Effect of Different Class C Fly Ash Compositions on the Properties of the Alkali-Activated Concrete

Abstract

Class C fly ashes from two different coal-fired power plants were used to manufacture alkali-activated concrete. The workability and the compressive strength were studied in this paper. The workability was measured by the slump test. The compressive strengths at different ages of 1, 7, and 28 days were measured. Three different curing regimes including elevated heat curing at 70 °C, laboratory ambient curing at 23 ± 2 °C, and moist curing in the moisture room at 23 ± 2 °C were applied to identical mixtures to investigate the curing regime effects. Both types of fly ashes showed high slump of 212.5 and 225 mm. The results revealed that the compressive strength of the specimens that cured at the ambient or moist conditions increased with increasing the calcium content in the fly ash. However, the compressive strength of the specimens that were cured at 70 °C decreased when increasing the calcium content of the fly ash. The compressive strength of the concrete based on fly ash having higher calcium content at 28 days reached to 34.78, 36.62, and 51.46 MPa for oven-, ambient-, and moist-cured specimens, respectively. Furthermore, the compressive strength of the concrete based on fly ash having relatively lower calcium content at 28 days reached to 36.43, 30.79, and 47.45 MPa for oven-, ambient-, and moist-cured specimens, respectively.