Good afternoon. Welcome to PCI's webinar series. Today's presentation is Guidelines for the Use of Ultra-High Performance Concrete, UHPC, in Precast and Pre-Stressed Concrete. My name is Royce Covington, Manager of Member Services at PCI, and I'll be your moderator for this session. Before I turn the controls over to our presenter, I have a few introductory items to note. If you need anything, please feel free to contact me by replying to your registration confirmation or send an email to marketing at pci.org as shown on your screen. Earlier today we sent an email containing handouts for today's presentation. The handouts are a PDF of the PowerPoint that will be shown, detailed instructions to access your certificate, and a webinar attendance sign-in sheet, which is only for locations with more than one person viewing. Please have all attendees at your location fill in the sign-in sheet and send to PCI per the instructions on the form. 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Any questions about the content of this webinar should be directed to PCI. Questions related to specific products or publications will be addressed at the end of the presentation. Our presenter for today is John Lawler, a principal with the consulting firm Wyss Janney Elstner in Northbrook, Illinois, where he has worked his entire 21-year career. His practice areas include structural evaluation and repair and materials evaluation and research, especially as these topics relate to concrete structures and innovative materials like UHPC. John was co-principal investigator on the recently completed PCI research project titled Implementation of Ultra-High-Performance Concrete and Long-Span Precast Pre-Tensioned Elements for Concrete Buildings and Bridges. He is a licensed professional engineer and is a member of PCI's Concrete Materials Technology Committee and TAC. I'll now turn the controls over so that we can begin our presentation. All right, thank you, Royce, and thanks to everyone for joining in on the discussion today. As Royce said, my name is John Lawler. I'm with WJE, where I work in our laboratories here in Northbrook, Illinois. The focus of my presentation will be the guidelines for the use of UHPC in precast and pre-stressed concrete that were recently finalized by PCI's Concrete Materials Technology Committee and that have since been published through PCI. Before I talk about the guidelines, though, I wanted to talk a little bit about their origins. In recognition of the great potential of UHPC, in 2018, PCI funded a research project. The title of the research project is what's shown on the screen there, Implementation of UHPC in Long-Span Precast Pre-Tensioned Elements for Concrete Buildings and Bridges. The principal investigator for the project was Mayor Todd Gross at eConstruct. He led the structural design efforts, while I was a co-PI and led the materials efforts with my colleagues here at WJE. So, as the title of the project implies, the overall goal was to create enough information to allow for the production and structural design of big members, big UHPC members, specifically bridge girders that could be up to 250 foot in span length and building floors that might have 60 foot by 60 foot bays. There were two components to the project, a materials component and a structural component. On the material side, the intent was to provide guidance on how to design and produce cost effective UHPC mixtures. As part of this, WJE worked with participating precasters to produce UHPC with local materials using existing production facilities. On the structural side, the goal was to provide design guidance to structural engineers that is straightforward to use and supported by worked out examples. As part of the development of that guide, some full-scale structural testing was performed on samples that the participating precasters built using the UHPC mixtures that were developed. So, to quickly outline the materials efforts, the project was divided into two phases. In phase one, we worked with six participating precasters to develop and or characterize a UHPC mixture. Phase two then included working with those precasters to produce components that were used for structural testing in support of the structural design guideline development and then testing the UHPC materials themselves to determine the properties of the UHPC that was produced. And as a side note, the structural testing was done at a few different locations, but the picture shown on the slide here is one of the structural specimens being tested here in WJE's lab. So, while the full research project produced a substantial report that was finalized in 2022, finalized last year, there were two materials related deliverables. Guidelines for production intended to be used by PCI member plants and others interested in producing UHPC for structural applications. And the second component was a guide material specification intended to be used by specifiers of UHPC. These deliverables then became the foundation for the document that was adopted by the CMT committee, whose members carefully reviewed and refined the document before it was published. So, those are the origins of the guidelines, which start with an introduction of why we are interested in UHPC in the first place. So, I expect most of you are familiar with UHPC, but as a quick reminder, the three properties of UHPC that differentiate it from more conventional concrete are the compressive strength, the tensile strength, and the durability. Of these, the two that really separate UHPC from conventional concrete are the tensile performance and the great durability. UHPC is stronger in tension to the point that the tensile capacity can reliably be used in the design of structures. And its highly refined pore structure can keep out chlorides and water and resist many of the mechanisms that limit the life of concrete structures. Where does this performance come from? First, it's the fibers. They bridge cracks and provide the ductility even when the matrix itself starts to crack. Second, UHPC is produced with a low water cementitious ratio. And as well known with most cementitious materials, the less water you have, the more dense the matrix can be. Third, UHPCs contain supplementary materials, especially silica fume. And these bring useful properties of the mix. Perhaps most importantly, they allow for the fourth item here, which is particle packing. This is the concept that the materials are combined in a manner that minimizes the void space within the matrix. In other words, smaller particles can fit within larger particles, which can in turn fit within larger particles. This results in a dense matrix that improves the strength and the durability. Optimized particle packing also contributes to workability since it reduces the free space within the particles where water exists. So for a minimum amount of water, you can still coat all the particles and still get a workable material. One way to group UHPCs, the kinds of UHPCs that could be used, is to think about prepackaged materials versus mixes based on locally available materials. Prepackaged materials are those that have been commercialized. They may come in a super sack and are generally the type of UHPC that has seen the most use to date. Prepackaged material suppliers are generally very selective regarding the raw materials that they use, and so can achieve better batch consistency and perhaps better performance. In addition, since they are pre blended, the mixing times can be lower than the local material based mixtures. However, a key disadvantage of the prepackaged materials is the high cost. Now all UHPC is going to be more expensive than typical concrete, but one method to address its high cost is to produce UHPC with local materials. Developing local materials based mixtures gives an opportunity to tailor the performance of the UHPC to what's important. For example, as I'll talk about in a minute, compressive strength is generally not the most important property of UHPC for flexural members, and that can be considered in the way that we develop the UHPC mixture. However, local material based mixtures do require obviously local expertise and certainly verification testing to ensure that the target material properties are actually achieved. But given the controlled environment that we actually have within precast plants, that lends itself very well to address the challenges of UHPC based on local materials. So if you're a new plant starting to look at using UHPC, the things you may be thinking about include mixture development, production, and testing and qualification. And so the guidelines for use of UHPC cover these things thoroughly. As I mentioned a minute ago, the use of local materials was really a focus here. This was identified as a primary means to reduce cost of UHPC, which we saw as a potential barrier to implementation. The cost of the UHPC mixes produced for this project was about $800 or less for the raw materials. This was just a couple years back, but that about $800 is the number that we were kind of targeting, which is a significant reduction compared to pre-bagged materials. Despite the fact that we were focusing on the local materials in order to produce the UHPC, some new materials did need to be identified for this use, and that includes a fine sand, a super plasticizer well suited to UHPC, and possibly a supplemental material. And I'll talk more about how those materials were selected in a second. We also focused on supporting the use of existing batching plants, including materials handling and mixers. Again, this was consistent with the goal of making the implementation of UHPC as easy and as accessible as possible. So for the purposes of the trials performed as part of the PCI project, some manual operations were still needed for material that was not typically used by a given plant. For example, fiber addition was generally done by hand. Generally, the mixers were operated at up to about 60% of capacity, but the existing batching equipment, given that limitation, the existing batching equipment was used successfully. So, our conclusion here is that it was possible to get started with UHPC without really a major capital investment, although we do certainly recognize that modifications to plant operations may become useful to improve efficiency as a plant matures in its production of UHPC. So beyond the introduction to the guidelines, let's talk about a bit more of the specific content that you'll find in it. Section 2 defines PCI UHPC. So what is PCI UHPC? It's a type of UHPC optimized for precast, pre-stressed concrete. And by optimized, we mean that the focus is on the performance characteristics that are most important for the application of long span elements. So in addition to requirements for flow for a self-leveling consistency, we have a compressive strength of 17.4 KSI at service, which is equivalent to 128, excuse me, 120 megapascals. And we have a recommended strength at release of 10 KSI, though that can be adjusted by the designer. While easier to test and familiar to most of us, the compressive strength can actually be de-emphasized for UHPC, since it's really the tensile and flexural strength that is the important parameter, since that's what really adds to the capability of precast concrete beyond what we're used to. So for this project, we've adopted flexural strength as a measure of that property. And we are looking at first peak and ultimate peak strengths of 1,500 and 2,000 PSI. To ensure post-peak ductility, there is also a requirement that the peak is at least 125% of the first peak, and the flexural strength is at least 75% of the first peak at a deflection of 0.08 inches. Section three of the guidelines covers materials and mixture proportioning. This section starts by providing some background description on the materials technology behind UHPC, which I just covered a few slides ago. The guide then gets into providing recommendations for selecting materials for UHPC. The emphasis is on particle packing as a means to achieve the overall performance and also thinking about compatible chemistry to ensure we get good initial workability. The cements, a variety of cements have been used in UHPC, but in general, a low C3A and moderate fineness are desirable properties. Silica fume is a part of nearly all structural UHPCs because they provide the smallest particles in the particle packing process. A high silica content which contributes to reactivity is desired. Supplemental materials are another component of UHPC mixes. Note, and I corrected myself earlier in this presentation, it's not necessarily supplemental cementitious materials. The material doesn't have to be cementitious to be included in the mix because we're using these supplemental materials more to achieve that particle packing than necessarily to include some cementitious properties. The sand is typically finer than typical concrete sands. A masonry sand, though, which can often be obtained from concrete sand producers, will generally work well. For structural applications, the fibers are typically going to be a high strength steel with a high aspect ratio of greater than about 60. And finally, one of the most important aspects of a UHPC is finding a super plasticizer compatible with the other materials. Polycarboxylates are the most common, and it's important that this is an efficient material because we've got high volumes of powder in our UHPC. In the PCI UHPC project, a range of different materials were used. In terms of cement, most precasters were able to use their usual cement type, including one UHPC that was based on a Portland limestone cement, that's a type GUL. Mixes with type 3 cements were also used, but tended to have reduced workability retention. Supplemental materials, they range a little bit here. Some were cementitious, but not all. And in each case, the materials were something that the precaster already had on hand. All right, the fibers, we looked at a range of lengths of fibers. Selection of fiber length had an impact on workability and the flexural and tensile performance for some mixtures, and I'll come back to that a little bit. The admixtures, there were a wide variety of materials used to achieve the target performance characteristics. One of the focuses was enhanced workability retention, and so that sometimes required a second high range water reducer, specifically focused on providing that workability retention. While many precasters were able to use materials from their usual admixture supplier in some cases just because of material compatibility some precasters Actually looked at using alternate sources of admixture Once the materials were selected then the next step is to go through the mixture development process There are three basic approaches on how one could develop a mixture I'm really going to talk about the third here because that is the the most efficient approach and the one that that we talked about Most in the the guidelines. I'm going to go into what this looks like in the next couple of slides So so once the materials are identified for a given application here There's really a three-step process to the mix development The first step is to examine the various combinations of materials based on their particle size distributions So many of you I expect are familiar with gradation reports for aggregates That tells you the different sizes of particles present in a sample of sand And the relative percentages of materials that fall within those various size fractions So that's shown as a yellow line on this particular curve But we can get the same type of information for other solid materials like cement and silica fume Then we can if we have a certain mix in mind looking at the various proportions the the relative proportions of those materials we can establish a combined gradation that represents all of the sizes of particles that that may be present for that that combination So to use the the particle packing model then We adjust the relative amounts of those materials until we have a good match between our combined material gradation and a theoretical target that defines an optimally graded mixture So the green line here is the target based on a model by Andreessen and Anderson So if we look at where we are with this particular set of materials, you'll see we're kind of missing that green line And in some of the the larger particles if we add more of the smaller particles add more fines We can move the curve to the left. But if we go too far, we're gonna miss the green line a little bit there So really what we're trying to do is find that best balance the curve that I'm showing here, which most closely matches the target So once we have those those relative Proportions of materials identified. The second step is to take the materials into the lab and work on small-scale batches to determine the high-range water reducer type and dosage required to get a self-consolidating consistency described by a spread of nine inches Once we did that we then verified the potential compressor strength of the mix on cubes without fibers So These are some of the mixes that were developed for the various pre casters labeled a through e as part of the the PCI research project the mortar batches showed potential strengths of 23,800 to nearly 28,000 psi Which was definitely encouraging but it is important to acknowledge that these are potential strengths based on a mortar produced in the lab And actual production in the plant may result in in lower strengths for a range of reasons including We've got less efficient mixing processes at larger scales But taking it into the plant and actually seeing what could be achieved. There is the the third step in the process Where we can then go ahead and introduce fibers and evaluate flexural performance So These are the the final phase one mix designs developed using the procedures that are outlined in the guidelines You'll see that the cementitious components included the silica fume the limestone and slag We have large doses of admixture, especially the high-range water reducer But all fibers here contained 2% by volume of steel fiber And the low water to binder ratios We're relatively consistent across the different materials all just a little bit below about 0.2 And note when we're talking about water to binder here We're referring to the binder as if it includes all the powder whether it's a cementitious or just a filler material Section 4 of the guidelines then talks about material properties of UH PC And how the UH PC itself is tested Giving a summary of the different types of tests used and how they differ from or were modified from the tests that we would use on conventional concrete We've also defined three categories of testing depending on how the different tests will be used Qualification testing which would be done during trial trial batching to pre qualify a mix against a certain specification Acceptance testing that would be done during production to verify performance and then potentially informational testing that Supplemental testing to provide information for the designer or verify type of performance To generate results generally not used for either qualification or acceptance And I'll talk more about the categories of the testing when I come back to talk about the guide specification So given that tensile performance of UH PC is key for structural applications it's obviously vitally important that the tensile properties including strength and ductility be characterized in a reliable and Generally straightforward manner a few different methods have been developed for testing tensile performance of Concrete the uniaxial tension test shown in the picture on the screen here is the most direct test of tensile performance measuring both strength and ductility And while a method has recently been approved as AASHTO T397 at the time we developed this guideline and specification There was not a standardized method available This is an equipment intensive method and is quite challenging or can be quite challenging to to run At the other end of the the spectrum in terms of characterization of tensile properties is a double punch test this involves Basically using a compression machine with a steel punch on either end of a cylinder And loading that in compression and measuring the response This is a relatively simple test to run but it only gives a rough approximation of the the post peak performance a Balance between these two methods is ASDM C1609 the flexural test Conducted with the appropriate standardized fixture that limits friction at the roller supports This method allows both the strength and the ductility to be characterized in a relatively straightforward manner So with the goal of keeping things as practical practical as possible for the PCI project We selected this as the basis for our efforts Through inverse analysis The tensile strain response can be estimated from the flexural testing performance And would be appropriate to to interpret Conservatively, but overall the the intent of us using this particular testing approach Is that if the minimum flexural performance limits that I've referenced earlier under the definition of PCI UHPC Can be met then the structural design guidelines that were developed as part of this project will be applicable you All right in section 5 of the guidelines Guidance on the production itself is given This was developed based on best practices specifications and observations from the pre caster experiences The top X covered range for materials handling to curing and I'm going to touch on a few here UHPC production obviously starts with with batching and mixing Generally, you're going to see a unique process for each plant depending on Their equipment and other aspects of the facility there But generally general guidance would include dry blending of the powders With the sand and this is done to break up the silica fume and get things well dispersed prior to addition of the water at some plants we found that early addition of about 30% of the super plasticizer and the mixed water Actually increased the initial flow spread and reduced total batch time But in general you want to make sure you get the powders well dispersed before you add the water once that all is in the mixer that you need to Let the mixing action occur Distribute all the the materials. It'll start in a relatively dry That the material will have a dry aspect in the mixer and then eventually it will turn and become a fluid self-consolidating self-consolidating material at which time would be appropriate to go ahead and add fibers Some of the important factors in terms of controlling production Is controlling moisture since there's so little moisture in the mix. It's important to consider all the sources of the water including both Sand and the super plasticizer Super plasticizers might be as much as 60% water and given the large amounts of super plasticizer. We're using that starts become important Temperature is the other Aspect that can be controlled The effectiveness of admixtures and the retention of the workability We're getting from the admixtures is really dependent on the temperature of the mix An ideal target is about 50 to 80 degrees And cooler temperatures can be achieved through the use of ice or otherwise chilled mixing water One of the challenges with UHPC production is fiber addition If the fibers are added too quickly, they are prone to balling or clumping Adding fibers over a grating or a mesh to help break up the clumps as they come out of the bag Was key for the participating pre casters if if the material wasn't broken up like that you get Clumps or balls as shown in the two pictures on the left here so the The use of a grating like this was key But it was still a slow process and was often the longest component of the the mixing cycle You Once the UHPC is mixed it's obviously got to get transported to the forms and placed UHPC can be placed from a ready mix truck a Tucker built or from a bucket Whatever equipment is used. It's important to be thinking about avoiding cold joints when you're talking about placement At cold joints the fibers may not be distributed to bridge across a joint As you can imagine after the UHPC is placed the fibers on a surface Do not really end up sticking up out of that surface And then when the next batch is placed against that surface the new fibers are unlikely to penetrate through into the old surface So that could produce a weak plane within the concrete. That's a potentially problem Avoiding cold joints can be achieved by using a single point of placement And we did this in some of the components that were produced as part of the project Achieving flows of more than than 20 feet But for for bigger for longer elements Following the point of placement is likely to be the the best approach It's also possible to agitate a surface to encourage the blending of fibers between two two lifts, but that's Obviously labor-dependent and and must be done conscientiously in order to avoid problems Another concern for larger elements is how to get enough material to the forms so that you do get a continuous placement process One option is to combine multiple batches in a ready-mix truck where the batches can be thoroughly mixed So we've got more material that can be placed in in a certain in one time This can also be useful if the first batch is a little bit off from the target flow for example The second batch can be used to adjust such that the final material is kind of midway through the process So the final material is is kind of midway between the two batches For larger product products the guidelines talk about strategies Beyond what I just described there As well as other considerations that could include methods to extend the the working time of the UH PC So there's more flexibility with the placement procedure And then methods to reduce batching times so that continuous production can be maintained All right now to talk about finishing for a second Because of the limited moisture in the UH PC. It's sensitive to drying from the surface shortly after placement If this happens, it can form a skin sometimes called an elephant skin It's sort of a crust on the surface That's that's unsightly and as such it's important to act quickly after placement to Strike off the surface and then cover the the UH PC Spiked rollers can help break up any surface skin That that wants to develop Break up trap voids and help get a uniform surface that's What the gentleman in the picture is is using right there. It's a spiked roller an evaporation reducer can also be applied to Freshly finished surfaces to reduce surface drying For curing there are generally two approaches that can be used with UH PC Historically and when I say historically i'm talking about some of the pre-bag mixes out there a post-cure Thermal treatment has been applied to UH PC and that involves heating the concrete up to 194 degrees fahrenheit for 48 hours with with steam An alternative approach is to use more standard curing Which can include only ambient curing or curing with application of external heat in accordance with the temperature limits of MNL 116 Depending on the environment a heat of hydration due to large quantities of cement in UH PC can however Generate significant temperature increases and that can help accelerate strength Um But that really depends on your environment if you've got thin elements or elements that are cast in colder weather External heating will likely be be helpful So to talk about these options a little more A big advantage of the post-cure thermal treatment is that it develops strength more quickly And usually results in a greater final strength than ambient curing it also locks in most of the potential volumetric changes due to creep and shrinkage that occur early in the life of a concrete So that the structural element is less likely to change Once it's installed in service However, the post-cure thermal treatment certainly does require a special effort on behalf of the producer And as I mentioned in some environments the internal heat of hydration combined with warm ambient temperatures may be enough to achieve the desired properties An example of that might be florida. So there are really two options here and it will depend on The the pre-caster environment and the the material performance requirements to determine which one is is best Finally the guidelines include guidance on quality inspection and testing during production In the center, you see a flow spread test. That's the standard method for evaluating the workability of UH PC And this is a consistency of of nine inches. That's the flow that we've been targeting On the right is a test fixture for flexural testing Incorporating freely rotating rollers to to limit friction Which is very important to get good results There are a number of of test frames that can be used in in various laboratories for doing flexural testing But not all of them allow free rolling and if you don't have free rolling That that will impact the the measured response in the flexural test All right now to shift gears if you are a material specifier Um, you may be more interested in the guide specification Uh, this document talks about materials qualification and qc testing And lays out some some general requirements for for fabrication This document actually shows up as the appendix For the guidelines and was prepared to be useful both Kind of in the building environment as well as in in transportation structures There is an introductory section In the appendix here that that talks about how the various pieces are intended to be combined but what we anticipate is for Specifications that are built around the the csi master format the information Would be used in part one and part two for So part one being general part two being products For a transportation specification the information would be used in maybe section two materials and section three construction Um One of the key ideas for specifying uhpc is the materials identity card The concept here is that each unique uhpc would have its own materials identity card This is the primary submittal for uhpc And identifies the parameters that will influence the uhpc properties including the source materials the mixture proportions And the production procedures including the mixing process and curing since all of those may have impact the performance It then becomes the reference for future understanding of how that uhpc will be produced and how it will perform the document Also provides the producer the means to demonstrate compliance with the specified properties again It would be the basis for a submittal So as I mentioned earlier, uh, the tests kind of fall into three categories depending on their purpose Which could be qualification acceptance or information? The items highlighted on this slide here in orange are the testing required for qualification And these would be the minimum properties expected to be on the materials identity card a goal here of approach is to keep the Qualification limited of the minimum required to adequately demonstrate performance and durability therefore we've limited to include only compressor strength flexural strength and for durability the c1202 rapid chloride permeability test. However, a specifier is obviously able to specify minimum requirements for qualification for other materials, such as other durability tests if there are specific durability concerns in the application. The acceptance tests would be done during production and would be used to demonstrate that the UHPC would meet the requirements that were the basis for qualification. We've also included unit weight testing as a means for ensuring consistency on a batch-to-batch basis. Finally, the third category is informational testing. A specifier could also decide to include testing of other properties for informational purposes without defining minimum requirements. An example of this might be that the specifier would require testing for module spasticity, which is important for design, but maybe they would not require or list either minimum or maximum on that particular property. All right, to qualify a mix based on strength, the guidelines have adopted the approach taken in ACI 301 for qualification of concrete compressive strength. I'll note that this is the same approach used in the AASHTO LRFD bridge construction specification, which references AASHTO M241, which is actually based on ACI 301. So basically, the idea is that to reliably meet the specified strength, the average strength based on repeated tests of the concrete from a given mix and production process must be sufficiently high so that the risk of failing to meet the specified strength is acceptably low, say one in 100 times. So in this approach, there are two options for determining what that required average strength is, depending on whether statistical data is available for the production of that specific mix. For conventional concrete, if prior testing data is not available, we can use an overdesign prescribed based on industry's historic understanding of conventional concrete and its testing. But unfortunately, we don't have that historical data available for UHPC. So we need to go the route of looking at available data and get specific data for production of that specific UHPC. And we can adopt the statistical approach for mixes with strengths of over 5,000 psi, which is a generic approach. From test records, then we would need the average and standard deviation of the strength performance for that mix. We can then apply a k factor, that's an adjustment that can be applied for smaller sample sizes if we have a smaller sample size. So this does require some amount of upfront testing. But this is really the only approach consistent with the ACI process here that is applicable for UHPC. So the other wrinkle here is for UHPC, we also need to consider both compressive and flexural testing. So for the guide specification, we've generalized this approach to define what we've called the strength as F sub X. ACI at minimum requires at least 15 tests, where each test is defined as three specimens. But we have proposed determining this value from nine tests with an approximate k factor, excuse me, with appropriate k factor, so that the low risk of failure is maintained. We've also indicated that the samples must come from a minimum of three batches to capture batching variability. This means that a minimum of 27 specimens, that is nine tests, must be prepared and tested to have the basis to legitimately qualify UHPC in a manner consistent with that ACI or AASHTO approach. Finally, the guide spec touches on various fabrication items. For the most part, we looked at the existing PCI MNL 116, that's the QC manual for structural precast products, and only identified items related to UHPC that were beyond the scope of that document of MNL 116. Finally, the specification includes a program for routine acceptance testing specific to UHPC, including the plastic properties and the mechanical properties, including compressive strength and flexural strength and ductility, which are obviously key for performance. So to wrap up my presentation, I wanted to come back to the experiences of the participating precasters and share a little bit more about their successes. While the initial efforts for many of the precasters started with the information that was in early drafts of the guidelines, the lessons that we learned working with the precasters during the project were also incorporated into the final version of the document of the guidelines with the intent of making it a better resource for future producers. So this slide shows the phase two mixture proportions. In general, these followed what was developed in phase one based on that particle packing approach, but there were some adjustments made by the precasters as they learned more about what worked and what didn't, particularly as it related to the admixtures. Just about all precasters introduced some type of workability modifying or similar admixture. Another thing that varied was the fiber length, not the amount, but the length, and this was largely driven by the availability of fibers, but it gave us an opportunity to see how fiber length impacted performance. The fibers were most commonly either 20 or 13 millimeters long depending on the product, except for precaster F, who also used some 25 millimeter fibers. This is a histogram of the compressor strength measured for each tested batch from the precasters in phase two. The vertical line represents our specified strength of 17.4. Each marker on these plots represents the average of three test specimens. The filled circles are standard cured, that is the standard PCI curing procedures that may have included application of heat at the bed, while the Xs receive the full post-cure thermal treatment. In this plot, you'll see a lot of purple dots. These are for precaster E, which produced the greatest number of UHBC batches for our program. So, a notable observation from this plot is that the lower strength here occurred for this mix when there was no external heat supplied. When external heat was applied, this mix performed substantially better. So, that was one of the lessons learned during the execution of the batching process. This is a similarly formatted set of data. This is the peak flexural strength compared to the target of 2.0 KSI. There were just a few tests below the target property for this, excuse me, the target value for this property. Though looking at this a little closer, we saw that the batches with the lower strength were fabricated with 13 millimeter fibers. For the precaster E mix, the longer fibers that they used and some subsequent batches actually increased the flexural performance. So, overall, we've been successful with the UHBC produced at the six precasters that participated in this project. About a dozen new shapes were designed to make efficient use of the material properties of UHBC, and those were fabricated and then tested. The participating precasters certainly deserve credit in the success of the project. Each had to address different challenges working with their own facilities, but we want to recognize bringing their existing expertise in concrete production and using the problem-solving skills, they certainly figured it out. So, in addition to the successful construction of the elements I showed on the previous slide, you know, the UHBC materials themselves generally achieved the performance requirements of PCI UHBC on a batch-by-batch basis. The UHBC mixes definitely saw benefits in heat curing, and especially the post-cure thermal treatment. The confidence, the likelihood in meeting those performance minimums, and as I alluded to earlier, the performance improved as the precasters gained experience with the production process. So, this really leads to the final conclusion that based on, you know, a mature production process, we certainly anticipate that all the precasters that participated using the mixes developed through this process and following the approaches outlined in the guideline documents, we certainly would anticipate that they could be successful in meeting the design targets for PCI UHBC. And with that, I'll conclude my presentation here and be happy to answer any questions. Thank you, John, for a great presentation, and we have quite a few questions, so I'll try to get to them as quickly as possible. The first question is, correct me if I'm wrong, but the UHBC seems to have a higher cement content than conventional concrete, a higher carbon footprint. Is that correct? On a per cubic yard basis, it certainly does have a higher cement content than conventional concrete. However, given the improved mechanical performance of the material, the cross-sections in an element that is designed to take advantage of those properties, the cross-section can be as much as 50 percent, or excuse me, as low as 50 percent of what you would get with conventional concrete. So, you may be using half the total concrete that you would with a conventional material. The other factor related to the environmental impact of UHBC is the durability that can be achieved with UHBC. You know, a conventional concrete structure may last 50 to 75 years. With the UHBC, given the very high durability, and there's some folks who would suggest that chlorides really just don't, and there's testing done to explain this or to observe this, chlorides really don't penetrate through UHBC to get to reinforcing steel, for example, to cause corrosion. So, UHBC structures may last two, three, four times longer than a conventional concrete. So, when you put all of those together, the environmental impact of UHBC may actually come out looking better than a typical conventional concrete component. Okay, thank you very much. Next question is, what type of mixers were used in the lab for the mixes? In the lab, we started with just a simple mortar mixer, a benchtop mortar mixer, and when we started to play with batching larger scale, we used a planetary mixer. But the various plants, the mixers ranged substantially. Some of them were also larger scale planetary mixers, some horizontal shaft mixers. There is also a mixture manufacturer out there that has developed a particular mixer that imparts a very high shear into the mixing process. So, there's lots of different ways that UHBC can be mixed. I mean, it can even be mixed in a ready mix truck, but generally the efficiency of the mixer, the amount of shear that can be generated within the material is really going to influence your batch time. So, a very high shear mixer might produce that UHBC, get that turn in the mix in a matter of a few minutes, while mixing in a ready mix truck might take you half an hour. Thank you very much. This is another one. It's pretty good. When do you anticipate IBC and ACI to actually allow members to optimally design with UHBC, meaning with thinner members and less reinforcement than ACI 318 currently allows for? That is a difficult question to answer. I hope the answer is soon. I guess what I can say is that on the transportation side of things, AASHTO committee T10 has been looking carefully at the recommendations that were developed by this PCI UHBC project in combination with some recommendations that were developed by FHWA. That's probably the most mature area of development relative to design. And so, it's an ongoing discussion right now how to kind of harmonize the recommendations, take out the best parts of both to come to a place where there is an adopted design specification for UHBC on the bridge side. That hopefully is happening. I've heard that there will be adopted within the year. On the building side, things are moving a little bit slower. There is work happening through ACI committee 239 to develop design guidelines. And there is actually at PCI underway right now the formation of a committee on structural design that's just kind of getting off the ground. But the expectation is or the intent is to be able to think about UHBC design from a precast perspective for buildings specifically so that there is going to be progress in that area as well. Okay, this next one is a two-part question. Does length of fiber affect compressive strength and to what percentage does the fiber increase tensile strength? So, fibers generally have limited impact on the compressive strength. So, I don't anticipate there'd be a substantial impact associated with the length of the fiber. In terms of the second part of the question, well, Royce, could you repeat the second question? The second question is to what percentage does the fiber increase tensile strength? Increase, okay. So, comparing it against conventional concrete, you know, the tensile performance we usually think about as having kind of two components. One is the strength, that is the total amount of stress that can be taken before it actually starts to crack. And that can be described as the first crack strength. Then we have the ultimate strength, but again, a strength parameter. And then the other component is the ductility. How much total energy can that material carry? And for UHBC to perform structurally, you really need both. So, in terms of the impact of the fiber, it really depends on the type of the fiber, but you know, you might get two or more times the strength due to fibers. But in terms of ductility, it could be 10, 20, many more times the ductility. So, both of those properties of the tensile performance really come from the fibers. And as I've tried to imply throughout my presentation here, that's what's the really important part of UHBC performance. Okay, we've got time for a couple more questions, I believe. This one is, since heat curing is required, how do we specify heat curing on actual projects for fields, say for bridge decks, are in closure or precast elements for bridges? So, there have been some attempts made to essentially warm UHBC when it's been placed in the field. But as one might imagine, that's challenging. You know, our focus here has been about structural precast elements, where there is more control over the UHBC product, and that heat curing is possible. In the field, you know, the type of UHBC you might want to use would be different from what might be used in a precast plant. In a field application, you may want to look more at a pre-bag type approach, for example, where things are better controlled. You're not going to have the capabilities of a well-controlled batch plant in the field. So, there's a number of components of field UHBC production that are different, and certainly heat curing is something that's much harder to do in the field. All right, thank you so much. It looks like that's all the time for questions that we have. On behalf of PCI, I would like to thank you for your great presentation and all attendees for your participation. All unanswered questions will be forwarded to Mr. Lawler. As a reminder, certificates of continuing education will appear on your account at www.rcep.net within 10 days, and a recording of today's webinar will be uploaded to PCI's learning management system. A pop-up survey will appear immediately after this program ends. If you have any further questions about today's webinar, please email marketing at pci.org with the title UHPC. Thank you again, have a great day, and please stay safe.

Ultra-High Performance Concrete

UHPC

Precast Concrete

Pre-Stressed Concrete

Concrete Materials Technology Committee

Mixture Proportioning

Particle Packing Concept

Production Process

Testing and Qualification