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Submission date: 8.9.2017

Word count: 4,226 words text

Number of figures and tables: 9 figures and 2 tables

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Title: Development of advanced temperature distribution model in hot mix asphalt patch repair

Author 1

Juliana Byzyka, BEng, MSc, PhD Candidate, MIET, AFHEA

Department of Civil and Environmental Engineering, Brunel University, London, UK

ORCID number: 0000-0002-5570-8909

Author 2

Denis Albert Chamberlain, BSc, DIC, MSc, PhD, MCS, FICE

Department of Civil and Environmental Engineering, Brunel University, London, UK

Author 3

Mujib Rahman, BS, MSc, PhD, CEng, MCIHTFCIHT, MICE, FHEA

Department of Civil and Environmental Engineering, Brunel University, London, UK

Contact details for the corresponding author:

Name: Juliana Byzyka, BEng, MSc, PhD Candidate, MIET, AFHEA

Contact address: Brunel University, Kingston Ln, Uxbridge, Middlesex UB8 3PH, London,

United Kingdom.

Tel: +44 7475 71 9051

E-mail address: juliana.byzyka@brunel.ac.uk

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Abstract

The performance of hot-mix asphalt patch repair is greatly reduced due to inferior compaction at

the interface. It is known that the faster loss of temperature at the interface is one of the primary

reasons for inferior compaction. A novel Controlled Pothole Repair System (CPRS) has been

developed as part of this study. The CPRS uses infrared heating technology with enhanced

features compared to many existing infrared systems. In parallel, a three dimensional finite

element thermal model capable of modelling the loss of temperature during patch repair process

has been developed. The first part of the paper presents the functionality of CPRS including

experimental results to demonstrate various features of the system. In the second part, the

numerical results are compared against experimentally measured values from a patch repair in

a controlled laboratory condition. The tests are done to measure the influence of no preheating

and preheating of the existing surface on the temperature loss. The results showed more than

80% agreement between simulation and actual measurements. It also shows, preheating of the

existing surface can significantly reduce temperature loss at the interface, thus allowing more

time for repair and the possibility of achieving better compaction.

KeywordsRoads & highways, thermal effects, failure

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Introduction

Pothole distresses appear in the form of small or large bowl shaped holes in asphalt pavements

(Lavin, 2003; Caltrans Division of Maintenance, 2008). Usual causes of potholes are weak

pavement caused by poor workmanship, inadequate drainage, and failures caused within the

base or sub-base (Lavin, 2003). Potholes are a water dependent phenomenon promoted by

traffic loading. They emerge from a sequence of cracking, and small and large scale ravelling

that develops to potholes (Dawson, 2008; Thom, 2008). Due to pothole dependency on water,

they usually appear after wet weather conditions, freezing and thawing, the latter dramatically

enhancing pothole development (Lavin, 2003; Thom, 2008).

Potholes are repaired by two main methods, commonly named as pothole filling and patching

(Lavin, 2003). Usually, pothole filling is performed as an emergency repair using cold asphalt

mixes, mainly during winter, until a permanent repair (hot mix asphalt repair) is executed. Poorly

executed repair methods cause early failure and associated high costs. Further outcomes of

failed pavements that generate significant public dissatisfaction on the ground of unsafe roads

(Thom, 2008), are poor riding conditions and high vehicle repair bills from vehicle damage. The

success of repairs depends on factors such as compaction, thermal segregation and inter

bonding between pothole fill and host asphalt materials.

Previous research on potholes has evaluated the quality of repairs in terms of compaction and

temperature values occurring before and after compaction in both a laboratory environment and

field projects (Rahman and Thom, 2012). Other research has studied pothole patching materials

mainly during winter season (Dong, Huang and Zhao, 2014), revealing a strong connection

between thermal segregation and poor compaction that lead to pothole premature failure

(Byzyka, Rahman and Chamberlain, 2016).

The current study forms initial stages of a wider research that is being developed by the authors

on pothole repair failures associated with inadequate bonding between the host pavement and

the new hot asphalt repair fill. The paper reveals the development of a novel infrared system,

referred from now on as Controlled Pothole Repair System (CPRS), that uses radiant heat to

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preheat an excavated and clean pothole prior to its repair. This is targeted to support a strong

interface bonding between the host pavement and the new hot asphalt mix fill (HMA) for longer

lasting hot pothole repairs. The study does not consider on this phase cold asphalt pothole

repairs. A laboratory based heating study demonstrates CPRS heating capabilities in pothole

excavation preheating with consideration of cooling influences, this compared with the

development of finite element (FE) thermal model of the heating process by the CPRS. It is

intended that such modelling tool will be used to simulate a variety of pothole repairs under

different weather conditions, which are limited in a laboratory environment, and further form part

of the future control algorithm for the heater.

2. Research objectives

Considering the need to achieve adequate bonding at the interface between the host pavement

and pothole fill materials when hot patching is executed, the study’s hypothesis holds that

controlled preheating of the interfacing perimeter and base surfaces of the pothole excavation,

in addition to the repair fill, is the route to enhanced repair performance.

The research objectives are:

1. To develop a novel prototype CPRS.

2. To examine the CPRS performance in the context of pothole preheating.

3. To use the laboratory outcomes to calibrate an FE modelling tool of the repair heating

process.

3. Parameters affecting pothole repairs

By traditional repair methods, the repair material is transported hot from the mixing plant to the

repair site. An appropriate transportation vehicle is vital for securing asphalt temperature levels

(Ter Huerne, 2004). Depending on the method of transport, distance to the site and climatic

conditions, the temperature of the placed repair material may be close or below that required to

form a durable repair. The reason is that thermal segregation is initiated (Lavin, 2003; Thom,

2008; McDaniel, Olek, Behnood, Magee and Pollock, 2014; WSDOT, 2013) which impacts on

compaction during the pothole repair process (BSI, 2015). Improper compaction results in an

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inadequate bond between the host pavement and the repair fill asphalt, which is frequently

reported for winter time pothole repairs (Nazzal, Kim and Abbas, 2014). However, proper

compaction offers high bonding between bitumen and aggregate, high friction between

aggregate particles, high density, strength and resistance to repair deformation (Hartman,

Gilchrist and Walsh, 2001; Commuri and Zaman, 2008; Kassem, Liu, Scullion, Masad,

Chowdhury, 2015).The geometry and preparation of the repair excavation impact also on

compaction and potential interface bonding between the host pavement and repair hot fill

asphalt materials. A lack of well-defined excavation geometry coupled with the absence of an

interbonding tack coat is commonly accepted to lead to reduced repair performance (Thom,

2008; McDaniel, Olek, Behnood, Magee and Pollock, 2014). Thus, five parameters affecting

pothole repairs emerge, all shown in Figure 1.

Figure 1. Main parameters affecting pothole repair performance and durability

4. Infrared repair systems

Several heater systems are reported for executing pothole repairs. Studies are reported on

enhancing pothole performance and durability through seeking higher interface bonding. Clyne,

Johnson and Worel (2010) undertook real world evaluation of a microwave pothole patch repair

system for surface heating to 115 oC with ambient temperature near to 0 oC. Approximate

heating time is not reported. The findings showed pothole preheating had little influence on

repair durability (Clyne, Johnson and Worel, 2010).

A Canadian study in 2011 researched infrared heating for cracked asphalt pavement repairs.

The system covered a large area using multiple heaters and the heating process included high

and low heating of the cracked area for 3 to 5 minutes with maximum heating not exceeding 190

oC. The heating time is noted to be dependent on climatic conditions, mix type, condition of the

excavation and initial asphalt temperature (Uzarowski, Henderson, Henderson and Kiesswetter,

2011). Asphalt Reheat Systems LLC (Asphalt Reheat Systems, 2016) further suggests

dependency of heating time on the age of host asphalt. Extracted cores revealed effective

compaction, no degradation and strong interbonding between the host pavement and fill

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materials. The study concluded that infrared heating technology is efficient, cost-effective and

durable for more than 13 years (Uzarowski, Henderson, Henderson and Kiesswetter, 2011).

A study by Freemen and Epps (2012) used infrared heating to complete 83 crack repairs, with

outcomes assessed by comparing extracted core properties in the host pavement and crack fill.

The weather temperatures during the repairs ranged between 15 oC to 21 oC, with host

pavement temperatures in the 20 oC to 31 oC range. Average patching time was 56 minutes with

infrared heating to 190 oC. Repaired sites were visited after 5 and 12 months of completion and

discovered generally good bonding with instances of shoving and settling failures (Freemen and

Epps, 2012).

Nazzal, Kim and Abbas (2014) evaluated winter pothole patching methods using a commercial

infrared asphalt patching. Sixty repairs were studied with the infrared patching method

evaluated in terms of patch performance, productivity and cost-effectiveness. The average

patching duration with infrared technology was 20 minutes with 3 - 10 minutes preheating. The

study suggests that the pothole surface should be pre-heated at temperatures between 135 oC

to 190 oC. Almost the same values were also suggested by Uzarowski, Henderson, Henderson

and Kiesswetter (2011) and Freemen and Epps (2012). Further, Nazzal, Kim and Abbas (2014)

suggest a space between heater and higher point of pavement surface of 254 mm, this to avoid

burning the asphalt surface.

5. Developmental CPRS

Successful use of infrared heating in asphalt repairs has, potentially, multiple significant

controlling parameters affecting outcomes with it. This consideration moves the research

agenda well beyond the simplistic surface temperature monitoring used to control current

commercial patch repair work. The controlling influence of each parameter needs to be

thoroughly understood and the most significant combined in an optimised control algorithm.

In the current CPRS research, parameters under investigation include plan geometry and depth

of evacuated pothole excavation, ambient temperature, host pavement temperature, host-fill

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interface temperature (using extractable thermocouples), formation time surface temperature,

heater offset and applied heat pattern including surface scanning parameters. In addition to the

completed repair performance parameter, repair time and total energy consumption (LPG

powered) are optimisation goals. Here we report work on the first consideration, pre-heating of

the repair excavation.

The main advances over the presented heater are (i) multiple heating elements that configure to

accommodate different sizes and shapes of pothole repairs, (ii) independent precise

temperature control of individual heater elements, (iii) precise motion controlled passage of the

heating elements over the repair surface, (iv) distributed subsurface temperature measurement

over the base and perimeter interfaces between the host and repair fill material, (v) Short

message service (SMS) messaging on system activity, including temperature and time base and

(vi) Global positioning system (GPS) enabled remote location.

Further, the prototype equipment has a small format and low weight appropriate for easy

transportation. It could be operated with a single lane closure, for example. Working towards

minimum fuel consumption within the optimisation research will be advantageous for repairs in

remote locations. The provision of the scanning mode, combined with overall mobility, will

enable both crack and patch repairs to be addressed. The CPRS is presented in Figure 2 and

its operation process in Figure 3.

Figure 2. (a) CPRS plan view and section sketches and (b) CPRS prototype

Figure 3. CPRS operation process

6. Initial trials

To understand how the CPRS heats the surfaces of the pothole excavation, three cycles of

experiments were executed.

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6.1 Cycle 1│ Temperature Distribution below Heater

A non reflective, thermal insulation board was marked out (Figure 4(b)) as per the matrix design

shown in Figure 4(a), this was positioned below the heater at an offset of 300 mm below the

heater plate. Thermocouples were located on the indicated 49 positions of the matrix design. A

series of five temperature measurements each of 5 minutes in duration were completed, these

capturing temperature distribution developed by the heater when operated at 20 % to 100 %

heat power. The ambient temperature during the experiments ranged between 25 oC – 32 oC.

Real time temperature measurements were captured using thermocouples connected to a multi-

channel data logger. The temperature distribution outcomes are presented in Figure 5. It should

be noted that the heater temperature is time dependent.

Figure 4. Set up of Cycle 1 of experiments (a) matrix design and (b) physical implementation of

matrix

Figure 5. Cycle 1 experimental outcomes: temperature distribution after 300 seconds of heater

operation between 20 % and 100 % heat power

6.2 Cycle 2│Temperature Distribution on Heater Plate

This cycle of experiments dealt with temperature measurements on the heater plate when

operating between 20 % and 100 % full heat power. The results not only enhanced

understanding of the heater operation but supported calibration of the finite element modelling.

Due to temperature differentials on the heater plate in Cycle 1 experiments, temperature

measurements on the heater plate were captured by dividing it into five areas (Figure 6(a)). The

ambient temperature ranged between 23 oC to 27 oC.

The results for all five heat powers (20 % - 100 %) are presented in Figure 6(b). Each contour

(key provided in figures) demonstrates the change in temperature over heater plate for the

stated heat power settings, operated between 25 seconds and 350 seconds. The x-axes and y-

axes of the contours in Figure 6(b) show the point of temperature sampling related to Figure

6(a) at corresponding times.

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Figure 6. Cycle 2 experimental outcomes (a) point measurement sketch and (b) infrared

detected temperature distribution after 300 seconds on heater plate when operating between 20

% and 100 % heat power

6.3 Cycle3│ Temperature Distribution in Pothole Excavation

Infrared heating is applied to a 450 mm (W) x 450 mm (L) x 75 mm (H) of 20 mm Dense

Bitumen Macadam (DBM) mix sample with a pothole of 300 mm (W) x 160 mm (L) x 45 mm (H)

(Figure 7(a and b)). The asphalt mix was designed to BS EN 13108 (BSI, 2010). The distance

between heater plate surface and the highest point of the asphalt sample was 254mm as

suggested by Nazzal, Kim and Abbas (2014). The ambient and asphalt sample surface

temperatures were approximately 25 oC. The results are presented in Figure 7(c) and (d). They

reveal the heating time of the pothole area up to 160 oC under the described conditions for 60 %

and 80 % of full heat power. Cooling times from 160 oC to 80 oC for both occasions are also

included. It should be noted that the CPRS starts operating after 21 seconds to 25 seconds.

This is a provision for future investigation and may depend on the ambient temperature or other

parameters.

Figure 7. Cycle 3 experimental outcomes (a) 20mm DBM sample, (b) sketch of temperature

measurement points and heating temperatures, and heating and cooling time of pothole

excavation for (c) 60 % and (d) 80 % heat power

7. CPRS simulation and validation

A finite element modelling was run for 60 % heat power, this being an idealisation of the third

cycle of laboratory experiments. The aim is to develop a tool that accurately predicts the

relationship between temperature produced by the radiant heater and heating time for a given

heater offset from the pavement surface.

To build the thermal simulation model of the heater – air space – pavement system, and design

the 3D geometries Ansys Workbench 16.2 and Creo Parametric 3.0 software were used. The

model incorporates two 3D geometries; the host pavement and the CPRS heater presenting

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Cycle 3 of laboratory experiments. The analysis was built using steady state thermal analysis for

applying geometry initial temperatures and thermal transient analysis for infrared radiation

heating of the pothole excavation. Mesh convergence test was carried out for both geometries

to ensure results. The final overall mesh included 24,344 elements.

The simplified FE thermal model of the study does not consider solar radiation, surface icing,

rain, evaporation and condensation that may have an effect oninfluence the temperatures of the

asphalt pavement. Two boundary conditions are defined. The first is surface to surface radiation

and the second is adoption of perfectly insulated boundary surfaces. The initial temperature of

the asphalt slab and the heater applied in the model were measured during the second cycle of

experiments and are equal to 25 oC (equal to ambient temperature) and 30.5 oC respectively.

The heater model was developed by containing five areas fully bonded between them (Figure

6(a)). The temperature measurements on heater plate from the third cycle of laboratory

experiments are applied to each area of the model simulation and are presented in Table 2.

Further, Figure 8 shows the model design, its mesh and pothole temperature distribution FE

results. The FE model is then validated by comparing temperature measurements between the

four points of Figure 7(b) for a time duration of 220 seconds all presented in Figure 9.

Table 1. Simulation model summary of parameters

Parameters Description3D geometries Host pavement of 450 mm x 450 mm x 75 mm

Pothole of 300 mm x 160 mm x 45 mmHeater is built by 5 areas: areas 1 & 5 of 165 mm x 65 mm x 104 mm and areas 2, 3 & 4 of 165 mm x 110 mm x 104 mm (decided by the authors)

Analysis type Steady state thermal analysisTransient thermal analysis – Radiation analysis surface to surface

Boundary and other conditions

Host pavement initial temperature: 30.5 oC; room and heater initial temp.: 25 oCHeater plate temperature as per Table 2Conditions: Radiation surface to surface & perfectly insulated boundary conditions

Asphalt properties Density: 2400 kg/m3 (Thom, 2008)Thermal conductivity: 2 W/m K (Thom, 2008)Specific heat capacity: 920 J/kg K (Thom, 2008) Emissivity: 0.967

Heater properties (Resistalloy Trading Limited, 2016)

Density: 7150 kg/m3

Thermal conductivity: 16 W/m KSpecific heat capacity: 460 J/kg K Emissivity: 0.70

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Table 2. Temperature values applied on the five areas of the heater plate defined in Figure 7(a)

Time (sec) Area 1 (oC) Area 2 (oC) Area 3 (oC) Area 4 (oC) Area 5 (oC)25 724 652 618 648 59940 731 731 878 816 81260 790 867 879 854 91590 800 863 878 901 925

120 884 881 909 914 917150 857 867 930 905 926180 865 852 952 909 932210 869 893 939 933 930240 800 913 923 933 919

Figure 8. Simulation model and results (a) Simulation model geometries and mesh and (b)

Temperature distribution of pothole excavation boundaries and bottom surfaces

Figure 9. Simulation validation – Comparison of temperature values of four points between

Cycle 3 of experiments and simulation results (a) Point 1, (b) Point 2, (c) Point 3 and (d) Point 4

8. Observations and future work

8.1 Observations

This study presents the development of a novel CPRS that offers the ability to preheat a pothole

excavation in a controlled manner, prior to repair filling and compaction, for longer lasting

pothole repairs. The study focused on the initial development, understanding CPRS operation

and the pothole excavation heating process in a laboratory controlled environment. Three cycles

of laboratory tests and one FE thermal model were evolved. The following were observed:

● Whilst 100 % heating power results in notably higher temperatures in the central region of

the heater plate than on its boundary, use of 20 % and 60 % heat power produces a

relatively uniform temperature distribution.

● Due to the uneven temperature distribution at higher power settings (80 % - 100 %), it is

suggested that at 254 mm distance between heater plate and pavement surface, pothole

excavation heating using 20 % - 60 % heat power is preferable.

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● Pothole heating experiments by the CPRS further demonstrated significant temperature

differentials between the excavation base and its boundary with the host pavement. This

suggests the risk of inadequate heating of the perimeter boundary in pothole repairs, thus

supporting the authors’ hypothesis that preheating of the whole pothole area is a significant

provision towards increasing pothole repair performance and durability. FE simulation

results confirm this.

● At 60% heating power, a total time of 240 seconds was needed to heat the 300 mm x 160

mm x 45 mm pothole excavation to 160 oC under laboratory conditions. The following

cooling time from 160 oC to 80 oC was 160 seconds.

● At 80 % heating power, a total time of 180 seconds was needed to similarly heat the same

pothole excavation, with following cooling time of 240 seconds to 80 oC.

● Finally, the 3D FE thermal model gives a good correlation when compared with the cycle 3

experimental outcomes. The model is in close agreement with the actual heating process

of the CPRS.

8.2 Future Work

Future research requirements include completion of a second phase of laboratory experiments

in simulating pre-heated artificial pothole excavations of various depths to identify temperature

feedback controls within the repair build, mainly using extractable thermocouples. After this,

traditional and pre-heated patching will be evaluated using shear bond strength test and wheel

tracking test. The patching material will be decided after measurement of thermal conductivities

of three dense graded asphalt mixtures (20 mm DBM, Asphalt Concrete (AC) - 14 and AC - 6)

and one asphalt binder which will be measured at room temperature, elevated temperatures

and freezing conditions. The measurements and the results of the analyses will be used to

calibrate and validate the FE patching modelling.

Acknowledgements

We acknowledge the financial support of International Chem-Crete Corporation, Texas, and the

assistance of MSc student Mohammad Ghate in laboratory work.

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Figure captions

Figure 1. Main parameters affecting pothole repairper formance and durability

Figure 2. (a) CPRS plan view and section sketches and (b) CPRS prototype

Figure 3. CPRS operation process

Figure 4. Set up of Cycle 1 of experiments (a) matrix design and (b) physical implementation of

matrix

Figure 5. Cycle 1 experimental outcomes: temperature distribution after 300 seconds of heater

operation between 20% and 100% heat power

Figure 6. Cycle 2 experimental outcomes (a) point measurement sketch and (b) infrared

detected temperature distribution after 300 seconds on heater plate when operating between

20% and 100% heat power

Figure 7. Cycle 3 experimental outcomes (a) 20mm DBM sample, (b) sketch of temperature

measurement points and heating temperatures, and heating and cooling time of pothole

excavation for (c) 60% and (d) 80% heat power

Figure 8. Simulation model and results (a) Simulation model geometries and mesh and (b)

Temperature distribution of pothole excavation boundaries and bottom surfaces

Figure 9. Simulation validation – Comparison of temperature values of four points between

Cycle 3 of experiments and simulation results (a) Point 1, (b) Point 2, (c) Point 3 and (d) Point 4

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