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Standard Aggregate Materials for Alkali-Silica Reaction Studies

L. Struble / M. Brockman

Preliminary studies have been carried out to identify candidate materials for use as a standard reactive aggregate in alkali-silica investigations. The materials studied included several commercial glasses, an opal, a quartzite, a rhyolite and a calcined flint. Candidate materials were tested for their expansion in mortars prepared using either a high-alkali or a low-alkali cement, a nonreactive limestone sand, and some proportion of reactive material. Tests were carried out according to ASTM C441-81, Standard Test Method for Effectiveness of Mineral Admixtures in Preventing Excessive Expansion of Concrete Due to the Alkali-Aggregate Reaction, and ASTM C227-87, Standard Test Method for Potential Alkali Reactivity of Cement-Aggregate Combinations (Mortar-Bar Method). The proportion of limestone replaced by each reactive material was varied so as to bracket the pessimum proportion (i.e., the proportion of reactive material producing the highest level of expansion). Mortar-bar expansion levels were measured throughout reaction periods of approximately 6 months to 1 year. Expansion results are presented and discussed. Based on the studies, the Vycor, fused quartz, fused silica, and calcined flint appear suitable as standard reactive materials; the calcined flint appears especially promising.