The Bennington evening banner. (Bennington, Vt.) 19??-1961, 1912-07-13

successive cultivation of the soil, and
II this soil Is used in the construction
OF a 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 variable
factor, as 1t may range all the way
from fine. dust-like particles TO coarse
grains and gravel and may be perfect
ly clean or mixed with loan and other
material In consequence OF these wide
differences In the materials consttut-
Ing sand.clay roads 1t 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,
1t possesses practically no binding or
cementing power. The grains of sand,
instead of cohering in tough mass
under the impact OF traffic and the ac-
ton OF water, remain loose and shift
ing. Fine sand when dry Is easily
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
II 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 place by
water the clay IS known as residual
clay" The sedlmentary clay, having
been carried in the form of fine par
tlcles, 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 powerful binder, but does not
possess the quality of hardness. II Is
evident that in the construction of a
sand-clay road the important property
In the clay is its Elasticity or tendency
to become sticky and elastic when
mixed with water. The clays which
are most plastic are called ball
-
which IS possessed by clays in widely
varying degrees is the porosity or ca
pacity for rapid absorption of winter
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
ily be seen that the plastic or ball clays
will form a 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 IL 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 I'm others, and 1t must
he apparent that the clays which ex-
pand the least are preferable for road
building.
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 I'll the voids between
the angular fragments OF stone and
when wet serve as cement or binder
The grains OF sand may be likened to
the angular fragments OF stone and
clay 20 the rock dust binder. In the
Most successful sand-clay road Just a
sufficient amount Of clay Is used to an
the voidt between the grains OF sand
In this way the sand sustains the
wear. while the clay serves as a
binder. " too much sand Is used the
result viii he loose sand on the sur
face: IL too much clay is used the sur
face Of the road will be,ome sticky
after rains.
The best mixture 81 sand and clay
can be made when the materials are
wet. and particularly is this true Of
the plastic OF ball ciays.
n the clay j. a plastic or ban clay
much greater effort viii be necessary
TO obtain a complete mixture. IL Il Il
q shaking clay the mixture viii D.
much more readily obtained This