CSA cement is anhydrous calcium sulfoaluminate (C4A3S) and dicalcium silicate (C2S) mainly composed of limestone, bauxite and gypsum with appropriate composition as raw materials and calcined at low temperature (1300~1350℃). Clinker composed of minerals is a hydraulic cementitious material with a series of excellent properties such as early strength, fast hardening, low alkalinity, etc.
A series of CSA cements have been developed from the research of anhydrous calcium sulfoaluminate C4A3S composite minerals, this series includes ordinary CSA cement and high iron CSA cement (also known as iron sulfate cement).
The production process of CSA cement and ferroaluminate cement is exactly the same, the only difference is that the content of iron phase minerals in the two is different.
Ordinary CSA cement: fast-hardening CSA cement R·SAC high-strength CSA cement H·SAC expanded CSA cement E·SAC self-stressed CSA cement S·SAC low alkalinity fast-hardening CSA cement
High iron CSA cement: fast-hardening iron aluminate cement R·FAC high-strength iron aluminate cement H·FAC expanded iron aluminate cement E·FAC self-stressed iron aluminate cement S·FAC
3. Process characteristics of CSA cement production
Compared with the traditional Portland cement, the CSA cement production process greatly reduces the amount of limestone in the raw meal, the heat consumption for decomposing CaCO3 is greatly reduced, the emission of CO2 is greatly reduced, and the clinker firing temperature is relatively low, the theoretical heat consumption is low, the firing range is wide, and energy is saved.
4. The rate value of CSA cement
Three coefficients: alkalinity coefficient Cm, aluminum-silicon ratio N, aluminum-sulfur ratio P
Alkalinity coefficient Cm: It indicates the degree of saturation of silicon oxide, aluminum oxide and iron oxide in clinker to form C4A3S, C2AF and C2S. The range of Cm is generally 0.95-0.98, which must be less than 1 (in the coefficient of CSA cement, f-CaO cannot exist, otherwise the cement will set rapidly).
Aluminum-sulfur ratio P: indicates the ratio of alumina content to sulfur trioxide content in clinker, reflecting the appropriate ratio of alumina and sulfur trioxide to form C4A3S. General control P<3.86.
Al-Si ratio N: It represents the ratio of alumina content to silica content in clinker, and also reflects the ratio of C4A3S and C2S in clinker. Generally control N>3.
5. The ingredients of CSA cement
The dosage of CaO: In CSA cement, the CaO required to form clinker minerals is designed according to the shortage.
Because if the amount of CaO added exceeds the amount required to form clinker minerals, f-CaO will be formed, resulting in rapid setting and low strength of clinker; at the same time, under high calcium conditions, the hydration rate of C4A3S will be reduced. greatly accelerated.
The amount of SO3 added: In CSA cement, the amount of SO3 required to form clinker minerals is designed to be excessive.
Since SO3 is always volatilized during the calcination of CSA cement clinker, if the amount of SO3 is insufficient, it will directly affect the formation of C4A3S. In the calculation of ingredients, SO3 should be excessive by about 10%.
6. Mineral composition of CSA cement clinker
The minerals in CSA cement clinker are mainly C4A3S, C2S, C4AF, and generally there are also a small amount of free gypsum (f-CaSO4), periclase (MgO) and perovskite (CaO·TiO2 or CT).
When the calcination is not normal or the ingredients are improper, there are also a small amount of calcite (2CaO·Al2O3·SiO2 or C2AS), calcium sulfosilicate (4CaO·2SiO2·CaSO4 or 2C2S·CaSO4), free lime (f-CaO) and aluminate Calcium (C12A7, CA), etc.
A small amount of mineral free gypsum (free CaSO4) periclase (MgO) perovskite (CaO TiO2) when the calcination is not normal or the ingredients are improper: calcite (2CaO Al2O3 SiO2) calcium sulfosilicate (4CaO SiO2 CaSO4) Free lime (free CaO)
7. Characteristics and application of CSA cement
CSA cement is characterized by early strength and high strength, high frost resistance, corrosion resistance, high impermeability, expansion performance, and low alkalinity.
At present, it is mainly used in: winter construction projects, emergency repair and emergency construction projects, preparation of shotcrete, production of cement products and prefabricated concrete components, preparation of shrinkage-compensating concrete and impermeability projects, production of fiber-reinforced cement products, etc.
CSA cement is a new variety series in the history of cement development in the world today. CSA cement is still in the period of application and promotion, but it has shown a very optimistic development prospect at present.