Protection of reinforced concrete beams retrofitted by carbon fibre-reinforced polymer composites against elevated temperatures

This paper presents the outcome of the first part of a 3 year project aiming to investigate the effect of elevated temperatures on carbon fibre-reinforced polymer (CFRP) retrofitted structures. Accordingly, different protecting mixes to be used as thermal insulating covers were proposed and evaluated. This experimental program addresses a series of indirect fire tests on reinforced concrete beams retrofitted with CFRP laminates exposed to a temperature of 900 °C (1652 °F) after being protected with ten types of special mortar covers. Materials known for their low coefficient of thermal conductivity were added in certain ratios to form mortars for these protective covers. Tests were carried out in a test furnace designed to produce the standard temperature–time curve specified in ASTM E119–95a. Scale effect was considered by proper adjustment of the exposure time to fire test. Temperature at the CFRP level, just below the protecting covers, was monitored to determine the efficiency of the covers in reducing heat transfer during the fire test. Furthermore, mechanical bending load tests were performed on specimens before and after fire tests to determine reduction in flexure failure load of the specimens due to indirect fire exposure. This reduction was found to vary from 10% to 48% for different tested coatings. In spite of the high damage in the protection covers expressing the lowest performance, reinforced concrete beams were still unaffected and could be restrengthened to return to their original status. Recommendations showing proper thicknesses of application and necessary precautions to be taken when using CFRP in retrofitting reinforced concrete structures to enhance their fire resistance were presented.