---
title: "NDT circumstances; ultrasonic pulse velocity test"
subject: "Concrete Technology and Masonry Structure"
chapter: 5
key: "semester_5/concrete_technology_and_masonry_structure:ndt-circumstances-upv"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/ndt-circumstances-upv
site: BCT Engineering
---

# NDT circumstances; ultrasonic pulse velocity test

Concrete Technology and Masonry Structure · Chapter 5: Testing of concrete and quality control

- Asked in: 2082 Bhadra, 4 marks
- Video: [Ultrasonic pulse velocity test of Concrete](https://www.youtube.com/watch?v=XFhsFoewejo) — R B Singh Civil Engineering Academy
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/ndt-circumstances-upv
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-5

## Question

What are the circumstances under which non-destructive testing of concrete is carried out? Explain the ultrasonic pulse velocity test in detail.

## Short answer

NDT is used when cube results are doubtful, compaction is suspect, records are lacking, for assessment of old or damaged structures, and to check uniformity. The UPV test measures pulse travel time; velocity V = L/T, with >4.5 km/s excellent, <3.0 poor. Stength is estimated from a pre‑established correlation curve, accuracy about ±20%.

## Answer

#### Circumstances for NDT
- When the cube/cylinder results fail the acceptance criteria (IS 456, Cl. 16) or are doubtful.
- Suspected poor compaction, honeycombing, voids, or cracks in the member.
- Lack of quality-control records, or specimens that were not properly cured.
- Assessment of old structures for change of use, extension, and rehabilitation.
- Damage by fire, earthquake, impact, corrosion, chemical or freeze-thaw attack.
- Checking uniformity of concrete, early stripping time, and cover/rebar location.
- Monitoring strength gain or deterioration over time.

#### Ultrasonic pulse velocity (UPV) test (IS 13311 Part 1)
**Principle:** the velocity of an ultrasonic pulse through concrete depends on its density and elastic properties. Sound, dense concrete transmits the pulse faster than porous or cracked concrete.

**Apparatus:** pulse generator and receiver with two transducers (usually 54 kHz), a timer reading to 0.1 microsecond, a coupling gel, and a reference calibration bar.

**Procedure**
1. Calibrate the instrument on the reference bar.
2. Clean the surface and apply grease or gel to ensure good acoustic contact.
3. Put the transducers on the concrete, either **directly** (opposite faces, most reliable), **semi-directly** (adjacent faces) or **indirectly** (same face, least reliable).
4. Measure the path length $L$ and the transit time $T$.
5. Calculate the velocity:

$$
V = \frac{L}{T}
$$

Take several readings and average them. Avoid paths parallel to reinforcement, as steel carries the pulse faster.

**Quality of concrete (IS 13311 Part 1)**

| Pulse velocity (km/s) | Quality |
|---|---|
| Above 4.5 | Excellent |
| 3.5 to 4.5 | Good |
| 3.0 to 3.5 | Medium |
| Below 3.0 | Doubtful (poor) |

**Strength estimation:** a correlation curve between $V$ and the compressive strength of cubes of the same mix (made and tested in the laboratory) is used. The accuracy is only about ±20%, because moisture, aggregate type, age and reinforcement also change $V$. Better accuracy is obtained by combining it with the rebound number (SONREB method).

**Uses:** uniformity of concrete, locating voids and cracks, depth of surface cracks, deterioration by fire, frost or chemical attack, and dynamic modulus.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. When is NDT carried out?
   A. Always instead of cube tests
   B. When cube results fail acceptance or are doubtful, or for old or damaged structures
   C. Only for fresh concrete
   D. Only to measure slump
   Answer: B. NDT is used for doubtful or failing results, old or damaged structures. (Key point: NDT circumstances)

2. What does pulse velocity depend on?
   A. Colour
   B. Cement brand only
   C. Density and elastic properties of concrete
   D. Slump
   Answer: C. Denser, sounder concrete is faster. (Key point: UPV principle)

3. What is the accuracy of UPV strength estimation and how is it improved?
   A. ±1%; use alone
   B. ±50%; use thicker transducers
   C. ±20%; use higher frequency
   D. ±20%; combine with rebound number (SONREB)
   Answer: D. Moisture, aggregate, age and steel affect V, so SONREB improves it. (Key point: Accuracy)

4. According to IS 13311 Part 1, a pulse velocity of 4.0 km/s indicates concrete of what quality?
   A. Good
   B. Excellent
   C. Medium (doubtful)
   D. Poor
   Answer: A. 3.5 to 4.5 km/s is Good; above 4.5 is Excellent. (Key point: UPV quality grading)

## Related in Concrete Technology and Masonry Structure

- [Ultrasonic pulse velocity test](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aupv-test-interpretation) — Concrete Technology and Masonry Structure, chapter 5, asked 2×
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