Effect of alkali metal sulfates on hydration properties of alpha-calcium sulfate hemihydrate for 3D printing

Abstract

Three-dimensional printing (3DP) technology is an important means of achieving decorative convenience, personalization, and functional integration for future building construction. However, the setting time and hydration process of calcium sulfate hemihydrate (HH) present chanllenges for the 3DP application. This study aims to investigate the accelerating effect of alkali metal sulfates accelerators on the hydration transformation of HH into calcium sulfate dihydrate (DH). The setting time, conductivity, Ca2+ ion concentration, size distribution, and zeta (ζ) potential of gypsum slurries with different accelerators were measured. The results demonstrated that the accelerators significantly enhanced the hydration process of αlpha-calcium sulfate hemihydrate (α-HH). On the effect of accelerators, the setting times of gypsum slurries containing 30 wt% lithium sulfate (LS), sodium sulfate (NS) and potassium sulfate (KS) were accelerated by 82.56 %, 86.06 % and 97.13 %, respectively, compared to the control sample. The crystal particle sizes of hydration products decreased, and the absolute values of ζ potential increased to 1.85 mV, 3.1 mV, and 5.3 mV, respectively. The X-ray photoelectron spectroscopy (XPS) analysis revealed a shift in the peak values of the hardened specimens towards higher electric fields. This was accompanied by improved ion dispersion within the slurry, resulting in enhanced supersaturation of calcium sulfate dihydrate and crystallization of the crystal nuclei. Thus, the suitable accelerators can effectively achieve rapid solidification and hardening of high-fluidity gypsum slurries.