论文总字数：31847字

摘 要

混凝土是当今建筑材料中使用最大宗和最广泛的土木工程材料，但由于其在建造过程中对于模具的需求导致材料耗费，能源资源的浪费及人工成本等大大提高。近些年，随着3D打印技术的快速发展，将混凝土技术与3D打印技术相结合，不仅降低建造成本，提高施工效率、节约自然资源，同时也大大增加了建筑设计的自由度及增加建筑设计的复杂性。但其对于可打印的混凝土材料的各项性能有更高的要求。针对3D打印混凝土逐层累加的成型过程，其硬化力学强度必然存在各向异性特征。且作为建筑构件的基体，其不仅要满足强度需要，耐久性能也必须满足实际工程的要求。因此，本文针对建筑3D打印构件，对硬化3D打印混凝土的基本力学性能，各向异性及耐久性开展研究，以期为混凝土3D打印技术在实际工程中的应用提供理论支撑。

本文通过抗压、抗折及抗拉强度实验，研究3D打印混凝土的硬化基本力学性能和各向异性，基于压汞实验（Mercury intrusion porosimetry，MIP）和X射线断层扫描实验（Computer Tomography，CT）扫描，观察其孔隙大小及分布。同时进行干燥收缩、干湿循环、冻融循环和氯离子侵蚀实验，对比观察3D打印混凝土和对应配合比的浇筑混凝土的耐久性。

试验结果表明：3D打印混凝土和对应配合比的浇筑混凝土相比，抗压和抗折强度更高、抗拉强度更低；存在明显的各向异性，根据加载方向不同抗压和抗折强度大小呈T1gt;T2gt;T3分布，可选用交叉打印路径成型降低各向异性。3D打印混凝土干缩应变在800微应变左右，持续时间一般不超过90d；150次冻融循环后，质量损失率最高1.87%，表面只出现坑蚀；氯离子渗透系数1.8710^-12m²/s~ 3.410^-12m²/s；干湿循环过程中抗压强度呈先升后降趋势，前90次循环强度持良好。上述结果说明，除抗拉强度和抗氯离子侵蚀能力外的基本硬化性能和耐久性，3D打印混凝土均优于浇筑混凝土。基于上述结果，进行MIP和CT测试进行验证。最终得出结论：3D打印混凝土存在显著力学各向异性，但硬化性能和耐久性不会成为实际工程应用的限制因素。

关键词：3D打印混凝土;力学性能;各向异性;耐久性能

Study on Anisotropy and Durability of 3D Printing Concrete

Abstract

Concrete is the largest and most widely used civil engineering material in building materials nowadays, but because of its demand for moulds in the construction process, material consumption, waste of energy resources and labor costs are greatly increased. In recent years, with the rapid development of 3D printing technology, the combination of concrete technology and 3D printing technology not only reduces construction costs, improves construction efficiency and saves natural resources, but also greatly increases the freedom of architectural design and increases the complexity of architectural design. However, it has higher requirements for the properties of printable concrete materials. In view of the cumulative forming process of 3D printing concrete layer by layer, its hardening mechanical strength must have anisotropic characteristics. As the base of building components, it not only meets the strength requirements, but also the durability requirements of practical projects. Therefore, in this paper, the basic mechanical properties, anisotropy and durability of hardened 3D printing concrete are studied for building 3D printing components, in order to provide theoretical support for the application of concrete 3D printing technology in practical engineering.

In this paper, the basic mechanical properties and anisotropy of 3D printing concrete are studied by compressive, flexural and tensile strength experiments. Based on Mercury intrusion porosimetry (MIP) and X-ray tomography (CT) scanning, the pore size and distribution are observed. At the same time, the experiments of drying shrinkage, drying-wetting cycle, freezing-thawing cycle and chloride ion erosion were carried out to observe the durability of 3D printing concrete and the corresponding mix proportion of pouring concrete.

The experimental results show that the compressive and flexural strength of 3D printed concrete is higher and the tensile strength is lower than that of the corresponding mix proportion of poured concrete. There is obvious anisotropy. According to the different compressive and flexural strength of the loading direction, the distribution is T1 gt; T2 gt; T3, and the cross printing path can be chosen to reduce the anisotropy. The drying shrinkage strain of 3D printed concrete is about 800 micro-strain and lasts less than 90 days. After 150 freeze-thaw cycles, the highest mass loss rate is 1.87%, and only pitting corrosion occurs on the surface. The chloride ion permeability coefficient is 1.87*10^-12m²/s~3.4*10^-12m²/s. The compressive strength increases first and then decreases, and the first 90 cycles are good. The above results show that besides tensile strength and chloride ion corrosion resistance, 3D printed concrete is superior to cast concrete in basic hardening performance and durability. Based on the above results, MIP and CT tests were carried out to verify the results. Finally, it is concluded that there is significant mechanical anisotropy in 3D printing concrete, but hardening performance and durability will not be the limiting factors in practical engineering applications.

Keywords: 3D printing concrete; hardened properties; durability; anisotropy;

目 录

摘 要 I

Abstract III

第一章 绪论 1

1.1研究背景 1

1.2国内外研究现状 2

1.2.1国外研究现状 3

1.2.2国内研究现状 5

1.3存在的问题 8

1.4研究内容及技术路线 8

1.4.1研究内容 8

1.4.2技术路线 9

1.5创新点 9

第二章 原材料及试验方法 10

2.1原材料 10

2.1.1水泥 10

2.1.2细集料 11

2.1.3掺合料 11

2.1.4聚丙烯纤维 11

2.1.5减水剂 11

2.1.6增稠剂 11

2.1.7水 11

2.2试验方案 11

2.2.1配合比设计 11

2.2.2试样准备 12

2.2.3成型及养护 13

2.3试验方法 13

2.3.1抗冻实验 13

2.3.2抗氯离子渗透试验 15

2.3.4干湿循环 17

2.3.4干燥收缩 17

2.3.5抗压及抗折强度试验方法 18

2.3.6抗拉强度试验方法 19

2.3.7压、拉和弯曲各向异性 19

2.4本章小结 20

第三章 3D打印混凝土基本力学性能研究 21

3.1抗压强度 21

3.2抗折强度 22

3.3抗拉强度 22

3.4本章小结 23

第四章 3D打印混凝土各向异性研究 24

4.1抗压和抗折各向异性 24

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