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,
This paper presents the results of a study on the mechanical properties and durability of concrete made with high volume fly ash -HVFA- blended cement produced in a cement plant. The test results obtained were compared with those of a control concrete made with a commercially available ASTM Type I cement; the control concrete had a 28-day compressive strength comparable to that of the concrete made with the HVFA blended cement.
The results showed that in order to obtain similar slump and air content to those of the control concrete the use of HVFA blended cement required increased dosages of the superplasticizer and the air-entraining admixture. This resulted in some delay in the initial and final setting times of concrete.
The use of HVFA blended cement resulted in lower compressive and flexural strengths at early ages -before 28 days- and higher mechanical properties after 28 days as compared with those of the control concrete made with ASTM Type I cement. The concrete made with the HVFA blended cement developed a 1-day compressive strength of 13 MPa -compared to 19 MPa for the control concrete- which is considered more than satisfactory for formwork removal.
The use of the HVFA blended cement improved significantly the durability characteristics of the concrete; the only exception was the resistance to the de-icing salt scaling as determined in ASTM C 672 test.
Technical Report Author: Nabil Bouzoubaa, Benoit Fournier, V.M. Malhotra, D.M. Golden