Note.—These specifications conform to the common practice of laying the sidewalk in two courses.
In the author’s judgment this is neither necessary nor desirable. He believes that it would be better and somewhat cheaper to use a single course of concrete four inches in thickness. He suggests for this concrete the ratios of one cement, two sand, and three and one-half stone, the latter to be crushed to pass a screen with five-eighths inch square openings.
Tamping will bring a sufficient quantity of mortar to the surface to permit of satisfactory finishing. While the materials for such a single course of four inch concrete would cost somewhat more, the saving in cost of labor would, at usual prices of material and labor, make the single-course construction somewhat cheaper, while the solid four inches of richer concrete would make the walk much stronger. In fact, a single course of such concrete three inches thick would be sufficient in a great majority of cases. While the surface might not have the glazed appearance common in the two-course work it would be really better for use—a polished and slippery surface on sidewalks is not desirable.
140.The hydraulic concrete sidewalk shall be ... feet in width and its outer edge shall be ... feet fromthe outer face of the street curbing. It shall be constructed with two courses of Portland cement concrete as hereinafter specified.
141. Excavation and Grading.—The ground to be occupied by the sidewalk shall be excavated or filled to a sub-grade which after being compacted shall be ... inches[79]below the finished surface of the sidewalk. The sub-grade shall be neatly dressed to a plane surface sloping downward toward the street one-fourth inch in one foot horizontal, and to such longitudinal gradients as the engineer may prescribe. The completed sub-grade shall project four (4) inches in excavation and eighteen (18) inches in embankment on each side beyond the edges of the completed sidewalk. After the grading is completed the surface shall be compacted by rolling or ramming.
142. Drainage Course.—Upon the sub-grade prepared as specified in Section 141 a drainage course composed of broken stone, gravel or boiler-plant cinders, ... inches[80]in thickness shall be laid. Broken stone for this purpose may be of any durable stone crushed to such size that all will pass through a screen with two inch openings. Crusher-run material may be used unless it contains an excessive quantity of fine material. Gravel for the purpose may be any sound durable gravel all of which will pass through a two inch screen and be retained upon a one-fourth (¼) inch screen. If cinders are used they must be good boiler-plant cinders from which the ashes have been screened out. The cinders must be thoroughly drenched with water at least one week before they are placed in the sidewalk.[81]
143.This drainage material shall be placed on the sub-grade and properly graded. After grading it shall be thoroughly compacted by ramming or rolling, and its surface shall be brought to a plane parallel to and ... inches below the designed surface of the sidewalk, after which the surface inequalities may be leveled up with screenings or small gravel.
The bottom of the drainage course shall be connected with the street drains or sewer inlets by three-inch hard drain pipe at such points, not more than three hundred feet apart, as will drain all standing water out of the drainage course.
144. Concrete, Bottom Course.—The bottom course of concrete ...[82]inches in depth, shall be constructed and placed in accordance with Sections 28, 29, 30, 31, 32, 33, 34, 35 and 36 of these general specifications, except that the maximum size of the crushed stone shall not exceed one-half the thickness of the bottom course of concrete and the concrete shall be uniformly composed of one part Portland cement, three parts sand and six parts of crushed stone. Its upper surface shall be brought to a plane parallel to and one inch below the designed sidewalk surface.
145. Surface or Finishing Course.—The surface or finishing course shall be of concrete, one inch thick, composed of one part Portland cement, one and one-half parts sand and two and one-half parts of hard, durable stone, crushed to such sizes that all will pass through a screen having openings one-half (½) inch square and none will pass through a screen having openings one-eighth (⅛) inch square.[83]This concrete shall be made as specified in Sections 28, 29, 30, 31, 32, 33, 34, 35 and 36 except in the particulars named in the preceding paragraph. Care must be taken to make the mixing very thorough. The quantity of water used in this concrete shall be just sufficient to make a moderately wet mixture, and care shall be takento make the different batches as nearly as practicable of the same consistency.
The surface concrete shall be spread over the bottom-course concrete before the latter has begun to set,[84]properly graded, well compacted by ramming, and its upper surface brought to the true designed plane and surface of the sidewalk by the use of straight-edges and troweling,[85]after which the surface shall be lightly gone over with a wire broom or brush to slightly roughen the surface. The finished plane of the sidewalk shall have a transverse downward slope toward the street of one-fourth (¼) inch to one foot of horizontal width. At no place shall the thickness of the surface-course be less than three-fourths of one inch. The outer top corners of the sidewalk shall be rounded off with a suitable tool to a radius of three-fourths (¾) inch.
146. Forms.—Substantial and suitable forms of wood or iron shall be furnished and used by the contractor to support the concrete until it is hard set, when they shall be removed at his expense.
147. Expansion Joints.—After the laying of both courses of concrete is completed expansion joints at right angles to the sidewalk, and not more than four (4) feet apart shall be constructed in the sidewalk in the following manner: the joint will be located by a line on the surface of the sidewalk and a straight-edged cutting tool one-fourth (¼) inch thick will be used to cut entirely through both courses of concrete, accurately along the line marked out, entirely across the sidewalk, after which a T-shaped trowel or tool shall be used to smooth and compact the cut surfaces for a depth of one inch, and to round off the corners of the sidewalk blocks to a radius of one-fourth (¼) inch.[86]
Where the ends of the sidewalk abut against the curbing a clearexpansion joint one and one-fourth (1¼) inches wide shall be left between the sidewalk and the curb.
148.After the concrete laying is completed it shall be protected from use or injury until the concrete is set hard enough to withstand travel, and it shall be kept continuously damp for at least five days after the concrete is laid.
149. Weather.—Concrete in sidewalks shall not be laid in freezing weather nor shall frozen materials be used in the work. Completed work must be securely protected from frost for at least seven days after the concrete is laid. Any concrete sidewalk that shall become frozen within that period of time shall be wholly taken up and replaced with new work, at the expense of the contractor.
150. Regrading.—Directly after the concrete is completed, the forms removed, and the work inspected by the engineer, the space between the outer edge of the sidewalk and the street curb shall be excavated or filled up and dressed to a plane one inch below the top of the sidewalk and the top of the street curb; and the space on the inner side of the sidewalk shall be graded to a plane one inch below and parallel to the surface of the sidewalk for a distance of two feet back from the edge of the sidewalk and completed with a slope of one and one-half to one to the natural surface of the ground. Where this regrading requires filling up the filling material, for a depth of four inches from the surface, shall be good, rich surface soil.
151.Should any defects due to faulty material or workmanship develop in the sidewalk within one year after the completion of the same the contractor shall repair or reconstruct all such defective places at his expense, doing the work in accordance with these specifications.
152. Measurement and Payment.—Concrete sidewalk will be measured and paid for by the square foot of completed sidewalk surface, and the unit price per square foot shall cover the entire cost of the work, including grading, drainage work, all material and labor, forms, and the regrading or dressing up after the completion of the concrete work; except that the drain pipe used will be paid for per linear foot at the price named in the contract which price shall cover the cost of furnishing and putting the pipe in place complete.