IS 516:2021 Part 5/Sec 1 is the Indian Standard (BIS) for methods of tests for strength of concrete - part 5: non-destructive testing of concrete - section 1: ultrasonic pulse velocity. This code covers the non-destructive testing procedure for assessing the quality of concrete using the Ultrasonic Pulse Velocity (UPV) method. Engineers use it to evaluate concrete homogeneity, detect internal voids or cracks, and estimate the dynamic modulus of elasticity in existing structures without causing damage.
Specifies the method for determining the ultrasonic pulse velocity in concrete.
Test setup, rejection criteria, quality grades (R-value bands), calibration frequency and direction corrections.
| Reference | Value | Clause |
|---|---|---|
| Hammer type | Schmidt rebound hammer (Type N — standard impact) | Cl. 4 / IS 13311 Pt 2 ref |
| Test surface preparation | Smooth, ground if rough; remove laitance | Cl. 6.2 |
| Test grid — points per location | Min 9 (typically 12) | Cl. 6.4 |
| Spacing between points | ≥ 25 mm (and ≥ 25 mm from edge) | Cl. 6.4 |
| Discard outlier rule | Reading differing > ±6 from mean rejected | Cl. 7.1 |
| Quality grade — R ≥ 40 (horizontal) | Very good / hard layer | Cl. 8 (Table) |
| Quality grade — R 30–40 | Good | Cl. 8 (Table) |
| Quality grade — R 20–30 | Fair | Cl. 8 (Table) |
| Quality grade — R < 20 | Poor / doubtful | Cl. 8 (Table) |
| Direction correction — vertical (downward) | + correction (refer hammer chart) | Cl. 7.2 |
| Calibration — frequency | Before/after each project (anvil block) | Cl. 5.2 |
| Calibration anvil — required reading | 80 ± 2 (typical N-type) | Cl. 5.2 |
| Min concrete age | 14 days (for trustable correlation) | Cl. 6.1 |
| Member thickness — min | 100 mm | Cl. 6.1 |
| Use — strength estimate ONLY with site correlation | Direct strength from R is unreliable; use cube correlation | Cl. 8.1 |
IS 516 Part 5 Section 1:2021 is the method for ultrasonic pulse velocity (UPV) testing of concrete — a non-destructive test that sends an ultrasonic pulse through concrete and, from the transit time over a known path, derives the pulse velocity to assess concrete quality, uniformity, and the presence of cracks, voids and deterioration without coring. It superseded the UPV provisions of the older IS 13311 Part 1.
It sits in the assessment stack:
Pulse velocity rises with the density, soundness and continuity of concrete (a faster path = denser, defect-free concrete; a slow or lost signal = cracks, voids, honeycombing or deterioration). IS 516 Part 5 Sec 1 fixes the method and a quality-grading band by velocity (broadly: very high velocity ≈ excellent concrete; descending bands → good / medium / doubtful):
The engineering point: UPV is a comparative quality and integrity tool, not a strength meter. It is superb at finding *where* concrete is bad and *how uniform* a structure is; converting velocity to MPa requires a correlation built from companion cores/cubes — a generic chart is not acceptance evidence.
Scenario: an element with surface cracking / suspected honeycombing under query.
Step 1 — grid the element: mark a test grid; use direct transmission (opposite faces) wherever access allows — it is the reliable arrangement.
Step 2 — couple & measure: apply couplant, measure transit time, compute velocity over the known path at each grid point.
Step 3 — map quality & defects: high, consistent velocity → sound, uniform concrete; local low velocity or lost signal → cracks, voids or honeycombing — UPV *locates* the problem zones.
Step 4 — correlate, don't guess strength: if a strength estimate is needed, take cores from representative zones, build a site-specific velocity–strength correlation, and combine with IS 516 Part 5 Sec 2 rebound (the standard combined-NDT approach).
Step 5 — decide per IS 456: use the mapped integrity + correlated/core strength for the acceptance/repair decision.
UPV told you *where* and *how uniform*; cores told you *how strong* — used together they answer the question, used alone UPV does not.
1. Reading UPV as a strength test. It measures quality/integrity; strength needs a site-specific correlation with cores — generic charts are not acceptance.
2. Using indirect (same-face) transmission then trusting it. Indirect is the least reliable, surface-only arrangement; prefer direct where access exists.
3. Ignoring reinforcement on the path. A pulse travelling along/near a bar reads falsely high — plan paths to avoid steel or correct for it.
4. Not accounting for moisture/temperature/coupling. Saturated concrete, poor couplant or extreme temperature bias velocity — control and report conditions.
5. Single readings instead of a grid. UPV's strength is *uniformity mapping*; one reading proves little — its value is the spatial pattern.
IS 516 Part 5 Section 1 is current (2021) and the modern home of UPV testing (replacing IS 13311 Part 1), and UPV is one of the most useful diagnostic tools on a forensic or QA job — fast, non-destructive, and excellent at answering *is this structure uniform* and *where is the bad concrete*. The persistent misuse is treating it as a strength test: velocity grades quality and integrity, and any strength figure must come from a site-specific correlation with cores, ideally combined with rebound hammer (the standard combined-NDT method). Use direct transmission, lay out a grid, keep reinforcement off the path, control moisture/coupling, and let UPV do what it is good at — mapping uniformity and locating cracks, voids and deterioration — while cores and IS 516 Part 1 supply the strength the IS 456 decision actually needs.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Standard Compressive Strength Specimen Type (Primary) | Cube | Cylinder | ASTM C39/C39M |
| Compressive Strength Loading Rate (Stress/time) | 14 N/mm²/minute | 0.25 ± 0.05 MPa/s (approx. 15 ± 3 N/mm²/min) | ASTM C39/C39M |
| Curing Temperature for Standard Specimens (Water/Moist Curing) | 27 ± 2 °C | 23 ± 2 °C | ASTM C31/C31M (referenced by C39/C39M) |
| Flexural Strength Test - Span-to-Depth Ratio (Third-Point Loading) | 4 (e.g., 600 mm span for 150 mm depth) | 3 (e.g., 450 mm span for 150 mm depth) | ASTM C78/C78M, EN 12390-5 |
| Number of Layers for Compaction of 300mm High Cylinders (by rodding) | 6 layers (approx. 5 cm deep each) | 3 layers (approx. 10 cm deep each) | ASTM C31/C31M |
| Maximum Time from Curing to Compressive Test | Within 30 minutes | Within 15 minutes | EN 12390-3 |