Experimental Study On Durability Of Concrete Cylinders Strengthened With Basalt Fiber Reinforced Polymer Sheets

BFRP attracted people's attention and was applied gradually to civil engineering due to its good mechanical properties and cut-price production cost. During the recent decade, Fiber Reinforced Polymer or plastics has been widely used as material for strengthening existing civil infrastructures. People's research attention focused on CFRP and GFRP. BFRP are studied gradually by experiments for scientific,safe, inexpensive application.But, the research had just started because of no enough long application time. How about the durability of FRP strengthened RC structures in environments? How to carry out durability design for FRP strengthened RC structures in environments? These questions must be paid more attention and solved reasonably before FRP is used in environments. Based on the research background, experimental researches have been carried out in the dissertation on durability of BFRP composite and BFRP strengthened concrete cylinders, including the following work:1.BFRP sheet were tested in longitudinal tension subjected to the test environments such as freeze-thaw cycles and freeze-thaw cycles in sodium chloride solution. The law of BFRP composites performance deterioration , the effects of different environmental conditions and exposure time on durability of BFRP composites are studied. The experimental results indicate that tensile strength and elongation decrease and elastic modulus increases when subjected to the two test environments. Single environment shows more effect on BFRP tensile strength than compound environment. Compound environment shows more effect on BFRP elongation and elastic modulus than single environment. The result indicate that compound environment is more easier to cause material embrittlement than single environment. Based on experiment result, a grey forecast model of BFRP relative tensile strength under environmental effect is presented.2.The axial compressive experiment of BFRP strengthened RC cylinders is carried out in the test environments. The effects of different environmental conditions, exposure time (cycle times), reinforcement method, adhesive layers, concrete grade of strength on durability of BFRP strengthened RC cylinders are studied. Experimental results show that, retained strength rate of BFRP entirely wrapped concrete cylinders is more higher than BFRP strips strengthened concrete cylinders under each environmental condition and the rate of unconfined concrete cylinders is the lowest. Vertical deformation ability of two types of confined concrete cylinders decrease under each environmental condition and the ability of BFRP entirely wrapped concrete cylinders is more higher under the same conditions. In terms of improving strength, earthquake-resistant capacity and durability of the concrete structure, the entire wrap manner is better than partial wrap manner. Degradation mechanism of BFRP strengthened RC cylinders under freeze-thaw cycles and freeze-thaw cycles in sodium chloride solution are also studied.3.Based on durability experiment and existed rule of lateral expansion coefficient with steady value in the ultimate state, the effects of environments on tangent Poisson ratio- longitudinal stress curves and tangent Poisson ratio are studied.The experiment results showed that tangent Poisson ratio- longitudinal stress curves changed regularly because of the environment effects. based on the discussions on the environment influence factors of ultimate tangent Poisson ratio of BFRP-confined concrete circular column, environment variable was introduced in analyzing the influence by aggressive environments and calculation formulas for ultimate tangent Poisson ratio under aggressive environments were presented.The analytical results are in good agreement with the test results.4.Several typical models including stress,strain for circular-section concrete confined by FRP are listed, and the models of stress,strain for peak point are compared according to experimental datas under aggressive environments.Based on the existed calculating models of stress,strain for peak point of concrete confined by FRP, introduced environment variable, the new models of stress,strain for peak point are presented considering environment influence factors, which provides data and theory for durability design of FRP strengthened RC structure under environments.