Tips for Pouring Concrete in Cold Weather​

From link.

Construction doesn’t stop when the temperatures drop. But pouring concrete in winter conditions does pose some unique challenges you must be prepared for.

The ideal temperature to pour concrete is between 10˚C and 15˚C (50˚F and 60˚F). When the temperature drops below 10˚C, the chemical reactions needed to set and strengthen concrete slow down significantly. And when the temperature drops below freezing, the setting and strengthening stops.

When it’s too cold, concrete won’t develop its desired strength. And when freshly poured concrete freezes during the first 24 hours, it can lose 50 percent of its potential 28-day strength.

On top of not strengthening, concrete can freeze and expand in freezing temperatures, resulting in cracks. But with the right precautions, you can still pour concrete in cold weather and protect it from cold weather damage.
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Things to Consider with Cold Weather Concrete Pouring​


If there are specific strength requirements for the concrete, make sure to protect the concrete at the required temperatures. You will also need to make sure the concrete sets before it is exposed to freezing temperatures.

Consider using the following to ensure your concrete is protected:
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  • Hot water to mix cement.
  • Extra cement to make the reaction hotter and cause faster hydration.
  • A squeegee or a shop vac to remove bleed water quickly.
  • Warm, dry materials that have been kept in a warm, dry location.
  • Concrete mixes that set quickly—additives (accelerators) that speed up the setting time. But avoid additives with calcium chloride if using steel-reinforcements since it can cause rusting and lead to cracks in the concrete.
  • Heated enclosures that are windproof and weatherproof to protect concrete in cold weather. And if you use combustion heaters, vent these outside to prevent carbonation.
  • Insulated forms and temporary covers to provide sufficient insulation in beams, walls, and columns.

Things to Avoid When Working with Concrete in The Winter​

When pouring concrete in winter, do not:


Let Fresh Concrete Get Cold/Freeze​


Concrete needs warm temperatures (minimum 10˚C) to cure and reach its desired compressive strength. And it will freeze at -4˚C.

If it’s too cold, the concrete won’t cure at all. So be sure to keep the concrete warm with heaters while curing in winter.


Pour Concrete on Frozen Ground​


Fresh concrete closest to the frozen ground will cure slower than the concrete surface, so the bottom will stay soft and the top will set. Also, when frozen ground thaws and settles, it will cause concrete to crack.

To avoid pouring concrete on frozen ground, use heaters to warm up the ground first, or place concrete blankets or black plastic on the ground for a few days before pouring.


Use Cold Tools​


Cold tools, especially cold forms, can alter the strength and quality of concrete. So be sure to keep your tools warm and out of the cold by storing them inside when not in use.


Remove Formwork Early On​


Avoid removing formwork when concrete is too cold and hasn’t reached its desired strength. Otherwise, the concrete might collapse.


Seal Concrete Below 10˚C​


Since concrete needs to be kept at a minimum temperature of 10˚C to cure properly, avoid sealing the concrete until it has fully cured. If the temperature is below 10˚C, take precautions and consult with a concrete supplier about the best practice for sealing.


Ignore the Temperature of the Concrete​


You must monitor the temperature of concrete in cold weather to prevent freezing, slow curing, and poor-quality concrete.


Tips for Pouring Concrete in The Winter​


Use these tips to ensure you have a quality pour in cold weather:

  • Schedule and determine the cold weather protection measurement of the concrete mix.
  • Keep record of the concrete temperature and the exterior temperature.
  • Do not pour concrete on snow, ice, or frozen ground.
  • Use heaters to thaw frozen ground before pouring concrete.
  • Keep dry concrete mix and tools inside and warm until the concrete is mixed and ready to pour.
  • Use a concrete mix with the right amount of air entrained voids to prevent damage from freezing and thawing.
  • Use accelerating additives in the concrete mix to make concrete cure faster.
  • Use a concrete mix with a water reducer or a low slump and minimal water-to-cement ratio to limit bleeding and reduce the setting time.
  • Request heated ready mixed concrete from your local concrete suppliers to help the concrete develop early strength. Or, request 100 lbs of extra cement for each cubic yard of concrete.
  • Place concrete as soon as possible after mixing.
  • Use concrete curing blankets or heated enclosures to maintain concrete temperatures above 10˚C (50˚F) for three to seven days.
  • Do not finish the concrete if bleed water is present.
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cplchanb said:
Looks good.
How many more pillars do they have to form? Are the concrete guide ways being prefabbed and shipped to site?
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vic said:
I thought all of the pillars were finished, but I noticed this week there were some still to be done near Campbell Park, as seen above in "Looking south from Antler St." photo.
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Putting together some of the last forms today. By my count there are 3-4 pairs left.

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ProjectEnd said:
Not necessarily for the grade separation, but does anyone know if the bridge rehab on Innes Ave has anything to do with the double tracking or corridor improvements?

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I don't think so......... I stand corrected as per @crs post below

Its a City of Toronto project.


I don't see a material reference to the bridge in the project documents regarding the Grade Separation, though I've only given the most cursory look.
 
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Interesting, the drawings in the report refer to 'CN E Track' and 'CN W Track' but when looking at aerial photos from the time, there only appears to be one. Does anyone know when double tracking up the Newmarket sub was abandoned and removed?
 
ProjectEnd said:
Interesting, the drawings in the report refer to 'CN E Track' and 'CN W Track' but when looking at aerial photos from the time, there only appears to be one. Does anyone know when double tracking up the Newmarket sub was abandoned and removed?
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The main line was only ever single track in the last century,, but there may have been yard trackage from St Clair up to the Belt Line and beyond once upon a time. CN employee timetables up into the 1970's indicate that the siding at St Clair Ave extended up to MP 5.5 - Innes is MP 5.65 - with a crossover at the north end, suggesting that the yard trackage continued northwards. A Service Track is still mentioned in a 1993 ETT. So it may have remained up to Innes... likely in the weeds….into the late 1990s

- Paul
 
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crs1026 said:
The main line was only ever single track in the last century
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The junction with CPR might have been single track, but just south of there at Dupont there was still the remnants of a second track in 2020. Presumably this is part of the area covered by the plans (the GO service would be on the west track).
 
nfitz said:
The junction with CPR might have been single track, but just south of there at Dupont there was still the remnants of a second track in 2020. Presumably this is part of the area covered by the plans (the GO service would be on the west track).
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There are lots of pictures on the internet, and old documents, that show a service track on the east side of the main line from south of Dundas up to the CPR. The Knob Hill Farms outlet was previously a factory with rail sidings, and the loading ramp for CN‘s short lived auto-rail service was right there.
Further north, it’s clear that there was a siding/service track from south of St Clair on the east side of the main line all the way to Downsview. It would be the “East” track shown in those diagrams of the Innes Ave bridge. The main line would be the “West” track in the diagram.
That track alignment dates from when the St Clair grade separation was built, which my dusty memory thinks was around 1930 (I’m connectivity challenged so can’t look it up)
The question was, when was the "east track" torn up. I would say some time between 1993 and 2002, based on the documents I have access to. But it would likely have been left unused for some years before that. And, if the distinction matters, it was never a main track….clearly, from Parkdale northwards the main line was always single track working.
FWIW the Vintage Toronto site on Facebook just added a whole album of interesting pictures taken along Davenport, with several shots of the old Davenport station and the TTC-CN diamond at the level crossing on Davenport Road. Somewhere I have seen a whole album of shots of the St Clair grade separation under construction. They seemed to get a lot more done faster with horses and small steam engine excavators than ML can accomplish with P3 contracts and multimillion dollar budgets. The St Clair bridge is still in use a hundred years later.

- Paul
 
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