Evaluation of Rutting, Fatigue, and Moisture Resistance of Low-Energy Asphalt Mixtures Modified by Crumb Rubber

Low-energy asphalt (LEA) mixture, as an alternative to hot mix asphalt (HMA) due to its lower mixing temperature, has advantages such as reducing energy consumption and environmental pollutants. LEA has poor performance characteristics due to the presence of water in its manufacturing process and low mixing temperature. All the studies about LEA have been focused only on investigating the performance of this asphalt mixture, and the effect of additives in its modification is one of the research gaps in this field. Therefore, the use of crumb rubber (CR) and determining its optimal percentage in modifying the performance characteristics of LEA is considered an innovation of this research. In this research, the performance characteristics of LEA modified by 10%, 15%, and 20% CR were evaluated. In order to examine the rutting behavior, moisture sensitivity and fatigue resistance, dynamic creep, indirect tensile strength (ITS), and four-point bending beam tests were applied, respectively. The results of creep curves and flow numbers (FNs) indicated that modifying LEA by 15% increased the rutting resistance by 1.92 and 2.3 times, respectively, compared to the HMA specimen at the stress level of 207 and 310 kPa. Moreover, the evaluation of the creep strain slope revealed that modifying LEA significantly reduced stress sensitivity. ITS test showed an increase in tensile strength ratio by 22% in the specimen with 10% CR compared to the unmodified specimen. In the evaluation of fatigue resistance, while LEA containing 10% CR had almost similar results to the HMA specimen, other specimens represented a shorter fatigue life, so that with the increase in CR percentage, the fatigue life decreased. Determination of fatigue life by energy ratio and Rowe and Bouldin criteria showed similar results. Finally, by determining the plateau value (PV) in the ratio of the dissipated energy change method, the lowest PV was assigned to the 10% CR-modified LEA and HMA specimens, respectively.