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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:
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.
Keywords
Roads & 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 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 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 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 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.
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.
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.