154142Fine Aggregate

For fine aggregates, a rounded particle shape and smooth texture have been found to require less mixing water in concrete and for this reason are preferable in HPC. The optimum gradation of fine aggregate for HPC is determined more by its effect on water requirement than on physical packing. A sand with a fineness modulus (FM) below 2.5 gives the concrete a sticky consistency, making it difficult to compact. Sand with an FM of about 3.0 gives the best workability and compressive strength. Thus, it is helpful to increase the fineness modulus. The amounts passing the No. 50 and 100 sieves should be kept low, but still within the requirements of ASTM C 33, and mica or clay contaminants should be avoided.

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