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Tomography - Ultrasonic Technology

How to overcome GPR Void Detection issues

When encountering post tensioned ducts and or highly reinforced concrete containing congested reinforcement patterns, GPR will fail to detect voidage within the post tensioned duct or behind the reinforced steel.

In these instances Ultrasonic Technology must be employed to discover any hidden voids and defects.

Tomography Pundit Live Array - Proceq

This is where we introduce the 'Pundit Live Array' Tomography; this technology utilises a multi array ultrasonic approach to overcome the reflective issues that metallic objects create when GPR is employed. Tomography enables HTA to accurately pick up hidden defects (ie the results of poor grouting within post tensioned ducts) and voids in such circumstances.

It is vital to have the training to read the data and interpret all the information available, digital, visual and experience to provide definitive answers for the client.


Tomography can be used for the following

This list is not exhaustive, however it gives a good idea of the range of applications that GPR can be applied to.

  • Grouting Defects within Post Tensioned Structures
  • Detection of Voids within Concrete
  • Detection of Cracks within Concrete
  • Investigations of Fibre Reinforced Concrete
  • Investigations for Potential Air Gaps
  • Ascertain Material Thickness

Fibre Reinforced Concrete Slab

A case study.

Knowing what lies beneath is paramount!

Here is an example of what our hidden defect detection and subsequent breakouts can uncover.

The consequences can be severe if such investigations are not carried out by competent engineers. A load placed on this concrete could damage both the asset and lives.


With steel-fibre-reinforced concrete becoming more prevalent in construction, problems can arise in determining potential defects, such as voidage due to clumping of the fibres.

Warren Thomas of Henderson Thomas Associates outlines how ultrasonic pulse technology (tomography) overcame the issue of detecting the presence of such voids in a fibre-reinforced concrete slab.


Read our full article featured in the Concrete Magazine

The ground-bearing slab within this particular warehouse under investigation was some 6500m²in area and problems had been detected while drilling holes into the slab for the insertion of a racking anchorage system.

Download a PDF of the Concrete Magazine April 2020 edition here


Watch Tomography via the Pundit Live Array in action

In this video you can see our engineer scanning for rebar and marking them in chalk once the GPR has indicated where they are. This technique massively reduces the amount of exploratory drilling and breakouts that traditionally were employed.

Watch more videos of the HTA crew at work by clicking here


Want to know more about Tomography Applications?

Take advantage of our Open Door Policy

Even if you do not end up using HTA we are happy to advise on the best course of action for the outcome you wish to achieve.

It is impossible for one company to carry out every project, however we can share our expertise far and wide.

Call: 01555 771 525 or Email: testing@hendersonthomas.co.uk