Normally we're able to pour garage slabs all the way to Thanksgiving. This year however, Mother Nature didn't cooperate. This November was so cold we had to stop pouring garage slabs and wait for warmer weather. We still needed to get a couple of jobs done so we went into cold weather mode.
First, a Warning about de-icing chemicals
At this point I want to remind all my customers to keep deicing chemicals off the surface of all exterior concrete during the first winter, especially your garage slab and driveway. Deicers can lead to spalling of newer concrete. In fact I'd recommend never putting de-icing chemicals on your concrete, but that's just me!
Cold weather concrete
The first thing for cold weather construction is to protect the ground from freezing. Never, I mean never place concrete on frozen ground.
We can control the concrete temperature for proper curing but not the ground so its critical we don't allow the ground to freeze.
To accomplish this we cover the ground with insulated cement curing blankets with an R-value of 5. Then we cover the blankets with a standard blue tarp or black poly to keep any snow or rain off the area we want to work. Don't worry if it snows, in fact several inches of snow or more will act as natural insulation, keeping the ground that much warmer.
Then you pray and wait for warmer weather. As long as the ground doesn’t freeze you can still pour when the temperature gets above 32 degrees.
Once the slab has been poured we need to protect it until the concrete can handle the cold on its own.
Once the concrete has gained strength to 500-psi compressive strength it can handle the cold on its own. If the concrete stays at 50 degrees or more it should reach 500-psi compressive strength the second day. Its important to note, we're not talking about 50 degrees air temperature we're talking about 50 degrees cement temperature.
Cold Weather Garage Slab Mix
- Cemstone, our ready mix producer will use hot water heated to about 65 degrees when it leaves the plant.
- We'll order a slump at or less than 4.
- We'll use air-entrained concrete to reduce bleeding and protect the slab from freeze thaw cycles.
- Concrete accelerators may be used to get the cement to set up faster.
- To make the chemical reaction hotter we'll add extra cement. Typically we'll use (high-early strength) cement, which hydrates more quickly.
In Conclusion, is a slab poured in cold weather as strong as one poured in May?
At the end of the day, after all the precautions I'm often asked if cold weather cement will be as strong as other cement? The answer is YES.
Although concrete gains strength more slowly, the overall strength of cold weather cured concrete will be the same as concrete cured at 70 degrees. It just happens at a slower rate.