Q.: Because it resists corrosion, calcium aluminate cement has been suggested for use in floors in a food processing plant. Some of these floors are above grade. Isn't it true that calcium aluminate loses strength drastically as it gets older? If so, it doesn't seem to be a good choice for a suspended floor.

A.: Hydrated calcium aluminate cements do undergo something called conversion a process by which the hydrates slowly change their crystal structure. Unfortunately, in this process the concrete becomes weaker. Knowledgeable designers overcome this problem by designing accordingly. They call for a mix that will still have the strength needed after it has changed its crystalline structure.