aggregates exhibit
peculiarities or the traffic conditions are unusual. It is desired to
emphasize that the purpose is to obtain concrete of the desired
strength and there can be no such thing as "standard" proportions.

=Measuring Materials.=--In considering the methods employed for
measuring aggregates, emphasis should be placed on the futility of
rigid requirements for the aggregates, both as regards quality and
range of sizes, if the materials are carelessly proportioned at the
mixer. If even reasonably near uniform wearing qualities are to be
secured throughout the entire area of the concrete road surface,
successive batches of concrete must be alike, and to insure that, the
aggregates including the water in each batch of concrete must be mixed
in exactly the same proportions. The aggregates are measured in
various ways, all essentially alike in that the intent is to insure
exactly the same amount of each ingredient for each batch of concrete.

One method is to place bottomless boxes in wheelbarrows, fill the
boxes level full and then lift off the box. Another is to use a
wheelbarrow with a bed of such shape that the contents will be a
multiple of 1 cubic foot when level full. For the larger jobs, the
aggregates are hauled in industrial cars, each having sufficient
capacity for a batch of concrete. The car body is provided with a
partition so as to separate the fine and coarse material.

The water is measured in a tank which automatically refills to the
same level each time it is emptied and when adjusted for a mixture
will introduce the proper amount of water for each batch. It is highly
important to use the least amount of water that will produce workable
concrete.

=Preparation of the Earth Foundation.=--The concrete road is generally
placed directly on the natural soil which has been brought to the
proper cross section. Some engineers advocate that in preparing the
subgrade, the earth be thoroughly rolled; others prefer not to roll
the subgrade. If fills of considerable depth are constructed, they
should either be rolled as built or else should be allowed to settle
for some months before the concrete road is placed, preferably the
latter.

=Placing the Concrete.=--The concrete is placed between substantial
side forms of a height equal to the thickness of the concrete road
slab at the edge, and is shaped roughly by means of shovels.

Various methods have been developed for striking the surface to the
ex