Author Instructions for Extended...

A NOVEL CONTROL POTHOLE REPAIR SYSTEM USING RADIANT HEATFOR LONG LASTING PATCH REPAIRS

Juliana Byzyka, Corresponding AuthorBrunel UniversityStation Road, Uxbridge, Middlesex UB8 3FG, United KingdomTel: +44 7475 719 051 Email: [email protected]

Mujib RahmanBrunel UniversityKingston Ln, Uxbridge, Middlesex UB8 3PH, United KingdomTel: +44 7894 339 752 Email: [email protected]

Denis Albert ChamberlainBrunel UniversityKingston Ln, Uxbridge, Middlesex UB8 3PH, United KingdomTel: +44 7808 760 796 Email: [email protected]

Word count: 5450 words text + 8 figures x 250 words (each) = 7,450 words

Submission date: 30/07/2016

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Byzyka, Rahman, Chamberlain

ABSTRACTPotholes are localized depressions developed in asphalt pavement between surface and base courses of asphalt concrete (AC) pavements. Potholes are a water dependent phenomenon increased by traffic loading. Typical pothole repair methods includes temporary and permanent solutions that are highly affected by detracting factors like such as thermal segregation, leading to inferior compaction, and poor bonding between old and new layersasphalt and others. To control these factors, Poorly executed repair methods promote early pothole repair failure, high repair costs, and unpleasant or even dangerous road networks. Hence, it is important to improve repair methods. This study aims at developing adequate bonding between old and new AC mix when a pothole repair is executed. To achieve this, aa novel prototype Control Pothole Repair System (CPRS), suitably modified for laboratory experimentation, has been developedbuilt. The CPRS includes three core features: (a) flexible repair design, (b) multiple, motion controlled radiant heating units that operate within a 443mm by 1.50m working envelope and (c) a Short message service (SMS)/Global positioning system (GPS). The reported study relates the initial development of CPRS and trials with it. Outcomes demonstrate the importance of preheating and strict heating provisions to the boundaries of patch repairs, both affecting the strength and durability of hot asphalt repairs. The laboratory outcomes are also used to effectively calibrate a 3D finite element modelling tool of the heating process.

Keywords: Asphalt, Pothole repair, Control Patch Repair System, Interface bonding, Radiant heat, Finite Element Modelling

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INTRODUCTIONPothole distresses appear in the form of small or large bowl shaped holes in asphalt pavements (1, 2). Usual causes of potholes are weak pavement caused by poor workmanship, inadequate drainage, and failures caused within the base or sub-base (1). Potholes are a water dependent phenomenon promoted by traffic loading. They emerge from a sequence of cracking, and small and large scale ravelling that expands to potholes (3, 4). Due to pothole dependency on water they usually appear after wet weather conditions, freezing and thawing, the latter dramatically enhancing pothole development (1, 4).

Potholes are repaired by two main methods, commonly named as pothole filling and patching. Pothole filling is considered as a temporary pothole repair method and is further divided to throw and go, throw and roll, semi-permanent and injection. Patching is defined as a permanent repair method and apart from potholes it may be used for other asphalt pavement distresses known as alligator cracking, pavement depressions, rutting, corrugations and slippage cracks (1). Usually, pothole filling is performed as an emergency repair, mainly during winter time, until a permanent repair is executed. Poorly executed repair methods cause early failure and associated high costs. Further outcomes are failed pavements that generate significant public dissatisfaction on the ground of unsafe roads (4), inappropriate riding conditions and high vehicle repair bills for road users. The success of repairs relies on factors such as compaction, thermal segregation, bonding between new and old asphalt mix and others.

Rahman and Thom (5) studied the performance of asphalt patch repairs in both laboratory environment and field projects. They evaluated the quality of repairs in terms of compaction process and temperature values before and after compaction. Dong, Huang and Zhao (6) studied pothole patching materials that are mainly used during winter season. They completed both a 6-month field investigation and laboratory tests. Factors such as patch repair size and depth, traffic level and speed limit, and freeze condition were analyzed. The results indicated that during the laboratory experiments, the patch repair materials were significantly affected by temperature, compaction process, and wheel load. A previous study by the authors of this paper (7) presented performance of ten field pothole repairs executed in United Kingdom in winter and summer time by three different contractors. This revealed the strong connection between segregation, compaction and pothole performance. A return visit to the repair sites after three months, showed locations where thermal segregation had already occurred, mainly at the interface between the existing and repair asphalt material.

RESEARCH OBJECTIVESThe present study responds to the needs to achieve adequate bonding at the interface between existing and new hot asphalt materials when patching is executed. The study’s hypothesis holds that preheating the surfaces of the pothole perimeter and base, the hot placed repair performance is enhanced. The research objectives are:

(1) To develop a novel prototype Control Pothole Repair System (CPRS), suitably modified for laboratory experimentation.

(2) Undertake initial trials and report outcomes. (3) To use the laboratory outcomes to calibrate a finite element modelling tool of the repair

heating process.

FACTORS AFFECTING POTHOLE REPAIRSBy traditional repair methods, the repair material is transported hot from the mixing plant to the repair site. Unfortunately, depending on the method of transport, distance to site and climatic conditions, the temperature of the placed repair material may be close or below that required to form a durable repair. Furthermore, the possibility of good post placement compact may be eliminated for such repairs as also the bond between the host and repair asphalt. It is also apparent that the method of transportation can affect thermal segregation (1, 4, 8, 9). Therefore, five parameters affecting pothole repairs emerge, all shown in Figure 1:

1 - Transportation methodThe transportation of hot asphalt mix is a route usually between asphalt production plant and one or several repair sites. The hot asphalt material is carried in a truck throughout the duration of all repairs. Appropriate transportation vehicle is vital on securing asphalt temperature levels (10). The

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transportation method affects both aggregate and thermal segregation which impact on compaction during the pothole repair process (11). The latter leads to premature failure of the pothole repair (7, 10).

2 - SegregationThe term segregation includes both temperature segregation and gradation segregation. Stroup-Gardener and Brown (12) refer to also a third type of segregation that is mainly appeared in stone matrix asphalt (SMA) mixes and is named as aggregate-asphalt segregation. Among gradation and thermal segregation, the first term is defined as non-uniform distribution of course and fine aggregates in the asphalt matrix whilst the second term is referred as the existence of temperature differentiations or else known as cold spots in the asphalt mix surface (12). Gradation segregation may be visually identified. However, thermal segregation is only possible to be evaluated by other means such as thermal imaging (13).

Thermal segregation is of more interest on this study due to its strong relationship with interface bonding between the host and new repair asphalt materials. On these repairs, thermal segregation occurs throughout (a) hot mix asphalt transportation between asphalt plant and repair sites, (b) placement of the material in the pothole void and (c) compaction of the placed material. The influence of thermal segregation during completion of these three steps is that inadequate compaction and weak interface bonding between new and old asphalt mix may occur (7). The commonly accepted cessation temperature of 80oC, seems to be the last favorable asphalt mix temperature for acceptable compaction (7, 14, 15, 16).

Stroup-Gardener and Brown (12) studied both types of segregation in terms of segregation definition, and appropriate methods and specifications that could offer the ability to detect segregation and evaluate its effect on hot mix asphalt (HMA) properties and pavement performance. Rahman et al. (13) evaluated the impact of thermal segregation on acceptable compact and therefore pothole repair future performance. A previous study by Byzyka, Rahman and Chamberlain (7) similarly concluded that locations where thermal segregation occurred the patching operation had failed prematurely.

3 - CompactionCompaction is the process of asphalt mix densification or change in volume. It is affected by previous stages in the pothole repair process and constitutes a significant factor in achieving strong pothole repairs in terms of surface smoothness (10), and pothole repair durability. Surface smoothness relates on achieving road users’ satisfaction. Durability is linked to reducing the number of repetitions of completed pothole repairs and reducing pothole repair costs. Proper compaction offers high bonding between bitumen and aggregate, high friction between aggregate particles and therefore high density. A strong mix with the described characteristics reduces asphalt pavement deformation (17, 18, 19). The positive and negatives effects of it on hot mix asphalt stability are acknowledged by many researchers in the field in their reported work. Relevant studies are presented by Delgadillo and Bahia, Hartman, Gilchrist and Walsh, Commuri and Zaman, Kassem et al. and Sousa et al. (14, 17, 18, 19, 20).

4 - Interface bonding between old and new mixFailure in interface bonding has been reported for winter time pothole repairs (21). The temperature difference between the existing hot asphalt pavement and new repair materials is significant, possibly creating a low strength interface/boundary that can easily start to lose mix in few months of operation (7). This allows water to penetrate and further develop the pothole repair failure. Other aspects that strong interface bonding relies on are interface roughness and host pavement age. The latter is included as pavement age has a direct relationship with the heating regime applied by the pothole repair system. Addressing the interface issue is not only important from repair cost point of view but also being able to offer adequate riding conditions for road users. An issue that has attracted a number of researchers (21, 22, 23) is use of preheating of the pothole surface. However, further research is necessary to confirm the influence of this on repair performance and durability.

5 - Pothole geometry and repair preparation

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The geometry and preparation of the repair excavation impact on compaction and interface bonding between the host and repair hot asphalt materials. Lack of well-defined excavation geometry coupled with absence of an interbodning tack coat are commonly accepted to lead to reduced repair performance (4, 9).

FIGURE 1 Main parameters affecting pothole performance and durability.

EXISTING INFRARED REPAIR SYSTEMSDebonding of pothole repairs can be caused by temperature differentials between the host and asphalt materials (Figure 1) during the pothole repairs. Several studies exist on enhancing pothole performance and durability in terms of higher interface bonding. Clyne, Johnson and Worel (24) studied the use of taconite aggregates as high quality paving aggregates in asphalt and concrete mixtures. Part of the study was the evaluation of a microwave pothole patch repair system on real life pothole repair projects. The ambient temperature during the repairs was around 0.55 oC. The pothole repair surface and the material were heated up to 115.55oC. Approximate heating time is not stated. The results of the study showed a low percentage change in pothole repair durability between preheated and non-heated patch repairs (24).

A Canadian study in 2011 researched the use of infrared heating in cracked asphalt pavement repairs. The system, which had the ability to cover a large area, comprised by a number of heaters. The heating process included high and low heating of the cracked area for 3 to 5 minutes each with the high temperatures being applied first. The authors underline the importance of the repair area being heated to not greater than 190oC. The time to heat the area is noted to be dependent of weather conditions, asphalt mix type, clean repair area (water and debris removed) and asphalt starting temperature (22). Asphalt Reheat Systems LLC (25) mentions also a dependency of heating time with the age of the asphalt surface being repaired. Results obtained from cores revealed appropriate densities and therefore effective compaction, with no degradation and strong bonding between the host and repair asphalt materials. The study concluded that infrared heating technology is efficient, cost-effective and can offer crack repairs that perform well for 13 or more years. However, to establish a detailed crack repair process with infrared heating that fully replaces conventional crack repair methods further research is necessary (22).

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A study by Freemen and Epps (23) that made use of infrared heating was completed in 83 longitudinal crack patching operations in asphalt pavements in San Antonio, Texas. The study reports that the repair operations were completed during weather temperatures of 15oC to 21oC. Pavement surface temperatures observed on these weather conditions ranged between 19.5oC and 30.5oC. The average patching time duration was 56.3 minutes and the average surface temperature after infrared heating application was approximately 189.7oC. The effectiveness of crack patch repairs by using infrared heating was defined by testing cores of the repaired and unrepaired areas (23). All the repaired sites were visited after 5 and 12 months of completion. The visits revealed repaired sites that performed well but also sites that had started to fail mainly by shoving and settling. However, the investigation showed good bonding and repair ability to perform patching during cold weather.

Nazzal and Kim (21) evaluated winter pothole patching methods among which infrared asphalt patching was included. In total 60 repairs were studied and infrared patching evaluated in terms of patch performance, productivity and cost-effectiveness. To undertake infrared patching, the researchers used an existing industrial infrared asphalt heater. The average patching duration using infrared technology was measured to be around 20 minutes with 3 to 10 minutes allocated to preheating. The study suggests that the excavated pothole surface should be pre-heated at temperatures between 135oC to 190oC. Almost the same values were also suggested by Uzarowski et al. (22) and Freemen and Epps (23). Further, Nazzal and Kim (21) suggest a space between heater and higher point of pavement surface of 254mm to avoid burning the asphalt surface. It is supported that height less than the reported one would burn the asphalt surface.

DEVELOPMENT OF CONTROL POTHOLE REPAIR SYSTEM (CPRS)As apparent in the above, a number of prototype and commercially operated pot hole repair heaters exist. However, the use of infrared technology is not fully understood in respect to the relationships between the applied heating regime in terms of heating pattern, temperature increase and dwell times over the repair area and the internal thermal response of the fill asphalt, especially at its interfaces with host material. Taking an optimization point of view, this also has substantial implications of energy consumption in the repair.

A new concept Control Pothole Repair System (CPRS) has been suitably modified for laboratory experimentation in the study. This CPRS includes (a) multiple heating elements that configure to accommodatedto accommodate different sizes and shapes of pothole repairs, (b) independent precise temperature control of individual heater elements, (c) precise motion controlled passage of the heating elements over the repair surface, (e) distributed subsurface temperature measurement over the base and perimeter interfaces between the host and repair fill material, (f) Short message service (SMS) messaging on system activity, including temperature and time base and (g) Global positioning system (GPS) positioning. The CPRS is presented in Figure 2 and its working envelope in Figure 3.

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FIGURE 2 Control Pothole Repair System (CPRS).

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FIGURE 3 Control Pothole Repair System (CPRS) working envelope (a) CPRS Plan view and (b) CPRS Section A-A.

CPRS core feature 1 – Flexible repair designThe CPRS consists of a support frame of 1.55m (W1) x 1.60m (L1) dimensions with four wheels that support two independently controlled heating elements of 455mm (W3) x 165mm (L2) size. The height of the frame is adjustable allowing minimum and maximum heights from the surface of the heater ranging between 223mm (H) and 443mm (H). The CPRS also contains four micro switches that allow the heaters to operate on three different heating areas (refer to Figures 2 and 3 for all the above information). All the parts of the CPRS are wired to a central operating unit that includes a motion controller. This CPRS design offers the following advantages:

(1) It can be transported by any appropriate in size truck to the pothole repair sites.(2) It can be manually positioned from the operator above the pothole surface due to the

wheels that accompany the system.(3) Its small relatively size and its operating system allows the repair to be completed by the

closure of one only lane.(4) It is possible to heat potholes surfaces of different dimensions due to three operating

heating areas and the use of two heat control units which may operate individually.(5) Its height is adjustable and thus same quality of radiant heat is applied on each pothole

repair occasion.(6) It has controlled heat energy supply and therefore radiant heat regulation at any time.

CPRS core feature 2 - Radiant heat control unitsEach heater unit is connected with a heat energy supply that ensure sufficient working pressure at all times. The operating temperature of the heater units can be preset or real-time controlled using thermocouple feedback. Static, ramped or variable heating patterns can be operated with the heaters.

The heaters make use of radiant heating or else known as infrared heating. Infrared heating applies to processes where energy is transferred directly to a solid body by electromagnetic waves. Infrared heating difference from conductive heating is that heat is absorbed by the solid body and not lost in the surrounding air achieving faster and more effective heating.

CPRS core feature 3 - Short message service (SMS)/ Global positioning system (GPS)The SMS and GPS is delivered by the SMS controller located inside the central operating unit. The device is designed for remote control, back to base monitoring and fault finding. The CPRS transmits its GPS coordinates on pre-programmed mode. Its correct operation is achieved by a four band GSM transmitter/receiver and highly sensitive GPS receiver that offers correct operation and GPS resolution requirements. The device also has an onboard battery and flash memory. The first offers independent operation and the second delivers protection of data if the battery or power supply fails. Further, the sealing unit of the SMS controller protects it from severe environmental conditions, dust and moisture such as occurring on paving sites.

INITIAL TRIALSTo comprehend the operation of the CPRS and the temperature distribution of pothole area under infrared heating prior to its repair, three cycles of experiments were executed.

Cycle 1 - Temperature distribution under heating unitA non reflective insulated board was marked (Figure 4(b)) as per the matrix design shown on Figure 4(a) and located below the heater of the CPRS at a distance of 300mm. The position of the heater is also indicated on Figure 4. Thermocouples were then located on the indicated 49 positions of the matrix design (Figure 4(b)). Five series of temperature measurements of 5 minutes in duration were completed with each series representing temperature distribution developed by the heater when operating at heat energy supply percentages of 20%, 40%, 60%, 80% and 100%. Real time temperature measurements were received by using a data acquisition device and a laptop. The room temperature during the experiments ranged between 25oC – 30oC. The results for each described series

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of experiments for this cycle are presented on Figure 5. The two axis of each graph represent the matrix design of Figure 4(a). The results demonstrate heating distribution along heater’s width and length.

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FIGURE 4 Description of the first section of experiments (a) Matrix design and (b) Insulated board marked as per the matrix design including thermocouples

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FIGURE 5 Temperature distribution after 100sec, 200sec and 300sec of heater operation at (a) 20% heat energy, (b) 40% heat energy, (c) 60% heat energy, (d) 80% heat energy and (e) 100% heat energy.

Cycle 2 - Temperature distribution on the heating unitOn this part, the temperature distribution on the surface of the heater is measured when operating at heat energy percentages between 20% - 100%. The aim of these measurements was to highly understand temperature distribution on the heater plate during different heat energy percentages supply and to use the results for properly calibrating the finite element modelling included on current paper. The temperature was measured by using an infrared thermometer gan. The thermometer was properly calibrated with the emissivity of the heater surface material equal to 0.70 (26). The results from the previous section showed different heating distribution below the heater. For this reason temperature measurements were taken from the heater by dividing it into five areas (Figure 6(a)). One measurement was taken from each area which is assumed later in the simulation model that represents

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the temperature of the whole area from where it was measured. The reason of this assumption was the difficulty presented during the measurements due to high heating levels.

The results are presented on Figure 6 and each contour surface presents the change in temperature of the heater plate for each chosen time interval between 25sec and 350sec. The x-axis of each contour surface shows the point of temperature measurement related to Figure 6(a) and the y-axis shows the time in seconds. The temperature levels are demonstrated by different colors which values are included on the right hand of the contour surfaces.

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FIGURE 6 (a) Heating unit sketch. Demonstration of five areas of temperature measurements

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of heater surface during 5 minutes of operation at (b) 20% heat energy, (c) 40% heat energy, (d) 60% heat energy, (e) 80% heat energy and (f) 100% heat energy.

Cycle 3 - Temperature distribution in the pothole area under heating unitInfrared heating is applied on an asphalt slab of 450mm (W) x 450mm (L) x 75mm (H) with a pothole of 300mm (W) x 160mm (L) x 45mm (H). The asphalt mix used was 20mm Dense Bitumen Macadam (DBM) and was designed as per BS EN 13108 (27). The height between heater surface and the highest point of the asphalt slab was chosen to be 254mm (21). This consideration supports to derive initial results. The results, which are presented on Figure 7, reveal temperature distribution inside the pothole area and asphalt slab surface when CPRS is supplied by 60% and 80% heat energy, significant temperature differentiations between the pothole bottom surface, the pothole boundaries and the asphalt slab surface. Further, heating time up to 160oC and cooling time from 160oC to 80oC are also suggested for the described pothole repair preheating processes.

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Heating time at 60% heat energy Cooling time at 60% heat energy

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FIGURE 7 Demonstration of experimental work and results (a) Asphalt slab and points of temperature measurements (b) Heating temperatures, heating and cooling time for 60% and (c) for 80% heat energy application.

INITIAL SIMULATION OF CONTROL POTHOLE REPAIR SYSTEM OPERATION AND ITS VALIDATIONThis section presents the finite element modelling built for simulating the third cycle of laboratory experiments. The aim is to develop a modelinglymodeling tool that accurately predicts the relationship between temperature (which is developed by the radiant heating emitted by the heaters of the CPRS), time and appropriate height for heating between pothole surface and heater surface for a given repair task.

To build the simulation model and design the pavement section along with one heater Ansys ANSYS Workbench 16.2 and Creo Parametric 3.0 software were used. Both softwaresoftware are broadly used for simulation and three dimensional (3D) designs. One simulation model is presented for 60% heat energy. The model includes an asphalt slab with a pothole in the middle and a heater with same dimensions and distance between them as per Cycle 3 of laboratory experiments’ part. The analysis was built by using steady state thermal analysis for applying initial temperatures to the bodies of the model and thermal transient analysis for simulating the infrared heating process. Mesh convergence test was carried out to ensure results. The final mesh included 24.344 elements, 57.040 nodes and a total running time of 17min 27sec.

Regarding model conditions, it is assumed that no heat is lost from the asphalt slab, the initial temperature of the slab and the heater applied in the model were measured during the second cycle of experiments and were equal to 25oC (equal to ambient temperature) and 30.5oC respectively. The heater model was developed by containing five areas fully bonded between them as per the execution of temperature measurements on the second cycle of experiments (Figure 6(a)). The results from the latter are applied to each area of the model simulation and are presented on Figure 8(a). Further, Figure 8 shows the model design, simulation results and simulation validation. The simulation is validated by comparing temperature measurements between the foursfour points of Figure 7(a).

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FIGURE 8 Demonstration8 Demonstration of simulation model and results (a) Simulation model design and properties (b) Temperature distribution of asphalt slab and pothole area for 60% heat energy application and (c) Simulation validation.

OBSERVATIONS AND FUTURE WORKThis study presented the development of a novel Control Pothole Repair System (CPRS) that offers the ability to preheat a pothole area prior to its repair with the aim of increasing its durability. The study focused only on the initial development, high understanding and initial trials of thethe operation of CPRS and heating process. Three cycles of initial laboratory tests and a simulation model were evolved.

The first experimental cycle studied the temperature distribution developed under the heating unit of the CPRS. It was noted that, along heater’s length, the heating was divided in to three heating areas with the middle area having the highest temperature values. Further, it was also seen that heat energy supply percentages of 80% and 100% developed high temperature concentration in the middle of the heater in contrast with 20%, 40% and 60% heat energy supply that heating distribution was more evenly spreaded on most of the heater areas. The results further suggested that by heating a pothole by using 20% - 60% heat energy would probably be more heat efficient than using 80% - 100% heat energy. Furthermore, due to not evenly developed heating distribution it is important to appropriately locate the heater above the pothole for successful overall heating.

The second cycle of experiments concentrated on temperature distribution developed on the heater plate of the heating unit. The results showed a continuous increase in temperature with the passage of the time. This change however appeared to become more steady and to develop less temperature values differentiations for the 20% heat energy heater operation after 180sec, for the 40% heat energy after 60sec and for the 60%, 80% and 100% heat energy operation after around 120sec. Further, the results also supported the results of the first cycle of experiments showing higher temperatures in the middle area of the heater and lower at the two ends of the heater surface. Both cycles of experiments demonstrated the importance of understanding the operation of the CPRS which highly affect the heating time, heating efficiency and repair costs for each pothole repair occasion.

The third cycle of experiments demonstrated an initial understanding of the temperature distribution of a pothole area under infrared heating and under laboratory conditions. The experiment included a slab of 20mm DBM mix of a total 0.0152 m3 and a pothole of an approximate volume of 0.00216 m3 which were subjected to infrared heating of 60% and 80% heat energy supply at a distance of 254mm. The slab was subjected to infrared heating until it reached a maximum of 160oC and measured cooling time until it reached around 80oC. The results showed that in the occasion of infrared heating applied by 60% heat energy the maximum settled temperature was achieved after 240sec and for 80% heat energy after 160sec. The cooling time on these occasions was measured equal to 180sec and 240sec respectively. Further, the results demonstrated the differences in temperatures between pothole bottom surfaces, pothole boundaries and slab surface.

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The finite element modelling built for simulating the last cycle of experiments demonstrated a same reaction of temperature differentientials between pothole areas and top asphalt surface. Experimental measurements and simulation results were compared against four same points presenting a good correlation between them with a difference in results around 15.6%. However, the results are promising and the model reacts properly on simulating the heating process.

Future research will focus on studying infrared heating application by the CPRS to potholes of different dimensions, depths and under different temperature conditions of those presented on current study, developing detailed heating processes for each pothole repair occasion, evaluate heated and non- preheated pothole repairs and integrate the finite element modelling.

ACKNOWLEDGEMENTSWe acknowledge the support on the research of Mr. Radi Al-Rashed andfrom International Chem-Crete, and the contribution from final year student at Brunel University Mohammad Ghate.

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