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Ensuring Successful Cold Weather Concrete Pours
February 5th, 2019
Let’s face it, we’re used to starting construction in the New England winters. But the truth is this timing isn’t ideal for anyone. The weather is unpredictable and can throw off a construction schedule, while winter conditions add to project costs.
Ideally, you would plan your project to be done with any concrete work before the temperature falls below 40 degrees. But we know this isn’t always realistic, so read on to learn how to protect your winter concrete, the risks associated with doing concrete work in cold weather and how we ensured optimal results on a recent project.
Winter Concrete Protection
The key to successfully completing concrete work in the winter is to let the concrete fully cure before exposing it to the freezing weather. If the proper temperatures are maintained, this typically happens the second day after a pour. There are several ways to prevent the concrete from freezing, however the owner pays more money to cover these winter conditions.
Winter conditions related to cold weather concrete include but are not limited to:
- Plastic sheathing to create temporary enclosures
- Temporary heating to keep the space warm
- Blankets to cover footings and pours
- Extra labor hours for snow and ice removal
- Additional lighting to help with visibility during shorter, winter days
We typically carry an allowance for winter conditions based on what phase the project will be in between late November and early April.
Winter Concrete Risks
Even though pouring concrete in cold weather is fairly common, there are still serious risks associated with it.
- Early freezing of concrete can result in a reduction of up to 50% of its ultimate strength.
- Concrete that’s exposed to repeated freeze-thaw cycles while it’s still curing is susceptible to expansion, cracking, scaling and crumbling.
- Concrete is vulnerable to thermal shock, which can cause it to crack.
Case Study: athenahealth West Garage
When working on the parking garage at athenahealth, we started foundations in the middle of January. The cast-in-place concrete specification required us to create a Cold Weather Concrete Quality Control Plan. It covered everything from approved mix designs to delivery requirements to temperature monitoring to how and when to protect the concrete. We worked with our subcontractors to create a comprehensive plan to ensure the best possible outcome.
The parking garage’s foundation used 10,000 cubic yards of concrete that we poured over eight weeks starting in mid-January. It was imperative that we placed the concrete in accordance to our Quality Control Plan.
One of the unique pieces of our Quality Control Plan was the use of internal, Bluetooth-enabled concrete sensors, where we could measure both internal and surface temperatures of all concrete placements. We installed the sensors at approved cubic yardage intervals, or pours, and recorded the temperatures twice a day in a daily log for the engineers to review. This worked extremely well and gave all team members confidence in the high quality of the concrete placement scope. This temperature monitoring coupled with our lean planning allowed us to place all the concrete on schedule and without any quality issues during the coldest time of the year.