While pouring concrete in cold weather can present some challenges, it is a common practice. When outside temperatures drop to 40 degrees Fahrenheit and below, the water in a concrete mixture can freeze, affecting the stability and strength of the concrete. The American Concrete Institute (ACI) publishes guidelines for properly mixing, pouring, and curing concrete in cold weather. The document we refer to is the ACI 306R-10, “Guide to Cold Weather Concreting.”
Before starting your building project, we recommend that you perform a construction site inspection in NJ and the surrounding region to determine if the soil conditions are adequate for a foundation or slab, especially in winter when the ground may be frozen. Earth Engineering Incorporated can help you determine if there are unstable conditions due to freeze-thaw variabilities. Let’s explore some of the most important tips and instructions for concreting in cold weather.
Preheat Materials and Use Hot Water
If your crew is mixing concrete onsite in cold weather, it is beneficial to use heated water and concrete components that are stored in a warm, dry place. This practice helps to maintain the mix’s ideal temperature and ensures that the concrete is workable. Using water that has been warmed to around 140 degrees Fahrenheit will reduce setup time by up to 25%. According to the ACI, this is critical for preventing the concrete from freezing.
On larger projects, you will likely be ordering your concrete premixed that will be delivered by a supplier in an agitator truck. When below 40 degrees outside, the supplier will use hot water and properly store Portland cement and aggregate. Concrete generates its own heat. Therefore, it will remain warm inside the barrel until it arrives at your job site. Our team of inspectors is certified by the American Concrete Institute to test both concrete and reinforcing steel for placement in cold weather.
Add Accelerators and Low-Temperature Additives to the Mix
Accelerators are additives that help concrete to set more quickly while developing the desired strength during cold weather. One of the most popular low-temperature additives is calcium chloride. According to the Portland Cement Association, calcium chloride can increase the hardening rate by up to 30% when added following the ACI 306R-10 recommended proportions.
It is critical that your concrete and additives are specified correctly by an engineer who understands the proper proportions of all components of the concrete mix so as not to compromise its stability and desired strength once cured.
Insulate and Protect Freshly Poured Concrete
It is always a good idea to protect freshly poured concrete from the elements. This is especially important in winter when temperatures are cold, and there is the potential for sleet, snow, and even hail. Formwork that is properly designed and inspected by a field engineer is the first step in protecting the concrete.
When temps drop below 40 degrees, the addition of insulation blankets plays a vital role in maintaining proper curing temperatures. These thick tarps and mats are wrapped around a vertical structure or placed over a slab to retain the heat of the concrete while also preventing surfaces from freezing. The purpose is to keep the concrete at a steady temperature of at least 50 degrees Fahrenheit for a period of 2 days to speed up curing time and reduce the risk of thermal cracking.
Let the Site Professionals Assist You in the Winter
Construction schedules don’t always go as planned and are often delayed due to weather and supplier issues. If you find yourself challenged by cold temperatures and the need to meet a deadline, rest assured that cold weather concreting is achievable. Before beginning any site work, including earth moving, excavation, and foundation construction in NJ and PA, reach out to the geotechnical engineers and geologists at Earth Engineering Incorporated for, guidance on pouring concrete in cold weather and testing services we can provide for your unique project conditions.