Research On Prevention Technology Of Dry Shrinkage Cracks Of Concrete Bridges

At present,concrete structural bridges account for a large proportion of highway systems.Due to the drying shrinkage of concrete materials and the combined effect of external loads,surface dry shrinkage cracks are easily formed in the initial stage of maintenance.The further expansion of such cracks not only affects the aesthetics of the bridge structure,but also reduces its durability and safety,and jeopardizes the safety of the highway system.Therefore,it is particularly important to study the prevention and control technology of surface dry shrinkage cracks in concrete structures.This paper is based on the concrete humidity field theory,used a combination of experimental research and finite element numerical simulation to measure the early internal temperature and humidity changes and dry shrinkage deformation of concrete structures,and discussed the determination of the relevant parameters in the concrete moisture differential equation,further explored the effect of surface sealing treatment on the cracking load of reinforced concrete structures and the deformation and stress of concrete bridge structures.(1)Through the shrinkage test of concrete specimens under three conditions of outdoor environment,closed environment and dry environment,the influence of ambient humidity on the humidity field,shrinkage deformation and early basic mechanical properties of the concrete structure was analyzed.The test results show that: The early shrinkage deformation of the specimen increases with decreasing ambient humidity.The lower the ambient humidity,the faster the internal wet diffusion rate and the more the internal relative humidity decreases.The wet diffusion of the concrete structure gradually decreases from the surface to the center of the test piece.The surface moisture diffusion is most obvious,and the internal humidity changes slowly.Adopting the method of sealing the surface of the wrapped aluminum foil helps to increase the tensile strength and elastic modulus of the test piece,but the improvement of the compressive strength is not obvious,and at the same time,the early shrinkage deformation of the test piece can be effectively reduced.(2)The ADINA finite element software was used to simulate the dry shrinkage deformation of the dry set specimens.The measured data were used to determine the value of the humidity convection coefficient and the shrinkage coefficient in the humidity field equation.The analysis results are as follows: The humidity gradient of the concrete specimen shows a gradual change from the surface to the interior and the internal humidity decreases slowly.The shrinkage deformation of the test specimen decreases with the increase of the ambient humidity,which is the same as the test result.The higher the ambient humidity,the greater the proportion of early contraction to the final contraction value.When the humidity reaches a certain range,the shrinkage of the test piece does not increase after 100 days.(3)Through the tensile test of reinforced concrete,the cracking conditions of the axial stress of the specimen under the two curing conditions of closing and drying were compared.The conclusions are as follows: The tensile strength of the closed cured specimens was higher,and the cracking load was 16.2% higher than that of the dry curing group.The width of the crack after unloading is also smaller than that of the dry curing group,indicating that surface sealing can effectively improve the crack resistance of the structure.(4)Through the finite element simulation of the tensile process of reinforced concrete specimens,the load-elongation curve was obtained and compared with the measured values.The results show that: The finite element model can simulate the tensile cracking of the specimen,which is in good agreement with the experimental conditions.The calculated cracking load is slightly higher than the measured value.