Important Considerations of Cold Weather Concreting

Cold weather concreting is the process by which concrete is laid, dried and maintained in low temperature climates. According to studies, cold weather has an adverse effect on the concrete’s qualities, such as its appearance, durability, and strength. To prevent flaws in concreting and to ensure optimal laying of concrete in cold weather, there are certain precautions necessary.

Hence, it is highly advisable to know how these factors can affect cold weather concreting and learn the best way to get strong, durable structures.

In this blog, we will discover important points of concreting in cold weather, including learning the objectives, principles and strategies of cold concreting, effect of cold weather on concrete, and precautions for optimal concreting in cold weather.

What is Cold Weather Concreting?

Generally, cold weather concreting is defined as – The time when the average daily ambient temperature is below, or expected to stay below 5 degree-Celsius for more than 3 days constantly. In this context, the mean of the lowest and highest temperatures recorded between midnight and midnight – for 24 hours – is considered as the average daily temperature.

However, if the temperature of the region reaches over 10 degree-Celsius for over 12 hours within any 24-hour period, then the period is not considered cold weather in the construction industry.

Hence, construction experts have discovered the use of heaters, insulating equipment, and curing compound to ensure best concreting in cold climate areas.

Temperature of Fresh Concrete

Cement mixing is mainly a chemical process, apart from the physical act of combining water and cement together. The rate of chemical reaction during the mixing of concrete is highly dependent on the ambient temperature. In addition, the entire process is exothermic, meaning it creates its own heat during the curing, which can last for up to 3 days.

In fact, concrete continues to remain warm if it is laid under ideal conditions. For instance, concrete tends to cure completely when it is laid at warmer temperatures and hydration is also easier.

According to construction experts, it is important to know that sections of thick concrete tend to cool gradually as they eventually lose heat. This also effectively helps avoid cracks from developing in the concrete, by lowering the temperature difference between the outer edges and central portion of the laid concrete.

Apart from this, there are numerous options available in the market when it comes to buying the best curing compound for cold weather concreting. For instance, Sakshi Chem Sciences manufactures top-quality concrete curing material for best results.

Objectives and Principles for Cold Weather Concreting Procedures

To ensure the best results from concreting, there are certain measures and principles that need to be followed, as per industrial experts. The main concern of concreting in cold weather is to prevent damage from premature freezing, which happens when the cement hardens but the concrete is still saturated. This step ensures that the concrete gains the appropriate strength, and prevent cracks that develop due to frequent fluctuation in ambient temperature.

In 1962, T. C. Powers discovered the perfect rule for cold weather concreting. Powers shows that concrete with compressive strength of 500 psi has water saturation level lower than the critical point. This usually occurs over 48 hours if the temperature is over 10 degree-Celsius. This makes the concrete stronger and sufficiently dry to undergo a single freezing cycle of freeze/thaw temperatures successfully.

Strategies for Cold Weather Concreting

Here are some strategies for successful cold weather concreting by our construction experts –

Preparing concrete for cold weather

The first step towards achieving optimal strength in concrete during cold weather starts with preparing it with the steps described below:

• Prepare a feasible plan for cold weather concreting before the temperatures drop significantly.
• Organize the necessary materials and equipment for concreting in cold weather at the site before the cold weather arrives.
• Choose air-entraining concrete for certain areas, such as slabs and other flat surfaces, if the region is experiencing frequent freeze-thaw cycles.
• Make sure to remove any frost, ice or snow from the surface and reinforcing components beforehand.
• You can also regularly check the weather conditions, surface temperature and air quality at least twice a day for best concrete preparation.

Pouring concrete in cold weather

Once the concrete is prepared using the above-mentioned steps, the next step is to know how the pour concrete properly in cold weather:

• Unless the temperature is over freezing limit, you should avoid pouring concrete around large areas.
• Using high early-strength concrete is highly advisable in cold weather by construction professionals.
• Do not use ‘anti-freeze’ solutions to lower the freezing point of concrete.

There are also certain conditions when construction experts recommend avoiding the use of cold weather admixtures that have soluble chlorides, such as:

• If concrete contains pre-stressing strands or aluminum as it can cause corrosion faster.
• If you do not want the troweled area of concrete to become discolored.
• If galvanized steel will be joined with cold weather concrete surface.

Protecting concrete in cold weather

Once you know how to prepare and pour it, your next step is to ensure protecting the concrete in cold weather with the following steps:

• Some of the protection methods recommended by construction experts include using enclosures, adjusting concrete admixture or curing compound, supplemental heat, etc.
• Make sure to protect the laid concrete against damage from freezing for at least 72 hours.
• If structural safety is a priority in the building, then you need to offer protection to the cold weather concrete for a longer period of time to ensure optimal strength development.
• Even when freezing temperatures are not expected, you should prevent the concrete surface from freezing with the necessary precautions for the first 24 hours at least, once it is laid.
• You can remove protective components if the temperature of the concrete surface is less than -6.6 degree-Celsius.

Curing concrete in cold weather

Now that you’ve learned about protecting cold weather concreting, you should also know the major tips from professional builders regarding proper curing of the concrete, including:

• Concrete should be cured completely to avoid losing moisture and the resultant weakening.
• If you are using heated enclosures to protect the concrete surface, then make sure to give moisture by heating with steam or simple spraying. Make sure to allow the concrete to cool slowly in order to avoid cracking of the concrete surface from abrupt temperature change.
• Leave the formwork in place for as long as the project allows for optimal strength in the concrete.
• Until the concrete acquires the desired strength, you should re-shore as frequently as possible.
• Concrete which is laid in winter or fall should be kept from exposure to de-icing salts, especially from parked vehicles.
• When the concrete is cured using curing compound at lower than 15.5 degree-Celsius, then you can use water retarders and water reducers to prolong the curing time in cold weather.

Cold Weather Concreting – Common Mistakes

Despite its growing popularity, many builders and contractors tend to have several misconceptions about concreting in cold weather. Besides this, there are some necessary precautions that need to be taken if you want to prevent concrete from getting damaged in cold weather. According to construction experts, the level of protection for concreting should rise when the temperature drops.

Here are some of the common mistakes to avoid during cold weather concreting –

Delay in laying concrete

Transporting or moving concrete should be carefully planned in cold weather conditions. For instance, you should ensure that the cold weather concrete is delivered on time. It is also advisable to heat water and aggregates at ideal temperatures while mixing concrete for cold weather.

An effective method to heating is using hot water blends, or blending the sand in cooler areas, and even warming the sand before mixing in the cement.

Failing to monitor temperature

Another common mistake contractors experience with cold weather concrete is that they fail to monitor the temperature of the mixture constantly. It is recommended to use temperature sensors that make it easier and more efficient to check the concrete’s temperature at frequent intervals.

Laying concrete on frozen surfaces

At times, concrete may be laid on frozen and cold ground. However, the concrete may develop cracks or even break apart, when the ground thaws. Besides this, the concrete layer closest to the ground tends to cure slower than the layer on the surface. As a result, the upper surface of a slab will harden quicker than the bottom portion, which can also cause crusting and cracking in the concrete.

Letting concrete freeze

Ideally, the temperature of laid concrete in cold weather should be around 10 – 21 degree-Celsius to achieve the expected strength. In contrast, fresh concrete in cold weather fails to gain the desired level of strength if it freezes before reaching the 500 psi benchmark. To prevent this, it is advisable to air-entrain the exterior concrete at the minimum required strength before the freezing and thawing cycle begins.

Mix Design Adjustments in Cold Weather Concreting Procedures

Here are some adjustments in mix design you can try for best quality cold weather concrete:

Adding more cement

Some cement manufacturers use Type I and Type II cements for cold weather concrete, while other may choose to use Type III, which is highly early strength cement. Type III is finely grounded cement and also reacts faster with water and other aggregates, which ensures higher early compressive strength.

Adjusting admixtures

Another tip to enhance cold weather concreting efforts is the choice of admixtures used. According to experts, you should choose additives for concrete used in cold weather according to the specific requirement of the building project.

For instance, it is recommended to lower the quantity of water reducer in the concrete when it is poured in cold weather. Besides this, you should also use less water-reducing retarder for ideal cold weather concrete.

Effect of Cold Weather on Concrete

Some of the significantly damaging effects of cold weather on concrete are:

• Longer curing and setting time as extremely low temperatures obstruct the hydration of cement.
• Lower strength development as cold weather adversely impacts the development of concrete strength.
• Higher risk of cracking because frequent temperature fluctuations can cause thermal stress that results in the cement surface to develop cracks.
• Swifter surface deterioration as quick freeze-thaw cycles can cause spalling and scaling in the concrete.

Cold Weather Concrete Placements

It is strongly recommended to follow the detailed guidelines when laying cold weather concrete for best end results. Firstly, you should regularly monitor the levels of heat in the concrete when the ambient temperature falls considerably low.

Next, you can make adjustments to the proportions of curing compound, admixtures, and other aggregates in the concrete. Lastly, you can use pre-heated aggregates in water to maintain an ideal temperature range in the concrete before it is laid.

What happens when concrete freezes?

Concrete experiences significant damage when it freezes. For instance, the water in the concrete expands when it form ice. This process causes increased internal pressure and results in minor cracks on the surface of the concrete.

Apart from this, the ice crystals forming inside the concrete create tiny gaps. This results in increasing the concrete’s porosity, and causes unwanted water retention. The increased porosity of the concrete also worsens the damage caused by the usual freeze-thaw cycle on cold weather conditions.

Precautions for Cold Weather Concreting

Let’s quickly check out the main precautions required for cold weather concreting:

• Remove any ice and snow from surface before laying the concrete
• Heat water and cement aggregates before mixing concrete
• Protect concrete by coverings, heated enclosures and similar insulation techniques
• Avoid wet curing during cold weather conditions
• Control temperature gradient so it stays within the advisable limit

Conclusion

Cold weather concreting is a special process through which concrete poured in low temperatures is laid, cured and formed perfectly. It requires learning certain precautions, such as maintaining the water levels in the cement and using special insulation equipment to hydrate the cement completely.

It is highly recommended by construction experts to use good-quality curing compound, such as those manufactured by Sakshi Chem Sciences, for best results.

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