Thermal activation of multi-recycled concrete powder as supplementary cementitious material for repeated and waste-free recycling

Utilizing powder generated during concrete recycling process is considered crucial for achieving complete recycling of concrete waste. However, integrating recycled concrete powder (RCP) often reduces cementitious mixture performance. This study aims to enhance RCP characteristics through thermal activation, facilitating its recycling as cement replacement over multiple recycling cycles. RCPs from three cycles of concrete recycling were heat-treated at 200 degrees C, 400 degrees C, 600 degrees C, and 800 degrees C for 2 h, and their chemical composition was analyzed before and after treatment. Subsequently, the RCPs replaced cement in mortar by 10 %, 20 %, and 30 %. Various properties of the mortars, such as flow, mechanical strength, water absorption, and drying shrinkage, were tested. The results showed a general decline in mortar properties with increasing RCP replacement ratios and recycling cycles. However, RCPs activated at 600 degrees C and 800 degrees C enhanced compressive and flexural strengths by up to 19 % and 16 %, respectively, and enhanced shrinkage resistance by 19 %. Particularly, the three-times RCP activated at 800 degrees C achieved mechanical performance comparable to standard mortar at 10 % replacement, meeting strength grading requirements per industry standards. This study demonstrates a viable pathway for the repeatable and waste-free recycling of concrete, contributing to more sustainable construction practices.