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.
4. Placing a smooth dowel bar 1-1/2 inch in diameter with
appropriate dowel chairs, expansion caps, and 1/2 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.
Figure
258.A – Slot Sawing Equipment
Figure
258.B – 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. A clean,
newly exposed concrete surface free of spalls, laitance, and all contaminants
detrimental to achieving an adequate bond will be left. 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 be done to the specified width
of 2-1/2 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 ensure that the dowel, when installed with a
1/2-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 2-1/2 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 1 foot (0.3 m) centers in
each wheel path, as shown in BP-2.6.
Figure
258.C – Saw Cuts for Three Slots
Figure
258.D – Concrete Removal by Light Weight Jack hammer
Once sawing is complete, the
concrete is carefully removed from the 2-1/2 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
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 the control of dust generated by blasting operations.
Figure
258.E – Dry Abrasive Blasting
Figure
258.F – 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 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.
Figures
258.G – 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 1-1/2 inches
(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 1/2 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).
Figure
258.H – Portable Mortar Mixer
Figure
258.I – Filling Slots with Patching Mix
The patching materials are
mixed in the field with 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 (or as directed by the
Engineer) is required before placing any vehicle loads on the repair.
Figure
258.J – Internally Vibrating Patch
Figure
258.K – 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 1/2-inch
wide, preformed filler board) for compliance.
4. Document all materials used (sealant, patching
material, etc.).
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.