Physico-chemistry of silica / Na silicate interactions during consolidation. Part 2: Effect of pH

This work aims to study the effect of the pH of a sodium silicate solution on the consolidation of silica-based aggregates at low temperature (70 °C). A diluted solution obtained by adding 50 wt% of distilled water into a concentrated commercial solution was used as starting solution. Solutions with an increasing pH values were prepared by alkalinizing the diluted solution with solid NaOH. This leads to the depolymerization of silicate species present in solution. Consolidated materials were obtained by impregnating silica sand with the solution. In order to increase the surface reactivity, the sand was also functionalized by a prior basic attack. Results reveal that the increase in the pH value or the functionalization of the sand surface leads to improve mechanical properties of materials suggesting chemical reactions between the components confirmed by FTIR experiments. Actually, the ν_asSi-O-Si broad band with a sharp peak located around 1015 cm^-1, shifts firstly to lower and then to higher wavenumber characteristic of dissolution / precipitation reactions. Moreover, the enhancement of the pH value induces intra-granular break characterized by SEM observations confirming the best consolidation. However, these samples are more soluble in water related to the excess in sodium that induces more ionic bonds.