Considerations on the effect of temperature, cation type and molarity on silica degradation and implications to ASR assessment

Abstract

This paper addresses parameters influencing the effectiveness of accelerated ASR testing. Amorphous Pyrex glass powder was subjected to alkali-rich solutions with different temperatures (20, 40, 60 and 80 °C), cation types (Na, K and Na + K) and concentrations (1 and 3 M). Visual assessment, phase assemblage and chemical analyses were performed through SEM, XRD, XRF and FTIR. The data indicates that the degradation of silica was strongly affected by complex interactions and the combined effect of all parameters. The increase in temperature induced a greater reduction in the degree of crystallinity and the Na + K solution was found to be the most effective on silica degradation. Synthesized gels produced at higher temperatures and molarities are both microstructurally and macrostructurally different than one synthesized at milder conditions. It follows that extrapolations based upon accelerated test conditions should be made with care and also consider the effect of these parameters on the gel’s structure as they can adversely affect expansion mechanisms.