determination of bond strength of cfrp sheets, exposed to temperature changes, wetting and drying, and freeze-thaw cycles, using twist-off method

nowadays frp composite sheets for structural repair, as an efficient and cost-effective technique for restoring and upgrading the load bearing of concrete structures are have become very common. in addition to high strength to weight ratio and the use of frp sheets while structure is in use, these sheets have good fatigue resistance. furthermore, their easy application is also an undeniable advantage. when exposed to cyclic temperature changes, wetting and drying and freezing and thawing, the frp retrofitted structures do not show acceptable durability. although, considerable researches have been reported on failure modes and increment of strength and changes in ductility of the frp strengthened elements, but experimental data on their durability are scarce. hence, this investigation focuses on the durability of these sheets under temperature changes, wetting and drying and freeze - thaw cycles. during this investigation, crfp sheets were glued to all 8 surfaces of 15×15cmconcrete cubes for every environmental condition. at the end of every thirty cycles, adhesional strength of cfrp sheets were determined using the twist-off method. the results show that, while the effects of wetting and drying and temperature changes on the cfrp/concrete interfacial adhesion are not considerable, the decreasing effect of freezing and thawing is enormous.