Refractory cement, also known as aluminate cement, is a hydraulic cementitious material made by calcining bauxite and limestone as raw materials to obtain a clinker with calcium aluminate as the main component and alumina content of about 50%, and then grinding it. Aluminate salt water mud is often yellow or brown, and some are gray in color. The main minerals of aluminate cement are calcium aluminate (CaO · Al2O3, abbreviated as CA) and other aluminates, as well as a small amount of dicalcium silicate (2CaO · SiO2). The colors are mostly gray and white.
According to the national standard (GB/T 201-2015), the density and bulk density of aluminate cement are similar to ordinary Portland cement. Its fineness is a specific surface area of ≥ 300m2/kg or 45 μ Screen residue ≤ 20%. Aluminate cement is divided into four types: CA-50, CA-60, CA-70, and CA-80. The setting time and strength of each type of cement shall not be lower than the standard requirements.
Aluminate cement includes three types of cement: calcium aluminate, barium aluminate, and barium zirconium aluminate. Among them, barium aluminate cement has the characteristics of fast hardening, high strength, and high fire resistance. Aluminate cement sets and hardens quickly. The 1-day strength can reach over 80%.
Aluminate cement has a high hydration heat and a concentrated heat release. The hydration heat released within 1 day accounts for 70% to 80% of the total amount, causing a higher temperature rise inside the concrete. Even when constructed at -10 ℃, aluminate cement can quickly set and harden, and can be used for winter construction projects.
Under ordinary hardening conditions, aluminate cement has a strong resistance to sulfate corrosion due to the absence of tricalcium aluminate and calcium hydroxide in the cement paste and its high compactness.
Aluminate cement has high heat resistance. If fire-resistant coarse and fine aggregates (such as chromite) are used, heat-resistant concrete with a service temperature of 1300~1400 ℃ can be made.
In addition, the mixing of aluminate cement with Portland cement or lime not only produces flash setting, but also causes concrete cracking and even destruction due to the formation of highly alkaline hydrated calcium aluminate. Therefore, during construction, it is not allowed to mix with lime or Portland cement, nor to use it in contact with unhardened Portland cement.
