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High aluminum cement, also known as aluminate cement, commonly referred to as bauxite cement, includes grades 625#, 725#, and 925#. It is a hydraulic cementing material made by mixing bauxite and lime in a certain proportion, then calcining and finely grinding the mixture. It is often used as a binder for refractory castables.
High aluminum cement contains different amounts of aluminum and calcium, and is classified into CA-50, CA-70, and CA-80. CA-50 high aluminum cement is yellow and its raw materials are bauxite and limestone. CA-70 high aluminum cement has fewer impurities, and its setting properties and refractoriness are better than those of CA-50 refractory cement. It is used as a binder when formulating low-cement refractory castables. CA-80 high aluminum cement has an aluminum content of 80% and contains α-AL2O3 micropowder. CA-80 high aluminium cement is used as a binder in high-grade refractory castables. The high aluminum content of CA-70 and CA-80 cement improves the setting speed and mid-temperature strength of refractory castables. Additionally, the low calcium content extends the service life of the refractory castables' strength at later stages.
The higher the alumina content, the higher the refractoriness; the lower the alumina content, the higher the calcium oxide content. Adding high aluminum cement as a binder allows the refractory castable to be demolded within 24 hours. High aluminum cement affects the flowability of the refractory castable, the construction process, and demolding time. Improper use can significantly impact the construction of the refractory castable.
The use of high aluminum cement falls into three stages: dissolution, nucleation, and precipitation. For example, CA-50 high aluminum cement is generally used in medium and low-grade refractory castables. CA-50 aluminium cement has the weakest strength at 800°C. Therefore, if the furnace lining's working temperature is 800°C, it is the most awkward temperature—not high enough to use ordinary refractory castables, necessitating the use of low-cement castables. Low-cement castables have low calcium content, good strength at intermediate temperatures, and excellent strength in later stages.
CA-70 and CA-80 high aluminum cements, with their high aluminum content and lower addition ratios, are often used in low-cement refractory castables. This not only enhances the strength of the castables but also reduces their calcium content, while improving performance at mid-range temperatures.
Therefore, when adding high aluminum cement to refractory castables, one must consider not only its binding effect but also the working temperature to decide whether to use CA-50 high aluminum cement or CA-70 and CA-80 high aluminum cements.
