CAREER: Tailoring Rheological Behavior and Interlayer Properties of 3-D Printing Concrete

该学院早期职业发展(CALEAR)奖是研究3-D混凝土打印，通过自动化过程逐步添加新混凝土来构建整个结构元素和结构。建筑业的进展是渐进的。这项新技术有可能彻底改变我们建造和修复基础设施的方式。与传统的静态模板浇注相比，三维混凝土打印的主要优势之一是消除了模板的使用和加固所需的振动。这可以减少因模板而产生的材料和人工成本，减少材料浪费，缩短施工时间，并减少人为错误。同时，无成形和无振动铸造对实现最终结构的预期性能、适用性和美观性提出了重大的材料工程挑战。该奖项支持基础研究，为开发专门为3-D打印应用量身定做的混凝土系统提供必要的知识，其中新鲜混凝土必须既可打印，又必须在凝固后显示所需的特性。这项工作将很容易被整合到一个更广泛的外展和教育项目--基础设施加工和技术流变学(P.R.I.N.T.)中，以向人们灌输基础设施中的颠覆性创新在多学科的科学和工程研究中具有坚实的基础。3-D混凝土打印的关键挑战包括实现沉积混合料的足够形状稳定性、预测工作时间和控制打印速度。该项目的目的是通过识别和表征基本流变参数来解决这些问题，以定量描述新鲜水泥基材料的可逆和不可逆硬化行为，然后将这些参数与材料系统对印刷过程的结构响应联系起来。通过实施旨在模拟印刷过程的稳态和准静态剪切流变学方案来表征达到设定的粘弹性特性，从而提出混合设计方法，以提高沉积后印刷层的形状稳定性和控制工作时间。泵送压力和印刷速度之间的关系将建立在糊料的稳态流变特性的基础上，模拟润滑层和砂浆的剪切诱导颗粒迁移动力学。此外，层层3D混凝土打印引入了对夹层的额外考虑，这对这种建筑技术来说是新颖和独特的。由此得到的印刷样品中间层的微观结构将被表征，然后通过调整材料的粘弹性属性和相变进行细化，然后与印刷元件的最终机械性能联系在一起。

This Faculty Early Career Development (CAREER) award is to study 3-D concrete printing, incremental addition of fresh concrete through an automated process to build entire structural elements and structures. Advances in the construction sector have been incremental. This novel technique has the potential to revolutionize the way we construct and repair our infrastructure. One of the major advantages of 3-D concrete printing over conventional static formwork casting is the elimination of the use of formwork and vibration typically necessary for consolidation. This can reduce material and labor costs due to formwork, reduce material waste, cut construction time, and reduce human error. At the same time, form-free and vibration-free casting presents a significant materials engineering challenge to achieve the desired performance, serviceability, and aesthetics of the final structure in place. This award supports fundamental research to provide needed knowledge for the development of concrete systems specifically tailored for 3-D printing applications, where the fresh concrete must be both printable and exhibit the desired properties once it sets. The work will be readily integrated into a broader outreach and education program, Processing and Rheology for Infrastructure and Technology (P.R.I.N.T.), to instill that disruptive innovations in infrastructure have strong underpinnings in multidisciplinary science and engineering research.Key challenges of 3-D concrete printing include achieving sufficient shape stability of the deposited mix, predicting working time, and controlling print speed. The aim of the project is to address each of these issues by identifying and characterizing fundamental rheological parameters to quantitatively describe the reversible and irreversible stiffening behavior of fresh cement-based materials, then tie these parameters to the structural response of the material system to the printing process. The viscoelastic properties up to setting will be characterized by implementing steady-state and quasi-static shear rheological protocols designed to simulate the printing process, from which mix design methodologies will be proposed to enhance shape stability of printed layers after deposition and control working time. A relationship between pumping pressure and print speed will be formulated based on the steady-state rheological properties of pastes modeling the lubrication layer and shear-induced particle migration kinetics of mortars. Further, layer-by-layer 3-D concrete printing introduces an additional consideration of the interlayer, which is novel and unique to this construction technique. The resulting microstructure of the interlayer in printed samples will be characterized and then refined through adjusting the viscoelastic properties and phase change of the material, then tied to the final mechanical performance of the printed element.