Features Of Granulated Blast Furnace Slag (GBFS) Granulated Blast Furnace Slag or GBFS is formed when Blast Furnace Slag or BFS is successively at a fast rate quenched from the furnace rather than left for cooling. It has a density of about 60% to 70% that of natural sand. This material has a much increased resistance to sulfate attack. This eventually leads to better performance in countering acids of any type. In GBFS, no type of reaction related to alkali and silica occurs. Also the material provides a huge saving in connection to carbon dioxide emission which is an extra boon. What constitutes GBFS are its properties that consist of durability, appearance, higher ultimate strength than concrete which is made up of Portland cement and high sustainability level of the product made out of this material.