The Influence Of Curing Conditions On Shrinkage And Mechanical Properties Of 3D Printed Cement Mortar

3D concrete printing technology is a new construction technology for layer by layer of concrete buildings based on the principle of "additive manufacturing".3D concrete printing technology have many advantages,such as high efficiency,fast,cost saving,environmental protection and breaking through traditional design restrictions,which is regarded as an important direction of the future development of the construction industry.However,3D printing technology is no systematic and comprehensive test specification standard characterization performance parameters,compared with the traditional pouring construction,which need to further study.Thus,the study on rheological energy,volume deformation and mechanical properties of3 D printing cement mortar materials under different curing conditions is more significance need for research.First of all,the rheological properties of printable cement mortar were studied by means of rheological experiment and 3D printing workability.The effects of water-cement ratio,silica fume and thickener on the working properties of 3D printing cement mortar were investigated.The results show that the fluidity of 3D printing cement mortar increases with the increase of water-cement ratio.Silica fume,methyl cellulose ether and rubber powder can all improve the viscosity and yield stress of 3D printing cement mortar.According to the test of the rheological properties of cement paste and combined with the actual printing effect,this experiment gives a range of rheological parameters that can be printed by cement mortar,and determines the mix ratio of this test.Different curing conditions also have a great influence on the mechanical properties of 3D printing specimens.It is found that the compressive strength of the specimens cured with film mulching is always higher than that of natural curing.The size and development trend of the compressive strength of the specimen are related to the content of silica fume.Among the three groups,the specimen with the content of 10% silica fume has the best compressive strength.The effect of film curing on the strength of specimens mixed with silica fume is more obvious than that of natural curing.Steam curing makes silica fume play a good role,and the24-hour strength of steam curing is similar to the 28-day compressive strength of natural curing.Due to the special construction technology of 3D printing,the compressive strength of the specimen loaded in the vertical printing direction is greater than that in the parallel direction.In order to characterize the degree of anisotropy,the anisotropy index is also introduced in this experiment.it is found that the flexural strength has no obvious anisotropy compared with the compressive strength,and the compressive strength anisotropy of 3D printed specimens under natural curing is more obvious than that of film curing.The effects of natural curing and film curing on the interlaminar bond strength of 3D printing specimens were studied.Due to the special forming process,the connection interface between layers of 3D printing specimens is relatively weak.The interlaminar bond strength of 3D printing specimens mixed with silica fume under film curing is also higher than that of natural curing.Finally,the effects of raw materials,admixtures and curing conditions on the shrinkage of 3D printing cement-based materials were studied.It is found that silica fume will increase the shrinkage deformation value o f the specimen.The addition of thickener also aggravated the shrinkage to some extent.The shrinkage deformation of 3D printing specimen under film mulching curing is smaller than that under natural curing.