Feasibility of Applying Attapulgite, Sodium Bentonite and Nano-Silica as a Viscosity Modifier Admixture for 3D Printing of Gypsum-Based Materials (2025-04)¶

Viscosity modifier admixtures (VMAs) are essential for 3D printing materials, but commonly used organic VMAs often compromise the mechanical properties of gypsum-based materials. To address this, three inorganic VMAs—attapulgite (ATP), sodium bentonite (NB), and nano-silica (NS)—were systematically compared with hydroxypropyl methyl cellulose ether (HPMC) to evaluate their applicability in 3D printing gypsum building materials. The results showed that ATP, NB, and HPMC reduced slurry fluidity, while NS enhanced it at low dosages. All VMAs significantly increased yield stress but inorganic VMAs had minimal impact on plastic viscosity. Although the addition of VMAs reduced 2-hour wet strength and compressive strength, inorganic VMAs caused significantly less reduction than HPMC. NS and HPMC lowered the hydration exotherm peak, with NS accelerating its occurrence. At 1% dosage, NB and ATP reduced the maximum exothermic peak, but higher dosages caused earlier and higher peaks. Microstructural analysis revealed that 5% NS resulted in short, thick gypsum crystals, while 0.5% HPMC led to curly flaky structures. Compared to HPMC, NS excelled in enhancing mechanical properties, NB improved workability and mechanical performance, and ATP demonstrated superior workability, mechanical properties, and printing performance. These findings highlight the potential of inorganic VMAs for developing high-performance 3D printable gypsum materials.