Virginia citizen. (Irvington, Va.) 1891-1921, 1907-10-11

as lt is only necessary TO mix sample
with The proper amount of water and
allow it to dry out in the sun. If the
mixing with sand is properly done the
bad effect of high shrinkage can be
largely overcome.
The Mixing OF Sand and Clay.
The best sand-clay road is one in
which the wearing surface is composed
of grains of sand in contact in such
way that the voids or angular spaces
between the grains are entirely filled
with clay, which acts as binder. Any
excess of clay above the amount neces-
sary to fill the voids in the sand is
detrimental If small section taken
from the surface of any well-constructed
sand-clay road is examined with mag
nifying glass, the condition of contact
which exists between thegrains of sand
and the small proportion of clay which
is required to fill the voids may be seen.
Wherever this proper condition of con-
tact exists for few inches in thickness
upon the surface of road. it will bear
comparatively heavy traffic for a long
time, even when the subsoil is sand or
clay.
All the experiments that have been
made by this Office indicate that the
materials should not be mixed in dry
state, but that they should be thorough
ly mixed and puddled with water. 1t
makes little difference by what method
the stirring or mixing is done, so long
as it is thorough and proper proportions
of the materials are obtained. If an
excess of clay is used in the mixture,
the grains of sand which are not in con-
tact are free to move among and upon
each other, so that no particle exerts
more resistance to pressure than if the
entire mass consisted of clay alone. On
the other hand, ifan insufficient amount
of clay is used, the mixture will lack
binding power and will soon disintegrate.
We may now outline the methods
which hare been used to obtain the
proper contact mixture, although it will
be necessary to discuss separately the
methods of treating shaking and nom
shaking varieties of clay. It will readily
be seen that it is less economical to haul
sticky orplastic clay and spread it upon
sand than it is to haul sand and spread
it upon clay. The clay is difficult to
dig and handle and usually comes out
in Jumps, which. if placed upon the
road-bed and covered with sand, are
apt to remain unbroksn unless great
care is taken in the mixing. The bad
effects of Jumps of clay in a sandy sub
soil and the effects of traffic on such a
mixture are illustrated in figures and 4.
Figure l shows a cross section of a
road into which Jumps of clay have been
worked. Figure shows the displace-
ment of these Jumps when subjected to
the prolonged action of traffic, and the
resulting formation of deep ruts and
general disintegration of the surface.
1t has been pointed out that thorough
stirring and pudding are absolutely es-
sential to successful sand-clay construc-
tion. This is most easily brought about
Immediately after hard or prolonged
rain, the clay having been previously
spread and the larger Jumps broken up
as completely as possible. The surface
should then be covered with few
inches of sand and plowed and narrowed
thoroughly by means of turning plow
and a cutaway or disk harrow. This
stage of the work will of course be
found somewhat disagreeable, leading,
as it does, to the formation of a thick,
pasty mud; but it is the only practicable
way in which the necessary mixing can
be accomplished. Many experiments
have been tried with dry mixing of the
clay and sand, but all have been more
or less unsuccessful. In cases where
the plowing and narrowing are con-
sidered too expensive, the mixing may
be left otraffic. This, however, inevi-
tably leads to muddy road surface for
long time, although finally tits posi-
BILE, by proper distribution of the
sand upon the clay, to bring about a
fairly good result, even by this simple
method.
In case a shaking clay IS used, very
much less pudding is required, as there
are practically no Jumps to be broken
up and the mixing can easily be done
with the harrow after rain. SHAKING
clays do not usually make as effective
binders as the more plastic clays; there.
fore in dry weather the road surface
becomes more dusty. 1t will be seer
that the best clay for this kind of con.
struction is one which slakes sufficiently
easily to enable the Jumps to be readily
Gross section of road showing Jumps of clay