CASE STUDY:
Dowel Bar Retrofits Find Success in Western States
Aging concrete highways across the U.S. combined with limited budgets can create quite a challenge for state Departments of Transportation. The need for improving concrete roadways is great, with many U.S. concrete pavements reaching 50 years of age. However, complete road replacement isn’t always an option. In recent years, dowel bar retrofit (DBR) has emerged – particularly in the Western U.S. -- as a superior-performing and cost-effective rehabilitation technique for extending the life of concrete pavements.
DBR is a means of rehabilitating pavements by inserting epoxy-coated dowel bars into an existing concrete pavement to provide better load transfer across the joints, extending pavement life by at least 15 years. In recent years, the method has found great success throughout the western U.S., with more than 1 million dowels installed on California, Idaho and Washington highways. Examples of this success can be found throughout the state of Washington, which initiated some of the first DBR projects in the nation.
“We have effectively rehabilitated more than 400 lane miles of highway pavements with dowel bars since 1992, with very little performance problems,” said Jeff Uhlmeyer, State Pavement Engineer for the Washington State Department of Transportation (WSDOT).
When compared to other rehabilitation techniques and complete pavement reconstruction, DBR remains cost-effective.
“DBR has added a cost-effective solution to rehabilitate concrete pavements,” said Uhlmeyer. “It’s the solution of choice to rehabilitate faulted concrete roadways. If the distress goes too far, reconstruction by another means becomes the option.”
Benefits of DBR
In the DBR method, epoxy-coated steel dowel bars are inserted into slots cut across the pavement’s joints or cracks to transfer load. The process typically involves saw-cutting the pavement across the joint or crack, jack-hammering and cleaning out the slots, placing the dowel bars into the slots and then backfilling with a non-shrink concrete mixture (grout). Finally, the pavement is diamond-ground to restore smoothness. By linking slabs together at transverse cracks and joints, loads are evenly distributed across the crack or joint, which is critical for long-term roadway performance.
According to the International Grooving & Grinding Association, benefits of the procedure include:
- Long lifespan of 15 to 20 years when constructed properly;
- Friendly to the environment. DBR repairs the existing surface with very little new material required. Also, keeping the pavement light (instead of making it black with an asphalt overlay) reduces the heat island effect. Because the pavements reflect more light, they reduce the roadside lighting requirements.
- Accommodating to the public: Projects can be completed during off-peak hours with short single-lane closures.
- Flexible: DBR only has to be applied to the lanes that show distress, whereas other applications require treatment of the entire roadway.
- Easy to bid: A simple design process allows projects to be designed and advertised in a fraction of the time required for competitive processes.
- Safety: diamond grinding enhances surface friction and safety. In Wisconsin, researchers found that the overall wet weather accident rate for diamond-ground surfaces was only 57 percent of the rate for non-ground surfaces.
- Smooth: Diamond ground roadways typically have a smoothness level equal to or better than original construction.
- Cost-effective: DBR is considered cost-effective since it is only applied to the faulted lane, while an asphalt overlay would be required on all lanes and shoulders, significantly increasing costs unnecessarily. When utilizing the asphalt overlay option, guide rails, overhead signs and bridges may need to be raised, increasing overall project costs.
Recent studies led by Linda M. Pierce, Senior Engineer, Applied Pavement Technology, Inc., as well as Stephen T. Muench, Assistant Professor, the University of Washington, have indicated DBR as a highly effective, cost-efficient method for repairing aging concrete roadways. A review of approximately 380,000 DBR slots with an average age of 9 in-service years in Washington found the presence of cracking, spalling and debonding of the patching material nearly non-existent. These findings indicate DBR’s effectiveness as a long-term repair method.
Certain materials requirements can help ensure a successful DBR project. Rapid Set DOT Repair Mix from CTS Cement is one product that has been used as a patching material for DBR. Rapid Set DOT Repair Mix meets the following DBR material requirements.: achieve a minimum compressive strength of 3,000 psi in three hours and 5,000 psi in 24 hours (ASTM C-39); meets the shrinkage requirement of four days, 0.13 percent maximum (ASTM C-157); and develop bond strength of 1,000 psi in 24 hours (ASTM C-882).
Rapid Set DOT Repair Mix has a history of proven performance on DBR projects and is often used as the patching material in DBR projects because of its ease of use, speed, high bond strength and extreme durability.
Dave King, President of Tualatin Valley Short Load, Portland, Ore., is a materials provider who has supplied the patching material for 250 thousand dowel bars in the last four years. For these projects, the prime contractor has most often selected Rapid Set DOT Repair Mix as the patching material. King uses volumetric mixers to mix the material on site.
“One of the most important things on DBR projects is the timing of the work,” said King. “We’re always keeping in mind how fast that lane has to be open and how quickly they can get the pour out. To get the highest amount of production, we need to work as late into that lane closure as we can. If we use Rapid Set DOT Repair Mix, we can work all the way to 45 minutes before the lane needs to open and be confident that we can open without damage to the dowel bars or experience concrete failure.”
Case Study 1: Spokane, US 195
To extend the life of a 5-mile stretch of northbound US 195 in Spokane, Wash., a concrete pavement dating to the mid 1960s, DBR was the repair method of choice. A major artery connecting Spokane to Lewiston, Idaho, US 195 had numerous concrete panels that had experienced faulting over the years due to the loss of load transfer. The outside lane, with panels maintaining vertical differences up to ¾-inch, required rehabilitation while the less traveled inside passing lane did not.
Work began March 15 of 2010 and was complete three months later in June. Prime contractor on the $2.5-million project, Acme Concrete Paving, Inc. of Spokane, installed 8,500 dowel bars between the existing concrete panels in the northbound lanes. The project was underway during daytime hours, and northbound traffic was reduced to one lane in some areas during construction.
Workers saw cut the dowel bar slots, removed the existing concrete, cleared the slot of all debris, installed the dowel bar assembly and placed the patching material, Rapid Set DOT Repair Mix. Approximately 100 tons of Rapid Set DOT Repair Mix were mixed and placed on site using mobile mix trucks.
“Our goals were to improve the ride for the public, extend the life of the pavement and get it done with the least amount of impact to the traveling public,” said Jim Allen of Acme Concrete Paving. “The patching material was key in helping us meet these goals.”
Once the steel bars were installed and sealed into the pavement, workers used a diamond grinder to smooth the surface of both lanes, realign the edges of the panels and get rid of ruts developed from studded tires. In addition, Acme made a number of partial depth spall repairs, and the shoulders received a new seal coating.
Acme made similar repairs to another stretch of US 195’s northbound lanes in 2007, installing 12,000 dowel bars and making partial depth spall repairs for the $3-million project.
Case Study 2: Bellevue, Wash.
In October of 2008, $100 million of repairs were completed along the I-405 corridor in Bellevue, Wash., a rapidly growing city just east of Seattle, across Lake Washington. Goals were to improve traffic congestion, improve safety, increase travel speeds during peak commuter hours, improve freight movement throughout the corridor and implement meaningful environmental improvements.
Acme Concrete Paving worked as a subcontractor to Guy F. Atkinson Construction LLC, Broomfield, Colo., on the I-405 project. Acme installed 25,000 dowel bars, made 28 panel replacements and partial depth spall repairs. Work was performed at night, between 10 p.m. and 5 a.m., to minimize disruption to the public along this heavily traveled roadway. Should the roadway not open on time, Acme would incur fines of $10,000 for every 15 minutes late.
“The short amount of time we have to work is always the biggest challenge,” said Allen.
Rapid Set DOT Repair Mix was chosen as the patching material for the DBR slots; Rapid Set Cement was used for the panel replacements. The project required 300 tons of Rapid Set DOT Repair Mix and was mixed and placed on site using mobile mix trucks.
“We used Rapid Set to meet our opening requirements,” said Allen. “We were able to place concrete panel replacements at 2 a.m. and open the lanes to traffic at 5 a.m. We were able to work on the dowel bars up to an hour before lane opening.”
With short timeframes for work, Allen has found a couple of ingredients for success: an experienced and well-trained crew and dependable suppliers. Over the years, Allen has developed a crew of key men, such as his finishers and mobile mix truck operator. He hires other workers locally and trains them on the job.
“Materials delivery scheduling is an important consideration to make on a DBR project, due to the often time-critical nature of the road repair work,” said Allen. “Working with suppliers that can deliver the product you order on time is crucial.”
The US 195 and I-405 DBR projects were completed successfully on time. Future work in Washington includes DBR on the I-82 corridor in southeast Washington.
As all states address the repair of aging concrete pavements, they can look to examples in Washington and throughout the West for DBR as the repair method of choice. For many concrete pavement rehabilitation projects, DBR can offer the ideal solution when long-lasting, cost-effective repairs are desired.
About CTS Cement Manufacturing Corporation | Rapid Set®
CTS Cement Manufacturing Corporation is the largest manufacturer of specialty fast-setting cement and shrinkage-compensating cement in the United States. As the leader in advanced cement technology, CTS provides innovative products to the construction industry through continual research and development. Rapid Set® is a brand of fast setting cement products well known for its versatility and high performance. It gains structural strength in one hour, has superior durability, and low shrinkage. Rapid Set® offers a full line of premium products for concrete repairs and new construction projects.
For more information, visit www.ctscement.com.
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