A novel gypsum-based self-leveling mortar produced by phosphorus building gypsum

Due to the higher 30-min slump loss and the lower 1-day strength of phosphorus building gypsum (PBG), its use for gypsum-based self-leveling mortar is limited, which makes its recycling low value-added and ineffective. In this work, PBG is modified by adding calcium sulfoaluminate cement 42.5R (S) and three types of ground granulated blast furnace slags (GGBSs), which are ordinary GGBS (OG, d(50) = 11.3 mu m), ultrafine GGBS A (UA, d(50) = 3.67 mu m) and ultrafine GGBS B (UB, d(50) = 2.65 mu m), to prepare PBG-based self-leveling mortar (PSLM). When adding S alone, the 30-min slump loss and 1-day strength of PSLM are the highest. GGBS replacing S can decrease 30-min slump loss and 1-day strength. The 30-min slump loss decreases with smaller GGBS particle size. The increase in hydration degree caused by the decrease in GGBS particle size does not cause an obviously negative effect on the slump of PSLM. UA and UB can reduce 30-min slump loss to less than 3 mm by decreasing plastic viscosity growth and yield stress. When the mix proportion of S and GGBS is optimum, the hydration reactions of S and GGBS promote each other, which ensures the higher 1-day strength. The hydration degrees increase, the microstructure becomes denser, and the 1-day strength increases with smaller GGBS particle size is. A novel PSLM with good performances meeting the requirements of JC/T 1023-2007 (Gypsum-based self-leveling floor compound) can be prepared by adding S and UA/UB, which is beneficial for the comprehensive utilization of phosphogypsum. (C) 2019 Elsevier Ltd. All rights reserved.