Fort Worth weekly gazette. [volume] (Fort Worth, Tex.) 1882-1891, 1889-08-29

est dimensions, through a ring two and a
half inches in diameter. Macadam pro-
! ferred the test of weight, and insisted
that no stone should weigh more than six
ounces-which is the weight of cube of
one and half inches of hard, compact
limestone. His overseeTs were provided
with a small pair of scales and six
ounce weight, in order to test the largest
stones.
It is fact, however, that the correct
| principles of modern road-building are
not due to either Macadam or Telford,
but to q French engineer, Tresaguet,
! who anticipated them in every detail by
! about thirty years. In a memoir pre-
/ pared in I775 Tresaguet advocated the
! small angular fragments of broken stone
1 of Macadam, and the rough paving
/ foundation of Telford. He built the
high-roads from Paris to Toulouse, and
| from Paris to the Spanish frontier. His
views were adopted by all French en-
! gineers at the end of the last century,
and it was in accordance with them that
the Simplon and other great roads over
| the Alps, rs well as the principal roads
of France, were built under Napoleon.
The excellence of broken stone roads
caused their universal adoption in the
first half of this century, and in only
| been made upon them to the present
| day. The first is in regard to the man
ner of breaking the stone. Macadam
caused the stone TO be broken by hand
on the side Of the road, the size and
weight of the hammer being carefully
| specified. Now they are much more
| quickly and cheaply broken by machine.
| Two classes of stone-crushers have been
devised for this purpose. The first,
usually known as the Blake, consists
| essentially of q strong iron frame,
near one end of which is q NOV
able jaw of iron. By means of a
toggle- Joint and an eccentric this
jaw is moved back and forward a slight
distance from the frame. As the jaw re-
cedes the opening increases and the
stone descends; as it approaches the
frame the stone is crushed The second
class is known as the Gates, and consists
of a solid mass of iron shaped somewhat
like a bell, which is supported within an
iron cone. By means of an eccentric
shaft q rocking and rotary motion is
given to the bell, so that each point of
its surface is successfully brought near
to and removed from the surface of
the cone, which causes the stone
to descend and to be crushed as before.
The machines are driven by steam en-
gines and are of various sizes, capable of
crushing from ten to two hundred tons
per day. By regulating the width of
opening between the jaws, or within the
cone, the size to which the stone can he
broken is correspoEdingly regulated; and
by the use of revolving screens with
openings of various sizes, the stones of
different sizes can be separated and de-
Iivered in separate piles of One-half inch,
one inch, two and One-half inches, etc.
The other improvement is in the use of
rollers to consolidate the road and give
smooth, uniform surface. instead of al
lowing this work to be slowly and pain
fully performed by the vehicles
using if. Horse-rollers were introduced
about 1894, and steam-rollers about 1860.
There was for sometime a discussion as
to the relative economy and merits of the
two kinds of rollers. but this has been
settled in favor Of steam rollers, OF
steam rollers there are three principal
varieties, the first, known as the Bal
laison, or Gellerat, designed in France,
the second, known as the Ayeling and
Porter, designed in England, and the
third, known as the Lindelof, designed
in America. OF these the Ayeling and
Porter is the best for macadam roads land
the IindeIof for rolling plastic pave
ments.
Macadam roads are now everywhere
constructed on substantially the same
principles. The ground is first cleared
and levelled Of the prescribed width,
and, if necessary, eXcavated to the depth
OF the road covering. All roots Of trees
and soft, spOngy spaces not affording a
firm bearing are removed and their
places filed with good gravel or broken
heavy roller, in order thoroughly to
compact it. If the Telford foundation is
used, it is placed on the rolled earth in
the form of irregular stones from six 10
eight inches in size, carefully placed in
position and forming Il rough pave
ment, on which the macadam metal
is placed If the TelfOrd found alton
is not used, the metal is placed directly
on the earth, in uniform layer not eX-
ceeding SIX inches in depth. This is then
thoroughly cOmpacted by rolling with a
heavy roller for several hours, until the
metal will not yield under the roller.
Another layer of broken stone of the
same depth is then placed on the first and
compacted in the same manner. Finally
a layer of from one to two inches in depth |
of very fine broken stone or gravel, not |
exceeding three-fourths of an inch in
largest dimensions, IS spread on the sur |
face, and this in turn is compacted by |
rolling. The road is then ready for use.
The rolling is greatly facilitated and the |
compactness of the road increased by |
thoroughly sprinkling each layer in con- |
nection with the rolling. In many cases |
the total thickness of the macadam is |
only eight inches, instead Of twelve to |
thirteen inches, as above described.
The cost of such roads depends chiefly /
on two factors, the price of labor and |
the price of broken stone. In addition |
to this is the cost of culverts and bridges, |
which must be provided for any road, |
whatever the road surface may be. The |
price of broken stone varies from seventy |
cents to two dollars per ton, depending !
on the character Of the stone and the |
distance which it has to be hauled. For
a road thirty feet wide and nine inches |
thick, about fifty-five hundred tons are
required for each mile in length. The |
cost of the road surface alone is about |
twelve thousand dollars per mile. The
cost of embankment, excavation, cul-
verts, drains, stone cutters, etc, may
carry the cost up to seventy thousand
dollars per mile.