Improving the methodology for preventing alkali-silica reaction (ASR) in concrete

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Date

2024-08

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University of New Brunswick

Abstract

Alkali-silica reaction continues to be a challenging issue in the field of concrete technology. This chemical reaction between alkalis of portland cement and reactive silica in aggregate leads to the expansion and cracking of concrete. Ever since the discovery of ASR by Thomas Stanton there have been hundreds of studies focusing on preventing ASR. The most obvious approach is to use an aggregate that does not contain reactive silica. If a non-reactive aggregate is used in concrete the reaction does not occur. In areas where rocks contain at least one form of reactive minerals, using a non-reactive aggregate means transporting aggregate from another location which influences the cost-effectiveness of the solution. Therefore, other ASR preventive measures have been explored. The most common means are: (1) use of supplementary cementing materials (SCM), and (2) limiting the alkali loading of concrete mixtures. Various test methods have been developed to evaluate the efficacy of SCMs in reducing ASR expansion. The most widely used ASR test called the concrete prism test (CPT) was known to be the best indicator of field performance of concrete. However, in recent years a disconnect has been discovered between the outcome of the laboratory test and the expansion of concrete blocks exposed to ambient temperature for several years. This dissertation presents the data from several laboratory test methods and the correlation of those tests with the field performance of concrete mixtures made with similar materials to investigate the reliability of ASR laboratory tests by using the long-term data as a benchmark. A new approach is proposed for selecting ASR preventive measures. The new approach consists of testing the aggregate to determine the alkali threshold above which the ASR can occur. This new approach also includes testing the amount of alkalis present from the combination of portland cement and SCM that are available for the reaction initiation. The amount of alkalis is measured using a novel test method proposed in this dissertation. Combining the results of the two proposed methods provides a prescriptive prevention approach that can be used to determine the ASR susceptibility of a specific concrete mixture.

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