IMPROVEMENTS IN THE CONSTRUCTION OF PAVEMENTS OR FLOORS OF THE CLASS GENERALLY KNOWN AS ASPHALTE PAVEMENT OR FLOORS."
Year: 1871

page_text: LETTERS PATENT to Henry Bessemer, of Queen Street Place, Cannon
Street, in the City of London, for the Invention of "IMPROVEMENTS
IN THE CONSTRUCTION OF PAVEMENTS OR FLOORS OF THE CLASS GENERALLY
KNOWN AS ASPHALTE PAVEMENT OR FLOORS."
PROVISIONAL SPECIFICATION left by the said Henry Bessemer at
the Office of the Commissioners of Patents, with his Petition, on
the 4th July 1871.
I, HENRY BESSEMER, of Queen Street Place, Cannon Street, in the
City of London, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN THE CONSTRUCTION OF PAVEMENTS OR FLOORS OF THE CLASS
GENERALLY KNOWN AS ASPHALTE PAVEMENT OR FLOORS," to be as follows:-
This Invention has for its object improvements in the construction
of pavements or floors of the class generally known as asphalte pave-
ment or floors.
Asphalte and other bituminous or pitchy matters have long been
employed in combination with small stones, sea beach shingle, sand,
and other matters for forming pavements and floors, the latter substances

page_text: being mixed with the bituminous or pitchy matters while they are kept
in a fluid state in large cauldrons having a fire beneath them. The
semi-fluid mixture thus obtained is then run or spread in a plastic state
on the surface to be paved or floored. The space to be covered is usually
divided into large narrow sections by strips of wood so that on the
solidification of the materials in one section a similar strip or section
may be formed immediately adjoining it, and so on progressively until
the required surface is covered.
Now when any of the aforesaid bituminous or pitchy matters are
mixed with small stones or sand or such like mineral matters in such
quantities as to allow the mixture to be readily stirred by a ladle or
other instrument in an open cauldron and be afterwards poured or
otherwise laid down in a semi-fluid or plastic state it is found that the
heat of summer is sufficient to cause the mixture to become soft and
be impressed by the passage of carriage wheels or other heavy bodies.
over it, and thereby much of its value and usefulness is destroyed.
It will also be observed that this mode of using asphalte or other
bituminous matters renders it necessary that a very large proportion of
the mass should consist of these expensive materials.
"
Now according to my present improvements I fuse asphalte and any
other bituminous, pitchy, or tarry matters alone or combined together.
I then run the fluid matter into a "pugmill" or into a basin in which
"hedge runners are made to revolve, and I there add to the fluid
matters mineral substances in the state of powder. The substances may
consist of limestone in its natural state or burned, sulphate of lime either
raw or burnt, chalk, burned clay, sand, and Portland, Roman, or other
cement, all of which are to be granulated or in powder. I cover the
pug-mill or other mixing apparatus with a jacket or casing, and heat
it by a flue or otherwise so as to raise the temperature almost to the point
at which the bituminous or other pitchy matters are decomposed, and
in this highly heated state I work or knead the materials by powerful
machinery until a large proportion of the dry solid substances are com
pletely incorporated and a stiff dough is produced. This dough is then
discharged from the pug-mill and is allowed to cool, after which it is
crushed by rollers, edge-runners, or stamps. When thus reduced to a
granulated state or in the form of a powder, I proceed to form it into
a pavement or floor by the application of heated rollers or heated rammers,
by means of which it may be consolidated and formed into a compact

page_text: mass extending over any desired length of roadway, and of such a thick-
ness as the amount of traffic renders desirable. I prefer first to heat-
the surface on which the powder is laid, and to heat the powder also in
a churn having a fire beneath it. In some cases before employing the
powdered compound, I moisten it with petroleum or other volatile hydro-
carbon which acts as a solvent for the time and is soon got rid of by
spontaneous evaporation. The substratum on which this powdered.
compound is laid may be a good cement or lime concrete or an old
stone pavement, or in some cases a surface to receive it may be formed
of cast-iron plates firmly united together and made to present a rough-
ened or undercut surface, so that a comparatively thin coating of the.
powdered composition will be held on and make a solid and even pavement:
suitable for carriage and foot ways and for paving yards, stables, and
floors for many other purposes. These artificial paving materials may
be mixed with natural asphaltic rock, and the mixed materials in the.
state of powder or granules may be used in constructing pavements in
the manner described.
The mineral substances are to be added to the bituminous, pitchy, or
tarry matters in such proportions that the mixture when heated to a tem-
perature somewhat below that at which the bituminous materials will
be decomposed shall lose its fluidity and assume the consistency of a
stiff dough. In order to obtain this condition the quantity of mineral
substance required to be added will vary according to its absorbent
power and its state of subdivision; materials of the cement class, such
as Portland, Roman, or gypsum cement, will unite with a fluid bitumen
in about the proportion of from 20 to 50 per cent. with beneficial results.
Whereas with ground limestone from 15 to 20 per cent. may be used
with advantage, but in all cases the temperature of the climate in which
the material is to be used will modify these proportions. In all cases
the point to be aimed at is to get as much solid matter into the compound
as is consistent with its retaining sufficient power of cohesion when
pulverized and compressed in a heated state.
No claim is intended to be made under this Specification for any
nooment of annamatue

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Henry Bessemer in the Great Seal Patent Office
on the 3rd January 1872.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, HENRY
BESSEMER, of Queen Street Place, Cannon Street, in the City of London,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Fourth day of July, in the year of our
Lord One thousand eight hundred and seventy-one, in the thirty-fifth.
year of Her reign, did, for Herself, Her heirs and successors, give and
grant unto me, the said Henry Bessemer, Her special license that I,
the said Henry Bessemer, my executors, administrators, and assigns,
or such others as I, the said Henry Bessemer, my executors, adminis-.
trators, and assigns, should at any time agree with, and no others,.
from time to time and at all times thereafter during the term therein;
expressed, should and lawfully might make, use, exercise, and vend,
within the United Kingdom of Great Britain and Ireland, the Channel.
Islands, and Isle of Man, an Invention for "IMPROVEMENTS IN THE CON-
STRUCTION OF PAVEMENTS OR FLOORS OF THE CLASS GENERALLY KNOWN AS ASPHALTE
PAVEMENT OR FLOORS," upon the condition (amongst others) that I, the
said Henry Bessemer, my executors or administrators, by an instrument.
in writing under my, or their, or one of their hands and "seals, should.
particularly describe and ascertain the nature of the said Invention,
and in what manner the same was to be performed, and cause the same
to be filed in the Great Seal Patent Office within six calendar months
next and immediately after the date of the said Letters Patent.
NOW KNOW. YE, that I, the said Henry Bessemer, do hereby declare
the nature of the said Invention, and in what manner the same is to
be performed, to be particularly described and ascertained, in, and by the:
following statement thereof, that is to say :-
⚫ This Invention has for its object improvements in the construction of
pavements or floors of the class generally known as asphalte pavement:
or floors.
Asphalte and other bituminous or pitchy matters have long been
employed in combination with small stones, sea beach shingle, sand,
and other matters for forming pavements and floors, the latter substances
being mixed with the bituminous or pitchy matters while they are kept
:

page_text: in a fluid state in large cauldrons having a fire beneath them. The
semi-fluid mixture thus obtained is then run or spread in a plastic state
on the surface to be paved or floored. The space to be covered is usually
divided into long narrow sections by strips of wood, so that on the
solidification of the materials in one section a similar strip or section
may be formed immediately adjoining it, and so on progressively until
the required surface is covered.
Now when any of the aforesaid bituminous or pitchy matters are
mixed with small stones or sand or such like mineral matters in such
quantities as to allow the mixture to be readily stirred by a ladle or
other instrument in an open cauldron and be afterwards poured or
otherwise laid down in a semi-fluid or plastic state it is found that the
heat of summer is sufficient to cause the mixture to become soft and be
impressed by the passage of carriage wheels or other heavy bodies over
it, and thereby much of its value and usefulness is destroyed. It will
also be observed that this mode of using asphalte or other bituminous
matters renders it necessary that a very large proportion of the mass
should consist of these expensive materials.
"
68
Now according to my present improvements I fuse asphalte and other
bituminous pitchy or tarry matters alone or combined together. I then
run the fluid matter into a pug mill" or into a basin in which "edge
runners are made to revolve, and I there add to the fluid matters
mineral substances in the state of powder. The mineral substance
which I prefer to employ is limestone in its unburned or natural state
dried and reduced to powder, and by its incorporation with bituminous
or tarry matter in the manner herein-after described I am enabled to
form a hard coherent mass having the general properties and character-
istics of the natural asphaltic limestone rock, and which compound by
way of distinction I call "artificial rock asphalte." In the production
of this material I first proceed to break the large masses of limestone in
one of "Blake's patent stone breakers," or by other suitable apparatus,
after which the fragments are reduced to powder under "edge runners
or between crushing rolls. The crushed limestone is then passed through
a circular or drum sieve by means of which the fine powder is separated
from the coarser particles, which may then be returned to the crushing
rolls to be further pulverized.
"
I next proceed to mix and incorporate with the ground limestone
about as much bituminous or pitchy matter as is contained in tho

page_text: natural Val de Travers asphaltic rock and known in this country as rock
asphalte. The quantity of bituminous or pitchy matter to be employed
with the limestone or other pulverized mineral substances is subject to
variation from several causes; thus when coal tar is mixed with mineral
pitch or asphalte, the temperature at which the mixture softens under
the influence of summer heat will depend on the quantity of the fluid
tar in the compound, and the extent to which a block of artificial
asphaltic rock would be indented by a given weight at a given tempera-
ture will also depend much on the state of division of the mineral
substances employed, or their more or less. absorbent properties, and
the proportion which they bear to the bituminous or pitchy matter
employed.
And in addition to these modifying causes the climate in which these
pavements are to be laid will influence the proportions in which the
materials should be employed. I do not therefore confine myself to any
exact rule of proportions for the mixture of bituminous or pitchy
matters with the pulverized mineral substances, as the manufacturer
will in practice vary, these to some extent in order to utilize such
native material as is readily accessible in the locality of his works, also
adapting them to sustain the average summer temperature of the place
in which the pavements are to be made and the nature of the traffic
passing over the pavement, footway, or floor to be covered.
As a general rule I may state that a good material for roads in England
may be obtained by first mixing from two to three hundredweight of
coal tar with two and a half hundredweight of mineral pitch, and after-
wards adding thereto from sixteen to twenty hundredweight of dry
pulverized limestone.
The manufacturer will observe that the greater the quantity of pul-
verized mineral matter employed in proportion to the bituminous or pitchy
matter the harder and more dense will be the material produced, and
the less expensive will it become, at the same time it will be less liable.
to become softened by summer heat. He will therefore in practice use
as little pitch, tar, or asphalte as is consistent with the production of a
material which when pulverized shall have the property of cohesion
by heat and pressure, and be capable of forming a solid and durable
pavement.or floor.
I would further observe that the use of coal tar in this manufacture
not only cheapens the compound but lessens the brittleness of the

page_text: mineral pitch or asphalte used with it, and renders the materials more
tough and coherent; but it must be borne in mind that too large a
quantity of the coal tar will cause the pavement to soften in summer
time and yield to the pressure of wheels passing over it.
For the purpose of producing artificial asphaltic rock it may in some
cases be found preferable to carry on the inspissation of coal tar until
its fluidity is considerably lessened, and to use this concentrated tar
alone or with a lessened quantity of mineral pitch or asphalte, instead
of using coal tar and pitch in the state in which they are met with in
commerce.
In the manufacture of artificial asphalte rock according to my Inven-
tion I prefer to employ a. pugmill consisting of an upright cast-iron
cylinder having a stout vertical shaft working in it, and driven by a
· pair of bevilled wheels from a horizontal overhead shaft. The pugmill
cylinder will be provided, as usual, with fixed blades projecting inwards,
and the revolving shaft will also have inclined blades projecting from it,
whereby a powerful mixing and kneading acțion will be obtained. The
pugmill cylinder is to be provided with an iron jacket of such a size
as to entirely enclose the sides and bottom of the cylinder, leaving a
space of about four or five inches between the pugmill and the jacket.
A small fire-place may be constructed below the pugmill, and the
products of combustion be made to circulate in the jacket before named,
or in lieu of this direct application of a fire hot air or superheated steam
may be employed in the jacket for the purpose of heating or keeping
heated the materials under operation in the pugmill.
In proceeding with the manufacture of artificial asphalte rock
according to my Invention I then highly heat the pitchy or tarry matter
to be employed in a cauldron situated, by preference, above the level of
the pug mill, and I also prefer to heat the limestone powder in a churn
or by other suitable means or apparatus also situated above the level of
the pug mill. I am thus enabled to let down into the heated pug-
mill a charge of powdered lime and a predetermined measure of the
bituminous matter both in a heated state, the two materials running in
together, while the central shaft of the pug mill is in motion; the
incorporation of the materials will thus be speedily effected.
I would here observe that I prefer to employ a temperature of about
250 to 300 degrees Fahrenheit in the pugmill, and to use so much of
the limestone in proportion to the quantity of bituminous or pitchy

page_text: -matter employed that the mixture when powerfully kneaded in the
pugmill shall form a stiff tenacious dough, and not a fluid or semi-fluid
mixture, resembling that melted in open cauldrons in the street, as
practised when paving streets with fluid or plastic asphalte. When
the materials have been sufficiently worked and kneaded in the pug-
mill a door opening near the bottom of it will allow the mass to be
forced out by the action of the inclined blades; the heated mass may
be received in an iron barrow, and wheeled to the cooling and crushing
house. Here it may remain exposed for twenty-four hours and become
cooled down to the temperature of the surrounding atmosphere, and
thus formed into hard masses of artificial asphalte rock, which is to be
again crushed and reduced to powder. This may be done in a manner
similar to that already described in the reduction to powder of the
original limestone, or in any other suitable manner.
In this pulverized
condition the material may be employed in constructing or forming
pavements or floors by means of heat and pressure, as already known
and practised in paving with the "Val de Travers rock asphalte" in a
powdered and heated state.
Although as before stated I prefer to employ limestone in its natural
state for general purposes and also from the cheapness of this material
in many localities, I nevertheless desire it to be understood that my
Invention consists also in the employment of burned lime, chalk, sulphate
of lime, and Portland, Roman, or other building cements, such matters
being used alone or mixed with each other in any desired proportions
in combination with pitch, tar, or other asphaltic matter, provided that
the aforesaid mineral substances are kneaded and incorporated with such
bituminous or pitchy matter in a heated state, and after cooling are
"reduced to powder for the purpose of forming pavements or floors by the
consolidation of such powdered compounds by means of heat and pressure.
I would here observe that such pavements may be conveniently made
by the application of heated rollers or heated rammers by means of
which the material may be consolidated and formed into a compact mass
"extending over any desired length of roadway, and of such a thickness
as tlie amount of traffic renders desirable. I prefer first to heat the
surface on which the powder is laid and to heat the powder also in a
churn having a, fire beneath it. In some cases before employing the
powdered compound I moisten it with petroleum or other volatile
- hydrocarbon which acts as a solvent for the time, and is soon got rid
- of by spontaneous evaporation. The substratum on which this powdered

page_text: compound is laid may be a good cement or lime concrete or an old stone
pavement, or in some cases a surface to receive it may be formed of
cast-iron plates firmly united together and made to present a roughened
or undercut surface, so that a comparatively thin coating of the powdered:
composition will be held on and make a solid and even pavement
suitable for carriage and footways, and for paving yards, stables, and
floors, and for many other purposes.
These roughened or undercut plates may either extend entirely over
the whole surface of a pavement or roadway, or they may be made to:
cover portions of it only, in which case I prefer that the iron plates
should be made long and narrow and be laid in lines so as to form a.
surface for the wheels of carriages to run upon, while granite or other
pavement occupies the space between the lines of plates. When thus:
partially covering a roadway with iron plates to receive the asphalte I.
bed them on good lime concrete, and I prefer to form on such plates a
raised edge or flange along the two opposite sides of the plates so under-
cut as to firmly retain the material. Such flanges may rise up to or
nearly to the same level as the top surface of the asphalte, or to the
level of the intermediate stone or other pavement.
I desire also to state that the artificial asphalte rock powder manu-
factured in the manner hercin-before described may be used alone as a
paving material, or it may be mixed with other powder obtained by
crushing natural asphalte rock, so that the properties of the natural
rock powder may be modified and altered as may be found desirable;.
thus in those cases where an insufficient quantity of asphaltic matter
exists in the natural rock powder a quantity of artificial rock may be
made in which the asphaltic matter is in excess of what is required, and
thus by mixing the desired quality may be obtained. So also natural
asphaltic rock having an excess of bituminous matter may be improved
by an admixture with the artificial compound having a less quantity of
bituminous or pitchy matter than would be necessary if used alone, and
in any case the mixture of the artificial with the natural rock powder
may be made for the purpose of reducing the cost of pavements or floors
made therefrom.
Having thus described my said Invention, and the manner in which
the same may be carried into operation, I would have it understood that, -
-
First. I claim the construction of pavements or floors substantially as
described by the mixture or incorporation of limestone with pitch, tar,
1

page_text: or other bituminous matter whilst in a heated state, and by the reduction
of the mass so obtained when cooled to a state of powder, which powder
is then consolidated by heat and pressure to form the pavement or
floor.
Second. I claim the construction of pavements or floors substantially
as described by the mixture or incorporation of mineral matters such as
burnt lime, chalk, sulphate of lime, Portland, Roman, or other building.
cement with pitch, tar, or other bituminous matter whilst in a heated
state, and by the reduction of the mass so obtained when cooled to the
state of powder, which powder is then consolidated by heat and pressure
to form the pavement or floor.
Third. I claim in the construction of pavements or floors the employ-
ment of artificial rock asphalte used in combination with pulverized
natural asphaltic rock, substantially as described..
Fourth. I claim in the construction of pavements or floors the employ-
ment of iron plates with roughened or undercut surfaces filled, covered,
or coated with a mixture of mineral substances and pitch, tar, or other
bituminous matters substantially as described.
In witness whereof, I, the said Henry Bessemer, have hereunto set
my hand and seal, this Third day of January, in the year of our
Lord One thousand eight hundred and seventy-two. ·