Sulphoaluminate cement is an important branch of China's special cement industry, which includes fast-setting Sulphoaluminate cement (with a mixture ratio of less than 15% of cement clinker), low-alkalinity Sulphoaluminate cement (with a mixture ratio of 15% to 35% of cement clinker), self-stress Sulphoaluminate cement, and expansive Sulphoaluminate cement. It is a special cement variety with independent intellectual property rights in China. The main components of Sulphoaluminate cement are C2S, anhydrous calcium sulfoaluminate, and mixtures (such as stone powder and gypsum). This concrete material has several excellent properties such as early strength, fast setting, and low alkalinity.
Currently, most of China use hard gypsum as a mixture for fast-setting and low-alkalinity Sulphoaluminate cement. However, in the early stages of the Sulphoaluminate cement development, gypsum was generally mixed with dihydrate gypsum. When introduced, dihydrate gypsum could increase the strength by 3-5MPa. But too much gypsum can cause the strength components in cement to turn into expansive components, which can cause cracking and even destruction. Compared to dihydrate gypsum, hard gypsum dissolves slower and is more dangerous for late expansion. Therefore, the amount of gypsum added to the cement should be less than 15% for fast-setting and low-alkalinity Sulphoaluminate cement.
The initial purpose of adding limestone to the Sulphoaluminate cement was to reduce the early hydration heat and overcome the flexural shrinkage caused by this. Compared to other mixtures, the decrease in strength was smaller. Later, it was found that adding a certain amount of limestone could reduce the alkalinity of the cement phase, which led to the development of low-alkalinity Sulphoaluminate cement known today.
Sulphoaluminate cement is used in GRC (glass fiber reinforced cement) products. 70% of China's Sulphoaluminate cement production is used in GRC products. GRC products refer to glass fiber reinforced cement and concrete products, and to ensure durability, Professor Cao Yongkang of the China Building Materials Academy first proposed the "double insurance" technology route by using alkali-resistant glass fibers and low-alkalinity Sulphoaluminate cement.
Sulphoaluminate cement is used in fast repair materials. In special engineering fields that require high early strength, such as 1h and 2h strength, Sulphoaluminate cement is commonly used because of its fast setting and early strength characteristics in fast repair materials.
Sulphoaluminate cement is used in special mortar materials. At present, the silicon-sulfoaluminate-gypsum system is extensively used in cement-based self-leveling materials, which fully utilize the advantages of the ternary system and ensure early strength and volume stability in the later period.