Behavior of thermally protected RC beams strengthened with CFRP under dual effect of elevated temperature and loading

Strengthening of reinforced concrete elements by externally bonded FRP is becoming increasingly popular in construction industry. Utilizing FRP offers several desirable attributes, such as resistance to corrosion, high strength-to-weight ratio, and electromagnetic neutrality. However, FRP materials have some disadvantages. In case of external strengthening with FRP which is directly exposed to the environment, efficiency of bond between FRP and concrete surface is affected by temperature. Current research work was carried out to investigate behavior of strengthened RC beams subjected to dual effect of elevated temperature and loading. The experimental program consists of two phases. First one comprises investigating thermal properties of six different cement-based mixes incorporating Perlite and Vermiculite in order to find out the most appropriate mix that possesses both low thermal conductivity and adequate strength. In the second phase, the obtained mix was applied as cement rendering to protect different reinforced concrete beams against elevated temperature. The beams were divided into four main groups in order to explore the flexural behavior of both unstrengthened and strengthened beams with CFRP subjected to dual effect of heating and loading. Results showed that a layer of 50 mm thickness of Perlite mortar can be used to protect CFRP strengthening system against 500 °C for three hours. Strengthened protected beams exhibited insignificant capacity loss when loaded under 500 °C for 3 h and cooled in ambient air, then loaded up to failure. When similar beam was subjected to the same loading and heating condition except that cooling was not allowed, a reduction in capacity by 22% was observed.