Corrosão das armaduras: o que muda com a nova NBR 17277? Parte 02 - Live 43

Added: 2026-05-25

[00:00:01]How to size a cathodic protection system?

[00:00:04]What is cathodic protection? How does it work? What are the types of cathodic protection? When should we use it? When you should not use it.

[00:00:12]You'll see all of this in today's video.

[00:00:14]Hi, my name is Marília Araújo, I'm a civil engineer and specialist in building pathology, ladies and gentlemen. So, welcome! Why? Because every Thursday at 12 noon we have a free lesson that I deliver here for you. So you can't complain about the free content I provide, which is a lot of high-quality content that I give you to specialize in. This class is aimed at engineers and architects who want to work or are already working in the field of building pathology.

[00:00:46]Welcome, everyone. They are arriving. Sergio Cordeiro from São Paulo. Vittor is here. Manuela, let's go. The fifth technique is a success. I'm anxious.

[00:00:57]Hey, it's me!

[00:01:01]Very good, ladies and gentlemen. So, let's go, shall we? Without further ado, today we're going to talk about Catholic protection. A new rule is coming out this year, which I already mentioned in the last live stream, so the last live stream was great, you guys hit the goal, and that's why I'm bringing you part two here. If you haven't watched the last live stream yet, when this one is over, come back to my profile and watch the one where I talked about cathodic protection and corrosion of reinforcement bars. But I'll give you an overview here without any problem, so you can understand. My team is already putting up the slides, and as soon as they get ours, I'll present to you, okay? But the first image I put on the slide is an image of cathodic protection itself. Okay, so in the last class I talked to you about cathodic protection, what it is, how it works, and why cathodic protection is good, especially when we start talking about corrosion of reinforcement bars, and the different types, right? We talked about the drain effect, and now I'm going to explain to you what it is. So I brought photos of this type of corrosion protection for the reinforcement bars. It's a type of protection that is extremely widely used in various factors and sectors. And you'll understand why, okay? So, when a concrete structure suffers corrosion of the reinforcement, it is usually due to two factors. What are the two factors? Carbonation, which I mentioned to you, or chloride pore attacks, will cause the concrete to start cracking, bulging, and flaking due to the increased volume of corrosion products, because corrosion will generate these expanded volumes. Beauty?

[00:02:42]Oh, very interesting, because you're talking about the topic of my thesis; I fell in love with pathology in the final stretch of college.

[00:02:48]Look how cool that is, right? That's a responsibility too. So, I'm going to put this one here for you guys. My team has already put up the slides. So, let's go.

[00:02:59]Let me put it on. Ah, here it is. Okay, I've added the slides here for you to see. So, we're talking about part two. What I'm going to start by talking about in this second part is exactly how it works. So the crux of the matter is how this repair works, which is different from traditional repairs— not that traditional repairs are useless, but you also have to know the correct way to do it, because otherwise we'll remove everything, do the treatment, and then create a new layer of corrosion. And the part that was in good condition starts to corrode. And that's where the problem lies, okay?

[00:03:36]So here in this image we can see... concrete that is contaminated, the concrete that he started to repair, right? So, this happened, and then, uh, we do this galvanic protection installation, which is this little yellow part, this little yellow square, which is like the galvanic protection installation for cathodic protection before closing the repair. And it's precisely the beige component, the component I'm showing you in the center of the image. This element is typically composed of zinc, which has a much more negative electrochemical potential than steel. So, I'll show it to you guys here too, okay? I think it's in the next picture. Let me grab the next picture here, okay? Here, look. So, we apply this cathodic protection material, which has a much more negative electrochemical potential than steel. In practice, folks, all that happens is that the zinc will sacrifice itself to protect the armor. And that. Then he will become the anode of the system. We already talked about this in the last live stream, and that's why I'm going into more detail with you all.

[00:04:44]So in the meantime, the armor behaves as a cathode and it will stop corroding. So I removed the anode part from that armor and replaced it with a sacrificial metal, which is zinc, precisely so that it would undergo corrosion, okay? So, instead of the metal losing electrons from corrosion, it will be the zinc that undergoes this oxidation-reduction process, right? Beauty? Here, folks, it's pretty easy for you to understand, right? It's just like a summary of the last class, okay? So here I've brought some photos for you showing what cathodic protection actually looks like.

[00:05:20]So here, this first photo you're seeing is nothing more than the cathodic protection placed there to protect the metal parts. So, as we can see here, she's doing it before the concrete is poured. So, we can use this cathodic protection before pouring the concrete or something like that to preserve it and extend its lifespan. We can use it later, I'll show you. We can use it to solve a problem when we have some potential for corrosion. Don't worry, I'll explain everything to you, stay with me, okay? So, to protect this metal reinforcement, we use, right, this solution that I told you about, which is the placement of galvanic anodes, right, for cathodic protection, where we simply connect high- potential zinc to this reinforcement, okay?

[00:06:14]So, these anodes, which are activated alcohols, are provided with a mortar encapsulation. So, as you can see here in the second picture, I have the zinc, which is the anode that will be sacrificed, but this anode also has to be encapsulated with mortar.

[00:06:33]Marília, with mortar, what type? How does it work? I'll tell you everything. I'm just giving a quick summary here. Therefore, it needs to have a high pH, ​​because remember from the last class when we talked about how a pH below that of concrete is what causes depassivation and corrosion of the reinforcement bars. So, this cementitious matrix that we're going to put there, right, which is in that little photo, is precisely what will have a higher pH in order to keep it permanently activated within the concrete. Therefore, the potential difference between the anode and the steel gives rise to a protective electric current that exits the anode and reaches the metal reinforcement. Beauty? Hey guys, are you getting it? Is everyone with me? It has n't been difficult so far, has it? Awesome! So here I brought a little photo for you of the area we use most, because it's our area of building pathology, specifically the repair area. So how will the repair actually work for us to do that? I also want to welcome Luís Paulo, who 's here, and he helped me a lot by answering some questions and explaining things a bit more. He, folks, was simply the guy who spearheaded this regulation, this regulation that we're talking about now. And he's here on our live stream. I called him to talk, and he said, "Marília, I can't because the guy is simply in Alaska, you have to respect that, right?" And then he spearheaded that regulation. So, his company is a pioneer here in Brazil; he's the one that resells these anodes, this cathodic protection. I'll explain a little more to you, okay? But thank you so much for participating here in our live stream.

[00:08:17]So here's an example of how it works. We're going to connect these tiles to the structure.

[00:08:24]So here, I even took this little photo from one of his presentations, which is from his company, ICE, which is corrosion engineering and installations. Yeah, they do that. The guy is tough.

[00:08:37]Really, Ana? The guy is tough. So here's this picture, what is it? Well, that's where we can use Catholic protections, which are even included in the regulations, okay?

[00:08:46]So, in certain applications, we can use it even before we actually build the structure. Why? To increase lifespan. Marília, in what situations is the density of iron higher? Look, there are two ways here. This first one here that you see in the first picture, we have a more elongated anode shape, because it will be used exactly where we have a denser shape of those structures.

[00:09:17]So, where I have a lot of hardware, I can even use these longer anodes, which will use the same core as that structure and the same encapsulation, alkali-activated and the same fastening wires. And then we incorporate that into the project along with the structure. Look how cool that is, right? Well, then we have other issues as well, right? So, installing anodes in new structures is very important so that we can actually have greater durability and prevent corrosion of the reinforcement bars. Who here has ever seen these anodes, you know, the sacrificial ones, this cathodic protection being performed?

[00:09:56]People, why does this need to be spread so widely? So that in new constructions we don't have so many problems with corrosion of the reinforcement bars, for example, right?

[00:10:05]So, in cases where we know that over time the concrete will absorb pollutants, especially in humid locations, underground areas, areas with higher levels of aggressiveness, contaminated by chlorides, or marine structures, for example, we can indeed install anodes, and it's important that this be done during construction. And why during construction, Marília?

[00:10:34]Precisely so we could place a sacrificial anode there. We put a sacrificial anode there, and that sacrificial anode will provide greater durability to the service life. Are you all understanding this? So, the first practical application I 'm presenting here is anodes installed in new construction projects. So, when we install the anode in new constructions, it will remain dormant. It's as if he were just lying there, sleeping inside the concrete. And it will only start working when the weapon, when or if there is, you know, moisture there, and the pollutants, the CO2, start to reach the metal parts. And that will prevent corrosion of the reinforcement bars, which will have a longer lifespan. This is very important, everyone. Look, look at the importance of what you are learning now, for free.

[00:11:31]Look how important this is. This is before the concrete is poured. This is very important.

[00:11:36]Then we have this other little photo here. Let me pass this over to you. We have this other photo here, which is being taken during a repair. So here we are, we've seen the potential for corrosion that may exist. So, to prevent corrosion— because yes, we can perform a corrosion potential test, I'll explain it to you. We start installing these anodes precisely to avoid any kind of problem. Oh, the genuine article. I have already installed marine structures. Look how cool! Very good. Adriana didn't know him. Legal. Awesome! So, when we talk about this type of protection, we can use it both before construction— pay attention, let's say before construction—and when we start to see that there is a potential for corrosion, that is, I did my inspections and from those inspections I saw that there is a potential for corrosion. I can do it, or I can do it when we're carrying out a structural recovery there, right? So I've brought here three methods that we can already use, and this other method here is a structural recovery. And here, you see us placing this sacrificial anode here. Beauty? So far, so good, right? Beauty?

[00:12:59]So here we've already understood that yes, we can use this in various ways, not only when we already have a structure with corrosion there. And then we need to evaluate the structures in the design and construction phases. So when it comes to Marília, the Catholic protection is envisioned in structures that haven't been built yet. And it's in item 6.3.2 of the standard. So, we're going to do an assessment that is preventative in nature.

[00:13:27]Remember in the first class when we talked about the difference between cathodic prevention and cathodic protection? There is this difference that we talked about in the last class, and it's even in the standard as well. So, this item 6.3.2 two of the standard, it outlines the assessments we need to make to determine whether or not cathodic protection is actually necessary. So, the first thing we need to look at are the construction characteristics, the thickness of the covering, the water-cement ratio, the type of cement, as these determine the permeability and the time it takes for corrosion to begin. We 'll need to analyze all of this. Subsequently, the design lifespan, long-lasting structures, and harsh environments are more likely to be affected. Therefore, cathodic prevention is justified, meaning I'll apply it even before construction so that we can prevent this corrosion. Next, the corrosiveness of the location, then C4 or higher, NBR ISO 9223 or class 3 and 4, NBR611.

[00:14:38]So, when we have a level of aggression, as I mentioned earlier, a very high level of aggression, we have a much greater probability of having any kind of problem, right?

[00:14:51]So, we can also do this kind of prevention and keep a record of past events. So, if I have experience with similar projects in the region, I know that there is proximity to the sea, I know that there are saline soils there, the CO2 is high, and the electric traction system is also high. So I'll also apply cathodic protection. Beauty? So far, everyone's with me, OK?

[00:15:17]Excuse my voice, I got sick, I caught it from my little one. But continuing on, Marília, when is cathodic protection indicated?

[00:15:26]Do you remember the difference? Protection and prevention. We were talking about prevention, let's talk now about Catholic protection, when is it always indicated? So, the standard defines six situations in which the installation must be considered; at least one must be present to justify the system. So here we have item one, which is new structures existing in regions with chlorides C4 or higher, class TR and 4. This includes coastal works, bridges over the sea, and port terminals. The next one we have here is rehabilitation of structures with corrosion or internal construction projects. So, insufficient cover, low- quality concrete, I'm rehabilitating, in other words, that structure of mine already has a problem and I'm going to rehabilitate that structure with corrosion. It also applies. What else? Well, we have localized rehabilitation here to prevent corrosion from the incipient, draining effect. We explained the drain effect in the last class, okay? So it's also important for us to have analysis of structures influenced by electrical traction leakage current or neighboring PCs, other structures with active corrosion or probability of corrosion, and specialist analysis. So all these situations are situations that the standard also brings here for you.

[00:16:51]I even brought the item from the standard, okay? And she talks about it. Good practice. Always document that a given situation regarding item X justifies its application. This justification should be included in the project's descriptive report, okay? So, that's a summary of the key concepts for us to delve into sizing here, which is what I want to discuss with you. So, passive layering and depassivation, we've already talked about that. We've already talked about the thinning effect. Galvanic system versus impressed current. Here I'm going to focus a lot on the galvanic system because impressed current is a much more complex system, and it's not so common for us to have a diagnosis before specification, right? Beauty? So, in order for us to do this, I told you that we might have a potential for corrosion. So, if we have a corrosion potential, we need to understand how we measure that corrosion potential and resistivity, which are distinct things, okay? Therefore, corrosion potential is different from resistivity. But before talking about corrosion potential, resistivity, and all that, I need to at least give you a brief overview of the PB diagram. What is it, right? It's applied to corrosion, right, of the reinforcement bars there, corrosion, uh, the effects of what it is. And I 'll explain this diagram a little more to you, okay? It is also called the potential versus pH diagram. It is a pH versus e diagram. It has several names, but it's the Porbex diagram. Porbex, right? It's a thermodynamic map, as you can see, that shows three zones, and I'm going to explain each one of them. So, pay attention because this isn't difficult, okay? You will, if you leave here understanding this diagram, because so far we've only done a summary of the last lesson. If you leave here understanding this diagram, then this lesson already makes sense, okay? It's a thermodynamic map, as I said, that answers a fundamental question.

[00:18:53]Marília, what is the fundamental question that this diagram will answer? Given the pH, here's the question. Given the pH of the medium and the electrochemical potential of the metal, will the steel corrode, passivate, or is it immune? That's basically what this diagram will answer, okay? And how is he going to respond to that? This diagram was proposed in 1974, right? Well, regarding the 25ºC water-bar iron system, which was proposed a long time ago—I wasn't even born yet—it has become an essential tool for us to understand how reinforcement corrosion works. And that's what I want to bring to you, okay? We have two main axes, so we 'll have two variables. If we have a diagram with two axes, we necessarily have two variables, right, that will govern the behavior of the iron. Basically, that's it. So, we have here, folks, a horizontal axis which is the pH. What is pH?

[00:20:06]We also talked last time about a measure of acidity or alkalinity that we have of the electrolyte in the pores of the concrete. We talked about this in the last class as well. And we have the vertical axis.

[00:20:18]So we have the horizontal axis, which represents pH, and we have a vertical axis, which represents the electrochemical potential of the steel relative to the reference electrode.

[00:20:29]Pay attention here, okay? Normally, I'll tell you which electrodes are used, but normally this electrode is always saturated, and there are some electrodes that we typically use. Well, by combining these two pieces of information, we'll define three zones in which the steel can be operating.

[00:20:48]We have the first zone here, which is this orangey zone you're seeing, which is the passivation zone, right? Uh, not the orange one, sorry, the green one is the passivation zone.

[00:21:03]So, this passivation zone that you have here is when the pH is elevated above 11.5, look, we can see here when the pH is elevated and the potential is in an intermediate range.

[00:21:18]This is the passivation zone, meaning there is no corrosion, right? PH, he's even done that, and then he continues. So its potential will be in an intermediate range. Steel spontaneously forms a protective layer of oxides called a passivating film, which, as I mentioned, is what protects reinforced concrete from acid. Remember when we talked about this? Well, this layer is transparent, obviously, right? So we ca n't see it there, but it also has very high omic resistance.

[00:21:52]So it doesn't completely prevent corrosion, but it reduces the rate, and the low values ​​that the metal can exhibit remain unchanged. So basically, this first zone we're talking about is the passivation zone, the zone that's in good condition, okay?

[00:22:08]Okay, there's no corrosion, the area is just good. Then we have a corrosion zone, which is this part here, the little orange one I told you about, okay?

[00:22:17]So, when the pH drops or the corrosion potential rises beyond the passive zone, the thermodynamic conditions allow for the active dissolution of iron, okay? And then there will be rust formation, volumetric expansion, cracks, chipping, all of that. Then the steel will destroy itself.

[00:22:43]One minute. And then we have the third zone, which is the immunity zone, which is this little purple zone here that I'm showing you. So, when the potential is sufficiently negative, the iron becomes thermodynamically stable. at any pH, whether acidic, neutral, or whatever. Why? Because for that to happen, we're going to need those two factors, the two variables we talked about. So, the dissolution of the metal is thermodynamically impossible when we're talking about this, right? This is the zone where we'll take our steel when we start applying cathodic protection; this is where we'll leave our steel. So, in cathodic protection, we go to the immunity zone. Did you understand? I was very fast. Are you guys understanding? Yes or no? Comment below, Marília. I understand.

[00:23:37]Marília is moving very fast. Explain it to me again. Did you understand? I explained the three zones to you here. Just leave a comment below letting me know if I should follow you or not? You all understand, right? If I went too fast, let me know. Okay, then. We have three zones here in our diagram. So, Maril, what do we need to understand?

[00:23:59]Why? Because we need to understand where we are and where we want to be. I'll give you an example now, which is these little balls that I put here for you, okay?

[00:24:08]So, uh, I want you to observe these points marked here. We have point A, point B, and point C, right?

[00:24:17]It's like the deterioration and recovery of a reinforced concrete structure. In other words, I'm having a problem and I'm going to recover it according to standard 1727.

[00:24:30]OK? You understand, right? Yes, I understand.

[00:24:34]Okay, then everything's fine. I'll keep going from here. So it's like the whole process that we go through.

[00:24:41]So deterioration will happen, we'll start doing the tests, and we'll recover this concrete cabinet structure. So this point A here is the healthy condition. So the pH of the concrete is between 12 and 13. So we can see here, at point A, the concrete is between 12 and 13. The natural potential of the steel is around -2 V, -0.2 V there, more or less, right? So it's between -0.4 and 0.0.

[00:25:11]So we're in there. And the armor is well within the passivation zone, which is the zone we talked about, the first zone we talked about. As long as the pH remains high, we won't have corrosion. Yes or no? But we saw that what depassivation does is lower the pH of the concrete. What are you all going to do about this? Remember last class? CO2, that is, if I don't have protected concrete, CO2 will enter the pores of the concrete, because concrete is porous, right? Pay attention, this isn't difficult.

[00:25:44]CO2 will enter the pores of the concrete and corrosion will occur. So, what do I need to do with both of them? Either way, I'll continue keeping my pH elevated there, right? Or we're going to have some problem with corrosion of the reinforcement bars. So, the armor will be well inside. Beauty?

[00:26:03]When we move on to point B, which is this reddish point, it's a critical condition because carbonation has started to occur. This is exactly the penetration of CO2 that I mentioned to you, which will react with the calcium hydroxides present in the concrete and form calcium carbonate, okay? Then it will reduce the pH to 8.9 there. So it's between 7 and 10. Let's suppose it's eight, right, the pH of the concrete. Or we could also have an action of chloride, okay? But let's just talk about the carbonation part, okay? Therefore, the potential may drop or the pH may decrease. We have these two factors. Either movement that crosses that boundary, into the corrosion zone, will be very damaging, since at point B, the reinforcement will actively rust there, let's say. So, what do we have to do? We have to put it at point C, which is the next point we're going to talk about now, which is the restoration, that is, I've already restored it, it's already out of the zone of power or not, in the spotlight, right, of being able or not to go to the corrosion zone. And I restored it. How do you do this restoration? Today we're discussing cathodic protection, which is the new standard we're introducing to you, ISO 1727. So, how does it work? We're going to install sacrificial anodes, as I mentioned before, or we're going to use impressed current, but here we're going to focus specifically on the placement of sacrificial anodes. And then we'll be able to get this back into the immunity zone.

[00:27:54]Hey everyone! So, we're going to do this here, see? We're going to do this so that we don't have any problems like this, okay? Everything's great here, right?

[00:28:07]OK? Awesome! So, by doing this, we begin to understand. Understanding this, we start to... oh, Marilha, so now I understand. Now tell me this, what does this have to do with corrosion potential? In the diagnostic practice, as I even included in the slide for you, measuring the corrosion potential of the reinforcement with a surface reference electrode and estimating the pH of the concrete cover, right? Then we can use the model to shape the reinforcement from the diagram and infer its condition. What condition is my armor in today? So we can measure the potential, by having this knowledge. So, how do I measure potential? I'll tell you all about it here as well. So, by measuring the potential, having this knowledge, I can put it inside this diagram here, OK? Right? Beauty. Come on, come on. Can I go deeper? I'll go deeper. And that's where the difference lies between concrete resistivity testing and corrosion potential. Marília, what is the difference between the two? Let's go.

[00:29:17]Let's start with the concrete resistivity test, which I'll explain to you. He assesses the quality and compassion of the material.

[00:29:29]So we see if the concrete has difficulty allowing CO2, or whatever pollutants, to enter, or not. So, we're going to indirectly measure the risk of corrosion.

[00:29:45]So, the corrosion potential is a completely different method, because it's an electrochemical method that allows us to verify whether the steel reinforcement is already undergoing active corrosion at the time of the test or not. So, they are different exercises, but the two exercises are complementary, and it's very important that we have both in our practice, right? Because both tests will often be used together, right, to diagnose the health of structures, electrical resistivity, and everything else. OK? Let's continue here.

[00:30:24]Okay, let me move the slide forward here, Adriana. I'm trying to process it, Maria.

[00:30:29]Okay, there's a lot of content, but you can pause here later, okay?

[00:30:33]So, the electrical resistivity of the concrete, which we will measure, will indicate the resistance of the concrete to the passage of ionic current. The lower the resistivity, the greater the ionic mobility and the greater the corrosive activity. In other words, the lower the resistivity, the greater the likelihood of corrosion, right? It is also the fundamental input data for sizing the cathodic protection system. And here I've brought exactly what we have in relation to resistivity, the numbers. So, if we have a resistivity greater than 200, which is very low, with creatinine, atmospheric corrosion, from 100 to 200, the probability of corrosion is low. From 50 to 100, moderate; from 10 to 50, high; and less than 10, very high, concrete, it's saturated, intense corrosion. In other words, the lower the resistivity, the greater the corrosive activity. They are inversely proportional.

[00:31:46]Okay, everyone, are you understanding this?

[00:31:50]Julio works on an oil production platform. We use impressed current cathodic protection for hull protection. Other vessels use sacrificial anodes, usually made of zinc. Look, that's what we're talking about here. Very good. How is the test performed to determine resistivity? That's what I'm going to show you now, doctor. We have some tests, right? I've brought the Un method here for you, which involves placing four electrodes. So, this is the most commonly used method in the field, where a low-frequency current is injected between the external electrodes, and the potential difference between the internal electrodes is measured. Here's the formula for you, and here's an example of how we can do it, OK?

[00:32:40]So this is how we measure resistivity. Marília, and how are we going to measure the corrosion potential?

[00:32:46]Therefore, this potential for corrosion is even easier, which is why I always recommend to my students that they have this equipment to prepare technical reports and everything else, because we can obtain a much more precise diagnosis. So, what do we need to have a potential measuring device? It's super cheap, okay guys? High impedance voltmeter.

[00:33:07]So, we're going to have a multimeter there, it's a requirement of the standard, all of this is in accordance with the standard, okay?

[00:33:14]Reference electrode, so we'll have a saturated electrode there for aerial and buried structures, and we'll also have another type of electrode for submerged structures, in contact with the reinforcement. So we'll need a stainless steel pin or an electrical cable previously connected to the reinforcement and in contact with the concrete. So, damp foam, a damp sponge, or conductive gel is used to ensure electrical contact between the handheld electrode and the surface, right? So what are the reference electrodes that we have? Marília, I also brought the reference electrodes here so you all know which reference electrodes we can use. for this potential corrosion test. And we also have the interpretation of potentials. So, according to the standard, right? This standard is an international standard that we can use before installing any cathodic protection system; the potentials indicate the current state of corrosion. The standard adopts the numerical magnitude technique as a reference for the saturated electrode. He even brought up the item from the standard as well. So we have the most positive result between 200 and less, indicating active corrosion. So we have passive armor, uncertain zone, and active corrosion, and each of them has its own probability of having corrosion or not, right? I also got all of this from the standard. So, before we start the sizing, I've brought something really cool for you: a field checklist. So, before the measurements, what do I need? The voltmeter is calibrated, the reference electrode is in good calibrated condition, the electrode solution has been verified, armature access points have been identified in the design, and the measurement loop is in place. What do we need to do next? So I brought this little checklist here for you, because here at the company we always have checklists, right? So I brought this checklist here for you all as well. Okay? And now, Marília, what are the types of years for galvanists? Which?

[00:35:18]How am I going to select the material?

[00:35:21]Because, okay, I need to determine the dimensions, but I also need to select the material. What materials are we going to use? What are the different types of anodes, and how does the selection process work? So, I've written this here for you all: the anode is the central component of the galvanic system. It is what generates the protective current when it oxidizes spontaneously. Choosing the wrong type is one of the most common mistakes on the field. Okay, then. What do we need to know? What are the types?

[00:35:49]So, we have zinc, which is the most commonly used, but we also have others. We have magnesium, we have aluminum, we have carbonic acid, okay? So, we normally use zinc the most, but we also have other electrochemical potentials that we can use as well, okay? And one very important thing: applying zinc directly to concrete doesn't work. So we need to have a mandatory activation mortar for the year of the embedded elements. Marília, what are the types of mortars?

[00:36:18]The regulation also brings this to you, okay?

[00:36:21]So, the year of disassembly and concrete work in the long term. They have to be supplied encapsulated with a special mortar, which I also mentioned at the beginning of our class; without it, the zinc undergoes the formation of basic zinc carbonate and stops working. So, it won't be useful for anything. So, here we have the type, electrical resistivity, pH, and quantity of the activator. So, these are the minimum requirements for us to have this mortar, and for this mortar to be part of these zones, okay?

[00:36:57]Here are the types of anodes. So, we have anodes for exposed structures, anodes for hidden structures, and for hidden surface structures, that is, surface-embedded structures. And I brought an example for each of you, just so we can go over it. Beauty? We've arrived where I wanted to be. Have you understood so far? Then you might ask: "Marília, okay, but to make this kind of protection, I need a dimensioning. For example, how am I going to know how many of these little anodes we're going to need for this protection without dimensioning?" Isn't it? We need a plan for this. And this standard is so comprehensive that it even includes instructions on how to size it correctly. And then you ask me, Maria, how am I going to size it correctly?

[00:37:46]I'll even share the standard here with you so we can explain it a little more, but before sharing it, I'll tell you the formulas that the standard provides. So, what does the formula, the standard, bring about? Here first, I'll pass this according to the standard, which is better. So, we have the following situation, pay attention here. Pay attention here now, because this is too good to be true. We have the following situation, okay?

[00:38:16]Let's suppose you have a reinforced concrete beam that belongs to the superstructure of a road bridge located in a coastal region, and it is exposed to the marine atmosphere, that is, it is an area with a very high degree of aggressiveness. Well, after the technical inspection, I'm reading the statement here, it was found that the reinforcement is already in an active corrosion process. Let me put the problem statement here for you. I'll share my screen here.

[00:38:55]Let's share the screen.

[00:39:04]Full screen.

[00:39:06]Oh, I'm going to share my entire screen with you all here. Here's the statement.

[00:39:10]Uh, a reinforced concrete beam belongs to the superstructure of a road bridge located in a coastal region. It is exposed to the marine atmosphere.

[00:39:20]Following the technical inspection, it was found that the reinforcement bars are already undergoing an active corrosion process. The electrochemical potential measured in these areas means that the corrosion process is already active.

[00:39:31]Remember that diagram we talked about, the one I explained to you? What zone is it in? Corrosion zone, right?

[00:39:39]Electrochemical potential measured on the reinforcement bars and complementary tests confirm corrosion of moderate intensity. To contain the progression of deterioration and extend the lifespan of the structure without the need to replace the beam, a cathodic protection system was installed using sacrificial zinc electroplating, in accordance with ABNT guidelines. So what do we need to do now? We need to put it into perspective. So, what is the purpose of this calculation? Design the galvanic cathodic protection system for the beam, determining the total impressed current, the required zinc mass, and the number of anodes. No, what are these things you haven't talked about yet? Relax, I promised you wouldn't get lost, so pay attention. In this standard, I'm bringing the standard to you. The standard already specifies the calculation steps. So, the first calculation step we have here is the total protection current demand.

[00:40:41]So, the first thing we need to do is determine the total protection current demand. Beautiful, Marille? What information will I need?

[00:40:48]Let's go. What does the rule say? She says she needs an S, right? What is the S? It is the surface area of ​​the steel reinforcement. Next, I'll need a J, which is the current density of steel without the coating.

[00:41:03]And I'll need a K, which is a slack factor. The only thing the standard doesn't tell us is this slack factor. So, the slack factor is kind of going to be based on feeling, right? Ah, it's 1.2, 1.3, it's the slack factor, it's the fear factor that we engineers call the fear factor. It's like this, man, I'm not 100% sure, so I'm going to put a margin of safety here to make sure the structure is really sturdy.

[00:41:31]So, let's go. Knowing this, he provides this input data. So, I have a total armature area of ​​180 m², and a current density of 0.012.

[00:41:45]and a slack factor of 1.2. What are we going to do now? We're going to multiply these little guys, right? So I'm going to need to tell you what S is right now. What is the S here? S is 180 m².

[00:42:01]So we're going to put it here, see?

[00:42:04]Let's calculate it together.

[00:42:09]What is the value here?

[00:42:16]180 times. So I took the area of ​​the armature multiplied by the current density, which is 0.02. So my J is 0.02.

[00:42:33]Sorry about the lyrics, guys.

[00:42:37]And we have a slack factor of 1.2. Cagarça factor here 1.2. We could put more, or less. The rule doesn't say. I even made a little table here that I think makes sense to use, but, you know, it will depend on each person. We don't have any set norms, okay, folks? It was just a little table I made here. So, a slack factor of 1.2 is 1.1 to 1.2, a project with precise field data, with a good database, and is the most common use. 1.3 to 1.5, incomplete field data, complex structure, very aggressive environment. I posted this here, but it hasn't been confirmed yet. I even asked some colleagues if we could use this or not, okay? But beautiful. So, we have this input data here. That's when we start to have our full protection chain. So, having this here, multiply it for me, folks.

[00:43:32]180 x 0.02 x 1.2. Multiply that for me. Let me see if you're here.

[00:43:40]Okay, fine. Go ahead, multiply that for me, and I'll get the result here, and I'll multiply it here so we can do it together.

[00:43:50]Let's go.

[00:43:54]Let's go. Okay. So, I'm going to delete the result of this one.

[00:44:05]Beauty?

[00:44:07]So, the first result gives 2 V50 92 amp. So, what do we have? It equals 2.660.

[00:44:25]We're going to get closer here, okay? It's not very pretty. We're going to get closer here. Beauty? After that, the standard itself states that we have a next step, which is the mass of anodes, which is shown here, the calculation of the mass of anodes. So, this step is going well, it's very didactic. Okay, so we completed the anode mass step. And why did we calculate all this, Marília?

[00:44:49]We need to put this into the second formula, which is what the second formula will ask for. So, what is the second formula?

[00:44:56]Well, 8760 times the lifespan of the anodes expressed in years times the value we just discovered divided by u, which is the utilization factor of the dimensional anodes, and times, and, oh, Marília, we have this U times, and we have... Here it is.

[00:45:19]So, we have here, the zinc utilization factor, which is 0.85. The question is already giving us trouble, isn't it? And the current carrying capacity of zinc is also giving us that information on the matter. So, we're just going to multiply this here, right? This is going to turn out the same. Let me get the values ​​here because otherwise it's going to look too bad. This will all come out the same; if we calculate it, it will equal 742 kg, right? So, we're going to have the calculation of the mass of the years. Ah, I have a nicer one, since I can't type here. Let me stop here so I can show you the prettiest one that's already been calculated.

[00:46:03]I made it really nice, okay? Beauty. I'll be back here, okay? So here, we're going to do uh 8760 times T times what we just found. So this calculation will remain as is. We've reached the total number of years. Part three, step three as required by the standard. What is step three of the standard?

[00:46:28]Definition of the type of mass, number of anodes and spacing. So we need to know what the spacing is, what type it is, and everything else. And to get to that point, it's M over MA. So, this is the total anodic mass expressed in kilograms that we just found. So we're going to put it up right away. Then it goes down onto the individual anodic mass. So let's go back here. So we're going to put the value we just found here and divide it by m. What does MA mean here? Let's put here that he has already given us the year of the chosen one. So, when we're going to do it, we need to know what type of year we're going to choose, according to the manufacturer's catalog. Oh, Marília, where's the manufacturer's catalog?

[00:47:16]Where can I get that? Here, Vector Corrosion is the manufacturer that, well, it seems like they have a manufacturer here in Brazil, but that Luiz I told you about, who's the head of the standard, he has the representation here in Brazil for this brand, which is a Canadian brand, it seems, something like that, I'm not sure exactly, okay? So here, look, there's a catalog for us to choose which year we're going to use, okay? Based on that, we'll have the individual mass of each anode, because having the total mass I need and the individual mass, I'll know what spacing I have. So we come here, to the number of anodes.

[00:48:01]So, if I have here and the number of anodes is going to be NM over MA, then I have 361 anodes, that is, I'm going to use 361 of these here, for example, units of this one, okay? If I choose this one, that makes 361 of these.

[00:48:19]And then we'll have the average spacing. If I have an area of ​​180 m², which he already gave me here, the total area of ​​the armor to protect 180 m², and I also have the number of anodes, we will have the spacing per anode, that is, one anode every 22 cm. Are you all understanding so far? Let me see your comments here. Are you understanding so far? Yes or no? Do you understand? Let me know if you're lost, if you understand. Great, okay? So, if it's great, it's because I understand.

[00:48:53]Beauty? Let's continue here. So far, I've determined the number of sacrificial anodes I'm going to use. I've already found out the spacing between each of these anodes. And now we're going to do a verification.

[00:49:08]Why? Up here we need to check the electrical resistance of the anode and in the middle of the concrete. And then the equation talks about that, look. The equation here talks about that. So, checking the current by ans, the formula is here too. So, what are we going to need? A is the final current supplied by the anodes, expressed in amperes. It is the potential for project protection. It is the closed-circuit angle potential and the electrical contact resistance. So, we're going to need to do that verification now.

[00:49:43]So, what are we going to have now? Okay, here, from the data, we'll have the resistivity here. So here, the resistivity of the concrete is already given. Why?

[00:49:55]Because we've already measured it on the field. So, we've already seen the resistivity of concrete. We already measured it with that meter I showed you before. See how everything is falling into place now.

[00:50:05]Oh, according to this meter here, let me see if I can find it.

[00:50:13]Hmm. Here it is. According to this one, you 'll also have this material here, including what's shown here for you. This is material that I created to make available only to my students. Only. So, we've already measured the resistivity here, right? Beauty? So, we already have that number. Let's come back here.

[00:50:35]So, what are we going to see now?

[00:50:37]Where? Come back here. Come back here. What are we going to see now? We're going to do that verification. So, I started doing the check here and arrived at this value. Next, we'll move on to the next check here. What's the next check we have? Next check. Hey, where is it? Okay? Okay, let me see what the formula is.

[00:51:04]N times, oh, here it is. So, we're going to check the injected current. How are we going to arrive at that formula? First, we need to get our RA (student registration number). And then I'll find my RA, which will be 25 x 2 x 10. Marília, what does 2 x 10 mean?

[00:51:24]10 is L. L has already been given here too, look. Where? Here, look. L, dimensions of the year of the cylindrical session. So, we took the resistivity of the concrete, we took the dimensions of the cylindrical shape, the radius, length, and everything else. So, we have a radius of 1.5 and we also have another length. Uh, uh, the project's protection potential, the area's structure, we've already looked into that as well, and so on. Beauty? So here's where I started doing the calculation, okay? And then we put all the values ​​here. I found this.

[00:51:57]And we're going to check the current supplied, which is precisely the formula I showed you. We did all of this to arrive at the RA, which is this formula here, from the standard. So, we've arrived here at RA.

[00:52:10]How do we get to that RA, Marília? RA is the electrical resistance of the contact of the year, of the express. So, we're going to need to get to that RA.

[00:52:19]Here's the formula for RA, OK? So, we arrive at the formula for RA.

[00:52:26]We arrived at the RA and checked the current supplied. OK? Is that all, Marília? It's not over. Why? Because we need to check if the IF value is less than the total I value. Like this?

[00:52:41]Explain to me what this is. When we have this here, we always need to verify if the number of anodes calculated from the zinc mass is necessarily sufficient to provide the required protection current.

[00:52:56]Considering the electrical resistance imposed on the concrete. If the system is deemed insufficient, we need to resize it until that situation occurs, okay?

[00:53:09]So, we always need this ifja to be greater than or equal to the total I. What is it, again, let's remember here, what is this total I here? It's the total protection current. What does she always have to be, people? bigger. The total protection current must always be less than the current actually supplied by the anode array.

[00:53:40]So we always have to check if this current here and this current here. So this last step is crucial because even if the initial calculation based on current density indicates that a certain number of anodes will be sufficient, the high resistivity of the concrete may limit the actual current delivered, requiring an increase in the number of anodes until the system is approved. So here, when we went to check, where was it? Let's check it out.

[00:54:07]We went to get it here, look, the IF that we found, that is, the current that we found here, will be 1 1.315.

[00:54:19]And the other one we picked here, look, the total we found was 2.6, which means it's not correct, the sizing is insufficient. So, what can we do? Increase the number of anodes or use the anode with the greatest mass and area, okay? And then when we did the verification here, it was approved. What lesson can we learn from this? The verification calculation, step four, is crucial. The initial current density can indicate the number of anodes, but verification by RA density may require adjustments. In this case, the high resistivity of the concrete, which was 25, increased the RA and reduced the current supplied by each anode, requiring almost double the initially calculated values. Look, guys, how important sizing is. Can you see this, everyone? Look how important this sizing is. This is a lesson, folks, and it's going very deep, very deep, so you can understand the step-by-step process, okay? Ana Carolina is even asking here, " When are you going to open a new DAP course?" The DAP group, folks, it's opening soon, and let me tell you, we're even going to have a free course on profiting from building pathology, which will precede the opening of the pathology domain. So, sign up. On June 15th we will open the classes, and before the classes open we will hold an immersion course on profiting from building pathology. Beauty? I hope you enjoyed today's lesson and that you understood it. Do you have any questions, guys, that I didn't answer because I was just flipping through messages and didn't get a chance to see if you had any questions or anything like that?

[00:56:21]If you have any questions, ask them here, and I'll answer at least one, if there is one. Oh, great, thank you.

[00:56:28]I hope you all understood a little more about this rule, right?

[00:56:33]Then, Júlio said: "I haven't had the opportunity to read the standard yet. We know that the sacrificial anode will deteriorate over time. What is the lifespan of the mentioned pads? It depends on the calculation and the aggressive environment. We also have to calculate to see what the lifespan is. This calculation of the lifespan, right? To see this, we can determine, according to the resistivity of the concrete, the pH of the concrete, and we can verify how long it will last. Okay?

[00:57:04]Did you understand, everyone? I think it was a super in-depth lesson where we did a dimensioning together. I think that's the best part, okay? And we need to study the standard, we need to analyze the standard, because this is a very complete standard, that we can study, that we can analyze. The only thing I didn't find in the standard itself was the issue of the safety factor that I mentioned to you, the safety factor, right? But otherwise, it's very well explained there, right? So there's nothing else to worry about." There are significant difficulties for us to see. If you take this lesson here, the previous lesson, and this lesson, and look at the standard over there, you'll see that it's a standard that we can apply to real life, okay?

[00:57:52]Francisco de Quadros, have you already executed and monitored these services? What difficulties did you notice? Well, the main difficulty we have is in the dimensioning.

[00:58:03]If we do a good dimensioning, if we have a good project, we won't have any difficulties. Why? Because the material will arrive, it's easy to install, we 'll basically do the same repair there. And the difficulty is more in the project itself than in the execution. Okay?

[00:58:22]That's it, everyone. Any more questions?

[00:58:25]Anything you're unsure about? Yes or no?

[00:58:30]OK. Great. So, I hope you enjoyed it. If you have any more questions, anything, I'm here to answer them. A kiss, bye, bye, and see you in the next lesson. M.