Passive House Cold weather concrete pour
I working on the development of 5 passive houses in Minneapolis (6A). We got delayed in the process and are now pouring concrete in “cold weather conditions”. I have our concrete sub really worried about this pour b/c of the cold weather and is looking to add winter charges for heating the slab. I would normally be all for it but we are building a passive house. and the slab sits in an insulated form. 5-6″ of EPS surround the entire slab the only part open to the air is the horizontal finished slab. (imagine a yeti cooler with the top open) The insulation is Averages R 24. My thought is that if we cover the top with concrete blankets that will keep enough heat in to keep the slab warm enough to cure.
Another thought would be to add sheets of EPS ontop of the blankets. we happen to have extra foam for the wings to be installed later we could cover the top of the slab and make a lid. THose would be R-24 as well.
I am thinking a heat loss calc would needed but unsure how to go about it.
Replies
There are a few variables which are independent and will be hard to control.
The ground temperature before the pour, (and that of the insulation).
Air temperature during the pour, and before additional blankets and insulation are placed. (and then after the pour)
Starting temperature of the concrete solid components and water before combining.
Time between initial combination of concrete solids with water and placement.
Heat generation rates of the concrete from the hydration process. (will vary with the cement used)
What might work for a sunny placement day with first overnight temps in the 20s would not work for colder conditions.
https://www.giatecscientific.com/concrete-temperature-testing/
These folks have some info on measuring the process and making decisions based on real-time data to guide whether supplemental heat is needed.