Effects of recycling agents and methods on the fracture and moisture resistance of asphalt mixtures with high RAP contents

Abstract

The design guidelines for recycled asphalt mixtures recommend rejuvenating the oxidized binder by adding recycling agents, which are viscosity and, consequently, temperature-reducing additives. As it is a component of recent use in pavement and its variety, there has yet to be a consensus on the determination of the recycling agent content or the ideal moment of its addition in the recycled asphalt mixture production process. This study aimed to analyze the fracture and moisture performance of asphalt mixtures with the addition of high contents of RAP (25%, 50%, 75%, and 100%) and two recycling agents (ADCAP WM and residual engine oil) in stages distinct from the production of recycled asphalt mixture (directly to the RAP and directly to the virgin asphalt binder). The recycling agents were added at 12%, 15%, and 18% residual engine oil by mass of RAP and 2%, 2.5%, and 3% of ADCAP WM by the total mass of asphalt binder. The asphalt mixtures were submitted to mechanical tests of tensile strength, resilient modulus, ice and thaw cycles, bending fracture, and fatigue life. The results showed that adding residual engine oil in the asphalt binder enables using up to 75% of RAP. In the case of ADCAP WM additions, identical additions of RAP can be performed. Mixtures with ADCAP WM showed higher consumption of fracture energy, while blends with residual engine oil showed a lower slope of the post-peak curve. Conditioning by the freeze–thaw (F-T) cycle method increased the susceptibility of mixtures to the deleterious effect of water. Statistical analyzes showed that the parameters RAP content, recycling agent, and time of addition of the recycling agent presented adequate significance for the analyzed tests. The maximum RAP content to be applied should be 75%, and adding ADCAP WM directly to the binder showed slightly better results than the other combination.