COST of pavements varies widely with local conditions, particularly the diTtli and character of the foundations, the kind and quality of the wearing surfaces, the inclusion (or absence) in the contract of maintenance guarantees, and the freight rates. The variations are even great er when the cost of grading is included. For comparative purposes the cost of grading, drain ing, and curbing should be omitted; and the maintenance guarantees, if any, should be de scribed. In fact, without full details relating to the various factors involved, comparative figures of cost are often worse than useless. Roughly, the cost per yard of asphalt and granite was, in 1900, about $2.25 to $2.75; brick, $1.50 to $1.75; all for American cities, and excluding both extremes. With sand foundations and second or third class work the prices would be less, but the tendency is to insist on concrete foundations and good work generally for all three kinds of pavements, asphalt, granite, and brick ranking in the order named in this par ticular. The best wood pavements. on con crete, cost about the same as brick. The life of pavements, or the period for which they may be used without renewing the wearing surface, is given by Tillson as follows: granite blocks, 25 to 20 years; Belgian blocks, 20 years: asphalt and cobble, each 18 years; brick, 15 years; wood, 10 to 15 years; macadam, S years.
Toor.s for paving work include hammers, ram tilers, tamping irons, crowbars, sand and gravel screens, and brooms. besides special asphalt tools and machinery and a variety of tools and ma chines common to road and other work, such as rollers and concrete-mixers. The graders, scrapers, and other apparatus used in preparing the earth sub-grade, and also the rollers used to compact the natural earth and various classes of paving material, will be deseribed under ROAD AND STREET Al ACIIINERY. Concrete-mixers are
described under CONCRETE. Pavers' hammers have a head at one end for pounding the blocks, and a sort of combination chisel and scoop at the other, to facilitate the preparation of the sand cushion and to pry out or loosen single blocks in the setting. Different-shaped ham mers are used for cobble than for squared stones, and still different ones for brick. Ran»ners, also, vary in shape and weight, according to the character of the blocks for which they are de signed. For stone. the weights are 40 to 45 pounds; for brick, 25 to 30 pounds; for earth, about 20 pounds. Several shapes of tamping irons are used for street asphalt. to facilitate work along curbstones and to meet other spe cial needs. These rammers have cast-iron heads and wooden handles. The smoothing irons are of the same materials, but are slightly convex to the pavement, and are mounted on handles curved at the lower end. Both the tamping and smoothing irons are heated in fire-boxes, mounted on wheels. Screens for sand and gravel are of the familiar type used by masons, con sisting of wire meshes of the desired size, mounted in wooden frames. The brooms used for brushing sand and gravel into joints are short and stiff, of rattan, wood fibres, or wire. The Perkins surface heater, used in repairing sheet asphalt, is composed of gasoline burners, surrounded by wire and asbestos cement. The burners are supplied from a gasoline tank mounted on wheels, the same mounting also serv ing as a support to the burner frame and mat when the heater is being wheeled about. When in use, the burner frame rests on the as phalt pavement, with a small air space below the mat.