There are water soluble suiphates in some soils, such as plastic clay, which react with ordinary cement and in time will weaken concrete. It is usual practice, therefore, to use one of the sulphate-resistant cements for concrete in contact with sulphate bearing soils.
Portland blast-furnace cement.
This cement is more resistant to the destructive action of suiphates than ordinary Portland cement and is often used for concrete foun dations in plastic clay subsoils. This cement is made by grinding a mixture of ordinary Portland cement with blast-furnace slag. Alternatively another type of cement known as ‘sulphate resisting cement’ is often used.
Sulphate resiting Portland cement.
This cement has a reduced content of aluminates that combine with soluble suiphates in some soils and is used for concrete in contact with those soils.