Many different forms of kiln are used for burning Portland cement.
At the bottom of the kiln is a grate of iron bars, and on this wood and coke are piled to start the fire.
The heat passes from the melting furnace into the annealing kiln.
More efficient is the Gill kiln which uses coke as a fuel.
The annealing kilns are large fire-brick chambers of small height but with sufficient floor area to accommodate four or six large slabs, and the slabs are placed directly upon the floor of the kiln, which is built up of carefully dressed blocks of burnt fireclay resting upon a bed of sand; in order to avoid any risk of working or buckling in this floor these blocks are set slightly apart and thus have room to expand freely when heated.