By studying the effect of different dosages of hydroxypropyl methylcellulose (HPMC) on the printability, rheological properties and mechanical properties of 3D printing mortar, the appropriate dosage of HPMC was discussed, and its influence mechanism was analyzed combined with the microscopic morphology. The results show that the fluidity of mortar decreases with the increase of the content of HPMC, that is the extrudability decreases with the increase of the content of HPMC, but the fluidity retention ability improves. Extrudability; shape retention rate and penetration resistance under self-weight increase significantly with the increase of HPMC content, that is, with the increase of HPMC content, stackability improves and printing time is prolonged; from the point of view of rheology, with With the increase of the content of HPMC, the apparent viscosity, yield stress and plastic viscosity of the slurry increased significantly, and the stackability improved; the thixotropy first increased and then decreased with the increase of the content of HPMC, and the printability improved; the content of HPMC increased Too high will cause the mortar porosity to increase and the strength It is recommended that the content of HPMC should not exceed 0.20%.
In recent years, 3D printing (also known as “additive manufacturing”) technology has developed rapidly and has been widely used in many fields such as bioengineering, aerospace, and artistic creation. The mold-free process of 3D printing technology has greatly improved material and The flexibility of structural design and its automated construction method not only greatly saves manpower, but also is suitable for construction projects in various harsh environments. The combination of 3D printing technology and the construction field is innovative and promising. At present, cement-based materials 3D The representative process of printing is the extrusion stacking process (including the contour process contour crafting) and concrete printing and powder bonding process (D-shape process). Among them, the extrusion stacking process has the advantages of small difference from the traditional concrete molding process, high feasibility of large-size components and construction costs. The inferior advantage has become the current Research hotspots of 3D printing technology of cement-based materials .
For cement-based materials used as “ink materials” for 3D printing, their performance requirements are different from those of general cement-based materials: on the one hand, there are certain requirements for the workability of freshly mixed cement-based materials, and the construction process needs to meet the requirements of smooth extrusion, On the other hand, the extruded cement-based material needs to be stackable, that is, it will not collapse or deform significantly under the action of its own weight and the pressure of the upper layer. In addition, the lamination process of 3D printing makes the layers between layers In order to ensure the good mechanical properties of the interlayer interface area, the 3D printing building materials should also have good adhesion. In summary, the design of the extrudability, stackability, and high adhesion is designed at the same time. Cement-based materials are one of the prerequisites for the application of 3D printing technology in the field of construction. Adjusting the hydration process and rheological properties of cementitious materials are two important ways to improve the above printing performance. Adjustment of the hydration process of cementitious materials It is difficult to implement, and it is easy to cause problems such as pipe blockage; and the regulation of rheological properties needs to maintain the fluidity during the printing process and the structuring speed after extrusion molding.In the current research, viscosity modifiers, mineral admixtures, nanoclays, etc. are often used to adjust the rheological properties of cement-based materials to achieve better printing performance.
Hydroxypropyl methylcellulose (HPMC) is a common polymer thickener. The hydroxyl and ether bonds on the molecular chain can be combined with free water through hydrogen bonds. Introducing it into concrete can effectively improve its cohesion. and water retention. At present, the research on the effect of HPMC on the properties of cement-based materials is mostly focused on its effect on fluidity, water retention, and rheology, and little research has been done on the properties of 3D printing cement-based materials (such as extrudability, stackability, etc.). In addition, due to the lack of uniform standards for 3D printing, the evaluation method for the printability of cement-based materials has not yet been established. The stackability of the material is evaluated by the number of printable layers with significant deformation or the maximum printing height. The above evaluation methods are subject to high subjectivity, poor universality, and cumbersome process. The performance evaluation method has great potential and value in engineering application.
In this paper, different dosages of HPMC were introduced into cement-based materials to improve the printability of mortar, and the effects of HPMC dosage on 3D printing mortar properties were comprehensively evaluated by studying printability, rheological properties and mechanical properties. Based on properties such as fluidity Based on the evaluation results, the mortar mixed with the optimal amount of HPMC was selected for printing verification, and the relevant parameters of the printed entity were tested; based on the study of the microscopic morphology of the sample, the internal mechanism of the performance evolution of the printing material was explored. At the same time, the 3D printing cement-based material was established. A comprehensive evaluation method of printable performance in order to promote the application of 3D printing technology in the field of construction.
Post time: Sep-27-2022