Performance in fire of small-scale CFRP strengthened concrete beams

When strengthening concrete members with fiber-reinforced plastic (FRP) materials the strengthening is, typically, undertaken to carry live load. This live load is assumed to remove itself from the strengthened member in the event of a fire. Thus, the fire performance of the FRP is not important. However, if the strengthening system was designed such that the FRP took some of the dead load, then the performance in fire would become important. In this series of tests, 24 reinforced concrete beams were cast. They were divided into eight sets of three. The sets were split into fire tested and control. In the control group were an unstrengthened control set, a set strengthened with bonded carbon FRP (CFRP) plates, and a set with bonded CFRP plates with bolted anchorages. In the fire-tested group were an unstrengthened control set, a set strengthened with bonded CFRP plates, a set with bonded CFRP plates with bolted anchorages, a set strengthened with bonded CFRP plates and a cementitous fire protection system, and a set with bonded CFRP plates with bolted anchorages and a cementitous fire protection system. The unloaded beams were then subjected to a cellulosic fire in a furnace. The adhesive on the unprotected beams was destroyed by the fire, as was the resin in the CFRP plate. On the strengthened beams with a cementitous fire protection system the adhesive was destroyed by the fire but the resin in the CFRP plate was undamaged. All the beams were tested in four-point bending to determine their load capacity and stiffness. Of the non-fire-tested beams the control beams were weakest and the strengthened beams were stronger and stiffer, there being no significant difference between the bolted and nonbolted beams. The fire-tested beams were load tested postfire exposure. Of the fire-tested beams the control beams had the same properties as the non-fire-tested control beams. The unbolted beams had the same strength regardless of fire protection. One of the bolted beams with fire protection was stronger than those without fire protection but not as strong as the nonfire-tested beams. It can be concluded that the strengthening system in the unprotected beams was destroyed in the fire test. Where fire protection was provided this protected the resin in the CFRP plate but not the adhesive bonding the plate to the beams. Bolts helped to keep the plate attached to the beam but did not provide as good a connection as the adhesive.