ASPHALT PLANTS, used to prepare the mate rial for laying sheet asphalt pavements, include melting kettles, sand-heaters, mixers, and vari ous accessories. The asphalt arrives at the plant in barrels. These are cut away and the asphalt and the residuum oil or other flux. are heated and thoroughly mixed in the kettles. The mixing may he effected by revolving paddles, or by pumping in air at the bottom of the kettles. The sand is dried and heated in jacketed revolv ing cylinders, fitted with angle bars to keep the sand well agitated. The drum is set at a slight angle, so the sand will find its way out. It falls into elevators, which take it to a bin on or above the mixing platform. In case pulverized lime stone cannot be had in the vicinity of the plant a limestone-grinding mill is provided. All the ingredients being ready, the asphaltic cement, sand, and limestone are admitted to the mixer. This is an iron box, with a capacity of S or 16 cubic feet. Two parallel revolving shafts, each fitted with steel blades. and revolving in oppo site directions, are placed in the bottom of the box and effect a thorough mixing of the several materials. When mixed, the finished paving ma terial is dumped from the mixer into a cart or wagon and hauled to the street.
Reif I: ASPHALT PAVEMENTS are composed of crushed limestone o• sandstone. naturally im
pregnated with bitumen. If the natural product does not linVe the desired proportion of hitu minons matter this is rectified by mixing a richer or poorer rock with the first. The mix ture is powdered. sifted. then kept heated for two hours at 300° to 325° F., after which it is carted to and spread upon the street. After a light rolling. followed by hand tamping, the sur face is covered lightly with hydraulic cement and rolled with a steam roller. The European rock asphalt pavements are all made from bitu minous limestone, hut in America both sand stone and limestone bituminous rock are used, sometimes mixed together. Little trouble from cracking arises with the rock asphalts; tlicy are generally considered more durable and more slip pery than the artificial asphalt mixtures. In Paris sonic of the asphalt pavements are pre pared by adding enough to the rock as phalt to bring the total bitumen up to 15 or 18 per .
• • • • it The mixture is heated to such a sistency that it can be spread or floated into a layer about one and one-half inches deep. It is not 'Idled. Other asphalt pavements in Paris a re compressed.