Dowel bar retrofit for lasting road repairs
The area where the load transfer retrofit tests were to be constructed on I-75 was rehabilitated in 1976 by GDOT maintenance forces but significant increases in joint faulting had redeveloped by 1980. The original plan to cut the slots for the dowels utilized a specially built carbide tipped Rotomill mandrel, but an early field trial showed that this method of concrete removal created too much damage to the joints. The GDOT then decide to cut the slot perimeters using diamond saw blades removing the remaining concrete with lightweight jack hammers as is done today. Core holes were drilled for the placement of the other devices.
Performance evaluations were made in January 1982, September 1982, and March 1983. Static weight and Dynaflect load transfer measurements were made along with horizontal joint movement measurements, faulting measurements, slab cracking, and visual observations of the load transfer devices for bond failures and spalling, cracking, etc., of the patching materials.
The results from the test installations showed that retrofitted dowel bars were the best means of reestablishing load transfer to existing joints determining that three dowels should be placed in the outside wheel path and two dowels in the inside wheel path. It also stated that retrofit dowel placement in the inside wheel path could possibly be eliminated once long term performance data became available. It was also recommended that joints with large slab movements should be stabilized though undersealing prior to placing dowels.
DBR in Washington State
In Washington State, plain jointed concrete pavements constructed prior to the 1990’s did not contain dowel bars across the transverse joints. After being in-service for 30 or more years, a significant number of the Washington State concrete pavements had developed transverse joint faulting, many with average faulting greater than ½ in. Since sufficient funding was not available to reconstruct the faulted and rough concrete pavements, in 1992 the Washington State Department of Transportation (WSDOT) initiated a study to investigate the cost effectiveness of load transfer restoration techniques. Since then, WSDOT has dowel bar retrofitted more than 626 lane miles or approximately 1,322,000 bars, of faulted concrete pavements.
Since its inception in Washington State, DBR projects have also included diamond grinding of the entire project length, and to the extent necessary, full-depth replacement of concrete panels with two or more cracks, partial-depth spall repair, crack sealing, and for all but one project, resealing transverse and longitudinal joints. It must also be noted, that when WSDOT initiated DBR there existed a sizeable (approximately 600 to 800 lane miles) backlog of concrete pavements in need of rehabilitation. Due to this backlog, the majority of which were on the heavily traveled interstate system, WSDOT conducted DBR in a worst-first manner, implying that projects that received DBR first, were in the worst condition (primarily heavily faulted).
According to WSDOT research, the average construction costs for DBR was approximately 16 percent less (2006 dollars) than the typical cost of a four-inch asphalt overlay, which is the minimum recommended overlay depth for rehabilitating a faulted concrete pavement. The success realized by WSDOT has promoted widespread acceptance of the process and as a result, 20 states and one Canadian province have completed numerous successful projects.
DBR application, in conjunction with panel replacements and diamond grinding, has proven to be an effective rehabilitation treatment for faulted concrete pavements. Based on the review of approximately 380,000 DBR slots in Washington State, the presence of cracking, spalling and debonding of the patching material was nearly non-existent, indicating that superior construction and inspection practices have led to long-term performance. It was determined that Washington State has experienced very little DBR slot-related distress, with less than 3 percent of all DBR slot distress combined on any given project and typically less than 1 percent on all projects. Further, after reviewing DBR performance, it was found that 5 of the 21 projects examined showed superior longer-term performance as compared to all other DBR projects. This was due in part to applying the DBR process to pavements earlier in the rehabilitation cycle and therefore with much less faulting.
Based on the findings in Washington, DBR is a highly effective solution for long-term pavement repair. Critical to the success of DBR projects are appropriate specifications and construction inspection processes, as well as contractors firmly establishing themselves in DBR construction techniques, bringing a high level of experience and quality consciousness to the project. As all states seek ways to repair aging concrete pavements, DBR can be the ideal solution when long-lasting, cost-effective repairs are desired.
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