A systematic review of factors affecting properties of thermal-activated recycled cement

The cement industry is currently faced with the great challenge of reducing its vast carbon footprint toward sustainability. With the findings on the rehydration behaviors of thermal-activated hardened cement paste, cement, the ‘glue’ of concrete, originally considered a non-renewable resource, now could complete a closed-loop of its whole life cycle. The up-to-date investigations on thermal activation, rehydration kinetics and microstructure phase development of thermal-activated recycled cement (RC) are summarized in this paper. Factors affecting the fresh properties (water demand and setting time), mechanical properties, volume stability (shrinkage and creep) and durability of RC paste and RC concrete are coherently analyzed. The factors considered include properties of mother concrete (degree of hydration, degree of carbonization, existence of SCMs, inert siliceous fines and fine aggregate powder), thermal activation methods (target temperature, heating rate and cooling rate), grinding method and particle size distribution of RC, and post-processing measures (adding superplasticizers, retarders and SCMs). An optimum method for producing RC from waste hardened cement paste was proposed based on the findings in this study to achieve similar properties as OPC. The findings confirm that RC could provide engineers with a novel and eco-efficient solution for the sustainable development of the construction industry. [Display omitted]