高触变混凝土设计方法与形成机理研究

In this project, a new type of high thixotropic concrete with instantaneous standup is designed and prepared based on the ideal of rapid structural buildup and breakdown from the kid’s cards toy. In concrete matrix, a special mineral admixture with card shape is chosen and incorporated to achieve instantaneous coagulation upon the removal of shear stress, which is very key to obtain a sable geometry of 3D printing concrete. In the present study, different types of layer clay minerals are selected and tested. Card shape particles with nanometer thinness are scaled off from these clay minerals by means of physical, chemical or mechanical methods and used as the mineral admixtures of 3D printing concrete. Then different types of ion (+, -) is selectively charged on the sides and faces of nano-size clay particles respectively, resulting in an obvious improvement in the rate and capacity of interparticle links. By using the microscopy, viscometer, rheometer, the whole process involving the coagulation, dispersion and re-coagulation between card clay particles and cement particles are systematically measured and characterized with or without shear stress. The important factors influencing the thixotropy are analysised. The detailed structural building and breakdown behavior is numerically simulated by using computer technology. The comparability and partnership amongst various constituents in high thixotropic concrete are established. The microstructure adjusting method is also proposed. This will provide strong scientific bases to design and prepare 3D printing concrete.

项目以儿童卡片玩具可快速组装和拆卸的思想，来设计可快速站立的高触变混凝土。通过在混凝土中引入片状外掺料，利用片状外掺料和水泥快速搭接形成絮凝结构，实现混凝土的快速“站立”，解决3D打印混凝土大流动与外观保持的难题。项目将优选多种粘土矿物，采用物理、化学或力学方法剥离纳米厚度的片状粘土作为外掺料，通过选择性吸附技术在片状粘土端部和面部浓集不同种类电荷，提高片状外掺料的搭接能力和速度。综合采用光学显微镜、旋转黏度计、混凝土流变仪等测试与表征片状粘土粒子和球形水泥颗粒复合搭接-破坏-重构形成絮凝结构的过程、速率及耗能大小，分析影响混凝土触变性能的关键因素及其规律；并利用计算机模拟技术，对混凝土卡片状絮凝结构的形成和重构进行模拟和仿真。研究混凝土各组分间配伍与相融性关系，建立高触变混凝土的微结构特征，提出调控方法，成功制备出可快速站立的高触变混凝土，为3D打印建筑材料的设计与制备奠定科学基础。

项目创新地提出了以儿童卡片玩具可快速组装和拆卸的思想，来设计可快速站立的高触变混凝土。通过在混凝土中引入片状外掺料，利用片状外掺料和水泥快速搭接形成絮凝结构，实现混凝土的快速“站立”，解决3D打印混凝土大流动与外观保持的难题。. 1）建立了层状粘土矿物的优选优化及其片状粒子的剥离与表面处理方法，采用物理、化学或力学方法从粘土矿物上剥离出纳米厚度的片状粘土作为外掺料，明显提高片状外掺料的搭接能力和速度。. 2）定量测试与表征了片状粘土粒子和球形水泥颗粒复合搭接-破坏-重构形成絮凝结构的过程、速率及耗能大小，分析了影响混凝土触变性能的关键因素及其规律；并利用计算机模拟技术，对混凝土卡片状絮凝结构的形成和重构进行模拟和仿真。. 3）设计加工了大型混凝土3D打印机，研究混凝各组分间配伍与相融性关系，建立高触变混凝土组成设计方法，揭示了微结构特征，提出组成调控方法，成功制备出可快速站立的高触变混凝土。. 4）深入剖析了可打印性能、力学性能、干燥收缩性能以及抗冻性、抗氯离子渗透、抗硫酸盐侵蚀和抗碳化等耐久性能，在实际工程中进行了示范应用，为3D打印建筑材料的设计与制备奠定科学基础。