The Cecil Whig. [volume] (Elkton, Md.) 1841-current, 1889-10-05

roads to France, were built under Ma
poleon.
The excellence of broken stone roads
caused their universal adoption in the
first half of this century, and in only
two particulars have any Improvements
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.
These machines are driven by steam
engines and are of various sizes, capa.
BILE of crushing from ten to two hundred
tons per day. BY regulating the width
of opening between the jaws, or within
the cone, the sizes to which the stone
can be broken is correspondingly regu-
lated and by the use of revolving
screens with openings of various sizes,
the stones of different sizes can be sep
arated and delivered 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 a smooth, uniform surface instead
of allowing this work to be slowly and
painfully performed by the vehicles u.s.
ing it. Horse rollers were introduced
about 1884 and steam rollers about
1860. There was for some time dis
cussion as to the relative economy and
merits of the two kinds of rollers, but
this has now heen settled in the favor
of the steam rollers. Of steam rollers
there are three principal varieties, the
first, known as the Ballaison, or Gellerat,
designed in France the second known
as the Aveling and Porter, designed in
England, and the third, known as the
Lindelof, designed in America. OF
these the Aveling and Porter is the
best for macadam roads, and the Lin
delof for rolling plastic pavements.
Macadam roads are now everywhere
constructed on substantially the same
principles. The ground is first cleared
and leveled of the prescribed width,
and, If necessary, excavated to the
depth of the road-covering. All roots
of trees, and soft and spongy spaces
not afiording firm bearing are re-
moved and their places filled with good
gravel or broken stone. The surface
is then rolled with a heavy roller, in
order to thoroughly compact it. If the
Telford foundation is used, it is placed
on the rolled earth in the form of irreg-
ular stones from six to eight inches in
size, carefully placed in position and
forming rough pavement, on which
the macadam metal Is placed. If the
Telford foundation is not used, the
metal is placed directly on the earth,
in uniform layer not exceeding six
inches in depth. This is then thor
oughly compacted by rolling with a
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 com.
pacted in the same manner. Finally a
layer of from one to two inches in
depth of!svery fine broken stones or
gravel, not exceeding three-fo -fourths of
an inch in the largest dimensions, is
spread on the surface, 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 connection
with the rolling. In many cases the
total thickness of the macadam is only
eight inches, instead of twelve to thir-
teen inches.
The cost OF such roads depends
chiefly on two factors, the price of labor
and the price of broken stone. In ad-
dition 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 10 cents to 81 per ton, de-
pending on the character of the stone
and the distance which it has to be
hauled. For road 80 feet wide and
9 inches thick, about $500 tons are
required for each mile In length. The
cost of the road surface alone is about
SI2, 1000 per mile. The cost of EN-.
bankment, excavation, culverts, drains,
stone cutters, etc., may carry the cost
up to $4,000 per mile.
These figures might even be lncreas-
ed in the case OF roads traversing a
mountainous district, where expensive
embankments, cuttings in rock and
earth. retaining walls, ETC., would be
necessary. The laying out of such
roads calls for the same surveys and the
same engineering skill as in the laying
out of railways.
The shape or cross-section to be
given to the road has been the subject
of much discussion in the past. Roads
which are much rounded in the centre
shed the water very easily, but, on the
other hand, they are very uncomfort-
able for vehicles. There has also been
much dispute as to whether the cross
shape of the road should be a curve, or
should consist of two straight lines
meeting at the centre. 1t is now gen.
orally conceded that the cross section
should be curve, and that the height
of the road should be about one six
| tieth of its width > . in roads % feet