Bend & Re-Bend Test (Bendability of Reinforcement)
IS 1786 makes the bend and re-bend test (method per IS 1599) a mandatory acceptance: the bar is bent around a mandrel whose diameter scales with bar size and grade with no surface cracking, and the re-bend test (age then bend back) exposes strain-ageing embrittlement. A bar can pass tensile strength yet fail bend/re-bend — and such steel cracks exactly at stirrup bends and hooks.
Key Requirements
•Bend around the specified mandrel diameter (scales with bar size and grade) — no cracks on the outer surface
•Re-bend test: bend, artificially age, bend back — exposes strain-ageing embrittlement
•Mandrel diameter is grade/size-specific — using too generous a mandrel makes the test meaningless
•Acceptance is strength (Clause 7) AND bend/re-bend together
•Failure rejects the lot regardless of strength — bars that crack when bent are unusable for stirrups/hooks
Practical Notes
✓Site corollary: over-tight bar-bender pins (below the IS 1786/IS 2502 mandrel) or re-bending already-bent bars reproduce the very failure the test screens for.
✓Re-bend (after ageing) is the more severe, more important check — it catches steel that embrittles over time after cold bending.
Common Mistakes
⚠Accepting rebar on tensile strength alone, skipping bend/re-bend.
⚠Using an over-generous mandrel so a fail looks like a pass.
⚠Site bar-bending below the specified pin diameter, cracking bars at hooks.