Study on the performance of CFRP strengthened corroded steel members

Abstract

Most of the metallic structures such as offshore platforms and railway bridges are now in the need of retrofitting due to corrosion. One of the efficient ways of strengthening these structures is by using (Carbon Fibre Reinforced Polymer) CFRP materials. Since the weakest link in this system is the bond between the adherends, the effect of pre-corrosion level of the steel elements on the bond characteristics and durability performance of the strengthened units should be properly evaluated. Even though there are many research studies on bond durability none of them has used corroded steel plates for bond strength evaluation and considered the inherent surface characteristics of the corroded steel surfaces. Therefore, this study aimed at investigating the bond performance of CFRP bonded corroded steel plates which are subjected to different ageing conditions and surface roughness characteristics.

A total of one hundred and twenty-eight conditioned and non-conditioned double strap joint specimens were tested. Both corroded and non-corroded steel plates and two different surface preparation methods were used to witness the importance of the surface texture properties. Scanning Electronic Microscopic (SEM) analysis was carried out to determine the surface characteristic properties of the corroded/non-corroded steel plates. The short-term bond performance was evaluated along with different bonding configurations. In the long-term analysis, six different environmental exposures; seawater, wet/dry cycles, open tropical environment, and distilled water at three different temperature levels, 25 o C -30 C and 3 o C were considered for conditioning. Residual bond strengths of the conditioned test specimens were evaluated after 6- and 12-month exposure periods at ambient temperature. A numerical model was developed to estimate the stress-strain variation of CFRP/steel specimens along the bond line. Bond-slip curves were evaluated to estimate the interfacial fracture energy of CFRP/steel composites. Moreover, experimental results were compared with the analytical results obtained from Hart-Smith model and a theoretical relationship between the failure modes was derived.

Test results indicated a major influence of surface roughness on the long-term performance of CFRP/steel joints. CFRP strengthened corroded steel joints showed a residual bond capacity of about 90% in seawater immersion and 111% in tropical environmental condition suggesting its suitability to adopt CFRP technique in these exposures. After 12 months of exposure duration, a similar bond degradation was observed of about 31% in distilled water immersed specimens at ambient temperature and about 60% in dry/wet cyclic condition irrespective of the pre-corrosion level. During an exposure period of 12 months, the rate of bond degradation was found to be less than 20% for cold water immersed specimens with non-corroded steel plates. The interfacial fracture energy of CFRP/steel composites exposed to hot humid environments indicated a significant reduction of 78% compared to control test specimens.