Comparison of Asphalt Mixes Containing Reacted and Activated Crumb Rubber (RAR) and CRM Binders

Crumb rubber has been utilized to enhance properties of bitumen and asphalt mixtures. This, which consists of particles from scrap tires of passenger cars and trucks, has conventionally been used in wet processing methods to prepare crumb rubber modified (CRMs). However, these processes require special equipment and long mixing times with bitumen which makes it difficult to be used extensively in asphalt pavements. A new approach of the application of crumb rubber in asphalt mixes is to use it in the form of reacted and activated rubber (RAR). This is a rubber-based asphalt mixture modifier that contains bitumen, rubber powder, and some chemical additives. The product that is in powder form, is prepared in advance and can easily be mixed with hot aggregates in conventional hot mix asphalt (HMA) plants. The purpose of this paper is to evaluate performance of a dense-graded asphalt mixture, containing this modifier and compare it with the control HMA and a conventional wet processing CRM mix. Laboratory tests included semicircular bending (SCB) and rutting tests. Tensile strength ratio (TSR) parameter was determined for moisture susceptibility assessment purposes. The results indicated that RAR is a compatible rubber modifier with significant potentials to enhance properties of asphalt mixes. In fact, at optimum content, it increased the indirect tensile strength of the modified mix by 21%, compared with conventional HMA. In SCB test at 25 degrees C, samples modified with RAR exhibited a maximum load of 4.38 kN, which was slightly higher than the corresponding CRM sample that was 4.19 kN. Rutting tests indicated that rubber-modified mixes exhibited four times better rutting resistance than the control HMA. Samples containing RAR and those of CRM, after 10,000 cycles, showed rut depths of 1.3 and 1.2 mm, respectively. Overall, the samples modified with RAR exhibited similar or slightly better performance than the conventional wet processing CRM mixes.