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

Columbia University, New York NY

Investigators

Abstract

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.