BACKGROUND OF THE INVENTION Many outdoor surfacing applications have employed asphalt for its weather resistance and superior mechanical properties under heavy loads. Asphalt is a dark cementitious material composed predominantly of bitumens. Most asphalts are now produced from the refining of petroleum and are used primarily in paving and roofing applications. At normal service temperatures asphalt is viscoelastic; at higher temperatures, it becomes viscous.

The water resistance of asphalt layers is essential to its durability. Asphalts that have a low content of soluble salts show a low water absorption.

When asphalt picks up water, it softens and blisters.

Bacteria and fungi are also known to attack the very low molecular weight portion of bituminous materials.

Exposed asphalt films have, additionally, been known to harden and crack when exposed to ultraviolet radiation.

Asphalt-mastics are known to include mineral (including glass) fillers which are added to influence their flow properties and reduce costs. Mineral- filled films show proven resistance to flow at elevated temperatures, improved impact resistance and better flame-spread resistance. Fillers may also increase the water absorption of asphalt, and can include ground limestone, slate flowers, finely divided silica, trapped rocks, and mica. Opaque fillers offer protection from weathering, and asbestos filler, because of its fibrous structure can be added to improve toughness. Asbestos fibers have also been added to asphalt paving mixes to increase the resistance to movement under traffic, and in roofing materials, for fire-retardant purposes.

Numerous approaches have been suggested for reinforcing and/or waterproofing asphalt and concrete pavement and similar structures, including both new and existing structures. Most involve sequential installation of several layers at the job site. For example, the Road Glass system, a product of Owens- Corning Fiberglass, involves melting asphalt-based mastic onto the targeted surface, followed by the application of a fiberglass layer, and then, an additional layer of asphalt mastic is provided to produce a composite reinforced structure.

Nonwoven fabric such as Petromat manufactured by Atlantic Construction Fabrics, Inc. is used primarily for waterproofing road bases prior to application of asphalt wear course layers. Petromat is a needle punched nonwoven polypropylene geotextile. The fabric is heat bonded, meaning the fibers are fused on one

side to prevent bleed through of the tack coat and water from reaching the underlying road layers.

Petromat has comparatively low modulus of elasticity and thus provides limited reflective cracking resistance.

U. S. Patent No. 4,151,025 discloses a method for waterproofing concrete bride decks including cleaning the bridge deck, applying primer to the deck, applying a membrane to the primer followed by a tack coat and a layer of asphalt. The membrane includes a lower layer of uncured elastomer, a fabric layer and an upper layer of cured elastomer. The membrane is heated to about 175°F and rolled prior to placement of the tack coat to bond the lower layer of uncured asphalt to the bridge deck. The fabric layer is a single layer of open-mesh, natural or synthetic fabric. The fabric is not disclosed as being high strength or high modulus material nor is it pre-impregnated or otherwise pretreated to enhance its or the membrane's strength or other physical characteristics.

U. S. Patent No. 4,699,542 describes a system including method and apparatus for reinforcing asphaltic overlays applied to underlying pavements. A tack coat is initially applied to the pavement followed by a layer of resin-impregnated, open-mesh, semi-rigid fiberglass fabric. An asphaltic mixture overlay is then applied to the fabric. The fiberglass fabric has a high modulus of elasticity which improves the strength of the asphaltic overlay and inhibits propagation of reflective cracks in the overlay.

Resin impregnation serves to coat the glass strands and protects them from degradation arising from internally induced and externally applied harm such as friction between the strand filaments and corrosion

associated with invasion by water, particularly high pH water created by the use of salt on roads.

U. S. Patent Nos. 4,957,390,5,110,627,5,246,306 and 5,393,559 disclose systems similar to U. S. Patent No. 4,699,542. Rather than using a tack coat, the resin-impregnated glass fabric is adhered to the underlying pavement by a pressure or heat activatable adhesive carried by fabric.

U. S. Patent Nos. 5,152, and 5,273,804 disclose methods for reinforcing a paved roadway surface using an open mesh/fabric laminate. The paved roadway surface is produced by applying a tack coat to an underlying road base followed by the laminate which is placed fabric side down on the road base. A second tack coat is then applied to the laminate followed by a layer of asphalt. The preferred fabrics are indicated as needled continuous filaments or staple fibers although woven or knitted fabrics could be used. The mesh structure is preferably polypropylene or polyester mesh. The fabric is provided to promote adherence of the laminate to the road base. It is mechanically bonded to the mesh at thickened mesh nodules, whereby the fabric is spaced somewhat from the strands of the mesh. The spacing of the mesh from the fabric enables overlying asphalt aggregate to penetrate the mesh and interlock with the strands of the mesh and thereby reinforce the roadway surface.

Although providing some degree of reinforcement, polypropylene, polyester or similar plastic meshes have comparatively low Young's moduli of elasticity, i. e., on the order of about 10,000 to about 200,000 psi. Such low modulus materials experience far greater strain and creep under comparable loads than, for example, glass fiber meshes which have Young's moduli typically ranging from about 1,000,000 about

4,000,000 psi, and thus have limited capacity to resist new and reflective cracking in the asphalt overlayers versus higher modulus materials.

Polyfelt Geosynthetics Group markets a product known as PGM-P which is a composite reinforcement for asphalt. PGM-P includes uncoated fiberglass fabric stitched to nonwoven fabric. Lacking coating, the fiberglass fabric is exposed to corrosive environmental agents and its filaments are subject to damage do to friction and abrasion which tends to cause cutting of one glass filament or fiber by another. Moreover, the uncoated glass is susceptible to damage caused by the asphalt roadway construction process and application equipment. Similar products, which use uncoated, uncrimped synthetic fabric instead of uncoated fiberglass fabric, are disclosed in U. S.

Patent Nos. 4,472,086 and 4,540,311.

Chomarat & Cie of Cheylard, France, markets a product under the name Rotoflex which is a composite roadway fabric including a coated, fiberglass laid scrim sandwiched between two layers of nonwoven material. The fabric may be placed either side down and the nonwoven material facilitates adherence of the fabric to a tack coat. A disadvantage of Rotoflex fabric is that provision of the nonwoven materials both above and below the fiberglass scrim is that the aggregate commonly present in asphaltic concretes cannot effectively penetrate the nonwoven material and interlock with the scrim in a manner to fully exploit the high modulus/low creep characteristics of the scrim.

An advantage exists, therefore, for a roadway fabric which possesses a desirable combination of features which incorporate the high modulus/low creep characteristics of fiberglass material with the

waterproofing and tack enhancing characteristics of nonwoven material.

SUMMARY OF THE INVENTION The roadway fabric according to the invention is a composite assembly which consists essentially of a first layer of open mesh, bi-axially oriented high modulus/low creep fiber material secured to a second layer of substantially water-resistant material. The first layer is pre-impregnated with a resinous substance which is compatible with asphalt and the roadway fabric is preferably disposed with the water- resistant material facing downwardly to enhance adhesion of the fabric to the underlying roadway substrate. The open mesh of the first layer is operable to interengage with the aggregate present in asphalt concrete. In so doing, the high modulus/low creep characteristics of the open mesh material are exploited to inhibit cracking in the overlying asphalt, either in the form of new cracking or reflective cracking resulting from cracks in the underlying road structure. The second layer of water- resistant material promotes adherence of the roadway fabric to, as well as waterproofing of, the underlying road surface.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross sectional view of a fabric according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, the composite roadway fabric according to the present invention may be deployed in new and existing roadway installations and preferably includes a first layer 10 constructed as a scrim or knit grid, desirably an open mesh, bi-axially oriented, fiber fabric having a tensile strength of at

least about 250 pounds/inch, and preferably greater than 300-500 pounds/inch which is preferably thermally stable to at least 400F. The grid may be formed of strands of continuous filament glass fibers, having moduli of elasticity of at least about 1,000,000 psi, though other high modulus fibers such as polyamide fibers of poly (p-phenylene terephthalamide), known as KEVLAR, may be used. Various deniers and grid patterns can be used so long as the patterns provide a sufficient mechanical strength to the resulting structure and are easily penetrated by molten asphalt.

ECR or E glass rovings of weights ranging from about 300 to about 5000 tex are preferred. These strands, which are preferably low-twist (i. e., about one turn per inch or less), are formed into grids with rectangular or square openings, preferably ranging in size from 0.25 to about 0.5 inch on a side, though grids ranging from 0.125 inch to six inches on a side may be used. The grids are preferably stitched or otherwise fixedly connected at the intersections of the crosswise and lengthwise strands. This connection holds the reinforcement in its grid pattern, prevents the strands from spreading out unduly before and during impregnation, and preserves the openings.

The large grid openings permit the asphalt mixture to encapsulate each strand of yarn or roving completely and permit substantial interengagement between aggregate in the asphalt concrete and the grid-like first layer 10. This permits substantial transfer of stresses from the asphalt wear course or the road substrate to the glass fibers, thereby increasing the strength of the asphalt wear course.

The first layer 10 has a high modulus of elasticity 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.

The fixed connections at the intersections of the grid also contribute to the strength of the grid because they permit forces parallel to one set of strands to be transferred in part to the other set of parallel strands. At the same time, this open grid construction makes possible the use of less glass per square yard and therefore a more economical product.

For example, a presently preferred grid weighs about 12 ounces per square yard, although 4 to 18 ounces per square may be used. By comparison, some prior art roadway reinforcement structures employed fabrics having weights of about 24 ounces of glass per square yard.

Stitching the grid intersections together on warp-knit, weft-insertion knitting equipment using 70 to 150 denier polyester is preferred. However, other methods of forming grids with fixedly-connected intersections may be utilized. For example, a nonwoven grid made with thermosetting or thermoplastic adhesive may provide a suitable grid.

Once the grid is formed, and before it is laid in place on paving, a resin is applied. That is to say, the grid is"pre-impregnated"with resin.

The viscosity of the resin is selected so that it penetrates into the strands of the grid. While the resin may not surround every filament in a glass fiber strand, the resin is generally uniformly spread across the interior of the strand. This impregnation makes the grid compatible with asphalt, imparts a semi-rigid nature to it, and cushions and protects the glass strands and filaments from corrosion by water and other elements. The impregnation also reduces abrasion between glass strands or filaments and the cutting of one glass strand or filament by another, which is particularly important after the grid has

been laid down but before the asphalt overlayment has been applied.

While drying or curing the resin on the grid, the strands may be somewhat flattened, but the grid-like openings are maintained. For example, in a preferred embodiment, a rectangular grid may be formed, with the rovings flattened to about 1/16 inch, whereby the thickness of the rovings after coating and drying was about 1/32 inch or less.

Many resins can be used for impregnating the grid, provided they are such that adhesives can be bonded to them well. Primary examples are asphalt, rubber modified asphalt, crosslinked and uncrosslinked acrylics and polyvinyl alcohol, unsaturated polyesters, vinyl ester, epoxies, polyacrylates, polyurethanes, polyolefins, and phenolics which give the required rigidity, compatibility, corrosion resistance and thermal stability. They may be applied using hotmelt, emulsion, solvent, thermal-cure or radiation-cure systems. Alternatively, an asphaltic emulsion modified with a polymeric material, such as an acrylic polymer, can be padded onto the grid and thermally cured. Such modification of the asphalt makes it possible to achieve a coating which is less brittle at low temperatures.

The composite roadway fabric according to the invention further preferably comprises a second layer 30 of material which may be a woven or, more preferably, a nonwoven fabric that is substantially resistant to passage of water therethrough. It should be thermally resistant to at least 400°F and functions to waterproof the underlying roadway while enhancing adherence of the composite fabric structure to the roadway. A presently preferred nonwoven fabric, because of its ready availability and relatively low cost is needle-punched polypropylene fabric such as the aforementioned Petromat product. Other suitable

nonwoven fabrics include spun bonded materials, knitted materials and needle-punched polyester. The preferred weight of the nonwoven fabric is about 2 to 8 oz/yd, and more preferably, about 3 to 5 oz/yd However, the actual grade, composition, or source of nonwoven fabric is not of great concern so long as it has been employed in or can be demonstrated to be of beneficial use in roadway waterproofing applications.

Composite roadway fabric structures according to this invention may be manufactured by many processes.

For example, the first layer 10 and second layer 30 may be mechanically attached together by stitching 40, stapling or the like. Alternatively, a pressure and/or heat sensitive adhesive 20 may be applied to one or both of the first and second layers 10,30 and they may thereafter be pressed together, with simultaneous application of heat if necessary. As a further alternative, the second layer 30 may be united with the first layer 10 by the resinous substance which impregnates the first layer 10. That is, the first layer 10 may be impregnated and coated by the resin and the second layer 30 may be contacted and become bonded with the first layer 10 upon curing of the resin. Still further, asphalt emulsion may be sprayed onto the first and second layers 10,30, or by dipping these layers through a molten mastic tank having a temperature of about 400°-420°F. The first and second layers 10,30 can be unwound from a pair of rolls during such coating and bonding and the resulting coated composite fabric can be dried at ambient temperature or sent through a drying oven prior to cutting and rolling the mastic into a convenient form, such as a roll or patch.

Preferably, however, a pressure sensitive adhesive 20 such as that described in U. S. Patent No.

5,110,627 (the disclosure of which is incorporated herein by reference) is used as the agent for binding

the first and second layers 10,30 of the composite fabric to one another. Suitable adhesives include synthetic elastomeric and synthetic thermoplastic adhesives. Included among these are acrylics, styrene-butadiene rubbers, tackified asphalts and tackified olefins.

When performing road rehabilitation using the composite fabric, normal surface preparation of the underlying asphaltic concrete or Portland cement concrete road surface, including base repairs, crack sealing, pothole filling, and the like, is performed.

A tack coat may be applied to the road surface and the fabric is unrolled and pressed against the roadway surface. The composite fabric may be disposed on the underlying road surface with the first grid layer facing downwardly. More preferably, the composite fabric is installed with the grid facing upwardly to maximize interengagement of the grid with the aggregate constituents of the asphalt overlayer. In lieu of a tack coat applied to the road surface, a coating of any of the aforementioned adhesives may be pre-applied to that surface of the composite fabric which contacts the underlying roadway to promote adherence thereto. A similar tack coat or adhesive may also be applied to the other surface of the composite fabric to promote adherence of the fabric with the asphalt overlayer. Following placement of the composite fabric and any tack coats/adhesives on the underlying road surface and/or composite fabric, a layer of asphalt concrete of suitable thickness and composition, e. g., about 50 mm of HL 1 asphaltic concrete, may be applied using conventional equipment and techniques.

The resulting reinforced roadway structure effectively waterproofs the underlying road structure and resists new and reflective crack formation in the asphalt overlayer.

Although the invention has been described in detail for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.