The river press. [volume] (Fort Benton, Mont.) 1880-current, 1912-07-10

produced by the front wheels and that
I.:actically the entire disturbance OF
the road is produced by the rear or
driving wheels. If the effect were pro-
duced by suction or vacuum the action
of both front and rear wheels should
be somewhat similar at least. Il seems
apparent to the writer. therefore, that
the road best adapted to motor traffic
is the road which will best resist this
powerful tractive shear. 1t has already
been demonstrated that no plain mac
adam road il capable OF resisting this
force.
The efforts of progressive highway
engineers are thus directed primari-
~ toward the preservation Of u stone
surfaced roads and the construction Of
dustless roads by the use Of a binder
more powerful than stone dust and.
secondly. to minimizing or mitigating
the dust nuisance.
For the purpose of discussing intelli-
gently the experiments thus far con-
Quoted with special binders the term
dust ~preventives" has been applied
to all of the various binders having for
their main object either suppression or
the prevention of dust. These may be
divided into two classes, temporary
and permanent. The temporary binders
serve merely as palliatives and require
frequent renewal. The permanent bind
ers, so called, enter into the structure
of the road as a Constituent element
and are either Incorporated with the
| other materials at the time of the con-
struction or applied later by a surface
treatment.
In the class Of temporary binders
may be included water. salt solutions.
light oils and tars and oil and tar
emulsions. waste sulphite liquors. etc,
while the permanent binders include
the heavy petroleums and tars. pitches
and numerous oil. tar and asphalt prep
%arations. The value of salt solutions,
which have been used to some extent
lies in the microscopic character of the
dissolved salt, which, having consider
able affinity for water, keeps tue roao
surface in a moist condition long after
a surface treated with water alone
would have become dry through evapo
ration.
The light oils and tars as we'll as the
oil and tar emulsions depend for theil
effect upon a comparatively small
amount of true binding base left upo1
the road surface after the volatil,
products have e%vaporated. These ma
terials prove effective only so long a:
they retain their binding power. Whel
the binding power is destroyed it i
necessary to apply more material.
The heavy oils and tars differ from
the lighter products in that they con
tain a much greater amount of tru
binding base. The results are, there
fore, Of a more lasting character AM
hence the name permanent binders.
The semisolid and solid preparation
usually contain a still greater amour
b Of binder. With some few exception
all of the true binders are bitumens.
t The usual method Of applying thes
materials to the road surface is b
y sprinkling. The temporary binders ca
+ usually be applied cold, but the perma
nent binders because of their niue
greater viscosity must be heated unit
r sufficiently fluid. In England an
France the use of coal tar is practice
u to a large extent, and their methods 9
application have been highly developed
n Machines are in general use which ar
Il self propelling and in which the tar
u heated and applied to the road surfac
as a spray under high pressure. Thes
d so called 'tar %sprayers" are not onl
very economical in the use of tar, bt
a insure a more even distribution al
d better penetration Of the road surfae
than it is possible to obtain in almo:
d any other way.
In the construction of dustless roac
y the crucial question is that OF cost. TT
effort must be to develop a form {
y construction which will withstand ia:
le automobile traffic and at the same tin
be within the financial Of tt
1t community. This Is largely being dor
y at present by the use Of a bitumino,
e. binder instead of rock dust. The tW
g methods generally employed are know
Re as the penetration and the mixin
e methods. In the former the hot liqu:
Is binder is sprinkled or sprayed over ii
e. stone and allowed to penetrate throue