When a Type I-II cement is specified, does it mean you use one cement that's a compromise between the two types, or does it mean the concrete supplier has the option of using either a Type I or a Type II cement?
Cement manufacturers can make a single cement that meets the ASTM C 150 specification requirements for both Type I and Type II cements. It's called a Type I-II or Type I-and-II cement and isn't a compromise because all of the standard chemical and physical requirements for both types are met. If Type I-II cement is being used to reduce heat of hydration in a structure, rather than to produce moderate sulfate resistance, an optional C 150 chemical requirement should also be specified. This optional requirement limits the sum of tricalcium aluminate and tricalcium silicate percentages to 58% for the cement. All Type I-II cements may not meet the optional requirement.