CA1240873B - Composition for reinforcing asphaltic roads and reinforced roads using the same - Google Patents

Abstract

Abstract of the Disclosure A reinforcing semi-rigid, resin impregnated continuous filament fiberglass is incorporated into a paved road or surface to provide increased strength and resistance to cracking.

Description

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 ~24~373 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 0~

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 ~LF'd `~ 3 7 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 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.

Claims (5)

1. A prefabricated composite for reinforcing roadways comprising an impregnated, semi-rigid, open grid of continuous filament fiberglass strands, said strands being fixedly connected at their intersections before the composite is impregnated, and said impregnating material being applied to the grid before the composite is placed at the roadway, wherein said grid is capable of being imbedded in or adjacent to an underlayment roadway layer.

2. The composite of Claim 1, wherein the impreg-nating material comprises an asphaltic material.

3. The composite of Claim 1, wherein the con-nections are stitches of continuous filament polyester or other textile threads.

4. A process for reinforcing roadways in which a) an underlying layer of pavement is covered by an asphaltic tack coat, b) an impregnated, semi-rigid, open grid of con-tinuous filament fiberglass strands is laid on top of the tack coat, said strands being fixedly connected at their intersections before the composite is impregnated, and said impregnating material having been applied to the grid before the grid is placed on the underlying layer of pavement, and c) a layer of asphaltic mixture is spread on top of the grid.

5. A roll of composite for reinforcing asphalt layers in roadways, the roll comprising an impregnated, semi-rigid, open grid of continuous filament fiberglass strands, said strands being fixedly connected at their inter-sections before impregnation and said roll being of a width, length, and rigidity adapted for continuously unrolling and laying the grid over substantial widths of a roadway during fabrication of the roadway.