Q.: Bagged cement labelled "Type I/II" is being sold in our area. Is this a new type of cement in ASTM C 150?

A.: ASTM C 150, "Standard Specification for Portland Cement," covers eight basic types of cement Types I through V, and air-entraining Types IA, IIA, and IIIA. For each cement type, limits may be set for chemical composition and physical properties. Type I cement is general purpose, and Type II is for moderate sulfate resistance and moderate heat of hydration. Type I cement does not have specified limits on several chemical compounds and has the same limits as Type II for some others. To achieve sulfate resistance and limit heat of hydration, Type II cement limits the content of tricalcium aluminate (C3A) to 8%, and the sum of tricalcium silicate and tricalcium aluminate (C3S + C3A) to 58%. The physical requirements for Types I and II are almost the same, except that Type II is permitted to gain strength somewhat more slowly.

Type I/II portland cement satisfies requirements for both Type I and Type II. Strength requirements meet those for Type I, and composition requirements meet those for Type II. The dual-type cement can be used where either type is specified. It cuts down on the costs of producing and storing two cements. It's also helpful on projects where out-of-town designers specify Type I, but local practice is to use Type II. Type I/II can be used without requesting a substitution for the specified material.