Utilization of ultrafine solid waste in the sustainable cementitious material for enhanced performance

Traditional Portland cement production processes are associated with significant carbon emissions, making them a contributor to climate change. Moreover, the disposal of industrial solid waste, such as phosphogypsum (PG), poses environmental challenges. To address these issues, this study investigates the feasibility of utilizing these waste materials to produce high-performance cementitious materials with reduced environmental impacts, namely composite solid waste-based regenerated ultrafine cementitious materials. The results demonstrate that ultrafine phosphogypsum (UPG) delays heat release during paste hydration. More UPG leads to the delayed heat release and better early strength. The compressive strength of 3 days can reach 27.23 MPa, which is 152.83% higher than that of 10.77 MPa in the control group. Hydration products in the ultrafine ground granulated blast furnace slag-ultrafine steel slag-ultrafine phosphogypsum (UFS-USS-UPG) system mainly include ettringite and C-S-H gel. Ultrafine powder boosts early strength due to its high reactivity and surface area. Later strength gains result from continuous UFS hydration and products interconnection. The pH changes of pastes in four stages, closely match heat release. A rapid pH drop coincides with the main heat release peak, the peak of the main heat release peak occurs at the lowest pH. The production of 1 t of ultrafine powder is cost-effective, approximately 200 RMB, while simultaneously reducing CO2 emissions by about 600 kg compared to the traditional Portland cement production. Overall, this study highlights the potential of these composite solid waste-based regenerated ultrafine cementitious materials as a sustainable and economically viable alternative to traditional Portland cement production, with significant benefits for early strength development and carbon footprint reduction.