Recycling and valorization of hydrated cement blends in mortars via semi-dry carbonation – The role of waste glass, granulated blast furnace slag and fly ash

The recycling technology of demolished concrete wastes in building materials manufacture provides a possibility of achieving sustainable constructions. Carbonation pre-treatment helps to enhance the performance of recycled concrete fines effectively. To investigate the effects of semi-dry carbonation on the utilization of recycled concrete fines containing supplementary cementitious materials (SCMs) in new concrete production, recycled blended cement paste powder (RBCPs) containing granulated blast furnace slag (GBS), fly ash (FA), or recycled glass powder (RGP) were prepared in the lab. The performance of mortars produced by carbonated recycled blended cement paste powder (C-RBCPs) and RBCPs blended cement were evaluated. C-RBCPs exhibited superior performance in workability and mechanical properties of prepared mortars compared to carbonated OPC powder. The results indicated that the RBCPs exhibited a lower carbonation degree (less than 53.4%) and CO2 uptake compared to OPC samples due to the lack of available Ca in the originally blended cement after incorporation of GBS, FA and RGP. As the main carbonation products, calcite, aragonite, and vaterite were all observed in C-RBCPs, the category of SCMs exhibited visible influences on the crystal format of calcium carbonate, as well as the reactivity of C-RBCPs in blended cement mortars. Overall, the semi-dry carbonation can promote the reactivity of C-RBCPs efficiently. The effects of the SCMs category should be considered in the recycling processes of cement wastes. The application of GBS, FA, and RGP in blended cement can help to achieve excellent sustainability of C-RBCPs blended mortars after semi-dry carbonation pre-treatment..