Collaborative Research: Engineering Fracture Response and Transport Behavior in Additively Manufactured, Layered Concrete Materials

本研究致力于开发性能增强的新一代3D打印胶凝材料。在基础设施和住房建设中，正在开发分层的3D打印混凝土组件。然而，由于机械性能和耐久性不太令人满意，这些部件在建筑业的广泛采用受到了阻碍。因此，更好地了解和提高3D打印混凝土材料的性能是当务之急。这项研究将从根本上了解3D打印混凝土在微米级的内部布置，并探索层沉积以定制这些新型材料的内部结构，提高力学和断裂性能，以及长期耐久性和安全性。这项研究将推动知识的边界，带来变革性的工程解决方案、广泛的影响和可转移到使用混凝土的大规模应用中的建议，如家庭、建筑、道路和桥梁。这项研究的发现有可能改进传统的混凝土基础设施，如提前养护和滑模施工。教育和推广活动将为学生(包括研究生、本科生和K-12学生)提供机会，了解土木工程领域的新方向和职业前景。研究将在几个时间和空间尺度上实现对3D打印混凝土物理的基础了解。材料表征将在挤压、3D打印和硬化阶段进行，使用中子射线照相术、微型计算机断层照相术、X射线衍射以及界面区和细丝的元素图。这项研究将回答有关挤压过程中涉及的机理的基本问题，例如所谓的“润滑层”的形成。研究将检验这种富水层在沉积前、沉积后(在编织/粘合期间)可以去均质和控制管/桶内的空间水分布的假设方式，以及围绕界面的孔隙网络和水合物的空间形态和连通性。然后，这些知识将被用来告知设计材料的内部结构，目标是定制断裂响应和传输行为。通过对内部螺旋结构界面的弱属性进行工程设计，本研究将基于线弹性断裂力学原理来提高3D打印胶凝材料的混合模式断裂韧性。通过设计故意缺陷和定制孔隙网络的形态，这些材料中的流体传输行为将得到控制。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This research focuses on the development of a new generation of 3D-printed cementitious materials with enhanced performance. Layered, 3D-printed concrete components are being developed in infrastructure and housing construction. However, broad adoption of these components by the construction industry is impeded by less-than-satisfactory mechanical properties and durability. As such, there is an urgency to better understand and improve performance of 3D-printed concrete materials. This research will gain fundamental understanding of the internal arrangements of 3D-printed concrete at the micron scale and explore layer deposition to tailor the internal structure of these novel materials and enhance mechanical and fracture properties, as well as the long-term durability and safety. This research will push forward the boundaries of knowledge, leading to transformative engineering solutions, broad implications, and recommendations transferable to large-scale applications where concrete is used, such as homes, buildings, roads, and bridges. Findings from this research has the potential to improve conventional concrete infrastructures, such as advancing curing and slip-form construction. The educational and outreach activities will provide opportunities for students (including graduate, undergraduate, and K-12 students) to learn about new directions and career prospects in civil engineering.The research will achieve a foundational understanding of the physics of 3D-printed concrete in several temporal and spatial scales. Material characterization will be conducted during extrusion, 3D-printing, and hardening stages using neutron radiography, micro-computed tomography, X-ray diffraction, and elemental mapping of interfacial zones and filaments. The research will answer fundamental questions about the mechanisms involved in the extrusion process, such as the formation of a so-called “lubrication layer”. The research will examine the hypothesized ways in which this water-rich layer can de-homogenize and control the spatial water distribution within the tube/barrel prior to deposition, after deposition (during the knitting/bonding), and the spatial morphology and connectivity of the pore network and hydrated compounds surrounding the interfaces. The knowledge will then be used to inform designs of the internal architecture of the material with the goal of tailoring fracture response and transport behavior. By engineering the weak attributes of the interfaces with internal helical architectures, this research will enhance mixed-mode fracture toughness in 3D-printed cementitious materials based on linear elastic fracture mechanics principles. By engineering intentional flaws and tailoring the morphology of the pore network, the fluid-transport behavior in these materials will be controlled.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.