The Research On The Concrete Crack Along Duct Of Post-Tensioned Beam In High And Cold Region

In recent years, with vigorous development of economic construction and the policy of development in our country, transportation foundation facilities developments get the fast fierce development, and the rail communication network of perfect is most important. In developments of the railroad bridge, prestressed concrete is acquired extensive application,because it has much advantage ,such as high load bearing capacity,good tension crack capacity and durability.However concrete is cement-based materials, belonging to the brittleness material essentially, which make pretressed concrete appear crack when it surfers low tensile stress.The partial bridge appeared crack in the congstuction of Qinghai-Tibet Railway,which is in high and cold region and execrale environment .Thereinto,The longitudinal crack along duct of 32 m post-tensioned prestressed concrete beam was more serious. After investigation and statistical dnalysis, it was considered that the crack appeared mostly because frost heaving of grouting and the great temperature stress of the high altitude environment of Qinghai-Tibet Railway. However, it is need further research to know the tensile stress maked by frost heaving of grouting materials, whether the main reason of crack is frost heaving or not, the main factors for frost heaving and how The weather reason influences the beam.This paper proceeded the frost heaving experimental investigation of grouting materials to obtain the frost heaving mechanism,which was aim at environment, weather and the characteristic of grouting materials. The experimental investigation studyed on the effect and primary and secondary factors of water-cement ratio , curing time , curing temperature on bleeding ratio and setting time of grouting materials, studyed on the rules and effect of all factors on degree of shrinkage and volume deformation of grouting materials,magnitude of volume deformation of grouting materials after frost heaving, the frost heaving stress for experimental beam, the temperature difference and stress of prestressed concerte beam when environment temperature drops much. According to the rults of experiment and calculation ,the crack of partial bridge in Qinghai-Tibet Railway was analyzed ,the main factors was given.At the same time, some effictive measures and theoretical gist for this crack was proposed for post-tensioned prestressed beam in high and cold region.