What happens if concrete freezes during curing time?

April 28, 2023

What happens to concrete if it freezes during the curing process? This is a question that many construction professionals may ask when working in cold environments. The freezing of concrete can have a significant impact on its strength, durability, and overall performance. 

This article will explore the consequences of frozen concrete during the curing process and shed light on how to tell if concrete froze during curing. 

Read more: Learn about the long term effects of hot climates and cold climates on concrete and how to pour concrete in freezing conditions.

The concrete curing process

Concrete is a versatile building material used in various construction projects, from bridges and roads to buildings and dams. One of the most critical aspects of using concrete is ensuring that it cures properly, a process that involves the hydration of cement particles to form a strong bond between the aggregate materials. This creates a hardened structure that can withstand the forces and stresses it will encounter throughout its service life.

For freshly poured concrete to reach its full strength the curing process must be allowed to continue for at least 28 days. If the concrete freezes during the curing process the curing will stop.

Can concrete freeze while curing? 

The answer is yes, and if concrete freezes during the curing process, it can lead to several issues that can compromise its structural integrity and long-term performance. The following points will discuss the various problems that can arise when concrete freezes during the curing process:

1. Delayed Hydration

As mentioned earlier, the curing process involves the hydration of cement particles. If the concrete is exposed to freezing temperatures, the water in the mix starts to freeze, slowing down the hydration process. The cement particles cannot react effectively with the water, leading to a slower rate of strength gain. This can result in weaker concrete with reduced durability and a higher risk of cracking.

2. Expansion of Water 

At what temperature does concrete freeze? Typically, concrete begins to freeze when its temperature falls below 32°F (0°C). As water freezes, it expands by approximately 9%. This expansion can generate internal stresses within the concrete matrix, potentially causing micro-cracks to form. These cracks can compromise the structural integrity of the concrete and make it more susceptible to damage from external factors such as freeze-thaw cycles.

3. Reduced Bonding 

What happens if concrete freezes during the curing process in terms of bonding? The freezing temperatures can affect the bond between the cement paste and the aggregate materials in the concrete. As the water freezes, it can create a barrier between the cement paste and the aggregates, reducing the overall strength of the bond. This can result in a weaker and more porous concrete structure, making it more susceptible to wear and tear.

4. Compromised Workability 

Frozen concrete can also become more challenging to work with, as the freezing temperatures can make the mix more rigid and less pliable. This can lead to difficulties in placing and compacting the concrete, potentially affecting the overall quality and finish of the final product.

Read more: Can you lay concrete in the rain and what is the best weather to pour concrete?

Road and some trees during a blizzard

How to tell if concrete froze during curing

To determine if freshly poured concrete is frozen, look for the following signs:

  1. Slower setting time: Freshly poured concrete that is freezing will take longer to set and harden, as the chemical reactions that cause it to cure are slowed down by cold temperatures.
  2. Bleeding water: As the water in the concrete mix freezes, it may cause excessive bleeding, where water pools on the surface of the concrete. This can indicate that the concrete is freezing or has frozen.
  3. Inconsistent texture: Frozen areas within the concrete may create an uneven texture or color, as the freezing process disrupts the normal curing process.
  4. Surface frost or ice: If the surface of the freshly poured concrete starts to develop frost or ice, this is a clear indication that it is freezing or has already frozen.

Considering the potential issues that can arise when concrete freezes during the curing process, it is essential to take appropriate preventive measures to ensure a high-quality, durable structure. It is also possible to measure the temperature of concrete in order to know when it is time to start taking some precautions.

Read more: Read up on how humidity affects fresh concrete, tips on how to place concrete in hot weather and underwater concreting.

Frequently asked questions

How long does concrete need to be protected from freezing?

Concrete needs to be protected from freezing during the first 24 hours. 

Will concrete crack in cold weather?

Since the concrete contracts in lower temperatures, very cold weather can cause cracking. The same goes for hot temperatures where concrete will expand. Both expansion and contraction of concrete will eventually cause cracks.

Is it OK to put salt on concrete?

Salt harms concrete by causing chemical changes that weaken it. It also makes the metal inside the concrete rust, which leads to cracks. Lastly, salt increases the cycles of freezing and thawing, causing damage to the concrete surface.

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