Dry weather is essential whilst this class of roadway is in course of construction, and they require careful watching, as, upon the skin becoming broken, the whole roadway soon breaks up. They have, however, many advantages over ordinary macadamised roadways when finished, not the least of them being their imperviousness to moisture, and the ease with which they are cleansed.
[12] The first road “engineer” in this country was John Metcalf of Knaresborough, who was born in 1717, and who, although totally blind, was the first person to introduce a methodical system of road repairs. Vide ‘Roads and Road Makers,’ by Henry Alexander Glass.
[13] Vide ‘A Treatise on Roads,’ by Sir H. Parnell (1833).
[14] The total width of roadway being thirty feet.
[15] It is necessary to give a new roadway more convexity than it will have when finished, for however carefully it is raked or attended to when being rolled, the top is sure to flatten and spread towards the haunches.
[16] Instead of parallel lines it is sometimes well to place these stones diagonally from centre to kerb or “herring-bone” fashion, thus greatly facilitating the under drainage.
[17] In metalling a road it is better to put on the coats gradually, than to give the whole thickness of metal at once.
[18] The method adopted in Chicago, U.S.A., for forming their roadways is as follows:—The road bed is prepared of the proper contour and well-rolled with a 15-ton steam roller until it is even, firm, and compact; on this bed rubble stone is carefully placed by hand with its broadest surface downwards, then 12 inches of metal are added 6 inches at a time, thoroughly rolled to bond it well, it is then topped with 4 inches of crushed trap rock or some other equally hard stone, which will not disintegrate through the action of the weather, nor pulverise under the pressure and wear of vehicles upon it; this is again, thoroughly well rolled so as to compact and bind it together.
[19] “If roads be kept dry they will be maintained in a good state with proportionally less expense. It has been well observed that the statuary cannot saw his marble, nor the lapidary cut his jewels without the assistance of the powder of the specific materials on which he is acting; this, when combined with water, produces sufficient attrition to accomplish his purpose. A similar effect is produced on roads, since the reduced particles of the materials, when wet, assist the wheels in rapidly grinding down the surface.” Parnell’s ‘Treatise on Roads,’ 1883. More modern writers have likened macadamised roadways to “stone mills on which the stones are ground into dust when dry, or mud when wet.”