Interactions between silica sand and sodium silicate solution during consolidation process

This work is based on the knowledge of the consolidation of silica sand with an alkaline solution in order to determine the mechanisms that occur during the drying of sand and various alkaline solution mixtures. The investigations concern effects of sand distribution size, dilution of sodium silicate solutions and drying temperature of the mixtures on consolidation behaviour. The thermal analysis performed on fresh mixtures show a release of free-water from diluted silicate solution during the consolidation. SEM observations and compressive strength tests results indicate that interactions between sodium silicate binder and silica sand depend on drying temperature. Consequently two consolidation mechanisms are proposed: at low drying temperature (70 °C), sodium silicate acts as a thin layer of glue covering sand grains and bind them to each other, while at high temperature (150 °C), dissolution–precipitation reaction occurred in the mixture consolidating more strongly the granular system. The increase of Si/Na molar ratio in a sodium silicate solution containing silica sand is in accordance with the proposed mechanism.

Research Highlights
► The grains size and silicate solution dilution affect the silicate content in the granular system.
► The mechanical cohesion is improved with a small grain size and/or a weakly diluted silicate solution.
► For a low drying temperature silicate forms an adhesive bond which cracks easily.
► The drying temperature imposes the physical chemistry of the consolidation. Therefore, two consolidation mechanisms were observed: - at 70 °C, the formation of a silicate glass - at 150 °C, a dissolution–precipitation phenomenon.