Every commuter has experienced it at some point. Cruising along an interstate when you come to a grinding halt as crews are patching pavement. Suddenly the expressway becomes a stress-way.
Precast concrete paving slabs were developed to alleviate those stressful daytime lane closures, and several states have started using the product to ease traffic jams on the interstate. While some states have been using the paving slabs for years, others are just now getting into the game and have been pleased with the results thus far.
Test project in Indiana
Indiana prides itself on being called the “Crossroads of America” with four major interstates spanning the state. Like other states, Indiana has been dealing with deteriorating roads and bridges, but recently invested heavily into its infrastructure.
As more projects are coming online, the Indiana Department of Transportation is looking at ways to improve the process and is testing precast paving slabs in both interstate and urban settings.
As INDOT was looking at possible projects, U.S. 40 in Richmond rose to the top of the list. For starters, it’s a 100-year-old section of the historic National Road US Route 40 that never had a major reconstruction project. It was also a project INDOT had been talking about for nearly 20 years.
“We’re on the low-risk side of the scale,” said Robert Gill, project engineer with INDOT. “We don’t want the first panel we place to be on Interstate 70 and it not work out. Nobody likes that idea.”
Half the road was going to be shut down as part of the project anyway, so it made sense for INDOT to try paving slabs.
“If a panel shows up and there’s something wrong with installation, construction or anything, we were already taking the lane so it doesn’t cost us long term,” Gill said. “If something doesn’t go quite right, we have time to adjust. It’s an experiment; so let’s experiment with it.”
Photo courtesy of The Fort Miller Co. Inc.
Choosing the project
It’s easy to say paving slabs are the perfect remedy for interstate projects, but what do you do when you’ve got a project in an urban setting with utilities underground?
Sure, crews can cut into the slabs to get the work done, but that can be an intensive process. Enter removable urban paving (RUP) slabs that are designed to allow utility companies to easily remove slabs, access their lines and reinstall the same slab back in its original location.
Dan Moellman, P.E., senior product engineer with Fort Miller, said the RUP slab is new, with the project in Richmond being its second use. Moellman’s team did a presentation for INDOT and other interested parties prior to the project.
“There were a lot of skeptics in the room,” he joked. “People wondered if it would be completed in the required time frame. Nobody in Indiana had done this before, and they need an entrepreneurial vision to tackle this new technology.”
Gill noted that several parties had to buy into the project for it to be a success.
“The precast industry has to say, ‘Yes, we want to be involved with this project,’” he said. “The contractors have to build up their installation expertise; the utilities have to be on board. It’s not like I can just say, ‘Well, we know what we’re doing, go to it.’
“There’s more to it than that, and so far we’ve had that response.”
Moellman was hoping for just a few intersections since it was going to be a test project. Instead, INDOT decided to do six-tenths of a mile of U.S. 40 through the heart of Richmond.
“We were thinking it was just a starter project,” he said. “Everything was coming together, and I kept wondering if it was actually going to happen because it was such a huge project. They wanted to do a showcase project, and that really kicked it off and got things going.”
Joys of urban construction
Image courtesy of The Fort Miller Co. Inc.
“When you saw through the joints, the Super-Dowel pipe dowels are cut in half,” Moellman said. “You can drill out and access the four coil lifting inserts and remove the slab. Each Super-Dowel has an internal nut welded to each end. With the slab removed, engage the nut in the half-dowel remaining in the pavement with a threaded rod and remove the half-dowel. Clean the hole and epoxy in a new Super-Dowel. Remove grout from bottom slots and grout ports on the removed panel. Regrade bedding material, reinstall the slab and grout in place to re-establish load transfer. Typically, on continuous slab installations, you cast dowels into one slab and have them meet with the bottom slots on the next slab. That works fine if you don’t have to remove them.”
Gill is quick to note how problems with underground utilities are far too common with urban construction projects.
“For this one, there was a 100-year-old bank of phone lines that would have taken a year to move to the elevation the project would have required had we used a traditional paving job,” he said. “So by using these slabs, it saves us a year in waiting.”
Even though the panels are removable, many of the utilities in the area moved their lines outside the pavement area to minimize future work. Gill likes that INDOT is getting experience in removing the paving slabs, but this project is also allowing utility companies to gain experience as well.
Photo courtesy of The Fort Miller Co. Inc.
NCI President John Lendrum said they had never produced paving slabs before, but they were eager to learn about it.
“This project was a good opportunity for us to get into production of paving slabs and learn what it takes to make slabs on a large-scale basis,” he said. “So we really looked at this as an opportunity for us to learn.”
Since NCI typically produces utility vaults, this project created some additional challenges for its team. For instance, the tolerances were much tighter than they were accustomed to, and the design of the slabs were unique with some being trapezoidal and having cutouts for manholes or other existing utilities.
“It was good to set up a project with some experienced production leaders and quality control people,” Lendrum noted. “We trained with Fort Miller, and they helped us set up for production so that certainly helped, and it worked out well for us.”
The sheer number of slabs created a logistical problem for the NCI team as well.
“Just the logistics of how you move fresh slabs and don’t damage them, storing them to prevent them from being damaged,” Lendrum said. “When you’ve got 1,100 slabs, you have to have proper documentation of what you’re doing, how you store them. All those things are very important.”
In addition to ensuring a proper mix and reorganizing the production area for maximum efficiency, NCI had another thing to factor – the cold weather. The majority of the slabs were cast during the harsh winter months so blanketing and proper curing of curing the slabs was equally important.
“We did our training on the front end well,” Lendrum added. “We finished the project with a remarkably low number of errors and problems.”
Since there was so much engineering and training on the front end, the installation has gone extremely smooth. At the start of the project, crews estimated installing around 40 panels per day, but on their best days, they can get close to 50.
Gill noted the biggest challenge is scheduling the installation around other activities like ensuring not too many streets are closed at one time since the project is near a fire station.
“The panels have gone in as well as we could have hoped,” he said. “We feel like it’s as good as we can expect if not better than we expect.”
Photo courtesy of The Fort Miller Co. Inc.
By all accounts, the project has been a success for all parties.
In addition to saving the public on travel time, Gill noted the quality control and durability of precast slabs is greater than most concrete patching jobs which use an accelerated-curing concrete, that can deteriorate quicker.
“With panels, those are made a week ago, a month ago, so you don’t need to use accelerated concrete,” he said. “We don’t have to worry about set time because it cured ages ago. What that allows is that we can come out on a Monday night, take our lane, cut our hole, place the panel, grout it up, and we’re good to go.
“You never have a daytime restriction.”
Lendrum liked getting into precast paving slabs and hopes to add them to his company’s product line, but the project was also beneficial for his younger employees.
“The most immediate return is focusing our production people on accuracy and productivity,” he said. “That’s something we can readily transfer to the other products we’re making. We see some gains in that regard because of all the training we did.
“It’s a great way to take some young people, get them promoted and move them up in our plant.”
INDOT is looking at a few other test projects, and Gill has enjoyed talking shop with a lot of visitors – a benefit he really didn’t see coming.
“The whole point of this project is experimental engineering so we’re not talking about budgets or politics or anything like that, we’re talking engineering,” he said. “And that’s been really nice. It’s been a pretty rewarding project so far.
“It’s not every day you get to do an urban reconstruction project on a 100-year-old road.”
Matt Werner is the managing editor of Precast Solutions magazine and NPCA’s communications manager.
Acknowledgement: The article has been reprinted/reproduced from National Precast Concrete Association (http://precast.org/) with its due permission.