Effects of crumb rubber content and curing time on the properties of asphalt concrete and stone mastic asphalt using dry process

Along with the rapid increase in the number of road vehicles, a large amount of waste tires have been created, causing negative effects to the environment. Many attempts have been made to effectively reduce this type of solid waste including the reuse of recycled rubber powder from waste tires as an additive for improving the performance of asphalt mixtures. In this work, the authors aim to study the effects of crumb rubber (CR) on the mechanical properties, especially the rutting resistance, of CR modified asphalt concrete (AC) and stone mastic asphalt (SMA) by varying two factors-namely, the content of additive and the curing time. The dimension of used CR ranges from 0 to 2.36 mm, which is not too coarse for promoting the CR-bitumen interaction and not too fine for facilitating the production of CR. The content of CR was increased gradually from 0 to 3% to examine the effects of CR content on the engineering properties and determine the optimal content in the mixture. It was observed that the optimal content is 1.5-2%, while the optimal curing time that contributes to the maximal increase in the mechanical characteristics of both mixtures could not be determined. In the range of 0-5 h of curing time, the longer the asphalt mixture is maintained at a high temperature, the better the performance of mixture will be. Ageing was found to have influence on the performance of asphalt mixtures; however, its effects are not as important as those of CR modification.