Phase Composition of Hydrated DSP Cement Pastes

Cement pastes densified with small particles (DSP) containing up to 48% silica fume by weight of cement, and hydrated to up to 180 d at room temperature, have been analyzed using TMS-GPC, TGA, and ²⁹Si NMR to quantitatively estimate the amount of unreacted cement, Ca(OH)₂, and residual silica fume, respectively. Using a mass balance approach, the CaO/SiO₂ and H₂O/SiO₂ molar ratios of the C-S-H in the samples were calculated. For samples containing silica fume, the values of CaO/SiO₂ lie between 0.9 and 1.3, depending on the degree of hydration and silica fume content, whereas for samples without silica fume they were 1.6. Silicate polymerization analysis using TMS-GPC suggests that the molecular structure of the C-S-H is similar to that formed in conventional hydration. No cross-linking species were found, but the fraction of higher polymers (above octamer) increases as the CaO/SiO₂ ratio decreases.