Experimental Study On Size Effect Of Splitting Tensile And Flexural Properties Of Steel Fiber Reinforced Concrete(SFRC)

As a kind of quasi-brittle materials,the mechanical properties of concrete are closely related to its geometric size.For the concrete,the main nominal performance like compressive strength,splitting tensile strength and flexural strength could decrease with the increase of specimen section size.The size effect of concrete strength is not only related to the mixture ratio and strength gradation of the specimen,but also its geometric size.At present,the design of concrete structures in our country mainly refer to the calculating formula of the small-size specimen test study for the calculation of strength of concrete.In recent years,the requirements for concrete material become higher and higher with the development of all kinds of engineering.In order to improve the mechanical properties of concrete in different applied fields,it has turned out a workable plan to add a certain amount of steel fibers to concrete mixture to improve its mechanical properties.In the research of size effect on the splitting tensile strength and flexural strength of concrete at home and abroad,it is mostly on the basis of the steel fiber volume ratio and single concrete matrix strength,but the study of specimen geometry size is relatively insufficient.To obtain the difference in the splitting tensile strength and compressive strength for SFRHSC specimens of different size,this paper mainly carry out the research on the size effect of splitting tensile strength and flexural properties of steel fiber reinforced concrete.The main research contents are as follows:1.Size effect of splitting tensile strength of steel fiber reinforced concreteIn order to study the size effect of splitting tensile strength of steel fiber reinforced concrete,the concrete specimens of 36 100mm×100mm×100mm and 36 150mm×150mm×150mm and 36 200mm×200mm×200mm were fabricated.Each type of specimen containing the C30 and C60 two strength grade;each strength grade contains 0,0.75%,1.5% three different steel fiber volume ratio;curing 7d and 28 d under the standard curing condition according to the curing age.The test is referring to the Standard Test Method for splitting tensile strength of steel fiber reinforced concrete.Through the splitting tensile strength test of above several concrete cube specimens,the influence of the steel fiber volume fraction,curing age and concrete strength on the splitting tensile strength is analyzed.The size conversion coefficient of splitting tensile strength of steel fiber reinforced concrete under different concrete matrix strength is obtained and the calculation formula of splitting tensile strength of steel fiber reinforced concrete under different intensity is fitted by linear fitting method.The results show that the splitting tensile strength of steel fiber reinforced concrete cube specimen has size effect phenomenon.Under the same conditions,the tensile strength of the nominal splitting tensile strength of the small size specimen is higher than the larger size specimen.In addition,the size effect of splitting tensile strength of steel fiber concrete will be more obvious with the increase of concrete strength.2.Size effect of flexural properties strength of steel fiber reinforced concreteIn order to study the size effect of flexural properties strength of steel fiber reinforced concrete,the concrete specimens of 36 100mm×100mm×400mm and 36 150mm×150mm×550mm were fabricated.Each type of specimen containing the C30 and C60 two strength grade;each strength grade contains 0,0.75%,1.5% three different steel fiber volume ratio;curing 7d and 28 d under the standard curing condition according to the curing age.The test is referring to the Standard Test Method for flexural properties strength of steel fiber reinforced concrete.Through the flexural properties strength test of above several concrete cube specimens,the influence of the steel fiber volume fraction,curing age and concrete strength on the flexural strength is analyzed.The size conversion coefficient of flexural properties strength of steel fiber reinforced concrete under different concrete matrix strength is obtained and the calculation formula of flexural properties strength of steel fiber reinforced concrete under different intensity is fitted by linear fitting method.It is shows that the Bazant size effect rate based on energy release has a good applicability for the analysis of flexural properties strength of steel fiber reinforced concrete by coMParing the test value and the calculated value.In addition,the test also provides theoretical support for the application of steel fiber reinforced concrete in engineering.