Transport properties of high volume fly ash or slag concrete exposed to high temperature

In this study, transport properties of high volume fly ash or slag incorporated concretes after exposure to high temperature were investigated experimentally. Concretes with the content of 0%, 30%, 50%, 70% and 90% fly ash or slag were prepared and moist cured until 28 days. Fly ash and slag concrete samples were exposed to high temperatures at 400 °C, 600 °C and 800 °C for an hour in a computer controlled, electrically heated kiln. Then, the specimens were left to cool down to the laboratory temperature. Subsequently, absorption, void ratio, sorptivity, chloride ion permeability and compressive strength tests were carried out on the specimens. Test results showed that transport properties of concrete increased significantly after exposure to 400 °C, as well as, compressive strength dropped remarkably. Test results also revealed that inclusions of fly ash or slag influenced the transport properties considerably. It is concluded that a blend of, at about, 30-50% fly ash and 50-70% slag as a cement replacement is found to be the optimal content for exposure to high temperature. Rapid chloride permeability test results revealed that slag concrete bound more chloride than fly ash concrete. Slag concrete behaved better than fly ash concrete did under high temperature exposure for all case, some of slag concrete even behaved better than Portland cement concrete in terms of compressive strength reduction.