Omaha daily bee. (Omaha [Neb.]) 187?-1922, 1905-08-27

ways, with iron or steel surfaces, dis
tributing their loads through the medium
of ties or planks, to the earth surface, the
macadam roads developed about 100 years
ago, with depths of broken stone. varying
with the traffic, and depending for their
efficiency upon compacting the aggregates:
first on the traffic which took years, and
later. upon great road rolling machinery,
which crushed and forced the various ag-
gregates to a wedged and compact mass,
developing a smooth surface.
1t was contended even by railway build
ers, that rOadbeds should have a certain
elasticity to be practical II is now clearly
demonstrated that the firmer and more I'M
yielding the foundation, the more durable
1t will be. The toughest steel bent back
and forth by continuous vibrations, will
break. Rock foundations yielding to COM
preston impacts will ultimately crush the
particles and the greater and more numer-
Gus the volds, the quicker the change OF
shape and final destruction. The theory
of the need of elastic foundations is erron-
eous, the elastic requisites should be in
the spring of the carriages and rolling
stock, and not the roadbed The con-
struction of the so-called bltullthic pave
ment, which is really a macadam with a
bituminous binder, recognizes the need OF
reducing voids by grading the aggregates
so as to reduce the voids from 40 to below
20 per cent, and finally I'LL this 20 per cent
with tar or other bituminous binder.
Faults of Macadam.
In the construction of macadam pave
ments it is conceded that next TO the earth
road the need Of a large crown is impera-
tive. Why? For the same reason as in the
case Of an earth road, TO shed water so as
to minimize its destructive effect. Expert
ence has demonstrated that, all things con-
sdered. the most economic covering for
road purposes upon soil capable of imme-
date consolida ton into monolith form IS
concrete of sand, cement and stone. Tn
like the old Roman road, this can be made
more uniform with less material and skilled
labor by the use of small, broken stone
which, with various grades OF sizes and the
mortar of sand and cement, produces a
compact and uniform mass.
The more ready action OF the elements
upon what Is known as natural cement
makes the so-called portland cement pre-
ferable for exposed concrete work It's
great cost. until within the last few years
has barred its use largely in our paving
works Since, however. It's cost has been
largely reduced by the increase OF its man
ufaeture in this country. its advantages
for paving are recognized and it's use is
becoming more general.
Concrete as outlined could be made for
country roads and pavements were Il not
that the broken limestone soon wears
smooth and, like the European asphalts
becomes too slippery. For this reason
thus far, IL is used as an intermediate
layer 10 distribute the wheel load TO the
| earth. whenever the upper three OF -four
inches can be economically made into a
composite OF cement and sand, with pro
visions TO resist the forces OF expansion
and contraction, we will have sandstone
monolith pavement capable 20 continuously
resist the action Of water, and yet furnish
a footing which never can become slippery
| Until then a composite covering OF sand
with bituminous cementing material known
as asphalt" will be used
Qualities of Asphalt.
Experience has shown that asphalt from
| Trinidad Venezuela, California, and
numerous other sections OF the country
/ 90 per cent OF whose bitumens are soluble
| in boiling naptha, possess SUFFICIENT adhesiv,
/ oementlng qualities 20 make a proper paw,
/ ing cement. Experience has further de
veloped that the actual and necessary
| quantity OF bitumen thus soluble TO max,
proper paving mixture. shall range be
| tween the extremes Of 10 and IS per cent
! BY weight The exact proportion MI