36 BULLETIISr 1077, U. S. DEPAETMENT OF AGEICULTUEE. 



loading is essential and a tunnel may be desirable, but for a single- 

 mixer operation open bins are believed to be preferable. Indus- 

 trial cars may be loaded from open bins either by chutes on the sides 

 of the bins or by running the cars directly under the bins and 

 loading from traps. (See Fig. 1, PI. VI.) After the aggregates are 

 loaded into the batch boxes the train is run past the cement house, 

 where the required number of sacks of cement are dumped into the 

 boxes. The cement house should be provided with a loading plat- 

 form at apjproximately the same elevation as the top of the batch 

 boxes. 



A 24-inch gauge is commonly used on industrial railways for 

 pavement construction and the track is generally laid along one 

 shoulder of the road. Passing switches are provided where neces- 

 sary. Both steam and gasoline locomotives are used to furnish trac- 

 tive power. The limiting factor in industrial railway hauling is 

 the rate of grade. On sustained grades exceeding 2^ per cent the 

 speed and capacity of trains begins to be measurably reduced. On 

 a 6 per cent grade the capacitj'^ is reduced to approximately one- 

 fifth of the amount generally hauled on grades of less than 2| per 

 cent. The capacity on grades may be increased by the use of geared 

 locomotives, but a locomotive of this type is much slower than a 

 direct-acting locomotive. The great advantage of industrial railway 

 hauling lies in the fact that the subgrade is not cut up by hauling 

 over it, and that hauling is affected comparatively little by weather 

 conditions. The delay on account of bad weather, therefore, is 

 reduced to a minimum. Another important advantage is that the 

 aggregates are kept clean and material is not Avasted on the subgrade. 



Attempts have been made to haul batch boxes on trucks and on 

 wagon trains, but they have not generally been successful. A der- 

 rick independent of the mixer is necessary to discharge the boxes 

 and it has been found that there is not suiRcient room on the sub- 

 grade to maneuver these large machines or wagons without losing a 

 considerable amount of time. 



A combination of batch-box truck haul and industrial railway 

 haul, however, has proved very satisfactory under certain conditions. 

 Where the begimiing of the pavement is a mile or more from the un- 

 loading plant and the road from the plant to the work contains 

 grades as high as 5 or 6 per cent, an all-industrial-railway haul is not 

 feasible. However, if the road from the plant to the work is in 

 good hauling condition, trucks may be used to haul batch boxes to 

 the beginning of the new pavement, where the boxes may be trans- 

 ferred by means of a portable overhead crane to an industrial railway 

 train for the rest of the trip to the mixer. The transfer of 4 batch 

 boxes from a truck to the industrial cars may be effected in from 5 to 

 7 minutes. (See Fig. 1, PI. VII.) The pavement in this case is 



