The Bennington evening banner. (Bennington, Vt.) 19??-1961, 1912-07-08

tires. all contribute to produce the et'
feet. the most conclusive experiments
seem TO warrant the assertion that the
great tractive force or shear exerted
bv the driving wheels Of motorcars is
the main factor of injury.
A series of tests conducted by the
United States office of pubic roads IN
1908 produced some interesting results
along this line. Cars of various weights
and types were run over measured
course at different rates of speed and
right angle photographs taken of each
run. A sixty horsepower car stripped
for racing. weighing with its driver
and mechanician about $500 pounds
was driven over this stretch OF road at
rates of speed varying from five to six
ty miles per hour the speed being in
creased five miles per hour for each
trip over the road. Up TO fifteen miles
an hour little or no effect was produced
on the road but from twenty miles an
hour the effect was striking with each
increase in speed. These demOnstra-
llubS pIONeu ludt Htlfc VI hO ShSNt -
produced by the front wheels and that
practically 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. II 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. Ii has already
been demonstrated that no plain mae
adam road is capable of resisting this
force
The efforts OF progressive highway
engineers are thus directed primari,
ly toward the preservation of our 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
10 all of the various binders having 70,
their main object either suppression OF
the prevention of dust. These may be
divided into two classes, temporary
and permanent The temporary binders
serve merely as palliatives and require
In
ars, so called. enter into the structure
0f 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 ~ temporary binders
may Toe included water. salt solutions.
light oils and tars and oil and tar
emulsious, waste sulphite liquors. etc.
while the permanent binders include
the heavy petroleums and tars. pitches
and numerous oil, tar and asphalt prep.
uratlons. 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 the road
surface In moist condition long after
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 their
effect upon a comparatively small
amount OF true binding base left upon
the road surface after the volatile
products have evapOrated. These ma
terials prove effective only so long as
they retain their binding power When
the binding power is destroyed il is
necessary TO apply more material.
The heavy oils aud tars differ from
the lighter products in that they con.
tain n much greater amount Of true
binding base. The results are. there
fore. of a more lasting character and
hence the name permanent binders. 81
The semisolid aud solid preparations
usually contain a still greater amount
OF binder. WIN some few exceptions
all of the true binders are bitumens.
The usual method OF applying these
materials to the road surface is by
sprinkling. The temporary binders can
usually be applied cold, but the perma-
nent binders because OF their much
greater viscosity must be heated until
sufficiently fluid. In England and
France the use Of coal tar is practiced
to large extent. and their methods OF
application have been highly developed
Machines are in general use which are
self propelllng and in which the tar is
heated aud applied to the road surface
as spray under high pressure. These
so called tar sprayers" are not only
very economical IN the use Of tar, but
insure a more even distribution and
better penetration Of the road surface
than Il is possible % obtain I'm almost
any other way.
In the construction OF dustlcss roads
the crucial question Is that OF cost The
effort must be 10 develop a form of
fcoustruction which will Withstand fast
automobile traffic and at the same time
I be within the financial resources Of the
community. This Is largely being done
E az present by the use 81 bituminous
f binder instead Of rock dust. The two
methods generally employed are known
as the penetration and the mixing
o methods. In the former the bot LIQUID
binder is sprinkled OF spray ever the