Greg , they are called breeze blocks because they come from the same mould in effect and look the same , so your assumption is correct . Traditional names die hard , don’t they ?
The Fly Ash that used to be used for this has better uses when you can get it , it is now deemed too good for building blocks .
I think that may come down to the use of pulverised coal whereby the fly ash is more fine and regular ; the older straight coal fired power stations produced the irregular hard glassy stuff which made such good building blocks with a better compression strength than contemporary concrete and also blunted all my drills when trying to hang pictures on the wall .
I understand that one use of the fly ash from powdered coal is in cladding in nuclear power plants , but I have no idea exactly how .
Mike Brit