Flexural strength of fly ash concrete under elevated temperatures

Concrete elements exposed to fire undergo temperature gradients and, as a result, the surface layers spall, exposing steel reinforcement. Relatively few studies have been undertaken on heat-induced changes in fly ash concrete. The structural property of concrete that has been studied most widely as a function of heat exposure is compressive strength. Less attention has been given to flexural strength as influenced by heat exposure. Therefore, to investigate the effect of temperature on the flexural strength of fly ash concrete, the present study was carried out with M28, M33 and M35 grades of concrete. Concrete specimens 100 mm × 100 mm × 500 mm with partial replacement of cement by fly ash (10%, 20% and 30% replacement levels) were heated to 100°C, 200°C and 250°C for 1 h, 2 h and 3 h duration in an electric oven. The specimens were tested for flexural strength in the hot condition immediately after removing from the oven. The fly ash concrete showed consistently the same pattern of behaviour as that of concrete without fly ash under elevated temperatures during flexure. The fly ash concrete with fly ash content up to 20% showed improved performance compared with the specimens without fly ash by retaining a greater amount of its strength.