Experimental Study On Drawing Properties Of Multi-Type Single And Double Steel Fibers-Uhpc Matrix

Ultra-High Performance Concrete(UHPC)is a cement-based composite material composed of cementitious materials,fine aggregates,admixtures and water.The overall performance of the concrete will also change,such as the amount of a certain mineral admixture,the size of the water-binder ratio,the addition of admixtures,and the amount of steel fiber will affect the compressive strength,flexural strength and mixing of ultra-high performance concrete.fluidity of the compound,etc.When the steel fiber ultra-high performance concrete is subjected to external force,the fiber forms a skeleton effect inside the UHPC matrix.to transmit.It can be seen that the drawing properties of steel fibers and their interfacial adhesion with the UHPC matrix are the key to the reinforcement,toughening and crack resistance of UHPC by steel fibers,and the fiber drawing test is the most important for studying the drawing properties of steel fibers-UHPC matrix.Commonly used test methods,most of the current pulling test research mostly uses single fiber pulling,but when the actual UHPC is subjected to external force,the fibers inside the matrix are in a complex stress state,and there is a strong coupling between the fibers.The fiber pull-out test can only express the mechanical properties of a single-fiber pull-out member,but cannot objectively describe the stress state of the fiber-reinforced concrete during the cracking process.Therefore,this paper started the fiber pull-out test,based on the single-fiber pull-out test,and carried out research on the double-fiber pull-out test at the same time,in order to clarify the effects of curing methods,fiber types and fiber spacing on the pull-out performance of single and double fibers.Laws and coupling between fibers.The main work of the paper is as follows:(1)Starting from the conventional curing system of UHPC,the mechanical properties of UHPC and the drawing properties of steel fibers under different curing methods and curing ages are studied.The research results show that:1)The curing method and curing age will affect the mechanical properties of UHPC.Water bath curing and steam curing can significantly improve the compressive and flexural strength of UHPC.Standard curing has a poor effect on improving the strength of UHPC.The strength of the matrix increases with the curing age.2)The curing method and curing age will also affect the drawing performance of the steel fiber and its bonding performance with the UHPC matrix interface.The tensile properties of the fibers and the bonding properties of the steel fiber-UHPC matrix interface are better with the increase of curing age.3)Under the SEM observation,the specimens cured by steam curing and water bath curing have higher matrix density,better bonding between aggregate and gel material,and more stable interface transition zone.For specimens cured by standard curing,the aggregates inside the matrix are The bonding with the gel material is poor,and there is cracking in the interface transition zone,and the cracks often develop and extend along the edge of the aggregate.(2)Using the double-fiber drawing test as a method,an experimental study was carried out on the influence of the type,diameter and double-wire spacing of the steel fiber on the drawing performance of the steel fiber under the double-fiber drawing.The test results show that:1)There are four failure modes in the double-fiber pull-out test:double-fiber pull-out,single-fiber pull-out+single-fiber breaking,no double-fiber pull-out,and double-fiber breaking.Double fiber drawing.2)Under double wire drawing,the fiber type and diameter will affect the drawing performance of steel fibers.For steel fibers of different types of fibers:end-hook copper-plated steel fibers>straight round copper-plated steel fibers>straight round non-plated steel fibers Copper steel fiber.3)After many repeated tests,it is found that the drawing performance between the steel fiber and the UHPC matrix changes in a "wavy" shape as the fiber spacing increases.For example,the S0.2 fiber specimen changes in a "wavy"shape;S0.3 The fiber specimen is "M" shape;FS0.2 and H0.3 are "N" shape;FS0.3 is "W"shape.4)A layer of matrix particles is attached to the surface of all fiber-embedded sections.The matrix tunnels are damaged to varying degrees.There are micro-cracks and holes in the fiber channels,and a large number of broken particles are distributed.H0.3,S0.3,and FS0.3 are pulled out.There is matrix spalling nearby,and the matrix tunnel damage of H0.3 specimen is the most serious,followed by S0.3 and FS0.3,and the damage of S0.2 and FS0.2 is the lightest.(3)Starting from the single-fiber and double-fiber experiments,through the comparative analysis of the test results,load-slip curves and SEM observations of single-fiber and double-fiber,the purpose is to clarify the drawing of different types of single-fiber and double-fiber in UHPC matrix.Influence law of performance and coupling between multifibers.The test results show that:1)The bond strength of the double-fiber drawing test is not a simple superposition of single-fiber drawing,and the superposition between fibers is closely related to the fiber spacing.2)Although the double-fiber pull-out test overall improves the pull-out load and strength of the specimen,the overall pull-out performance is higher than that of single-fiber pull-out,but it reduces the ultimate load and pull-out work of a single fiber,and reduces the fiber strength.The utilization rate reduces the drawing performance of a single fiber.3)In the SEM observation,a layer of matrix particles is attached to the surface of all fiber-embedded sections.In the matrix tunnel after the fibers are pulled out,it can be observed that there are micro-cracks and holes in the fiber pores,and a large number of broken particles are distributed.The matrix tunnels of H0.3,DH0.3,S0.3 and DS0.3 specimens are more seriously damaged,and the distribution of matrix debris and cracks is obvious.For S0.2 and DS0.2 specimens,the interior of the tunnel is relatively smooth,and the matrix The debris is small,the number is small,and the number of holes is small,but there are also micro-cracks,and the cracks are fine and not many in number.