Laboratory Study On 3D Printing Technology For Concrete Vertical Shaft Lining

In china,the depth of the new mine shafts is growing continuously,and the formation passing through becomes more complex.The traditional pouring lining technology is difficult to adapt to the development trend and requirements of the intelligent lining building,but the 3D printing concrete technology can figure out that.Therefore,it is of great significance to carry out the study of 3D printing shaft lining technology.The research on 3D printing technology of concrete shaft lining has not been reported.Unlike the 3D printing concrete structure on the ground,the 3D shaft lining not only needs high strength,but also requires high impermeability.In this dissertation,the structure of the 3D printing system for the vertical shaft lining is proposed,and the 3D printing system for the shaft lining model is integrated and developed.On this basis,the indoor test research on the 3D printing technology of high strength and high permeability shaft lining is carried out.Firstly,the printing properties of the printing materials are evaluated by the performance indexes such as fluidity,extrude,constructability and early strength.The range of the performance index of the concrete material to meet the printability is given.Secondly,in order to meet the requirements of high strength and high permeability,the printing process without layered interface is obtained,which makes the strength and impermeability of the printed concrete sample higher than that of poured sample,it also reveals the mechanism of improving the strength and impermeability of the printed concrete.The microstructural analysis and the analysis of three-dimensional X ray CT microimaging show that the pores in the printed concrete are mostly small holes(equivalent diameter 0-50 mm),while the pores in the poured concrete are mostly large holes(equivalent diameter 50-200 mm).Also the porosity of the printed concrete is about 20% lower than that of the poured concrete,which means the printed concrete is more compact.Smaller pores and lower porosity are the main mechanisms for improving the strength and impermeability of printed concrete specimens.Finally,an experimental study on the bearing capacity and impermeability of 3D printed model of concrete shaft lining is carried out.The model is impermeable until the surrounding water pressure is up to 8.8MPa.It shows that the printed model has good bearing and anti-seepage performance,and has achieved the expected effect.In this study,the strength grade of 3D printed concrete specimens is up to C70,and the 3D printed concrete shaft lining model does is impermeable below 8.8MPa water pressure.It is feasible for 3D printing concrete shaft lining with high strength and high permeability.The research results in the dissertation have important reference value and guiding significance for the development of 3D printing technology for underground structures.