Portland Slag Cement is equivalent to OPC in mechanical strength, setting and hardening and serves as an alternative to OPC with the additional advantage of mild sulphate resistance. Slag cement is ground slightly finer than OPC. This is a blended type in which OPC (55 to 60%) and granulated blast furnace slag (40 to 55%) are inter ground / blended, with about 4% gypsum additive. This is manufactured in cement factories situated near steel factories from which granulated slag is obtained.