Clinker (waste)

Clinker often forms a loose, dark deposit consisting of waste materials such as coke, coal, slag, charcoal, and grit.

It is laid and rolled, and forms a hard path with a rough surface that presents less risk of slipping than most loose materials.

However, if laid without sufficient adhesive, it needs frequent rolling and addition of more clinker to maintain the path in good condition if it is subject to heavy foot traffic.

Aerobic microbes soon grow in hollows in the clinker, where they kill harmful anaerobic bacteria in the water and remove much of the offensive organic waste.

For example, in the Powder River Basin is covered by clinkers from coal-seam fires, i.e., "baked, welded and molded rocks formed by the natural burning of coal beds.