The Bemidji daily pioneer., 1912-03-26

successive cultivation OF the soil, and
if this soil is used in the construction
Of q road it is known as ''top soil road"
There are many varieties OF clay and
consequently wide. variation in the
characteristics of sand-clay road.
The quality of the sand is a variable
factor, as il may range all the way
from fine, dust-like particles to coarse
grains and gravel and may be perfect
" clean or mixed with loan and other
material. In consequence of these wide
differences in the materials CONSTITUTE
ing sand-clay roads it is impossible to
maintain a uniform standard as to
quality of the road or methods of con-
struction.
Not all but most sand consists of
tiny grains Of quartz. While quartz
is one of the hardest minerals known,
it possesses practically no binding or
cementing power. The grains Of sand
instead of cohering in a tough mass
under the impact of traffic and the ac-
ton Of water, remain loose and shift
displaced by the wind, which pro
duces In this way the ever shifting
sand hills. No road is so difficult to
travel as one through fine sand
If clay has been carried in small
quantities by running water and de-
posted as sediment it is known as
"sedimentary clay" If the feldspathic
rock has been disintegrated in place1by.
water the clay is known as residual
clay" The sedimentary clay, having
been carried in the form of fine par
ticles. is finer grained than the residual
clay and is more sticky and plastic.
In CONTRAST With sand, which possesses
no binding power, but is very. hard.
clay is a powerful binder, but docs not
possess the quality of hardness. 1t is
sand-clay road the important property
in the clay is it's Elasticity or tendency
to become sticky and elastic when
mixed with water. The clays which
are most plastic are called "ball
clays:" Another important property
which is possessed by clays in widely
varying degrees is the porosity or ca
pacity for rapid absorption of water.
Clays which possess this quality in
the highest degree fall to pieces under
the action OF water. These clays
are called shaking clays." 1t will read
lily be seen that the plastic or ball clays
will form better and more powerful
binder for sand-clay roads than will
the shaking clays; but, on the other
hand, they will be much more difficult
to mix, as they disintegrate with far
less rapidity. - ~
The shrinkage of clay is an impor.
tant characteristic in connection with
the building Of roads. When water Is
mixed with clay expansion results, and
when the water evaporates the clay
contracts: This characteristic of ex-
pansion is much more pronounced in
some clays than in others, and it must
be apparent that the clays which ex-
pand the least are preferable for road
building. s'
The theory Of the sand-clay road Is
very similar to the theory Of the mac
adam road In the latter rock dust
and screenings fill the voids between
the angular fragments Of stone and.
when wet et-serve as cement or binder.
The grains Of sand may be likened to
the angular fragments of stone and
clay to the rock dust binder. In the
most successful sand-clay road Just
sufficient amount of clay is used to fill
the voids between the grains Of SAINT.
In this way the sand sustains the
wear. while the clay serves as d
binder. If too.much sand is used the
result will be loose sand on the sur
face; If too much clay is used the sur
face Of the road will become sticky
after rains.
The best mixture Of sand and clay
can be made when the materials are
wet, and particularly is this true of
the plastic or ball clays. 'Ss#
It the clay is Il plastic or ball clay
much greater effort will be necessary
TO obtain d complete mixture; IL 1t Is
4 shaking clay the mixture will be
much more readily obtained. This
Kind of clay is not as satisfactory,
however, az the ball clay, a. tts bind
n .3--58 --4.s-1.-.s.