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Post Tensioned Special Inspections 'PTSI'

Get the 'HTA 3 Step PTSI Approach'

Adopted by Network Rail, TFL & Leading Consultants

The HTA 3 Step process has transformed the Post-Tensioned Special Inspection process. Utilising GPR and Tomography we reduce structural damage while locating tendons, their profile and subsequent detection of any hidden defects.

HTA have over 30 years of bridge investigation experience offering a Multi Disciplined & Skilled Approach removing the necessity of having numerous sub contractors on site and their subsequent management.

Step 1: Location of Tendon Ducts, Depth & Profile

Negating unnecessary asset damage from traditional exploratory stitch drilling

It is imperative to ascertain where the tendon ducts are, their depth and the profile of the duct within the concrete. Which HTA carried out with Ground Penetrating Radar 'GPR'.

Without GPR engineers would (and still do today) drill the concrete via guesswork to locate the tendon and its running profile, resulting in considerable damage to the asset.

By taking advantage of this NDT technology HTA reduce asset damage, time on site and increase engineer safety.

The following video shows GPR being used to locate Tendons, depth & their profile.

Step 2: Detecting Hidden Grouting Defects via Ultrasonics

Using Tomography via Proceq's Pundit Live Array

Having ascertained the tendon duct location and its profile, HTA are then in a position to scan the entire tendon duct for grouting defects, particularly voidage.

We undertake this process using Tomography in the form of the Proceq Pundit Live Array.  This NDT device uses Ultrasonics which enable any voidage within tendon ducts to be detected.

This multi device approach and a good understanding of how this technology works is the only practical way to diagnose voidage, potential corrosion and failure when carrying out PTSI works.

The following video shows the Pundit Live Array being used to detect hidden grouting defects.

Step 3: Targeted Localised Opening Up

Confirming the digital data with accurate breakout

Confirming Non-destructive Testing Data with Targeted Intrusive Investigations

Confirmation of a potential void location from step 2. Localised intrusive investigations are undertaken to expose the tendon duct sheath.


On exposure of the sheath a careful opening is carried out to allow an internal inspection, as can be seen below.

Localised breakout - Henderson Thomas Associates

The Result

Below we have highlighted confirmation of the digital data along with localised breakouts. At two separate locations we exposed the tendon to confirm a well grouted tendon within its sheath and hidden voidage at another location and their associated scans.

A UK First! HTA carry out R&D of the Pundit Live Array

Initial Research and Development of the Pundit Live Array was carried out by HTA in 2017. The 'HTA 3 Step Approach' has since been adopted by Network Rail, TFL and Leading Consultants.

Details of this first trial can be seen below

GPR & Ultrasonic Tomography result from Henderson Thomas Associates

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.

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