Volume 36, Issue 6 (November 2008)
Influence of Selected Mix Design Factors on the Thermal Behavior of Lightweight Aggregate Asphalt Mixes
Lightweight aggregate (LWA) asphalt mix has been found to have lower thermal conductivity and thermal diffusivity compared to a conventional asphalt mix. Given these beneficial thermal properties, a LWA-asphalt mix can reduce frost penetration into the underlying pavement layers. It is therefore postulated that the LWA-asphalt mix can reduce damage associated with frost heave. This paper investigates the effects of binder grade and coarse aggregate content on the thermal properties of LWA-asphalt mixes. The effects of three asphalt binder grades (PG58-28, PG64-28, and PG70-28) and three aggregate gradations were investigated. The thermal conductivity was found to vary from 0.77 to 0.87 W/m°K for the LWA-asphalt mixes having bulk density in the range of 1585–1653 kg/m3 and air voids 3.5–4.5 %. Thermal diffusivity was determined to vary from 2.1 × 10−7 m2/s to 2.6 × 10−7 m2/s and a standard deviation of 0.18 × 10−7 m2/s. Specific heat capacity was found to be in the range of 1990 J/kg⋅°K to 2360 J/kg⋅°K, with a standard deviation of 130 J/kg⋅°K. Coefficients of variation for thermal conductivity, thermal diffusivity, and specific heat capacity were found to be 3.2, 6.1, and 7.6 %, respectively. These results show that the three thermal response variables vary in a very narrow range. It is concluded that the beneficial thermal properties of LWA-asphalt mixes appear to be insensitive to variation in asphalt binder grade and aggregate gradation.