Effect of waste glass powder on quartz sand autoclaved material: strength, hydration products and microstructure

Waste glass is a high-quality siliceous material for autoclaved material, but its effect as the substitution for quartz sand is variable and not sufficiently clarified. To better apply the waste glass in the autoclaved material, the single and combined effect of waste glass and quartz sand as siliceous material on compressive strength is evaluated, and the transformation of hydration products and microstructure is ascertained based on the comprehensive analysis of XRD, FTIR, TG-DSC and ²⁹Si NMR tests. The results indicate that the compressive strength of the autoclaved materials with waste glass is generally higher than that with quartz sand, and the optimum Ca/Si ratio for the waste glass autoclaved material is 0.7, lower than 0.9 for quartz sand autoclaved material. As a single siliceous material, waste glass inhibits the formation of tobermorite and benefits the production of amorphous and highly polymerized C-S–H. At the fixed Ca/Si ratio of 0.7, the partial substitution of waste glass improves the compressive strength of quartz sand autoclaved material by increasing the yield of tobermorite, and the compressive strength reaches the maximum value at the substitution ratio of 20%. A higher waste glass replacement ratio will then be adverse to the formation of tobermorite and decrease the compressive strength. With the increase of the waste glass replacement ratio, the compressive strength presents a three-stage development process. Boosting the formation of tobermorite at a low replacement level of waste glass or highly polymerized C-S–H at a high enough replacement level of waste glass are two feasible approaches to enhancing the strength of autoclaved materials.