The Preparation And Properties On Alkali-activated Cementitious Material For 3D Printing

The application of 3D printing technology in construction industry is limited to materials,The performance requirements of printing technology are different from those of traditional cement-based materials.Fly ash and slag are excited by sodium hydroxide and sodium silicate in order to produce paste which meets printing conditions.As a new green material,alkali-activated cementitious material has excellent engineering and technical properties,and it has the potential to be used in 3D printing because of its characteristics of early strong and quick setting.In this paper,orthogonal and parallel experiments are used to optimize the mix ratio scheme to prepare alkali excitation materials which can satisfy the printable performance.The effects of relative amount of raw materials,alkali components and sol ratio on their basic properties were analyzed.The microstructure was analyzed by SEM and XRD,and the relationship between microstructure and macro-properties was discussed.The performance and constructability of printing paste are studied.The results show that:1.Alkali-activated slag/fly ash system is used as 3D printing material for building,which has basic printable properties,good working performance,excellent apparent effect and considerable accumulative layers.When the flowability is in the range of 170-190mm and the number of accumulative layers is more than 4 layers,the comprehensive performance is good.2.The theoretical optimum ratio for 3D printing is as follows:the mass ratio of fly ash to slag is 3:7,the sol ratio is 0.48,alkali The content of Na₂O is 5%and the modulus is 1.4.3.The alkali content has the greatest influence on the initial fluidity and the early strength of the slurry,fly ash content has the least effect on the initial fluidity.When the content of fly ash increases from 0 to 50%,the strength of system decreases,and the fluidity decreases first and then increases.In order to obtain better fluidity and mechanical properties,the reasonable values of sol ratio and cement sand ratio are 0.46-0.48 and0.9-1.2,respectively.When the modulus of water glass increases from 0.8 to 1.4?the alkali content is 6%?,the fluidity of the slurry increases and the flexural strength and compressive strength increase.When the alkali content of Na₂O is increased from 3%to6%?the modulus of water glass is 1.2?,the fluidity of the slurry decreases,and the compressive strength increases first and then decreases.4.20min is the best printing time from mixing to initial setting.The layered loading environment and printing rate are simulated,and the function of p/s curve is fitted,which can calculate the plastic bearing capacity,print layer number and print height.