Development of a Quality Control Method and Guidelines for Hot Mix Asphalt Using Recycled Concrete Aggregate

Each year, about 122 million tons of aggregates, a major structural component of pavement, are used in asphaltic mixtures in pavement construction. At the same time, aging U.S. infrastructure produces around 200 million tons of demolition waste each year, half of which is concrete debris. Therefore, introducing recycled concrete aggregate (RCA) as hot mix asphalt (HMA) aggregate could not only relieve the disposal pressure but also result in considerable reductions in cost, energy usage, and greenhouse gas emissions in the paving industry. A limited number of studies regarding the use of RCA to substitute virgin aggregate in HMA (RCA-HMA) exist. More importantly, the findings reveal discrepant or even contradictory results, regarding the effects of RCA on almost all the volumetrics and performance indicators of RCA-HMA. Because RCA is different from virgin aggregate, as RCA particles are at least partially covered by a residual cement mortar (RCM) layer, the attached RCM in RCAs from different concrete sources could significantly differ in terms of content, porosity, and distribution on the RCA surface. This study aims to determine the characteristics of RCA and RCM, such as RCM content, specific gravity, and absorption, and to evaluate their effects on the volumetrics and performance indicators of RCA-HMA. This research evaluates the variation in the properties of RCA and RCM obtained from different sources and their effects on RCA-HMA’s performance. The research revealed the properties of RCA from different sources vary significantly. It is insufficient to predict the volumetrics and performance of RCA-HMA using only the information of RCA, such as RCA replacement rate and gradation. Information pertaining to the RCM’s properties, such as the RCM content, specific gravity, and absorption, is critical for the prediction of the RCA-HMA properties, including optimum binder content (OBC), voids in mineral aggregate (VMA), voids filled with asphalt (VFA), resistance to permanent deformation, and moisture damage susceptibility. The results of this investigation can help to ensure reliable performance of RCA-HMA in practice by controlling the properties of RCM in the RCA