Effects of Moisture on Properties of Concrete Exposed to Elevated Temperature

Concrete is often damaged on exposure to fire causing significant loss in strength. Although the subject has been extensively investigated, the physics of fire damage is still not known exactly, especially the effect of water inside concrete that can evaporate, causing internal pressure and cracking. This paper explores the influence of some practical cases of moisture states on the performance of concrete after exposure to heating. This research focusses on the effect of three moisture states, namely, dry, saturated, and moist, on the behavior of normal and high strength concretes (NSC and HSC) at high temperatures. As the moisture states may be dependent on the size of concrete specimens, two sizes of cylinders of 150 × 300 and 100 × 200 mm were used. The moisture states were differentiated in terms of unit weight, weight loss, and relative humidity inside concrete. The relative humidity was measured at different depth of concrete cylinder to establish the variation of moisture inside concrete test specimens. The exposure temperatures were: ambient, 300 °C, and 600 °C. The condition of test specimens after heating was assessed in terms of cracks, spalling, and compressive strength. Although no effect of moisture could be observed at 300 °C, significant effect of moisture was noted at 600 °C with the almost dry conditions being the most favorable in minimizing the strength loss.