Geotechnical and geochemical studies of Eocene limestone of Kohat formation for its use as concrete aggregates
Abstract
The Eocene limestone of the Kohat Formation is well exposed in the Kohat, Hangu and Bannu districts. It is cream to gray in color, hard, compact, well-bedded and fossiliferous. The limestone of Kohat Formation has been evaluated mineralogically, chemically and physically, for its use as concrete aggregates during present study.
Mineralogically, the studied limestone is dominantly calcite with abundant fossil shells. Fine-grained quartz, chalcedony, clay, dolomite and opaque phases are present in minor amount. The limestone generally has fine to medium-grained granular mosaic with microfossils. Deleterious minerals for concrete are generally found in the argillaceous variety of the studied limestone. Chemically, the studied limestone (by weigh) is classified as high-calcium limestone, with CaCO3 between 81.23 and 98.93%. The average chemical compositions of various cements manufactured in N.W.F.P., are within the ASTM limits. The alkali-silica reactivity graph of the limestone's aggregates also confirms the petrographic observations. Physical properties (i.e., soundness, water absorption, Los Angeles abrasion and specific gravity) are generally in accordance with the ASTM standards for aggregates to be used in concrete.
The studied limestone of the Kohat Formation except its argillaceous variety, found in the eastern part of the study area, is generally free of dolomitization and has no other deleterious substances as far as the durability of concrete is concerned. This Eocene limestone of the Kohat Formation is, therefore, recommended for its use as concrete aggregates.
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