CHP 4:CONSTRUCTION OF ROADS

BY: R.V. K

TYPES OF PAVEMENTS•Un Surfaced–Earthen roads–Gravel roads•Surfaced–Bituminous Road–Cement Concrete Road•Un Conventional–Block Pavement

Further classification

Flexible Pavements– Earthen Roads–Gravel Roads–Bituminous Roads

Rigid Pavements–Reinforced Concrete– Plane Concrete Roads

FLEXIBLE PAVEMENT RIGID PAVEMENT

Types of Pavements

Wheel Load Distribution

Flexible Rigid

Properties Flexible Rigid Design Principle

Empirical method Based on load distribution characteristics of the components

Designed and analyzed by using the elastic theory

Material Granular material Made of Cement Concrete either plan, reinforced or prestressed concrete

Flexural Strength

Low or negligible flexible strength

Associated with rigidity or flexural strength or slab action so the load is distributed over a wide area of subgrade soil.

Normal Loading

Elastic deformation Acts as beam or cantilever

Excessive Loading

Local depression Causes Cracks

Stress Transmits vertical and compressive stresses to the lower layers

Tensile Stress and Temperature Increases

Design Practice

Constructed in number of layers.

Laid in slabs with steel reinforcement.

Temperature No stress is produced Stress is produced Force of Friction

Less. Deformation in the sub grade is not transferred to the upper layers.

Friction force is High

Opening to Traffic

Road can be used for traffic within 24 hours

Road cannot be used until 14 days of curing

Surfacing Rolling of the surfacing is needed

Rolling of the surfacing in not needed.

LOAD DISTRIBUTION

PAVEMENT MATERIALSDifferent materials are used in different typesof pavements• Soil• Aggregates (natural, artificial)• Bitumen, Tar, Emulsion, Cutbacks• Modified bituminous binders • Bituminous mixes

• Cement• Cement concrete (plain, reinforced, prestressed)• Stabilized materials• Recycled materials

Tests

• Tests on soil-CBR test• Tests on agg- Abrasion,Impact,Shape test• Tests on bitumen-Penetration,Softening,flash

n fire point etc

EARTHEN ROADS

General Terms used in Earthwork of Roads

1. Borrow Pits2. Balancing Earthwork3. Lead & Lift4. Spoil Bank

Borrow Pits• Small pits dug parallel to the road alignment

on both sides of the road formation to draw extra earth required to fill in embankment.

Spoil Bank

• Extra earth excavated and to be dumped on the road sides in road in cutting.

• Dumped in regular shape for future use.

Balancing Earthwork

• While constructing road, it is desirable for a segment of road, that the quantity of earthwork in cutting and embankment should be nearly equal if the soil available is good for the use.

• If possible, keeping in mind the limiting values of gradients and curves, the alignment is so fixed to have the equal quantity of earthwork in cutting and banking.

• This is known as balancing earthwork.

Lead & Lift

• Lead: Horizontal distance travelled by the earth to be moved for banking or dumping.

• Lift : Vertical distance travelled by the earthwork after excavating.

Construction Procedure for Earthen Road• Preparation of Sub-Grade: Arranging sub-grade in

proper gradient & camber.• The sub-grade is rolled & watered to have OMC &

compacted to MDD.• Over it, a layer of soil 10cm thick is sprayed, rolled,

& finished to have required camber & gradient.• 4-5 days curing.• Opening to traffic.• Watering for 10 days after opening to traffic.

Sub-GradeSoil Layer 10 cm Thick

Marking Road Levels & Boundaries

• Marking the centre line of alignment on ground with the help of theodolite.

• Marking carriageway, shoulder, berms, borrow pits & road boundaries.

• Putting pegs & clearing stakes in the sides & cleaning the area within the clearing stakes.

Construction Steps

• Clearing & Grubbing: It includes removing any unwanted material i.e. tree roots, grass, loose soil, Preparing the leveled surface

• Stripping off the top of soil to avoid the plant growth on the road.

• Excavation: if the existing material is not suitable for the road, other suitable material is dumped in the excavated portion.

• Embankment preparation

Sheep Foot Roller

SOIL STABILIZED ROADS

soil stabilized roads • Step1 Stabilization

Soil stabilization is the process whereby soil and related materials are made stronger and more durable by mixing with stabilizing agents. The common method to achieve soil stabilization are:a) Stabilization by compactionb) Mechanical stabilizationc) Stabilizing by the use of stabilizing additives like cement, lime, bitumen and many other stabilizers available in the market. Alternatively, you may use TopSeal-SoilStabilizer a Soil Stabilizer & Strengthener.

• 100% Environmentally safeNon-toxic, non-flammable non-corrosive, non-allergenicWater-based liquid form

Step 2 SeaIing•

The stabilized soil surface is then sealed with TopSeal SOIL SEALANT, providing a waterproof layer to prevent rain water penetration into the soil and keep the road in condition at all times. A stabilized soil road in dry condition will perform in its best condition with TopSeal Soil Sealant covered on soil surface, making it dust free and mud free at all times.

• Waterproof.No erosion by rainwater & trafficMaintain soil/gravel road strength even during rainy seasonsDust & mud freeMinimum maintenanceNot slippery, overcoming hilly road problemsSeal stabilized soil surface using Top Seal Soil Sealant

Step 3Maintenance

• Patching any pothole or depression by mixing roadside soil with TopSeal-SoilStabilizer, followed by sealing a layer of TopSeal Soil Sealant on the affected area. Maintenance can be done as and when required for long-lasting road.Pothole & Depression Maintenance

WBM Roads

Definition: The pavement base course made of crushed or broken aggregates mechanically interlocked by rolling and voids filled by screening and binding material with the assistance of water

Salient Features of WBM Roads

• WBM means Water Bound Macadam.• The word Macadam comes from the name of

Scottish Engineer John L. Macadam.• Wearing surface is formed by cleaned,

crushed aggregates which are spread and rolled by sprinkling water.

Salient Features of WBM Roads

• Low cost• Thickness range: 8cm to 30 cm• Camber : 2.5% to 3% OR 1:36 to 1:48• Surface is better than earthen road but rough

as compared to bituminous or Concrete roads• Can be used as Base Course for Bituminous or

Concrete roads.

Salient Features of WBM Roads

• Low cost• Thickness range: 8cm to 30 cm• Camber : 2.5% to 3% OR 1:36 to 1:48• Surface is better than earthen road but rough

as compared to bituminous or Concrete roads• Can be used as Base Course for Bituminous or

Concrete roads.

IRC Recommendations for Course Aggregate Grading for WBM Roads

Grading No Size Range (mm) Sieve Size (mm) % Passing the sieve by weight

1

2

3

90 to 40

63-40

50-20

10080634020

8363504020

6350402010

10065-8525-600-150-5

10090-10030-700-150-5

10095-10035-700-100-5

IRC Recommendations for Grading of Screenings

Classification Grading

Size of Screenings mm

Sieve sizemm

% by weight passing the sieve

A

B

12.5

10.0

12.510.04.750.15

10.04.750.15

10090-10010-30

0-8

10085-10010-30

Construction Procedure of WBM Roads

• 1. Preparation of Sub Grade• 2. Preparation of Base Course• 3. Intermediate Layer• 4. Wearing Surface• 5. Shoulders

Sub Grade

Base CourseIntermediate Course

Wearing Course ShoulderShoulder

Precautions in Rolling WBM Roads

• Roller to be used- 8-10 Tonnes• Rolling should be done from edges to the centre• The successive rolling strips should be overlapped• Length of each rolling should be <=200m.• Water should be sprinkled and not poured by

buckets• The rolling should be done for 80 passes or until

the aggregates are broken.

RIGID PAVEMENTS :

Pavements usually constructed using plain or unreinforced cement concrete slabs having high flexural strength.

It serves as good and durable wearing surface as well as an effective and strong base course of highway pavements.

WHERE ARE RIGID PAVEMENT PROVIDED ?

Rigid pavements are usually provided when road stretch is subjected to adverse conditions:1. Very heavy rainfall.2. Poor soil conditions3. Poor drainage4. Extreme climatic conditions5. Combinations of some of these conditions

which may lead to development of cracks in pavements.

MATERIALS FOR CONSTRUCTION OF CC PAVEMENTS :

Portland cement : --OPC of grade 43.--OPC of grade 53.--Portland pozzolona cement with fly ash (20 per cent)Portland slag cement.2. Coarse aggregates :

Los angeles abration value < 35 %

Combined flakiness and Elongation index

<35%

Water absorption <3%

soundness For Na2So4 <12%For MgSo4 <18%

Fine aggregates : clean natural sand / crushed stones /combination of both.It should be free of clay ,coal and ignite. Well graded with 100% passing 10 mm sieve.

WATER: Water used for mixing and curing of concrete shall be clean and free from injurious amount of oil, salt, acid, vegetable matter or other substances harmful to the finished concrete. It shall meet the requirements stipulated in IS:456.

Chemical Admixtures : conforming to IS:9103 and IS:6925 shall be permitted to improve workability of the concrete and/or extension of setting time, on satisfactory evidence that they will not have of any adverse effect on the properties of concrete with respect to strength, volume change, durability and have no deleterious effect on steel bars.

Reinforcement:• steel dowel bars (rounded) with yield

strength 240 MPa are used for the load transfer across in expansion and construction joints.

• Plain or twisted steel bars are used as tie bars are used as tie bars at longitudinal joints.

• Basic Components of CC Pavements:

• --soil subgrade.• --drainage layer.• --sub-base course generally constructed using

lean cement concrete or ‘dry lean concrete’• --separation membrane laid on top of base

course.• --CC pavement slabs Using ‘ paving quality

concrete’ (PQC)• --construction of different types of joints in

CC pavements.

• DIFFERENT TYPES OF CC PAVEMENTS:

Jointed Plain Concrete Pavement (JPCP)• – does not use any reinforcing steel

Jointed Reinforced Concrete Pavement (JRCP)• – Reinforcing steel placed at mid height and discontinued at the

joints.

Continuously Reinforced Concrete Pavement (CRCP)• – This method is very costly and generally not used in India.

Pre-stressed Concrete Pavement (PCP)• – Comprises new and innovative construction methods

Among these Plain CC pavements are most commonly used.

Equipments required for the different phases of concrete road construction:

Three wheeled or vibratory roller for compaction purpose

Shovels, spades and Sieving screens

Concrete mixer for mixing of concrete

Formwork and iron stakes

Watering devices - Water Lorries, water carriers or watering cans

Wooden hand tampers for concrete compaction

Cycle pump/pneumatic air blower for cleaning of joint

Mild steel sections and blocks for making joint grooves for finishing purpose

• METHODS OF CONSTRUCTION OF CC PAVEMENTS :

1. Construction by Slip Form Paver2. Construction by Fixed Form Paver. 3. Construction by Fixed Form and labour oriented method of paving. • Basically different operation involved in construction of CC

pavements slabs are :

a) spreading prepared concrete mix to desired thickness, grade and cross profiles.

b) Compacting.c) Finishing the surface to desired surface profile.d) Texturing.e) Curingf) Cutting of construction joints and longitudinal joints.

TYPES OF JOINTS IN CC PAVEMENTS:

A) Longitudinal joints ( parallel to traffic flow).

B) Transverse joints ( perpendicular to traffic flow) -- Contraction joints -- Expansion joints. -- construction joints.

• Longitudinal joints

• During initial period of curing ,shrinkage cracks usually develops in CC pavements ,when length or width of the slabs exceeds 4.5 to 5 m width or more.

• Hence longitudinal joints are provided whose spacing depends on width of traffic lane . For instance if width is 3.5 or3.75 , then spacing of longitudinal joints is also 3.5 or 3.75m respectively.

CONTRACTION JOINTS :

• These are purposely made weakened planes which relieve the tensile stresses in the concrete Caused due to changes in the moisture content (Drying shrinkage) and/or temperature and• Prevent the formation of irregular cracks due to restraint in free contraction of concrete .

Purpose of joints in Concrete Roads

1. To absorb expansion & contraction due to variation intemperature. 2. To avoid warping of slab edges3. To grant facility in construction .

Construction of contraction joints :• They are formed initially by sawing a groove of 3-5 mm with up to about one-fourth to one-third the slab which facilitates the formation of a natural crack at this location extending to the full depth.

Two methods of construction of contraction joints:1. As ‘plain joints without dowel bars’.

2. With dowel bars.

Expansion joints

• There are full-depth joints provided transversely into which pavement can expand, thus relieving compressive stresses due to expansion of concrete slabs, and preventing any tendency towards distortion and buckling.• They are allows expansion of slabs due to temperature.• A joint filler board of compressible material is used to fill the gap between the adjacent slabs at the joint.• The height of the filler board is such that its top is 23-25mm below the surface of the pavement.• The joint groove is filled by a sealant .

CONSTRUCTION OF EXPANSION JOINT WITH LOAD TRANSFER DOWEL BARS

1. A steel bulk head with drilled holes at desired intervals is provided to support end of slabs adjoining expansion joint such that dowel bar can be inserted up to mid-length and held in correct position.

2. Concreting is done , filler board is inserted through gap of expansion joint ,so that dowel bars are properly placed in position .

3. Now filler board will be 25mm below the surface of slab.4. Wooden strips of 20x25 size and 25 mm depth are placed on top of

filler to fill gap during concreting .

5. After concrete is cured for a period of 14 days ,wooden strips are removed and gap is thoroughly cleaned .

6. The sealant is heated ,poured in gap of joint, above filler board. Top of sealant shall be at same level as adjoining pavement surface.

EFFECT OF REINFORCEMENT IN CONCRETE PAVEMENTS

WORKING OF EXPANSION JOINTS :

• During hot climate CC slab expands towards the gap provided at expansion joint, due to which filler board and joint sealer gets compressed and pushed up.

• Dowel bars also move along with the slab, occupying the space in the metal cap attached at the end of each dowel bar.

• AND, During cold climate slabs contracts and gap increases and dowel bars also move along with slab.

• The compressed filler board may partly recover and joint sealer moves down.

JOINT SEALERTop portion of gap at expansion joint above the joint filler is sealed to prevent entry of water and grit into pavement through expansion joint

The sealer should be impermeable and flexible to accommodate slab movements , sealant should not flow in hot season or become brittle in winter.

Rubberized bitumen is commonly used.

Hence, for effective sealing of joint for a long period, it is essential that sealing compounds posses these properties :1. Adhesion to cement concrete edges.2. Extensibility without fracture.3. Resistance to ingress of grit.4. Durability.

Some sealants are:• Hot poured rubberized Asphalts (Thermoplastic type)• • Cold applied poly sulphide sealants( performs well for 5 to 7 years). • Cold silicone Sealants(performs well for 10 years.)

QUALITY CONTROL DURING CONSTRUCTION:

1. CA samples collected should be tested to specified tests in the laboratory to decide suitability.

2. Grading of CA and FA for mix is checked and compared with specified gradation.

3. Samples of fresh CC mix are collected ,cube and beam specimen prepared and tested according to standard test and checked with acceptance criteria.

4. Side slabs of pavements is checked to find hungry/honeycombed surface such surfaces are finished with cement mortar.

5. Regularity of finished pavements is checked with a 3m straight edge, 6 to 12 hours after laying , maximum permissible number of irregularities of 4 mm and 7 mm sizes in a 300 m stretch are 20 and 2mm.

• Unevenness index or roughness index is measured using bump indicator, along the wheel path of each lane; the average value of unevenness index shall not exceed 2200 mm/Km length of highway.

OPENING TO TRAFFICThe entire surface of newly laid pavement is carefully examined for :1. Fine cracks have developed on surface2. Non-uniform settlements of CC slabs has

taken place near abutments or along high embankments.

If any such defect is noticed ,then corrective measures may be taken up.

A newly constructed CC pavement stretch shall be opened to traffic only after a minimum curing of 28 days.