New Measurement of Thermal Properties of Superpave Asphalt Concrete

Reliable implementation of transient temperature prediction models for asphalt pavements has been impeded by lack of reliable thermo–physical properties data. The existing methodology based on ASTM C177-85 is not conducive to asphalt concrete specimens due to the difficulty to meet the slab requirements of the standard. This paper discusses a new laboratory procedure for the determination of thermal properties of asphalt concrete specimens. The new device can accommodate small specimens derived from either laboratory compacted $150\mathrm{mm}$ diameter briquettes or cores from in-service pavements. The effect of compaction on thermal properties was tested by compacting the briquettes to 67, 99, 133, and 212 gyrations using the superpave gyratory compactor. Thermal conductivity $\left(\lambda \right)$ was determined after the experiment reached steady state, whereas thermal diffusivity $\left(\alpha \right)$ was determined during the transient state. Analytical curve fitting technique was applied to the test data to compute the thermal diffusivity. Thermal conductivity of laboratory compacted Superpave hot-mixed asphalt was observed to vary from $1.4\text{to}1.8\mathrm{W}∕\mathrm{m}\mathrm{K}$ for dense graded mixtures (corresponding to $\mathrm{2,295}–\mathrm{2,450}\mathrm{kg}∕{\mathrm{m}}^3$ bulk densities and 3–7% air voids). Thermal diffusivity was observed to range from $4.4\text{to}6.4\times {10}^{-7}{\mathrm{m}}^2∕\mathrm{s}$ . These values are much narrower and consistent than presented in the literature. The thermal properties were then examined for possible correlation with resilient modulus, Marshall stability and flow, and bulk density. It was found that there was no correlation between asphalt concrete thermal properties and physical properties.