Item No. 432
Concrete Sidewalks
432.1 Description
This item shall govern the construction of Portland cement concrete sidewalks as herein specified, on an approved subgrade and in conformance with the lines, grades and details indicated on the Drawings or as established by the Engineer or designated representative.
432.2 Submittals
The submittal requirements of this specification item include:
A. Class A p.c. concrete mix design,
B. Type of Installation (i.e. Type I, Type II, etc.) and construction details (i.e. cushion layer, base, reinforcing steel, joints, curing membrane),
C. Identification of the type, source, mixture, Pure Live Seed (PLS) and rate of application of the seeding.
432.3 Materials
(1) Portland Cement Concrete
Portland cement concrete shall be Class A conforming to Specification Item No. 403, "Concrete for Structures".
(2) Reinforcement
Reinforcement shall conform to Specification Item No. 406, "Reinforcing Steel".
(3) Expansion Joint Materials
Expansion joint materials shall conform to Specification Item No. 408, "Expansion Joint Materials".
(4) Membrane Curing Compound
Membrane curing compound shall conform to Specification Item No. 409, "Membrane Curing".
432.4 Construction Methods
The subgrade shall be excavated in accordance with, “Excavation”, prepared in accordance with “Subgrade Preparation”, shaped to the lines, grades and cross section as indicated on the Drawings or as directed by the Engineer or designated representative and thoroughly compacted. A granular cushion of a minimum thickness of 2 inches but maximum thickness of 5 inches, composed of crusher screenings, gravel and sand, crushed rock or coarse sand, shall be spread, wetted thoroughly, tamped and leveled. The granular cushion shall be moist at the time the Portland cement concrete is placed.
If the subgrade is undercut by more than 4 inches or the elevation of the natural ground is more than 4 inches below "top of subgrade", then a necessary backfill/embankment layer of an approved material shall be placed and compacted with a mechanical tamper. Hand tamping will not be permitted.
Where the subgrade is rock or gravel, 70 percent of which is rock; the 2-inch cushion need not be used. The Engineer or designated representative will determine if the subgrade meets the above requirements.
Sidewalk forms shall be constructed of metal or well-seasoned wood not less than 2 inches in thickness, with a section satisfactory to the Engineer or designated representative. The forms shall be clean, straight, and free from warp with a depth equal to the thickness of the finished work. All forms shall be securely staked to line and grade and maintained in a true position during the deposition of Portland cement concrete. Before p.c. concrete is placed, the forms shall be thoroughly oiled with a light form oil.
Expansion joint material ¾ inch thick, shall be provided where the new construction abuts an existing structure, sidewalk or driveway. Similar expansion material shall be placed around all obstructions protruding through the sidewalk. The expansion joint material shall be placed vertically and shall extend the full depth of the p.c. concrete. Maximum spacing of expansion joints shall be 40 feet as indicated on the Drawings or as directed by the Engineer or designated representative. Weakened plane joints shall be spaced at 5 feet on center. Normal dimensions of the weakened plane joints shall be ¼ inch wide and ¾ inch deep. All joints shall be constructed perpendicular (90 degrees) to the centerline of walk and shall match any previously placed concrete joints.
Reinforcement for sidewalks shall consist of polypropylene fibrillated fibers, 1 layer of 6 x 6 - W1.4 x W1.4 wire fabric or #3 bars, placed not more than 18 inches on center both directions. All reinforcement shall be placed equidistant from the top and bottom of the p.c. concrete. Care shall be exercised to keep all steel in its proper position during placement of the p.c. concrete. Splices in wire fabric shall overlap sufficiently to allow two pairs of transverse wires to be tied together and no splice of less than 6 inches will be permitted. Splices in the #3 bars shall have a minimum lap of 12 inches.
Where driveways cross sidewalks, additional reinforcing shall be placed in the sidewalk as indicated on the Drawings.
Portland cement concrete shall be placed in the forms and spaded, tamped and thoroughly consolidated until it entirely covers the surface and has a monolithic finish. The top surface shall be floated and troweled to a uniform smooth surface; then finished with a broom or wood float to a gritty texture unless indicated otherwise on the Drawings or as directed by the Engineer or designated representative. The outer edges and joints shall be rounded with approved tools to a ¼-inch radius. Care will be exercised to prevent loss of dummy joints or rounded edges when applying the brush finish.
Portland cement concrete sidewalk ramps shall be stamped or formed to produce a finished surface with detectable warnings in accordance with the requirements of the American Disabilities Act and Texas Accessibility Standards (TAS), including Sections 4.29.2 and A4.29.2. The p.c. concrete sidewalk ramps shall be constructed in accordance with appropriate Details.
Detectable warning for the ramps shall consist of raised truncated domes with a diameter of nominal 0.9 inch, a height of nominal 0.2 inch and center-to-center spacing of nominal 2.35 inches and shall contrast visually with adjoining surfaces, either light on dark or dark-on-light. The material used to provide contrast shall be an integral part of the walking surface.
When indicated on the Drawings or directed by the Engineer or designated representative the finished concrete, while still plastic, shall be stamped with an impression. The stamp shall be of approved design. The impressions shall be placed at or near street intersections at a distance, which does not exceed 350 feet or as directed by the Engineer or designated representative.
At the proper time after finishing, the surface shall be protected by a membrane, compound curing agent or by wetted cotton or burlap mats, conforming to Item No.409, "Membrane Curing". The sides of the p.c. concrete shall be cured in the forms. If the forms are removed during the curing process, the curing shall be continued by the placement of fill against the exposed concrete edges or by other procedures conforming to Item No. 410, "Concrete Structures". The top 4 inches of fill shall be clean topsoil conforming to Item No. 604, "Seeding for Erosion Control".
Existing sidewalk that is scheduled for removal and replacement shall be removed and the underlying material shaped to the lines, grades and cross section as indicated in the drawings or as directed by the Engineer or designated representative. The removal and/or relocation of obstructions, including but not limited to signs, trash cans and benches on concrete pads, abandoned manholes, sprinkler control valves and landscaping, shall be performed, as indicated on the drawings, in a manner acceptable to the Engineer or designated representative. Removal and/or relocation of obstructions will be considered incidental work to this item and will not be paid for directly.
Existing PVC pipe drains in and behind curb shall be removed and replaced as required in new sidewalk and/or curb and gutter. In areas of proposed sidewalk construction, where curb and gutter is to remain in place, existing PVC pipe shall be cut far enough behind the back of curb to allow sufficient room for joint fittings to connect to new or salvaged PVC pipe.
The Contractor shall be responsible for removing and replacing mailboxes that are located in the construction area, while assuring that mail delivery will not be interrupted as a result of the construction activities. Mailboxes shall not be laid on the ground.
All necessary excavation, filling and grading of the slopes adjacent to the completed concrete sidewalks will be considered incidental work pertaining to this item and will not be paid for directly. The adjacent excavation and grading of the slopes shall be done in a manner acceptable to the Engineer or designated representative.
432.5 Measurement
Accepted work performed as prescribed by this item will be measured by the square foot of surface area of "Concrete Sidewalk". Accepted work performed as prescribed by "Sidewalk Ramps" will be measured per each for the type of ramp indicated on the Drawings.
432.6 Payment
No direct measurement or payment will be made for the work to be done or the equipment to be furnished under this item, but shall be considered subsidiary to the particular items required by the bid.
End