Large fans cool the clinker after it leaves the kiln. The clinker may be stockpiled for future use, or it may be reground at once in ball or tube mills. A small amount of gypsum is added to the clinker before the regrinding. This final grinding produces powdery portland cement that is finer than flour. The cement is stored in silos until it is shipped.
Unpackaged cement is shipped by railroad, truck, or barge.
The ancient Romans developed cement and concrete similar to the kinds used today. Their cement had such great durability that some of their buildings, roads, and bridges still exist. The ash produced a hydraulic cement that hardened under water. People lost the art of making cement after the fall of the Roman Empire in the A.D. 400's. In 1756, John Smeaton, a British engineer, again found how to make cement.