Improvements in Concrete Pavements.
Year: 1887

page_text: Improvements in Concrete Pavements.
A communication from Aзzi LORENZO BARBER, of Columbia Heights, Washington,
in the District of Columbia, United States of America.
I, ALFRED JULIUS BOULT of 323 High Holborn in the County of Middlesex,
M.L.M.E. do hereby declare the nature of this invention and in what manner the
same is to be performed, to he particularly described and ascertained in and by the
following statement:―
This invention relates to certain improvements in concrete pavements.
The object of this invention is to thoroughly lock or cement the different layers or
stratas of which the pavement is composed more especially to form a bond of union
between the upper or wearing course and the intermediate or binding course so that
there will be less liability to crack and disintegrate under the influences of heat, cold
or moisture.
In the drawing is shown a transverse sectional view of a pavement laid according
to this invention.
In carrying out this invention the road bed is graded to the proper depth upon
which is placed a layer of cement concrete A, said concrete being made of Portland
or other good hydraulic cement, clean sharp sand and broken stone, brick or gravel
and laid to the depth of three or more inches, the thickness of this layer being
dependent on the probable traffic of the road or street to be paved.
The proportions of ingredients used in this concrete base may be varied, but it is
preferred to use them in the following proportions
----
One measure of hydraulic cement and two measures of clean sharp sand free from
clay or other extraneous matter is mixed with a suitable amount of water to form a
mortar.
Broken stone, or hard broken brick or gravel of the proper size, either separate or
combined, is soaked or saturated with water, and while in this saturated condition is
mixed with the mortar above described the quantity of broken stone being such as
will give a surplus of mortar when the concrete is rammed down on the road bed.
The mixing of the broken stone with the mortar may be done by hand or with
suitable machinery such mixing being carried on until each piece of broken stone or
other material used is completely coated or covered with the mortar.
The cement concrete thus formed is then spread at once on the previously prepared
road bed and thoroughly compacted by ramming until the free mortar appears upon

page_text: the surface. The upper surface of this layer or bed of concrete is finished with a
smooth surface and so shaped as to correspond to the curvature of the crown or upper
surface of the pavement. When this foundation layer or course of hydraulic concrete
has set or become sufficiently hard, the cementing or locking course B is placed
thereon which is composed of the following materials -
Broken stone about one inch in largest diameter is thoroughly screened in order to
free it from dust is heated by passing the same through revolving heaters and while in
this heated condition is mixed by means of machinery or otherwise, with the residuum
of coal tar distillate which is known in the trade as No. 4, or any other number, or
with coal tar product and asphaltum and petroleum oil combined until each stone is
perfectly and evenly coated with the bituminous matter, care being exercised, in order
to avoid a surplus of the bituminous material. About one half gal. of the coal tar
product is used for each cubic foot of broken stone this amount being sufficient to
firmly bind the broken stone together without having a surplus of the bitumenous
material to run down and fill the voids between the broken stone.
Instead of using broken stone, gravel and sand mixed together may be used, or a
combination of broken stone, gravel and sand, when the same is coated with the
bitumenous compound.
A layer of suitable thickness of the broken stone, thus prepared is laid on the
hydraulic concrete base A and rolled or compacted in any suitable manner so as to
form a substantial bed for the top or wearing course C.
The top or wearing course C is composed of refined Trinadad or other suitable
asphaltum, heavy petroleum, or the residuum of petroleum, fine sand, and powdered
carbonate of lime, mineral dust, or any other finely divided mineral material. The pro-
portions of the above mentioned substances will depend upon the character and traffic
of the street, and in some cases the carbonate of lime or mineral dust may be omitted;
this will depend on the quality of the sand.
In order to protect the sides of the pavement from the deteriorating effects of
moisture and the urine of animals, the same is coated with coal tar cement or other
resinous pitch which is ironed in and smoothed down with hot smoothing irons on and
into the surface or wearing course C.
This strim of coal tar is shown at D and extends outward from the curb, a distance
of about two feet more or less and when laid as described effectually protects the
gutters from rapid disintegration.
The advantage of a pavement laid in the manner described is that the bitumenous
matter employed in cementing the broken stone of the middle or binding course B
will cause the wearing surface or top layer to adhere thus forming a solid or com-
paratively solid mass, which increases the strength of the pavement and at the same
time will be pliable enough to prevent the cracking of the surface layer.
Having now particularly described and ascertained the nature of this invention, as
communicated to me by my foreign correspondent, and in what manner the same is to
to be performed, I declare that what I claim is :-
1. A concrete pavement consisting of a base of hydraulic concrete an intermediate
or binding course of broken stone coated with bitumenous material and a top or wearing
surface of bitumenous concrete as described.
2. A concrete pavement consisting of a base of hydraulic concrete an intermediate
layer or binding course of broken stone coated with bitumenous material and a top or
wearing surface of asphaltic concrete.
Dated this 20th day of December 1887.
W. P. THOMPSON & BOULT,
Agents.