Performance and carbon emission of recycled micropowder-based cementitious materials

Urban renewal has brought about a large amount of construction waste, generating concrete micropowder as a by-product, which poses significant pressure on the ecological environment. Herein, a green high-performance recycled micropowder (RMP)-based cementitious material is developed using the simplex centroid design method. A systematic study of the mechanical properties, microstructure characteristics, and carbon emission is conducted using mechanical tests, isothermal calorimetry, XRD, FTIR, TG, SEM, and LCA. The findings indicated that the transformation of quartz and C₂S crystal patterns and the decomposition of dolomite occur in RMP following mechanical-thermal activation. There is a notable reduction in particle size and an increase in microstructure density. When the RMP dosage is 0–10 %, slag dosage is 15–35 %, and cement dosage is 65–85 %, the system achieves its highest 28-day compressive strength, exceeding 70 MPa, sufficient for most engineering scenarios. The early activity of RMP can be attributed to the rapid reorganization of the dehydrated phases, including CaO and MgO, and the gradual rehydration of the dehydrated amorphous C-S-H phase and polycrystalline reactive C₂S. The subsequent activity is attributed to the reappearance of pozzolanic activity. The incorporation of slag and RMP results in a reduction in the early exotherm and a decline in the hydration rate of the system. Furthermore, the introduction of RMP and slag achieves a 48 % reduction in carbon emissions and a 29 % reduction in total costs per unit strength.