Research And Control On Printing Performance Of 3D Printing Cement-based Materials

As a new rapid prototyping technology,three-dimensional printing(3DP)has the advantages of forming speed and high efficiency.In recent years,it is not only widely used in the fields of aerospace,electronic devices and biological materials,but also a popular research object in building field.In recent years,the material of 3DP is still limited to metal,plastic and on the like,although 3DP equipment has made an important breakthrough.And cement-based building materials commonly used are currently less studied as for 3DP material.The most important property of 3DP material is the printability.In this paper,the printability parameters of 3DP materials are studied for the way of powder printing.The effects of different treatment processes on the flow properties of the composite powders were investigated by means of changing grinding method,adding grinding aid or quartz fine sand.And the continuous flowability of cement powder was realized.The effect of different content of admixtures on the coagulation time of sulphoaluminate cement was also studied,to achieve the coagulation time of cement powder controllable.The solid foundation is laid for the applications of sulphoaluminate cement in the field of 3DP.The main conclusions are as follows:The flow performance of the composite power(1)The effect of grinding methods on the flowability of cement powder is obviously different.The addition of grinding aid can significantly improve the flow property of the composite powder.The continuous flowability of the composite powder which grinded by adding the grinding aid can be achieved when only a little quartz fine sand was added.When the content of grinding aid is 0.5%,the flow property of the composite powder is the best,then is 0.2% and the 1% is worst.The flow property of composite powder by alcohol wet grinding also can be improved,and the best grinding time is 30 min.However,ordinary dry grinding method has no obvious effect on the flow property of the composite powder.Furthermore,it is found that the composite powder of which the internal porosity is less than 75% has a continuous flowability.And the better the flow property is,the closer the internal porosity is to 71%.Regulation of curing time of composite cement powder:(1)The basic formula of cement powder was determined by compound of cement and addition of lime.We can see that a small amount(<10%)of ordinary Portland cement is favorable to the early coagulation hardening of the sulphoaluminate cement system.The effect of lime on the composite cement system which is compounded with a small amount of quartz sand(5%)(SS System)or a large amount of quartz sand(50%)(LS System)is very obvious,resulting in a remarkable reduction in the coagulation time of composite powder slurry.(2)Study on the control of curing time of composite powder system with different admixtures:In SS System,the curing time decreases: A salt>C salt>B salt.While in LS System,the curing time decreases: A salt>B salt>C salt.The effect of A salt in two systems both is especially obvious,can significantly improving the coagulation time of composite cement powder system.From the overall perspective,the initial preparation of the composite cement powder slurry can be controlled in 1.17 min-4min and final curing time in 1.5 min-5min,through changing admixtures,adjusting the dosage of admixtures and other means.