Holding SmartRock on the Jobsite during winter

Cold Weather Concreting

For many construction companies, it is approaching the time of the year when dropping temperatures play a massive role in your workers day to day operations, especially where concrete is involved. Concrete temperature monitoring becomes more critical in cold weather as low temperatures decrease the rate of strength development during curing. For this reason, accurate and consistent temperature monitoring of your in-situ slab is important so that the quality of your structure is optimal.

What is Cold Weather Concreting

In the American Concrete Institute (ACI) 306: Guide to Cold Weather Concreting “cold weather” is defined as three or more consecutive days of low temperatures, specifically outdoor temperatures below 40 degrees F (4 degrees C) and air temperature below 50 degrees F (10 degrees C) for more than any 12-hour period.

Learn About the Five Phases of Heat Evolution in Concrete.

Concrete Construction Site Using SmartRock2

Why Should You Care About Proper Cold Weather Concreting Practices?

Temperature is typically measured to make sure the concrete is in compliance with certain specifications that define an allowable temperature range. Typical specifications require the temperature of the concrete during placement to be within a range of 10°C to 32°C (50°F to 90°F). However, different specified limits are provided depending on the element size and ambient conditions (ACI 301, 207). The temperature the concrete exhibits during placement affects the temperature of concrete during the next hydration phase.

By closely monitoring temperature variances in your concrete element during curing you will ensure that the strength, quality, and durability of your structure is acceptable. If cold weather concreting practices are not followed according to specifications, you risk running into numerous issues and possibly even structural damage. Among these problems include;

  • Freezing of concrete at early ages,
  • Lack of required strength,
  • Rapid temperature changes,
  • Inadequate protection of the structure and its serviceability, and
  • Improper curing procedures.

5 Tips for Controlling Concrete Temperature in Cold Weather

Installing internal electric heating:

This requires using embedded coils and insulated electrical resistors.

Optimize Your Concrete Mix:

Using low-heat cement; aggregate substitutes such as fly ash, limestone, or slag; and low water-to-cementitious materials are all good ways to optimize your concrete mix for heat retention in cold weather.

Use Insulation:

Layering helps maintain the heat that is generated from the concrete. Like heating blankets or forms, this allows you to control temperature differentials between the core and the surface of your slab.

Cool Concrete Before Placement:

This can be done using chilled water, chipped or shaved ice, or liquid nitrogen.

Cool Concrete After Placement:

Use embedded non-corrosive cooling pipes prior to concrete placement. This removes heat by circulating cool water from a nearby source.

Concrete Construction Site Using SmartRock2

Optimizing Your In-situ Concrete for Cold Weather

  • When working with early-age concrete, temperatures should be above freezing or within 10 degrees F (-12 degrees C) of the minimum required temperature.
  • The required temperature of concrete is >5 degrees C (40 degrees F) for 48hrs (ACI 306)
  • The desired strength of concrete before freezing is 3.5 MPa/500 psi (ACI 306). Concrete that is below 3.5 MPa/500 psi can lead to cracking because it does not have the strength to resist the expansion of water due to ice formation.
  • To protect concrete from freeze damage all concrete surfaces need to be protected within the first 24 hours of being placed.
  • When removing ice, the volume of ice should not be more than 75 percent of the batch water (NPCA).

7 Common Mistakes to Avoid During Cold Weather Concreting

To help you avoid structural issues and project delays, it is important to familiarize yourself with the do’s and don’ts of cold weather concreting. Take a look at these 7 common mistakes to avoid when pouring concrete in cold weather.

  1. Pouring Concrete on Frozen Ground

When pouring your concrete, the placement of your slab factors into the effectiveness of the concrete curing conditions. Frozen ground can settle when thawed, causing the concrete to crack. The fresh concrete closest to the ground will also cure slower than the surface, meaning the top of your sets while the bottom stays soft. This is a problem because concrete with different temperature gradients doesn’t develop strength adequately, leading to cracking and possible structure disaster.

  1. Allowing your Concrete to Freeze

Concrete should be kept warm (around 10°C), in order to cure properly. Fresh concrete can freeze at -4°C, so it is important to warm fresh concrete until it has the proper compressive strength measurement. This can be done more efficiently using a concrete temperature and maturity meter, such as SmartRock.

Cold Weather Concreting

 

  1. Using Cold Tools

It is just as important to keep your tools and building materials warm as it is the concrete. If forms or tools are too cold, it could alter the concrete that comes into contact with them. This can negatively affect the strength development of your slab.

  1. Not Using Heaters

Concrete needs to stay warm in order for strength to develop and continue curing. If your slab gets too low in temperature, curing stops altogether. Portable heaters deliver extra heat into the ground and directly on the concrete, ensuring concrete keeps curing and gaining strength. Be careful when using heat; improperly heating the concrete can result in a weak structure.

  1. Sealing Concrete When it’s Too Cold

Concrete sealers make your concrete more resistant to weather exposure and other outside elements. If you are placing concrete in cold weather, it is advised to get a sealer that works well in extreme weather conditions based on the recommend of the producer/manufacturer. Sealing typically should not be done if the temperature is below 10°C (50°F).

  1. Misjudging Daylight

During the colder months, the amount of daylight lessens. It is essential to use your time wisely, as running behind schedule could lead to more problems. Daylight will not only give you an abundance of light, it will also result in warmer temperatures. If concrete must be poured before or after the sun has passed, be sure to follow #4 on this list.

  1. Not Using Real-time Temperature Sensors

For these techniques to make a valuable difference, you must be able to monitor and report on the changing temperatures of your concrete structure. Traditionally wired systems, such as thermocouples and loggers, are used. In most of these systems, however, wires stick out from the concrete and need to be protected from damage onsite. The data loggers that are attached to the ends of thermocouples may also experience malfunctioning at very low temperatures. Moreover, the manual installation process for these types of sensors, along with the time-consuming data collection process, becomes more difficult in cold weather conditions. More specifically, when heat blankets are used, it is a challenge to lift them and find the end of the temperature cables to collect data.

Real-time Temperature Sensors
Real-time Temperature Sensors

Wireless temperature sensors, like SmartRock, are designed to address these cold weather concreting challenges. One of the benefits of fully-embedded sensors during cold weather concrete temperature monitoring is the elimination of a physical connection to data loggers, which are required when using wired systems. This allows sensors to remain protected in the concrete and eliminates the hassle of having to find the sensors beneath protective blankets. It also eliminates potential malfunctioning from cold temperatures and exposed wires.

Monitoring Your Concrete in Cold Weather with Wireless Sensors

SmartRock’s ability to monitor the effects of the in-situ concrete and ambient temperatures make it easier to control concrete curing and ensure optimal strength gaining conditions. They provide real-time data on temperature and strength during all stages of the curing process, from early-age to hardening. These measurements upload directly on the free SmartRock app (available for both iOS and Android devices), where they can be downloaded and shared with any team member. From there, you can view the minimum and maximum temperature values and track the temperature and strength history of your pour.

Optimizing Your In-situ Concrete for Cold Weather with SmartRock

Not only does SmartRock make your job of monitoring temperature easier, it also allows you to know more information about your concrete than ever before. With the SmartRock app and its’ Giatec 360 desktop dashboard, it is easy to check the temperature gradients of your in-situ concrete so you can ensure that the core and surface of your slabs are consistently curing. Equipped with real-time results, contractors can improve the heating process, decrease energy costs, and save time in their project schedule by knowing when to move on to subsequent construction operations, such as; formwork removal or post-tensioning.

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