Reaction mechanisms of alkali-activated glass powder-ggbs-CAC composites

This paper discusses the alkali activation reaction and the alkali-silica reaction (ASR) of the alkali activated cement (AAC) using glass powder (GP) as the major precursor and glass cullet (GC) as the fine aggregate. For the AAC, the proportion of GP was fixed at 75% by weight and different dosages of ground granulated blast furnace slag (GGBS) and calcium aluminate cement (CAC) were incorporated. The main reaction product of the alkali-activated glass powder and slag was an amorphous gel N-(C)-A-S-H according to scanning electron microscopy (SEM)-back scattered electron (BSE) result. New crystalline phases including zeolite and katoite were detected by X-ray diffraction (XRD) in the AAC pastes after the incorporation of CAC in addition to the N-(C)-A-S-H gel. The compressive strength of the AAC mortar was increased with the increase of CAC dosage when the CAC content was lower than 10%. But further increase of the CAC content decreased the strength of the alkali-activated mortar due to the formation of zeolite and katoite loosening the microstructures. The alkali-activated glass/slag cement suffered from severe expansions due to ASR and the expansion exceeded 1000 micro strain after 14 days of alkaline immersion. The addition of CAC significantly decreased the ASR expansion.