June 9th, 2011
CONCRETE SHOWCASEPreserve Infrastructure, by Catherine Higgins.
A recent UDOT showcase demonstrated a quick and effective way to repair concrete pavement using precast panels.
Precast concrete elements are commonly used for bridge girders, decks or associated structures like MSE walls. Use of Precast Concrete Panel Systems to repair or build pavement is gaining popularity across the country but is not yet widely used. The construction process for repairing pavement involves removing the damaged concrete, preparing the road base then placing, leveling and grouting concrete panels into place.
UDOT has been using two PCPS to replace damaged pavement – a proprietary system available locally from one contractor and a non proprietary system detailed in UDOT’s Standard Specifications. With the support from FHWA Highways for Life, UDOT held a workshop and on-site demonstration to showcase a newly designed non-proprietary panel. Over two hundred attendees from across the United States took advantage of the opportunity to learn about design, construction and installation of the new panels.
At the workshop, designer Dave Eixenberger with T.Y. Lin International gave a lot of credit to Dave Gilley with Harper Pre-cast “who was a big, big help.” Eixenberger started the design process by looking at other PCPS projects and assessing lessons learned. His objective was to develop another tool to “provide a cost-effective and durable pavement product.” Working with Gilley, Eixenberger eventually designed a standardized panel intended to minimize construction costs and simplify installation.
The new panel is 12 by 12 feet square and 9 inches thick. Uncoated black steel rebar provides reinforcement to support lifting the 17,000 pound panel. The unique aspect of the design is the inclusion of leveling bolts that are commonly used in bridge deck construction. After placement, the bolts are turned against steel panels on the sub-base to achieve correct elevation. Four bolts are placed in each panel during the casting process. Six grout ports are also included in each panel.
Gilley experimented with different methods of preparing the sub-base and two grout options by setting up mock roadway trials at the pre-cast yard. Gilley and his crew arrived at some important lessons learned: A thin, firm sub-base is needed to prevent grout displacement and an adequately wide leveling bolt panel is crucial. As for grout options, concrete urethane type grouts were tried and found to flow and fill equally well. The final decision was to select urethane grout for the demonstration project. With a cure time of 20 minutes, urethane is much quicker than concrete grout which means travel lanes can be opened sooner.
The on-site portion of the showcase took place on the south-bound on-ramp to I-215 at 3900 South. Because UDOT requires work to be done with as little disruption to traffic as possible, “This process is schedule critical,” explains Gilley. “You need to get all of your ducks in a row.” Kilgore Construction crews had been placing panels during three previous nights so the process was executed with precision.
Daniel Hsiao, UDOT Research Division Project Manager who oversaw panel testing, design and the showcase event compares the new system to UDOT’s use of ABC construction methods. “We took bridges off the critical path — now we have to speed up the pavement,” says Hsiao.
As with bridges, using PCPS offers the advantage of a speedy repair which is great for road users. Using a cast-in-place method involves closing lanes and waiting for concrete to cure before traffic can resume. With PCPS, the cure time takes place is off site, so traffic lanes can be reopened soon after installation. And, another panel option in Utah will help support a competitive bidding environment, which conserves limited funding.
Other project personnel:
UDOT Project Manager: Matt Zundel, Region Two
Resident Engineer, John Montoya, Region Two
Information about the showcase will be posted on the UDOT website. Check the UDOT Blog for and update about project information documents.