What is ultrasonic tomography of concrete?

It is a non-destructive testing method that analyses the internal structure of concrete through the reflection of elastic wave pulses. The recorded reflections are processed to produce B-scan sections and, through grid acquisitions, three-dimensional representations of the element under investigation.

What does the pulse-echo method mean?

The pulse-echo method involves emitting short elastic wave pulses and recording their reflections. Reflections occur at surfaces with an acoustic impedance contrast relative to the surrounding material, such as discontinuities, voids or elements with different properties.

What can ultrasonic tomography reveal?

Depending on acoustic contrast and acquisition conditions, ultrasonic tomography can reveal cavities and voids, cracks, discontinuities, internal delaminations, metallic elements and anomalies in the internal configuration. A response is never guaranteed in advance: it depends on geometry, material and appropriate survey design.

What is the difference between a B-scan and a 3D reconstruction?

A single acquisition produces a vertical section of the investigated volume, called a B-scan. Repeating acquisitions on a predefined grid allows the data to be combined into a three-dimensional representation of the analysed portion of the element.

Can ultrasonic tomography be used on prestressed elements?

It can be used to analyse elements containing prestressing cables or strands, after assessing the element's geometry and thickness, available concrete cover, the most suitable viewing direction and possible shadowing from highly reflective elements. Preliminary validation on a known portion of the structure is appropriate in many cases.

Technical guide · Methodology

Ultrasonic tomography of concrete

Seeing inside a structure through the response of ultrasonic waves.

Ultrasonic tomography analyses the internal structure of concrete through the reflection of elastic wave pulses, producing B-scan sections and, through grid acquisitions, three-dimensional representations.

Talk to a technician Explore bridge and viaduct investigations

What is ultrasonic tomography?

Ultrasonic tomography is a non-destructive testing method based on the pulse-echo principle: short elastic wave pulses are applied to the structural element and the response reflected by the material is analysed.

Reflection occurs where the wave path encounters a change in the properties of the medium. Response intensity depends on acoustic impedance contrast: the greater the difference between the concrete and the encountered element, the more pronounced the recorded reflection.

Pulse emission
Short elastic wave pulses are generated and propagate within the concrete element.
Reflection
The pulse is reflected at surfaces that interrupt material continuity.
Acoustic impedance contrast
The magnitude of the reflection depends on the acoustic impedance contrast between the concrete and the element or discontinuity encountered.
Signal acquisition
The reflected signal is acquired and recorded with its corresponding travel times and amplitudes.
Response processing
The acquired data are processed to produce a representation of the investigated volume's response.

Pulse-echo principle of ultrasonic tomography — Tomographic acquisition on a concrete element: pulses emitted at the surface are reflected by internal discontinuities and recorded again from the same side of the element.

How acquisition works

The information pathway, from the emitted pulse to the three-dimensional representation, follows a sequence defined during survey design.

Ultrasonic pulse

Emission of elastic waves into the material.

Reflection

Response at acoustic contrasts.

Acquisition

Recording of the reflected signal.

B-scan

Section of the investigated volume.

Grid acquisition

Repetition on a defined grid.

3D reconstruction

Three-dimensional combination of the data.

In the system documented in Novatest campaigns, an array of 12 sensors operates alternately as transmitter and receiver, generating many path combinations at each position. This characteristic relates to the specific system used and must not be regarded as a property shared by all tomographic systems.

What it can reveal

The information obtainable depends on the acoustic contrast between the elements present and the concrete, as well as acquisition conditions. Detectability of an anomaly therefore cannot be assumed in advance.

Cavities and voids

Volumes without material or with a filling different from the surrounding concrete.

Cracks

Separation surfaces that may generate a detectable reflection.

Discontinuities

Internal variations in material configuration or compactness.

Internal delaminations

Separations between layers or between materials with different properties.

Metallic elements

Reinforcement, inserts and other embedded elements with high acoustic contrast.

Internal configuration anomalies

Deviations from the expected or documented geometry of the element.

From B-scan to 3D representation

A single acquisition produces a section of the investigated volume, called a B-scan. Repeating acquisitions on a defined grid allows the data to be combined into a three-dimensional representation of the analysed portion of the element.

B-scan obtained using ultrasonic tomography — Single acquisition
B-scan section: recorded reflections are displayed as a function of position and depth, showing the response of the investigated volume.

Three-dimensional reconstruction using ultrasonic tomography — Grid acquisition
Three-dimensional reconstruction obtained by combining successive grid acquisitions, displaying the internal configuration of the analysed portion.

When GPR precedes tomography

In specific documented campaigns, ground-penetrating radar was used first to reconstruct the element's internal geometry, locate reinforcement and embedded elements, and guide subsequent tomographic acquisition towards relevant areas.

The two methods provide different types of information: their combination is a documented example of an investigation strategy, not a mandatory procedure or a sequence applicable in every context.

GPR

Location and geometry

Ultrasonic tomography

Further investigation of internal characteristics

Data correlation

Integrated interpretation of the acquired information

Example of a documented strategy: GPR guides the investigation, tomography examines the element's response in more detail, and data correlation supports technical assessment.

Applications to prestressed structures

In elements containing prestressing cables or strands, ultrasonic tomography can contribute to analysing the internal configuration, provided that the investigation is designed with the element's characteristics in mind.

Preliminary assessment of the element's geometry and thickness, verification of available concrete cover and choice of viewing direction decisively influence the quality of the information obtainable.

Preliminary assessment of element geometry and thickness
Verification of adequate concrete cover for the investigation objective
Possible shadowing from highly reflective near-surface elements
Reasoned choice of viewing direction
Preliminary validation on known portions of the structure, where possible

Limitations and applicability conditions

Technical note

Geometry of the investigated element
Thickness of the portion to be analysed
Concrete quality and homogeneity
Contact surface conditions
Presence of coatings or finishes
Highly reflective elements
Signal attenuation at depth
Shadowing caused by near-surface elements
Need for preliminary tests, where required

Ultrasonic tomography is a diagnostic tool: result quality depends on appropriate survey design and data interpretation.

Application example: Via Mario de Bernardi Viaduct

In 2019 Novatest carried out a diagnostic campaign on the Via Mario de Bernardi viaduct near Fiumicino Airport, aiming to obtain information on the internal configuration of the existing structural elements.

The campaign used ultrasonic tomography, GPR and digital radiography. This page focuses on tomography's contribution and its methodological relationship with ground-penetrating radar investigations.

GPR provided preliminary information on the internal configuration, while tomography enabled a more detailed examination of the element's response through ultrasonic acquisitions.

Explore the full bridge and viaduct investigation case:

Integrated diagnosis of bridges and viaducts

Ultrasonic tomographic acquisition on a concrete viaduct deck — Tomographic acquisition at height on concrete viaduct elements: measurement positions were defined using preliminary information acquired on site.

Equipment

The campaigns described used the A1040 MIRA tomographic system. Equipment nevertheless remains a supporting element: result quality depends on survey design and technical interpretation of the acquired data.

When should ultrasonic tomography be chosen?

Ultrasonic tomography can be considered when it is necessary to:

Further investigate previously reported internal anomalies
Analyse concrete elements
Investigate discontinuities of unknown nature
Obtain sectional or three-dimensional information
Further investigate areas already identified using other methods

The method must be selected according to the diagnostic objective, the structure and operating conditions.

Frequently asked questions

What is ultrasonic tomography of concrete?: It is a non-destructive testing method that analyses the internal structure of concrete through the reflection of elastic wave pulses. The recorded reflections are processed to produce B-scan sections and, through grid acquisitions, three-dimensional representations of the element under investigation.
What does the pulse-echo method mean?: The pulse-echo method involves emitting short elastic wave pulses and recording their reflections. Reflections occur at surfaces with an acoustic impedance contrast relative to the surrounding material, such as discontinuities, voids or elements with different properties.
What can ultrasonic tomography reveal?: Depending on acoustic contrast and acquisition conditions, ultrasonic tomography can reveal cavities and voids, cracks, discontinuities, internal delaminations, metallic elements and anomalies in the internal configuration. A response is never guaranteed in advance: it depends on geometry, material and appropriate survey design.
What is the difference between a B-scan and a 3D reconstruction?: A single acquisition produces a vertical section of the investigated volume, called a B-scan. Repeating acquisitions on a predefined grid allows the data to be combined into a three-dimensional representation of the analysed portion of the element.
Can ultrasonic tomography be used on prestressed elements?: It can be used to analyse elements containing prestressing cables or strands, after assessing the element's geometry and thickness, available concrete cover, the most suitable viewing direction and possible shadowing from highly reflective elements. Preliminary validation on a known portion of the structure is appropriate in many cases.

Do you need to check what is inside a structural element?

The choice of method depends on the investigation objective, the element's geometry and operating conditions.