Pozzolan Cementing Efficiency Factor

The DOE Method, used by Firstmix, suggests that the effect of the addition of Pozzolan to the cement on the strength of a concrete mix may be modelled by using a Pozzolan Cementing Efficiency Factor.

The Pozzolan Cementing Efficiency Factor is defined as the ratio of the cementing efficiency of Pozzolan to the cementing efficiency of the cement to which the Pozzolan is added. In Firstmix, following the DOE method, for concrete mixes containing Pozzolan the equivalent Free water/Cement Ratio, from which the concrete strength is predicted, is calculated as:

wcempoz/(cem + cef x poz)

Where:

cef = Pozzolan cementing efficiency factor.

cem = Weight of cement.

poz = Weight of Pozzolan.

wcempoz = Free water content (weight).

Since Pozzolans generally act as retarders, the Pozzolan cementing efficiency factor is usually negative for test ages of 7 days or less, since initially the strength of concrete containing Pozzolan is less than the strength of concrete which does not contain Pozzolan. The DOE Method recommends that concrete mixes, in which Pulverized Fuel Ash is the Pozzolan, should be designed on the basis of their strengths at 28 days but Firstmix allows the user to specify Pozzolan cementing efficiency factors for a range of test ages.