Thermochemical activation of low-grade sand washing sludge and its application in cement-based materials

Sand washing sludge (SWS), a typical solid waste from the sand manufacturing process of natural minerals, has caused serious environmental problems due to its accumulation. To reuse SWS as supplementary cementitious materials, this study investigates the structural changes of thermochemically activated SWS and its effect on cement hydration. The results show that the synergistic activation of calcination and calcium enrichment led to the formation of new silicate minerals in SWS, and that thermochemically activated SWS exhibited higher reactivity compared to SWS800 treated with calcination at 800 °C. According to the results of the setting time and heat release of the fresh pastes, it can be found that thermochemically activated SWS promoted the hydration reaction and shortened the setting time. When the incorporation of A2-SWS800 was 10 %, the compressive strength of M-A2S8 specimens at 3 and 28 days was 20.6 MPa and 36.0 MPa, respectively, which was 24.8 % and 26.8 % higher than that of M-S specimens at the same age, respectively. From the environmental perspective, with the increasing addition of thermochemically activated SWS, the embodied energy and CO2 emissions of cementitious materials gradually decrease. These works are important guidance for the recycling of SWS and the decarbonization of the building materials sector. •The sand washing sludge is treated with calcined and calcium-enhanced synergistic activation.•The physicochemical properties and structural changes of activated sand washing sludge were investigated.•The incorporation of activated sand washing sludge promoted the hydration reaction and improved the strength.•The recycling of sand washing sludge in an efficient way was realized.