In　recent　years,　thin　fiber　reinforced　polymer　(FRP)　composite　sheets　have　been　successfully　used　in　strengthening　deficient　concrete　structures.　Although　the　short　term　performance　of　these　FRP　sheets　has　been　satisfactory,　their　long　term　durability　performance　remains　yet　to　be　confirmed.　The　bond　strength　between　FRP　and　its　concrete　substrate　is　one　of　the　critical　design　factors　due　to　the　composite　action　requirement.　In　this　paper,　the　effects　of　hot　temperature　(100　and　180　degrees　C)　on　the　deterioration　of　bond　strength　and　the　changes　in　failure　modes　are　presented　and　discussed.　Three　possible　failure　modes　are　considered　in　this　study:　cohesive　in　the　concrete　substrate,　mixed,　and　adhesive　at　the　interface.　Therefore,　the　true　bond　strength　between　concrete　and　FRP　can　only　be　measured　when　the　failure　mode　is　adhesive.　Under　the　control　conditions　at　room　temperature,　the　true　adhesive　strength　exceeds　6　MPa,　which　is　adequate　for　most　engineering　applications.　A　combination　of　high　temperature　and　low　humidity　is　the　most　detrimental　to　bond　strength.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.