The success of a thin-bonded
patch depends on complete removal of all unsound or damaged material, adequate
bond between old and new concrete, use of “low slump” air-entrained concrete, and
proper curing. Successful patching
depends on strict adherence to all requirements.
This work involves bonded
patching of Portland cement concrete pavements in areas designated by the
Engineer and includes:
1. Marking repair areas using aerosol spray paint;
minimum payment is 2 square feet (0.2 m2) for each area.
2. Saw cutting the perimeter of all areas marked for
repair.
3. Removing loose and unsound concrete and asphalt
patching materials from within the repair area.
4. Removing sound concrete to obtain a minimum depth of
1-1/2 inch (38 mm).
5. Preparing the surface by cleaning bonding surfaces
using abrasive blasting.
6. Applying a bonding grout for Type A, B, or C patches.
7. Mixing, placing, finishing, and curing Type A, B, or C
patch material.
8. Checking surface for trueness using 10 foot (3 m)
straightedge.
Type A patches require high
early strength cement, 701.05. Type B patches require quick setting concrete
mortar, 705.21
Type I or II. Type C patches require
quick setting concrete mortar, Type II.
Fine aggregate must meet the
requirements for concrete aggregate specified in 703.02.
Coarse aggregate must meet
the requirements for concrete aggregate specified in 703.02
and be No. 8 size.
Curing compound must meet the
requirements of 705.07.
Air entraining admixtures
must conform to 705.10.
Prepackaged mortar material
must conform to the requirements of 705.21.
Equipment must be milling
machines, concrete saws, jackhammers, or other approved equipment that is
capable of removing the existing surface material. Chipping hammers may not be
heavier than 35 pound (16 kg) class.
Oil and moisture free
compressed air is required to clean and abrasive blast prepared areas.
An on-site concrete mixer
with a minimum capacity of 2 cubic feet (0.06 cubic meters) is required to mix
the patching material.
Figure
256.A – Areas to be Repaired are Marked by the Engineer
Figure
256.B – Perimeter of the Repair is Saw Cut a Minimum of 1 Inch Deep
The limits of the damaged
area must first be determined and the repair area be established beyond the
deteriorated area and into sound concrete.
A steel rod or steel chain may be used to “sound” the surface to determine
hollow and deteriorated concrete. The
Engineer marks the limits of all bonded patches with spray paint provided by
the Contractor.
Figure
256.C – Pavement Removal with Jackhammer
Figure
256.D – Pavement Removal by Milling Machine
The repair area should be
square or rectangular. The perimeter
should be outlined by sawing to a vertical depth of approximately 1 inch (25
mm) to avoid feathered edges that usually spall. Additional saw cuts within the outlined area
aid the breakup and removal operation.
The Contractor must remove all unsound concrete materials and all loose
or disintegrated concrete within the marked area. Sound concrete must be removed to the minimum
required depth within the patch area.
Concrete may be removed by jack hammering or milling. The minimum depth of a repair is 1-1/2 inches
(38 mm) except for the perimeter saw cuts which require a 1 inch (25 mm)
minimum. During removal operations,
remove any reinforcing steel within the patch area by cutting or with a torch.
Figure
256.E – Abrasive Blasting of Repair Areas
After removal of pavement within
the repair area, the area must be cleaned of all loose material, dirt, dust,
asphalt, etc. by abrasive blasting and blowing out with oil- and moisture-free
compressed air. If water is used for
cleaning, it must be mopped out thoroughly before abrasive blasting. Abrasive blasting of the bonding surfaces
must be done after the area has dried. The Contractor must comply with all
state, regional, and local government agency requirements regarding control of
dust generated by the abrasive blasting operation.
Type B and C patching
materials that do not use water as an activator may require additional surface
preparation. Check the manufacturer’s
instructions to ensure surface preparation is done correctly.
If a bonded patch area is
adjacent to a transverse or longitudinal joint, the joint must be reestablished
by using a joint board or form that extends below the level of the patch and is
as wide as the joint. This board is to
be removed about an hour after placing the patching material.
Figure
256.F – Adjacent Joints are Formed Prior to Placing the Patching Material
For Type A patches, prepare a
grout of equal parts by volume of Portland cement, sand, and water to a
consistency of a thick paint or slurry.
The grout should be brushed and scrubbed into the dry and clean bonding
surfaces of the exposed concrete. Grout
should be placed immediately prior to placing the patching material. Excess grout should not be allowed to collect
in low spots. Ideally, the grout should
have a uniform thickness of 1/16 to 1/8 inch.
For Type B and C patches, the
bonding grout should be mixed and applied per the manufacturer’s
requirements.
Figure
256.G – Portable Mortar Mixer used to Mix Bonding Grout and Patching Material
Figure
256.H – Bonding Grout is Brushed into the Dry Patch Area
The plans will specify the
type of patching material to be used. In
all cases, after placing the patching material, screed patches 12 feet and less
in length, parallel with the centerline and patches longer than 12 feet,
perpendicular to the centerline.
While the patch material is
still plastic, the surface of the patch should be checked with a 10 foot
straightedge to ensure the final surface is flush with the edges of the
adjacent pavement. The straightedge is
to be placed parallel to the centerline and drawn across the patch while
checking for any high or low areas. High
or low spots that exceed 1/8 inch in 10 feet are to be immediately
corrected. After making any corrections,
recheck the surface to ensure that there are no variations more than 1/8 inch
high or low in 10 feet.
The surface of the completed
patch is to be textured in the same manner as the adjacent pavement.
Type A patching material is
to be mixed in the field using 701.05
high-early-strength cement (Type III).
Ready mixed concrete is not permitted.
Use only enough water to make it cohesive and cause sufficient air
entrainment. One part of cement is
combined with 1-1/2 parts of sand and 1-1/2 parts of No. 8 sized coarse
aggregate and enough water to obtain a slump practical to place in the patch
area. Only the minimum amount of water
is to be used and the slump must not exceed 4 inches. A low slump mix will reduce shrinkage of the patch
and ensure a good bond to the surrounding concrete. An air entraining admixture is used to obtain
8 ± 2 percent air content.
Place the patching material while the grout is
still wet, and vibrate the concrete in place after the patch area is slightly
overfilled. Strike off the concrete to
the elevation of the adjacent concrete.
This type of patching
material is a quick-setting mortar that comes prepackaged. The patching material must be pre-approved
and must comply with 705.21
as Type I or II material.
Mix and place the material
according to the manufacturer’s directions.
Add coarse aggregate, as needed, according to the manufacturer’s
instructions. Place the mortar mixture in
the patch area. If the manufacturer’s
requirements specify using bonding grout, place the mixture while the bonding
grout is still wet. Slightly overfill,
vibrate, and strike off the concrete.
Figure
256.I – Patching Material Placed and Consolidating with an Internal Vibrator
Figure
256.J – Patching Material Screeded Off Flush with Surrounding Pavement
This type of patching
material is also a quick-setting mortar that comes prepackaged. The patching material must be pre-approved
and must comply with 705.21
as Type II material. Mix and place the
material according to the manufacturer’s directions. Add coarse aggregate, as needed, according to
the manufacturer’s instructions. Place
the mortar mixture in the patch area. If
the manufacturer’s requirements specify using bonding grout, place the mixture
while the bonding grout is still wet.
Slightly overfill, vibrate, and strike off the concrete.
Figure
256.K – Application of Curing Compound to New Bonded Concrete Patch
Figure
256.L – Completed Bonded Patches
Type A patches must be cured with
a white-pigmented, liquid membrane-forming compound conforming to 705.07
and applied at a rate of 150 square feet per gallon (1 Liter per 3.7 square
meters). The amount of curing required
and used is to be documented. A modulus
of rupture of 400 psi (2.8 Mpa) must be obtained prior to opening to traffic. Record the times and results of all beam
breaks.
Cure Type B and Type C
materials according to manufacturer’s directions.
Project personnel must
measure the repair areas and calculate the area in square feet (square meters)
of completed and accepted work. If a
measured area is less than 2 square feet (0.2 square meters), the Engineer will
increase pay to 2 square feet (0.2 square meters).
Pay the contract price for
accepted quantities per square feet (square meters) of Item 256,
Bonded Patching of Portland Cement Concrete Pavements, Type A, B, or C.
1. Locate, mark, and record areas to be replaced.
2. Document the method used to remove the existing
surface material and unsound concrete, size of jackhammers, depth of repair
area, removal of reinforcing steel, and method of cleaning.
3. Document type of grout, mixing, and application.
4. Document type of patch material, mixing, placement,
screeding, surface check, texturing, and curing.
5. Document the times and results of beam breaks.
6. Measure and calculate the area of the repair for
payment.
7. Document on CA-D-6
or other approved form.