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Durability Issues of Calcium Sulphoaluminate Cement Concrete

Understanding of calcium aluminate powder and calcium aluminate cement

Calcium aluminate powder (raw material for water purifier) mainly consists of CaO, AL2O3, and Fe2O3, and has strong activity. Adopting the one-step acid dissolution method can save a lot of labor and electricity for the production of water purifiers, greatly reduce costs, and has the advantages of simple process equipment and easy mastering. It is an ideal material for the production of basic aluminum chloride and polyaluminum chloride products. Calcium aluminate powder is a grayish-white powder. The main components are a mixture of dicalcium aluminate (CaO·2A1203) and monocalcium aluminate (CaO·A1203). It is slightly soluble in water, and the water solution is alkaline with a pH value of about 11.

Calcium aluminate powder has high activity and reacts strongly with inorganic strong acids. It can be activated at room temperature and has a high release of heat, and the solubility of aluminum oxide can reach more than 90%. Using it as raw material to produce liquid or solid polyaluminum chloride can simplify the process, reduce costs and improve product quality, which is adopted by most polyaluminum chloride manufacturers as raw materials.

Calcium aluminate cement is a cement with monocalcium aluminate or dicalcium aluminate as the main mineral component. It is made of natural bauxite or industrial alumina and calcium carbonate (limestone) in a certain proportion, through calcination or electric melting. It can also be made by melting iron bauxite and limestone together. In practical use, many different labeled calcium aluminate cements can be seen, and the labels represent the strength reached after the cement is cured for a certain period. For example, calcium aluminate cement with CA as the main mineral is generally labeled with the strength reached after 3 days of curing, while the calcium aluminate cement with CA2 as the main mineral is labeled with the strength reached after 7 days of curing.

Understanding the durability issue of sulphoaluminate cement concrete

Due to the differences in component characteristics, sulphoaluminate cement concrete is naturally superior to silicate cement in some aspects, such as shrinkage and shrinkage crack control, resistance to freezing and thawing damage, alkali-aggregate reaction, and resistance to sulfate erosion. However, the academic community has not reached a consensus on the transport properties, carbonation resistance, and corrosion protection of steel bars in sulfoaluminate cement concrete. These differences are attributed to the variability of the chemical composition of sulphoaluminate cement and the service environment. Some studies have found that although some sulphoaluminate cement concrete does not resist carbonation and chloride ion erosion as well as silicate cement concrete, its strong internal self-drying ability allows it to protect the steel bars in concrete structures well in marine tidal environments.

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Durability Issues of Calcium Sulphoaluminate Cement Concrete