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It is to be expected that the influx of preheater/precalciner technology will result in a general increase in portland cement alkali level. High-alkali cement is associated, in general, with rapid early strength development and disproportionately lower 28 day strength in mortar cubes in accordance with ASTM Compressive Strength of Hydraulic Cement Mortars (C 109). Too, alkali cements react more readily with reactive aggregates. While portland cements tend to be increasing in alkali content, sources of unreactive aggregates tend to be decreasing.
The literature suggests that the use of fly ash can mollify the reaction of alkalies in both strength development and in alkali-aggregate reactivity. Usually it is necessary to add the fly ash in addition to portland cement to accomplish the task, to maintain adequate strength development.
The use of finely ground water-granulated blast-furnace slag as a replacement for portland cement up to 65% can markedly reduce the alkali aggregate reaction and improve compressive strengths at the age of 28 days and beyond. To a significant degree, this procedure could help offset the quality problems often associated with cements of high-alkali content produced by energy efficient kiln systems. Finely ground water-granulated blast-furnace slag can be produced using only about one fifth the energy needed to produce an equal weight of portland cement.
Executive vice-president, Atlantic Cement Company, Inc., Stamford, CT
Stock #: CCA10255J