Alkali Etching Tests on Concrete Aggregates
Willard H. Parsons and Herbert Insley
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A test for determining the reactivity of an aggre- gate with high-alkali cements is described, which consists of microscopic examination of polished sur- faces of rocks and minerals after etching in various alkaline hydroxide and sulfate solutions. Pure opal, opaline chert and opaline limestone are readily etched, while volcanic glass, certain feldspars, chal- cedony, calcite, and dolomite are slightly etched under some of these test conditions. Photomicrographs of etched rocks and minerals are included.