Alkali Carbonate Reaction Products Found by Petrographic Examination of Mortar Bars and Prisms of Carbonate Aggregate after Use in Expansion Tests

摘要

Mortar bars prepared under the ASTM cooperative test series for alkali carbonate reaction were examined by three procedures: (1) Optical methods using reflected light, (2) Optical methods using transmitted light (thin sections), (3) X-ray powder diffraction methods. The reaction products from rock prisms prepared under the same program were examined by X-ray diffraction and by optical methods. X-ray examination of the most expansive aggregates from the mortar bars failed to detect any brucite. However, some type of dedolomitization reaction was indicated. The reaction products from the treated prisms indicate that the minerals of the hydrotalcite-sjogrenite groups (complex magnesium carbonate hydroxides) can be the chief products of alkali dedolomitization near the surface of the prisms of dolomitic carbonate aggregate, and that brucite can be the major dedolomitization product in the interior of the aggregate. (Author)