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


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

Author(s): G. Vivian Walters and Thomas R. Jones

Publication: Special Publication

Volume: 126


Appears on pages(s): 941-954

Keywords: alkali-silica reactions; calcined clay; concretes; expansion; metakaolin; pozzolans; Materials Research

Date: 8/1/1991

A recent report claimed that ASR expansion was suppressed when calcined clay was added to concrete used in hydroelectric dam construction containing reactive aggregates. The authors report a laboratory study on the effectiveness of metakaolin in preventing ASR. Samples of metakaolin were prepared by calcining china clay (relatively pure kaolin) and several ball clays, all collected from Southwest 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 that expansion of 0.450 percent at 12 months. Prisms in which up to 25 weight percent of the OPC was replaced by calcined clay have been monitored over a period of 18 months and have shown no expansion or deleterious surface appearance. As a result of these tests, it is concluded that expansion due to ASR is completely suppressed when sufficient metakaolin is added to the concrete formulation. Metakaolin does not reduce the ultimate compressive strength of the concrete, provided that the feed clay is relatively free of impurity minerals.