Experimental Study On The Bonding Performance Of Printed Concrete And Reinforcement

At present,3D printing concrete technology is getting more and more applications.Different from ordinary cast-in-place concrete,3D printed concrete materials need to have a certain degree of fluidity,maintain shape and rapid development of strength without external force,and have good durability after forming.In the aspect of component forming technology,3D printing concrete is also different from cast-in-place concrete,which often uses layered overlay printing technology,that is,the printing head is used to extrude the concrete strip and stack layer by layer.Because the material and technology of printing concrete is very different from that of ordinary cast-in-place concrete,the study of the bond performance between printing concrete and steel bar is of great significance to guide the printing process and reinforcement design of printing concrete.Firstly,on the basis of literature reading and field investigation,the appropriate mix ratio of 3D printing concrete is determined.Based on the central pull-out test,the effects of two traditional factors,the diameter of steel bar,the strength of printed concrete material,the printing path and the placement mode of steel bar on the bond performance between steel bar and printed concrete were studied.Through the central pull-out test,the influence of different factors on the bond performance between steel bar and 3D printed concrete and the corresponding ultimate pullout capacity are obtained.The test results show that the diameter of steel bar has the greatest influence on them,followed by the strength of printed concrete.In the aspect of printing process,the printing path has a great influence on the test results,and the way of steel bar placement has the least influence on both.The bonding effect between the steel bar and the printed concrete is the best with the printing path along the grain and the embedded steel bar in the way of embedding steel bar.In the test,the relative slip between the free end of the steel bar and the concrete was collected simultaneously,and the load-slip curve was drawn to obtain the bond-slip constitutive model.The calculation and simulation are carried out by Abaqus finite element software.The test specimen model was established,and the nonlinear spring element method and the bonded area element method were used for calculation.Comparing the calculated load-slip curve with the experimental data curve and the curve under the constitutive relationship,the results show that the three trends are the same,and the influence of anchoring length and anchoring position change is further analyzed by finite element.The calculation results show that under the same slip,as the anchorage length increases,the maximum stress and ultimate load of the steel bars increase.When the anchoring position is in the middle,there is no obvious change in the stress distribution around the anchoring section;when the anchoring position is close to the two ends,the stress at both ends of the anchoring zone is higher.In order to further explore the law of grip and force transfer between steel bar and printed concrete,the test method of drawing stress and strain with slotted strain gauge on the inside of steel bar was designed.The test results show that the bond strength between the steel bar of the printed specimen and the printed concrete is more than 20% higher than that of the transverse printed specimen.On the basis of summarizing the previous calculation methods of bond stress,combined with the actual situation of this paper,the previous calculation theory is improved.By comparing the bond stress distribution curves of the specimens with different fabrication methods,it is found that the bond stress distribution curve of the printed specimen along the grain is more consistent with that of the cast-in-place specimen,in contrast,the bond stress distribution curve of the transverse print specimen will appear on the local low side.Through the study of this paper,3D printing concrete with cement,sand,PVA fiber and cellulose ether as the main raw materials is designed,and on this basis,pull-out tests are carried out to study the bond properties between steel bar and printed concrete.Through the analysis of the test data,the influence of different factors on the bond properties is determined,and the bond stress distribution trends of along-grain printing,cross-grain printing and cast-in-place specimens are determined.