Evaluation of recycled concrete aggregate in asphalt mixes

Abstract

This paper investigates the feasibility of using recycled concrete aggregate (RCA) as a replacement to the natural aggregates (NAs) in hot mix asphalt (HMA). RCA was collected from two different sources (new concrete cubes used for quality control testing during construction, and old demolished building) to investigate the impact of material degeneration on the engineering properties of the mix. Basic engineering properties were determined for both RCA and bitumen for the preparation of HMA mixes. Different mix designs were conducted using the conventional Marshall method with 100% RCA or substituting the coarse natural aggregates (retained on the US Standard Sieve No. 4) by RCA. Performance of the investigated mixes in terms of stability, flow, loss in abrasion, loss of stability, and indirect tensile strength was evaluated. Moreover, the investigated mixes were characterized by the image processing and analysis system (IPAS) software to investigate the aggregates characteristics such as contact zone properties, orientation, and segregation. Results showed that the new RCA coarse aggregate had lower bulk specific gravity, higher liquid limit with no plasticity, higher pH values and lower Los Angeles Abrasion values compared with the old RCA. Also, new and old RCA showed higher water absorption than the specification maximum limits, which had a significant effect on the optimum bitumen content. Using of the 100% new RCA, increased the stability, and flow compared with other mixes. In terms of abrasion loss, loss of stability and indirect tensile strength, all results were within the specification limits. Required fracture energy was lower for the 100% new RCA. The results of the IPAS software showed that the HMAs containing new RCA yielded the best performance in terms of aggregate-to-aggregate contact zone properties, resistance to permanent deformation, and less stress concentrations in comparison with those of other mixes, old RCA, new RCA/NA, and old RCA/NA, respectively.