Asphalt pavements are laid as follows; A foundation is formed of cement or lime concrete, varying from 6 to 9 inches in thickness, according to the traffic. The mineral rock in its natural state, and without admixture with other in gredients, after being broken into small lumps, is brought to a state of dry powder by subjecting it to considerable heat in revolving ovens; it is then put into iron carts with close-fitting covers, and brought on to the works, taken out, laid over the surface, and whilst hot compressed with heated irons into one homogeneous mass without joints. The finished thickness varies from 2 to 2 1/4 inches, according to the traffic of the place in which it is laid, and it further compresses and consolidates under the traffic. Val de Travers liquid asphalt is laid upon a concrete bed 6 inches thick, the asphalt surface being 1 1/2 inch thick. The rock is first ground to a fine powder, and being then placed in caldrons, from 5 to 7 per cent. of bitumen is added to dissolve it; heat being then applied, it forms into a semi-fluid or mastic state, and when in that condition about 60 per cent, of grit or dry shingle is added to it, and after being thoroughly mixed together, the compound is spread over the concrete in one thickness.
With Limmer asphalt, a concrete foundation 9 inches thick is first formed, and the asphalt is used in certain proportions by the judgment of those directing the work; it is broken up and mixed with clean grit or sand of different sizes according to the place in which the pavement is to be laid; a small quantity of bitumen is then added to the materials, which are placed in caldrons on the spot, made liquid by heat, and the compound is run over the surface and smoothed with irons to the proper slopes and curvatures. It is run in two thicknesses, the lower stratum being made with grit of a larger size than that of the upper. The total thickness of the asphalt, when finished, is from 1 1/2 to 2 inches.
Barnett's Liquid Iron Asphalt can be made either of natural or artificial asphalt, mixed with pulverised iron ore or sesquioxide of iron, and a small proportion of mineral tar. The materials are put into a caldron which is brought on to the works, and are made into a liquid state by heat, run over the surface, and smoothed in the same way as the other liquid asphalts mentioned; the thickness usually laid is about 2 inches.
Made by mixing with fine breeze, or small coke, just enough of thick refuse coal-tar to make it somewhat sticky; put a thin layer on the smooth and hardened surface, on this spread a couple of inches of metal, or pebbles, or coarse gravel, then a thin layer of the prepared breeze, covered lightly with fine gravel, and beat or press together. It is cheap, slightly elastic, and durable.
(a) The terraza floors used in Italy at the present day are made in the following manner: - 1st coat; a concrete, consisting of common lime 1/4, sand and fine gravel 3/4, laid 6 inches thick and well beaten with wooden rammers; after two days in that climate, it is sufficiently dry for the next coat. 2nd coat; a terraza, consisting of pounded brick or tile 1/6, common lime 2/6, sand 3/6, of the consistency of mortar, laid 1 1/4 inch thick, well beaten with a light flat rammer. After two or three days it is hard enough for the next coat. 3rd coat; a similar terraza, but with the grit of broken stones instead of sand in it, laid on like a coat of plaster with a trowel. After this has been laid for one day, a layer of small hard broken stones is pressed into it; these stones should be of some substance that will take a polish, and be of uniform size (they are passed through a gravel screen), about that of a walnut: these being afterwards rubbed to a smooth even surface with some smooth hard stone, form a kind of mosaic-work. The stones are frequently selected by colour, and laid in the third coat to a rough pattern.
(6) Dig the earth out about 8 inches, fill in with coarse gravel and stones, well rammed, and levelled about 5 inches. Mix Portland cement to the consistence of cream and pour over, spreading it with a stiff broom; when hard, mix finer gravel with cement and water, and fill up to within 3/4 inch of the surface; when hard, mix clean sharp sand and Portland cement, half-and-half, with water to about the thickness of mortar, and finish, slightly rounding. It should not be walked on for a day or two. Cement must be Portland, and fresh.