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ASTM Tentative Definition of the Term Aggregate (C 58 - 28 T), defined aggregates as follows: “Aggregate—In the case of materials of construction, designated inert materials which when bound together into a conglomerated matrix forms concrete, mastic, mortar, plaster, etc.” It has long been recognized that aggregates might contain impurities that are not inert in portland cement concrete. For example, ASTM Standard Method of Test for Organic Impurities in Sands for Concrete (C 40), was published as a tentative method in 1921. Actually, an aggregate may be inert in one matrix, for example, plaster of Paris, and reactive in another, such as, portland cement paste. Over the years concrete technologists have found that it is unsafe to assume that crushed stone and natural aggregates, from sources without service records, will prove to be inert in portland cement concrete. Lerch  has reviewed the early efforts to develop test methods for the purpose of evaluating the potential reactivity of aggregates in portland cement concrete. These efforts resulted in the following methods. 1. C 227, Standard Method of Test for Potential Alkali Reactivity of Cement Aggregate Combinations (Mortar Bar Method). 2. C 289, Standard Method of Test for Potential Reactivity of Aggregates (Chemical Method). 3. C 295, Recommended Practice for Petrographic Examination of Aggregates for Concrete. 4. C 342, Standard Method of Test for Potential Volume Change of CementAggregate Combinations.
Hansen, W. C.
Consulting chemist, Valparaiso, Ind.