Note: Descriptions are shown in the official language in which they were submitted.
Composition for Reinforcing Asphaltic Roads
and Reinforced Roads Using the Same
Background of the Invention
1~ Field of the Invention
This invention relates to reinforcing roadways with a
prefabricated reinforcing composite, an~d primarily to
reinforcing asphaltic conrete overlays on Portland
concrete or other underlying pavements to prevent cracks
and other defects, wllich had previously appeared in the
underlying pavement, from reappearing in the overlay.
Thermal expansion or contraction is the primary cause of
such cracks in the underlayment reappearing in the
overlay. This phenomena is generally referred to as
~reflective~ cracks. The prefabricated reinforcing
composite is a resin-impregnated, semi-rigid, open grid of
continuous fiberglass filaments. The crosswise and
lengthwise intersections of the grid are stitched together
or otherwise fixedly connected. In use, the underlying
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pavement is coated with an asphaltic tack coat; the
semi-rigid, open grid of this invention is then unrolled
over the tack-coat; and an asphaltic mixture overlay is
applied. Composites of asphaltic materials and fiberglass
have shown superior resistance to reflective cracking and
other defects.
2. Description of the Prior Art
Various methods and composites for reinforcing asphaltic
roads and overlays have been proposed. U.S. Patent No.
2,115,667 of Ellis (1937) refers to the use of flexible,
woven, tape-like strips or ribbons of fiberglass, 1/2~ to
1" wide, which are interwoven at right angles to produce a
netting with openings ranging from one to three inches
square. These interwoven, flexible tapes are laid on a
bed of asphalt and tied together at their intersections by
means of wire staples. Another layer of molten asphalt is
laid on top of the tapes, followed by crushed stone and a
top coat of asphalt. The art has also used narrow strips
(4 to 44 inches wide) of a loosely woven fabric made of
flexible fiberglass roving (weighing 24 ounces per square
yard) in the repair of cracks in pavement. These are not
impregnated with resin, and do not have grid-like
openings. They are laid down on top of a tack coat,
followed by application of asphaltic concrete, but they
are too expensive and too flexible to be practical to lay
over substantial portions of a roadway and, because of
their flexibility, like the unimpregnated structures of
Ellis, would be difficult to handle if installed over
substantial portions of a road where they could be
subjected to traffic from paving vehicles and personnel as
the overlayment is put down. Also the lack of adhesion
between underlayment and overlying layers is a problem
because of the essentially closed nature of the fabric.
Also in the prior art are rigid plastic grids, such as
shown in U.S. Patent No. 4,168,924. These have the
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disadvantage that they cannot be continuously unrolled and
are therefore difficult to install, and while they may use
fiberglass as a filler for the plastic, they do not have
the strength and other desirable characteristics of
continu~us filament fiberglass strands.
Summary of the Present Invention
In making, maintaining and repairing paved roads and
surfaces, particularly when placing an asphaltic concrete
overlayment on top of an older pavement which has cracked,
a tack coat of emulsified asphalt, liquid asphalt, or hot
asphalt may be applied to bind the underlying layer of
pavement, which may or may not be asphalt based, to a
layer of asphalt mixture pavement. An asphaltic mixture,
typically consisting of hot mix, or hot laid asphaltic
concrete may then be laid down continuously using paving
equipment desighed for the purpose.
In this invention a prefabricated resin impregnated,
semi-rigid, open grid of continuous filament iberglass
strands is placed on top of the tack coàt and thereafter
buried and imbedded in the roadway under the asphaltic
concrete overlayment. Incidentally, the words ~roads~ and
Rsurfaces" are used here in a broad sense to include
sidewalks, driveways, parking lots and other such paved
surfaces.
The grid is formed of continuous filament rovings of
fiberglass. ~1e prefer ECR or E glass rovings of 2200 tex,
though one could easily use weights ranging from about
1000 to about 5000 tex. These rovings are formed into
grids with rectangular or square openings, prefera~ly
ranging in size from 3/4~ to lx on a side, though grids
ranging from 1/8~ to six inches on a side may be used.
The grids are preferably stitched at the intersections of
the crosswise and lengthwise strands to hold the grid
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shape, prevent the rovings from spreading out unduly, and
to preserve the openings, which are believed to be
important in permitting the overlayment to bind to the
underlying layer and thereby increase the ~trength of the
composite. At the same time, it makes possible the use of
less glass per square yard and therefore a more economical
product; for example, we prefer to use a grid of about 8
ounces per square yard, though 4 to 18 ounces per square
may be used, but some prior art fabrics had fabric
contents of about 24 ounces of glass per square yard.
While we prefer stitching these intersections together on
warp-knit, weft-insertion knitting equipment using 70 to
150 denier polyester, other methods of forming grids with
fixedly-connected intersections may be utilized. For
example, a non-woven grid made with thermosetting or
thermo-plastic adhesive may provide a suitable grid.
Once the grid is formed, an asphaltic coating or resin is
applied to impart a semi-rigid nature to it. This coating
also makes the grid compatible with asphalt and protects
the glass from corrosion by water and Qther elements in
the roadway environment. In drying, the rovings may be
flattened, but the grid-like openings are maintained. For
example, in a preferred embodiment using 2200 tex rovings,
a rectangular grid was formed, with openings of about 3/4
inch by one inch, and the rovings flattened to about 1/16
inch to 1/8" across. The thickness of the rovings after
coating and drying was about 1/32~ or less.
Many resins can be used for this purpose, such as asphalt,
rubber modified asphalt, unsaturated polyesters, vinyl
ester, epoxy, polyacrylates, polyurethanes, polyolefines,
and phenolics which give the required rigidity,
compatibility, and corrosion resistance. They may be
applied using hot-melt, emulsion, solvent, or
radiation-cure systems~ One curing system used for a
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coating and found satisfactory was thermally cured.
For example, a 50~ solution of 12n-195C (boiling point)
asphalt was dissolved in a hydrocarbon solvent using a
series of padding rollers. The material was thermally
cured at 175C and a throughput speed of 30 yds./min. The
pick-up of asphalt material was 10-15% based on original
glass weight.
The grid when coated is semi-rigid and can be rolled-up on
a core for easy transport as a prefabricat~ed continuous
component to the place of installation, where it is rolled
out continuously for rapid, economical, and simple
incorporation into the roadway. For example, it can be
placed on rolls 15 feet wide containing a single piece 100
yards or more long, which makes it practical to use this
grid on all or substantially all of the pavement surface,
which is cost effective because it reduces labor costs.
(Where cracks occur in random fashion, mechanized laying
of narrow strips of fabric is impossible, and it is costly
to place narrow strips over each crack by hand.)
The above described reinforcement invention can be rolled
out on a roadway which has previously been coated with
tack coat. Once laid down it is sufficiently stable,
prior to placing the overlayment on it, for vehicles and
personnel to drive or walk on it without displacing it.
The large grid openings permit the asphalt mixture to
encapsulate each strand of yarn or roving completely and
permit complete and substantial contact between underlying
and overlaid layers. The product has a high modulus and a
high strength to cost ratio~ its coefficient of expansion
approximates that of road construction materials, and it
resists corrosion by materials used in road construction
and found in the road environment, such as road salt.
