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Effects of Cold Weather on Concrete

Every contractor who regularly works with concrete in cold or temperate climates knows that cold weather can ruin the placement of new concrete and damage concrete structures and surfaces over time.

But why does this happen? What are the effects of cold weather on concrete? 

Read on to explore what cold weather does to concrete and precautions to avoid the worst damage. 

How Does Cold Weather Damage Fresh Concrete?

Although the cold can damage concrete at any stage, freshly placed concrete is most susceptible to weather. Saturated or badly designed concrete is tough to work with in cold weather, so consider your environment when deciding on the mix. 

Concrete becomes solid through a reaction called hydration. When cement powder comes into contact with water, this reaction is what begins a crystallization process. The crystallization speed depends on the ambient temperature where you work with concrete. When it's hot, the reaction can happen quickly — sometimes too quickly — and when it's cold, the reaction slows down.

This reaction is good to a point, with slow crystals forming stronger concrete. However, below 14°F, the crystals stop growing entirely. Additionally, time is a factor. Under average temperatures, concrete will strengthen in 24 hours. Leave it too much longer, and the higher the chance of a cold snap that could freeze the concrete. 

Concrete needs internal crystallization to resist the pressure of frozen water within it. A minimum compressive strength of 500 pounds per square inch is essential, or there will be freeze damage. 

When it's below 14°F, freezing will likely coincide with crystallization pausing and weaken your concrete further internally with a 'plastic state freeze.' This is a danger for newly placed concrete, which is why White Cap always advises the use of curing blankets to our customers.

The Freeze-Thaw Cycle

Moisture damages all unsealed or poorly sealed concrete via the freeze-thaw cycle. Cold weather affects concrete when the water has entered through its porous surface, as well as when concrete is freshly placed. 

When water freezes, it expands by 9%. Over time, the expansion of water freezing inside a structure cracks concrete internally. In areas with cold winters, this happens repeatedly and can cause further serious issues over time, such as spalling and scaling.

Below is a little more on spalling and scaling, as well as how unmanaged snow, rain, and ice can damage concrete even long after it is placed.

How Does Cold Weather Damage Poorly Sealed Concrete?

While water passing through concrete isn't inherently harmful to the material, the freeze-thaw cycle is. 
Cold Weather Concreting - Freeze Thaw Bridge Damage

It is best to minimize even a sealed concrete surface's contact with snow and ice if possible (shoveling snow, deicing using a concrete-safe salt-free deicer, etc.). 

If these precautions aren't taken, the effects of cold weather on concrete include:

1. Spalling

Spalling is a common issue with concrete. It happens when areas of a flatwork slab delaminate from the substrate. It can be caused by the freeze-thaw cycle and worsened by rebar corrosion (which can also be caused by contact with water and ice). Initially, spalling looks like acne scars on the surface of concrete, but as the problem gets more serious, large chunks of concrete can come loose, revealing the inner surface of the concrete and any damaged rebar/mesh. 

2. Scaling
Scaling is when thin layers of exterior concrete come away. They usually appear as delicate flakes on the surface of concrete slabs. Initially, scaling is a minor issue, but as the inner layers of concrete are exposed, the problem can worsen. 
Cold Weather Concreting - Spalling and Scaling

3. Cracking
All concrete is at risk of internal and eventually external cracking via repeated exposure to the freeze-thaw cycle. Still, poorly mixed and badly designed concrete is in the most danger. Salt worsens the problem, so don't salt concrete paths and driveways in the winter.

Precautions to Take When Working With Concrete in the Cold

If you know it will be less than 40°F for three days while placing concrete, know your concrete will be hard to work with. The effects of cold weather on freshly placed concrete include a much slower curing time and plastic freezing.

There are a few ways to guard against these effects, like using curing blankets and designing concrete with cold weather in mind.

Concrete Design
Concrete designed for cold weather should include additional cement for strength and to add internal heat, low slump to avoid excessive bleed, and you shouldn't add much fly ash as it slows curing time.

No matter the temperature when you lay concrete, fly ash should always be kept under 25% in areas with cold winters. This is because the ash makes concrete more susceptible to scaling and spalling later on if it is repeatedly exposed to the freeze-thaw cycle.
Before You Place 
Consider a heated mixer for cold-weather concrete placement. A warm mix will help negate the effects of cold weather on concrete, especially if you keep in the heat with curing blankets, and the additional cost is minimal compared to repairing or replacing concrete later. 

You should also think ahead when placing concrete on newly excavated earth. Keep the earth's natural warmth in by laying curing blankets before you're ready with your concrete. 

After You Place
Finally, after completing the placement and finishing and allowing the bleed water to evaporate, you should cover concrete with insulated curing blankets for 72 hours. This allows the temperature to stabilize, at which point you can remove the blankets so your concrete can air dry and continue curing until it reaches the necessary psi for the project. 

Repairing the Effects of Cold Weather on Concrete

Concrete repair and restoration should be avoided by taking the precautions outlined above whenever possible. That being said, some damage is inevitable over time due to the effects of cold weather on concrete.

The good news? 

Most damage can be repaired. Early signs of cracking, spalling, and discoloration can all be dealt with through careful repair, even if they result from poor construction or curing.  

If you need help with repair techniques, finding the root cause of a concrete issue, or want to discuss the perfect material for the job, get in touch with one of our White Cap experts.

Why White Cap?

White Cap has been working with industry-leading professionals in construction for over 35 years. In fact, many of our highly trained sellers and specialists worked in the construction industry themselves before joining the White Cap family. Our local experts are always happy to help, and as they know the area, they can answer questions about dealing with weather conditions better than anyone else.

With over 400 stores across the US and online shopping options, you can always depend on White Cap to help you get the job done. If you're interested in buying or renting from White Cap, request a quote or get in touch today.
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