Any hard, inert waste material, or by-product of industry is suitable for use as aggregate material. Chief among these is blast furnace and steel slag, as well as slag from non-ferrous smelters. Most of slag for aggregate use is air cooled, and the resulting clinker is crushed and sieved. Follow the SLAG link for more information
Crushed old concrete is a local source of aggregate. The quality of the aggregate is a function of the type of concrete, and the condition of the concrete used. Although recycled aggregates can be used in a variety of road construction applications, product variability and strength characteristics usually limit their use to road base, backfill, and asphalt pavement. Quality of the products containing recycled material is often source dependent, and indiscriminant blending may lead to inferior performance.
Examine the economics of recycled aggregate production.
The general use of waste material in construction is evaluated in this paper
