Resist Attacks

LOUISE: Well hello all, and welcome to Markham’s latest podcast episode! I’m Louise Kirk, part of the Markham marketing team in Australia, and it’s great to have you listening today. Continuing our Invisible Strength series, we’re looking into the science of how concrete can Resist Attacks.

With us virtually today is Martin Prestidge, Sales and Marketing manager of our Industry and Infrastructure department. Martin joins us from the Markham headquarters in Napier, New Zealand. Martin, welcome aboard. Please introduce yourself to the audience!

MARTIN: G’day Louise, thank you for having me along! Yes, I’m Martin Prestidge, been with the company for a bit over 10 years. As Louise said, I’ve been working in the industry infrastructure sector – civil projects, marine, mining. Pretty much anywhere we’re trying to increase the service life of concrete, whether that’s existing or new construction.

LOUISE: That’s very good, thanks Martin! And working with Martin is Doug Hamlin, our Research and Development expert. Doug, tell the audience about yourself.

DOUG: You have covered it fairly well there, Louise. But yes, I’m Doug Hamlin – been with Markham for just over 10 years. And yes, I work in a similar field to Martin in the infrastructure-industry side; working with asset owners, so engineers and the like. And yes, I also do look after the research and development side of things, technical side of things here at Markham.

LOUISE: Excellent, thanks Doug. Now, Doug, you spend a lot of time considering the science of concrete deterioration. Can you give us an outline of your observations?

DOUG: Yes, sure. As I’m sure everyone will appreciate, who’s listening to this podcast, that it is a very wide, far reaching topic. There’s many different attack mechanisms, things like that. But I guess in the main, the premature deterioration of concrete structures is really the most expensive in terms of asset management of concrete structures, concrete assets. So that’s their structures that have been designed and constructed with the, you know, 50 or 100 year design life. They’re getting to, you know, maybe half that and starting to show signs of deterioration.

And I guess so that’s the main thing I’ve observed in terms of asset management. In terms of damage or deterioration of the structures, there’s many, many different ways, concrete can break down. But there’s always one common and key factor, and that’s the fact that moisture moves can move through concrete. So that’s really concrete’s biggest flaw, for all its good, all its benefits, it does let moisture move through.

And this moisture by itself is not an issue. But when it becomes an issue is when it carries contaminants through the concrete as well. So that carries things like chlorides, sea salts; it can carry carbonic acid from, you know, the carbon dioxide in the air, into the concrete. And that can cause reactions and feed reactions inside the concrete. And that’s really when it becomes an issue.

So you know all these, we should say 95% of the issues associated with concrete, can be tied back to the fact that it lets moisture migrate through it – if that makes sense.

LOUISE: Yes it does. Right, when you say challenging environments, what situations do you mean?

DOUG: We touched on the chlorides, you know, like a seawater or marine environment, so that would be the most common one. There’s a lot of concrete structures in their environment, and it’s probably the one with most familiar with.

But there are also things … we’ve got carbonation, for example, that basically affects every concrete structure that’s built. That’s because there’s carbon dioxide in the air mixes with moisture – however, wherever, that may come from – and it forms an acid and eats away at the concrete. Eventually, it gets to the reinforcing steel and causes corrosion.

And there are also things like, you take effluent tanks or wastewater treatment plants, and we’ve got, you know, acidic material in contact with the concrete. And see the hydrogen sulphide and microbial corrosion there. And then you’re also looking at things like … where you’ve got fertilisers and minerals sitting on the concrete itself.

And you know, basically concrete is a high pH material and there’s a lot of things that come into contact with it that are lower pH, and that, you know, naturally wants to balance out and it breaks the concrete down.

Yes, I guess putting that into practical projects that things like sewage, water treatment, fertiliser, plants, that type of thing. But Martin, what’s your thoughts on?

MARTIN: That yeah, thanks Doug covered it pretty well. Yes, so it’s like you say, it’s anywhere where there’s potential for contaminants to become soluble and be carried inside the concrete. So pretty much the issue is the contaminants being able to ingress in the concrete.

So you’ve got permeable concrete, and then moisture migration, but if the contaminants are soluble, they could get carried in, carried down to the depths of steel and accelerate the corrosion.

LOUISE: So that’s what you mean when we’re talking about attacks on concrete.

MARTIN: I guess the cost implications is the need … like you’re saying that the early deterioration … see it’s the need for unplanned repairs or remediation earlier in the design life than what would normally be expected. So we’re seeing concrete coming under attack, and the durability isn’t quite there to handle it, and they’re having to expend money to help resist these attacks earlier than you’d normally expect in the asset owner’s maintenance cycle.

And then you’ve got the other issue with unplanned repairs, which is disruptive. So you’ve got to take the asset offline. Whether that’s traffic downtime, or it’s a wastewater treatment plant. That sort of thing.

LOUISE: Thanks, Martin. Tell us about what treatments you would recommend.

MARTIN: Yes, thanks, Louise. So we recommend treating with a hydrogel: colloidal silica hydrogel treatment. Whether that’s retro-treating to an existing structure, or including it as an admixture, or surface-applied during construction.

This deeply penetrates and immobilises the moisture. So we were speaking about the way contaminants have been carried into the concrete through moisture. If you can stop that moisture transmission inside the concrete, any moisture moving in or out, you’ve cut off the pathways for the contaminants. You slow the oxygen rate down. You remove the moisture and remove the soluble contaminants. So those three things in itself will decelerate the corrosion considerably. The hydrogels are highly reactive colloidal silica, and it gets in and reacts with the calcium hydroxide in the porosities of the concrete. And it just forms a gel inside the concrete that completely blocks those capillaries and messes up with those transmission lines, really, for the contaminants to get in.

LOUISE: Well, it sounds a very simple approach, just immobilise the moisture! Is that all there is to it?

MARTIN: Yes, Doug would have some comments on this, but that is the best way of protecting a structure.

DOUG: 100%! And it’s like you say, that’s all there is to it? Well, yes, it is. It is a simple principle, but you know, immobilising that moisture has many practical benefits.

So just going back to the colloidal silica hydrogels for a minute there. So if we just looking at when they’re applied to an existing structure for the minute – these treatments are nil VOC, so they don’t have any volatile organic compounds or solvents, if you like, in the product. So when applying them it means a lot less PPE and requirements for the installers. You know, applying it over waterways and that type of thing, there’s much less need for catch-and-contain.

And the other thing is, when they’re applied to concrete it’s a case of getting back to the bare concrete surface. So removing any previous coatings, dirt, dust, grime, that sort of thing – general a high-pressure water-blast is enough. And then they’re spray-applied, a number of wet-on-wet coats, so it’s not waiting for, you know, 24 hours between coats.

And so what that ends up meaning for you and for the structure, for the asset, is that there’s a real minimal amount of downtime required to treat the structure, and, you know, obviously all these structures are there for a reason. Generally, it’s because they’re making money for you as the client or as the asset manager.

But yes, getting back to that – it is really that simple, that moisture migration through concrete. If we can stop that, we stop, you know, most of the problems associated there.

And we would always recommend having a structure assessed as early on as possible in its life. That’s things like, you know, maybe getting some chloride readings or assessing the permeability of the concrete, because there is a lot of things that happened to concrete that you don’t see until it’s too late. So there are things like the corrosion process on the steel starts a long time, or can be, you know, manifesting itself a long time before it shows any signs on the surface of the concrete.

But at the same time, you can actually monitor the levels of the chlorides and get an indication of where that process is up to, and so that’s really why we strongly recommend having those assessments conducted as early on as possible in the structures life you know to give you a clear picture or … a clear picture of where you are, where your structure’s sitting in what … you know, what you might need to do in terms of proactive maintenance or reactive maintenance. If it’s, you know, too far down the track.

LOUISE: Oh, that’s excellent advice.

Well, thank you so much. Martin and Doug for joining us today. And to all our listeners, we welcome any questions or feedback you have on today’s topic, or even if you have a specific project you want to talk about.

If you want to find out more, please go to our website www.markhamglobal.com. We do our best to respond to all inquiries within a day. We are also happy to take suggestions for topics in the future. What are your concrete pain points in the field? How can we help to educate the industry?

Thank you so much for listening and don’t miss out next episodes!