Effects of elevated temperature curing on glass transition temperature of CFRP/ concrete bond

Abstract

Strengthening of existing structures made out of concrete, all around the world is an increasing requirement due to many reasons like aging, insufficient maintenance, and the degradation due to environmental impact, as well as due to increases of the applied loads and due to requirement of complying with the modern standards. Carbon Fiber Reinforcement Polymer, CFRP, one of the budding and potential technologies in the structural strengthening process. As such lots of researchers who wish to continue their higher studies and knowledge gaining in structural engineering have involved researchers in structural strengthening using CFRP. Laying CFRP fabrics and composites using epoxy adhesives, along the external surfaces of structural elements are the popular method for a strengthening of structural capacities. These externally laid CFRP fabrics are subjected to elevated temperatures due to environmental conditions. The exposure to such elevated temperature affects the strength of the CFRP/Concrete bonds, because of the low glass transition temperature (Tg) of these epoxy adhesives that have been used to create the bond between CFRP and concrete substrate. A slight increment of Tg is also contributed to enhancing environmental resistance of strengthened outdoor members which directly expose to the environmental fluctuations. Curing of the CFRP/epoxy/concrete bond in an elevated temperature environment may enhance the bond performance while improving its Tg. However, it is important to ensure a safe temperature range in curing without affecting the performance of the concrete part of the system. This study focuses on determining the safe temperature range, which may be used as raised temperature curing of the CFRP/Concrete composites and determination of bond characteristics for the corresponding temperature applied for curing. A total of twenty-five single strap joints were prepared under two different curing conditions. The impact of curing at moderately elevated temperature (75°C) on CFRP/Concrete bond strength was examined for both ambient and elevated temperature conditions.