223 - Heat-induced delamination in CLT with Antonela Čolić

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<v Wojciech Wegrzynski>Hello everybody, welcome to the Fire Science Show.

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<v Wojciech Wegrzynski>The science of construction, civil engineering, is a very interesting one.

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<v Wojciech Wegrzynski>My mentor at the Building Research Institute, Professor Czonesky, used to say that we often do focus on our research on discovering why something works, not necessarily inventing new things, and this is true for the construction because you know 100 years ago they didn't have finite element method, they did not have your codes, but yet they were building buildings, many of which are still standing till this day.

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<v Wojciech Wegrzynski>And discovering why that is came later.

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<v Wojciech Wegrzynski>And in this case it it kind of continues.

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<v Wojciech Wegrzynski>I remember a few years ago we were been doing with OFR a very big experimental project on timber slabs which had different adhesive used in them.

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<v Wojciech Wegrzynski>And indeed in those experiments you could observe a big difference, big change in performance of the of the ceiling with the different type of adhesive use.

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<v Wojciech Wegrzynski>And and that was quite a surprise to me.

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<v Wojciech Wegrzynski>I was not I have not expected such an obvious measurable outcome of this experiment, yet it happened.

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<v Wojciech Wegrzynski>Now I must say I have not understood why exactly that happened, why exactly there was that big difference, and it appears it was quite an interesting research project to understand why.

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<v Wojciech Wegrzynski>And as you can imagine, today in my podcast I have someone who's been working on the answer of why this measurable difference was observed, and that is Dr.

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<v Wojciech Wegrzynski>Antonela Čolić from the OFR.

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<v Wojciech Wegrzynski>Antonela has just finished her PhD on mass timber and uh the and all the interesting things that happen at the glue line in the cross-laminated timber.

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<v Wojciech Wegrzynski>So in this podcast episode we go very deep into the glue line and we try to answer uh why adhesives work and at what conditions they fail.

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<v Wojciech Wegrzynski>We go into thermal, mechanical, moisture, all the interesting things that that happen into the timber, all powered through the science, all based on scientific research, multiple experiments across the scales.

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<v Wojciech Wegrzynski>I think it's a very interesting episode, I'll bite you have to be warned, it's a little bit more technically difficult because we really go deep into the the glues and uh and technology, but well, if I have one chance to do an episode about at his in the fire science show, let it be a good one.

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<v Wojciech Wegrzynski>So let's spin the intro and jump into the episode.

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<v Wojciech Wegrzynski>Welcome to the Firescience Show.

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<v Wojciech Wegrzynski>My name Wojciech Wegrzynski, and I will be your host.

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<v Wojciech Wegrzynski>This episode is brought to you in partnership with OFR Consultants, the UK's leading independent fire engineering consultancy.

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<v Wojciech Wegrzynski>With a multi-award-winning team and offices across the country, OFR are experts in fire engineering committed to delivering pre-eminent expertise to protect people, property, and the planet.

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<v Wojciech Wegrzynski>Applications for OFR's 2026 graduate program are now open.

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<v Wojciech Wegrzynski>If you're ready to launch your career with a supportive forward-thinking team, visit OFRconsultants.com to apply.

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<v Wojciech Wegrzynski>You will join a worldless organization recognized for its supportive culture and global expertise.

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<v Wojciech Wegrzynski>Start your journey with OFR and help shape the future of fire engineering.

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<v Wojciech Wegrzynski>Hello, everybody.

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<v Wojciech Wegrzynski>I'm joined today by Antonela Čolić from the OFR Consultants.

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<v Antonela Čolić>Hello, Antonela.

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<v Antonela Čolić>Hey, hi, Wojek.

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<v Wojciech Wegrzynski>I'm very happy to have you in the podcast and I'm thankful that you've agreed to discuss your very recent PhD.

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<v Wojciech Wegrzynski>Congratulations.

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<v Antonela Čolić>Thank you.

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<v Antonela Čolić>Thank you.

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<v Antonela Čolić>Thanks.

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<v Wojciech Wegrzynski>And uh I really want to talk about the lamination today in a relationship with the CLT and structural timber in general.

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<v Wojciech Wegrzynski>And I'm kind of stressed because I don't, I'm not even sure if I'm supposed to use the word lamination in this interview.

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<v Wojciech Wegrzynski>So am I am I allowed to use delamination in here?

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<v Antonela Čolić>Uh yeah, we were gonna call it lamination, but it's heat-induced delamination.

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<v Wojciech Wegrzynski>Okay, what's the Kvet?

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<v Antonela Čolić>So the delamination is the one that we actually use in the ambient conditions, and when we test products for the detachment of the bond line due to the environmental conditions, which is drying and heating in normal, I mean like everyday drying and heating.

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<v Antonela Čolić>And then heat-induced one is due to the presence of external heating sources, fire.

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<v Antonela Čolić>So those are the elevated temperatures.

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<v Antonela Čolić>But we can call it for the simplification today, the lamination.

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<v Antonela Čolić>I think it's just really important to make the distinction at the beginning.

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<v Wojciech Wegrzynski>Yeah, thank you very much because there were some extremely complicated terms uh we started to use to this, uh, which definitely have their merit, and we will definitely go into that merit, but there's also uh power in simplicity, and if everyone calls it lamination, it's lamination for me.

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<v Antonela Čolić>I do, I do, I do, I do.

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<v Antonela Čolić>Yeah, yeah.

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<v Wojciech Wegrzynski>Yeah, so it's a very interesting phenomenon.

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<v Wojciech Wegrzynski>Um, can you give me a little bit of background how you've ended up doing this as your uh PhD at the University of Edinburgh?

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<v Antonela Čolić>Yeah, yeah, yeah.

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<v Antonela Čolić>I mean, uh to be honest, like it's it's it's a cliche, but like when I was a kid as well, I was always impressed by glue.

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<v Antonela Čolić>And how can you add a substrate that is completely different, the two things, and then just glue it together?

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<v Antonela Čolić>And I was like, always thought like that's never gonna work.

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<v Antonela Čolić>And yeah, I always thought like you have to take your nail and nail your stuff into this.

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<v Antonela Čolić>It's like it's I I always believe more in mechanical fixing, but yeah, glues for some reason they do work, and then um when COVID happened, I worked on this small literature review with uh with Luke.

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<v Antonela Čolić>I worked from Croatia, I'm originally Croatian, and I kind of got into the topic then, and then I that was during my IMFSE period, and then I got to do master thesis with Luke.

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<v Antonela Čolić>So after that, Luke, I'm I'm really glad.

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<v Antonela Čolić>Uh he asked me whether I want to do a PhD with him, and then we ended up doing a PhD as well together, and it's such an expensive topic that actually we started as one of the future work topics from Felix Wiesner's work.

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<v Antonela Čolić>So when he graduated, he graduated in 2018, and that's when I started with my IMFC.

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<v Antonela Čolić>So it was just a continuation of of work.

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<v Wojciech Wegrzynski>Fantastic.

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<v Wojciech Wegrzynski>Well, MFSC that explains a lot.

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<v Wojciech Wegrzynski>Actually, I missed that part in the bio, but here comes the missing puzzle.

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<v Wojciech Wegrzynski>Great, yeah, great.

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<v Wojciech Wegrzynski>And I also had a Felix in the podcast ages ago, eons ago, like 200 episodes ago, we've talked about moisture and know that this is also an important part of your considerations.

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<v Wojciech Wegrzynski>But uh let's let's get into that.

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<v Wojciech Wegrzynski>First, perhaps let's try and settle the difference between the char fall-off and the heat-induced lamination.

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<v Wojciech Wegrzynski>Because I assume those are two different processes, two different manifestations.

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<v Antonela Čolić>No, no, no, that's very important.

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<v Antonela Čolić>Clarification, and thanks for asking.

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<v Antonela Čolić>So the difference is that the heat-induced lamination is the detachment of the pieces of lamella which haven't completely char.

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<v Antonela Čolić>So that means that the char layer hasn't progressed to the bond line yet, meaning that it happened at the temperatures which are lower than the typical 300 degrees isotherm that we take for the paralysis of wood.

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<v Antonela Čolić>So that means that you have the reduction of the composite action even before the char has progressed to the bond line.

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<v Antonela Čolić>Uh, char fall-off is just the char falling off.

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<v Antonela Čolić>That can happen even in solid timber.

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<v Antonela Čolić>It can be just small pieces of char that are detached in the matrix of the timber itself.

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<v Antonela Čolić>So the char fall-off in the glute or CLT or any laminated product, that can happen before the char has reached the bond line, just the char falling off, or when it reaches the bond line, the whole charce falling off or progress the bond line, any any char detachment.

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<v Antonela Čolić>And the difference is A, when it occurs, and B how it affects structural mechanics.

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<v Antonela Čolić>So if you have heat-induced lamination, you still do have some mechanical properties preserved of your bond line at the point when you're losing it.

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<v Antonela Čolić>For the char fall-off, once once the char progresses, you've lost all of your structural capacity.

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<v Antonela Čolić>Char has no load-bearing property whatsoever.

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<v Antonela Čolić>So that means that with a heat-induced delamination, you're progressively losing your cross-section, which is really important for residual load-bearing capacity of your structure.

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<v Wojciech Wegrzynski>Well, with char you lose the protective insulative layer, so there's also like consequences of losing that.

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<v Wojciech Wegrzynski>But indeed, it already had no uh structural load-bearing capacity of any sort.

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<v Wojciech Wegrzynski>Um, I think we maybe, maybe should have stepped back a once before to even define the bone line, because like we're we're we're gonna like discuss some very high-level things in a minute.

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<v Wojciech Wegrzynski>Let's define why bone line is important and how does it mechanically affect the properties of your cross-laminated timber at a large scale?

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<v Wojciech Wegrzynski>Is it only to keep the lamellas in place or does it have a bigger role?

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<v Antonela Čolić>Well, the bone line itself is this interface between timber and adhesive.

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<v Antonela Čolić>So it's not interface, it's the phase.

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<v Antonela Čolić>It's it's kind of inter intermixed because it adhesive penetrates timber differently in different regions.

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<v Antonela Čolić>So there is no this like clear line where you can say, oh, it's just the adhesive failure.

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<v Antonela Čolić>So when you when you have the failure at the bond line and you have the two pieces of wood in your hands, you will see that on both sides you have some splinters of wood.

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<v Antonela Čolić>That means that there is this like weird phase in which you had this detachment, meaning that it's very important how your adhesive actually interacts with timber and that it's not only the adhesive, that it's also the timber that you choose for bonding of your element.

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<v Antonela Čolić>So that's the bond line definition when I ref refer to it as such.

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<v Wojciech Wegrzynski>And uh does it play any role in mechanical response of the timber or just it must in that case?

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<v Antonela Čolić>Yeah, of course.

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<v Antonela Čolić>Yeah.

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<v Antonela Čolić>So the way we design our structure is you you have this composite action, and that means that the element, when it's bonded, it behaves as one unit.

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<v Antonela Čolić>So it behaves essentially as solid timber.

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<v Antonela Čolić>So there is no distinction across the cross section.

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<v Antonela Čolić>And if there is a distinction that is made between the glue laminated timber and cross-laminated timber, where in the crosswise-oriented lamella, they have reduced elastic modulus.

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<v Antonela Čolić>But in in the glue lam, everything goes in the one direction, all over the lamellas.

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<v Antonela Čolić>So the the elastic modulus is the same across the cross section.

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<v Antonela Čolić>But with the bond line, we never, as a structural engineer, I never had to take that into account that the bond line can have, depending on the adhesive choice, different elastic modulus.

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<v Antonela Čolić>You just take it as the same across the whole timber.

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<v Antonela Čolić>So in ambient conditions, you say that it plays no role, which adhesive you choose.

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<v Antonela Čolić>You test the element as a whole.

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<v Antonela Čolić>But then in the fire conditions, this was already found by Emberly back in the days, I would say five, six years ago, and Jose Torero, bond line, the failure mode in the element, in the structural element changes.

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<v Antonela Čolić>So if it tests it in the ambient conditions, the failure is in is in timber.

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<v Antonela Čolić>Once you start heating the element, the failure mode changes and it goes to the bond line.

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<v Wojciech Wegrzynski>So if you put force on your CLT slab in ambient, it will most likely break like a solid timber would.

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<v Antonela Čolić>Yeah, it yeah, it depends on which product you you test.

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<v Antonela Čolić>Which engineered wood product you test, yes.

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<v Wojciech Wegrzynski>I don't know how many large CLT structures I've burned, but now I realize I've never crushed one without fire.

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<v Wojciech Wegrzynski>So a non-fire failure is extremely you know uh exotic to me.

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<v Wojciech Wegrzynski>I've never seen it fail without fire.

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<v Wojciech Wegrzynski>It's probably funny to say, but yeah, that that that that's the case.

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<v Wojciech Wegrzynski>But I've seen a lot of char fall-offs and I a lot of uh the lamination.

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<v Wojciech Wegrzynski>So from that perspective, I'm I'm safe to carry on this discussion.

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<v Wojciech Wegrzynski>Um maybe let's cover the adhesives then.

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<v Wojciech Wegrzynski>What types of adhesives are used in this uh in this type of constructions?

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<v Wojciech Wegrzynski>Do they have anything special to them?

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<v Wojciech Wegrzynski>And basically, how how how does that world look like?

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<v Antonela Čolić>Yeah, yeah.

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<v Antonela Čolić>So like back in the 50s, we had only glue-laminated timber, which are which which we use usually for beams and columns, and those are the line elements that we use.

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<v Antonela Čolić>And we used to bond them with usually melamine urea formaldehyde, MUF, and that worked really well for like 40 years.

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<v Antonela Čolić>But then in the late 1990s, the CLT was patented, and CLT had to use a different type of adhesive.

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<v Antonela Čolić>And the reason for that is that MUF it cures with the application of heat and the pressure.

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<v Antonela Čolić>And you can imagine that once you have the larger elements as CLT, you have this big amount of energy that you would need to cure such element, which is opposing to our sustainability idea and the reasons why we are using timber in the first place.

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<v Antonela Čolić>So our the the new adhesive we came up with is one component polyurethane, and that adhesive it cures with the presence of water, which is naturally within timber.

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<v Antonela Čolić>So it takes the moisture from the timber itself, and then you apply the pressure.

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<v Antonela Čolić>So that would go good.

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<v Antonela Čolić>You have also reduced formaldehyde emission, which was another restriction.

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<v Antonela Čolić>And then we used the one component polyuretine for for years, but then in the early 2000s, around 2010, we realized that this adhesive doesn't perform that well in fire.

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<v Antonela Čolić>The reason we figured that out is because we started building more complex and larger mass timber buildings and using more and more CLT.

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<v Antonela Čolić>So then the research ramped up and we tested more and more products, and we realized that we need to figure out how to deal with this issue of heat-induced delamination, which was now a new phenomena occurring in CLT structures.

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<v Antonela Čolić>So around 2020, we came up with this new adhesive, new one component polyuretin adhesive, commonly known as HBX.

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<v Antonela Čolić>And we came up with a new testing method which proved that this adhesive works.

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<v Antonela Čolić>So everyone now implemented that adhesive, and we were like, okay, fine, we are good.

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<v Antonela Čolić>But then I spent four years of my PhD trying to figure out what are the conditions under which actually this adhesive works and why is that said.

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<v Wojciech Wegrzynski>Fantastic.

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<v Antonela Čolić>Sorry, that was like a long, widened answer.

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<v Antonela Čolić>A really simple question.

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<v Wojciech Wegrzynski>Well, no, no, that that that's that's a good historical like uh like you would expect from someone who just did their PhD on something.

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<v Wojciech Wegrzynski>Like you probably know more about those adhesives than uh the most people in the industry, which which is again expected.

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<v Wojciech Wegrzynski>Thank you, thank you um for that.

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<v Wojciech Wegrzynski>So now let's maybe try how the failure in that bond line may occur.

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<v Wojciech Wegrzynski>So so uh what's the buildup to the uh to the failure and then how how the the failure itself happens?

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<v Antonela Čolić>So the reasons for failure can be either in intrinsic or extrinsic.

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<v Antonela Čolić>So intrinsic ones are what is the type of the adhesive you are using, and what is the chemical composition of the adhesive you're using, what is the type of the wood you're using, and what is the morphology between the two.

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<v Antonela Čolić>So that's everything that's happening, happening on the front of like what is the choice you're making.

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<v Antonela Čolić>And then you have the extrinsic ones, and those are the external conditions that are applied on your bone line.

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<v Antonela Čolić>So you have three things that are happening at the same time.

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<v Antonela Čolić>First one is the thermal penetration.

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<v Antonela Čolić>So you have the thermal wave passing through and exposing your adhesive and timber naturally to some form of thermal degradation.

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<v Antonela Čolić>Then you have also the mechanical stresses that are naturally induced due to the load that you applied on your structural element.

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<v Antonela Čolić>Then you have the thermomechanical effect, which is shrinkage and swelling, which that is induced now.

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<v Antonela Čolić>And then you have the moisture movement, which is a really important one.

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<v Antonela Čolić>Due to the presence of pressure gradients and the thermal gradient, you have the movement of this moisture from the heating source towards the bond line.

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<v Antonela Čolić>So your bond line is at one point, it finds itself in this complex thermohydromechanical state due to the all of this effect, and it's and it's exposed to the complex set of stresses.

00:16:22.399 --> 00:16:24.720
<v Wojciech Wegrzynski>And let's start with the intrinsic ones.

00:16:24.720 --> 00:16:29.919
<v Wojciech Wegrzynski>I'm really interested in the uh compatibility between the glue and the timber.

00:16:29.919 --> 00:16:31.440
<v Wojciech Wegrzynski>So, what can go wrong in there?

00:16:31.440 --> 00:16:36.159
<v Wojciech Wegrzynski>I I the most of CLT I've ever seen was uh spruce.

00:16:36.399 --> 00:16:36.879
<v Antonela Čolić>Yeah.

00:16:37.200 --> 00:16:40.720
<v Wojciech Wegrzynski>But in in my laboratory, there's a researcher, Dr.

00:16:40.720 --> 00:16:51.200
<v Wojciech Wegrzynski>Pavel Sullich, and he's done a lot of research on locally sourced timber of different types, because you've also mentioned that we need uh CLT.

00:16:51.200 --> 00:17:08.720
<v Wojciech Wegrzynski>Uh you said it between the lines, but we need CLT for sustainability reasons, and I fully uh fully agree with that, though I'm not sure if importing it through the continent from one factory in a very remote location is if that is the essence of sustainability.

00:17:08.720 --> 00:17:12.720
<v Wojciech Wegrzynski>I think the future is like more locally produced CLT.

00:17:12.960 --> 00:17:14.079
<v Antonela Čolić>I completely agree, yeah.

00:17:14.160 --> 00:17:20.799
<v Wojciech Wegrzynski>Yeah, and I think the companies who are who are doing this also agree because I see the factories popping all over the place.

00:17:20.799 --> 00:17:22.400
<v Wojciech Wegrzynski>Uh that's that's great news as well.

00:17:22.400 --> 00:17:23.279
<v Wojciech Wegrzynski>But anyway, uh Dr.

00:17:23.279 --> 00:17:28.799
<v Wojciech Wegrzynski>Sulik is looking into uh locally sourced timber, different types of timber in in Poland.

00:17:28.799 --> 00:17:34.640
<v Wojciech Wegrzynski>Like I'm not sure if he was testing mechanical response, because that's perhaps where he would observe some differences.

00:17:34.640 --> 00:17:39.519
<v Wojciech Wegrzynski>But in terms of their fire response, it was very interesting to see different.

00:17:39.519 --> 00:17:46.000
<v Wojciech Wegrzynski>But he was making his CLT on his own, like you know, literally uh gluing uh different timbers together and pressing them.

00:17:46.000 --> 00:17:49.599
<v Wojciech Wegrzynski>Anyway, what can go wrong between the adhesive and timber?

00:17:49.599 --> 00:17:52.319
<v Wojciech Wegrzynski>Where is the risk of incompatibility between them?

00:17:52.640 --> 00:17:57.519
<v Antonela Čolić>So, first is the choice whether you go with a softwood or the hardwood.

00:17:57.519 --> 00:18:03.440
<v Antonela Čolić>So the thickness of the selves of naturally between the two are very different.

00:18:03.440 --> 00:18:09.680
<v Antonela Čolić>And that will then uh influence the infiltration of the adhesive in timber itself.

00:18:09.680 --> 00:18:14.160
<v Antonela Čolić>And you can have this effect that we call starved bond line.

00:18:14.160 --> 00:18:29.039
<v Antonela Čolić>So if you have in hardwood, it can occur that like your your your adhesive just penetrates so deeply into the hardwood that your bond line itself is starved, like if you don't you don't have anything anymore because it just like travels so deeply inside.

00:18:29.039 --> 00:18:32.480
<v Antonela Čolić>And that's when you also have the gaps in the bond line as well.

00:18:32.480 --> 00:18:39.599
<v Antonela Čolić>And then when it comes to the the the softwood itself, uh we tested Norway spruce and radiata pine.

00:18:39.599 --> 00:18:47.519
<v Antonela Čolić>And the two we we found the differences between the two just due to the presence of different latewood and early woodwood ratios.

00:18:47.519 --> 00:18:56.240
<v Antonela Čolić>So radiata pine was uh I did those experiments back in uh Australia, and radiata pine there, those are the trees that grow very fast.

00:18:56.240 --> 00:19:02.319
<v Antonela Čolić>So the presence of the latewood, uh which is usually the during the winter times, is is is really low.

00:19:02.319 --> 00:19:06.240
<v Antonela Čolić>And the early wood, which is spring and summer, that's that's really high.

00:19:06.240 --> 00:19:11.519
<v Antonela Čolić>But the latewood is the one that is responsible for your mechanical response of your timber.

00:19:11.519 --> 00:19:13.200
<v Antonela Čolić>And it's really, really cool.

00:19:13.200 --> 00:19:25.359
<v Antonela Čolić>But like I think that this morphology aspect of it all needs to be further explored and it needs to, you know, like timber has its own natural variability, and you just need to know how to account for it.

00:19:25.359 --> 00:19:34.480
<v Antonela Čolić>You you can't go into so many details to see, like, oh, is my bond line gonna be really close to the late wood or early wood and in which ratio?

00:19:34.480 --> 00:19:52.319
<v Antonela Čolić>But I think we we kind of need to figure out how to account, or it would be at least fun to do research to to try and account for that natural variability of timber and and how close to the bond line this latewood and early wood is, because it does define the the response of your bond line.

00:19:52.559 --> 00:19:54.720
<v Wojciech Wegrzynski>Yeah, that's what I wanted to ask, actually.

00:19:54.720 --> 00:20:06.400
<v Wojciech Wegrzynski>I wonder if the the type of timber is the defining thing, because you you may have it like stored outdoors versus stored indoors, like different moistures of the timber plank when it's glued.

00:20:06.400 --> 00:20:17.839
<v Wojciech Wegrzynski>You may have it like uh a very anisotropic piece of timber, like the the like even within one tree, you will have a diversity of different structures in in the in the single planks.

00:20:17.839 --> 00:20:30.799
<v Wojciech Wegrzynski>I also understand that CLT technology was meant to kind of get rid of this issue by you know just having a lot of different planks together and eventually all the things even it itself out.

00:20:30.799 --> 00:20:38.480
<v Wojciech Wegrzynski>Are those like conditions at which the timber was stored before building in the CLT uh also playing a role in the bond line?

00:20:38.559 --> 00:20:39.920
<v Antonela Čolić>Uh definitely, yeah, yeah, yeah.

00:20:39.920 --> 00:20:41.039
<v Antonela Čolić>No, no, for sure.

00:20:41.039 --> 00:20:44.079
<v Antonela Čolić>And it's it's how was a timber stored before manufacturing?

00:20:44.079 --> 00:20:45.200
<v Antonela Čolić>How is it stored?

00:20:45.200 --> 00:20:48.079
<v Antonela Čolić>How is it pressed during much manufacturing?

00:20:48.079 --> 00:20:52.799
<v Antonela Čolić>What is the dispense of the of the adhesive on the assembly line?

00:20:52.799 --> 00:20:56.240
<v Antonela Čolić>What is the then the storage after the manufacturing?

00:20:56.240 --> 00:21:06.880
<v Antonela Čolić>And then what are the using conditions in which like your your your timber is going to behave differently in the kitchen and in the living room, in in depending on where you are, what are your conditions of use?

00:21:06.880 --> 00:21:16.960
<v Antonela Čolić>All of that affects what is the moisture content in your timber, and yeah, naturally, like when the moisture starts traveling, what is the pressure that affects the bond line.

00:21:17.279 --> 00:21:24.160
<v Wojciech Wegrzynski>So this kind of narrows the technology into factories where it would be very well controlled, I presume.

00:21:24.559 --> 00:21:25.759
<v Antonela Čolić>Yeah, we do believe that.

00:21:25.759 --> 00:21:36.799
<v Antonela Čolić>I think Danny and Mike from OFR they did some research on whether the different supplier in Europe, if you choose different supplier, whether that would affect the consequential chart fall off.

00:21:36.799 --> 00:21:38.640
<v Antonela Čolić>Is that what they were studying?

00:21:38.640 --> 00:21:42.880
<v Antonela Čolić>And they didn't find much difference between the three different suppliers.

00:21:42.880 --> 00:21:48.240
<v Antonela Čolić>Uh, but you know, that was the only study I know of that that that did that.

00:21:48.720 --> 00:21:55.200
<v Wojciech Wegrzynski>Well, large large-scale experiments with CLT are quite an expensive game, I would say.

00:21:55.200 --> 00:21:57.119
<v Wojciech Wegrzynski>And you know that I know that very well.

00:21:57.519 --> 00:22:03.920
<v Antonela Čolić>Just to add, there is no study to my knowledge that compares different species across the world.

00:22:03.920 --> 00:22:09.839
<v Antonela Čolić>So the three suppliers we use Danny and Mike used in their study, those are all from Europe.

00:22:09.839 --> 00:22:16.000
<v Antonela Čolić>So it's highly likely that those are all spruits or like same-ish softwood.

00:22:16.000 --> 00:22:24.720
<v Antonela Čolić>So at least if we are referring to that study, we can say, okay, we are safe in Europe, but you can't compare the standards and the methodologies across the globe.

00:22:25.119 --> 00:22:26.240
<v Wojciech Wegrzynski>Let me ask you a question.

00:22:26.240 --> 00:22:36.720
<v Wojciech Wegrzynski>I it it's like curveball, so uh you may say you don't want to answer it, but can you actually glue hardwood to softwood and it's gonna work, or is no one knows?

00:22:37.039 --> 00:22:38.720
<v Antonela Čolić>I would not personally recommend.

00:22:39.200 --> 00:22:39.440
<v Wojciech Wegrzynski>Okay.

00:22:39.839 --> 00:22:40.240
<v Antonela Čolić>Why?

00:22:40.240 --> 00:22:41.359
<v Antonela Čolić>I've not not.

00:22:41.359 --> 00:22:43.519
<v Antonela Čolić>It's just completely different microstructure.

00:22:43.759 --> 00:22:44.000
<v Wojciech Wegrzynski>Okay.

00:22:44.160 --> 00:22:46.960
<v Antonela Čolić>So so the cells are very different around the bone line.

00:22:46.960 --> 00:22:49.839
<v Antonela Čolić>Uh your adhesive is gonna interact differently.

00:22:49.839 --> 00:22:56.640
<v Antonela Čolić>The mechanical interlocking, which is how your adhesive penetrates the cell itself, is gonna be different.

00:22:56.640 --> 00:23:00.000
<v Antonela Čolić>The infiltration through the cell is gonna be different.

00:23:00.000 --> 00:23:09.279
<v Antonela Čolić>So, you know, we already have a lot of, I mean, a lot of, I know don't want to make it uh existential, but there are already issues if you bought bond softwood to stuff to it.

00:23:09.279 --> 00:23:14.960
<v Antonela Čolić>So we need to figure that out a little bit better before we progress to the combination of softwood and hardwood.

00:23:15.279 --> 00:23:21.359
<v Wojciech Wegrzynski>And uh last one, are the surfaces prepared in any way for that?

00:23:21.359 --> 00:23:27.119
<v Wojciech Wegrzynski>Like, do you do any any time I I don't know English words for processing timber.

00:23:27.119 --> 00:23:32.720
<v Wojciech Wegrzynski>Is there any processing that's done to the surface before adhesive is applied?

00:23:33.039 --> 00:23:37.839
<v Antonela Čolić>I believe it has to be sanded, but I uh yeah, I think that that's the extent of manology.

00:23:37.839 --> 00:23:48.799
<v Antonela Čolić>I do believe that some some people depending on adhesive, primers can be used that first applied on on timber, but like the specific mechanical change of the surface of timber, I'm not sure.

00:23:49.440 --> 00:23:50.960
<v Wojciech Wegrzynski>Okay, let's move to extrasy.

00:23:50.960 --> 00:23:56.880
<v Wojciech Wegrzynski>So you said it's thermal penetration, mechanical, including thermal mechanical response and moisture.

00:23:56.880 --> 00:23:58.640
<v Wojciech Wegrzynski>Let's take them one by one.

00:23:58.640 --> 00:24:03.920
<v Wojciech Wegrzynski>So, how does thermal penetration affect the bond line leading to its failure?

00:24:04.240 --> 00:24:11.279
<v Antonela Čolić>So the way we studied this is we started from micro scale and then we went to the intermediate scale.

00:24:11.279 --> 00:24:16.960
<v Antonela Čolić>So in the micro scale, we only studied how the thermal penetration changes the adherent.

00:24:16.960 --> 00:24:20.640
<v Antonela Čolić>Adherent, when I say I mean adhesive and timber.

00:24:20.640 --> 00:24:28.559
<v Antonela Čolić>And then I'll just give a quick overview of like the complete scope, and then we can dissect what happened at each extrinsic stage.

00:24:28.559 --> 00:24:31.039
<v Antonela Čolić>So that was the the micro scale.

00:24:31.039 --> 00:24:44.720
<v Antonela Čolić>Then we went to the small scale where we had such a thin element, we did a little shear laps where which allowed us to take out of the equation the moisture movement, and we could then study only thermomechanical response.

00:24:44.720 --> 00:24:51.359
<v Antonela Čolić>Then we went even larger, where I only had the heating of the timber and the moisture movement.

00:24:51.359 --> 00:24:58.960
<v Antonela Čolić>And we did some experiments where we exposed those little um timber to neutron flow in the neutron beam.

00:24:58.960 --> 00:25:10.160
<v Antonela Čolić>And then the last aspect was the intermediate scale, where we did thermo hydromechanicals, and those are where you have the presence of all three moisture movement and thermal gradient and mechanical stresses.

00:25:10.160 --> 00:25:12.319
<v Antonela Čolić>So let's now go from the start.

00:25:12.319 --> 00:25:14.319
<v Antonela Čolić>Thermal penetration.

00:25:14.319 --> 00:25:19.359
<v Antonela Čolić>The way we studied that was through two different microscale tests.

00:25:19.359 --> 00:25:27.920
<v Antonela Čolić>Those are thermogravimetric analysis, where you heat something and it loses mass, and as it loses mass, you can see what are the thermal degradation uh stages.

00:25:28.240 --> 00:25:32.559
<v Wojciech Wegrzynski>Did you do TGA in uh nitrogen or in oxygen?

00:25:32.880 --> 00:25:33.519
<v Antonela Čolić>We did both.

00:25:33.519 --> 00:25:35.759
<v Antonela Čolić>We did both in nitrogen and oxygen, yeah.

00:25:35.920 --> 00:25:36.160
<v Wojciech Wegrzynski>Okay.

00:25:36.319 --> 00:25:40.480
<v Antonela Čolić>And the second one is differential scanning calorimetry.

00:25:40.480 --> 00:25:46.960
<v Antonela Čolić>Uh, and that one is essentially at a heat flow, you get the response which can be exothermic or endothermic.

00:25:46.960 --> 00:25:53.200
<v Antonela Čolić>Uh, and you it's telling you what is the molecular movement in your polymer chain when you're observing your adherent.

00:25:53.200 --> 00:26:02.480
<v Antonela Čolić>So we in those two microscale methods, we tested separately adhesive films that we produce out of one component polyuretane and muf.

00:26:02.480 --> 00:26:07.359
<v Antonela Čolić>But I'll stick, I'll I'll take MUF today out of the equation because it would just complicate the story.

00:26:07.359 --> 00:26:10.559
<v Antonela Čolić>So I'll just refer to the two one component polyuretane.

00:26:10.960 --> 00:26:11.279
<v Wojciech Wegrzynski>Okay.

00:26:11.519 --> 00:26:25.119
<v Antonela Čolić>So we did the testing of the adhesive films, and then we also took the sawdust from the Norris spruce and from Radiatopine, and then we tested each of them separately to see what is the thermal response.

00:26:25.119 --> 00:26:43.119
<v Antonela Čolić>So what happened is when we compare the behavior between the two adhesives, we could see in TGA tests that in the range from 200 to 220, for the HBS, you had this little plateau uh when you check your DTG curve.

00:26:43.119 --> 00:26:49.119
<v Antonela Čolić>And that plateau usually means that the material is experiencing some sort of softening.

00:26:49.119 --> 00:26:55.680
<v Antonela Čolić>But we couldn't confirm it because it's such a small temperature range, only from from 200 to 220.

00:26:55.680 --> 00:27:12.319
<v Antonela Čolić>So then we tested it in DSC, and then what we observed in that same range for the HBS is that you have a little drop, and it's an endothermic drop, and that confirmed to us that the material has experienced some softening.

00:27:12.319 --> 00:27:25.279
<v Antonela Čolić>So those two just those two simple micro-scale methods were really indicative of the behavior, and it gave us the answer why HBS usually fails around between 200 to 240 degrees.

00:27:25.279 --> 00:27:29.680
<v Antonela Čolić>It was really clear that it's due to this transition, softening transition.

00:27:29.680 --> 00:27:39.119
<v Antonela Čolić>But then before I even go to that softening, the DSC method also allowed us to see what is the glass transition temperature.

00:27:39.119 --> 00:27:43.599
<v Antonela Čolić>And this occurred for both adhesives, HBS and HBX.

00:27:43.599 --> 00:27:50.000
<v Antonela Čolić>And uh before you your material reaches the glass transition, it's kind of in a vibrant glassy state.

00:27:50.000 --> 00:27:55.839
<v Antonela Čolić>And once it reaches the glass transition, your polymer change chains, they start to move against each other.

00:27:56.400 --> 00:28:00.400
<v Wojciech Wegrzynski>Sorry, is this done on the glue itself or glue on the timber?

00:28:00.640 --> 00:28:02.559
<v Antonela Čolić>No, no, this is all now just the adherent.

00:28:02.559 --> 00:28:03.440
<v Antonela Čolić>Just the adherent.

00:28:03.440 --> 00:28:05.039
<v Antonela Čolić>Just the adhesive film.

00:28:05.039 --> 00:28:13.039
<v Antonela Čolić>And you could see the uh so glass transition temperature, once you reach it, the polymer change, they start to move against each other.

00:28:13.039 --> 00:28:18.799
<v Antonela Čolić>And depending on the chemical composition of the adhesive, they can undergo additional crosslinking.

00:28:18.799 --> 00:28:38.000
<v Antonela Čolić>So what we saw is that for the HBX adhesive, once it reaches this glass transition temperature, it does experience some crosslinking because the stiffness of the element it just which we observed in later stages in different experience uh experiments, it just plateaus.

00:28:38.000 --> 00:28:47.839
<v Antonela Čolić>Whereas for HBS, there is nothing, like it just keeps the viscous behavior just continuous and the polymer chains they keep like moving against each other.

00:28:47.839 --> 00:28:55.200
<v Antonela Čolić>So that for the cases HBS leads then to a softening temperatures, but for HBX it doesn't.

00:28:55.200 --> 00:28:59.440
<v Antonela Čolić>HBX just chars, whereas HBS softens.

00:28:59.599 --> 00:28:59.920
<v Wojciech Wegrzynski>Okay.

00:29:00.240 --> 00:29:04.240
<v Antonela Čolić>This is kind of a small explanation of these like thermal degradation stages.

00:29:04.240 --> 00:29:12.160
<v Antonela Čolić>There is a paper we published on that uh in the International Journal for Adheses, and I think that's quite useful to better understand actually.

00:29:12.480 --> 00:29:17.519
<v Wojciech Wegrzynski>Yeah, that's the exact paper uh that is in front of my eyes.

00:29:17.519 --> 00:29:46.960
<v Wojciech Wegrzynski>Um, from a practical perspective, uh, as a fire engineer, if I do a thermal analysis of heat penetrating my timber element, and I just want to have a ballpark number to say, okay, it's most likely going to fail at this temperature, taking the lower bound of the range of softening, which you indicated at around 200 ish degrees, is that a reasonable approximate?

00:29:46.960 --> 00:29:53.440
<v Wojciech Wegrzynski>How would an engineer apply that exquisite piece of knowledge you you just gained into practice?

00:29:53.759 --> 00:30:11.680
<v Antonela Čolić>Well, that that is really important because the what actually my whole piece of work showed is that just Doing the micro scale methods, just this thermal analysis, it's not sufficient to tell you at which temperatures, what are your what is your performance criteria, what is your critical bond line temperature.

00:30:11.680 --> 00:30:12.960
<v Antonela Čolić>That is not sufficient.

00:30:12.960 --> 00:30:20.799
<v Antonela Čolić>The reason for that is because you have these influences of the structural stresses and moisture movement, which we later observe on the larger scale.

00:30:20.799 --> 00:30:36.640
<v Antonela Čolić>But if someone is asking me what is the temperature that I should use as a critical temperature in my models, for example, where I'm doing uh estimating what is the heat release rate curve, then I need to account for some additional fuel load that is that is added.

00:30:36.640 --> 00:30:43.440
<v Antonela Čolić>If you really want to be super conservative, you can use the glass transition temperatures for both HBS and HBX.

00:30:43.440 --> 00:30:45.519
<v Antonela Čolić>For HBS, that's 160.

00:30:45.519 --> 00:30:48.079
<v Antonela Čolić>For HBX, that's 190.

00:30:48.079 --> 00:30:51.599
<v Antonela Čolić>But that that's really super, super conservative.

00:30:51.599 --> 00:30:56.960
<v Antonela Čolić>If you want to lose it a little bit, you could go with softening temperature for HBS.

00:30:57.759 --> 00:31:08.559
<v Wojciech Wegrzynski>That's the reason I I mean it's sometimes okay to be super conservative, but sometimes being super conservative is a fancy word for saying I'm wrong.

00:31:08.559 --> 00:31:17.039
<v Wojciech Wegrzynski>And uh if you want to have a really detailed image of your the structural response of the element, perhaps you're being overly conservative with that.

00:31:17.039 --> 00:31:37.920
<v Wojciech Wegrzynski>And as you said, there are other factors to consider which uh we will go in a second, but 180 versus 190 versus let's say 220 sounds not like a big difference, but in the in the realm of progression of thermal front into your structural element in a real fire, that can be difference of let's say 190 could be at a peak and 220 is never reached.

00:31:37.920 --> 00:31:46.079
<v Wojciech Wegrzynski>That that's a possibility in a fire for sure, or it could be a 15-minute difference between these fronts uh propagate, it all depends on the fire.

00:31:46.079 --> 00:31:52.960
<v Wojciech Wegrzynski>So so it it actually, while it's a little difference in temperature, timber is an excellent insulating material.

00:31:52.960 --> 00:31:54.559
<v Wojciech Wegrzynski>So that's quite a difference, actually.

00:31:54.799 --> 00:31:55.359
<v Antonela Čolić>I do agree.

00:31:55.359 --> 00:31:57.839
<v Antonela Čolić>Yeah, it has really good thermal conductivity.

00:31:58.160 --> 00:32:04.559
<v Wojciech Wegrzynski>Let's try to do mechanical stresses uh and and how that affects the lamination.

00:32:04.559 --> 00:32:06.720
<v Wojciech Wegrzynski>First, uh a cheeky question.

00:32:06.720 --> 00:32:09.519
<v Wojciech Wegrzynski>Do you need mechanical load for lamination to happen?

00:32:09.759 --> 00:32:11.200
<v Antonela Čolić>That's such a good question.

00:32:11.440 --> 00:32:13.680
<v Wojciech Wegrzynski>It's not mine, it's right.

00:32:14.799 --> 00:32:23.200
<v Antonela Čolić>No, it's it's it's really good because what happened actually is uh this is this is the study we presented at Interflan.

00:32:23.200 --> 00:32:37.519
<v Antonela Čolić>So bone limb performance was usually tested through large-scale experiments, but those larger scale experiments which prove that the new adhesive, HBX adhesive work, are more often than not loaded with really low load, structural load.

00:32:37.519 --> 00:32:45.680
<v Antonela Čolić>So then I was wondering, what if this adhesive performs only up to the certain stage, after a certain structural load?

00:32:45.680 --> 00:33:00.640
<v Antonela Čolić>So in our larger scale experiments, what we did is we induced higher load and we figured out that once you induce really high shear stresses, the lamination occurs in both HBS and HBX.

00:33:00.640 --> 00:33:14.240
<v Antonela Čolić>Whereas at small scale experiments that we did, and I say small scale are the ones that are just 30 millimeters, like they're really small shear lab samples where you have no presence of any moisture transfer.

00:33:14.240 --> 00:33:20.400
<v Antonela Čolić>When we did those experiments, those were stressed at only 6% of shear strength, little veneers glued.

00:33:20.400 --> 00:33:22.319
<v Antonela Čolić>And HBX performed well.

00:33:22.319 --> 00:33:24.079
<v Antonela Čolić>It didn't delaminate at all.

00:33:24.079 --> 00:33:32.000
<v Antonela Čolić>Like you didn't even have the bond line failure at 300 degrees, and if it failed, it failed outside of the bond line in timber itself.

00:33:32.000 --> 00:33:42.319
<v Antonela Čolić>So whereas HBS continuously failed at those often temperatures that I was talking about, and that it would just disintegrate in the bond line uh phase.

00:33:42.319 --> 00:33:54.079
<v Antonela Čolić>So those were the small-scale experiments where I had no presence of any moisture movement, and at six percent we saw no, like we really saw good performance of HBX.

00:33:54.079 --> 00:34:01.680
<v Antonela Čolić>But then later, on larger scale, in I call it larger scale, but actually it's intermediate scale, we did two sets of experiments.

00:34:01.680 --> 00:34:11.119
<v Antonela Čolić>One was the shear lap samples, which were half meter, around half meter, and then the other ones were the cantilever beams, which were 1.2 meters.

00:34:11.119 --> 00:34:18.559
<v Antonela Čolić>And uh, you could see in the shear lap samples, we stretched it at 20% of shear strength, and all of them delaminated.

00:34:18.559 --> 00:34:27.599
<v Antonela Čolić>No matter the heat flux, we applied 50, which was 50 kilowatts per meter square with a radiant panel that was representative of flaming combustion.

00:34:27.599 --> 00:34:39.360
<v Antonela Čolić>We also had 25 smoldering combustion, representative of, and in both cases, in all cases, independent, regardless whether you use S or X, it all the laminates.

00:34:39.360 --> 00:34:44.559
<v Antonela Čolić>And then we said, okay, 20% of shear stress, the strength that's really high.

00:34:44.559 --> 00:34:55.519
<v Antonela Čolić>We did the analysis of what is I run the survey through the cost Helen action among the practitioners to see what is the usual law that we apply in our structures.

00:34:55.519 --> 00:35:04.159
<v Antonela Čolić>And actually, the the shear, the the maximum shear that we we could see that was used in practice was ranging somewhere around 6%.

00:35:04.159 --> 00:35:12.000
<v Antonela Čolić>But the rolling shear, which is another different type of failure that it can have in CLT, that one was going up to 13%.

00:35:12.000 --> 00:35:24.960
<v Antonela Čolić>So what we decided is okay, we're gonna use these values now in our last set of experiments, the cantilever beam, to see how the increase of the structure load affects heat in use delamination.

00:35:24.960 --> 00:35:29.039
<v Antonela Čolić>And what we realized is that the heat flux is the main driving parameter.

00:35:29.039 --> 00:35:35.119
<v Antonela Čolić>So once you have 50 kilowaspermeter square, all of them delaminate, independent of the load that you put.

00:35:35.119 --> 00:35:40.559
<v Antonela Čolić>But when you have on the 25 kiloes per meter square, the increase of the load does matter.

00:35:40.559 --> 00:35:45.440
<v Antonela Čolić>So we tested it at 6% of shear strength and 12% of shear strength.

00:35:45.440 --> 00:35:55.360
<v Antonela Čolić>And you could see that for HBX, once you increase the load, it really does define what is your behavior after you experience the heat-induced delamination.

00:35:55.760 --> 00:36:00.719
<v Wojciech Wegrzynski>One thing that that's interesting to me related to mechanical response and the lamination.

00:36:00.719 --> 00:36:06.960
<v Wojciech Wegrzynski>So before the delamination, the plank of timber is still load-bearing, right?

00:36:06.960 --> 00:36:16.639
<v Wojciech Wegrzynski>It still has some because uh two 200, how how much uh of load-bearing capacity of timber you would lose around 200, like more than half of it?

00:36:16.880 --> 00:36:19.440
<v Antonela Čolić>Yeah, it would be more than half at 60 degrees.

00:36:19.440 --> 00:36:26.880
<v Antonela Čolić>You're already, I don't know by hand, but I think like you're you have less, but 40, if I remember correctly.

00:36:26.880 --> 00:36:28.960
<v Antonela Čolić>Like that's that's like really, really low.

00:36:28.960 --> 00:36:31.360
<v Antonela Čolić>Uh, but then you kind of stay on that.

00:36:31.360 --> 00:36:36.639
<v Antonela Čolić>And I think that yeah, it at 200, you're still on like 20, 30, something like that.

00:36:36.639 --> 00:36:38.079
<v Antonela Čolić>Don't take me my word.

00:36:38.559 --> 00:36:40.000
<v Wojciech Wegrzynski>Don't quote don't don't quote us in.

00:36:40.000 --> 00:36:41.599
<v Wojciech Wegrzynski>I don't want to end up in jail.

00:36:41.599 --> 00:36:54.400
<v Wojciech Wegrzynski>So I assume that uh I'm being this hundred percent, uh, 300 degrees is like zero, so there there must be some residual load bearing uh left before your glue is exposed uh to temperatures at which uh the bond line would fail.

00:36:54.400 --> 00:37:06.719
<v Wojciech Wegrzynski>It must be quite interesting from the mechanical like the load-bearing partways, because you suddenly lose a part of your structure that was load-bearing, so you suddenly quite significantly reduce the cross-section of your element.

00:37:06.719 --> 00:37:12.800
<v Wojciech Wegrzynski>And because it's a cross-laminated timber, the next plank is in a different direction.

00:37:12.800 --> 00:37:17.360
<v Wojciech Wegrzynski>So it is not gonna necessarily behave the same as the one that just fell.

00:37:17.360 --> 00:37:27.840
<v Wojciech Wegrzynski>So the logic when we were doing you know those large-scale experiments with OFR for many real-world projects, we were and we always done them uh loaded.

00:37:27.840 --> 00:37:35.440
<v Wojciech Wegrzynski>Uh, we were like, okay, if we have five layers of timber in the CLD, we literally have the three load-bearing layers.

00:37:35.440 --> 00:37:37.760
<v Wojciech Wegrzynski>That was a rough approximation.

00:37:37.760 --> 00:37:56.880
<v Wojciech Wegrzynski>Uh and basically when we got into the third one, you know, when the third one became exposed, which means it starts drastically reducing its load-bearing capacity, we were really stressed because that meant we only have one plank at ambient at which all the load is.

00:37:56.880 --> 00:38:01.360
<v Wojciech Wegrzynski>And this is usually the point at which the structures start making sounds.

00:38:01.360 --> 00:38:10.480
<v Wojciech Wegrzynski>I really do not like my structures making sounds, like I like them to be silent, not moving, not deflecting, and definitely not making sounds.

00:38:10.480 --> 00:38:18.639
<v Wojciech Wegrzynski>So perhaps this is outside of your scope, but where are you looking into how the the static uh load distribution changes when the planks fall?

00:38:18.639 --> 00:38:21.039
<v Wojciech Wegrzynski>That doesn't could be an interesting study.

00:38:21.360 --> 00:38:22.159
<v Antonela Čolić>No, no, for sure.

00:38:22.159 --> 00:38:29.280
<v Antonela Čolić>Yeah, I mean the stress distribute distribution in your element completely changes, and it's very different for CLT and uh GLULAN.

00:38:29.280 --> 00:38:44.000
<v Antonela Čolić>So, yes, what we did is in in uh both of our intermediate scale experiments is is we we tracked the the strain in the bond line itself, and we did that by using the digital image image correlation.

00:38:44.000 --> 00:38:55.760
<v Antonela Čolić>Um, not sure how much you know about it, but essentially you you you speckle the surface of your element in little dots, and you have your camera which is recording it, and you're just tracking how those dots move.

00:38:56.000 --> 00:39:00.719
<v Wojciech Wegrzynski>I I I love the technique, but it never works in fire lab because of all the smoke and dusting.

00:39:01.039 --> 00:39:02.079
<v Antonela Čolić>Smoke, exactly, yes.

00:39:02.079 --> 00:39:08.480
<v Antonela Čolić>But we kind of tried to isolate it and we did get some results, so that was really, really nice, I guess.

00:39:08.480 --> 00:39:34.400
<v Antonela Čolić>Uh and and and what we noticed uh is that even though the elastic stress that you impose on your element, which is due to the imposed load, even though your imposed load is very, very low, what happens is that when when you start heating your element on your bone line, due to the shrinkage and swelling, you have the normal normal strain which is acting on your bone line.

00:39:34.400 --> 00:39:36.800
<v Antonela Čolić>And that's just due to the heating of your element.

00:39:36.800 --> 00:39:45.360
<v Antonela Čolić>And that strain increases magnificently, much higher than the strain that is caused only due to the presence of the structural load.

00:39:45.760 --> 00:39:49.519
<v Wojciech Wegrzynski>Can you expand on thermo mechanical response to shrinking and expansion?

00:39:49.519 --> 00:39:56.159
<v Wojciech Wegrzynski>Um, will there be a difference in shrinking or expanding at the bone line versus the virgin timber that's next to it?

00:39:56.159 --> 00:39:58.559
<v Wojciech Wegrzynski>Does this cause additional stresses?

00:39:58.800 --> 00:39:59.360
<v Antonela Čolić>Yeah, yeah, yeah.

00:39:59.360 --> 00:40:15.679
<v Antonela Čolić>So when you check the strain profile across your cross-section, it's just like the peaks are immense in the bond line itself, and then it relaxes in the middle of the plank, and then it again peaks in the bond line itself, meaning that the bond line is doing its work, it's it's it's taking a lot of strain.

00:40:15.679 --> 00:40:16.320
<v Antonela Čolić>Yeah.

00:40:16.960 --> 00:40:23.840
<v Wojciech Wegrzynski>And is this also like something you would connect with the ability to withstand or promote the delamination?

00:40:23.920 --> 00:40:30.480
<v Antonela Čolić>Or yeah, I mean, definitely, and it's really promoted in the so it depends how stiff your adhesive naturally is.

00:40:30.480 --> 00:40:33.039
<v Antonela Čolić>HBX is stiffer than HBS.

00:40:33.039 --> 00:40:42.079
<v Antonela Čolić>We saw that in our ambient test, the displacement that we we got from the HBX was smaller than the one that we got from uh HBS.

00:40:42.079 --> 00:40:50.400
<v Antonela Čolić>Um, and then naturally later in our experiments, there was a difference between the two and how they take the the strain and the bond line.

00:40:50.400 --> 00:40:56.719
<v Antonela Čolić>The strain that was experienced by HBS was higher than the one that was experienced in HBX.

00:40:56.719 --> 00:41:07.440
<v Antonela Čolić>And then the cool thing about the last part of our study is the in CLT, you have the big contribution of the fact that the lamellas are cross-oriented.

00:41:07.440 --> 00:41:13.440
<v Antonela Čolić>So you you you naturally in timber have a different shrinkage in in tangential and radial direction.

00:41:13.440 --> 00:41:23.679
<v Antonela Čolić>And then if you also cross-oriented, that then it's even more promoted because you have also the different orientation of your drains of timber.

00:41:23.679 --> 00:41:31.920
<v Antonela Čolić>Whereas in GLULAM, everything flows in the one direction, so you wouldn't expect that to influence your adhesive that much.

00:41:31.920 --> 00:41:48.719
<v Antonela Čolić>But then if we we when we compared in the glue lamp, because in the last set of experiments we tested both CLT and GLULAM to see what is the contribution of just the adhesive, because in glue in GLULAM you take out this problem of timber and differential shrinkage of the timber itself, right?

00:41:48.719 --> 00:41:55.840
<v Antonela Čolić>So in the GLULAM, also see that the HBS has higher strain than HBX.

00:41:55.840 --> 00:42:01.679
<v Antonela Čolić>So it is the adhesive difference as well as the contribution of uh of timber.

00:42:01.679 --> 00:42:04.559
<v Antonela Čolić>I I hope that came somewhat clear.

00:42:04.559 --> 00:42:08.079
<v Antonela Čolić>It's really hard to like explain strain in words.

00:42:08.559 --> 00:42:13.519
<v Wojciech Wegrzynski>People have people have been warned that we're gonna talk about high-level stuff on the online.

00:42:13.519 --> 00:42:16.000
<v Wojciech Wegrzynski>So yeah, you signed for that.

00:42:16.000 --> 00:42:18.800
<v Wojciech Wegrzynski>It was your choice to listen to this podcast, it's your fault.

00:42:18.800 --> 00:42:20.800
<v Wojciech Wegrzynski>Let's talk about the moisture movement.

00:42:20.800 --> 00:42:24.000
<v Wojciech Wegrzynski>I've covered that with Felix, but I would uh love a refresh on that.

00:42:24.239 --> 00:42:26.800
<v Antonela Čolić>Oh, that's that's so cool.

00:42:26.800 --> 00:42:31.440
<v Antonela Čolić>I love it, and it's so non-discovered, and I know know so little about it.

00:42:31.440 --> 00:42:34.320
<v Antonela Čolić>And and our experiments just show how little we know.

00:42:34.719 --> 00:42:35.920
<v Wojciech Wegrzynski>It's so hard to measure.

00:42:36.159 --> 00:42:41.039
<v Antonela Čolić>Yeah, so what we did is we did the experiments in um in France.

00:42:41.039 --> 00:42:51.679
<v Antonela Čolić>We have a big uh uh nuclear reactor, and the way this method works is essentially you you have your element, you heat it from one side, and your moisture starts to move.

00:42:51.679 --> 00:43:19.199
<v Antonela Čolić>Simultaneously, you point out the neutron beam through your sample, and it's kind of like doing x-rays for humans, but it's instead of checking the bones, you're checking the position of the hydrogen because these neutrons they are interact with the hydrogen in your element, and what you get on the back side is this image of what is the position of your hydrogen at every single moment of your heating.

00:43:19.199 --> 00:43:30.400
<v Antonela Čolić>And simultaneously you're rotating your sample, and as you're rotating it, you get this 3D image of what is the position of the moisture throughout the whole cylinder that we tested.

00:43:30.400 --> 00:43:39.840
<v Antonela Čolić>And what we saw is that as the moisture progresses towards the bond line, but once it passes the bond line, the the front movement is bilinear.

00:43:39.840 --> 00:43:46.559
<v Antonela Čolić>So it has one increased rate up to the bond line, and then it reduces once it passes the bond line.

00:43:46.559 --> 00:43:53.119
<v Antonela Čolić>The two reasons for that are first it's further away from the heating source, so the pressure gradients are naturally different.

00:43:53.119 --> 00:43:55.599
<v Antonela Čolić>And the second is the presence of the bond line.

00:43:55.599 --> 00:44:02.400
<v Antonela Čolić>So bond line does like the movement of moisture is not the same in the laminated timber and the solid timber.

00:44:02.400 --> 00:44:07.119
<v Antonela Čolić>And then we wanted to see what is the difference between HBX and HBS.

00:44:07.119 --> 00:44:12.000
<v Antonela Čolić>Is there a difference in the the bond line retention around the adhesive itself?

00:44:12.000 --> 00:44:22.480
<v Antonela Čolić>And what happened is that actually both of them do have the retention of the moisture front at some point, but HBX keeps that moisture for the longer period.

00:44:22.480 --> 00:44:39.440
<v Antonela Čolić>So then later, when we did our large scale, intermediate scale experiments, we saw that it looked like HBX fails at lower temperatures, but actually those were not lower temperatures due to thermal penetration, it was due to this retention of the moisture.

00:44:39.440 --> 00:44:50.639
<v Antonela Čolić>So that's why it's so hard to say that the bond line temperature at failure was this and that, because it's that the system behaves really, really differently at every single scale.

00:44:50.960 --> 00:44:51.119
<v Wojciech Wegrzynski>Right.

00:44:51.119 --> 00:44:57.360
<v Wojciech Wegrzynski>I'm just amazed, like you get to do you get to do experiments in nuclear facilities with Timber.

00:44:57.360 --> 00:44:58.079
<v Wojciech Wegrzynski>That's so cool.

00:44:58.480 --> 00:44:58.800
<v Antonela Čolić>Yeah, yeah.

00:44:59.119 --> 00:45:09.599
<v Wojciech Wegrzynski>But we had to keep it at like 270 degrees, yeah, because fire and but the the the butt I assume the samples had to be fairly small size, so we were not able to load them either.

00:45:11.039 --> 00:45:20.320
<v Antonela Čolić>There are methods to load them, but that then you're like entering so many complexities, and we just wanted to dissect this hydrothermal response.

00:45:20.320 --> 00:45:30.000
<v Antonela Čolić>So we didn't want to introduce load as well, but there is a way to introduce, they have instron that you can use whilst doing this screening as well.

00:45:30.000 --> 00:45:41.679
<v Antonela Čolić>But yeah, I mean we we we opted not to do so, and the the the size was 20 times 50 millimeters, so it was just a cylinder, like it's it's really fine, yeah.

00:45:42.000 --> 00:45:47.679
<v Wojciech Wegrzynski>So you we have these three components the the thermal penetration mechanical stress moisture.

00:45:47.679 --> 00:45:54.639
<v Wojciech Wegrzynski>Like how how do you now make out of these three variables one telling you uh how bad it is?

00:45:54.719 --> 00:45:57.039
<v Antonela Čolić>Like that well, that that's a good question.

00:45:57.039 --> 00:46:10.960
<v Antonela Čolić>So so the larger scales are telling you what the response of your material could be at specific conditions, and then the smaller scale experiments they tell you why is that happening.

00:46:10.960 --> 00:46:27.440
<v Antonela Čolić>So so the reason why the HBX had lower failure temperatures is not because it's weaker or whatever, it's because there is the moisture that is being retained stopped at the bond line.

00:46:27.440 --> 00:46:33.519
<v Antonela Čolić>And you can only see that if you do different types of experiments, and now we know why that happens.

00:46:33.519 --> 00:46:51.760
<v Antonela Čolić>Or when we see that that the HBS fails at 200 degrees, we know now why it fails at 200 degrees, and this is very important for the development of the future adhesives because if you know what that your product works, you also want to know why it works.

00:46:51.760 --> 00:47:04.000
<v Antonela Čolić>You don't want to stop there because at some point it's not gonna work because we are gonna maybe increase the structure load, or we're gonna say, oh, isocyanates are now awful, like let's not have that many isocycles.

00:47:04.000 --> 00:47:06.000
<v Antonela Čolić>You know, you never know what a future holds.

00:47:06.320 --> 00:47:16.159
<v Wojciech Wegrzynski>Well, that I think that's an interesting question because you if you don't have nitrogen in your fuel, you're not gonna produce cyanides in your smoke.

00:47:16.159 --> 00:47:20.559
<v Wojciech Wegrzynski>If you have nitrogen there, then you probably will produce that.

00:47:20.559 --> 00:47:34.079
<v Wojciech Wegrzynski>So so a question of a large-scale impact of that and overall smoke toxicity, for example, out of polyurethane uh glues in timber, perhaps that's a question that will be asked in the future.

00:47:34.079 --> 00:47:42.159
<v Wojciech Wegrzynski>Uh at this point, I'm not sure if it would be a strong contributor given the little amount and how late into the fire it would go.

00:47:42.159 --> 00:47:48.079
<v Wojciech Wegrzynski>But yeah, I can imagine such questions being uh brought up someday.

00:47:48.079 --> 00:47:49.840
<v Wojciech Wegrzynski>Perhaps it's a valid research question.

00:47:49.840 --> 00:47:54.559
<v Wojciech Wegrzynski>Um, jumping back from um lamination to to char fall off.

00:47:54.559 --> 00:48:00.000
<v Wojciech Wegrzynski>In your paper, you defined it that it can happen below the bond line, at the bond line, above the bond line.

00:48:00.000 --> 00:48:09.119
<v Wojciech Wegrzynski>Uh, have you seen any outcomes of using the different types of glue in the progression of that?

00:48:09.119 --> 00:48:14.559
<v Wojciech Wegrzynski>Any trend that with HPX again it happens way above the the bond line?

00:48:14.960 --> 00:48:16.880
<v Antonela Čolić>So that's really relevant.

00:48:16.880 --> 00:48:22.639
<v Antonela Čolić>So that was our latest finding that we now submitted a paper, it's under review.

00:48:22.639 --> 00:48:32.480
<v Antonela Čolić>So what happens is that once you have heat-induced delamination in both adhesives, it is very different what happens later.

00:48:32.480 --> 00:48:44.400
<v Antonela Čolić>So in HBS, you have this lamination, and then the char lamella starts to peel off from the surface, and you get really, really soon the char fall-off at the bond line.

00:48:44.400 --> 00:48:52.159
<v Antonela Čolić>Whereas for the HBX, the delamination happens, but the crack propagation and the crack itself is not as wide.

00:48:52.159 --> 00:48:57.519
<v Antonela Čolić>The bond line still sticks together, and the charred fall-off happens outside the bond line.

00:48:57.519 --> 00:48:59.119
<v Antonela Čolić>It happens before the bond line.

00:48:59.119 --> 00:49:05.280
<v Antonela Čolić>So you still have some charred layer that is later protecting your bond line.

00:49:05.280 --> 00:49:10.880
<v Antonela Čolić>So the reduction of the cross-section is much slower for HBX than uh HBS.

00:49:11.119 --> 00:49:18.400
<v Wojciech Wegrzynski>Well, you you said it yourself based on the TGA and the TG that the the HBS would uh soften and HBX would char.

00:49:18.400 --> 00:49:30.400
<v Wojciech Wegrzynski>So I assume HBX would uh like become a different type of char within the char, but it's still like the the the carbon matrix is close enough to each other, so they they kind of form a continuous thing.

00:49:30.400 --> 00:49:52.400
<v Wojciech Wegrzynski>Well, that that's a fantastic explanation because again, I've seen this and with my own eyes in the experiments we've done with OFR years ago on on the slabs that were under uh thermal load, and and we have seen a difference, quantitative difference between the char fall off between uh slab that was built with HBS and HBX.

00:49:52.400 --> 00:49:55.119
<v Wojciech Wegrzynski>On the side note, then Quick had a great idea.

00:49:55.119 --> 00:49:58.079
<v Wojciech Wegrzynski>Let's put a beam inside of the slab, and it changed everything.

00:49:58.079 --> 00:50:09.920
<v Wojciech Wegrzynski>Uh point where I've started to regret myself being a fire engineer because we had some stuff sorted out, and then we put like one little element inside, and that's where it means everything's changing.

00:50:09.920 --> 00:50:16.320
<v Wojciech Wegrzynski>Yeah, but but yeah, there's uh there's a World Timber conference paper on the effect of the beam as well.

00:50:16.320 --> 00:50:20.000
<v Wojciech Wegrzynski>Um I think we've covered most of it.

00:50:20.000 --> 00:50:24.880
<v Wojciech Wegrzynski>Please tell me how now this translates to your real-world projects.

00:50:24.880 --> 00:50:31.039
<v Wojciech Wegrzynski>Uh, did your engineering practice change given the findings of your PhD and your colleagues?

00:50:31.039 --> 00:50:37.280
<v Wojciech Wegrzynski>Did they incorporate any of this in their reasoning when discussing with clients about the CLT timber?

00:50:37.519 --> 00:50:41.599
<v Antonela Čolić>Well, we are more careful about the specification of the adke itself.

00:50:41.599 --> 00:50:49.840
<v Antonela Čolić>There are also some other things that we are recommending, such as lamella thickness or uh having the two lamellas in the CLTs which are spanning in the same direction.

00:50:49.840 --> 00:51:02.639
<v Antonela Čolić>And then if we are uh introducing uh the temperatures in our model models, we are internally discussing what the temperatures should be, depending on the on the consequence class of the project or the building we handle.

00:51:02.639 --> 00:51:08.800
<v Antonela Čolić>And in essence, PHV also offers you like you cover a lot of statistical methods to go through your data.

00:51:08.800 --> 00:51:19.119
<v Antonela Čolić>So later on when you're doing your work, that that is really really helpful when you're analyzing the data that is out there, you can just focus on your own work, like you have to incorporate the world outside of you.

00:51:19.119 --> 00:51:22.480
<v Antonela Čolić>So yeah, uh it's you have a wider view on the problem.

00:51:22.800 --> 00:51:29.599
<v Wojciech Wegrzynski>Yeah, yeah, I think you you've also mentioned you have to care about the where the CLT is used, kitchen office, a swimming pool, I guess.

00:51:29.599 --> 00:51:32.000
<v Wojciech Wegrzynski>Uh, do do you also take that into consideration?

00:51:32.000 --> 00:51:35.519
<v Wojciech Wegrzynski>How much moisture will there be in the everyday use of the timber?

00:51:35.519 --> 00:51:37.760
<v Wojciech Wegrzynski>Is this a factory consider right now?

00:51:38.079 --> 00:51:49.599
<v Antonela Čolić>Well, to be honest, I've not worked on a project that had such a various uh disparity in the moisture in itself, but I'm sure if such uh project occurs, that that's something that we should consider, definitely.

00:51:50.000 --> 00:51:52.079
<v Wojciech Wegrzynski>One last question cost action.

00:51:52.079 --> 00:51:52.719
<v Wojciech Wegrzynski>Was it fun?

00:51:52.960 --> 00:51:54.639
<v Antonela Čolić>Oh my god, that was strange.

00:51:54.639 --> 00:52:00.559
<v Antonela Čolić>Like I was just so lucky because it started when I my PhD started and it finished when it's finished.

00:52:00.559 --> 00:52:02.079
<v Antonela Čolić>It's like a four-year thing.

00:52:02.079 --> 00:52:07.119
<v Antonela Čolić>So, like they have this thing called STSM, it's like short-term scientific mission.

00:52:07.119 --> 00:52:14.400
<v Antonela Čolić>So they essentially funded my travels to Australia and my travels to Canada because Felix Wiesner was one of my supervisors.

00:52:14.400 --> 00:52:17.440
<v Antonela Čolić>So I kind of followed the guy across the world.

00:52:17.440 --> 00:52:25.360
<v Antonela Čolić>So we worked together in at the UQ uh with David Lang and Sergio Zarate and Thomas Bravo, which are such a great team.

00:52:25.360 --> 00:52:36.320
<v Antonela Čolić>And I got to work in that institution and then I did two types of experiments there, like the micro-scale ones, the TGA stuff I did there, intermediate sheer lab stuff I did there.

00:52:36.320 --> 00:52:45.440
<v Antonela Čolić>And then I managed to go to Canada to work there with Felix, where I did my survey on the loads that are involved in practice.

00:52:45.440 --> 00:53:14.159
<v Antonela Čolić>So essentially it ended up being three research publications, three chapters of my PhD, and also like learning from the other people because they have these like cost meetings yearly or or two times a year in different countries in Europe, where you gather and you present the work and you get to know what is the robustness, how does that affect the design, how does the durability affect the design, what is the influence of the moisture, and you realize that it's not fire only that matters.

00:53:14.159 --> 00:53:19.360
<v Antonela Čolić>And it it was just such a great idea, led by a really good group of young researchers.

00:53:19.360 --> 00:53:27.039
<v Antonela Čolić>It doesn't matter whether they're young researchers, so it was it was it was really good and very international, which I I love.

00:53:27.519 --> 00:53:32.239
<v Wojciech Wegrzynski>I got a little exposure to that cost action, it was called called Cost Action Helen.

00:53:32.239 --> 00:53:35.760
<v Wojciech Wegrzynski>Uh, I'll probably drop a link into the the show notes.

00:53:35.760 --> 00:53:46.880
<v Wojciech Wegrzynski>Uh I mean i I was surprised with the amount of work out there, so I eventually like uh did not contribute that much, but I remember some meetings uh with I remember you from the beginning, yeah, yeah.

00:53:47.039 --> 00:53:48.639
<v Antonela Čolić>In the beginning meetings you were there.

00:53:48.639 --> 00:53:50.239
<v Antonela Čolić>Come on, do yourself some credit.

00:53:50.480 --> 00:53:53.599
<v Wojciech Wegrzynski>I I I I was there, but I was like more like slowing down.

00:53:53.599 --> 00:53:55.039
<v Wojciech Wegrzynski>People are writing their drafts.

00:53:55.039 --> 00:53:58.960
<v Wojciech Wegrzynski>But uh I remember Ian uh doing great work, Chamit doing great work.

00:53:58.960 --> 00:54:10.000
<v Wojciech Wegrzynski>Like it was really I I enjoyed it thoroughly, and I'm I'm really happy there are finally tangible outcomes of that work because I know just uh a book chapter has appeared out of that work, and I assume there will be more coming.

00:54:10.079 --> 00:54:13.280
<v Antonela Čolić>So yeah, it was just published like this week, so yeah, great timing.

00:54:13.280 --> 00:54:14.320
<v Antonela Čolić>Yeah, great timing.

00:54:14.400 --> 00:54:20.400
<v Wojciech Wegrzynski>Yeah, so I I just wanted to bring this up because you know a lot of young researchers are listening, they're wondering what are the possibilities.

00:54:20.400 --> 00:54:36.559
<v Wojciech Wegrzynski>I'm not sure everyone is aware of cost actions and what kind of possibilities those actions do, but I think they're very, very good ways to get into the international research in the general scope if you're interested.

00:54:36.559 --> 00:54:55.599
<v Wojciech Wegrzynski>And I also, if if you're listening to this and you're now curious about the the cost actions, I had an episode with uh Nieves Fernandez Anis, and she was also a participant of Cost Action, and actually in that interview, I think we spent uh like 15-20 minutes talking about cost actions in general.

00:54:55.599 --> 00:55:04.320
<v Wojciech Wegrzynski>So, yeah, there's some there's a lot of uh testament about uh uh about testimony about uh how good cost actions are, and I would recommend that.

00:55:04.320 --> 00:55:06.320
<v Wojciech Wegrzynski>Antonella, uh well, thank you.

00:55:06.320 --> 00:55:13.519
<v Wojciech Wegrzynski>Thank you so much uh for uh uh coming to the Fire Science show and highlighting so much about the bond line failure.

00:55:13.760 --> 00:55:14.719
<v Antonela Čolić>No, you're well welcome.

00:55:14.719 --> 00:55:15.360
<v Antonela Čolić>I enjoyed it.

00:55:15.360 --> 00:55:16.320
<v Antonela Čolić>This, of course, yeah.

00:55:16.480 --> 00:55:20.559
<v Wojciech Wegrzynski>I I'm I'm a little worried like Gordian is gonna be so happy about this episode.

00:55:20.559 --> 00:55:26.000
<v Wojciech Wegrzynski>I just want to say, in no way, in no way Henkel did affect this podcast episode.

00:55:26.239 --> 00:55:30.400
<v Antonela Čolić>Yeah, Henkel they no Henkel was they were great contributors, especially Gordian.

00:55:30.400 --> 00:55:33.760
<v Antonela Čolić>Like that guy is just so helpful and open to discuss.

00:55:33.760 --> 00:55:36.159
<v Antonela Čolić>He was genuinely curious about whether the product works.

00:55:37.360 --> 00:55:39.199
<v Wojciech Wegrzynski>The same the same experience when we were doing that.

00:55:39.199 --> 00:55:48.320
<v Wojciech Wegrzynski>So this was absolutely like that there was no product placement in this podcast episode, just honest uh scientific discussion between uh two researchers.

00:55:48.320 --> 00:55:52.159
<v Wojciech Wegrzynski>I felt I need to make this statement after all the praise we gave.

00:55:52.159 --> 00:55:54.320
<v Wojciech Wegrzynski>But anyway, Abdullah, thank you so much for coming.

00:55:54.639 --> 00:55:56.320
<v Antonela Čolić>Thank you, thank you for your time, Poi Chick.

00:55:56.559 --> 00:55:57.920
<v Wojciech Wegrzynski>Uh that's it, thank you for listening.

00:55:57.920 --> 00:56:02.239
<v Wojciech Wegrzynski>Surprisingly, a lot of things happening at this uh bond line interface.

00:56:02.239 --> 00:56:22.800
<v Wojciech Wegrzynski>For me, the surprise or new finding was that it's not just you know a single line that that's in between the timber, it actually affects the timber, and uh the blue line and timber form some sort of composite together, which it's not just line, it it is deeper and it kind of makes sense.

00:56:22.800 --> 00:56:31.039
<v Wojciech Wegrzynski>It makes sense that it works, uh but it also like makes difference to how I uh understand the failure at that place.

00:56:31.039 --> 00:56:40.000
<v Wojciech Wegrzynski>Yeah, and then the last research was definitely a deep dive into the subject and there's like further reading if you need some more technical details.

00:56:40.000 --> 00:56:46.320
<v Wojciech Wegrzynski>We always scratch the surface at the fire science show, and there's always more waiting for you if you need that.

00:56:46.320 --> 00:56:59.920
<v Wojciech Wegrzynski>I think for your engineering practice and you know just the basics, we've covered most of the important things, but if you really want to understand the differences between the HBS and HBX glues, well you have to read more.

00:56:59.920 --> 00:57:09.280
<v Wojciech Wegrzynski>And finally, it's it's interesting that you know those differences are fairly small, but yet uh enough to impact the large scale.

00:57:09.280 --> 00:57:20.239
<v Wojciech Wegrzynski>Also, like I I need to learn more about putting more lamellas in the same direction, same orientation, and that that's probably something I would like to explore for the future episodes because I find that interesting.

00:57:20.239 --> 00:57:26.880
<v Wojciech Wegrzynski>I guess this helps you get your load bearing capacity in the correct direction that you need it more.

00:57:26.880 --> 00:57:32.079
<v Wojciech Wegrzynski>And uh something we've not tested yet so far in large scale, I think.

00:57:32.079 --> 00:57:37.119
<v Wojciech Wegrzynski>So I'm probably interested in that uh in that aspect of the design.

00:57:37.119 --> 00:57:42.559
<v Wojciech Wegrzynski>Anyway, that would be it for the comprehensive adhesive episode of the Fire Science Show.

00:57:42.559 --> 00:57:50.239
<v Wojciech Wegrzynski>I hope you've learned something new today, and I'm really happy we were able to share this exciting PhD journey of Antonella Cholica.

00:57:50.239 --> 00:57:54.320
<v Wojciech Wegrzynski>And yeah, I hope we will be able to share more stories like that.

00:57:54.320 --> 00:58:11.360
<v Wojciech Wegrzynski>I'm super, super happy to host especially fresh PhD students, or fresh doctors actually, fresh fresh PhD graduates in the fire science show because I find those people to be extremely knowledgeable about the area they have just finished uh researching for many years.

00:58:11.360 --> 00:58:21.679
<v Wojciech Wegrzynski>Therefore, they usually are the number one source of information in very specific areas of the fire science, and I would love to cover more of them.

00:58:21.679 --> 00:58:31.119
<v Wojciech Wegrzynski>So if you know someone who is willing to share their PhD journey and explain to me what they have found, I am more than keen to listen.

00:58:31.119 --> 00:58:32.559
<v Wojciech Wegrzynski>Anyway, that's it.

00:58:32.559 --> 00:58:36.159
<v Wojciech Wegrzynski>Thank you for being here with me this Wednesday and next Wednesday.

00:58:36.159 --> 00:58:39.760
<v Wojciech Wegrzynski>Uh well, another Wednesday, another fire scientific episode waiting for you.

00:58:39.760 --> 00:58:40.239
<v Wojciech Wegrzynski>Thank you.

00:58:40.239 --> 00:58:40.880
<v Wojciech Wegrzynski>Bye.