Influence of activation of fly ash on the mechanical properties of concrete

The use of high volume fly ash as a partial replacement of cement in concrete reduces environmental pollution and conserves natural resources. This study presents the results of an experimental investigation to find out the effect of chemical activation of class F fly ash to overcome the low early strength problem. The replacement ratio of Portland cement with fly ash was 40%. Four different chemical activators were used in the study; 2.5% Na2SO4, 2.5% NaOH, 3.0% (Na2SiO3 and CaO) by ratio (1:8) and 4% Aquis Na2SiO3. Concrete strength was investigated at room temperature and after exposure to elevated temperature. Glass fibers were added by ratio 0.7% to improve concrete ductility. Test results indicated that aquis Na2SiO3 activator is the superior activator for fly ash in view of enhancing concrete compressive, splitting tensile and flexural strengths at early ages. Besides, a significant increase in concrete strength was obtained at elevated temperatures. Adding glass fibers in the ratio of 0.7% by weight of cementitious material with activated FA by using aquis Na2SiO3 greatly enhances the splitting tensile and flexural strengths at normal and elevated temperature.