Mechanochemical activation of recycled concrete fines to produce supplementary cementitious materials

Leveraging “end of life concrete” as a resource, not waste, is a critical milestone in achieving circularity and meeting the sustainability targets outlined in the Sustainable Development Goals. However, current industrial practices remain limited, with most concrete waste being crushed and discarded, including the fine fraction known as recycled concrete fines (RCFs). This study investigates the reactivity of mechanochemically activated (MCA) RCFs as a potential supplementary cementitious material. Reactivity was assessed using Frattini, R3 calorimetry test, and Strength Activity Index (SAI). All methods confirmed that mechanochemical activation effectively enhanced the reactivity of RCFs, with an optimal grinding duration of 20 min. Mortar results showed a compressive strength improvement of 35% (at 20% cement replacement) relative to the untreated RCF blend. The results further indicated that particle size distribution affects the measured reactivity, emphasizing the need to distinguish the filler effect from intrinsic chemical reactivity. Overall, the findings highlight the potential of MCA as an effective and sustainable strategy for valorizing fine concrete waste in circular cementitious systems.