A Concrete Solution to Freeway Repair: D7 Road Tests an Innovative Precast Panel Strategy
Click on photos to enlarge and read captions.
On an unseasonably warm day in March, about 40 people — Caltrans staff and contractors — and numerous construction vehicles were gathered on a coned-off section of westbound I-210 just east of SR-2 for a pavement demo. But this wasn’t just any pavement demo. Three broken concrete slabs were about to be repaired using an innovative new strategy developed by Caltrans Maintenance staff and an enterprising small business contractor. Up to this point, only a small group of people had ever seen this done. An even smaller group understood how it worked. That was about to change.
More on the demo in a minute. First, some background. There are two basic methods to replace broken concrete freeway slabs: cast-in-place (usually using rapid-strength concrete) and precast concrete panels. As the name suggests, with cast-in-place repairs, the broken slab is removed and concrete is pumped into the roadway cavity. With precast concrete, the panels are cast and cured at a fabrication facility and then placed at the repair location.
District Materials Engineer Kirsten Stahl has been advocating for the use of precast panels as an emergency maintenance strategy since 2001.
“When a slab breaks up on a high-traffic freeway, we need to be able to fix it fast,” said Stahl, who provided invaluable support in developing base specifications for the panel design used in the I-210 demo. “If we have these panels stored at a maintenance yard nearby, we can drop them in and open to traffic an hour later.”
Precast panel repairs initially are more expensive than cast-in-place, but they’re also more durable, which means they’re cheaper in the long run and require fewer maintenance closures. The dicey part of working with precast panels is the installation. Grinding and leveling the panels can be difficult and time-consuming. But that’s changing, thanks to Maintenance Design Manager Debbie Wong,* Maintenance Area Superintendent Ed Toledo, Baltazar Siqueiros of Baltazar Construction, and Stahl. Working together, they’ve developed a better way to install precast concrete panels.
The Wong/Toledo/Siqueiros/Stahl strategy was inspired by slow, tedious slab replacements in Toledo’s area, requiring lengthy closures and sometimes resulting in failed panels. The key to the new strategy is a clever piece of hardware, a leveling lift, that Siqueiros developed. The leveling lift allows panels to be installed quickly and relatively easily without extensive grinding. Essentially, it allows the panel to be raised up and down using a screw-like mechanism.
Wong made some modifications to the hardware and panel design, and then, after getting approval from Deputy District Director of Maintenance Dan Freeman, it was time to road test it. The first batch of panels using the new system was installed on westbound I-210 during a miserable weekend in November 2012.
“It was cold and raining — probably the worst possible conditions for a test run,” said Wong. “But we figured if we could make it work here, it would work anywhere.”
And it did work — quite well, in fact. Despite some equipment issues, the hardware functioned as intended and the work proceeded quickly. Wong said crews installing panels without a leveling lift can typically complete 124 feet of repairs in a night. With the leveling lift, they can do 500 feet.
With the first successful installation under their belts, crews installed another 40 panels in eight hours on northbound I-5 near Lake Hughes Drive and 40 more on I-210 near Lake Avenue. Which brings us to the I-210 demo project in March. With the strategy working so well, it was time for show and tell. Wong invited contractors and Caltrans staff (including folks from District 12) out to I-210 to see exactly how to install a precast panel with a leveling lift. Up to this point, only Baltazar Construction knew how to do it; other contractors needed to learn the technique.
So how, exactly, does it work? With apologies to engineers and the technically inclined, here’s How to Install Precast Concrete Panels with Leveling Lifts in Six EZ Steps:
Step 1: Mark and measure the precast panel layout. Cut the damaged slab into chunks, which will then be lifted out of the roadbed. In the video below, this process looks like removing big, concrete brownies from a pan.
Step 2: Grind the roadbed so it’s a bit deeper than the thickness of the panel, which in this case, was 8.5 inches. Clean up debris.
Step 3: Lay thick plastic sheeting in the cavity, kiddie-pool style. This will keep the grout from oozing into places where grout shouldn’t ooze.
Step 4: Using a crane, place the concrete panel in the excavation (the hole in the roadway). The panels and excavation can be trimmed to fit before placing them, if necessary.
Step 5: Level the panel so it’s even with neighboring slabs by adjusting the leveling screws in the corners. This is sort of like leveling a tripod by adjusting the height of the legs.
Step 6: Pump rapid-setting, self-leveling grout under the panel and — ta-da! — open to traffic. The dowel bars that fit into the dowel joints connecting the panels can be installed up to 48 hours later, if necessary.
The steps listed above are, of course, an oversimplification, but installing concrete panels using this method is considerably simpler than the standard method.
“Since we can cut the excavation to fit the panel, level the panel with screws, and grout it to achieve the necessary depth, we don’t need surveys,” said Wong. “It’s a huge time savings. We can close the lane, install the panel and reopen to traffic all within three hours.”
Not only do the panels install quickly and thereby minimize closures and exposure of crews to live traffic, they can also be removed and reused somewhere else. Additionally, they can be installed in any weather and they last a long time.
“We know we won’t have to go back out and replace them in year or two,” said Toledo. “These panels can last 50 years. They’ve got a much longer life-cycle than any cast-in-place solution.”
After the demo on I-210, a second demo was performed in District 8 a week later, followed by installation of another 28 panels on northbound I-405 near LAX.
Panels continue to be placed using the leveling lift system while the team perfects the process. (A patent is pending.) Leveling lift installation is not yet widely used by Caltrans, but if the panels that have been installed so far hold up well, it could be. It could be because innovative, committed Caltrans employees working with an excellent contractor knew they could improve upon a standard practice, and then they put in the time an effort to actually do it. There are now hundreds of panels on District 7 freeways testifying to their ingenuity, and by the looks of it, many more to come.
*Debbie Wong is currently District Claims Engineer, but still assists Maintenance with special projects.