Methodology for formulating low-carbon printable mortar through particles packing optimization

Abstract

High packing density is one of the key factors for obtaining ultra-high-performance cementitious materials in the hardened state. Packing density also plays a role in the fresh state, influencing various properties of dense suspensions, including rheological properties and stability, which are highly important in 3d printing applications. The maximum packing density of a specific mixture can be estimated by considering the geometrical properties and proportions of each component using the compressive packing model (CPM). This paper aims to utilize the CPM as an efficient tool for designing cementitious materials specifically tailored for large-scale 3D printing of mortar in bi-component printing systems, with a focus on maximizing the performance-to-environmental impact ratio. Two different sets of mixtures were prepared for this study. Set A consisted of cement, sand, and silica fume, while Set B utilized cement, multiple sands, and multiple limestone fillers. Within each group, various mixtures were tested on a small scale to validate their rheological properties, particularly the yield stress. Pumpability, extrudabilty and buildability were evaluated by utilizing these mixtures in different printing sessions. Additionally, the compressive strengths of these mixtures were characterized. Finally, a method for designing a printable mixture is presented, and efficient and printable formulations with low cement ratio are proposed and printed.