Investigation of the fracture resistance of warm mix asphalt mixtures containing steel slag aggregates at low temperatures

The use of waste materials and Warm Mix Asphalt (WMA) technology in asphalt pavements has several advantages. Low-temperature cracking is one of the most common failures of WMA mixtures. Hence, the primary objective of this study is to evaluate the fracture toughness and fracture energy of asphalt mixtures containing a chemical WMA additive and steel slag aggregates. The steel slag aggregates were substituted at percentages of 0%, 25%, 50%, and 75% by the volume of coarse aggregates. To this end, a three-point bending fracture test was carried out under pure modes I, II, and mixed mode I/II, as well as at three low temperatures (0°C, − 10°C, and − 20°C), using Edge Notch Disc Bend (ENDB) specimen. The results of this study show that the reduction in test temperature leads to an enhancement in fracture toughness and a decrease in the fracture energy of specimens. The lowest fracture resistance is observed under mixed mode I/II; therefore, the risk of cracking in WMA in mixed mode I/II was more significant than in other modes. Additionally, an increasing trend in fracture toughness and fracture energy for WMA mixtures was observed by increasing the percentage of steel slag aggregates. By increasing the slag percentage to 75%, fracture toughness and fracture energy under pure mode I were increased by 35% and 16%, respectively. Therefore, the incorporation of 75% coarse steel slag is recommended to enhance the fracture resistance of WMA mixtures at low temperatures.