Effect of nano molybdenum disulfide (Nano-MoS2) on fracture behavior of Warm mix asphalt (WMA)

Abstract

Warm mix asphalt (WMA) has been developed for producing cleaner products than other asphalt mixtures. However, fractures caused by structural factors (microcracks caused by insufficient mixing of bitumen and aggregates at lower construction temperature) and environmental factors (microcracks caused by freeze–thaw cycles (FTCs) and aging process (AP)) lead to the formation of low temperature cracking (LTC) and intermediate temperature cracking (ITC), which is intensified by the loading factor. The present study aimed to evaluate and compare the short and long-term fracture behavior of WMA (containing vertical and angular cracks) using semi-circular bend (SCB) geometries under mode I loading conditions at low and medium temperatures. In order to improve the fracture behavior of WMA, an eco-friendly additive called molybdenum disulfide nanoparticles (Nano-MoS2) was used. The results showed that the mixture reinforced with 0.3 and 0.6% nano-MoS2 had better fracture resistance (Fracture Energy (GF) and Fracture Toughness (KIC)), Fracture Flexibility (Flexibility Index (FI), Toughness Index (TI), and Cracking Resistance Index (CRI)), and fracture toughness (Tensile Stiffness Index (TSI) and Tensile Strength (TS)) than the sample without additives under short-term and long-term conditions at temperatures of −15 and + 15 °C. Under 3FTC, the reduction of three indices KIC, GF, and Pmax (in agreement with the hypothesis), decrease in stiffness (in agreement with the hypothesis), and increase in the flexibility of the mixtures (against the hypothesis) was achieved. In addition, the increase of the three indices KIC, GF, and Pmax (against the hypothesis), increase of stiffness (agree with the hypothesis), and decrease of flexibility of the mixtures (agree with the hypothesis) were obtained under 6AP. After the addition of nano-MoS2 to the WMA, a large part of the reduction in the fracture indices was compensated due to the application of FTD cycles. Therefore, the mixture reinforced with nano-MoS2 had better long-term performance under mode I at low and medium temperatures (compared to the sample without additives and at the beginning of the design year). On the other hand, the long-term performance results showed that SCB samples containing vertical and angular cracks were more affected by 3FTC than 6AP. This result indicated the use of FTD cycles to evaluate the long-term performance of WMA mixture to achieve a better design.