POURING CONCRETE in HOT WEATHER can be challenging.

Summer is a great time to start construction projects. Managers and crews are eager to take advantage of the longer daylight hours and warmer weather.

Crews are eager to do as much as they can with fall and winter approaching.

While there are fewer problems in summer, excessively high temperatures can also cause problems.

Concrete can be installed in temperatures up to 90 degrees. You will need to adjust the mix and the installation process to handle the heat.

This article will explain how to pour concrete in hot weather.

DOES HEAT AND HUMIDITY IMPACT CONCRETE?

The setting time and strength for concrete mixes can be greatly affected by summer heat. It all depends on where you live. Summers can be quite humid.

Although the heat is not particularly severe, it can make concrete pouring more difficult due to the combination of higher temperatures with airborne moisture.

If you don’t take special precautions, heat and humidity can affect the strength of concrete.

CONCRETE CHALLENGES IN THE WARMER MONTHS

Although most people enjoy the summer heat, concrete can be difficult to pour in hot weather.

Concrete cures best when it is between 70deg and 80deg F. However, if you reach 90deg F or higher, you will start to have problems.

Hot weather in concrete is more than temperature.

Hot weather also includes days with low relative humidity and high wind speeds. This can make it difficult to pour concrete.

FINISHING DIFFICULTY

Concrete sets faster in hot weather, making it difficult to finish and level it 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

Fluid concrete can be moldable with strategically placed control joints after it has been poured. 

As the material shrinks and hardens, these joints prevent random cracking. 

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

When the water absorbs the slab, crystals are formed.

Concrete that is cooler takes longer to hydrate, and crystals take more time to form and strengthen.

This is because the temperature rises faster and the mixture has less time to hydrate and form crystals. The mix can then be compressed to high strength.

It is important to take steps to ensure that hot-weather concrete does not lose strength or durability.

INCREASED CRACKING RISK

Evaporation is increased by hot weather, wind, dry conditions, and other factors such as dry weather. 

These environmental factors can pose a serious threat to your concrete slab’s top layer. 

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 in ideal conditions, a wet slab’s volume will differ from a dry slab.

Concrete poured in hot conditions will show a greater volume change. 

The biggest reason for shrinkage is increased evaporation at higher temperatures. 

Shrinkage can also be caused by the temptation to add more water. The volume change at the set is greater the wetter a mixture.

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

Water is leached from concrete during a pour and into the surface that you are pouring onto. _

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

In hot weather, it is important to schedule pours at the coolest time of the day. 

This time period is often found in the morning. 

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 10deg 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.

Reduce the time you mix the mixture after adding the water. Over-mixing can lead to more water loss via evaporation.

TIP #4: ADMIXTURES

Concrete additives are concrete mixtures that alter the physical properties of the slab. 

They can increase concrete strength and offer corrosion protection. 

Some specific things to look for in admixtures include:

  • Set Retardation
  • Air-Entrainment
  • Hydration Stabilizers
  • Water Reducers

TIP #5: ALL HANDS ON DECK

You will need to schedule your crews in advance so you can have as many people as possible for 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

You can protect concrete from the elements by monitoring wind forecasts and sun patterns. 

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.

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