ABSTRACT
In this research, the influence of aggregates sizes, cover to reinforcement thickness, concrete age, exposure period on the mechanical properties of normal concrete (NC) subjected to different elevated temperatures were investigated. Two types of concrete (combined aggregates concrete and single aggregate size concrete) were used to determine the residual compressive strength, while only combined aggregate concrete was used for flexural strength of reinforced concrete prisms. Fire resistance of the concrete cubes and concrete prisms specimens in terms of residual compressive and bending strength was studied. Five different temperatures level of 1000C, 3000C, 5000C, 7000C and 9000C were used and they were maintained constant for four different exposure periods of 30mins, 60mins, 90mins and 120mins.The residual compressive strength as percentage of the strength of the unheated specimens ranged between (95-120%) at 1000C, (70 -101%) at 3000C, (45-60%) at 5000C and (0-10%) between (7000C -9000C). Exposure time above 1hour had significant effect on the residual compressive strength of concrete; however, the effect was so pronounced at early age concrete and single and bigger aggregates size concrete (20mm) when the temperature increased. Generally, the flexural strength was found to be more sensitive to high temperature exposure than compressive strength. The residual flexural strength was in the range of (85-90%), (50-75%) and (25-40%) at 1000, 3000C and 6000C respectively. The results clearly showed the influence of concrete cover to reinforcement on the residual deflection and tensile strength of concrete prisms specimens. The respective deflection recorded for the three different concrete cover of 20, 25 and 30mm at 1000C and heated for 60min are (15, 20 and 23mm). The deflection was (20, 22 and 29mm) at 3000C when heated for the period of 60min, and the deflection was (31, 34 and 40mm) at 6000C when heated for the period of 120min respectively