March 2014

The Indian Roads CongressE-mail: [email protected]/[email protected]

Founded : December 1934IRC Website: www.irc.org.in

Jamnagar House, Shahjahan Road,New Delhi - 110 011Tel : Secretary General: +91 (11) 2338 6486Sectt. : (11) 2338 5395, 2338 7140, 2338 4543, 2338 6274Fax : +91 (11) 2338 1649

Kama Koti Marg, Sector 6, R.K. PuramNew Delhi - 110 022Tel : Secretary General : +91 (11) 2618 5303Sectt. : (11) 2618 5273, 2617 1548, 2671 6778,2618 5315, 2618 5319, Fax : +91 (11) 2618 3669

No part of this publication may be reproduced by any means without prior written permission from the Secretary General, IRC.

Edited and Published by Shri Vishnu Shankar Prasad on behalf of the Indian Roads Congress (IRC), New Delhi. The responsibility of the contents and the opinions expressed in Indian Highways is exclusively of the author/s concerned. IRC and the Editor disclaim responsibility and liability for any statement or opinion, originality of contents and of any copyright violations by the authors. The opinions expressed in the papers and contents published in the Indian Highways do not necessarily represent the views of the Editor or IRC.

Volume 42 NumbeR 3 maRCh 2014 CoNTeNTs IssN 0376-7256

INDIaN hIGhWaYsa ReVIeW oF RoaD aND RoaD TRaNsPoRT DeVeloPmeNT

Page

2-3 From the editor’s Desk - “Roads - Engine of Growth for Economy, Employment & Empowerment”

4-5 Membership Form A-1

6 Membership Form A-2

7 KUDOS to IRC Secretariat

7 New Publications Released

8 Effect of Type and Quantity of Binder on Rutting Characteristics of Bituminous Mix Vijay B. Kakade and M. Amaranatha Reddy

15 Properties of Porous Friction Course Mixes for Flexible Pavements A.U. Ravi Shankar, S.N. Suresha and G.M.V.S. Saikumar

26 BenefitsofMechanisticApproachinFlexiblePavementDesign Nagrale Prashant P and More Deepak

34 Design, Construction and Performance of Porous Asphalt Pavement for Rainwater Harvesting Prithvi Singh Kandhal and Sapan Mishra

50 Innovative Idea to Calculate the Tilt of a Well KNSP Kamaraju

53 Acceleration and Deceleration Behaviour of Truck on Indian Highway P.S. Bokare and A.K. Maurya

69 Dispute Avoidance Practices on Construction Contracts S.K. Dhawan

73-79 Circular Issued by MORT&H

80 Tender Notice of NH Circle, Madurai

81 Tender Notice of NH Circle, Tirunelveli

82 Tender Notice of NH Circle, Tirunelveli

2 INDIAN HIGHWAYS, MARCH 2014

Dear Readers,

Do the road sector deserve a better attention and more importance than what it has been given? Do we really take into account the positivities which may emerged if higher attention along with higher level of investment in terms of budgetary support is given to road sector? How these issues connected with the road sector have relevance on the economic growth and empowerment of the people may be the question(s) which may come in any one’s mind. This requires a deeper introspection on the opportunities and potential of growth which gets generated by the road sector.

How many times do we consider the road sector as a potentially job creating sector? Normally it is perceived as a sector to create majority of job for unskilled/semi-skilled work force. However, the time has changed and with every passing day it is opening up more and more opportunities for skilled and high skilled work force in the allied areas like material conservation, environment conservation & protection, tourism, healthcare, textiles,capitalgoods,automobiles,financing,etc.Therateofreturntotheeconomyoneverypercentageofcomparativeinvestmentmadeintheroadsectoroveratimeperiodneedsquantificationbothindirectandindirect terms. However till that is achieved, the perceptible difference it is making on a broader assessment prospectiveclearlyjustifiesthecontinuousincreaseinattentiontobepaidandinvestmenttobemadeintheroad sector.

Can we dream of empowering people in the villages or in remote areas without providing them connectivity with better roads? Can they be empowered if they are not connected with the tehsil or district headquarters or with educational or healthcare institutions or with market/mandis, etc. How do we ensure the inclusive developmentofpeopleinrealsenseiftheessentialroadconnectivityhavingfairlevelofefficiencyisnotprovided? These issues are enumerated to provoke thoughts in respect of the level of attention the road sector deserves & needs to be given on regular basis to allow realistic empowerment of people at grass root level.

Inthecurrentdifficulteconomicscenariobothatthenationallevelaswellasatthegloballevel,itmaybea wise view if due consideration is given for capturing the smallest possibility of increasing the economic growth as well as improving the employment opportunities. The road sector offers not a small but a very big scope of taking the contracting economy to a growth path. With the recent introduction of guidelines by IRC, the road sector can become a major player of creating wealth from the waste. There has been a lot of concern about the disposal of plastic waste and the concern have reached to that level at which the related industrial units are getting closed down resulting into the contribution towards unemployed work force. The road sector today with the new guidelines comes to the rescue of not only this industrial segment but also offers new employment opportunities which gets created from the usage of waste plastic in the road construction. The direct and indirect saving to the economy resulting to contribution towards economic growth needs to be given due consideration in the policy and programme framework.

Similarly, huge scope is available for use of other type of waste/byproducts generated from industrial/mining activities and also from municipality areas. The potentiality of their usage require intensive and extensive researchactivitiesacrosscountrysoas tocater todifferentspectrumoftrafficintensity,soilconditions&geological conditions, etc. This in turn result into employment opportunities both at the research institutions

From the editor’s Desk

RoaDs – eNGINe oF GRoWTh FoR eCoNomY, emPloYmeNT & emPoWeRmeNT

eDIToRIal

INDIAN HIGHWAYS, MARCH 2014 3

level as well as in industrial units which may come up as a result of capitalizing /commercializing the researchresults.Thereisaneedtobridgethegapbetween“thelabandthefield”intheroadsector,whichmay get addressed if the opportunities as existed are duly considered and captured. This may also require corresponding skills development for the technicians and supporting manpower. This cascading generation of employment opportunities by the road sector at different levels may help to some extent the absorption of existing unemployed work force. A win-win situation for the economy.

There are number of similar openings which road sector has the potential to offer to the economy provided these chances do not go wanting. The scepticism which is coming in the way of introducing and encouraging new technology, methodology, technique and material through experimental pilot projects needs to be overcomed. The road sector is not a short term investment sector. In the process of road building, the assets are created for the society and for the nation. Such asset creating activities should not be perceived with a myopic vision but with a vision of creating the asset which should serve the purpose over the design life period without carrying out major augmentation/realignment. The two concepts namely “life cycle cost of facility” & “technical audit offinancialdecisions”aretheneedofthehourwhichneedstobepracticedintheroadinfrastructuresectorin today’s context.

DowehaveeverquantifiedthescopeofaddingintotheGDPgrowthrate, if therateofaccidentsaswellas the rate of road accidents deaths is reduced by 50% within the period of 3 years which is achievable and not impossible. The creation of safer roads and safe road transport system may not only results in saving of unwarranted expenditure but may also result into channelizing huge investment including surplus (resulting from safe roads) into other productive segments of the economy. How much we are saving by curtailing the safety features in the road & road transport segment(s) and how much we are losing in terms of GDP growth by creating unsafe roads & road transport system based on myopic concepts needs a thorough review. The safer roads on a broader assessment may result in positive contribution of 2 to 3 % in terms of GDP which should be considered on top priority in the current scenario.

The road sector not only deserves a better consideration alongwith out of box thinking to overcome the unwarranted impediments and bottlenecks, which are resolvable in a productive manner. The perception about road sector requires a thorough overhaul, as it not only provides employment opportunities in the core sector related activities but also has abundant scope of providing commercial opportunities and employment in large number of allied areas including that of energy conservation which may also boost the economy besides resulting into inclusive growth leading to empowerment of people at large.

Througheffectiveandefficientroadnetworkconnectivitytotheremotestareasofthecountry,thedreamofhaving Panchayati Raj system along with inclusive growth & development of people can be achieved at a faster pace.

“Vision without action is a day dreaming” “Action without vision is a nightmare”

(A Japanese proverb)

Place : New Delhi Vishnu shankar Prasad Dated : 20th February, 2014 Secretary General


KuDos To IRC seCReTaRIaT

To, 18-02-2014

The Editor, Indian Highways, Delhi

What an amazing task! 74th annual session of IRC concluded on 24-1-2014 and its Report has appeared in February2014issueofIndianHighwayswhichisbeingpublishedinthefirstweekofeverymonth.Thismeansthatthecompilation,editing,finalisationoftheReportinallrespectshasbeenachievedinarecordtime of mere 10 days. An impossible task has been accomplished by Secretary General and his supporting staff.Besides the quality ofReport is also not a sketchy one. It is complete and flawless covering theproceedingsoftheentiresession,fromfirsttofinishincludingphotographswiththeircaptions.Thisisanonerous task almost beyond anybody’s physical and mental capacity. Please accept my congratulations.

N.G. Vakharia Ahmedabad, Gujarat

LM - 2922 E-mail: [email protected]

NeW PublICaTIoNs ReleaseD

1. IRC:6-2014 - “StandardSpecifications andCodeofPractice forRoadBridges,Section-IILoads andStresses” (Revised Edition) (Price Rs.700/- + Rs.40/- for postage & packing charges)

2. IRC:78-2014-“StandardSpecificationsandCodeofPracticeforRoadBridges,SectionVII-Foundationsand Substructures (Revised Edition) (Price Rs.700/- + Rs.40/- for postage & packing charges)

3. IRC:115-2014 - “Guidelines for Structural Evaluation and Strengthening of Flexible Road Pavements UsingFallingWeightDeflectometer(FWD)Technique”(PriceRs.300/-+Rs.30/-forpostage&packingcharges)

4. IRC:SP:55-2014-“GuidelinesonTrafficManagementinWorkZones”(FirstRevision)(PriceRs.900/-+ Rs.40/- for postage & packing charges)

5. IRC:SP:62-2014 - “Guidelines for Design and Construction of Cement Concrete Pavements for Low Volume Roads” (First Revision) (Price Rs.600/- + Rs.30/- for postage & packing charges)

6. IRC:SP:100-2014 - “Use of Cold Mix Technology in Construction and Maintenance of Roads Using Bitumen Emulsion” (Price Rs.900/- + Rs.40/- for postage & packing charges)

7. HRB SR No.23-2014 – State-of-the-Art Report: Design and Construction of Rockfall Mitigation Systems (Price Rs.900/- + Rs.40/- for postage & packing charges)


eFFeCT oF TYPe aND QuaNTITY oF bINDeR oN RuTTING ChaRaCTeRIsTICs oF bITumINous mIX

Vijay B. KaKade* and M. aMaranatha reddy**

* Research Scholar** Associate Professor, E-mail: [email protected]

absTRaCTRutting is one of the most common type of failure observed on high volume bituminous pavements in India and Viscosity Grade bitumen (VG 30) is a most common binder used for construction and these could not provide desirable performance. Modifiedbinders, both polymer and crumb rubber, have been also used in the construction mainly to address rutting failures. Though these binders have shown improved performance over VG 30 binders, it is not clearly understood the effect of type and amount of modifiedbinderontheperformanceofmixes.Althoughruttinginbituminous mix depends on many factors such as size, gradation, surface texture of aggregates, type and amount binder etc, it is importanttofindouttheroleofthebinderintheperformanceofthe mixes.

Keeping the above in view, performance of three commonly used modifiedbinderswereevaluatedforbinderrheologicalparameterG*/sinδassociatedwith ruttingbehaviourusingdynamic shearrheometer. Bituminous mixes prepared at 0.5% incremental binder contents either side of the optimum binder content were evaluated to study the effect of type and quantity of binder on rutting performance of the mixes. A mid-point aggregate gradation of a wearing course of Indian highways, bituminous concrete, as per Indian Roads Congress specifications was considered. Ruttester was used to evaluate the relative rutting susceptibility of the mixes. Correlation between rut depth measured and binder content or air voids for each type of binder was developed. Relative rutting performance of bituminous concrete mix at different binder content for all types of binders was evaluated and presented. BasedonthestudyitwasobservedthatPolymerModifiedBinder(PMB 40) performed better compared to other binders considered in this study. Also with increase in binder content beyond certain limit, rutting susceptibility of the bituminous mixes increased irrespective of type of binder used but the effect was less in case of PMB 40 mixes.

1 INTRoDuCTIoN

1.1 background

Permanent deformation or rutting in bituminous mixes depends on numerous factors such as aggregate gradation, shape and quality of aggregate, quantity and

quality of binder, volumetrics of mix such as amount of air voids and Voids in Mineral Aggregates (VMA), filmthickness,temperature,constructionpracticesandenvironmental conditions ((Lynn et al, 2007; Sengoz and Topal, 2007; Lee et al, 2008). Of these, quantity of binder is one the most important parameters that should be carefully chosen for better pavement performance. Variation in the binder content for given type of aggregate and gradation results in change in air voids content in the mix. Studies reported that air voids less than 3% led to failures such as rutting and bleeding (Archilla and Madanat, 2001) and more than 8% resulted in oxidation, moisture damage etc (Brown, 1990; Solaimanian et al, 1993; Williams et al, 1999). Excess asphalt binder or low air void content in the mix leads to loss of internal friction between aggregate particles and thereby rutting due to shear deformation occurs. Uzarowski et al. (2004) and Archilla and Madanat (2001) reported that high level of asphalt content was more susceptible to rutting than thelowasphaltcontentsandmodifiedbindershowedbetter resistance to rutting than neat binder.

Although the rutting tendencies of a pavement are influenced primarily by aggregate and mixproperties, type and properties of binders are most important parameters that have significant affecton mix properties (Lundy and Sandoval- Gil, 2004; Uzarowski et al 2004, Jun et al 2005). In order to minimize rutting and raveling distresses, it is a general practice to restrict the air voids in the mix to around 8% during construction (in-place) and upon secondary compactionbythetraffic(in-service)to3%(Robertset al, 1996). Being an important parameter, some of the mix design procedures have adopted air void as the main criteria for selection of optimum binder content

Civil Engineering Department, Indian Institute of Technology, Kharagpur-721 302, India

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(MS-2, 1994; SP-2, 2001). However the mix design criteria practiced in India as per Ministry of Road Transport and Highways guidelines (MoRT&H, 2001) considersstability,flowandothervolumetricsofmixincluding air voids as the selection criteria for arriving at Optimum Binder Content (OBC) expecting the mix to perform better in resisting both fatigue and rutting at OBC. However majority of the Indian highways, designed and constructed under stringent quality control, have shown premature failures such as rutting and bleeding indicating the need of proper mix design, including re-look into criteria for selection of optimum binder content (Interim Report, Reddy, 2007). Use of incorrect amount of binder that affects air voids in the mix was the causative factor for failures of some of the pavements in India (Rao, 2009). Limited studies have been conducted to find out effect of bindercontent on performance of Indian mixes. Awanthi et al, 2008 evaluated fatigue and rutting performance of mixes prepared with different binders under varied compaction efforts to get different air voids. However no studies have been reported on effect of different modified binders and variable binder contents onrutting susceptibility of mixes.

Variation in air voids in the mix is possible by changing either binder content or compaction effort (Brown, 1990). Limited studies have been carried on tolerance limits of binders that vary air voids in the mix. Therefore, the main focus of the present work is to study the effect of binder content on rutting characteristics of the mix as it addresses the use of improper quantity of binder in the mix which is a common problem in India.

In the present study, three types of commercially availablemodifier binders PMB-40, PMB-70 (SBS-polymer with 4% content) and CRMB-60 (Crumb RubberModifiedBinder-rubbercontentof6%)wereconsidered. Rheological parameters such as complex modulus(G*)andphaseangle(δ)ofthesebinderswereevaluated using dynamic shear rheometer. Bituminous Concrete (BC) samples for mid-point aggregate

gradation as per MoRT&H guidelines (2001), were prepared with same source of aggregates and three modifiedbindersatbindercontentof0.5%incrementon either side of optimum binder content. The samples were prepared using same compactive effort (75 blows from Marshall hammer) and same source of aggregates and gradation but at different binder content. An indigenously developed wheel tracker, IITKGP Rut tester was used to evaluate the rutting susceptibility of mixes. Correlations were developed between air voids content and rutting observed from the mixes. From the test results, conclusions were drawn on effect of type of binder and variation in binder content on the rutting performance of mixes.

2 eXPeRImeNTal DeTaIls

2.1 aggregate

Crushedcoarseaggregate,fineaggregateandmineralfillerwereprocuredfromRampurquarryinthestateof West Bengal, India. Table 1 presents the properties of aggregates considered in the present study.

Table 1 Physical Properties of aggregates

Property Tested Test Result

(%)

Specifications moRT&h (2001) (%)

Aggregate Impact value 12.0 Max 24

Los Angeles Abrasion value 17.3 Max 30

Flakiness Index 23.5 Max 30

Elongation Index 24.4 Max 30

Water Absorption 0.90 Max. 02

Specificgravity 2.8735 ………….

2.2 aggregate Gradation adopted

Mid-point gradation for Bituminous Concrete (BC) gradation-I, a dense gradation, as per MoRTH guidelines (2001) was selected for the present investigation. Fig. 1 show the aggregate gradation used along with suggested upper and lower limits as per MoRT&H guidelines.

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Fig. 1 Aggregate Gradation used for Bituminous Concrete Mix

2.3 binders used

Two SBS Polymer Modified Binder (PMB- 40#, PMB -70#) and one Crumb Rubber ModifiedBinder (CRMB-60*) were used in the investigation. Properties of binders are given in Table 2.#40and70 refers to penetration value; * 60- refer to softening point value.

Table 2 Properties of binder Considered

Property evaluated Types of binderPmb40 Pmb70 CRmb-60

Penetration @ 25ºC, 100 gm, 5 sec, (dmm)

41 58 43

Softening Point, (ºC) 74 63 65

Viscosity at 150ºC, (Poise)

8.2 4.8 8.9

2.4 marshall mix Design for optimum binder Content

Table 3 presents the Marshall parameters and resulting optimum binder content for mix prepared with bituminous concrete mid-point aggregate gradation with different binders.

From the above results, it was observed that optimum binder content for all binder mixes is close to 5% (by weight of mix). Air voids are ranging from 4.0 to 5.1% and these are almost in the range of MoRT&H guidelines (2001) i.e 3 to 5%.

Table 3 marshall Parameters and optimum binder Content for mixes Prepared with Different binders

mix Type (binder used)

stability (kg)

Flow (mm)

obC (%)

bulk Density (kg/m3)

air Voids (%)

Vma (%)

VFb (%)

PMB 40 1780 3.6 4.85 2.550 5.1 15.6 66.3PMB 70 1605 3.9 4.85 2.541 4.8 15.8 70.0CRMB 60 1495 4.6 4.90 2.530 4.6 16.4 68.1MoRT&H Specification

9.0 (min) 2 to 4 --- ---- 3 to 6 14 (min) 65--75

2.5 Rheological studies on binders

Rheological parameters such as G*/ sin δ and zeroshear viscosity and Multiple Creep Stress Recovery (MCSR) are some of the parameters used to explain the rutting potential of binders. Superpave binder specificationusesG*/sinδparametertoaddressruttingfailure (SP1, 2003). In addition to the above, number of researchers have tried to correlate binder rutting parameter (G*/sin δ) withmix rutting evaluated bywheel tracking devices (Stuart and Izzo 1995; Stuart et al. 2000; Shenoy et al. 2003; D’Angelo and Dongre 2004; Youtcheff et al. 2004). Therefore, in the present

study, rutting potential of binder was evaluated by meansofG*/sinδvaluesofunagedbinders.

Binder tests were conducted in the temperature range of 40 to 82ºC at 6°C increment with angular frequency of 10 rad/s using Dynamic Shear Rheometer (DSR). GenerallyhighertheG*/sinδsignifiesmoreresistanceto rutting.

2.6 evaluation of bituminous mixes using IIT KGP Rut Tester

The indigenously developed IIT KGP Rut Tester was used to perform the rutting test on the bituminous

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mix samples (Reddy, 2011). Mixes were prepared at optimum binder content and other binder contents as well with 0.5% intervals. The test was performed at 50ºC and a load of 2000 N was applied (back and forth) through a steel wheel of 50 mm diameter for 5000 to study the relative rutting performance of the mixes. Three samples were prepared and tested to include the sample variation for each type of bitumen.

3 eXPeRImeNTal ResulTs aND DIsCussIoN

3.1 superpave binder Rutting Parameter (G*/sin δ)

Fig. 2showthevariationofG*/sinδvaluewithtesttemperature for unaged binders measured at 10 rad/s angular frequency.

Fig.2G*/sinδVersusTemperatureatFrequencyof 10 Rad/s for Different Binders

From the above figure, it was observed that PMB-40has highestG*/sin δ value as compared to othermodified binders (PMB-70; CRMB-60). Therefore,PMB 40 binder showed higher resistance to rutting at alltemperatures.AsperSuperpavespecifications,G*/sinδvalueforunagedbindersshouldhaveaminimumof 1 kPa. From the results on binders considered in the present study, all binders are satisfying the above requirement up to 76ºC.

3.2 effect of binder Content on Rutting

Binder content was varied from 4 to 6% with 0.5 % increment (by weight of the total mix) while preparing

the samples. Relative rutting test results measured at 50ºC using IIT KGP rut tester are given in Table 4.

Table 4 Rutting Test with Different Types of binders and binder Content

mix (binder Type)

Rutting (mm) in mixes with binder Content (%)

4.0 4.5 5.0 5.5 6.0CRMB 60 3.85 3.58 3.42 4.68 5.12PMB 40 3.28 2.75 3.85 4.27 4.64PMB 70 3.36 3.14 3.38 4.67 4.94

Effect of binder type and content on rutting susceptibility of BC mixes is shown in Fig. 3.

Fig. 3 Effect of Binder Type and Content on Rutting Susceptibility of BC Mixes

With decrease in binder content from OBC, all the mixes have resulted in increase in rutting but less compared to rutting Observed for Binder Content above OBC (5%). Generally for a low binder content mix will have higher air voids and low air voids for high binder content. At lower air voids, bitumen acts as lubricant and thereby more rutting at higher binder contents. Mixes prepared using with PMB 40 have resulted in less rutting at all binder contents (lower and higher of OBC) and showed less effect even beyond OBC compared to other mixes.

3.3 effect of binder Type on Rutting

As optimum content of bituminous concrete mix considered in the present study using different binders was found to be close to 5% by weight of mix, samples

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were prepared at this binder content and evaluated for relative rutting susceptibility at 50ºC. Fig. 4 shows the test results.

From the test results, mix prepared using PMB 40 binder found to be better than CRMB 60 mix.

Fig. 4 Rutting at Obinder Content of Different Binders

3.4 effect of air Voids on Rutting

In order to study the effect of air voids on rutting of bituminous concrete mixes, varying binder content (4 to 6%) were considered keeping the aggregate gradation and compactive effort same during preparation of mix samples to get different air voids in the mix. Samples were subjected to rutting evaluation using rut tester under same test condition. The results of air voids content of bituminous mixes for different types of binders and binder content are shown in Figs. 5 to 8 along with rut depths.

Fig. 5 Air Voids Vs Rut Depth for PMB 70 Mix

Fig. 6 Air Voids Vs Rut Depth for PMB 40 Mix

Fig. 7 Air Voids Vs Rut Depth for CRMB 60 Mix

Fig. 8 Air Voids Vs Rut Depth for all Binders

The correlations between rut depth and air voids have showed similar trends for all types of binders. At low void content, the rut depth observed was more and this value decreased till 8% air voids and beyond this there was increase in rutting value. This implies that at higher binder content (lower air voids) than optimum binder content the severity of rutting was found to be

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higher than that of lower binder contents for all types ofbinders.Atairvoidcontent,modifiedbindershaveshown lower resistance to rutting implies that excess binder leads to problems.

The rutting values for three mixes below 3% and above 7% are shown in Figs. 9 and 10.

Fig. 9 Air Voids (<3%) Vs Rut Depth for Different Mixes

Fig. 10 Air Voids (>7%) Vs Rut Depth for Different Mixes

From Fig. 9 and 10, it is clear that the rut depth, for air voids below 3%, rutting in the mixes was more compared to air voids greater than 7% for all mixes indicating that at lower air voids in the mixes leads to higher rutting. However performance of the PMB 40 mix was found to be better at both lower and higher air voids compared to other binders.

4 CoNClusIoNsAnefforthasbeenmadeinthisstudytofindouttheeffectoftypeofmodifiedbinderandquantityofbinderon relative rutting susceptibility of Indian bituminous mixes.Forthreetypesofmodifiedbindersconsidered,rutting characteristics were evaluated using Dynamic Shear Rheometer. Bituminous concrete mixes were prepared at varied binder content to obtain different air voids in the mix and evaluated for their rutting susceptibility. Correlations were developed for air voids and resulting rut depth of the mix. From these studies, following conclusions have been drawn. ● From the Dynamic Shear Rheometer

test results on binders, it was found that at a 10 rad/s PMB 40 binder offered highruttingresistance(higherG*/sinδvalue) at all temperatures. This indicates that performance of PMB 40 expected to be better in rutting than othermodifiedbinders.

● From rut tester results on bituminousconcrete mixes prepared at OBC, PMB-40 mix demonstrated lower rutting susceptibility followed by PMB-70, CRMB-60. Similar conclusion was made from binder study also.

● At higher binder content (air voids <3%), all mixes resulted in higher rutting compared to lower tolerance limit (air voids >7%) indicating the severity of rutting at higher binder content due to shear deformation. However, performance of PMB 40 mix was found to be better at all air voids contents compared to CRMB 60 and PMB 70 mixes.

● From the study conducted on mixes,it can be concluded that binder content limit beyond optimum has effect on rutting. However, PMB 40 binder appears to perform better compared to othermodifiedbindersevenatbothlowerand higher binder contents of the range considered.

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ReFeReNCes1. Awanti, S, Amarnath, M, S & Veeraragavan, A., 2008.

Effect of Air Voids on Permanent Deformation Characteristics of SBS Polymer Modified AsphaltConcrete Mixtures for Paving Applications. Proc., of 5th International Transport Conference, Wuppertal, Germany.

2. Archilla, A, R., & Madanat, S, M.( 2001). Estimation of Rutting Models by Combining Data from Different Sources, Journal of Transportation Engineering, American Society of Civil Engineers, 126(4), 291-299.

3. Brown, E,R. (1990). Density of Asphalt Concrete-How Much is Needed?, NCAT (90-3), National Center for Asphalt Technology, Auburn University, Auburn, USA.

4. D’ Angelo, J., & Dongre, R. (2004). Development of a Performance Based Binder Specifications in the UnitedStates, Proc., of 3rd Eurasphalt and Eurobitume Congress, Vienna.

5. Jun,Y,Haibin Z., Juan, C., Guochao,Q.,Weiyu, P.,&Yiwen, Y.( 2005). Study of Rutting Resistance of Asphalt Surfacing Mixtures, Proc., of the 24th Southern African Transport Conference (SATC2005), Pretoria, South Africa, 768-777.

6. Lee,S,J.,Amirkhanian,S,N.,Known,S,Z.(2008).Effectof Compaction Temperature on CRM Mixture Made with the SGC and the Marshall Compactor, Journal of Construction and Building Materials, (22), 1122-1128.

7. Lynn, T., Robert, S., Peter, J, Wu, Y., & Jared, D. (2007). Effect of Aggregate Gradation on Volumetric Properties of Georgia’s Hot Mix Asphalt, Transportation Research Record 1998, Transportation Research Board, Washington D.C, 123-131.

8. Lundy, J, R., & Sandoval-Gil, J,A. (2004). Permanent Deformation Characteristics of Oregon Mix Using the Asphalt Pavement Analyzer, Report (340), Oregon Department of Transportation, Research Unit 200, Hawthorne SE, USA.

9. MoRT&H(2001). Specification for Road and BridgeWorks, Ministry of Road Transport and Highways, 4th Edition, Indian Roads Congress, New Delhi, India.

10. MS-2 (1994). Mix Design Methods for Asphalt Concrete and Other Hot Mixes, Asphalt Institute, 6th Edition, USA.

11. Rao, S,K.(2009). Asphalt Paving Mix Design for Heavily TraffickedRoads,Proc.ofShortTermCourseonPavementMaterials, Design and Evaluation, Indian Institute of Technology Kharagpur, Kharagpur.

12. Reddy, K,S. (2007). Interim Report-Investigation of Rutting Failure in Some Sections of National Highway-2 Between KM. 317 and KM. 65, Transportation Engineering Section, Civil Engineering Department, IIT Kharagpur, India.

13. Reddy, I.S., & Reddy M.A. (2011). “Low Cost Device for Evaluating Rutting Characteristics of Bituminous Mixes”, Journal of Indian Roads Congress, New Delhi, Vol.39 (3), 51-62.

14. Roberts, F. L., Kandhal P, S., Brown, E, R., Lee, D, Y., & Kennedy, T, W. (1996). Hot Mix Asphalt Materials, Mixture Design, and Construction. NAPA Education Foundation, Lanham, MD. 2nd Edition.

15. Sengoz, B., & Topal, A.(2007). Minimum Voids in Mineral Aggregate in Hot-Mix Asphalt Based on Asphalt Film Thickness, Journal of Building and Environment (42), 3629-3635.

16. Shenoy, A., Stuart, K., & Mogawer, W. (2003). Do Asphalt Mixtures Correlate Better with Mastics or Binders in Evaluating Permanent Deformation? Transportation Research Record 1829, Transportation Research Board, Washington, D.C., 16-25.

17. Solaimanian, M., Kennedy, T.W., & Elmore, T.W.(1993). Long Term Evaluation of Stripping and Moisture Damage in a Asphalt Pavements Treated with Lime and Anti-Stripping Agents, Texas Department of Transportation, Report (CTR 0-1286-1F), Center of Transportation Research, University of Texas at Austin, USA.

18. SP-1(2003). Superpave Performance Graded Asphalt BinderSpecificationandTesting,SuperpaveSeriesNo.1,3rd edition, Asphalt Institute, USA.

19. SP-2(2001). Superpave Mix Design, Superpave Series No. 2, 3rd Edition, Asphalt Institute, USA.

20. Stuart, K, D., & Izzo, R, P.(1995). Correlation of Superpave G*/ sin δ with Rutting Susceptibility fromLaboratory Mixture Tests, Transportation Research Record 1492, Transportation Research Board, Washington, D.C., 176-183

21. Stuart, K, D., Mogawer, W, S., & Romero, P.(2000). Validation of Asphalt Binder and Mixture Tests that Measure Rutting Susceptibility, Report of FHWA- (RD-99-204), Federal Highway Administration, U.S. Department of Transportation.

22. Williams, R, C., & Prowell, B,D.(1999). Comparison of Laboratory Wheel-Tracking Test Results to West Track Performance, Transportation Research Record 1681, Transportation Research Board, Washington D.C, 121-128.

23. Uzarowski, L., Paradis, M., &Lum, P.(2004). Accelerated Performance Testing of Canadian Asphalt Mixes using Three Different Wheel Rut Testers, Proceedings of the Transportation Association of Canada (TAC) Annual Conference, Quebec

24. Youtcheff, J, Stuart, K., Al-Khateeb, G., & Shenoy, A.(2004). Understanding the Performance of Polymer Modified Binders, Proc., of the 3rd Eurasphalt and Eurobitume Congress, Vienna.


PRoPeRTIes oF PoRous FRICTIoN CouRse mIXes FoR FleXIble PaVemeNTs

a.U. raVi ShanKar*, S.n. SUreSha** and G.M.V.S. SaiKUMar***

* Prof. & Head, E-mail: [email protected]** Asst. Prof., E-mail: [email protected]*** P.G. Student, E-mail: [email protected]

absTRaCTPorous Friction Courses (PFCs) are open-graded bituminous mixtures used as surfacing or wearing courses over sound dense bituminous mix surfaces of highway and runway pavements. These are provided to serve as surface drainage layers to improve the pavement skid-resistance and to mitigate hydroplaning effect during wet-weather conditions, in addition to attenuation of vehicle tyre noise. Number of research findings on characterization of PFCmixes reported the use of Superpave Gyratory Compactor (SGC). Major differences were observed in the design gyrations (Ndesign) and the design aggregate gradations. This paper summarizes the laboratory investigation on effect of aggregate gradation on the mix design (with regard to volumetric properties, permeability, unaged abrasion loss, and drain down) and performance properties (including aged abrasion loss, moisture susceptibility, and rutting) of PFC mix with neat bitumen and waste plastic asmodifier.

1 INTRoDuCTIoN

Open-graded mixes are composed of relatively uniform graded aggregate and bitumen or modifiedbinders, and are mainly used to serve as drainage layers, either at the pavement surface or within the pavement structure (FAA 2001). Open-graded mixes used as surface drainage layers are termed as Porous Friction Courses (PFC). Normally, the thickness of PFCs varies in the range of 25-40 mm with a minimum air voids content of 18 percent. PFCs are also called by different names by various agencies around the world, like Porous Asphalt (PA), Open-Graded Friction Course (OGFC), Open Graded Asphalt (OGA), etc. (Suresha et al. 2007). PFCs arefoundtooffermultiplebenefits like,betterskid-resistance, reduced splash and spray, and improved night-visibility during wet-weather conditions, in

addition to mitigation of hydroplaning (Halstead 1978; Nicholls 1997; Huber 2000). Moreover, the negative-texture of PFC surfaces enables considerable reduction in traffic tyre-noise (Suresha et al. 2007).Open-graded mixes are highly recommended for high-speed road-corridors (Huber 2000) and runway pavements (FAA 1997).

These mixes are designed to resist mainly two modes of deterioration i) raveling, and ii) clogging of pores. Verhaeghe et al. (1994) carried out studies on porous asphalt mixes and suggested that the selected aggregate gradation should result in at least 20% voids in the compacted mix. Mallick et al. (2000) conducted studies on OGFC mixes with different percentages of materials passing 4.75 mm sieve and reported that a gradation with not more than 20% passing 4.75 mm sieve is sufficient to achieve stone-on-stone contactconditions, capable of providing adequate permeability in OGFC mixes. Use of larger-sized aggregate grading providessuperiorperformancethanfinergradedmixesin terms of hydraulic conductivity (Nicholls 1997). Current design procedures also include a method of evaluating the degree of stone-on-stone contact. An OGFC must have a skeleton of coarse aggregate with stone-on-stone contact to minimize rutting (Brown and Cooley 1999). The aggregate gradation and binder content plays a major role in ensuring the hydraulic efficiencyanddurabilityofthemix.

The lower surface area due to the use of uniformly graded aggregates and the low quantity of fillermaterials used result in the draining of bitumen-mastic (draindown) from PFC mixes during mixing, storage, transport, and laying operations. To mitigate the

Department of Civil Engineering, National Institute of Technology Karnataka, Surathkal

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problemofdraindown,useoffibresorwasteplasticsas modifiers (stabilizers) to the mixes are widelyrecommended (Huber, 2000). This consequently requires an increase in the binder content, which further improves the durability of the mix. Further, it increases the stiffness of bitumen-mastic minimizing the amount of draindown.

Many road agencies in the United States recommend the use of these layers for safety (Huber 2000), while many European countries widely use these as quiet pavements. Road agencies in countries like Japan (Nielsen et al. 2005), Australia (NAS 2004), New Zealand(TNZ2007),andSouthAfrica(Sabita1995)recommend the open-graded mixes to achieve both safety and tyre-noise-attenuation. OGFCs have been experimented widely in the United States over the past 50 years (Huber 2000). European experiences with porous mixes demonstrated its potential applications on high-speed road facilities that also produced exceptionally quiet pavements (Focus 2005). Porous pavements of Japan are known for their structural and acoustic durability (Nielsen et al. 2005). The Federal Aviation Administration (FAA) recommends PFCs as one of the technique for improvement of runway pavement skid-resistance and mitigation of potential of hydroplaning (FAA 1997).

Research findings on open-graded mixes are rarelyreported from India (Suresha 2004; Jain et al. 2007). The findings reported by Punith et al. (2004) andSridhar et al. (2005) seems to be foremost, which are based on the studies conducted to characterize polymer and fibre modified open-graded frictioncourse mixtures (Suresha 2004). Suresha (2008) performed an extensive research on various aspects ofPFCmixesandfindingsofthesamecanbefound

elsewhere (Suresha et al. 2009a, 2009b, 2009c, 2010a, 2010b, 2010c).

2 objeCTIVe aND sCoPe

The main objective of this study is to evaluate the mix design and performance properties of PFC mixes corresponding to the gradation suggested by Suresha (2008). The mix design properties considered are volumetric properties, permeability, unaged abrasion loss, and draindown. The performance properties considered are aged abrasion loss, moisture susceptibility, and rutting. Various tests were performed on the cylindrical shape PFC specimens prepared by the Superpave Gyratory Compactor (SGC) to evaluate all the properties as mentioned above, except resistance to rutting.

3 maTeRIals aND meThoDoloGY

3.1 materials

The Porous Friction Course (PFC) mixes corresponding to aggregate gradation shown in Table 1 were investigated.Coarseandfineaggregatesobtainedfrom(Granite aggregate) local stone crushing plants were used in this study. Ordinary Portland Cement (OPC) blendedwithstonedust,wasusedasthemineralfiller.The quantity of OPC was limited to 2% by mass of the total aggregates. Straight-run paving grade bitumen used in the present investigation, was supplied by theMangaloreRefineryandPetrochemicalsLimited(MRPL), Mangalore. The physical properties of coarse aggregates, and paving-grade bitumen were determined in accordance with Indian Standard (IS) test methods. The test results are presented in Table 2.

Table 1 aggregate Gradation Recommended by suresha (2008)

IS Sieve Size, mm 19 13.2 9.5 4.75 2.36 0.075% Passing 100 90 - 95 25 - 65 10 - 17.5 7.5 - 11.5 2 - 5

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Table 2 Properties of Coarse aggregate and bitumen

material Properties Is test method Test resultsCoarse Aggregate

Combinedflakinessandelongationindex,% 2386 P(1) 28.1Aggregate impact value, % 2386 P(4) 20.1Los Angles abrasion value, % 2386 P(4) 26.6Water absorption, % 2386 P(3) 0.15Soundness: Magnesium sulphate, % 2386 P(5) 0.2 1

Bitumen Specificgravity,at27ºC 1202 1.01Penetration at 25ºC, 100 g, 5 s., 1/10 mm 1203 89Penetration at 4ºC, 200 g, 60 s., 1/10 mm 1203 43Softening point, (R&B), ºC 1205 46Ductility at 27ºC, cm 1208 90Lossonheating,thinfilmoventest,percentbymassRetainedpenetrationafterthinfilmoventest,25ºC, 100 g, 5 s., 1/10 mm, % of original

9382 62

3.2 Concept of aggregate locking Point

The design of PFC mix was carried out by using the Superpave Gyratory Compactor (SGC). From the SGC approach, it is found that the design gyrations (Ndesign) have been specified by various agencies. Varadhan(2004) and Jaiswal (2005) adopted the compaction level corresponding to the gyration at the aggregate locking point (NLP), at which the aggregate skeleton “locks” together and further compaction results in aggregate degradation without any significant achievement ofcompaction (Prowel and Brown 2007). The aggregate lockingpointconceptwasfirstproposedbytheIllinoisDepartment of Transportation (Pine 1997), in order to prevent over-compaction and subsequent degradation of aggregates in the SGC. Vavrik and Carpenter (1998) providedarefineddefinitionforNLP, where it is said to correspondtothefirstgyrationinthefirstoccurrenceof three gyrations of the same height proceeded by two sets of two gyrations with the same height. The NLP can be taken as (Ndesign) for SGC approach.

3.3 experimental DesignPFC mix corresponding to the gradation and three Binder Contents (BC) of neat bitumen were investigated. Cylindrical specimens of 100 mm in diameter for the selected PFC mix were prepared by the Superpave Gyratory Compactor with 50, 80, 120

& NLP gyrations. To prepare a cylindrical specimen of 100 mm Diameter (D), loose hot PFC mix was compacted by applying at different gyrations, using a Superpave Gyratory Compactor (SGC). Each specimen thus prepared constituted 1000 g of the aggregate in additiontopre-definedquantitiesofBC.In total,96cylindrical PFC specimens that constituted minimum of three replicate specimens for the experimental mix were prepared to evaluate the volumetric properties, coefficientofpermeability(K),Cantabroabrasionloss(Unaged (UAL), Aged (AAL), Wet (WAL)) abrasion losses, and moisture-susceptibility.

4 eValuaTIoN oF PFC mIX

4.1 aggregate locking Point

The influence of gyration levels on the mixcorresponding to the gradation and for the binder contents of 4.5, 5.0 and 5.5% by mass of the total mix was evaluated. In total, nine PFC specimens with three replicates for each were compacted using the SGC to a maximum gyration level of 120 (N120). The locking point (NLP) for eachmixwas identifiedand presented in Table 3. The NLP of most of PFC mixes tested were found to vary between 50 and 75. A similar study performed by Vardhan (2004) on friction course mixes with granite-aggregates has reported NLP

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values in the range of 76 - 96, where the NLP values were identified according to the recommendationsof Vavrik and Carpenter (1998). It may be observed that in the present study, the Los Angeles Abrasion (LAA) value of aggregates used was lesser than 30%,

while Vardhan (2004) adopted aggregates with LAA values up to 50%. The difference in the results of the NLP is inferred to be mainly due to the above reason.

Table 3 Gyrations Corresponding to locking Point (NlP)

Binder content, % 4.5 5.0 5.5NLP of individual specimens 62 63 58 66 65 67 67 70 70

4.2 Volumetric Properties

The volumetric properties of compacted specimens tested included the bulk specific gravity (Gmb), percent air voids (Va), and the Voids in Coarse Aggregate (VCAm). The Gmb was determined using the geometric measurements of the diameter (D) and mean Length (L), and the mass of the specimen in air. The theoretical maximum density (Gmm) of the uncompacted mix was determined in accordance with ASTM D 2041(2011). Va was then determined using the corresponding values of Gmb and Gmm using Eq.(1). Presence of stone-on-stone contact condition in the compacted PFC mix was evaluated based on the VCAm and the percentage of voids in coarse aggregate of the coarse aggregate alone (VCAd) determined using the dry-rodded test procedure. The VCAd and VCAm values were computed using Eqs. (2) and (3), respectively. Stone-on-stone contact condition in the mixwasconfirmedwhentheratioofVCAm to VCAd was found to be lesser than unity.

Va = 100 × 1−

GG

mb

mm ... (1)

VCAd = GG

CA w s

CA w

γ γγ− ... (2)

VCAm = 100 – GG

Pmb

CACA×

... (3)

Where,

GCA = bulk specific gravity of the coarseaggregate;

γs = bulk density of the coarse aggregate fraction in the dry-rodded condition;

γw = density of water; PCA = percentage of coarse aggregate in the total

mixture.

For tests conducted on mix, the mean values of test results corresponding to the Gmb, ratio of VCAm to VCAd, and Va are presented in Table 4. The mean value of VCAd is 52.56%.Themeanbulk specificgravityof compacted mixes (Gmb) ranged between 1.933 g/cc and 2.040 g/cc. The mean values of Va for the mix varied from 23.8% and 27.8%, The mean voids in coarse aggregate mix VCAm ranged between 43.8% and 46.5%. The ratios between VCAm and VCAd presented in Table 4,confirmthepresenceofstone-on-stone contact condition in the coarse aggregate skeleton in all the experimented mix combinations tested. Thus, the mix ensures adequate stability to resist the plastic deformation.

Table 4 Volumetric Properties

bC (%)

Gmb at Va (%) at VCam (%) at VCam/VCad N50 NlP N80 N120 N50 NlP N80 N120 N50 NlP N80 N120 N50 NlP N80 N120

4.5 1.97 2.00 2.02 2.01 26.2 25.10 24.6 24.8 45.4 44.60 44.1 44.4 0.872 0.85 0.84 0.845.0 1.97 1.98 2.03 1.99 26.4 26.1 24.1 25.8 45.5 45.3 43.8 45.0 0.870 0.86 0.83 0.865.5 1.93 2.02 2.01 2.04 27.8 24.5 25.6 23.8 46.5 44.1 44.4 43.6 0.88 0.84 0.85 0.83

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4.3 Permeability

The hydraulic conductivity of compacted specimens tested is expressed in terms of the coefficient ofpermeability (K), determined using the falling-head method. PFC specimens prepared using SGC, at gyrations of 120, were inserted into the standard Marshall mould. The circumferential contact area between the specimen and the mould was covered using paraffin wax on either side to prevent theleakage of water. Care was taken to avoid clogging of voidsduetoparaffinwaxinthespecimen.Thecollarplaced on the mould-specimen assembly, made water tight at the interface, acted as a water reservoir. Water was then allowed toflow through the specimen andthe average time (tm) taken for a drop in water level from 70 mm to 30 mm was recorded in seconds. The typical setup for permeability test using falling-head method is shown in Fig. 1.

Fig. 1 Typical Permeability Test Setup

The coefficient of permeability (K, m/day) of thecylindrical specimen of 100 mm diameter (D) and of mean length (L, mm) was calculated using the expression as in Eq. (4) for the falling-head permeability approach.

K = 198.9792 (a L/A tm) Tc log10[(h+h1)/(h+h2)] ... (4)

Where,

a and A are cross-sectional areas of collar (internal) and specimen respectively (mm2); h is the thickness of specimen (mm); and Tc is the temperature correction for viscosity of water (= 0.83- 0.89, for the test temperature in the range of 25 - 28ºC).

The individual permeability (K) values for the mix tested varied in the range from 45 to 155 m/day. Thus, themixsatisfiedthepermeabilitycriteriathatKshouldbe more than 8.7 m/day (0.01 cm/s) for good drainage condition (Chen et al. 2004). Table 5 indicates the mean K values of 12 mixes tested. It is generally accepted that the permeability is directly proportional to the porosity (percent air voids, Va). Here too, the variations in the permeability seem to be similar to that of trends of air voids.

Table 5 Permeability (K) Values

Binder content, % 4.5 5.0 5.5Mean values of K (m/day) 146 136 47

4.4 Cantabro abrasion Test

The Cantabro abrasion test method is used to ensure adequate durability of the compacted PFC specimen. Nowadays, most of the agencies recommend this test as a compulsory or as an optional test for the mix design of PFCs. The SGC compacted, at NLP, PFC cylindrical specimens were directly tested according to Cantabro abrasion test method. This test can be conducted on unaged specimens, aged specimens, and wet conditioned specimens and the corresponding abrasion losses are termed as Unaged Abrasion Loss (UAL), Aged Abrasion Loss (AAL), and Wet Abrasion Loss (WAL) respectively.

4.4.1 Unaged Abrasion Loss (UAL)

The unaged abrasion loss of PFC mix tested by placing a compacted specimen in a Los Angeles abrasion drum (Fig. 2 (C)) without any abrasive charges, and machine is operated at a speed of 30 to 33 revolutions per

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minute for 300 revolutions. The operating temperature should be 25 ± 5ºC. Fig 2 (a) and (d) shows how the condition of specimen before subjecting to Cantabro abrasion and after the abrasion respectively. Before placing the specimen in Los Angles Abrasion drum initial weight of specimen is taken (A) and later after 300revolutionsfinalweightofspecimenistaken(B).

Loss in the specimen weight is expressed in percentage of ratio of weight of disintegrated particles to the initial weight of the specimen (Eq. 5) and expressed as the abrasion loss. Table 6 indicates the mean unaged abrasion loss values.

% Loss = (( A – B ) / A ) * 100 ... (5)

(a) Unaged PFC Specimen

(c) Specimens (Unaged/Aged) Subjected to Abrasion Test

(b) Specimens Subjected to Aging Process

(d) Specimens After Abrasion TestFig. 2 Specimen Before and After the Cantabro Test

Table 6 unaged abrasion loss (ual) Values

Binder content, % 4.5 5.0 5.5Mean values of UAL (%) 22.2 19.9 19.1

4.4.2 Aged Abrasion Loss (AAL)

Aging is accomplished by placing triplicate specimens in a forced draft oven, set at 60ºC, for 168 h (7 days). The specimens are then cooled to 25ºC and stored for

4 h prior to conducting the Cantabro abrasion test. Fig. 2(b) shows the cylindrical specimen placed in oven for simulating aging. Table 7 indicates the mean aged abrasion loss values.

Table 7 aged abrasion loss (aal) Values

Binder content, % 4.5 5.0 5.5Mean values of AAL (%) 32.97 23.28 22.26

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4.4.3 Wet Abrasion Loss (WAL)

Specimens were saturated by submerging in water and kept at a temperature of 4ºC for period of 15 h (Fig. 3). These specimens were immediately transferred into the hot water bath for thawing to a temperature of 60ºC for a period of 24 h (Fig. 4). This cycle of freeze-thaw was performed twice. After two cycles of moisture-conditioning, the specimens were kept in a cold water bath to bring down the temperature to 25ºC before subjecting to the Cantabro abrasion test. Table 8 indicates the mean wet abrasion loss values of moisture-conditioned specimens.

Fig. 3 Specimens in Freezer

Fig. 4 Specimens in Hot Water Bath

4.5 moisture-susceptibility

The moisture-susceptibility of PFC mixes was also evaluated using the retained tensile strength or Tensile Strength Ratio (TSR) method. In total six replicate specimens were prepared for each mix, compacted at

NLP, as per the experimental design. Three of the six replicates, were subjected to indirect tensile strength tests in dry-condition (ITSd). The remaining, three specimens of each mix was then subjected to wet-conditioning, and the indirect tensile strengths (ITSw) were evaluated. The wet-conditioning of the compacted PFC specimens was performed as per AASHTO T 283 withminormodifications. The specimens were firstsaturated by submerging in water and kept at water freezing temperature for about 15 h. The frozen specimens were immediately transferred into the hot water bath for thawing to a temperature of 60ºC for 24 h. After two such cycles of moisture conditioning, the specimens were kept in a cold water bath to bring down the temperature to 25ºC before testing. The mean ITS values of each mix for the dry and wet conditioned specimens were used to compute the tensile strength ratio (TSR). The following equations were used to compute ITS and TSR.

ITS = 2×× ×

PL D

u

π ... (6)

TSR = ITSITS

w

d×100 ... (7)

Where,

Pu = ultimate load required to fail specimen in the indirect tension test;

ITSw = mean indirect tensile strengths of wet conditioned specimens; and

ITSd = mean indirect tensile strengths of dry conditioned specimens.

The mean Indirect Tensile Strengths (ITS) of dry and wet conditioned PFC specimens and the Tensile Strength Ratios (TSR) of mixes are provided in Table 8.

The individual values of ITSd for the mixes were found to be in the range from 133 to 154 kPa. When, triplicate specimens were subjected to wet conditioning, the individual ITSw value was found varied between 126 and 154 kPa. According to ASTM D 7064(2004), the Tensile Strength Ratio (TSR) of PFC mixes should be at least 80%, so as to ensure resistance to moisture-susceptibility.

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Table 8 Results of moisture susceptibility Tests

BC (%)ITSd (kPa) ITSw (kPa) TSR WAL (%)

Individual Mean Individual Mean (%) Individual Mean

4.5151

146137

144 98.8-

--133 154 -153 142 -

5.0136

148151

139 94.529.0

28.4153 126 26.5154 142 29.6

4.6 Draindown Test

The PFC mixes are featured by coarser gradation and with higher binder contents compared to conventional dense bituminous mixes. The coarser gradation ensures higher air voids ratio and good hydraulic conductivity, while higher binder content imparts durability to themix by providing a thicker binder film over theaggregates. Increase in the binder content in PFC mixes will have a tendency to cause draindown of bitumen binder during mixing, storage and/or transportation. This will cause non-uniform distribution of bitumen anddeficientbindermixthatresultinraveling.Mixeswith excessive binder content causes bleeding, loss in permeability, and flushing and rutting (Kandhaland Mallick 1999). Hence, it is necessary to limit the binder content to avoid the subsequent problems of binder draindown.

The draindown characteristics of uncompacted bituminous mixes are evaluated using basket drainage test [(AASHTO T305 (2001); ASTM D 6390 (2005); MCSBW (2001)], which is similar to the Schellenberger basket drainage test. A sample of the uncompacted hot PFC mix will be placed in a wire basket, which is placed on a plate of known weight. The entire test set-up is placed in an oven for a specifiedperiodoftimeattheproductiontemperature.At the end of the heating period, the basket containing the sample is taken out from the oven along with the plate and the weight of the plate is determined. Fig. 5 shows the sketch of wire-basket, while Fig. 6 shows the test set-up used.

Fig. 5 Sketch of Wire-Basket

Fig. 6 Basket Drainage Test Set-up

The amount of draindown is considered to be that portion of material that separates itself from the sample as a whole and gets deposited on the plate. The wire basket to be used for this test is made of wire-mesh of 6.3 mm opening (0.25 inch). The depth of the wire-basket is 165 ± 16.5 mm, and the width is 108 ± 10.8 mm, with a basket bottom 25 ± 2.5 mm from the bottom of the wire basket assembly. The binder drainage loss is calculated by using Eq. (8).

Drainage loss, % = [(D-C) / (B-A)] *100 ... (8)

Where, A is the initial weight of empty wire basket

(g); B is the weight of wire basket and sample (g);

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C is the initial weight of empty catch plate or container (g); and

D is the weight of catch plate or container plus drained material.

The draindown tests on uncompacted PFC mix for a binder content of 5.0% was performed using the basket drainage test as per ASTM D 6390 (2005). The reason for performing the drainage test at a binder content of 5.0% was because; the results of volumetric properties, permeability, andunaged abrasion loss are satisfied.The tests indicate that the mixes with binder content intherangefrom4.5%to5.0%satisfiedtheoptimalmix criteria. Also, the mix with 5.0% binder content is likely to give a higher draindown value. Hence, the draindown tests were performed only on mixes with 5.0% binder content. The draindown test revealed that with neat bitumen the draindown was more than 0.3%. But, using waste plastics with a dosage of 0.4% of total weight of mix, resulted in the draindown value less than 0.3%.

4.7 Rutting

Porous asphalt exhibits a high resistance to permanent deformation due to stone-on-stone contact condition in the coarse aggregate skeleton. Huet et al. (1990) carried out comparative tests on porous asphalt made withpurebitumen;SBSmodifiedbitumen andpurebitumenwithmineral fibers on a test track.Overallrut depth after 600,000 cycles was about 5 mm with aslightadvantagegoingtotheSBSmodifiedbinderssections. Mallick et al. (2000) conducted tests on the four specimens prepared at design bitumen contents, all of the rut depths were less than 5 mm after 8000 cycles.

In the present study Immersion Wheel Tracking Device (IWTD) has been used to perform the rutting simulation. A rectangular slab specimen of 600 × 200 × 50 mm dimensions was prepared for a binder content of 5.0% and bulk density corresponding to NLP. The rut tests were conducted at a contact pressure of 0.7 MPa, speed of 0.468 kmph, and temperature of 50ºC. The testing was conducted continuously for about 6000 to 9000 passes (7 to 10 hours). These test conditions (parameters) vary depending upon the type of wheel-tracking devices

(Xiao et al. 2007; Kandhal and Cooley 2006; Shen et al. 2005; Jackson and Baldwin 2000). The vertical deformations under the wheel, at the centre of the slab specimen were continuously measured by Linear Variable Displacement Transducers (LVDTs) and recorded at regular intervals. The mean Rut Depth (RD) value for each Wheel Pass (WP) was computed from the two LVDT readings.

The trend between RD and Number of Wheel Passes (NWP) for the mix is shown in Fig. 7. It is evident fromthefigurethemixwillundergopost-compactionconsolidation to a depth in the range from 0.5 to 1.5 mm at the end of 500 wheel passes. The stripping of bitumen from the aggregate surface was not observed along the wheel path during the entire test period. The rut depth at 9500 cycles was found to be less than 6 mm.

Fig. 7 Rut Depth of PFC Mix

5 CoNClusIoNsThe following conclusions were drawn from the present study:1. The PFC mixes compacted at the gyration

level of N120 has exhibited good volumetric properties and permeability. Air voids content werefoundtobemorethan20%andcoefficientof permeability more than 100 m/day for the mixes at a binder content of 5.0%.

2. The mixes with Neat Bitumen (NB), for binder content of 5.0% and compaction level of NLP, the mean values of UAL and AAL were found to be within the acceptable limits of 20% and 30% respectively (ASTM D 7064, 2004).

3. The resistance to moisture-induced damage was found to be appreciable both in terms of TSR and WAL.

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4. Mix modified with the Waste Plastics (WP)helped in reducing drain down loss to below 0.30%.

5. The locking points (NLP) of most of the PFC mixes tested were found to vary between 50 and 75 gyrations, and the mixes compacted at NLP were found to provide consistent variations in the volumetric properties.

6. The results of the Immersion Wheel Tracking Tests (IWTT) indicated that the PFC mixes offer better resistance to rutting, when compared to that of other dense bitumen mixes as reported (Punith and Veeraragavan 2007; Xiao et al., 2007; Kandhal and Cooley, 2006; Shen et al., 2005; Jackson and Baldwin, 2000).

7. In the IWTT, there was no sign of stripping observed for the mix tested. Thus, the mix testedwasfoundtohavesufficientresistancetobinder-stripping due to mechanical action and exposure to moisture.

8. Themix of this gradation satisfied the stone-on-stone contact condition. This can be related to the presence of more quantity (> 20%) of aggregates passing 4.75 mm sieve (Mallick et al. 2000).

ReFeReNCes1. AASHTO T283. (2007). Standard Method of Test for

Resistance of Compacted Hot Mix Asphalt (HMA) to Moisture-Induced Damage, American Association of State HighwayandTransportationOfficials,Washington,D.C.

2. AASHTO T305. (2001). Standard Method of Test for Determination of Draindown Characteristics in Uncompacted Asphalt Mixtures, American Association of StateHighwayandTransportationOfficials,Washington,D.C.

3. AI (2001). “Superpave Mix Design.” SP-2. 3rd Ed., Asphalt Institute, Lexington.

4. ASTM D 2041 (2011). Standard Test Method for Theoretical Maximum Specific Gravity and Density ofBituminous Paving Mixtures, West Conshohocken, P.A.

5. ASTM D 6390. (2005). Standard Test Method for Determination of Draindown Characteristics in Uncompacted Asphalt Mixtures, West Conshohocken, P.A.

6. ASTM D 7064. (2004). Standard Practice for Open-Graded Friction Course (OGFC) Mix Design, West Conshohocken, P.A.

7. Brown, E.R., and Cooley, L.A. (1999). “Designing Stone Matrix Asphalt Mixtures for Rut-Resistant Pavement.” Report 425, National Cooperative Highway Research Program, Transportation Research Board, Washington, D.C.

8. Chen, J.S., Lin, K.Y., and Young, S.Y. (2004). “Effects of Crack Width and Permeability on Moisture-Induced Damage of Pavements.” J. Materials in Civil Engineering, 16(3), 276-282.

9. Federal Aviation Administration (FAA). (1997). “Measurement, Construction, and Maintenance of Skid-Resistant Airport Pavement Surfaces.” Advisory Circular No. 150/5320-12C, U.S. Department of Transportation, Washington, D.C.

10. Federal Aviation Administration (FAA). (2001). “Hot Mix Asphalt Paving Handbook.” Advisory Circular No. 150/5370-14A, U.S. Department of Transportation, Washington, D.C.

11. Focus (2005). “Quiet Pavements: Lessons Learned from Europe.” <www.tfhrc.gov/focus/apr05> (Jul. 18, 2005).

12. Halstead, W.J. (1978). “Open-Graded Friction Courses for Highways.” Synthesis of Highway Practice 49, National Cooperative Highway Research Program, Transport Research Board, Washington, D.C.

13. Huber, G. (2000). “Performance Survey on Open-Graded Friction Course Mixes.” Synthesis of Highway Practice 284, National Cooperative Highway Research Program, Transportation Research Board, Washington, D.C.

14. Huet, M., Boissoudy, A.D., Gramsammer, J.C., Bauduin, A., and Samanos, J. (1990). “Experiments with Porous Asphalt on the Nantes Fatigue Test Track.” J. Transport Research Record-1265, 54-58.

15. IS 1201 – 1220 (1978). Methods for Testing Tar and Bituminous Materials. Bureau of Indian Standards, New Delhi.

16. IS 2386 (P1 – P8)(1963). Methods of Test for Aggregates for Concrete. Bureau of Indian Standards, New Delhi.

17. Jackson, N.M., and Baldwin, C.D. (2000). “Assessing the Relative Rutting Susceptibility of HMA in the Laboratory with the Asphalt Pavement Analyzer.” International J. Pavement Engineering, 1(3), 203-217.

18. Jain, P.K., Mohan, S., and Sengupta, J.B. (2007). “Optimization of Porous Bituminous Concrete Through the Use of Special Binders and Development of Design Guidelines.” Highway Research Bulletin, 77, Indian Roads Congress, New Delhi, India, 11-22.

19. Jaiswal, L. (2005). “Development and Evaluation of Permeable Friction Course Mix Design for Florida Conditions.” M.E. Thesis, Graduate School of the University of Florida, F.L.

20. Kandhal, P.S., and Cooley, L.A. Jr. (2006). “Simulative Performance Test for Hot Mix Asphalt Using Asphalt Pavement Analyzer.” J. ASTM International, 3(5), Paper ID JAI 12255, 9.

TeChNICal PaPeRs


21. Kandhal, P.S., and Mallick, R.B. (1999). “Design of New-Generation Open-Graded Friction Courses.” Report No. 99-3, National Center of Asphalt Technology, Auburn, AL.

22. Mallick, R.B., Kandhal, P.S., Cooley, L.A. Jr., and Watson, D.E. (2000). “Design, Construction, and Performance of New-Generation Open-Graded Friction Courses.” J. Association of Asphalt Paving Technologists, 69, 391-423.

23. Manual for Construction and Supervision of Bituminous Works (MCSBW). (2001). Ministry of Road Transport and Highways, Indian Roads Congress, New Delhi, India.

24. National Asphalt Specification (NAS). (2004). 2nd Ed., Australian Asphalt Pavement Association, Kew Victoria, Australia.

25. Nicholls, J.C. (1997). “Review of UK Porous Asphalt Trials.” Transport Research Laboratory: Report 264, London, U.K.

26. Nielsen, C.B., Bendtsen, H., Andersen, B., Larsen, H.J.E. (2005). “Noise Reducing Pavements in Japan – Study Tour Report.” Danish Road Institute: Technical Note 31, Road Directorate, Denmark.

27. Pine, W.J. (1997). “Superpave Gyratory Compaction and the Ndesign Table.” Internal Report to the Illinois Department of Transportation.

28. Prowel, B.D., and Brown, E.R. (2007). “Superpave Mix Design: Verifying Gyration Levels in the Ndesign Table.” Report 573, National Cooperative Highway Research Program, Transportation Research Board, Washington, D.C.

29. Punith,V., S., and Veeraragavan, A. (2007). “Behaviour of Asphalt Concrete Mixtures with Reclaimed Polyethylene as Additive.” J. Materials in Civil Engineering, 19(6), 500-507.

30. Punith,V.,S., Suresha, S.N., Veeraragavan, A., Raju, S., and Bose, S. (2004). “Characterization of Polymer and Fiber Modified Porous Asphalt Mixtures.” 83rd Annual Meeting (CD-ROM), Transportation Research Board, Washington, D.C.

31. Shen, D.H., Kuo, M.F., Du, J.C. (2005). “Properties of Gap-Aggregate Gradation Asphalt Mixture and Permanent Deformation.” J. Construction and Building Materials, 19, 147-153.

32. Southern African Bitumen Association (Sabita). (1995). “The Design and Use of Porous Asphalt Mixes.” Manual 17, Roggebaai, South Africa.

33. Sridhar, R., Suresha, S.N., Bose, S., and Veeraragavan, A. (2005). “StudyofPolymerandFibreModifiedOpenGraded Friction Courses.” J. Indian Roads Congress, 514, 66 (2), 291-318.

34. Suresha, S.N. (2004). “Characterization of Polymer and FibreModifiedOpen-GradedFrictionCourseMixtures.”M.E. Thesis, Bangalore University, India.

35. Suresha, S.N, Varghese George and Ravi Shankar, A.U. (2007). “Investigation of Porous Friction Courses (PFC) and Mixes: a Brief Overview” Indian Highways Vol. 35, No.7, pp. 21-43.

36. Suresha, S.N. (2008). “Experimental Investigations on the Properties and Developments of Design Guidelines for Porous Friction Course Mixes.” Ph.D. Thesis, NIT K Mangalore, India.

37. Suresha S.N., Varghese George, and Ravi Shankar, A.U. (2009a). “A Comparative Study on Properties of Porous FrictionCourseMixeswithNeatBitumenandModifiedBinders,” Construction and Building Materials, 23 (3), pp. 1211-1217.

38. Suresha S.N., George Varghese, and Ravi Shankar, A.U. (2009b). “Characterization of Porous Friction Course Mixes for Different Marshall Compaction Efforts,” Construction and Building Materials, 23 (8), pp. 2887-2893.

39. Suresha S.N., Varghese George, and Ravi Shankar, A.U. (2009c). “Evaluation of Properties of Porous Friction Course (PFC) Mixes for Different Gyration Levels.” Journal of Materials in Civil Engineering, 21(12), pp. 789 -796.

40. Suresha S.N., Varghese George, and Ravi Shankar, A.U. (2010a). “Laboratory and Theoretical Evaluation of Clogging Behaviour of Porous Friction Course (PFC) Mixes,” International Journal of Pavement Engineering, 11 (1), pp. 61 -70.

41. Suresha S.N., Varghese George, and Ravi Shankar, A.U. (2010b). “Properties of Cellulose Fibres and Waste Plastics Modified Porous Friction Course Mixes.” TheBaltic Journal of Road and Bridge Engineering, 5(3), pp. 156-163.

42. Suresha S.N., Varghese George, and Ravi Shankar, A.U. (2010c). “Effect of Aggregate Gradations on Properties of Porous Friction Course Mixes.” Materials and Structures, 43(6), pp. 789-801.

43. Transit New Zealand (TNZ). (2007). “Specificationfor Open Graded Porous Asphalt.” SP/SP11 070704, <http://www.transit.govt.nz/technical/specifications.jsp>(Jan.28, 2008).

44. Varadhan, A. (2004). “Evaluation of Open-Graded and Bonded Friction Course for Florida.” M.E. thesis, Graduate School of the University of Florida, F.L.

45. Vavrik, W.R., and Carpenter, S.H. (1998). “Calculating AirVoidsatSpecifiedNumberofGyrationsinSuperpaveGyratory Compactor.” J. Transportation Research Record-1630, Asphalt Mixtures: Stiffness Characterization, Variables, and Performance, 117-125.

46. Verhaeghe, B.M.J.A., Rust, F.C., Vos, R.M., and Visser, A.T. (1994). “PropertiesofPolymerandFibre-ModifiedPorous Asphalt Mixes.” Asphalt Review, 13 (4), 17-23.

47. Xiao, F., Amirkhanian, S., and Juang, C.H. (2007). “Rutting Resistance of Rubberized Asphalt Concrete Pavements Containing Reclaimed Asphalt Pavement Mixtures.” J. Materials in Civil Engineering, 19(6), 475-483.


beNeFITs oF meChaNIsTIC aPPRoaCh IN FleXIble PaVemeNT DesIGN

naGrale PraShant P* and More deePaK**

* Professor & HOD** M.E. Student

absTRaCTThe present work was undertaken to evaluate the benefit ofmechanisticapproachinflexiblepavementdesign.Twotypesofsoils (soil-A and soil-B) were selected in study. The number of laboratorytestswasconductedonthesesoilsfortheirclassification.The static triaxial test was conducted on these soils as well as on otherpavementslayersmaterialataconfiningpressureof40kPa.The results obtained from static triaxial test were further used in finite elementmodeling of the flexible pavement as per Indianpractice code IRC:37-2001.

To understand the response of pavement, the finite elementmodelingiscarriedoutonmultilayeredflexiblepavementsrestingon subgrade soil – A and B using commercial software ANSYS. The vertical compressive strain developed at the top of subgrade soil was further used for estimation of number of cycles taken by pavement. The study shows that the pavement resting on subgrade soil -A modeled as per IRC:37-2001 for a traffic intensity of150 msa may take 694 msa. i.e. almost 4.62 times more than conventional practices.

1 NeeD meChaNIsTIC aPPRoaCh PaVemeNT DesIGN

The flexible pavements in India are designed andconstructed based on CBR value of subgrade soils. Once the 4 days soaked CBR value of subgrade soil and traffic intensity for which pavement is tobe designed known is the thickness of other layers can be directly read out from the chart given by IRC:37-2001. The major drawback of this method is that the pavement can be designed upto traffic intensity of 150 msa. Also, the suitability of aggregate for the pavement layers is decided based on

guideline given by Indian Standard Specification.For example; the aggregate having crushing value less than 45% can be accepted as a sub base and base course material.

Suppose there are two aggregates such as aggregate-A and aggregate-B having crushing value 8% and 44% as per guideline both these aggregates can be accepted as a sub base and base coarse material but looking to properties, aggregate-A is much stronger than aggregate-B and if the pavement designed with aggregate-A will be over designed. Keeping in view the above draw backs of existing methods it is urgent need to develop the mechanistic – empirical pavement (M-Epavement)designapproachfordesignofflexiblepavements. This methodology has better capability to characterization of different material properties and loading conditions and has ability to evaluate different design alternatives on economic basis.

1.1 how Does mechanistic Pavement Work?

The following description is necessarily somewhat genericandbasedprimarilyontheanalysisofflexiblepavement; however the system has been designed in a modular fashion, which with the modular nature of the software, allows the same elements of design with type-specificsub-modules.TheM-Epavementdesignguide performs a time-stepping process, illustrated in thefigurebelow:

CED, Sardar Patel College of Engineering, Andheri (W), Mumbai

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2 lITeRaTuRe ReVIeW

Stephen F Brown (1997), developed the concept of effective stiffness deterioration to deal with fatigue cracking in pavement design, Theyse et.al. (1953), concluded subgrade permanent deformation based on the data generated from a series of Heavy Vehicle Simulator (HVS). Pavement performance data is generated over the long-term that may be used to investigate pavement behavior in general and calibrate mechanistic empirical design models. The mechanistic empirical method of design is based on the mechanics of material that relates an input, such as a wheel load, to an output or pavement response, such as stress or strain. The response values are used to predict distress from laboratory test and field performance data.Dependence on observed performance is necessary because theory alone has not proven sufficient todesign pavements realistically. With a view to have unified approach for working out design of flexiblepavement in the country the IRC first brought outguidelines in 1970 with the name of (IRC:37-1970). Thesesguidelinefurthermodifiedin1984and2001and published with the name of (IRC:37-1984) and (IRC:37-2001). Now IRC:37-2001 is in use for design of flexible pavements in India. This practice codewas developed from original CBR method given by California Division of Highway in 1934.

Many researchers are of the opinion that the design offlexiblepavementinvolvestheinterplayofseveralvariables such as wheel loads, traffic, climate, andterrain and subgrade conditions. During the literature review it was found that a very few research work has beendoneintheareaofmodelingofflexiblepavementand its economics with conventional practice by using commercial software ANSYS.

3 eXPeRImeNTal PRoGRamTwo types of soils were selected for this study. The soils have been referred to as Subgrade Soil-A and Subgrade Soil-B. The index properties; liquid limit, plastic limit, plasticity index, and other important soil propertiesasperAASHTOandUSsoilclassificationsystem have been presented in Table 1. The soil-A was silty-clay of low plasticity (A-2-4) and soil-B was sandy- silt (A-3). Chandra and Mehndiratta (2002), reported that confinment in the pavementdue to shoulder and surrounding soil is in the range of 26 to 40 kPa, hence Triaxial test were conducted on subgrade soils as well as different pavement layer materialsatconfiningpressureof40kPa,stress-straincurve drawn and the value of initial tangent modulus calculated, the same value further used as input parameter in Finite Element Modeling of flexiblepavement. Table 2 shows the value of initial tangent modulus and poison’s ratio for subgrade soil and other pavement layer materials.

Table 1 Properties of the subgrade soil

Properties soil - a soil - bMaximum Dry Density 17.70 19.30Optimum Moisture Content 14.00 11.30SpecificGravity 2.21 2.40Liquid Limit (%) 28.00 --Plasticity Index (%) 8.10 --D50 (mm) 0.11 --Fraction Passing 75 micron 32.00 7.00CBR (%) 1.96 6.30Initial Tangent Modulus (kg/cm2) 111.80 162.10ClassificationasperAASHTO A – 2 - 4 A - 3Typical name Silty clay of

Low plasticitySandy – silt

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Table 2 Value of Initial Tangent modulus of other Pavement layers

subbase base Dbm bCE – value (kg/cm2) 701.20 992.00 2696.70 4033.30

μ-value 0.30 0.30 0.50 0.50

DBM – Dense Bitumenous Macadam, BC – Bitumenous concrete

4 FINITe elemeNT aNalYsIs

Finite element method was used to analyze the pavement section resting on subgrade soils. The software ANSYS was used for finite elementmodeling. The pavement section was modeled as a 2-D axisymmetric problem and 8-noded structural solid element was used for the analysis. The stresses and deformations within the pavement section and vertical strain at top of the subgrade were captured.

Afive-layer flexible pavement systemwasmodeledand analyzed. Fig. 1showsthetypicalmodelforfive-layeredflexiblepavementrestingonsubgradesoil-ASimilar models were developed for pavement resting on subgrade soils-B. The thickness of each layer in the pavement was modelled as per lndian practice code IRC:37-2001. For design traffic of 150 msa,the thicknesses of each layer in the pavement section resting on subgrade soil-A and soil-B are presented in Table 3.

Table 3 Pavement Composition for Traffic Intensity of 150 msa (IRC:37-2001)

subgrade soil

CbR (%)

subgrade (mm)

sub base (mm)

base (mm)

Dbm (mm)

bC (mm)

Total (mm)

Soil A 2 500 460 250 215 50 1475Soil B 6 500 260 250 160 50 1220

Fig. 1 2-D Axisymmetric Finite Element Model Used In Present Study

A pressure equal to single axle wheel load has been assumed to be applied at the surface and distributed over a circular area of radius 15 cm. For application of FEM in the pavement analysis, the layered system of infiniteextentisreducedtoanapproximatesizewithfinitedimension.Therighthandboundaryisprovidedat 110 cm from outer edge of the loaded area, which is more than 7 times loaded area.

The elasto-plastic analysis was carried out to evaluate the primary response of the pavement resting on subgrade soils. The multilinear isotropic hardening model (MISO) available in ANSYS was used to evaluate the stresses, strains and deformations within the pavement sections. The mixed incremental method is used in present study for elasto-plastic analysis of 2-D axisymetric finite element model. This method

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combines the advantages of both the incremental and the iterative schemes. The external load, here, is applied incrementally, but after each increment, successive iterations are performed to achieve equilibrium.

In general, for the jth load increment, the state of deformation, stress and strain at the end of (j – 1)th load increment is known, i.e. {δ}j–1, {ε}j–1, {σ}j–1 are known, the subscripts (j – 1) refers to the load increment. The general procedure of this method is follows,

i) Forthefirstiterationofthejth load increment,

∆ ∆F Kj j j{ } = { }−

11

1δ ... (1)

which can be solved to obtain,

∆ ∆δ{ } = { }−1

11

j j jK F ... (2a)

obtain, ∆ ∆ε δ{ } = [ ]{ }1 1j jB ... (2b)

and ∆ ∆σ δ{ } = [ ]{ }1 1j jD ... (2c)

ii) Accumulated displacements, strains and stresses at the end of 1th iteration can be expressed as,

δ δ δ{ } ={ } +{ }−

11

1j j j∆ ... (3a)

ε ε ε{ } ={ } +{ }−

11

1j j j∆ ... (3b)

σ σ σ{ } ={ } +{ }−

11

1j j j∆ ... (3c)

iii) Obtain the principal stresses, σ pj

{ }1 and strains,

ε pj

{ }1 and then,

Etj1 and v ft

jp

jp

j1 1 1= { } { }( )σ ε, ... (4a)

and D D E vtj

tj[ ]= ( )

1 1, ... (4b)

iv) Equilibrated force vector will then be given by,

F B D B dveqj t j

v{ } = [ ] [ ][ ]{ }∫1 1δ ... (5a)

Therefore, the residual force vector,

ψ{ } = { } −{ }( )1 1 1

j jeq

jF F ... (5b)

v) Check for convergence,

ψ ψ1 1

0 5

1 1

0 5 100

j T j

j T jF F

{ }{ }

{ }{ }

× ≤

.

. Tolerance Limit ... (6)

In general, for any ith iteration of the jth load increment, force-displacement equation system will be -

ψ δ{ } = { }−−

ij j

ijK1

1 ∆ ... (7a)

where [K j – 1] is the constant stiffness matrix obtained from the state of stress and strain attained at the end of the (j – 1)th load increment.

Therefore,

∆ ∆δ ψ{ } = { }− −

ij j

ijK 1 1 ...(7b)

∆ ∆ε δ{ } = [ ]{ }ij

ijB ... (7c)

∆ ∆σ σ{ } = [ ]{ }ij

ijD ... (7d)

The accumulated state of deformation, strain and stress is given by,

δ δ δ{ } ={ } { }−

ij j

ij1 ∆ ... (8a)

ε ε ε{ } ={ } { }−

ij j

ij1 ∆ ... (8b)

σ σ σ{ } ={ } { }−

ij j

ij1 ∆ ... (8c)

The state of principal stresses and strains will be given

by σ p i

j{ } and ε p i

j{ } respectively, and the tangent

modulii by E vtij

tij, and the elasticity matrix,

D D E vtij

tij[ ]= ( )

, ... (9)

The equilibrated force vector,

F B D B dveq i

j T

v{ } = [ ] [ ][ ]∫ ... (10)

and the residual force vector,

ψ ψ{ } ={ } −{ }−ij

ij

eq i

jF1

... (11)

The check for convergence will be given by,

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ψ ψ

ψ ψ

ij T

ij

ij T

ij

{ }{ }

{ }{ }

× ≤

− −

0 5

1 1

0 5 100

.

. Tolerance Limit ... (12)

the equilibrium and therefore the convergence for jth load increment is considered to have been achieved when this force residual is bellow certain tolerance level, otherwise iteration are continue until the above iterationsatisfied.Oncetheconvergenceisachieved,the next increment 1

1+∆ jF is applied and the process

isrepeateduntilthefinalloadlevelisreached.Inthismethod, the equilibrium can be achieved at the end of every load increment. It makes use of a variable stiffness matrix for each new load increment while maintaining it constant within a given load increment so as to achieve convergence and therefore the equilibrium iteratively.

5 eValuaTIoN oF beNeFITs

The proposed methodology is a mechanistic-empirical designapproachfordesignofflexiblepavementusedto evaluate the number of cycles taken by pavement with varying layer thicknesses of subbase and base. It has a better capability of characterizing different material properties and loading condition, and has the ability to evaluate alternatives on an economics basis.Structuralfailureinaflexiblepavementisoftwotypes, namely surface cracking and rutting. Cracking is due to fatigue caused by repeated application of load intheboundedlayergeneratedbythetraffic,itisdueto horizontal tensile strain developed at the bottom of bituminous layer which have been considered as chief elements of the pavement failure. Rutting is due to accumulation of pavement deformation in various layers along the wheel path.The scope of present study is restricted to rutting being the failure criterion, IRC:37-2001 considers a rut depth of 20 mm to be a failurecriterionforflexiblepavementandtheruttingin the following equation is,

N20 = 4.1656 ×

−10 184 5337

εz

.

... (13)

Where,

N20 = Number of cumulative standard axles to produce rutting depth of 20 mm.

εz = Vertical compressive subgrade strain (micro strain) at top of subgrade.

5.1 Pavement Response

The 2-D axisymmetric finite element model wasdeveloped for the pavement resting on subgrade Soil-A and Soil-B in commercial software ANSYS and pavement response within pavement and vertical compressive strain developed at the top of subgrade was captured also the parametric study was carried out for two different cases.

Case-I: Keeping all other layers constant, the thickness of sub base varied and vertical compressive strain developed at top of subgrade soil - A and subgrade soil – B captured.

Case-II: Keeping all other layers constant only the thickness of base varied and vertical compressive strain developed at top of subgrade-A and subgrade –B captured.

Table 4 and 5 shows the variation of pavement response. i.e. vertical compressive strain, vertical compressive stress and deformation at top of subgrade Soil - A and Soil – B. The result shows that the value of vertical compressive strain and deformation at the top of subgrade consistently increases with decrease in the thickness of subbase for a constant thickness of Base course and DBM course. Similarly the value of vertical compressive strain and deformation increase with decrease in the thickness of base for constant value of subbase thickness and DBM thickness.

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Table 4 Variation of Pavement Response at the Top of subgrade soil - a

base = 250 (mm), Dbm = 215 (mm) subbase = 460 (mm), Dbm = 215 (mm)subbase

(mm)εz

(micron)σz

(kg/cm2)δz

(mm)base(mm)

εz (micron)

σz (kg/cm2)

δz (mm)

460 1212.40 0.1399 0.556 250 1212.40 0.1399 0.556450 1219.50 0.1390 0.558 225 1231.30 0.1412 0.561425 1238.10 0.1418 0.563 200 1252.10 0.1433 0.566400 1258.50 0.1438 0.568 175 1274.90 0.1455 0.573375 1280.60 0.1461 0.574 150 1300.10 0.1481 0.579350 1304.80 0.1485 0.580 125 1328.10 0.1509 0.586325 1331.20 0.1511 0.586 100 1359.20 0.1541 0.594300 1360.20 0.1541 0.593 75 1394.00 0.1576 0.604275 1391.90 0.1573 0.601 50 1433.10 0.1616 0.614250 1429.60 0.1607 0.610 25 1477.00 0.1661 0.625225 1465.40 0.1646 0.618 0 1528.40 0.1713 0.638

Table 5 Variation of Pavement Response at the Top of subgrade soil-b


(mm)εz

(micron)σz

(kg/cm2)δz

(mm)base (mm)

εz (micron)

σz (kg/cm2)

δz (mm)

260 1184.80 0.1903 0.473 250 1184.80 0.1903 0.556250 1202.60 0.1929 0.477 225 1233.20 0.1974 0.561225 1250.50 0.1999 0.489 200 1287.40 0.2054 0.566200 1303.70 0.2077 0.501 175 1348.20 0.2144 0.573175 1363.10 0.2164 0.515 150 1416.60 0.2245 0.579150 1429.30 0.2261 0.530 125 1494.00 0.2359 0.586125 1503.50 0.2370 0.547 100 1581.80 0.2489 0.594100 1586.60 0.2491 0.566 75 1681.90 0.2637 0.60475 1679.80 0.2629 0.587 50 1796.70 0.2808 0.614

The value of vertical compressive strain at the top of subgrade soil - A and soil - B for a standard pavement section modeled as per IRC:37-2001 found to be 1212.40 micron and 1184.80 micron respectively. This value increase to 1360.20 micron when only subbase varied from 460 mm to 300 mm and it increase to 1359.20 micron when only base is varied from 250 mm to 100 mm for a pavement resting on subgrade soil - A also, this value increase to 1586.60 micron when only subbase varied from 260 mm to 100 mm and it increase to 1581.80 micron when only base is varied from 250 mm to 100 mm for a pavement resting on subgrade soil - B.

5.2 effect on service life

Considering rutting as a failure criterion, the number of cycles taken by the pavement section resting on subgrade soil - A and soil - B is evaluated using rutting equation and the results shown in Table 6 and 7. The number of cycles taken by the standard pavement section resting on subgrade soil – A and soil – B was 694.301 msa and 770 714 msa. Whereas, for constant other layers, only subbase thickness was varied to 450 mm, 350 mm and 250 mm, the number of the cycles taken by the pavement was reduce to 676.169 msa, 497.664 msa and 328.913 msa respectively. Similarly for constant other layers, only base thickness was

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varied to 200 mm, 100 mm and 50 mm. the number of the cycles taken by the pavement reduced to 599.945 msa, 413.533 msa and 325.699 msa respectively. Similar variation was observed for pavement section resting on subgrade soil B and presented in Table 7. It indicates if the pavement is modelled by mechanistic

– empirical approach considering actual properties of subgrade soils and other pavement layers the thicknesses of layers required may be much lower than the pavement designed as per Indian Practice code IRC:37-2001.

Table 6 Variation of Vertical Compressive strain at Top of subgrade and Number of Cycle Taken by Pavement Resting on subgrade soil-a


(mm)εz

(micron)(NR)

(msa)base (mm)

εz (micron)

(NR) (msa)

460 1212.40 694.301 250 1212.40 694.308450 1219.50 676.169 225 1231.30 647.284425 1238.10 631.322 200 1252.10 599.945400 1258.50 586.237 175 1274.90 552.816375 1280.60 541.747 150 1300.10 505.873350 1304.80 497.664 125 1328.10 459.289325 1331.20 454.460 100 1359.20 413.533300 1360.20 412.157 75 1394.00 368.751275 1391.90 371.280 50 1433.10 325.287250 1429.60 328.913 25 1477.00 283.699225 1465.40 294.023 0 1528.40 242.942

Table 7 Variation of Vertical Compressive strain at top of subgrade and Number of Cycle Taken by Pavement Resting on subgrade soil-b


(mm)εz

(micron)(NR)

(msa)base (mm)

εz (micron)

(NR) (msa)

260 1184.80 770.714 250 1184.80 770.714250 1202.60 720.331 225 1233.20 642.775225 1250.50 603.433 200 1287.40 528.895200 1303.70 499.570 175 1348.20 429.052175 1363.10 408.196 150 1416.60 342.821150 1429.30 329.226 125 1494.00 269.355125 1503.50 261.724 100 1581.80 207.914100 1586.60 205.078 75 1681.90 157.42375 1679.80 158.317 50 1796.70 116.698

6 CoNClusIoN

From the present study it is observed that mechanistic approach is a valuable tool for design of flexiblepavement. It gives more realistic thickness of pavement layers. Following important conclusion are drawn from the present study.

1. The value of vertical compressive strain and deformation at the top of subgrade consistently

increases with decrease in the thickness of subbase for a constant thickness of Base course and DBM course.

2. The value of vertical compressive strain and deformation at the top of subgrade consistently increases with decrease in the thickness of base for a constant thickness of subbase course and DBM course.

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3. The value of vertical compressive strain at the top of subgrade soil - A and soil – B for a standard pavement section designed as per IRC:37-2001 for atrafficintensityof150msaare1212.40micronand 1184 micron respectively; the corresponding number of cycles taken by the pavement are 694.301 msa and 770.714 msa respectively.

4. The number of cycles taken by the standard pavement section resting on subgrade soil – A was 694.301 msa. For constant other layers, if only subbase thickness varied from 460 mm to 450 mm, 350 mm and 250 mm. the number of the cycles taken by the pavement is reduce to 676.169 msa, 497.664 msa and 328.913 msa respectively.

5. The number of cycles taken by the standard pavement section resting on subgrade soil – B was 770.714 msa. For constant other layers, if only subbase thickness varied from 260 mm to 200 mm, 150 mm and 100 mm. the number of the cycles taken by the pavement is reduce to 499.57 msa, 329.226 msa and 205.078 msa respectively.

ReFeReNCes1. Stephen F Brown (1997), “Achievements and Challenges

in Asphalt Pavement Engineering”, ISAP - 8th International Conference on Asphalt Pavements - Seattle, pp 1 - 22.

2. H. L. Theyse, T. P. Hoover, J. T. Harvey, C. L. Monismith and N. F. Coetzee (1953), “A Mechanistic-Empirical Subgrade Design Model Based on Heavy Vehicle Simulator Test Results”, ASCE Geo Institute, 1801 Alexander Bell Drive Reston, VA 20191-4400 USA pp 195 – 202.

3. S L Webstar (1992),”Geogrid Reinforcement Bases Course for Flexible Pavements for Light Aircrafts”, Technical Report GL 93-6, ASCE Waterway Experiment Section, Vicksburg Mississippi, USA, pp 886 – 887.

4. P P Nagrale, S. Chandra and Prof M N Viladkar (2006), “BenefitsofFibreReinforcedSubgradeSoilsinFlexiblePavement”, Journal of the Institute of Engineers India, vol- 87, May 2006, pp 53 – 57.

5. S. Chandra, H. C. Mahindiratta (2002), “Effect of Shoulder on Life of Flexible Pavements”, HRB – 67, Indian Road Congress, New Delhi, 2002, pp 37 – 46.

6. IRC:37-2001. ‘Guideline for the Design of Flexible Pavements’. Indian Roads Congress, New Delhi, 2001.

7. Ministry of Road Transport and Highways (MORTH). “Specifications for Road and Bridge Works”. IndianRoads Congress, New Delhi, Section 400, pp 100 – 104.


DesIGN, CoNsTRuCTIoN aND PeRFoRmaNCe oF PoRous asPhalT PaVemeNT FoR RaINWaTeR haRVesTING

PrithVi SinGh Kandhal* and SaPan MiShra**

* Associate Director Emeritus, US National Center for Asphalt Technology, Auburn University, Alabama, USA E-mail: [email protected]** Executive Engineer, Jaipur Development Authority E-mail: [email protected]

absTRaCTMulti-storied commercial and residential buildings, which significantlyincreasethedemandforwatersupply,areincreasinglybeing constructed in urban India. In many states of India such as Bihar, Delhi, Gujarat, Haryana, Punjab, Rajasthan and Tamilnadu, the ground water is plunging at an alarming rate. Responsible town planners, architects and civil engineers must be proactive and integrate rainwater harvesting techniques in the design of all types of buildings, parking lots and low-trafficked roads/streets. For example, Public Works Department (Buildings and Roads) engineers can integrate government buildings with porous asphalt parking lot. This would recharge the ground water in over-exploited/critical areas of India. The revolutionary technology presented in this paper addresses that very need.

The porous asphalt pavement which can be used for parking lot or low-trafficked roads/streets works like this. The top 75 mmasphalt layer is specially designed to make it porous. Rainwater goes through it rapidly without any ponding. The water is then stored in an underlying open-graded stone bed, which is about 225 mm thick. From there, water percolates slowly into the underlying soil. The porous parking lot or street can be integrated with a roof rainwater harvesting system in the buildings adjacent to it by diverting the roof water to the stone bed. Recently, the Jaipur Development Authority has constructed the first everporous asphalt parking lot in India. This paper gives the details of its design, construction and performance.

1 INTRoDuCTIoN

Multi-storied commercial and residential buildings, which significantly increase the demand for watersupply, are increasingly being constructed in urban India. However, additional water supply is hardly available. The Central Ground Water Board (CGWB) has identified about 800 regions in India in whichground water level is plunging at an alarming rate. These regions are located in Rajasthan, Madhya Pradesh, Punjab, Haryana, Gujarat, Bihar, Delhi and Tamilnadu.

According to the 2004 data of CGWB, for every 125 units of ground water being taken out in Jaipur, only 100 units are replenished by rain. It is estimated that the ground water level in Jaipur is falling at the rate of about one meter every year.

According to the CGWB, all underground water will be depleted in Jaipur in about 10 years’ time1. There is some water in rocks below 100 meters but that water contains harmful elements in it and may not be safe for drinking.

There is an urgent need to act now to recharge the ground water in over-exploited/critical areas of India. The Ground Water Advisory Council on ArtificialRecharge of the Ministry of Water Resources has suggested that there is a need to develop separate technologiesforrechargespecificallyforurbanareas.This paper addresses that very need.

The ground water problem was also felt in the US in urban areas, where rainwater simply runs off without charging ground water. The Franklin Institute of Philadelphia, Pennsylvania was tasked in early 1970s to develop technologies to address the problem of plungingwater table inurbanareas.Thefirstauthorhad the privilege of brainstorming with the Franklin Institute researchers in developing the concept of porous asphalt parking lot for urban areas2. This concept was tried in some pilot projects and was very successful. The concept was later fully developed in the 1980s. It was also successfully tried on a road in Chandler, Arizona. At the present time it is being used in many states of the US primarily for storm water

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management3. The State of California has built over 150 projects since 1980. About 95% of rainwater falling on a porous asphalt parking lot goes to recharge ground water. Even in case of open ground with vegetation in rural areas, only about 33% of rainwater goes to recharge ground water primarily due to evapo-transpiration losses. This percentage is believed to be significantlylowerinhotclimateofRajasthan.

This proven concept of building porous asphalt pavements was declared Outstanding Engineering Project in 2000 by the American Society of Civil Engineers.

Responsible town planners, architects and civil engineers must be proactive and integrate rainwater harvesting techniques in the design of all types of buildings,parkinglotsandlow-traffickedroads/streets.For example, Public Works Department (Buildings and Roads) engineers can integrate government buildings with porous asphalt parking lot4,5. This would recharge the ground water in over-exploited/critical areas of India. The revolutionary technology presented in this paper addresses that very need.

2 CoNCePT oF PoRous asPhalT PaVemeNT TeChNoloGY

This technology is based on building porous asphalt pavements which can be used for parking lots, recreationalareas,orlow-traffickedstreetsandroads.The porous asphalt pavement works like this Fig. 1. The top 50-100 mm thick asphalt layer is specially designed to make it porous. Rainwater goes through it rapidly without any ponding at the surface. The water is then stored in an underlying open-graded stone bed also called stone reservoir. From there, water percolates slowly into the underlying natural soil (subgrade). There is hardly any evaporation loss. Porous parking lots or streets can be integrated with roof rainwater harvesting systems in the buildings adjacent to it as explained later. There is no need to bore deep wells or construct deep pits.

Fig. 1 Schematic of Porous Asphalt Pavement

A typical cross-section of the porous asphalt pavement system is shown in Fig. 2. The pavement consists of the following components from top downwards:

Fig. 2 Typical Cross-Section of Porous Asphalt Pavement System

● Open-graded, porous asphalt course 50-100 mm (typically 75 mm) thick

● 12.5mmnominalsizeaggregatechokinglayer 25-50 mm thick (this is placed over the stone bed so as to stabilize it and facilitate asphalt paving over it)

● Clean,uniformlygraded40-75mmsizecrushed aggregate compacted layer to act as a water reservoir (typically it is 225 mm thick and contains more than 40% voids to accommodate rainwater)

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● Non-wovengeotextiletoseparatethesoilsubgrade and water reservoir course so that soil particles do not migrate from the subgrade into the stone water reservoir course thus choking it. Alternately, a 75mmthickstonefiltercourseconsistingof 10-25 mm size aggregate can be provided if good aggregate gradation control can be maintained.

● Uncompacted natural soil subgrade(bed)

As mentioned earlier, rooftop rainwater harvesting systems of the buildings adjacent to porous parking lots or streets can be integrated into the porous asphalt pavement. A typical rooftop rainwater harvesting system for buildings consists of the following elements:

1. Vertical down pipes for carrying the water from the roof to ground level and a horizontal pipe system for connecting all down pipes.

2. Asiltingpitfittedwithasteelscreen

3. A soaking well with cement ring and shaft filled with filter media consistingof large stone, medium size stone and coarse sand.

If the rooftop rainwater harvesting is integrated with the porous asphalt pavement, item 3 above is not required. The water from the rooftop is carried directly to the stone water reservoir and dispersed there through a series of perforated water pipes. (Fig. 3). This way, the stone reservoir does not experience any localized flooding.Thissystemalsomeansnosoakingwellorbore hole which involves considerable cost. In case of streets, water from the roof top of the buildings on the street can all be diverted to the stone water reservoir course. Another major advantage of this technology is that the water recharging the underground water is pure and free of contaminants.

Fig. 3 Roof Rainwater Harvesting Integrated with Porous Asphalt Pavement (Courtesy NAPA)

It should also be mentioned that porous cement concrete can also be used in lieu of porous asphalt but this paper is limited to the use of the latter.

3 DesIGN, CoNsTRuCTIoN aND maINTeNaNCe GuIDelINes FoR PoRous asPhalT PaVemeNTs

Detailed guidelines for constructing porous asphalt pavementforparkinglotsandlowtraffickedroadsorstreets for rainwater harvesting are given in Appendix. Some brief highlights are given below.

It is recommended that the in-situ soil permeability infiltration rate is 12.5 mm per hour. However, 2.5 mm per hour is acceptable by suitably increasing the thickness of the stone reservoir course. In Jaipur, the infiltration rate of the local soil is significantlyhigher than 12.5 mm per hour. Soil investigations should be carried out by boring and/or test pit to test for permeability, determining the depth of high water table, and determining depth to bedrock. Porous asphalt pavement is not suitable if (a) local soil is clayey; (b) bedrock is close to pavement; and (c) location has high water table. Also, porous asphalt pavement should not be constructed at a location subjected to blowing sand. That is, the adjacent ground should either be paved or covered with grass.

Compacted stone reservoir layer should be placed directlyonnaturalsoilsubgrade(bed)becausefillisnotrecommended.Althoughaflatsoilbedispreferred,slope of natural soil bed should be limited to 5 percent.

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This would ensure that water at the bottom of stone reservoir layer does not flow; rather it percolatesdownwards. If the slope is steeper, a terraced parking lot can be considered.

The thickness of compacted stone course (containing about 40% voids) should be designed to accommodate intensity and amount of rainfall prevailing in the region. Typical designs are made for 6 months/ 24-hour rain storms. Conservative designs are based on 20-year/24 hour rain storms, which can range from 35 mm to 400 mm in 24 hours. Typically, stone reservoir is about 225 mm (9 inches) thick, which can store 40% of 225 mm = 90 mm (3.7 inches) of rainfall temporarily. Obviously, the thickness is increased if additional water (from rooftop or adjacent dense road surface) needs to be accommodated.

The structural design of the pavement including the compacted stone reservoir course and porous asphalt wearing course should be based on traffic using thefacility. Normally, porous asphalt pavements are recommended for parking lots, recreational areas, and low-trafficked roads (with limited truck use).Both the porous asphalt course and the stone bed are structurally strong to withstand car and occasional trucktraffic.Thisisbecausebothderivetheirstrengthfrom stone-on-stone contact6.

Work site should be protected from heavy equipment so that the natural soil subgrade (bed) is not compacted otherwise its permeability may be reduced. Before placingthestonereservoirlayer,placeafilterfabricover the soil bed so that soil particles do not migrate upwards and clog the stone reservoir layer. As an alternate,astonefiltercourseconsistingof12.5mmstone particles has been found quite suitable. Place the porous asphalt course last on the entire project so that it is protected from construction debris. It should also be protected from soil laden runoff.

Before placing the 50-100 mm thick porous asphalt course, place 25 to 50 mm thick layer of 12.5 mm size stone to stabilize the surface of the stone reservoir course and facilitate paving operation.

The porous asphalt course should be designed as per established guidelines contained in the US Manual on Design, Construction and Maintenance of Open Graded Asphalt Friction Course (OGFC)6. Incidentally, OGFC is used in the US as a wearing course on interstate highways, ranging in thickness from 20 to 25 mm. The objective of laying OGFC on dense graded asphalt course is to provide a skid resistant pavement during rains. Rainwater quickly penetratestheOGFCsurface,flowsatitsbottomandemerges from its edge on to shoulders. Not only the OGFC prevents hydroplaning of motor vehicles during rains, it also provides a quieter pavement throughout the year6,7,8.

Normally, the asphalt mix would have 6 percent bitumen by weight of mix. It is recommended to use polymer-modifiedbitumensothattherenodraindownof binder in the trucks transporting the porous mix fromplanttopavingsite.Trafficshouldberestrictedfor 24 hours after construction of the porous asphalt wearing course.

The dramatic performance of porous asphalt pavements in the US is clearly visible in Figs. 4, 5 and 6. Fig. 4 shows a parking lot which is porous where the cars are parked whereas the driveway between the parked cars is dense asphalt. During rain, water is standing on the driveway but has percolated into the porous parking area. Fig. 5 shows two parking lots just after rain. The one in the background is conventional dense asphalt parking lot whereas the one in the foreground is a porous asphalt parking lot. Their relative appearance after rain is so very clear.

Fig. 6 shows view of a highway in Chandler, Arizona during rain. The left lanes were constructed with porous asphalt and the right lanes were constructed with conventional dense asphalt. After 20 years in service, the porous asphalt on this highway is still functional. This highway is in semi arid region of Arizona with very low rainfall similar to Rajasthan.

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Fig. 4 View During Rain: Driveway is Dense Asphalt with Water Ponding on it; Parking Area on the Right is Porous Asphalt with

no Water (Courtesy NAPA)

Fig. 5 View Just After Rain: Parking Lot in the Background is Dense Asphalt with Water Still Ponding on it; Parking Lot in the

Foreground is Porous Asphalt (Courtesy NAPA)

Fig. 6 Highway in Chandler, Arizona During Rain; Left Lanes are Porous Asphalt and Right Lanes are Conventional Dense

Asphalt (Courtesy NAPA)

It is absolutely clear that the porous asphalt technology works. Ninety-five percent of the rainwater fallingon porous asphalt pavement goes to recharge the ground water. Therefore, its effectiveness in capturing rainwater is very close to paved catchment areas.

4 DesIGN, CoNsTRuCTIoN aND PeRFoRmaNCe oF PoRous asPhalT PaRKING loT IN jaIPuR

The Jaipur Development Authority (JDA) had planned to construct a conventional dense graded asphalt parking lot at the Gandhi Nagar Railway Station in Jaipur. It was decided to include an experimental porous asphalt area (about 85 m by 4 m) as part of thelargeparkinglot.Itisbelievedtobethefirsteverporous asphalt pavement constructed in India for rainwater harvesting.

The land where parking was developed by the JDA was initially a garbage dumping yard. It was cleared and reclaimed to construct the parking lot to serve public at large.

Fig. 7 shows the cross section of the porous asphalt parking lot on the left and that of the conventional dense graded asphalt parking lot on the right. The two types of parking lot pavements were divided by constructing a cement concrete partition wall as showninthefigure.

Fig. 7 Cross Sections of Porous Asphalt Parking Lot (Left) and Dense Asphalt Parking Lot (Right) Partitioned

by a Concrete Wall

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The porous asphalt parking lot for rainwater harvesting was designed and constructed as follows.

subgrade

The existing subgrade was tested for its average water infiltration capacity, which was determined to be 46.5 mm/hour (1.83 inches/hour) which is well above the minimum reasonable water infiltration rate of 12.5 mm/hour (0.5 inch/hour).

After removing the garbage, excess soil was excavated to the required level and grade keeping about 150 mm (6 inches) soil to be excavated last. This was done to keepthefinalsubgraderelativelyuncompactedfromthe construction equipment.

stone Filter Course

Itwasnecessarytoprovideastonefiltercoursebetweenthefinishedsubgradeandthestonereservoircoursesothatfinesfromsubgradedonotmigrateupwardsintothe stone reservoir course thereby reducing its storage capacity.

The thickness of the stone filter coursewas 75mm (3 inches). The gradation of the aggregate actually used in this course is given in Table 1; it met the AASHTO 57 gradation. The filter course wascompacted lightly with a 2-ton steel wheel roller to maintain its integrity and avoid compacting the natural subgrade.

Table 1 Gradation of stone Filter Course

sieve size, mm

Recommended % Passing

(aashTo 57)

actual % Passing

37.5 100 10025 95-100 95

12.5 25-60 364.75 0-10 42.36 0-5 2

stone reservoir course

The function of the stone reservoir course is to temporarily store rainwater which percolates slowly into the natural subgrade below. The actual gradation of the clean stone used in constructing this course is given in Table 2 it met the recommended AASHTO 2 gradation.

Table 2 Gradation of stone Reservoir Course

sieve size, mm

Recommended Percent Passing

(aashTo No. 2)

actual Percent Passing

75 100 10063.5 90-100 9250 35-70 4838 0-15 819 0-5 2

0.150 0-2 1.5

The total thickness of the stone reservoir course was 365 mm (14.4 inches). Being the first ever porousasphalt parking lot in India, it was designed very much on the safe side. It was laid and compacted in two lifts with an 8-ton steel wheel roller. Four roller passes were applied in static mode and there were no roller marks. Rolled stone reservoir course was tested for effectiveness by poring water over it from a bucket; water disappeared from the surface instantly.

stone Choking Course

The stone choking layer is placed on the stone reservoir course so as to fill and level its open large surfacevoids and to make it stable and smooth for asphalt paver. It was placed in 50 mm (2 inches) thick layer and compacted well with an 8-ton steel wheel roller in static mode only until a smooth surface was obtained for paving above it. The gradation of this course was same as that of the stone filter course as given in Table 1. The finished, rolled surface was tested bypouring water over it; water disappeared instantly from its surface.

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The sampled bituminous mix was analyzed for bitumen content and gradation by conducting extraction test. Both dry and washed gradations were determined. Test results are given in Table 3.

Table 3 Gradation of Porous asphalt mix Produced

sieve size, mm

Required Percentage

Passing as Per NaPa Is-115

Percentage Passing

actual, Dry Gradation

Percentage Passing

actual, Wash Gradation

19.00 100 100 100

12.5 85-100 82 96

9.5 55-75 60 86

4.75 10-25 18 25

2.36 5-10 9 10

0.075 2-4 1.3 3.2

Type of bitumen: Although VG-30 paving bitumen meeting IS 73 is used in conventional paving, stiffer bitumen is needed for porous asphalt parking lot so that (a) there is no drain down of the asphalt binder within truck when this open-graded mix with high bitumen content is transported from the plant to the pavingsite,and(b)thereisnoscuffingwhenwheelsof a parked vehicle are moved with power steering. Therefore, Polymer Modified Bitumen (PMB) Grade 40 complying with IS:15462 was used on this project. Table 4 gives the test properties of the bitumen used.

Table 4 Properties of Pmb 40 used on Project

Properties Specification measured Value

Penetration at 25ºC, 0.1 mm 30-50 45Softening Point, ºC, min 60 60.3Elastic Recovery of half thread of ductilometer at 25ºC, % , min

75 66.5

Flash point, ºC, min 220 285Separation , difference in softening point, ºC, max

3 1.7

Fig. 8 Stone Reservoir Course Being Spread Over Stone Filter Course

Fig. 9 Choking Stone Layer in Place (Left) Ready for Laying Porous Asphalt; Dense Asphalt Completed on Right Side

Porous asphalt Wearing Course

Different blending proportions of the three aggregates available at the asphalt batch plant were tried so that the combined aggregate met the desired range of gradation for porous asphalt. The following proportions met the requirement: 15 mm aggregate (60%); 10 mm aggregate (32%); and stone dust (8%).

A trial batch of 1200 kg was made at the batch plant with 6 percent bitumen using 720 kg 15 mm aggregate; 384 kg of 10 mm aggregate; and 96 kg of stone dust. The mix temperature was 120 C (248 F).

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Properties Specification measured Value

Test of residue

Increase in softening point, C, max

Reduction of penetration at 25 C, max.

Elastic recovery of half thread in ductilometer at 25 C, percent, min

5

35

50

1.5

33

57

Viscosity at 150ºC, Poise, min

3.9 5.4

The design bitumen content was 6.0 percent by weight of the mix. High bitumen content is used in this open gradedmixsothatthickerfilmofbitumenisobtainedto avoid premature oxidation of bitumen. One percent liquid anti stripping agent by weight of bitumen was used to minimize stripping. This dosage was confirmed by conducting 24-hour static immersiontest in distilled water in accordance with IS:6241.

Three mix samples were compacted in Marshall moulds with 50 blows on each side. The moulds containing compacted specimens were placed under water tap for testing relative water infiltration rate.Table 5 gives the test results for information, which are reasonable based on visual observation.

Table 5 Relative Water Infiltration Rates for Compacted Porous mix

mix sample No.

mould Number

Time Taken for 25 mm Deep Water to Drain,

secondsI 1 7.60I 2 6.45I 3 6.25II 1 6.27II 2 7.45II 3 5.90

Schellenberg binder drainage test was conducted (see guidelines for procedure) on two different trial mix samples. Drain down of 0.12 and 0.14 percent

were obtained, which were well below the acceptable maximum limit of 0.3 percent.

Fig. 10 Schellenberg Binder Drainage Test

Compacted Marshall specimens were tested for average bulk specific gravity (Gmb) which was determinedtobe2.070.Maximumspecificgravityofthe loose mix (Gmm) was determined by ASTM D 2041 and was found to be 2.471. Air voids were calculated from Gmb and Gmm values. Average air void content in compacted Marshall Specimens was determined to be 16.2 percent, which met the minimum 16 percent requirement to ensure adequate permeability of the porous asphalt mix.

Although there is no requirement for Marshall Stability andflow,thesetestswereconductedforinformationonly. The average Marshall stability was determined to be 323 kg and the average Marshall flow wasdetermined to be 4.85.

On the day of scheduled laying of porous asphalt, there wassometrafficprobleminthecityofJaipur.Itwasnot certain as to how much time the truck will take to reach paving site within the city some 25 km away from the hot mix plant outside the city. Considering this unforeseen problem and high temperature of the mix (120 C) it was arbitrarily decided to lower the bitumen content from 6.0 to 5.5 percent so that there is no bitumen drain down problem in the truck during transit. When the truck arrived at the paving site and

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emptied the mix on to paver, it was observed that there was no bitumen drainage at the bottom of the truck.

The porous asphalt was laid in one lift to obtain compacted thickness of 75 mm. It was compacted with 8-ton steel wheel roller in static mode. Only four passes were made and there were no roller marks.

Stonereservoirwasprovidedwithanoverflowoutletby extending this course beyond the porous asphalt course (Fig. 14). This was done so that water does not exert any pressure underneath the porous asphalt course in case stone reservoir course gets choked and its storage capacity is reduced from unforeseen circumstances.

Fig. 11 Porous Asphalt Paving in Progress Over Stone Choking Layer

Fig. 12 Porous Asphalt Lay Down and Compaction

Fig. 13 Completed Parking Lot: Porous Asphalt on Left and Dense Asphalt on Right

Fig. 14 Extension of Stone Reservoir Course at the Edge of ParkingLotforOverflow

Fig. 15 Close-up of Porous Asphalt Pavement Surface

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After the compacted porous asphalt mat cooled to ambient temperature, its general permeability was tested by pouring water on it from a bucket. Water disappeared almost instantly.

The parking lot was completed in October 2012. In absence of rain at that time, a water tanker was brought in to check the relative permeability of the porous asphalt and the conventional dense graded asphalt pavements. As expected, water from the hose pipe was rapidly penetrating the porous asphalt surface andwasjustflowingonthedenseasphaltsurface.Thecomparison can be seen in Figs. 16 and 17.

Fig. 16 Water from Tanker Hose Readily Penetrating Porous Asphalt Surface

Fig. 17 Water from Tanker Hose Simply Flowing on Dense Asphalt Surface

Later, the porous asphalt parking lot was observed during the first two heavy rains of the monsoonseason on 11 and 27 June 2013. Rainwater was

almost disappearing on the porous asphalt surface andwas flowing on the conventional dense asphalt.This relative stark difference can be seen in Figs. 18 and 19. Therefore, it has been verified in the field that porous asphalt is performing really well as expected.

Fig. 18 Relative Performance of Porous Asphalt (Right) and Dense Asphalt (Left) During Monsoon

Rain in June 2013

Fig. 19 General View of Porous Asphalt (Right) and Dense Asphalt During Monsoon Rain in June 2013

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It is estimated that this porous asphalt test section measuring only 85 m by 4 m would recharge the groundwater by over 2 lakhs liters per year considering average annual rainfall of 640 mm in Jaipur. If the whole JDA parking lot (3,545 sq m area) was built with porous surface it would have recharged the groundwater by over 22 lakhs liters per year9.

It is hoped public and private agencies in India would construct porous asphalt parking lots/low-traffickedstreets and roads, in areas where the groundwater level is depleting.

5 CoNClusIoNs aND ReCommeNDaTIoNs

Porous asphalt pavement is one of the responses to plunging ground water table in Jaipur and elsewhere in India. It can be integrated with the roof rainwater harvesting system effectively and economically. According to experience in the US, properly designed and constructed porous asphalt pavement can last more than 20 years. Such a pavement can be used for parking lots, recreational areas, and low-volume roads and streets.

The first ever porous asphalt pavement in India forrainwater harvesting has been constructed successfully by the Jaipur Development Authority in October 2012. Its design, construction and performance have been described in the paper.

Government should encourage (and mandate in critical areas) construction of porous asphalt pavements in urban areas. Town planners, architects and civil engineers should be proactive by incorporating this unique rainwater harvesting system while designing government buildings, residential buildings, commercial buildings, parking lots and roads in new townships.

aCKNoWleDGemeNT

Fig. 1 through 6 are courtesy of US National Asphalt Pavement Association (NAPA). Permission given by Mr. Kuldeep Ranka, Commissioner, Jaipur DevelopmentAuthorityforconstructingthisfirsteverporous asphalt parking lot in India is appreciated.

ReFeReNCes

1. Mathur, R. P. Regional Director, Central Underground Water Board. Presentation Made at the Water Resources Workshop held in Raj Bhawan of Jaipur on 4 November 2009.

2. Thelen, E. and L. F. Howe. Porous Pavement. The Franklin Institute Reserch Laboratories, 1978.

3. Jackson, N. Design, Construction and Maintenance Guide for Porous Parking Lots. National Asphalt Pavement Association, Information Series IS-131, October 2003.

4. Kandhal, P. S. Presentation made at the Water Resources Workshop Held in Raj Bhawan of Jaipur on 4 November 2009 presided by H. E. Governor S. K. Singh.

5. Kandhal, P.S. A Revolutionary Technique of Rainwater Harvesting Integrated into the Design of Buildings and Parking Lots. Water Digest Magazine, March-April 2011, New Delhi, India.

6. Kandhal, P.S. Design, Construction and Performance of Open-Graded Asphalt Friction Courses. National Asphalt Pavement Association, Information Series IS-115, May 2002.

7. Kandhal, P.S. and R.B. Mallick. Open-Graded Friction Course: State of the Practice. Transportation Research Board, Transportation Research Circular Number E-C005, December 1998.

8. Roberts, F.L., P.S. Kandhal, E.R. Brown, D.Y. Lee, and T.W. Kennedy. Hot Mix Asphalt Materials, Mixture Design and Construction. NAPA Education Foundation, Lanham, Maryland, Second Edition, 1996.

9. Kandhal, P.S. Role of Permeable Pavement in Groundwater Recharge. Presentation at the Rajasthan State Workshop on Water Conservation: Issues and Challenges. Held in Jaipur by the Centre for Science and Environment (CSE), 7 February 2013.

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aPPeNDIX

GuIDelINes FoR CoNsTRuCTING PoRous asPhalT PaVemeNT FoR PaRKING loTs aND loW TRaFFICKeD RoaDs oR sTReeTs FoR RaINWaTeR haRVesTING

1 INTRoDuCTIoN

These guidelines deal with the basic outline for the design, construction and controls needed for constructing porous asphalt pavement for parking lotsand low-traffickedroadsorstreets for rainwaterharvesting. The porous asphalt pavement shall be constructed as per project drawings under the guidance of the Engineer.

The porous asphalt pavement consists of the following starting from the bottom upwards: subgrade; stone filter course; stone reservoir course; stone chokinglayer; and porous asphalt course. Guidelines for constructing these different courses or layers are given below in that order.

2 subGRaDe

Subgrade should be allowed to remain natural and uncompacted to maintain its permeability. No excessiveconstructiontrafficshouldbepermittedonthe subgrade. It is advised to excavate for the desired subgrade level (at least the last 150 mm or 6 inches) when all preparations have been made for laying the stonefiltercourseandthestonereservoircourse.

If there are any depressions in the subgrade which needtobefilledandlevelled,usepermeablesandandcompact it lightly.

The slope of the finished subgrade should not exceed 5 percent. In case of steeper slope, terraced parking lots need to be considered. Subgrade soil should be such that it can drain water within 48 to 72hours.Infiltrationcapacityofsubgradesoilsusedin the past in the US has ranged from 2.5 mm/hour to 76 mm/hour (0.1 inch/hour to 3 inches/hour). A rate of 0.5 inch/hour is considered very reasonable. Subgrade with clayey soils is not desirable.

3 sToNe FIlTeR CouRse

The stone filter course is provided between thesubgradeandthestonereservoircoursesothatfinesfrom the subgrade do not migrate upwards into the stone reservoir thereby reducing its storage capacity. It also provides some platform for laying the stone reservoir course.Note : Although nonwoven geotextile fabric has been used

between the subgrade and the stone reservoir for this purpose, some clogging of the geotextile material has been reported from the fineswashed down on itssurface.

Typically,thestonefiltercourseis75mm(3inches)thick and the following AASHTO 57 gradation given in Table 1 is used.

Table 1 Gradation of stone Filter Course (aashTo 57)

sieve size, mm Percent Passing37.5 mm (1.5”) 100

25 mm (1”) 95-10012.5 mm (1/2”) 25-60

4.75 mm 0-102.36 mm 0-5

After spreading the stone filter course aggregate onthe prepared subgrade, only light rolling should be done with a 2-3 ton roller.

4 sToNe ReseRVoIR CouRse

The function of the stone reservoir course is to temporarily store rainwater which percolates slowly into the natural subgrade below. Its AASHTO Gradation 2 consists of large uniformly graded aggregate particles 40 mm to 65 mm (1.5 to 2.5 inches) in size with about 40% voids to accommodate rainwater. The stone should be clean. Desired gradation is given in Table 2.

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Table 2 Gradation of stone Reservoir Course (aashTo No. 2)

sieve size, mm Percent Passing75 mm (3”) 100

63.5 mm (2.5”) 90-10050 mm (2”) 35-70

38 mm (1.5”) 0-1519 mm (0.75”) 0-5

0.150 mm 0-2

The thickness of this course is designed to hold rainwater during a 25-year, 24-hour rain storm. Its minimum thickness is 230 mm (9 inches). It should empty within 72 hours. Its thickness is designed based on expected rainfall and desired structural strength.

Stone reservoir course should be laid and compacted in 150 mm to 180 mm (6 to 8 inches) lifts and rolled in static mode only with a light roller (about 5 ton) until no roller marks are visible and it is true to the desired grade. Test the rolled stone reservoir course by pouring water over it, water should disappear instantly from its surface.Note : The stone reservoir course should be provided with an

overflowoutletsothatinextremecasessuchaschoking,water does not exert any pressure underneath the porous asphalt course thus damaging it. Overflow can beprovided by extending the stone reservoir course like an apron by about 0.45 to 0.6 m (1.5 to 2 feet) beyond the overlying porous asphalt pavement course. In case of kerbed parking lot, a suitable outlet control structure with internal weir and an outlet channel or pipe should be provided.

5 sToNe ChoKING laYeRThe stone choking layer is placed on the stone reservoir course so as to fill and level its open large surfacevoids and makes it stable and smooth for asphalt paver. Normally, it is placed in 50 mm (2 inches) thick layer and compacted well with a light (about 5 ton) roller in static mode only until a smooth surface is obtained forpavingaboveit.Testthefinished,rolledsurfacebypouring water over it, water should disappear instantly from its surface.

The stone choking layer consists of either a clean, single size aggregate (12.5 mm) as given in Table 3 or AASHTO 57 gradation given in Table 4.

Table 3 Gradation of stone Choking layer (alternate 1- single size)

sieve size, mm Percent Passing12.5 mm (1/2”) 1009.5 mm (3/8”) 0-5

Table 4 Gradation of stone Choking layer (alternate 2- aashTo 57)

sieve size, mm Percent Passing37.5 mm (1.5”) 10025 mm (1”) 95-10012.5 mm (1/2”) 25-604.75 mm 0-102.36 mm 0-5

6 PoRous asPhalT CouRse

Do not apply any tack coat before placing the porous asphalt course; it is likely to reduce its permeability. The porous asphalt course is usually placed in 75 mm (3 inches) thickness in one lift. After compaction in thefielditmusthaveatleast16%airvoidstoprovidethe desired porosity and permeability.

Specifications for Dense Graded BituminousMixesIRC:111-2009 shall generally be followed to produce and lay porous asphalt with the additional/special requirements noted herein.

6.1 Gradation

It is important that the gradation given in Table 5 is strictly adhered to obtain the desired porosity and permeability.

Table 5 Gradation of Porous asphalt Pavement mix

sieve size, mm Percent Passing19 mm 100

12.5 mm 85-1009.5 mm 55-75

4.75 mm 10-252.36 mm 5-10

0.075 mm 2-4

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6.2 Type of Paving bitumen

Although VG-30 paving bitumen meeting IS 73 is used in conventional paving, stiffer bitumen is needed for porous asphalt parking lot so that (a) there is no drain down of the asphalt binder within truck when this open-graded mix with high bitumen content is transported from the plant to the paving site, and (b)thereisnoscuffingwhenwheelsofaparkedvehicleare moved with power steering. Therefore, a Polymer ModifiedBitumen (PMB)Grade40complyingwithIS:15462 should be used.

6.3 bitumen Content

Bitumen content by weight of mix should be 6 percent. Thickerfilmsofbitumenarenecessaryintheporousasphalt pavement with over 16% air void content so that bitumen does not get oxidized prematurely in service.

6.4 anti stripping agent

A suitable anti stripping agent should be mixed in the proposed bitumen. It is necessary because water will pass through the porous asphalt pavement. The effectiveness of the anti stripping agent should be tested with the 24-hour static immersion test in distilled water as per IS:6241 or 10-minute boiling test given in Annexure A.

6.5 mix Temperature

Since the open graded porous asphalt mix contains relatively higher bitumen content, the bitumen can drain down to the truck bed if the mix temperature is too high. That would result in either fatty or too lean mix spots during paving. It is recommended to make the mix in 95-120 C (200-250 F) temperature range to minimize bitumen drain down during transportation. Establish the mix temperature so that drain down does not exceed 0.3 percent if determined by the drain down test given in Annexure B or C. If the drain down exceeds 0.3 percent even at relatively low mix temperatures, increase the amount of material passing 0.075 mm sieve but not to exceed 4 percent. Examine

the truck bed after unloading the mix into paver to confirmthereisnoactualdraindownproblem.

6.6 mix Design

Compact the mix using aggregate gradation given in Table 5 and 6.0 percent bitumen binder by weight of mix in Marshall mould with 50 blows on each side. Make three specimens. Allow the mix to cool completely in the moulds (in a refrigerator if needed) before extracting the specimens without any damage. Determinethebulkspecificgravityofthecompactedspecimens by geometrical measurements. Determine the maximum specific gravity of the loose porousasphalt mix as per ASTM D 2041. Calculate the percent air voids in compacted specimens using bulk specificgravityandthemaximumspecificgravity.Airvoids should be at least 16 percent to ensure reasonable porosity and permeability.

Before extracting the specimens from the moulds, conduct an approximate water permeability check. Hold the mould containing specimen under a water tap. Water should readily pass through the compacted porous asphalt. If not, revise the gradation of the aggregate.

6.7 Paving and Compaction

Trucks carrying the porous asphalt should be covered with tarpaulin because the mix has tendency to cool at a faster rate. The 75 mm thick porous asphalt should be paved in single lift and compacted promptly with an 8-10 ton roller in static mode only. Only 2-3 passes are needed to compact the porous asphalt course. Do not use pneumatic tired roller. Too much compaction would reduce its porosity and permeability.

Examine the truck bed after the mix has been emptied on to paver to see if there is any binder drain down. If so, the paved surface would have either fatty spots or lean spots. Decrease the mix temperature immediately to prevent any further drain down.

After the porous asphalt is compacted, make a permeability check by pouring water on its surface, the water should disappear immediately. If not, there

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is something wrong in terms of mix composition (bitumen content and gradation) and/or compaction. Until this test is successful, paving work shall not proceed any further.

Donotallowanytrafficonthepavedsurfaceatleastfor 24 hours.

7 maINTeNaNCe oF PoRous asPhalT PaRKING loT

Place a sign board at the porous asphalt parking lot so that its surface is not sealed by any means in future. If needed, the parking lot can be patched lightly; not more than 10 percent of the surface area.

The parking lot should be reasonably protected from excessive wind blown soil or sand; mud tracking from adjacent areas; and construction debris to maintain its permeability.

Overflowoutletfromthestonereservoircourseshouldbe checked periodically to ensure it is functional.

If the permeability of porous asphalt is reduced drastically for some unforeseen reason, it can be reclaimed, recycled and relaid,

aNNeXuRe a oF aPPeNDIX

boiling Water Test for Detecting Presence of anti stripping agent in bituminous mixes (after asTm D 3625)

This boiling water test shall be conducted at least twice at random on each day of bituminous mix production to detect if an anti stripping agent (such as hydrated lime or liquid anti strip) has been used in the mix in required dosage to prevent stripping of the bituminous mix. Mix samples should also be taken at the paving site and test conducted everyday right at the paving site.

Follow the procedure as given below:

1. Boil distilled water in a glass beaker of 1000-2000mlcapacityfilledabouthalf.

2. Place about 250 grams of fresh bituminous mix into the boiling water.

3. After the water resumes boiling, continue boiling for 10 minutes.

4. Cool water to room temperature, decant (drain off) water, and spread the bituminous mix on a white paper towel.

5. Examine the mix for bituminous coating. At least 95% of aggregate surface should retain bituminous coating. Any thin, brownish, translucent areas are considered coated.

6. Reject the mix if bitumen coating is found to be less than 95 percent.

aNNeXuRe b oF aPPeNDIX

outline of asTm D 6390, “Determination of Drain Down Characteristics in uncompacted asphalt mixtures”

a. scope and summary of Test

This method determines the amount of drain down in an uncompacted asphalt mixture sample when the sample is held at elevated temperatures, which are encountered during the production, transportation, and placement of the mixture. This test is especially applicable to open-graded asphalt mixtures (such as open-graded friction course and porous asphalt) and gap-graded mixtures such as stone matrix asphalt (SMA).

A fresh sample of the asphalt mixture (either made in the laboratory or from an asphalt plant) is placed in a wire basket. The wire basket is hung in a forced draft oven for one hour at a pre-selected temperature. A catch plate of known mass is placed below the basket to collect material drained from the sample. The mass of the drained material is determined to calculate the amount of drain down as a percentage of the mass of the total asphalt mix sample.

b. Testing equipment

1. Forced draft oven, capable of maintaining temperatures in a range of 120 to 175 C with +/- 2 C of the set temperature.

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2. Plates to collect the drained material 3. Standard wire basket meeting the dimensions

shown in Figure 1. A standard 6.3 mm sieve cloth shall be used to make the basket. The dimensionsshownin thefigurecanvaryby+/- 10 percent.

4. Balance readable to 0.1 gram

C. Testing Procedure 1. For each mixture to be tested, the drain

down characteristics shall be determined at two temperatures: at the anticipated plant production temperature and at a temperature 10 C higher than the anticipated production temperature. Duplicate samples shall be tested at each temperature. Therefore, a minimum of 4 samples shall be tested.

2. Weigh the empty wire basket (Mass A). 3. Place in the wire basket 1200 +/- 200

grams of fresh, hot asphalt mixture (either prepared in the laboratory or from an asphalt plant) as soon as possible without losing its temperature. Place the mix loosely in the basket without consolidating it. Determine the mass of the wire basket plus sample to the nearest 0.1 gram (Mass B).

4. Determine the mass of the empty plate to be placed under the basket to nearest 0.1 gram (Mass C).

5. Hang the basket with the mix in the oven preheated to a selected temperature. Place the catch plate beneath the wire basket. Keep the basket in the oven for 1 hour +/- 5 minutes.

6. Remove the basket and catch plate from the oven. Let cool to ambient temperature. Determine the mass of the catch plate plus the drained material to the nearest 0.1 gram (Mass D).

7. Calculate the percentage of mixture which drained to the nearest 0.1 % as follows:

Drain down (percent) = (D-C)/(B-A) multiplied by 100

Where, A = mass of the empty wire basket, g B = mass of the wire basket plus sample, g C = mass of the empty catch plate, g D = mass of the catch plate plus drained material, g

8. Average the two drain down results at each temperature and report the average to nearest 0.1 percent.

Fig. 1 Wire Basket Assembly for Drain Down Test

aNNeXuRe C oF aPPeNDIXThe schellenberg binder Drainage Test 1. Determine the mass (A) of an empty 850-ml

glass beaker, approximately 98 mm diameter by 136 mm high, to the nearest 0.1 gram.

2. Pour approximately 1 kg of the mix immediately into the glass beaker after mixing at the anticipated field mixingtemperature. Re-weigh the beaker together with mix (B) to the nearest 0.1 gram.

3. Place the glass beaker with a glass or tin cover in an oven maintained at 170 C + 1 C for 1 hour + 1 minute.

4. At the end of 1-hour period, immediately remove the glass beaker from the oven and empty the beaker without the use of any shaking or vibration. Re-weigh the beaker (C) to the nearest 0.1 gram.

5. Calculate the percentage of binder drain down (definedas thepercentageofmassofthe mix deposited in the beaker) as follows:

Binder Drain down (percent) = (C-A) / (B-A) multiplied by 100


INNoVaTIVe IDea To CalCulaTe The TIlT oF a WellKnSP KaMarajU*

* General Manager (Structures), GMR Project of Hunugund, Hospet, Karnataka. E-mail: [email protected]

1 INTRoDuCTIoN

It is obvious that the tilt of a well steining plays a crucial role in the safety of the well foundation bridge. Through the well steining only, the load of the bridge will be transmitted to the foundation soil. This load will be transmitted safely to the foundation soil through the well steining as far as the well steining is normal/vertical or the tilt is in permissible limits. Hence, it is very much necessary to ascertain the tilt judiciously.

As per MORT&H specifications the resultant tiltshould not more than 1 in 80. Up to 1 in 50 is also allowed with reduction in payment. In no case it is allowed more than 1 in 50. In case tilt is more than 1 in 50, we must have to resort to the redesign of that well/well cap in view of the safety.

2 PRoCeDuRe To FIND ouT TIlT

At present the following procedure is in practice to findoutthetiltofawell.

AspertheMORT&Hspecification,theleveldifferenceof steining on either side of well at the same length (height) from the bottom of well ie from cutting edge (A Scale is being painted on all the 4 sides on outer surface of the well. i.e along X-X & along Y-Y axis as the sinking is progressing. Scale position is shown in Fig. 1) will be collected at points E & F as shown in Fig. 1 and Tilt will be calculated as per the procedure stipulated below.

ABCD are the 4 initial points on the well on X-X axis and on Y-Y axis respectively as shown in plan of

figure1while thewell isnothavingany tilt.Letusassume a small tilt has come in the well while sinking, so that the positions of points “ABCD” on the well will come to the position “EFGH”. That means A&B are the initial points on X-X axis will have taken a position E&F after tilt, which is shown on section of figure1.Nowwearegoing to take the levelsof thepoints of E&F, so that the difference of these levels will be equivalent to “hx”.

To calculate the tilt, the factor being used is shown below from Fig. 1.

i.e. Tilt along X-X axis (Fig. 1) Tx=TANα

Half of the difference in reduced level of same points on steining along X-X axis =

(hx/2)

Radius of the well R

i.e. Tilt along Y-Y axis (Fig. 1) Ty=TANα

Half of the difference in reduced level of same points on steining along Y-Y axis =

(hy/2)

Radius of the well R

Resultant Tilt : T = Tx Ty( ) + ( )2 2

The above calculation is totally dependent on the level difference of those points on scale hx and hy (since radius of well R is a constant), which are manually done by the contractor. But there is a chance of manipulation by the contractor in the preparation of scale to show the well is within permissible tilt/no tilt and generally happens in site. The manipulation cannot be found by anybody, once the well progresses down into the soil or ground.

To avoid such manipulation an innovative idea is formulatedtofindoutthetiltexactly.

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Fig. 1

3 PRINCIPleThis works on the principle that normal drawn at the centre of the cross section of the well at top always falls at the centre of the bottom of the well as long as there is no tilt in the well. i.e. If we hang a plumb bob “QP “from the top at the centre of the well, it will touch the bottom at the centre “O” as shown Fig. 2 as long as there is no tilt in the well. In other words the distance between the plumb line and the inner periphery of the well on either side should be the same.

Fig. 2

If there is any tilt in the well, the plumb line will not touch at the bottom of well at centre ‘O’. In other words the distance between the plumb line and the inner periphery of the well on either side will not be equal.

Based on above principle, an innovative Idea has been developed to calculate the tilt.

4 INNoVaTIVe PRoCeDuRe To CalCulaTe TIlT oF Well

Dewater the well for at least 3 m of depth from top of well, if required. Two threads are to be tied along X-X axis and Y-Y axis dividing the well in 4 equal sectors along cross section of well as shown in plan of Fig. 2. Let us call them as Top Thread lines. Tie two more threads as explained above at approximately two metre below from the top thread lines with the help of sticking tape or by any other means. Let us call them as bottom thread lines. (We can insert steel spikes/steel rings at the time of casting of steining at every 2 m interval to tie these threads).

Take plumb bob having thread length approximately 3 m. Put a mark on thread line of plumb bob just above plumb ball as shown in Fig. 3. Now release the plumb from the centre of the well, which is the intersection point of top thread lines. The plumb bob will touch at the intersection point of bottom thread lines, if there is no tilt in the well. But because of the tilt, it will not touch the intersection point of bottom thread lines at centre and hence match the mark on the thread line of the plumb bob with bottom thread lines along X-X axis at point ‘R’ and measure the difference “ x” from the centre as shown Fig. 2. Similarly, we can measure the difference along Y-Y axis as “y”.

Fig. 3

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Find out the distance ‘L’ between the top and bottom thread lines tied along cross section. This can be measured along the length of plumb-bob also.

Now the calculation is very simple. The formula is

TiltalongX-X Tx=TANα=

Difference in X-X direction “x”

Distance between top & bottom thread lines or measured length of plumb bob” L”.

TiltalongY-Y Ty=TANα=

Difference in Y-Y direction “y”

Distance between two thread lines or measured length of plumb bob “L”.

Resultant tilt : T = Tx Ty( ) + ( )2 2

This has been achieved from the rule of similar triangles as shown in Fig. 2 and as per the calculation explained below:

5 CalCulaTIoN

From Fig. 1Tilt TANα=hx/(2R)OR(hx)/D

From Fig. 2wecanobservesimilartriangles∆AEQand∆QPR.TheyaresimilartrianglesbecauselineABand line QP are perpendicular to each other. Because of the tilt in the well the line AB has taken the position of line EF and line QP has taken position of line QR and hence they are also perpendicular to each other. Therefore,angle∟AQEandangle∟PQRareequalfrom the rules of similar triangles. Assume further theyareequaltoα.

ThereforeAE/AQ=PR/PQ=TANα

TANα=(h/2)/R=x/L

Tofind out the ‘α ‘we are using ‘x’ and ‘L’ insteadof ‘h’ and ‘R’, where ‘h’ and ‘R’ being used by the MORT&H procedure.

With the above procedure we can eliminate the manipulation error in calculation of Tilt.


aCCeleRaTIoN aND DeCeleRaTIoN behaVIouR oF TRuCK oN INDIaN hIGhWaY

P.S. BoKare* and a.K. MaUrya**

* Research Scholar, E-mail: [email protected]** Assistant Professor, E-mail: [email protected]

absTRaCTAcceleration and Deceleration (A/D) characteristics of vehicles are important for intersection design, acceleration deceleration lane design, traffic simulation modeling, vehicular emissionmodeling, instantaneous fuel consumption rate modeling, etc. Heterogeneous traffic stream consists of vehicles with widevariation in their physical dimensions, weight to power ratio and dynamic characteristics which affect their acceleration and deceleration behaviour in traffic stream. Truck is the majorcomponentoftrafficcompositiononIndianhighways.Thepresentstudy aims to analyze the acceleration and deceleration behaviour of trucks which are approximately 20% in composition on Indian roads. This study was conducted on Nagpur-Mumbai Express Highway at Wardha, India. Drivers were asked to accelerate their vehicles from stop to their maximum speed and then to zero speedinshortesttimeandtheirspeedprofilesduringaccelerationand deceleration profiles are collected usingGlobal PositioningSystem at 1 second time interval. Various A/D parameters like A/D distance, A/D time, mean and maximum A/D rates and speed at maximum A/D are reported in study. A negative exponential model for acceleration and dual regime model for deceleration are proposed. Various statistical tools are used to validate the A/D models.

1 INTRoDuCTIoN

Traffic,inmostofthedevelopingcountries,includingIndia, is heterogeneous which consist of vehicles with wide variation in their physical dimensions, weight to power ratio and dynamic characteristics. This heterogeneity results in difference in performance of various categories of vehicles as regards to their capacity to accelerate and decelerate. Poorly accelerating and decelerating vehicles develop resistance to movement of efficient vehicles. TheAcceleration and Deceleration (A/D) capability of vehicle, however, depends on its engine capacity, power to weight ratio, driver behavior, road conditions, etc. The drivers’ response to signal or other control measures depend largely on their A/D capability.

Further, vehicle’s A/D characteristics play vital role in vehicular emission modeling, instantaneous fuel consumption rate modeling, deceleration lane design, trafficsimulationmodeling,etc.Henceitisimportantto have better understanding of acceleration and deceleration behavior of vehicles5.

Most of the existing A/D models4; 10; 11; 12; 20 consider homogenous traffic stream (which isnot the case inIndia) and are based on A/D behaviour at signalized intersections. Some of the studies8; 20 formulated A/D models based on old data sets (of 1968 and 1985) due to lack of accurate and recent data. The vehicle technology and driver response to control devices have changed since then. Literature review yields limited studies15; 17 related to A/D behaviour for Indiantrafficstreams.Inthesestudies,speeddataarecollected using either radar gun or based on manual measurement of travel time which limits their scope to get complete acceleration or deceleration profilesof vehicle. Hence there is a need to study the A/D behaviour of vehicles on Indian roads using advanced equipments (like GPS) to get accurate and complete A/Dprofilesofvehicles.Thispaperpresentsthestudyof A/D behaviour of trucks (as trucks constitute the significantproportionofhighwaytraffic18) on straight and level road using Global Positioning System (GPS). This study reports typical A/D parameters for trucks like maximum and mean A/D values, speed at which they occur, A/D distances and time etc. Existing A/D models are also evaluated for their suitability in describing the collected A/D data of trucks on Indian Highway.

Department of Civil Engineering, Indian Institute of Technology, Guwahati, Assam

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2 ReVIeW oF eXIsTING a/D moDels

Many researchers4; 8; 10; 11; 12; 20; 21 have worked on A/D modeling of vehicles. Literature review yields two types of A/D models - kinematic and dynamic. This study focusses on kinematic models. The section is divided in two subsections describing various acceleration and deceleration models.

2.1 acceleration models

Kinematic acceleration models reported in literature can be grouped as follows, 1. Single regime acceleration model.

Constant acceleration model. Linear decay acceleration model. Polynomial acceleration model.

2. Multi regime acceleration model.Fig. 1 shows typical acceleration speed plot for above models11.

Fig.1SpeedandAccelerationProfileforDifferentModelsLikea) Constant Acceleration b) Linear Decay c) Polynomial

d) Dual Regime

2.1.1 Single Regime Acceleration Model

In this group of model, A/D behaviour of vehicles are described/modelled using single relationship for entire speed range of vehicles (refer Fig. 1a, 1b and 1c).

a Constant Acceleration Model: This model is the simplest among all model presented in Fig. 1. It assumes that vehicles keep accelerating at constant rate (as determined from Equation III-A) through entire acceleration process.

... 1

where, aavg is average acceleration rate (m/s2), x is distance covered, (m) in time t, (s), t is time required tocoverdistancexortoreachavelocityfromυitoυf, υi isstartupvelocity(m/s)andυf is velocity (m/s) at time t.

Field observations on acceleration show that vehicle acceleration is never constant, however, it continuously changes over the time, distance and speed8. Studies reported that vehicles have higher acceleration rates at lowerspeeds.Althoughmostof trafficsimulationpackages use constant acceleration models for the sake of simplicity12. Constant acceleration model can be best suited only when vehicle maneuvers in one particular gear at maximum acceleration rate. However the model is greatly in error while accelerating up through the gears10.

b Linear Decay Model: This model assumes that acceleration linearly reduces (from a maximum acceleration at zero speed) with increase in speed (refer Fig. 1b). Model presents vehicle acceleration behavior by a relationship a = α – β * υ where a and υ are acceleration (m = s2) and speed (m = s) respectively, represents maximum acceleration when speed is zero and β is slope of the line or rate at which acceleration decreases with

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increase in speed. Gary Long13 reported that values of β (slope) are similar for each type of vehicles and α value increases with decrease in weight to horse power ratio. This indicates that the maximum accelerating capacity increase with decrease in weight to horse power ratio.

Dockerty6 reported that actual motorists acceleration values are not maximum at t = 0 but they are zero at t = 0 and rapidly increase to its maximum value at a time t after t = 0. Dockerty6 obtained acceleration values with α =1.49 and β = 0.1455 for trucks. Dey et al.17 also modeled the acceleration behaviour of trucks at signalized intersection. They obtained α = 0.4758 and β = 0.0312 for trucks on Indian highways.

c Polynomial Model: Ackelik and Biggs20 proposed a nonlinear polynomial relation between acceleration and time as given below:

a(t) = ramθ(1 – θm)2 m > –5 ... 2

where, a(t) is acceleration rate (m/s2) at time t, am is maximum acceleration (m/s2), θ is time ratio t = ta, t is acceleration time (s), ta is total time of acceleration (s), m is parameter that depends on initial and final speed, acceleration time anddistance, and r is parameter that depends on value of m. This model overcomes the unrealistic assumption of high acceleration at beginning. They pointed out following requirements for a realistic acceleration model (as shown in Fig. 2).

1. SpeedprofileshouldindicateanSshape.

2. Acceleration rate must be zero at the start and end of acceleration run.

3. Jerk (rate of change of acceleration with time) should be zero at the start and end of acceleration.

Fig. 2 Acceleration Speed Plot-Polynomial Model, Akcelik and Giggs, 1987

2.1.2 Multi Regime Acceleration Model

This group of models use a combination of above single regime models to describe the acceleration behaviourofvehiclesforspecificspeedranges.Figure1d shows a dual regime model which utilizes two different constant acceleration models for different speed range to describe acceleration behaviour of vehicle. Chowdhury15 suggested dual regime model for vehicle acceleration process in which different linear decreasing models (linear models with different slopes) are used for different regime.

Bham and Benekohal8 suggested dual regime model of following form:

... 3

where, a1 and a2areaccelerationratesforthefirstandsecond regime respectively. This model is similar to Chowdhury15 model.

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2.2 Deceleration models

Similar to acceleration models, existing deceleration models can also be grouped in single and multi regime models. However, literature review yields less studies on deceleration behaviour of vehicles as compared to acceleration behaviour. Various studies reported different deceleration rates for vehicles like Gazi et al.7 suggested a deceleration rate of 5 m/s2 whereas Parsonson19 found a deceleration rate of 3 m/s2. Mean deceleration rate was found to vary from 2.1 to 4.2 m/s2 with a mean approach speed of 50.6 to 62.4 km/h by Wortman et al.25. Studies conducted by Wortman et al.25 indicated that vehicles do not decelerate at uniform rate but the deceleration rate depend on their approach speed. ITE‘s Traffic EngineeringHandbook2, suggests that a deceleration rate up to 3 m/s2 is comfortable for passengers cars. Akcelik and Biggs20 also suggested non uniform deceleration rate depicting a polynomial behavior between deceleration and speed. Samuels and Jarvis24 suggested a constant deceleration model. Bennet and Dunn4 found that the driver‘s deceleration rate depends on driving speed. Drivers with higher speed decelerate at higher rate than drivers at slow speed. They developed a regression model to show deceleration as a function of approach speed and deceleration time as given in Equation 4.

υ = υa – a0υat2 ... 4

where, υisvehiclespeed(km/h),υa is approach speed (km/h), t is deceleration time (s), a0 is a constant parameter. They concluded that drivers decelerate over a same distance irrespective of speed, resulting in higher deceleration rate with higher speed. However, their conclusion that driver deceleration is maximum at the end of deceleration maneuver contradicts the concept of zero jerk at the end of deceleration maneuver reported by Akcelik and Biggs20.

Later in 2005, Wang et al.10 proposed following relation between current speed and deceleration time basedonspeedprofileofvehiclescollectedbyGlobalPositioning System (GPS):

υ =4.6899+0:050υa – 7.583t2, ... 5

where,υisspeed(km/h),υaisapproachspeed(km/h)andtisrelativedecelerationtime(0≤t≤1).Relativedeceleration time is ratio of deceleration time of trip to total deceleration time. No clear relationship between average and maximum deceleration rates and approach speed were observed. However drivers with high approach speed decelerate over a longer time and distance similar to observation made by Akcelik and Biggs20. Several other researchers15;18 have reported acceleration and deceleration values of different vehiclesonIndianroadsatspecificspeedsonly(notfor entire speed range). Arasan3 has proposed constant acceleration model for different speed range. Due to different A/D rates in different speeds, the number of discontinuities in model increases. Further, as highlighted before that to measure the speed of vehicles these studies uses either radar gun or based on manual measurement of travel time which limits their scope to get complete acceleration or deceleration profilesof vehicle. Further these methods lead to average A/D values between two data collection points not the actual A/D values corresponding to a speed.

Though, several attempts were made to model acceleration and deceleration using various data sets, owing to variations in methods of collecting data, vehicle types considered in study, driving conditions, road conditions and the driver behavior, the suggested modelsmaynotbesuitablefortrafficplyingonIndianhighways. Further the Indian traffic is generallyheterogenous with weak lane discipline which further reduces the applicability of existing A/D models in Indian context. A/D studies conducted in India have used old/traditional method of speed data collection which may not provide an accurate and complete acceleration or deceleration profiles of vehicles.Therefore, in the present work, A/D behaviour of trucks is analyzed based on speed data collected using GPS.

3 DaTa ColleCTIoN aND aNalYsIs

The assessment of vehicle behaviour can well estimated by observing it in actual traffic stream.But owing to limitations of resources sometime it is

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difficultandimpossible.InIndia,trafficstreambeingheterogenouswithweaklanediscipline,itisdifficultto observe consistent acceleration and deceleration behaviour at intersections. Moreover, the presence of variety of vehicles with variation in their sizes and operating characteristics, impact the movement of other neighboring vehicles. Data collection in such situation is difficult.Most often the exercise resultsin an inconsistent data14. An alternative is to observe vehicle behaviour over a selected short stretch and under controlled conditions16. Data collection in present work is undertaken in controlled manner and efforts are made to ensure that A/D behaviour of vehicles is not affected by any external factors. Drivers were told that collected data will be used only for study and research purpose and not for enforcement purpose to reduces the possible bias in driver’s speeding behaviour.

3.1 Data Collection

The study was conducted on 1.5 km stretch of a four lane (divided) Nagpur-Mumbai Highway on the outskirts of Wardha Town, about 80 km from Nagpur (India). The geometry of the road was fairly straight and vertical layout was fairly level. Entire surface was fair during data collection. The study was conducted on sunny days with dry pavement conditions. Test stretch of road was free from intersection, side encroachment, pedestrian movements, etc. All types of vehicles (like trucks, cars, motorized three wheelers and motorized two wheelers) run over this highway facility. Being a newly build facility, traffic volume was very lowensuringfreeflowconditionforvehicles.

GPS were installed in vehicle before conducting the experiment to collect speed and position data of vehicle at 1 second logging interval. All the drivers were asked to speed up from stop condition to achieve their desired speed (maximum speed at which driver feel safe for a given road geometry and environmental condition; hereafter referred as maximum speed) as early as possible and then they were allowed to drive at their maximum speed for some time. Further

drivers were asked to slow down to stop condition in the shortest possible time.

All the tripsweremadeduring freeflow traffic andall the vehicles used in this study were randomly sampledwithinvehiclesofreal trafficstreamplyingon that road. A total of 66 medium size trucks (10 to 12tonnecapacity)speedprofilesdatawerecollected.Acceleration-deceleration data was computed from second by second speed data using following formula:10;11.

where, a(t2) and d(t2) are the acceleration and deceleration respectively (m/s2) at time t2, υ1 and υ2 are the speeds (m/s) at time t1 and t2 (sec) respectively. The acceleration process ended when the increment in speedis≤0.5m/scontinuouslyfornextfiveseconds.The starting of deceleration process is defined fromthe time onwards where the deceleration values calculatedfromformulaare≥0:1m/s2 continuously for next five seconds11. At the end of deceleration process vehicle’s speed become zero. Acceleration and deceleration profiles were separated usingabove method. Figs. 3(a) and (b) present speed profiles (speed-time scatter) during acceleration anddeceleration. Idealized speed profiles (speed valuesare averaged over every one second) for acceleration and deceleration maneuver are also presented in Figs. 3(c) and (d). Main observations from Fig. 3 are;

1. Some trips do not start at zero speed as seen in speed scatter in acceleration maneuver. Since the logging interval of GPS is 1 second, the speed data is lost between successive seconds. Similarly for the same reason some trips in deceleration maneuver do not terminate at zero speed.

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2. Different drivers choose different cruising speed. This results in different maximum speed at the end of acceleration maneuver. The time taken to complete acceleration maneuver also varies with driver.

3. For the reason stated in (2) above, the speed at starting of deceleration maneuver is different for different drivers.

4. Maximum speed of vehicle observed during acceleration maneuver varies from 15.9 m/s to 9.09 m/s with an average maximum speed being 13.08 m/s. Other researchers11;5) also reported similar truck speed.

5. Time taken to complete acceleration maneuver (completion of acceleration maneuver is determined as mentioned earlier in this section) varied from 45 seconds to 60 seconds. This time

depended on the amount of acceleration applied by driver during maneuver (indicated by slope of speed profile inacceleration maneuver).

6. Time taken to complete deceleration maneuver varies from 18 seconds to 47 seconds. This indicates that the drivers apply different deceleration rates (indicated by varying slopes of speed profile of drivers) in decelerationmaneuver.

7. Idealized speed profiles in accelerationand deceleration do not follow ’S’ shape (implying zero acceleration at the beginning and end of acceleration maneuver) as also reported by Akcelik and Biggs20. This is because the ’S’ shape profilereportedbyAkcelikandBiggsisanidealcaseanddifficulttoobtainedinfieldexperiments.

(a) Speed Scatter During Acceleration

(c) Idealized Plot of Speed-Time During AccelerationFig. 3 Scatter and Idealized Plot of Speed During acceleration and Deceleraion

(b) Speed Scatter During Deceleration

(d) Idealized Plot of Speed-time During Deceleration

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3.2 Data analysis

The GPS speed and position data for 66 truck trips wascollectedinfreeflowcondition.Atotalof1716data points in acceleration and 1471 data points in deceleration were collected. Raw speed data obtained from GPS is smoothen using exponential smoothing method to minimize GPS error9.

The acceleration-deceleration speed profile datawas analyzed for various parameters like maximum and mean speed, acceleration and deceleration time and distance, maximum and mean acceleration and deceleration rates and speed at maximum acceleration and deceleration. Table I presents above parameters corresponding to acceleration and deceleration maneuver.

Table I Various Parameters of acceleration and Deceleration maneuver

maneuver Type

maximum speed Range

(km/h)

maximum speed (m/s)

mean speed (m/s)

a/D* Time (sec)

a/D* Distance

(m)

speed at maximum a/D* (m/s)

maximum a/D* Rate

(m/s2)

mean a/D* Rate

(m/s2)Acceleration 20-30 8.18 5.18 11 56.98 2.77 0.75 0.28

30-40 11.05 5.78 17 98.26 1.53 1.01 0.2940-50 13.24 7.62 34 259.08 1.27 0.96 0.2450-60 15.95 10.32 35 361.2 1.08 0.87 0.24

Deceleration 20-30 7.51 4.43 13 57.59 4.20 1.02 0.4730-40 10.46 5.84 18 105.12 3.01 1.01 0.4040-50 13.26 7.32 18 131.76 4.33 0.92 0.3250-60 14.55 7.92 25 198.00 5.80 0.88 0.35

* Acceleration/Deceleration

Table I presents the parameters of acceleration and deceleration maneuver of trucks. Parameters corresponding to each maximum speed range are determined after averaging the corresponding parameters of all trips which falls in that maximum speed range.

It is seen from Table I that there is a marked difference in acceleration behaviour of trucks with their maximum speed. Trucks with lower maximum speed range exhibit lower acceleration distance and time. Speed at which maximum acceleration is achieved reduces with increase in maximum speed range. This implies that drivers driving at higher speed employ higher acceleration at early stage of their acceleration maneuver. No consistent relationship is observed between maximum speed and acceleration (maximum and mean) rate.

Similar to acceleration behaviour, trucks exhibit lower deceleration distance and time for lower maximum speed range. No clear trend is observed between

maximum speed range and speed at which maximum deceleration occurs. No consistent relationship is also observed between maximum speed and deceleration (maximum and mean) rate similar to acceleration maneuver. Fig. 4. presents the acceleration versus speed plot for truck acceleration maneuver. The main observations from Fig. 4 are:

Fig. 4 Acceleration Speed Scatter

1. Acceleration value decreases with in-crease in speed of trucks. This implies

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that drivers use higher acceleration during startup. Similar observation is also reported by other researchers11;8;9;20.

2. The maximum acceleration value for truck observed for any trip is 1.008 m/s2. The maximum accelerations of all trips are computed and average maximum acceleration value of 0.73 m/s2 is observed. The average maximum acceleration values reported by Arasan3 and Dey17 are 0.79 m/s2 and 0.4758 m/s2respectivelyforIndiantraffic.These studies used radar gun or travel time to measure the speed of vehicle at definite locations and these speed dataare used to determine the acceleration values between two locations which gives average acceleration. Therefore, these reported maximum acceleration values are closer to average maximum acceleration value of current study. Acceleration studies from other countries like Gary Long13 reported the maximum acceleration values are 0.45 m/s2 to 2.95 m/s2 (depending on load to horsepower ratio) of trucks show higher than that is observed in the current study.

Fig. 5 presents the deceleration versus speed plot for truck deceleration maneuver. The main observations from Fig. 5 are:

Fig. 5 Deceleration Speed Scatter

1. The maximum deceleration rate observed for any truck trip in this study is 1.31 m/s2 which does not exceed maximum deceleration rate of 3 m/s2 recommended by ITE’s TrafficEngineering Handbook2 and 3.4 m/s2 recommended by ASHTO1.

2. Unlike acceleration, deceleration shows a different trend with speed. At the beginning of deceleration maneuver (at higher speed) deceleration increases up to certain level and then starts decreasing to become zero at zero speed. The speed at which maximum deceleration occurs is termed as ’critical speed’. The critical speed in case of trucks varies from 3.01 m/s to 5.80 m/s which is approximately of approach speed (the speed at which driver start decelerating). This is consistent with Wang et al.10 observation that vehicles achieve maximum deceleration rate at around 11th to 12th second in 15 second deceleration maneuver.

4 aCCeleRaTIoN moDelING

An idealized plot of acceleration-speed relationship (refer Fig. 4) is presented in Fig. 6 by averaging acceleration values over every 1 m/s speed interval. It can be observed from idealized acceleration-speed relationship (refer Fig. 6) that employed acceleration monotonically reduces with increase in vehicle speed

Fig. 6 Idealized Plot of Acceleration-Speed

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which can be described by single regime models. Therefore, two single regime models - (i) linear decay model and (ii) negative exponential model are proposed to described the observed acceleration-speed behaviour. Both models are calibrated for present data set and predicted acceleration values are compared with acceleration values computed from observed speed values (refer Fig. 6). Residual Sum of Squares (RSS) and various other error tests, such as Root Mean Square Percent Error, Mean Percent Error (MPE), Positive and Negative Percent Errors (PMPE and NMPE) and Maximum Absolute Error were used to asses the suitability of both models for present acceleration data set8. The error tests are used to assess the suitability of models since error tests do not need assumption of independence of variables on each other. Also the assumption of normality of variables, which forms the basis of many statistical tests, is not applicable to error tests. The errors are computed using following formulae8;

... 6

where, is predicted value from model, is observed value and N is number of observations. Percent error provides the deviation of model values from observed values in percentage and is a

quantitative measure of deviation. Since in mean error the positive and negative error may cancel out each other, the positive and negative percent error is calculated separately. These errors indicate overstating or understating of model. Maximum absolute error is yet another measure stating the absolute error of each data point and examining the maximum of that8. The reason for carrying out number of error tests is that no single test identifies the problems inmodel.Theresults of error tests for both models are presented in Table II to compare their suitability. Error test results of both models (presented in Table II) show that negative exponential model perform better than linear decay model (i.e. has lower errors) in all error tests. Also Pearson Correlation value of 0.719 for acceleration-speed data indicates low strength for linear relationship. Hence the negative exponential model is chosen for description of collected data and evaluated further in details.

4.1 Negative exponential acceleration model

The general form of the proposed negative exponential model is as follow:

a = k1 × ek2 × υ ... 7

where, a is acceleration (m/s2) at time t, υ is speed(m/s) at time t and k1, k2 are the model parameters to be evaluated from field data. Model parametersk1 and k2 are 0.666 and – 0.13 respectively obtained fromlinearregressiontechniquesandthecoefficientof regression is 0.92 which indicates good correlation between acceleration and speed of trucks.

Table II error Tests on models

model Type Rms Rms % % mean error PmPe NmPe absolute maximum error

Linear Model 0.016 22.84 0.12 24.85 14.49 0.22Negative Exponential Model

0.011 9.17 0.087 11.23 6.15 0.17

4.2 acceleration model Diagnostic

While ascertaining the statistical correctness of proposed model following assumptions are tested22,

1. Error terms are independent, and

2. Error terms are approximately normally distributed.

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Residual analysis is conducted to detect the violations of independence of errors and quantile plots are used to detect violation of normality of errors22. Residuals (difference between acceleration values calculated from observed speed values and calculated using model) are computed and plotted against predicted acceleration values (see Fig. 7a). The plot shows that residuals are uniformly spread over predicted values and do not show any trend. This depicts uniform variance of errors over predicted values, indicating independence of error terms. Since the data is observed over time, the residuals are also tested over time. Fig. 7b presents plot of residuals against time. The plot shows no trend over time depicting no dependence of errors over time.

(a) Residual vs Predicted Values

(b) Residual vs Time

Fig. 7 Residual Analysis

Fig. 8 presents the quantile plot showing observed acceleration values on X axis and predicted acceleration values on Y axis. Quantile plot shows satisfactory clustering around (45º) straight line indicating that

variables are normally distributed. This satisfiesanother assumption of regression.

Fig. 8 Quantile Plot

Paired t-test is also conducted to test the means of acceleration computed using observed speed values and accelerationcomputedfrommodelat5%significancelevel. Test result shows that there is no significantdifference in the mean of acceleration computed from observed speed and mean of acceleration obtained from proposed model.

4.3 speed and Position from acceleration model

The acceleration model equation reported above (referEquation7)isusedtofindspeedandpositionofvehicle at time t. The relations are derived as below;

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The idealized modeled speed and position are then computed from above equations and compared with observed idealized speed and position. Figs. 9a and 9b presents the observed idealized position trajectory (obtained by averaging the position values of different trips obtained from GPS over every 1 second time interval) and idealized speed profile (obtained byaveraging speed of different trips over every 1 second time interval) of a vehicle observed in this study. Modeledpositiontrajectoryandspeedprofileisalsoplotted in Figs. 9a and 9b. Kolmogorov-Smirnov two sample test is performed to compare the observed and modeled position trajectory and speed profile.The test result indicates that both samples come from populations having identical cumulative frequency distribution and match with respect to location, dispersion and skewness.

(a) Observed and Modeled Trajectories

(b) Observed and Modeled Speed

Fig.9ObservedandModeledTrajectoriesandSpeedProfiles

It can be concluded from above statistical test results that proposed model suitably describes the acceleration-speed relationship of present data set.

5 DeCeleRaTIoN moDelING

Scatter plot of deceleration-speed data points of truck is already presented in Fig. 5. Idealized plot of deceleration versus speed is obtained from scatter plots where deceleration values are averaged over every 1 m/s speed interval and presented in Fig. 10. Scatter plot and idealized plot of deceleration-speed data points (refer Figs. 5 and 10) indicate a strong relationship between deceleration and speed. Initially deceleration increases with decrease in speed and after achieving a maximum value, deceleration starts decreasing with further decrease in vehicle’s speed. Speed at which the maximum deceleration occurs is referred as ’critical speed’. Hence, it is more logical to model deceleration as a function of speed rather than as a function of time. This view is also supported by Bham and Benekohal8, Long13. Therefore, in present work, deceleration rate is modeled as a function of vehicle speed.

Fig. 10 Idealized Plot of Deceleration-Speed

Literature review yields no model describing deceleration-speed relationship during deceleration maneuver. However, Wang et al.10 proposed deceleration model based on relationship between approach speed and deceleration time as discussed earlier (refer Equations 4 and 5). This model is developed using speed data collected using GPS. Firstly, this model is calibrated with the present data

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set. Later, observed speed values are compared with computed speed from the Wang et al.10 model. A two sample Kolmogorov-Smirnov test is applied to check whether observed and predicted speeds are from same continuous distribution23. Test results indicates that two sets (observed and predicted) of speed have different cumulative distribution. This implies that Wang et al.10 modelisnotsufficienttodescribethepresentdataset.Therefore, a new model is required to describe the observed deceleration-speed relationship.

On observation of deceleration-speed relationship, it is felt that a dual regime model may be suitable for observed deceleration speed relationship (refer Fig. 10). Regime I can be referred to the region with speed > critical speed and regime II can refer to the region with speed critical speed. Dual regime model offers computational simplicity and reduces simulation time as compared to polynomial model model8;10). Hence the dual regime model is explored in detail in present study. The regimes are separated at critical speed (in present data set the critical speed is 3.49 m/s) where deceleration is maximum. Only limitation with the the dual regime model is that it has one point of discontinuity at critical speed. The Pearson correlation values are computed to ascertain the strength of linear relationship between deceleration and speed for both regimes. The Pearson correlation values are – 0:92 for regime I and 0:961 for regime II. This indicates that linear relationship (with opposite slopes) may exist between deceleration and speed in both regimes. The strength of linear relationship in regime I is weaker than that of regime II. Further, to ascertain the form of the model in both regimes, Residual Sum of Squares (RSS) are calculated for various deceleration-speed model like linear, second order polynomial and negative exponential for both regimes. The appropriate model is one which yields minimum value of RSS. The RSS values for different model forms are shown in Table III. It is observed from Table III that for Regime I, RSS values are minimum for negative exponential model and for Regime II for linear model. Hence, negative exponential and linear models are opted for regime I and regime II respectively.

General forms of these models are presented in Equation 9.

Table III Residual sum of squares (Rss) Values for Different model Forms

model Type Regime I Regime IILinear 0.066 0.006Negative Exponential 0.031 0.100Second Order Polynomial 0.038 0.036

... 9

where, d1 and d2 are deceleration rates (m/s2) in Regime I and Regime II respectively, k1 and k2 are model parametersforRegimeI,αisminimumdecelerationrate (m/s2)whenspeediszeroforRegimeIIandβisrateofchangeofdecelerationwithspeedυ(m/s)forRegime II.

These models are fitted to observed speed data indeceleration maneuver for calibration of model parameters. The resulting model parameters are k1 = 1.587, k2=0.017andcoefficientof regression, r2=0.834forregimeIandα=0.104,β=0.225and r2 = 0.92 for regime II. Plot of observed and modeled deceleration-speed relationships are presented in Fig. 11. It is seen from the Fig. 11 that predicted critical speed (speed at which deceleration is maximum) by models is 3.52 m/s while observed critical speed is 3.49 m/s. The average maximum deceleration value predicted by model is 0.891 m/s2 as against observed value of 0.805 m/s2. Further, the deceleration predicted by model at the beginning of deceleration maneuver is 0.138 m/s2 whereas the observed value is 0.06 m/s2 (refer Regime I as deceleration maneuver starts from maximum speed). The point of discontinuity is observed at the critical speed of 3.52 m/s. At this speed, where two regimes meet, the deceleration predicted by regime I is 0.879 m/s2, whereas by regime II is 0.851 m/s2. Except this point, the model is continuous. Hence, it is observed that model predicts critical speed, average maximum deceleration and deceleration

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at beginning of deceleration maneuver with fair accuracy and with only one point of discontinuity. In other multiregime models the points of discontinuity are more.

Fig. 11 Modeled Plot of Deceleration-Speed

5.1 Deceleration model Diagnostic

Various diagnostic tests, similar to that acceleration models, are used to check correctness of deceleration model. Residual analysis is carried to check the statistical correctness of model. Plot of residuals against predicted deceleration, for trucks, are presented in Fig. 12. This shows that residuals are uniformly distributed against predicted values depicting uniform variance of errors, which is one of the assumption in regression. The quantile-quantile plot for predicted versus observed deceleration for both regimes are obtained and presented in Figs. 13a and 13b. Clustering of points around a 45 line for both regimes indicate that the variables are normally distributed, which is an assumption in regression analysis. Regime II has less points due to its shorter span. Paired t-test is used to test the means of computed and observed deceleration for Regime I and Regime II at5%significance level.Thecomputeddecelerationis obtained from deceleration-speed relationship presented in Equation 9. Test result shows that there is nosignificantdifference in themeanofdecelerationcomputed from observed speed and mean of deceleration obtained from proposed model.

Fig. 12 Plot of Residuals Against Predicted Values

(a) Quantile Plot, Regime I

(b) Quantile Plot, Regime II

Fig. 13 Quantile Plots

5.2 speed and Position from Deceleration model

The deceleration model equation reported above for Regime-I and Regime-II (refer Equation 9) is used to find speed and position of vehicle at time t. The relations are derived as below;

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... 10

during deceleration maneuver in this study. Modeled position trajectoryandspeedprofile (obtainedusingfor Regime-I and Regime-II using Equation 10 and 11) is also plotted in Figs. 14a and 14b. Kolmogorov-Smirnov two sample test is performed to compare the observed and modeled position trajectory and speed profile. The test result indicates that both samplescome from populations having identical cumulative frequency distribution and match with respect to location, dispersion and skewness. It can be concluded from above statistical tests results that proposed model suitably describes the deceleration-speed relationship of present data set.

(a) Observed and Modeled Trajectories

(b) Observed and Modeled Speed

Fig.14ObservedandModeledTrajectoriesandSpeedProfiles

6 CoNClusIoNsThe Acceleration/Deceleration (A/D) model of vehicles are useful in many traffic application likedesign of deceleration lanes, signalized intersection design, instantaneous fuel consumption, emission modeling, etc. In the present study, data for entire A/D maneuver of trucks has been collected using advanced equipments like GPS for the first time on Indianhighway. Existing models of A/D are evaluated for their

Further, Figs. 14a and 14b present the observed idealized position trajectory (obtained by averaging the position values of different trips obtained from GPS over every 1 second time interval) and idealized speedprofile(obtainedbyaveragingspeedofdifferenttrips over every 1 second time interval) of a vehicle

... 11

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suitability and new accurate and simple A/D models are proposed to describe the observed acceleration speed and deceleration-speed relationships of trucks onIndianhighways.Themainfindingsofthisstudyare as follows:

1. Trucks with lower maximum speed range exhibit lower A/D distance and time during A/D maneuver.

2. The maximum acceleration values for trucks varied from 1.01 m/s2 to 0.57 m/s2 which is higher than acceleration values reported by Arasan3 and Dey17 (0.79 m/s2 and 0.4758 m/s2

respectively) for Indian traffic. Older studiesused radar gun or travel time to for speed measurement of vehicles at definite locations.Therefore, these speed data provide the average acceleration of vehicle between two locations instead of maximum acceleration value of vehicle.

3. In the acceleration maneuver, it is observed that acceleration values decreases with the increase in speed. Therefore, a negative exponential acceleration model of form at = k1e

k2υ (where at is acceleration at time t second, υ is speed in m/s and k1 and k2 are model parameters) is proposed to describe the observed truck’s acceleration-speed relationship. It is evident from statistical tests that proposed model describes the acceleration-speed relationship satisfactorily.

4. In deceleration maneuver, initially with decrease in speed deceleration increases and after achieving a maximum value, deceleration falls with further decrease in vehicle’s speed towards the end of maneuver. Speed at which the maximum deceleration occurs is referred as ’critical speed’. Therefore a dual regime model is proposed to describe deceleration-speed relationship observed in this study. Negative exponential and linear models are found suitable for regime I (speed > critical speed) and regime II ( speed critical speed) respectively.

5. Maximum deceleration rate is observed as 1.31 m/s2 which is less than the maximum

deceleration rate of recommended by ITE’s TrafficEngineeringHandbook2 and AASHTO1 (3 m/s2 and 3.4 m/s2).

6. Observed and modeled position trajectories and speedprofilesmatchedwithinbothaccelerationand deceleration maneuvers.

Simple and accurate A/D models of vehicles help in developing better simulation models, fuel consumption and emission models. Further, the present study may be extended to A/D modeling of all class of vehicles generally observed on Indian roads. Impact of different vehicle and driver characteristics on their A/D behaviour can also be explored.

ReFeReNCes1. AASHTO, (2004). A Policy on Geometric Design of

Highways and Streets, Washington D.C.2. TrafficEngineeringHandbook,5th Edition, Institution of

Transportation Engineers, Washington D.C., 2000.3. V. Thamizh Arasan and Reebu Zachariah Koshy.

MethodologyforModelingHighlyHeterogeneousTrafficFlow. Journal of Transportation Engineering, ASCE, 131:544–551, 2005.

4. C.R. Bennett and Dunn R.C. Driver Deceleration BehaviouronaFreewayinNewZealand.TransportationResearch Record: Journal of Transportation Research Board, 1510:70–74, 1995.

5. SarochBoonsiripant.SpeedProfileVariationasaSurrogateMeasure of Road Safety Based on GPS-Equipped Vehicle Data. PhD thesis, Georgia Institute of Technology, 2009.

6. A. Dockerty. Accelerations of Queue Leaders from Stop Lines. Traffic Engineering and Control, Vol. 8, No.3:150155, 1966.

7. A. Maradudin Gazis D.R., Herman R. The Problem of the AmberLightTrafficFlow.OperationResearch,8,No1,1960.

8. G. Bham and R. Benekohal. Development, Evaluation and Comparison of Acceleration Models. 81st Annual Meeting of Transportation Research Board, Washington D.C., pages 1–42, 2002.

9. F. Dion H. Rakha, M. Snare. Vehicle Dynamics Model for Estimating Maximum Light Duty Vehicle Acceleration Levels. In 83rd Transportation Research Board Meeting, pages 1–22, 2003.

10. H. Li J. Ogle J. Wang, K. Dixon. Normal Deceleration Behavior of Passenger Vehicle at Stop Sign Signaled Intersection Evaluated with in-Vehicle Global Positioning System Data. Transportation Research Record, 1937:120–127, 2005.

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11. H. Li J.Wang, Karen K D. and J.Ogle. Normal Acceleration Behaviour of Passenger Vehicles Starting from Rest at all Way Stop Controlled Intersections. Transportation Research Record, Journal of Transportation Research Board., 1883:158–186, 2004.

12. C. Lee and T. Rioux. Texas Model for Intersection. University of Texas at Austin, 1:1–10, 1977.

13. Gary Long. Acceleration Characteristics of Starting Vehicles. Transportation Research Record, 1737:58–70, 2000.

14. Arif Mehmood. Determinants of Speeding Behaviour of Drivers in al Ain (United Arab Amirates). ASCE Journal of Transportation Engg., 135, No 10:721–729, 2009.

15. S.K.Rao M.L. Raichaudhari. Acceleration Characteristics of Vehicles at Signalized Intersection. Indian Highways, Journal of Indian Roads Congress, pages 35–37, 1989.

16. M. Snare. Dynamic Model for Predicting Maximum and Typical Acceleration Rates of Passenger Vehicles. Master’s Thesis, Virginia Polytechnic Institute and State University, 2002.

17. P. Biswas P. Dey. Acceleration of Queue Leaders at Signalized Intersection. Indian Highways, Journal of Indian Roads Congress, pages 49–54, 2011.

18. S. Gangopadhyay P. Dey, S. Chandra. Speed Studies on Two Lane Indian Highways. Indian Highways, Journal of Indian Roads Congress, pages 9–18, 2008.

19. A.SantiagoP.S.Parsonson.TrafficSignalChangeIntervalMust be Improved. Public Works, 1980.

20. D.C.BiggsR.Akcelik.Acceleration ProfileModels forVehicle in Road Traffic. Transportation Science, 21, No 1:36–54, 1987.

21. M. Besley R. Akcelik. Acceleration and Deceleration Models. In 23rd Conference of Australian Institute of Transport Research, Monash University Melbourne, Auatralia., 2002.

22. R.J. Freund and W.J. Wilson. Statistical Methods. Academic Press, 2003.

23. R. Johnson. Probability and Statistics for Engineers. Pear, 2000.

24. S.E. Samuels and J.R. Jarvis. Acceleration and Deceleration of Modern Vehicles. Technical Report, Australian Road Research Institute, Report 86., 1978.

25. Fox T.C. Wortman R.H. An evaluation of Vehicle DecelerationProfiles.JournalofAdvanceTransportation,8, No 3, 1994.


DIsPuTe aVoIDaNCe PRaCTICes IN CoNsTRuCTIoN CoNTRaCTs

S.K. dhawan*

* Former Chief Engineer, C.P.W.D., E-mail: [email protected]

1 It is often said “Prevention is better than cure” so it is with disputes. The focus should be on preventing the disease rather than curing it subsequently. There is dichotomy with our construction contracts in this country. Client is keen on getting the work completed within the prescribed time schedule and conforming to therequiredstandardsandspecificationsandwithleastcost. The contractor on the other hand is interested in theworktobecompletedatthemaximumprofit.

Constructions projects are developed in an open environment where variables like soil, unforeseen site conditions,weather andnatural disaster are difficultto control. Successful Project Management would require both client and contractor working together towards completion of the project within the budget, on schedule with required quality and safety and also with minimum disputes and litigations. Cost and time involved in arbitration has been worrying the engineering profession as the department has to payinterestoverclaimsafterthepaymentofthefinalbill.

2 A construction project, over the years, has been characterized by:- a) Contractors bidding competitively to get

the work and then achieve maximum profit.

b) Project contains unknowns/uncertainties and the owners like to transfer all the risks to contractor.

c) Use of poorly made tender documents d) Unfair/one sided contract documents. e) A project involves number of agencies

which do not have coordination.2.1 Some common issues leading to disputes are:-

i) Poor and unfair documentation in general, designs,drawingsandspecificationsetc.

ii) Internal and external uncertainties

iii) Unfair allocation of risk

iv) Delay/failure in:-

● Handing over the site free fromencumbrances

● Getting clearance from statutorybodies including forest and environment clearance etc.

● Arranging power connections,permits etc.

● Issue of working drawings,structural drawings, service drawings etc.

● Givingdecisionsandapprovals

● CertificationofBills/Payments

● Settlement of Rates for extraitems, extra quantities beyond deviations.

v) Delay can be due to:-

● Slowprogressand timeextensionetc.

● OtherContractors/Sub.Contractorsworking on the Project

● SomeExternalinfluence

3 Dispute avoidance practices can be divided into two stages:-

- Pre-award stage

- Post-award stage

Pre-award stage - Pre tendered stage

- Tendered stage

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3.1 Pre tendering Stage

- Survey and investigations - Designandspecifications - Availability of Site - Tender Process should be fair and unbiased - Contract documents- General Conditions and Special conditions etc. - Risk management - Dispute Resolution mechanism - Availability of Funds

3.2 Tendered Stage

● Thetenderdocumentsshouldeffectivelyconvey the owner’s requirements and the tenderers should seek all clarificationsduring pre-bid meetings

● KeepawatchonAbnormallyHighRate/Abnormally Low Rate (AHR/ALR) items anticipating fluctuations in thequantities.

● To inspect the project site beforetendering.

● Avoid unrealistic time period for thecompletion which results in extension of time (ET) and thus, ‘time no longer remains the essence of the contract’.

● Reject unrealistically or absurdly lowrates on scrutiny, as under quoting has brought failures to some projects.

3.3 Post contract award stage (Construction management)Site Management * Site manager (EE) and contractor should work out the requirement of materials, equipment etc. * Maintain progress report and regular monitoring

* Should not allow to sublet the work without the approval of the client * Sort out conflicts related to quality and safety Standards * Preparation of work programme and Review * Team work- develop team spirit * Timely payment * Timely decisions * Genuine claims arising fromsitedifficulties,price escalation and variations should be settled quickly.Claims should be well supported by facts. This implies keeping relevant records.

- Liquidated damages:- Should be applied as a last resort when there is real loss to the owner due to excessive delay.

- Communication:- Meeting of Senior Engineer with contractor at site may ensure smooth progress during execution.

4 Contract administration4.1 ● Jointly identify, understand, appreciate

and agree to each other’s goals and priorities,

● Contractor to understand time, costand quality requirements of the owner department.

● Ensure reciprocal help (contractor /department)

● Understandtherightsandobligationsofboth the parties,

● Agreetorealisticworkprogramme, ● Contractortoadheretoqualityassurance

procedures, ● Adheretothesafetystandards. ● Promptattentiontocorrespondence,

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● Prompt assessment and processing ofclaims,

● Checksontimelimits, ● Keep good project records

(Documentations), ● Periodic training and awareness

programme ● Timely decisions without fear and

favour, ● Developteamspirit, ● Appreciategoodwork.4.2 Trust, goodwill and co-operation:- For successful completion open and honest communication, trust, good will should exist between the contractor and the department. A working knowledge of the contract agreement removes many disputes.

4.3 Owner/Department Breaches - The common breaches of contract, from the parties are:-

Common inadequacies like delay in handing over the site free from encumbrances, supply of materials, working drawings, designs, failure/delay in making payment against running Account Bills, extra items, substitute items, payment of mobilization and machinery advances, delay in approving the specialize contracts and suppliers, failure to obtain environment clearances before award of work, failure to shift utilities (Services), approval of cutting of trees, land acquisition, removal of encroachment etc.

5 Contractors breaches5.1 ● Abandoning of work or failure to

complete the work ● Delayincompletion ● Use of substandard materials and

substandard work methodologies ● Failuretosubmitplannedprogress ● Unauthorizedsub-letting ● Failuretoinsureasrequired ● Failuretoensuresafety ● Failure to employ qualified engineers

causing damages to property or work of another contractor

● Misappropriation through extraconsumption of stipulated materials and failure to account for or return such materials.

5.2 Inadequate Information about the site

Survey the site/property to ascertain details like type of soil, ground water condition, availability of water for construction, availability of materials for construction and lead involved, availability of borrow pit areas, approaches to the site etc.

In the case of major projects, the tender documents invariably enjoined up on the bidders to inspect the site of work in order to familiarize themselves with the ground conditions but, also use such information in preparing their detailed bids.

example:- In a case involving the construction of school building for a certain owner, it was provided that the contractor should be entitled to enter the site immediately so as to complete the work by the agreed date. The only access to site was from the road and the soil between the road and site was soft, as such, the contract incorporated a provision that contractor should lay a temporary slip road-way from road to the site of work and subsequently provide a permanent path way. The contractor was forced to suspend the work after commencing it because of threatened injunction from adjoining owner who claimed that the road was his property. Even though 3rd party claims were unfounded and the contractor resumed and completed the work. The contractor claimed damages for the losses suffered due to delay caused by 3rd party action. It was held by the court that there was no implied warranty by the owner against wrongful interference by 3rd party for the free access to the site.

In another case involving the widening of the existing National Highway, the contract was allotted without the full availability of site.Awrong certificate wasgiven with regard to acquisition and possession of land. A large number of trees and structures existed in the right of way of the road. The stipulated completion of project was 30 months. But, land could not be acquired fully even after a lapse of more than two years. Similarly a delay was caused by the State Government

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for according permission to cut the trees. The clause regarding the machinery advance as contained in the contract stipulated that the machineries could not be disposed of by the contractor and exemption in the event of custom duty was given under the express condition. Since the machinery was idle in the face of availability of site, the contractor suffered losses. Even the manpower was idle.

5.3 Delay in a approving variation:-

In the above mentioned case the item of tree cutting was not included in the agreement. The grubbing of stump and root of the trees was responsibility of the contractor. The State Forest Department while giving permission to cut the trees, told the owner of the project to cut the trees and deposit them in the ware house department of the forest department. The owner ordered to start cutting the trees and simultaneously moved a proposal for the determination of the rate of tree cutting. The contractor started cutting trees and submitted rates of tree cutting which was not approved by client even after cutting of the trees are over. Ultimately a very low rate was sanctioned which was not accepted by the contractor, who took the matter in the dispute adjudication board, who gave a ruling in favour of the contractor, though the rates claimed by the contractor were moderated by the board.

5.3.1 In other case the contractor was asked to take up the work of reinforced earth walls for approaches of theflyoversonacertain reachofNH.Thisworkwas not included in the B.O.Q. The work involved the strengthening of foundation of R.E. walls. The client took a stand after the completion of work that the work of the foundation of R.E. wall was not payable even though the engineer had recommended the payment of work in question based on which the running payments were released by client, but, suddenly the recovery of amount of question was ordered and affected on the plea that the vigilance department had ordered the recovery of payment in view of the provision of the agreement. This is a classic example where the contractor kept on doing the work on the assurance of the engineer that the payment would be ultimately made.

5.3.2 On account of improper interpretation of contract

When the matter was referred by the contractor to Dispute Adjudication Broad (DAB), the client took a plea that the payments recommended by the engineer was based on provisional rates and that the same were liable to be cancelled subsequently. The provision in the agreement provides that the engineer can order thevariationsubjecttotheconditionthatthefinancialvariation of such variation is less than 1 % of contract price and the total value of variation should not exceed 10% of the contract. Even though both these conditions have not been violated, yet client went ahead with e recovery of the payment in question. The contractor won the case in the DAB. However, client hasfiledappealbeforetheArbitalTribunalagainsttherecommendations of DAB.

6 CoNClusIoN

Various stages of any project are as follows:- i) Preplanning, ii) Planning, iii) Execution, iv) Closure of the contract.If preplanning goes wrong there may be more than 100% error in the cost of construction. Faulty planning may cause over run by as much as over 50%. Therefore, these two stages of any project formulation are very important. The drafting of the tendered conditions is equally important. The job should not be left to the raw hands. The persons drafting the tender conditions should be fairly experienced in the various aspects of contract management. A poorly drafted contract is bound to create friction between the planning team and fieldteamwhoareboundtoindulgeinablamegameon account of faulty work caused by implementation ofadeficientcontract.

The project management team in the field shouldcomprise of experienced personnel at different levels in the hierarchy of the team. Last, but not the least, the watch word is vigilance. Any vigilant owner will see to it that the project is completed within the projected time and cost. There is no substitute to alertness.

March 2014

Documents

Transcript of March 2014