Pre- and post-cracking behavior of asphalt mixtures under modes I and III at low and intermediate temperatures

Abstract

The pre- and post-cracking resistance of asphalt mixtures depends on factors such as the coherence of the soft asphalt matrix (SAM) section, which should be considered. The SAM section can achieve more coherence through the suitable additives. In fact, the additives increase the interlocking of aggregates by increasing the coherence of the SAM section; conclusively, the pre- and post-cracking resistance of the pavement increases. This study was intended to investigate the pre- and post-cracking behavior of two types of modified asphalt mixtures, namely Hot Mix Asphalt (HMA) and Warm Mix Asphalt (WMA), using indicators of pre-peak fracture energy (Gfpre-peak), post-peak fracture energy (Gfpost-peak), Tensile Stiffness Index (TSI), and Tensile Strength (TS) at temperatures of −18 °C and + 25 °C (under modes I and III). Thereby, 5 HMA mixtures and 5 WMA mixtures containing different percentages of polyester fibers and calcium lignosulfonate were prepared. Subsequently, two geometries called symmetric specimen ENDB and asymmetric specimen ENDB, typifying mode I and III the loading conditions, were extracted from the desired mixtures, and then they were tested. According to the results, the fracture behavior of HMA and WMA mixtures was changed by increasing the coherence of the SAM section. Moreover, the resistance to elastic deformations for HMA and WMA mixtures containing additives was improved by using TSI and TS indicators. The results of the statistical analysis showed that there was a good correlation between the TSI and TS indices with the Gfpre-peak index, which indicated the relationship of the Gfpre-peak index with stiffness (resistance to elastic deformation). In addition, the regression relationships with higher R2 values indicated that the stiffness of the asphalt mixture can be estimated using ENDB geometry. Therefore, the slope of the load–displacement curve obtained from the ENDB geometry can be used as a measure to calculate the stiffness of the asphalt mixture. Finally, considering all the results, it can be argued that for the HMA and WMA mixtures, the mixtures containing 0.25% polyester fiber and the mixture containing 0.25% polyester fibers + 6% calcium lignosulfonate had a better fracture behavior (pre- and post-cracking resistance) under mode I and III loading conditions (at temperatures of −18 °C and + 25 °C).