Experimental and Statistical Investigation of the Effect of Nano ${\mathrm{Al}}_2{\mathrm{O}}_3$ on Asphalt Mixture Resistance against Low Temperature Cracking and Moisture Susceptibility

Improving asphalt mixtures has become increasingly important due to the rise in traffic volume, high maintenance costs, and the challenges associated with their implementation. Previous studies have examined various additives and modifiers. This study investigated the effect of nano ${\mathrm{Al}}_2{\mathrm{O}}_3$ on two significant potential damages in asphalt pavements: low-temperature cracking and moisture sensitivity. The results of this study can be used to propose a suitable solution to minimize the probability of these failures occurring in asphalt pavements. Moreover, this study examined the impact of loading modes, temperature, and crack type on the fracture toughness of asphalt mixtures. In addition to exploring pure mode I and pure mode II, four distinct mixed modes (I/II) were also studied because, usually, this mode is the critical mode of the asphalt mixture. Temperature was another variable observed to validate the elasticity of asphalt mixtures at low temperatures. Lastly, the study investigated the effect of incorporating nano ${\mathrm{Al}}_2{\mathrm{O}}_3$ on the fracture toughness of the asphalt mixture under different temperatures and crack geometries. To achieve the objectives of this study, the semicircular bending and indirect tensile tests were conducted. The results showed that adding 0.6% nano ${\mathrm{Al}}_2{\mathrm{O}}_3$ can increase the crack resistance of asphalt mixtures by up to 12%. Additionally, the study demonstrated that incorporating 0.6% nano ${\mathrm{Al}}_2{\mathrm{O}}_3$ can decrease the vulnerability of asphalt mixtures to moisture by 5.1%. The response surface method technique was employed to analyze the laboratory data statistically. A reduced cubic model was utilized to assess the relationship between independent factors (loading mode, temperature, crack type, and nano ${\mathrm{Al}}_2{\mathrm{O}}_3$ content) and fracture toughness due to its superior fit with the laboratory results Next, sensitivity analysis was used to find the effect value of each parameter on the fracture toughness of the asphalt mixture. The sensitivity analysis results showed that the loading mode, temperature, crack type, and use of nano ${\mathrm{Al}}_2{\mathrm{O}}_3$, respectively, will significantly impact the fracture toughness of the asphalt mixture.