A Comparison of On-Site and Elevated Temperature Cure of an FRP Strengthening Adhesive
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FRP strengthening is critically dependent upon the bonding adhesive. The adhesive used is typically an ambient cure epoxy with a glass transition temperature as low as 60°C. This paper describes the performance of bonded FRP strengthening within real compartment fires (the Dalmarnock Fire Tests), one of which was allowed to grow past flashover. The aim of these real fire tests was to complement the laboratory-based fire tests on FRP strengthened members that are currently being undertaken at various research centres. In this study, externally bonded plate and near-surface-mounted FRP strengthening were applied to the ceiling of a concrete structure. The FRP was protected using either an intumescent coating or gypsum boards, alongside FRP that was left unprotected. The tests demonstrated the vulnerability of FRP strengthening during a real compartment fire. The glass transition temperature was rapidly exceeded in the bonding adhesive for all samples. The near-surface mounted strengthening and the gypsum board protected strengthening was in a visibly better condition after the fire.
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Externally bonded fibre reinforced polymer (FRP) has been proven to be a successful strengthening technique for deteriorated and aged structures. In the last two decades, an extensive number of studies have been dedicated to investigating this strengthening method. Therefore, it is considered to be extremely time-consuming for researchers to go through most of these studies. The aim of this paper is to provide an extensive review of a considerable number of papers in which a special emphasis is placed on the finding of the most recent papers. The paper focuses on the bond behaviour, testing techniques and models used to assess bonding strength. The deterioration of the FRP due to moisture has been also examined. Finally, flexural, shear and fatigue behaviours of this strengthening technique have been intensively reviewed. It was concluded that silane coupling agents can be used to enhance bond characteristics of poorly treated surfaces under moisture effect. It was also found that FRP can be used to extend the fatigue life of concrete beams. Finally, the review also showed that the Pellegrino and Modena model provides a good prediction of the shear strength of FRP-strengthened concrete beams.
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This paper presents the strengthening effect and the behavior of reinforced concrete slab strengthened with Carbon Fiber Reinforced Polymer (CFRP) grid. Parameters involved in this experimental study are FRP grid reinforcement quantity, repair mortar thickness, presence of anchor, and the location of strengthening. Generally, flexural members strengthened with reinforcement material (sheet, plate) made of Fiber Reinforced Polymer (FRP) have the failures, such as delamination failure debonding failure before reaching the maximum stress of FRP reinforcement. However, in this study there are various failure types with increasing the strengthening reinforcement. On the moderate strengthening level, there is a failure in the interface of carbon FRP grid because of the excessive shear deformation. On the other hand, there is a failure in shear on the high strengthening level. With the increasing of FRP grid reinforcement, the strengthening effect in flexure increased, but the ductility decreased. By limiting the strengthening level, it can be achieved to prevent shear failure, to increase the efficiency in strengthening, and to improve the ductility.
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This paper presents the results of an experimental investigation into the influence of temperature on small scale concrete specimens, strengthened with externally bonded Carbon Fiber Reinforced Polymers (CFRP). Debonding of the CFRP, due to high shear stresses in the concrete at the interface with the adhesive, governs the failure of these specimens at room temperature. Temperature changes however will affect the bond properties of the CFRPadhesive-concrete joint, both due to the significant difference in the Coefficient of Thermal Expansion (CTE) between concrete, adhesive and CFRP and due to the change of the material properties with increasing temperatures. Both effects can affect the load level at which debonding occurs. Especially the adhesive shows a significant decrease in strength and stiffness when the temperature reaches the glass transition temperature (Tg). To investigate the influence of temperature on the debonding of externally bonded CFRP, two different test setups were used; a double-lap shear test setup and a three point bending test setup. Test results have shown that a change in temperature affected both the failure load and the type of failure, especially when the Tg of the adhesive was reached.
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The use of externally-bonded fiber-reinforced polymers (FRPs) to strengthen reinforced concrete (RC) structures is now widely recognized. However, a concern that continues to discourage the use of FRPs in many applications is their susceptibility to high temperature and fire. Although recent studies have shown that the fire endurance of appropriately designed and insulated FRP strengthened RC members is satisfactory, the specific performance of FRP systems at, and after exposure to, high temperature remains largely unknown. The results of tests on the residual properties after high-temperature exposure of various available FRP strengthening systems for concrete are reported; these include: tension coupon tests, single-lap FRP-to-FRP bond tests, direct tension FRP-to-concrete bond tests, and pull-apart FRP-to-concrete shear bond tests after exposure to temperatures up to 400°C . The data show that the allowable exposure temperatures for residual performance of externally bonded FRP systems lie between the glass transition temperature (Tg) and the thermal decomposition temperature of the resin systems used. The potential consequences for fire-safe design of FRP strengthened RC members are discussed. Material properties during a fire event are not specifically addressed.
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