Reducing Portland Cement in Design Mix - options?

The contractor brought up a concern of the 50% and 30% Slag Cement requirements in the specs for a 4500 psi interior slab. They are concerned with the amount of time that a mix design of this nature takes to come up to strength, especially as we get into the cooler months. They have encountered this same spec on other projects and have always been able to get approval to use straight cement. The project is in CT/MA

You should work with the concrete supplier to meet the target strength (e.g., with accelerators), although keep in mind that the overall goal is to reduce the cement content. Optimizing the aggregate grading is another good option to significantly reduce cement. Otherwise if it can be precast you shouldn’t have any issues.

@matt.dalkie - what sort of options are available?

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As a ready mix supplier I can say that we regularly provide slag mixes with 30-50% replacement even in cooler months. Understanding the proper use of admixtures can assist in initial set times and ultimate strengths. I’d recommend meeting with the ready mix supplier and contractor to discuss options. Many times it is just that the contractor is in an older mind set of “that’s the way we’ve always done it” and they haven’t necessarily kept up with the advancements in admixtures.