Laboratory framework for understanding mix formulation for 3D printed cementitious materials

Over the recent years, additive manufacturing has gained significant traction in the arena of automated construction application via 3D printing of concrete. Unlike the regular concrete construction, 3D printing of concrete is carried out through extrusion of cementitious materials controlled digitally to print out pre-assigned architectural and structural components. Current research is focused on efficient automation of 3D concrete printers and printability of such structures. However significant fundamental research on rheology of such cementitious mixtures are absent. Before a large scale print job is undertaken it is crucial to predetermine the rheological properties and printability of the cementitious mixtures. The commonly used rheological model for fresh state concrete is the Bingham model. Since 3D printed cement-based materials are variant in mixture designs due to incorporation of various powder additives and chemical admixtures to achieve the unique processing methods that are needed for printing, an appropriate rheological model for 3D-printed mixtures is still missing. It is vital to study the flow properties and the way these properties changes with time of fresh 3D printed cementitious mixtures in order to understand the extrudability, stability and buildability of printed layers. This research presents the preliminary results aimed at characterizing the rheological properties of cementitious mixtures used for 3D printing purposes. Mix designs consisting of limestone powder, sand and chemical admixtures were formulated for understanding the rheological properties of manually controlled, printed mixtures. This is the initial phase for outlining optimum mixture design which can be employed for scaled up 3D printing construction based off the laboratory testsCivil, Architectural, and Environmental Engineerin