CONCRETE FOR ROADS AND PATHWAYS.

New Zealand Journal of Agriculture, Volume XVIII, Issue 2, 20 February 1919, Page 92

CONCRETE FOR ROADS AND PATHWAYS.

By the Public 1

Works Department.

Concrete for the formation of roads and pathways must be hard, strong, and solid, for the purpose of standing wear and distributing the load over the foundation. The foundation on which the concrete is to be laid should be, if necessary, consolidated by rolling.

The thickness of the concrete is determined by the nature of the traffic, varying from 8 in. down to in. If, however, the layer of concrete is to be as thin as i|in. the size of the large stones must be reduced to less than that. specified hereafter. The cement should comply with all the requirements of the British standard specification. As packed in New Zealand each bag contains 1241 lb.--that is, eighteen bags per ton. Cement weighs a little more than . 90 lb. per cubic foot, but for ease of calculation and to facilitate memorizing it is convenient to adopt 90 lb. as the weight of a cubic foot. One bag of cement will therefore contain 1-38 cubic feet. The sand must consist of sharp, angular grains of evenly graded sizes ; such that the whole will pass through a riddle having holes J in.. square, and be retained upon a standard sieve containing 2,500 meshes to the square inch. It should be derived from hard, tough rock, and be perfectly clean.

The coarse material in the “ aggregate ” may consist of either broken stone or shingle, broken stone being preferred. The dimensions will vary, but the whole should pass through a riddle having apertures in. square in the clear, and be retained upon a riddle having apertures J in. square in the clear. The stone must be hard, .tough, and perfectly clean. The materials are gauged by measure in the proportions of one of cement, two and a half of sand, and five of stone or shingle. They should be mixed together with a minimum quantity of fresh, clean water until they assume an even colour throughout, so as to provide for the concrete being placed in position and compacted' with a moderate amount of ramming. The foregoing specification will provide a roadway or pathway suitable for moderate traffic and restricted loads. If the wheeled traffic is likely to be heavy, then the surface will require protecting by a carpet of bituminous asphalt. If it is desired to omit the asphalt and rely upon the concrete, then a surface dressing of cement mortar consisting of one part cement and two parts sand should be applied. It may be added that the whole subject of concrete roads is still under study, most of the • work carried out up to date being of an experimental character.