Strength development and deterioration mechanisms of foamed asphalt cold recycled mixture based on MD simulation

•The molecular model of foamed asphalt cold-recycled mixture was presented.•Moisture reduce the bonding strength among the components of mixtures.•Bonding between RAP and new asphalt is greater than that between RAP and cement. The recycling and reuse of asphalt pavement have become requirements for environmental protection. Foamed asphalt cold-recycling technology is drawing extensive attention and being widely applied. Foamed asphalt cold recycled mixture has advantages such as energy savings, reduced asphalt content, and low transportation costs, and it has the characteristics of both rigid and flexible pavement. However, foamed asphalt mixtures are complex in composition, as it includes recycled asphalt pavement (RAP), water, new asphalt, aggregate, and cement. Therefore, the interaction mechanisms between recycled asphalt pavement and cement or foamed asphalt within the presence of water in the mixing, curing and service procedures will play a key role in determining the development and deterioration of strength of foamed asphalt cold recycled mixture, which was however not well clarified. This study firstly specified the decrease of strength of foamed asphalt cold recycled mixture when considering the effect of water in field project. It was found that the strength of foamed asphalt cold recycled mixture increased along with the decrease of water content during the curing procedure, and decreased by 15–20% through the winter frost. Then the interaction between RAP and cement or foamed asphalt within and without the presence of water had been analyzed with molecular simulation method. The mechanisms of strength development and deterioration of foamed asphalt cold recycled mixture were clarified from the point of view of molecular interaction. The simulation results indicate that the adhesion strength between RAP and cement is greater than that between RAP and new asphalt. The presence of water simultaneously weakens the adhesive bond strengths between RAP and cement and RAP and asphalt.