Research Progress on Rheological Property Control of 3D Printable Concrete

Concrete 3D printing technology has attracted much attention in the construction industry due to its high degree of automation, efficiency, and cost-effectiveness. However, this technology imposes stricter requirements on the rheological properties of concrete. The material must exhibit a good fluidity during pumping and extrusion stages, while also demonstrating a superior buildability during the deposition phase. It is thus essential for production of high-performance 3D printable concrete and ensuring its printability to clarify the evolution mechanisms and underlying principles of rheological behavior.

This review firstly introduces the key rheological parameters and testing methods for 3D printable concrete, and then discusses the evolution mechanisms of rheological properties from the perspectives of interparticle forces and hydration reactions. The influence of typical solid waste materials (i.e., steel slag powder and recycled brick powder with distinct physical and chemical characteristics) on the rheological performance and the fundamental mechanisms are analyzed. In addition, the effect of shear action occurred during the printing process on the rheological properties is also illustrated.

The evolution of rheological properties in cement-based materials is governed by a complex interplay of colloidal interparticle forces (i.e., the van der Waals and electrical double-layer forces) and cement hydration, altering the solid volume fraction and C-S-H interactions. While hydration dominates static yield stress growth after the acceleration period, the relative contributions of colloidal versus hydration effects beforehand remain debated. In a macroscopic scale, concrete rheology is determined via a synergy between the paste properties and the aggregate volume fraction. The system transitions from being paste-dominated to governed by aggregate contact forces once a critical volume fraction is exceeded. The plastic viscosity and yield stress are quantitatively described by the Krieger-Dougherty and Chateau–Ovarlez–Trung models, respectively. Solid waste materials further modulate rheology by altering the water film thickness via changes in particle packing and specific surface area and by influencing the yield stress development rate through modifications to surface energy, liquid phase ionic strength, and hydration kinetics. The existing research sufficiently addresses the impact of mix proportions. However, a significant knowledge gap persists for the time-dependent rheological evolution under the complex shear history inherent to 3D printing processes. Future work should thus focus on elucidating the underlying microscopic mechanisms and developing quantitative models that couple shear effects with multiple material parameters to enable a precise rheological control.