Accelerating Early Strength in GGBS (Slag) Concrete

BRENDAN:

G’day and kia ora, everybody. Thank you very much for coming along to join us today for the latest MARKHAM online event, our webinar on Accelerating Early Strengths in GGBS (Slag) Concrete. Sorry, I'm going to call it slag concrete, because GGBS is rather a bit of a mouthful!

With us today we’ve got Hayden and Doug. We'll just get this slide deck cranking; because unfortunately at this stage of my career, I haven't worked out anything that works quite as well as a slide deck, for all its limitations. Everybody seeing that OK? And can everybody hear us? Please be free to drop a comment... G’day, Mark. Thank you very much, very good!

So we've got Hayden and Doug with us. If you've been on some of our webinars in the past you’ve possibly met them before. They'll introduce themselves in a little bit more detail as we get in. And you do have a Question button and a Comments button in the toolbar at the bottom of the screen.

The agenda today revolves around slag concrete.

[1] How did we get here? The use of slag and other SCMs;

[2] Challenges for high-slag mixes; and

[3] Introducing a targeted practical response to improve the mix.

The burning question here, the underlying discussion point through this is, Can we make slag concrete act like traditional GP mixes? And without further ado - Hayden, I think you're going to take us away! ... or have I got that wrong?!

HAYDEN:

Thanks, Brendo. And g’day, everybody, good to see everyone jump on these sessions. They’re always good; they’re always interactive. So the more questions and chat we can have through these, the better. We all learn together. Obviously this is an open platform we can all join in.

So, I'd be pretty interested - just to kick off - if everyone can just hop on the chat, maybe. Say by this time next year, 12 months ahead, what percentage of your concrete mixes would you see containing SCMs? Is it like 20% of your mixes? 50%? 75%? Be pretty interested in that. It is a movement forward in New Zealand, Australia and beyond. And just be really interested to get a bit of a gauge. So just pop that in the chat. What percentage of your mixes would contain SCMs? But yes, just while you're doing that, we'll just jump in at...

This is interesting, the notes coming through. Yes. I think it's definitely a growth market and a change. Some big ones - 70%, 25%, 50%. That's good. But we're very much seeing this, OK. It's being used around the globe - the use of supplementary cementitious material, SCM. And it's climbing and climbing. And here obviously is the strive to reduce carbon is, you know, this whole green movement, and it's a good thing. And we're here to back it.

And that's probably our point of view is, How can we make these mixes perform the best they can be? Fly ash has been used a lot. And now what we're focusing on in this session is blast furnace slag as a cement replacement. And getting it to that point where everybody's comfortable, we know how it performs, we know how it works, and we can get it as close as we can to GP mixes or what the market's used to, so to speak. So it performs the same. And the guys placing it on site are familiar with how it behaves and acts; and we get the same consistent finish. So I guess that our overall purpose of this - making sure specifiers, or those sitting boundaries or goals, performance requirements, right at top level through to actually practically placing and getting the right finish on site - everyone's aligned, everyone's getting the right information, and we're all pulling together. So that's where we're at. It's a big focus for MARKHAM. It’s obviously a big focus for the industry, reducing cement and getting more out of SCMs. It does present its challenges though. And Doug might take you through some of those points.

DOUG:

Yes. Thanks, Hayden. And yes, good comment there on the ... We're seeing a lot more of the GWP potential, global warming potential, being specified in mixes. We definitely see that. We’re asked for it for our products, regularly. And it's something we can contribute positively, towards that. So, yes, with high-slag mixes - really just looking at some of the challenges now, obviously with the caveat that some... You get different supplies of slag, you get different materials you’re working with. They’re not always present, but we do ... From our research, and talking to customers from UK to Australia to New Zealand, these are some of the things that have come up.

And so round the finish times, set times, you know, getting that, waiting for that time to be able to strike formwork. So whether that's lifting precast panels, whether that's striking formwork on site, things like that. We are seeing that strength gain is a lot slower. Sometimes it can be hours in a precast setting. It could be days on a site setting. And that obviously plays into program disruptions or, you know, pushing that construction schedule out.

The cold weather does affect that. Slag is quite dependent on temperature to hydrate and activate, you know, create that strength there. And then the actual placing and finishing is different as well. So it can have less bleed, it can have late bleed. And you know, when you get a crew, concrete layers that are used to laying GP or standard concrete - when they come in... A lot of the time, it's when they haven't been told that there's a low-carbon mix or a high-slag mix. And they treat it like a normal mix and, you know, run into some problems there.

We've also heard of problems with some of the PCE water reducers where they sort of stop working after a certain period of time and all the water starts rising to the top. So, yes, there's a lot of challenges there to think about. The good news is, we are a good way down the track, with a lot of these problems.

And what we're focusing on is really is that early strength. And then, you know, at a later date, the workability of these concretes as well. So, yes, that really plays into what Brendan mentioned, Can we make slag concrete act like traditional GP mixes? I think we can get it close. I don't know if we will ever get it the same, but yes, we're very motivated as a company to get them closer to GP mixes.

HAYDEN:

Yes. Without going crazy on costs and integration and product etc. But keen to see from the audience as well, is there any main sort of challenges that we haven't touched on? I know even things like surface durability has been an issue for some, you know, it behaves different. What's long term? What's the concrete going to do? Is it more... You know, what's abrasion resistance? Those sort of things. Waterproofing, you know, are we able to achieve the same long-term results? Those things. But yes, pop anything in the chat. We would be interested to see some of the specific challenges you’re maybe having with some of these higher slag or SCM mixes in general. Be good.

So I suppose really we wanted to touch on. They’re good challenges and that's what we want to overcome as a group here and in the industry. And how do we do that? So if you want to jump the slide, Brendan, there?

This is something we've been working on for quite some period of time now. And based off a lot of research, a lot of history of what we've been able to do with concrete in different areas. And then getting a group of decent intelligence together, some good heads around the table, and working at what we need to do to get this concrete working the best it can.

And yes, introducing for those who haven't seen it, the CONQOR A80 liquid admixture, a strength... Purely focused on early strength development, this one. Batched at the ready-mix plant; obviously back end of the ready-mix process, and really kicking in that early strength push that's needed.

Exactly what Doug was saying. You know, you get that formwork released earlier, you've been able to strike that. Precast is a big one, you know, being able to utilize your precast beds more; more production, more program, you know, better efficiency there. Those sort of things are huge.

Cold weather is a huge one. And some of the traditional slag activators, we do know - as we all do - they have been limited in their ability in colder weather. So this was obviously a key focus for us as well, to make sure we're working consistently in different conditions and consistency across multiple different slags, different versions of products through Australia and New Zealand as well.

And then... So that's been a big one. And we've really tried to maintain it as a liquid. Obviously we know there's a lot of different activators out there. You know, you can get powders and grinding, into your actual finished product, etc. The integration of a liquid, the storage of it, the practicality of it, has come across strong from feedback. And that's why we’ve stuck with that as well.

So this is a... yes, this is something we're focusing on quite well now and getting a lot of uptake. Have you got any thoughts on that, Doug?

DOUG:

No, I was just going to say you can dial a liquid up a lot easier, compared to something that's added into the fly ash or slag at the earlier stage. So it's pretty versatile there.

HAYDEN:

Yes. And even had feedback on that, as around the quality control of that. You know, being able to plumb in a liquid, up through your ready-mix plant, up through your lines. It comes out on your batching sheets etc. It’s very consistent, you get a consistent response every time. So obviously proof in the pudding. We need to show some numbers on what it’s doing, Doug, if you want to jump into this space?

DOUG:

Yes, keen! So yes, obviously the first step where we start in proving these products is in the lab, you know, small scale lab samples, moved to bigger mixes there.

And then obviously, the real test is what happens when you put it on the back of an agitator truck and do a field scale mix. Do we see the same gains across those two...? You know, is there any gaps in those two tests there?

So we've done a lot of in-house testing. I think we're approaching about 100 mixes now. And more just sort of picked like a 40 MPa mix and then just tested many different quantities of the A80; different products, different things there. And we're seeing around a 50 to 70% increase in the lab. The 1-in-7 days we're generally seeing a little bit higher. And then 28 days, it does drop back a little bit, but we're still seeing an increase there. So it's giving that... it's getting closer to, you know, that traditional 28 days as the finished concrete strength mark, where, you know, construction can carry on; that type of thing. And then on the... seeing a similar sort of improvement at 30 MPa. We do drop back a little bit there. Obviously there's more water, things like that, in the mix. You do see that reduction in increased strength there. We do kind of take the philosophy that a lot of these low-carbon mixes are going into higher MPa’s anyway. So they're going into infrastructure projects, government work, that type of thing.

And then with field trials - obviously some of these we can’t always share because we are under NDAs with the ready-mix companies, things like that. But what we have done at our own... We’ve physically got concrete trucks to our head office here in Napier, and cast some samples.

We are seeing that around about that 40% increase, at seven days, was where we saw the definite increase. We also saw it earlier, and that's something that we have seen earlier with ready-mix companies, but obviously we can't share that as we’re under confidentiality here. But what we are seeing is that one-day increase, out in the field, which gives that assurance that both lab and field are matching.

The question I just see there [Can we talk about timing of strength gain as precast needs 18 hour strength? – Justin]- Thanks, Justin - around the 18 hours: we have we have done some at earlier than 24 hours, 18 hour mark, and we are still seeing improvements. We currently have got a program underway to be a bit more rigid around, you know, getting different MPa’s at 18 hours, at 24 hours, particularly for that precast market, using a precast mix. So that is coming. And yes, but early indications have shown we're getting some good results there. So, yes. Thanks for the question. That's good. Anything else on that one?

HAYDEN:

No, I was just going to say, probably some of the products we have tried in the past have had good initial kick, you know, day one, day three. But then long term, be detrimental to your specified or designed strength. So, you know, if you're trying to hit ‘X’ at 28 or 56 days, some products can be detrimental to that point. It's one thing we have very much carried in our R&D as well. And make sure that you're still hitting your design strengths.

There was a good question - we’ll answer some of these as they come in, but we’ll need to check at the end, we'll make sure that we’ve answered everyone. But the question is, If I only use 35% slag, will it affect strength...? [If I only use 35% slag, will it affect the strength increase compared to your data? – Verna] That’s good. We've pushed this right up to the limits. Or not limits, but relatively high, you know, 80% slag replacement.

And with the view of, you know, Can we still activate and get that responsive at that level? As we come back down, we very much see the gains. Because obviously you got cement and things working. That hydration is helping there as well. So as far as that, yes. We would see more, probably, in that space, on those slags. Any other comments on that one?

DOUG:

No, that's good. As far as the control mix - There was a 50% replacement there with slag mix. We can send you the actual mix later, for anyone that wants it there. But yes. That was what we would have said is like the baseline. And then yes, as Hayden mentioned, gone up and down from there.

HAYDEN:

Yes. Quite a bit of verification testing underway as well now, with different different groups across Australia and New Zealand. But yes, really sort of focused on... I'll be interested in any comments on this - running 40, 50, 60 MPa, and then 50%-65% replacement.

But do you think - This is for the audience now, do you think it would be better to see some more data around lower replacement levels, you know, 30-40% as well? I'd be interested in any comments on that. But, yes, we do know it's had good results.

But we are... exactly what Doug was saying. So this is where, as a company, we don't like to just say, here's a product that, you know, ‘one size fits all’ scenario. It needs to work for you, needs to work for your materials. Your aggregates, your... wherever you’re sourcing your slag from. Those sort of things, making sure it activates the same. So we really promote the ability of field trials, you know, working up and down with different dosage rates on different mixes, those sort of things, to maximize efficiency, from a commercial sense, but also from what you need to hit from a performance point of view.

Keep those comments and questions coming in, it’s fantastic! We'll get to those soon. One other big thing is integration and support with the actual set up into plants. This has been a good focus, I think. We touched on a couple of these points before, but having reach right across from bases in Perth, Sydney, Melbourne, Brisbane, and then through New Zealand. We can hit all the metro areas as well.

But then the liquid additive, being very easy to store, transport, you know, those sort of things, and then integrate into your actual plants, providing with bulk tank integration with lines etc. So it's part of your command unit or whatever you're using. Dorner or the likes. That’s probably one thing there. Just a note at the bottom of that slide, we've always got new products in development.

One of the next things we're working on, and would be keen on working with you all on this - we know workability is an issue; and a lot of these higher slag mixes, you know, they can become sticky, especially when we're pumping for distance or just getting them into where it needs to go. So the combination of early strength activation combined with a workability admixture, two-in-one type of approach there, is next off the rank. So watch that space. We'll be diving into that.

But there's a lot more questions that we'll go through now. But that's what we're up to. And I suppose that's the key to keep in mind right now is, Let's make the proof in the pudding, so to speak. And we would really love to engage in, you know, product and some field trials with you, those sort of things.

Anyway Doug, should we jump into some of these good comments here?

DOUG:

Yes, keen! I’m seeing a question there around the... I think it's quite important to address - I might have not made that super clear earlier - talking about polycarboxylates. [If precast moves to inclusion of Conqor B80 to help achieve early strength does that mean polycarboxylates can be dropped? – Loch] So we're not saying we're replacing those with the A80 product. We work alongside them and we help them work against some of those impacts. We help that early strengths and things. We might even better help some of that late bleed with some of the other work we're doing, down the track. But definitely not a replacement. So we fit in with what your standard mix is. We just make it better; if that makes sense there.

HAYDEN:

And from what we're seeing, yes, no issues with all the other mainstream additives. So it's good.

DOUG:

That's cool. The question around the, again, on the precast numbers, which we touched on that earlier, [1 day strengths not so relevant to precasters - need 18 hour numbers. – Justin] it's definitely something we are getting some more data on. We have seen improvements. We just want to get it verified independently. And we'll bring that back to the precast market there, and to yourself. Justin. So yes, thanks for the feedback there. Yes.

And probably better to wait until we say if we can hit that 15 MPa. We would certainly like to. And you know it really has to, to be practical for precasters. But yes, we'll do some more work on that and come back to you there.

HAYDEN:

Couple of questions around dosing. [When is it added? Is it when the concrete is being batched? – Mark V] [What is dose sequence? – Verna] It's good. So at the benching plant, and at the back end of the mixing process. So you've got all your mix sitting there, and in goes the product; and obviously revolutions to get that mixed in. So pretty standard.

We have got a bunch of - for those that know us and work with us - a lot of colloidal silica based type products, which go in at the start of the mixing process with the mix-water. This CONQOR A80 is different to that. It gets batched at the end there.

[What would be the ideal dose rate for 40MPa with 50% slag? – Jacinta] It does vary on the content of your slag, how much you’ll need, and the reactivity of your product you're working with. But, yes, 1-2% of your content is probably pretty effective from what we're seeing.

DOUG:

Yes, I was going to mention that, we're not talking a very high dose rate there, of admixture.  It's sort of in the 2-4 litres per cubic metre, that sort of range; depending on your... obviously, depending on your mix and slag content there. So yes, we would always look at that and advise you for a particular mix or what you're trying to do there rather than just a... I mean, there's obviously a guide on the technical data sheet. But yes, we'd want to make that work for you there.

And yes, just on the dose sequence, it is added at the back end of the mixing process. So you do put your water reducers, your other admixtures in; then your dry materials, mix it up and then add CONQOR A80, and send the truck on its way, for a short mix. So yes, we don't want it right at the start like we do for some of our other admixtures there.

HAYDEN:

Yes. that's good. [Definitely 30% for precast. – Justin] And yes, thanks, Justin, 30% slag replacement for precast; noted. We’ll probably do a little bit more work around that one for you as well - that's good - just for verification.

That's good. [Cost is always key. What is range per m³? – Justin] Cost is always key. Massively so. And this is always something that stays in the back of our mind as well. Obviously, we want to perform like GP, but we can't have it blowing out over the top with cost. So many projects... Obviously MARKHAM's been in the project space for a long time; and everyone wants to support green, you know, low carbon, until they see the proposal. So it's always been a focus of ours as well. From a cubic metre range – it does depend obviously on dosage but we're looking at – I don't know, $7 or 8, 9 bucks maybe, to get what you need there. But yes, that'll change on everyone’s mix obviously. But yes something like that. Hopefully that helps.

Sorry. Just reading through - do you want to do that one?

DOUG:

Yes. I was just thinking about that as we go. [We use a lot of S50 65% slag for pours where early-age thermal/restraint cracking is a significant risk, but early stripping is requested - does this accelerator significantly affect the early-age temperature profile? - Andy] So, using a lot of 65% slag for pours where early age thermal/restraint cracking is also a significant risk, or is a significant risk; but early stripping is requested. Does this accelerator significantly affect the early age temperature profile? Short answer is I wouldn't expect it to, but we do need to do some work, you know, with some temperature probes, things like that, as well. We're very much just focused on the best strength at this stage. I haven't seen anything that would cause concern at this stage. But yes, it is something we need to look at, especially for mass pours there. So yes. Thanks. Thanks for your question there, Andy, we’ll...

Yes. Jacinta, hopefully we covered that in your ... as far as ideal dose rates. I'd say, without knowing your mix totally, somewhere around three litres, maybe, per cubic metre; somewhere in that vicinity would be close; 40 MPa, 50% slag.

BRENDAN:

I’ve got a question for you, Hayden and Doug. You've used the terms ‘accelerator’ and ‘activator’ almost interchangeably. Are they the same thing?

HAYDEN:

Yes, sorry about that. Probably have. No, they are slightly different. Doug, you can jump into that.

DOUG:

Yes so... My apologies if I have slipped there. The accelerator generally is working with the cement or with the GP itself to accelerate the hydration of the concrete. The activator is working with the slag itself to kick that into gear sooner, effectively. And with what we're doing with the CONQOR A80, we are activating it and getting that getting that to kick into gear to start hydrating quicker than normal. There's a small part where it... I mean, just by the nature of it, is helping the GP as well. But its main function is to work with that slag and activate it. So yes, thanks, Brendan. It's good to get that clarified, because there is a difference there.

HAYDEN:
Good ol’ terminology in our industry!

[Is there any lab trial data available to share with clients especially on strength gain over time graphs? – Jacinta] Jacinta, that's good; lab trial data on the strength profiles over time. It's something we've been putting together now. So no issue to share that with you. We have got lab data. But it's very, very easy to control to the millilitre in a lab, if you know what I mean, as everyone would appreciate here. So it’s easy to get consistent results. What we're done right now is doing a lot more in the field, and collating a lot of those results. So we think that's probably a better way to display the performance. So yes, we’ll absolutely get that out and make it available when it's ready to roll.

DOUG:

Yes. And you touched on it earlier too, but there’s different sources of GGBS, different cements, materials. Everything. It all has an impact there. And so yes, that's... I strongly encourage that field trial just to see what you... what the impacts are we actually have on that mix. It's something that we're keen to be a part of, and, you know, provide the admixture, be part of those trials so we can keep building that picture there.

HAYDEN:

Was there any... Go on Brendan.

BRENDAN:

No, I was just going to say, offering field trials. It was sort of our wrapping-up message, wasn't it? I’ll just put this up again.

HAYDEN:

Yes, absolutely. We like to work with the industry to make this work and, you know, offering product, technical help etc, to work in with your specific mixes. And that's really the point we're up to now. There’s a lot of companies going through this phase at the moment. Obviously, it's a hot topic out there to make sure... Especially heading into these cooler months again, as well, on this side of the globe; and making sure we're all set up and doing the right thing for our mixes.

I'll be pretty interested if there's any specific challenges we have overlooked or haven't touched on. We normally fire out an email straight after this as well. So if something comes to mind, looking back on. A response to that would be good as well.

BRENDAN:

There’s just a question come in there on micro-cracking and VPVs. [Is there currently any indication of a reduction in micro cracking and VPV's? I would think not in early days? – Loch]

DOUG:

Yes. We haven't done the VPVs yet. It's not as much of a focus for the early strength there. I mean, it would be done as part of the mix validation or certification processes there. But, you know, we haven't looked at that yet. I mean, it's easy to do. We will at some stage.

And the micro-cracking is really what we're talking about with the field trials. I believe that's the true test there. The fact that we are hydrating it earlier, we're not letting that... we're kicking that hydration process off faster. It's not letting that mix-water evaporate as much as it normally does. So yes. But again, that's something we want to really show and prove in the field, before we claim anything with that.

And yes, just the comment there. [Elevated temperature accelerated curing has significant adverse effects on durability parameters due to development of a coarser pore structure. Has any work been done to look at similar effects? – Andy] Elevated temperature, accelerated curing has significant adverse effects on durability. 100% agree there. The development of a coarser pore structure. No, again, we haven't looked at the temperature profiles as yet. Yes. Appreciate that feedback. We’ll incorporate that into the next round of trials, if you like, for that.

HAYDEN:

Yes, that's a good point there. That’s good, Andy. Is it - just to make sure I’ve got your thought there - is that for precast heated beds? Or something further than that, that you're referring to? Just drop a note in there, I’d be interested. But yes, it's good. Good point. Yes. Nothing is showing that it's elevated by any means. And then, as I touched on the long... the next... [Mostly steam-cured precast. – Andy] Steam-cured precast. Yes. That's good.

The next product off the ranks, just gaining momentum now, is the slag activator, followed by a blend of our colloidal silica technology. And just touching on that micro-cracking, moisture retention side. They obviously work hand in hand for, you know, to combat some of that long-term or longer phase curing, if you know what I mean. So it keeps hydrating the cement and obviously works to negate some of that. So I think that will be a key there.

[Precast in Auckland doesn't require heated beds – Justin] Good point. Yes, a lot of precast is still not using heat there; and some various methods of curing across Australia and New Zealand in precast. So we need to consider all.

DOUG:

And I guess overall the point around the durability, it will form part of the next stage there to make sure there's no negative effects. The early indicators are no. But yes, we obviously want to get that verified before we sit here and say that there's no effects or anything there. So that's interesting.

[Some recent testing gave a factor of 3 difference to ambient cure in chloride penetration. – Andy] And yes, that’s something that's very important. Obviously curing in that space is always important. And yes, we don't want to be doing anything that's affecting the good work that that's doing there. So yes. No, I appreciate that. It's been a really, really good session. Appreciate everyone's questions there.

Hayden did you have anything else you wanted to ...?

HAYDEN:

No, I agree, appreciate it. These always work best when it's interactive like this. So thanks everyone that's commented and jumped on. We’ll fire out an email; give us some feedback; tell us where we need to do a helluva lot better. And yes, more importantly, if it tweaked any thoughts, we’d be interested to join you or have a chat, see what you're doing. And maybe get some of the product through your plant, or your operation there. And have a play with your specific mixes. But yes, we just wanted to go over all that, and we appreciate the input. Thanks, everybody.

DOUG:

Thanks very much.

HAYDEN:

Have a good day.