Study On The Shear Characteristics Of UHPC-NC Interface

Ultra High Performance Concrete(UHPC)is widely used in structural reinforcement because of its ultra-high mechanical properties and excellent durability.Obviously,the interface between UHPC and substrate concrete is its weakest point,and the damage of the interface is often preceded by the reinforcement under load.Ultra-high performance concrete and normal concrete interface(Normal Concrete,NC)adhesion performance is critical.Many scholars at home and abroad have conducted a large number of studies on the shear properties of the UHPC-NC interface,which have not yet fully considered the influence of the keyway parameters,the volume admixture of steel fibers,the number of keyways,and the type of interfacial agent on the shear properties of the interface.In this paper,the shear resistance of UHPC-NC interfacial adhesion has been thoroughly explored through theoretical and experimental studies,and the main works are:(1)Mechanical properties tests of concrete materials were carried out.Referring to the Standard for Test Methods of Physical and Mechanical Properties of Concrete(GB/T50081-2019)and Reactive Powder Concrete(GB/T 31387-2015),the cube compressive strength test,prismatic compressive strength test and static compressive elastic modulus test of ordinary concrete and ultra-high performance concrete were carried out to obtain the test parameters and provide parameters for finite element simulation.(2)Consider the influence of keyway parameters on the shear performance of UHPC-NC interface,and carry out the optimal setting of keyway parameters.Referring to the Design Specification for Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts(JTG3362-2018),"Z"-shaped UHPC-NC direct shear specimens with different depths(t),widths(w)and angles(?)were designed to carry out single-keyway UHPC-NC interfacial shear performance tests under the influence of keyway parameters.The relationship between the keyway parameters and the interface shear bearing capacity is obtained,the load-slip curve is analyzed,and the optimal solution of the single keyway parameters is determined to provide a reference basis for practical engineering.(3)Considering the effects of steel fiber volume dosing,keyway quantity and interfacial agent on the interface shear performance,the study of UHPC-NC interface shear performance under the influence of multiple factors was carried out.The multi-factor interfacial shear performance test is carried out to analyze the damage morphology of the specimen,the characteristics of the interfacial load-slip curve,the interfacial crack morphology and its ultimate shear bearing capacity,to determine the influence of each factor on the shear performance,and to provide parameters for the calculation formula of the UHPC-NC interfacial shear bearing capacity under the action of multiple factors and the 3D finite element simulation of the UHPC-NC shear specimen.(4)Consider the factors affecting the shear performance of the interface and carry out the derivation of the formula for calculating the shear bearing capacity of the UHPC-NC interface.Through the UHPC-NC interface shear test,the calculation parameters such as interface agent influence coefficient and multi-bond groove influence coefficient are obtained.Based on the basic assumption of shear damage,the formula for calculating the shear bearing capacity of UHPC-NC interface under the action of multiple factors is proposed.The parameters obtained from the test are brought into the interface shear bearing capacity calculation formula and compared with the test results.By analyzing the mean value and standard deviation of the calculated shear bearing capacity and the test shear bearing capacity,it is verified that the formula can be used to predict the shear bearing capacity of UHPC-NC interface under the action of multiple factors.(5)Numerical simulation of the shear performance of UHPC-NC interface based on the shear test of UHPC-NC interface under the action of multiple factors.Based on the composite material theory,the ordinary concrete is regarded as a two-phase non-homogeneous composite material composed of mortar matrix and irregular aggregate;the ultra-high performance concrete is regarded as a two-phase non-homogeneous composite material composed of concrete matrix and steel fiber reinforcement,and the Python code of steel fiber and irregular aggregate is written by random placement method,and the code is imported into the finite element software based on the secondary development of ABAQUS The three-dimensional shear model was completed.The interface parameters obtained from the test are given to the model for calculation to simulate the shear damage process of ultra-high performance concrete-ordinary concrete,and finally the finite element simulation results are compared with the shear test results of UHPC-NC interface under the action of multiple factors to verify the validity of the three-dimensional shear model of steel fiber and irregular aggregate established based on the secondary development of Python-ABAQUS.