Estimation of Optimum Compaction Temperature for PMA and WMA Mixtures by Volumetric Property Evaluation

Abstract

Abstract The optimum compaction temperature (OCT) is defined as the temperature at which asphalt provides proper viscosity in an asphalt mixture. For normal asphalt, the proper viscosity level has been suggested as 280 ± 30 mm2/s by the American Association of State Highway and Transportation Officials (AASHTO). This suggestion has been effectively utilized in selecting the OCT of normal hot-mix asphalt (HMA). However, because polymer-modified asphalt (PMA) and warm-mix asphalt (WMA) have been used recently, it is difficult to apply this method in general. This study evaluates important volumetric properties (air void ratio and void filled with asphalt) of HMA and WMA mixes. The three binders evaluated included 64-22 and 76-22 for HMA and 70-22 for WMA for dense-graded asphalt mixtures compacted using a Superpave gyratory compactor. The OCT at which the optimum asphalt content could be obtained was determined for the three binders. The OCTs obtained via volumetric property evaluation were 20 °C and 38 °C lower than the values determined via the AASHTO method for PMA and WMA. In mechanical performance comparisons, the mixture compacted at the lower OCT was not inferior to the mixture compacted at a higher OCT. It is therefore concluded that the OCT should be determined based on the volumetric property of mixtures, because compaction is not solely a function of viscosity, especially for PMA and WMA mixtures.