The Republican., 1900-11-15
THE USE OF GRAVEL.
Road Building Instructions PrOmul-
gated by the WiscOnsia state
Experiment Station.

AS gravel is the material chiefly
used for the improvement OF country
roads, the following instructions
taken from bulletin issued by the
Wisconsin experiment station will be
of interest to many of our readers:
1t occasionally happens that nat
ural gravel beds are found which pos
sess the right characteristics for max
ing roads, and when the gravel is just
right excellent roads may be made
from it.
There are several important feat
ures which a good road gravel must
possess:
l. There must be one prevailing
size of pebble in sufficient quantity so
that when thoroughly rolled they
press against one another.
2. There must be enough of the
hEer sizes ot coarse sand and fine
gravel to fill the voids between the
coarser gravel.
3. There must be enough of fine
| loan to fill the voids between the
coarse sand and fine gravel and retain
" VI NdlCl " Olhb
the sand grains together and prevent
their rolling.
4. The coarse and fine gravel and
the sand must be made up of more or
less angular fragments in order that
| fiat faces of rock may set together
and thus lessen the danger of rolling
| and of crushing under the weight of
the LOAD.
1t is not possible to give specific,
! concise directions for identifying a
good road gravel, but a man who has
seen and worked with it readily rec
ognizes it.
1t will be apparent at once that the
several characteristics which have
been pointed out are not likely often
to occur together in just the right
ratios; and so there will be all pos
sible gradations from the ideal gravels
to those which will not answer at all.
Indeed it must be said that most
gravel beds have had the finer mate
rials so completely washed out that
only clean sand and gravel remain;
and when this is true it is useless to
try to make road with it. Such ma
terials can only be used to temper a
road which is too clayey in its texture
by reducing its water capacity.
1t happens in the majority of cases
that much of the gravel is too large
and too rounded to permit close pack
ing and fast binding. When this is
true much better qualities may be
secured by using either the crusher or
the screen, or both together. 1t will
be at once apparent that where much
of the gravel is too coarse, to run il
through the crusher so as to reduce
the material to a more uniform size
and at the same time to increase the
angularity of the fragments will make
a much better road material to use
either by itself, to build a road of OF
as tempering material.
There are many deposits of gravity
clay which it might appear would
make a good road material. but the
principle must be kept always in minC
that too much of too fine materia
will take in and retain so much water
that the binding quality OF the water
is lost. -nese gravelly clays occur il
many of the hills of the glaciated por
tions of the United Dtates and through
which roads are often cut.
In the construction of gravel road
as in that of a stone road, it is o.
prime Importance to secure first o.
all properly shaped and thoroughly
rolled and firmed roadbed before any
gravel is laid on. When this has beer
done, and a suitable gravel has beer
found, the next step is to spread even
ly over the surface and thoroughly
roll layer which, when finished, viii
measure three inches thick.
In the rolling it will be importan'
to firm the outer edges of the grave
first in order that the rolling may no
force it outward and destroy the slope
Should the gravel be too dry to pacl
it must be moistened or the work b,
suspended to take advantage of the
rains.
To make a good road there should
be not less than three three-inch Law
ers, and usually four will be better
Of course a road six inches thick will
be great improvement, and Otter
where Inc travel is light and tn,
roadbed thoroughly made three inche.
of good gravel, well placed, will make
a great improvement in the road
serving as a wearing surface.