| Concrete box girder structures has been widely used in engineering due to its big stiffness and small structure.Now,premature deterioration often make the service life performance of concrete structure shorter in practical engineering.It is not because of lack of strength,but the drop and injury of long-term performance.At present,the research about long-term degradation of solid concrete member under the single environment factor has been more mature.But most of the studies have not considered load effect and a two-dimensional diffusion characteristic due to unique space of box girder structure.So this paper has carried on the study of carbonation and chloride ion erosion characteristics considering concrete box girder load effect,At the same time,this paper has also carryed on the chloride ion penetration test of box girder structure.At last,it reveals the quantitative influence law of concrete box girder about carbonation and chloride ion erosion on the basis of the shear lag effect of box girder.The main researchs and results of this paper are as follows:(1)Study the various factors which affect the performance of concrete carbonization and analyze the concrete carbonation rate influence affected by sustained load.Through the measured data contrast we can find that which model takes into account the cement,stress levels,as well as the relationship between natural and accelerating carbide has highest precision,it conform to the actual service environment and is easy to used to the actual artifacts.(2)Concrete box girder structures is different from the previous simulation of solid beam.Due to the spatial structure characteristics of box girder,the carbonization time of cross section is different.the starting time value of carbide of the inside edge is greater than the outer edge.The starting time value of roof is significantly greater than floor area,the biggest difference is 68%.At the same time,the carbonization time of each section of concrete box girder are affected by the stress and water cement ratio.The water cement ratio is greater the carbonization time is smaller.Within a certain range,the compressive stress increases carbonization starting time,on the contrary,the tensile stress will reduce carbonization starting time.(3)Study the various factors which affect the performance of diffusion of chloride ion in concrete,analyze the diffusion coefficient of chloride ions affected by sustained load on the basis of experiment,it is concluded that which model takes into account the time,adsorption capacity,temperature and curing environmental factors is closer to the experimental value,and the precision is higher.Due to the shear lag effect of box girder,the diffusion coefficient values is different from the simulation solid beam of laboratory.the diffusion coefficient of each cross section is different,the diffusion coefficient value of the inside edge is greater than the outer edge edge diffusion coefficient value is less than the outer edge.At the same time,the diffusion coefficient value are affected by the stress,water cement ratio,and the environment variety.The water cement ratio is greater,the diffusion coefficient is bigger.The diffusion coefficient value of soaking condition is greater than the dry-wet circulation state.Within a certain range,the compressive stress will decrease the diffusion coefficient values,on the contrary,the tensile stress can increase the diffusion coefficient value.(4)Due to the spatial structure characteristics of box girder,to the marine environment,the chloride ion diffuse from cross section inside and outside two directions,the chloride ion diffusion is multidimensional.Considering the two-dimensional diffusion,the density of box girder section is bigger than one dimensional diffusion state.And the distribution of density are affected by the stress,water cement ratio,and the environment variety.The water cement ratio is greater,the density is bigger.The density of soaking condition is greater than the dry-wet circulation state.Within a certain range,the compressive stress will decrease the density values,on the contrary,the tensile stress can increase the density values.(5)The calculated theoretical value using the improved two-dimensional diffusion theory is probably same to the measured values,but the difference of the box girder roof and floor edge and junction is large.It shows that the two-dimensional theoretical calculation formula which this paper propose is rough.The diffusion status on the edge of the box girder roof,floor,and the junction may be more complex. |
