How To Work With Concrete In The Winter Cold
Practically everything is harder to do in the harsh winter cold. If you’re not freezing your hands off, mobility and versatility are greatly impaired because of thick gloves and clothing layers. Concrete workers and masons have it worse. Not only is the safety risk higher, but they have to battle strong winds and sleet while mixing, pouring, and forming cement. To make matters even worse, low temperatures are not concrete’s friends.
What happens to concrete in extreme cold?
The short answer to this is that the concrete’s strength will be compromised. The damage done to concrete is immediate and permanent, no matter what you do to fix it. You can try to warm it up or cure it, but the damage has already been done. That’s why the only way to save concrete during cold weather is to prevent the damage.
If fresh concrete freezes, or if it freezes before it has attained enough strength to withstand forces associated with cold water, the concrete loses more or less 50% of its comprehensive strength.
Helpful Tips For Working With Concrete In Winter
Contrary to popular belief, it is possible to place successfully, finish, and cure concrete in extremely low temperatures (even sub-zero temperatures). It just needs a little extra work. From prepping, placing, and curing, a few precautions need to be taken.
Prepping
- Do not misjudge daylight
Keep in mind that days are “shorter” in the winter, and the amount of sunlight lessens. Now while it’s okay to work at night, sunlight also means warmer temperatures. With that, wisely plan your project and organize your concrete tasks to get the most out of sunlight.
2. Preheat materials
When the months start to get colder, it can help preheat at least one of the constituent materials, like water and aggregates, to ensure the concrete is at a proper temperature when it’s poured. Onsite, you can use hot water and/or keep the aggregate stored in a warm indoor area before mixing. But some ready-mix companies generally send out concrete from their plant in trucks at about 65 degrees Fahrenheit.
3. Adjust mixture components if needed
Even though you’ve done this countless times, not all jobs are the same — Concrete jobs are varied because of factors like the crew’s skill and cement quality. In this case, temperature and climate are your biggest issues, so you may need to adjust the mixture components. Usually, it involves increasing the cement content ratio or using a 2% ratio of an accelerating chemical mixture like calcium chloride.
4. Use Portland cement Type III.
High moisture content in cement can cause corrosion problems in steel reinforcement. Portland cement Type III aids in setting that does not reduce the quality of the concrete.
5. Do not use fly ash or slag cement.
When working with concrete on colder days, avoid using slag cement or fly ash. This is because these generate less internal heat and set up slower.
Placing and Pouring
- Employ a project management system that has the crew stay longer on site
Winter might mean longer work hours for the crew. When concrete is exposed to lower temperatures, it takes more time to set initially. So, adjust the finishing crew’s work schedules for them to be present for a longer time.
2. Use windbreaks
As the name implies, windbreaks act as a barrier to reduce and redirect wind, protecting both the concrete and the workers. Winds can drop the temperature quickly and hasten evaporation. Windbreakers of about 6-feet are enough to prevent these.
3. Consider heated enclosures
In more extreme cases, heated enclosures may be needed. You can use rigid-plastic commercial ones or make it with canvas tarps, wood, or polyethylene sheets, then use electric heaters to get the best results.
If you choose to use fuel-burning heaters, go for indirect-fired heaters — warm air is funneled int from burner unit placed outside the enclosure. Alternatively, you can use a hydronic system. Through hoses or pipes, a warm mixture of water and glycol circulates through the enclosure.
4. Do not pour concrete on frozen ground.
When frozen is thawed, it can settle and cause the concrete to crack. This weakness occurs because the fresh concrete closest to the ground cures much slower than the surface, which means the bottom remains soft while the top of the slap sets. The problem is the strength of concrete with varied temperature gradients does not develop.
With that, heat the ground with heaters or other means of increasing temperature.
5. Do not use cold tools.
Similar to the cold ground coming into contact with fresh concrete, cold tools have the same effect. Cold tools can alter the concrete and negatively affect its strength.
6. Be mindful of the temperatures.
Keeping track of the temperature is of utmost importance. Concrete must be poured and placed at a temperature of no less than 40 degrees Fahrenheit and kept there for how long it’s appropriate for the type of concrete and its purpose.
One day at a temperature of at least 40 degrees Fahrenheit is enough for high-early strength concrete that will not be exposed to freeze-thaw cycles. Conversely, concrete foundations and structures that are intended to carry heavy loads early on need 20 days at the minimum at least 50 degrees Fahrenheit.
Cement curing is an exothermic reaction, meaning that it produces some heat itself. Therefore, there are often when trapping the heat with insulating blankets or polyethylene sheets is sufficient.
Curing
- Keep the type of cement in mind.
Cure the concrete for the time recommended for the type used.
The ACI Committee 308 recommends the following:
● ASTM C 150 Type I cement — 7 days
● ASTM C 150 Type II cement — 10 days
● ASTM C 150 Type III cement — 3 days
● ASTM C 150 Type IV or V cement — 14 days
● ASTM C 595, C 845, C 1157 cements — variable
2. Leave forms in place
If the crew used forms, advise them to leave them in place for as long as possible. This is because it will retain heat and can stave off the concrete from drying too fast. Edges and corners vulnerable, but forms can help keep heat.
3. Consider using live steam.
Low humidity levels are common in cold weather and this can cause concrete to dry too quickly. To solve this, consider having live steam pumped into the enclosure around the concrete.
4. Wait for bleed water to evaporate before finishing.
A common concrete mistake is finishing before all bleed water completely evaporates, creating a layer or sheen of water on the surface.
Concrete is poured and placed in cold climates sets and cures much slower, which also means that bleeding starts later than expected. There also tends to be more bleed water compared to regular concrete placement. The key here is to be patient and wait for all bleed water to evaporate before finishing fully.
5. Verify concrete temperature and do not let your concrete freeze
It was previously mentioned that concrete needs to be poured and placed at at least 40 degrees, but it’s essential to keep track of the temperature while curing. Utilizing an infrared temperature gun can quickly deliver accurate results — ensure that it is maintaining a 40-degree temperature at the minimum during the curing period.
It’s vital to note that concrete should never be allowed to freeze within 24 hours of its pouring and placing.
Working with concrete in cold weather does take extra time, effort, and care than it usually does in warmer months. But neglecting to follow these procedures will lead to a concrete project failure.
6. Be alert for the concrete cooling too rapidly
Be vigilant in guarding against the concrete cooling too fast, particularly when active heating is discontinued. One of the most common ways is to lower the temperature in the enclosure gradually. The keyword here is “gradually.” Abruptly changing the temperature can damage the concrete, specifically cracking.
For projects with a smaller surface area of concrete, you can cover it with insulated blankets. For larger structures, it’s recommended that gradual cooling for several days or weeks is needed.
7. Do not seal concrete if it’s cold.
To make the concrete more resistant to outside elements, such as weather exposure, sealers are used. And because cold weather is not favorable to work with concrete in, make sure you choose a sealer that works well in harsh weather conditions, in this case, cold weather. Moreover, sealing concrete should be done at a temperature of at least 50 degrees Fahrenheit, nothing less.
Managing construction projects with concrete contractor software
Using concrete contractor software positively impacts your day to day life, workwise. It increases efficiency, improves productivity, and reduces the chance of reworking.
Concrete contractor software allows concrete contractors to fluidly update data, such as drawings, budgets, and change orders to avoid any mistakes on the field and (digital) paper. Documents are also safely stored on the cloud and can easily be shared with your crew members.
More than that, you can stay on schedule and on budget. With this tool, you can correctly deploy resources, dispatch crew members, and review production reports. Reviewing the reports can help you analyze what equipment to use, identify issues, and immediately solve them.
All in all, project management software proves to be highly beneficial.
