How Does Fire Affect Concrete Structures?

How Does Fire Affect Concrete Structures?

January 27, 2022

We all know the devastation fires cause on siding, roofs, walls and other wooden parts of a home, but we don’t always think of what those flames can do to a concrete foundation or a concrete structure in general. After all, concrete should be tough enough to handle anything, right?

Unfortunately, that’s not the case. This post will cover what fire does to concrete and how we conduct a fire-damaged concrete assessment:

  • Spalling: Concrete contains water, and that water turns to steam as the temperature of concrete rises in a fire. If the evaporation rate is high enough and the permeability of the cement paste is low, spalling occurs. Spalling isn’t necessarily a concern unless the structure behind the concrete is damaged. An in-depth investigation should be performed to ensure the steel supports are unharmed.
  • Cracking: Cracking occurs when the hot concrete is extinguished with water by firefighters or a sprinkler system. These cracks can develop parallel to the floor or ceiling or only in the fire-affected zone. Cracks may seem small on the surface but can penetrate deeply into the concrete, which is why an engineering evaluation of fire damage to concrete foundations is essential.
  • Discoloration: Concrete can also change colors when exposed to high temperatures in a fire. The surface often starts to turn pink when the surface temperature climbs above 570°F and then a whitish buff color as the temperature rises. This color change indicates that the concrete is seriously structurally compromised.

Evaluating fire damage

There are four main ways we conduct an engineering evaluation of fire damage to concrete foundations. These are the steps your engineering team will take after a fire:

  • Visual: The easiest way to tell that something’s wrong with the concrete is just by taking a look at it. We start by performing a thorough visual inspection to see where the cracks are and how deep they run into the concrete.
  • Audible changes: Believe it or not, concrete actually has a different sound when struck with a hammer after it’s damaged in a fire. Healthy concrete produces a high-frequency ringing when struck, while fire-damaged concrete only produces a dull thud sound.
  • Fracture mechanics: Even healthy concrete can crack over time, but these cracks typically occur in a plane through the aggregate. If we notice cracking that breaks around the aggregate, we can confirm that the concrete has undergone significant fire damage.
  • Relative concrete strength: Finally, we use a rebound hammer on the concrete to test its surface strength. This test is the best way to determine the concrete’s structural integrity after a fire.

Is your concrete in good standing?

Whether you’ve recently had a fire or if it’s just been a while since your concrete structure has been examined, now’s a good time to hire our team for an evaluation. Our structural engineers at High Plains Engineering & Consulting, LLC are experts at performing a fire-damaged concrete assessment, so you can trust that our findings will be accurate. Contact us today to see what we can do for you.

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