Experimental And Numerical Study On The Relationship Between Fibre Distribution And Mechanical Properties Of SFRC

Concrete is the most widely used building material in the world,and the mechanism of its components has always been a research hotspot.Concrete can be considered as a three-phase composite material consisting of aggregate,cement mortar and the interface transition zone(ITZ).The mechanical properties of concrete are determined by the properties of each component.However,it is known that ITZ is the weakest area of concrete,and the impact of its strength on the concrete has always been the focus of the research.With the fast development of infrastructure construction of China,the difficulty of construction has increased.As a result,there is an increasing demand for advanced construction technology.When the conventional concrete with improved ITZ strength cannot meet the requirements of structures,steel fibre reinforced concrete(SFRC)has been promoted accordingly.At present,the mechanical properties of concrete at the meso-scale level as well as the promotion and application of SFRC have been widely studied and many research results have been achieved.However,there are still many problems that have not been fully resolved yet.For instance,the properties of aggregates and mortars on the concrete strength and elastic modulus can be studied through mechanical tests,but it is difficult to quantify the influence of ITZ on it,because it is too small to study via traditional test.In addition,the spatial distribution of steel fibres has obvious effects on the mechanical properties of SFRC.However,due to the limitations of experimental conditions and the large demand for manual labour work,there is no complete theory of the spatial distribution of steel fibres on the mechanical properties of SFRC.Because of the above-mentioned problems,this dissertation intends to study the influence of ITZ on the mechanical properties of concrete as by means of particle element numerical simulation;then to study the spatial distribution of steel fibres in SFRC by conducting image processing analysis as well as inductive test;in addition,this dissertation also studies the effect of spatial distribution of steel fibres on the post-crack behaviour of SFRC via the multi-directional double splitting test(MDST)and finite element numerical simulation.The main study and innovation of the dissertation are presented as the following four aspects:1)The second chapter proposes a method for generating aggregates and establishes an inversion formula between the meso-parameters and macroparameters under the Flat-joint Model(FJM).Based on the particle element model of concrete,the numerical simulation on concrete uniaxial compression and the Brazilian splitting test were performed,and the process and results of the tests are introduced in this chapter.The simulation results are basically consistent with the strength obtained by the mechanical tests,which explains the correctness of the model.In addition,under the precondition that the numerical simulation meets quasi-static loading,in this chapter,a new numerical simulation loading method,which greatly shortens the simulation time,is also proposed.2)The third chapter introduces the inductive test and image processing analysis which are performed on different types of SFRC cubic specimens.The spatial distribution of steel fibres in different types of specimens is obtained based on the experimental results.And a calculation method to evaluate the steel fibre content is proposed according to the image processing method.In addition,in order to reflect the similarity of the spatial distribution of the steel fibres obtained by the inductive test and image processing,the phase coefficient is introduced in this chapter.Therefore,the destructive test results verify the correctness of the non-destructive test results,providing evidence for the promotion and application of inductive test.3)In the fourth chapter,based on the experimental results of different mechanical properties of the SFRC specimens loaded in different directions,a multi-directional splitting test(MDST)method is proposed.And the method is used to analyse and calculate the fibre distribution in the three axes of SFRC.In addition,based on the inductive test results of samples extracted from the prismatic beams under different wall-effects,concluded conclusion can be drawn that as the wall-effect decreases,the proportion of the steel fibre distribution in the long axis increases,and the content of the fibres in the middle of the beam is greater than the fibre content at the boundary;through the mechanical properties of the SFRC specimens,it was found that the increase of the steel fibre content has no significant influence on the initial crack strength of the specimens,in spite of whether it is three-point bending test or the splitting test.However,with the increase of fibre content,SFRC shows a significant difference in post-crack performance and a positive correlation with fibre content.This chapter verifies the accuracy of MDST in predicting fibre distribution through the results of inductive test,and both test results show a good correlation.4)In the fifth chapter,based on the fibre distribution obtained in SFRC in the chapter four,a hooked-end steel fibre model which conforms to the actual distribution is generated,and a SFRC model is established using the finite element software ABAQUS.Without considering the interfacial bonding behaviour between steel fibre and concrete matrix,the simulation curve obtained by using this model agrees well with the load-displacement curve measured in the test in the ascending part,which verifies the correctness of the model.