Evaluation of low and intermediate temperatures fracture indices for modified Warm mix asphalt (WMA) using edge notched disc bend (ENDB) specimen

Abstract

Fracture toughness and fracture energy have been used as the main fracture indices to evaluate asphalt mixtures' fracture resistance. Recently, some cracking-related index parameters such as Flexibility Index (FI), Toughness Index (TI), and Cracking Resistance Index (CRI) have proposed the brittle behavior of asphalt mixtures by normalizing the fracture energy obtained from the load–displacement curve. Although previous studies have evaluated fracture indices in a limited range of temperature conditions and on a limited number of geometries, this study tried to evaluate different fracture indices on Warm Mix Asphalt (WMA) using Edge notched disc bend (ENDB) geometry (pure mode I and III) at low and intermediate temperatures. Besides, environmentally friendly additives, including Calcium Lignosulfonate (CL) and polyester fibers (PE), were used in different percentages jointly and separately to improve WMA mixtures' fracture performance. The results showed that although the risk of cracking of pure mode III was higher than pure mode I based on the toughness results, nevertheless, more fracture energy was required to fracture the sample in pure mode III than pure mode I. For the modified WMA mixture, the fracture toughness and fracture energy in both pure modes I and III had a similar procedure and were affected by the presence of PE at −18 °C. At +25 °C, the fracture energy in pure mode I and III were higher for samples containing 0.25% PE-6% CL than for all samples. Finally, considering all the results, 0.25% PE-6% CL mixture due to higher fracture toughness, higher fracture energy, and a more flexible fracture (based on all three indices FI, TI, and CRI) in pure modes I and III were recommended to use WMA at temperatures of −18 °C and +25 °C.