What Is A Dowel Bar Retrofit?
What Is A Dowel Bar Retrofit?
Dowel Bar Retrofit (DBR) is a way to strengthen cracks in road pavement by inserting steel dowels into cuts made across the cracks. This technique has been effectively used by transportation departments in several U.S. states to fix issues with older jointed concrete pavements.
The typical process involves cutting and removing portions of the pavement to make room for the dowels, then filling the cuts with a type of concrete that does not shrink and smoothing out the surface with diamond-grinding.
States are upgrading older highways by installing epoxy-coated dowel bars through a process called retrofitting. This process involves cutting slots in the concrete, inserting the bars, filling the slots with grout, and then smoothing the surface by diamond-grinding.
This method is expected to greatly extend the time before resurfacing is needed and improve ride quality. Compared to Asphalt Overlay, Dowel Bar Retrofit is known to last at least ten years longer.
History Of Dowel Bar Retrofit?
When a vehicle drives on concrete roads with joints, the weight is placed on the edges of the panels where they are most vulnerable to cracking.
In the past, steel rods (dowel bars) were used to transfer the load across the joints, but these were prone to corrosion and required frequent replacement. Instead, aggregate interlock was relied upon to distribute the load, but over time this led to cracks and displacement of the panels.
Contemporary highway construction now uses dowel bars coated with epoxy to prevent corrosion and maintain the integrity of the road.
Process Of Dowel Bar Retrofit
The materials and steps needed for dowel bar retrofit include dowels, bond breaker, expansion caps, dowel bar support chairs, foam core insert, caulking filler, non-shrink concrete backfill material and submittals.
The dowels must be smooth, round, made of epoxy and bond breaker coated steel that conform to requirements. The bond breaker should be applied to all surfaces of the dowel bar. The expansion caps are placed at each end of the dowel bar and the support chairs hold the dowels in place during backfill operations.
The foam core insert is used to fix the joint or crack, while the caulking filler prevents backfill material from flowing into the joint or crack. Rapid set concrete patching materials are recommended as the non-shrink concrete backfill material.
The process includes saw cuts in the pavement, removal of debris and existing concrete, installation of retrofit dowels, and diamond-grinding the pavement surface.
Problems of Dowel Bar Retrofit
If not properly executed, Dowel bar retrofits can result in significant issues, typically stemming from inadequate workmanship. These issues can be prevented by adhering to specifications and closely monitoring the work.
The use of heavy jackhammers can lead to cracking of the concrete near the slots, while a lack of caulk or poor caulk application in joints and cracks can cause cracking in those areas. Additionally, voids in the grout particularly beneath the dowel bar can result in the failure of the grout.