The construction industry faces unique challenges when working in cold weather, especially when dealing with cement-based materials like concrete and mortar. If you've ever poured concrete in freezing temperatures, you know it’s not as simple as just waiting for it to set. The cold can slow down hydration—the chemical reaction that gives concrete its strength—leading to delays, weaker structures, and long-term durability issues.
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So, what can you do to ensure your concrete and mortar perform well in chilly conditions? This article breaks down the science behind cold weather’s impact on cement, shares best practices for working in low temperatures, and highlights research-backed strategies to keep your projects on track.
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Cement and Mortar: The Basics
Cement primarily consists of calcium silicates (C3S and C2S), aluminates, and ferrites. When mixed with water, it forms calcium silicate hydrate (C-S-H) gel, the key component responsible for concrete’s strength. Mortar, a mixture of cement, fine aggregates (sand), and water, acts as a binding agent in masonry. While hydration is an exothermic process, it is also highly temperature-sensitive. Optimal curing occurs between 10 °C and 25 °C. When temperatures fall below this range, reaction rates slow, delaying setting time and strength development.
However, cold weather can throw a wrench in the hydration process, leading to slower reaction rates and even freezing risks.
If fresh concrete freezes before it sets, the results can be disastrous—cracks, weak spots, and durability problems down the line. Here’s what happens when temperatures drop:
- Slower Reaction Rates: As the temperature goes down, hydration slows down. Research shows that at 5 °C, concrete takes twice as long to gain strength as it does at 20 °C. This delay can be a big deal for projects that rely on early strength development.
- Risk of Freezing: If water inside the mix freezes, it expands and disrupts the matrix, creating microcracks. If this happens within the first 24 hours, compressive strength can drop by up to 50 %.
- Long-Term Durability Issues: Cold weather can lead to incomplete hydration, leaving unreacted cement particles. This increases permeability, allowing moisture and de-icing salts to seep in, leading to freeze-thaw damage and corrosion of embedded steel.
Best Practices for Cold-Weather Concreting
To keep your concrete strong and durable despite the cold, you’ll need to take extra precautions. The goal is to prevent freezing, maintain adequate curing temperatures, and ensure strength development. Here’s how:2,3
1. Pre-Placement Preparations
- Make sure forms, subgrades, and reinforcement are ice-free and warmed above freezing.
- Use heated aggregates and warm mixing water to keep the mix temperature in a safe range.
- Cover the subgrade with thermal blankets before placement to prevent heat loss.
- Aim for an initial mix temperature of 10–20°C to kickstart hydration.
2. Temperature Control and Insulation
- Use insulating blankets, form insulation, and heated enclosures to keep temperatures stable.
- Be cautious with heaters—proper ventilation is key to avoiding surface carbonation.
- Protect exposed edges and thin sections with extra insulation.
- Remove insulation gradually to prevent sudden temperature drops that could cause cracking.
3. Curing Techniques
- Avoid traditional moist curing in freezing temperatures, as added water can freeze and damage the concrete.
- Use membrane-forming curing compounds and insulated covers to retain moisture safely.
- Keep formwork on longer to slow cooling and protect curing conditions.
- Set up windbreaks and evaporation retarders to prevent moisture loss in cold, dry air.
4. Mix Design and Admixtures
- Use accelerators like calcium nitrate or calcium chloride to speed up hydration and strength gain.
- Add air-entraining agents to improve freeze-thaw resistance and minimize cracking risks.
- Consider high-early-strength cement or reduce fly ash content to promote faster strength development.
- Adjust the water-cement ratio to maintain workability while avoiding excess water that could freeze.
- Some studies suggest that phase change materials (PCMs), such as paraffin, can help regulate concrete temperature, delaying freezing by 6 to 8 hours—perfect for short cold spells.
5. Scheduling and Monitoring
- Use lower slump concrete to reduce bleed water and setting delays.
- Extend curing times to ensure concrete reaches proper strength before removing formwork.
- Monitor curing progress with maturity sensors and in-place strength testing.
- If possible, schedule concrete placement during the warmest part of the day to maximize curing efficiency.
Case Studies and Real-World Examples
Cold-weather concreting requires proven strategies to ensure successful construction. Various case studies highlight effective methods like thermal insulation and chemical accelerators. The following examples demonstrate the practical applications of these techniques in challenging climates.
Thermal Blankets in Norwegian Bridge Construction
In Norway, insulated blankets were used on a bridge deck to retain heat and prevent freezing. This method maintained hydration temperatures and ensured proper strength gain despite sub-zero conditions. Heated enclosures were also used in extremely cold periods to keep ambient temperatures above freezing. Research confirmed that insulated curing significantly improved early strength development. These measures enabled successful concrete placement in Arctic conditions without compromising quality.3
Accelerated Curing in Canadian High-Rise Construction
In Canada, contractors used non-chloride accelerators and insulation for winter high-rise projects. Accelerators sped up hydration, allowing timely formwork removal even in freezing weather. Heated mixing water and insulated formwork kept fresh concrete at optimal temperatures. The combination of thermal protection and chemical admixtures ensured that the concrete reached the required strength levels. This approach allowed continuous winter construction while meeting structural and durability standards, demonstrating the effectiveness of a well-planned cold-weather concreting strategy.4
Industry Standards and Guidelines
If you're working with concrete in cold weather, you don’t have to figure it all out on your own—industry standards are here to help. These guidelines are designed to keep your concrete strong, durable, and resistant to freezing conditions. Here are some of the key ones to know:
- ACI 306R-16: This standard from the American Concrete Institute defines cold weather as temperatures below 4°C and provides detailed recommendations for protecting concrete during curing. It emphasizes keeping concrete above freezing until it gains sufficient strength to resist damage from freeze-thaw cycles.
- CSA A23.1: The Canadian Standards Association outlines similar principles, requiring insulation, heated enclosures, or protective covers to maintain adequate curing temperatures. It also mandates a minimum strength of 7 MPa before exposing concrete to freezing conditions, ensuring durability in harsh climates.
- ASTM C31: This standard specifies how to properly cure and test concrete specimens in cold weather. It requires maintaining temperatures between 16–27°C for the first 24–48 hours to provide accurate strength assessments.
- ASTM C94: This guideline establishes minimum delivery temperatures for concrete in cold weather to prevent premature setting and ensure proper hydration. Following these specifications helps contractors maintain consistent quality, even in challenging conditions.
Following these standards isn’t just about checking boxes—it’s about making sure your concrete stands the test of time. With the right precautions, you can keep your project on track, even when the temperatures drop.5
Conclusion
Cold weather doesn’t have to mean trouble for your concrete work—as long as you plan ahead. Managing temperature, using the right mix, and extending curing times can go a long way in preventing hydration issues and freeze-thaw damage.
With climate variability on the rise, new solutions like phase change materials and energy-efficient heating systems are becoming game-changers. Sticking to proven industry standards like ACI 306R-16 and ASTM C31 gives you a solid foundation (literally) for successful cold-weather concreting. Stay prepared, follow best practices, and your concrete will hold up no matter how low the temperatures go.
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References and Further Reading
- Hammontree, H., Oh, E., & Moler, P. (2020). Temperature Effect on the Compressive Behavior and Constitutive Model of Plain Hardened Concrete. Materials, 13(12), 2801. DOI:10.3390/ma13122801. https://www.mdpi.com/1996-1944/13/12/2801
- Cold Weather Concreting. ACI 360R. American Concrete Institute. https://www.concrete.org/Portals/0/Files/PDF/University/306R-16_excerpt.pdf
- Nilimaa, J., & Zhaka, V. (2023). An Overview of Smart Materials and Technologies for Concrete Construction in Cold Weather. Eng, 4(2), 1550-1580. DOI:10.3390/eng4020089. https://www.mdpi.com/2673-4117/4/2/89
- Sedaghatdoost, A. (2023). COLD WEATHER CONCRETE: CURRENT PRACTICES AND INNOVATIVE MIX DESIGNS AND PROTECTION METHODS. The University of Manitoba. https://mspace.lib.umanitoba.ca/server/api/core/bitstreams/635f9f55-70c5-47c5-8c1a-d0ed3422ae09/content
- Concrete in Practice: What, Why & How? NRMCA. https://www.nrmca.org/wp-content/uploads/2021/01/27pr.pdf
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