Evaluation of fracture behavior of modified Warm Mix Asphalt (WMA) under modes I and II at low and intermediate temperatures

Cracking is considered to be one of the most important distress of the Warm Mix Asphalt (WMA) mixture, which can occur in different climatic conditions due to a lack of proper bonds between aggregate and bitumen. Since the WMA mixture consists of coarse aggregates in different parts of the asphalt layer, cracks can develop and grow at an angular position. Therefore, this study investigates the fracture behavior of WMA mixtures under vertical (Pure mode II) and angular (Pure mode I) cracking states using a semi-circular bend (SCB) sample at −18 °C and +25 °C using the fracture mechanics method. To improve the WMA mixture's performance, additives of Calcium Lignosulfonate (CL) and waste Polyester (PE) fibers, which were economically justifiable, were used separately and simultaneously in different percentages. According to numerical-experimental results, the proposed samples in both pure mode I (angular crack) and pure mode II (vertical crack) were able to model the WMA's fracture behavior and therefore can be used as suitable specimens for studying the pure mode crack deformation of WMA at intermediate and low temperatures. The results also showed that the coarse aggregate distribution in the ligament section of the specimen had a significant contribution in improving the WMA mixture's fracture performance. As a result, fracture energy (GF), fracture toughness (KI and KII), The Flexibility Index (FI), Cracking Resistance Index (CRI), and the Toughness Index (TI) depended on the type of additive used in the WMA mixture. Finally, 0.25PE-6CL, 0.25PE, and 6CL mixtures had the best results in terms of fracture mechanics.