Laboratory Investigation of the Effect of Nano-ZnO on the Fracture and Rutting Resistance of Porous Asphalt Mixture under the Aging Condition and Freeze–Thaw Cycle

Abstract

Porous asphalt (PA) mixture is a hot mix asphalt with an open gradation that has a high amount of air void in its structure. Although this high volume of empty space in PA has several road safety and environmental benefits, it causes some performance drawbacks like reducing PA mixes’ resistance against rutting and cracking and increasing sensitivity to aging and moisture conditions. This study aims to evaluate the rutting and intermediate-temperature cracking behavior of PA mixes modified with various percentages of nano-ZnO (NZ) (0%, 2%, 4%, 6%, and 8%) under laboratory aging conditions and freeze–thaw (F-T) cycle by performing wheel track and semicircular bending (SCB) tests. It can be inferred from the wheel track results that while the aging process positively affects the rutting behavior of the PA mixtures, the F-T cycle decreases PA mixtures’ rutting resistance because moisture deteriorates the adhesion between bitumen and aggregates. From the SCB test results, both the aging and F-T cycle negatively impact the crack resistance of the PA mix. Moreover, the results indicate that adding NZ improves PA mixtures’ performance against permanent deformation and cracking by an average of 50%. The optimum content of the NZ modifier in PA mixes was 6%.