Experimental Study of the Effect of High Service Temperature on the Flexural Performance of Near-Surface Mounted (NSM) Carbon Fiber-Reinforced Polymer (CFRP)-Strengthened Concrete Beams.

Younes Jahani,Cristina Barris,Lluís Torres,Marta Baena,Javier Gómez

doi:10.3390/polym13060920

Abstract

This paper presents a study of the effect of high service temperature (near or beyond glass transition temperature (Tg) of structural epoxy adhesive) on the behavior of near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP)-strengthened reinforced concrete (RC) beams. The study includes experimental work as well as analytical and numerical analysis. To this end, fourteen beams have been tested up to failure in two different series. In series 1, specimens with three different CFRP areas have been tested at two different temperatures (i.e., 20 and 40 °C). In series 2, and with the aim of evaluating the effect of higher temperatures, only one CFRP area was tested under four different temperatures (i.e., 20, 60, 70, and 85 °C). Experimental results are evaluated in terms of load–deflections, failure modes, and bond performance. Furthermore, the experimental load–deflection curves are satisfactorily compared to both analytical predictions and finite element (FE) numerical simulations. In both cases, shrinkage and temperature effects on the short-term response of flexural elements have been accounted for. No significant reduction in stiffness and ultimate load was observed for specimens being tested up to 60 °C (in the range of epoxy Tg), showing FRP rupture failure in all of them. For specimens under 70 and 85 °C, the failure mode changed from FRP rupture to FRP end debonding and concrete crushing, respectively.

Highlights

In the past decades, fiber-reinforced polymer (FRP) materials have been produced in different configurations and have been widely used for different purposes, such as the strengthening of reinforced concrete (RC) structures
In the externally bonded reinforcement (EBR) technique, the FRP is bonded to the previously prepared concrete surface, usually with an epoxy resin, while in the near-surface mounted (NSM) technique, a groove is cut in the concrete cover and the FRP bar or strip is inserted and bonded using groove filler, which is typically an epoxy adhesive or a cement grout
The performance of the NSM strengthening system relies on the bond capacity of the joint between concrete and FRP material, which in turn depends on the properties of the adhesive, among other parameters

Summary

Introduction

Fiber-reinforced polymer (FRP) materials have been produced in different configurations and have been widely used for different purposes, such as the strengthening of reinforced concrete (RC) structures. In addition to experimental work, finite element methods have been widely used to simulate the FRP-strengthened beams and columns under different loading and environmental conditions [36,37,38,39,40,41,42,43] In these studies, different types of FRP material (i.e., carbon, glass, and basalt) have been considered as NSM or EBR reinforcement, and both the flexural and shear performance of the strengthened members have been validated. The present work aims at studying the effect of relatively high service temperature (near and beyond Tg) on the flexural performance of NSM carbon FRP (CFRP)-strengthened RC beams when different strengthening areas of CFRP are used For this purpose, an experimental program has been carried out, and results are analyzed in terms of flexural behavior, failure modes, and bond performance along the FRP laminate. The load was applied under displacement control mode at a rate of 0.6 mm/min

Instrumentation

Findings

Methodology