Use of Efficiency Factors in Mix Proportioning of Fly Ash Concrete

Abstract

In the first revision of IS: 10262, 2009 an illustrative example of concrete mix proportion ing using fly ash as one of the ingredients has been added. Merely a numerical example without theoretical backup leads to number of queries in the mind of the designer, who has no other option but to follow the steps empirically. To incorporate fly ash @ 30 % of total binder content an increase of 10 % has been envisaged on the binder content of control concrete. This does not seem to be justified as the fly ash used can have a wide variation in properties, which has not been taken into consideration at all. On the other hand, if some guidelines are provided on the basis of the efficiency factor of fly ash, at least a good first hand estimate of the fly ash content equivalent of the cement replacement percentage can be obtained. Even if such relationships are available for one type of fly ash, whose properties are known, an estimate of the cement equivalence of fly ash can be obtained for the fly ash used. This will help in reducing the number of trial mixes needed to arrive at the desired concrete mix. The present paper is a humble effort in this direction and deals with fly ash concrete mixes having water binder ratios ranging from 0.4 to 0.6, binder contents varying from 300 to 450 kg/m³ and fly ash binder ratios ranging from 0.0 to 0.5. Efficiency factors have been derived and parameters affecting the efficiency values have been identified. Typical ranges of efficiency values with respect to those parameters have been provided which can act as useful tools in the mix proportion ing of fly ash concrete.