Ohio Concrete

Concrete Testing At The Core Of The Maumee River Crossing

From 2002 through 2007, the distinct sounds of hydraulic drills, bull dozers and front end loaders became familiar to the traffic goers of Toledo, Ohio. Fru-Con Construction Corporation, a general contractor headquartered in St. Louis, Missouri, was in the process of constructing a new bridge over the Maumee River that was poised to be a lasting landmark for the city. As part of a program to modernize Interstate 280, the six-lane, $220 million bridge, boasts a 1,225 foot main span and cable stay consisting of 156 individual strands, the biggest and strongest ever used on a cable-stayed structure. It was made from 14,000 tons of epoxy coated reinforcing steel, 3,900 tons of steel post-tensioning cables and 186,000 cubic yards of concrete. To help with this record-breaking project, Fru-Con contracted the services of Ohio Concrete Sawing & Drilling of Sylvania, Ohio.

On Friday, July 19, 2002 the last day of a grueling week of the busiest month of the year, Ohio Concrete Sawing & Drilling received a phone call from Fru-Con at 4:30 p.m. Fru -Con needed two holes drilled, each approximately 70 feet deep and two inches in diameter. At the moment, the proper equipment to perform such a sizeable task was at one of Ohio Concrete’s other branches. Therefore, they immediately sent someone to their facility in Columbus, Ohio to retrieve special core bits allowing them to drill to the desired depth. At 7:00 a.m. the next day, Saturday, operators began drilling the first 2” holes on the Maumee River Crossing.

Fru-Con uses a special testing technique called cross-hole sonic logging (CSL) testing to show possible anomalies within the 8’ diameter piers supporting the bridge. The CSL testing works by sending an electric pulse from one tube cast in the foundation pier to another tube within the pier through the use of a sending and receiving probe. The time it takes for the pulse to travel is recorded, and velocities are calculated at one-inch increments. Sent by e-mail, the results which are interpreted by Conrad Felice, a geotechnical engineer in Seattle, Washington, give a profile of the entire foundation pier from top to bottom. Twelve total profiles are taken within each 8' diameter pier.

CSL testing has become an acceptable manner of determining the integrity of concrete in the last ten years. It is the first step in determining the integrity of the concrete after the foundation pier is complete. However, this method of testing is not always successful due to slurry interfering with the electric pulse. Therefore, core drilling is a secondary test to CSL. Core samples are taken to determine if there are any voids present within the foundation pier as well as to demonstrate compressive strength at different intervals in the caisson.

Because a core drill allows the operator to drill only as deep as the bit, Continental tubing is used. Continental tubing is hollow tubing threaded on each end and allows the drill operator to drill very deep holes without continually retrieving the cores. When the core drilling is complete, the 2” core pieces are removed from the tubing and aligned in order from top to bottom. Then, the pieces are tested to make sure the foundation pier is solid and the concrete meets the Ohio Department of Transportation’s specifications.

Fru-Con has been very pleased with the service of Ohio Concrete. Matt Hogan, a manager for Fru-Con, said, “Ohio Concrete Sawing’s service to this project has been outstanding both in the timely response to requests to perform the coring as well as the experience shown while working on site.”

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