The effect of utilization of RCA on volumetric properties of asphalt mixtures

The need for sustainable asphalt mixture design is becoming a priority within pavement industry. This trend is necessitated by high rate of construction and demolition waste, pressing demand on landfill sites. Recycled Construction Aggregate (RCA) is one of the potential options for utilization in pavement construction. Therefore, the feasibility of partial substitution of virgin aggregate in hot-mix asphalt (HMA) with RCA is investigated in this research project. RCA differs from virgin aggregate because of the cement paste which is attached to the surface of the virgin aggregates as well as the variety in its composition. This highly porous cement paste and the variation in quality of RCA results in the lower particle density and higher porosity, and subsequently higher bitumen absorption and wet/dry strength variation. However, the test results demonstrate that some parameters such as flakiness Index and particle shape have a smaller value in RCA compared to virgin aggregates. These parameters are two dominant characteristics which have significant impact on asphalt mixture strength and stability. This paper presents some of the results of an investigation on the feasibility of utilization of RCA in asphalt mixtures. For this purpose, firstly, a preliminary experimental study is conducted to evaluate the properties of RCA as an alternative for natural aggregate in asphalt mixture under different combination and percentages with virgin aggregates. The aggregate properties studied in this preliminary level were flakiness index, particle shape, water absorption and particle density, wet/dry strength variation, crushing value, and weak particles. Based on the results obtained from the aggregate specification tests on unbound RCA, in the second step, different asphalt mixtures incorporating substitutions of coarse virgin aggregate with 25% and 50% RCA were prepared and evaluated through gyratory compaction method; the optimum bitumen contents were found to be 5.1%, 5.8 and 6.2% of C320 bitumen, respectively.