Alkali – carbonate reaction: significance of chemical and mineral admixtures

This Paper deals with the effect of admixtures on the expansion of concrete prisms caused by alkali-carbonate reaction (ACR). The alkali-reactive aggregates were dolomitic limestones from the Pittsburg quarry, Kingston, ON. Admixtures used included accelerators, retarders, an SNF-type superplasticizer (modified sulphonated naphthalene formaldehyde condensate), an air-entraining agent (AEA) and several Li and Ba compounds. The effect of 9% Ca(OH)₂ and of 20% silica fume (SF), and the combined effect of both these materials, was also investigated. Expansions smaller than those of controls were shown by prisms containing the accelerators, the retarders, SF, the Li salts at early ages and two of the three Ba salts. Some increases in expansion were shown by prisms containing Ca(OH)₂, the superplasticizer, one Li salt and one Ba compound. The AEA had no significant effect on expansion. The effect of admixtures on the expansion of prisms caused by ACR was often different from that of similar admixtures on the expansion of prisms caused by alkali–silica reaction.