Flexural Behavior of Reinforced Concrete Beams Covered by Gypsum Layers and Exposed to Elevated Temperatures

The paper presents results of exposure of normal concrete to elevated temperatures (400 and 700) °C covered by layers (gypsum and plaster) with different thicknesses (10 and 20) mm. The casted specimens for each type of test were divided into three groups. The first was without covering the concrete surface with gypsum, while the second and third groups were covered with gypsum of the outer surface with a thickness of 10 and 20 mm, respectively. The experimental results found that the ultimate load capacity and the first crack load of RC beams were improved by using gypsum layers through 400°C. At thickness 10 and 20 mm, the (P cr and P u ) loss was about (8 and 6) % and (1 and 7) % respectively, compared to the concrete not covered with gypsum, the loss rate is about (25 and 13) %, and this is clear evidence of the benefit of gypsum in reducing the Elevated Temperatures directly to concrete. As for the temperature of 700, the reduction in (P cr and P u ) was about (57 and 22) % and (31 and 16) % and (10 and 15) % at 0, 10, 20 mm gypsum thickness, respectively. Through the figures shown in the paper, which were obtained from the experimental side of the research, the load-deflection curves improved when the gypsum thickness increased during the specimens' exposure to fire. Where the relationship between them at a temperature of 400°C in a thickness of 20 mm was better than 10 mm when exposed to fire, so by increasing the thickness of the gypsum, the occurrence of deflection is less because it protects the surface of the concrete from direct exposure to heat and thus prevents the occurrence of cracks in the outer surface of the concrete.