Engineered\nBlended Thermoactivated Recycled Cement:\nA Study on Reactivity, Water Demand, Strength-Porosity, and CO<sub>2</sub> Emissions

Annually, 1 Gt of cement waste is produced, constituting\none-fourth\nof recent cement production and surpassing the availability of most\nsupplementary cementitious materials (SCMs). It is known that the\nthermoactivation of cement waste (heating to 500 °C to drive\noff water molecules and hydroxyl units) recovers cement reactivity.\nHowever, from literature we show that this reactivity is insufficient\nfor adequate strength gain due to the high surface area and, hence,\nhigh water demand of thermoactivated recycled cement (RC). Instead,\nas proposed herein, RC used as the dominant component (>75% wt)\nwithin\nan optimized particle packing system (<20% wt of micronized Portland\ncement) yields an engineered recycled cement (eRC) with comparable\nearly- and late-age strength gain behavior to ordinary Portland cement\n(OPC). Evaluation of CO<sub>2</sub> emissions reveals that eRC emits\n198–320 kgCO<sub>2</sub>/t, which is substantially lower than\nthat of scalable blended Portland cements. Deploying this technology\ntogether with other strategies, such as CO<sub>2</sub> capture by\ncarbonation of cement waste, can mitigate 61% of projected 2050 CO<sub>2</sub> emissions of the cement industry (2.31 Gt of CO<sub>2</sub>/year).