Bridge Inspection Techniques Practice Test 2026 – Complete FHWA NSTM Exam Prep

Concrete delamination is when layers of concrete separate from one another, usually caused by corrosion of embedded reinforcing steel. As steel corrodes, rust products take up more space, pushing apart surrounding concrete and creating voids between lift’d layers or near joints. On the surface this can look intact, but the interior has a hollow or weak zone.

You detect it first by tapping the surface: a delaminated area often sounds dull or hollow compared with sound concrete. Because tapping alone isn’t definitive, you confirm with nondestructive testing such as ground-penetrating radar, which can locate internal voids, map their extent, and verify that layer separation exists beneath the surface.

This is different from cracking caused by drying shrinkage, which is a surface or near-surface crack from moisture loss, and from simply removing a surface seal, which is a weather‑proofing issue at the surface rather than internal layer separation.