2013-09-19 / Front Page

DOT resumes construction on Fortson-Dorn Bridge

Work resumed Monday, September 9, on the construction of the new Fortson-Dorn Bridge, which spans the Savannah River, connecting Lincoln and McCormick counties.

Construction ground to a halt last winter when issues arose related primarily to the bridge supports, also known as columns or bents.

At the time, James “Jimmy” Smith, Georgia DOT engineer for the East Central District, said, “One issue involves the very soft soils that we have discovered beneath the supports and another has to do with the ambient temperatures of the bent concrete seals as the concrete cures or sets.”

Ambient temperature is that of the water at the depths of the concrete seals.

“The water is approximately 80 feet deep at some of the bents, which results in some very cold water relative to the temperature of the curing concrete,” Smith continued. “The temperature differential has caused stresses in the seals being evaluated.”

The problem has since been traced to Delayed Ettringite Formation (DEF), a chemical reaction that can occur when poured concrete overheats while curing. DEF is rare, and there is no record of it ever having occurred on a bridge project in Georgia. It can, however, result in the concrete weakening and cracking.

“The average size of the seals, which are located on the bents at the bottom of the lake, is 30 x 30 x 30,” according to Smith. “When the concrete was poured, the first two or three feet on the outside cooled quicker, while the internal temperature remained very high. This temperature differential allowed DEF to take place.”

Consequently, the DOT has decided that six existing columns for the new bridge should be rebuilt using a new design that will be incorporated into the entire project.

The DOT and its contractor for the project, Scott Bridge Company of Opelika, Alabama, are in the process of completing the revised work plan and schedule, which is anticipated to be finalized within a month. Details of the revised schedule will be available at that time.

In other items of information, the public should note that short delays can be expected at the bridge as intermittent single lane closures will be used. Since heavy equipment will be entering and exiting the roadway, motorists are asked to use caution, reduce their speed, and be alert to changing traffic conditions.

The historic Fortson-Dorn Bridge was constructed in 1938 and renovated in 1952.

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