This article was downloaded by: [John Emery] On: 30 April 2014, At: 11:37 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK International Journal of Pavement Engineering Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gpav20 Light-coloured grey asphalt pavements: from theory to practice ab b b c d John J. Emery , Peijun Guo , Dieter F.E. Stolle , Jessica Hernandez & Lixin Zhang a Shiloh Canconstruct Limited, CaledonONCanada L7E 0P5 b Department of Civil Engineering, McMaster University, HamiltonONCanadaL8S 4L7. c LVM Inc., TorontoONCanadaM9 W 5W8. d Terraprobe, BramptonONCanadaL6T 3Y3. Published online: 28 Mar 2013. To cite this article: John J. Emery, Peijun Guo, Dieter F.E. Stolle, Jessica Hernandez & Lixin Zhang (2014) Light-coloured grey asphalt pavements: from theory to practice, International Journal of Pavement Engineering, 15:1, 23-35, DOI: 10.1080/10298436.2013.782402 To link to this article: http://dx.doi.org/10.1080/10298436.2013.782402 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions International Journal of Pavement Engineering, 2014 Vol. 15, No. 1, 23–35, http://dx.doi.org/10.1080/10298436.2013.782402 Light-coloured grey asphalt pavements: from theory to practice John J. Emerya,b, Peijun Guob*, Dieter F.E. Stolleb, Jessica Hernandezc and Lixin Zhangd a Shiloh Canconstruct Limited, Caledon, ON, Canada L7E 0P5; bDepartment of Civil Engineering, McMaster University, Hamilton, ON, Canada L8S 4L7; cLVM Inc., Toronto, ON, Canada M9 W 5W8; dTerraprobe, Brampton, ON, Canada L6T 3Y3 (Received 15 May 2012; final version received 11 February 2013) Downloaded by [John Emery] at 11:37 30 April 2014 This paper presents the technological development and application of hydrated lime in treating the surface of asphalt concrete to develop light-coloured, grey asphalt pavements. When appropriately applied on the surface of fresh asphalt concrete, hydrated lime makes the surface grey, significantly increases its albedo and effectively reduces the pavement’s temperature caused by hot weather. Two application case studies are presented, focusing on how to ensure hydrated lime’s long-term effectiveness on the surface of asphalt pavements and take into account the effect of the subsequent reduced temperature on the resilient modulus of asphalt concrete in the design of long-life flexible pavements. The increased asphalt concrete modulus, owing to lowered temperature, can reduce the design thickness of the asphalt concrete without sacrificing pavement performance. This also has a positive influence on reduced pavement heat island effects. It is concluded that the appropriate use of hydrated lime on asphalt pavement surfaces is an effective and economical method to produce lightcoloured, grey asphalt pavements. Keywords: long-life flexible pavement; albedo; temperature effect; light-coloured asphalt pavement 1. Introduction Hydrated lime has been used as a relatively inexpensive, readily available, safe additive in hot mix asphalte (HMA) for some time. When used as an additive in HMA mixes, hydrated lime creates multiple benefits and contributes to the improvement of a mix’s mechanical and rheological properties (Little and Epps 2001) including a significant reduction in stripping potential (moisture susceptibility), the major current use; somewhat reduced design asphalt binder content; improved toughness and resistance to low temperature cracking; reduced age hardening (decreased rate of oxidation) of the asphalt binder and increased mixture stability, durability and dynamic modulus. As a result, the use of hydrated lime has been shown to reduce distresses and to extend the service life of asphalt pavements. The advantage of using hydrated lime on the black asphalt concrete surface has not been investigated systematically, even though it also has multiple advantages through improvements in pavement performance. For some time, hydrated lime was applied on highperformance asphalt concrete surfaces to toughen the pavement’s surface, accelerate the ‘curing’ process, and hence prevent early tire scuffing (race track surfaces for instance) (Emery 2007). This technology was used in the construction of several car and motorcycle race tracks in Canada, including Shannonville Motorsport Park, Toronto Molson Indy Race Track and Calabogie Race Track (Figure 1(a)). Unfortunately, the hydrated lime in these projects did not stay very long on the surface of *Corresponding author. Email: [email protected] q 2014 Taylor & Francis conventional asphalt concrete pavements because its long-term effectiveness requires a ‘sticky’ surface such as that a polymer-modified asphalt (PMA) binder provides. In addition to increasing the resistance of an asphalt concrete surface course to early tire scuffing, hydrated lime on the black asphalt concrete surface makes its colour lighter to develop a grey asphalt pavement, significantly increasing its albedo (fraction of solar radiation energy reflected from the road surface). The increased albedo can effectively reduce the surface temperature of the pavement, which in turn somewhat enhances its frictional resistance owing to the increased stiffness of both asphalt concrete and tired rubber (Luo 2003; Baran 2011) and significantly reduces any runoff-water temperature (Van Buren et al. 2000) and/or heat island effects. As anticipated from asphalt binder rheology, the resilient modulus (Mr) of the asphalt concrete increases as a result of the lowered pavement temperature, which in turn improves the rutting resistance and fatigue endurance of the pavement (ARA 2004; NCHRP 2004; El-Basyouny and Witczak 2005; Kawakami and Kubo 2008). An early example of using hydrated lime on an airside asphalt concrete pavement surface to decrease its hot weather temperature was reported in 2003 (Emery 2003, 2007). The objective of this paper is to demonstrate the temperature reduction potential of hydrated lime application (or equivalent light-coloured materials, such as agricultural lime and fly-ash) to the surface of new asphalt concrete and incorporating the increased asphalt concrete 24 J.J. Emery et al. Downloaded by [John Emery] at 11:37 30 April 2014 Figure 1. Lime-treated pavements of the Calabogie race track (photo courtesy of Calabogie Race Track). Mr in flexible pavement designs. A brief review of the reduction of hot weather pavement temperatures using hydrated lime is presented first. Two application case studies are provided thereafter, focusing on how to effectively apply hydrated lime to the surface of asphalt concrete pavements and then incorporate the enhanced asphalt concrete Mr in the American Association of State Highway and Transportation Officials (AASHTO) mechanistic-empirical (M-E) flexible pavement design method. The increased Mr allows a reduction in asphalt concrete layer thickness without sacrificing pavement lifecycle performance. 2. Reduction of hot weather pavement temperatures in grey asphalt pavement Using hydrated lime to reduce black body solar energy absorption is not new. For example, limewash has long been used to paint objects (e.g., tree trunks, pipes) white to help keep them cool. Dr Steven Chu, the US Secretary of Figure 2. Energy and a Nobel prize-winning scientist, has even suggested making all roofs and pavements white or light coloured to help reduce global warming by both conserving energy and reflecting sunlight back into space. According to him, it would be the equivalent of taking all the cars in the world off the road for 11 years (Connor 2009). Dr Chu’s statement is in line with the data of Akbari (2011), who estimated that the world-wide CO2 offset of cool roofs and pavements is in the range of 44– 78 GT CO2, which would offset emissions from all cars for 18 –32 years (Akbari and Matthews 2010; Akbari 2011). As illustrated in Figure 2, which shows a schematic pavement cross-section and the heat-related processes that affect the pavement structure, the pavement temperature greatly depends on how solar energy heats the pavement and how the pavement influences the air above it (Sun et al. 2006). In general, the temperature of the pavement is affected by many factors, such as solar energy, solar reflectance, material heat capacities, surface roughness, heat transfer rates, thermal emittance, wind and permeability (Ting et al. 2011). The albedo of new black asphalt pavements is as low as 0.05, which increases to 0.1 –0.15 for aged asphalt concrete (Bolz and Tuve 1973; Levinson and Akbari 2001). Comparing this with 0.35– 0.40 for new Portland cement concrete (PCC) and 0.2– 0.3 for aged PCC (Bolz and Tuve 1973; Levinson and Akbari 2001), one may expect that if asphalt pavements are made off-white grey in surface colour using hydrated lime (or equivalent such as limestone dust or cement kiln dust), the pavement temperature will significantly reduce. It should be noted that the change in albedo for all exposed surfaces is very important to climate change, particularly for cold regions (light, fresh snow compared to dark, bare soil for instance). The effectiveness of applying hydrated lime on asphalt concrete surfaces to reduce pavement temperatures has Heat-related characteristics and processes in a pavement. Source: Adapted from Sun et al. (2006). International Journal of Pavement Engineering 25 (a) Surface temperature (˚C) 70 60 Black 20g/m2 35g/m2 50g/m2 75g/m2 100g/m2 125g/m2 150g/m2 50 40 30 20 0 2 4 6 8 Time (hours) (b) Figure 4. Structure of heat-shield pavements. Source: Adapted from Kubo et al. (2006). Surface temperature (˚C) 50 40 Black 50g/m2 100g/m2 30 150g/m2 20 0 2 4 6 Time (hours) (c) Pavement temperature (˚c) 40 50 60 70 0 20 Depth (mm) Downloaded by [John Emery] at 11:37 30 April 2014 60 40 60 80 100 g/m2 Black 100 Figure 3. Change in surface temperature between black unmodified asphalt concrete and those modified with different hydrated lime concentrations in (a) laboratory tests, (b) in situ tests and (c) temperature profiles of laboratory HMA specimens with different surface hydrated lime concentrations at peak surface temperature. Source: Adapted from Abu-Halimeh (2007). Table 1. been confirmed in laboratory and in situ tests reported by Abu-Halimeh (2007) and Abu-Halimeh et al. (2008). Different amounts of hydrated lime were placed uniformly on the surface of asphalt concrete with the concentration varying between 20 and 150 g/m2 to investigate dosage influences on hot weather asphalt concrete temperatures. Thermal couples were installed in the asphalt concrete at different depths, and the surface temperature was measured using an infrared camera. As shown in Figures 3(a) and (b), in both laboratory and in situ tests, the surface temperatures of asphalt concrete with the surfaces treated using different amounts of hydrated lime were much lower than the untreated ones. Higher reductions in the surface temperature took place as more hydrated lime was used to produce whiter surfaces, with as high as a 148C temperature reduction being achieved in approximately 4 h at higher hydrated lime concentrations of 100– 150 g/m2. The asphalt concrete temperature profile as shown in Figure 3(c) demonstrates a decrease of pavement temperature with depth when a surface is treated using hydrated lime. It should be noted that the decrease of pavement temperature in Figure 3(c) is generally consistent with the Bell’s equation and measured data in the literature (e.g., Lukanen et al. 2000). The hydrated lime treated asphalt concrete surface is almost as effective in decreasing the absorption of solar radiation and reducing pavement temperature as proprietary heat-shield asphalt pavements based on current Japanese research (Kubo et al. 2006; Kawakami and Kubo 2008). As illustrated in Figure 4, the heat-shield asphalt pavement is coated by a layer of special paint containing Comparison of the heat shield material and hydrated lime. Temperature decrease Albedo of treated HMA surface Cost Heat shield material Hydrated lime (concentration 100– 150 g/m2) Approximately 158C 0.4 – 0.5 $1.7– 3.2 (estimated) Up to 148C 0.3 – 0.4 $0.15– 0.20 Downloaded by [John Emery] at 11:37 30 April 2014 26 Figure 5. J.J. Emery et al. Hydrated lime-treated asphalt pavements: the taxiway of Pearson International Airport. Source: Adapted from Emery (2007). hollow ceramic particles and special pigment. It reduces the absorption of solar radiation and energy from the atmosphere, and hence reduces accumulated heat in pavements. Compared to conventional asphalt concrete, heat-shield pavements have surface temperatures approximately 158C cooler. However, the cost of heat-shield asphalt pavements is very high owing to the expensive coating materials. The experimental data in Figure 3 shows that appropriate application of hydrated lime on an asphalt pavement surface would have temperature reductions similar to the relatively expensive heat-shield pavements. Table 1 provides a brief comparison of the heat shield material and the hydrated lime. It should be noted that other approaches have been used in engineering practice to increase the albedo of asphalt pavements (US Environmental Protection Agency 2008; Tran et al. 2009). Typical methods include chip seals with light-coloured aggregate, surface gritting using lightcoloured aggregate, sand/shot-blasting and abrading pavement surface and using light-coloured aggregates in the asphalt mix. It has been reported that using a lightly coloured aggregate can raise the albedo of new asphalt concrete to 0.15 – 0.20. The measured albedo of new limestone chip seals is in the range of 0.2– 0.3, which then declines with age. Shot blasting, which can remove the asphalt coatings from a new asphalt pavement surface and expose the natural colour of light-coloured aggregates (such as limestone aggregates) used in the asphalt mixture to improve the pavement surface reflectivity, can raise the albedo of new asphalt concrete to 0.2 (Tran et al. 2009). This value is the same as the typical albedo of a worndown asphalt concrete pavement with the aggregates being revealed. It should be recalled that the albedo of unbound limestone aggregate could be as high as 0.3– 0.45 (Bretz et al. 1992; Tran et al. 2009). It should be emphasised that the use of hydrated lime is intended to effectively reduce the early stage albedo of new asphalt pavements, while in the long term, the albedo of the hydrated lime-treated asphalt pavements is expected to be similar to the worndown pavements that have exposed aggregates. 3. Case studies 3.1 Toronto Pearson International Airport Taxiways Taxiways A and H (originally PCC with cement-stabilised base, CSB) at the Toronto Pearson International Airport were upgraded in 2001/2002 by placing 125 mm of HMA on top of the existing PCC pavements. After being upgraded for less than 2 years, the composite pavement (mainly Taxiway A) developed asphalt concrete distresses of concern with potential loss of functional serviceability. Various types of distress, including asphalt concrete rutting, shearing and extensive progressive shoving in heavy aircraft, slow, taxi wheel paths, were identified due to an unfortunate combination of factors: a prolonged hot (near record) weather period and slow moving heavy aircraft on fresh HMA, including Antonov AN 124 air freighters carrying imported steel and interface slippage on a geogrid. The repair programme included removal of the HMA overlay down to the concrete surface for the 27 Downloaded by [John Emery] at 11:37 30 April 2014 International Journal of Pavement Engineering Figure 6. (a) Hourly spectra of single axle/dual tire loadings and (b) single axle load distribution measured on an expressway adjacent to the Da’an to Jiliao Expressway. middle width of the taxiway, transversely grinding the exposed concrete surface as well as cleaning the surface and application of polymer-modified surface course HMA. The lower and the upper course HMAs incorporated PG 64-28 and PG 70-28 (polymer-modified) with air voids of 3 –5%, respectively. In order to reduce both pavement temperatures during the summer and the black body absorption of radiation from the sun and aircraft engines, hydrated lime was applied on the finished HMA upper surface course. It is important to appropriately apply hydrated lime on the finished HMA surface so that the hydrated lime sticks on the surface for a long time to maintain a uniform offwhite surface condition. A special provision was developed describing the procedures to place hydrated lime on the new HMA surface (see Appendix). More specifically, immediately after paving and completion of compaction, when the asphalt concrete was still warm following conventional finish rolling, a light application of hydrated lime (100 g/m2) was applied to the asphalt Downloaded by [John Emery] at 11:37 30 April 2014 28 J.J. Emery et al. pavement surface using a small rotary spreader. The applied hydrated lime was then rolled into the pavement surface with multiple passes of a light, unballasted, rubbertire roller. The hydrated lime and rolling process was repeated, as necessary, to achieve a uniform off-white, grey surface colour condition. Care was taken to avoid creating a dusty condition when spreading the dry hydrated lime. Rather fortuitously, it was found in this case study that the hydrated lime were essentially bound as a long-term surface coating, which was attributed to the surface course HMA incorporating PMA. This confirmed that the use of PMA and the correct procedures for the application of dry hydrated lime was the two key factors for the success of this project. The PMA provided a very sticky surface to hold the dry hydrated lime and to effectively make the pavement surface grey. The effectiveness of the procedures developed in this airport pavement project and the durability of the lightcoloured asphalt pavement surface have been clearly demonstrated through monitoring of the project with Google Earth and during flight operations. As shown in Figure 5, after almost 7 years, the surface colour of the asphalt pavement area treated using hydrated lime is close to that of adjacent PCC pavements and much lighter than that of conventional asphalt pavements. For the marked areas in Figure 5, the greyscale (0 for black and 1 for white) of pavements is 0.034 (Patch of HMA pavement, Area 1), 0.375 –0.445 (Areas 2 –5, hydrated lime-treated HMA pavements), 0.526– 0.533 (Area 6, PCC pavements) and 0.159 –0.242 (Areas 7 –8, aged HMA pavements without surface lime treatments). Even though the HMA in this project used a light-coloured aggregate (crushed limestone), after 7 years when the natural colour of the light-coloured aggregate was exposed, the area without hydrated lime surface treatment was found to still be darker than the treated area, and the greyscale values of lime-treated asphalt concrete had almost the same level of greyscale as the PCC pavements. Testing by the airport maintenance department reported no difference in the surface skid resistance between the pavement areas with or without hydrated lime treatment. In addition, the pavements have no significant distresses after three successive hot summers of 2005– 2007. 3.2 Da’an to Jiliao Expressway With the successful use of hydrated lime for the surface treatment of asphalt concrete pavements to produce light coloured asphalt as demonstrated in the Toronto Pearson International Airport Project, this technology was then implemented in the design and construction of the Chinese Da’an to Jiliao Expressway long-life flexible pavements. This Project is a 26.78-km section in Ruyang County, Henan Province, China, of the new Erlianhaote to Guangzhou Expressway. The four-lane tolled expressway has a truck design speed of 100 km/h (cars 120 km/h) and includes twin tunnels (12.5 m in width and approximately 2.1 km in length), many culverts/small bridges and two large, low-level bridges. To demonstrate the benefits in terms of enhancing the quality and long-term performance of expressways, as well as to promote implementation of Superpave HMA and long-life flexible pavements in China, based on North American technology transfer, this Project incorporated Superpave HMA and was designed as a 30-year long-life flexible pavement structure. In addition to the Superpave and M-E design methodology, the Project design adopted several new concepts, including high performance granular base/subbase, light-coloured asphalt to deal with the high summer temperatures and the typical severe overload of Chinese heavy trucks, pavement structure quality monitoring that made use of deflection testing (Benkelman beam and FWD) together with Dynamic Cone Penetration testing of the high-performance granular base/subbase layers. Overview details of the long-life flexible pavement analysis and structural design, including traffic data and analysis, climate and pavement temperature information and materials characterisation within the framework of the M-E design method, are summarised below. 3.2.1 Traffic data and information The axle load spectra of different axle types required for the design of long-life flexible pavements were established from bus and truck traffic monitoring for eight days (24 h per day) at a comparable adjacent expressway and toll station with weigh-in-motion scales. Figure 6 presents the hourly spectra of single axle/dual tire loadings and the corresponding axle load distribution. Similar data for single axle/single tire loadings were also developed. The analysis of the axle load spectra provided the traffic volume of 13,900/day with 42% trucks in which 40% exceeded the Chinese standard axle load of 100 kN. The design traffic data were determined by considering three loading scenarios: 100th, 98th and 95th percentile of the traffic loadings. When determining the truck load on the design lane, a 50:50 directional split was used with the percentage of heavy vehicles in the design lane assumed to be 80%. A composite growth factor of 3.8% was used to calculate the design equivalent single axle loads (ESALs). 3.2.2 Climate and pavement temperature information The hourly mean air temperature data in the area of the Project was collected from two nearby weather stations (Zhengzhou and Ruyang) for five days every month (12th – 16th) between 2004 and 2005. The recorded International Journal of Pavement Engineering Table 2. Season No. weeks No. days % 29 Number of days per year in various temperature ranges. 1 , 258C 2 25 –358C 3 35 – 408C 4 40 – 458C 5 .458C Total 25 175 48 6 42 12 7 49 13 11 77 21 3 21 6 52 365 100 calculated using the climate information from Zhengzhou (Year 2004 and 2005), and several methods (Dickinson 1971; Wahhab 1994; Bosscher et al. 1998) were used to convert the air temperature data to pavement temperatures. Downloaded by [John Emery] at 11:37 30 April 2014 monthly mean high-air temperatures of this region during July to September were 30.1– 31.58C, with the monthly maximum being 39.5 –39.98C. The pavement temperatures, which are higher than the air temperature, were then Figure 7. Variation of deformation with the number of loading cycles for different asphalt concrete samples in APA. Without lime 47.5 45.0 38.0 32.0 30.0 41.0 38.5 32.5 28.5 26.5 With lime Without lime 45.0 42.5 35.5 29.5 27.5 37.0 34.5 30.5 24.5 22.5 40.0 37.5 30.5 24.5 22.5 30.5 28.0 23.0 17.0 15.0 With lime Without lime With lime 32.5 30.0 23.0 17.0 15.0 Without lime With lime 21.5 19.0 20.0 15.0 15.0 22.5 20.0 20.0 15.0 15.0 Without lime ,258C An algorithm was developed to determine the pavement temperature profiles with depth based on measured data at different locations in China. In order to incorporate the influence of temperature for the pavement performance analyses and simultaneously simplify the design process, the pavement surface temperatures were grouped into five ‘seasons’ of similar temperatures (, 25, 25– 35, 35– 40, 40 –45 and . 458C), with the number of weeks for each season being calculated as presented in Table 2. The pavement surface temperatures in each of the five seasons were then used as the input to determine the pavement temperature profiles with depth for each season. It should be noted that the pavement temperatures could be divided into more groups to get somewhat improved results. To deal with high summer temperatures and the severely overloaded heavy trucks reflected by the data shown in Figure 6, the long-life flexible pavement designs included an alternate with hydrated lime coating of the upper (surface) course Superpave HMA (. 30 million ESALs mix design) to reduce pavement temperatures in the hot seasons and to enhance the stiffness of asphalt concrete. Even though the reduction of the pavement surface temperatures could be as high as 148C at the air temperature of 34.3– 36.68C (Figure 3), it was assumed for this Project that, for the scenario with hydrated lime, a 18C (cool weather season) – 58C (hot weather season) reduction in the pavement surface temperatures (with a similar reduction in the temperature profile with depth) could be readily achieved. This assumption was considered to be conservative based on Figure 3. Table 3 presents the estimated variation of pavement temperatures with depth for the two scenarios with and without hydrated lime. 3.2.3 0 cm, 8C 2 cm, 8C 7 cm, 8C 15 cm, 8C 25 cm, 8C .458C 35 – 408C 25 – 358C 40 – 458C 5 4 3 2 1 Depth (cm) Pavement temperature variation with depth, with and without hydrated lime surface coating. Table 3. Downloaded by [John Emery] at 11:37 30 April 2014 42.5 40.0 35.0 30.0 29.0 J.J. Emery et al. With lime 30 Mechanistic characteristics of HMA AC-13/SP 12.5, AC-20/SP 19 and AC-25/SP 25 were selected as upper (surface), middle and lower course HMA, respectively, using Marshall and Superpave asphalt mix design methods jointly, meeting the JTG D50/JTG F40 (Marshall) and AASHTO R35-04 (Superpave) requirements. The final HMA Marshall/Superpave mix designs are summarised in Table 4. To deal with the high, hot weather, pavement temperatures and the heavy truck loadings in the Project, two asphalt binders, namely A70 (PGAC 64-22) and the polymer-modified SBS 1-D (PGAC 70-22), were selected to get high rutting resistance of the surface and middle course hot-mix asphalt. The mechanistic characteristics of the three asphalt concretes were determined at the mix design stage. Tests were carried out to determine the rutting resistance using the Asphalt Pavement Analyzer (APA) and fatigue endurance and Mr using the Nottingham Asphalt Tester (NAT), generally following relevant AASHTO designations. International Journal of Pavement Engineering Table 4. 31 HMA mix designs. (a) AC 13/SP 12.5 FC2 HMA mix design for surface course: asphalt binder SBS 1-D (PG 70-22) Aggregate (basalt) gradation percent passing (mm) Asphalt binder content (%) Marshall Superpave Marshall 5.5 5.2 4.9 16 13.2 9.5 4.75 2.36 1.18 0.6 0.3 0.15 0.08 100 94 84.8 49.4 29.9 20.6 14.5 10.2 7.3 5.5 100 97.7 79 49.4 37.6 27 17 10.4 8.3 6.9 (b) AC 20/SP 19.0 HMA mix designs for intermediate course: asphalt binder SBS 1-D (PG 70-22) Aggregate (limestone) gradation percent passing (mm) Asphalt binder content (%) Downloaded by [John Emery] at 11:37 30 April 2014 Marshall Superpave 4.2 4.3 Note 26.5 19 16 13.2 9.5 4.75 2.36 1.18 100 100 98.5 99.7 89.7 90.7 76.6 77.2 55.8 55.3 37 36.5 24.6 23.4 18.1 17 (c) AC-25/SP 25.0 HMA mix designs for lower course: asphalt binder A70 (PG64-22) Aggregate (limestone) gradation percent passing (mm) Asphalt binder content (%) Marshall Superpave 3.8 3.8 37.5 26.5 19.0 16.0 13.2 9.5 4.75 2.36 1.18 0.60 0.30 0.15 0.075 100 100 98.2 98.1 86.6 85.8 77.1 76.2 67.8 66.8 54.4 53.4 35.9 35.0 24.8 23.8 20.1 19.1 15.3 14.3 10.0 9.0 7.4 6.4 5.4 4.5 Rutting resistance from APA tests. The APA allows for an accelerated evaluation of rutting potential after volumetric design. APA tests on various HMA samples were performed at different high Superpave temperatures (58, 64 and 708C). For clarity, Figure 7 presents the APA test results at temperatures of 588C and 708C only. All of the asphalt concretes are seen to meet the recommended deformation resistance requirements for the Project at 588C and to exhibit good rutting resistance at up to 708C, with the frictional surface course AC-13/SP 12.5 (basalt aggregates and incorporating the polymer modified SBS 1-D) having satisfactory rutting resistance. The difference in the APA test results is attributed to the aggregate structures, percent air voids and the type of asphalt binder. Use of the polymermodified SBS 1-D, which has high softening point temperature of 758C, is particularly important for the rutting resistance of the surface and middle course hot-mix asphalt. The APA test results for submerged asphalt concrete samples were also carried out, and the results all indicated a good resistance to stripping, noting the AC-13/SP 12.5 incorporated 1% hydrated lime. The overall laboratory APA testing of the asphalt concrete samples confirmed that these HMAs met the requirements of the Project. Mr and fatigue endurance of HMA from NAT. The Mr of different HMA samples at different air voids (AV ¼ 4.0% and 7.0%) and asphalt binder contents (AC ¼ 3.8%, 4.0% and 5.5%) was determined using the NAT. Figure 8(a) summarises the NAT test results for the asphalt concrete samples (for clarity, only the results for samples of AV ¼ 4.0% are presented). In general, the Mrs of all HMA samples decrease with an increase in temperature, following log Mr ¼ a1 2 a2T with the coefficient a2 in the range of 0.038– 0.05. These Mrs are favourable, being at the high end of typical Mr values for quality asphalt concretes (see, e.g. Croney and Croney 1997). However, the exponential decreases of Mr with increasing temperature result in a factor 2.4– 3.2 for a 108C increase in temperature for a2 ¼ 0.038 –0.05. The fatigue endurance of the AC-25/SP 25 lower HMA course was also determined in the NAT for HMA of different air voids and asphalt binder contents, as shown in Figure 8(b). The number of load repetitions to failure decreases with the increase of tensile strain using the transfer function N f ¼ c1 ð1t Þ2f 2 with f2 ¼ 6.109 and 6.875 for AV ¼ 7.0% and 5.0%, respectively. It should be noted that practical experience has indicated the typical field fatigue endurance to be approximately 100 times greater than the laboratory-determined fatigue endurance for quality asphalt concretes (Croney and Croney 1997). 3.2.4 Characterisation of granular base/subbase and subgrade/select subgrade materials The characterisation of the subgrade and granular base/subbase materials was performed by comprehensive laboratory tests, including modified Proctor compaction, California Bearing Ratio tests and Mr testing following relevant AASHTO designations (AASHTO T180/T99, Downloaded by [John Emery] at 11:37 30 April 2014 32 J.J. Emery et al. Figure 8. Variation of (a) resilient modulus and (b) fatigue endurance of different asphalt concrete samples tested using the Nottingham Asphalt Tester. AASHTO T193 and AASHTO T307-99). It should be noted that the use of the Mrs of all materials is an essential component of flexible pavement design using a M-E method such as AASHTO M-E. In order to quantify the influence of moisture content on the Mrs of these materials, the Mr tests were carried out at moisture contents in the range of wopt ^ 2%. In addition, the results of material testing were used to select the aggregate structure of granular base/subbbase materials to achieve the best performance (highest resilient modulus) possible by appropriate gradation adjustment. 3.2.5 Pavement structural design For this project, the pavement structural design included various analyses to access the likelihood that the critical pavement responses may exceed predefined thresholds. PerRoad 3.2 (Timm 2004) was used to determine the fatigue life of the asphalt concrete, and KENPAVE (Huang 2003) was used to determine the stresses and strains at critical locations in the pavement structure. Both PerRoad and KENPAVE require Mrs and Poisson’s ratio of all material layers. The Mr of asphalt concrete is a function of pavement temperature, which varies with depth and whether hydrated lime is used for surface treatment or not. The effect of lime is simulated using the Mrs of the HMA concrete at reduced pavement temperature levels. The recommended 30-year pavement structure design for the flexible asphalt pavements was 30 cm of high quality Superpave HMA, 20 cm of crushed rock base, 40 cm of crushed rock subbase and 80 cm of select subgrade material. Details about the materials character- International Journal of Pavement Engineering Table 5. PerRoad pavement design results (AADT ¼ 13,900). Traffic (%) 100 98 95 Percent below critical (%) With lime Without lime 90.1 91.1 92.0 91.7 92.2 93.0 satisfactory long-life flexible pavement design for the Project traffic and climate conditions analysed. When the surface is treated with hydrated lime, the percentage below the 70-m1 critical strain level is at least 1% lower than that for conventional asphalt concrete. 3.2.7 Downloaded by [John Emery] at 11:37 30 April 2014 isation and the selection of Mrs for pavement structural design have been previously presented (Emery 2007). 3.2.6 Likelihood of excessive strain responses PerRoad, a mechanistic-based pavement design and analysis programme that utilises layered elastic analysis with a statistical modelling procedure (Monte Carlo simulation) to estimate stresses and strains within asphalt pavements (Timm 2004), was used to assess the likelihood that critical pavement responses may exceed predefined thresholds: the horizontal tensile strain of 70 m1 at the bottom of the asphalt concrete to control fatigue cracking and the vertical compressive strain of 200 m1 at the top of the select subgrade material to control structural rutting. For high truck traffic volume pavements, the threshold strains should not be exceeded more than 5–10% of the time. The likelihood analysis for excessive strain responses was performed for different scenarios when considering 30 cm of Superpave HMA for 100th, 98th and 95th percentile traffic loadings with and without hydrated lime surface coating. The results showed that the vertical strain at the top of the select subgrade material was below the limit of 200 m1 in all loading cases, and the horizontal strain at the bottom of the asphalt layer was below the 70-m1 level for about 90.1 –93.2% of the loadings for all scenarios examined. Table 5 presents the summary of horizontal tensile strains at the bottom of HMA with AADT ¼ 13,900. Therefore, the 30 cm of HMA was considered to be a Figure 9. 33 Analysis for critical stresses and strains The KENPAVE program was used to compute the horizontal tensile strains at the bottom of the asphalt concrete layer and the vertical compressive strains at the top of the select subgrade material for the two critical hot seasons (T ¼ 40–458C and T . 458C), with the axle load of 70, 90, 110 and 140 kN for the single axle/single tire and 160, 200, and 240 kN for the single axle/dual tire configurations. Both scenarios with and without hydrated lime were again evaluated, with the results summarised in Figure 9. For all loading scenarios with different pavement temperatures, the vertical strains at the top of the subgrade and select subgrade materials are seen to be consistently smaller than the critical value of 200 m1. The tensile strains at the bottom of HMA may exceed the critical value of 70 m1 under heavy truck loadings but not exceed the fatigue endurance. 3.2.8 Benefit of surface hydrated lime coating To demonstrate the benefit of using hydrated lime on asphalt concrete surface, parametric studies were carried out to examine the performance of asphalt pavements (without lime treatment) by adjusting the Mr of the granular base layer. When the Mr of the granular base layer is increased from 350 to 400 MPa, the tensile strain at the bottom of HMA is reduced by 5 – 6%. Using a hydrated lime coating on the Superpave HMA surface course to reduce pavement temperature and increase the stiffness of the asphalt concrete is found to also reduce the tensile strains by approximately the same amount. When the KENPAVE pavement analysis results: tensile strain at the bottom of HMA (pavement surface temperature of 40 – 458C. 34 J.J. Emery et al. Downloaded by [John Emery] at 11:37 30 April 2014 Figure 10. Effect of hydrated lime and the resilient modulus of granular base on tensile strains at the bottom of HMA (pavement surface temperature ¼ 40 – 458C). pavement surface temperatures are in the range of 40 – 458C, the combination of increasing the granular base Mr by 50 MPa and using hydrated lime surface treatment can reduce the tensile strains at the bottom of the HMA by up to 10 – 12%, as seen in Figure 10. The benefit of applying hydrated lime on the surface of fresh asphalt concrete pavements to reduce the hot weather pavement temperatures is demonstrated by the tensile strain distributions at the bottom of the asphalt concrete for different temperature reduction scenarios, which is found to have the same effect on tensile strain reduction as an increase in granular base M r. For the relatively conservative assumption about the reduced pavement temperatures adapted (by only 1 – 58C), the surface hydrated lime coating can reduce the tensile strains at the bottom of the HMA by 5– 6%, which is equivalent to increasing the Mr of granular base materials by 50 MPa (from 350 to 400 MPa). Additional simulations showed that the effect of applying hydrated lime was equivalent to a 12.5-mm increase in the HMA thickness in terms of the tensile strains at the bottom of the HMA for this Project. By taking into account the additional cost of PMA for the HMA surface course and hydrated lime, the reduced asphalt concrete thickness implies significant savings. 4. Concluding remarks Hydrated lime, when appropriately applied on the surface of fresh asphalt concrete, makes the asphalt pavement surface grey, which in turn significantly increases its albedo and effectively reduces the hot weather pavement temperatures. The use of polymer-modified surface course HMA and the correct procedures for the application of dry hydrated lime are two essential factors to ensure the long-term effectiveness of the surface hydrated lime coating. The reduction in hot weather pavement temperatures effectively enhances the stiffness of asphalt concrete, resulting in significant improvement in its rutting resistance and fatigue endurance. When implemented in the M-E design of the asphalt pavement structures, the surface hydrated lime coating is equivalent to reducing the HMA thickness or increasing the Mrs of granular base layer materials when maintaining the same pavement performance. While not discussed here, as an effective and economical method to make light-coloured, grey asphalt pavements, this technology also has the potential to reduce urban heat island effects and to enhance environmental conditions. It should be noted that instead of hydrated lime, other equivalent materials, such as limestone dust, cement dust and fly-ash, may be used to make grey (light-coloured) asphalt using the same technology. However, hydrated lime is favoured in terms of its availability, reasonable cost, ease of application and multiple functions in enhancing the properties of surface course asphalt concrete. A laboratory study is being carried out to investigate the effectiveness of using these alternative by-product materials and develop improved application techniques to generate light-coloured grey asphalt concrete surfaces. In situ tests will also be performed with the albedo of asphalt concrete surfaces treated using different concentrations of the various materials measured using a pyranometer, a device for determining the albedo of a surface. The durability of the alternative by-product materials to maintain a light-coloured surface will be specifically examined. Acknowledgements Partial funding provided by the Natural Sciences and Engineering Research Council of Canada is gratefully acknowledged. Support from Shengzhen Kang and Xiaozhong Li, Henan Expressway Development Limited, Zhengzhou, Henan, China, is also appreciated. References ARA Inc., 2004. Guide for mechanistic-empirical design of new and rehabilitated pavement structures. Champaign, IL: NCHRP. Abu-Halimeh, I., 2007. Surface colour effects on the thermal behaviour and mechanistic properties of hot mix asphalt, Thesis (MSc). McMaster University. Abu-Halimeh, I., Stolle, D.F.E, Guo, P., and Emery, J., 2008. Surface colour effects on the thermal behaviour and mechanistic properties of asphalt pavements. In: Annual conference of canadian technical asphalt association, November 17 –18, Saskatoon, Canada. Akbari, H., 2011. Cool roofs and cool pavements to cool the world, heat islands, and buildings: a lucrative way to slow global warming. In: Greenbuilding Brasil, Conferência internacional & EXPO, August 29 – 31, São Paulo, Brazil. Akbari, H. and Matthews, D., 2010. Global cooling updates: reflective roofs and pavements. In: Proceedings of the 3rd international passive and low energy cooling for the built environment, September 29 – Oct 1, 2010, Rhodes, Greece. Downloaded by [John Emery] at 11:37 30 April 2014 International Journal of Pavement Engineering Baran, E., 2011. Temperature influence on skid resistance measurement. In: 3rd International surface friction conference, safer road surfaces – saving lives, 15 – 18 May, Gold Coast, Queensland, Australia, 18 p. Bolz, R.E. and Tuve, G.L., eds., 1973. CRC handbook of tables for applied engineering science. Boca Raton, FL: CRC Press. Bosscher, P.J., Bahia, H.U., Thomas, S., and Russell, J.S., 1998. The relation between pavement temperature and weather data: a Wisconsin field study to verify the Superpave algorithm. In: Transportation research record: journal of the transportation research board, no. 1609. Washington, DC: Transportation Research Board of the National Academies pp. 1 – 11. Bretz, S., Akbari, Rosenfeld, H., and Taha, H., 1992. Implementation of solar reflective surfaces: materials and utility programs. Berkeley: University of California LBL Report 32467. Connor, S., 2009. Obama’s climate guru: paint your roof white! The Independent. Climate Change, 27 May 2009. Available from: http://www.independent.co.uk/environment/climatechange/obamas-climate-guru-paint-your-roof-white1691209.html [Accessed 16 March 2011]. Croney, D. and Croney, P., 1997. The design and performance of road pavements. London: McGraw-Hill Book Co. Dickinson, E.J., 1971. Temperature conditions in bituminous surfacings at a site near Perth during a period of one year. Australian Road Research, 4 (7), 33 – 36. El-Basyouny, M.M. and Witczak, M., 2005. Development of the fatigue cracking models for the 2002 design guide. In: Paper presented at the annual meeting of the transportation research board, Washington, DC. Emery, J., 2003. Asphalt specification for airfield pavement. In: Presentation at Summer Winter Integrated Field Technologies (SWIFT) conference, Toronto, September 11, 2003. Emery, J., 2007. Grey asphalt surfaces. In: 52nd annual conference, the Canadian Technical Asphalt Association, November, Niagara Falls, Ontario. Huang, Y.H., 2003. Pavement analysis and design. Prentice Hall. Kawakami, A. and Kubo, K., 2008. Development of a cool pavement for mitigating the urban heat island effect in Japan. In: International symposium on asphalt pavements and environment, August 18 – 20, Zurich, Switzerland. Kubo, K., Kido, H., and Ito, M., 2006. Study on pavement technologies to mitigate the heat island effect and their effectiveness. In: 10th international conference on asphalt pavements, August, Quebec City, Canada. Levinson, R. and Akbari, H., 2001. Effects of composition and exposure on the solar reflectance of portland cement concrete. Berkeley, CA: Lawrence Berkeley National Laboratory Report LBNL-48334. Available from: http://www-library. lbl.gov/docs/LBNL/483/34/PDF/LBNL-48334.pdf Little, D.N. and Epps, J.A., 2001. The benefits of hydrated lime in hot mix asphalt. Arlington, VA: National Lime Association. Available from: http://www.lime.org/ documents/publications/free_downloads/benefits-hydratedlime2006.pdf Lukanen, E.O., Stubstad, R., and Briggs, R., 2000. Temperature predictions and adjustment factors for asphalt pavement. Washington, DC: Federal Highway Administration Report FHWA-RD-98-085. Luo, Y., 2003. Effect of pavement temperature on frictional properties of hot-mix-asphalt pavement surfaces at the Virginia Smart Road, Thesis (MSc). Virginia Polytechnic Institute and State University. NCHRP, 2004. Guide for mechanistic-empirical design of new and rehabilitated pavement structures, Project 37-1A. Washington 35 DC: National Cooperative Highway Research Program, Transportation Research Board, National Research Council. Sun, L., Qin, J., and Jia, L., 2006. Temperature distribution prediction model for asphalt pavements. In: Proceedings of the 10th international conference on asphalt pavements, Vol. 2, 25 – 34, August, Quebec City, Canada. Timm, D.H., 2004. PerRoad perpetual pavement design software. NCAT: Auburn University, Auburn, Alabama. Ting, M.K., Koomey, J., and Pomerantz, M., 2011. Life-cycle costs and market barriers of reflective pavements. Available from: http://enduse.lbl.gov/Projects/pavements.html. [Accessed 16 March 2011]. Tran, N., Powell, B., Marks, H., West, R. and Kvasnak, A., 2009. Strategies for design and construction of high-reflectance asphalt pavements. Transportation Research Record: Journal of the Transportation Research Board, No., 2098, 124– 130. US Environmental Protection Agency, 2008. Reducing urban heat islands: compendium of strategies, cool pavements. Available from: http://www.epa.gov/heatisland/resources/ pdf/CoolPavesCompendium.pdf Van Buren, M.A., Watt, W.E., Marsalek, J., and Anderson, B.C., 2000. Thermal enhancement of stormwater runoff by paved surfaces. Water Research, 34 (4), 1359– 1371. Wahhab, H., 1994. Asphalt pavement temperature related to arid Saudi environment. Journal of Materials in Civil Engineering, 6 (1), 1– 14. Appendix: Special Provision – application of hydrated lime This Special Provision describes the procedures to be followed to apply hydrated lime to the surface of the hot-mix asphalt surface course immediately after paving and completion of compaction. All MSDS and safety requirements must be observed throughout. The procedures described should be modified in the field, as necessary, to meet the intended purpose of toughening the surface and providing a uniform, light-coloured surface. (1) The surface course asphalt paving work is to be carried out in conformance with the overall Project requirements. (2) A light application (‘dusting’) of hydrated lime shall be applied to the asphalt pavement surface subsequent to the conventional finish rolling (compaction). The applied hydrated lime shall then be consistently rolled onto the asphalt pavement surface with multiple passes of a light, unballasted, rubber-tired roller. The hydrated lime application and rolling process shall be repeated, as necessary, to achieve a uniform ‘off-white’ surface colour condition. Guidance note: The hydrated lime can be applied dry using a common garden fertiliser spreader(s) (a rotary spreader is recommended, not a broadcast spreader to keep the hydrated lime as close to the asphalt pavement surface as possible). The gate opening on the spreader should be sufficient to apply a consistently uniform, light application. Care must be taken to avoid creation of ‘dusty’ conditions. Alternatively, the hydrated lime can be mixed with water and applied as a light slurry; however, the slurry will then have to be permitted to dry before the rolling-in operation.