ABSTRACT
Many civil engineering structures are subjected to deterioration due to aging and exposure to harsh environments. Over the past four decades, fiber reinforced polymers (FRP) have been increasingly used for strengthening, repair and refurbishment of bridge structures, and more recently, in the manufacture of whole/hybrid FRP bridges. In such applications, adhesive bonding is usually the preferred joining technique. Although, the short-term behavior of FRP/steel bonded joints has been extensively studied, the subject of the durability has not been researched to the same degree.
Today, uncertainties regarding the durability aspects of adhesively bonded FRP/steel joints used in bridges present a major obstacle to their growing application. The lack of knowledge regarding the long-term performance is currently compensated by applying a multiple of large safety factors to the strength of FRP materials, which dramatically increases the material usage and reduces the design efficiency.
The aim of this research work is to shed some light on the durability and long-term performance of adhesively bonded Carbon-FRP/steel joints with emphasis on effects of temperature, de-icing salt solutions and moisture on mechanical behavior of such joints. This aim was realized by conducting long-term experiments on CFRP/steel double lap shear joints subjected to various temperature ranges, humidity levels and solutions. The specimens and exposure conditions were carefully designed to reflect configurations and environmental conditions expected in bridge applications. Forty joint specimens were aged in simulated de-icing salt solution (SW) and deionized water (DW) at 20° C and 45°C for up to eighteen months. Complementary material characterization tests were also conducted to study the moisture diffusion kinetics, and moisture dependent mechanical properties.
The test results of hygrothermally aged joints indicate a clear change of failure mode from cohesive to interfacial or interlaminar FRP failure, see Figure 1. Even though all the joints exhibited increasing load-bearing capacity during the first six months, the failure load of specimens aged at 45°C started to degrade afterwards. Prolonged exposure in salt water at 45°C caused FRP damage that led to the lowest joint strength with 35% reduction. Thus, although salt water was found to be less damaging to the adhesive material compared with distilled water, it had more deleterious effects on the strength of CFRP material, particularly at higher temperatures. Examples of different failure modes of tested joints. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig179_1.jpg"/>
