Abstract: Anhydrite is one of the important admixtures to improve the mechanical properties of steam-cured concrete. In this paper, the effect of anhydrite content on the compressive strength, hydration products, porosity, microstructure and durability of steam-cured concrete was studied by mechanical properties, X-ray diffraction, thermogravimetric analysis, mercury intrusion test, scanning electron microscopy, chloride ion penetration and freeze-thaw cycles tests. The results show that anhydrite improves the linear expansion rate of steam-cured concrete. When the content of anhydrite increases from 0% (mass fraction) to 25%, the linear expansion rate increases from 0.03% to 0.25% after steam-curing for 6 h. When the anhydrite content is 15%, compared with the blank sample, the 3 and 28 d compressive strength of steam-cured concrete are increased by 14.4% and 10.5%, respectively. The incorporation of anhydrite helps to increase the amount of ettringite and hydrated calcium silicate (C-S-H), refine the pore, reduce the number of harmful pores, densify the internal structure of steam-cured concrete, and improve its chloride ion penetration resistance. With the increase of anhydrite content, the amount of ettringite in system increases significantly, and the risk of later cracking increases. When the content of anhydrite is higher than 15%, the frost resistance of steam-cured concrete decreases obviously. The content of anhydrite should be controlled at 5%~10%, at this time steam-cured concrete has better mechanical properties and durability.

Key words: anhydrite, steam-cured concrete, expansion rate, mechanical property, microstructure, durability