Bottom ash that comes from incineration is refined by separating its metals for recycling. After this, slag gravel, which is comparable with crushed rock, is refined out of the mineral material which replaces natural sand and crushed rock in earthworks. Slag gravel is used as construction material for many purposes.
In the production of soil cement, a mixture of slag gravel and ash from the burning of biofuel is used as a substitute for cement, which reduces the carbon dioxide emissions of the construction industry. Finer slag gravel can also be used as a filler for pipe trenches.