Evaluation of Moisture sensitivity of asphalt mixtures modified with nanomaterials (ZnO and SiO2)

One of the most common damages in asphalt mixtures is due to the destructive effects of moisture on the cohesion of asphalt binder and adhesion of asphalt binder-aggregate which is called moisture damage. There are several different approaches for improving adhesion and reducing moisture sensitivity in asphalt mixtures. One convenient approach is modifying the asphalt binder with suitable agents. In this research, the effects of two types of nanomaterials in two different percentages (nano ZNO and SiO2), two types of aggregates (granite and limestone), and one base asphalt binder were evaluated. To assess the effect of nanomaterials, the indirect tensile cyclyc loading (similar to resilient modulus test) in dry and wet conditions and surface free energy (SFE) tests have been used. Moisture sensitivity index, which is the percentage of the aggregate surface exposed to water as calculated by using the measured SFE and indirect tensile cyclic results, was considered an index for the moisture susceptibility of mixtures. Mechanicaltest results used in this study show that using nanomaterials significantly improves the moisture strength of samples made with the modified asphalt binder in comparison with the control samples. Results of surface free energy theory show that the nanomaterials increase the cohesion free energy of the asphalt binder that decreases the probability of the occurrence of cohesion failure in the mastic. Also, nanomaterials decrease the acid component and increase the base component of surface free energy of the asphalt binder which increases its adhesion with the aggregates that are prone to moisture damage.