Closed-loop recycling of C&D waste: Mechanical properties of concrete with the repeatedly recycled C&D powder as partial cement replacement

Abstract

Studies have been conducted on the repeated recycling of recycled coarse aggregates and recycled fine aggregates obtained from concrete waste, but no research has been conducted on the repeated recycling of recycled powder as a partial replacement for cement, which is pointed out as a major source of CO2 in the concrete industry. This paper investigates the closed-loop recycling potential of construction wastes by evaluating the effects of repeated use of concrete powder generated in the production of recycled aggregates on the selected fresh and hardened mechanical properties of concrete. Through a series of concrete making and crushing, once-, twice-, three times-recycled concrete powder of less than 150 μm was collected and used as a partial replacement for cement in concrete matrices at replacement levels of 10%, 20% and 30%. According to the experiment results, the replacement ratio and the number of recycling of concrete powder are parameters that affect the properties of concrete, and in particular, the replacement ratio is more affected than the number of recycling. The strength of concrete containing 10–20% concrete powder surpassed the target strength by up to 21% over three times of recycling, and the cost and environmental benefits increase in proportion to the number of concrete powder recycling. This study can contribute to the valorization of construction waste by providing a new initiative for multi-recycling of concrete powder and a closed-loop recycling system for construction waste.