Optimizing the pretreatment conditions for waste glass sand in mortar focusing on the alkali-silica reaction mechanism

Using waste glass sand (GS) in concrete has the potential to address the depletion of natural sand resources and environmental issues, however, the degradation of concrete performance caused by the physical properties of GS hinders its practical application. Although mitigation of the negative effects through GS pretreatment has been considered, elucidating the reaction mechanisms and determining optimal pretreatment conditions remain essential. Thus, this study aimed to develop an effective pretreatment method for GS and investigate the reaction mechanisms occurring during the pretreatment process. GS was pretreated using an NaOH solution, a combination of NaOH and CaO solutions, and an NaOH solution for 1 or 3 d followed by a CaO solution. The effect of pretreated GS (TGS) on the compressive strength and alkali–silica reaction (ASR) expansion of mortar was evaluated. Additionally, the cost estimations and carbon emissions were evaluated to verify the optimization of the pretreatment conditions. The reaction products present in TGS exhibited different chemical ratios, depending on the pretreatment conditions, and affected the mechanical properties of the mortar differently. Among the conditions, pretreatment of GS immersed in a NaOH solution for 1 d followed by its immersion in a CaO solution for 2 d (N1C2) was the most effective, improving compressive strength by approximately 34 % and reducing ASR expansion by approximately 55 % compared to untreated GS. Additionally, due to its short pretreatment period, the N1C2 condition exhibited the lowest energy requirement and carbon emissions, demonstrating its potential as the optimal pretreatment condition.