Dense-Graded Hot Mix Asphalt with 100% Recycled Concrete Aggregate Based on Thermal-Mechanical Surface Treatment

Abstract

Construction and demolition (C&D) waste has been annually generated in high volume due to a mega-scale of the construction industry. It causes the environmental problem of waste management requiring numerous landfill disposal areas. C&D waste can be mainly used as recycled concrete aggregate. However, C&D materials are needed for more effective utilization. Applications in road pavement are recommended to overcome this problem. Therefore, this study examined the use of recycled concrete aggregate (RCA) as a full replacement for natural aggregate (NA) in a hot mix asphalt (HMA) mixture for a heavy-duty asphalt surface. A modified thermal-mechanical beneficiation method was employed to improve the RCA abrasion resistance to meet the Los Angeles abrasion (LAA) requirements for HMA aggregates. Then, the heavy-duty dense-graded HMA was mixed with beneficiated RCA (BRCA) (HMA-BRCA). The HMA mixture with NA (HMA-NA) was utilized as a benchmark. A series of laboratory performance tests on the Marshall stability and flow, resilient modulus (MR), dynamic modulus, and tensile strength ratio (TSR) was performed in conjunction with x-ray diffraction (XRD) analysis. Test results revealed that HMA-BRCA demonstrated better Marshall stability and flow and had a better MR than HMA-NA. However, HMA-BRCA and HMA-NA demonstrated almost identical dynamic modulus characteristics. Nevertheless, HMA-BRCA was more susceptible to moisture than HMA-NA, as indicated by the substandard TSR of HMA-BRCA. Further analysis showed that the breakage of BRCA particles during the mixing and compaction processes led to tighter packing of the HMA aggregate matrix, which was the cause for the improved strength, modulus, and deformation characteristics of HMA-BRCA. Furthermore, a relatively thinner asphalt binder film and the presence of calcite (retained from the original mortar) lead to the poor moisture damage resistance of HMA-BRCA. Therefore, moisture susceptibility is an issue when RCA is used in an HMA mixture, even though the RCA was treated to meet all HMA aggregate requirements. A solution by using an antistriping agent would be carefully considered.