Tarif Jaber, Jaber Engineering Consulting, Inc.
In many states, it is widely believed that the use of advanced materials such as high performance concrete (HPC) is only feasible near large cities. Many engineers, contractors, and the industry in general believe that the special training, workmanship, and supervision required are only available in populous areas.
The Green River Bridge project illustrates that you can successfully place HPC in remote areas, provided that you are willing to handle the materials properly and use weather conditions, such as temperature, to your advantage. Performance results to date show that the choice and methods of application were a success. The Utah Department of Transportation (UDOT) will reap the benefits of HPC for years to come in an extended service life of the bridge and reduced lifecycle costs.
Green River Bridge
Located at Ouray (Uintah County with a population of 26,000) in northeastern Utah at an elevation of 4666 ft (1422 m), the Green River Bridge is a two lane, five span bridge with a concrete deck originally 7-1/2 in. (190 mm) thick supported by four lines of steel girders. It has a total length of 405 ft (123 m) and was constructed in 1960. The bridge is used primarily by oil tankers that are suspected of frequently exceeding the posted load limits. The bridge deck surface had deteriorated significantly and needed repair.
The UDOT considered several options and chose to install a 2-in. (50-mm) thick HPC overlay to restore the integrity of the bridge deck surface and extend its service life. A full-depth replacement was not used because of the cost and environmental impact on the Green River. An HPC overlay was selected to provide an economic rehabilitation method, stiffen the superstructure, and provide 1-1/2 in. (38 mm) of additional cover to the original reinforcing steel. Silica fume was included in the concrete to reduce the permeability and steel fibers were used to control shrinkage cracking.
To obtain the best conditions, the project team chose a cool evening on May 17, 2003, for the HPC placement. The work took place at night to lessen problems with wind and temperature. On a cloudy night, with no wind and an air temperature of 60°F (16°C) at 1:30 a.m., the conditions were ideal for bridge deck placement.
Deck Preparation
The old concrete deck surface was first milled down approximately 1/2 in. (13 mm) to achieve a good rough, clean surface. Deteriorated areas in the old deck were outlined with a saw cut then chipped out with a 16 lb (7.3 kg) pneumatic hammer. These “cutouts” varied in size from 18×18 in. to 2×4 ft (460×460 mm to 610×1220 mm). The exposed reinforcement was sandblasted and the sand removed. The specifications called for keeping the deck wet for three hours prior to the placement. Subsequently, it was decided to soak the deck earlier and then let it dry out for three hours to achieve a saturated surface dry condition. Prior to concrete placement, a slurry of cement, silica fume, sand, and water was scrubbed vigorously into the deck and the cutout areas.
HPC
The batch plant was approximately 40 miles (64 km) from the project. The first truck arrived on site at 2:00 a.m. with concrete having a 6 percent air content, 5 in. (125 mm) slump, and a temperature of 60°F (16°C). Subsequent trucks arrived at 30 to 45 minute intervals. The concrete was screeded with a vibrating triangular-shaped screed. It was then bull floated and steel troweled. The first tining of the finished surface began at about 3:45 a.m. and by 6 a.m. half of the deck had been placed, tined, and received a curing compound. Between noon and 1:00 p.m., the crew placed wet burlap, wetted down the entire deck area, and covered it with plastic sheeting, which remained in place for 7 days.
Human Resources are Key
An evident contributor to the success of this project was the dedication by everyone at the site to doing their jobs well. The placement crew was large enough to match the size of the job, the foremen had good concrete experience, the finishers were diligent, and the other workers were energetic. At times when the placement was going slowly, the finishers had too much time. The crew worked hard at doing a good job and were proud of their work. Although some normal HPC practices were not followed, the final product was successful. In the end, the attention to the project and the willingness to do a good job prevailed.
End Result
The decision made by the UDOT district office to take on the challenge of an HPC project has paid off. Six months after construction, the entire bridge deck overlay showed no signs of cracking. It is expected that the use of HPC with its increased durability will prolong the life of the bridge beyond that anticipated for the original structure.
While many state departments of transportation claim they cannot do HPC in remote areas, this project speaks to the contrary. This may seem like another simple HPC application on a bridge deck, but in fact it underscores the reality that achieving HPC is only a matter of selecting the right material for the project and following good concrete practices … and nothing more.
