Harsco sell graded steel slag at selected locations across Pittsburgh area. Material is available for pick up from our manufacturing sites. Steel slag is a construction aggregate which is an alternative to crushed rock, gravel or limestone. It is commonly used as a structural fill material, or for constructing/surface dressing of roads and driveways. Also, we developed and markets a calcium and magnesium silicate soil amendment and conditioner, which is formulated so that the silicon (Si) is soluble and readily available to crops, turf and plants.