Episode Preview with TTI's Tom Scullion (audio, 27s):
Full Episode (audio):
February 14, 2023Episode 51. One Size Doesn’t Fit All: Maintaining our roadway infrastructure demands a varied scientific approach.
FEATURING: Tom Scullion
America’s roads were built to last, but they weren’t built to last forever. New research is taking a forensic approach to maintaining and repairing our surface transportation infrastructure.
About Our Guest
Manager, TTI's Flexible Pavements Program
TTI Senior Research Engineer Tom Scullion is a Texas A&M University System Regents Fellow and manager of TTI’s Flexible Pavements Program. He’s studied pavements for more than 40 years for a variety of sponsors and pursues current research interests in pavement design, high-performance thin overlays, non-destructive testing, full-depth reclamation and soil stabilization. Among other applied research innovations, Tom supervised the development of ground-penetrating radar interpretation software for the Texas Department of Transportation and provides training on this and other pavement technologies for the department.
Bernie Fette (host) (00:14):
Hello again. This is Thinking Transportation — conversations about how we get ourselves and the things we need from one place to another. I’m Bernie Fette with the Texas A&M Transportation Institute. If we judge things on appearance alone, it’s easy to think that streets and highways are almost indestructible, strong enough to bear the weight of countless cars and trucks day after day and year after year without fail. And though many of us don’t realize it, there’s a lot of science, chemistry, and engineering that goes into keeping those driving surfaces in good shape. That’s our topic today with Tom Scullion, a senior research engineer at tti, and an expert in pavement maintenance and repair. Tom, I know you’ve been super busy and you’ve been traveling a lot. We’re really grateful you could make time to join us today. Thanks, Tom.
Tom Scullion (guest) (01:14):
Bernie Fette (01:16):
I know we’re gonna try to talk about a number of new things in your work today, what you can do to help roads stand up to the vibrant energy industry in Texas, environmentally friendly ways to, to repair pavements. Yep. I was hoping though, that we could start at a more basic level, particularly for listeners who don’t know anything about road building. Those of us who don’t think about roadway maintenance unless we run over a pothole. So can you give us a picture of the major steps that go into building a street or highway?
Tom Scullion (01:50):
Yeah. Most of my experience, vast majority of my experience has been in Texas and I, I think when we talk about building roads in Texas, it’s not one size fits all. We’ve got a state here with just about everything. If you go from east to west — in east Texas, you have some really poor soil conditions and you have a lot of rainfall. You go to west Texas and you have very good soils, very good subgrade materials, very little rain. That’s an ideal situation. You go to south Texas and you have very pleasant climates. You go up to the panhandle and we get several feet of snow. Mm-hmm. <affirmative>. So like I said, road building in Texas is not one size fits all. Texas is blessed with some of the worst soils in the whole United States. Uh, that is these expansive clay materials that we find anywhere east of Interstate 35. Okay. Uh, these are the soils that when they get wet, they expand, and when they get dry they shrink and crack. All of these issues I’m bringing up now are to do with the challenges of building roads in the state of Texas.
Bernie Fette (03:04):
Tom Scullion (03:05):
Now, road building really started maybe a hundred years ago, and the big drive back then was to get the farmers out of the mud. And the first thing you have to do with these roads that we built was you have to have a stable foundation.
Bernie Fette (03:24):
Tom Scullion (03:24):
Now, if you’re working on this very poor soils that we have, how do you get a stable foundation? Well, you have to chemically treat it. So Texas probably uses more lime than the rest of the whole United States together because of the very sorry, nature of the soils that we have to build it on.
Bernie Fette (03:44):
Okay. And so you have to do a lot of things to that soil. And when we’re talking about soil, we’re talking about more than just the dirt. You’re talking about the clay, you’re talking about the rocks that are in it, the other organic matter like roots and grasses and such. Yes. All of the things that you’re talking about have to be done to make the soil essentially more stable.
Tom Scullion (04:02):
That’s right. Okay. We need a, a stable foundation. Right. To put a road on it. Now, when we started, the vast majority of that payment structure in the rural areas was this lime stabilized subgrade where we needed it, six inches of limestone material, and then what was a surface dressing, which is just a shot of asphalt and a layer of rocks placed on top. Okay. Those things, if they’re designed properly, really got the farmers out in the mud, so that’s okay. Kind of where we started. Now, the other thing which drives the whole payment design side of things is the amount of traffic on the roads. And I’m sure you’ve heard the statistic before for the last, oh, I don’t know how many years, there’s been a statistic that there’s a thousand people a day moving to Texas.
Bernie Fette (04:51):
Right, right. And they all bring their cars and trucks.
Tom Scullion (04:54):
They’ll bring in two cars with them. And so then we have many more vehicles on the roads and subsequently because of the influx of people coming here, we need new roads, but we also need new buildings and highways and schools and all this kind of good stuff. So that drives the whole economy, the construction economy, not just of roads, but of buildings that’s putting more load on the roads that needs to be, you know, accounted for.
Bernie Fette (05:19):
Because a lot of the same things that you’re using to build roads, you’re also using to build those, those office buildings. Yeah. And schools and such. Yeah. Okay.
Tom Scullion (05:27):
The basic road system was really put in for the farmers, but then when we have this tremendous growth and then we have the focus on moving the cities, we’ve gotta modify things to handle those situations.
Bernie Fette (05:38):
Okay. So you started out with this goal of getting the farmer out of the mud. Mm-hmm. <affirmative>, and we’ve proceeded to a more modern Texas where urban areas are growing at an extremely fast clip. Mm-hmm. <affirmative>, uhhuh, <affirmative>. Those things taken into consideration once you’ve built that, that stronger foundation for those roads and put the surface on them and put those roads into use, how long can you reasonably expect those roadways to last before the pavement needs to be maintained or fixed?
Tom Scullion (06:09):
When these things are initially designed there, there’s two types of pavements that you see when you move to the cities. One is asphalt pavements, right. Where we have a layer of the black stuff, which covers our base material. Our base material is usually, typically just a layer of limestone, aggregates that is compacted and whatever. Then we put certain thicknesses of asphalt on top of that. What has become really popular in the urban areas is the other type of payment that we see a lot of is concrete payments.
Bernie Fette (06:40):
Right. And you’re getting to, one of the questions I was hoping to ask is why we have those two different types.
Tom Scullion (06:45):
The feeling right now with with folks like the Texas Department of Transportation is that when we get into the urban areas, and I’m talking about the urban areas of Houston, and I’m talking about the urban areas of Dallas. Mm-hmm. <affirmative>, that’s where we have requirements on there. Man, man, we want to get in there. We want to do whatever we’re building and we don’t want to come back for 30 years. The consensus is that the concrete pavements in those brutal conditions usually hold up better. Okay. You know, or give us those long life. Now there’s a whole history of road building in the urban areas and I think, uh, the Texas Department of Transportation has really done a, a good job of designing payments to last in those areas. They go through this foundation stuff again, when you get into the areas of Houston, because Houston’s on some pretty poor soils. They go with lime stabilized layers, uh, base layers, and then they’ll put 12 to 14 inches of concrete as the wearing surface. Mm-hmm. <affirmative>, those typically, you know, don’t give you any problems till after at least 20 years. Their design life is normally 30 years. That’s what they’re designed for.
Bernie Fette (07:59):
Okay. As opposed to asphalt roadways, which you can expect to last about how long?
Tom Scullion (08:05):
Normally the asphalt roadways are designed for 20 years. Um, and the expectation in the design process is you will not do anything to these roads for 15 years. At 15 years you’ll have to do some resurfacing. You know, you should just have like a surfacing problem where you need to come and redo the surface of the road because maybe it’s got some minor cracks in it. Mm-hmm. <affirmative>, or maybe it is got some skid resistance type problems. So for a national payment, normally in year 15 when they’re built for this urban situation, normally in, in that situation you’ll be coming to do some milling and a, a new surfacing after say 15 years.
Bernie Fette (08:47):
You’re talking about the differences between concrete and asphalt pavements, how long they last. One of the things that a typical traveler is probably most familiar with whenever they encounter a maintenance issue is the pothole. Mm-hmm. <affirmative>. Mm-hmm. <affirmative>. And so just to give us a little bit of a engineering 101 or road maintenance 101 explanation, why do potholes happen?
Tom Scullion (09:12):
I would say that the main reason is the combination of, um, overloaded vehicles and bad weather, heavy rainfall. And you know, we have a hard time regulating the loads that drive on these roads, especially, you know, the energy sector stuff going on and what have you. But sometimes the roads, maybe there were designs for a certain level of traffic, and we’ll talk about this later too. And the level of traffic might have gone up by a factor of 10 and there’s 10 times more loads on the road and what have you. Now, if we’re talking about potholes in asphalt pavements, normally what happens is because of the traffic on it in the environment and what have you, you get some kind of cracking going on. Okay. Then what happens is you get rainfall going in there, the surfacing is supposed to protect the base from wearing out. Now if that surfacing cracks, you get rain into it, you get moisture into that limestone base down there, all things go bad. So increased traffic loads, payments that will never designed for those roads, surface cracking, water getting in, but you have potholes.
Bernie Fette (10:21):
Right. And you mentioned the extra load on roadways that weren’t built to handle those roads. You specifically mentioned roadways in the energy sector, Permian Basin and other parts of Texas as well. And not just Texas, but anywhere in the United States where the roadways were built for a particular type of traffic, perhaps cars and pickups and maybe the occasional tractor, but now they’re standing up or those roads are trying to stand up to much, much heavier loads. Mm-hmm. <affirmative> due to circumstances that were not foreseen years before when they were designed and built. What are some of the challenges that you’re running into there, especially since those are relatively recent developments in Texas and and how have you been dealing with those?
Tom Scullion (11:06):
Yeah, that’s what I’ve been dealing with Bernie for the last 10 years, and that’s when the energy boom really kicked off in both south Texas and in the Odessa area. Mm-hmm. <affirmative>, Permian Basin. Mm-hmm. <affirmative>, and as I say, those roads were never built for the loads that are on them. The energy guys are what drives the economy of Texas. So we need to, you know, accommodate this stuff. And so the challenges that were put in there is that you have a road that was designed for 500 cars a day, and all of a sudden that road is carrying 500 trucks an hour. I mean, the roads in both areas, south Texas, in the Odessa area were totally destroyed. The farm to market network over there was totally destroyed. Mm-hmm. <affirmative>. So we got into working with the Texas Department of Transportation to say, well, what the heck can we do? Well, TxDOT made the challenge even more interesting because they said, okay, you guys, you need to come up with a fix. We need to widen these roads, we need to strengthen these roads. But the one kicker on top of that stuff is whatever you folks do, we’re putting the energy sector traffic on it that night. So whatever repairs you come up with, you’ve gotta get outta the way at five o’clock and we’re putting the energy sector loads on it.
Bernie Fette (12:29):
So fix it right. And fix it fast.
Tom Scullion (12:31):
Fix it fast. That has been what we have been working on intently for the last seven or eight years at least. And what we do, these are roads in rural areas where you really need to figure out how to take the existing structure and strengthen it. But you’ve also got that additional requirement on it of, you know, um, how can we put the traffic on it early? And we’re talking about fully loaded energy sector trucks here. Okay. We’re talking about going in there, doing something to the road, mixing it up, leveling it out, and then within two hours putting traffic on it. The traditional approaches didn’t work.
Bernie Fette (13:09):
And just for a perspective, you were having to accelerate procedures to a degree. Yeah. Leveling things out, fixing it, and two hours later putting traffic on it in the past, or if this was not an energy sector roadway, how much time would be allowed for the processes that you’re talking about?
Tom Scullion (13:26):
Oh, you can keep the road closed for two or three days while you get everything looking pretty and make sure everything is gonna hold up and what have you.
Bernie Fette (13:34):
Two or three days versus two or three hours. Yeah.
Tom Scullion (13:36):
Yeah. This, okay, this, remember what we’re talking about here is minor roadways in the boonies where there is no detour available.
Bernie Fette (13:44):
Tom Scullion (13:44):
And you’ve got major energy sector development going on along the route.
Bernie Fette (13:50):
Because time is money.
Tom Scullion (13:51):
Get in there, fix it, and get outta the way. Right. There’s a challenge. Okay. Now what we’ve been doing and what we’ve promoted and what is working very well is coming up with a combination of different materials. And this gets into a lot of things. This gets into the whole concept of improving our pavement recycling processes. Mm-hmm. <affirmative> Recycling is where we come and evaluate the existing structure, mix it all up with a huge reclaimer, put some kind of stabilizer into it, we will then compact it and roll it. We will not put a surfacing on it, but then we’ll put the traffic on it. So the challenge for us is what kind of treatment can we apply to this thing to facilitate this rehabilitation option?
Bernie Fette (14:37):
So you’re grinding up an old roadway, you’re mixing in newer materials, and then using that combined product to build a new driving surface. Right?
Tom Scullion (14:46):
Yes. Well, it is gonna eventually have some kind of surfacing on it. Okay. But we want to make it stable enough that we can drive on whatever we finished at the end of that day.
Bernie Fette (14:57):
Even if it doesn’t have an asphalt surface on top.
Tom Scullion (14:59):
It doesn’t have an asphalt, it doesn’t have a seal coat. Nothing. It’s on a treated material.
Bernie Fette (15:03):
You’re just driving on the base material.
Tom Scullion (15:05):
That’s right. That’s
Bernie Fette (15:06):
Right. Okay. Okay.
Tom Scullion (15:07):
Bottom line on what we’ve been promoting is that we knew that our, our standard stabilizers cement wouldn’t work because it kind of set up as fast. So what we’ve done in the last seven or eight years at least, is come up with a combination of cement in asphalt.
Bernie Fette (15:23):
Tom Scullion (15:23):
<affirmative>, We have two products. One is 1% cement and foamed asphalt, and that’s just another story in itself. Or we have 1% cement and an asphalt emulsion. We mix these two things together and we come up with the best of both worlds, I think. Okay. Because when we do this and we compact that thing, you gain strength, the asphalt will help you with the waterproofing because the last thing you want is to finish the construction and then you get three inches of rain that night. Right. And then you’re putting these trucks onto it. So whatever you do has gotta have the strength and it’s gotta have the ability to shed water if it gets rained on. The energy sector is still booming and it’s still really, really booming in the Odessa area. And I think we put several hundred million worth of this material down in the last five years. They’re rebuilding all the roads in Odessa, and this combination of fold EPP recycling with an asphalt cement combination is really working well for these people.
Bernie Fette (16:29):
So I’m hearing you talk about challenges that current modern road builders are having to deal with that were not an issue more than a century ago. Yeah, that’s true. Okay. On the flip side of that, what sorts of things did the early road maintainers have to contend with that DOTs don’t have to worry about today? What’s the converse? And yeah. I’m thinking in part about horse manure as one example, <laugh>. So what were the things from previous ages, early days of road building that we have today that they didn’t have to contend with over a hundred years ago?
Tom Scullion (17:09):
Well, I, I’m thinking about the great advances that have been made, you know, okay, where, where, where, where are these things? And I, and I really think the advances have been made in the terms of the equipment that we have available now. I mean, this maybe is not known, but there’s a lot of money in this road building and making sure it’s permanent. Um,
Bernie Fette (17:30):
Great. Let’s, let’s talk a little about those advancements then. Yeah. Specifically in the time that this has been your life’s work. Mm-hmm. <affirmative>, Can you start with talking a little about ground penetrating radar? Talk about that a little bit because just the name itself sounds pretty fascinating and then you can go from there.
Tom Scullion (17:46):
Yeah. I’ve been around this technology since the late eighties and I think I, the best way to explain it is to think that we’re road doctors. What this technology does, if for a layman’s point of view is X-ray the road, okay. We can go along at highway speed, use this technology to go and shoot into the pavement to tell us what we have there. And often we go to roadways and we really, like I say, it might be a 50 year old road and it’s been maintained and there’s all kinds of things going on. And then we put a very thin surface over it. So what’s beneath the surfaces? We’ve got no clue. Right. So we needed a technology that would help us get through this whole process of rebuilding these roads, strengthen these roads. So before you do that, you say, well, what we got, well, we don’t know what we’ve got. The last thing you wanna do is get a contractor out there to do a lot of repair work where he is gonna grind things up and hit a major change. You know, and the main benefits of this technology we’re talking about, the ground penetrating radar is no surprises. Okay. We want to fully understand what we have beneath the surface so we can effectively treat it. The technology itself is very fascinating because it was developed by the U.S. military in the 1970s for land detection.
Bernie Fette (19:09):
To, to find landmines. Okay.
Tom Scullion (19:12):
Yeah. Now, back in the sixties and seventies, the landmines were all metal, but they changed from being metal in the eighties to be much smaller plastic mines. So the military decided that the technology, they developed a very good technology, wasn’t appropriate for the application they needed, had to move on to something else. Mm-hmm. <affirmative>. So that technology was released for applications and that’s where we jumped into it with a few small companies to say, well, what can we do with this stuff? Mm-hmm. <affirmative>, at the moment, we mount this radar antenna on front of a vehicle and it’s four foot in front of the vehicle, and we travel down the road at 70 miles an hour and we can take a reading every foot as we go down and we can measure the thickness of the road and we can tell you if there’s any defects in that road beneath the surface. We’re looking down to about two foot beneath the surface. And so we essentially get an x-ray of the road at 70 miles an hour. Every one of these pavement rehabilitation strategies or projects I get involved with, we use this technology as step number one. We have a picture of what the animal is that we’re trying to rehabilitate here.
Bernie Fette (20:24):
And having those readings is important because it’s the quickest and most efficient way for you to find out what is happening below the surface. Yeah. This helps you and the contractors who are hired to fix the roadways helps to know exactly where the problems are so that you can Yeah. Put the dollars where they do the most good, right? Yes,
Tom Scullion (20:47):
Yes, that’s right.
Bernie Fette (20:47):
That’s right. Okay. Which leads me to the point that road building is a pretty expensive endeavor. Mm-hmm. <affirmative>. So can you talk a little about how all of these advancements, and I know we’re talking about just one now, but just this one for example, how does it help to stretch transportation budgets, whether we’re talking local or state or federal transportation budget levels?
Tom Scullion (21:08):
Yeah. I’ve been doing this stuff for a long time and I think in Texas we really have put together the set of tools that let you do it right. And it’s not just us here at the Texas A&M Transportation Institute. The technologies we’ve been developed have been fully implemented statewide around the state of Texas. The main thing Bernie, is man, no surprises. Okay. We don’t want to get into projects, start turning it over and find out. It’s completely different from what we had. When you have these kind of surprises that you come to on projects, man that can eat your lunch, when it comes to getting these things done the way they should be done.
Bernie Fette (21:48):
I mentioned in that last question, something about the federal transportation dollars. Mm-hmm. <affirmative> and speaking of the federal level mm-hmm. <affirmative> Congress passed an ambitious piece of legislation. Yes. Last year, the Infrastructure Investment and Jobs Act. How does that collection of policies address roadway maintenance in this country?
Tom Scullion (22:10):
Yeah. We, we will have to see. The focus of that policy is really welcome. I mean, we really need to explain to the public that man, the, these roads were designed for 30 years and a lot of these roads out there and now 60 years old, they’ve lasted a lot longer. And they’re held together with band-aids is what? What’s happening without the emphasis put on it by this policy, you know that DOTs will never have enough money to do everything they need to do. So what they do with these older roads is they put band-aids on them, which means that they have to come back every three to five years instead of having them money to fix them properly. Right. So that’s what you see a lot of, Bernie, going on there, is that you have a road that’s cracked up. We go out and do the design and we give them two options. We say, well, if you want a bandaid to hold this thing together for four years, I can give you that. But if you really want to fix this thing for 20 years, you’ve gotta spend a lot more money. Well, that money was never available. Now the fact that the feds have come in there and you know, encouraged a thorough investigation that’s really welcome. But whether we’ll ever have enough money to do all the fixing that we need to do, that’s another question.
Bernie Fette (23:24):
Because the, the roads we’re talking about, they were definitely built to last, but they were not built to last forever.
Tom Scullion (23:30):
Well, just the length of time and the amount of traffic on them with the issues of the number of people coming to Texas, and then with the issues of the special development, energy sector development, agricultural development, and all this other things, the amount of traffic and the loads of traffic have all increased substantially. They were designed 30, 40 years ago. They were never in design for that level of traffic.
Bernie Fette (23:54):
So much of what we’ve touched on, we could do several hours of discussion on all of this. I know, Tom. So as I’m trying to wrap up our conversation, I’m, I’m wondering, can you share your thoughts on what you see as being the biggest research needs for the near future? We’ve talked a little about advancements over the past several decades. Where is the next big thing likely to come from?
Tom Scullion (24:18):
Of course, Bernie, the big thing for the next 10 years is gonna be this environmental stuff, this carbon footprint. How do we change our whole operation to give us a smaller carbon footprint? So the whole industry needs to look at this whole environmental side of things now. Mm-hmm. <affirmative>, I think just adding on to what we spoke about earlier, where we contribute on that area, there has to be worked on materials and whatever, but you think of the carbon footprint from rebuilding roads where you take everything away and build a new road to what I’ve been telling you earlier, which is recycling. Mm-hmm. <affirmative>, I think there’s gonna be a big boom in this area of recycling. You know, when the road wears out, one of the things you can do is get rid of the whole road and then build a new one. Mm-hmm. <affirmative>. Well that takes a lot of energy. You’ve gotta know the materials, you’ve gotta take ’em away. You’ve gotta bring new materials in, you’ve gotta mine them. Well, there’s a lot of energy and a lot of cost there.
Bernie Fette (25:19):
And a lot of environmental implications.
Tom Scullion (25:22):
Yes. If you can do what I’m talking about, which is look at the existing roadway with the technologies we have. Look at ground penetrating radar, falling weight, deflectometer, and come up with a very good long-lasting design by grinding up what’s there and treating it. Somehow the environmental impact is minimal compared with the full reconstruction process. So I think very, that’s the focus and the future because of the federal push and you know, this is the global warming and all this kind of stuff going on here. It really is gonna come impact the road building industry.
Bernie Fette (25:56):
Lastly, Tom, what is it that keeps you showing up to work every day?
Tom Scullion (26:02):
Well, maybe I fooled a lot of people over the years, or sounding, but a lot of people think I know what I’m talking about. Maybe it’s my funny accent. They told me that 50 years ago, Bernie, that this thing is gonna peter out. And I’m still here, man, and I’m still busier now than I was 50 years ago. I’ve got to the position where people trust me. Mm-hmm. <affirmative>, and whenever we have a problem, if something doesn’t hold up, it was designed for 20 years and we’re seeing problems in five years and we’re seeing problems in two years. I get called in to do what’s called forensic investigations. We did one just this week in the Odessa District, and these are the challenging things where roadways fail. If roadways never fail, you don’t learn anything. But if a roadway is supposed to last 20 years and you have problems in one year, you go in and figure out what the heck happened here. Mm-hmm. <affirmative>. So I do about one of these a month, and that’s truly where we learn things. If the road is designed for 20 years, you build in and it performs perfectly. You don’t learn anything. A lot of the advances we’ve made in the last 15 years has been caused by digging into failures, understanding the failures, and implementing changes so it doesn’t happen again. That’s why I come to work, because I do a lot of these forensics, and when we do these forensics investigations, that’s where we learn things.
Bernie Fette (27:28):
We’ve been visiting with Tom Scullion, a senior research engineer at tti, and by his own definition, one of the road doctors who is working to keep your daily travels is smooth and pothole free as possible. Tom, thanks very much for being with us. This has been fascinating.
Tom Scullion (27:48):
Alright, thank you Bernie.
Bernie Fette (27:50):
The process of building a roadway seems simple enough. Lay out the base material and cover it with asphalt. But keeping those pathways in good condition is far more complicated than it might appear. Maintaining a stable transportation infrastructure requires careful investment and scientific precision. Because the roads and bridges we drive upon every day were certainly built to last, but they were not built to last forever. Thanks for listening. Please take just a minute to give us a review, subscribe and share this episode, and we hope you’ll join us again next time for a conversation with Tim Lomax. When Tim was a young boy, his mother told him to go out and play on a freeway. He used that advice to launch a 46-year career in transportation research thinking Transportation is a production of the Texas A&M Transportation Institute, a member of the Texas A&M University System. The show is edited and produced by Chris Pourteau. I’m your writer and host, Bernie Fette. Thanks again for listening. We’ll see you next time.