Durability Test Of Wet Joint Mechanism Sand-UHPC Applied To Transverse Multi-Beam Bridge

With the popularization and development of assembly-type technology,assembly-type construction methods are widely used in China.Assembly-type bridge members are prefabricated in factories,and they are usually connected by wet joints in the field,prefabricated construction methods are more and more used in urban bridges and high-speed bridges.Due to the cold winter and large temperature difference in northern China,the durability of bridge wet joints is more prominent.The use of rain and snow frost and de-icing salt puts forward higher requirements for its durability.In this paper,the wet joints of the transverse multi-beam system bridge of Yaoluanxi Expressway are taken as the research object to enhance its durability and prolong its service life.Considering the cost economy in combination with the actual construction,the research idea of using ultra-high-performance concrete（UHPC）with manufactured sand as the main fine aggregate as the wet joint filling material is proposed.The manufactured sand selected in the test is limestone manufactured sand which is easy to obtain and cheap.Considering the construction requirements and environmental protection,UHPC manufactured sand is designed and prepared and its durability is studied.The main research contents are as follows:1.The test of the material properties of the manufactured sand was carried out.The UHPC mix proportion test was carried out for the manufactured sand.The optimal mix proportion was selected by comparing the basic mechanical properties and working performance.The compressive strength of the 28d age was 135 MPa,and the expansion degree of the mixture was 650 mm.2.The durability test blocks were prepared according to the relevant specifications,and the rapid freeze-thaw cycles of 5%NaCl solution freeze-thaw and pure water freeze-thaw were carried out.The changes of apparent morphology,compressive strength,dynamic elastic modulus and mass of UHPC under freeze-thaw cycles were studied and analyzed.The freeze-thaw damage mechanism of manufactured sand UHPC was clarified by scanning electron microscopy（SEM）test.The relationship model between the relative dynamic elastic modulus of salt frost damage and the number of freeze-thaw cycles was established after the attenuation constant K was corrected.Suggestions for the application of UHPC in transverse multi-beam wet joints were put forward.3.The RCM test of manufactured sand UHPC after freeze-thaw damage was carried out.The variation of chloride ion diffusion coefficient of UHPC under water freezing and 5%NaCl solution freezing and thawing was studied and analyzed.The chloride ion diffusion coefficient of UHPC increases nonlinearly with the number of freeze-thaw cycles,and the relationship between them is quadratic polynomial.The relationship between D_RCM,S under water freezing cycle and D_RCM,Y under salt freezing damage was proposed,and the influence of salt freezing on chloride ion diffusion was simply expressed.