Pouring concrete can be a finicky process. Many factors impact how well the concrete cures and its ultimate strength. One of the most important considerations is the temperature when pouring concrete. The ideal temperature to pour concrete is between 50-90°F. Pouring concrete outside of this temperature range can cause issues with curing and lead to weak, crumbly concrete. In this article, we’ll discuss the best practices for pouring concrete in various temperatures.
Why Temperature Matters for Pouring Concrete
Temperature impacts how concrete cures. Concrete cures through a chemical process called hydration. When water is added to cement, a reaction occurs that allows the concrete to harden.
Hydration is temperature dependent. The ideal temperature for hydration is between 50-90°F. Hydration occurs more rapidly at higher temperatures and more slowly at colder temperatures.
If concrete cures too quickly or too slowly, it can have negative impacts:
- Curing too quickly leads to weak, brittle concrete. The cement paste does not have time to properly hydrate and bond. This leaves air pockets and cracks.
- Curing too slowly increases chances of frost damage. Cold temperatures can cause water in the concrete to freeze and expand, damaging the curing concrete. Slow curing also delays strength gain.
That’s why monitoring the temperature when pouring concrete is so important. The temperature should be controlled to allow for proper curing and strength gain.
Ideal Temperatures for Pouring Concrete
The best temperature range for pouring concrete is 50-90°F. Within this range, the concrete will hydrate at an ideal rate to gain strength properly.
50-70°F
This is the optimal temperature range for pouring concrete. Hydration proceeds steadily, allowing the concrete to gain strength on a predictable timeline.
Concrete poured in this temperature range will:
- Have reduced chances of cracking and cold joints
- Cure evenly throughout the slab
- Gain strength predictably over 7-28 days
At lower temperatures, you may need to use an accelerating admixture to speed curing. But overall, this is the best temperature range for concrete work.
70-90°F
As temperatures climb above 70°F, concrete begins curing more rapidly. The quicker curing can lead to issues if proper precautions aren’t taken.
At these warmer temperatures:
- The concrete setting time is reduced. This decreases workability.
- The concrete gains strength quickly, but results in lower ultimate strength.
- Risk of plastic shrinkage cracking increases.
If pouring concrete in warmer temperatures, it’s important to have plans to manage the heat:
- Use ice or chilled water when mixing to keep concrete temperatures low
- Spray forms with cool water before concrete placement
- Begin curing immediately after finishing
- Erect sun shades over concrete after pouring
With active measures to manage heat, quality concrete pours can still be achieved in this temperature range.
Problems With Pouring Concrete in Extreme Temperatures
Once the temperature moves outside the 50-90°F range, potential issues arise. Here’s how to handle concrete pours in extreme heat or cold.
Pouring Concrete in Cold Weather (<50°F)
Cold temperatures slow the curing of concrete. This can lead to strength gain issues and increased chances of frost damage.
To manage cold weather concrete pours:
- Use an accelerating admixture in the concrete mix
- Pour concrete in the warmer part of the day
- Prevent evaporative cooling by shielding the pour from wind
- Keep concrete at 50°F+ until cured using insulation or heating
With proper cold weather plans, concrete can be poured down to near freezing temperatures. But extra care must be taken to ensure proper curing.
Pouring Concrete in Hot Weather (>90°F)
In extreme heat, concrete cures rapidly, resulting in decreased strength and increased cracking. Proper planning is critical for hot weather pours.
Strategies for managing hot weather concrete include:
- Cool concrete ingredients before batching
- Add water-reducing retarder admixtures
- Pour concrete at night or early morning
- Spray forms and subgrade with cool water before placement
- Install sun shades and wind breaks after finishing
- Begin curing immediately with water spray or wet burlap
Hot weather concreting requires experience to perfect. But with an understanding of how heat impacts concrete, quality pours can be achieved even in extreme temperatures above 90°F.
FAQs About Pouring Concrete in Various Temperatures
What temperature is too hot to pour concrete?
There is no absolute cut-off for maximum concrete pouring temperature. With proper planning, concrete can be poured up to 100°F or above. However, as the temperature exceeds 90°F, the risk of problems increases. Above 90°F, take extra measures for cooling and curing to prevent cracking and achieve desired strength.
What temperature is too cold to pour concrete?
Concrete can be poured at near freezing temperatures if special precautions are taken. These include using accelerators, pouring in the warmest part of day, shielding from wind, and adequately insulating. Once temperatures drop below 20°F, concrete placement becomes infeasible without heated enclosures.
How do I calculate the concrete temperature?
Concrete temperature is estimated by averaging the temperature of the individual ingredients. Take temperature readings of the cement, water, and aggregates. The overall concrete temperature is the average of these components. A field measurement of the concrete temp can also be taken after batching.
Can you pour concrete at 100 degrees?
Yes, it’s possible to pour quality concrete at 100°F and above. The challenges are rapid setting, increased shrinkage, and lower ultimate strength. To manage, cool the concrete as much as possible and cure immediately after placement. Experience with hot weather concreting techniques is recommended before placing concrete at such high temperatures.
What happens if concrete freezes while curing?
If concrete freezes before properly curing, major strength and durability issues can occur. The expanding frozen water ruptures the cement paste, leaving voids and cracks. Concrete damaged by early freezing will need to be removed and replaced. Preventing premature freezing is critical for cold weather pours.
Can you pour concrete when it’s raining?
It’s best to avoid pouring concrete in the rain. Rainwater can wash away cement paste leading to weakened areas called rain damage. If rainfall is light, concrete pours may be feasible if the slab is properly covered immediately after screeding. Heavy rain necessitates postponing the pour.
Best Practices for Pouring Concrete in Any Temperature
Proper planning and concrete practices are key for a successful pour in any weather conditions:
- Test concrete ingredients – Check aggregate moisture and adjust mixes accordingly. Test cement for age and alkali silica reactivity.
- Use air entrainment – Air bubbles provide space for water to expand when freezing, preventing damage. Air entrainment is strongly recommended for outdoor concrete.
- Cure properly – Begin curing immediately after finishing to lock in moisture. Continue curing for a minimum of 7 days.
- Monitor conditions – Track precipitation, humidity, wind, and temperatures in the hours before the pour and throughout curing.
- Prevent evaporation – Use wind breaks, sun shades, and mist spray to prevent the concrete surface from drying out.
- Order extra concrete – Have 10-15% more concrete than estimated available for the pour to allow rapid placement.
With monitoring and planning, quality concrete can be poured and cured even in non-ideal temperatures. An experienced concrete contractor will have the necessary techniques to adjust for any type of weather conditions.
Conclusion
Temperature plays a critical role in proper concrete curing and strength development. The ideal temperature range for pouring concrete is 50-90°F. Within this range, the concrete will hydrate at an appropriate pace.
In cold weather, measures must be taken to accelerate curing and prevent frost damage. Strategies include using admixtures, insulating, heating, and pouring in the warmer part of day.
Hot weather concreting brings the challenges of rapid setting, increased shrinkage, and lowered strength. Proper planning, cooling methods, and prompt curing can aid in a successful pour.
With careful monitoring and adjustments, concrete pours can be completed successfully even in extreme cold or hot temperatures. An experienced concrete contractor will have the skills and knowledge required to tailor materials, techniques, and curing to the ambient conditions. By understanding the impact of temperature, you can ensure your next concrete pour cures properly and reaches its designed strength regardless of the weather.
More Resources
The Effect of Temperature on Concrete Curing