Comparison of waste glass and fly ash as silica sources for autoclaved materials

The effect of fly ash (FA) and glass powder (GP) as siliceous materials on the strength, hydration products and microstructure of autoclaved materials are investigated. The results indicated that GP is more beneficial to the growth of compressive strength than FA. At the Ca/Si ratio of 0.7, the compressive strength of the GP mixture is 95.7 % higher than that of the FA mixture, and the compressive strength presents a monotonously increasing trend with the increase of the GP replacement ratio for FA. The silica in GP has a higher reactivity than FA to form more hydration products. The main hydration product in the GP mixture is mainly the amorphous C-S-H with a lower Ca/Si ratio, which is difficult to crystalize and transform into tobermorite. FA facilitates the formation of tobermorite, and with the substitution of GP for FA, the fibrous tobermorite is displaced by sheet-like tobermorite and even the foil-like phases at a high GP substitution ratio. Furthermore, the hydration products in the GP mixture have a lower density than that in the FA mixture, but it is conducive to reducing the porosity of the autoclaved material. The low porosity is an important reason that GP as siliceous raw material is eligible for preparing high-strength autoclaved material.