Performance Evaluation of Carbon Fiber-Reinforced Polymer-Repaired Beams Under Corrosive Environmental Conditions

ACI Structural Journal, Jan/Feb 2007 by Maaddawy, Tamer El, Soudki, Khaled, Topper, Timothy

This paper presents results of an experimental study designed to evaluate the performance of reinforced concrete beams repaired with carbon fiber reinforced polymer (CFRP) sheets under corrosive environmental conditions. A total of 16 beams, 152 × 254 × 3200 mm each, were tested. One beam was used as a control while 15 beams were initially corroded electrochemically for 50 days that corresponded to approximately 9% steel mass loss. Following the initial corrosion, one beam was tested to failure while 14 beams were repaired with a flexural CFRP sheet along with a continuous wrapping or an intermittent wrapping. Following repair, two repaired beams were tested to failure while 12 beams were subjected to additional corrosion exposure for up to 310 days that corresponded to a maximum steel mass loss of approximately 34%. Six beams were exposed to additional corrosion under a sustained load to simulate a service condition. Test results showed that the beams of intermittent wrapping had a higher steel mass loss rate and thus a lower strength than the beams of continuous wrapping. The presence of the sustained load and associated flexural cracks during the post-repair corrosion exposure slightly increased the steel mass loss rate, which further reduced the beam yield load but it had no noticeable effect on the beam ultimate strength.

Keywords: concrete; corrosion; repair; steel; sustained.

(ProQuest Information and Learning: ... denotes formulae omitted.)

INTRODUCTION

Corrosion of steel reinforcement is the most common durability problem of reinforced concrete (RC) structures. Evidence of the vulnerability of RC structures to damage by corrosion is witnessed in field situations, despite the recommendations and precautions specified by current codes of practice. Significant reductions in beam strength and stiffness due to corrosion of steel reinforcement have been reported in the literature by many researchers.1-3 Numerous studies reported a deterioration of bond at the steel-to-concrete interface caused by the lubricant effect of corrosion products and by cracking of the concrete cover.4-6 Hence, there is a need for a durable and cost-effective repair system that can counteract the reduction in beam strength caused by corrosion and maintain the bond at the steel-to-concrete interface. Wrapping a beam with carbon fiber reinforced polymer (CFRP) sheets have been shown to control corrosion cracking and spalling of concrete cover.7-8 The ability of a CFRP repair to improve the structural strength of RC beams when applied at minor levels of corrosion damage was reported in previous studies.9-11 Some researchers reported data that confirmed the ability of CFRP wrapping to reduce corrosion activity of steel reinforcement, even under harsh environmental conditions. 12-14 Figure 1 summarizes the benefits of using CFRP sheets to repair corroded RC elements.

To date, very little information is available in the literature concerning the performance of CFRP-repaired beams when exposed to corrosive environmental conditions after repair. The effect of using a continuous wrapping rather than an intermittent wrapping on the post-repair performance has received little attention in previous studies. The effect of the presence of flexural cracks caused by a sustained load during the post-repair corrosion phase on the steel mass loss rate and the overall structural performance was also not addressed in previous studies. The present work is the second phase of a research program aimed at investigating the short- and long-term structural performance of corrosiondamaged RC beams repaired with externally-bonded CFRP sheets. In a previous study carried out by the authors, the viability of using CFRP sheets to repair RC beams at different levels of corrosion damage was investigated.15 Results of this study showed that the ultimate strength of a severely corroded beam (approximately 31% steel mass loss) was increased to a level even higher than that of a control beam after the application of externally-bonded CFRP sheets. In this paper, the performance of CFRPrepaired beams when exposed to additional corrosion after repair with and without a sustained load is examined.

RESEARCH SIGNIFICANCE

This paper reports results of a test series designed to evaluate the structural performance of CFRP-repaired beams under corrosive environmental conditions. The main objective is to provide data that describes the effect of corrosion with and without a sustained load on the post-repair structural performance of RC beams repaired with externally-bonded CFRP sheets. Valuable information concerning the effect of CFRP repair scheme on the steel mass loss rate and the lateral CFRP-strain caused by the expansion of corrosion products is reported. Results of the current study will help practicing engineers in estimating the residual strength of CFRPrepaired beams at any level of corrosion damage after repair.

EXPERIMENTAL PROGRAM

Test specimen

Figure 2 shows details of the test specimen. The test specimen was a reinforced concrete beam, 3200 mm long, 152 mm wide, and 254 mm deep. Two No. 15 deformed steel bars were used as tensile steel reinforcement while two 8 mm diameter plain bars were used as compression steel reinforcement. The ratios of the areas of the tensile and compression steel reinforcement to that of the effective concrete section were 1.04 and 0.26%, respectively. The beams were tested in four-point bending with an effective span of 3.0 m and a shear span of 1.0 m. Corrosion was restricted to the middle 1400 mm of the tensile steel reinforcement to simulate a flexural-critical corroded beam. To represent a severely chloride-contaminated concrete, salt was added to the concrete used to cast the middle 1400 mm of the bottom third of the beam such that the concrete within that zone had approximately 2.25% chloride ions by weight of cement. A tubular stainless steel bar was placed inside the specimen at a distance 80 mm away from the bottom soffit of the beam to act as a cathode during the accelerated corrosion process. The shear reinforcement consisted of 8 mm diameter stirrups placed at 80 mm on center (OC) in the shear span and at 333.33 mm OC in the constant moment region with a clear cover of 25 mm. As shown in Fig. 3, CFRP repair schemes included flexural strengthening with a longitudinal CFRP sheet that corresponded to a CFRP reinforcement ratio of 0.31% in addition to CFRP wrapping. Over the middle 1500 mm of the beam, continuous or intermittent transverse CFRP sheets were wrapped around the cross section to improve the bond at the steel-to-concrete interface. In the shear span, three U-shaped CFRP strips were wrapped around the cross section to act as end anchorages for the longitudinal CFRP sheet, to prevent peeling off for the longitudinal sheet, and to avoid any premature shear failure due to an increase in flexural strength after repair. The analytical model developed by the authors16 was used to ensure that the repaired beams will fail by rupture of the longitudinal CFRP sheet after yielding of the tensile steel reinforcement.