Enhancing the Printability of 3D Printing Limestone Calcined Clay Cement Using Hydroxyethyl Cellulose Admixture and Silica Fume (2025-04)¶

Limestone calcined clay cement (LC3) is an eco-friendly alternative for sustainable construction. However, its fresh material and rheological properties pose challenges for 3D printing, necessitating the evaluation and optimization of printability. While hydroxypropyl methylcellulose-based viscosity modifying admixtures (VMA) are widely used in 3D concrete printing to improve buildability, their application in LC3 leads to a reduced printability window (open time). This study explores the potential of hydroxyethyl cellulose (HEC)-based admixtures and silica fume (SF) to enhance extrudability, open time, and buildability in 3D printing LC3 mixtures. The mixtures comprised cement, limestone, metakaolin (calcined clay), and a polycarboxylate-based high-range water-reducing admixture, with varying LC3, HEC, and SF percentages evaluated over time. Experimental investigations included flow table tests, Vicat setting time measurements, and 3D printing assessments. Results revealed that higher LC3 or SF contents shorten both initial setting time and open time while enhancing buildability. Conversely, incorporating HEC extended the initial setting time, 0.5% HEC prolonged open time and maintained the targeted filament width up to 120 min, and improved buildability. Polynomial and Gaussian process regression were applied to optimize the mixture composition and identify the ideal printing time. The optimal percentages for maximum buildability were determined to be 1% HEC, 6% SF, and a printing time of 20 min.