The tests in accordance with the ASTM C227 (mortar bar test) have been carried out to investigate the effects of calcium nitrite (CN), fly ash, microsilica and their combination on the alkali-silica reaction (ASR). The chemically combined water, X-ray diffraction and compressive strength of each batch of specimens were also measured to explore the mechanism of these effects. The results show that both mineral admixtures and the CN solution have positive effects in preventing ASR expansion. It is found that the addition of a CN solution in this experiment has additional effects, being favourable for strength development. © 1999 Thomas Telford Ltd.