64 and 65), while in others the asphalt is laid to the curb, a space of 12 to 15 inches along the curb being covered with a thin coating of asphalt cement.
Asphalt laid adjoining center-bearing street-car rails is quickly broken down and destroyed. This defect is not peculiar to asphalt. All other materials when placed in similar positions are quickly worn. Granite blocks laid along such tracks have been cut into at a rate of more than half an inch a year. The frequent entering and turning off of vehicles from car tracks is one of the severest tests that can be applied to any paving material; moreover, the gauge of trucks and vehicles is frequently greater than that of the rails, so one wheel runs on the rail and the other outside. The number of wheels thus travel ing in one line must quickly wear a rut in any material adjoining the center-bearing rail.
To obviate the destruction of asphalt in such situations, it is usual to lay a strip of granite block or brick paving along the rail. This pavement should be of sufficient width to support the wheels of the widest gauge using the street.
The burning of leaves or making of fires on asphalt pavements should not be permitted, as it injures the asphalt, and the paving com panies cannot be compelled to repair the damaged places without compensation.
Asphalt Blocks. Asphalt paving blocks are formed from a mix ture of asphaltic cement and crushed stone in the proportion of 8 to 12 per cent of cement to 88 and 92 per cent of stone. The materials are heated to a temperature of about 300° F., and mixed while hot in a suitable vessel. When the mixing is complete, the material is placed in moulds and subjected to heavy pressure, after which the blocks are cooled suddenly by plunging into cold water.
The usual dimensions of the blocks are 4 inches wide, 3 inches deep, and 12 inches long.
Foundation. The blocks are usually laid upon a concrete founda tion with a cushion-coat of sand about I inch thick. They are laid with their length at right angles to the axis of the street, and the longitu dinal joints should be broken by a lap of at least 4 inches. The blocks
are then either rammed with hand rammers or rolled with a light steam roller, the surface being covered with clean, fine sand; no joint filling is used, as, under the action of the sun and traffic, the blocks soon become cemented.
The advantages claimed for a pavement of asphalt blocks over a continuous sheet of asphalt are: (1) That they can be made at a factory located near the materials, whence they can be transported to the place where they are to be used and can be laid by ordinary paviors, whereas sheet pavements require special machinery and skilled labor; (2) that they are less slippery, owing to the joints and the rougher surface due to the use of crushed stone.
Asphalt Macadam—Bituminous Macadam. Recently it has been proposed to use asphalt as a binding material for broken stone. There are two patented processes—the Whinery and the Warren— which differ slightly in details.
The advantages claimed for these methods are: (1) The first coat will be materially less; (2) it will offer a better foothold for horses; (3) it will be at least as durable as the ordinary sheet asphalt; (4) it will not shift under traffic and roll into waves; (5) it will not crack; (6) it can he repaired more cheaply and with less skilled labor than can the ordinary sheet asphalt.
The principal dimensions of a five-ton roller are as follows: roll or steering-wheel 30 to 32 inches diameter.
Rear roll or driving-wheel 18 Width of front roll 40 " " " rear " 40 Extreme length 14 feet.
" height 7 to S feet.
capacity SO to 100 gallons.
Coal " 200 pounds.