---
title: "Non-destructive tests in buildings"
subject: "Building Technology"
chapter: 11
key: "semester_6/building_technology:ndt-building"
source: https://www.bctengineer.com/q/semester_6/building_technology/ndt-building
site: BCT Engineering
---

# Non-destructive tests in buildings

Building Technology · Chapter 11: Earthquake protection & Retrofitting in building

- Asked in: 2072 Asoj, 6 marks
- Video: [Non-Destructive Testing in Construction Materials | GATE CE](https://www.youtube.com/watch?v=mHxWLOV0QIM) — Ekeeda GATE & ESE
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/ndt-building
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-11

## Question

Describe non-destructive test in building structure.

## Short answer

Non-destructive testing assesses concrete strength, uniformity, and defects like voids or cracks without damage. Key methods: rebound hammer for surface hardness, ultrasonic pulse velocity for internal flaws (velocity <3.0 km/s is doubtful), cover meter for rebar location, and half-cell potential for corrosion probability.

## Answer

**Non-destructive testing (NDT)** assesses the strength, quality and condition of a building's materials and members without damaging them, so the structure can stay in service. It is used for quality control, for assessing damage and ageing, and before retrofitting.

#### Common NDT methods
1. **Rebound (Schmidt) hammer test (IS 13311 Part 2):** a spring-loaded plunger hits the concrete surface; the rebound number relates to surface hardness and approximate compressive strength. It is quick and cheap, but it is affected by surface moisture, carbonation and smoothness, and it gives only the surface strength.
2. **Ultrasonic pulse velocity (UPV, IS 13311 Part 1):** measures the travel time of an ultrasonic pulse through the concrete. Concrete quality by velocity: above 4.5 km/s excellent, 3.5-4.5 good, 3.0-3.5 medium, below 3.0 doubtful. It detects voids, cracks and honeycombing.
3. **Cover meter (profometer):** an electromagnetic device that locates rebars and measures cover and bar spacing.
4. **Half-cell potential test:** shows the probability of rebar corrosion by measuring electrical potential.
5. **Carbonation test:** a phenolphthalein spray shows the depth of carbonated concrete (pink = alkaline, colourless = carbonated).
6. **Penetration (Windsor probe) and pull-out tests:** partially destructive tests that estimate strength.
7. **Radiography, ground penetrating radar and infrared thermography:** detect voids, delaminations, moisture and rebar layout.
8. **Core test** (partially destructive) is used to calibrate the above methods.

The results of different methods are combined for a reliable assessment.

## Check yourself

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

1. What defines non-destructive testing?
   A. Assesses strength and quality without damaging the member
   B. Tests specimens to failure
   C. Needs demolition of the member
   D. Can be done only in labs
   Answer: A. NDT lets the structure stay in service. (Key point: NDT definition)

2. What does a rebound hammer measure?
   A. Rebar corrosion potential
   B. Surface hardness related to approximate compressive strength
   C. Depth of cover
   D. Internal voids
   Answer: B. Rebound number relates to surface hardness; it is affected by moisture, carbonation and smoothness. (Key point: Rebound hammer)

3. UPV of 4.0 km/s indicates concrete quality of:
   A. Excellent
   B. Doubtful
   C. Good (3.5-4.5 km/s)
   D. Poor
   Answer: C. Above 4.5 excellent, 3.5-4.5 good, 3.0-3.5 doubtful, below 3.0 poor. (Key point: UPV)

4. Which pairing is correct?
   A. Half-cell locates bars; cover meter detects corrosion
   B. Both measure compressive strength
   C. Both measure carbonation
   D. Half-cell detects corrosion probability; cover meter locates rebars and cover
   Answer: D. Half-cell measures electrical potential for corrosion; cover meter is electromagnetic. (Key point: Half-cell and cover meter)

## Related in Building Technology

- [Destructive and non-destructive tests](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aretrofit-destructive-tests) — Building Technology, chapter 11

## Related in other subjects

- [Destructive and non-destructive tests in masonry](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Adestructive-ndt-masonry-list) — Concrete Technology and Masonry Structure, chapter 10
- [Non-destructive tests on insulators](https://www.bctengineer.com/question.md?key=semester_8%2Fhigh_voltage_engineering%3Anon-destructive-insulator-tests) — High Voltage Engineering, chapter 7, asked 4×
- [Non-destructive tests for masonry](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Andt-masonry-tests) — Concrete Technology and Masonry Structure, chapter 10, asked 3×
- [Destructive tests of concrete](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Adestructive-tests-concrete) — Concrete Technology and Masonry Structure, chapter 5