Engineered Blended Thermoactivated Recycled Cement: A Study on Reactivity, Water Demand, Strength-Porosity, and CO₂ Emissions

Annually, 1 Gt of cement waste is produced, constituting one-fourth of recent cement production and surpassing the availability of most supplementary cementitious materials (SCMs). It is known that the thermoactivation of cement waste (heating to 500 °C to drive off water molecules and hydroxyl units) recovers cement reactivity. However, from literature we show that this reactivity is insufficient for adequate strength gain due to the high surface area and, hence, high water demand of thermoactivated recycled cement (RC). Instead, as proposed herein, RC used as the dominant component (>75% wt) within an optimized particle packing system (<20% wt of micronized Portland cement) yields an engineered recycled cement (eRC) with comparable early- and late-age strength gain behavior to ordinary Portland cement (OPC). Evaluation of CO2 emissions reveals that eRC emits 198–320 kgCO2/t, which is substantially lower than that of scalable blended Portland cements. Deploying this technology together with other strategies, such as CO2 capture by carbonation of cement waste, can mitigate 61% of projected 2050 CO2 emissions of the cement industry (2.31 Gt of CO2/year).