Understanding Materials and Processing Related Effects in 3D Printing of Sustainable Cementitious Materials

水泥材料的3D打印或数字制造可以直接从数字模型自动生产连续层的建筑元件或整个结构。自动化和控制的最新进展使3D混凝土打印技术成熟，使坚固的建筑成为可能。这一过程有可能减少现场劳动力和能源需求，加快施工过程，并降低施工相关风险。除了降低成本和加快施工速度外，3D打印在建筑中的一个主要优势是它有可能通过创新的几何形状来增强建筑性能，而这是无法实现的。该项目的前提是，随着水泥材料3D打印的广泛接受，重点将转向材料设计和加工，以确保性能，长期耐用性和可持续性。可持续的无水泥粘结剂体系如碱活化粘结剂可被设计为提供用于基于挤出的加工的有利性质（例如，早期硬化），这将通过有针对性的实验和计算机模拟在本项目中使用。其目标是将3D打印可持续粘合剂系统的材料设计与打印过程本身联系起来。研究成果将使碱活化粘合剂能够在3D打印混凝土元件中使用，并为工业企业开辟新的途径。 该项目利用多个学科的知识（粘合材料的化学，颗粒介质的流动，材料加工，计算建模），为可持续混凝土元件的3D打印的科学和工程做出贡献。该研究将包括用于3D打印的碱活化粘合剂的成分操作，以实现理想的流变和早期硬化反应。将评估糊剂性质（颗粒类型及其化学性质和尺寸、活化剂化学性质、流变助剂）和挤出机特性（尺寸和几何形状、挤出压力）的影响，包括它们的相互作用，以更好地理解印刷材料的流变性。基于离散单元的数值模型将用于：（i）阐明影响流动的颗粒尺度过程，（ii）准确预测流动行为，以及（iii）建立颗粒尺度机制和过程级挤出流变学之间的联系。这项研究也将大大有助于我们理解和潜在的缓解液相迁移，超载相关的不稳定性和分层效应，这是基于挤出的3D打印所独有的。这些综合活动将增强我们对高性能可持续混凝土粘结剂系统3D打印中材料设计和加工效果的基本理解。

3D printing or digital fabrication of cementitious materials enables automated production of building elements or whole structures in successive layers, directly from digital models. Recent advances in automation and control has enabled maturing of 3D concrete printing technology to make robust construction possible. This process has the potential to reduce on-site labor and energy requirement, speed up the construction process, and reduce construction-related risks. A major advantage of 3D printing in construction, apart from cost reduction and acceleration of construction, is its potential to provide enhancements in building performance through innovative geometries that otherwise cannot be realized. This project builds on the premise that, with wider acceptance of 3D printing of cementitious materials, the emphasis will shift to materials design and processing to ensure performance, long-term durability, and sustainability. Sustainable cement-free binder systems such as alkali-activated binders can be designed to provide advantageous properties for extrusion-based processing (e.g., early stiffening), which will be utilized in this project through targeted experiments and computer simulations. The objective is to link the material design of sustainable binder systems for 3D printing and the process of printing itself. The research outcomes will enable the use of alkali-activated binders in 3D printed concrete elements, and open new avenues for industrial ventures. This project harnesses knowledge from multiple disciplines (chemistry of binding materials, flow of granular media, materials processing, computational modeling) to contribute to the science and engineering of 3D printing of sustainable concrete elements. The research will include compositional manipulations of alkali-activated binders for 3D printing in order to achieve desirable rheological and early-age stiffening response. The influence of paste properties (particle types and their chemistry and sizes, activator chemistry, rheology aids) and extruder characteristics (sizes and geometry, extrusion pressure), including their interactions, will be evaluated to better understand the resulting rheology of the printed material. Discrete element-based numerical models will be used to: (i) elucidate the particle-scale processes influencing flow, (ii) accurately predict the flow behavior, and (iii) establish the link between particle-scale mechanisms and process-level extrusion rheology. This study will also contribute significantly to our understanding and potential mitigation of liquid phase migration, overburden-related instability, and layering effects which are unique to extrusion-based 3D printing. The integrated activities will enhance our fundamental understanding of material design and processing effects in 3D printing of high-performance sustainable concrete binder systems.