false
Catalog
Webinar: Durable Bonded Post-Tensioning
Webinar: Durable Bonded Post-Tensioning
Webinar: Durable Bonded Post-Tensioning
Back to course
[Please upgrade your browser to play this video content]
Video Transcription
All right, guys, let's get this webinar going. So good morning to the West Coast and good afternoon to those out East again. Welcome back to the Post-Tensioning Institute's monthly webinar for October already. My name is Kyle Boyd, and I'm again the moderator for today's session. I'm also the chair of the Education Committee, EDC 130. And like we've said before, if this is a repeat time joining us, we are the committee that sponsors this monthly webinar. For those of you that this is your first time joining us, we do host this webinar every month at the same exact time. So the second Wednesday of every month at 1 o'clock Eastern, 10 o'clock Pacific time out there. As you can see, today's topics around durable bonded post-tensioning. So this is a material topic, kind of similar to what we talked about last month, which was a material topic. But this is one that's often used in bridges here. And we're excited to get into the bridge world a little bit. We've done a lot of building topics and we're really excited about doing bridges and materials this week. So it's material that's used often, but not always in the bridge world. Last month we did the material that was used in retaining type structures, rock and soil anchors. And then we'll talk about where we're going in the future months here, which is going to be slab on ground provisions, because we've gotten a lot of requests for those. Bridges is something, as we get feedback on every webinar, it's one that we continue to see requests for more and more bridge presentations. You guys asked for it, this is us trying to respond to that bridge topic and we're pretty excited to be able to do that. Before we get too far into anything, we do have to always go through those initial housekeeping slides at the very beginning. So the first one is the best one, which is everyone that's on here, you're getting a continuing education grant for free through RCEP. The only thing you have to do is you have to be on the webinar for the entire duration and then it'll be emailed to you at the end. I'll go over in a couple of slides what we'll do in case you have to drop off early. The next one's our copyright material slide. This is just one that's saying, you know, this is owned by the Post-Tension Institute. If you guys do want access to any of this information, just reach out to us afterwards and we can tell you what we can and can't provide. We'll give you all the contact information and it's just, you know, keeps the legal team happy by putting this slide in there. The next one being our webinar protocol. So you're all listening and you're all muted and cameras are off. So obviously that means we can't hear you, we can't see you. If you have questions, ask them through the Q&A feature and I'll be moderating those questions at the very end of the webinar there. So all you have to do is just write them in there. I can see them as you guys are asking them. We'll do our best to respond to as many as we can. If we can't, we'll give you guys the links or email addresses to where you can ask those questions there. I already talked about, you have to be on the webinar for the entire time to get that continuing education grant. That's for free. However, if you do have to drop off early or one of your colleagues missed the webinar, have no fear. You can go online and you can watch this that's recorded for free on PTI's website. So you go to the website, you go to our education side of things. We have all these webinars from all the months. You can go on, you can watch them. There's a quiz you have to take at the end, usually about 10 questions. After you answer those 10 questions, you'll get your free PDH. I know a lot of states, we're getting close to December and there's a lot of renewals coming up. For all you guys that are sweating, that's a way to start getting some of your credits there. All right. With that, I'm going to introduce today's speaker. So today's speaker, once again, we have a powerhouse presenter and it's Mr. Bob Swart. He's the Vice President at Structural Technologies and anyone in the industry obviously knows who Structural Technologies is. As you can see, based on what he has up here, he's got four years of experience in the design of new existing structures, implementing post-tensioning, especially in the bridge world. Once again, today's topic is a material one that's often, but not always used in bridges. He's very, very active in the professional community, especially ASPE, which is the American Segmental Bridge Institute, which co-does a lot of things with the Post-Tensioning Institute, ACI, and the Post-Tensioning Institute, PTI, obviously today's sponsor here. He was the past president of PTI. So you guys are getting a presentation from some of the old pop brass that we used to have. Currently, he's the chair. So he's the head of M50, which is Specs for Multi-Strand and Grounded Post-Tensioning. He's also a voting member of M10 and DC45, M's are material committees, D stands for our design committees that we have on there. So again, the material and design side for that. So with that, we really didn't have anybody more qualified than Bob who could be presenting on this topic today, and I'm going to hand it over to him and let him dive in for you. Okay. All right. Thank you, Kyle. Today, I'm going to talk about bonded post-tensioning and what the industry has done to improve the overall performance and durability of bonded post-tensioning. There have been some issues with bonded PT in the past, and I'm going to go through what those were, some of them, and then how the industry got together and what responses we orchestrated to help improve and address those issues. So one of the first jobs we encountered issues on was the Mid-Bay Bridge. This project is in Florida. They've had several projects like this where they've had some external bonded tendons that were grouted fail due to corrosion, and the reason for the failure was due to poor grouting practices and poor grouting materials. They also had some issues with their grout materials, as well as some of the details they used in their anchorage protection were not the best. So we'll talk about some of those and how we can correct those issues. Another project, another similar issue, this is the Verena Enon Project in Virginia where they had similar issues with poor grouting practices. They also had bleed water collecting at the anchorages that resulted in corrosion. In some of the cases, the voids were discovered and an attempt was made to re-grout those locations, and unfortunately, the grout they put back in place actually promoted corrosion. So that'll be one of the things you want to look at if you do find voids in tendons is to make sure that the material you're putting back into the tendons is compatible with the existing grout. We've also encountered partially grouted tendons where the grout, where the tendons basically weren't grouted or were just partially grouted, maybe during the grouting operation the equipment broke down, was never completely grouted. As we were investigating these issues, one of the things that we learned is that the way the grout flows through tendons is if you're injecting from this end, your grout will flow up to the high point, and then when it reaches the high point, then it rolls down to the bottom, and then it would back up, and when that happens, it could create a void in here. So we were finding a lot of voids at high points and issues with corrosion there, and then it would go up to the anchorage up here, and if there was any excess water or bleed, then it would collect at these high points as well. We also took a look at the materials themselves, and looking at the segregation of materials where the grout components separate, certainly bleed water is an issue with grouted tendons, the earlier grouted tendons that were done back in the 70s, 80s, and early 90s. What we discovered also is that the strand itself promotes the bleed water by wicking the water out of the grout and pulling it up to the top. That was another issue for some of the voids. There was poor training for some of the crews and lack of oversight of the grouting operation. In a lot of cases, the grouting operation is an afterthought. The crews go out there that really aren't highly trained in the grouting of the tendons. So this was another area that we identified as causing potential issues with grouted tendons. Also looking at the materials, some of the HDPE pipe that was used for external tendons wasn't appropriate and ended up having some splitting issues, either due to overpressurizing when it was grouting or just through environmental derivation, and then some of the repair methods that were used to correct those were not the best. We also saw some issues with incomplete grouting of anchorages. This could probably be due to bleed water collecting in the grout caps. Earlier systems that were done back in the 70s, 80s, early 90s had grout caps that fit on the face of the anchor head and didn't entirely encapsulate the anchor head. So they would remove those grout caps, and here you can see where the strand tails were left exposed due to bleed water when it was grouted. You also see that these tendons on the right, these anchors on the right are rather than expansion joints, so any kind of void that's in the anchor itself, if it's not fully protected and it rains, there's an opportunity for that moisture to recharge that cavity and promote the corrosion within the tendon. So as these issues began to appear in the 90s, the industry got together, and primarily through PTI and ASPE, and gathered stakeholders from owners, engineers, contractors, and suppliers, and we took a hard look at what the issues were, not just grouting issues, but entirely look at all aspects of the post-tensioning system, from the design of the components to the materials that were being used and specified to the equipment that was being employed to either inject or stress tendons to the details, not only for the installation but as protection as well, and the procedures and training and QC processes. We took a holistic view at these areas and came up with a strategy to address those, and those strategies came out as specifications, both the M50 specification for multi-strand and grouted post-tensioning, and then the M55 specification, which specifically deals with the grouting of post-tension structures. There's some other documents out there that are also very helpful, FHWA had a document prepared called Post-Tensioning Tendon Installation and Grouting Manual that was, I believe, written by John Corvin. It's a very good document, and there's some other documents that were done in Europe. The FIB bulletins 70 and 75 really address polymer duct post-tensioning systems for post-tensioning. One of the first things we took a look at is defining protection levels for the tendons, PL1, PL2, and PL3 were the three levels of protection. This follows pretty closely the same protection levels defined in Europe, where PL1 is the lowest level of protection, and this is going to be used in an environment where it's not a very aggressive environment, and there's multiple levels of corrosion protection provided by the structure itself. PL2 is probably most commonly used here in the U.S., where we provide the encapsulation of the strand in the plastic ducts, and then PL3 is our highest level of protection for the post-tensioning, and this would be electrically isolated tendons. I can talk a bit more about that shortly. The PTI document defines these. There's some other documents out there that can help designers determine which PL level they should be selecting for their project that we can provide in the future. So when we looked at the anchorages, one of the first things we took a look at is how the grout caps fit over the anchor head, as opposed to fitting on the face, and then specifying a non-metallic grout cap that stays permanently on the anchor and completely covers the anchor head. We also wanted to incorporate provisions to be able to inspect the anchorage behind the anchor head after it's been grouted to confirm that it has been fully grouted, that there is no voids behind the anchor head. We also specified in the PTI document that the bearing plate should be galvanized, and that the trumpet connection needs to be a mechanical connection to the bearing plate itself and the duct system as well. So here you see an example of a PL2 anchorage with a permanent grout cap. A lot of the grout accessories and fittings are designed to screw into the different ports. Up here in this little caption right here, this is an EIT tendon. It's essentially the same as a PL2 with the exception that we've added a non-metallic plate between the bearing plate and the anchor head to isolate the main tensile element, and then you have some wires that go out through a port that allows you to measure the resistance between the main tensile element, the strand, and the surrounding rebar and concrete to see if there's any breakdown in the encapsulation. We also looked at the duct systems, the earlier duct systems that were used primarily in the 70s, 80s, and 90s was a metal duct. It's a galvanized metal strip that's rolled into a duct shape. It's a spiral configuration typically, and then it's duct tape at the joints. This is a pretty standard duct that we would use in that time frame. I think some states still use metal ducts, and I think we still see metal ducts used in some splice gritter applications. In the late 90s, middle of the late 90s, we started looking at plastic ducts. The original plastic ducts we looked at had a sinusoidal profile similar to what you see here in the middle, and that worked okay, but it didn't have any longitudinal stiffness, so it was very difficult to profile correctly. The industry began to develop purpose-designed duct systems for post-tensioning, and these duct systems have corrugations at a certain spacing that are deep enough so that you have an interlock between the grout on the inside of the tendon and the surrounding concrete, but also allows some flexibility, but it's also fairly stiff, so you can't profile it. We also required that the ducts be capped so that when they're shipped to the job sites that there's not a chance for debris or animals or anything like that to crawl inside the tendons and then unintendedly be built into the structure. In these materials, the plastic duct can either be polypropylene or polyethylene. We've seen in colder climates that you might want to consider using polyethylene, but typically the systems we use here in the U.S. are polypropylene for our duct systems. We also looked at the couplers that are used to couple the plastic duct systems, and the intent there is that the coupler is not the weak point in the system. There are several different systems out there, different coupler designs, but they're all purpose-designed connections. They're not relying on duct tape to make the connection watertight. We've also integrated ports into these couplers so that you can have your grout vents or drain at your low points without having to cut a hole in the duct and tape on a saddle. A lot of the other features we've built into the system as it's been developed is easy, quick connects to the grouting hose when we're grouting and integration of the grout hose into the valves themselves. We also looked at segmental construction. For those of you that are familiar with precast segmental construction, this is where we would cast elements off-site, truck them to the site, and then glue them together. And across these joints, you have the potential for communication between ducts or ingressive water in service. So we've developed ductless couplers that go across these segmental joints, and they've been tested. There's a performance criteria within the PTI documents and FIB documents that defines the performance requirements to ensure that when these segments are glued together using these segmental duct couplers that we maintain the integrity of the encapsulation across these joints. We've also developed other types of duct coupler systems. This one is intended to be used with precast elements that can have variable width gaps between the elements, whether it's an inch gap or it could be 18 inches. This allows for the integrity of the duct system to be in place but gives the flexibility for different widths, closure pores, or joints between the segments. There's also quite a bit of testing that goes into these systems, and it's defined in the documents from anchorage load transfer tests, which basically defines the amount of load that you have to transfer into the surrounding concrete and what spiral size you need for your anchorage system to work. The anchorhead efficiency test really tests the wedge-strand anchorhead interaction to make sure that the wedges and the strand can achieve 95 percent of AUTs or MUTs in a testing lab. Depending if it's an unbonded system or a bonded system, if it's an unbonded system, you may also have to do some fatigue testing where you do a 500,000 cycle test followed by a 50-cycle test at varying stress ranges. The duct material, there's requirements on the duct material as far as UV resistance, and there's a whole barrage of performance tests that have to be done on the duct from abrasion resistance to impact resistance to indentation. What you see in the lower right is a test of a coupler to show that it's not going to kink as it's being profiled in the form. So here they've got a coupler at midpoint of the radius, and here at the top you can see they're going to drop a, what they call a tup, down through the duct and then pull it back up. And if it passes without hanging up, then it passes. So a lot of tests is done like this to ensure that the system is going to work correctly when it gets into the field. There's also pressure tests that we do with the grout, the duct and the grout caps to ensure that they'll withstand the grouting pressures. And we also want to make sure that we're going to be able to have good traceability of the materials so we can trace, you know, what material goes into what location of the structure. Whether it's strand or grout, we want to be able to trace all the materials as well. And this is defined in the PTI documents. And we are in the, PTI is in the process, and I think we're very close to launching our multi-strand system pre-qualification program. And the intent of this program is to be able to have a pre-qualified list of post-tensioning bonded systems that states and owners can look to that, and with assurance that these systems have been tested and are certified to meet the requirements of the PTI documentation and specs. So once that gets up and going, that will give an owner a place to go for that. Right now, all the states or a lot of states have their own individual qualification program that they have to maintain. So this would be an advantage to a state to be able to call on PTI's pre-qualified system list and with assurance that the systems that are listed have been tested thoroughly. We also took a hard look at the grout itself. This is obviously one of the issues that we identified in those earlier projects that I showed you. Typically back in the 80s and 90s, we were using just a cement type one, type two, and water with an admixture like interplast. And the crews that were doing it were maybe the laborers. And if the grout got a little hot or thick, then they would just add some more water during the process. That caused some problems. But we've now shifted away for the most part with the PTI document to a prepackaged grout. And we've arrived at this because there's a couple of things that go on with these grouts. One is the source of the cement has a big impact on how the grout performs. A type one cement from one supplier can vary widely from a type one cement from another in how it performs with the admixture. So by getting prepackaged grout from a specific vendor, then we know that they're pulling the cement and the admixtures from a consistent source so that the product should be very consistent when it gets to the job site and we're using it. And there's some very specific requirements as far as storage on site and that type of stuff that needs to be followed to make sure that the grout stays fresh. And recently, Florida has begun to use a flexible filler for their post-tension tendons. For the most part, there's a couple of cases where they might still use a grout for filling their tendons. But they've switched to this for a number of reasons. One is for corrosion protection, but also for the possibility of being able to remove and replace tendons in the future if there is ever a need to do that. This is a relatively new application for post-tensioning. This use of flexible fillers has been used in the past here in the U.S. on nuclear power plants. A lot of nuclear power plants that were built back in the 70s and 80s have flexible filled tendons so that they can pull a tendon out and inspect it. It's all part of their renewal certification program that they go through. But just like any material, there's going to be things we don't know that we're going to learn about. But it seems like it's meeting the needs for the Florida DOT. We also looked at equipment. The earlier grouting equipment that we used for post-tensioning was just a paddle mixer that didn't really impart a lot of energy into the grout. Basically, turn the grout slowly and it seemed to do the trick for cement and water grouts. But as we started going to these more pre-packaged grouts that are thixotropic, we needed to use a pumping system that put more energy into the grout so that we could get all the particles wetted correctly. Then we began to shift over to these colloidal mixers which put a lot of shear into the grout and do a better job of mixing it. We also have developed pumps for pumping the flexible filler. This typically shows up to the job site in heated drums or actually heated tankers trucks. When the flexible filler is melted, it's pretty much like a water. Then you can inject it into the tendons or you can use a pump like what we show up here in the middle. These are flexible filler pumps that we've had manufactured. The other thing that we've developed too is to address any kind of voids that are discovered in tendons is a method for being able to measure the volume of the void by pulling a vacuum. Then we can mix a grout and then we can inject that grout back into the tendon and measure the volume we're able to put back into the tendon to understand how full have we made this tendon. We also looked at a lot of the details for making sure the tendons get installed correctly. One of them is the location of vents and drains. Obviously you want to have your vents at your low points. We've called out for high point vents to be on either side of the high point to make sure any kind of trapped air is allowed to escape. There's a process of going back. You grout a tendon, you have to come back and burp the tendon to make sure you purged all that trapped air in there. There's some guidance in the document about where you should be installing vents and drains. We've also provided some details on how to protect the end of the anchorage. Right now the PL2 has a permanent plastic grout cap. If you have an anchor that's going to be exposed and you would pour it back with an epoxy grout and then that gets covered with elastomeric as well. We've done a lot to improve the details for protecting the anchorage at the ends. There's also some details that talk about how you address the grout vents that come out of the top of the slab to make sure that they're properly sealed as well. There's also some details in there about using Diablos for external tendons. In some cases we still do see steel deviation pipes at deviation points for external tendons. What this requires is for a pipe to be bent to a certain radius, then set into forms. In many cases these tendons are not just going straight up and down, they're actually at an angle going up to the diaphragm. You have to rotate this deviation pipe a certain amount to make sure it's lined up with the tendon anchorage at the diaphragm. If that's not done correctly, then you end up with a spall like you see here in the lower left. Or you could even end up with broken strands if the angle break is sufficient enough to do that. With a Diablo, what a Diablo is, is basically it's a void that's basically the shape of a bell of a trumpet, for lack of a better word. The angle break as it comes out of the Diablo needs to be larger than the angle that the tendon is actually going to see as it goes from the deviation point up to the diaphragm. This allows the tendon to basically follow its natural path from the low point up to the diaphragm. Another advantage is that the HDPE pipe just passes right through the Diablo and keeps on going, so there's not a need for a coupler such as this on either side of the diaphragm or the deviation block. We see this most of the times now on our projects. Occasionally, we still see steel pipe, but this is, in our opinion, is a superior solution for external tendons that are deviated. Another thing that the document addresses that we think is really important for communication, not only amongst the crew, but with the contractor, between the installer, the contractor, the system supplier, the inspectors, and the owners to have well-defined written procedures for the installation of the post-tensioning that addresses every aspect of the field work from receiving materials, handling materials, storage of materials, installation of materials, documentation that needs to be done during the installation, whether it's strain installation logs or stressing logs or grouting logs. Those are all part of the written procedure. These written procedures typically, at least ours, include a job hazard analysis. What are the hazards that the crews and the inspectors around them might face when doing this operation? There's also an environmental hazard analysis as well in case there's any potential contamination that could get into the environment. This is addressed in these work plans as well. So, these are a really good tool to communicate what we're going to be doing, when we're going to be doing it, and how we're going to be doing it. Training is also a really big improvement that's been made for bonded post-tensioning. Both PTI and ASBE have really stepped up and provided really top-shelf training for installers of post-tensioning with the PTI Level 1 and Level 2 for the installers or technicians, and then the ASBE grouting training. This has really gone a long way to really improve the overall quality of the installation of grouted post-tension tendons. The other thing that PTI has done also is they have implemented an inspector training program as well. We've seen in the past where a crew has gone through the PTI training and the ASBE training, but the inspector may not be familiar with the latest that we've learned. That instructs a crew that if something happens during a grouting operation that we need to flush a tendon. Well, we know from our experience now that flushing tendons is not a good practice. Not only does it blow holes through the grout that's in there and makes it into like a Swiss cheese, but it also traps a bunch of water in the tendon. Whenever you go back to grout the tendon, we're going to have to deal with that as well. So, I think it's great that we've got a training program for inspectors as well. That really helps to improve the overall quality of the post-tensioning once it's installed. As far as quality, I'll talk more about that. I think there's a couple things we can do in here. One is define the traceability requirements for post-tension materials. That's not on the list there, but that's one of the things we need. It's clearly defined in the PTI documents is the need to have clear defined traceability of all the materials that go into the post-tension tendon. So, if there's ever an issue identified, we can go back and identify where in the structure and which tendons are affected by whatever suspect materials are in there. Mock-ups are a great tool for indoctrinating new crew members, inspectors, contractors, everybody into the process, particularly with regards to grouting. Going through a grouting mock-up really helps get everybody on the same page as far as what's going to happen, where it's going to happen, when it's going to happen. Doing this with the contractor helps make sure we've got the source of the water figured out. All these things worked out ahead of time so it doesn't happen when we're up to actually doing production grouting. Also, installation logs, as I mentioned earlier, these would be in the work plans. I think it's important to document which pack of strain is put into which tendon. Grouting logs, when you're doing fluidity tests or mud balance tests, we want to document all that kind of information. If there's ever any doubt about what was done, then we can go back and reference this information. That rolls right into field testing as well. What you see here on the right, they're doing a flow cone test here. Behind it is a wet density measurement tool. Once you've stressed and grouted your tendon, there's also the post-grouting inspection where you go back and drill in through the inspection ports a certain number of anchorages to determine if there is any issues with voids behind the anchors or even some high points you can inspect. If there is, you have a strategy to repair those as well. How effective has this been? I think this graph really shows what the impact has been of these improvements to bonded post-tensioning. This is an excerpt from an article that was published in Aspire back in 2019. I think this was also presented at a couple of conferences as well. Bruce Osborne is one of our superintendents. Over his career, he's collected information on all the tendons he has inspected. Of those tendons that he's inspected, how many did he find voids? Tendons he's inspected, how many did he discover actual failures? You can see for bridges that were tendons that were installed and grouted in the 70s and 80s, there was a fair number of voids in these tendons. Also, there were some failures as well. As you go into the 90s, tendons that were installed in the 90s, you start to see an improvement in the quality of the grouting these tendons but there's still some tendons or some voids so they may be you know hold over from the old old way of doing things but if you look at the tendons that were installed in 2000 to 2009 of the 5,200 tendons that Bruce inspected he found five voids and no failures so to me that really demonstrates that you know the measures that have been put in place through the PTI documents as these training have really had the desired impact to improve the overall durability and quality of the post-tensioning installed there's also some other emerging technologies that are being looked at they haven't made them made their way into the into the codes yet but a couple of them are like inline density meters this this is a tool that's used in the oil and gas drilling industry where they need to make sure they understand the density of the the muds that they're injecting into the ground as they're drilling these wells so it's it's been around a long time I think there was some testing done recently by Andrea Shocker and some of her folks on different different tools that do this but that looks to me like a promising way of us being able to just attach this tool to the end of a grout plant or that at a discharge at the end of a tendon and measure the density of the grout as it's flowing out and having a having a record of that we've also been looking at using grout sensors installing grout sensors into the duct into the anchorages that can measure if there was a void in the tendon if the grout tendon is fully grouted it can also sense the quality of the grout if it's gotten hard if it's soft so it gives some information there and it can also be measured through through time if you want to come back in a year or ten years and verify that the grout is still in good shape then you can you can you can have a have a way of doing that without having to drill into it there's also been some looking at epoxy coated strands for post-tensioning there have been a couple of state cable bridges built recently or currently under construction using epoxy coated strand for the stays I understand in Japan they use a lot of epoxy coated strands for external tendons that are unducted and ungrouted and there's going to be a demonstration project we're going to be installing epoxy coated strands in the next month or two I think the hurricane that came through a couple weeks ago has slowed things down on the site so we'll be out there probably November ish putting in epoxy coated strands that are unducted and ungrouted and then there'll be some more information on that is as that gets done and there's also been some talk about potentially using stainless steel strands I haven't seen that used on any jobs yet but I understand that they've used it in some precast applications as far as new technologies that are are available out there this this is a this is an excerpt from a durability survey that was published by as the American Segmental Bridge Institute a couple years ago and what you see on the left in figure three is basically it gives you the distribution of different types of structures bridge structure types between concrete continuous concrete pre-stressed concrete steel continuous steel that's the distribution of the different number of structures by type on the right this figure four gives you this same distribution but it but it breaks down the the structure type by or rating by the the rating of for rating from the how they rate bridges so what this shows me is that post-tension structures while we've had some issues that have been pretty widely publicized you know the industry is really in which industry is really I believe dealt with it still shows that post-tension structures in pre-stressed structures really perform you know very well if you look at the segmental bridges which are point one two percent of all the bridges of those point one two percent only none of them but only point zero three percent of the bridges rated as poor or segmental it's the same with the pre-stressed concrete where you've got thirty point five percent we're only 22 percent are rated poor so you can see that there's a real indication there that the the pre-stressed and post-tension bridges really perform quite well so in closing what I just want to say is that as we just talked about the PT structures are outperforming other structure types and the improvements to post-tensioning durability have have had the desired results we've seen really a you know that the survey that was done by Bruce really shows that we're we're making the the improvements we want to have with the durability and bonded post-tensioning unfortunately there the older structures that are currently out there that were built in the 70s 80s and 90s may continue to still see issues and so we need to be looking at that as we're inspecting these bridges and dealing with anything we might find so that's all I have all right well we got a few questions here to go through Bob first one being on you showed the slide of segmental bridges and where they came together there's a coupler mechanism right there not that coupler mechanism there's a question that has to do is there any sort of inspection that's required prior to grouting of that or any way to verify the quality of that joint yeah that's a very good question there is typically we like to do an air test before we grout so it would be a pressure test that we would we would pressurize the tendon before we grout it and that does a couple things it helps to identify any any potential leaks in the encapsulation so if there is so at a segment if there is a leak we'll be able to find it and we'll be able to address it yeah that's something we do I should have mentioned that nice another question has to do with you showed the flexible fillers with that wax has our DOTs why are we accepting that versus grout can you talk a little bit about kind of pros and cons there and how you guys shifted towards that I we we haven't we've seen one project maybe two projects outside of Florida that have used flexible filler we just completed we have a project out in Yellowstone that's precast segmental that is it's this columns and they are flexible filled and and they had a different reason for using the flexible filler there wasn't a corrosion related thing but it had to do with wanting flexibility of the structure under a seismic event they didn't want a bonded tendon they were afraid it might yield the strands so they wanted to have some flexibility there and I think there was a job in Minnesota that used flexible filler but I'm not sure about that there may have been others but typically I think the states are wanting to see more about the flexible filler before they jump into it and quite frankly I think with the improvements that have been made with bonded post-tensioning I don't know that you get the value or the you know for the additional cost plus you know with with the flexible filler when you have splice girders you know splice girder you know very thin webs and when we do post-tensioning and we grout those and that that those voyage where those ducks are get filled either with strand or grout so they can do the full cross-section of the girder if it's flexible fill then you end up with these voids in there so it really takes a large section of the of the sheer capacity away from this which it's almost entirely you know stop the splice girder bridges in Florida with the flexible filler sure it would be you know I think we're waiting to see how things turn out in Florida okay we have another question that has to do with the delay time from installation 20 actually do the grouting requirements out there on you know how long can it be exposed if it's exposed for something like four months before being grouted you know issues potential losses anything like that can you talk to that a little bit yeah there are time frames in the PTI document that specifies how how soon you should grout after you've completed the stressing operation but there are cases you're building a segmental bridge in Minnesota and it's you know 30 degrees you can't grout when it's 30 degrees so there are materials out there there's VPI powders that you can blow into the tendon that provide corrosion protection that you can that you can do to extend that period all right another one has to do with grout sensors how widely are they being used in the u.s. right now is there more information out there on that oh you froze on me there another one has to do with grout sensors and how often it's being used in the u.s. if there's more information out there we did a demonstration project down in Houston last year but I'm not aware of any other applications here in the u.s. it was more of a proof of concept does it work I know they've used them in Europe which is where we we got ours from our VSL international folks over there question on the mock-up is that something that needs to be from the design side or the local jurisdiction put into the design contract specs is that something that installer should be holding as a cost what's your advice to just give that more widely implement I would think if it's in the spec if it's in the spec that the mock-up needs to be done then it gets priced in and it's everybody's on the same playing field so that would be my recommendations that it is to include that as a spec requirement that a mock-up needs to be done so that really goes back to the design side making sure that that gets included yep I think you have a similar response for this question but it has to do with you talk about level one and two installers and inspectors out there and using that more widely throughout the industry can you elaborate on how well that's being actually implemented on projects throughout the USA ways to make sure that that truly becomes a hundred percent industry standard you know a lot of the lot of the bridge projects were involved they with they have requirements for ASB grout training certification and PTI you know level two for your superintendent and foreman and certain percentage of your crew have to have PT you know the PTL level one I think that's great when the inspector when the designers and owners put that in their specifications and then that's really really helps to make sure they're gonna get trained people out there on the job site doing the work last one before we go on to show them what the future presentations are gonna be it's an easy one for you all says it's great information dot dot dot thanks Bob okay I'll have to get back to you on that one so Bob I want this is Tim here I wanted to jump on and just add to what you already brought up but just to kind of expand upon good points you made so as you mentioned the CRT 70 program the certification program you talked about which is great that you mentioned it that post-tensioning systems quality testing certification program we actually have our first two systems currently undergoing audit so the good news is starting in August we've gotten some submittals and that program is underway with auditing and then ultimately before we get to the end of the year here we should have our first couple of systems make their way into the registry which is going to be great so it's been great to see that correlation between that program and what m50 has done in the m50.3 specification that you touched on and then just also the flexible filler which you've talked about quite a bit you know just for folks out there in the audience we have a flexible filler subcommittee that's a subcommittee of m50 that's busy at work creating material spec installation specs and things like that that relate to that product as much as it may or may not expand upon the industry it's certainly in in the process of being accommodated by PTI and their specs and then lastly as you talked about emerging technologies the beauty of and I'll let you say more about this but the beauty of those emerging technologies with EIT tendons epoxy strand other various other expand expanding upon those durability improvements maybe maybe you could touch on the m50 committee cycle that's ongoing to update from 2019 till 2026 for example what's happening with m50 integrating all those new things into the spec yeah I think I'll touch base first only on the on the the the flexible filler subcommittee I think I apologize for not mentioning that that's you know we've whether whether it's our preferred method of doing tendons or not it's really you know part of PTIs being a leader in the industry and providing guidance if an owner wants to use that that we want to be the resource PTI wants to be the resource so they can go to to get good information so they do a good job on their project as far as integrating new technologies and we were inviting speakers to come to the committee to talk about what their new technologies whether it's stainless steel strand or epoxy we are going through a another cycle of our spec I hope we're hoping to have the next spec out in the next year or so so as we as we come across new technologies we want to bring those into the into the document and take advantage of them I don't know if that's what you meant me to say that's good no yes one of the heavy add to that that's great any other questions come in nothing else so we can kind of go through our look ahead for the next few months here so at the end of every one of these webinars we always like to present what the next three webinars are that we have lined up for there and so last month like I said was a material topic today was material slash bridges on there now we're gonna go into PT slab on ground we've had an overwhelming number of requests for PT slab on grounds this is definitely one of those classic you asked we listened type of responses it's a very very broad deep topic with a lot to talk about so we're going to be doing lots of side on ground presentations likely in 2025 as well the first one being November 13th and that's gonna be the fundamentals of PT slab on ground from the geotechnical side because obviously that's one of the most important things to understand before you can start into the concrete post-tension design itself is truly having a strong grasp on that geotech side so we're gonna kick things off with our slab on ground series with geotech and then after that in December we're going to go into the structural side of things from there in January we're gonna go vertical and we're gonna be talking about parking structures and within parking structures a hot topic today is electric vehicles and the weights electrical vehicles obviously are much heavier than traditional vehicles and how do you account for that in design there's a lot of questions coming out there so we're gonna have Walker consultants kind of giving a presentation on EV weights and kind of where we're headed as an industry there and so this one's more on the hot topic within the industry as a whole there so we're looking forward to those next three presentations as I said at the very beginning those three presentations are at the same exact time so it's the second Wednesday of every single month it is at 1 o'clock Eastern 10 o'clock Pacific watch it for some of the year you should always begin the invite for it sometimes the auto filter to your other inbox in there so just keep an eye out for it they all have the free PDH credits and just like me there's a lot of folks we're getting towards the end of the year we have a lot of PDHs to complete before renewals come up so great opportunity to knock some of those out with that you guys can see information to get a hold of us with further questions both the speaker and the industry as a whole the post-tension industry as a whole that's up there we thank you guys for the time and we look forward to seeing you again next month have a good rest of your day you
Video Summary
In October's webinar by the Post-Tensioning Institute, Kyle Boyd introduced the session focused on durable bonded post-tensioning, particularly in bridge construction. The discussion highlighted improvements in post-tensioning systems to enhance performance and durability. Bob Swart from Structural Technologies detailed past issues related to poor grouting practices and material choices that led to corrosion and structural failures. The presentation addressed how industry stakeholders, including PTI and ASPE, collaborated to improve post-tensioning systems through specifications, better materials like prepackaged grout, and advanced equipment such as colloidal mixers.<br /><br />The introduction of protection levels (PL1 to PL3), advancements in anchorage and duct systems, and testing measures were discussed. Training programs for installers and inspectors were emphasized as key improvements, ensuring that grouting and installation procedures are properly executed. The session also considered new technologies, such as epoxy-coated strands and flexible fillers. The audience was informed about upcoming PTI webinars focusing on PT slab-on-ground fundamentals, structural aspects, and the impact of electric vehicle weights on parking structures, scheduled for the upcoming months.
Keywords
post-tensioning
bridge construction
durability
corrosion prevention
grouting practices
construction materials
structural technologies
training programs
new technologies
×
Please select your language
1
English