Abstract
An experimental work was carried out to investigate the use of a non-standard high calcium fly ash in concrete. The response of the same fly ash to the accelerated curing was also explored. With three different cementitious material contents, a total of 48 concretes were produced. The water/ cement ratios were varied from 0.40 to 0.87. Compressive strengths of the moist cured cube specimens cast from the concrete mixtures made with 0%, 15%, 30% and 45% replacement of normal Portland cement with fly ash were measured at 28 days and 3 months. Accelerated compressive strengths were also measured using warmwater method and boiling-water method in accordance with the relevant ASTM and Turkish Standards. Despite the fact that the fly ash used was a non-standard, the laboratory test results showed that it could be utilized in concrete production at a replacement level between 15% and 30% by weight basis because fly ash concrete developed comparable or higher compressive strength than that of corresponding normal Portland cement concrete. The laboratory test results also indicated that the accelerated curing could be used to predict the compressive strength of fly ash concrete with 85% correlation coefficient. The amount of fly ash was found to be immaterial in the strength prediction. The relation between warm-water method and boiling-water method was of linear form with 93% correlation coefficient.
Highlights
Using fly ash in concrete is accepted widely in the world due to the fact that it modifies the properties of the concrete in both fresh and hardened state
Fly ashes classified as high calcium and low calcium fly ashes according to its CaO content (6)
If the CaO content is less than 10% the ash classified as low calcium or class F (7)
Summary
Using fly ash in concrete is accepted widely in the world due to the fact that it modifies the properties of the concrete in both fresh and hardened state. The physical properties and chemical composition of fly ash change due to the type of coal and the factory where the coal was burned. The daily changes in the physical property and chemical composition can be seen for a speciflc ash (5). Fly ashes classified as high calcium and low calcium fly ashes according to its CaO content (6). If the CaO content is less than 10% the ash classified as low calcium or class F (7). If the CaO content is more than 10% the ash classified as high calcium or class C (7). The use of fly ash according to its physical property and chemical composion are picked up in different standards. The ASTM (7) restricts the amount ofSiO^+Aip^+Fep^ to =50% for high calcium fly ash and =70% for low calcium fly ash
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