IS 516:2021 Part 5/Sec 2 is the Indian Standard (BIS) for methods of tests for strength of concrete - part 5: non-destructive testing of concrete - section 2: rebound hammer. This standard specifies the method for assessing the in-situ compressive strength, uniformity, and surface hardness of hardened concrete using a Rebound Hammer. It is a non-destructive testing (NDT) code frequently used by structural and quality control engineers to quickly evaluate existing concrete structures.
Specifies the method for determining the rebound number of concrete using a rebound hammer.
Velocity grading bands, transducer frequency, path lengths and direct/indirect test modes.
| Reference | Value | Clause |
|---|---|---|
| Method | Ultrasonic Pulse Velocity (UPV) | Cl. 4 / IS 13311 Pt 1 ref |
| Transducer frequency — typical concrete | 20 kHz – 150 kHz (50 kHz common) | Cl. 5.2 |
| Path length — direct transmission (min) | 100 mm | Cl. 6.3 |
| Couplant — typical | Petroleum jelly / grease (for smooth contact) | Cl. 6.4 |
| Quality grade — V > 4.5 km/s | Excellent | Cl. 8 (Table 1) |
| Quality grade — V 3.5–4.5 km/s | Good | Cl. 8 (Table 1) |
| Quality grade — V 3.0–3.5 km/s | Doubtful / Medium | Cl. 8 (Table 1) |
| Quality grade — V < 3.0 km/s | Poor | Cl. 8 (Table 1) |
| Calibration — reference bar | Steel bar of known velocity (~5.9 km/s) | Cl. 5.3 |
| Test mode — direct (preferred) | Transducers on opposite faces | Cl. 6.2 |
| Test mode — semi-direct | Adjacent faces (90°) | Cl. 6.2 |
| Test mode — indirect (surface) | Same face — least accurate | Cl. 6.2 |
| Reinforcement effect — correction | Avoid bars in path; use shielded chart if unavoidable | Cl. 7.2 |
| Min concrete age | 14 days | Cl. 6.1 |
| Resolution — time measurement | 0.1 µs (or finer) | Cl. 5.2.1 |
| Number of readings per location | Min 3 (mean reported) | Cl. 6.5 |
| 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 |