U.S. patent application number 15/766960 was filed with the patent office on 2018-10-18 for geogrid made from a coextruded multilayered polymer.
This patent application is currently assigned to TENSAR CORPORATION, LLC. The applicant listed for this patent is TENSAR CORPORATION, LLC. Invention is credited to William Stanley SHELTON, Manoj Kumar TYAGI.
Application Number | 20180298582 15/766960 |
Document ID | / |
Family ID | 58488480 |
Filed Date | 2018-10-18 |
United States Patent
Application |
20180298582 |
Kind Code |
A1 |
SHELTON; William Stanley ;
et al. |
October 18, 2018 |
GEOGRID MADE FROM A COEXTRUDED MULTILAYERED POLYMER
Abstract
An integral geogrid includes a plurality of interconnected,
oriented strands having an array of openings therein that is
produced from a coextruded multilayer polymer sheet starting
material. By virtue of the construction, the coextruded multilayer
sheet components provide a crystalline synergistic effect during
extrusion and orientation of the integral geogrid, resulting in
enhanced material properties that provide performance benefits to
use of the integral geogrid in soil geosynthetic reinforcement.
Inventors: |
SHELTON; William Stanley;
(Lithonia, GA) ; TYAGI; Manoj Kumar;
(Fayetteville, GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TENSAR CORPORATION, LLC |
Alpharetta |
GA |
US |
|
|
Assignee: |
TENSAR CORPORATION, LLC
Alpharetta
GA
|
Family ID: |
58488480 |
Appl. No.: |
15/766960 |
Filed: |
October 6, 2016 |
PCT Filed: |
October 6, 2016 |
PCT NO: |
PCT/US2016/055768 |
371 Date: |
April 9, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62239416 |
Oct 9, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B32B 3/266 20130101;
B32B 2250/24 20130101; B29C 48/0018 20190201; B29C 48/08 20190201;
B32B 27/32 20130101; B32B 2250/03 20130101; E02D 3/005 20130101;
E02D 17/202 20130101; E02D 29/02 20130101; E02D 2300/0084 20130101;
B32B 27/08 20130101; B29C 48/185 20190201; B29C 48/304 20190201;
E02D 17/20 20130101; B29C 48/21 20190201 |
International
Class: |
E02D 17/20 20060101
E02D017/20; E02D 29/02 20060101 E02D029/02; B29C 47/00 20060101
B29C047/00; B29C 47/06 20060101 B29C047/06; B29C 47/12 20060101
B29C047/12; E02D 3/00 20060101 E02D003/00 |
Claims
1.-28. (canceled)
29. An integral geogrid comprising a plurality of interconnected,
oriented strands having an array of openings therein, the integral
geogrid being produced from a multilayer polymer starting sheet
having layers of different materials and formed in a single
coextrusion.
30. The integral geogrid according to claim 29, wherein the
oriented strands have been uniaxially or biaxially stretched.
31. The integral geogrid according to claim 29, wherein the
coextruded multilayer polymer starting sheet includes a first
layer, a second layer, and a third layer, with the first layer and
the third layer being arranged on opposite planar surfaces of the
second layer.
32. The integral geogrid according to claim 29, wherein the
coextruded multilayer polymer starting sheet has a thickness of
from about 2 mm to about 12 mm.
33. The integral geogrid according to claim 31, wherein the first
layer has a thickness of from about 0.5 mm to about 4.5 mm, the
second layer has a thickness of from about 1 mm to about 9 mm, and
the third layer has a thickness of from about 0.5 mm to about 4.5
mm.
34. The integral geogrid according to claim 31, wherein the first
layer has a material of construction of a high molecular weight
polyolefin, the second layer has a material of construction of a
broad specification polymer, and the third layer has a material of
construction of a high molecular weight polyolefin.
35. The integral geogrid according to claim 34, wherein the high
molecular weight polyolefin of the first layer is a polypropylene,
the broad specification polymer of the second layer is a
post-industrial polypropylene, and the high molecular weight
polyolefin of the third layer is a polypropylene.
36. The integral geogrid according to claim 29, wherein the
plurality of interconnected, oriented strands includes transverse
strands interconnected by substantially longitudinally oriented
strands.
37. The integral geogrid according to claim 29, wherein the
integral geogrid is configured for structural or construction
reinforcement purposes.
38. A starting material for making an integral geogrid comprising a
multilayer polymer starting sheet having layers of different
materials and formed in a single coextrusion, and having holes or
depressions therein that provide openings when the starting sheet
is uniaxially or biaxially stretched.
39. The starting material according to claim 38, wherein the
coextruded multilayer polymer starting sheet includes a first
layer, a second layer, and a third layer, with the first layer and
the third layer being arranged on opposite planar surfaces of the
second layer.
40. The starting material according to claim 38, wherein the
coextruded multilayer polymer starting sheet has an initial
thickness of at least 2 mm.
41. The starting material according to claim 38, wherein the
coextruded multilayer polymer starting sheet has a stretched
thickness of from about 0.2 mm to about 9 mm.
42. The starting material according to claim 38, wherein the
coextruded multilayer polymer starting sheet once stretched
exhibits an increased flexural stiffness and torsional rigidity
relative to the flexural stiffness and torsional rigidity of a
non-coextruded sheet having a substantially same starting
thickness.
43. A soil construction comprising a mass of particulate material
strengthened by embedding therein an integral geogrid as claimed in
claim 29.
44. A method of strengthening a mass of particulate material,
comprising embedding in the mass of particulate material the
integral geogrid as claimed in claim 29.
45. A method of making an integral geogrid, comprising: providing a
multilayer polymer starting sheet having layers of different
materials and formed in a single coextrusion; providing a patterned
plurality of holes or depressions in the coextruded multilayer
polymer starting sheet; and orienting the coextruded multilayer
polymer starting sheet having the patterned plurality of holes or
depressions therein to provide a plurality of interconnected,
oriented strands and to configure the holes or depressions as grid
openings.
46. The method according to claim 45, wherein the coextruded
multilayer polymer starting sheet having the patterned plurality of
holes or depressions therein is oriented by uniaxial or biaxial
stretching.
47. The method according to claim 45, wherein the coextruded
multilayer polymer starting sheet includes a first layer, a second
layer, and a third layer, with the first layer and the third layer
being arranged on opposite planar surfaces of the second layer.
48. The method according to claim 45, wherein the coextruded
multilayer polymer starting sheet has an initial thickness of at
least 2 mm.
49. The method according to claim 45, wherein the first layer has a
thickness of from about 0.5 mm to about 4.5 mm, the second layer
has a thickness of from about 1 mm to about 9 mm, and the third
layer has a thickness of from about 0.5 mm to about 4.5 mm.
50. The method according to claim 45, wherein the first layer has a
material of construction of a high molecular weight polyolefin, the
second layer has a material of construction of a broad
specification polymer, and the third layer has a material of
construction of a high molecular weight polyolefin.
51. A method of providing an integral geogrid construction,
comprising: uniaxially or biaxially stretching a starting material
that is a multilayer polymer starting sheet having layers of
different materials and formed in a single coextrusion, and having
a patterned plurality of holes or depressions therein, to provide
an integral geogrid having a plurality of oriented strands and a
plurality of grid openings; and embedding the integral geogrid in a
mass of particulate material.
52. The integral geogrid according to claim 29, wherein the
integral geogrid is a triaxial integral geogrid.
53. The method according to claim 45, wherein the integral geogrid
is a triaxial integral geogrid.
54. The method according to claim 45, wherein the integral geogrid
is a uniaxial integral geogrid.
55. The method according to claim 45, wherein the integral geogrid
is a biaxial integral geogrid.
56. The method according to claim 45, wherein the integral geogrid
includes a color identification layer.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of priority to U.S.
Provisional Application for Patent No. 62/239,416 filed Oct. 9,
2015.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates generally to integral geogrids
and other oriented grids used for structural or construction
reinforcement and other geotechnical purposes, More particularly,
the present invention relates to such integral geogrids made from a
coextruded multilayer polymer sheet in order to achieve
enhance& stiffness characteristics, as well as other desirable
characteristics as disclosed herein.
[0003] This invention also relates to the method of producing such
integral geogrids. Lastly, the present invention relates to the use
of such integral geogrids for soil and particulate reinforcement
and methods of such reinforcement.
[0004] For the purpose of this invention, the term "integral
geogrid" is intended to include integral geogrids and other
integral grid structures made by orienting (stretching) a polymeric
starting material in the form of a sheet or a sheet-like shape of a
requisite thickness and having holes or depressions made or formed
therein.
2. Description of the Prior Art
[0005] Polymeric integral grid structures having mesh openings
defined by various geometric patterns of substantially parallel,
orientated strands and junctions therebetween, such as integral
geogrids, have been manufactured for over 25 years. Such grids are
manufactured by extruding an integrally cast sheet which is
subjected to a defined pattern of holes or depressions followed by
the controlled uniaxial or biaxial stretching and orientation of
the sheet into highly oriented strands and partially oriented
junctions defined by mesh openings formed by the holes or
depressions. Such stretching and orienting of the sheet in either
uniaxial or biaxial directions develops strand tensile strength and
modulus in the corresponding stretch direction. These integral
oriented polymer grid structures can be used for retaining or
stabilizing particulate material of any suitable form, such as
soil, earth, sand, clay, gravel, etc.
[0006] and in any suitable location, such as on the side of a road
or other cutting or embankment, beneath a road surface, runway
surface, etc.
[0007] Various shapes and patterns of holes have been experimented
with to achieve higher levels of strength to weight ratio, or to
achieve faster processing speeds during the manufacturing process.
Orientation is accomplished under controlled temperatures and
strain rates. Some of the variables in this process include draw
ratio, molecular weight, molecular weight distribution, and degree
of branching or cross linking of the polymer.
[0008] The manufacture and use of such integral geogrids and other
integral grid structures can be accomplished by well-known
techniques. As described in detail in U.S. Pat. No. 4,374,798 to
Mercer, U.S. Pat. No. 4,590,029 to Mercer, U.S. Pat. No. 4,743,486
to Mercer and Martin, U.S. Pat. No. 4,756,946 to Mercer, and U.S.
Pat. No. 5,419,659 to Mercer, a starting polymeric sheet material
is first extruded and then punched to form the requisite defined
pattern of holes or depressions. The integral geogrid is then
formed by the requisite stretching and orienting the punched sheet
material
[0009] Such integral geogrids, both uniaxial integral geogrids and
biaxial integral geogrids (collectively "integral geogrids," or
separately "uniaxial integral geogrid(s)" or "biaxial integral
geogrid(s)") were invented by the aforementioned Mercer in the late
1970 s and have been a tremendous commercial success over the past
30 years, totally revolutionizing the technology of reinforcing
soils, roadway underpavements and other civil engineering
structures made from granular or particulate materials.
[0010] Mercer discovered that by starting with a relatively thick,
substantially uniplanar polymer starting 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 whose centers lie on a
notional substantially square or rectangular grid of rows and
columns, and stretching the starting sheet either unilaterally or
biaxially so that the orientation of the strands extends into the
junctions, a totally new substantially uniplanar integral geogrid
could be formed. As described by Mercer, "uniplanar" means that all
zones of the sheet-like material are symmetrical about the median
plane of the sheet-like material.
[0011] In U.S. Pat Nos. 3,252,181, 3,317,951, 3,496,965, 4,470,942,
4,808,358 and 5,053,264, the starting material with the requisite
pattern of holes or depressions is formed in conjunction with a
cylindrical polymer extrusion and substantial uniplanarity is
achieved by passing the extrusion over an expanding mandrel. The
expanded cylinder is then slit longitudinally to produce a flat
substantially uniplanar starting sheet.
[0012] Another integral geogrid is described in U.S. Pat. No.
7,001,112 to Walsh (hereinafter the "Walsh '112 patent"), assigned
to Tensar international Limited, an associated company of the
assignee of the instant application for patent, Tensar
International Corporation, Inc. (hereinafter "Tensar") of Atlanta,
Georgia. The Walsh '112 patent discloses oriented polymer integral
geogrids including a biaxially stretched integral geogrid in which
oriented strands form triangular mesh openings with a partially
oriented junction at each corner, and with six highly oriented
strands meeting at each junction (hereinafter sometimes referred to
herein as "triaxial integral geogrid").
[0013] It is intended that the present invention be applicable to
all integral grids regardless of the method of starting sheet
formation or of the method of orienting the starting material into
the integral geogrid or grid structure.
[0014] The subject matter of the foregoing U.S. Pat. Nos.
3,252,181, 3,317,951, 3,496,965, 4,470,942, 4,808,358, 5,053,264
and 7,001,112 is expressly incorporated into this specification by
reference as if the disclosures were set forth herein in their
entireties. These patents are cited as illustrative, and are not
considered to be inclusive, or to exclude other techniques known in
the art for the production of integral polymer grid materials.
[0015] Traditionally, the polymeric materials used in the
production of integral geogrids have been high molecular weight
homopolymer or copolymer polypropylene, and high density, high
molecular weight polyethylene. Various additives, such as
ultraviolet light inhibitors, carbon black, processing aids, etc.,
are added to these polymers to achieve desired effects in the
finished product and/or manufacturing efficiency.
[0016] And, also traditionally, the starting material for
production of such an integral geogrid has typically been a
uniplanar sheet that has a monolayer construction, i.e., a
homogeneous single layer of a polymeric material.
[0017] While an integral geogrid produced from the above-described
conventional starting materials exhibits generally satisfactory
properties, it is structurally and economically advantageous to
produce an integral geogrid having a relatively higher degree of
stiffness suitable for the demands of services such as geosynthetic
reinforcement or having other properties desirable for particular
geosynthetic applications.
[0018] Therefore, a need exists for a starting material not only
that is suitable for the process constraints associated with the
production of integral geogrids, but also that once the integral
geogrid has been produced and is in service, provides a higher
degree of stiffness than that associated with conventional geogrid
starting materials or provides other desirable properties not
available with current monolayer integral geogrids.
SUMMARY OF THE INVENTION
[0019] To attain the aforementioned higher degree of stiffness and
other desirable characteristics, the present invention employs a
coextruded multilayer polymer sheet as the starting material for
the fabrication of the integral geogrid.
[0020] The experiments described herein support the inventors'
theory that by virtue of the inventive construction, the coextruded
multilayer sheet components provide a crystalline synergistic
effect during extrusion and orientation, resulting in enhanced
material properties that provide performance benefits to use of the
integral geogrid in soil geosynthetic reinforcement.
[0021] According to one embodiment of the present invention, a
starting material for making an integral geogrid includes a
coextruded multilayer polymer sheet having holes or depressions
therein that provide openings when the starting material is
uniaxially or biaxially stretched.
[0022] According to another embodiment of the present invention, an
integral geogrid includes a plurality of highly oriented strands
interconnected by partially oriented junctions and having an array
of openings therein that is produced from a coextruded multilayer
polymer sheet. According to one embodiment of the invention, the
integral geogrid is a triaxial integral geogrid.
[0023] According to still another embodiment of the present
invention, a soil construction includes a mass of particulate
material strengthened by embedding therein an integral geogrid
produced from a coextruded multilayer polymer sheet.
[0024] According to yet another embodiment of the present
invention, a method of making a starting material for an integral
geogrid includes providing a coextruded multilayer polymer sheet,
and providing holes or depressions therein.
[0025] According to another embodiment of the present invention, a
method of making an integral geogrid includes providing a
coextruded multilayer polymer sheet, providing holes or depressions
therein, and uniaxially or biaxially stretching the coextruded
multilayer polymer sheet having the holes or depressions therein so
as to provide a plurality of highly oriented strands interconnected
by partially oriented junctions and having an array of the openings
therein. According to one embodiment of the invention, the method
produces a triaxial integral geogrid from a coextruded multilayer
polymer sheet.
[0026] And, according to yet another embodiment of the present
invention, a method of strengthening a mass of particulate material
includes embedding in the mass of particulate material an integral
geogrid produced from a coextruded multilayer polymer sheet.
[0027] Accordingly, it is an object of the present invention to
provide a starting material for making an integral geogrid. The
starting material includes a coextruded multilayer polymer sheet
having holes or depressions therein that provide openings when the
starting material is uniaxially or biaxially stretched.
[0028] Another object of the present invention is to provide an
integral geogrid having a plurality of highly oriented strands
interconnected by partially oriented junctions and having an array
of openings therein that is produced from a coextruded multilayer
polymer sheet. An associated object of the invention is to provide
an integral geogrid characterized by a higher degree of stiffness,
a greater strength, and other desirable characteristics.
Specifically, an object of the present invention is to provide a
triaxial integral geogrid from a coextruded multilayer polymer
sheet.
[0029] Still another object of the present invention is to provide
a soil construction that includes a mass of particulate material
strengthened by embedding therein an integral geogrid produced from
a coextruded multilayer polymer sheet.
[0030] Yet another object of the present invention is to provide a
method of making a starting material for an integral geogrid that
includes providing a coextruded multilayer polymer sheet, and
providing holes or depressions therein.
[0031] Another object of the present invention is to provide a
method of making an integral geogrid. The method includes providing
a coextruded multilayer polymer sheet, providing holes or
depressions therein, and uniaxially or biaxially stretching the
coextruded multilayer polymer sheet having the holes or depressions
therein so as to provide a plurality of highly oriented strands
interconnected by partially oriented junctions and having an array
of the openings therein. The method can employ known geogrid
fabrication methods, such as those described in the aforementioned
U.S. Pat. Nos. 4,374,798, 4,590,029, 4,743,486, 5,419,659, and
7,001,112, as well as in other patents. Specifically, an object of
the present invention is to provide a method of making a triaxial
integral geogrid from a coextruded multilayer polymer sheet.
[0032] And, still another object of the present invention is to
provide a method of strengthening a mass of particulate material by
embedding in the mass of particulate material an integral geogrid
produced from a coextruded multilayer polymer sheet.
[0033] These together with other objects and advantages which will
become subsequently apparent reside in the details of construction
and operation as more fully hereinafter described, reference being
had to the accompanying drawings forming a part hereof, wherein
like reference numbers refer to like parts throughout. The
accompanying drawings are intended to illustrate the invention, but
are not necessarily to scale.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 illustrates a coextruded uniplanar multilayer sheet
starting material for an integral geogrid, before holes or
depressions are formed therein according to one embodiment of the
present invention.
[0035] FIG. 2 is a perspective plan view of the starting material
sheet shown in FIG. 1 that has the holes punched therein for
forming a triaxial integral geogrid of the type shown in the Walsh
'112 patent.
[0036] FIG. 3 is a side view of a section of the starting material
sheet shown in FIG. 2.
[0037] FIG. 4 is a plan view of a section of the triaxial integral
geogrid produced by biaxially orienting the starting material sheet
shown in FIG. 2.
[0038] FIG. 5 is a perspective view of the section of the triaxial
integral geogrid shown in FIG. 4.
[0039] FIG. 6 is an enlarged perspective view of the section of the
triaxial integral geogrid shown in FIG. 4.
[0040] FIG. 7 is a side cross-sectional view of the section of the
triaxial integral geogrid shown in FIG. 4.
[0041] FIG. 8 is a table summarizing aperture stability modulus
properties for an experimental triaxial integral geogrid produced
from a 3 mm coextruded uniplanar multilayer sheet starting material
such as shown in FIGS. 1-7 to be compared with similar properties
of a triaxial integral geogrid commercially available from Tensar
as a TriAx.RTM. TX140.TM. geogrid.
[0042] FIG. 9 is a table comparing various product properties of
triaxial integral geogrids commercially available from Tensar
(produced from extruded monolayer sheets) with corresponding
various product properties of experimental triaxial integral
geogrids as shown in FIGS. 4-7 produced from coextruded uniplanar
multilayer sheets according to the present invention.
[0043] FIG. 10 is another table comparing various product
properties of triaxial integral geogrids commercially available
from Tensar (produced from extruded monolayer sheets) with
corresponding product properties of experimental triaxial integral
geogrids produced from coextruded uniplanar multilayer sheets
according to the present invention.
[0044] FIG. 11 is a perspective view of a section of a triaxial
integral geogrid according to another embodiment of the present
invention.
[0045] FIG. 12 is a plan view of the section of the triaxial
integral geogrid shown in FIG. 11.
[0046] FIG. 13 is a side cross-sectional view of the section of the
triaxial integral geogrid shown in FIG. 11.
[0047] FIG. 14 illustrates a coextruded uniplanar multilayer sheet
starting material for an integral geogrid, before holes or
depressions are formed therein according to another embodiment of
the present invention.
[0048] FIG. 15 is a perspective view of a section of a triaxial
integral geogrid associated with the starting material sheet shown
in FIG. 14.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0049] Although only preferred embodiments of the invention are
explained in detail, it is to be understood that the invention is
not limited in its scope to the details of construction and
arrangement of components set forth in the following description or
illustrated in the drawings. The invention is capable of other
embodiments and of being practiced or carried out in various
ways.
[0050] Also, in describing the preferred embodiments, terminology
will be resorted to for the sake of clarity. It is intended that
each term contemplates its broadest meaning as understood by those
skilled in the art, and includes all technical equivalents which
operate in a similar manner to accomplish a similar purpose.
[0051] And, as used herein, the terms "coextruded," "coextruding,"
and "coextrusion" are used according to their commonly accepted
definition, i.e., pertaining to a single-step process starting with
two or more polymeric materials that are simultaneously extruded
and shaped in a single die to form a multilayer sheet.
[0052] The present invention is directed to uniaxial, biaxial, and
triaxial integral geogrid structures produced from a coextruded
multilayer polymer sheet as the starting material. The coextruded
multilayer polymer sheet starting material can be, for example,
uniplanar, or can be non-uniplanar, depending upon the particular
characteristics that are desired for the multilayer geogrid
structure that is to be fabricated therefrom. According to a
preferred embodiment of the invention, the coextruded multilayer
polymer sheet starting material is uniplanar or substantially
uniplanar.
[0053] The invention is based on the fact that extrusion of the
coextruded multilayer sheet consisting of different polymeric
materials or other extrudable materials at varying percentage
content when converted to uniaxial, biaxial, and/or triaxial
integral geogrids via a sheet punching and oven stretching process,
produces a finished product that has unique characteristics
relative to the traditional uniaxial, biaxial, and triaxial
geogrids for purposes of soil reinforcement and other geotechnical
applications.
[0054] FIG. 1 illustrates a coextruded multilayer sheet 100 used as
a starting material for an integral geogrid according to one
embodiment of the present invention, before the sheet has been
through-punched or depressions formed therein.
[0055] As shown in FIG. 1, the coextruded multilayer sheet 100 is a
three-layer sheet embodiment of the invention. That is, preferably,
sheet 100 includes a first layer 110, a second layer 120, and a
third layer 130. The first layer 110 and the third layer 130 are
arranged on opposite planar surfaces of second layer 120,
preferably in a uniplanar or substantially uniplanar configuration.
Further, while the three-layer configuration of sheet 100 is shown
for purposes of illustration, the invention contemplates the use of
a sheet having multiple layers arranged in various configurations,
multiple layers having various combinations of thicknesses, and
multiple layers having various materials of construction, all as
dictated by the particular application in which the integral
geogrid is to be employed. For example, while the three-layer
configuration of sheet 100 is shown for purposes of illustration,
the invention also contemplates the use of coextruded sheets having
more than three layers. In general, the layer configuration, the
layer thicknesses, and the materials of construction of the layers
are selected to provide not only ease of fabrication of the
integral geogrid, but also an integral geogrid having the desired
degree of stiffness and other performance properties.
[0056] As described above, the coextruded multilayer sheet 100 used
as the starting material for an integral geogrid according to the
present invention is preferably through-punched, although it may be
possible to use depressions formed therein instead. According to
the embodiment of the starting material in which depressions are
formed in the sheet, the depressions are provided on each side of
the sheet, i.e., on both the top and the bottom of the sheet.
Further, the depressions extend into each layer of the coextruded
multilayer sheet.
[0057] In the particular embodiment of the invention shown in FIG.
1, the 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 in a
manner known to those skilled in the art of extruding multi-layer
sheets.
[0058] According to a preferred embodiment of the invention, the
overall thickness of the sheet 100 is from about 2 mm to about 12
mm and, according to a more preferred embodiment of the invention,
the overall thickness of the sheet 100 is from about 2 mm to about
6 mm.
[0059] With regard to the individual thicknesses of the sheet
layers, according to a preferred embodiment of the invention, the
thickness of the first layer 110 is from about 0.5 mm to about 4.5
mm, the thickness of the second layer 120 is from about 1 mm to
about 9 mm, and the thickness of the third layer 130 is from about
0.5 mm to about 4.5 mm, keeping in mind that the overall thickness
of the sheet 100 is from about 2 mm 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 mm to about 2 mm, the
thickness of the second layer 120 is from about 2 mm to about 5 mm,
and the thickness of the third layer 130 is from about 0.5 mm to
about 2 mm.
[0060] In general, the material of construction of the first layer
110, the second layer 120, and the third layer 130 may be the same
as each other, 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 as
each other, or may be different from one another. More preferably,
material of construction of the second layer 120 is different from
the material of construction of both the first layer 110 and the
material of construction of the third layer 130.
[0061] And, in general, the layers of the sheet are polymeric in
nature. For example, the materials of construction may include high
molecular weight polyolefins, and broad specification polymers.
Further, the polymeric materials may be virgin stock, or may be
recycled materials, such as, for example, post-industrial or
post-consumer recycled polymeric materials. And, the use of one or
more polymeric layers having a lower cost than that of the
aforementioned high molecular weight polyolefins and broad
specification polymers is also contemplated. The use of such a
lower cost polymeric layer may result in a cost savings of
approximately 20% to approximately 30% relative to the use of, for
example, a polypropylene layer.
[0062] 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, a
polypropylene ("PP"). And, according to the same preferred
embodiment, the material of construction of the second layer 120 is
a broad specification polymer, such as, for example, a virgin PP,
or a recycled PP, such as, for example, a post-industrial PP or
other recycled PP. However, depending upon the particular
application of the integral geogrid, polymeric components having a
material of construction other than polypropylene may be included
in the coextruded multilayer sheet.
[0063] FIGS. 2 and 3 illustrate the coextruded multilayer sheet
starting material 100 of FIG. 1 that has holes 140 punched therein
for forming the triaxial integral geogrid 200 shown in FIGS. 4, 5,
and 6. The size and spacing of the holes 140 are as disclosed in
the Walsh '112 patent. The triaxial integral geogrid 200 includes
highly oriented strands 205 and partially oriented junctions 235,
also as disclosed in the Walsh '112 patent. The upper layer 130 of
the starting material 100 has been stretched and oriented into the
upper layer 230 of the strands 205 and junctions 235. Similarly,
the third or lower layer 110 of the starting material 100 has been
stretched and oriented into the lower or underneath layer 210 of
the strands 205 and junctions 235. As the first layer 130 and third
layer 110 are being stretched and oriented, the second or middle
layer 120 is also being stretched and oriented into middle layer
220 of both the strands 205 and junctions 235.
[0064] The invention also relates to a method of making the
above-described triaxial integral geogrid 200. The method includes:
providing the coextruded multilayer polymer sheet 100; forming a
plurality of holes or depressions in the coextruded multilayer
polymer sheet 100 in a selected pattern, such as in accordance with
the disclosure of the Walsh '112 patent; and biaxially stretching
and orienting the coextruded multilayer polymer sheet having the
patterned plurality of holes or depressions therein to form an
integral geogrid having a plurality of interconnected, oriented
strands between partially oriented junctions and to configure the
holes or depressions as grid openings.
[0065] In general, once the coextruded multilayer polymer sheet 100
has been prepared with holes or depressions, the triaxial integral
geogrid 200 can be produced from the sheet 100 according to the
methods described in the above-identified patents and known to
those skilled in the art.
[0066] To demonstrate the enhanced characteristics and properties
of the inventive integral geogrid produced from the coextruded
multilayer sheet, comparative tests were performed.
[0067] FIG. 8 is a table summarizing aperture stability modulus
properties for an experimental triaxial integral geogrid produced
from a 3 mm coextruded sheet starting material to be compared with
similar properties of a triaxial integral geogrid commercially
available from Tensar as a TriAx.RTM. TX140.TM. geogrid. The
experiment was performed according to the testing protocols of ASTM
D7864, i.e., the "Standard Test Method for Determining the Aperture
Stability Modulus of Geogrid." The aperture stability testing was
performed on triaxial integral geogrid samples made from a 3 mm
thick coexruded multilayer sheet that included 50% BSR ("broad
specification resin") that had been punched. and stretched. The
first i.e., lower, layer 110 of the coextruded multilayer sheet had
a material of construction of a high molecular weight polypropylene
(PP) and a thickness of 0.75 mm; the second, i.e., middle, layer
120 had a material of construction of a broad specification PP and
a thickness of 1.50 mm; and the third, i.e., upper, layer 130 had a
material of construction of a high molecular weight PP and a
thickness of 0.75 mm.
[0068] For the experimental laboratory-prepared triaxial integral
geogrid made from the coextruded multilayer sheet, the average
value for a moment of 20 cm-kg was 70 cm-kg/deg. Conversely, for
the non-coextruded, i.e., monolayer sheet, specifically from six
tests of the standard Triax.RTM. TX140.TM. geogrids, the average
value of the tests was 2.86 cm-kg/deg, with a range of 2.52 to 3.14
cm-kg/deg, substantially below the average value recorded for the
experimental multilayer samples.
[0069] FIG. 9 also illustrates various product properties of
triaxial integral geogrids produced from monolayer extruded sheets
with corresponding product properties of triaxial integral geogrids
produced from coextruded multilayer sheets according to the present
invention. In the tests summarized in FIG. 9, the monolayer sheets
were processed to have the configuration of the triaxial integral
geogrid described in the Walsh '112 patent. Such a triaxial
integral geogrid is commercially available from Tensar, and is
known as the TriAx.RTM. TX160.TM. geogrid.
[0070] For the comparative experiments shown in FIG. 9, coextruded
3-layer sheets in 4.6 mm finished sheet thicknesses were prepared.
The various sheets incorporated different loadings of
post-industrial polypropylene (PP) content, and each of the
coextruded 3-layer sheets was then processed into a triaxial
integral geogrid comparable to Tensar's TriAx.RTM. TX160.TM.
geogrid.
[0071] With regard to FIG. 9, each of the 4.6 mm coextruded
multilayer sheets included the following layer compositions: Sample
(1) a first or upper layer 130, as described above, of 34% virgin
polypropylene (PP) and black masterbatch ("MB," i.e., black carbon
to provide a black color to the product for UV protection)/a second
or middle layer 120, as described above, of 32% post-industrial
PP/and a third or lower layer 110, as described above, of 34%
virgin PP and MB; and Sample (2) 25% virgin PP and MB/50%
post-industrial PP/25% virgin PP and MB.
[0072] The thickness of each of the above-described layers for the
various sheet Samples (1) and (2) is as follows. For the 4.6 mm
multilayer sheet Sample (1), the thicknesses of the layers were,
respectively: 1.56 mm/1.47 mm/1.56 mm. For the 4.6 mm multilayer
sheet Sample (2), the thicknesses of the layers were, respectively:
1.15 mm/2.30 mm/1.15 mm.
[0073] As is evident from the results presented in FIG. 9, the
resultant experimental triaxial integral geogrids produced from the
above-described punched and oriented 4.6 mm coextruded 3-layer
sheet samples resulted in a product, versus the standard
monolayered Triax.RTM. TX160.TM. geogrid with the approximate
equivalent starting sheet thickness (4.7 mm), that exhibited
substantially higher product stiffness as measured per standard
Tensar low strain tensile modulus testing, flexural stiffness
testing, and aperture stability testing. The 0.5% and 2.0% strain
tensile modulus test values were more than 30% stronger for the
experimental triaxial geogrids produced from the 4.6 mm coextruded
3-layer starting sheet than from the conventional Triax.RTM.
TX160.TM. geogrids produced from the 4.7 mm monolayered sheet.
Similarly, the flexural stiffness measured more than 33% higher for
the experimental triaxial geogrids produced from the 4.6 mm
coextruded sheet than the standard Triax.RTM. TX160.TM. geogrid
made from a 4.7 mm monolayered starting sheet.
[0074] FIG. 10 is another table comparing various product
properties of triaxial integral geogrids produced from monolayer
sheets commercially available from Tensar with corresponding
product properties of experimental triaxial integral geogrids
produced from coextruded multilayer sheets according to the present
invention. In the tests summarized in FIG. 10, the monolayer sheets
were also processed to have the configuration of the triaxial
integral geogrid described in the Walsh '112 patent. Such a
triaxial integral geogrid is commercially available from Tensar,
and is known as the TriAx.RTM. TX140.TM. geogrid.
[0075] For the comparative experiments shown in FIG. 10, coextruded
3-layer sheets in 3.0 mm finished sheet thicknesses were prepared.
The various sheets incorporated different loadings of
post-industrial polypropylene (PP) content, and each of the
coextruded 3-layer sheets was then processed into a triaxial
integral geogrid comparable to Tensar's TriAx.RTM. TX140.TM.
geogrid.
[0076] With regard to FIG. 10, Sheet "SN20140407" had the following
composition: 32% broad specification 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., lower) layer 110.
Sheet "SN20140408" had the following composition: 50% broad
specification resin in the second (i.e., middle) layer, and 25%
high molecular weight PP in the first layer and in the third layer.
Sheet "SN20140409" had the following composition: 60% broad
specification resin in the second (i.e., middle) layer, and 20%
high molecular weight PP in the first layer and in the third
layer.
[0077] The thickness of each of the above-described layers for
Sheet SN20140407, Sheet SN20140408, and Sheet SN20140409 is as
follows. For the 3 mm multilayer Sheet SN20140407, the thicknesses
of the first, the second, and the third layers were, respectively:
1.02 mm/0.96 mm/1.02 mm. For the 3 mm multilayer Sheet SN20140408,
the thicknesses of the layers were, respectively: 0.75 mm/1.5
mm/0.75 mm. For the 3 mm multilayer Sheet SN20140409, the
thicknesses of the layers were, respectively: 0.6 mm/1.8 mm/0.6
mm.
[0078] As is evident from the results reported in FIG. 10, the 3.0
mm starting sheet thickness with post-industrial PP content of 32%
(SN20140407), 50% (SN20140408), and 60% (SN20140409), when
converted to a finished triaxial integral geogrid, exceeded the
only specified tensile modulus test for Triax.RTM. TX140.TM.
geogrid produced from a 3.7 mm thick sheet which is 220 kN/m in the
transverse direction ("TD"). FIG. 10 also shows that each of the
coextruded samples, starting with the thinner 3.0 mm sheet, met or
exceeded the average tensile modulus values of standard Triax.RTM.
TX140.TM. geogrid produced from a 3.7 mm sheet.
[0079] Again, the experiments described herein support the
inventors' concept that by virtue of utilizing a multi-layer
construction for the starting material sheet, the coextruded
multilayer sheet components can provide a crystalline synergistic
effect during extrusion and orientation, thus providing enhanced
material properties in the resultant integral geogrid and
performance benefits when using the resultant integral geogrid in
soil and other geotechnical applications.
[0080] Other possible embodiments of the instant invention can
include, for example, (1) multilayer coextruded polymer sheet
starting materials having significantly higher levels of
post-industrial and post-consumer PP resins, i.e., PP resins that
have a relatively low cost, (2) foaming agents to provide a foamed
or expanded second (i.e., middle) layer, (3) one or more relatively
low cost layers that include bulking agents or fillers, (4) a color
identification layer within the integral geogrid, and (5) a 3-layer
coextruded polymer sheet with HDPE outer layers and an amorphous
and crystalline polyester inner layer sandwiched therebetween. Each
of the above examples would provide an enhancement or satisfy a
need for an integral geogrid having enhanced geosynthetic aggregate
reinforcement, cost reduction and/or identification properties.
[0081] More specifically, as indicated above, one possible
embodiment of the instant invention could include the use of a
foaming agent to provide a foamed or expanded second or middle
layer. FIGS. 11, 12, and 13 are directed to such an embodiment 300,
in which the second or middle layer (here designated as 320) of the
coextruded multilayer sheet forms an expanded or "foamed" structure
That is, according to this embodiment of the invention, a chemical
foaming agent is mixed with the polymer that is extruded to form
the second layer. The heat that is generated to melt the polymer
decomposes the chemical foaming agent, which results in the
liberation of a gas. The gas is then dispersed in the polymer melt,
and expands upon exiting the die. As a result, the second layer is
expanded or foamed (see FIG. 13, which is a side cross-sectional
view of the section of the integral triaxial geogrid shown in FIG.
11.)
[0082] According to this embodiment of the invention, as with the
above-described first embodiment, 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 as each other, or may be
different from one another, 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.
[0083] 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 also may include
desirable physical and chemical properties of the foamed layer per
se.
[0084] As indicated above, one possible embodiment of the instant
invention could include the use of a color identification layer
with the integral geogrid. For example, the American Association of
State Highway and Transportation Officials ("AASHTO") requires, in
conjunction with the National Transportation Product Evaluation
Program ("NTPEP"), a product marker for geosynthetic reinforcements
associated with walls, slopes, and fills over soft ground.
[0085] The above-described color identification layer could be, for
example, a polymeric layer having a color that differs from the
color of an adjacent, or an associated, co-extruded layer. The
color identification layer could be an inner layer or an outer
layer of the integral geogrid, or the integral geogrid could
include multiple color identification layers of either the same
color or a variety of colors. The color identification layer could
be a solid color, or could have a pattern, such as incorporating a
stripe. The color and/or chemistry of the color identification
layer is selected, of course, based upon the requirements of a
particular application of the integral geogrid.
[0086] In addition to the above-described use of the integral
geogrid's color identification layer for compliance with AASHTO and
NTPEP standards, the color identification layer can also serve to
provide source identification of the integral geogrid.
[0087] As indicated above, while the three-layer configuration of
sheet 100 has been shown for purposes of illustration, the
invention also contemplates the use of coextruded sheets having
more than three layers. For example, the coextruded sheet can be 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
arranged on opposite planar surfaces of middle layer 420,
preferably in a uniplanar or substantially uniplanar configuration.
The first outer layer 440 and the second outer layer 450 are
arranged on opposite planar surfaces of, respectively, first inner
layer 410 and second inner layer 430, preferably in a uniplanar or
substantially uniplanar configuration.
[0088] In the particular embodiment of the invention shown in FIG.
14, the 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 that forms the second outer layer 450, in a manner
known to the those skilled in the art of extruding multi-layer
sheets.
[0089] In general, the material 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 as each other, or may be 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. In summary, depending upon the particular service
application in which the integral geogrid made from the sheet 400
is to be employed, various combinations of materials of
construction for the above-described five layers may be used.
[0090] FIG. 15 is a perspective view of a section of a triaxial
integral geogrid 500 associated with the starting material sheet
400 shown in FIG. 14. The triaxial integral geogrid 500 includes
highly oriented strands 505 and partially oriented junctions 535.
After holes have been punched in sheet 400, the first outer layer
440 and the second outer layer 450 of sheet 400 have been stretched
and oriented into, respectively, the first outer layer 540 and the
second outer layer 550 of the strands 505 and junctions 535.
Similarly, the first inner layer 410 and the second inner layer 430
of sheet 400 have been stretched and oriented into, respectively,
the first inner layer 510 and the second inner layer 530 of the
strands 505 and junctions 535. And, as the first outer layer 440
and the second outer layer 450, and the first inner layer 410 and
the second inner layer 430 are being stretched and oriented, the
middle layer 420 is also being stretched and oriented into middle
layer 520 of both the strands 505 and junctions 535.
[0091] As also indicated above, one possible embodiment of the
instant invention could include the use of one or more relatively
low cost layers that include bulking agents or fillers. The
inclusion of such bulking agents or fillers in the layers of the
integral geogrid create a product having a thicker, i.e., loftier,
profile, which can lead to enhanced performance of the integral
geogrid in certain service applications. Depending upon the service
application in which the integral geogrid is to be employed, such
bulking agents or fillers, may include, for example, one or more of
CaCO.sub.3 (calcium carbonate), talc, CaSiO.sub.3 (wollastonite),
nano-fillers, multi-wall carbon nanotube ("MWCNT"), single wall
carbon nanotube ("SWCNT"), glass fibers, and aluminum hydrate.
[0092] As described earlier above, the use of one or more polymeric
layers having a lower cost than that of high molecular weight
polyolefins and broad specification polymers is contemplated. In an
embodiment in which such a lower cost polymeric layer also includes
the aforementioned bulking agent or filler, a cost savings of
approximately 20% relative to the use of, for example, a
polypropylene layer, may result.
[0093] And, of course, use of the above-described foam layer can
also create a product having a thicker, i.e., loftier, profile,
which can also lead to enhanced performance of the integral geogrid
in certain service applications. Contemplated embodiments of the
invention include those in which one or more of the foamed layers
are used in conjunction with one or more layers that include the
bulking agents or fillers.
[0094] In general, the instant invention is based on employing the
coextrusion techniques and materials described herein to modify and
enhance certain physical, chemical, and/or mechanical properties of
an integral geogrid so as to improve the performance of the
integral geogrid in a particular application thereof.
[0095] The foregoing is considered as illustrative only of the
principles of the invention. Further, since numerous modifications
and changes may readily occur to those skilled in the art, it is
not desired to limit the invention to the exact construction and
operation described and shown.
* * * * *