Investigating effects of using nanomaterial on moisture susceptibility of hot-mix asphalt using mechanical and thermodynamic methods

One of the main reasons of premature damage to the asphalt layers of flexible pavements is the damage caused by moisture which is also called moisture damage or stripping. Stripping is defined as the loss of resistance and strength induced by moisture. Various methods have been used to decrease this type of damage using anti-stripping materials as the most common method. Problems associated with the practical application of anti-stripping materials coating aggregates and adverse effect of using bitumen-modifying additives have motivated us to investigate the effect of using styrene-butadienestyrene nano-composite as a new anti-stripping additive in hot-mix asphalt. In this study, besides applying modified Lottman test as a conventional test for moisture susceptibility, surface free energy methods were also utilized to determine the mechanism by which the considered nanomaterial affected cohesion and adhesion properties of asphalt mix components. Materials used in this study included two types of aggregates with different hydrophilic degrees (limestone and granite aggregates), bitumen with 60-70% penetration grade (PG 64-22), and SBS nano-composite with two different percentages. Results of the modified Lottman test showed that use of nano-composite improved the resistance of the asphalt mix manufactured by two types of aggregates used in this study. Also, the results of measuring surface free energy components of bitumen indicated that use of nano-composite increased the force required for producing the aggregate's stripping in the bitumen, which further improved the strength of the asphalt mix against moisture damage.