A. Required Specifications:
1. Concrete: All sidewalks shall be constructed of four thousand (4,000) pounds per square inch minimum strength air entrained concrete at least four inches (4") thick and not less than six inches (6") thick where motor vehicles may cross. (Ord. 2014-7, 9-23-2014)
2. Joints: Dummy joints shall be located not more than six feet (6') apart or distance from expansion-contraction joints which shall be not more than eighteen feet (18') apart.
3. Slope: Finished sidewalks shall have a slope toward the street of one-fourth inch (1/4") per foot ending at the top of curb; provided, that sidewalks located away from the curb pursuant to section 7-2-2 of this chapter shall have the same slope.
B. Recommended Specifications: Since property owners must repair or replace sidewalks in poor condition, it is recommended that sidewalks be constructed in the following manner for maximum life and durability:
1. Subgrade Preparation:
a. Remove from the site all organic matter such as grass, sod, roots, etc., and grade the ground. Dig out soft or mucky spots; fill them with soil similar to the rest of the subgrade or with granular material such as sand, gravel, crusher fines, crushed stone or slag and compact thoroughly.
b. All fill materials should be uniform, free of vegetable matter, large lumps or stones and frozen soil. Compact these materials in layers not more than five inches (5") thick until the site is at final grade with uniform hardness. It is best to extend the fill at least one foot (1') beyond the slab edge to prevent undercutting during rains and high winds. Unless fill material is well compacted, it is advisable to leave the subgrade undisturbed. Undisturbed soil is superior as a support for a concrete slab versus soil that has been dug out and poorly compacted. Subgrade compaction can be done with hand tampers, rollers or vibratory compacts.
c. A dry spot on the subgrade absorbs more water from the concrete slab than does an adjacent moist spot. This, in turn, may result in dark and light spots in the concrete finish. Hence, the subgrade shall be in a uniformly moist condition at the time of concreting. If necessary, dampen it by spraying with water. However, there should be no free water standing on the subgrade, nor should there be any muddy or soft spots when concrete is being placed.
d. On any new construction, the subgrade compaction should be ninety five percent (95%) of the standard ASTM laboratory method D-698. Compaction tests should be conducted on each one foot (1') lift of fill and on every three hundred (300) linear feet of sidewalk.
2. Concrete Recommendations:
a. Maximum Size Aggregate: Gravel, crushed stone, etc., should not exceed one-third (1/3) slab thickness. Accordingly, four inch (4") slabs can use three-fourths inch (3/4") or one inch (1") top size, but one inch (1") is recommended. The one inch (1") aggregate should meet ASTM C-33, 57 stone; the three-fourths inch (3/4") aggregate, 67 stone.
b. Minimum Cement Content: In this area, concrete is exposed to a number of freeze-thaw cycles and sometimes to the use of deicers. Therefore, it is advisable to use a minimum cement content of six (6) bag, five hundred sixty (560) pound per cubic yard or four hundred ninety five (495) pounds of cement per cubic yard with "Possolith", a water reducing, set controlling admixture conforming to ASTM C-494 71, type A (water reducing), type D (water reducing and retarding) and type E (water reducing, accelerating).
c. Maximum Slump: This should not exceed four inches (4"). A four inch (4") slump will give a good, workable mix. Stiffer mixes are harder to place and finish by hand but can be used to advantage with mechanical placing and finishing equipment.
d. Compressive Strength: Compressive strength at twenty eight (28) days should be three thousand to three thousand five hundred (3,000 to 3,500) pounds per square inch. In some instances, cement content higher than given in subsection B2b of this section may be necessary to obtain three thousand to three thousand five hundred (3,000 to 3,500) pounds per square inch concrete.
e. Air Content: An air entraining agent to provide six percent (6%) entrained air by volume should be in all concrete exposed to the outside and subjected to freezing, thawing and deicing salts. The air entraining agent may be MBVR and should conform to ASTM C-260.
3. Placing Concrete:
a. Concrete should be placed at a four inch (4") slump one inch (1"). It should be struck off with a straight edge or a strike off tool. Following strike off, the concrete should be bull floated or darbyed to fill voids left by the straight edge and to embed all particles of coarse aggregate slightly below the surface.
b. A "jitter bug" or hand tamper is not necessary for concrete placed between a three inch (3") and five inch (5") slump.
c. Control joints should extend into the slab one-fourth to one-fifth (1/4 to 1/5) of the slab thickness. For a four inch (4") thick slab, the joint should be a minimum of three-fourths inch (3/4") deep. In sidewalks, control joints should be spaced at intervals equal to the slab width.
d. Following the edging and placing of control joints, there should be final surface floating to remove any imperfections left in the surface by the previous operation. Following this final floating, the concrete should be given a coarse, transverse scored texture by drawing a broom across the surface.
4. Curing Of Concrete: All concrete work should be cured for a minimum of seven (7) days to increase the strength and durability of the concrete. The following methods of curing are advisable: water curing, water retaining (waterproof paper), mechanical barrier (polyethylene sheets) or a chemical membrane (liquid curing compounds) conforming to ASTM C-309. Alternate wetting and drying of concrete should not be permitted.
5. Seasons To Place Concrete:
a. Concrete sidewalks subject to freezing weather should be placed and cured far enough in advance to provide approximately four to five (4 to 5) weeks of drying out before freezing and thawing begins, unless precluded by a tight construction schedule and cold weather concrete practices, ACI 306-66, are met.
b. Cold weather concreting should begin in the fall, from the time of the first frost or when the average daily, high and low, temperature falls below forty degrees Fahrenheit (40°F) (4.5°C) for more than one day. Cold weather concreting practices should remain in effect until spring when the average daily, high and low, temperature rises above forty degrees Fahrenheit (40°F) (4.5°C) for more than three (3) consecutive days.
c. When concrete is placed during cold weather, the temperature of the mix should not be less than sixty degrees Fahrenheit (60°F), nor more than eighty degrees Fahrenheit (80°F) at the time of placing. Aggregates or water, or both, may be heated, but the water should not be hotter than one hundred seventy five degrees Fahrenheit (175°F) and aggregates should not be used which are hotter than one hundred fifty degrees Fahrenheit (150°F). Before concreting is started, remove ice, snow and frost.
d. When concrete is being placed in cold weather and temperature may be expected to drop below thirty five degrees Fahrenheit (35°F), a supply of straw, insulated curing blankets or other suitable material should be provided along the line of work. At any time when the air temperature may be expected to reach the freezing point during the day or night, the material so provided should be spread over the concrete to a sufficient depth to prevent freezing of the concrete. Concrete should be protected from freezing temperatures until it is at least five (5) days old. Concrete injured by frost action should be removed and replaced. (Ord. C66-149, 7-12-1977)