We're getting pretty close to starting our build now and the foundation for our addition is going to be ICF's. My architect is telling me we need 28 days curing time before building on them but my SIP supplier said if I use a higher strength concrete I can cut that down to 7 days. Would that be 4000psi or 27mpa concrete????

Anyone have any info or anything to add that might help me here. I don't mind paying a little extra to get things going.

Sean

What?  No this does not make sense.  Unless you have a special circumstance, and sips are not that circumstance that I am aware of, standard construction loads for the upper section will only increase over a period of time, as the concrete cures.  I would not recommend starting the next day, however 3-7 day cure time, is lots.  You wont be adding the weight of the entire house, contents, snow, and live loads immediately after construction.  Unless you have a special circumstance, your architect is wrong.

7 days is about 60% of the strength, so you need 1.7x stronger concrete.

5000 psi instead of 3000 would meet that spec and be stronger in the long run.

But I would agree - it will be well past 28 days before it is fully loaded anyway.

Thanks for the info. this helps a lot.

 

I really regret this architect I hired, if we weren't so close I'd move on, I'm getting pretty tired of his "games".

 

Sean

Your SIP supplier is correct, concrete strength is to 75% after 7 days.

I'm probably way late on this, but I only recently re-upped. The 28 day answer is given because that's how long it should take the mix to reach it's *design compressive strength*. Assuming this is a continuous footing foundation (resting on ground), the compressive strength has little to do with any concern of failure. The 3-7 days will most certainly get you everything you need to get going on the walls. I wouldn't advise driving your backhow back and forth across it, but you should otherwise have no problems. Yes, a higher strength desigh mix will get you to the 3000 mark sooner, but why? It probably doesn't need it (need more soil info to know for sure), and higher strength concrete, if achieved by more cement, will have more shrinkage cracking. Type III, high early strength, cement is a better approach when you need quicker, but not stronger, set. When you can get it.

Actually you're right on time, should be ready to pour this week. Thanks for the info, I'll mention it to my concrete guy and see what he says.

Sean