Influence of temperature on bond–slip characteristics of concrete containing fly ash

Abstract

This paper deals with the bond–slip characteristics of concrete containing fly ash after the concrete is exposed to elevated temperatures. M40 concrete with 0%, 15% and 25% fly ash content and 8-mm-diameter ribbed bars were considered for the present study. Specimens were heated to different temperatures (ambient—28 °C, 200 °C, 400 °C, 600 °C and 800 °C) and cooled under air cooling and water cooling environment. Standard pullout test has been carried out on specimen, and the bond–slip relationship was observed. It could be observed that compared to OPC concrete, the loss in bond strength of concrete after exposure to elevated temperatures is less in concrete with fly ash content, primarily due to the additional formation of C–S–H with the presence of silica in fly ash at elevated temperatures, and is dependent on the fly ash content. It has further been observed that the ductile behavior of bond–slip after the peak bond strength of ribbed bars reduces when concrete is exposed to elevated temperatures. The micro-cracks formed in concrete due to the thermal shock induced because of sudden cooling with water after exposure to elevated temperatures reduces the bond strength of concrete and is dependent on the fly ash content in concrete. Most of the available equations for the prediction of bond strength of concrete after exposure to elevated temperatures do not consider the influence of fly ash in concrete and hence they underestimate the bond strength. With the present experimental data, an equation has been proposed to predict the bond strength of concrete containing fly ash after it is exposed to elevated temperatures.