Hydration kinetics and products of Portland cement incorporating polyhedral oligomeric silsesquioxane (POSS)

Polyhedral oligomeric silsesquioxane (POSS), as an organic-inorganic hybrid material with tunable functionality, is innovatively applied in this study to regulate cement hydration and microstructural evolution. The hydration kinetics, hydration products, and compressive strength of Portland cement incorporating four POSS, including octamethyl-silsesquioxane (POSS-A), octavinyl-silsesquioxane (POSS-B), octaphenyl-silsesquioxane (POSS-C), and poly methylsilsesquioxane (PMSQ), were systematically studied. Through isothermal calorimetry, XRD, and TGA analysis, the results reveal that POSS influences hydration via synergistic physical filling and chemical interactions. Specifically, POSS-A and POSS-B enhance early hydration in the first three days, promoting the formation of calcium hydroxide (CH), and facilitate secondary hydration by consuming CH at later hydration stages. In contrast, POSS-C and PMSQ retard hydration by prolonging the induction period. Mechanical tests indicate that optimal POSS-A or POSS-B incorporation (0.2% ∼ 0.6%) enhances 28-day compressive strength, whereas excessive content slightly reduces performance. All POSS types exhibit excellent colloidal stability in alkaline environments, ensuring uniform dispersion and improving the fluidity of mortar. This work demonstrates the potential of POSS for designing high-performance cement-based materials through the tailored control of hydration. • Effects of four POSS materials on cement hydration and performance were evaluated. • The NG-I-D kinetics model revealed the hydration reaction mechanism of POSS-cement. • POSS modulates cement hydration through physical-chemical synergistic effects. • POSS-A/B enhances hydration and strength, whereas PMSQ/POSS-C delays both.