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Specifications for Laying

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SPECIFICATIONS FOR LAYING Below are the specifica tions employed for asphalt block pavements on carriage ways, in the City of Washington.* Road-bed. The space over which the pavement is to be laid hav ing been excavated to the proper depth below the surface of the pave ment when completed, any objectionable or unsuitable matter below the bed will be wholly removed, and the space filled with good gravel or sand compactly rolled or rammed. The bed will be trimmed so as to be parallel to the surface of the pavement when completed, and the entire road-bed will then be thoroughly compacted by rolling with a roller weighing at least ten tons, or by thorough ramming at places which can not be reached by the roller. No extra allowance will be made for trimming and rolling.

Foundation. Two forms of foundation are used—con crete and gravel. The specifications are as follows, those for the concrete being abridged.

Concrete Base. This will be four inches thick when compacted, and will be made of broken stone and gravel, sand, and natural cement in such proportions that the quantity of gravel will be equal to the volume of voids in the broken stone; and the sand and the cement, mixed in the pro portion of one part cement and two parts sand, will be 20 per cent in excess of the volume of the voids in the combined gravel and broken stone. Upon the concrete will be laid a course of fine sharp sand, half an inch thick, to serve as a bed for the blocks. Special care will be observed to make the sur face of the sand exactly parallel to the surface of the pavement when com. pleted.

Gravel Base.

Upon the mad-bed prepared as above is to be laid a course of bank gravel, screened from all pebbles measuring more than one and one half inches in their largest dimension, of such a depth as to give five inches in thickness when compacted by rolling and ramming. Upon the gravel will be spread a .layer of fine sharp sand two inches in thickness, to serve as a bed for the blocks. Special care will be observed to make the surface of the sand exactly parallel to the surface of the pavement when com pleted.

Placing the Blocks.

The blocks will be 4 X 12 inches on top and five inches deep,* and a variation of one quarter of an inch from these dimensions will be sufficient grounds for rejecting any block. The blocks

must be square and have sharp corners, and blocks having chipped or rounded edges will be rejected.

The blocks will be laid by pavers standing or kneeling upon the blocks already laid, and not upon the bed of sand. Each course will be formed of blocks of a uniform width and depth. The blocks will be laid with their length at right angles to the axis of the street; and shall be so laid that all longitudinal joints shall be broken by a lap of at least four inches. Each course ef blocks will be driven against the course preceding it by a heavy wooden maul, in order to make the lateral joints as tight as possible. The longitudinal joints will be closed by pressing on a lever inserted at the end of the course adjoining the curb, and keying with a block cut to the required size.

When laid, the blocks will be immediately covered with clean, fine sand entirely free from loam or earthy matter, perfectly dry, and screened through a screen having 20 meshes to the inch. The blocks will then be rammed by placing an iron plate, 24 inches by 8 inches, and inch thick, over four blocks, and striking on the plate with a rammer weighing not less than 45 lb. The ramming will be continued until the blocks reach a firm, unyielding bed and present a uniform surface, with the required grade and crown. Any lack of uniformity of the surface must be corrected by taking up the blocks, increas ing or decreasing the sand bedding, and relaying them. When the ramming is completed, a sufficient amount of fine, dry sand, as above described, will be spread over the surface and swept into the joints.

The contractor will be permitted, if he so desires, to use the District steam roller No. 1 on this work. The men and material for its use are to be sup plied by the District, and are to be paid for by the contractor during such use.

It is better to lay asphalt blocks in hot rather than in cool weather. If the weather is cool, the blocks are firm and do not fit closely together; and consequently the edges chip or flow into the joint, thus making the upper surface of the block rounded and the pavement rough and comparatively noisy.