New Approach to Inhibiting Alkali-Aggregate Expansion
W. J. McCoy and A. G. Caldwell
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Investigators have studied for a decade the chemical reactions between high-alkali cement and siliceous mineral constituents of some aggregates towards deterioration of concrete. Papers on this subject indicate a consensus that there are just two possible remedial measures when reactive aggregates are used - low-alkali cement or substitution of a pozzolanic material for 20 to 30 percent of the portland cement. Investigative work foucused off the beaten path of pozzolans and lowering cement alkali content resulted in experimental data which indicate that small amounts of certain materials added to high-alkali cement have an inhibiting effect on expansion reaction. For example it has been found that 1 percent or less of specific salts will reduce expansion more than 75 percent in Pyrex glass mortar bar tests using a small percentage of opal and quartz sand as aggregate. Additional information indicates that small amounts of certain proteins (0.2 percent or less) added to the cement appear to have a greater inhibiting effect on the expansive reaction than is obtained by comparable air entrainment effected by the conventional air-entraining agents. Such inhibitors appear to have no appreciable detremental effect on the properties of the high-alkali cements as determined by ASTM specification tests for cement.