PORTLAND 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, PI. 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. 
, Vactors are usually used in conjunction with a train of 4 or 5 
.ottom-dump specially constructed wagons each with a capacity of 
about 5 cubic yards. The success of the tractor train is due to 
tie large quantity which it is possible to haul at one time. (See 
.'ig. 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 dumped 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 may 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 
