Surface Colour Effects on the Thermal Behaviour and Mechanical Properties of Hot Mix Asphalt

Abstract

The focus of the study was to evaluate the effect of placing hydrated lime on the surface of asphalt concrete pavement. The study assesses the influence of hydrated lime on both the peak surface temperature as well as the temperature profile of the pavement with depth. The amount of lime that would yield the optimal temperature reductions without placing excess ineffective material was selected. To address the aforementioned goal, eight Superpave mix samples were prepared in the lab and compacted at the design compaction temperature to achieve a relatively consistent percent of air voids. All samples were compacted using a vibratory compactor to simulate real field construction procedures and conditions. To examine the effect of hydrated lime, surface temperatures as well as with-depth temperature measurements were made with an infrared camera, and thermocouples buried into the pavement, respectively. The same tests were performed at a field site with a newly laid down pavement. To minimize variables, the field Hot Mix Asphalt (HMA) pavement was of the same design as that used to prepare the lab samples. The effect of temperature on the mechanical properties of HMA mixtures used in Ontario; namely Superpave SP12.5FC2 PG64-28, SP12.5FC2 PG70-28, SP19.0, and Stone Mastic Asphalt (SMA), was assessed. The mechanical properties studied include rutting susceptibility, fatigue resistance, and resilient modulus. Thirty two samples were prepared in the laboratory and compacted at the design compaction temperature and percent air voids. For each mix, two samples were used to test rutting susceptibility, three samples were used to test fatigue resistance, and three samples were used to test the resilient modulus of the mixes. With regards to rutting, the samples were tested in the Asphalt Pavement Analyzer (APA) at four different temperatures in order to give a complete rutting versus temperature profile. Three samples of each mix were tested to measure the resilient modulus at different temperatures using the Nottingham Asphalt Tester (NAT). Lastly, the fatigue resistance for each mix was assessed in the NAT with each of the three samples tested at a different strain to provide a complete picture of the mix behaviour when subjected to fatigue. The stiffness characteristics of the newly laid down in-situ pavement was determined using the Light Weight Deflectometer (LWD). Results indicate that placing 100g/m^2 of hydrated lime on the surface of the hot mix asphalt pavement was the optimum surface treatment while avoiding the placement of excess ineffective material. This level of surface treatment led to temperature reductions that significantly improved the mechanical properties of asphalt concrete. Using the increased resilient modulus, consistent with the temperature reductions, it was shown, by carrying out an analysis using KENLAYER, that the design life of a pavement could be increased from approximately 25 to 33 years, from 20 to 30 years and from 12 to 20 years corresponding to cool, intermediate and hot weather conditions, respectively.