Portland Slag Cement is blended cement consisting of intimately inter-ground mixture of Portland cement clinker and granulated blast furnace slag, or an intimate and uniform blend of Portland cement and fine granulated blast furnace slag, together with required quantity of gypsum, in which the amount of slag constituent is within the specified limit. Using ground slag to replace a portion of clinker in manufacturing Portland cement is a useful method to make concrete better and more consistent. Among the measurable improvements are: