(85c) Tailoring Tricalcium Silicate Hydration and Microstructure Using Engineered Layered Double Hydroxides with Tunable Composition and Anion Exchange Capacity

The hydration behavior and microstructural evolution of tricalcium silicate (C₃S), a principal phase in Portland cement, were systematically investigated in the presence of nano-uniform layered double hydroxides (LDHs) synthesized with varied compositions. These LDHs were designed using different divalent metals (Ca²⁺ and Mg²⁺), interlayer anions (NO₃⁻, CO₃²⁻, and SO₄²⁻), and tailored M²⁺/M³⁺ molar ratios (2, 3, and 4 in Mg-based systems). Results from isothermal calorimetry showed that the inclusion of Mg–Al LDHs with CO₃²⁻ significantly accelerated the early hydration of C₃S, advancing the main hydration peak by over 2 hours. TGA and XRD analyses confirmed increased formation of calcium-silicate-hydrate (C-S-H) and portlandite in LDH-modified systems compared to controls. Moreover, SEM images revealed a denser and more refined C-S-H morphology in samples containing Mg–Al LDHs with SO₄²⁻ interlayers, while LDHs with higher M²⁺/M³⁺ ratios promoted more uniform microstructures. These findings highlight the ability of compositionally engineered LDHs to modulate C₃S hydration kinetics, enhance microstructural development, and serve as multifunctional nano-additives for advanced cementitious materials.