Effect of elevated temperatures on a fiber composite used to strengthen concrete columns

Externally applied composite reinforcement can be used to provide additional strength or ductility to concrete members as part of a seismic retrofit or repair to a structure, but the composite reinforcement may be exposed to elevated temperatures. In this study, concrete cylinders were wrapped with a composite reinforcing system, exposed to a range of elevated temperatures and allowed to cool. Subsequent compression testing of the cooled cylinders indicated there was no statistically significant loss of strength until the treatment temperature was more than 30°C above the glass transition temperature of the epoxy. Additionally, the predominant mode of failure of the composite system changed from hoop split to seam debonding at the same temperature. This study also examined the role of a fire-protective coating that forestalled the onset of the transition of failure modes by almost 30°C.