EFFECTIVENESS OF MINERAL ADMIXTURES IN REDUCING ASR EXPANSION

This paper investigates the effectiveness of eight mineral admixtures in reducing the alkali silica (te) reactivity of cement mortar, The ad mixtures include one class F fly ash, a condensed silica fume, a groun d fiberglass, three glass containing waste materials, and two inert fi llers (carbon and calcium carbonate). Mortar bar expansion, the change in evaporable water content, the evidence of reaction and the composi tion of reaction products were studied. It was found that shale is the only reactive component of the sand and the effectiveness of admixtur es in reducing alkali-silica reaction depends largely on the chemical composition of the admixtures. Ground fiberglass is very effective in controlling the alkali silica reaction, while inert fillers have only a ''dilution effect''. It is thought that admixtures reduce ASR expans ion by two reactions: (1) pozzolanic reaction that reduces the permeab ility of concrete and entraps some fraction of the alkali ions; (2) al kali silica reaction that consumes most of the available alkali ions a nd thereby prevents the reaction between alkalis and aggregate.