Sustainability and Performance

BRENDAN:

G'day and welcome aboard everybody. Thank you very much for joining us today. And we're back in the room with the team from Napier there, Hayden and Doug, who we’ll introduce as we go along. And we're focusing today on sustainability - not at the expense of performance. We’re talking about advanced concrete admixtures. And very quickly I'll just bring up the slide deck, and away we go!

So yes, as I say, Hayden and Doug, who some of you will have met before. And they’ll introduce themselves as we go along. And there’s a questions and comments field in the bottom of your toolbar.

The agenda today relates to, What are the impacts of the various SCMs in current use? You might well ask what an SCM is! How can we optimize performance of the resulting concrete? Can we preserve the surface integrity and the durability of that concrete? So as I say, questions and comments at any time using the Q&A button at the bottom. And if you'd like to start the ball rolling, we'd love to hear from you in the comments. What concrete additives do you currently use? So, Hayden, do you want to take us away with the first topic.

HAYDEN:

Thanks, Brendo, and good morning all. Good evening, if anyone else is on that side of the globe. But I appreciate everyone coming on. It's such a good topic out there at the moment. And it's good to be part of it. So yes, Hayden Prestidge, based out of Napier. I work across Australia and New Zealand, in the ready-mix concrete space for MARKHAM. Been here about ten years or so. But I really wanted to jump into ... Obviously there is a very noticeable drive in lowering the carbon footprint of concrete production and it's becoming... it's gaining a lot of momentum. Obviously there's a lot of authorities, governments, a lot of projects driving for a large reduction in cement. And it's all pushing momentum and energy into looking at cement replacements.

And there's Supplementary Cementitious Materials. And that is SCM, for those unaware of the acronym. So we do use a few acronyms. That's an industry one, but you'll be aware of that. So that, What is an SCM? It's basically anything that... it's a binder, to try and move away from cement. So it's replacing cement with some things. You know, slag is a common one. Blast furnace slag. There’s fly ash, you know, that comes out of the production of coal, etc. Or there’s, you know, people looking at calcined clays. Different products that are coming that can act and react and cause a replacement of concrete... cement.

And then you can also move into areas to reduce the GWP - there’s another acronym, Global Warming Potential - that's another one to look at, which is in this topic as well. But then there's people looking at crushed rock; different manufactured sands etc; to try and pull back and reduce the carbon impact of concrete. So it’s just interesting; I think there's about 4 billion tonnes of cement produced annually, globally. In every tonne that's produced there’s about 0.9 of a tonne of carbon emissions produced. So that's a lot globally. And that equates to about 8% of total emissions in the world. So it is a topic. It is a topic we need to be behind, get in behind. And that's what this is for.

We can get concrete. There's still a lot of people that say, hang on, just take me back to the good old GP. You know, the good old cement days. But we can get concrete to that point. And this is what this discussion’s about, is how to get it there. Using SCMs does have challenges. And no doubt you'll all have challenges in your minds, right from designing; through to production of concrete; through to placing and finishing. So let's have a bit of a look at some of those. Brendan, if you want to jump to the next slide.

So the long and short of it is, all these cement replacements do act and behave different in the concrete. And it's not that, you know, a lot of us wouldn't be aware of how that can react; and the times; the reactivity; what's needed to make the strength go off, etc. It’s all different to what we’ve lived and breathed in the concrete industry. And some might be struggling with some of the traditional approaches out there. And then, like I said, there's some benchmarks and the goal setting done by corporates and authorities on cement replacement and lowering carbon, you know; people pushing a 70-80% replacement, which is very interesting and good.

A lot of research and development in there.

But these are some of the challenges that we're seeing. We'll just run through them quickly. Powdered sort of replacements that, you know, even from a safety point of view, there's a lot of handling and, you know... obviously these are micro, nano sized powders that are harmful. And then the quality control of adding those. How do we get them into the batch right? And then the demand on the mix or the, you know, the demand on the water or things like that? Strength development is notably a big topic in the industry, how do we get our early strengths, you know, if we can't use our cements etc?

Piling is an interesting one. When you get things like moisture loss and you get a lack of cohesion in a mix. That can result in real poor quality piling work. There's challenges, a lot of challenges through to the placing and finishing of concrete. And that's largely probably because we haven't had training - effective, intelligent training through that on how to treat a different mix in a different way, especially with SCMs. You get different bleed; and you can get different workability; different in how it closes at the surface; how its porosities work, etc. Working time and workability is pretty important. And that is different to normal GP concrete.

So what we're seeing is issues. People that are familiar with good workable concrete from cement are being challenged with these replacements. Bleed delays are important. Like I said before, how they react, how they demand on water; and they might get quite a different process there. And you get secondary bleed or delayed bleed type work that comes up and that causes durability issues long term. So spray concrete's another one. No doubt you'll be familiar with some of those, but I'd love any questions on these or any other challenges that you see, just pop it down the chat and we'll get to them at the end as well. But that’s some of the things we see, you know. When you're pumping, is it flowable? Is the mix right? How's it reacting with those pump pressures? Is it causing rebound? Is it closing off? You know, those sort of things. Is it setting right to stick to the wall?

So that's some of the things you see. And really all that goes into the durability and integrity of the concrete being challenged long term. But I don’t know if, Doug, you’ve got any comments on that?

DOUG:

No, that's good. It's a good outline, thanks. Yes. If we could go to the next slide there, Brendan. Thanks for joining, everyone. I'm Doug Hamlin, work in the research part of MARKHAM. So the... Looking at how we optimize these mixes, overcome some of these challenges: there are really two items I want to focus on, of what Hayden's just been going over, and that is the early strength gain of these mixes, being one of the biggest challenges.

And then secondly, the workability of these concretes. So there's really three ways that we can we can look at this. Either we say, I accept that it's a totally different material. It behaves differently. It finishes differently, closes up, everything, all those things that... you know. It's a completely different and new material and we need to, you know, essentially retrain everybody on how to deal with these mixes.

The second one is what we see already happening; is that yes, they are replacing 30% of the cementitious [content] with, say, fly-ash or slag; or it might be higher, whatever it is. But they're also increasing the GP cement, so as to make sure we get that early-age strength and workability in the concrete.

And essentially what we're doing there is that you're still using more cement than you need to. SCMs obviously have a slower strength gain. So typically what you would see at 28 days on a standard GP concrete, you're saying at around 56 days. And if you take that back upstream, in terms of getting on to slabs, that type of thing, for construction workers to carry on, you're just sort of looking from one day out to 2 to 3 days.

So there's some delays there which need to be taken into account. And then the third option that we can look at is specialized admixtures. The hydrogel admixtures are the ones that we look at; we specialize in. And that is to get the concrete, these SCMs concretes, behaving more like a GP concrete.

So this is in terms of, you know, how they place on site; the workability. We've done a lot of concrete there where the workability is, you know, it's pumping nice. It's placing nice. You're not getting that late bleed out of the concrete. It's more like a standard concrete in terms of that.

Durability is another area. So the SCMs themselves, especially slag concrete, it has a higher durability anyway. We can take that and further increase that with the use of hydrogels. So you're getting the best in terms of protection there. The only any issue, as I've mentioned, is that that early strength gain isn't there. So while the end result is great, the logistics and the critical pathways in the construction are affected, in terms of getting that... getting a construction program on track or keeping it on track.

So, yes, that's really the options out there in the industry. Just touching back on that cement point again - another side effect of that. So you know, obviously increasing your GP and putting SCMs in as well, is that you're hitting those early strengths, well and good; but then when you get out to 56 days and plus you're actually hitting well above what you need to in terms of your strength in the concrete. And most of you would say... or you might think that's a good thing.

That's not necessarily, because engineers do have maximum strength that they want structures to get to. So they don't want it being too strong, too brittle. They do need it to, you know, be in that sort of strength range for the engineering designs, the earthquake, seismic designing, that type of thing. So yes, something to bear in mind there.

If we could go to the next slide and have a bit of a deeper dive into hydrogels and how they affect the SCMs. Firstly, they are a liquid admixture. So they're much easier to dose on site and safer for the staff there. And being nil VOC, they're not giving off any solvent smells, that type of thing.

This is also true when you're coming through to placing and that type of thing. So you're not getting anything abnormal there. And, you know, the safety: it's not a crystalline silica product. So that's a colloidal silica which is fundamentally different and basically comes down to the shape of the particles. So there's no silicosis risk and that type of thing with these materials.

The workability, as I've mentioned. So being a... they're essentially a sphere in shape, or circular. And that helps the rheology and workability within the mix. The mix is essentially lubricated. So when you're placing and finishing and that type of thing, it's flowing; pump pressures - you can lower pump pressures on a standard pour, like we've got on the photo there. Also for shotcrete, sprayed concrete, that type of thing, you can bring back that pressure so there's less effect on the gear. Also when you're screeding, raking concrete around, it's not stiff and sticky, the concrete. So when you're... The end result is you get a more quality finish and quality concrete. It's all around the reinforcing steel where it needs to be. It's finishing off nice at the top. You're getting a good surface. And you know, that workability is improved. And yes, I've mentioned the durability is enhanced as well, which is obviously a further sustainability benefit there. Hayden, do you want to touch on the surface challenges with these mixes?

HAYDEN:

Yes, sure. And just a reminder to keep firing questions in. We’ll have a good session at the end just to go over specific points that you've all got, because that’s always the best part of these sessions, is when we discuss actual challenges that you're facing. So just pop them down there, and we'll get to them soon. So yes, surface durability.

Well, durability and concrete integrity as a whole is very important, obviously. There's a lot of modeling, a lot of history with GP concrete. And there's challenges. There's concerns. There's hesitations in the market of, How long will my structure last? You know, I've got cement replacements. I'm looking at this geopolymer concrete, you know, really pulling back on cement, etc.

What's the long term outlook for my structure? If it's in the marine zone or carbonation; those sort of things. Those sort of things are very valid. Hesitation. But one thing I just wanted to touch on is the surface durability; and that's quite interesting. The structure... the concrete matrix itself should be pretty protected.

But what you can find - because it reacts, because of these cement replacements etc react different with water; they let go; and some of the admixtures in there etc, as I touched on earlier, you can get those sort of delayed bleeds and different finishing things and you might see different coloration etc on the surface. You've probably seen that in some of the mixes. That's all on this topic. And that can result in a lot less strength at the surface. And that's subject to wear; you get machinery running over, you get traffic over it; and that's subject to wear. You think of a car park structure where you got [vehicles] turning on every corner, those sort of things. You'll notice wear quicker, if it's not done right.

So these are some of the things that need to be considered. And these are some of the things that we need to overcome, because otherwise, you know, we can reduce cement, we can reduce carbon. But if we’re building the structure again, prematurely to what it should have been, we haven't really overcome anything in the industry. We've just used more cement again. So those are some of the things to think about. There's ways to increase that abrasion resistance, etc. And we're finding colloidal silica is a good way of overcoming that. So just to touch on this. Anything to add on that, Doug?

DOUG:

No, no, it's just... Actually there is. Just what you said about the durability of the matrix itself, that's typically with... especially with blast furnace slag, you're not getting that... It's actually getting a better result than standard concrete. It's just that surface. And it has to do with the, like you say, the way it finishes, and can sort of bleed differently, those sort of things.

So yes, if we wanted to wrap things up now. As we've gone over, we want to push for these low carbon mixes. They are here to stay. And that's good in terms of the sustainability of the concrete; reducing that global warming potential and, you know, achieving a more sustainable result overall.

And we really want to be able to do that without having impact on the performance of the concrete. So in terms of GP concrete, we're getting that same workability, same placing, performance; and then obviously long term performance of the concrete as well. We want to achieve that, you know, get that as close as possible as we can there.

So yes, the challenge we would really like to leave with you today, before we get on to the questions here, is, Is there a need for performance of these low carbon concretes - that's whether it's durability, surface, wear, placing, those sort of things - to be compromised with the use of these supplementary cementitious materials in the concrete?

We don't think so. And it's an area where we're committed to developing further, and getting these concretes closer to standard concretes. But obviously there's a few challenges that we've gone over, that we need to take into account and think about. But yes, the good news is we believe it can be done. And look forward to getting to your questions now!

BRENDAN:

Thank you very much! Sorry, go along, Hayden.

HAYDEN:

No, that's good. There's already a couple of points in there, but just... How does Markham reduce rebound in spray concrete without compromising performance?

BRENDAN:

Yes. Go ahead, give us that one.

HAYDEN:

So it's interesting. So we do a lot with underground constructions; shotcrete basements, those sort of projects. And it's really interesting... You'll see the same even on line pumping, or pumping vertically up, you know, structures etc. Essentially what's happening is, by the inclusion of colloidal silica hydrogel that Doug was speaking about, it lubricates the mix, in short.

It provides a... we call it a hydrogel. And so it stays in the gel form and just helps the rheology; but it also helps it stay together. So it holds it together, so it gets a quality concrete; but it lubricates it, so it flows, pumps and places better. So what that does as far as reducing rebound is you can wind back - and we've seen this numerous times - wind back the pressures on your pumps and your equipment. So you get an advantage there as well. Which ultimately reduces things like rebound, because you're not firing it at the wall as hard; but also the cohesion, holding it together and setting up that concrete. So hopefully that makes sense.

BRENDAN:

Very good. We had a couple of questions which came in before the session, very much appreciate that. Antony was asking about any product updates; and experience with Global Warming Potential, which I think you touched on before. Do you want to talk about EPDs, I guess?

HAYDEN:

Yes, Global Warming Potential is very valid and it should be looked at. A lot of concrete ready-mix producers have now got EPDs, Environmental Product Declarations on their mixes - or their standard ones. I believe every product that goes into concrete should have EPDs as well. And that obviously dictates your global... Every product comes out with a number on it. So you can calculate your Global Warming Potential. And it is a factor that's being looked at more globally, which is good. And it's actually a number that can be actually put into... into actual numbers, which is something we haven't really had before.

So there's a drive obviously from, you know, different projects, or sustainable, councils etc, to reduce or get down to target levels. It's a way to calculate that now to make sure you're in that framework. That's really good. But we believe it can be done, obviously, by pulling back on cement, replacing it with these things and putting it in. Hopefully that makes sense on that one. Anything to add to that, Doug?

DOUG:

No, you've covered that well.

BRENDAN:

Antony's also got a question on the waterproofing of old foundations and spalling repairs. I guess it's something that occasionally we involve admixtures in that kind of situation. I was thinking of that old wharf that MARKHAM did many years ago.

DOUG:

Yes. Yes, that is an option there. Another area we get involved in is the sprays. So we can protect the original concrete, and then any repairs have an admixture in them to protect them as well, from ingress of contaminants; whether it's chlorides; or protect from carbonation, that type of thing. Yes. So like you say, Brendan, it’s slightly different to what we're going over today, but it'll be good to send some... a bit more detailed information out after this, I think.

BRENDAN:

That's good. Just a question from Carlos came in, as I say, before the session, on corrosion. Aspects of corrosion in post-tensioned concrete and the most common tests to detect it? Did you want to just say a word on that? It bears on making the concrete last longer. I suppose it would relate to what you just mentioned about spray applied treatments.

DOUG:

Yes. That is an area of concern, especially because once you get that corrosion happening on those tendons or on those strands, it's almost too late. You can't do a traditional repair, where you take out the rebar, weld it together and go again.

So it really does... I agree with you, Brendan, it really highlights the need to protect the concrete itself as much as possible, to stop those contaminants getting into the concrete. Moisture, even moisture getting into the concrete so it can start that corrosion process. So, yes, that's really all we can do from our side. We're not so much into the testing area. But yes, we're more about the preventative side of things.

HAYDEN:

Yes, all I was thinking... I mean, corrosion pretty much... Contaminants or moisture and chlorides really. And if you can take those out of the equation, you're doing well. There is surface tests you can do on permeability. There are different tests you can do there. You can take cores. Know what your chloride profiles are at different depths. Especially thinking around the depth of the tendons. And so you need to do that. But that's probably something you could monitor.

But long and short of it is, durability essentially, we think, comes down to allowing... how much allowance of moisture can get into the structure. And if you can take that out, if you can stop moisture moving, and take that out of the equation, you're doing a good job to get that. But obviously these all come in from these cement replacement examples. And if we're not getting things right, you are allowing different paths, and contaminants and moisture to get into the concrete. And you can result in premature loss. So yes.

Question there around, How does colloidal silica hydrogel admixture enhance durability? So we’ve probably touched on it roughly in what I was just saying. The hydrogel essentially set ups in the porosity, and blocks the porosity, to stop moisture migration, essentially, It grows more calcium-silica-hydrate, and really densifies that concrete matrix; and protects it against contaminants; acids, chlorides, those sort of things that get into the concrete.

DOUG:

Yes. I was going to say that the cement, efficiency of your cement, has increased as well. So in those early stages, you're getting more ‘bang for your buck’, if you like, out of the cement. And that creates a more lubricated, creamy mix. And then obviously that hydrogel in the concrete helps it place nice. And then, yes, as Hayden’s mentioned, the calcium-silica-hydrate formation is accelerated or sped up. So yes. And you're getting a more denser, less permeable concrete. So yes, that's how that increases that durability there.

Any other questions there, Brendan?

BRENDAN:

...any other points that you wanted to ... here we are. Thank you, Samson! That's much appreciated. [Samson – Thanks to all… very valuable information 😊]

HAYDEN:

Yes. Just interested if there's any other specifics around cement replacements, or what people are finding, and what people are trying to overcome. But we'll be doing a series of these anyway, so it'll be good to have everyone on board. We’ll fire out an email as well, after this. So come back with any specifics, or something that might jump into your mind. And we’re happy to chat it through from what we've seen.

BRENDAN:

Yes, I was just going to say we will definitely send out a follow-up email. We’ll put a couple of links on there with some related information. And if anybody's got a project-specific question or a case-specific question, we would be happy to have a look at that with you. Thank you very much to everybody that has joined, and appreciate the questions that were coming in. It’s been really good.

HAYDEN:

It's good.

DOUG:

Thank you guys.

HAYDEN:

Thank you. Very good.

BRENDAN:

Thank you. Yes.