Improvements in Asphaltic Pavements and the like.
Year: 1897

page_text: Date of Application, 12th Apr., 1897-Accepted, 29th May, 1897
COMPLETE SPECIFICATION.
Improvements in Asphaltic Pavements and the like.
I, CLIFFORD RICHARDSON, of No. 122 East 34th Street, in the City, County
and State of New York, U.S.A., Chemist, do hereby declare the nature of this
invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
This invention relates to that well-known class of asphalt pavements and like
surfaces in which a natural or artificial bitumen, or both combined, is mixed with
a mineral aggregate of sand, either silicious or calcareous, and fine mineral dust or
hydraulic cement, for the purpose of making a bituminous concrete which when
properly combined, laid and compressed, shall form a pavement surface.
Asphalt pavements have been laid for many years under different formulas by
many different parties, but heretofore it has never been found practicable to
produce pavements uniform in character. It has been found by all of those who
have engaged in this business that pavements laid upon the same formula will not
be alike; that some will be excellent in quality, durable and in every way
effective, while others laid upon the same formula will fail to come up to the
standard requirements in many respects. Many efforts have been made from time
to time to discover the cause of this difference in pavements of the same
composition of materials, but without success. In the course of many experiments
and trials, I have discovered that the grading of the sand in a pavement
composition is not, as heretofore supposed, a mere matter of convenience and
dependent upon the particular kind of sand used, but that it is a inatter which is
absolutely essential to secure a pavement of uniform quality, and I have discovered
that by properly grading the sand, as I shall hereafter set forth, using other
materials in proper and in most cases well-known proportions, I am enabled to lay
pavements which shall be substantially alike in all respects, and to adopt a formula
with the positive knowledge as to the character of the pavement which will result
therefrom.
I have further discovered that by properly grading the sand, I am enabled to
combine effectively therewith a larger proportion of bitumen without making a
pavement that will become too soft and liable to "creep," while securing a greater
degree of toughness and pliability than has heretofore been practicable with
pavements of requisite durability.
For the purpose of regulating the sizes of the particles of the mineral aggregate,
of which the mixtures consist to which this invention relates, a series of sieves is
employed, which are made with a sifting portion of brass cloth of the numbers
commonly known in the trade as Nos. 10, 20, 30, 40, 50, 80, 100 and 200 mesh,
and which pass particles having on the average a diameter of 085, 17, 24, 32,
50, 67, 100 and 200 millimeters. This series is selected because the average
diameters of the largest particles, passed by the different sieves, bear a numerical
relation to each other, being about 1, 2, 3, 4, 6, 8, 12, 24, the size of the largest
particle passed by the smallest sieve being taken as unity, but any other series of
sieves could be used in place of these with the same object in view, if they pass
particles within the same extreme limits of size. With these sieves the grading
of the mineral matter in an asphalt pavement, or of the sand and dust of which
it is composed can be determined and represented in percentages, as hereinafter
illustrated..

page_text: Experience with such pavements as have worn the best shows that they have
accidentally been made with sand containing but a small proportion of coarser
sized particles. Further experimental tests have shown me that it is desirable to
have the mineral aggregate rich in particles of the size passing the 200, 100
and 80 mesh sieves, and I have also found that mineral aggregates which contain
much fine material will carry more bitumen, will prove more dense and compact, and
will have better wearing properties than those made of coarser material and which
will carry less bitumen.
The present improvement in the making of asphaltic pavements consists,
therefore, in the grading of the mixture of sand and dust (by "dust" I mean any
earthy matter that will pass through a sieve having at, least 100 meshes to the
inch) by means of sifting and varying the proportions of the material employed,
so that the resulting surface mixture shall contain at least 35 per cent. and preferably
a larger amount of material which will pass an 80 mesh sieve..
The grading of this 35 per cent. or more of sand in the mixture is preferably as
follows:
10 per cent. or more passing à 200 mesh sieve or smaller than 085 millimeters in
average diameter;
10 per cent. or more passing a 100 mesh sieve but not a 200;
15 per cent. or more passing an 80 mesh sieve but not a 100.
Not more than 15 per cent. of the material used should be so large as to fail to
pass a 40 mesh sieve, preferably less, and but a small amount, or none, should fail
to pass the 10 and 20 mesh sieves.
In combination with such graded mineral aggregates, I add the bituminous
cement in such amount as to give over 10.5 per cent. (and preferably more) pure
bitumen, soluble in carbon bisulphide, or as much as well-known tests will show
that the mixture will carry without becoming "sloppy" when hauled upon the
.work.
As an illustration of one of the best graded mixtures made according to my
invention the following will serve :

page_text: 3. An asphalt pavement or like surface containing bitumen and mineral matter,
in which the latter contains definite proportions of different grades, at least
35 per cent. of the mineral matter consisting of particles capable of passing, some
through a 200 mesh sieve, others through a 100 mesh sieve, and others through
an 80 mesh sieve, substantially as described.
10L 15 A 1907
PHILIP M. JUSTICE,
Chartered Patent Agent, London,
For the Applicant.