Characterization of Recycled Aggregates in Existing Pavement Base Layers

The use of recycled pavement materials in transportation infrastructure projects has contributed positively to maintaining a sustainable flow of construction materials and sources. Geotechnical properties of recycled pavement materials play a major role in the suitability of such materials for use in civil infrastructure. This study aimed at evaluating the properties of recycled concrete aggregates (RCA) and reclaimed asphalt pavements (RAP) used as base layer materials in existing hot mix asphalt pavements (with service life of more than 8 years) and comparing them with virgin crushed aggregate (CA) base materials of similar service life. Coring of flexible pavement surface layers at 18 pavement sites was performed to expose the base course layer materials for sampling and testing. Then, the dynamic cone penetrometer (DCP) test was conducted in which the cone penetrated through base layers to the subgrade when possible. Thereafter, base materials were retrieved from the pavement sites for laboratory testing and evaluation. Laboratory tests consisted of particle size analysis, specific gravity and absorption, and Micro-Deval abrasion. Analysis of the particle size distribution showed the presence of high sand size fractions in both RCA and RAP base materials compared with virgin CA base materials. This indicated the recycled materials were crushed/milled to smaller size fractions or degraded under freeze-thaw cycles and traffic loads during the pavement’s service life, or both. The RCA base materials exhibited the highest absorption and mass loss in the Micro-Deval test. The DCP test results were used to predict California bearing ratio (CBR) and resilient modulus (Mr) of base materials. The predicted CBR and resilient modulus of the recycled base materials showed that RCA, RAP, and CA all had comparable strength and modulus values that were high. The investigated recycled RCA and RAP aggregates possessed properties that are comparable with the properties of the virgin CA.