Study On The Joint Durability Of Bridge Precast Section Beams By Freeze-thaw And Carbonization In North Hebei Region

The durability of concrete Bridges is affected by many factors in atmospheric environment,among which carbon dioxide erosion and freeze-thaw damage are the two main factors affecting the durability of concrete Bridges.In recent years,concrete bridge diseases have been emerging in the north of hebei province.As the weakest part of the concrete bridge structure,the joints of the precast section beam body of the bridge are the most vulnerable to erosion damage,which leads to the damage of other parts of the bridge structure,resulting in the decline of the durability of the bridge and shortened service life.In order to improve the durability of concrete bridge in hebei north areas of scientific rationalization proposal,this article selects the bridge prefabricated Duan Liang seam the research object,the control of the concrete specimen as a whole,is commonly used in preparation of the engineering of the joint types:direct wet juncture,cut hair wet juncture,epoxy resin adhesive joints such as three different classes of joints of concrete specimens,taking indoor freeze-thaw and two kinds of single and compound carbide test,studies the different types of joint seam between the durability of the change law of freeze-thaw damage model and set up different environment and carbonation damage model,and completed the life prediction under different environment.The main research conclusions are as follows:?1?Field investigation of concrete bridge diseases in north hebei region?taking zhangjiakou as an example?.The joints of precast section beam body of bridge are the first part of concrete bridge to suffer from disease and the most serious part of concrete bridge structure.?2?Under the action of single freeze-thaw,the apparent failure,mass loss,tensile strength and bending strength tests of four joints were comprehensively analyzed,and the results showed that:when freeze-thaw cycles were repeated for 200 times,the joints of direct wet joints and epoxy resin adhesive joints were completely cracked and the strength was completely lost.The overall pouring specimens and the hewn wet joints specimens still maintain the integrity of the specimens,and each strength index remains above 63%.The overall pouring specimens of the four types of concrete joints have the best durability under the freeze-thaw environment,and the hewn wet joints have the best durability among the three types of joints commonly used in engineering,while the direct wet joints have the worst durability.?3?Under single carbonation,the carbonation test of 28 days shows that:the joints of the direct wet joints are most seriously eroded by carbon dioxide,and the carbonation depth at the joints is up to 9.83mm.The joints of epoxy resin adhesive joints had the best carbonation resistance,and the carbonation depth at the final joints was only 1.93mm.The carbonation depth at the joints of the integral casting specimens and the gouged wet joints was 5.83mm and 6.48mm,respectively.The carbonation resistance of four joint types of concrete specimens from small to large is direct wet joint<gouged wet joint<integral casting<epoxy resin adhesive joint.?4?Under the combined action of freeze-thaw and carbonization,the damage degree of four concrete specimens with different joints is much higher than that of single test.Under the cyclic test mode,the relative dynamic modulus of concrete specimens with direct wet joints decreases to less than 75%when the freeze-thaw cycle is repeated for 100 times.The relative dynamic modulus of the whole casting specimen and the gouged joint specimen remains above 80%.The relative dynamic modulus of the hewn wet joints with epoxy resin decreased to 74%⁷8%.At 28 days of carbonization,the carbonation depth of the direct wet joints reached more than 1.5times that of the other three joints.The epoxy resin adhesive had the strongest carbonation resistance in the early stage of the cyclic test,and the carbonation depth increased faster than that of the whole cast specimens and the chiseled wet joints in the fourth cyclic test.The durability of four kinds of concrete specimens with different joints is the best,the wet joints with chiseled wool are the best,and the direct wet joints are the worst.?5?Based on the analysis and fitting of the test results,the freeze-thaw damage model:E _d=?₁ N²+?₂ N+1 and carbonization damage model:H_c=?₁t+?₂t²+t_c,under different environments were established.The results show that the durability of gouged wet joints is better than that of other joints.?6?The degree of damage caused by freezing-thawing failure was greater than that caused by carbonization,and the durability of specimens carbonized after freezing-thawing was worse than that of specimens carbonized after freezing-thawing.Epoxy resin adhesive has a strong anti-carbonization effect,but the effect is poor in freezing-thawing environment.In the construction process,the anti-carbonization ability of epoxy resin adhesive and the anti-freezing performance of gouging wet joints can be combined to effectively improve the durability of concrete Bridges.