What is concrete delamination and how can it be detected?

• A. Removal of surface seal.
• B. A type of cracking caused by shrinkage.
• C. Separation between concrete layers due to corrosion of embedded steel; detected by sounding (tapping).
• D. Separation between concrete layers due to corrosion of embedded steel; detected by sounding (tapping) and confirmed with nondestructive tests like ground-penetrating radar.

Answer: (D)

Concrete delamination is the separation between layers inside a concrete element caused by corrosion of the embedded reinforcing steel. As steel corrodes, rust formation expands, pushing adjacent concrete apart and creating internal voids that weaken the bond between layers. Because this condition often isn’t visible on the surface, inspectors use tapping or sounding to listen for hollow or dull tones over suspect areas, which suggests a delaminated zone beneath the surface. To verify and map the extent, nondestructive testing like ground-penetrating radar is used, since GPR can detect internal voids and changes in layer structure under the concrete and help pinpoint depth and area to repair.