EA042118B1 - METHOD FOR CREATING INTEGRATED GEOGRID FROM CO-EXTRUDED MULTILAYER POLYMER MATERIAL (VERSIONS) - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Technical Field of the Invention

The present invention relates generally to integral geogrids and other oriented grids used for structural or structural reinforcement and other geotechnical purposes. More specifically, the present invention relates to such integral geogrids made from a co-extruded multilayer polymer to achieve improved stiffness characteristics as well as any desired characteristics disclosed herein.

The present invention also relates to a method for manufacturing such integrated geogrids. Finally, the present invention relates to the use of such integral geogrids for reinforcing soil and granular material, and methods for such reinforcement.

For the purposes of this invention, the term integrated geogrid generally includes integral geogrids and other integral mesh structures made by orienting (stretching) a polymeric starting material into a sheet or sheet-like shape of a predetermined thickness, and having holes or depressions made or formed therein. .

2. Description of existing equipment

Polymer integral mesh structures having cell openings formed by various geometric patterns of essentially parallel, oriented strips and joints between them, such as integral geogrids, have been manufactured for over 25 years. Such meshes are made by extruding a cast sheet which is machined to form a pattern of holes or recesses, followed by controlled stretching in one or two axes and orientation of the sheet to form highly oriented bands and partially oriented joints defined by the cell openings formed by the holes or recesses. Such stretching and orientation of the sheet along one or two axial directions improves the strength and tensile strength of the strip in the respective direction of stretching. These integral oriented polymer mesh structures can be used to contain or stabilize any suitable type of particulate material such as soil, earth, sand, clay, gravel, etc. at any suitable location, such as on a road slope or other cut or fill for a road, runway, etc.

Various hole shapes and patterns have been experimented with to achieve a higher strength to weight ratio, or to achieve higher speeds in the manufacturing process. Orientation is performed with temperature and strain control. Some of the variables in this process include draw ratio, molecular weight, molecular weight distribution, and degree of polymer branching or crosslinking.

Well-known techniques may be followed in the manufacture and use of such integral geogrids and other integral mesh structures. As described in detail in U.S. Patents 4374798, Mercer, 4590029, Mercer, 4743486, Mercer and Martin, 4756946 Mercer and 5419659, Mercer, the original polymer sheet material is first extruded and then punched to form a given pattern of holes or depressions. Then an integral geogrid is formed by predetermined stretching and orientation of the punched sheet material.

Integral geogrids such as uniaxial integral geogrids and biaxial integral geogrids (together integral geogrids or individually uniaxial integral geogrids or biaxial integral geogrids) were invented by the aforementioned Mercer in the late 1970s and have had great commercial success in the last 30 years, completely revolutionizing the technology of reinforcing soils, roads, road bases and other building structures made from granular or granular materials.

Mercer has discovered that using the original relatively thick, substantially uniplanar polymer sheet, preferably on the order of 1.5 mm (0.059055 inch) to 4.0 mm (0.15748 inch) thick, having a pattern of holes or depressions with centers , lying on an imaginary, essentially square or rectangular grid of rows and columns, and stretching the original sheet either one-sided or along two axes so that the orientation of the strips is at the joints, you can make a completely new, essentially uniplanar integral geogrid. As Mercer describes, uniplanar means that all areas of the sheeting are symmetrical about the median plane of the sheeting.

In the U.S. patents Patent 3252181, 3317951, 3496965, 4470942, 4808358 and 5053264, the source material with a given pattern of holes or recesses is formed in connection with cylindrical polymer extrusion and essentially uniplanarity is achieved by passing the extruded material over the expanding spindle. The expanded cylinder is then longitudinally flattened to form a flat, substantially uniplanar parent sheet.

Another integral geogrid is described in U.S. Patent 7,001,112, Walsh (hereinafter the Walsh '112 patent), is issued to Tensar international Limited, an associate of the assignee of the patent application currently pending, Tensar International Corporation, Inc. (below in this Tensar document) Atlanta, Georgia. The Walsh '112 patent discloses oriented polymer integral geogrids, including biaxially stretchable integral geogrids, in

- 1 042118 which oriented stripes form triangular grid cells with partially oriented junctions at each corner, and with six highly oriented stripes occurring at each junction (hereinafter referred to as a three-dimensional integral geogrid in some cases).

The application of the present invention to all integral grids is proposed, regardless of the method of making the initial sheet or the method of orienting the initial material in the integral geogrid or mesh structure.

The subject matter of the above patents 3252181, 3317951, 3496965, 4470942, 4808358, 5053264 and 7001112 are expressly incorporated herein by reference as if the disclosures are set forth herein in their entirety. These patents are set forth as illustrative and are not intended to be inclusive or exclusive of other techniques known in the art for making integral polymer mesh materials.

Traditionally, polymeric materials used in the manufacture of integral geogrids have been a homopolymer or copolymer of high molecular weight polypropylene and high density, high molecular weight polyethylene. Various additives such as ultraviolet light inhibitors, carbon black, processing aids, etc. are used with these polymers to achieve desired parameters in the finished product and/or for manufacturing efficiency.

And also traditionally, the starting material for making such an integral geogrid is usually a uniplanar sheet that has a single layer construction, i.e., a homogeneous single layer of polymeric material.

Although an integral geogrid made from the conventional raw materials described above exhibits generally satisfactory properties, it is structurally and economically advantageous to manufacture an integral geogrid having a relatively higher stiffness to meet the requirements of a geosynthetic reinforcement service, or having other properties required for particular applications. geosynthetic applications.

Therefore, there is a need to provide a starting material that is not only suitable for the technological constraints associated with the manufacture of integral geogrids, but also one that, after the manufacture of the integral geogrid and during its operation, provides a higher stiffness index than the raw materials of conventional geogrids, or provides other desired properties that today's single-layer integral geogrids lack.

The essence of the invention

In order to achieve the aforementioned higher level of rigidity and other desired characteristics, the present invention uses a co-extruded multilayer polymer sheet as a starting material for the manufacture of an integral geogrid.

The experiments described herein support the inventors' theory that, through a patentable design, the co-extruded components of a multi-layer sheet provide a synergistic effect of crystal structure during extrusion and orientation, where the result is improved material properties, which provides preferred performance when applying an integral geogrid in a geosynthetic soil reinforcement.

According to one embodiment of the present invention, an integral geogrid stock includes a co-extruded multilayer polymer sheet, with holes or recesses therein that provide openings when the stock is stretched along one or two axes.

According to another embodiment of the present invention, the integral geogrid includes a plurality of highly oriented strips interconnected by partially oriented joints and having a group of openings, which is made from a co-extruded multilayer polymer sheet. According to one embodiment of the invention, the integral geogrid is a three-dimensional integral geogrid.

According to another embodiment of the present invention, the earth structure includes a body of particulate material reinforced by embedding an integral geogrid made from a co-extruded multilayer polymer sheet.

According to another embodiment of the present invention, a method of creating an integral geogrid starting material includes providing a co-extruded multilayer polymer sheet, and providing holes or depressions therein.

According to another embodiment of the present invention, a method for creating an integral geogrid includes providing a co-extruded multi-layer polymer sheet, providing holes or recesses in it, and stretching along one or two axes of the co-extruded multi-layer polymer sheet with holes or recesses in it to provide a plurality of highly oriented strips interconnected partially oriented joints and having a group of openings between them. According to one embodiment of the invention, the method produces a three-dimensional integral geogrid from a co-extruded multilayer polymer sheet.

And according to another embodiment of the present invention, the method of strengthening the mass of granular material includes embedding an integral geogrid in the mass of granular material,

- 2 042118 made from co-extruded multilayer polymer sheet.

Accordingly, it is an object of the present invention to provide a starting material for creating an integral geogrid. The parent material includes a co-extruded multilayer polymer sheet with holes or depressions therein that provide openings when the parent material is stretched along one or two axes.

Another object of the present invention is to provide an integral geogrid having a plurality of highly oriented strips connected to each other by partially oriented joints and having a group of openings, which is made from a co-extruded multilayer polymer sheet. A related object of the invention is to provide an integral geogrid having a higher level of stiffness, higher strength and other desired characteristics. Specifically, it is an object of the present invention to provide a three-dimensional integral geogrid from a co-extruded multilayer polymer sheet.

Another object of the present invention is to provide an earth structure that includes a body of particulate material reinforced by embedding an integral geogrid made from a co-extruded multilayer polymer sheet.

It is another object of the present invention to provide a method for making an integral geogrid starting material, which includes providing a co-extruded multilayer polymer sheet and providing holes or depressions therein.

Another object of the present invention is to provide a method for creating an integral geogrid. The method includes providing a coextruded multilayer polymer sheet, providing holes or recesses therein, and stretching along one or two axes of the coextruded multilayer polymer sheet having holes or recesses to provide a plurality of highly oriented strips interconnected by partially oriented joints and having a group of openings. The method may employ known geogrid fabrication methods, such as those described in the aforementioned U.S. Patent Nos. 4374798, 4590029, 4743486, 5419659 and 7001112 and other patents. Specifically, it is an object of the present invention to provide a method for creating a three-dimensional integral geogrid from a co-extruded multilayer polymer sheet.

Another object of the present invention is to provide a method for strengthening a body of granular material by embedding an integral geogrid made from a co-extruded multilayer polymer sheet into the body of granular material.

The foregoing, together with other objects and advantages, will become apparent from the detailed description of construction and use described hereinafter with reference to the accompanying drawings forming part of the description, with like reference numerals referring to like parts throughout. The accompanying drawings show the invention, not necessarily to scale.

Brief description of the drawings

In FIG. 1 shows a co-extruded uniplanar multi-layer integral geogrid sheet stock prior to being provided with holes or depressions in accordance with one embodiment of the present invention.

In FIG. 2 is a top isometric view of the starting material sheet of FIG. 1 with holes punched through it to form a three-dimensional integral geogrid of the type shown in the Walsh '112 patent.

In FIG. 3 is a side view of a portion of the raw material sheet of FIG. 2.

In FIG. 4 is a plan view of part of a three-dimensional integral geogrid made by biaxially orienting the raw material sheet of FIG. 2.

In FIG. 5 is a perspective view of part of the 3D integral geogrid of FIG. 4.

In FIG. 6 is an enlarged perspective view of a portion of the 3D integral geogrid of FIG. 4.

In FIG. 7 is a sectional view of the three-dimensional integral of FIG. 4.

In FIG. 8 is a table summarizing the properties of the aperture stability modulus for an experimental 3D integral geogrid made from a 3 mm co-extruded uniplanar multilayer sheet stock as shown in FIG. 1-7 for comparison with similar properties of the 3D integral geogrid commercially available and supplied by Tensar as the TriAx® TX140™ geogrid.

In FIG. 9 shows a table comparing various physical properties of the 3D integral geogrids commercially available and supplied by Tensar (made from extruded single layer sheets) with the corresponding properties of the experimental 3D integral geogrids shown in FIG. 4-7 made from co-extruded uniplanar multilayer sheets according to the present invention.

In FIG. 10 shows another table comparing various physical properties of 3D integral geogrids commercially available and supplied by Tensar (made from extruded single layer sheets) with corresponding properties of experimental 3D integral geogrids made from coextruded uniplanar multilayer sheets according to the present invention.

In FIG. 11 is a perspective view of part of a 3D integral geogrid according to another embodiment of the present invention.

In FIG. 12 is a plan view of part of the three-dimensional integral geogrid of FIG. eleven.

In FIG. 13 is a sectional view of the 3D integral geogrid of FIG. eleven.

In FIG. 14 shows a co-extruded uniplanar multilayer integral geogrid sheet stock prior to being provided with holes or depressions in accordance with another embodiment of the present invention.

In FIG. 15 is a perspective view of part of the 3D integral geogrid associated with the raw material sheet of FIG. 14.

Detailed Description of the Preferred Embodiments

Although only the preferred embodiments of the invention are described in detail, it is to be understood that the invention is not limited in scope to the details of construction and arrangement of components set forth in the following description or shown in the drawings. The invention may have other embodiments and may be implemented or carried out in various ways.

Also in the description of the preferred embodiments, the terminology has been re-sorted for clarity. Each term is understood to have its broadest meaning as understood by one skilled in the art and includes all technical equivalents that operate similarly for a similar purpose.

And as used herein, the terms co-extruded, co-extruded and co-extruded are used according to their usual accepted meanings, i.e., referring to a one-step process, starting with two or more polymeric materials that are simultaneously extruded and molded into a single die die to form a multilayer sheet.

The present invention is directed to uniaxial, biaxial and three-dimensional integral geogrid structures made from a co-extruded multilayer polymer sheet as a starting material. The co-extruded multilayer polymer sheet stock may or may not be uniplanar, for example, depending on the specific characteristics required for the multilayer geogrid structure to be made from it. According to a preferred embodiment of the invention, the coextruded multilayer polymer sheet stock is uniplanar or substantially uniplanar.

The invention is based on the fact that the extrusion of a co-extruded multilayer sheet consisting of different polymeric materials or other extrudable materials with different percentages, when converted into uniaxial, biaxial and/or three-dimensional integral geogrids, by punching the sheet and during the stretching process, gives a finished product that has unique characteristics compared to traditional, single axis, biaxial and 3D geogrids for soil reinforcement and other geotechnical applications.

In FIG. 1 shows a co-extruded multi-layer sheet 100 used as a starting material for an integral geogrid according to one embodiment of the present invention, before the sheet is punched through or recessed.

As shown in FIG. 1, the co-extruded multilayer sheet 100 is a three-layer sheet in an embodiment of the invention. That is, sheet 100 preferably includes first layer 110, second layer 120, and third layer 130. First layer 110 and third layer 130 are disposed on opposite planar surfaces of second layer 120, preferably in a uniplanar or substantially uniplanar configuration. Additionally, although a three-layer configuration of sheet 100 is shown for illustration, the invention contemplates the use of a sheet having multiple layers arranged in various configurations, multiple layers having different combinations of thicknesses, and multiple layers having different materials of construction, all dictated by a particular application, in which the integral geogrid is to be used. For example, although a three-layer configuration of sheet 100 is shown for illustration, the invention also contemplates the use of co-extruded sheets having more than three layers. In general, the configuration of the layers, the thicknesses of the layers, and the materials of construction of the layers are chosen to provide not only the convenience of manufacturing an integral geogrid, but also an integral geogrid having the desired level of stiffness and other performance characteristics.

As described above, the co-extruded multilayer sheet 100 used as the starting material for the integral geogrid of the present invention is preferably punched through, although depressions may be provided instead. According to an embodiment of the starting material in which depressions are made in the sheet, such depressions are provided on each side of the sheet, i.e., both on the top and bottom of the sheet. Additionally, the recesses extend into each layer of the co-extruded multilayer sheet.

In the particular embodiment of the invention shown in FIG. 1, sheet 100 is made by coextruding a first material that forms the first layer 110, a second material that forms the second layer 120, and a third material that forms the third layer 130,

- 4 042118 method known to a person skilled in the art for extruding multilayer sheets.

According to a preferred embodiment of the invention, the total thickness of sheet 100 is from about 2 mm to about 12 mm, and in a more preferred embodiment, the total thickness of sheet 100 is from about 2 mm to about 6 mm.

With respect to the individual thicknesses of the sheet layers according to the preferred embodiment of the invention, the thickness of the first layer 110 is from about 0.5 to about 4.5 mm, the thickness of the second layer 120 is from about 1 to about 9 mm, and the thickness of the third layer 130 is from about 0. 5 to about 4.5 mm, considering that the total thickness of the sheet 100 is from about 2 to about 12 mm. And according to a more preferred embodiment of the invention, the thickness of the first layer 110 is from about 0.5 to about 2 mm, the thickness of the second layer 120 is from about 2 to about 5 mm, and the thickness of the third layer 130 is from about 0.5 to about 2 mm.

In general, the materials of construction of the first layer 110, the second layer 120, and the third layer 130 may be the same or may be different from one another. Preferably, the material of construction of the first layer 110 and the material of construction of the third layer 130 may be the same or may be different from one another. More preferably, the material of construction of the second layer 120 is different from the material of construction of both the first layer 110 and the third layer 130.

And, in general, the layers of the sheet are polymeric in nature. For example, materials of construction may include high molecular weight polyolefins and general purpose polymers. Additionally, the polymeric materials may be recycled or recycled materials, such as, for example, polymeric materials from recycled industrial or municipal waste. And it is also proposed to use one or more polymeric layers having a cost lower than that of the above mentioned high molecular weight polyolefins and general purpose polymers. The use of such low cost polymer layers can provide cost savings of about 20% to about 30% over the use of, for example, a polypropylene layer.

According to a preferred embodiment of the invention, the material of construction of the first layer 110 and the third layer 130 is a high molecular weight polyolefin such as, for example, polypropylene (PP). And, in the same preferred embodiment, the material of construction of the second layer 120 is a general purpose polymer such as, for example, virgin PP or recycled PP, such as industrial waste PP or other recycled PP. However, depending on the particular application of the integral geogrid, polymer components having a material of construction other than polypropylene can be included in the composition of the co-extruded multilayer sheet.

In FIG. 2 and 3 show the co-extruded multilayer sheet stock 100 of FIG. 1 having holes 140 punched therein to form the three-dimensional integral geogrid 200 shown in FIG. 4, 5 and 6. The size and spacing of holes 140 are as disclosed in the Walsh '112 patent. The 3D integral geogrid 200 includes highly oriented lanes 205 and partially oriented joints 235, also as disclosed in the Walsh '112 patent. Top layer 130 of parent material 100 is stretched and oriented to transform into top layer 230 of strips 205 and seams 235. Similarly, third or bottom layer 110 of parent material 100 is stretched and oriented to transform into bottom or underlying layer 210 of strips 205 and seams 235. When the first layer 130 and the third layer 110 are stretched and oriented, the second or middle layer 120 is also stretched and oriented to transform both the strips 205 and the joints 235 into the middle layer 220.

The invention also relates to a method for creating the above-described three-dimensional integral geogrid 200. The method includes providing a co-extruded multilayer polymer sheet 100; forming a plurality of holes or depressions in the co-extruded multilayer polymer sheet 100 in a selected pattern, such as in the Walsh '112 patent disclosure; and biaxially stretching and orienting a co-extruded multilayer polymer sheet patterned with a plurality of holes or depressions therein to form an integral geogrid with a plurality of interconnected, oriented strips between partially oriented joints and to configure the holes or depressions as mesh openings.

In general, when the co-extruded multilayer polymer sheet 100 is prepared with holes or depressions, the three-dimensional integral geogrid 200 can be made from the sheet 100 according to the methods described in the above patents and known to those skilled in the art.

In order to demonstrate the improved performance and properties of a patentable integral geogrid made from a co-extruded multilayer sheet, comparative tests were carried out.

In FIG. 8 shows a table summarizing the properties of the aperture stability modulus for an experimental 3D integral geogrid made from 3 mm co-extruded sheet stock material for comparison with similar properties of a 3D integral geogrid commercially available and supplied by Tensar as the TriAx® TX140™ geogrid. The experiment was performed according to ASTM D7 864 test protocols, i.e., Standard Test Method for Determining the Aperture Stability Modulus of Geogrids. Aperture stability testing was performed on samples of a 3D integral geogrid constructed from a 3mm co-extruded multi-layer sheet that had a 50% BSR (general purpose resin) composition, which was punched and stretched. The first, i.e., bottom, layer 110 of the co-extruded multilayer sheet had high molecular weight polypropylene (PP) as material of construction and a thickness of 0.75 mm; the second, i.e., middle, layer 120 had as a material of construction PP of wide application and a thickness of 1.50 mm; and the third, i.e., the top layer 130 had high molecular weight PP as the material of construction and a thickness of 0.75 mm.

For the experimental, laboratory-prepared 3D integral geogrid made from a co-extruded multilayer sheet, position 5, the average value for a moment of 20 kg.cm was 3.70 kg.cm/deg.

In contrast, for non-co-extruded, i.e., single layer sheet, specifically across six tests of standard Triax® TX140™ geogrids, the average test value was 2.86 kg.cm/deg, ranging from 2.52 to 3.14 kg.cm /deg, essentially below position 10, the average value recorded for experimental multilayer samples.

In FIG. 9 also shows the various physical properties of 3D integral geogrids made from single layer extruded sheets with the corresponding physical properties of 3D, position 15 integral geogrids made from coextruded multilayer sheets according to the present invention. In the test summarized in FIG. 9, single layer sheets were processed to form the 3D integral geogrid configuration described in the Walsh '112 patent. This 3D integral geogrid 20 is commercially available and commercially available from Tensar and is known as the TriAx® TX160™ geogrid.

For the comparative experiments shown in FIG. 9, co-extruded three-layer sheets were prepared with a finished sheet thickness of 4.6 mm. The different sheets were formulated with different loadings of industrial waste polypropylene (PP) content, and each of the co-extruded three-ply sheets was then processed into a 3D integrated geogrid comparable to Tensar's TriAx® TX160™ geogrid.

With reference to FIG. 9, each of the 4.6 mm co-extruded multilayer sheets included the following layer compositions: sample (1) first or top layer 130, as described above, of 34% virgin polypropylene (PP) and black rubber (MB, i.e., black carbon to provide a black product for UV protection)/second or middle layer 120 as described above from 32% industrial waste PP/and third or bottom layer 110 as described above from 34% virgin PP and MB ; and sample (2) 25% virgin PP and MB/50% industrial waste PP/25% virgin PP and MB.

The thickness of each of the above-described layers for various sheets, samples (1) and (2), was as follows. For the 4.6 mm laminated sheet sample (1), the layer thicknesses were 1.56 mm/1.47 mm/1.56 mm, respectively. For the 4.6 mm laminated sheet sample (2), the layer thicknesses were 1.15 mm/2.30 mm/1.15 mm, respectively.

As is evident from the results presented in FIG. 9, the resulting experimental 3D integral geogrids made from the above-described punched and oriented 4.6mm co-extruded three-ply sample sheet yielded a product, compared to a standard Triax® TX160™ single-ply geogrid with an approximate equivalent strip of original thickness (4.7mm), which demonstrated substantially higher product stiffness as measured by Tensar's low mechanical strain test of tensile modulus, flexural stiffness, and aperture stability. The 0.5% and 2.0% tensile modulus values were more than 30% higher for experimental 3D geogrids made from 4.6mm co-extruded 3 ply base sheet than conventional Triax® TX160™ geogrids made from 4 .7 mm single layer sheet. Similarly, measured flexural stiffness values were 33% higher for experimental 3D geogrids made from 4.6mm co-extruded sheet than for standard Triax® TX160™ geogrids made from 4.7mm single ply base sheet.

In FIG. 10 is another table comparing various physical properties of 3D integral geogrids made from single layer sheets commercially available and supplied by Tensar with corresponding physical properties of experimental 3D integral geogrids made from co-extruded multilayer sheets according to the present invention. In the tests summarized in FIG. 10, single layer sheets were also processed to have the 3D integral geogrid configuration described in the Walsh '112 patent. This 3D integral geogrid is commercially available from Tensar and is known as the TriAx® TX140™ geogrid.

For the comparative tests shown in FIG. 10, 3.0 mm thick co-extruded three-layer finished sheets were prepared. The various sheets included differing loading contents of polypropylene (PP) from industrial waste and each of the co-extruded three-layer

- 6,042,118 sheets were then processed into a 3D integral geogrid comparable to the geogrid

Tensar TriAx® TX140™.

With reference to FIG. 10 Sheet SN20140407 had the following composition: 32% general purpose resin in the second (i.e., middle) layer 120 and 34% high molecular weight PP in the first (i.e., top) layer 130 and in the third (i.e., , bottom) layer 110. Sheet SN20140408 had the following composition: 50% general purpose resin in the second (ie, middle) layer, and 25% high molecular weight PP in the first layer and third layer. Sheet SN20140409 had the following composition: 60% general purpose resin in the second (ie, middle) layer and 20% high molecular weight PP in the first layer and third layer.

The thickness of each of the above layers for Sheet SN20140407, Sheet SN20140408 and Sheet SN20140409 is as follows. For the 3 mm Multilayer Sheet SN20140407, the thicknesses of the first, second and third layers were 1.02 mm/0.96 mm/1.02 mm, respectively. For the 3mm multilayer Sheet SN20140408, the layer thicknesses were respectively 0.75mm/1.5mm/0.75mm. For the 3mm multilayer Sheet SN20140409, the layer thicknesses were respectively 0.6mm/1.8mm/0.6mm.

As is evident from the results shown in FIG. 10, a 3.0 mm sheet of original thickness with 32% (SN20140407), 50% (SN20140408), and 60% (SN20140409) industrial waste PP content, when converted to a finished 3D integral geogrid, only exceeded the specified value of the modulus of elasticity test at tensile strength for a Triax® TX140™ geogrid made from 3.7mm sheet, which is 220 kN/m in lateral direction (TD).

In FIG. 10 also shows that for each of the co-extruded samples, starting with a thin 3.0 mm sheet, there is a match or exceeding the average tensile modulus of a standard Triax® TX140™ geogrid made from a 3.7 mm sheet.

Also, the experiments described herein support the inventors' concept that through the use of a multi-layer design for a sheet of raw material, the co-extruded components of the multi-layer sheet can provide a synergistic crystal structure effect during extrusion and orientation, thus providing improved material properties in the resulting integral geogrid and preferred performance of the resulting integral geogrid in soil and other geotechnical applications.

Other possible embodiments of the present invention may include, for example, (1) multilayer co-extruded polymer sheet stocks having significantly higher levels of PP resins from industrial and municipal recycling, i.e., PP resins that have a relatively low cost, (2) foaming agents to provide a foaming or expanding second (i.e., middle) layer, (3) one or more relatively low cost layers that include fillers or fillers, (4) a color identification layer in the integral geogrid and (5) a three-layer co-extruded polymer sheet with HDPE outer layers and an amorphous and crystallizable polyester inner layer sandwiched therebetween. Each of the above examples should provide an improvement or meet the requirements for an integral geogrid having improved geosynthetic aggregate reinforcement, cost reduction, and/or identification properties.

More specifically, as noted above, one possible embodiment of the present invention may include the use of a blowing agent to provide a foamable or expandable second or middle layer. Shown in FIG. 11, 12, and 13 relate to such an embodiment 300 in which the second or middle layer (here 320) of the co-extruded multilayer sheet forms an expandable or foam structure. That is, according to this embodiment, the chemical blowing agent is mixed with the polymer, which is extruded to form the second layer. The heat generated to melt the polymer decomposes the chemical blowing agent, resulting in the release of gas. The gas is then dispersed in the polymer melt and expands after exiting the die die. As a result, the second layer expands or foams.

According to this embodiment, as in the first embodiment described above, the material of construction of the first layer (here 310) and the material of construction of the third layer (here 330) may be the same or different from each other, although the same material is preferred. In general, the material of construction of the second layer 320 is different from the material of construction of both the first layer 310 and the material of construction of the third layer 330.

The advantages of the foamed embodiment of the finished integral geogrid according to the present invention not only include reduced raw material cost and reduced geogrid weight, but may also include the desired physical and chemical properties of the foamed layer in its pure form.

As indicated above, one possible embodiment of the present invention may include the use of a color identification layer with an integral geogrid. For example, the American Association of State Highway and Transportation Officials (AASHTO) requires, along with Transportation

Product Evaluation Program (NTPEP), a product marker for geosynthetic reinforcement associated with walls, slopes and infills over soft ground.

The color identification layer described above may be, for example, a polymeric layer with a color that is different from that of the adjacent or bonded co-extruded layer. The color identification layer may be an inner layer or an outer layer of the integral geogrid, or the integral geogrid may include multiple colored identification layers of the same color or different colors. The color identification layer may be a solid tone or may have a pattern, such as including a stripe. The color and/or chemistry of the colored identification layer is chosen, of course, based on the requirements of the particular application of the integral geogrid.

In addition to the above-described use of the integrated geogrid color identification layer to comply with AASHTO and NTPEP standards, the color identification layer may also serve to provide an integral geogrid identification source.

As stated above, although a three-layer configuration of sheet 100 is shown for illustration purposes, the invention also contemplates the use of co-extruded sheets having more than three layers.

For example, the co-extruded sheet may have a five-layer configuration, such as sheet 400 shown in FIG. 14. Sheet 400 includes a middle layer 420, a first inner layer 410, a second inner layer 430, a first outer layer 440, and a second outer layer 450. The first inner layer 410 and the second inner layer 430 are located on opposite planar surfaces of the middle layer 420, preferably in a uniplanar or substantially uniplanar configuration. The first outer layer 440 and the second outer layer 450 are located on opposite planar surfaces of the first inner layer 410 and the second inner layer 430, respectively, preferably in a uniplanar or substantially uniplanar configuration.

In the particular embodiment of the invention shown in FIG. 14, sheet 400 is made by coextruding a first material that forms the middle layer 420, a second material that forms the first inner layer 410, a third material that forms the second inner layer 430, a fourth material that forms the first outer layer 440, and a fifth material, which forms the second outer layer 450, known to the person skilled in the art by extruding multilayer sheets.

In general, the materials of construction of the middle layer 420, the first inner layer 410, the second inner layer 430, the first outer layer 440, and the second outer layer 450 may be the same or different from one another. For example, the middle layer 420 may have a first material of construction, the first inner layer 410 and the second inner layer 430 may have a second material of construction, and the first outer layer 440 and the second outer layer 450 may have a third material of construction. As such, depending on the particular application of the integral geogrid fabricated from sheet 400, various combinations of materials of construction may be used for the five layers described above.

In FIG. 15 is a perspective view of a portion of the 3D integral geogrid 500 associated with the raw material sheet 400 shown in FIG. 14. The 3D integral geogrid 500 includes highly oriented bands 505 and partially oriented joints 535. After punching holes in the sheet 400, the first outer layer 440 and the second outer layer 450 of the sheet 400 were stretched and oriented to transform into the first outer layer 540 and the second outer layer 550 of the strips 505 and the joints 535. Similarly, the first inner layer 410 and the second inner layer 430 of the sheet 400 have been stretched and oriented to transform into the first inner layer 510 and the second inner layer 530 of the strips 505 and the joints 535, respectively. And since the first outer layer 440 and the second outer layer 450, as well as the first inner layer 410 and the second inner layer 430 are stretched and oriented, the middle layer 420 is also stretched and oriented to transform into the middle layer 520 both strips 505 and joints 535.

As also indicated above, one possible embodiment of the present invention may include the use of one or more layers of relatively low cost, which include fillers or fillers. The incorporation of such fillers or fillers into the layers of the integral geonetwork creates a product having a thicker, ie, higher, profile, which may result in improved performance of the integral geonetwork in some applications. Depending on the intended application of the integral geogrid, such fillers or fillers may include, for example, one or more of the following CaCO ³ (calcium carbonate), talc, CaSiO ³ (wollastonite), nanofillers, multi-walled carbon nanotubes (MWCNT), single-walled carbon nanotubes (SWCNT), glass fibers and aluminum hydrate.

As described above, one or more polymer layers are contemplated at a cost lower than high molecular weight polyolefins and general purpose polymers. In an embodiment where the low cost polymer layer also includes the filler or filler mentioned above, the result can be a savings of approximately 20% relative to

- 8 042118 application, for example, a layer of polypropylene.

And, of course, the use of the above-described foam layer can also create a product having a thicker, ie, higher profile, which can also result in improved integrated geogrid performance in some applications.

Contemplated embodiments of the invention include those where one or more foam layers are used in conjunction with one or more layers that include fillers or fillers.

In general, the present invention is based on the use of the coextruding techniques and materials described herein to modify and improve certain physical, chemical and/or mechanical properties of an integral geogrid to improve the performance of an integral geogrid in its particular application.

The foregoing is considered to be illustrative of the principles of the invention only. Additionally, since numerous modifications and changes may occur to a person skilled in the art, it is not necessary to limit the invention to the specific construction and operation described and shown.

Claims (21)

CLAIM 1. A method for creating an integral geogrid, which includes obtaining, by one co-extruding, an initial co-extruded multilayer polymer sheet having at least co-extruded first, second and third layers of polymer materials, wherein the original co-extruded multilayer polymer sheet has an initial thickness of at least 2 mm, moreover the polymeric material of the first layer and the third layer has the first molecular weight and is each from 25 to 34 wt.% of the original sheet, and the polymeric material of the second layer has a second molecular weight different from the first molecular weight, and is from 32 to 50 wt.% of the original sheet, and the second layer is located between the first layer and the third layer; obtaining a plurality of holes or recesses of a selected pattern in the original coextruded multilayer polymer sheet and orienting the initial coextruded multilayer polymer sheet having a pattern of a plurality of holes or recesses in it, to obtain a plurality of oriented strips interconnected by joints, and to configure the holes or recesses in the form mesh openings in the space defined by oriented stripes and joints. 2. The method of claim 1, wherein the first layer and the third layer of the original coextruded multilayer polymer sheet are placed on opposite planar surfaces of the second layer of the original coextruded multilayer polymer sheet. 3. The method of claim 1, wherein the first layer, the second layer and the third layer are in contact both at the joints and along a plurality of strips. 4. The method of claim 1, wherein the starting co-extruded multilayer polymer sheet has a thickness of at least 2 to about 12 mm. 5. The method of claim 1, wherein the first layer and third layer of the original co-extruded multilayer polymer sheet are each about 0.5 to about 4.5 mm thick and the second layer is about 1 to about 9 mm thick. 6. The method of claim 1, wherein the polymeric material of the first layer and the third layer is virgin polypropylene, and the polymeric material of the second layer is industrial waste polypropylene or recycled polypropylene. 7. The method of claim 1, wherein the initial co-extruded multilayer polymer sheet having a pattern of a plurality of holes or depressions therein is oriented by uniaxial or biaxial stretching. 8. The method of claim 1, wherein the plurality of oriented strips includes transverse strips joined together by joints with substantially longitudinally oriented strips. 9. The method of claim 1 wherein the starting co-extruded multilayer polymer sheet has an oriented thickness of from about 0.2 to about 9 mm. 10. The method of claim 1, wherein the initial co-extruded multilayer polymer sheet, after orientation, exhibits increased flexural and torsional stiffness relative to the flexural and torsional stiffness of a non-coextruded sheet having substantially the same original thickness. 11. The method of claim 1, wherein the integral geogrid is a uniaxial integral geogrid. 12. The method of claim 1, wherein the integral geogrid is a biaxial integral geogrid. 13. The method of claim 1, wherein the integral geogrid is a triaxial integral geogrid. 14. A method for producing an integral geogrid structure, including stretching along one or two axes of the original material, which is the original coextruded multilayer polymer sheet having at least the first, second and third layers of polymeric materials coextruded and formed in one coextruding , wherein the original co-extruded multilayer polymer sheet has an initial thickness of at least 2 mm, wherein the polymer material of the first layer and the third layer has the first molecular weight and each makes up from 25 to 34 wt.% of the original sheet, and the polymer material of the second layer has a second molecular weight , different from the first molecular weight, and is from 32 to 50 wt.% of the original sheet, and the second layer is located between the first layer and the third layer, and the source material has many holes or recesses of the selected pattern in it to obtain an integral geogrid having many oriented lanes connected between along the joints, and a plurality of mesh openings in the space defined by the oriented strips and joints; and embedding an integral geogrid in a mass of granular material. 15. A method for creating an integral geogrid, including the following steps: coextruding the original multilayer polymer sheet having at least the first, second and third layers of polymeric materials, wherein the polymeric material of the first layer and the third layer has the first molecular weight and each makes up from 25 to 34 wt.% of the original sheet, and the polymeric the second layer material has a second molecular weight different from the first molecular weight and comprising from 32 to 50 wt.% of the original sheet, while the second layer has a foamed or expanded structure, and the original co-extruded multilayer polymer sheet has an initial thickness of at least 2 mm; making a plurality of holes or recesses of a selected pattern in the original co-extruded multilayer polymer sheet and orienting the initial coextruded multilayer polymer sheet having a pattern of a plurality of holes or recesses in it to obtain a plurality of oriented strips interconnected by joints, and to configure the holes or recesses in the form mesh openings in the space defined by oriented stripes and joints. 16. The method of claim 15, wherein the first layer and the third layer are placed on opposite planar surfaces of the second layer. 17. The method of claim 15, wherein the second layer has a thickness greater than either of the first layer and the third layer. 18. The method of claim 15, wherein after the orienting step, the first layer, the second layer, and the third layer are in contact both at the junctions and along a plurality of strips. 19. The method of claim 15, wherein the step of orienting the initial co-extruded multilayer polymer sheet having a pattern of a plurality of holes or depressions therein is carried out by uniaxial or biaxial stretching. 20. The method of claim 15, wherein the chemical blowing agent is mixed with a polymeric material that is extruded to form a foamed or expanded second layer. 21. A method for creating an integral geogrid, including obtaining an initial co-extruded multilayer polymer sheet having an initial thickness of at least about 2 mm and having adjacent co-extruded first, second and third layers of polymer materials, while the polymer material of the first layer and third layer has a first molecular weight and each makes up from 25 to 34 wt.% of the original sheet, and the polymeric material of the second layer has a second molecular weight different from the first molecular weight and constituting from 32 to 50 wt.% of the original sheet, while the original co-extruded multilayer polymer sheet is formed in one coextruding; obtaining a pattern from a plurality of holes or depressions in the original coextruded multilayer polymer sheet and orienting the original coextruded multilayer polymer sheet having a pattern of a plurality of holes or depressions in it, by stretching, to obtain a plurality of interconnected oriented strips and configuring holes or depressions in the form of openings grids.