Temperature Effect of Hydration and Microstructure of Tricalcium Silicate–Slag Powder Hydrated Composites: An Experimental and Molecular Dynamics Investigation

Slag powder is an effective and promising alternative to cementitious materials for improving the microstructure of cement composites due to its high environmental and economic benefits. The hydration products of cement–slag powder composites have a typical C-A-S-H gel structure. Especially, the hydration temperature significantly impacts the microscopic characteristics of C-A-S-H crystals, which directly determines the efficiency of the slag powder in modifying cementitious materials. In this paper, the microscopic characteristics of tricalcium silicate (C3S)–slag powder hydrated composites at 20, 50, and 80 °C were investigated, while the molecular structure and mechanical properties of C-A-S-H gels at different temperatures were simulated based on molecular dynamics. The results illustrate that the hydration degree of the C3S–slag powder composites is immensely improved with the increased temperature, while the MCL and Al[4]/Si values of the C-A-S-H gels are both increased. Meanwhile, the conversions of dissociative Al[6] to Al[4] and Al[5] in the C-A-S-H structure are promoted at high temperatures. Furthermore, the elevated temperatures cannot affect the "sandwich-like" microstructure of the C-A-S-H gel but are conducive to the polymerization of the aluminosilicate chains and the increasing proportion of Al[4] in the C-A-S-H crystal. Importantly, an increasing temperature leads to a C-A-S-H structure that has higher tensile ductility. This paper reveals the mechanism by which the environmental temperature affects the microstructure of C-A-S-H crystals and provides insights into the research and design of sustainable and environmentally friendly cement–mineral admixture composites with superior durability.