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

3D打印或数字制造胶凝材料可以直接从数字模型中自动生产连续层的建筑元素或整个结构。自动化和控制方面的最新进展使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打印在建筑领域的一个主要优势是，它有可能通过创新的几何形状来增强建筑性能，否则这是无法实现的。该项目的前提是，随着3D打印胶凝材料的广泛接受，重点将转移到材料的设计和加工上，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系统，如碱活化粘结剂，可以设计为基于挤压的加工提供有利的性能（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得到利用。目的是将3D打印的可持续粘合剂系统的材料设计与打印本身的过程联系起来。该研究成果将使碱活化粘合剂在3D打印混凝土元件中的使用成为可能，并为工业企业开辟新的途径。该项目利用了多学科的知识（结合材料的化学，颗粒介质的流动，材料处理，计算建模），为可持续混凝土元素的3D打印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，以实现理想的流变学和早期硬化响应。将评估浆料性质（颗粒类型及其化学性质和尺寸、活化剂化学性质、流变性助剂）和挤出机特性（尺寸和几何形状、挤出压力）的影响，包括它们之间的相互作用，以更好地了解打印材料的流变性。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）建立颗粒尺度机制与过程级挤压流变之间的联系。这项研究也将有助于我们理解和潜在的缓解液相迁移、覆盖层相关的不稳定性和分层效应，这些都是基于挤压的3D打印所特有的。综合活动将增强我们对高性能可持续混凝土粘合剂系统3D打印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.