The Effects of Surface Condition and Long-Term Environmental Exposure on the Bond Between CFRP and Steel

About the report

As the existing steel infrastructure inevitably continues to age and deteriorate, engineers are increasingly looking for innovative and effective methods for repairing and maintaining existing steel bridges, which are susceptible to corrosion damage when exposed to aggressive environments and deicing salts. Conventional methods for repairing steel bridges can be labor intensive and time consuming and add considerable weight to the existing structure. One alternative is to utilize carbon fiber reinforced polymers (CFRPs). Many studies have documented CFRP’s ability to enhance the strength of existing structures while having a high strength-to-weight ratio and the added benefit of being noncorrosive. However, most of these studies have focused on the bond behavior between CFRP and steels having a smooth surface condition, which is not representative of deteriorated structures in need of retrofitting. Further research has examined the durability of CFRP-steel bonds but under conditions that do not reflect the service life conditions for typical bridge applications.

This study examined the effects of the surface condition and environmental exposure on the bond between steel and two different CFRP materials, one having a normal modulus and the other an ultra-high modulus. The researchers evaluated the influence of corrosion and simulated corrosion pitting to determine whether structures with non-uniform surfaces are viable candidates for CFRP retrofits. In addition, the durability of CFRP-steel bonded, double-strap jointed specimens was investigated through laboratory hygrothermal aging and chloride exposure, as well as in situ environmental conditioning to multiple environments in Virginia. The study also included a small subset of fatigue-tested specimens, as well as a hypothetical in situ cost comparison to assess the economics of strengthening steel structures using the CFRP materials used in this project.

The results showed that although a corroded steel surface does require a longer bond length compared with a smooth surface, a pitted surface due to corrosion has no negative effect on the bond strength between CFRP and steel. Furthermore, exposure to chlorides does not appear to affect that bond strength. However, strength reduction factors for hygrothermal and environmental aging should be included in the design to account for exposure to given conditions. Nevertheless, CFRP is a cost-effective method for strengthening corrosion-damaged steel members with moderate levels of surface pitting. The research can be useful in the development of guidelines that will assist engineers determine if a CFRP retrofit solution is applicable in a given environmental setting and appropriate for the level of deterioration of the structure.

_{Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.}

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