119

D.—l

In case they deviate from the required crown they shall be immediately corrected. If the proper correction cannot be made they shall be discarded and new ones placed in service by the contractor. Rolling. —After the concrete is tamped as above specified it shall be rolled three times with intervals of from five to fifteen minutes between rollings. The roller shall be provided by the contractor, and shall be a hollow cylinder of smooth iron, not less-than 6 ft. long, and shall be from 9 in. to 12 in. in diameter, and weigh not less than 1 lb. per lineal inch. The roller shall be used transversely to roll off the excess water which comes to the surface of the concrete, and shall be used from 10 ft. to 20 ft. behind tho newly placed concrete. The roller shall be moved forward one-half its length each time across. Finishing. —After rolling with the hand-roller has been completed as specified, a straight-edge templet not less than 16 ft. nor more than 18 ft. in length, with a trowelling or smoothing surface not less than 8 in. nor more than 10 in. in width, shall be used with its length parallel to the centreline of the pavement, and operated from bridges with a combined longitudinal and transverse motion, planing off the high places and filling in the depressions. Final Finishing.-—Tho, surface of the concrete shall be finally finished smooth and true to grade with a canvas belt or trowel, as the engineer may direct. Finishing Edge of Pavement. —All. outside edges of the pavement shall be rounded to I in. radius. Testing Surface. —When a straight-edge 10 ft. long is laid on the finished surface of trie roadway and parallel with the line of the road, the surface shall in no place vary more than Jin. from the lower edge of the straight-edge. Cracks and Hair-checks. — In case fine cracks or hair-checks appear in newly placed concrete before it is thoroughly set, immediate steps shall be taken by the contractor to remedy this condition. Pavement which shows serious chocking shall, if required by the engineer, be removed by the contractor and replaced at his expense. Curing Concrete Pavement. Curing. —Fresh concrete shall be covered with heavy burlap laid directly on the pavement. This burlap covering shall, as soon as placed, be sprinkled with water by means of an adjustable gardenhose nozzle, so adjusted that it will spray, and it shall be kept wet until it is removed. The burlap may bo made up in mats approximately J 2 ft. in width and 4 ft. longer than the specified width of the pavement to be built, and placed by hand ; or it may be made up in mats 50 ft. in length and 2 ft. wider than the specified width of the pavement, and wound on spools supported on wheels running on the shoulders. The contractor shall provide with each mixer on the work sufficient burlap to cover the maximum amount of pavement laid in one day's run. This burlap shall be used exclusively for covering pavement, and shall be replaced by new burlap when ordered by the engineer. Earth Dykes. —After the concrete pavement has set sufficiently so that the earth will not become incorporated in the surface of the concrete the burlap shall be removed, earth dykes shall be constructed along each side of the pavement, and across the pavement at intervals not greater than 25 ft. In placing earth no teams or wheelbarrows shall be allowed on the concrete. The earth dykes shall bo built sufficiently high so as to hold at least 2 in. of water over the crown of the pavement. Earth for dykes shall be taken from outside the limits of the shoulders. These dykes shall be flooded with water immediately after they are built, and shall bo kept flooded for a period of fourteen days. The water shall then be allowed to evaporate. Earth Blanket. —Whore it is not feasible to flood the pavement for curing by means of earth dykes on account of grades or soil conditions, a blanket of earth or sand, 2 in. or more in thickness, shallbe placed on the concrete, and kept thoroughly wet for a period of fourteen days. After remaining in place for fourteen days the earth or other covering may be removed.

Authority : W. A. G. Skinner, Government Printer, Wellington.—l 924.