Preparation And Mechanical Properties Of 3D Printed Polymer Lattice Reinforced Cementitious Composite Materials

Cement-based materials are widely used in the field of civil engineering due to their high compressive strength.However,in concrete structures,the inherent brittleness and low tensile strength of cementitious materials require them to work together with steel bars with strong plasticity and high tensile strength.However,the construction strength and difficulty of traditional(high reinforcement ratio)steel reinforcement cages are high,and they are prone to corrosion in corrosive environments.The randomness of fiber distribution in traditional fiber-reinforced cementitious materials has to some extent constrained the development of cementitious materials.3D printing technology has promoted the manufacturing of complex lattice structures.lattice reinforced cement-based materials have the ability to improve the brittleness and ductility of cementitious materials,providing new solutions for the reinforcement of cement-based materials,which has aroused great interest among scholars.However,there is relatively little research on the performance of 3D printed lattice reinforced cementitious materials,and there is not much research on the factors that affect performance,failure mechanisms,and failure characteristics.There is a lack of effective characterization methods for the deformation and damage of lattice reinforced specimens under load,and it is necessary to continue to optimize structural design and experimental methods,and conduct research on maximum bearing capacity and failure modes.This study starts from a uniform lattice structure composed of a single unit cell,and investigates the bending and compressive mechanical properties of 3D printed polymer lattice reinforced cement-based composites with different structural forms;Starting from the graded lattice structure composed of gradient unit cells,the bending mechanical properties of 3D printed polymer graded lattice reinforced cement-based composites with variable volume fraction were studied.The main content is as follows:In the study of bending mechanics of 3D printed polymer lattice reinforced cementitious materials with different structural forms,the volume reinforcement ratio of five uniform lattices was controlled to be the same,and the three-point bending performance of uniform lattice reinforced cement mortar with different structural forms was tested.Compare the differences in mechanical properties between the control group and the lattice reinforcement group using AE and DIC methods.The results show that the response of uniform lattice reinforced cement mortar specimens under three-point bending load can be divided into initial compaction stage,elastic stage,plastic stage,brittle cracking stage,reloading stage,and failure stage.The cracking load of all lattice reinforced cement-based specimens cannot be significantly increased.Casting cementitious materials to the lattice can effectively reduce the number of AE Hits before brittle cracking and reduce the peak frequency of brittle cracking in cement mortar.The maximum strain of the lattice reinforced specimen during cracking is higher than that of the plain cement mortar specimen.In the study of compressive mechanics of 3D printed polymer lattice reinforced cementitious materials with different structural forms,the volume reinforcement ratio of six uniform lattices was controlled to be the same,and the compressive mechanical properties of cement mortar reinforced with uniform lattices of different structural forms were tested.Compare the differences in mechanical properties between the control group and the lattice reinforcement group using AE and DIC methods.The results show that the compressive strength of the uniform lattice reinforced cement mortar specimens is higher than that of the plain cement mortar group.Lattice reinforcement in cement-based materials can reduce the lateral expansion deformation of cement mortar under vertical compressive load,improve the compressive bearing capacity of cement mortar,and transform from a single large crack in plain cement mortar to a failure mode of multiple small cracks.The deformation mechanism of the lattice under uniaxial compressive load has little effect on the deformation mechanism of its reinforced cement mortar.The reinforcement mechanism of the lattice on cement mortar under uniaxial compressive load mainly includes limiting lateral expansion deformation,preventing the extension and expansion of internal cracks in cement mortar,and dowel action.In the study of bending mechanics of 3D printed polymer graded lattice reinforced cementitious materials,six volume fraction cells were designed based on Cubic cells,with bending and tensile deformation as the main deformation.Five graded lattice structures were designed based on the load characteristics of the three-point bending test;At the same time,a skin lattice structure and a uniform lattice structure were designed,and a control group of plain cement mortar was set up to comprehensively evaluate the bending mechanical properties of graded and uniform lattice reinforced cement-based materials.The results indicate that the arrangement of a uniform lattice with low volume fraction of single cells and a single layer lattice in the tensile zone cannot significantly improve the maximum bending bearing capacity of cement-based materials.Gradient lattices with high volume fraction across the mid-span cannot increase the cracking load of cement-based materials.But it can significantly improve the maximum bending bearing capacity of cement-based materials,improve cracking characteristics and failure modes,along with the lattice with skin.The failure modes of the cementitious composites reinforced with a graded lattice or a lattice with skin respectively changed from the brittle fracture failure of a single crack to the ductile failure of multiple cracks,and from the tensile failure of the plain cementitious matrix to the flexural shear failure of the lattice and cementitious matrix.The deformation mechanism of lattice reinforced cementitious specimens with skin is similar to that of beams without stirrups reinforcement in concrete structures.The deformation mechanism of graded lattice reinforced cementitious specimens is similar to that of beams with stirrups reinforcement in concrete structures.This study further demonstrated the feasibility of preparing 3D printed lattice reinforced cementitious materials.DIC and AE methods were used to reveal the strain field evolution,denaturation characteristics,crack formation and propagation,failure modes,and damage mechanisms of lattice reinforced cementitious materials under bending and compression.It was confirmed that 3D printed lattices can improve the ductility,delay cracking,and increase the maximum bending/compressive bearing capacity and deformation capacity of cementitious materials.