IMPROVEMENTS IN ROAD, STREET, TRAM, AND PATHWAY PAVEMENTS, AND IN THE COMPOSITION OF PAVING MATERIALS
Year: 1874

page_text: ROVISIONAL SPECIFICATION left by Aaron Van Camp and George
Clark at the Office of the Commissioners of Patents, with their
Petition, on the 2nd January 1874.
We, AARON VAN CAMP, of Washington, in the United States of
America, now residing at the Inns of Court Hotel, Holborn, and GEORGE
CLARK, of No. 10, Craven Buildings, Drury Lane, in the County of
Middlesex, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN ROAD, STREET, TRAM, AND PATHWAY PAVEMENTS, AND IN
THE COMPOSITION OF PAVING MATERIALS," to be as follows:
1
This Invention relates to the production of asphaltum concrete, to its
application in various ways and forms for the formation of street, road,,
or other pavements, and also in imbedding and fixing iron rails for tram-
ways in any such concrete or other bituminous pavement.
For the production of asphaltum concrete, which is the main object of
this Invention, we make use of asphaltum rich in bitumen in a heated
and sufficiently fluid state mixed with broken stone or rock, in
proportions varying with the per centage of bitumen the asphaltum
contains.

page_text: We find that asphaltum containing 60 to 80 per cent. of bitumen is
the material which most efficiently and economically answers the objects
in view as herein-after stated, as it admits of from 4 to 10 times its own
weight of broken and pulverised stone being combined and cemented
with it.
The rock or stone employed, which by preference is granite, limestone,
or rag, is crushed or otherwise broken in such a manner that it is sub-
divided, some part into pieces of from half an inch to an inch and a half
in length in angular forms, and the remainder into small particles also
angular and in part pulverised. The object of so preparing the stone or
rock intended to be mixed with asphaltum in a melted and semi-liquid
state, is effectually to imbed the sharp edges and points of the larger
pieces in the melted or softened asphaltum, and to fill up the interstices
between them with the smaller particles. The stone or rock thus
prepared is heated in an iron pan or trough to a temperature suitable to
assist the cementation thereof with the melted asphaltum, which as
before mentioned, being in a heated and proper fluid state, is gradually
poured into the iron vessel over the hot, broken, and pulverised stone or
rock, and all these materials are intimately mixed together by con-
tinuous stirring, until by this process and the action of heat applied to
the said mixing vessel, they are intimately incorporated with each other,
the whole forming one adhesive mass. This compound which when
cold will be asphaltum concrete at once hard and tough is now ready for
use.
As a flux to melt asphaltum and facilitate its combination with
broken and pulverised stone, we employ green dead oil of coal tar or the
residuum of petroleum distillation or crude petroleum, in proportions
varying from 15 to 30 per cent., more or less of the quantity of
asphaltum treated, according to the per centage of bitumen contained in
the asphaltum and the quantity of broken stone or rock combined with
the former. Any other suitable solvent may be used.
Before proceeding to describe the application of asphaltum concrete
for paving purposes, we wish to point out that one of its peculiar merits
is that being composed in a large proportion of hard broken stones in
angular forms, its surface when laid down and as it wears away will
continuously be sufficiently rough to prevent slipperiness, whereas the
surface of pavements made of rock asphalte, which contains a large
proportion of alumina, becomes slippery when slightly wet.

page_text: For the formation of asphalte pavements instead of rock asphalte
containing only 5 to 15 per cent. of bitumen, to which consequently only
a small quantity of rough material can be added, we make use of
asphaltum concrete made and prepared ready for use as above described
in the following manner:-The prepared concrete in a hot state is
transferred from the mixing pan or trough into iron buckets, barrows, or
carts, and being immediately removed to the ground to be paved, is there
shot down on the foundation previously prepared. It is then spread
over the foundation to any required depth, levelled, and pressed down with
tamping irons, and afterwards its surface being sprinkled with hard grit,
it is compressed and finished in the manner usually adopted in laying
down asphalte pavement.
.
To facilitate the mixing operations already described, the asphaltum is
previously formed into a mastic by melting it in its proper solvent by
the action of heat, and in some cases it will be found advantageous to
mix into the mastic a certain proportion of ground rock asphalte or of
finely crushed and pulverised limestone or chalk. The mastic thus
made is moulded into blocks of convenient size for use. These can be
readily melted and combined with any suitable quantity of broken rock
or stone.
For carriage pavements where the traffic is not heavy, for foot paths,
courts, and other places, coal tar pitch may be combined with asphaltum
in the mastic and in the mixing processes before described, but for any
kind of solid street or road pavement for heavy traffic asphaltum concrete
alone should be used, as any mixture of coal tar pitch tends to render
the pavement brittle and unreliable.
Asphaltum concrete made as above described is well adapted to be
formed into quarries or blocks of any suitable form and size, by casting
the hot mixture of asphaltum and broken stone in moulds, into which
the compound in its plastic state is compressed and solidified by
mechanical means. In this way we propose to produce asphaltum
concrete tiles or bricks available for paving or other purposes, and which
when so applied may be solidly connected together with fluid asphaltum
or other bitumen, or any suitable varnish or cement.
In forming tramways the rails may be firmly secured and held in
position without liability to vibration, by imbedding them in asphaltum
concrete. To effect this object, the mode of proceeding is to form rolled

page_text: or cast iron rails (on which the wheels travel) in connexion with a plate
running under the rail, to serve as a stand and support to the rail the
whole of its length. The entire rail with its supporting plate is im--|
bedded in asphaltum concrete or asphalte in a hot and plastic state, so
that the top of the rail shall be flush with the surface of the roadway.
For the passage of the flange of the wheels of the tram carriage, if the
flange projects from the side of the wheel, a channel of the proper depth
and width is made in the asphaltum concrete or asphalte along one side
of each rail, by means of a hot iron rod pressed into the asphalte and
completed with a hot iron tool of the proper form. Or the same object
may be effected by fastening to the side of each rail, where the channel
for the flange is to be formed, a moulding (having its section corre-
sponding to that of the required channel) of wood or plaster or other
material, or of metal with its surface prepared to prevent adhesion of the
asphalte. The rail with this moulding attached to it is imbedded in the
asphalte in the way before described, and when the asphalte is set hard,
the moulding is removed and the required channel for the wheel flange
is produced.
The supporting stand of the rail may have a spreading foot running
the whole length or a rib along the side, or it may be corrugated in
order to fix the rail more securely in the asphaltum. An ordinary
double T rail would answer the purpose.
For tram carriage rails having a channel on the surface in which the
flange of the wheel runs, no side channel in the asphalte paving is
required, and for this kind of rail we form the top of the rail on which
the wheels travel of a greater width than that usually adopted, say 4 or
5 inches, thereby giving the rail a better bearing on the asphalte on
which it rests.