Optimization of Fly Ash in Concrete

This report outlines the preliminary results of a research project aimed at optimizing the fly ash content in concrete. Such fly ash concrete would develop an adequate 1-day compressive strength and would be less expensive than the normal Portland cement concrete with similar 28-day compressive strength.

The results show that in a normal portland-cement concrete having a 28-day compressive strength of 40 MPa. it is possible to replace 50% of cement by a fine fly ash -~3000 cm2/g- with a CaO content of ~ 13% yielding a concrete of similar 28-day compressive strength. This concrete air-entrained or not can be designed to yield an early-age strength of 10 MPa. and results in a cost reduction of about 20% in comparison to the control concrete. In a case of a coarser fly ash -~2000 cm2/g- with a CaO content of ~ 4% substitution levels of cement by this ash could be from 30 to 40%. This concrete yields a 1- day compressive strength of 10 MPa. and 28-day compressive strength similar to that of the control concrete. The total cost of this concrete is about 10% lower than that of the control concrete. The above fly ash concrete are made without the use of a superplasticizer and are found to have higher resistance to chloride-ion penetration than the control concrete.

Technical Report Author: Nabil Bouzoubaa, Benoit Fournier, CANMET Energy Technology Centre, Natural Resources Canada,