IS 516 Part 5 covers non-destructive testing: Section 1 (ultrasonic pulse velocity) grades concrete quality, uniformity and locates cracks/voids; Section 2 (rebound hammer) gauges surface hardness. Neither is a direct strength test — a strength estimate requires a site-specific correlation with cores (IS 516 Part 6), ideally combining UPV + rebound. This consolidated the older IS 13311 NDT provisions.
Key Requirements
•UPV (Part 5 Sec 1): prefer direct transmission; keep reinforcement off the pulse path; grade quality by velocity bands
•Rebound hammer (Part 5 Sec 2): apply orientation correction; account for carbonation on old surfaces (over-reads)
•Strength is NOT read directly — build a site-specific correlation against cores (IS 516 Part 6); generic charts are not acceptance
•Use a grid and combine UPV + rebound for reliability (combined-NDT approach)
•Decide acceptance/repair per IS 456 using the correlated/core strength, not the NDT number alone
Reference Tables
Indicative UPV quality grading (verify against the current BIS edition)
Pulse velocity
Concrete quality (indicative)
Higher (≈ > 4.5 km/s)
Excellent
≈ 3.5–4.5 km/s
Good
≈ 3.0–3.5 km/s
Medium / doubtful
Lower (≈ < 3.0 km/s)
Doubtful / poor
Indicative bands only — use the grading table of the current IS 516 Part 5 edition.
Practical Notes
✓UPV maps where the bad concrete is and how uniform a structure is; cores tell you how strong it is — used together they answer the question, UPV alone does not.
✓Carbonation is the classic rebound-hammer error on old structures: a carbonated surface is hard and badly over-reads strength.
Common Mistakes
⚠Reading strength off a generic rebound/UPV chart instead of a site-specific core correlation.
⚠Trusting indirect (same-face) UPV transmission as if it were direct.
⚠Ignoring reinforcement on the UPV path (reads falsely high).