AASHTO re:source Q & A Podcast

Talking Balanced Mix Design with Illinois DOT

September 05, 2023 Brian Pfeifer and Brian Hill from the Illinois DOT Season 4 Episode 15
Talking Balanced Mix Design with Illinois DOT
AASHTO re:source Q & A Podcast
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AASHTO re:source Q&A Podcast Transcript

Season 4, Episode 15: Talking Balanced Mix Design with Illinois DOT

Recorded: August 11, 2023

Released: September 5, 2023

Host: Brian Jonson, AASHTO Accreditation Program Director, AASHTO re:source 

Guests: Brian Pfeifer, Engineer of Materials; Brian Hill, Hot Mix Asphalt and Aggregate Engineer, Illinois Department of Transportation

Note: Please reference AASHTO re:source and AASHTO Accreditation Program policies and procedures online for official guidance on this, and other topics. 

Transcription is auto-generated. 

[Theme music fades in.] 

00:00:02 ANNOUNCER: Welcome to AASHTO resource Q & A. We're taking time to discuss construction materials testing and inspection with people in the know.  From exploring testing problems and solutions to laboratory best practices and quality management, we're covering topics important to you. Now here’s our host, Brian Johnson.

00:00:22 BJJ: Welcome to AASHTO Resource Q&A. I'm Brian Johnson and today we are going to talk about something I've been hearing about for the last few years in the construction materials industry, especially with the DOT's, and that is balanced mixed design. would be today to talk about it as Brian Pfeifer, engineer of materials with the Illinois Department of Transportation. Welcome, Brian. [BP:  Thanks.] And Brian Hill, hot mix asphalt and aggregate engineer with also with the Illinois Dot welcome, Brian. [BH:  Thank you.] If you're counting, that is 3 Brians today on the episode, and no Kims. So Kim couldn't join us today to be the co-host, but she will be producing this. Which means that anything I say that is embarrassing will be included in the episode and anything I say that sounds remotely intelligent will be cut, as she often does. So we'll get into this, though. Let's start with Brian Pfeifer, what is balanced mix design for those who have never heard of it?

00:01:20 BP: OK. So for asphalt pavements, we're looking to find a balance and performance primarily between running and cracking. So we're trying to optimize our performance and for us it means. And try to balance our use of recycled materials as well and make sure that those recycled materials are used in a way that doesn't have a negative impact on performance, that it's you know we're getting the performance we're looking for and expecting. I think that's an important part I think in when it comes to sustainability to keep in mind that you may be adding a material or using a material that. Is appearing to make the mixture more sustainable, but if you don't get the longevity, if you don't get the durability or the out of it, then you're not realizing that improvement on sustainability so.  It's really about balancing between those two ends of performance.

00:02:09 BJJ: Now, Brian Hill, do you have? Anything else to add to that?

00:02:11 BH: The only thing that I would add is that we also include moisture resistance test and then when I'm modified AASHTO T283 just to make sure that we're considering moisture as well.

00:02:22 BJJ: OK, so I heard in addition to the moisture sustainability, performance, longevity, I didn't hear anything. About volume metrics which what used to be the target right for people when they were putting a mixed design together, what happened to volume metrics?

00:02:40 BP: Still definitely there. And in Illinois for our larger projects, we have a percent within limits specification with incentives and disincentives. So that's definitely still there and important and it's still a. Big issue.

00:02:51 BJJ: OK, that's something I was wondering about because in all these discussions that I was wondering if the term balanced mix design was a change in. Strategy for developing mixed designs or state highways and Interstate highways.  Or if it was just another term that is used like I didn't know if it represented a significant change to what you do or is it just a progression of what you were already working on.

00:03:22 BP: Yeah, I guess I'd kind of think of it more as a progression and it makes me wonder if I never really thought about that terminology before in. That way that it's. Focused on mixed designs, but really it's the mixture that we're, you know, trying to balance performance.

00:03:36 BJJ: With as far as recycled materials are concerned, have you increased the percentage of recycled asphalt pavement that is going into the mixes in Illinois?

00:03:48 BP: We have and actually that was what kind of prompted the research originally back in around 2013 or so, there were some increases made to the amount of rap and Ras as well reclaimed asphalt shingles and so. What in looking at our performance and kind of seeing some indications of some premature cracking that was a reaction that we had to and we had already implemented the Hamburg wheel on the running side of performance a few years before that or a year before that in 2012. So it really made us take a look at the cracking side of things by you know. Looking at the premature tracking and we saw that as potentially related to those increases in recycled. Materials. And then since we've implemented and and as part of our implementation effort and in collaborating with industry, we agreed to increase our recycled binder content by 5% on all of our mixes that that was you know, so now that we have those performance tests, we know that when recycled materials are used then. They're going to be still meeting our performance criteria then we feel more comfortable raising those.

00:04:56 BJJ: Limits. So as you raise those limits, do you have to make any other adjustments to account for that to make sure?  That you can avoid cracking Brian Hill you want.  To take that one.

00:05:06 BH: What we do in Illinois is at 20%, we have a grade bump down one grade both on the high temperature grade as well as the low temperature grade. So for example, if a mixed design had more than 25% or had 25% ABR and the contract plans called for a PG 6422 that contractor.  Would need to use a PG 58 -, 28 to adjust for the. Asphalt binder that's replaced.

00:05:33 BJJ: OK, so for those of you who are not. Familiar with asphalt special. Applications. Brian's talking about performance gridded Binder specifications, which is the liquid asphalt that goes into the mix, so it's not necessarily that you're adding more liquid asphalt, so you're changing the grade. Or are you also increasing the percentage of virgin asphalt binder that goes into the mix?

00:05:55 BH: That's not a requirement to increase the amount of virgin asphalt binder. That's more of a function of the process of meeting volume metrics as well as the balanced mix design criteria. So that will be a function of the contractors decisions with regard to the different materials that they use.

00:06:11 BJJ: Was wondering did it? The dot doesn't specify what the design or what the ingredients and percentages have to be.  Right. The contractor can determine what the what they feel is the optimal mix to provide the sustainability and the resilience you're looking for.

00:06:33 BP: Right. It's the contractors responsibility to to design the mix and to optimize based on their material sources based on their plant operations and to determine the most, you know, economic. Little Mix while still, you know meeting those volumetric criteria and performance criteria now too. So the performance criteria that is kind of added on and we had done the TSR, the the moisture sensitivity prior to this but yeah so it's kind of a little bit of extra to ensure performance.

00:07:03 BJJ: OK, so we've got more parameters that the contractor has to be concerned with right to to avoid the cracking. And the rutting problems. So let's talk about those. So those are, that sounds like there's some other tests that people have to worry about. You mentioned the Hamburg. What else is Illinois using to evaluate cracking?

00:07:22 BP: So for cracking, we're using the Illinois flexibility index test. And so that was something that came out of that early research. So in 2013, when we were looking at the amount of recycled material we were using and the brittleness of our mixes and the potential and propensity for premature cracking, then we worked with the. Illinois Center for Transportation at the University of Illinois that they handle our contract research. Program and so we worked with Professor Arkadi over at ICT and started a research project to take a look at the options out there and and what type of I think at that point there were a lot of questions, a handful of cracking tests that people were looking at but no one was really sure what kind of direction to take. So the University of Illinois through that. Research and have developed used. The semicircular bend test as a kind of a starting point and kind of evolved with that philosophy and help us to develop that Illinois flexibility index test and then then help us also then to develop the.

00:08:24 BJJ: Criteria. So Brian Hill, do you regularly perform the they also call that the ifit test, right?  That Illinois flexibility index test do you perform that, or does your laboratory perform that at the dot?

00:08:37 BH: So in the process of getting going with ifit evaluations, Central Bureau of Materials purchased devices for the district laboratories. So we have 9 districts within the state of Illinois. And so the district laboratories handle the day-to-day operational tests with regard to Ifit and Hamburg in terms of mixed design and production.

00:08:59 BJJ: Can you take us through that test a little bit just so that our listeners can understand what happens during that testing?

00:09:05 BH: Sure. So the owner flexibility index tests is completed at approximately 25 degrees Celsius. There is a temperature range, but at approximately 25 degrees Celsius, as Brian mentioned, it's a semicircular bend geometry. There is a a notch that is placed in the specimen to initiate a. Track at the end of that notch and such that it travels through the remainder of the ligament test is completed approximately 50 millimeters per minute, or two inches per minute, and then at the end of.  The test, the load versus displacement curve, is produced the area under that curve is integrated and then we look at the.  Post peak slope at the inflection point of that post peak slope such that we can calculate the flexibility index parameter.

00:09:54 BJJ: So people can understand what this looks like.  Like, imagine a an asphalt core that is sliced in half where you've got a semi circle instead of the entire core circular shape and there's a notch cut in it. So you can imagine what that looks like. So you've got a semicircle with just a notch in it and it's on a frame. That has supports on the outside part, away from the notch it with a point load above the center.  There. So it's kind of pushing down on that notch and that's where you get the does it typically fracture all the way through or does it stop when it starts to fail?

00:10:36 BH: By the time you get to .1 Kilo Newtons remaining, the test is finished and so more than likely it won't go all the way through. Otherwise you get unstable crack growth and and the device would actually stop itself. And we also have end plates on our devices in particular. So if you did have unstable.  That growth you may reach a point where. They would hit the end plates and then you'd actually have the load ramp back up because of the response.

00:11:03 BJJ: OK, now other than the index, is there any sort of subjective determination of how the cracking occurred in this test that tells you anything?

00:11:13 BH: I mean, you can look at it visually and see whether or not there's more failure with regard to the mastic. Whether it's more at the interface with the aggregate particles, you can also look at especially. Short term age versus long term aged specimens in general, the more tortuous a crack is, the more cracking resistance that particular sample or that particular mixture has. If it is a very straight crack without very much tortuosity then in reality that means that that crack is very quick to form and so therefore that mixture. Is relatively brittle.

00:11:48 BJJ: Typically when you test these specimens, is this all done before the material is laid down, or do you run this on cores that were taken from the edge of the roadway?

00:12:01 BH: We test both in mix design and production, but it's from loose mix that is compacted as part of research studies and as part of some of our pilot project work that we've completed. And we do test core. So I mean that is part of more of a of the research process. But not as part of the determination of whether someone is going to continue using that mix design or whether that mix design is going to go forward for you.

00:12:25 BJJ: Have you done any of this testing on failed roadway course? What's that process like if you have?

00:12:33 BH: We have, I mean.  I can't say that we've looked at a large number of roadways. That have. Necessarily use the term failed it. It's primarily looked at indications of both pavements that are early in their service life as well as with regard to research, looking at some that have performed poorly, some that are more in a moderate sense and some that are in a better category. I think that larger effort. And Brian Pifer, you can verify this. But the initial IFIT research study looked at payments that were in good, moderate and poor performance to evaluate and determine some level of metric with regard to where flexibility index would be.

00:13:11 BP: Right. Yeah. We had at one point asked all nine districts to submit cores from roadways that in relation to. To to cracking good performing pavements versus what they would consider poorly performing. So at that point it was just kind of a rough, I mean later on when we were actually correlating the ifit results in the lab to performance in the field that was done where transverse crack length was measured.  Over years and chores were taken then. But you, you do have to be careful about comparing the results you get from testing a core as compared to the loose mix. So those aren't the same numbers or they don't mean the same thing. So and I think Brian, you could maybe explain a little bit. More about that.

00:13:55 BH: As part of the. 2016 pilot projects that the department completed, there were 11 total projects and so testing was conducted generally on mixed design production and annual field course that were evaluated including post construction field course. So immediately after construction and as part of that process, it was identified that. There is a difference between loose mix versus field compacted specimens.

00:14:22 BJJ: Yeah. And I and I do want to point out I used the term failed and that's not really the right way to look at it because there's, you know, exhibited cracking is probably what I should have said because it's not like the road just disintegrates or collapses. And you know.  There are varying degrees. You know there could be small cracks, there could be bigger cracks, different types of cracks. When you drive around, is the traveling public, you're gonna see cracks on roadways, right? And there are ones that you can you can be you can think. Ohh well, that's normal. And there's ones you can say. Well, that's a that looks like a concern. How do you know the difference between normal and a concern?

00:14:55 BP: In relation to this subject, to correlate field performance with what the IFIT flexibility index is showing us, we would look at transverse cracked length and and in Illinois we've got a lot of our original pavements were built from concrete, joint and concrete, so. The transverse cracks or the cracks that reflect through that were in that concrete pavement and reflecting through the asphalt and then eventually, yeah, like you said, they they start out, you know, where you, you know hairline you could barely see them and really doesn't get to be a problem for the public until it's actually starting to come apart. And I think this is common across a lot of the OT.  Now and and focusing more on the preservation side of things and trying to have some treatments to be able to prevent that to treat the roadways before those cracks develop to that degree where they're causing problems opening up into potholes or.  Causing a lot of roughness. It is a way a convenient way for us to monitor performance and to correlate field performance with the test results.

00:15:55 BJJ: That's also a good point is that once you start seeing cracks, that dot considers to be unacceptable by their terms. Then they do have pavement preservation techniques that they can employ, you know, crack sealants and other ways to.  Stabilize that roadway or smooth out or improve the rideability and performance of that roadway without having to rip it out and rebuild. Let me ask you something else about the balanced mix design. So the reason why I had reached out to you to talk about this is Illinois is considered to be 100% implementing. The balanced mix design and you already talked about what that means, but how long will it be before you have a good handle on this and feel like, hey, this was the right thing to do? We're seeing improved perform.  Since we're happy with this, we can report back to the other DOT's and the Federal Highway Administration and say, hey, we've got something good here and we're proud of it.

00:16:53 BP: We've had a lot of success already. I think we, you know prior to implementation, we were really comfortable with that tie between field performance and test results. So we feel like we're getting better cracking resistance. We didn't really have a running problem, but we kind of knew that already. But that was because we had the Hamburg wheel. Test already implemented in 2012. So throughout this process you know we've been throughout implementation it's it's taken a quite a while quite a few years, but it's been a very deliberate process where we've worked closely with our districts that Brian had mentioned earlier you know getting the equipment for all nine districts, getting them experienced with testing we've also collaborated. Closely with our industry partners too, and had task force set up to talk about implementation along the way. There were a number of progressive contractors who got their own equipment, started doing testing, characterizing all of their mixes to see where they stood. And so, so yeah. And and then that that correlation with field performance and the the pilot projects that you know we we've really I think progressed a long ways through research and through collaboration already. So as far as you know proving it with field performance over a long period of time that that's going to take a number of years I think actually.

00:18:09 BP: Is now implementing A pavement management system that is really going to help. Closely track performance, but in failed performance you really have to take a a really close look. There are a lot of things that can happen with the pavement and it could be the underlying material.  It could, you know. Be different circumstances of the mix and placement. Compaction. A lot of things that can go wrong and you know a lot of things that need to go right.  To get the performance, you know that we see here. So I think overall things go very well and we see very good performance in our pavements in Illinois and we we saw that before. It's just we raised the bar even higher it.  With this effort, so but. But yeah, I think in the years to come we'll get more firm data. I think on that in looking at our payment management data. But I yeah, I think we have had a lot of.  Success so far,.

00:18:59 BJJ: yeah Now you mentioned the partnering with private industry with the development of this strategy.  Or the implementation of the additional tests and specifications around. And running and cracking. Is this something that the industry kind of moved together with you?

00:19:19 BP: I think we were ready to go and ready to implement a little bit faster than industry they did. We were, I think it was in 2020, January that we were planning to implement an industry, did ask for an extra year for shadowing. And I think I mentioned earlier that there were a number of contractors who really invested and they bought into it they. Kind of realized this was their direction, that we were headed and they were in agreement with that direction, I think. And so they did a lot of work and they even shared, you know, it's a competitive and.  History, but, and they didn't openly share all their data with their competitors or with their industry. But they did share, you know, data that it kind of redacted data that showed. And that's something too that we did. I think that helped the implementation effort. And Brian can speak to this more. There was a database that was developed that was.  All the district data, all of our Central materials data and all the contractors data and I don't know how many data sets we're up to now, but it's in the thousands.

00:20:17 BH: Yeah, we have comfortably over 4000 tests. That's there are multiple replicates per test set.

00:20:23 BJJ: That's a lot of.

00:20:25 BP: And we've helped workshops. We've got an Illinois by two in this paving conference that's hosted at the University of Illinois annually. And so we've had workshops that I think at least one year, maybe, if not two years and the contractors have presented their data, you know, along with ours. And I think it's really been a partnership throughout this.

00:20:44 BJJ: Yeah. Now one way that states have encouraged the implementation of new technologies or strategies has been through incentives.  Or warranties on roads or some kind of way that the contractor is incentivized to produce a a more stable or or long lasting roadway. Does Illinois do anything like that?

00:21:10 BP: We have incentives on the volumetric parameters and you know so for density that covers 40% of the incentive and then? Voids and VMA are the other two components, each at 30%, so we pay up to 105% and then also there's a this incentive side of that too, but really in analyzing that data, I know that that for the past few years we've been kind of reporting back to industry on where things stand and we're paying a fair amount and incentives. But we also realize we're getting a. Performance enhancement out of that, especially you know, we know that the density of the pavement is really a huge key and correlates directly that the studies have shown strong correlation between.  In place, density and performance, so you know, we feel like we're paying those incentives, but we're also getting a performance advantage in return. So at this point, it's just on the volumetrics that that we pay incentives and also assess disincentives. We haven't had any any kind of discussions yet on any incentives or disincentives.  For performance testing, there definitely be some challenges. We don't have the frequency of testing that we would need and that would be a challenge for us to have the resources to do that.

00:22:22 BJJ: It's a lot easier to go out there with a nuclear density gauge and get a lot of test points on density compared. To taking a core, preparing it for the rutting and the cracking testing, I mean, that's a lot of.

00:22:34 BP: Clarification on density. We do use cores for for our density. We feel like that's a more accurate measure of in place densities. It does leave a hole in the road, but it's pretty straightforward. Test to run as opposed to the performance test.

00:22:49 BJJ: Those district Labs, I mean, how much time are they spending on these performance? As compared to some of the other tests that they're doing.

00:22:57 BH: I think they're still completing more in terms of volume metrics than they are with performance tests. I mean performance. Us do take up a considerable amount of time, but with the testing intervals that we have for our different quality management programs, volume metrics still require more time in generality.

00:23:16 BP: But for the performance tests, we're just running those during mixed design, and then once during production. And really those for projects over 3000 tons.  We would just do a fake performance test. Samples at the beginning of the job, whereas our volumetrics those are being done, you know, samples are being taken throughout production.

00:23:36 BJJ: Brian, you're also the aggregate engineer. What kind of aggregate tests are you having the districts work on in addition to the hot mix tests?

00:23:45 BH: Districts conduct graduation testing. Quality testing is completed in the Central Bureau of Materials.

00:23:51 BJJ: What are they doing? Extractions or ignition and graduation? To see what's in the mix.

00:23:56 BH: Oh, in terms of the extracted material? Yeah, I mean, they're still conducting gradations there. We use either ignition oven or extraction. According to Illinois modified T164. We also allow asphalt content to be determined by nuclear method, which then wouldn't have that extracted graduation.

00:24:14 BJJ: Ohh, really? Yeah. You mentioned for the the balance mix design using the Illinois. This or specification for how you handle this? Is there an ash toe standard on the practice of developing A balanced mix design strategy at the dot? Is there like an M or in our standard that explains how you handle this?

00:24:38 BP: Yeah, there's a provisional standard, and I don't recall the number, but it's actually got the summary of the state dot. The current practices. Just because there are a lot of still quite a few different tracking tests and different running tests, that's something that's being updated as we speak through this round of of updates for the material standards. So it's.  Going to be continually updated. For a while I would imagine.

00:25:02 BJJ: Yeah, I think so. Hopefully we can eventually get to the point where we've got a single running test that people are satisfied with and a single cracking test that people are satisfied with because I think may not be a big deal where the contractors are kind of working in the one state all the time. But if you're working with multiple states. You really don't want to be in a situation where you're dealing with multiple testing protocols and different pieces of equipment, especially if you're looking at one state is saying, OK, you have to use this particular test and this equipment and then you have to use this whole other set.  Deep in this other state that you border, that would be pretty difficult. So it would be nice if we could come to some conclusion collectively in the states to say we really like this running test and we really like this cracking test. But I don't know if that'll ever happen.

00:25:55 BP: Yeah. We may end up being the outlier there. Actually with ifit we're, you know, heavily invested in it and.  But it seems like for other states, the predominant ideal CT is what's being commonly used. I guess not many of them have actually implemented that, but that's what they're looking to implement. But we've definitely invested heavily and and have those field performance correlations established with. I fit very comfortable with the test method and. What it tells us what we learned from it, and so.  We'd have a hard time, you know, moving from that. But yeah, I think I think Hamburg wheel is probably the more the predominant running tests, but there's also the ideal RT that that folks are looking at and Hamburg wheel to try to run that test on a frequent basis like during production that would be a a challenge so.  So yeah, it's it's hard to say.  It's definitely an evolving field.

00:26:48 BJJ: And just last week at the Committee on Materials abatements meeting, we heard about another running test that people are looking at. There are always going to be. The new ones coming up because somebody learned something new. So let me ask you this, what can Ashton do to help Illinois dot get more data or promote the use of of this strategy in Illinois and and beyond?

00:27:15 BP: Well, I think actually I've heard something just here in the last few weeks about the creation of a proficiency sample program for Hamburg wheel.  That's something that we do it within Illinois. We have round Robin programs we've had for hammered wheels since probably around that 2012 time frame. And then for ifit, we started a round Robin program in saying maybe around 2015 or so, and that includes a a number of contractor labs. All the districts are participating in that. You know as well. So and that was actually how the precision statement was developed for T393, right? We've worked with AASHTO and using.  Or round Robin data to establish that.

00:27:58 BH: I think we started high fit uniformity studies in 2017, but in terms of the precision limits that was developed, I believe with 2017 through 2019 data, so three different years worth of interlaboratory study work currently as of last year, we had 29 participants in our I fit round Robin and 32 participants in our Hamburg round Robin. But in terms of analyzing the data, it was just following that. The ASTM standard with regard to develop. That precision statement knowing that you know bias is not really a possible statement that can be created for asphalt mixture. Since there's no accepted baseline number.

00:28:34 BJJ: So when we implement this proficiency sample on Hamburg and I think we'll probably have to have one on a cracking test as well. At some point, it's good to know that. You already have that many participants, so you've got a sound population of laboratories for statistical analysis, and you can draw some conclusions from that. That would be encouraging for our program to know that, at least in your state, there are enough participants. So if that's the case, it can be assumed that throughout the US and and really throughout the world that we should have enough. Laboratories to participate in that program and come up with some reasonable data for providing ratings for people. What I would like to do is hopefully be able to compare some of these methods through the collection of that data. Maybe we can see how they compare and and if they're comparable then that's great and people can use what they want and you don't have to pick. Is there anything else you want to tell people about balance, mix design that we didn't cover today?

00:29:35 BP: If I can just kind of acknowledge some contributions we've had, number of folks retire in the last several years who have been heavily involved. Dave Lippert, Matt Mueller, and Jim Trepanier all retired in the last several years and were really instrumental in heavily involved with the evolution of this. I think Dave Lippert talked at a number of conferences here in Illinois. Before balance mix design was really a commonly used term. He was talking about Goldilocks analogy for asphalt mixes between running and cracking. So definitely some progressive thinkers there. And then also still working for us here. Tom's there, has contributed a lot over the years to that. He was actually our statewide Illinois dot. Engineer of the.  Year several years back. For his efforts in in this area, and then also I can't say enough about the contributions from the Illinois Center for Transportation and Professor.

00:30:26 BP: Al Qadi and his team there they are huge help to us and really instrumental not only in the you think of universities being involved with more of the theoretical or the research or the laboratory base, but they really did a lot of work to help us tie the field performance to the laboratory test too. So with a study that I think included.  Eight different pavement sections in the Chicago area and analyzing the thing they focused in on five to correlate with that transverse tracking and field performance. It's been a great partnership for us and they've they've really helped us turn research into a very practical and implementable set of results. So.  Appreciate all the work that they've done and I think we talked too about or collaboration with the industry definitely is it huge part of our ability to to move forward with this and and with our districts too. So a lot of folks had to come together to and we've also incorporated these performance tests into our training program. We we worked with Lakeland College here in Illinois for our quality management training program. So for the new technicians you know coming into the industry, they're learning about these performance.

00:31:36 BP: Yes, and and doing that through that training program. So we appreciate their efforts too. That's a big part of it as well. So wanted to acknowledge the Federal Highway administration too and the the assistance we've gotten from them and also we've been working with them really closely the last few years. They've published a few reports or sponsored. Some efforts we were the subject of a virtual site visit, along with a number of other states. There's a report published through the University of Nevada, Reno in 2020 that that highlighted us and several other. States and then we've been working. With Federal Highway.  And hosted the regional peer exchange here earlier this year, and then we're going to be hosting another one here in, in December. So we appreciate our federal partners and the collaboration.

00:32:23 BJJ: There now, Brian. Now is there anything that you would say to your peers at other DOT's?  That have not implemented balanced mix design. Any tips or any recommendations you have for them or words of encouragement to move in this direction?

00:32:40 BH: I guess I will.  Just simply say that you feel like there's a benefit to it. Feel like we've gotten more to a quote UN quote balance state with regard to cracking, running and moisture resistance. It does take a lot of time. It does take a lot of. Effort. But if anybody has any questions, by all means we're always open. If somebody wants to reach out and ask. Or to see how we've set up the database for cracking resistance, or how we've set up round Robin studies. But there's no time like the present to start collecting data because it takes a a large amount to really, truly understand.  How mixtures are performing in your state with those particular specifications and standards that are employed?

00:33:25 BP: And I think I may use the term earlier, like establishing A baseline of, you know, of where your mixes are. And I I would tell other states to or or advise that don't be afraid to raise that bar. I know that's something.  One of our districts in particular is presented data kind of showing where their contractors mixes were prior to implementation and then during that phase in you know the shadow year and then then after implementation and and really you may see results when you do look at the the performance that you're seeing. Also look at the the potential for raising that bar and and getting improved performance. We feel like and we're starting to get that kind of feedback and we this is our third season of full implementation. And right, Ryan, I think. And so we're now and we had a meeting with the our industry representatives a few weeks ago and just kind of talking through the different situations. You know you get out in the field, you get on projects, the sample fails, you retest, it fails again, what do you you know, how do you handle that and what do you do and and that was a concern.

00:34:30 BP: Early on, I think where they say, OK, you know, you're trying to shoot between. These two performance goals, routing and cracking. But what if that's so narrow that you're constantly getting failing results on one side or the other, or bouncing back and forth between them? So is there really room there? So that's really, I think is the balance that you want to try to find is, you know, getting the best performance you can on both sides of the equation.  But still leave enough room in the middle to, you know, for for variability and and we do feel like.  We're getting that kind of feedback so far that you know, the vast majority of our our samples are passing. The contractors have figured this out. They've figured out how to design their mixes, operate their plant and use the recycled material in a way that they can, you know, pass our tests and and be successful.

00:35:18 BJJ: Are there any resources that Illinois dot has that we can share as links?

00:35:23 BP: The the ICT research reports the Federal Highway sponsored report from University of Nevada, Reno. There's going to be, you know, for the regional peer exchange. I don't think that's published yet, but there'll be a report coming out from that one. But yeah, definitely we can.  Get some some links to.

00:35:41 BJJ: You we'll put links on our website under this episode and if you want to get in touch with Illinois dot about what they've done, we will put some kind of information about that on the website as well. So Brian and Brian, thank you so much for your time today and thanks again for sharing.  All this information.

00:35:58 BP: Thanks for having us.

00:36:00 BH: Thank you.

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