Performance evaluation of asphalt mixture using brake pad waste as aggregate

Utilizing brake pad waste (BPW) in asphalt mixture can not only reduce the consumption of natural mineral material, but also alleviate the environmental pollution problem caused by such solid waste. This paper concentrates on the feasibility and strategy of using BPW as aggregate in asphalt mixture. Firstly, BPW aggregate within five different particle sizes were separately used to replace the limestone aggregate or filler with different proportions (25%, 50%, 75% and 100%) in asphalt mixture by the volume control method. The corresponding optimum asphalt contents of 21 kinds of asphalt mixtures were determined by the Marshall design procedure. Due to its high asphalt-absorption, BPW aggregate would increase the optimum asphalt content of asphalt mixture, which depends on the particle size of BPW aggregate. To meet the Chinese Standard Specification for asphalt mixture, the maximum substitution proportions for the BPW aggregates of 0–0.075 mm, 0.075–2.36 mm, 2.36–4.75 mm, 4.75–9.5 mm, 9.5–16 mm were 75%, 50%, 25%, 100%, and 100%, respectively. On this basis, BPW mixture simultaneously using the BPW aggregate with different sizes and the corresponding maximum substitution proportions were prepared and evaluated by a series of laboratory tests as well. Results implied that BPW mixture (BPW-M) outperformed the limestone asphalt mixture (Control-M) in term of the moisture stability, the high-temperature performance, the low-temperature property, and the fatigue life. Furthermore, dynamic modulus test results indicated that BPW-M mixture was more stiffness at relative low frequency (high temperature) and more flexible at relative high frequency (low temperature). Overall, this study verifies the feasibility and provides a reference datum of using BPW materials as aggregate in asphalt mixture.