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 these 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 ½ 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 of Type A, B, or C patch material.
8. Checking surface for trueness using 10-foot (3 m) straightedge.
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. The chipping hammers used 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.
Picture 256.A - Areas to be Repaired are Marked by the Engineer
Picture 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 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.
Picture 256.C – Pavement Removal with Jackhammer
Picture 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 removal may be by jack hammering or milling. The minimum depth of a repair is 1-1/2 inch (38 mm) except for the perimeter saw cuts that require 1 inch (25 mm) minimum. During removal operations, remove any reinforcing steel within the patch area by cutting or with a torch.
Picture 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 re-established 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.
Picture 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.
Picture 256.G - Portable Mortar Mixer used to Mix Bonding Grout and Patching Material
Picture 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 with the centerline and drawn across the patch checking for any high or low areas across the patch. 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 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. The principal requirements are the use of only enough water to make it cohesive and sufficient air entrainment. One part of cement is combined with 1 ½ parts of sand and 1 ½ parts No. 8 size coarse aggregate and enough water to obtain a slump practical to place in the patch area. Only a 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% 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 1 or 2 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.
Picture 256.H - Patching Material Placed and Consolidating with an Internal Vibrator
Picture 256.I – 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 2 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.
Picture 256.J – Application of Curing Compound to New Bonded Concrete Patch
Picture 256.K – 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 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 for 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 method of removal of the existing surface material and of unsound concrete, size of jackhammers, depth of repair area, removal of reinforcing steel, method of cleaning.
3. Document type of grout, mixing, and application.
4. Document type of patch material, mixing, placement, screeding, surface check, texturing, curing.
5. Document 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.