There is a fine line between setting and freezing that needs supervision when working with concrete below 39°F. Water is a major constituent in concrete cement curing, and the exothermic reaction during mixing keeps the mixture relatively warm under normal conditions. Colder temperatures can cause the water in the concrete mix to freeze. Ice expands. If you have never seen the destructive power of ice, you have probably never forgotten a glass bottle full of water in the freezer too long.
In much of eastern Pennsylvania, snow does occur, but it doesn’t mean that Saint David’s, a city in the southwestern borough of Wayne, doesn’t feel the cold winters. Temperatures can go as low as 29°F, which is not an ideal temperature to cure poured concrete. Concrete requires water to remain liquid till a stage in its curing, after which it becomes indestructible; discard the advice below if you want rocky road crumble for dessert all winter.
- It’s important to use hot water when preparing your concrete mix. Concerning the consistency of the concrete mix, 65°F is a suitable mixing temperature.
- Remember, science taught us that air is a good insulator. The concrete mix is pumped through an air entrainment system designed to introduce air bubbles into the mixture. This a) keeps the concrete mix warm longer, and b) the air bubbles act as stress dissipators to mitigate any freezing or thawing as the concrete solidifies.
- More science: impurities introduced into a pure mixture will decrease its melting point (while increasing the boiling point- but that’s not our point!). To this advantage, sprinkle in some calcium chloride at two parts to a whole batch. As a bonus point, the salt will act as an accelerant to the concrete setting.
- Keep in mind that if this is a pre-fab rebar reinforced project, then the calcium chloride will corrode the rebar in the concrete over time. If you have a fussy client who likes things their way in the dead of winter despite being warned about using too much accelerant, have them sign a mechanic’s lien, so you are not responsible for the cookie crumble that follows come summers.
- Suppose your client is adamant about reading somewhere that fly ash or water reducers in cold weather help cure concrete better. DON’T! It makes the concrete worse.
- When concrete is setting, a thin film of water is expelled to the surface, which can freeze and damage the surface. This ‘bleed’ water needs to be promptly sponged up or wet vacuumed when the surface is firm enough to level.
- Now that the concrete is leveled bring out the heat! Concrete needs up to 48 hours to cure, and during this time, it needs to stay warm. Insulation blankets powered by induction coils or ventilated heating containment units can bring temperatures in harsh winters up to a soothing 50F which is more than enough to cure concrete.
At Advanced Paving & Masonry, this is just one of many anecdotes that have come in handy time and again for winter clients. If you are planning on a concrete project, try having it done before winter comes, or get in touch with us for a free estimate on our asphalt & concrete services in Saint David’s, PA.
Our advice isn’t just concrete; it’s pretty saintly too!