Expanded Slag

Slag’s application as a construction material dates to 1813 when it was used to produce roads in England. By the 1880s, blocks cast with slag were common as road building material in both the United States and Europe.

Lightweight blast furnace slag aggregates are produced as a nonmetallic byproduct in the smelting of iron and steel. Although there are several ways to produce slag, they all generally follow the same principles. The molten slag, at temperatures between 2,000 F and 2,500 degrees F (1,200 to 1,400 degrees C), is combined with carefully controlled amounts of water. This causes steam to form and also cools the slag. A cellular structure within the slag particles is formed from the expansive action of the entrapped water as it turns to steam and from reaction of small amounts of constituents in the slag with the water vapor. The slag is usually crushed after the cooling process.