When moisture in concrete is heated to steam and expands, what is this phenomenon called?

When moisture in concrete is heated to steam and expands, what is this phenomenon called?

• A. Pyrolysis
• B. Cracking
• C. Delamination
• D. Spalling

Answer: (D)

When moisture trapped in concrete is heated enough to turn into steam, it expands and builds up high internal pressure behind the surface. If the surface can’t vent or accommodate that pressure, the outer layer cracks and peels away. This outward breakage of the concrete surface is called spalling. It’s a distinct failure mode from plain cracking, which is just cracks forming in the material, delamination, which is layers separating, or pyrolysis, which is chemical decomposition rather than pressure-driven surface breakage. Spalling is a common hazard in fire conditions because rapid heating and trapped moisture can cause chunks of concrete to break off.

When moisture trapped in concrete is heated enough to turn into steam, it expands and builds up high internal pressure behind the surface. If the surface can’t vent or accommodate that pressure, the outer layer cracks and peels away. This outward breakage of the concrete surface is called spalling. It’s a distinct failure mode from plain cracking, which is just cracks forming in the material, delamination, which is layers separating, or pyrolysis, which is chemical decomposition rather than pressure-driven surface breakage. Spalling is a common hazard in fire conditions because rapid heating and trapped moisture can cause chunks of concrete to break off.