Concrete Mix - Combining different Brands or PSI strength

Hi DIYers -

In one of the 3 bases (where you place the oven on) concrete slab I accidently put one bag of Sacrete High Strength concrete mix ASTM C387 and another bag of the recommended 5000 plus High Strength Concrete Mix 80 pounds by Sakrete.

The 5000 plus went in first, rebar and then the ASTM C387 went in second. Is this OK? Or do I restart that one slab. I sure hope my goof does not cost me more work.

Thanks for your knowledge!

Hi @monty!

Both of the mixes in your photo are “high strength” concrete mixes. The Sakrete High Strength is tested to reach a load strength of 4,000 psi after 28 days curing; the 5,000psi mix obviously reaches 5,000 psi after that cure time.

Data Sheet for Sakrete High Strength Concrete Mix

Your higher-strength concrete went into the lower part of your slab, where it will be spanning the sidewalls of the block base.

But even if you’d used 4,000 psi concrete throughout the slabs, you’d be fine. In other threads on this forum you’ll find similar questions about concrete strength. The answer is that the concrete is intentionally “over-spec’ed”…you want something that sets up stronger than a standard mix, but “stronger” in this context means WAY stronger.

Also - the 5,000psi concrete is actually in the TOP part of your slab section, because the slabs are cast upside-down. Either grade of concrete is WAY more than strong enough to bear the load you’re placing on it.

Bottom line: You’ll be fine!

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Thank You!
Thank You!
Thank You!

I have been losing sleep thinking I needed to redo the one slab.



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