All right, I think that's pretty good, so we'll get started here. Good morning to the West Coast and good afternoon to those out east. Welcome back again to the Post-Tensioning Institute's monthly webinar for July. For any of you who have been to this before, you guys all know this webinar happens every month on the second Wednesday of the month at the same exact time throughout the year. It's a free webinar and you do get a PDH credit for it. So this month's topic is the evaluation and repair of existing post-tension concrete structures. I'm going to talk about that a little bit more here in a second, but before we do, I'll introduce myself. My name's Kyle Boyd. I'm the moderator for today's session. I've been the moderator for all the sessions so far. I'm also the chair of the Education Committee, EDC 130, for the Post-Tensioning Institute. That's the committee which sponsors this monthly webinar, and we're really in charge of trying to get the technical content out to everybody in the professional world there. So with today's topic, we're going into repair of existing structures, which is different from the design and the bridges that we've talked about previously. And I think anyone who's ever dived into this topic knows it can almost be a little bit more of an art than it is an exact science, because each building, each situation, each deterioration that you're working with, it's a snowflake. So this is a topic that I have a lot of interest in. It's one that I've spent a lot of time kind of diving into on unique situations that I've come across in my career, and pretty excited for us to be talking about today, and then also for PTI to be releasing a new document. Scott's going to be talking about that here as well. So before we dive in, we always have to go through those first few slides, and the first one is the continuing education aspect of today's presentation. RCEP is the agency that we use for continuing education. If you registered for today's webinar, and stay on for the entire time, you will get that one hour continuing credit for it. RCEP still does not have a great way yet for us to do group settings for if everybody's in a conference room. So on those, we recommend everybody individually registers, plays it on their computer, and then everybody can go into the conference room and watch there, and that way you can get the credit itself from that approach. But you do get that credit is sent out at the very end, and once again, it's through this RCEP program that you get there. We have a copyright material slide that we have to go through. All this says is, please don't copyright, plagiarize any of the material you see here. If you do want to see any of the material, we do give contact information at the end of the presentation. You can reach out to us, and we can get you what you need on there. Now, a couple just basic webinar protocol things I've already talked about, you know, being on for the entire time, you'll get that one hour PDA credit. Usually that's attendee. You are muted. Your cameras are off during this, so we can't hear you. We can't see you. Therefore, if you do have a question, you have to ask it via the Q&A feature that's on there. That Q&A feature will then pop up on my end. I'll be able to see the questions. If they're a good question that's a very explicit, direct question, I'll be able to ask that question at the end. Usually we have time for a few questions, and questions that don't get answered, there's also contact information that you can reach out, and we'll be happy to answer those questions. If for whatever reason you do have to step away from the webinar today, or one of your colleagues had to miss it, we do have all these listed on our website. You can go and watch them. There's a quiz at the end, and you do get that same PDH credit on there. So if you have to step away, or you missed it, good news is you can still get the credit on there. So with that, we can kind of jump into introducing our presenter today. You know, each month I feel like we've had really strong presenters, all of whom have been industry leaders, and real thought provokers within the Post-Tensioning Institute. And today's presenter is no different. It's Mr. Scott Greenhouse. He's from the Structural Group, and it's a very technical and specialized group, and one of the focuses is on PT design, repair, rehab, strengthening, all those, you know, uniqueness that we're going to talk about today. He's very senior. He's got over 32 years of experience within this topic itself. And then within the Post-Tensioning Institute, he's actually a legend of PTI, and what that means for those that aren't within PTI is that's really our Hall of Fame. So he's been inducted into our Hall of Fame. He's been a past president of PTI, and more notably, he is the chair of the committee that is responsible for repair, rehabilitation, and strengthening. And so Scott, you know, with all your experience at this point, I'm really going to turn it to you to talk about DC80, the documents you guys are presenting, and all the technical information with your 32 years of experience. Okay. Well, thank you, Kyle. I appreciate it. It's actually more like 40-plus years now, but who's counting? Happy to be here today to describe to you the Guide for the Evaluation and Repair of Unbonded Post-Tension Concrete Structures. What you see here on the screen is the very extremely new, soon-to-be-published guide, and what we're going to describe today is give you an overview of the contents of this guide, and I believe the guide will be available in the PTI bookstore next week. So look out for this guide. It's got a lot of great information, and what I'm going to describe today is just the highlights of the guide. So we're going to go over a few just basics on the PT systems that are historic PT systems, and then we'll dive right into the evaluation process and the repair process, and again, all these things I'm describing now are described in detail in the DC80.3 guide. So when we look at the historic systems, we're looking at the prestressing steel, that is the main PT component, along with the anchorages, whether it's a high-strength seven-wire strand. The current systems have been for quite some time, 270 KSI, but at the beginning there was 250 KSI systems, primarily half-inch diameter for unbonded PT, and we'll also be talking about buttonhead wire systems, which are designed, of course, with ASTM A421. They are 240 KSI systems, and they're quarter-inch wires with a field cold-torn buttonhead. Now these PT systems have evolved over quite some time to the systems that you might be aware of today, but back at the beginning of the PT systems, back in 1950s, there were systems such as we see on the left, which are buttonhead wire systems that are in paper sheathing. There's going to be things that we're going to describe about the paper sheathing and those type of systems, which made them particularly susceptible to corrosion. In the 60s, we went to single monostrand-type systems, very similar to the systems that we are aware of currently. We'll talk about the sheathing and some of the issues with those particular systems. In the 70s, we moved to extruded plastic sheathing, which is a much tighter-fitting sheathing around the prestressing steel. And in the 1980s, we started to see encapsulated tendon systems as we became more aware of the issues that could happen with corrosion with post-tensioning systems, and that has evolved into the encapsulated tendon systems that we're all aware of today. We talked about the sheathing of these systems, and this is important to understand when we're looking at the investigation and repair of the existing unbonded monostrand systems. So those paper-wrapped systems, whether they were the wire, individually wire systems, or monostrand systems, were wrapped in a kraft paper, and they had a lubricating grease, but that grease was simply there to allow the prestressing steel to slide within the sheathing, within the concrete, during stressing. And had very few anti-corrosion-inhibiting properties to it. So that was, you could imagine paper in concrete, that certainly presented a risk of deterioration should water and other deteriorating materials be able to access the prestressing steel. As monostrand systems became more in favor, and greater protection was required, the strand was pushed through a solid tube, as shown in the center left, or a heat-sealed tube, which is wound around the prestressing steel, encapsulates the grease around the prestressing steel, and it's heat-sealed. It's also called a cigarette wrap system. Both the heat-sealed and the push-through system do have a relatively large annular space around the prestressing steel, and that annular space provides an opportunity for water and other contaminants to get to the prestressing steel. And then the more current extruded HDPE systems are very tightly wound to the prestressing steel with grease, and they are much more durable than the systems that were used previously. So let's get into the evaluation of the unbonded post-tension concrete structures. And what we describe in our document is what the evaluation process looks like. And as an evaluator, you can go to any level of detail as described in DC 80.3, from looking at the history of the structure, we want to know about what that looks like. We could look at documents, we could look at service reviews, we could talk to people there. Once we get an idea of what we're dealing with with that particular structure, we'll enter into a field investigation, where we'll look at things visually, we'll do non-destructive evaluations, and we'll do some limited exploratory evaluations. We'll take samples from the structure, and we'll do a laboratory investigation on the system. And I'm going to go over this a number of times, these post-tension, we call it post-tension structures because it's not just the post-tensioning system, the post-tensioning system encapsulated in the concrete structure with mild reinforcing steel. And so we have to look at all the constituents of the structure, so we can get a better understanding of what the situation is. And once we gain the information from all these investigations, the structural engineer will do typically a structural analysis to determine what the load carrying capacity of the structure has been impacted in any way, and a report for the owner and others in terms of what the findings are of the evaluation process. So we start with looking at the history of the structure, certainly age, as we all age, as structures age, that we have a little bit of deterioration that occurs. And depending on where the structure is located, the weather conditions, the exposure conditions, the amount of deterioration could be greater. The type of PT systems that we just described earlier is important to know if we can tell that from either looking at the structure or looking at the drawings and the documents. And that will help us to get a good start on our design of our evaluation process. So if there are drawings available, some structures have drawings, some structures you have no drawings and you're just flying blind. But if you have architectural drawings, structural drawings, maybe if you're lucky, PT shop drawings which will tell you what type of system, what kind of forces were initially imparted into the structure. There might be stressing records. Some of these older structures, these structures are getting to be 40, 50, 60 years old now. There might be previous investigations or reports that were done on the structure. So those could provide a wealth of information and can streamline the current evaluation process. Structures of these ages might have loading or use changes over their history. So we want to know about that. And certainly we want to do some interviewing with the owners and the maintenance people who know the structure, live with it every day, know where the problems are, what kind of issues, is there a leakage in the garage, tell us about what types of things are happening. So that's our start as we do our field, as we do our document reviews. And that helps us to really map out what our field investigation is going to look like. And there's lots of tools in our toolbox for these field investigations. So we're going to do a visual investigation, which has a list of items here that we're going to look at. We'll talk about that some more in detail. And then a list of instrument testing that's described in the DC 80.3 document. Some or all of which may or may not be applicable to a particular structure, but there are a number of tools in our toolbox which will help us paint a picture of what the condition of the structure is. In my experience, there's no one particular instrument or testing methodology. It's usually a combination of different methodologies during our visual inspection and instrument testing and investigatory process that gives us a better idea of what's going on with a particular structure. Now we go into our field investigation, we want to start with a visual examination. So we're going to look at things like cracks and spalls, where water leakage might be happening. If we have extensive cracking in the structure, we would be concerned about that because post-tension structures are designed to have minimal amount of cracking. So that could indicate a loss of pre-stressing force within the structure. Grease stains on the soffits might tell us there's a breach in the sheathing system. If we have excessive deflections, that might also tell us that we have a lack of post-tensioning strength in the structure and other areas where there might be exposed tendons and areas that we're going to describe where there is a higher risk of damage to the post-tensioning system. We've certainly over the years have seen our fair share of damage that's been done to structures that have been repaired, modified, or retrofitted over their history. For a PT repair contractor, the core drilling mechanical contractors, they provide a lot of work. And you see some pictures here of structures where core drilling has occurred from the surface and certainly core drill is more than capable of cutting through a post-tensioning tendon. But we also can have damage that's done by mechanical electrical contractors and others that are fastening piping, plumbing, conduit to the soffit of slabs, which might impact a power actuated system, the post-tensioning system at its low point in the deviation. So certainly we want to look at areas where there have been penetrations. And certainly the most common issues that we face, the most that we're concerned about is corrosion of the PT system, whether it's a buttonhead wire system, which we see down in the bottom left, if it's the actual strand that's severely pitted, which we see in the upper left, we'll look at the anchorages and corrosion is not our friend. So we want to find out the best of our ability where corrosion is occurring and how ultimately we're going to be able to mitigate that corrosion. So where do I start? I've got this huge, massive structure. I don't know where to look. A lot of it's hidden. So we provide some areas that we call the vulnerable areas for PT tendons. Those are described here in this picture. So that's going to be any discontinuity, such as a crack, a construction joint, expansion joint, where water, moisture, contaminants can make their way into the structure. And structures that are particularly susceptible to corrosion are those that I described as the paper wrap systems or the push through heat seal, where there's ability for moisture to penetrate into the system or to damage that might've occurred during construction. All these things happen where moisture and other contaminants can get into the system. So those happen at construction joints, could be at a high point where there's lack of cover, the first low point of the tendon deviation away from an anchor, where if water does get into the anchorage, it's going to tend to pool at the low point, first low point in the interior span and expose slab edges that we see in structures and parking garages and balconies or areas where we're going to look for vulnerabilities of the post-tensioning system. Certainly the end anchors, back when they were not encapsulated, were particularly susceptible to water intrusion. The very last thing that's done on these post-tensioning jobs is to fill the grout pockets with some type of grout. The quality of the grout was often questionable. The workmanship, there was often a smooth grout pocket that the repair contractor or the new construction attempted to fill those voids against a smooth surface, which led to a poor bond. So what you might end up with is something you see on the left here, where the grout pockets obviously have signs of water and efflorescence leaking. And these older PT systems, where they were seating the wedges, they stripped the sheathing behind the anchorages so moisture can get back through a crack or some delamination on the edge, corroded the mild reinforcing steel, the backup bars, and also the pre-stressing steel right in the anchorage. We talked about expansion joints. Historically, as a repair contractor, we see a lot of nasty expansion joints. We chose a picture of a particularly nasty one here in a parking garage. And these are certainly areas where you want to take a close look at the structure. On the left-hand side, we see an expansion joint that has deteriorated. There was some repair that was done there. It's an armor-angled joint. And that repair has deteriorated, and the anchorage is exposed, and you can see heavy corrosion. So expansion joints, certainly an area we want to take a very close look at. We might also see a visual manifestation of a strand failing, which is an eruption through the slab. It could be through the bottom of the slab or the top of the slab that we could see in these pictures here. That could be caused by deterioration. It could be caused by a saw cutting or drilling or something that a contractor is doing. These are not that common. They are very interesting to see and very dramatic, but you don't see it that much. So if you have three quarters of an inch generally of cover or greater over the post-tensioning system, you will not generally see it break through the slab. Sometimes it'll come through the anchorage. You might've heard of strand flying across the street, and that has happened on occasion, but it is extremely rare. And the other thing that occurs is because the tendon is deviated within the slab. If there's any friction within the structure, will cause a broken strand to not break through. If there's corrosion by-products, that also creates frictions. So while you might not see that, a manifestation is shown here in this drawing. There could actually be tendon failures within the structure. So, and there's other areas that we've described in the DC 80.3 in terms of where to look visually, but this gives you an idea of what those visual areas we wanna look at. And as we described those areas of higher risk, then we move on to the non-destructive testing phase. And we're gonna describe a number of highlights from the document. These are just a few of them. There's more that are described. So it's up to you as the investigator to use the appropriate investigatory techniques. But in the repair and restoration field, this is one of our favorite. We give it the very scientific name of acoustic emission testing. So that's where we are taking a hammer or a chain and dragging it along a surface. And as maybe not sophisticated as this seems, this is a very accurate means of determining whether there is delaminations in the slab. Because what happens when reinforcing steel corrodes, it will expand the greater volume than its original mass, put a tensile force on the concrete, cause the concrete to crack and potentially create a plane of delamination. And when we strike it with a hammer, a brick hammer, like this technician is doing here, or a chain, we get a distinctive ringing sound, a hollow sound, which is different than when you knock the hammer against a solid surface. And then that could be marked. And that is indicative of a corrosion, a spalling or delamination that might be in the mild reinforcing steel and also might involve the prestressing steel as well. In terms of locating where the steel is in the structure, there's a variety of different ways we could do that. We could do that with a ground penetrating radar. GPR uses electromagnetic reflection to create subsurface images. And it's been shown to easily detect the location and depth of reinforcement. You can see some of the pictures here that the technicians can identify where reinforcing steel is, where post-tensioning steel is, or you could use a picometer, which many of you have seen on project sites in order to determine the location of where the reinforcing steel is or the post-tensioning steel. Because we need to know whether we do a further exploratory evaluation where the steel is in the structure. And these are some of the techniques that should be used when mechanical contractors and others are doing work within a post-tension slab. Another methodology that has been used, it's not that often used, but it is out there in the toolbox, is X-ray technology. And this gives a pretty accurate depiction of what the reinforcing steel looks like. You can see drawn on the structure surface here where the prestressing strand is. It's called cables. And this picture where the rebar is located. Using X-rays is a time-consuming and somewhat costly process. You do need two-sided access so you can get an image. And certainly there are safety considerations. You are using radiation to create the X-ray. So it might be required to evacuate a portion of a structure to do this type of investigation. So it's not used that often, but it certainly is a tool that's there and it can provide very accurate depiction of what the reinforcing steel system looks like within the structure. If we're looking for delaminations within a structure that you can't necessarily see on the surface, there's a number of techniques similar to the one here, impact echo, impulse response, where we would create some sort of a stress wave within the structure through an impactor that will travel through the concrete. And that's measured by software and sensor system. And if the impact wave travels completely through the structure, there's no discontinuity, void, honeycomb within the structure. But if there's a void delamination, then that time for travel is going to be reduced and that will be displayed to the operator. So we can look at structures and we could find where there are discontinuities, voids and honeycombs within the structure by using these techniques. And as we mentioned, we do have a system and within the post-tensioning is within the concrete system. And we, for our evaluative and the structural analysis process, may wanna know what the compressive strength of the concrete is. So we can extract samples. We can use a variety of different techniques such as a rebound hammer, which is shown here, a Windsor probe, pull-out testing, pulse velocity, variety of techniques to either get a qualitative test such as a rebound hammer or more accurate tests such as core and sampling and compressive tests. So we know what the compressive strength of the concrete is. We might have some idea of what it was planned to be by the drawings, but perhaps it could be much higher or in some cases lower than what was originally expected or specified. And that's important information to know as we move into the structural analysis phase. We could also do corrosion potential mapping, which is shown here on this drawing here. This corrosion potential mapping, which with a half-cell corrosion potential system, it provides a baseline for the threshold of corrosion activity within the structure. And the potential readings are taken by using a grid with a copper-copper sulfate reference electrode, which are shown here in the picture. And the half-cell potential technique indicates a likelihood of corrosion, which is shown in the bottom left, by measuring the electrical potential difference between the steel reinforcement and the portable reference electrode. You probably don't get a good solution for this for plastic sheath unbonded tendons, but if there's active corrosion going on in the mild reinforcing steel within the structure, this will give us a heat map, like you see on the right here, of where that corrosion might in actuality be happening. And because we have the laminations, those provide pathways for contaminants to get into the post-etching system. So we do wanna know what is the corrosion situation within the structure. And as we take the information that we have from our testing, we might move on to then our field investigation, which we call exploratory evaluation. This is where we're gonna get a little bit more into the structure itself. So the first thing we might do is just what we call a high point, low point inspection. This is described in our document. So we're gonna look at, if you might look at this picture and say, yeah, that's familiar. Those are the areas that we said are high risk. The areas that are cracks or high points, low points, first low point away from an anchorage, first low point away from an expansion joint. We might create an opening in the concrete that allows us to look at the post-tensioning system to remove the sheathing and directly visually inspect the condition of the pre-stressing steel. In our DC 80.3 document, we have provided a methodology for classifying the amount of strand corrosion that might be happening ranging from no corrosion at all to a severe pitting corrosion, which are shown in some of the drawings here. And we've defined as best that we can how those classifications will work based on the pit depth and the pit density. So if you're looking for a methodology of classifying the amount of corrosion, DC 80.3 provides that type of information for you. And if we want to look at some other methods of determining whether we have tension in the strap, there's a good old sort of semi-reliable screwdriver test, which again is not an overly sophisticated test. And it's sometimes been criticized as relying too heavily on the skill and strength of the operator. But what this involves is driving a flathead screwdriver with a hammer and attempting to pull apart or pry apart the individual wires of the seven wire strand. And if you could do that rather easily, you are generally have some sort of a strand failure within that particular post-tensioning tendon. So the attempt to create more consistency is shown on the bottom left here. That's called a slide hammer or calibrated hammer to provide a more consistent load into the pulling the wires apart. So this will give, it is a qualitative test. It will tell you, perhaps there's a wire breakage. It's still quite often used in the investigation phase. If there is corrosion on the pre-stressing steel away from this area, you might, or a failure, you might not be able to detect it using the screwdriver test because of the amount of friction that's built up within the pre-stressing steel strand. But it is a test that's used and it's just another tool in our toolbox to take a look at whether it might be under tension or not. Since that time, when we first started doing that, these tension testers have been developed and you can see those in use in this picture here. So section of concrete is removed. To provide a free length of cable, a load is applied through a device that hooks around the strand to deflect the cable. And that load is equivalent and the amount of deflection is equivalent to a force in the cable that is shown on a calibrated chart. So we can get a pretty accurate reading of whether there's tension in the cable or not. So this is a useful test to do in conjunction with a number of the other tests that we're doing. And because the anchors, particularly the live end anchors, are susceptible to corrosion being on the outside, generally often in the outside of the structure. So we wanna remove the grout. We wanna look at the condition of the strand tail, of the wedges, of the wedge cavity. We wanna take a look at, perhaps as shown on the left here, whether the grease cap was put in place properly or whether the tail was too long and it just destroyed the end of the grease cap. In the center section above the picture of the two anchorages is a intermediate anchorage. Obviously, we have to be very careful with removing concrete around the intermediate anchorages. But it is a place where we could see a lot of deterioration because they're generally gonna be a construction joint associated with that. Many oftentimes it's not sealed and water could get in and corrode the strand. As you can see, the corroded strand completely failed. And as we mentioned, we might need to take core sampling of the concrete to get an accurate reading of the constituents of the concrete and the strength of the concrete. And certainly we have to be careful and use the techniques we described for locating the steel before we take cores. And then we take that information and we move it on to the laboratory testing process. And so we wanna do laboratory tests on the various materials that make up the constituents of our structure. We do concrete testing, looking for chlorides to see if the chloride levels exceeded the strength of the concrete. We might wanna do a petrographic analysis where we assess the internal structure of the concrete and the integrity of the pace of the concrete, the air content, assess the water cement ratio. Might wanna look for carbonation. That's also a constituent of corrosion where calcium hydroxide and a cement paste mixes with carbon dioxide from the air. It forms calcium carbonate, which lowers the pH of the concrete and can cause corrosion of the mild reinforcing steel and the prestressing steel. And there's a number of tests that we can do on the post-tensioning components as well. We could do a tensile test to see if it meets the requirements. Perhaps it's a 95% of the minimum ultimate strength of the strand. We could do metallurgical tests to look at macroscopic and microscopic inspection of wedges and the steel surfaces and see if there's fractures in the wild, whether there's ductile fractures or brittle fractures. We could do hydrogen embrittlement testing to see if there's a brittle fracture potential. And that's through an FIB test. We could do energy dispersive spectrography where we're gonna determine what the constituents of the products, the actual materials that might be there. So we could detect whether there's a chloride ions or sulfites or some other corrosive material within the post-tensioning system or the grease. And the grease can be tested to see if it meets the PTI requirements. So this will give us more information about the condition of the post-tensioning system. And all this information can then be put into a structural analysis, in which case the structural engineer will look at the effect of the existing conditions on the load carrying capacity of the structure, whether there's estimating the loss of PT force, taking into consideration the cracks and spalls and deflections that we see, applying the appropriate codes and standards and engineering judgment, determine whether there's excess capacity for the original design. Maybe the structure needs to be short and loads restricted. So it's an important part of the process. It's taking all the information that we've gained from our investigation and putting it into a structural analysis. And ultimately then that ends up with an evaluation report, which goes through all the information that we see here. What was done? How was done? What are the results of the structural analysis? Are there concerns about the stability of the structure? What are the recommendations for repairs and the probable costs and those type of, and potential, what are some of the repair potentials that might be thought about during this evaluation process? So that gives us a sort of a brief overview of what's entailed in DC 80.3 of the evaluation process. And let's get a little bit now into the repair process. And this is again, described in detail within the document, where there's a lot of considerations in terms of how we look at the design. We're looking at the post-tensioning system, the concrete system, a lot of information that we've gleaned from the investigation phase. And we have several different approaches that we might take to repairs. You might say there might be no repair required. We found the system to be in pretty good shape. Or we might have some strands or some of the post-tensioning system that has deteriorated, but maybe it could be abandoned because we have excess capacity in the structure. But maybe there's a point at which we need to do repairs, either full length repairs or partial repairs to supplement the existing post-tension structure. Or we might have deterioration that has become so severe that a full structure needs to replace or sections of the structure need to replace. We've seen all those types of situations. And then perhaps we need to add extra strength to the structure or make up for a strength that has been lost. And that's when we get into the strengthening of structures and that can be done with post-tensioning as well. We're gonna hit that briefly today as well. So the important thing, and I want to stress this too, is when we're working with post-tension structures is to think about safety considerations. We are dealing with very high forces, tens of thousands of pounds of force. And so we have to really take into consideration the safety of the people performing the work, those inspecting the work, and of the general public. So our document describes in detail the expectations for written safety plans and the expectations for the contractors performing the work, their educational requirements and experience requirements. And certainly above all, in addition to safety of life and limb is the safety of the structure. The structural engineer will look at the condition of the structure and also needs to look at what happens to the structure during the repair process. Where are there areas that create potential for structural instability that's shown on some of these drawings on the right. And what have we learned through our structural analysis and the review process that says, these are the areas, these are the extensive repairs that we could do at one time, or perhaps we need to do more extensive shoring and support of the structure to ensure that it maintains a structural stability. We discuss how we should be talking about the safety of the structure as it turns to tensioning. The post-tensioning systems, those should be put right on the drawings that's as suggested here. Because tensioning, we're going to talk about this a little later of an existing structure is different than a new structure. So there's certainly certain safety considerations that are required. And absolutely removing concrete is a whole different ball game when we're dealing with post-tensioning. We want to use light impact hammers, whether it's a pneumatic hammer, 15 pound class or less, electric hammers. We want to stay away from certain zones where there are high compressive forces. That's kind of shown in the center picture here. We described that within the document because we don't want people to get hurt during this process. And the picture you see on the bottom left is a area where concrete was removed behind an anchor. The crew that was removing the concrete thought they were just dealing with corroded reinforcing steel, but they were actually looking at post-tensioning anchorages which failed explosively. And the anchorages shot out of the slab. And in this case, unfortunately, one of the workers was severely injured due to the explosive nature and the force release. So we want to be very careful around these areas. So we describe in detail how to take great care in the concrete removal and with the removal processes themselves, we'll refer to the ICRI, International Concrete Repair Institute guidelines for surface preparation and removal. I failed to mention that this is a joint document with ICRI. PTI and ICRI collaborated on this document. So the information regarding concrete repair is up to date. One cautionary note is, as we see on the bottom right here, that's with hydro demolition. We want to be very careful in using and probably trying to avoid the use of hydro demolition for post-tensioning systems because we could be driving high pressure water into the post-tensioning system. And as we get into the repair, there's a number of approaches that we could take for tendon repairs. Generally, if we're going to be repairing a tendon, there's some detensioning that might be required. So we have a couple of different methodologies here, a grinder or a saw, where a blade cuts a wire at a time until the other wires are overloaded and the tendon fails. And that has to be done, obviously, very, very carefully. A torch could be used similarly to a saw and the application of flame causes a local necking of the strand. Tension release is similar to the suddenness of a saw cutting but that's another methodology. Sometimes the wedges are burned out to detension the structure or in specialized cases, a custom-made detensioning ram, as we see on the right-hand picture here, could be utilized to detension a tendon, in this case, an external monostrand strengthening process. And if we want to mate an existing post-tensioning tendon to a new section of strand, there's a number of different splicing techniques that are described in the document. For monostrand, for button head wires, some involve utilizing a device like we see in the middle here. Some involve the ram. There's lots of different approaches and a lot of different tools that we could use when we splice tendons. A splice chuck is shown on the left. Combination system is shown in the upper right where we are working a monostrand system together with a button head wire system. This has become more common and can be engineered based on the number of wires in the system. A more common or the original methodology of splicing a button head wire is shown directly below that on the bottom right. That is a, what's commonly called in vernacular, a Y-splice and a jack is placed between these jacking plates and that way the load is imparted to the wires. And there's a device called center stressing anchors which we see on the left here that are also utilized to stress anchors from a center section when you don't have access to the anchorages. Lots of different ways to splice tendons. And in some cases, we might need to replace a tendon in its entirety. And what we see here is a couple of different projects where tendons have been replaced through a trenching mechanism where the concrete is removed and the strand is deviated as per the structural engineer's design. And we might abandon or remove the existing post-tensioning system. And in other cases, we might be able to pull out a strand with a winch or a jack from within its sheathing and push a new strand in or braze a new strand to an existing strand. And when we're pulling it out, we pull the new strand in. Or in some cases, we might use a smaller strand like a three-eighths inch diameter strand, just taking into consideration the lower effective force of a smaller strand. But there's certainly methodologies that have been developed for replacing tendons within structures. And when it comes to repairing anchorages, which we have to be able to do because that is certainly an area where we see a lot of deterioration, there are devices that are used to temporary lock off the tension in the structure. We see here some pictures of corroded anchorages. This might occur in the edge of a slab. This might occur in a balcony slab. And the lock off devices are put in place to hold the tension in this post-tensioning system, sort of inboard inside the structure, which allow us to cut or remove a section of deteriorated strand, add a splice coupler, and add a new encapsulated monostrand anchor in the exterior. As we mentioned, the tensioning is certainly a consideration. We have to look at very closely when these structures are originally stressed. There's a reduction in the prestressing force due to elastic shortening and friction, creep and shrinkage of the concrete. But when we have an existing structure, the creeping, shrinkage, elastic shortening has generally already occurred. So the jacking forces might be less in a repair than in an existing structure. And the structural engineer should take that in consideration and describe that to the contractor performing the work. We should be certainly considerate of the durability of our repairs. PTI specifies sheathing repairs, as we see here in this drawing, to ensure that we can re-establish the continuity of the sheathing on a repair where it's damaged or a section has been removed. There are devices that are available in the market, such as the one shown here, where a splice chuck is encapsulated within a HTPE plastic sheathing. And then the sheathing has waterproof tape. So we are attempting, in this case, to provide a completely continuous waterproof system. And again, when we are replacing anchorages, we want to replace them with the very latest water-resistant, waterproof, anchorage-encapsulated systems, such as the one shown here. We are going to be replacing the concrete. Again, we're going to refer back to our friends at ICRI for selecting methodologies for replacing concrete, whether we're pouring it, shooting it, forming it, pumping it. There's many methodologies that might be applicable for a particular project. So we want to refer to the ICRI manuals. And then an important final aspect, because a lot of deterioration we see, is due to poor consolidation or placement of the stressing pockets. Well, we want to make sure if we're repairing a structure that we do a good job replacing the stressing pockets. So we have to make sure the surface is roughened. We're cleaning it of bond-inhibiting materials. We're using a high-quality grout, as non-shrink as possible. And there's also been developed precast grout plugs, which you see here. They are, in essence, pre-shrunk concrete that are epoxied in place. The surface is roughened, and this provides a good opportunity to have a grout pocket filler, where there'll be a minimum amount of possibility for moisture intrusion. And we want to protect the concrete, ultimately, and any of the means that water is getting in, whether that's through cracks in joints, good expansion joint systems. When we're doing the repairs, we want to tool a joint around the perimeter and fill that with sealant, and then potentially put a membrane or a coating system. There's liquid-applied membranes. There's epoxy overlays. There's sheet-applied coatings. There's lots and lots of protective systems. So we're protecting not only the concrete structure and the mild-reinforcing steel, but we're protecting the post-tensioning system, most importantly, from further moisture ingress. So we do definitely talk about concrete protection systems. And finally, on the repair and investigative side, we could do acoustic monitoring of the system. These are systems that detect wire breaks in the structure. So sensors are placed onto the structure, generally piezoelectric devices that detect whether there's vibration caused by a wire breaking. That data is captured and differentiated, a wire break from other noise in the structure. It's transmitted digitally to a central processing unit. An alert can be issued to the structural engineer or the owner as to whether there is a wire break. So we just described the acoustic monitoring system. There's lots of applications and lots of new technologies regarding this. And finally, the last section that we have in our document talks about strengthening with post-tensioning systems. There's some major advantages with post-tensioning and external post-tension systems. It applies the active load directly into the structure. So it can supplement the existing capacity of that structure to really any degree. Now, you contrast this with other strengthening systems such as steel or concrete beams, concrete enlargement, FRP, wrapping. Those are passive systems. So unless there's jacking involved, the strengthened member will not mobilize the strengthening system without a deflection. So there are definitely benefits to using post-tensioning. We have to be careful, though, when we use post-tensioning for strengthening systems to make sure the capacity of the existing structure at the end anchorages can take the loads to prevent any cracking or crushing. There's lots of different approaches to external post-tensioning. Here's an external post-tensioning using monostrands for a precast double T. And here's an application of using post-tensioning with a concrete girder. The post-tensioning system has been added to the structure to increase its capacity. Center stressing anchors are shown in the center because there's not access to the anchorages, and then it's encased in concrete. So it's very, very flexible material for strengthening concrete structures. And finally, when we do external post-tensioning, we have to consider the fireproofing capabilities. It's often should be as what's specified for the original structure in terms of fire rating. There's fireproofing that can be placed, which we see here with some external monostrands processes. There are heat-resistive tendons available in the marketplace. You can see on the right here, which have multiple extrusions, but importantly include a intumescent fire retardant coating that's placed on the strand. So that was used in this structure here to provide the fire rating. So certainly when we do external PT, we have to have fireproofing considerations. And finally, when we complete the process, we should record what has happened during the structure evaluation, what's happened during the repair, where tendons have been repaired, removed, replaced. Create as-built drawings. As I mentioned, when we did the original investigation, we wanna look at other investigation repairs have been done. So if we can create a good history of what the investigation looked like and what the repairs look like, the owner of the structure, structural engineer will have a history that can be used in the future. So that's a sort of a quick overview of our document. And I will tell you, there's a lot more that's within the document. We covered it very fast, but this is just to give you a flavor. So if you're into repair and restoration work, then certainly we hope we can help you by you utilizing this new document. Awesome. Well, Scott, we've got quite a few questions here. Only time for a few of them, so I'm gonna just pick a couple for you. The first one has to do with re-threading a strand. So if you have a broken strand and extruded system and you're trying to re-thread a new one through, do you advise doing like a smaller diameter than welded to a bigger diameter? If you pull the bigger diameters, it's gonna be a lot easier to re-thread. If you pull the bigger diameters through, the original diameter, I should say, is there any issues with pulling that through? Well, in an extruded system, it could be quite difficult to remove the strand and pull a new strand in, has been done. Paper wrapped tendons are very difficult to remove fully. And it generally has to be removed in sections because the concrete just encapsulates the pre-stressing steel and just can't remove it. So yes, so when we pull through a new strand and we have raised an existing strand to the, a new strand to the existing strand and pulled that in. So you're pulling it out and pulling it in at the same time. Gotcha. Another question, and I know part of this is gonna have to deal with the grease caps and the encapsulation of everything, but is there a method that's preferred that minimizes for cutting tendon tails that is more susceptible to corrosion than others? Well, certainly there's tools that are available in the marketplace for cutting the tails, you know, to the right length. And you could find those in the, you know, there's certainly a number of PTI members who sell hydraulic cutting tools that will cut the strand tail to the right length. You know, and historically they were cut with a torch, which was not as accurate a cut. And what we've seen in many structures is when they attempt to fit the cap, the cap doesn't fit. So it's either the tail's too long or the cap doesn't seat properly. So yeah, so definitely you need to use the current technology that's out there to cut the tendon tails appropriately. All right, guys, we got a ton of questions coming in, really good questions. So you can see the information here and we're at the top of the hour, so we need to wrap things up. You can see the information here for reaching out to us. There's another slide for reaching out to PTI in general on there. The one question we're getting over and over again is will slides be made available? If you do wanna see slides at the very end, we do, like I said at the beginning, we do put this online. It's recorded, you can go watch it online anytime. We do not provide, however, individual PDFs of the PowerPoint just because of the free nature that we have in some directive within PTI itself. But you can watch the recording. This information is always available and is online so you can watch there. Coming up, we always show the next three webinars. As we say, it's always the second Wednesday of every month at the same exact time. Dual banded tendon layout for post-tension slabs is the next one coming up. It's a topic that's a one I personally really enjoy. I've spent a lot of time diving into and it's a huge progression for the post-tensioning industry as a whole within the building side of things. And that we're gonna have four different presenters from different backgrounds. One's academics, one's from PTI, one's real world practicing engineer, one's from software. So we're gonna get a pretty diverse, good conversation around doing dual banded layouts. Then we move away from buildings to alternative PT bar considerations and then we go to bridges in October. So those are the next three there on deck. Yeah, with that, like I said, we're out of time at the top minute past the hour now and we look forward to seeing everybody here on the second Wednesday in August. So talk to you guys later, have a good one.

Post-Tensioning Institute

Evaluation and Repair

Existing Structures

Post-Tension Concrete

Field Investigations

Non-Destructive Testing

Structural Analysis

Repair Techniques

Safety Considerations