Spalling of concrete in Type I buildings can contribute to early collapse primarily due to

• A. Loss of moisture in concrete reduces its fire rating.
• B. The added weight of broken pieces may cause overload.
• C. Reinforcing steel is exposed to the heat of the fire.
• D. It could create void spaces.

Answer: (C)

Spalling creates a direct fire exposure problem for the reinforcing steel. In reinforced concrete, the concrete cover serves as a shield that keeps the steel cooler during a fire. When spalling occurs, that protective layer is stripped away, allowing heat to reach the reinforcing bars much more quickly. As the steel heats up, its strength and ductility decline, and the bond between steel and surrounding concrete can weaken. In Type I construction, where the structure often relies on that steel for carrying significant loads, this rapid loss of steel capacity can lead to an early, more sudden collapse. Other effects like loss of moisture, extra debris weight, or void spaces may happen, but they don’t address the primary mechanism driving early failure: exposed reinforcing steel losing strength under heat.