Aniello Palmieri

Influence of High Temperature on Bond between NSM FRP Bars/Strips and Concrete

The use of near surface mounted (NSM) fiber reinforced polymers (FRPs) is being increasingly recognized as a valid technique strengthening of concrete members. In case of elevated temperature or fire exposure however, the bond between the bars and the concrete will be lost very quickly due to the adhesives low glass transition temperature. Although recent studies have shown that the fire endurance of appropriately designed and insulated FRP strengthened RC members is satisfactory, the performance of FRP strengthening systems at high temperature remains largely unknown. To study the bond behaviour at elevated temperature between the NSM FRP bars and concrete a series of 18 double bond shear tests were performed at Ghent University. Results show that the failure load of NSM FRP strengthened concrete structures and the bond strength are influenced at values of temperature equal to or beyond the glass transition temperature. Failure mode changed by increasing the temperature.

Fire testing of RC beams strengthened with NSM reinforcement

The weak performance of fibre reinforced polymer (FRP) strengthened members in fire is a primary factor hindering the widespread implementation of FRP strengthening technology in the construction industry. An investigation was undertaken to examine and document the performance of NSM FRP strengthened concrete beams under fire conditions. Six reinforced concrete beams were strengthened in flexure with NSM FRP bars and insulated with different insulation systems. The specimens were subsequently exposed to a standard fire under service load. The testing parameters of these elements include the use of different thermal protections (including different materials and geometric layouts of the protection) of the glued reinforcement. Member deflections and temperatures throughout the section were measured during fire testing. Tests results indicated that insulated NSM FRP strengthened beams can achieve a fire endurance of at least of two hours.

Basalt FRPs for strengthening of RC members

The use of FRPs to enhance the structural performance of RC members represents today’s common practice. This is mainly due to their high strength to weight ratio, corrosion resistance or ease of application. However, given the current circumstances, the construction industry is in need of a more viable alternative to the commonly used glass and carbon fibres. Hence, the paper discusses two experimental programmes investigating the use of relatively new basalt fibres for strengthening of both compression and flexural members. Application of shear strips in strengthening of an RC beam (University of Sheffield) has shown that even a small amount of basalt FRPs can successfully increase the ultimate load capacity as well as provide anchorage and reduce the brittleness of plate end debonding. Testing of FRP confined concrete cylinders (Magnel Laboratory) has proven basalt to be 14% more effective than glass, yielding an average compressive strength increase of 84% when compared to the unconfined cylinders.

Experimental investigation on bond of NSM strengthened RC structures

Near Surface Mounted (NSM) FRP reinforcement is being increasingly recognized as a valid alternative to externally bonded reinforcement (EBR) for enhancing the flexural strength and shear resistance of deficient reinforced concrete members. As this technology emerges, the structural behaviour of NSM FRP strengthened elements needs to be characterized, and bond between NSM FRP bars and concrete is the first issue to be addressed. This paper presents, as part of a study in the framework of a Round Robin Testing (RRT) programme, the results of a series of 27 double shear bond tests on NSM FRP strengthened concrete. Aim of this project is to investigate the feasibility of the adopted test method and to investigate the mechanism of bond between NSM reinforcement and substrate material. Experimental results confirm the efficiency and re-liability of the test method and the bond effectiveness of the NSM technique for strengthening RC members.