Definition - What does Ettringite mean?
Ettringite has a high mineral content of sulfate calcium sulfoaluminate. The former name for ettringite is "cement bacillus." It occurs naturally or is formed by sulfate attack on mortar and concrete. Bacillus is generally a bacteria that increases the compression strength of concrete through its biomass. The disintegration of concrete in seawater and sulfate solutions is due to the formation of ettringite. It is the main reaction product formed by the expanding form of sulfate attack.
Corrosionpedia explains Ettringite
Ettringite is also known as cement bacillus, which is the name of a naturally occurring mineral of the same composition and structure. The formation of ettringite or cement bacillus has been recognized as the cause of excessive expansion, cracking and even complete disintegration of concrete subjected to intensive sulfate attack.
Ettringite or cement bacillus has advantages and disadvantages, depending on the circumstances and conditions in which it forms. It is a product of the reaction between sulfate and calcium aluminate. It is an expansive compound, and is bigger in volume (is of smaller density) than its forming chemicals.
However, when ettringite is formed in an already hardened cementitious system, the tensile stresses that it creates lead to the expansion of the system as a whole, and this results in cracks that, at times, ultimately lead to total collapses.