Adding Life to Concrete – From Day One

NIKKI: Kia ora and g’day everyone, welcome to Markham’s latest podcast episode. Obviously, we’re very excited, and we’ve still got our training wheels bolted on! I’m Nikki Horn, Markham’s Project Manager for New Zealand, and it’s great to have you listening today.

This is the second topic of our series, Invisible Strength. We’re keen to get into the science and practical challenges of Adding Life to Concrete from Day One.

With me, as we walk through this topic is Wade Lanham, Project Consultant in our Sydney office. Wade, give a shout out to our audience!

WADE: Hey, hey, audience! Thanks Nikki, and yes, I’m excited about joining our new podcast series as well. It’s going to be practical stuff, learned through real experience, not just hypotheticals. Of course, we will dive a little into the science, although mostly keeping it really simple. We’re hoping to include relevant industry experts in future segments, but as Nikki says it’s just training wheels today!

NIKKI: That’s great, Wade, thank you. And also with us is Doug Hamlin, our Research and Development Manager – let the audience hear you, Doug!

DOUG: Thank you, Nikki, yes, I’m keen to help this series along with some practical insights! Back to you.

NIKKI: Awesome! So Wade, where exactly is today’s topic coming from? We’re talking about adding life to concrete from day one – can you give us some context?

WADE: Yes thanks Nikki. When we’re looking at a new structure, and we’re talking about adding life to it, we’re really thinking about how long that structure is intended to last – what is its planned service life?

So in the context of concrete, there are two sides to the coin. Firstly, how do we guarantee that service life will be achieved? Now that doesn’t mean, achieved with the help of expensive repair work later in its life. And of course, there’s a lot of research sunk into ensuring the concrete will endure the planned service life. But there are on-the-ground reasons why that doesn’t always happen.

The second aspect is, what if the structure is still in use beyond its planned service life? And let’s face it, suppose you have a structure with a 50-year service life, and it’s in active use when that 50-year mark hits, there’s not much motivation to demolish it. Now of course we’re not thinking about that when we’re building the new structure, but it’s these types of situations that Markham’s experience in concrete life has developed.

So the context comes from looking at structures later in their service life, and applying these lessons from their deterioration into new structures, how to maximize the concrete’s durability from day one.

NIKKI: Let’s talk about durability a bit more. I was waiting for you to use that word! It seems like plain logic, if the concrete is more durable, it will last longer. But concrete is naturally durable, isn’t it? And very qualified people spend a lot of time designing concrete mixes for increased durability. Is there something we’re missing here?

WADE: Well that’s the multi-million dollar question, isn’t it. And you’re right, there’s a good deal of industry headspace spent on the topic, and we don’t want to sound like we’re rubbishing those efforts either. But for all the backroom mix design, and even the best efforts at placement time on site, we’re still seeing premature deterioration. That is, structures needing significant repair to achieve their original planned service life.

There are a number of reasons why this happens.

You have to understand the deterioration cycle. Doug, can you give our listeners a quick outline of how this works?

DOUG: Yes sure thing. In short, the deterioration cycle happens by contaminants and reactive chemicals travelling into the concrete using microcracks, and these are carried by moisture. So these contaminants cause the steel reinforcing to corrode, or they might accelerate ASR or other expansive concrete reactions, and this cracking becomes more severe. So this means more contaminants, more moisture gets into the concrete, and so it goes on getting worse, exponentially! So it’s not a lineal gradual matter.

So often the first anyone realizes the concrete is deteriorating, is when they have corrosion stains seeping out of the concrete, or they start to see large cracks developing for no apparent reason. You know, it catches everyone a little bit by surprise.

WADE: Yes, that’s a really good little summary, Doug. I want to pick up on that expression you used, ‘microcracks’. Those fine cracks often develop at the curing stage and are often ignored, but they can spell early ageing for the concrete. High-quality curing – high quality hydration – it’s incredibly important for long term durability. And curing quality remains challenging to control on-site. So that’s reason number one for unexpected premature ageing, of course.

Secondly, this is the missing piece to the puzzle: bleedwater evaporation leaves micropores in the concrete, as the water leaves the concrete, it escapes. These pores are even less likely to be noticed than the microcracking, and they occur despite the best efforts of mix designers to reduce the impermeability of the concrete.

NIKKI: Oh, another keyword! Impermeability! When the concrete is more permeable, it will let in more of those contaminants, right? So the more impermeable the concrete is, the longer it will last.

WADE: Well, in the field this is often camouflaged as the concrete’s strength rating. People commonly think about durability as being linked to the strength. The higher the MPa rating, typically the higher the Portland cement content in the mix, and sometimes flyash and other fines are used to help close up potential porosities in the concrete. So a stronger concrete is usually a less permeable concrete – and lasts longer. But people don’t always realize that this is because the contaminants are being kept out.

But as we said, that bleedwater porosity will still occur to some extent, particularly if the mix design has a high water content. When it’s a high-cement mix, the placement team may be tempted to add a bit of extra water to make the mix flow a bit easier. But this leads to more bleedwater porosities after curing and takes away from the intended durability of that high-strength concrete. So there’s reason number two.

Two reasons why contamination can enter the concrete from day one – microcracking, and bleedwater porosity. Once the contamination is inside the concrete – carried in by moisture or moisture vapour, and moving around inside the concrete carried by moisture – then that cycle of deterioration we talked about is inevitable.

NIKKI: OK, can you give the listeners now an example of what you mean when you say ‘contaminants’?

WADE: In this context, contaminants include any chemical which will react with the concrete. Chlorides are a particular example. Chlorides are found in seawater and therefore affecting a lot of marine structures. It’s very common to see rust stains coming out of marine structures, because the chlorides have soaked into the concrete and reached the steel reinforcing, triggering corrosion. Then you get carbon dioxide, for example from exhaust fumes, which may affect concrete car parks, causing carbonation and causes a lot of dusting issues. There are other reactions that can cause expansive damage inside the concrete, forcing cracking from the inside out. And as Doug explained, the little cracks become big ones, and the damage is exponential. And potentially very expensive.

NIKKI: Very expensive and very scary. So you’re saying, premature concrete failure is often built in from day one. So what’s the answer to that? How do we stop that?

WADE: Stop the water moving through the concrete.

NIKKI: Is that all?

WADE: Yes! Sounds too simple, doesn’t it? We’ve already discussed that the contaminants are carried by moisture. Carried in, and carried around within the concrete.

So here it is. We’ve got unwanted and unexpected porosity and microcracks. That’s what we need to fix – or even better, prevent it from day one.

NIKKI: Awesome summary. So let’s ask Doug Hamlin, another expert, our research and development coordinator, to turn this around for us. Doug, what’s the secret? How can we close up those fine cracks, those invisible pores, that’s P-O-R-E-S, in the concrete, so moisture can’t get in or move around?

DOUG: Yes, sure, so I’m just going to give this in general terms, we won’t mention product brands here because that gets a bit sales-y. But the secret is hydrogel treatment.

So what we’re talking about here – listen carefully: this is the application of catalytic silica nanoparticles, that induce the formation of a C-S-H hydrogel within the concrete. That’s C-S-H, that’s calcium-silica-hydrate, that’s the same molecular formation the concrete itself is made up from, so that cement paste that binds everything together. Now the hydrogel picks up that moisture that causes the trouble, you know, that’s moving through the concrete, and immobilizes it. And then new moisture from the outside of the concrete can’t get in. And you know, reactions are arrested and prevented due to the lack of those active ingredients or the lack of those factors needed to make up that damage equation.

So that sounds complex, but that’s actual the simple version.

So I haven’t mentioned some other finer details, there are particulars around dosing or how it’s applied which make a big difference. And not all catalytic silicas or colloidal silicas are created equal – actually the best ones look like water because the particles are so fine.

NIKKI: I love that concept! Immobilize the moisture, arrest the deterioration! Hey, that really is simple. So bringing this round full circle, if hydrogel treatment is applied at the construction stage, it will enhance the long term durability of the structure by overcoming unwanted porosity or microcracking issues in the concrete.

DOUG: That’s right, yes, that’s the generic conclusion, yes. Of course, we’re talking about concrete that’s been mixed, poured and placed correctly according to industry best practice. Hydrogels won’t fix below-standard work, or severe rain damage, for instance. Or another thing we see sometimes is below-strength concrete. So there’s a little disclaimer there!

NIKKI: I’m quite often asked about a couple of those issues. Without going too far down that tangent, what do we do if we do have those issues?

DOUG: OK so if we take weather damage, for example – obviously each scenario or project needs to be reviewed on its own merits, but it depends how severe the damage is. A good hydrogel treatment penetrates 150mm into the concrete. So that’s very important when you’re talking about durability under loads. And then if you think about during construction, if the surface is damaged, whether that’s due to some preparation that’s been done, or some bolts that have been drilled into the concrete, that type of thing – but the hydrogel treatment remains in the concrete and can’t be removed or reversed out of that concrete. But yes as I said, every situation is slightly different, so if you do want to talk about your specific project, we’d definitely love to talk to you.

NIKKI: That’s absolutely true. If you want to find out more, please go to our website, www.markhamglobal.com. We do our best to respond to all enquiries within a business 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, don’t miss our next episodes!