Preparation And Mechanical Properties Of Extrusion-Curing 3D Printed Concrete

The 3D printing technology is an innovative manufacturing process which can realize the printing of solid model by adding materials layer by layer on the basis of 3D digital model.It has advantages of high automation,high generation efficiency and environmental protection.Compared with the traditional construction technology,the 3D printed concrete technology has higher requirements on materials,materials used for 3D printing should have good extrudability,constructability,workability and other performance indicators.At present,the research on 3D printed concrete is still in the early stage.In this thesis,the preparation and mechanical properties of 3D printed concrete are systematically tested and numerically simulated.The specific research contents are as follows:1.Comparison and selection of test equipment and material for 3D printed concreteThe composition and function of the control system,motor system,extruding system and data processing system of a extrusion-curing type 3D printing device developed by Harbin University of Science and Technology and Center for Spatial Structure Research in Harbin Institute of Technology was introduced in this thesis.And main process in the three stages of data preparation,concrete preparation and model print were given.According to the extrudability,constructability and workability,the cementitious material,aggregate,mineral admixture,additive and fiber used in 3D printing were compared and selected.2.Study on mixing proportion of extrusion-curing 3D printed concreteThe fluidity and collapse degree were chosen as the main evaluation indicators,and the setting time was regarded as the secondary item.A series of single factor experiments were conducted to investigate the effects of water-reducing agent,retarder and latex powder on the performance of 3D printed concrete,and the dosage or dosage range of each factor was determined.On this basis,the orthogonal combination test was used and 16 groups of mixture ratio were designed.The basic mixture ratio of 3D printed concrete was determined by analyzing the influence of fluidity,slump,compressive strength and bending strength.The fiber optimization tests were performed,and the influence of a low volume usage of basalt fiber and glass fiber on the 3d/28 d compressive and bending strength of the concrete was analyzed.Finally,the proportion of fiber for reinforcing the extrusion-curing 3D printed concrete was determined.3.Study on mechanical properties of the extrusion-curing 3D printed concreteUsing the determined mixture ratio of the fiber and the 3D printing technology of extrusion-curing,concrete specimens were prepared and the axial tension,axial compression and three point bending tests were conducted.The peak bearing capacity and load-displacement curve of the specimens were obtained,and the differences between failure mode and ultimate bearing capacity of the specimens under different loading mode were analyzed.By comparing with the cast-in-place concrete,mechanical properties of the 3D printed concrete were discussed.Based on the finite element software ABAQUS,the Cohesive bond element numerical simulation method was proposed and numerical simulation on the axial tension/compression of the 3D printed concrete were carried out,and the influence parameters of inter-layer bonding performance of 3D printed concrete were obtained.Four numerical models of beam elements were built and the mechanical properties of beams were analyzed by taking 3D printing forming method as variables.The effects of interlayer defects and interstrip defects on the mechanical properties of beam elements were investigated,and the advantages and disadvantages of different printing paths were discussed.