Synergistic effects of calcination temperature and curing conditions on the hydration and chemical shrinkage of dolomite powder waste pastes

Dolomite powder waste (DPW), abundant in calcium and magnesium elements, represents a potential raw material for concrete expansion agents. This paper shows the hydration properties of calcined dolomite powder waste (CDPW) under different curing temperatures and alkaline conditions. At the same time, the influence of CDPW on the chemical shrinkage characteristics of cement pastes under different curing conditions was analyzed. The intrinsic relationship between the expansion components and chemical shrinkage in the hydration products has been explored using XRD and TG quantitative analysis. SEM-EDS techniques are employed to systematically investigate the microstructural evolution of the samples after 28 d of reaction. The results indicate that within the calcination temperature range of 800–950 °C, the active MgO and CaO content in CDPW exhibits a synchronous increase with elevated temperature, subsequently inducing the formation of a brucite-portlandite complex during hydration. Substituting cement partially with 80 % 850 °C CDPW, the chemical shrinkage of the composite pastes after 28 d under standard curing conditions decreased by 50.98 % compared to cement pastes. In addition, chemical shrinkage is highly sensitive to curing temperatures and solution alkalinity. Although elevated temperatures and robust alkalinity environments accelerated the early hydration of the pastes, extreme conditions (high temperature and robust alkali) resulted in a reduction of the chemical shrinkage rate by 22.58 % compared to standard curing conditions. Microscopic analysis results reveal the crucial role of curing temperature on the degree of paste hydration reaction and product distribution. Under high-temperature and robust alkaline conditions, a synergistic effect exists between the concentrations of Ca(OH)2 and Mg(OH)2 and the rate of chemical shrinkage. This phenomenon is attributed to the unique embedding interaction between Ca2+ and Mg2+, which facilitates the formation of C-M-S-H gels and the optimization of the hydration product structure.