Wausau pilot. [volume] (Wausau, Wis.) 1896-1940, 1917-09-18
GRAVEL ROADTYpEs
Constitute About 0ne-Third of
Surfaced Roads in the
United States.
BEST SELECTION OF GRAVEL
Quality of Material Is Next in Impor-
lance to Proper Drainage-Clay Is
Poorest Cementing Material
We Have.

prepared by the United States Depart
ment of Agriculture.)
Roads that are artificially surfaced
with gravel, or with earthly material
in the composition of which gravel pre-
dominates, are called gravel roads.
This designation covers variation in
type which ranges from roads sur
faced with natural sand-clay mixture
containing a considerable percentage
of gravel to those having so-called
gravel macadam" surfaces, composed
almost wholly of pebbles and con-
structed in practically the same man
ner as first-class macadam roads. GRAY
ell roads constitute about one-third the
total mileage of surfaced roads in the
United States and are confined to no
especial section of the country.
In the following discussion of gravel
subject under the two general heads,
Selection of Gravel" and "Construc-
ton Methods"
Selection of Gravel.
Ordinarily the selection of gravel for
use in road surfacing must be confined
to local materials which are or can
be made suitable for that purpose.
Because Of high freight costs it seldom
happens that road gravel of even the
very best quality is transported by rail
a greater distance than about 100
miles from the source Of supply, and
In the vast majority of cases it is
hauled directly from pit to road in
wagons. Since the quality of gravel
varies to a considerable extent, some
times in different parts of the same
pit, it is essential that local road Off
Gals, who frequently are charged with
the selection of such material, should
have some knowledge of the relation
between the physical characteristics of
gravel and it's wearing qualities when
placed in road surface. While such
knowledge can best be gained by ac-
tual experience with different kinds of
gravel, there are certain general re-
the guidance of the inexperienced.
For example, the following excerpt
from Bulletin No. of the Michigan
state highway department presents in
very concise form the characteristics
which gravel for road Surfacing should
possess, in the judgment of the state
highway commissioner, in order to
meet the Michigan conditions.
Next to proper drainage, the most
important thing in building gravel
roads is to secure good quality of
gravel. Authorities have differed as
to the requirements of suitable road
gravels, most of them, in my opinion,
placing too much stress on the imme-
date packing qualities. Indeed, the
average township commissioner and
farmers generally have become so i'm
bued with the idea that it is necessary
to use q gravel that will pack quickly
that they have almost lost sight of
the fact that the only thing which
makes a gravel road better than an
earth road is the pebbles. real stones,
that it contains and is dependent up
on to bear up traffic and resist wear
Gravels that come from the pit with
the pebbles cemented together, even
though they contain no clay, will re-
cement in the road and become harder
than they were in the pit. Tests of
specimens of this kind always show
that there is much lime present and
usually some iron, both of which are
excellent cementing materials. Brief
ly, the experience of the state high
way department warrants the state
ment that there are few, if any, bank
gravels III Michigan that do not con-
tain enough limestone and other soft
pebbles which grind up under traffic
to furnish sufficient binder to cause
them to consolidate in a few months
time, if separated from the surplus
sand and earth, and properly treated
after applying to the road.
In accordance with these sugges-
tons, gravelS are considered valuable
for road purposes in the following
order:
1. Almost in direct proportion to the
percentage Of pebbles constituting the
mass.
2. In direct proportion to the value
as road metal of the rock fragments
constituting the pebbles.
3. In direct proportion to the value
as a cementing material under all con-
ditiOns of weather, of the finer par
ticles of earthly matter constituting
the filler or binder.
In general, the physical characters
tics of gravel which determine its
suitability for use in surfacing a road
are:
% The durability of the pebbles or
rock fragments, (2) the quality of the
binder, (3) the grading of the pebbles,
and (D the proportion in which the
binder material is present. While the
influence each of thaca factorS Shou1d