Pouring concrete in hot weather can be challenging.
Summer is an ideal time for construction projects, so managers and crews begin the season eager to maximize the longer daylight hours and the warmer weather.
With the threat of fall and winter looming right around the corner, crews want to accomplish as much as possible.
Fewer concrete problems indeed exist during the summer, but excessively hot temperatures can cause problems as well.
If you intend to install concrete in temperatures around 90 degrees, you'll need to adjust the mix and installation process to accommodate the heat.
In this article, we'll explain the steps you need to take to accommodate pouring concrete in hot weather.
Table of Contents
- Does Heat and Humidity Impact Concrete?
- Concrete Challenges in Warmer Months
- Finishing Difficulty
- Less Setting Time
- Reduced Strength
- Increased Cracking Risk
- Drying Shrinkage
- Pouring Concrete During The Warmer Months
Does Heat and Humidity Impact Concrete?
Summertime heat can dramatically impact the setting time and strength of the finished concrete mix. Depending on where you live, summers can also be known for their unbearable humidity.
While the heat itself may not be particularly extreme, the combination of higher temperatures and airborne moisture can pose a challenge for a concrete pour.
The heat and humidity can impact the strength of new concrete unless special precautions are taken.
Concrete Challenges in the Warmer Months
While most everyone enjoys the warm summer months, the temperature can make it difficult when pouring concrete in hot weather.
Concrete cures best in a range between 70° to 80° F., but as your temperature approaches 90° F, you'll start to run into problems.
In the world of concrete, hot weather is more than just temperature.
Days of low relative humidity, as well as days with high wind speeds, also are grouped into "hot weather" and can cause problems with pouring concrete.
Finishing Difficulty
Concrete sets much faster on hot weather days, which makes it very difficult to level and finish smoothly before it sets.
Your finished slab is more likely to have surface deformities and unevenness in the summer unless precautions are taken.
Less Setting Time
Freshly poured, fluid concrete mixtures can be molded with strategically spaced control joints.
These joints help control random cracking as the material hardens and shrinks.
During hot weather, your mix sets much quicker, so there will be much less time to place these joints correctly.
Time is of the essence.
Reduced Strength
Your slab becomes set during the hydration process when the water absorbs and crystals form.
Cooler concrete takes more time to hydrate and has more time for these crystals to form and strengthen.
When the temperature is higher, this process is sped up, and the mix has less time to hydrate, form crystals, and set to strong compressive strength.
Because of this, steps need to be taken to ensure hot weather concrete doesn't suffer decreased strength and durability.
Increased Cracking Risk
Hot weather, wind, and dry conditions all lead to increased evaporation.
These environmental factors pose a real threat to the top layer of your concrete slab.
As water is leached out of the surface layer by evaporation, the mix can become too dry and is more susceptible to surface cracking.
Drying Shrinkage
Even under ideal conditions, the volume of a wet slab will be different than that of a dry slab.
This volume change is even more significant when pouring concrete in hot weather.
Increased evaporation due to the higher temperature is the biggest culprit behind the shrinkage of a slab.
The temptation to add more water to a mixture can also create shrinkage. The wetter a mix is, the higher the volume change when set.
Hot Weather Concreting Tips
Don't worry; it is still possible to pour concrete in the warmer months without any issues or sacrifice of quality.
Here are a few tips to make sure your concrete job is successful during the warmer months.
Tip #1: Dampen Your Subgrade
During a pour, water is immediately leached out of your concrete and into the surface you are pouring on top of.
If you lightly hydrate the surface before you pour, you can help keep moisture in your mix during the hydration process.
Tip #2: Time Your Pour
During hot conditions, you should make sure you schedule your pours during the coolest part of the day.
This time frame often falls in the morning hours.
If your concrete is being mixed off-site and then delivered, try not to time your deliveries during peak heat.
Tip #3: Chill Your Water
Chilled water can reduce the concrete temperature by up to 10° F.
Hot water added to hot concrete won't do you any favors.
Having an industrial chiller on hand to chill your water before mixing will give you a significant advantage over mother nature.
Once the water has been added to the mix, reduce your mixing time. Over-mixing will create more water loss through evaporation.
Tip #4: Admixtures
Admixtures are concrete additives that alter the physical qualities of the finished slab.
They can improve concrete strength, offer corrosion protection, and slow down setting time, depending on the admixture used.
Some specific things to look for in admixtures include:
- Set Retardation
- Air-Entrainment
- Hydration Stabilizers
- Water Reducers
Tip #5: All Hands On Deck
Schedule your crews so that you have as many hands as possible when pouring in hot weather.
Due to faster set times, you will need as much manpower as possible to place forms, prep your sub-grade, smooth, set control joints, and level while your mix is still workable.
Tip #6: Use Sunshades and Windbreaks
Closely monitor sun patterns and wind forecasts so you can keep your concrete protected from the elements.
Placing sunshades and windbreaks can significantly decrease the threat of evaporation and give your slab more time during the hydration process.
Pouring Concrete During The Warmer Months
Although it does come with challenges, pouring concrete during the warmer months is still possible.
And it is often still better than pouring during the colder months.
Using the tips above should ensure your concrete job goes off without a hitch.
At STEVENS, we have the knowledge and experience to make sure that your concrete projects are done right the first time.
Click the button below to get started on your concrete project.
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