A hairline-to-fine longitudinal crack (width ≈ 0.2–0.5 mm) was observed along the top reinforcement in the negative moment region of a cantilever overhang slab. The crack runs parallel to the main tension rebar, approximately 50–100 mm from the face of the supporting beam.
: When steel reinforcement (rebar) is exposed to oxygen, moisture, and chloride ions, it begins to rust. Rust occupies more volume than the original steel, creating internal pressure that leads to "spalling" or cracks running directly parallel to the rebar line. toh rebar crack