Investigation on the roles of glass sand in sustainable engineered geopolymer composites

The use of fine silica sand negatively affects the sustainable and economic benefits of Engineered Geopolymer Composite (EGC). This paper proposes using glass sand to replace silica sand in producing sustainable EGCs. The influences of glass sand content and size on the properties and microstructure of the EGCs are evaluated. Results show incorporating glass sand increases the flowability of EGCs due to its smooth surfaces. Using 25 % of glass sand decreases the compressive and tensile strengths of the EGC due to the weakened glass-geopolymer interfaces. However, incorporating more fine glass sand can promote the geopolymerisation and remedy the weak glass-geopolymer interfaces, which eventually increases the strengths of EGCs. Decreasing the glass sand size improves both compressive and tensile strengths of EGCs, as this reduces the gap width between glass and geopolymer. Reducing the glass sand content or increasing the glass sand size is beneficial to the pseudo-strain hardening indices reflecting a higher tensile strain capacity, and the developed EGCs can attain a tensile strain capacity of 13.4 %. Increasing the glass sand size up to 1.18 mm or using 100 % of glass sand decreases the average crack width by around 25 % due to the facilitated crack initiation by the weak glass-geopolymer interfaces. Further increasing the glass sand size to 2.36 mm reduces the fibre bridging stress and increases the crack width. Overall, the fine glass sand with a size of 0.125–0.2 mm is easier to participate in the reaction than the coarse glass sand within 0.2–2.36 mm. All the EGCs incorporating glass sand achieve a tensile strain capacity over 7 %, and the tensile strain capacity of sustainable EGC can be adjusted through changing the glass sand size without significantly compromising its mechanical properties.