Effect of Particle Size of Quartz Sand Filler on Microstructure and Strength of Alkali-Activated Slag-Based Materials

Interaction between quartz sand and water glass has been investigated and characterized by using the Si/Na molar ratio to determine the role of silica in the polycondensation rate and mechanical properties of the synthesized materials as a function of quartz sand particle size. Results of atomic emission spectroscopy, SEM and compressive strength tests show that interactions between sodium silicate solution and quartz sand depend on the degree of dispersibility that determines the degree of amorphization of quartz sand. When using ordinary quartz sand sodium silicate solution acts as a thin layer of glue covering the grains of sand and weakly binds them to each other, while using finely ground quartz sand in the mixture there is a dissolution–precipitation reaction that modifies the surface layers of the particles and more strongly consolidating the granular system. The increase in the molar ratio of Si/Na in sodium silicate solution containing finely ground quartz sand occurs due to the increase in the proportion of amorphous quartz (according to XRD) and corresponds to the described mechanism. Then, samples of alkali-activated slag-based materials with a coarse ordinary quartz sand and finely ground quartz sand were synthesized, compared in terms of strength and the latter characterized by SEM, porosimetry, XRD. The increase of dispersibility and amorphization of quartz sand is established to favors to form consolidated of low-temperature curing materials based on alkali-activated slag and quartz sand with the significantly increased compressive strength from 30–44 MPa for mixtures based on ordinary coarse quartz sand to 95–140 MPa for finely ground slag/sand blended mixture.