Harsco sell graded steel slag at selected locations across Carlisle, PA, Harrisburg PA, Middletown PA, and Central PA. 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.