UHPC Shrinkage Simulation Based On Thermo-Hygro-Chemo-Mechanical Coupling Model

Ultra-high performance concrete(UHPC)as an excellent repair material is widely used in repair and reinforcement projects,which effectively guarantees the safety and durability of the existing structure.However,due to the large early shrinkage of UHPC,it is incompatible with the deformation of the old concrete,causing the repair system to fail.In order to better control the reliability of the repair system,the early contraction behavior of UHPC should be predicted in advance.The early shrinkage of UHPC is usually the result of the coupling of hydration,damp heat and stress of the cementitious material.This study uses the existing chemical-moisture-heat-mechanical coupling model to establish partial differential equations,obtains the necessary parameters of the equations through experiments,and finally uses the finite element method to solve the equations,so as to obtain the early shrinkage performance of UHPC and achieve prediction the goal of.The specific work carried out in this paper is as follows:(1)According to the early UHPC hydration reaction-relative humiditytemperature-stress interaction characteristics,with the help of the temperaturehumidity-chemical reaction-mechanical coupling model of ordinary concrete,the UHPC coupled partial differential equations are established.(2)Conducted mercury intrusion test analysis to study the early pore structure changes of UHPC at different ages with different shrinkage capacity;conducted thermogravimetric test analysis to study the early hydration reaction degree of UHPC at different ages with different shrinkage capacity;The corresponding relationship between the evolution of the UHPC pore structure and the hydration reaction at ages,the functional relationship between the volume fraction of UHPC pores and the degree of hydration reaction required to solve the coupled equations is given;the UHPC with different shrinkage capacities The mechanism of the volume fraction of fine pores and the degree of hydration reaction.(3)The functional relations obtained in the joint test and the established coupling equations are solved by using the finite element method to solve the coupling equations of 5 different working conditions,and the shrinkage performance of the UHPC under the corresponding working conditions is obtained.The results show that under various working conditions,the multi-physics coupling model in this paper can better predict the shrinkage performance of UHPC at the early age;for the common constrained shrinkage in actual repair and reinforcement projects,an evaluation based on the degree of damage is given The method has certain practical application value and can be used to predict the reliability of repair and reinforcement materials in repair projects.