Mechanics And Durability Experimental Research Of CFRP Strengthened Reinforced Concrete Structures

Using fiber-reinforced plastic (FRP) to strengthen or retrofit existing reinforced concrete members has become more and more popular in the last couple of decades. Carbon fiber-reinforced polymer (CFRP) materials have higher stiffness and enhanced durability characteristics compared to other composites and have been frequently used for applications in concrete structures. But due to the versatile applications of concrete in different construction fields, CFRP reinforced concrete structures may often be exposed to wetting and drying (W/D) cycles, sea-salts in hot-humid climates, freezing and thawing (F/T) conditions, and many other severe environments. Some difficulties still exist during field applications. Effects of these environmental factors on the long-term bond of CFRP composites to concrete are addressed through accelerated experiments. It is necessary to understand the mechanisms that composite structures degradation; not only to optimize material performance, but also to provide information that can be used in the design of accelerated aging tests.This paper presents accelerated aging test results of a durability study on CFRP reinforcing sheets for concrete structures. It was intended to study the effect of harsh environmental conditions such as wetting/drying cycling using sulfate solution on the performance of CFRP-bonded concrete beams and on the interfacial bond between the fiber and the concrete. CFRP sheets bonding to concrete prisms and strengthening reinforced concrete beams on the tension face were exposed to three different environments, and many conclusions have been obtained.1. The tensile property of CFRP sheets and concrete cylinders in sulfate solution were tested. Results showed that the sulfate solution had no effect on the tensile property of CFRP sheets and elastic modulus of concrete. The compressive strength of concrete in sulfate solution had an important relation with the corrosion damage time.2. The shear bond performance between the CFRP and concrete attacked by sulfate solution was tested. The result showed that the bond strength did not decrease.3. A total of 10 CFRP strengthened reinforced concrete beams were tested, and crack load,ultimate flexural capacity and failure modes were comprehensively studied. Based on those, the bending stiffness can be divided into three phases according to the cracks developments and rebar yielding. A deflection formula which deduced by the hypothesis with the test results. Therefore it may be used in practical engineering.4. Based on the test results of 9 reinforced concrete beams strengthened by externallybonding CFRP in two environments. Load-deflection curves of the beams were obtained in order to evaluate their maximum flexural capacity, stiffness, ductility and failure model. The performance of the accelerated aging beams was compared with those kept at room temperature. The result showed that temperature/humidity cycles and sulfate fog wet/dry cycles had bad influence on the performance of CFRP strengthened RC beams.