Bismarck daily tribune. [volume] (Bismarck, Dakota [N.D.]) 1881-1916, 1912-04-25

1 successive cultivation Of the soil, and
II this soil is used in the construction
Of road it Is known as top soil road. :"
There are many varieties Of clay and
consequently wide variation In the
characteristics of a sand-clay road.
The quality Of the sand Is a variable
factor, as It 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 c0nstitut-
Ing sand-clay roads it Is impossible to
maintain a uniform standard az 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 &C.
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 fne 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 place by
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 does not
possess the quality of hardness. It IS
evident that in the construction of a
sand-clay road the important property
in the clay is its Elasticity or teA1oacE
to become sticky and elastic wheA
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.
Olays 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
fly 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 in others, and it must
be 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 Ill the voids between
the angular fragments Of stone and
when wet serve as a cement or binder.
The grains Of sand may be Hkened to
the angular fragments Of stone and
clay to the rock dust binder. In the
most successful sand-clay road Just a
sumcient amount Of clay Is used to nll
the voids between the grains of sand.
In this way the sand sustains the
wear, while the clay serves al .