Thermal activation of Multi-Recycled Concrete Powder as Supplementary Cementitious Material for Repeated and waste-free Recycling

The utilization of powder generated during the recycling process of concrete waste is considered crucial for achieving the complete recycling of concrete waste. This study investigated the effect of thermal activation on using recycled concrete powder (RCP), produced from repeated recycling of concrete, as a supplementary cementitious material. RCPs obtained from three cycles of concrete recycling were heat-treated at 200 ℃, 400 ℃, 600 ℃, and 800 ℃ for 2 hours, and their chemical composition was analyzed before and after treatment. Subsequently, the RCPs were used to replace ordinary Portland cement in mortar by 10%, 20%, and 30%, and the fresh and hardened properties of the mortars, such as flow, mechanical strength, water absorption, and drying shrinkage, were tested. The results showed that as the replacement rate and the number of recycling cycles of RCP increased, the properties of the mortar deteriorated. However, heat treatment at 600 ℃ and 800 ℃ enhanced the strength and shrinkage resistance of the mortar. Specifically, the three-times RCP activated at 800 ℃ achieved mechanical performance similar to standard mortar at a 10% replacement rate without a decrease in strength grade. This study is expected to contribute to the repeatable recycling of concrete with zero waste.