Hydration Process and Long-Term Strength of Gypsum Slag Cement with High Content of Phosphogypsum

Abstract

Abstract: A large amount of phosphogypsum, ground granulated blast-furnace slag and slaked lime were employed to prepare the gypsum slag cement. The effect of phosphogypsum content on the hydration process and long-term strength of gypsum slag cement was investigated through hydration heat, chemical shrinkage, pH value of pore solution and compressive strength tests, combined with XRD and SEM-EDS. The results show that the third peak of heat release curves of cement pastes gradually decreases when the phosphogypsum content increases from 40% to 70% (mass fraction, the same below). The chemical shrinkage at 14 d increases from 0.066 mL·g^-1 to 0.193 mL·g^-1, and chemical shrinkage rate significantly increases during the early hydration stage (0~1 d). The pH value of pore solution tends to stabilize within 28 d. Compared with 28 d compressive strength, the 90 d compressive strength is enhanced by 12.3%~27.8%. XRD and SEM-EDS reveales that the cement pastes mainly consists of gypsum, quartz, ettringite and C-S-H gel. At the age of 28 d, the ettringite content decreases from 7.48% to 2.84%, and the Ca/Si ratio (molar ratio) of C-S-H gel increases from 1.08 to 2.24 with the increase of phosphogypsum.

Key words: phosphogypsum, gypsum slag cement, ground granulated blast-furnace slag, hydration heat, chemical shrinkage, hydration product, compressive strength

CLC Number:

TQ172

LIAO Yishun, WANG Kai, LI Hao. Hydration Process and Long-Term Strength of Gypsum Slag Cement with High Content of Phosphogypsum[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2023, 42(12): 4408-4415.

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