A suite of 10 synthetic sodium silica and sodium calcium silica gels was prepared to explore the basic mechanism of expansion of concrete by alkali‐silica reaction. Methods were developed for measuring the free swelling capacity and the maximum swelling pressure generated by these gels when they are allowed access to free water. Free swelling ranged from as little as 0.5 to as much as 80%, maximum swelling pressures recorded varied from as little as 0.1 to almost 11 MPa, the latter well in excess of the tensile strength of most concretes. The relations observed between alkali:silica ratio of the gel and its free swelling and swelling‐pressure characteristics were suggestive but not straightforward. The presence of calcium in the synthetic gels did not noticeably reduce their activity with respect to either test.
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Struble et al. (1981) studied this question.