Feasibility of using pretreated sodium silicate-bonded waste foundry sand as fine aggregates for construction mortar

Insufficient utilization of sodium silicate-bound waste foundry sand (SS-WFS) in construction is due to the presence of harmful residual sodium silicate film on the sand surface, which are detrimental to cement hydration. Based on previous research, this study proposes a pretreatment method using another industrial waste, calcium carbide slag (CCS), to effectively remove pollutants from sodium silicate-bounded waste foundry sand (SS-WFS). The feasibility of pretreated SS-WFS as an alternative to natural sand and optimal washing duration were investigated. The results demonstrate that pretreated SS-WFS exhibits promising potential as a substitute for 100% natural sand as a fine aggregate within the construction industry, while demonstrating comparable mechanical properties to those of natural sand mortar. The residual sodium silicate film on the surface of SS-WFS undergo secondary hydration, leading to the formation of hydration products with a low calcium-to-silicon ratio in interfacial transition zone. This enhances the mechanical properties of the mortar and improves its deformation characteristics. The optimal washing duration is determined to be 5 min with 1% CCS, and compared to RS-0, the mortar strength has increased by 70%. Extended washing duration may cause the depletion of beneficial components, such as active Si2O, from the sand surface.