The effects of portland cement alkali content, and replacement of portland cement with Class F fly ash, slag, or silica fume on alkali-silica reactivity (ASR) were studied by measuring the expansion of mortar bars made with Pyrex glass and stored over water at 38°C. Expansions were negligible with portland cements having alkali contents of 0.40% Na₂O equivalent or less. Above 0.40%, expansions of bars made with cement only expanded linearly with cement alkali content after 56 days in storage through 336 days. Regression analysis yielded correlation coefficients of 0.91 for the 56 and 336 day expansions. An expansion of 0.10% was established as the maximum expansion indicative of a mixture providing acceptable mitigation of ASR.

The replacement of cement having alkali content of 0.50% and above with pozzolan or slag was found to reduce expansion. A procedure for normalizing the expansions of pozzolan and slag batches to the regression of cement control batch expansions is presented that allows comparison between batches on an equivalent basis by factoring out inherent testing variability. The level of expansion achieved was related to the alkali content of the cement and the type and amount of mineral admixture or slag used. The materials tested, several Class F fly ashes, a slag, and a silica fume were effective in preventing expansions when used in appropriate amounts with respect to the alkali content of the cement used. The mitigation provided by the materials tested was greater than would have been achieved through simple alkali dilution. Preventive methods based on total cementitious alkali content discount the effectiveness of Class F fly ash, slag, and silica fume in mitigating ASR.