POETLAND CEMENT CONCRETE ROADS. 33 



The equipment used for hauling must fit in with the general 

 method of conducting the work. The proper hauling equipment 

 will depend upon which of the three general methods of operation 

 are employed. By the first method, the materials entering into 

 the construction of the pavement are hauled separately to the work ; 

 by the second, they are proportioned at the unloading plant; and 

 when the third method is used, the concrete is mixed at the unload- 

 ing plant and hauled to the road. If the first method of opera- 

 tion is employed the materials must be distributed on the sub- 

 grade (see Fig. 2, PL II) or placed in stock piles on the road. Teams, 

 trucks, tractors, or an industrial railway may be used for this haul- 

 ing. Team haul is generally not economical where the maxi- 

 mum haul exceeds 3 miles. The economy of truck haul depends 

 largely upon the condition of the road hauled over and the care ex- 

 ercised in the operation and maintenance of the trucks. It should 

 not be attempted on a sandy or sandy-loam grade. No class of 

 equipment used in pavement construction depreciates as rapidly as 

 motor trucks if they are improperly operated. Constant changing 

 of drivers and the overloading of the truck are two of the prac- 

 tices which contribute to this rapid depreciation. Trucks for this 

 class of hauling should be equipped with power dump bodies. 

 Tractors are usually used in conjunction with a train of 4 or 5 

 bottom-dump specially constructed wagons each with a capacity of 

 about 5 cubic yards. The success of the tractor train is due to 

 the large quantity which it is possible to haul at one time. (See 

 Fig. 1, PL II.) On account of the great width of pile which the 

 tractor train spreads, the proper distribution of the materials on 

 the subgrade is rather difficult. On roads of average width some 

 shoveling of the materials is necessary before the forms can be 

 set. An industrial railway may be used for delivering the material 

 to the subgrade, but when it is used, it would appear to be doubtful 

 economy to dump the materials on the subgrade and rehandle them 

 into the mixer when they can be handled directly into the mixer 

 from the industrial railway by the use of batch boxes. 



When the materials are proportioned at the unloading point, the 

 only practicable method of hauling is with trucks or by industrial 

 railway. Under this method of operation the properly propor- 

 tioned materials for each mixer batch of concrete are diunped di- 

 rectly into the mixer skip. Each batch, therefore, constitutes a 

 distinct unit and must be handled so that it is kept separate from 

 other batches. Trucks of various sizes m.ay be used for this work. 

 The light trucks are usually equipped to haul only one 4-sack batch. 

 Trucks of larger size, however, may be used by dividing the body 

 of the truck into compartments separated by swinging transverse 

 101130°— 22 3 



