Development Of 3D Printing Support Material For Shaft Lining

The technology application of 3D printing concrete has been widely studied in civil engineering industry,but still has several outstanding problems,in particular the printing layer accumulation and the waterproof of interlayers.To address this challenge,the dissertation develops materials of 3D printing concrete shaft lining,which could provide suitable materials for the research of high efficiency support technology of shaft lining.The main research achievements of this dissertation are as follows:Firstly,the effects of the amount of water reducing agent,accelerator,retarder,starch ether,thixotropic agent,and the fine modulus of sand on the concrete flow,slump,setting time and strength are analyzed by single factor and orthogonal test.According to that,the mix ratio of 3D printing concrete suitable for shaft lining is obtained.The test results show that the mix ratio makes the concrete has good extrudability.Adding appropriate amount of aluminate cement into ordinary portland cement or using the fast-hard sulphoaluminate cement can shorten the setting time greatly,thus the requirement of rapid condensation can be realized.Secondly,in order to get the best mix ratio of 3D printing concrete suitable for shaft lining,three indexes of extrudability,constructability and opening time are adopted to evaluate the printing performance of various mix ratios.The test results show that the single component of ordinary portland cement has better extrudability and longer opening time,but poor accumulation.The formula of aluminate cement on the basis of ordinary portland cement formula can not only meet the better fluidity and opening time,but also solve the problem of accumulation,which can be played more than 120 cm high in a short time and only produces a small deformation.The formulation of fast-hard sulphoaluminate cement cannot meet the printing requirements because the setting speed is too fast.The test establishes the performance characteristics of new mixed concrete suitable for printing,such as the fluidity,slump,opening time,penetration resistance value and yield strength,which provide the basis for the subsequent printing performance evaluation.Finally,the printing test results show that the defect of the printing block are less than that of pouring block.Specific performances: the density of the printing specimen is increased by about 0.4% and the porosity is reduced by about 3% to 10%.The permeability coefficient of the printing block is about 20% of the pouring block,and there is no obvious defect and cold joint between the layers.For the material strength,the strength of the printing block reaches 50 MPa ~ 60 MPa,which is 39.9% higher than that of the pouring block,the maximum compressive strength of the printing specimen for 28 days is 65.2MPa,which is greater than the 46.6MPa of the cast test block.The flexural strength of the printing specimen is 4.5 to 5MPa larger than the pouring block,4.5MPa.The splitting tensile strength of the printing block is 3.7 to 4.2MPa,which is larger than that of the pouring block,3.4MPa.In the hydrostatic test,the printing model can bear the maximum 9.74 MPa water pressure,which means the strength of the printing material meets the requirements.To sum up,the dissertation obtains the concrete material formula for the 3D printing of the shaft lining,the 3D printing concrete of this formula has good fluidity,rapid prototyping construction and sufficient opening time.The 3D printing shaft lining has a good integrity and satisfied strength,and the printing layer is tightly bonded without cold seam.The developed concrete formula provides the suitable material for the research of high efficiency support technology of shaft lining.