Research On Engineering Service Life Of Concrete Material For Highway Bridge

Concrete is the most widely used material in modern engineering construction.In highway bridge engineering,concrete bridges account for more than 90%.The national standard "Uniform Standard for Reliability Design of Engineering Structures"(GB 50153-2009)stipulates the design service life of 30 years,50 years and 100 years according to the scale and importance of the main structure of the bridge.Due to the low requirements of early bridge design codes,low load levels,low concrete grades,and aging of concrete bridges during service,increased vehicle loads,and increased environmental erosion,most of China's highway bridges have a service life of 25 to 35 years.The service life of concrete bridges is not optimistic.Concrete as the main material of the bridge structure,its long-term performance and engineering service life is the premise to ensure the long-term service performance of the bridge structure and realize the design service life.What is the engineering service life of concrete materials? Whether it can meet the 50-year,100-year or longer service life requirements requires research and demonstration,thus providing the necessary theoretical support for the realization of bridge design service life.Several aspects have been studied around the engineering service life of concrete materials.(1)The stability of cement hydration products in concrete was studied by fine microscopic mechanism analysis.The factors affecting the stability of calcium hydroxide,calcium silicate silicate and calcium sulphoaluminate in cement stone were analyzed from the perspective of chemical reaction at the cement hydration product level.The decrease of cement slurry pH value is the main reason for the deterioration of stability of hydration products.The pH decrease is mainly caused by the consumption and dissolution of calcium hydroxide in cement stone which is relatively unstable.In addition,the expansion of hydrated calcium sulphoaluminate with sulfate ions in the environment is also an important cause of concrete failure.On this basis,the factors influencing concrete stability in typical environment were analyzed.(2)Through the investigation and statistical analysis methods,the time-varying regularity of concrete strength in typical environment was studied,and the long-term variation curves of concrete strength in general atmospheric environment,marine environment,medium alkaline soil environment,saline soil environment and acid corrosive soil environment were obtained.After the concrete is hardened,the concrete becomes more compact and the performance continues to increase with the continuous hydration of the cementitious material for a long time.The extent and time of growth are related to the type,quantity and fineness of the cementitious material.Concrete is also subject to environmental erosion.When the environmental erosion is greater than the cement hydration growth,the concrete performance will decrease.According to the analysis of the influence of concrete strength deterioration on the bearing capacity of the bridge,the engineering service life of the concrete in the typical environment is obtained from the strength variation curve.(3)The effects of carbonation on surface deformation and cracking of concrete structures were studied by means of experiments and numerical simulations.And the relationship between shrinkage crack width and carbonization depth and time under different carbonization coefficients under the action of carbonization and shrinkage.The carbonization shrinkage coefficient,temperature linear expansion coefficient and dry-wet deformation coefficient of cement mortar were studied by accelerated carbonization test.The influence of carbonization and shrinkage on the surface cracking of concrete was simulated by ANSYS software.The relationship between the crack width and the carbonization time was analyzed,and the age at which the crack width reached the limit was obtained.In addition,the effect of the change of dry-wet deformation property of the carbonated mortar component on surface cracking was analyzed.