This work investigated the influence of three different lithium compounds, lithium carbonate (Li₂CO₃), lithium sulfate (Li₂SO₄) and lithium chloride (LiCl), on the hydration and mechanical properties of calcium sulfoaluminate (CSA) cement mixtures. Five concentrations of Li⁺, 0, 0.05, 0.11, 0.16 and 0.22 mmol/g of cement, were chosen, and then the proportions (by mass) of three lithium compounds were determined. Compressive strengths at 8 h, 24 h and 28 days were tested. Meanwhile, an early hydration heat test, thermogravimetric (TG) analysis, X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques were performed to study the influences of different lithium compounds on properties of CSA cement mixtures. The experimental results show that three lithium compounds can all accelerate the early hydration process of CSA cement. There is not a remarkable difference on the properties of CSA cement pastes with a different content of Li⁺. The anion of lithium compounds can also affect the properties of CSA cement pastes, the accelerating effects of LiCl and Li₂SO₄ are more significant than that of Li₂CO₃, but there is not a distinct difference between LiCl and Li₂SO₄.

Molecular insights into structural and dynamic properties of water molecules in calcium silicate hydrate nanopores: The roles of pore size and temperature

Steel slag is generally regarded as a supplementary cementitious material in cement-based materials, which is conducive to the realization of the goal of carbon peak and carbon neutralization. However, the lower cementitious activity and poorer volume stability of steel slag limit its high dosage in cement-based materials. In this paper, steel slag ultrafine powder (SSUP) was prepared in the laboratory through mechanical activation combined with grinding aids. Furthermore, the grinding time was optimized. The particle size, specific surface area, and microstructure characterization were evaluated for the SSUP compared with steel slag powder (SSP). The hydration properties of SSUP were studied by means of cement paste hydration heat and mortar strength. Meanwhile, the soundness of SSUP and SSP was compared by the Le chatelier soundness test. The process of preparing SSUP in the laboratory is as follows: the steel slag is ground by a horizontal ball mill for 50 min and then ground with a planetary ball mill mixing with the grinding aids for 15 min. The experimental results show that the hydration degree and rate of SSUP are better than that of SSP, and the activity index of SSUP is 94.19%, which is much higher than that of SSP (69.62%). The X-ray diffractometry (XRD) result shows that the content of the hydration products for SSUP is higher than that of SSP. The soundness test shows that the stability of SSUP is superior to that of SSP when the dosage is the same. Therefore, ultra-fining can effectively improve the cementitious activity and soundness of steel slag.