This is a rehabilitation technique that is normally specified to restore load transfer at faulted transverse cracks in older concrete pavements. It has also been used in new construction when dowel bar installing equipment on a concrete paving machine inadvertently fails to install dowels at contraction joints. Standard Construction Drawing BP-2.6 Dowel Bar Retrofit is to be followed when constructing this item of work.
The work involves the following:
1. Sawing the proper size slots across transverse cracks.
2. Cleaning the slots.
3. Injecting a silicone caulking filler to seal the crack and filler board as specified.
4. Placing a smooth dowel bar 1-1/2 inch in diameter with appropriate dowel chairs, expansion caps and ½ inch thick filler board in each slot.
5. Filling the slot with one of the specified cementitious patching materials.
6. Consolidating, finishing and curing the cementitious patching material.
7. Establishing a joint by sawing.
Equipment for sawing slots in the pavement must be power driven, gang type, assemblies with diamond saw blades that are capable of sawing a minimum of three slots at a time. Saws must not damage the existing pavement.
Picture 255.A – Slot Sawing Equipment
Jack hammers used to remove concrete from the sawed slots must be less than a 30 pound (13.6 kg) class.
Abrasive blast equipment used to clean debris from the slots must be capable of removing the saw slurry and other foreign material from the exposed surfaces of the sawed slot leaving a clean, newly exposed concrete surface free of spalls, laitance, and all contaminants detrimental to achieving an adequate bond. If wet blasting is used, ensure water blasting pressure with abrasives in the water is 10,000 psi (690 bar) or less.
The Engineer must mark the transverse cracks to be retrofitted with dowels. The Contractor will provide the spray paint. The Contractor must position the slots as shown in Standard Construction Drawing BP-2.6 Dowel Bar Retrofit.
The sawing must done to the specified width of 2-½ inches (65 mm) and to a length as needed to allow the centering of the dowel at the transverse crack. The slot must be sawed deep enough to assure that the dowel, when installed with a ½ inch tall prefabricated chair, is level and located at mid-depth in the concrete slab. The slots must be parallel to the centerline of the pavement. The contractor may make multiple parallel saw cuts within the 2 ½ inch width to facilitate removal of concrete, and to provide a level surface for the feet of dowel bar chairs. Six slots are to be cut in each lane at each crack, three slots at one foot (0.3 m) centers in each wheel path, as shown in BP-2.6.
Picture 258.B - Saw Cuts for Three Slots
Picture 258.C - Concrete Removal by Light Weight Jack hammer
Once sawing is complete, the concrete is removed carefully from the 2-½ inch slot using lightweight jack hammers (30 pounds (13.6 Kg) or less). Once concrete is removed, traffic must be kept off of the slots until the patching material is placed and cured.
It is permissible to do all of the sawing within an area and open the pavement for a period of time, but once the concrete is removed traffic must be prohibited from using the pavement.
Once concrete is removed from the sawed slots to the proper depth, cleaning of the slots can begin. Inspection should include checking the slot depth to ensure the bottom of the slot is level and to the proper depth. Cleaning must be done by approved abrasive blasting (wet or dry) which will produce a rough surface on the sawed faces of the slots. The Contractor’s abrasive blasting operation must not damage the surrounding pavement. Do not allow the Contractor to begin abrasive blasting operations unless reasonably available engineering controls are implemented to limit fugitive dust. The Contractor must conform to state, regional, and local government agency requirements regarding control of dust generated by the blasting operation.
Picture 258.D – Dry Abrasive Blasting
Picture 258.E – Blowing Out Slots - Air Blast
After cleaning the slots, caulk cracks at the bottom and sides of the slot with silicone material. The purpose of the caulking is to keep the patching material from entering the crack when placed in the slot. The caulking material must be forced into the crack under pressure. Care must be taken to be neat and not contaminate the cleaned slot face in adjacent areas.
Pictures 258.F - Dowels Installed in Prepared Slots at Transverse Cracks
Next dowel bars are placed into the prepared slots. Inspectors must ensure the Contractor follows these dowel placing requirements:
Dowels must be 1-½ inch (13 mm) in diameter and 18 inches (460 mm) long. The dowel is to be centered on the crack. Dowels must be epoxy coated steel or fiber reinforced polymer.
Coat each dowel with a thin coating of new light form oil just prior to installation in the slot.
Place an expansion cap on each end of the dowel prior to placing it in the slot.
Two dowel bar chairs are required for each dowel bar. The chair is to be placed parallel to the pavement surface. Normally the two dowel chairs are attached to each dowel prior to installation into the slot. These dowel chairs must firmly hold the dowel bar centered in the slot at the proper elevation of ½ inch (13 mm) from the slot bottom. Inspectors must reject any chair design that allows movement of the dowel bar during placement of the patching material.
The dowel must have the 1/2 inch (13 mm) thick preformed filler board centered on the dowel to maintain the crack across the slot, as shown in BP-2.6. This filler board must fit tight around the dowel and extend to the bottom and to the edges of the slot. The filler board must be maintained in a vertical position and be tight to all edges during placement of the patching material. Use the silicone caulking material on the bottom of the preformed filler to keep the patching material from flowing under it. The filler board must extend from the bottom of the slot to the surface of the pavement. If the filler board shifts during placement of the patching material the Contractor must redo the installation at no additional cost.
Once the dowels are in place at the proper location the Contractor must make several passes of an air blast throughout each slot to provide a dust free slot for adequate bonding of the patch material.
Next the patching material is mixed, placed, and cured per the material manufacturer’s directions. The patching materials specified are prepackaged, proprietary, cementitious materials which may allow the use of a certain amount of aggregate of a certain grading to be blended with each bag. The contractor must provide one of the approved patching materials listed on the Department’s Qualified Products List (QPL).
Picture 258.F - Portable Mortar Mixer
Picture 258.G - Filling Slots with Patching Mix
The patching materials are mixed in the field in a portable mixer. When the material is placed into the prepared slot it must be consolidated with an internal vibrator approved by the Engineer. The excess patching material is screeded off flush with the adjacent pavement. The surface is cured per the manufacturer’s directions however a minimum cure time of 4 hours is required before placing any vehicle loads on the repair, or as directed by the Engineer.
Picture 258.H – Internally Vibrating Patch
Picture 258.I – Patches Cured with Spray Cure
The Department will measure the quantity of Retrofit Dowel Bars by the actual number in the complete and accepted work.
Payment is full compensation for furnishing all materials including paint; sawing and cleaning the slots; installing dowel chairs, dowels, bond breaker material, dowel bar end caps, sealant/caulking material, filler material, and patching material.
1. Mark and document the locations of dowel bar retrofit.
2. Check and document equipment for compliance prior to commencing work.
3. Check and document all dowels (diameter, length and epoxy coating) and dowel hardware (expansion caps, dowel chairs and ½ inch wide preformed filler board) for compliance.
4. Document all materials used (sealant, patching material).
5. Document compliance to specification requirements (slot location, width and depth of slot, cleaning, dowel placement, chair placement, patch mixing and placement, curing, etc.).
6. Document the number of slots performed each day for payment.
7. Pay the unit bid price for Dowel Bar Retrofit.