73 CONCRETE CURBS AND SIDEWALKS
73-1 General
73-1.01 General
Section 73 -1 includes general specifications for constructing concrete curbs, sidewalks, and their appurtenances, such as gutter depressions and island paving; and curb ramps and driveways. Steel dowels, reinforcing steel, and welded wire reinforcement mus t comply with section 52.
73-1.02 Materials
73-1.02A General
Concrete for curbs, sidewalks and their appurtenances must be minor concrete containing at least 463 pounds of cementitious material per cubic yard. For extruded or slip form curb construction, the maximum aggregate size must be from 3/8 to 1 inch. The cementitious materia l content must be at least 505 pounds per cubic yard if a maximum of 3/8 -inch aggregate is used. Preformed expansion joint filler must comply with ASTM D1751. As an alternative , a semi -rigid, closed - cell polypropylene foam, pr eformed joint filler that complies with ASTM D8139 may be used. Mortar must comply with section 51 -1.02F. Form oil must:
1.Be commercial quality or an equivalent coating
2.Allow the ready release of forms
3.Not discolor the concrete
73-1.02B Detectable Warning Surfaces
Detectable warning surface must be on the Authorized Material List for detectable warning surfaces and must match yellow color no. 33538 of AMS -STD-595.
73-1.03 Construction
73-1.03A Ge neral
Construct contraction joints by (1) scoring concrete with a grooving tool and rounding corners with an edger tool or (2) saw cutting hardened concrete to a depth of at least 1 inch. Immediately apply curing compound to the exposed surfaces of saw cut joints. Construct expansion joints at each side of structures and at the ends of curb returns. Fill expansion joints with 1/4 -inch-thick preformed joint filler. Finish the concrete adjacent to expansion joints with an edger tool. Do not construct expansio n joints within 20 feet of an island nose. Shape the preformed joint filler to match the surface contour of the concrete.
73-1.03B Subgrade Preparation
Remove soft or spongy basement material to a depth of 6 inches below the subgrade elevation for curbs, gutter depressions, island paving, and driveways and 3 inches below the subgrade elevation for sidewalks and curb ramps. Backfill the subgrade with earth, sand, or gravel to produce a stable foundation. Apply water to the subgrade and thoroughly compact it before placing concrete. Prepare subgrade to required grade and cross section . Verify that the finished surface of the subgrade does not project into the concrete cross section at any point by:
1.Using a template supported on the side forms for the fixed form method
2.Measuring from the offset guide line or survey marks for the extruded or slip form method
73-1.03C Fixed Form Method
Set forms to the required alignment, grade, and dimensions. SECTION 73 CONCRETE CURBS AND SIDEWALKS Forms must:
1.Be smooth on the side placed against conc rete.
2.Have a straight upper edge.
3.Be rigid enough to withstand the pressure of fresh concrete without distortion. Use enough stakes, clamps, spreaders, and braces to ensure rigidity.
4.Be clean of debris and old concrete.
5.Coated with form oil bef ore placing concrete. You may use either benders or thin plank forms on curves, grade changes, or curb returns. Wet the subgrade and forms immediately before placing the concrete. Place the preformed joint filler at expansion joints in the correct positio n before placing concrete against the filler. Place and compact the concrete without segregation.
73-1.03D Extruded and Slip Form Methods
Wet the subgrade immediately before placing the concrete . Feed concrete into the extrusion machine at a uniform rate. Restrain forward travel of the extrusion machine to produce a well -compacted mass of concrete requiring no further finishing other than a light brushing. The brush may be filled with water. Do not finish the concrete surface with a brush application of grout. If you use a slip form machine, automatically control the alignment, grade, and cross slope by one of the following methods:
1.Sensing from preset string lines
2.String line control of the alignment and grade and automatic control of the cross slope The slip form machine must have traveling forms rigid enough to produce the required cross section. The machine m ust produce a dense, homogeneous concrete, true to grade and cross section and require minimum handwork. Consolidate the concrete with internal vibrators or other authorized method. Use a smaller, maximum size of aggregate with an extruded or slip form mac hine if it is required to produce concrete (1) free from surface pits larger than 3/16 inch in diameter and (2) with well -defined web marks of water on the surface. You may construct expansion joints by sawing through the concrete cross section to its full depth. The width of the cut must provide a tight fit for the joint filler. Insert preformed joint filler into sawed joints and mortar it in place. If a joint is cut before the concrete has hardened:
1.Protect the adjacent surfaces with close fitting, firmly suppo rted shields
2.Complete the saw cut and insertion of the preformed join t filler before curing the concrete If a joint is cut after the concrete has hardened:
1.Mortar preformed joint filler in place using heavy trowel pressure
2.Cover the exposed portions of the concrete in the vicinity of the saw cut with an additional application of curing compound After the concrete has cured, check the joint filler for a tight fit. If any loose joints are found, mortar the joint in place and recheck after the mortar has cured. Repeat as necessary to achieve a tight fit.
73-1.03E Curing
Cure concrete using the curing compound method with pigmented curing compound. Completely coat the exposed faces of the concrete with curing compound. SECTION 73 CONCRETE CURBS AND SIDEWALKS
73-1.04 Payment
Not Used
73-2 Curbs
73-2.01 General
73-2.02 Materials
Not Used
73-2.03 Construction
73-2.03A General
If curbs are constructed over existing pavement, use steel dowels and reinforcing steel or adhesive to anchor the curb to the existing pavement. Anchor steel dowels in drilled holes with mortar made from equal parts by volume of portland cement or portland limestone cement, sand, and water. You may use anchor bolts instead of anchored s teel dowels if authorized. If adhesive is used, remove all dust, loose material, or oil from the surface of the existing pavement by either wire brushing or blast cleaning. Construct contraction and expansion joints at right angles to the line of the curb. Space contraction joints at 20 -foot intervals. For curbs adjacent to existing concrete, align the curb joints with the existing concrete's pavement joints. The top and face of the finished curb must be true and straight. The top surface of the curb must b e uniform in width and free from humps, sags, or other irregularities. Clean any discolored concrete by abrasive blast cleaning or other authorized method. Except for curbs on structures, you may place curbs with an extrusion machine or a slip form paver i f:
1.Finished curb is true to line and grade
2.Concrete contains the maximum quantity of water that maintains the curb's shape without support
3.Required surface texture is attained Check the flatness of the top and face of the curb and the surface of the gutter with a 10 -foot straightedge. The surfaces must be flat to within 0.01 foot except at grade changes or curves.
73-2.03B Fixed Form Method
Set fixed forms the full depth of the back and face of the curb. The back forms may be construct ed with 1/2 -inch-thick bender boards. Cleat the back forms together as required to attain the full depth of the curb. Use form clamps to prevent interference with finishing activities. Before removing the forms, finish the surface true to grade with a stra ightedge float at least 10 feet in length. Operate the straightedge float longitudinally over the concrete surface. Remove the forms from the face of the curb from 1 to 6 hours after placing the concrete. Do not remove the forms if the concrete is plastic enough to slump. After removing the forms, immediately use a steel trowel to attain a smooth finish. The smooth finish must extend (1) to within 0.17 foot of the flow line or (2) to the flow line of a curb with an integral gutter. After smoothing the curb' s face, apply a fine -brush finish parallel to the line of the curb.
73-2.03C Extruded or Slip Form Methods
For an extrusion machine, use the Department's survey marks to determine the offset guide line for setting the grade for the top of the curb. The ex trusion machine must have a grade -line gauge or pointer that allows continual comparison between the curb placement and the offset guide line. SECTION 73 CONCRETE CURBS AND SIDEWALKS The machine must be capable of vertical adjustment during forward travel to construct curbs of varying height as determined by the offset guide line. You may operate the extrusion machine on rails or forms set at a uniform depth below the established grade of the top of curb.
73-2.04 Payment
Not Used
73-3 Sidewalks, Gutter Depressions, Island Paving, Curb Ramps, An D Driveways
73-3.01 General
73-3.01A Summary
Section 73 -3 includes specifications for constructing sidewalks, gutter depressions , island paving, curb ramps, and driveways.
73-3.01B Definitions
Reserved
73-3.01C Submittals
Submit a 5 -year manufacturer's replacement warranty against defects in a prefabricated detectable warning surface.
73-3.01D Quality Assurance
73-3.01D(1) General
Reserved
73-3.01D(2) Warranties
The 5 -year manufacturer's replacement warranty for a prefabricated detectable warning surface must cover defects in dome shape, color fastness, sound -on-cane acoustic quality, resilience, and attachment. The 5 -year warranty period starts at Contract acceptance.
73-3.01D(3) Quality Control
Reserved
73-3.02 Materials
Not Used
73-3.03 Construction
Construct expansion joints at:
1.All re turns and opposite expansion joints in the adjacent curb
2.60-foot intervals whe re there is no adjacent curb Construct contraction joints to create rectangular patterns from 12 to 20 square feet in the surface of sidewalks. Install a prefabricated detect able warning surface under the manufacturer 's instructions. Broom finish the surface of sidewalks, gutter depressions, curb ramps, and driveways. Make the broom finish perpendicular to the path of travel on surfaces used by pedestrians. You may apply water to the surface immediately before brooming. The finished surface must not vary more than 0.02 foot from a 10 -foot straightedge except at grade changes. If placing pavement around or adjacent to manholes, pipe inlets, or other miscellaneous structures in sidewalk, gutter depression, island paving, curb ramps, or driveway areas, do not finish the miscellaneous structures to final grade until the pavement is finished beyond the miscellaneous structure. If using fixed forms, strike off and compact fresh concre te until a layer of mortar is brought to the surface. Finish the surface with a float to grade and cross section and trowel smooth. SECTION 73 CONCRETE CURBS AND SIDEWALKS Leave forms in place for sidewalks, gutter depressions, island paving, curb ramps, and driveways for at least 12 hours after surface finishing. Clean any discolored concrete by abrasive blast cleaning or other authorized method.
73-3.04 Payment
The payment quantity for minor concrete (curb ramp) does not include detectable warning surface .
73-4 Textured Concrete and Colored C Oncrete Surfaces
73-4.01 General
73-4.01A Summary
Section 73 -4 includes specifications for texturing and coloring concrete surfaces. Texture concrete by imprinting with stamps, tools, brooms, or other methods to attain the pattern or impressions shown.
73-4.01B Definitions
Reserved
73-4.01C Submittals
Submit the manufacturer's data for the color hardener and curing and fini shing compounds for each color of a concrete surface colored by the dry -shake method.
73-4.01D Quality Assurance
73-4.01D(1) General
Reserved
73-4.01D(2) Quality Control
Construct test panels for textured or colored concrete under section 51 -1.01D(2)(c) .
73-4.01D(3) Department Acceptance
The Department accepts textured or colored concrete surfaces based on a visual comparison with the test panel.
73-4.02 Materials
Aggregate for textured or colored concrete surfaces must comply with the gradation req uirements for fine aggregate . Aggregate used in grout for textured and colored concrete surfaces must comply with the gradation requirements shown in the following table: Aggregate Gradation for Grout Sieve size Percentage passing No. 4 100 No. 8 90–100 No. 16 60–100 No. 30 35–70 No. 50 15–35 No. 100 2–15 Color pigments for the dry -shake method must comply with ASTM C979.
73-4.03 Construction
Protect the surrounding exposed surfaces during the placement, finishing, and curing of colored concrete. Screed the concrete to the grade and cross section shown, and strike off and compact the concrete until a layer of mortar is brought to the surface. Wood float the concrete to produce a uniform surface. For the dry -shake method, apply the color hardener in 2 applications while the concrete surface is plastic. Use at least 60 lb of hardener per 100 sq ft of concrete surface. Wood float the surface after each application of hardener. Trowel the surface only after final floating. SECTION 73 CONCRETE CURBS AND SIDEWALKS Texture the concrete while it is in the plastic stage. For a texture that requires a concrete stamp, use the stamp under the manufacturer's instructions. Do not texture or grout the grooved area and detectable warning surface on a curb ramp. Cure the concrete surfaces using the curing compound method with curing compound no. 6. Place any grout after the (1) initial curing of the textured concrete and (2) removal of curing seal and other deleterious substances. The method of removal must not stain or discolor a reas of textured concrete to remain exposed after grouting. Spread and consolidate the grout over the textured concrete under the manufacturer's instructions. Remove excess grout with a squeegee and damp burlap rags or other authorized method. Apply curing seal.
73-4.04 Payment
Not Used
73-5 73-9 Reserved
73-10 Existing Curbs and Sidewalks
73-10.01 General
Section 73 -10 includes specifications for performing work on existing curbs, sidewalks, and their appurtenances, such as gutter depressions and island paving.
73-10.02 Materials
Not Used
73-10.03 Construction
If you repair any part of a curb, sidewalk, curb ramp, driveway, or gutter depression, remove and replace the entire sect ion between contraction or expansion joints. At contraction joints, saw cut a true line at least 1 -1/2 inches deep before concrete removal. Removal of concrete includes the removal of detectable warning surfaces. Install a prefabricated detectable warning surface on an existing curb ramp under the manufacturer's instructions.
73-10.04 Payment
Detectable warning surface placed on existing concrete is paid for as a separate bid item.
73-11 73-15 Reserved
Source: California Standard Specifications, 2024 Edition. Pages 1053–1058 of 1,372.