Study On Optimizing Formula Of 3D Printing Concrete And Its Hardening Performance For Vertical Shaft Lining

With the progress and development of science and technology,3D printing technology has carried out a great deal of research in the field of building at home and abroad,very few people have studied in the field of vertical shaft lining,and the shaft lining is easy to leak at the joint seam,shaft lining poured can not meet the needs of intellectualization gradually.3D printing concrete technology will be an important way to realize automation,intellectualization and rapid construction of complex shaft lining in the future.In view of the fact that ordinary concrete does not meet the printing requirements and provides 3D printing supporting materials for vertical shaft lining.In this paper,single factor analysis test,orthogonal combination test and optimum design test were carried out to determine the reasonable mix proportion of 3D printing concrete,and the physical and mechanical properties of specimens with two printing processes were studied.Firstly,taking fluidity,slump and setting time as main evaluation indexes and compressive strength as secondary evaluation indexes,the effects of fineness modulus,sand-binder ratio,dosage of superplasticizer and R.SAC on printing concrete are analyzed by single factor,the optimum proportion or dosage range of each influencing factor was determined,based on single factor analysis test,the multi-factor orthogonal test was carried out,and the basic mix proportion of 3D printing concrete was determined.Considering the disadvantage of calcium formate and the influence of temperature of pouring shaft lining,anhydrous calcium sulfate was used in place of calcium formate.By adjusting mix proportion,the mix proportion of 3D printing concrete with ambient temperature of(20±2)°C and(24±2)°C was determined preliminarily.Finally,the reasonable mix proportion of 3D printing concrete with different environmental temperature was determined through the evaluation of extrusion,construction and mechanical properties.The 1d compressive strength of different mix proportion can reach 28 MPa,and specimens are kept in water at 50°C for three days,its compressive strength can reach more than 54 MPa.Secondly,the physical and mechanical properties of the specimens taken from two printing processes and the specimens poured were compared,it was found that the early compressive strength,flexural strength,splitting tensile strength and mechanical properties of specimens by the two printing processes decreased slightly,but improved slightly in the later stage,and there was no obvious anisotropy and different mechanical properties caused by the process due to layer upon layer pileing up.It was verified that the strength growth of hardened printing concrete was mainly affected by the microscopic pore structure by density and microstructure analysis,the printing concrete was rotated and compacted to improve the pore structure,reduced the porosity and improve the compactness.Finally,the vertical shaft lining is printed with the developed mix proportion of 3D printing concrete and its impermeability is studied.The horizontal loading of 6.8MPa can be withstood by the incomplete restraint at the end of the shaft lining,the shaft lining completely confined can withstand more than 11.4MPa.With the increase of horizontal loading,the difference of circumferential strain in the same or different layers of shaft lining increases gradually.Based on above research results,the mix proportion of 3D printing concrete with different ambient temperatures were put forward,which took into account the effect of fluidity,constructability and setting time,It was found that a good printing process does not cause a weak layer-to-layer to the printed structure.The impermeability and sealing performance of the vertical shaft lining by 3D printing was preliminarily determined.