Concrete subjected to elevated temperatures : a study of the effect of temperature (100°C - 600°C) on local limestone aggregate concrete

Abstract

Concrete is normally designed for normal operating conditions without considering the effects which high temperatures might have on the material and whether or not it would still be serviceable after such an exposure, as ina fire. The choice of an appropriate concrete mix could make the difference between a concrete structure being repairable and serviceable after an accidental fire, and it being totally beyond repair, with potentially serious consequences in terms of safety and economy.

All materials possess upper temperature limits for their structural usefulness, and concrete is no exception. The upper temperature limit for concrete based on Portland cement seems to be 600°C. Nevertheless, most commonly used

concretes lose considerable strength at much lower temperatures. Even when the surface might be exposed to temperatures exceeding 600°C, as in a fire, the bulk of the structure might be at lower temperatures which the concrete could be designed to withstand. In this way, a larger proportion of the structure would remain serviceable and repairable, bringing about significant economic benefits.

The aim of this study is to determine the effect on the compressive strength of concrete after exposure to different peak temperatures (100°C, 150°C, 200°C, 400°C, 600°C) for different periods. The exposure time is taken as the average time required for a fire to be dealt with once it has broken out. Furthermore, two methods of cooling are adopted: a slow rate of cooling (cooling in air) and a quick rate of cooling (quenching).

After exposure, the specimens are tested in uniaxial compression and the residual strength determined. This gives an indication of the damagesustained by the concrete when exposed to high temperatures. In general, high residual strength is indicative of sound concrete or at least of a repairable : structure.