Pure mode I fracture resistance of hot mix asphalt (HMA) containing nano-SiO2 under freeze–thaw damage (FTD)

Abstract

• Pure mode I fracture resistance of Nano-SiO2-modified asphalt mixture under FTD was evaluated. • The semi-circular bending and edge notched disc bend tests were performed on samples at ± 15 °C. • Nano-SiO 2 improved the behavior of LTC and ITC asphalt mixtures under mode I loading and FTD conditions. • Nano-SiO 2 improved the fracture energy and fracture toughness of asphalt mixture under FTD. • SCB geometry with an angle of 35°was critical due to lower average fracture toughness. In cold climates, increased traffic load has increased the damage caused by low-temperature cracks (LTCs) in asphalt mixes. Due to the viscoelastic behavior of asphalt mixtures, cracks caused by intermediate temperatures (ITCs) have led researchers to think more about improving the technical properties of asphalt mixtures with additives. On the other hand, asphalt pavements are affected by freeze–thaw cycles during their service life, a process that intensifies distress and reduces crack resistance. However, despite the effect of freeze–thaw cycles on the fracture behavior of LTCs and ITCs, this process has received less attention from researchers. Hence, in this study, the effect of Nano-SiO 2 on the occurrence of low and intermediate temperature cracks under freeze–thaw damage (FTD) conditions in asphalt mixtures has been investigated experimentally. For this purpose, Semi-Circular Bending (SCB) and Edge Notched Disc Bend (ENDB) tests were used under mode I loading to investigate the effect of Nano-SiO 2 on the crack resistance of the asphalt mixture (i.e., vertical and angular cracks) at temperatures of ± 15 °C. Before the fracture test, the samples were subjected to 0 and 3 FTD cycles to investigate the effect of these conditions on the long-term fracture resistance of the samples. The results showed that adding Nano-SiO 2 increased the brittleness of the mixtures, fracture energy, and fracture toughness of asphalt mixtures containing vertical and angular cracks in both 0 and 3 FTD cycles. Also, it was concluded that Nano-SiO 2 could recover a large part of the resistance reduced by the 3 FTD cycles; therefore, using Nano-SiO 2 additive improved the long-term behavior of LTC and ITC asphalt mixtures under mode I loading and FTD conditions. Finally, by comparing all the geometries used in this research, it was concluded that from the point of view of fracture energy, the ENDB geometry, and from the point of fracture toughness, the SCB geometry with an angle of 35°was critical due to lower average fracture energy and lower average fracture toughness, respectively (temperatures of ± 15 °C under 0 and 3 FTD cycles).