Correlation of reaction products and expansion potential in alkali-silica reaction for blended cement materials

This article will review how blended cements are effective in controlling the alkali-silica reaction (ASR) expansion by changing the chemical reactions, as well as improving the transport properties of concrete. Several models have been proposed to describe the mechanism by which ASR can damage cement-based materials. Nonetheless, the effect of blended cements on the morphology and chemical composition of reaction products needs better understanding. In this study, experimental data from the ASTM C1567 test method and microstructural studies, including an environmental scanning electron microscope (ESEM) and quantitative energy dispersive spectrometer (EDS), were used to develop a physico-chemical model based on the properties of different silicate glass structures. One type of reactive aggregate and several fly ashes with various properties were used. An analysis of the number of bridging and nonbridging oxygens in the gel network in acidic and basic environments provided further insight into ASR products. The distinction between “safe” and “unsafe” reaction products was discussed with the formation of smooth gels with Na-Si-O phase versus the dispersed platelets with Ca-Na-Si-O composition.