Crushed Rock, Ontario, Canada

In essence, steel slag is a synthetic mineral. It is a by product of the steelmaking process, and silicon and calcium make up the majority of it. It can be processed (which entails cooling, weathering, and crushing) into a variety of useful applications. Consequently, it qualifies as a green material made from a renewable resource.

But steel slag's exceptional qualities as a building material are what really make it useful. Steel slag's qualities for use in roads and other applications have long been understood by engineers.