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Interview: How multi-technology concrete testing delivers peace of mind

By Karolina Rzepiejewska-Malyska, June 11, 2019, 10:00 CEST

Concrete is one of the oldest and greatest inventions of humanity and remains one of the most impactful materials of all time. There are plenty of well-established but also modern technologies related to that construction material. This, in turn, translates into a plethora of business when it comes to the construction and quality assurance of new civil engineering structures, as well as the inspection of existing ones as required during their lifecycle.

In this interview we discuss with Warren Thomas, director at Henderson Thomas Associates (HTA). We learn his point of view on the innovation and advancements in the space of Non-Destructive Testing of structural concrete.

Warren, what kind of services does your company offer?

HTA offers an array of services related to the inspection of structures and infrastructure of any kind. This includes survey works, building investigations, etc. In addition, a big part of our work is related to the inspection of concrete highway structures, and in particular bridges.

Bridges. That’s interesting. Can you give us some insights related to bridge inspection?

Bridges can be of many types, each with its own inspection challenges. Especially post-tensioned bridges can hide many defects, specifically voids. However, similar defects can also be in car parks, power stations and other buildings. Now, when it comes to bridge inspection and investigation, one of the biggest threats related to their integrity and therefore lifetime are defects—voids—within the tendon ducts. These defects result from poor grouting practices during the structure’s construction. Being able to detect those grouting defects means that we can determine the risks they pose to the safety of the structure and the public. Our task is to inspect the structure effectively, precisely, and locate the tendons and then these voids non-destructively. We then operate like surgeons on the structure—we open the area and make the necessary repairs. The post-repair inspection is the last step of our service process, and a key part of delivering safety of the structure, safety of the public, and peace of mind.

And how do you do that?

The first step is to locate the tendon. In the past, we were looking at the technical drawings or used conventional cover meters. However, technical drawings are not always accurate or even available to begin with, and tendon ducts very often are too deep in the structure to be detected by cover meters. Then, we were using single-channel instruments and some really slow methods to estimate whether the tendon was grouted or not. This process was time-consuming and caused extensive damage to the structure. And this made the inspection process very expensive, considering time constraints such as the limited time we have available overnight to test e.g. rail structures used by the public intensively.

That sounds really challenging.

Indeed. It used to be. Over the past years we have used more and more sophisticated technology to get this done. Nowadays, we have a breadth of modern technologies in the form of Proceq solutions. Our excellent personnel together with our excellent NDT equipment by Proceq make our job really effective and allow us to fulfill the motto of HTA: “For definitive answers, not guesswork”.

How so?

Let me explain how we approach such an inspection job nowadays. First, we subscribe to Proceq GPR Live Unlimited—a best-in-class product that in subscription mode reduces our operating costs while providing continuous software performance improvements.  GPR Live focuses us in on the tendon that we want to look at. We start like this, because GPR is good at detecting metallic objects. The Stepped-Frequency Continuous-Wave GPR in Proceq GPR Live makes it exceptional at doing so deeper in concrete, and with great clarity.

So, now thanks to SFCW GPR technology we know where the tendon is, instead of assuming where it could be. Once this is done, we run Pundit Live Array Pro with its AI positioning along the profile of the tendon to accurately detect where the voids are.

That is exactly the breakthrough—since we started using Pundit Live Array Pro 18 months ago, we have been able to reliable find various defects. For example, we find grouting defects in tendon ducts, as I just mentioned. But we also find other defects, such as honeycombing and delaminations that GPR technology cannot detect.

This represents incredible progress. We have done jobs in the past, where by using other techniques we were not even able to determine the position of the tendon as accurately as we would like to.

That sounds like a multi-technology approach is the key to success...

Indeed. It needs to be said aloud: there is no single technology that would address it all. Period. The multi-technology approach is not an option. It’s an absolute must. If you want to eliminate guesswork and achieve peace of mind when inspecting concrete structures, adapt your toolbox to the work you do and the challenges you face in the field. Use Proceq GPR Live for metallic object detection and Pundit Live Array Pro for spotting defects within the investigated structure. Especially, if you continually strive to provide the right service, at the right time, at the right price, as we do.

What makes these devices special?

Apart from the obvious technical advantages of Proceq GPR Live and Pundit Live Array Pro, the great thing is that they are both wirelessly linked to the iPad. Both products use iPad apps for visualization, and follow the same software workflow principles, so it’s straightforward to use both on-site. Another thing is that both apps have a simple, yet powerful user interface. We also use the Logbook functionality a lot, and since we are a team, we also regularly share measurements with each other over the cloud, even across job sites. Altogether, these two products work great for inspecting post-tensioned concrete structures, which is an important service. I’d say, each of those is a brilliant bit of a kit that makes our services cutting-edge.

That’s very nicely said. Let’s talk about the future. You have been so many years in the NDT space. How do you envision the future of NDT? How far are we from what you consider to be your vision? How will this space develop?

What I am trying to do is to get across what the client sees. This means using more NDT technologies rather than having to extract cores, break them up, and do all kinds of intrusive work on a structure beyond the bare minimum that is necessary for the repair. That’s exactly what every structure or bridge owner wants: less damage to his structure. This we achieve with more brain power, the right combination of technologies, and cutting-edge NDT solutions. In fact, this is what this imaging kit is doing for us.

Great. So, if you had to transmit our readers a single idea from your experience in the concrete NDT space, what that would be?

More NDT, less intrusive testing!

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