Pouring concrete outdoors in this weather?

[Stabbsson]

Hello Byggahus!

I'm planning to cast a small slab approximately 130x70x10 outdoors as it will be a foundation for an air/water heat pump's outdoor unit. However, I have some questions regarding casting in the current weather conditions.

If I follow all the best practices, dig out all the topsoil down to about 50 cm deep, and create a gravel bed, use a geotextile, and even place some insulation at the bottom of the mold, along with reinforcement, of course. How long does it take for the concrete to reach 5 MPa? It's +5 and above during the day but can drop to 0 degrees at night. What will stand on the concrete weighs "only" 150 kg. Do you think it is feasible to use regular coarse concrete for this right now, or should I use cold-weather concrete, or simply wait until it is over 5 degrees even at night?

 

[bomm]

I would have used regular coarse concrete or taken a trailer to fetch ready-mixed concrete from the concrete station...

Use warm water so the "curing" starts faster and cover the concrete with plastic + insulation (polystyrene or concrete cover mat). This retains the heat and allows it to continue curing despite low temperatures at night. It's also good to use polystyrene in the formwork, as it insulates the edge.

The plastic retains moisture in the slab, so you don't need to water it.