Effects of elevated temperature on bond in reinforced concrete

Abstract

The practical situation which led to this investigation is the case of fires in reinforced concrete structures. Concrete is a good fire resistant material and after a fire has finished the structure itself can often remain standing. Therefore a choice is available between reinstating the fire damaged structure as, opposed to demolishing and reconstructing the whole of it. Often the former alternative can be quicker and cheaper, however, before reinstatement can begin it must be established that the damaged structure is suitable for such treatment. Hence-an assessment of its residual capacity for structural performance must be made. To do this knowledge of the properties of ' steel and concrete and the bond between them at temperatures experienced in fires must be known.

Such information on the two materials themselves is readily available, however, little is known about the response to heat treatment of the bond properties between them. Therefore the aim of this project was to investigate the effect of heat on the bond properties between the steel reinforcing bar and. the concrete.

To carry out this aim a review was made of heat effects on steel and concrete, within the context of fire resistance and reinstatement design. Also existing work on bond at ambient and elevated temperature was studied enabling the form of experimental procedure to be established.

The experiments themselves were on simple pull-out type specimens and looked at various parameters affecting the bond. From the results the effect of the bond reduction with respect to the anchorage and cracking in beams was examined This enabled the bond reduction, on subjection to heat treatment, to be quantified for possible application to the reinstatement and fire resistant design processes.