Experimental Study On Bond Performance Between GFRP Bars And The Coral Concrete Under Seawater Environment

Without destroying the natural environment,using coral debris as coarse and fine aggregate and sea water to mix concrete can solve the problem of the lack of conventional building materials for remote island reef projects.However,because the large amount of salt contained in the coral concrete can easily lead to the corrosion of steel,coral concrete engineering applications have been limited.At present,fiber reinforced polymer(FRP)bars have appeared as a practical alternative to steel for concrete reinforcement,due to their high strength,lightweight,corrosion resistance,and other outstanding characteristics,which could solve the corrosion problems caused by the large amount of salt contained in coral concrete and maintain good performance in marine environments.However,the lack of research on the bonding performance between FRP bars and coral concrete seriously affects the calculation and performance analysis of FRP reinforced coral concrete structure.In this paper,the bonding properties of GFRP bars and coral concrete,the factors affecting the bond performance at different temperature under seawater environment and the degradation rule of bond strength after immersion in high temperature seawater were expounded.The main contents and results of this study are as follows:1.At normal temperature,the bonding properties of GFRP bars and coral concrete were studied,including the form and mechanism of bond failure,and the factors that affect the bond strength.The results showed that the bond strength of GFRP and coral concrete can meet the general engineering needs.The bond process,characteristics of bonded slip curve,bond mechanism and failure modes of GFRP bars and coral concrete were similar to those of GFRP bars and ordinary concrete.Among the influencing factors,the bond length,relative thickness of cover layer,the diameter and surface condition of GFRP bars had great influence on bond strength and failure modes.2.The effects of seawater temperature on the bond properties of FRP bars and coral concrete were studied.The characteristics of the bond stress-slip curve,failure modes and mechanisms,and changes in the bond strength of FRP bar-coral concrete immersed in seawater were analyzed.The results showed that with increasing the seawater temperatures,the bonding performance decreased significantly,and the failure modes of the GFRP bar-bonded specimens gradually changed to bar fracture from pullout failure.The residual segments of the ?-s curves of some of the CFRP bar-bonded specimens showed a wave-like uptrend.Both the two kinds of the FRP bars' surfaces were obviously sheared and worn.3.The FRP bars after seawater immersion were observed by electron microscope.The results showed that the effect of the seawater immersion on the GFRP bars was significantly greater than that on the CFRP bars.after immersion at a high temperature,microcracks and voids appeared between the surface resin and fiber of the GFRP bars,and serious debonding and deterioration of glass fibers occurred gradually,too.4.The bond slip models of the existing FRP tendons and concrete were summarized.The rising segment of the ??s curve of GFRP bar-coral concrete was verified and analyzed by using the existing model.The results showed that the experimental curve was in good agreement with the CMR model curve.