Effect of Metakaolin on Alkali-Silica Reaction (ASR) in Concrete Manufactured With Reactive Aggregate

Abstract

This study is on the effectiveness of metakaolin in preventing ASR (alkali-silica reaction). Samples of metakaolin were prepared by calcining china clay (relatively pure kaolin) and several ball clays, all collected from South West England. Compression cube strength tests were carried out in which part of the cement content of a 1:6 mixture of aggregate and ordinary Portland cement (OPC) was replaced by calcined clay. Results showed that some of the mixtures containing calcined clay exhibited no reduction in the 28 day compressive strength even when 25 percent of the OPC was replaced. Tests for ASR were conducted using prisms produced in accordance with the Draft British Standard 812, Part 123, containing highly reactive natural aggregates which gave an expansion of 0.450 percent at twelve months. It is concluded that expansion due to ASR is completely suppressed when sufficient metakaolin is added to thee concrete formulation. Metakaolin does not reduce the ultimate compressive strength of the concrete, provided that the feed clay is relatively free of impurity minerals.