Thinking About Pouring Outdoor Concrete after September 15?

This is a great article sent to us today by Crushrite. For those readers who may be thinking of doing concrete work soon, it is worth reading! – Kenneth

Submitted by Crushrite

If you have poured or are considering pouring a sidewalk, driveway, or garage pad this year, then this article is for you.  Concrete in Saskatchewan is exposed every winter to salts and freezing and thawing. It needs to be as strong and durable as possible to withstand these harsh conditions.

Here’s how the Winter season is hard on concrete.

Ice: The formation of ice on flatwork causes a mechanical reaction in the concrete.  The ice melts, freezes inside the concrete capillaries, and then expands.  The harshest part of the year is the late Autumn and the early Spring because all of the moisture on the concrete is expanding and contracting as the concrete freezes and thaws.  Eventually, the stress of expansion and contraction can cause the concrete surface to fail, and this is known as Scaling.

Deicing Chemicals & Salts: When we use deicers on flatwork, they are normally advertised as:  “SAFE FOR CONCRETE”, or “WILL NOT CHEMICALLY ATTACK CONCRETE.”  While these statements are true, they are misleading. Deicers don’t cause a chemical reaction with the concrete: they raise the melting point of water, causing the ice to melt, and then the same mechanical reaction occurs as listed above, causing Scaling.   It’s a bit of a marketing ploy, and can cause issues in the concrete industry.

Magnesium Chloride: Magnesium Chloride is used for two things.  It is used as a dust preventer on gravel roads (the town of Esterhazy uses it), and it is also used by the Department of Highways as a deicer because it is extremely effective in eliminating black ice.  Unfortunately, this is a chemical that ACTUALLY ATTACKS CONCRETE. This product actively attacks the hydrated cement in the concrete to destroy the bond and deteriorate concrete.

Placing concrete in Saskatchewan may be a little trickier than the rest of the world, so here are some things to consider when pouring your concrete.

Pour after the frost is out of the ground, and before September 15: To reach its ultimate strength, concrete needs 28 days of weather that is above 10⁰C.  Concrete will even continue to get stronger every day while in the curing stage as long as the concrete is above 10⁰C.

If you pour your flatwork in the spring, after the frost is out of the ground, it will have 4 – 5 months to cure properly.

After September 15th, there aren’t many days where the ambient temperature remains above 10⁰C for the full 24 hours.  (At the time of writing, the ambient outdoor temperature is reaching below 10⁰C nightly).  Any concrete you pour after September 15th may not have that crucial 28 day curing period to reach ultimate strength before winter sets in, the time of year when it needs to be at its strongest.

Because of falling temperatures, Crushrite doesn’t recommend pouring outdoor flatwork after September 15th, and will not warranty any outdoor flatwork poured after that date.

Use Sask C2 Concrete mix: This concrete mix is a prescription created by and endorsed by the Saskatchewan Ready Mixed Concrete Association.  This mixture makes for an extremely durable concrete that will help withstand the effects of mechanical expansion of ice, and the deterioration caused by magnesium chloride.

Properly cure your concrete: When concrete is hardened, the more water that is present, the stronger your concrete gets. Here are some ways to cure your concrete properly:

  • If you have the ability, flood your concrete for three days with a continuous supply of water.  You can pond your concrete and flood it, or use sprinklers to ensure that the slab stays continuously wet for three days.
  • Use a curing compound.  This is a topically applied chemical that locks in moisture and eventually dissipates over time.
  • Use wet burlap or curing blankets.  Soak the burlap or curing blankets, because using these will ensure that the concrete stays wet continuously for the curing window

Pour with PMT: PMT is a pozzolanic admixture that breaks up the cement clusters in the concrete and allows them to fully hydrate, making the concrete stronger and more watertight.  This product allows the concrete to self-seal, making the concrete resist the harmful effects of ice and magnesium chloride.  We have been using PMT over the last two years and have seen great success.

Seal your concrete: Sealing your concrete to protect it from moisture is a great way to protect it. However, most sealers need to be applied at 10⁰C or above, and 28 days after the concrete was poured. New regulations on sealers make them more environmentally friendly, but sometimes less effective. We have some sealers that can stand the test of time at Crushrite, come and see which sealer is right for you.  (Of course, if you use PMT you don’t need a sealer.)

Following these guidelines will yield a durable concrete that will last you years.

Consider these two photos (below):  Figure 1 is a driveway poured with the proper strength, finished properly and wet cured for 3 days with curing blankets.  It was poured in 2006.  Figure 2 is a driveway that was poured in the late fall of 2013 and was air cured.

Figure 1

Figure 1 – Poured in 2006

Figure 2

Figure 2 – Poured in 2013

All of the problems of shale popping and scaling have occurred in Figure 2 within the past three years, while the driveway in Figure 1 has lasted for 10 years!

We at Crushrite want to provide you with concrete we can stand behind, both through our products and our knowhow. Remember September 15th when planning your outdoor flatwork, and speak to us about concrete that will survive the Saskatchewan winter.

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