Study On Bond Behavior Of High Performance Concrete At Different Ages

At present,the structure of the combined box girder is widely used,but from the operation status of the bridge,a large number of wet seam location are cracks,the emergence of cracks affect both the comfort of traffic and seriously affect the safety of the use of the bridge The Cracks in the new pouring concrete and post-pouring concrete interface,in the construction disturbance,environmental conditions,material properties and construction technology and other factors under the influence of the two concrete in the surrounding constraints under the conditions of the performance is more complex,so this The study of the problem has important practical and theoretical value.The bonding surface of concrete at different ages is the weak layer in the process of stress.When the interface in different ages of concrete is smeared Interface agentt,this measure can not only improve the adhesive surface of the concrete defects,thereby enhancing the bonding surface bonding properties,but also can have a waterproof effect on the bonding surface,prevending Rainwater infiltrates from the seams to improve durability.In the Engineering field these interface agent are commonly used:cement paste,cement mortar,fast iron aluminate cement slurry,expansion interface agent,epoxy mortar or epoxy resin interface agent and polymer interface agent,etc.In the actual project,the most widely used interface agent is cement paste.Moreover,the prefabricated sheet has long been contracted and deformed,and the elastic modulus is no longer changed with age.However,the new wet seam has just begun to hydrate.In the early phase of the concrete,the shrinkage deformation accounts for a large proportion of the total shrinkage deformation,therefore,additional tensile and shear stresses are generated inside the wet seam.When the additional stress is too large,cracks are inevitable.According to the above,this paper mainly concentrate on the following aspects:(1)The Interface Bindert was modified by adding cement,mineral powder and water to the polymer.By studying the effects of different polymer-cement ratio and the proportion of the Mineral powder,we will get the Match ratior with the best mechanical properties,and can stuy how the polymer-cement ratio and the proportion of the Mineral powder affect the mechanical properties of mortar.(2)Since the concrete at both ends of the wet seam being at different ages,the main shrinkage of the concrete at one end has completed,but the shrinkage deformation of the new pouring concrete has just begun.Therefore,a set of orthogonal tests is designed.Water-cement ratio?the content of the Mineral powder?the content of the fiber are selected as the three main influencing factors.Using the L9 orthogonal table,the optimal mix ratio of wet seam concrete is determined by measuring the early shrinkage value.And the measured data are analyzed to determine the main factors that affect the early shrinkage of high performance concrete.(3)The finite element model was established to simulate the stress distribution of Wet seam with different types of concrete under shrinkage and deformation,and the distribution position of thecrack is discussed.