Effects of Different Types of Gypsum on Compatibility Between Portland Cement and Alkali-Free Liquid Accelerator

doi:10.16552/j.cnki.issn1001-1625.2025.0563

Abstract

Abstract: Different types of gypsum can affect the compatibility between cement and alkali-free liquid accelerators in shotcrete. This study compared the effects of anhydrite, hemihydrate, and dihydrate gypsum on the macroscopic properties of cement by examining cement paste setting time and mortar compressive strength, with the addition of alkali-free liquid accelerator. The mechanism by which gypsum type affects cement hydration was revealed using microstructural testing methods, such as heat of hydration testing, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. The results indicate that, under the influence of an alkali-free liquid accelerator, the types of gypsum significantly impact the compatibility between cement and gypsum. The dissolution rates of gypsum decrease in the following order:hemihydrate, dihydrate, and anhydrite, with a lower dissolution rate contributing to a higher early heat release in the cement paste, thus accelerating the setting and hardening process. Moreover, the hydration of the cement becomes more complete, and a greater amount of calcium hydroxide and calcium silicate hydrate gel is produced in the hydration products, resulting in enhanced mechanical performance of the hardened mortar. However, the change of gypsum type in cement only affects the early hydration process and the microstructure of the hardened cement paste, with no significant impact on the mechanical properties, hydration products, and microstructure in the later stages of hydration. This study provides an important theoretical basis and practical reference for understanding the effects of different gypsum types on the compatibility between cement and alkali-free liquid accelerators.

Key words: gypsum, dissolution rate, alkali-free liquid accelerator, compatibility, ettringite

CLC Number:

TU528.042

LI Xiaopeng, ZENG Fanchao, WANG Qin, WANG Jian, XU Kexin, GUO Zhixiang. Effects of Different Types of Gypsum on Compatibility Between Portland Cement and Alkali-Free Liquid Accelerator[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2025, 44(12): 4314-4324.

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