Why Does Concrete Heat Up?

If you’ve ever tried to walk barefoot across a concrete sidewalk on a scorching summer day, then you already know just how hot concrete can get – but why does this happen?

Concrete gets hot in two main ways: through the curing process and via exposure to the sun.

Keep reading for an in-depth look at what curing is, how it turns concrete hot, and the role that sun exposure plays in changing concrete’s temperature.

How Hot Does Concrete Get?

Before we get into why does concrete get so hot, it’s important to touch on how hot it can turn, especially compared to other building materials. The table below uses the average temperature that concrete, wood, and grass can turn when they’re exposed to direct sunlight.

Concrete 175℉
Wood 90℉
Grass 80℉

Concrete retains heat much better than wood and grass, and even if it’s in the shade, concrete can still easily reach seventy to eighty degrees on a hot summer day.

How Hot Does Concrete Get?

What is Curing, and How Does It Affect Temperature?

The curing process occurs when you first pour concrete. Mix cement, sand, and aggregate together, and you’ll get concrete. When you add water to this combination, there’s a chemical reaction that occurs, which helps dry the concrete.

Curing is crucial for drying concrete after it’s poured, but the chemical reaction that helps dry that new sidewalk can also raise the temperature of the concrete too.

Most curing processes last around twenty-eight days, and once it’s as cured completely, the concrete will cool and return to a normal temperature.

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The temperature of concrete can depend on how much of it that you’re curing, but generally, every hundred pounds of curing concrete can raise the temperature by ten to fifteen degrees.

What is Curing, and How Does It Affect Temperature?

Why Does the Sun Turn Concrete Hot?

While curing can raise the temperature of concrete, it only turns it hot for the first month. After that, concrete that is hot is only hot a result of sun exposure and hot weather.

Unlike curing, a sunny day can heat your concrete any day of the year, especially during the summer.

And, most of the time, if hot concrete patios or poolsides are burning your feet, it’s due to sun exposure.

Concrete is one material that’s great at storing heat. Not only does it get hotter under the sun than other materials might, but it also releases heat more slowly too. So, it’s even easier for concrete to get hot and stay hot.

You can chalk concrete’s high heat capacity up to a couple of different factors. The ingredients of concrete make them especially great for storing heat energy, and the dull surface of the concrete is much better at absorbing sunlight than reflecting it.

During the day, a concrete sidewalk may absorb and store heat, energy, and sunlight and then slowly release it as the sun goes down.

Any heat that concrete materials have stored throughout the day will just go back into the atmosphere. This is why you may find cities and urban areas with sidewalks to be a few degrees hotter than places that don’t have them.

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Ways to Cool Down Concrete for Construction

Tips to keep concrete from becoming too hot include:

  • Using ice water to prepare your concrete.
  • Delay the mixing process until you are on the construction site.
  • Alternatively, use high range water reducers.
  • Avoid letting materials sit in trucks for long periods.
  • Using evaporation retardants, which slows down the setting process if the weather is going to be too hot.
  • Paint mixer drums white or a bright color to better reflect sunlight.

Even once the concrete has been poured and set correctly, there is still a risk that excessive hot weather may lead to cracks or other damage. So, it’s not uncommon for a waterproof sealant to get sprayed on top of setting concrete.

Final Thoughts on Concrete getting hot.