JP5397790B2 - Geocell for load bearing applications - Google Patents

Description

  The present disclosure relates to cellular confinement systems, also known as CCS or geocells suitable for use in load bearings, such as those present in roadways, railways, parking areas, and sidewalks. In particular, the geocells of the present disclosure retain their dimensions after multiple load and temperature cycles. Thus, the required infill containment is maintained throughout the design life cycle of the geocell.

  Cellular containment system (CCS) is a “honeycomb filled with granular infill, which can be non-viscous soil, sand, pebbles, gravel, crushed stone, or any other type of granular agglomerates An array of containment cells resembling a structure. CCS, also known as geocell, is mainly used for civil engineering applications that require little mechanical strength and rigidity, such as slope protection (to prevent erosion) or slope side support.

  CCS differs from other geosynthetics such as geogrid / geotextile in that the geogrid / geotextile is flat (ie, two-dimensional) and used as a planar reinforcement. Geogrids / geotextiles confine only for very limited vertical distances (usually 1-2 times the average size of the granular material) and are limited to granular materials having an average size greater than about 20 mm . This limits the use of such two-dimensional geosynthetics to relatively expensive granular materials (gravels, crushed stones and pebbles), which are low quality granular materials such as recycled asphalt, ground This is because there is little confinement or reinforcement of the concrete, fly ash and quarry waste. Conversely, CCS is a three-dimensional structure that provides confinement in all directions (ie, along the entire cross section of each cell). Furthermore, the multi-cell geometry provides a passive resistance that increases the holding force. Unlike two-dimensional geosynthetics, geocells contain and reinforce granular materials that have an average particle size of less than about 20 mm and, in some cases, materials that have an average particle size of about 10 mm or less.

Geocells are manufactured by some global companies including Presto. Presto's geocell, as well as most of its imitations, are made of polyethylene (PE). The polyethylene (PE) can be high density polyethylene (HDPE) or medium density polyethylene (MDPE). The term “HDPE” refers hereinafter to polyethylene characterized by a density greater than 0.940 g / cm ³ . The term medium density polyethylene (MDPE) refers to a polyethylene characterized by density of up to 0.940 g / cm ³ greater than the 0.925 g / cm ^3. The term low density polyethylene (LDPE) refers to polyethylene characterized by a density of 0.91 to 0.925 g / cm ³ .

  Geocells made from HDPE and MDPE are either smooth or textured. Textured geocells are most common on the market because their texture can add some friction between the infill and the geocell walls. Theoretically, HDPE can have a tensile strength (yield or tensile stress at the point of failure) of greater than 15 megapascals (MPa), but in practice its strength when samples are taken from the geocell wall and tested according to ASTM D638. Is insufficient for load bearing applications such as roadways and railways, and hardly reaches 14 MPa at a high strain rate of 150% / min.

  The low properties of HDPE and MDPE are clearly visible when analyzed by dynamic mechanical analysis (DMA) according to ASTM D4065: the storage modulus at 23 ° C. is less than about 400 MPa. Storage modulus degrades dramatically with increasing temperature and is below useful levels at temperatures of about 75 ° C., limiting its use as a load bearing reinforcement. These low mechanical properties are sufficient for slope protection, but not for long-term load bearing applications that are designed for business use over 5 years.

  Another way of predicting the long term creep-related behavior of polymers is the accelerated creep test by the stepwise isothermal method (SIM) according to ASTM 6992. In this method, the polymer sample is subjected to a constant load under a stepwise temperature program. The high temperature stage accelerates creep. This method allows extrapolation of the properties of the sample over a long period of time and even over 100 years. Normally, when PE and PP are tested, the load that results in 10% plastic deformation is referred to as “long-term design strength” and is used in geosynthetics as an acceptable strength for design. Since PE and PP are under the influence of secondary creep exceeding 10% plastic deformation, loads that cause plastic deformation exceeding 10% are avoided. Secondary creep is unpredictable and PE and PP tend to cause “penetration” in this mode.

  For applications such as roadways, railways, and storage and parking lots that are subject to heavier loads, such strengths of almost less than 14 MPa are insufficient. In particular, these geocells with low mechanical properties tend to have relatively low stiffness and tend to plastically deform at strains as low as 8%. Plastic deformation loses its containment potential of the cell, essentially the main reinforcement mechanism after a short period or a few vehicle passes (a few periodic loads). For example, when a strip taken from a typical geocell in the machine direction (perpendicular to the stitching surface) is tested according to ASTM D638 at a strain rate of 20% / min or even 150% / min, at 6% strain Is less than 13 MPa, the stress at 8% strain is less than 13.5 MPa, and at 12% strain is less than 14 MPa. As a result, HDPE geocells are limited to applications where the geocell is under low load and no load-carrying infill containment is essential (eg, in soil stabilization). Geocells are not widely accepted for load bearing applications such as roadways, railways, parking areas, or heavy container storage because they tend to plastically deform at low strains.

  When a vertical load is applied to a granular material substrate, a portion of the vertical load is converted to a horizontal load or pressure. The magnitude of the horizontal load is equal to the vertical load multiplied by the horizontal earth pressure coefficient of the granular material (also known as the transverse earth pressure coefficient or LEPC). LEPC is about 0.2 to quarry waste or recycled for good materials such as pebbles and crushed stones (generally lower hard particles, so compression is very good and least plastic) For more plastic materials such as processed asphalt (material with high fines content and high plasticity), it can vary from about 0.3 to 0.4. When the granular material is moist (eg, the roadbed and the lower roadbed are saturated due to rain or flood), its plasticity increases, resulting in higher horizontal loads and increasing hoop stress on the cell walls .

式中、ＨＳは、ジオセル壁の平均フープ応力であり、ＶＰは荷重によって顆粒状材料に対外的に適用される垂直圧力である。ＬＥＰＣは、横方向の土圧係数であり、ｒは平均セル半径であり、ｄは公称セル壁厚さである。 If the granular material is confined by the geocell and the vertical load is applied from the top by static or dynamic stress (eg pressure applied by vehicle wheels or train rails), the horizontal pressure will hoop in the geocell wall Converted to stress. The hoop stress is proportional to the horizontal pressure and the average cell radius and inversely proportional to the cell wall thickness.

Where HS is the mean hoop stress of the geocell wall and VP is the normal pressure applied externally to the granular material by the load. LEPC is the lateral earth pressure coefficient, r is the average cell radius, and d is the nominal cell wall thickness.

  For example, a cell wall thickness of 1.5 millimeters (including texture, the term “wall thickness” hereinafter refers to the cell wall cross-sectional peak-to-peak distance), an average diameter of 230 millimeters (granular material Geocells made of HDPE or MDPE having a height of 200 millimeters, sand or quarry waste (LEPC 0.3) and a vertical load of 700 kilopascals (kPa) are about 16 mm. Subject to megapascal (MPa) hoop stress. As can be seen from the hoop stress equation, larger diameters or thinner walls (advantageous from an economic manufacturing point of view) are subject to significantly higher hoop stress and are therefore reinforced when manufactured with HDPE or MDPE. Does not work as much.

  A vertical load of 550 kP is common on unpaved roadways. Significantly higher loads of 700 KPa or higher may be encountered on roadways (paved and unpaved), industrial roads, or parking areas for heavy vehicles.

  Because load bearing applications, especially roadways and railways, are typically subjected to a large amount of cyclic loading, the geocell walls need to retain their original dimensions under cyclic loading with very low plastic deformation. is there. The commercial use of HDPE geocells is limited to unload-holding applications as HDPE reaches its plastic limit at typical stresses typically found in strain and load bearing applications typically around 8% Is done.

  Increased stiffness and strength, low tendency to deform at high temperature, good retention of its elasticity above ambient temperature (23 ° C.), plastic deformation under repeated and continuous loads and / or long-term service It would be desirable to provide such a geocell that has a low tendency to yield.

  Disclosed in embodiments are geocells that provide sufficient rigidity and can accept high stress without causing plastic deformation. Such geocells are suitable for load bearing applications such as paved roads, roadways, railways, parking areas, airport runways, and storage areas. Methods for making and using such geocells are also disclosed.

  In some embodiments, a geocell formed from a polymer strip is disclosed, wherein at least one polymer strip is measured in the machine direction by dynamic mechanical analysis (DMA) according to ASTM D4065 at a frequency of 1 Hz at 23 ° C. When having a storage elastic modulus of 500 MPa or more.

  The at least one polymer strip may have a storage modulus of 700 MPa or more (including a storage modulus of 1000 MPa or more).

  At least one polymer strip has a stress at 12% strain of 14.5 MPa or higher (stress at 12% strain of 16 MPa or higher, or 18 MPa at 12% strain when measured according to the Izhar procedure at 23 ° C. Including the above).

The at least one polymer strip may have a coefficient of thermal expansion of no greater than 120 × 10 ⁻⁶ / ° C. at 25 ° C. according to ASTM D696.

  Geocells can be used for paved roads, roadways, railways or parking areas. Geocell is composed of sand, pebbles, crushed stone, gravel, quarry waste, crushed concrete, recycled asphalt, crushed bricks, building debris and rough stone, crushed glass, power plant ash, fly ash, coal ash, It can be filled with a granular material selected from the group consisting of blast furnace iron slag, cement production slag, steel slag and mixtures thereof.

  A geocell formed from a polymer strip is disclosed in another embodiment and has at least one when measured in the machine direction by dynamic mechanical analysis (DMA) according to ASTM D4065 at a frequency of 63 ° C. and 1 Hz. The polymer strip has a storage modulus of 150 MPa or more.

  The at least one polymer strip may have a storage modulus of 250 MPa or more (including a storage modulus of 400 MPa or more).

  Geocells formed from polymer strips are disclosed in yet other embodiments, and when measured according to the PRS SIM procedure, at least one polymer strip has a long-term design stress of 26 MPa or greater.

  The at least one polymer strip may have a long-term design stress of 3 MPa or more (including a long-term design stress of 4 MPa or more).

  These and other embodiments are described in more detail below.

  For purposes of illustrating exemplary embodiments disclosed herein, and not for purposes of limitation, a brief description of the drawings is as follows.

It is a perspective view of a geocell.

2 is a diagram illustrating an exemplary embodiment of a polymer strip used in a geocell of the present disclosure.

6 is a diagram illustrating another exemplary embodiment of a polymer strip used in the geocell of the present disclosure.

6 is a diagram illustrating another exemplary embodiment of a polymer strip used in the geocell of the present disclosure.

6 is a graph including stress-strain results of various cells of the present disclosure for a comparative example.

2 is a graph showing a stress-strain diagram for a geocell of the present disclosure.

6 is a graph illustrating the results of an exemplary cell vertical load test of the present disclosure relative to a comparative example.

FIG. 6 is a graph of storage modulus and Tan Delta versus temperature for a control strip.

2 is a graph of storage modulus and Tan Delta versus temperature for a polymer strip used in the geocell of the present disclosure.

  The following detailed description is presented to enable one of ordinary skill in the art to make and use the embodiments disclosed herein, and illustrates the best mode envisioned for carrying out these embodiments. However, various modifications are still apparent to those skilled in the art and should be considered within the scope of this disclosure.

  A more complete understanding of the components, processes, and apparatus disclosed herein can be obtained by reference to the accompanying drawings. These drawings are schematic illustrations based solely on convenience and ease of illustrating the present disclosure, thus showing the relative sizes and dimensions of the devices or their components, and / or exemplary embodiments. It is not intended to define or limit the scope.

  FIG. 1 is a perspective view of a single layer geocell. The geocell 10 includes a plurality of polymer strips 14. Adjacent strips are joined together by distinguishable physical joints 16. The connection can be made by joining, stitching or welding, but is generally done by welding. Each strip portion between the two joints 16 forms a cell wall 18 of an individual cell 20. Each cell 20 has a cell wall made from two different polymer strips. The strips 14 are joined together to form a honeycomb pattern from multiple strips. For example, the outer strip 22 and the inner strip 24 are joined together by the physical joint 16 so that it regularly spaces along the length of the strips 22 and 24. The pair of inner strips 24 are joined together by a physical joint 32. Each joint 32 is between two joints 16. As a result, when multiple strips 14 are stretched in a direction perpendicular to the plane of the strip, the strips bend in a sinusoidal fashion to form the geocell 10. At the geocell edge where the ends of the two polymer strips 22, 24 meet, the end weld 26 (also considered a joint) is short distance from the end 28 and stabilizes the two polymer strips 22, 24. A short tail 30 is formed.

  The geocells of the present disclosure are manufactured with polymer strips having specific physical properties. In particular, a polymer strip has a yield point when measured in the machine direction (perpendicular to the stitching surface of the geocell) at a strain rate of 20% / min or 150% / min. If not, it has a stress of 14.5 MPa or more at 12% strain. In other embodiments, the polymer strip has a strain of 10% or less at a stress of 14.5 MPa when measured as described. In other words, the polymer strip can withstand a stress of 14 MPa or more without reaching the yield point. Other synonyms for yield point include yield point stress, elastic limit, or plastic limit. If the polymer strip does not have a yield point, the stress is taken into account at 12% strain. These measurements relate to the tensile properties of the polymer strip in the machine direction at 23 ° C., not its bending properties.

Because many geocells are perforated, it is generally not possible to measure stress and strain according to ASTM D638 or ISO 527 standards. Thus, the measured values are measured according to the following procedure, which is a modified version of this standard and is referred to herein as the “Izhar procedure”. A 50 mm long and 10 mm wide strip is sampled in a direction (ie, machine direction) that is parallel to the ground and perpendicular to the stitching surface of the cell. The strips are clamped so that the distance between the clamps is 30 mm. The strip is then stretched by moving the clamps away from each other at a rate of 45 millimeters (mm) per minute and converted to a strain rate of 150% / min at 23 ° C. The load applied by the strip in response to this deformation is monitored by a load cell. The stress (N / mm ² ) is calculated at different strains (the strain is the increase in length divided by the original length). The stress is calculated by dividing the load at a specific strain by the original nominal cross section (strip width multiplied by strip thickness). Since the surface of a geocell strip is usually textured, the thickness of the sample is simply measured as the “peak to peak” distance averaged between three points in the strip. (For example, a strip having an embossed diamond-like texture with a distance of 1.5 mm between the top texture on the top side and the bottom texture on the bottom side is considered 1.5 mm thick). Such a strain rate of 150% / min is associated with paved roads and railways where each load cycle is very short.

In other embodiments, the polymer strip is
A strain of up to 1.9% at a stress of 8 MPa;
A strain of up to 3.7% at a stress of 10.8 MPa;
Strain of up to 5.5% at a stress of 12.5 MPa;
A strain of up to 7.5% at a stress of 13.7 MPa;
A strain of up to 10% at a stress of 14.5 MPa;
It can be characterized as having a strain of up to 11% at a stress of 15.2 MPa; and a strain of up to 12.5% at a stress of 15.8 MPa. The polymer strip can also optionally have a strain of up to 14% at a stress of 16.5 MPa; and / or a strain of up to 17% at a stress of 17.3 MPa.

  In other embodiments, the polymer strip has a stress of at least 14.5 MPa at 12% strain; a stress of at least 15.5 MPa at 12% strain; and / or a stress of at least 16.5 MPa at 12% strain. Can be characterized as a thing.

  In other embodiments, the polymer strip can be characterized as having a storage modulus greater than or equal to 500 MPa at 23 ° C. when measured in the machine direction by dynamic mechanical analysis (DMA) at a frequency of 1 Hz. . For tensile stress-strain measurements, the thickness for DMA analysis is measured as the “peak to peak” distance averaged between three points. The DMA measurements described in this disclosure are performed according to ASTM D4065.

  In other embodiments, the polymer strip can be characterized as having a storage modulus greater than 250 MPa at 50 ° C. when measured in the machine direction by dynamic mechanical analysis (DMA) at a frequency of 1 Hz. .

  In other embodiments, the polymer strip can be characterized as having a storage modulus of 150 MPa or more at 63 ° C. when measured in the machine direction by dynamic mechanical analysis (DMA) at a frequency of 1 Hz. .

  In other embodiments, it can be characterized as having a Tan Delta of 0.32 or less at 75 ° C. when measured in the machine direction by dynamic mechanical analysis (DMA) at a frequency of 1 Hz. These novel properties exceed those of typical HDPE or MDPE geocells.

  Dynamic mechanical analysis (DMA) is a technique used to test and characterize the viscoelastic properties of polymers. In general, an oscillating force is applied to a material sample and the resulting periodic displacement of the sample is measured against a periodic load. As the elasticity increases, the time lag (phase) between load and displacement decreases. From this, the pure stiffness (storage modulus) of the sample, as well as the dissociation mechanism (loss modulus) and their ratio (Tan Delta) can be determined. DMA is also discussed at ASTM.

Another aspect of the geocell of the present disclosure is a low coefficient of thermal expansion (CTE) relative to current HDPE or MDPE. CTE is important because expansion / contraction during thermal cycling is another mechanism that imparts additional hoop stress as well. HDPE and MDPE have a CTE of about 200 × 10 ⁻⁶ / ° C. at ambient (23 ° C.), and the CTE is even higher at higher temperatures than ambient. The geocells of the present disclosure have a CTE of about 150 × 10 ⁻⁶ / ° C. or less at 23 ° C., and in certain embodiments about 120 × 10 ⁻⁶ / ° C. or less at 23 ° C. as measured according to ASTM D696. It is. The CTE of the present disclosure has a low tendency to rise at high temperatures.

Another aspect of the geocell of the present disclosure has a low creep tendency under constant load. The low creep tendency is measured according to the accelerated creep test by the stepwise isothermal method (SIM) as described in ASTM 6992. In this method, the polymer sample is subjected to a constant load under a stepped temperature program (ie, the temperature increases over a predetermined period and is held constant). The high temperature stage accelerates creep. The SIM test procedure is applied to samples having a width of 100 mm and a net length of 50 mm (distance between clamps). The sample is loaded and heated by a static load according to a procedure that includes the following steps:

  This SIM procedure is referred to herein as the “PRS SIM procedure”. The plastic strain at the end of the procedure (the increase in length irreversibility divided by the initial length) is measured. Plastic strain is measured for different loads, and a load that produces a plastic strain of 10% or less is called a “long-term design load”. The stress associated with the long-term design load (the load divided by the original width multiplied by the original width) is the “long-term design stress”, the allowable hoop stress that the geocell can withstand for long periods under static loads. give.

  A typical HDPE geocell can afford little long term design stress of 2.2 MPa when subjected to the PRS SIM procedure.

  In some embodiments, a polymer strip according to the present disclosure is characterized by a long-term design stress of 2.6 MPa or more (including a long-term design stress of 3 MPa or more, or even 4 MPa or more).

  Unlike HDPE geocells, the geocells of the present disclosure can provide very good properties up to 16% strain, and in some embodiments up to 22% strain. In particular, geocells can provide an elastic response to stresses above 14.5 MPa, thus providing the properties required for load bearing applications. The elastic response ensures that the original dimensions are fully restored when the load is removed. Geocells provide infills with higher load holding capacity and increased repulsive force that returns to its original diameter under repeated loads (ie, cyclic loads). Furthermore, the geocells of the present disclosure can be used with granular materials that are generally not available for the roadbed and lower roadbed, as further described herein. The geocells of the present disclosure also allow good load retention and fatigue resistance under humid conditions, especially when using fine grained granular materials.

  The polymer strip may further comprise a polyethylene (PE) polymer, such as HDPE, MDPE, or LDPE, which has been modified as described below.

  The polymer strip may also include a polypropylene (PP) polymer. Most PP homopolymers are highly brittle and most PP copolymers are too soft for load bearing applications, but some grades of PP polymers are useful. Such PP polymers are stiff enough for load bearing applications, but geocells are soft enough to be folded. Exemplary polypropylene polymers suitable for this disclosure include polypropylene random copolymers, polypropylene impact copolymers, blends of polypropylene and elastomers based on ethylene-propylene-diene-monomer (EPDM) or ethylene alpha-olefin copolymers, and polypropylene block copolymers. Including. Such PP polymers are commercially available as R338-02N from Dow Chemical Company; PP71EK71PS grade impact copolymers from SABIC Innovative Plastics; and PP RA1E10 random copolymers from SABIC Innovative Plastics. Exemplary elastomers based on ethylene α-olefin copolymers include Exact® elastomers manufactured by Exxon Mobil and Tafmer® elastomers manufactured by Mitsui. Because PP polymers are brittle at low temperatures (below about −20 ° C.) and tend to creep under static or periodic loads, the disclosed geocells incorporating PP may have poor load retention. Yes, it may be even more limited in operating temperature than the geocell of the present disclosure incorporating HDPE.

  PP and / or PE polymers or any other polymer composition according to the present disclosure are generally modified through various processing processes and / or additives to obtain the required physical properties. The most effective treatment is post-extrusion processing either downstream from the extruder or in another process thereafter. Typically, low crystallinity polymers such as LDPE, MDPE, and some PP polymers require post-extrusion processes such as orientation, cross-linking and / or thermal annealing while high crystallinity polymers are Extruded as a strip and welded together to form a geocell that does not require the application of post extrusion processing.

  In some embodiments, the polymer strip comprises (i) a high performance polymer and (ii) a blend of polyethylene or polypropylene polymer (usually as a compatibilized alloy). The blend is generally an immiscible blend (alloy) and the high performance polymer is dispersed in a matrix formed by a polyethylene or polypropylene polymer. A high performance polymer has (1) a storage modulus greater than 1400 MPa at 23 ° C. when measured in the machine direction by dynamic mechanical analysis (DMA) at a frequency of 1 Hz according to ASTM D4065; or (2) a final of at least 25 MPa It is a polymer having a tensile strength. Exemplary high performance polymers include polyamide resins, polyester resins, and polyurethane resins. Particularly suitable high performance polymers include polyethylene terephthalate (PET), polyamide 6, polyamide 66, polyamide 6/66, polyamide 12, and copolymers thereof. High performance polymers are typically included at about 5 to about 85 weight percent of the polymer strip. In certain embodiments, the high performance polymer comprises about 5 to about 30% (including about 7 to about 25%) of the polymer strip.

  The properties of the polymer strip can be modified either before forming the geocell (by welding the strip) or after forming the geocell. Polymer strips are generally manufactured by extruding a sheet of polymer material and cutting the strip from the polymer material sheet, with modifications generally being made to the sheet for efficiency. The modification can be performed in-line in the extrusion process after the melt is formed into a sheet shape and the sheet is cooled below the melting point, or as a secondary process after the sheet has been separated from the extruder die. It can be carried out. The modification can be performed by treating the sheet, strip and / or geocell by crosslinking, crystallization, slow cooling, orientation, and combinations thereof.

  For example, a sheet having a width of 5 to 500 cm is stretched (ie, oriented) at a temperature in the range of about 25 ° C. to about 10 ° C. below the peak melting point (Tm) of the polymer resin used to produce the sheet. Also good. Since the orientation process changes the strip length, the strip can increase in length by 2% to 500% relative to its original length. After stretching, the sheet can be gradually cooled. The slow cooling can be performed at a temperature 2 to 60 ° C. lower than the peak melting point (Tm) of the polymer resin used for producing the sheet. For example, when an HDPE, MDPE or PP sheet is obtained, stretching and / or slow cooling is performed at a temperature of about 24 ° C to 150 ° C. When the polymer alloy is slowly cooled, the annealing temperature is 2 to 60 ° C. lower than the peak melting point (Tm) of the HDPE, MDPE, or PP phase.

  In some specific embodiments, the polymer sheet or strip is stretched to increase its length by 50% (ie, so the final length is 150% of the original length). Stretching is performed at a temperature of about 100-125 ° C on the surface of the polymer sheet or strip. The thickness decreases from 10% to 20% due to stretching.

  In other embodiments, the polymer sheet or strip is added by adding a free radical source to the polymer composition by irradiation with an electron beam after extrusion, or prior to melting or during melt kneading in an extruder. Cross-linked.

  In other embodiments, the properties required for the geocell can be obtained by providing a multilayer polymer strip. In some embodiments, the polymer strip has at least 2, 3, 4, or 5 layers.

  In some embodiments as shown in FIG. 2, the polymer strip 100 has at least two layers 110, 120, wherein the two layers are made from the same or different compositions and have at least one The layer is (1) a storage modulus greater than or equal to 1400 MPa at 23 ° C. when measured in the machine direction by dynamic mechanical analysis (DMA) at a frequency of 1 Hz according to ASTM D4065; or (2) a final of at least 25 MPa Manufactured with high performance polymers or polymer compounds with tensile strength. In an embodiment, one layer comprises a high performance polymer and the other layer comprises a polyethylene or polypropylene polymer, which is a blend of polyethylene or polypropylene polymer with other polymers, fillers, additives, fibers and elastomers or It may be an alloy. Exemplary high performance resins include polyamides, polyesters, polyurethanes; (1) alloys of polyamides, polyesters, or polyurethanes with (2) LDPE, MDPE, HDPE, or PP; and copolymers, block copolymers, three polymers Any two blends or combinations of (polyamide, polyester, polyurethane) may be mentioned.

  In other embodiments as shown in FIG. 3, the polymer strip 200 has five layers. Two of the layers are the outer layer 210, one layer is the core layer 230, and the two intermediate layers 220 join the core layer and each outer layer (ie, the intermediate layer as a tie layer). Act). This five-layer strip can be formed by coextrusion.

  In other embodiments, the polymer strip 200 has only three layers. Two of the layers are outer layers 210 and the third layer is a core layer 230. In this embodiment, the intermediate layer 220 is not present. The three layer strips can be formed by coextrusion.

  The outer layer can provide resistance to UV degradation and hydrolysis and has good weldability. The outer layer can be made from a polymer selected from the group consisting of HDPE, MDPE, LDPE, polypropylene, blends thereof with other compounds and polymers, and alloys. Such polymers may be blends with elastomers, especially EPDM and ethylene-alpha olefin copolymers. The core and / or outer layer can also be made from an alloy of (1) HDPE, MDPE, LDPE, or PP and (2) polyamide or polyester. Each outer layer may have a thickness of about 50 to about 1500 micrometers (microns).

  The intermediate (tie) layer can be made from a functionalized HDPE copolymer or terpolymer, a functionalized PP copolymer or terpolymer, a polar ethylene copolymer, or a polar ethylene terpolymer. In general, HDPE and PP copolymers / terpolymers contain reactive end groups and / or side groups that allow chemical bond formation between the intermediate layer (tie layer) and the outer layer. Exemplary reactive side groups include carboxyl, anhydride, oxirane, amino, amide, ester, oxazoline, isocyanate, or combinations thereof. Each intermediate layer may have a thickness of about 5 to about 500 micrometers. Exemplary interlayer resins include Lotader® manufactured by Arkema and Elvaloy®, Fusabbond®, or Surlyn® resin manufactured by DuPont.

  The core and / or outer layer may comprise polyesters and their alloys with PE or PP, polyamides and their alloys with PE or PP, polyester and polyamide blends and PE or PP and their alloys. Exemplary polyamides include polyamide 6, polyamide 66, and polyamide 12. Exemplary polyesters include polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). The core and / or outer layer may have a thickness of about 50 to about 2000 micrometers.

  In another embodiment, as shown in FIG. 4, the polymer strip 300 has three layers, an upper layer 310, a central layer 320, and a lower layer 330. The upper layer is the same as the aforementioned outer layer, the central layer is the same as the aforementioned intermediate layer, and the lower layer is the same as the aforementioned core layer.

  Geocells are generally embossed (texturized by pressing the extruded semi-solid into a textured roll) to increase friction with the granular infill or soil. The geocell may also be perforated to improve friction with the granular infill and drainage. However, embossing and drilling reduces the stiffness and strength of the geocell. Since these friction aids are usually present, it is necessary to give the geocell improved strength and stiffness by changing its polymer composition and / or morphology.

  The polymer strip may further contain additives to obtain the required physical properties. Such additives may in particular be selected from nucleating agents, fillers, fibers, nanoparticles, cured amine light stabilizers (HALS), antioxidants, UV light absorbers, and carbon black.

  The filler may be in the form of a powder, fiber, or whisker. Exemplary fillers include metal oxides such as aluminum oxide; metal carbonates such as calcium carbonate, magnesium carbonate or calcium carbonate-magnesium; metal sulfates such as calcium sulfate; metal phosphates; In particular talc, kaolin, mica or wollastonite; metal borate; metal hydroxide; silica; silicate; alumosilicate; chalk; talc; dolomite; organic or inorganic fiber or whisker; Inorganic particles; clay; kaolin; industrial ash; concrete powder; cement; or mixtures thereof. In some embodiments, the filler has an average particle size of less than 10 microns, and in some embodiments, also has an aspect ratio greater than 1. In certain embodiments, the filler is mica, talc, kaolin and / or wollastonite. In other embodiments, the fibers have a diameter of less than 1 micron.

  The nanoparticles can be added to the polymer composition for various processes. For example, inorganic UV-absorbing solid nanoparticles are not actually mobile and are therefore very resistant to leaching and / or evaporation. UV-absorbing solid nanoparticles are also transparent in the visual spectrum and are very uniformly distributed. As such, they provide protection without contributing to the color or tone of the polymer. Exemplary UV-absorbing nanoparticles comprise a material selected from the group consisting of titanium salts, titanium oxide, zinc oxide, zinc halides, and zinc salts. In certain embodiments, the UV-absorbing nanoparticles are titanium dioxide. Examples of commercially available UV-absorbing particles include Sachtleben ™ Hombitec RM 130F TN by Sachtleben, ZANO ™ Zinc Oxide by Umicore, NanoZ ™ Zinc Oxide by Advanced Nanotechnology Limited, and Zinc Oxide by azide by Advanced Nanotechnology Limited. It is.

  The polymer strip from which the geocell is formed is manufactured by various processes. In general, the process involves melting the polymer composition, extruding the composition through an extruder die as a molten sheet, shaping, optionally texturing the resulting sheet, and as required to obtain the desired properties. Processing the sheet, cutting the sheet into strips, and welding the strips formed from the sheets together, stitching, joining and riveting to obtain a geocell. First, various components, such as polymer resins and any desired additives, are usually melt kneaded in an extruder or co-kneader. This is for example a melt extruder, for example a twin screw extruder or a single screw extruder with sufficient mixing elements to provide the heat required for the polymer and shear with minimal degradation. Can be done. The composition is melt kneaded so that any additives are completely dispersed. The composition is then extruded through a die and pressed into a sheet form between metal calendars. Exemplary treatments provided downstream of the extruder die include sheet surface texturing, sheet perforation, orientation (unidirectional or bi-directional), electron beam or x-ray irradiation and thermal annealing. In some embodiments, the sheet is heat treated to increase crystallinity and reduce internal stress. In other embodiments, the sheet is treated by electron beam, x-ray, heat treatment, and combinations thereof to induce crosslinking in the polymer resin. Combinations of the above processes are also envisioned.

  Strips can be formed from the resulting sheet and welded together, stitched, or joined to form a geocell. Such methods are known in the art. The resulting geocell can retain its rigidity under load cycling that lasts for a long period of time.

  The geocell of the present disclosure is useful for load bearing applications that cannot be used with current geocells. In particular, the geocell can also use infill materials that are not normally suitable for load bearing applications for roadbeds, subbases and roadbeds.

  In particular, the geocells of the present disclosure are suitable for load bearing applications such as roadbeds and underlayers due to insufficient stiffness and relatively low fatigue resistance (in granular materials, fatigue resistance is also known as modulus). Infill materials that were previously unsuitable for use in roadbeds can be used. Exemplary granular infill materials that can be used here include quarry waste (fine fraction remaining after classification of good quality granular materials), ground concrete, recycled asphalt, ground brix, Examples include building debris and rough stone, ground glass, power plant ash, fly ash, coal ash, blast furnace iron slug, cement manufacturing slug, steel slug, and mixtures thereof.

  The present disclosure is further illustrated in the following non-limiting working examples, which are for purposes of illustration only, and this disclosure limits the materials, conditions, process parameters, etc. described herein. It is understood that the purpose is not.

  Some geocells were manufactured and tested for their impact on their stress-strain response, DMA properties and granular material retention capacity.

  In general, tensile stress-strain properties were measured by the Izhar procedure described above.

  Loads at various deflections were measured or converted to Newton (N). The deflection is measured in millimeters (mm) or converted to millimeters (mm). Stress is the original cross-section of the strip (the original width multiplied by the original thickness, where the thickness is the peak-to-peak nominal distance between the top and bottom surfaces, with the load at a specific deflection. Calculated by dividing by. Strain (%) was calculated by dividing the specific deflection (mm) by the original length (mm) and multiplying by 100.

Comparative Example 1
Geocells made from high density polyethylene (HDPE) commercially available from Presto Geosystems (Wisconsin, USA) were obtained and tested for their properties. The average cell wall thickness was 1.5 mm and the strip had a diamond-like vertical cell texture. The geocell was non-perforated. Its stress-strain response according to the Izhar procedure is shown in Table 2.

  At a strain of about 8% and a stress of about 13.4 MPa, the comparative example begins to experience severe plastic deformation and in fact reaches the yield point at a strain of about 8%. In other words, after releasing the stress, the sample did not recover its original length, but remained longer (permanent residual strain). This phenomenon is unsuitable for load-bearing applications, especially cellular containment systems for applications that are subject to many (10,000 to 1,000,000 or more cycles during the product life cycle), pavement and This is the reason why the performance of HDPE geocell deteriorates as a load support for railways.

The HDPE strip is extruded and embossed to give a texture similar to Comparative Example 1. The strip had a thickness of 1.7 mm and was then stretched (at the strip surface) at a temperature of 100 ° C., increasing its length by 50% and reducing its thickness by 25%. The stress-strain response of this HDPE strip was measured according to the Izhar procedure and is shown in Table 3.

  The strip of Example 1 did not have a yield point at stresses above 17 MPa and did not reach its plastic limit and maintained an elastic response up to 12% strain. The initial dimension recovery after releasing the load was close to 100%.

12% by weight polyamide 12, 10% by weight polybutylene terephthalate, 5% maleic anhydride compatibilizer polyethylene grafted (Bondyram® 5001 manufactured by Polyram), and 73% HDPE The high performance polymer alloy composition was extruded to form a textured sheet having a thickness of 1.5 mm. The stress-strain response of the strip formed from the composition was measured according to the Izhar procedure and is shown in Table 4.

  The strip of Example 2 did not have a yield point and did not reach its plastic limit and maintained an elastic response at stresses above 17 MPa up to 14% strain. The initial dimension recovery after releasing the load was close to 100%.

  FIG. 5 is a graph showing the stress-strain results for Comparative Example 1, Example 1, and Example 2. An additional point at (0,0) was added to each result. As shown, Example 1 and Example 2 did not have a sharp yield point and maintained an increase in stress without yielding to a strain of 12-14% at stresses above 17 MPa. Example 1 reached the yield point with a strain of 8-10% and a stress of about 14 MPa. This is interpreted as a wider range in which the elastic response is maintained. The fact that no yield point was observed in Example 1 and Example 2 is important when periodic loads are expected, and the ability to return to the original dimensions (and thus maximum infill containment) is also extremely important. .

  FIG. 6 shows Comparative Example 1 and a maximum strain of 1.9% at a stress of 8 MPa; a maximum strain of 3.7% at a stress of 10.8 MPa; a strain of maximum 5.5% at a stress of 12.5 MPa; Up to 7.5% strain at a stress of 7 MPa; Up to 10% strain at a stress of 14.5 MPa; Up to 11% strain at a stress of 15.2 MPa; Up to 12.5% strain at a stress of 15.8 MPa A graph showing the difference between the stress-strain results of the disclosed polymer strips characterized as having a strain of up to 14% at a stress of 16.5 MPa; and a strain of up to 17% at a stress of 17.3 MPa; is there. The left-hand region of the dashed line defines the stress-strain combination according to the present disclosure.

  Two cells were tested to show an improvement in the reinforcement of the granular material and an increased load holding capacity. These cells were single cells that were not complete geocells. As a control, one cell corresponding to Comparative Example 1 was used. For comparison, a cell was produced from the composition according to Example 2, textured and had a thickness of 1.5 mm.

The wall of each cell was 10 cm high, 33 cm between stitches, embossed, not perforated and had a thickness of 1.5 mm. The cell was open, its long “radius” was about 260 mm and its short radius was about 185 mm. A sand box 800 mm long and 800 mm wide was filled with sand to a depth of 20 mm. Table 5 shows the gradual distribution of sand.

  A cell was placed on the surface of the sand and filled with the same sand. The expanded cell had a roughly elliptical shape with a major axis of about 260 mm and a uniaxial of about 180 mm. Additional sand was then placed in the sandbox, surrounding the cell and filling the cell, with a 25 mm top layer covering the cell. The sand was then compressed to a relative density of 70%.

  A 150 mm diameter piston was placed above the center of the cell, increasing the load and applying pressure on the sand surface in increments of 50 kPa (ie, the pressure was increased by 50 KPa every minute). Deflection (piston penetration into the trapped sand) and pressure (vertical load divided by piston area) were measured.

Pistons were used for (1) sand only; (2) the cell of Comparative Example 1; and (3) the cell of Comparative Example 2. The results are shown in Table 6.

  The cell of Example 2 continued elastic behavior at pressures above 400 kPa, but did not show the cell of Comparative Example 1. Due to the yielding of the HDPE wall, confinement degradation was observed in the cell of Comparative Example 1. The yield point of Comparative Example 1 was at a vertical pressure of about 250 kPa, but when the average hoop stress was calculated at that vertical pressure (the average diameter of the cell was 225 mm), the value of about 13.5 MPa was can get. This number agrees very well with the yield point values obtained by stress-strain tensile measurements according to the Izhar procedure. The results showed that there was a strong significant correlation between stiffness and yield resistance (ability to hold hoop stress above 14 MPa) and ability to support large vertical loads. It should be noted that this test provided only a single load, but in practical applications the load to be supported is periodic. As a result, resistance to plastic deformation was very important and was not present in the cell of Comparative Example 1.

  FIG. 7 is a graph showing the results of Table 6. The difference in resistance to penetration (ie, how much vertical load the cell supported) is very clear.

  A polymer strip was produced according to Example 2.

  As a control, a 1.5 mm thick HDPE strip according to Comparative Example 1 was provided.

  The two strips were then analyzed by dynamic mechanical analysis (DMA) at a frequency of 1 Hz according to ASTM D4065. The control HDPE strip was tested over a temperature range of about -150 ° C to about 91 ° C. The control strip was heated at 5 ° C./min and the force, displacement, storage modulus, and tan delta were measured. The polymer strip of Example 2 was tested over a temperature range of about -65 ° C to about 120 ° C. The control strip was heated at 5 ° C./min and the force, displacement, storage modulus, and tan delta were measured.

  FIG. 8 is a graph of storage modulus (modulus) and Tan Delta vs. temperature for the control HDPE strip.

  9 is a graph of storage modulus (modulus) and Tan Delta vs. temperature for the polymer strip of Example 2. FIG.

  The storage modulus of HDPE decreases more rapidly than the storage modulus of Example 2. The storage modulus for the strip of Example 2 was about 3 times higher at 23 ° C. than the storage modulus of the HDPE strip. In order to obtain the same storage modulus that the HDPE strip has at 23 ° C., the strip of Example 2 should be heated to about 60 ° C., ie the strip of Example 2 has a good storage modulus. It remained.

  The Tan Delta of the HDPE strip begins to increase exponentially at about 75 ° C., which is indicative of elastic loss (ie, the material becomes too plastic and does not retain sufficient stiffness and elasticity), and the strip is viscous. It became thick and plastic. This is undesirable because the geocell can be heated even when placed underground (eg, in a roadway). Tan Delta for the strip of Example 2 maintained its properties at temperatures as high as 100 ° C. This property is desirable because it provides an additional safety factor. Since performance at high temperatures is a way to predict long-term performance at non-high temperatures (as described in ASTM 6992), HDPE begins to lose its elasticity and thus within about a few seconds at about 75 ° C. The fact of losing load bearing capacity gives specific insights regarding its low creep resistance and tendency to plastic deformation. Unlike HDPE, the composition according to the present disclosure suggests that it retains its elasticity at very high temperatures (low Tan Delta) and thus has the ability to retain its properties for many years and many load cycles .

Three strips were tested according to the PRS SIM procedure to determine their long-term design stress (LTDS). As a control, one HDPE strip was produced according to Comparative Example 1. The first test strip was made according to Example 2. A second test strip was made according to Example 2, but was then oriented at 115 ° C. and increased its original length by 40%. The results are shown in Table 7 below.

  As can be seen, both Example 2 and oriented Example 2 had higher LTDS compared to Comparative Example 1.

  While specific embodiments have been described, alternatives, modifications, changes, improvements and substantial equivalents that are not currently or can be foreseen can be recalled by the applicant or one of ordinary skill in the art. Accordingly, the appended claims, as filed and amended, are intended to embrace all such alternatives, modifications, variations, improvements and substantial equivalents.

Claims (18)

  A geocell formed from a polymer strip, wherein at least one polymer strip is at least 500 MPa when measured in the machine direction by dynamic mechanical analysis (DMA) according to ASTM D4065 at a frequency of 1 Hz at 23 ° C. Geocell with a storage modulus of.   The geocell according to claim 1, wherein the at least one polymer strip has a storage modulus of 700 MPa or more.   The geocell of claim 1, wherein the at least one polymer strip has a storage modulus of 1000 MPa or greater.   The geocell of claim 1, wherein the at least one polymer strip has a stress at 12% strain of 14.5 MPa or greater when measured according to the Izhar procedure at 23 ° C.   The geocell of claim 1, wherein the at least one polymer strip has a stress at 12% strain of 16 MPa or greater when measured at 23 ° C. according to the Izhar procedure.   The geocell of claim 1, wherein the at least one polymer strip has a stress at 12% strain of 18 MPa or greater when measured according to the Izhar procedure at 23 ° C. The geocell of claim 1, wherein the at least one polymer strip has a coefficient of thermal expansion of no greater than 120 × 10 ⁻⁶ / ° C. at 25 ° C. according to ASTM D696.   A pavement, roadway, railroad or parking area comprising at least one layer comprising the geocell according to claim 1.   Geocell is made of sand, pebbles, crushed stone, gravel, quarry waste, crushed concrete, recycled asphalt, crushed bricks, building debris and rough stone, crushed glass, power plant ash, fly ash, coal ash, 9. A pavement, roadway, railroad or parking area according to claim 8, filled with a granular material selected from the group consisting of blast furnace iron slag, cement slag, steel slag and mixtures thereof.   Geocell formed from a polymer strip, wherein at least one polymer strip is at least 150 MPa when measured in the machine direction by dynamic mechanical analysis (DMA) according to ASTM D4065 at a frequency of 1 Hz at 63 ° C. Geocell with a storage modulus of.   The geocell according to claim 10, wherein the at least one polymer strip has a storage modulus of 250 MPa or more.   The geocell according to claim 10, wherein the at least one polymer strip has a storage modulus of 400 MPa or more.   The geocell of claim 10, wherein the at least one polymer strip has a stress at 12% strain of 14.5 MPa or greater when measured according to the Izhar procedure at 23 ° C.   The geocell of claim 10, wherein the at least one polymer strip has a stress at 12% strain of 16 MPa or more when measured at 23 ° C according to the Izhar procedure.   11. A geocell according to claim 10, wherein the at least one polymer strip has a stress at 12% strain of 18 MPa or more when measured according to the Izhar procedure at 23 [deg.] C. The geocell of claim 10, wherein the at least one polymer strip has a coefficient of thermal expansion of no greater than 120 x ^10-6 / ° C at 25 ° C according to ASTM D696.   A pavement, roadway, railway or parking area comprising at least one layer comprising the geocell according to claim 10.   Geocell is made of sand, pebbles, crushed stone, gravel, quarry waste, crushed concrete, recycled asphalt, crushed bricks, building debris and rough stone, crushed glass, power plant ash, fly ash, coal ash, 18. A pavement, roadway, railway or parking area according to claim 17, filled with a granular material selected from the group consisting of blast furnace iron slag, cement slag, steel slag and mixtures thereof.

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