Effect of curing regime on polymerization of C-S-H in hardened cement pastes

The effect of two different curing regimes on the polymerization degree of C-S-H in hardened cement pastes within 28 d were investigated by measuring the chemical environments of ²⁹Si with magic angle spinning (MAS) nuclear magnetic resonance (NMR) and by analyzing the ²⁹Si NMR spectra with deconvolution technique. The experimental results indicate that, at curing regime of constant temperature of 20 °C, the polymerization of C-S-H increases and then decreases with curing age, and the Al/Si ratio increases gradually with curing age, furthermore, the two non-bridging oxygen bonds of bridging silicate tetrahedra in C-S-H structure mainly bond to H⁺. At curing regime of variable temperature, the polymerization of C-S-H firstly increases then changes slightly and subsequently decreases with the temperature from low to high and then to low, and the Al/Si ratio firstly increases then keeps invariant and subsequently slightly decreases. Moreover, the temperature decreasing is advantageous for the Ca²⁺ to be bonded to the bridging silicate tetrahedra and entering into the interlayer of C-S-H structure. The polymerization of C-S-H at curing regime of variable temperature is higher than that cured at constant temperature, but the curing regime of constant temperature is more beneficial to the substitution of Al³ for Si⁴⁺ than that of variable temperature.