Abstract: A cement of the same general characteristics of a normal Type I is provided which involves the intergrind of from 1 up to about 25 parts by weight of air-cooled iron blast furnace slag, and from over 75 up to 99 parts by weight of conventional Type I Portland clinker. Traditional set control additives, particularly such as sulfate provided through gypsum, are used in the new cement composition. It is particularly noted that the slag involved is air-cooled, as contrasted to an amorphous material obtained by water quenching. In some respects the new product is better than traditional Type I, and can thus be referred to as an improved Type I.