Supplementary cementitious materials (SCMs) can mitigate alkali silica reaction (ASR) but the level of cement replacement required is difficult to estimate for a particular SCM. The Chemical Index Model was recently proposed to estimate the relation between mortar expansion and the chemical compositions of cement and fly ash but has not been tested extensively for use with other SCMs. This study uses natural pozzolans and blast furnace slags, in addition to fly ashes, with two portland cements and a reactive aggregate to evaluate the effectiveness of the model to estimate 14-day ASTM C 1567 expansion. The reactivities of different oxides are discussed. Model parameters are calibrated for use with mortars containing slags or natural pozzolans. Improvements are suggested to the optimization strategy in the model. Errors in the estimated minimum cement replacement to limit expansion to 0.1% are significantly lowered when the calibrated model is used with these improvements. (C) 2018 Elsevier Ltd. All rights reserved.