Experimental Study On The Bonding Performance Of Corrugated Steel Fiber-Hybrid Fiber Concrete Matrix Interface

Steel-polypropylene hybrid fiber concrete(HFRC)is widely used in engineering due to its excellent basic mechanical properties.The fiber-concrete matrix interface is the connection link between fiber and matrix two-phase materials.The mechanical properties of fiber-concrete are closely related to the bonding properties between fiber-matrix interfaces.Given this,with the support of the Chinese National Natural Science Foundation(Grant No,51478367),the fiber-matrix interfacial properties in steel-polypropylene(PP)hybrid fiber reinforced concrete was studied by coupling of experimental investigation and discrete element simulation.The main work and results are summarized as follows:The main conclusions are as follows:(1)21 groups of steel-polypropylene hybrid fiber concrete pull-out specimens were designed to study the bonding performance of corrugated steel fiber-hybrid fiber concrete matrix by one-sided steel fiber pull-out tests.Taking peak pull-out force,bonding strength and pull-out work as the reference indexes of bonding performance,the change rule of bonding performance between steel fiber and concrete matrix with the major factors was analyzed.The peak pull-out force and pull-out work of corrugated steel fiber became the largest value when the steel fiber volume content was 1.5% and the polypropylene fiber volume content was 0.05 %.At the same time,the best reinforcement and toughening effect for concrete was obtained.When the embedded depth of steel fiber was small,the force of corrugated steel fiber pulled out from hybrid fiber concrete increased with the increase of the embedded depth of fiber,but when the embedded depth of fiber was greater than the optimal embedded depth(8mm),the bond strength would gradually decrease with the increase of the embedded depth.Matrix strength has a significant influence on the interfacial bond performance.The bond performance between corrugated steel fiber and hybrid fiber concrete matrix increased with the increase of matrix strength when the matrix strength is within the range of C40～C50.(2)The influence factors on the bonding performance of corrugated steel fiber-HFRC matrix were analyzed.The contact force of corrugated steel fiber was recorded through single steel fiber pull-out test and PFC discrete element numerical simulation,and the change rules of the bond between steel fiber and concrete matrix with the main influencing factors in the PFC model were analyzed:The increase of effective deformation modulus of parallel bond led to the decrease of the peak bonding force,and the peak bonding force would appear in advance.With the increase of bonding distance,the steel fiber could bond with more matrix particles nearby,so that the bonding effect between the steel fiber and the concrete matrix was better.The friction coefficient mainly affected the shape of the stick-slip curve and the peak bonding force.With the increase of the friction coefficient,the friction between particles increased and the bonding force increased.When the fiber diameter was thicker,the bonding force would be greater,but the bonding strength would be smaller.The interfacial bonding force increases with the increase of the aspect ratio of corrugated steel fiber.(3)The bonding mechanism of the fiber-matrix interface was also revealed by fiber pullout test and scanning electron microscope test.The chemical bonding force first increased and then decreased with the increase of fiber content.The friction increased with the increase of fiber content.The mechanical bite force increased with fiber incorporation and matrix strength increased.