Understanding and mitigation of plastic shrinkage cracking in 3D-printed concrete elements

点击翻译按钮获取中文摘要

The 3D-printing of concrete is expected to lead to a breakthrough in the construction industry, allowing the speedy, economic, formwork-free, and less labor-intensive fabrication of buildings and structures. However, there are several obstacles to be overcome before the new technology can be generally put into practice. Plastic shrinkage and the related cracking are such major challenges since they not only compromise the durability, serviceability, and aesthetics of printed elements, but as well they may compromise form stability and limit the geometrical precision of digital construction. The reasons for plastic shrinkage cracking risk’s becoming particularly pronounced in the context of 3D-printing are 1) lack of formwork to protect fresh material from water evaporation, 2) difficulty in using curing techniques, and 3) use of material compositions with increased paste content and higher initial stiffness in comparison to ordinary concrete. The aim of this project is to gain a thorough understanding of the mechanisms of plastic shrinkage deformations and the related cracking for 3D-printed concrete elements and structures produced by extrusion-based selective material deposition techniques. On this basis, efficient strategies to mitigate plastic shrinkage cracking are to be developed. These main objectives will be accomplished stepwise in achieving the following goals: 1) Developing adequate experimental approaches to quantifying plastic shrinkage and the resulting cracking in 3D-printed concrete; 2) Developing accurate experimental methods in determining genuine material properties such as bulk modulus, coefficient of permeability, water retention behavior, tensile strength, and degree of hydration in the context of extrusion-based selective material deposition; 3) Simulating plastic shrinkage and cracking by utilizing the determined material properties and experimental verification of the simulation results obtained using the developed setups for free and restrained plastic shrinkage; and 4) Analyzing cracking mitigation methods on the basis of the simulations and experiments and assessing their efficiency. The mitigation approaches will include use of Shrinkage Reducing Admixtures (SRA), Super Absorbent Polymers (SAP), accelerators, and curing agents.