The Marine Concrete Experience

CHARLES: Hello all, and welcome to MARKHAM’s latest online event, The Concrete Marine Experience. My name is Charles Currie and I’m based in the Napier, NZ, head office. Today I’m going to be interviewing Doug Hamlin, our R&D manager in the Infrastructure and Industry Department of MARKHAM. Doug, would you like to come on and introduce yourself?

DOUG: Sure thing, thanks, Charles. Yes, as Charles mentioned, I work in the infrastructure and industry space at MARKHAM; I’ve been here for about 10-1/2 years now. And currently not only working with engineers, asset owners in the infrastructure space with projects, extending the service life of concrete; but also looking at some of the research and development; projects and testing validation that we have going on.

So yes, something I’m very passionate about; extending the life of concrete. So back to you, Charles.

CHARLES: That’s great, awesome! So the learning outcomes for this session include: What are the challenges faced by marine concrete? And what can be done to meet these challenges in both new and existing concrete? And are there other structures for which this is also relevant?

Today’s session is about a quarter of an hour long, and then we’re going to open the floor to questions. So you’ll find a Q&A button in your floating toolbar at the bottom. Please put any questions you have in there as we go along, and any that we don’t cover during the presentation we will cover in our Q&A session at the end.

Just before we proceed though, we are going to run a brief welcome poll. Can you please share a bit of background about yourself? It just helps us tailor the presentation to our audience. Thank you.

Awesome, that’s great, thank you. Right, so let’s kick into it.

Doug, can you give us an overview of our topic? What are the challenges of marine concrete? And give us some context here.

DOUG: Yes, sure thing. So firstly, starting with the description of what a marine structure is: many of the codes and standards specify slightly different things, but in general we’re talking around 1.5 kilometres from the shoreline is classed as a marine structure. And then there’s also a further classification that says in a coastal area, which is up to 50 kilometres from the shoreline. Now the 1.5 km zone can be subject to … generally it’s water or airborne chlorides; so whether that’s a structure right on the coast, or whether it’s in a tidal inlet, something like that; whereas in that further you know up to 50 kilometres as more… is predominantly airborne chloride risk of attack.

Now, why these are at risk is because there are variable moisture levels in those zones, so there’s a lot of … especially in that tidal zone, you’ve got that wetting and drying effect every, you know, twice a day, and that’s where the concrete gets into a saturated state, and then it dries out; and then as it gets saturated again the chlorides are drawn in, and they move around and gradually increase their concentration and get through the concrete, you know, borne by the water that’s migrating through the concrete; and attack that reinforcing steel – start that corrosion process.

And then once that corrosion process of the reinforcing steel starts, it’s a very exponential process, so it doesn’t just gradually manifest. Once that propagation is actually started, and you’re seeing that cracking and staining, and maybe some minor spalling, the damage exponentially gets worse. So it’s a very harsh environment. We see it predominantly in a wharf marine structure.

And sometimes it’s to do with the quality of the structure when it starts; but generally, as a general rule, you will see some deterioration of the reinforcing steel corrosion on any given structure. And whether it’s in, you know, 10-20% of the structure, or whether it’s over the whole structure. So yes, I hope that helps, Charles.

CHARLES: Yes, that’s great. It does sound rather extreme as well. Can you help us with the operational challenges? Where do they come in?

DOUG: Yes, definitely. So I guess, thinking about the structures and what they are used for: a lot of these are port structures where we have… Even myself, yourself, on the audience and the webinar today, you’re waiting for things that you bought online to be delivered, to come through these ports. Whether it’s in business; we are heavily reliant on a port to, you know, shift that freight, shift that cargo. And then the shipping companies themselves; they can’t wait in port for longer than they need to; or they can’t be held out of port due to, you know, some urgent repairs. Things like that. And then if that is needed to be taken offline, that is very expensive for, you know, not only the port itself, that is, for the shipping companies themselves; it’s for us as consumers. Everything is delayed, and that downtime really costs money. So it’s really something you want to avoid.

Then you’ve got things like the loading on a port structure – carrying on using that as our example – so you’ve got the cranes; you’ve got the loaders; got trucks; everything moving around. You’ve got the impacts of when a container hits the deck from being unloaded from a ship. You’ve got where you might have, like, a logging operation and the abrasion or the abrasive wear of the loaders picking up those logs. There are so many different loading and impact loads that these structures incur. As well as, you know, where the mooring lines are tied up to the ship and the subsequent stresses that are associated there.

And what all these add up to is that they can cause further microcracking in the structure; and the more microcracking you get, the fast, the more, the quicker that contaminants and moisture can travel through your concrete and to get to that reinforcing steel. Is that good, Charles?

CHARLES: Yes, that’s fair enough! Can you explain the MARKHAM approach now what can be done to protect the concrete?

DOUG: Yes, absolutely! So at MARKHAM we work with a technology called hydrogels. But before I go into those in-depth, it’s really important: We’ve touched on the moisture movement, carrying contaminants through concrete. It’s really important to recognise the fact that even from the day the concrete is poured, even if it’s a very well designed concrete, there is still an element of bleed water that comes out of the concrete as it’s, you know, after it’s being poured. It’s going from that ‘plastic’ to the hardened state, and that leaves these channels or porosity pores through the concrete. Once the concrete’s hydrated and cured, the moisture can get back down those channels and ultimately reach the reinforcing steel. So that’s very important to mitigate that moisture movement through the concrete and that’s how we do that.

But that’s essentially what we do with the hydrogels. So they’re a spray-applied treatment. So once the structure’s been cleaned down, we’re getting back to absorbent clean concrete – spray-applied; and they penetrate into the concrete. They’re molecularly attracted to the alkaloids within the pore structures, and they draw themselves down; form a hydrogel within the concrete matrix, and mitigate the moisture migration.

Now what is really important to note is that they are working in that critical area; and when I say the critical area, that’s the area around the reinforcing steel. So traditionally, the focus has been on either making the reinforcing steel itself resistant to the corrosion; so still allowing moisture and fluids to get into the concrete; so things like cathodic protection, that type of technology. Or it’s been focused at the surface level only; so stopping the moisture, the chlorides getting in at that very surface barrier.

Now what’s important here is that both of those systems – the cathodic protection is very reliant on a continuous steel line; it’s also very expensive. And so yes, kind of, you know, scares away asset owners from going down that track.

The surface coatings – they are great on day one. As you get down that 3, 4, 5 year time period, there’s a good chance that they have been chipped or worn off the concrete surface. And with the loadings and things we mentioned. And then even just the weathering, the UV, after that five year time period, they’re starting to wear off and they’re not providing that protection into the concrete.

Whereas when you can actually form a hydrogel, and manage that moisture migration in that matrix in that coverage, in that cover concrete to the reinforcing steel, you’re really getting, you’re really targeting the problem, right where it actually matters and mitigating the mechanism for the damage. So that makes sense, Charles?

CHARLES: Yes it does. It’s really good, thanks. Are you able to talk about some actual examples we’ve been able to help with, Doug?

DOUG: Yes, definitely. I think there’s some we prepared earlier here! So the first one is Ohope Wharf in the southern Bay of Plenty. So this was constructed in the 1950s. It is mainly used for recreational, you know, fishing boats. It’s a great jumping off spot for the kids in the summer! And what was happening is, it had some repairs carried out about 15… might be a little bit longer than that… years ago, to maintain the structure in a safe condition. And you know, that’s well expected with that age structure in that environment. And then after 15 years, the repairs were starting to show signs of being a bit tired, they’d started to break out again in places and then started to break out beside the repairs. This is what we know as Incipient Anode Formation. So in essence the structure was repaired again; brought up to a satisfactory level, a safe condition; and then we protected their… the concrete elements, so that they don’t deteriorate any further from the current condition, and we can maintain that condition for the service life, you know, of the structure.

So we can move on to the next one there. This is obviously a very aggressive environment, where you’ve got not only the wetting and drying of the tidal zone there, we’ve also got the abrasion, the erosion of that water as it hits the concrete, the seawall, every day. So this was over in the UK. So exposed to, not only a damp environment but, you know, the constant thrashing, if you like, of the concrete from the seawater. And we’re showing some excellent results here; a very visual example of that, you know, protecting the concrete against that ingress; because what you would normally expect to see over time is that ingress; and start to see some spalls around the… off the reinforcing steel, particularly around the corners of the structure. And we’re not seeing that on this project.

If we could go to the next one there. So this one is slightly different. It’s into a new construction and this was over in Port Hedland, WA. Yes, very harsh environment to pour concrete; and the weather is, you know, almost tropical there and so very high temperatures. When you’re pouring concrete makes it hard to get a, you know, a good result from day one, and, you know, that long term durability. So with this one we not only… There was a few other things. Obviously, the mix design was a pretty sweet design. They used some stainless steel reinforcing in the worst areas. And then we cured the concrete with a hydrogel treatment. So right from day one, it was protected not only, you know, to help make you better, get a better result, but protected from the, you know, the chlorides in the airborne environment. And what even made it worse on this one is that it’s a salt loading berth, so there’s always that, you know, that salt dropping onto the wharf around loading areas; and that, as we all know, fast tracks the chloride penetration into the concrete. So that was a project where we got involved right at the design stage and specified them to be applied right at that curing point. And then to further safeguard they also, you can see on the picture there, we rolled some CONQOR Hydracure curing mats out as well and that that helped with, you know, that surface, maintaining that surface moisture, not letting that escape and, you know, leading on to cracking. So yes, that was a belt-and-braces approach there. And yes, good results there, with no deterioration as of yet. Normally they’re in the five to six-year time period before they’re having to do some repairs in that harsh environment.

So yes, if you move on.

CHARLES: Very good. So the learning outcome we haven’t touched on yet is, What other structure types have similar issues?

DOUG: Yes, it’s a good question. So typically we focus on the marine environment. It’s very obvious this area that is under attack from, you know, those aggressive chlorides and saltwater and it’s got that constant wetting and drying. But remember that the structures are … they can be exposed to chlorides up to 1.5 kilometres. And even further, in some areas… I know there’s some areas even here in New Zealand that the tidal inlets go a long way inland and can affect a lot of structures, particularly bridges in that zone where they’re wetting and drying. So that’s a classic example there. It’s an area we do a lot of work on. Coupled with the chlorides and damage, there’s other things on bridges. You’ve also got your loadings, which, you know, of course, cracking over time… could be cracking from day one with the conditions of the concrete pour.

But then there’s one main one that we haven’t touched on and that’s carbonation. So typically there is a higher volume of carbon dioxide around from the vehicles, that type of thing. And that mixes with moisture and forms a carbonic acid, which breaks down the pH of the concrete. And then eventually it gets to the steel and starts that same corrosion process.

Now another area is water infrastructure, so potable water reservoirs. And you might say, hey, they’re housing water, what’s the issue there? It’s a pretty neutral substance. But there is what’s called a soft water attack, and that’s where there’s a leaching effect that happens. And it pulls down the alkalinity of the concrete, which is it’s natural protection; and pulls the alkalis, the calcium hydroxides, out of the concrete; and eventually, that gets the… lowers the pH, gets to that steel and, you know, attacks that pacification layer and you get corrosion. And it’s not always in the obvious areas. I’ve seen this on the soffits of a reservoir roof, where it’s not actually even in direct contact with water, but where there’s condensation and it’s in a moist environment.

The other area is in sewerage infrastructure, so the likes of pipelines and tanks, that type of thing. And that’s about the acid attack; and we’re not saying we can fully stop the acid attack, by the use of hydrogels, but we can limit it to that surface. So normally what would happen is moisture would carry in the sulphuric acid from the sewer and carry it into the concrete and break down the microstructure; whereas it’s only limited to the surface, once it’s treated with the hydrogel. So it extends the service life or surface life of the structure.

CHARLES: Yes, that’s great.

DOUG: Enough there, Charles on that one?

CHARLES: Yes, thank you! Just before we finish, can you say something about these treatments in sensitive environments?

DOUG: Yes definitely, yes. So we’ll finish on that. So the areas we’re … so in this example on the screen here – it’s over waterways. Because the hydrogels are a colloidal silica product. They are naturally occurring materials. They don’t have any volatile organic compounds in them. So when you’re spray-applying over the waterways, that type of thing, they are very safe, not only for the marine life in the environment but safe for the users as well.

And coupled with that, if you think about… if you’re extending the service life of a structure, you are… It’s a very sustainable approach, so there’s not needing to be more carbon emissions spent on the repair materials or the waste of the original structure; or even the concrete for a new structure in some cases, and which is the reality.

And then the last point on that is, we have got for our key products in our range, we have got the ecolabel, Environmental Choice NZ, so that’s a certification process that we’ve got there. And it gives you that assurance for the environmental concerns; not only just about the products themselves but MARKHAM as a company. So hope that’s helpful there.

CHARLES: Yes, it’s really good. Thanks very much.

Looks like there’s been a couple of questions, so I’ll…

Do you work in regional parts of Queensland?

DOUG: Yes, that’s a good point. So as a company we are based, our head office is in New Zealand, but we have got offices across Australia. Our head office in Australia is in Sydney, and we have one in Melbourne, in Perth, and Queensland as well. And yes, we’ve got installers all over Australia, all over New Zealand, so any area that you’ve got a project, we can get a team to. We’ve got one in each state, team or teams in each state. In short, we can. Yes, good question.

CHARLES: Nice. This other one is Can other coatings and treatments be used alongside this?

DOUG: Yes they can. You don’t always need to … like, it is a standalone protection treatment. But if you are wanting to go to belt-and-braces; or you’ve got your wanting it to be a certain colour; or whatever the requirement may be. Yes, you can. Anything that’s compatible with concrete is compatible with AQURON treated concrete, or with hydrogel treated concrete, or the ones that we deal with anyway! And that’s because they are not adding anything to concrete that’s not naturally found there; they’re only creating more of that calcium silica hydrate hydrogel, and more of that cement paste. And so if it’s compatible with standard concrete, it’s definitely going to be compatible with hydrogel treated concrete.

CHARLES: Awesome! And one last one. What warranty is provided?

DOUG: Yes, that’s a great question. That’s something we haven’t touched on today. MARKHAM work on project-specific performance warranties. So based on the condition of a structure; based on, you know, things like the chloride readings, the permeability of the concrete, what it’s being used for, the environment. There’s a whole lot of factors. And then we can give you a performance warranty for a set number of years based on, you know, the current condition that we’ve assessed it.

And now this is only in relation to durability, so we’re not structural engineers; but in terms of durability, if you’re expecting to get, you know, say, for example, we’re expecting to get five years more out of a structure. If we can, you know, repair and treat it with the hydrogels, we can push that out to the 10-15 year time period and put a performance warranty on that with measurable things like chloride contents; like the permeability of the concrete. So yes.

CHARLES: Awesome, thanks Doug! Was there anything else you wanted to touch on before we closed?

DOUG: No, I think I’ve said enough there, Charles!

CHARLES: Sounds good. Well, that wraps us up for today. Thank you very much for coming along. We are going to be sending out an email with Doug’s contact details and you can also request the recording from today’s webinar. So have a great day and don’t miss out on our next webinar! Cheers!