BG2798U1 - Geosell for applications related to load maintenance - Google Patents

Abstract

The present object is a geosell that has high strength and stiffness and has a dynamic modulus of elasticity of 500 MPa or higher at 23 ° C; a dynamic modulus of elasticity of 150 MPa or greater than 150 MPa or greater at 63 ° C when measured in longitudinal direction by Dynamic Mechanical Analysis (DMA) at a frequency of 1 Hz; tension at stretching at 12% deformation 14.5 MPa or higher at 23 ° C; a thermal expansion coefficient of 120 x 10-6/oС or less at 25 ° C and / or a long-term design voltage of 2.6 MPa or more.

Description

(54) GEOB CELL FOR LOAD MAINTENANCE APPLICATIONS

(57) The present site is a geocell that has high strength and hardness and has a dynamic modulus of elasticity of 500 MPa or higher at 23 ° C; A dynamic modulus of elasticity of 150 MPa or greater than 150 MPa or higher at 63 ° C when measured in the longitudinal direction by Dynamic Mechanical Analysis (DMA) at a frequency of 1 Hz; tensile stress at 12% strain 14.5 MPa or higher at 23 ° C; a thermal expansion coefficient of 120 x 10 ' ^b / ° C or less at 25 ° C, and / or a long-term design voltage of 2.6 MPa or more.

claims, 9 figures

2798 UI (54) GEOD CELL FOR LOAD MAINTENANCE APPLICATIONS

Field of technology

The present site is a geocell that is suitable for use to maintain loads, in particular for the reinforcement of underlying layers of road surface and / or underlying layers of roads, road surfaces, storage areas, railways.

BACKGROUND OF THE INVENTION

The present disclosure relates to a cellular restraint system, also known as CCS or a geocell, that is suitable for use in maintaining loads such as those available on roads, railways, parking areas, and road surfaces. In particular, the geocells of the present disclosure retain their size after a large number of load cycles and temperature cycles; thus, the required backfill restriction is maintained during the design life cycle of the geocell.

A cell restraint system (CCS) is an array of restraining cells resembling the structure of a "honeycomb" that is filled with granular embankment, which can be unbound soil, sand, gravel, fine gravel, crushed stone, or any other type of granular filler. . Also known as geocells, CCSs are primarily used in construction applications that require low mechanical strength and rigidity, such as slope reinforcement (to prevent erosion) or to provide lateral slope support.

CCSs differ from other geosynthetic materials, such as geogrids or geotextiles, in that the geogrids / geotextiles are flat (i.e., two-dimensional) and are used as flat reinforcements. Geogrids / geotextiles provide a restriction only for very limited vertical intermediate spaces (usually 1-2 times the average grain size) and are limited to grain materials having an average size greater than about 20 mm. This limits the use of such two-dimensional geosynthetic materials to relatively expensive grains (fine gravel, crushed stone and gravel) because they provide little or no restriction or reinforcement for lower quality grains, such as recycled asphalt, crushed concrete, fly ash and waste. from quarries. In contrast, CCSs are three-dimensional structures that provide constraint in all directions (i.e., along the entire cross section of each cell). Moreover, the multicellular geometry provides passive resistance, which increases the load capacity. Unlike two-dimensional geosynthetic materials, the geocell provides restriction and reinforcement of granular materials having an average particle size of less than about 20 mm, and in some cases materials having an average particle size of about 10 mm or less.

Geocells are made by several companies around the world, including Presto. Presto's geocells, like those of most of its simulators, are made of polyethylene (PE). Polyethylene (PE) can be high density polyethylene (HDPE) or medium density polyethylene (MDPE). The term "HDPE" hereinafter refers to polyethylene having a density greater than 0.940 g / cm ³ , medium density polyethylene (MDPE) referring to polyethylene having a density greater than 0.925 g / cm ³ to 0.940 g / cm ³ . The term low density polyethylene (LDPE) refers to polyethylene having a density of 0.91 to 0.925 g / cm ³ .

Geocells made of HDPE and MDPE are either smooth or textured. Textured geocells are the most common on the market, as the texture can provide some additional friction between the geocell walls and the backfill. Although HDPE could theoretically have a tensile strength (tensile stress at the creep limit or breakage) greater than 15 megapascals (MPa), in practice when a sample is taken from a geocell wall and tested according to ASTM 0638, the strength is insufficient for load-bearing applications such as roads and railways, and even at a high strain rate of 150% / min, it will reach only 14 MPa.

The poor properties of HDPE and MDPE are clearly seen when tested by Dynamic Mechanical Analysis (OMA) according to ASTM

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04065: The dynamic modulus of elasticity at 23 ° C is less than about 400 MPa. The dynamic modulus of elasticity deteriorates significantly with increasing temperature, and decreases below the practically used levels at temperatures of about 75 ° C, thus limiting applications such as load-bearing reinforcements. These moderate mechanical properties are sufficient to protect slopes rather than long-term load-bearing applications that are designed to operate for more than five years.

Another method for predicting the long-term creep-related behavior of polymers is the accelerated step-by-step isothermal (SIM) creep test according to ASTM 6992. In this method, a polymer sample is subjected to a constant load according to a stepwise modification program. of temperature. The stages of elevated temperature accelerate creep. The method provides extrapolation of the properties of the sample over long periods of time, even for 100 years. Typically, when PE and PP are tested, the load that causes a plastic deformation of 10% is called the 'long-term design strength limit' and is used in geosynthetic materials as the allowable strength for structures. Loads that cause plastic deformation greater than 10% are avoided because PE and PP are subject to second-order creep above 10% plastic deformation. Second-line creep is unpredictable, and PE and PP tend to "cover with thin cracks" in this mode.

For applications such as roads, railways and heavy-duty storage and car parks, the given strength of only 14 MPa is insufficient. In particular, geocells with such moderate mechanical properties tend to have relatively low strength and tend to deform plastically at deformations lower than 8%. Plastic deformation causes the cell to lose its retention potential, which is essentially the main strengthening mechanism, after short periods of time or a small number of vehicle transitions (small number of cyclic loads). For example, when a strip of a typical geocell in the length direction (perpendicular to the seam plane) is tested according to ASTM 0638 at a strain rate of 20% / min or even 150% / min, the stress at 6% strain is less than 13 MPa, at 8% deformation is less than 13.5 MPa, and at 12% deformation is less than 14 MPa. As a result, HDPE geocells are limited to applications when the geocell is under low load and when a load-bearing load limit is not required (e.g., in soil stabilization). Geocells are not widespread in load-bearing applications such as roads, railways, parking lots, or in heavy container storage sites due to the strong tendency to plastic deformation at low stresses.

When the vertical load is applied to a granular substrate, part of this vertical load is translated into a horizontal load or pressure. The magnitude of the horizontal load is equal to the vertical load multiplied by the horizontal soil pressure coefficient (also known as the soil lateral pressure coefficient or LEPC) of the granular material. LEPC can vary from about 0.2 for good materials such as gravel and crushed stone (usually solid particles, finely divided, so the seal is very good and plasticity is minimal) to about 0.3 to 0.4 for more plastic materials, similar to waste from quarries or recycled asphalt (materials that have a high content of small particles and high ductility). When the granular material is wet (for example, by seepage from rain or flooding of the road surface and the ground base of the road), its plasticity increases, and increased horizontal loads develop, providing increased circular stress in the cell wall.

When the granular material is bounded by a geocell, and the vertical load is applied from above at the expense of static and dynamic stresses (such as pressure caused by a vehicle wheel or train rail), the horizontal pressure is translated into a circular stress in the geocell wall. The circular stress is proportional to the horizontal pressure and the mean radius

2798 UI of the cell, and is inversely proportional to the thickness of the cell wall.

___ VP * LEPC * r at —-------- d where HS is the mean circular stress in the geocell wall, VP is the vertical pressure applied externally to the granular material from the load, LEPC is the lateral pressure factor of the soil, d is the average radius of the cell and d is the nominal wall thickness of the cell.

For example, a geocell made of HDPE or MDPE having a cell wall thickness of 1.5 mm (including texture, and the term "wall thickness" refers hereinafter to the distance from the end point to the end point of the cross section of the cell wall), average diameter (when filled with granular material) 230 mm, height 200 mm, when filled with sand or quarry waste (LEPC 0.3), and vertical load 700 kilopascals (kPa), will experience a circular voltage of about 16 megapascals ( MPa). As can be seen from the circular stress equation, the larger diameter or thinner walls - which is an advantage in terms of production economy - are subjected to significantly higher circular stresses, and thus do not work well as reinforcement, when made of HDPE or MDPE.

Vertical loads of 550 kPa are common for unpaved roads. Significantly higher loads, such as 700 kPa or more, can be applied on roads (paved and unpaved) for heavy trucks, roads for industrial use, or parking areas.

Because load-bearing applications, especially roads and railways, are typically subjected to millions of cyclic loads, the geocell wall must retain its original dimensions under cyclic loads with very low plastic deformation. The commercial use of HDPE geocells is not limited to load-bearing applications, as HDPE typically reaches its limit of ductility at about 8% strain, and at stresses below normal stresses, available in most cases in load-bearing applications.

It would be desirable to provide a geocell that has increased hardness and strength, reduced tendency to deform at elevated temperatures, better preservation of its elasticity at ambient temperatures (23 ° C), reduced tendency to undergo plastic deformation at repetitive and continuous loads, and / or long periods of operation.

Short description

In embodiments, geocells are disclosed that provide significant hardness and can accept high stresses without plastic deformation. Such geocells are suitable for load-bearing applications, such as pavements, roads, railways, parking areas, runways, and storage sites. Methods for preparing and using such geocells are also disclosed.

In some embodiments, a geocell formed of polymer strips is disclosed, at least one polymer strip has a dynamic modulus of elasticity of 500 MPa or more when measured in the direction of length by Dynamic Mechanical Analysis (DMA) according to ASTM D4065 at 23 ° C and with a frequency 1 Hz.

At least one polymer strip may have a dynamic modulus of elasticity of 700 MPa or more, including a dynamic modulus of elasticity of 1000 MPa or more.

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

At least one polymer strip has a coefficient of thermal expansion of 120 x 10 ' ⁶ / ° C or less at 25 ° C according to ASTM D696.

The geocell can be used in a layer of road surface, road, railway line, or parking lot. The geocell can be filled with granular material selected from the group consisting of sand, gravel, crushed stone, fine gravel, quarry waste, crushed concrete, recycled asphalt, crushed bricks, construction waste and gravel, crushed

2798 UI glass, power plant ash, fly ash, coal ash, blast furnace slag, cement slag, metal - containing slag, and mixtures thereof.

In other embodiments, a geocell formed of polymer strips is disclosed, at least one polymer strip having a dynamic modulus of elasticity of 150 MPa or more when measured in the longitudinal direction by Dynamic Mechanical Analysis (DMA) according to ASTM D4065 at 63 ° C and with frequency 1 Hz.

At least one polymer strip may have a dynamic modulus of elasticity of 250 MPa or more, including a dynamic modulus of elasticity of 400 MPa or more.

In still other embodiments, a geocell formed of polymer strips is disclosed, at least one polymer strip having a long-term design voltage of 2.6 MPa or more, when measured according to the PRS SIM procedure.

At least one polymer strip may have a long-term design voltage of 3 MPa or more, including a long-term design voltage of 4 MPa or more.

These and other embodiments are described in more detail below.

Explanation of the attached figures

The following is a brief description of the drawings, which are presented in order to illustrate the exemplary embodiments disclosed herein, and not in order to be limited.

Figure 1 is a perspective view of a geocell.

Figure 2 is a diagram showing an illustrative embodiment of a polymer tape used in the geocells of the present disclosure.

Figure 3 is a diagram showing another illustrative embodiment of a polymer tape used in the geocells of the present disclosure.

Figure 4 is a diagram showing another illustrative embodiment of a polymer tape used in the geocells of the present disclosure.

Figure 5 is a graph comparing stress-strain results of different cells of the present disclosure with a comparative example.

Figure 6 is a graph showing a stress-strain diagram for the geocells of the present disclosure.

Figure 7 is a graph showing the results of a vertical load test of an illustrative cell of the present disclosure compared to a comparative example.

Figure 8 is a graph of the dynamic modulus of elasticity and Tan Delta versus temperature for the control strip.

Figure 9 is a graph of the dynamic modulus of elasticity and Tan Delta as a function of the temperature for the polymer strip used in the geocells of the present disclosure.

Detailed description

The following detailed description is provided to enable a person skilled in the art to create and use the embodiments disclosed herein and outlines best practices involving the implementation of these embodiments. Various modifications, however, will become apparent to those skilled in the art and should be considered in the context of this disclosure.

A more complete understanding of the components, processes, and devices disclosed herein can be obtained by reference to the accompanying drawings. These figures are merely a schematic representation based on the convenience and ease of demonstration of the present disclosure, and are therefore not intended to show the relative size and parameters of the devices or their components and / or to define or limit the illustrative embodiments.

Figure 1 is a perspective view of a single layer geocell. The geocell 10 comprises a plurality of polymer strips 14. Adjacent strips are joined together by separate physical connections 16. The connection may be made by bonding, sewing or welding, but is usually made by welding. A portion of each strip between two connections 16 forms a cell wall 18 of a separate cell 20. Each cell 20 has cell walls made of two different polymer strips. The strips 14 are joined together to form a honeycomb structure of multiple strips. For example, the outer strip 22 and the inner strip 24 are connected together by physical connections

2798 UI

16, which are separated at regular intervals along strips 22 and 24. A pair of inner strips 24 is connected together by physical connections 32. Each connection 32 is located between two connections 16. As a result, when a plurality of strips 14 are stretched in a direction perpendicular to the surfaces of the strips, the strips are bent sinusoidally to form the geocell 10. At the end of the geocell, where the ends of two polymer strips 22, 24 touch, the final weld 26 (also considered a connection) is made at a short distance from the end 28 to form a short tail 30 which stabilizes the two polymer strips 22, 24.

The geocells of the present disclosure are made of polymer strips that have certain physical properties. In particular, the polymer tape has a creep limit stress, or at 12% deformation when the polymer tape has no creep limit, of 14.5 MPa or more when measured in a longitudinal direction (perpendicular to the seam plane in the geocell cell) at strain rate 20% / min or 150% / min. In other embodiments, the polymer tape has a deformation of 10% or less at a stress of 14.5 MPa when measured as described. In other words, the polymer tape can withstand stresses of 14 MPa or more without reaching its creep limit. Other synonyms for creep limit include creep limit stress, elastic limit, or ductility limit. When the polymer tape has no creep limit, the stress is considered to correspond to 12% strain. These measurements refer to the mechanical properties of the polymer tape in the longitudinal direction, at 23 ° C, and not to its bending properties.

Because many geocells are perforated, stress and strain measurements according to ASTM 0638 or ISO 527 are generally impossible. Thus, the measurements are performed according to the following procedure, which is a modified version of the mentioned standards and is referred to herein as the "Izhar procedure". A strip 50 mm long and 10 mm wide is taken in a direction parallel to the ground level and perpendicular to the plane of the cage seams (ie in a longitudinal direction).

The strap is fastened so that the distance between the fasteners is 30 mm. The strap is then stretched by moving the fasteners away from each other at a speed of 45 millimeters (mm) per minute, equal to 150% / min, at 23 ° C. The load provided by the belt in response to said deformation is measured by a dynamometer. The stress (N / mm ² ) is calculated at different deformations (the deformation is an increase in length divided by the original length). The stress is calculated by dividing the load at a certain deformation of the initial nominal cross section (the width of the strip multiplied by the thickness of the strip). Because the strip surface of the geocell is usually textured, the thickness of the sample is measured as the end-to-end distance, averaged between three points on the strip. (For example, a strip having an embossed diamond-shaped texture and having a distance between the top texture of the top side and the bottom texture of the bottom side of 1.5 mm is considered to be 1.5 mm thick). This deformation rate of 150% / min is more typical for road surfaces and railways, where each load cycle is very short.

In other embodiments, the polymer tape may be characterized by:

deformation of at most 1.9% at a stress of 8 MPa;

deformation of at most 3.7% at a stress of 10.8 MPa;

deformation of at most 5.5% at a stress of 12.5 MPa;

deformation of at most 7.5% at a stress of 13.7 MPa;

deformation of at most 10% at a voltage of 14.5 MPa;

deformation of at most 11% at a stress of 15.2 MPa; and a deformation of at most 12.5% at a stress of 15.8 MPa.

The polymer tape may also have, optionally, a deformation of up to 14% at a stress of 16.5 MPa; and / or deformation of at most 17% at a stress of 17.3 MPa.

In other embodiments, the polymer tape may be characterized as having a stress of at least 14.5 MPa at a deformation

2798 UI mation 12%; stress at least 15.5 MPa at 12% deformation; and / or a stress of at least 16.5 MPa at a deformation of 12%.

In other embodiments, the polymer tape may be characterized as having a dynamic modulus of elasticity of 500 MPa or more at 23 ° C, measured in the longitudinal direction by Dynamic Mechanical Analysis (DMA) at a frequency of 1 Hz. As with strain-strain measurements, the thickness for DMA analysis is taken as the end-to-end distance, averaged between three points. The DMA measurements described in the present disclosure are performed according to ASTM D4065.

In other embodiments, the polymer tape may be characterized as having a dynamic modulus of elasticity of 250 MPa or more at 50 ° C, measured in the longitudinal direction by Dynamic Mechanical Analysis (DMA) at a frequency of 1 Hz.

In other embodiments, the polymer tape may be characterized as having a dynamic modulus of elasticity of 150 MPa or more at 63 ° C, measured in the longitudinal direction by Dynamic Mechanical Analysis (DMA) at a frequency of 1 Hz.

In other embodiments, the polymer tape may be characterized as having a Tan Delta of 0.32 or less at 75 ° C, measured in the longitudinal direction by Dynamic Mechanical Analysis (DMA) at a frequency of 1 Hz. These new properties are outside the range of typical HDPE or MDPE geocells.

Dynamic Mechanical Analysis (DMA) is a technique used to study and characterize the viscoelastic nature of polymers. As a rule, an oscillating force is applied to a sample of material and the resulting cyclic displacement of the sample is measured depending on the cyclic load. The higher the elasticity, the shorter the time interval (phase) between loading and displacement. From this, the exact hardness (dynamic modulus of elasticity) of the specimen can be determined, as can the scattering mechanism (dynamic modulus of mechanical losses) and the ratio between them (Tan Delta). DMA is also discussed in ASTM.

Another aspect of the geocell of the present disclosure is its reduced coefficient of thermal expansion (ETS) relative to current HDPE or MDPE. ETS is important because expansion / contraction during cyclic thermal action is another mechanism that also provides additional circular stresses. HDPE and MDPE have an ETS of about 200 x 10 ' ⁶ / ° C at ambient temperature (23 ° C), and this ETS is even higher at temperatures above ambient temperature. The geocell of the present disclosure has a CTE of about 150 x 10 ' ⁶ / ° C or less at 23 ° C, and in specific embodiments about 120 x 10' ⁶ / ° C or less at 23 ° C when is measured according to ASTM 0696. The ETS of the geocell of the present disclosure has a lower tendency to increase at elevated temperatures.

Another aspect of the geocell of the present disclosure is its lower tendency to crawl at constant load. A lower creep tendency is measured according to an accelerated creep test by the stepwise isothermal method (SIM), as described in ASTM 6992. In this method, a polymer sample is subjected to a constant load according to a stepwise temperature change program (ie. the temperature rises and remains constant for a predetermined period). In the stages with elevated temperature, the creep accelerates. The SIM test procedure is applied to a specimen with a width of 100 mm and a clear length of 50 mm (distance between fasteners). The sample is loaded with a static load and heated according to a procedure comprising the steps of:

Stage T time Celsius o'clock 0 23 0 1 30 3 2 37 3 3 44 3 4 51 3 5 58 3 6 65 3 7 72 3

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This SIM procedure is referred to herein as the "PRS SIM procedure". The plastic deformation (irreversible increase in length divided by the initial length) is measured at the end of the procedure. Plastic deformation is measured at different loads, and the load that causes plastic deformation of 10% or less is called the 'long-term design load'. The stress related to the long-term design load (said load divided by (initial width multiplied by the initial load)) is the "long-term design load" and provides the allowable circular stress that the geocell can withstand for a long period under static load.

A typical HDPE geocell, when subjected to the PRS SIM procedure, can provide a long-term design voltage of 2.2 MPa.

In some embodiments, the polymer tape 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 geocell of the present disclosure can provide significantly better properties up to 16% strain and in some embodiments up to 22% strain. In particular, the geocell can react elastically to stresses greater than 14.5 MPa, thus providing the necessary properties for load-bearing applications. The elastic reaction guarantees the full restoration of the original dimensions when the load is removed. The geocell will provide backfill with increased allowable load and increased recovery of its original diameter under repetitive loads (ie cyclic loads). Moreover, the geocell of the present disclosure can be used with granular materials, which as a rule cannot be used in basic road layers and in basic soils, as described hereinafter. The geocell of the present disclosure also provides the opportunity for better load-bearing capacity and fatigue resistance in humid conditions, especially when finely divided granular materials are used.

The polymer tape may include a polyethylene (PE) polymer, such as HDPE, MDPE or LDPE, that has been modified as further described below.

The polymer tape may also contain a polypropylene (PP) polymer. Although most PP homopolymers are too brittle and most PP copolymers are too soft for load-bearing applications, some types of PP polymers are useful. Such PP polymers may be hard enough for load-bearing applications, and still soft enough that the geocell can be folded. Illustrative polypropylene polymers suitable for the present disclosure comprise polypropylene uncoordinated copolymers, polypropylene impact resistant copolymers, mixtures of polypropylene with either ethylene-propylene-diene-monomer (EPDM) or an elastomer based on ethylene alpha-copolypropolin and copolypolypolepopol. Such PP polymers are commercially available as R338-02N from Dow Chemical Company; PP 71EK71PS brand impact resistant copolymer from SAB1C Innovative Plastics; and PP RA1E10 unordered copolymer from SABIC Innovative Plastics. Illustrative elastomers based on ethylene alpha-olefin copolymer contain Exact® elastomers manufactured by Exxon Mobil and Tafmer® elastomers manufactured by Mitsui. Because PP polymers are brittle at low temperatures (less than about minus 20 ° C) and tend to creep under static or cyclic loads, geocells of the present disclosure that include PP may carry less load and be more -limited in terms of their operating temperatures than geocells of the present disclosure that include HDPE.

The PP and / or PE polymers or any other polymer composition according to the present disclosure are generally modified by various processing processes and / or additives to achieve the required physical properties. The most efficient treatment is the post-extrusion treatment, either after leaving the extrusion machine, or as a separate process afterwards. As a rule, polymers with lower crystallinity, such as LDPE, MDPE, and some PP polymers will require post-extrusion.

2798 UI zion treatment, such as orientation, crosslinking, and / or thermal annealing, while polymers with higher crystallinity can be extruded as strips and welded together to form a geocell without the need for post-extrusion treatment.

In some embodiments, the polymer tape comprises a mixture (usually as a compatible alloy) of (i) a high quality polymer and (ii) a polyethylene or polypropylene polymer. The mixture is generally a non-miscible mixture (alloy), where the high quality polymer is dispersed in a matrix formed by the polyethylene or polypropylene polymer. A high quality polymer is a polymer having (1) a dynamic modulus of elasticity of 1400 MPa or more at 23 ° C, measured in the longitudinal direction by Dynamic Mechanical Analysis (DMA) at a frequency of 1 Hz, according to ASTM 04065; or (2) a maximum tensile strength of at least 25 MPa. Illustrative high quality polymers include polyamide resins, polyester resins, and polyurethane resins. Particularly suitable high quality polymers include polyethylene terephthalate (PET), polyamide 6, polyamide 66, polyamide 6/66, polyamide 12, and copolymers thereof. The polymer tape typically contains from about 5 to about 85 weight percent high quality polymer. In certain embodiments, the high quality polymer is from about 5 to about 30 weight percent of the polymer tape, including from about 7 to about 25 weight percent.

The properties of the polymer strips can be modified either before the formation of the geocell (by welding the strips) or after the formation of the geocell. The polymer strips are generally made by extruding a sheet of polymeric material and cutting strips of said sheet of polymeric material, and the modification is generally performed on the efficiency sheet. The modification can be done simultaneously with the extrusion process after the melt has formed as a sheet and the sheet has cooled to a temperature lower than the melting temperature, or as a secondary process after the sheet has been separated from the extrusion head. The modification can be done by processing the leaves, strips, and / or geocell by crosslinking, crystallizing, annealing, orienting, and combinations thereof.

For example, a sheet that is 5 to 500 cm wide may be stretched (ie oriented) at a temperature range of about 25 ° C to about 10 ° C lower than the maximum melting temperature (Tm) of the polymer resin. used to obtain the sheet. The orientation process changes the length of the tape so that the tape can be increased in length from 2% to 500% of its original length. After stretching, the sheet can be annealed. The annealing can be carried out at a temperature which is 2 to 60 ° C lower than the maximum melting point (Tm) of the polymer resin used to form the sheet. For example, if a sheet of HDPE, MDPE or PP is obtained, stretching and / or annealing is performed at a temperature of about 24 ° C to 150 ° C. If the polymer alloy is annealed, the annealing temperature is 2 to 60 ° C lower than the maximum melting point (Tm) of the HOPE, MDPE, or PP phase.

In some individual embodiments, the polymer sheet or strip is stretched to increase its length by 50% (i.e., so that the final length is 150% of the original length). The stretching is carried out at a temperature of about 100-125 ° C on the surface of the polymer sheet or strip. As a result of stretching, the thickness is reduced by 10% to 20%.

In other embodiments, the polymer sheet or strip is crosslinked by irradiating with an electron beam after extrusion or by adding a source of free radicals to the polymer composition before melting or during mixing of the melt in the extruder.

In other embodiments, the required properties of the geocell can be obtained by providing multilayer polymer tapes. In some embodiments, the polymer strips have at least two, three, four or five layers.

In some embodiments, as shown in FIG. 2, the polymer tape 100 has at least two layers 110,120, where two of the layers are made of the same or different compositions and at least one layer is made of a high quality polymer or polymer composite having (1) a dynamic modulus of elasticity of 1400 MPa or more at 23 ° C, measured in the longitudinal direction by Dynamic Mechanical Analysis (DMA)

2798 IU at a frequency of 1 Hz according to ASTM 04065; or (2) a maximum tensile strength of at least 25 MPa. In embodiments, one layer comprises a high quality polymer and another layer comprises polyethylene or polypropylene polymer, which may be a mixture or alloy of polyethylene or polypropylene polymer with other polymers, fillers, additives, fibers and elastomers. Illustrative high quality resins include polyamides, polyesters, polyurethanes; alloys of (1) polyamides, polyesters or polyurethanes with (2) LDPE, MDPE, HDPE, or PP; and copolymers, block copolymers, mixtures or combinations of any two of the three polymers (polyamides, polyesters, polyurethanes).

In other embodiments, as shown in FIG. 3, the polymer tape 200 has five layers. Two of the layers are outer layers 210, one layer is a core layer 230, and the two intermediate layers 220 connect the core layer to each outer layer (i.e., the intermediate layers serve as bonding layers). This five-layer strip can be formed by co-extrusion.

In other embodiments, the polymer tape 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 layers 220 are missing. This three-layer strip can be formed by co-extrusion.

The outer layers can provide resistance to degradation by ultraviolet light and hydrolysis and have good weldability. The outer layer may be made of a polymer selected from the group consisting of HDPE, MDPE, LDPE, polypropylene, mixtures thereof, and alloys with other composites and polymers. These polymers can be mixed with elastomers, especially EPDM and ethylene-alpha olefin copolymers. The core and / or outer layer may also be made of alloys of (1) HDPE, MDPE, LDPE, or PP with (2) polyamide or polyester. Each outer layer may have a thickness of about 50 to about 1500 μm (microns).

The intermediate (bonding) layers may be made of functionalized HDPE copolymers or terpolymers, functionalized PP copolymers or terpolymers, a polar ethylene copolymer, or a polar ethylene terpolymer. Typically, HDPE and PP copolymers / terpolymers contain functional end groups and / or side groups that provide the ability to form chemical bonds between the intermediate layers (bonding layers) and the outer layer. Illustrative reactive side groups include carboxyl, anhydride, oxirane, amino, amido, ester, oxazoline, isocyanate groups, or combinations thereof. Each intermediate layer may have a thickness of about 5 to about 500 pm. Illustrative intermediate layer of resins including Lotader® resins manufactured by Arkema and Elvaloy®, Fusabond®, or Surlyn® resins manufactured by DuPont.

The core and / or outer layer may contain polyester and its alloys with PE or PP, polyamide and its alloys with PE or PP, and mixtures of polyester and polyamide and their alloys with PE or PP. Illustrative polyamides contain polyamide 6, polyamide 66, and polyamide 12. Illustrative polyesters contain polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). The core and / or outer layer may have a thickness of about 50 to about 2000 pm.

In other embodiments, as shown in FIG. 4, the polymer strip has three layers: a top layer 310, a middle layer 320, and a bottom layer 330. The top layer is the same as the outer layer described above, the middle layer is the same as the intermediate layer described above; and the lower layer is the same as the core layer described above.

Geocells are generally embossed (textured by pressing a semi-solid mass after extrusion with a textured drum) to increase friction by granular filling or soil. Geocells can also be perforated to improve friction with granular backfill and water drainage. However, both the relief and the perforation reduce the hardness and strength of the geocell. Since these friction additives are usually present, it is necessary to provide increased strength and hardness of the geocell by changing its polymer composition and / or morphology.

The polymer tape may additionally contain additives to achieve the required physical properties. Such supplements can

2798 UI are selected from, inter alia, germ-forming agents, fillers, fibers, nanoparticles, spatially hindered amine (HALS) stabilizers, antioxidants, UV light absorbers, and carbon blacks.

The fillers may be in the form of powders, fibers, or filamentary crystals. Illustrative fillers include a metal oxide, such as alumina; a metal carbonate such as calcium carbonate, magnesium carbonate, or calcium magnesium carbonate; metal sulphate, such as calcium sulphate; metal phosphate; metal silicate - especially talc, kaolin, mica, or wollastonite; metal borate; metal hydroxide; silicon dioxide; silicate; aluminosilicate; chalk; talc; dolomite; organic or inorganic fibers or filamentary crystals; metal; inorganic particles coated with metal; clay; kaolin; industrial ash; concrete powder; cement; or mixtures thereof. In some embodiments, the filler has an average particle size of less than 10 μ, and in some embodiments, there is also a geometric size ratio greater than one. In some embodiments, the fillers are mica, talc, kaolin, and / or wollastonite. In other embodiments, the fibers have a diameter of less than 1 μ.

Nanoparticles can be added to the polymer composition for various purposes. For example, inorganic UV-absorbing solid nanoparticles have virtually no mobility and are therefore very resistant to leaching and / or evaporation. UV-absorbing solid nanoparticles are also transparent in the visible spectrum and are distributed very evenly. Therefore, they provide protection without any influence on the color or shade of the polymer. Illustrative UV-absorbing nanoparticles contain a material selected from the group consisting of titanium salts, titanium oxides, zinc oxides, zinc halides, and zinc salts. In more specific embodiments, the UV-absorbing nanoparticles are titanium dioxide. Examples of commercially available UV-absorbing particles are SACHTLEBEN ™ Hombitec RM 13 OF TN, from Sachtleben, ZANO ™, zinc oxide from Umicore, NanoZ ™ zinc oxide from Advanced Nanotechnology Limited and AdNano Zinc Oxide ™ from Degussa.

The polymer bands from which the geocell is formed are obtained by various processes. As a rule, the process includes melting the polymer composition, extruding the composition through an extruded head in the form of a molten sheet, shaping and optionally texturing the resulting sheet, processing the sheet as needed to obtain the desired properties, cutting the sheet into strips , and welding, sewing, bonding, or riveting strips formed from sheets together in a geocell. First, the various components, such as polymer resins and any desired additives, are mixed in the molten state, usually in an extruder or mixer. This can be done in, for example, an extruder, such as a twin-screw extruder or a single-screw extruder with sufficiently miscible elements, which provides the necessary heating and deformation with minimal destruction of the polymer. The composition is mixed in the molten state so that any additives are completely dispersed. The composition is then extruded through a head, and pressed between metal calendars in sheet form. Illustrative treatments provided after the extrusion head include sheet surface texturing, sheet perforation, orientation (in one direction or in two directions), electron beam or X-ray irradiation, and thermal annealing. In some embodiments, the sheet is heated to increase crystallinity and reduce internal stresses. In other embodiments, the sheet is processed to induce crosslinking in the polymer resin by electron beam, X-ray, heat treatment, and combinations thereof. Combinations of the above treatments are also provided.

Strips can be cut from the resulting sheet and welded, sewn, or tied together to form a geocell. Such methods are known in the art. The resulting geocell is able to maintain rigidity under prolonged cyclic loading for long periods of time.

The geocells of the present disclosure are suitable for load-bearing applications for which existing geocells cannot be used. In particular, in the current geocells can

2798 UI also to use bulk materials, which as a rule are not suitable for applications with load support for basic layers of road surface in basic soils and soils.

In particular, the geocells of the present disclosure allow the use of backfill materials that were not previously suitable for use in load-bearing applications, such as for road surfaces and base soils, due to their insufficient hardness and relatively poor fatigue resistance (in granular materials, fatigue resistance is also known as modulus of elasticity). Illustrative bulk granular materials that can now be used include quarry waste (fine fraction remaining after good quality grain sorting), crushed concrete, recycled asphalt, broken bricks, construction debris and construction waste, broken glass, power plant ash, fly ash, coal ash, iron - containing slag from a blast furnace, slag from cement production, steel slag, and mixtures thereof.

The present disclosure will be further illustrated in the following non-limiting working examples, it being understood that these examples are for illustrative purposes only and that the disclosure is not intended to be limiting to the materials, conditions, process parameters and the like cited herein.

Examples

Some geocells are prepared and tested for their stress-strain reaction, 5 DMA properties and their influence on the load capacity of granular material.

As a rule, the tensile-strain properties under tension are measured by the Izhar procedure described above.

Yu The load at different deformations is measured or translated into Newtons (N). The deformation is measured or translated into millimeters (mm). The stress is calculated by dividing the load by a specific deformation of the initial cross section of the strip (initial width multiplied by the initial thickness, where the thickness is the nominal distance from end point to end point between the upper surface and the lower surface). Deformation (%) is calculated by dividing the specific deformation (mm) by the initial length (mm) and multiplying by 100.

Comparative example 1

A geocell made of high density polyethylene (HDPE), commercially available from Presto Geosystems (Wisconsin, USA) was obtained 3θ and its properties were tested. The average wall thickness of the cell is 1.5 mm and the strip has a texture of diamond-shaped vertical cells. The geocell is not perforated. Its stress-strain reaction according to the Izhar procedure is shown in Table 1.

Table 1

Voltage (MPa) 7,874 th most common 10,499 th most common 12,336 th most common 13,386 th most common 13,911 th most common 14 14 14 Deformation (%) 2 4 6 8 10 12 14 16

At a deformation of about 8% and a stress of about 13.4 MPa, the comparative example undergoes severe plastic deformation and actually reaches its creep limit at about 8% deformation. In other words, after removing the stress, the specimen does not return to its original length, but remains longer permanently (permanent residual deformations). This phenomenon is undesirable for cellular containment systems for load-bearing applications, especially for those subjected to many (10,000-1,000,000 and more cycles during the product life cycle) and is the reason for the poor performance of HDPE geocells, as resistant load for road surfaces and railways.

Example 1.

The HDPE tape is extruded and stamped to provide a texture similar to Comparative Example 1. The tape is 1.7 mm thick, and then stretched at 100 ° C (on the surface of the tape) so that the length is

2798 UI increases by 50% and thickness decreases by 25%. The stress-strain reaction of this

HDPE tape is measured according to the Izhar procedure and is shown in Table 2.

Table 2

Voltage (MPa) 8 10.8 12.5 13.7 14.5 15.2 15.8 16.5 17.3 Deformation (%) 1.9 3.3 4.8 6 6.6 7.6 8.8 10.51 12

The tape of Example 1 retained the elastic strain response at 12% strain without reaching the creep limit and without reaching its ductility limit and at stresses greater than 17 MPa. The restoration of the initial dimensions after removal of the load is close to 100%.

Example 2.

Composition of high quality polymer alloy containing 12 wt% polyamide 12, 10 wt 10% polybutylene terephthalate, 5% polyethylene, with maleic anhydride additive for compatibility (Bondyram® 5001 manufactured by Polyram), and 73% HDPE is extruded to form textured sheet 1.5 mm thick. The stress-strain reaction of this band formed by the composition was measured according to the Izhar procedure and is shown in Table 3.

Table 3

Voltage (MPa) in 10.8 12.5 13.7 14.5 15.2 15.8 16.5 17.3 Deformation (%) 1.9 3.6 5.2 6.8 7.9 8.9 10 12 14

The tape of Example 2 preserves the elastic strain response at 14% strain and at stresses greater than 17 MPa, without reaching its ductility limit and at stresses greater than. The restoration of the initial dimensions after removal of the load is 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 (0,0) is added for each result. As can be seen, Example 1 and Example 2 have no island creep limit, and retain an increase in stress without creep limit to 12-14% strain at stresses greater than 17 MPa, while Comparative Example 1 reaches its limit of creep at 8-10% deformation and stress about 14 MPa. This translates into a larger range in which an elastic response is maintained. The fact that no creep limit is observed for Example 1 and Example 2 is important when the cyclic load is expected and the ability to return to the original dimensions (and thus the maximum backfill limit) is critical.

FIG. 6 is a graph showing the stress-strain results for Comparative Example 1 and a polymer strip of the present disclosure, which is characterized by the presence of a strain of at most 1.9% at a stress of 8 MPa; deformation at most 3.7% at a stress of 10.8 MPa; deformation at most 5.5% at a stress of 12.5 MPa; deformation at most 7.5% at a stress of 13.7 MPa; deformation at most 10% at a voltage of 14.5 MPa; deformation at most 11% at a voltage of 15.2 MPa; deformation at most 12.5% at a stress of 15.8 MPa; deformation at most 14% at a voltage of 16.5 MPa; and deformation at most 17% at a stress of 17.3 MPa. The area to the left of the dashed line determines the stress-strain combinations according to the present disclosure.

Example 3.

Two geocells were tested to demonstrate improved granular reinforcement and improved load-carrying capacity. These cells are single cells, not an entire geocell. A cell corresponding to Comparative Example 1 was used as a control. For comparison, the cell was made from a composition according to Example 2, textured, and 1.5 mm thick.

The walls of each cell are 10 cm high, 33 cm between the seams, embossed, non-perforated, and have a thickness of 1.5 mm. The cell opens so that its long "radius" is about 260 mm, its short radius is about 185 mm. A sandbox 800 mm long and 800 mm wide is filled

2798 UI up to 20 mm depth with sand. The distribution of the granulometric composition of the sand is presented in Table 4.

Table 4

Mains filter hole (mm) 0.25 0.5 0.75 1 2 4 Cumulative switching% 10-20 35-55 50-70 60-80 80-90 90-100

The cage is placed on the surface of the sand and filled with the same sand. The enlarged cell has an elliptical shape, about 260 mm along the long axis and about 180 mm along the short axis. Additional sand is placed in the sandbox to enclose the cage and bury the cage so that an upper layer of 25 mm covers the cage. The sand is then compacted to 70% relative density.

A piston with a diameter of 150 mm is placed above the center of the cell and the load is increased to provide a pressure increase of 1 θ sand surface by 50 kPa (ie the pressure increases every 1 min by 50 kPa). The displacement (penetration of the piston into the insulated sand) and the pressure (vertical load divided by the area of the piston) are measured.

The piston is used (1) only on sand; (2) per cell of Comparative Example 1; and (3) per cell of Example 2. The results are shown in Table 5.

Table 5

Vertical load (kPa) 100 150 200 250 300 350 400 450 500 550 Move to sand only (mm) 1 2 3 > 10 > 15 > 20 > 20 > 20 > 20 > 20 Move with cell from Comparative Example 1 (mm) 0.7 1.3 2 2.5 3 4 5 > 10 > 15 > 20 Move with a cell from Example 2 (mm) 0.6 1 1.1 1.7 2 2.5 2.9 4 5 7

The cell of Example 2 continued to have good elasticity performance at pressures greater than 400 kPa, while the cell of Comparative Example 1 did not. Due to the creep of the HDPE wall, a poor restriction was observed in the cell of Comparative Example 1. The creep limit for Comparative Example 1 appears at a vertical pressure of about 250 kPa, and if the average circular stress is calculated (average cell diameter is 225 mm ) at this vertical 4θ pressure, a value of about 13.5 MPa is obtained. This number is in very good agreement with the values of the creep limit determined by tensile strain measurements according to the Izhar procedure. The results shown there have a strong 45 and significant correlation between deformation and creep resistance (ability to withstand circular stresses greater than 14 MPa) and ability to withstand high vertical loads. It should be noted that this test provides only a single load, whereas in practical applications the load to be borne is cyclical. As a result, the resistance to plastic deformation is very important and is absent in the cell of Comparative Example 1.

FIG. 7 is a graph showing the results in Table 5. The difference in penetration resistance (ie how well the cell maintains the vertical load) is very clear.

Example 4.

A polymer tape was prepared according to Example 2.

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

The two bands were then analyzed by Dynamic Mechanical Analysis (DMA) at a frequency of 1 Hz according to ASTM 04065. The control HDPE band was tested in the temperature range of about -150 ° C to about 91 ° C. The control strip was heated to 5 ° C / min and the force, displacement, dynamic modulus of elasticity, and tan delta were measured. The polymer tape of Example 2 was tested in the temperature range of about -65 ° C

2798 IU to about 120 ° C. The control strip was heated to 5 ° C / min and the force, displacement, dynamic modulus of elasticity, and tan delta were measured.

FIG. 8 is a graph of the dynamic modulus of elasticity (modulus of elasticity) and Tan Delta depending on the temperature for the HDPE control strip.

FIG. 9 is a graph of the dynamic modulus of elasticity (modulus of elasticity) and Tan Delta as a function of temperature for the polymer strip of Example 2.

The dynamic modulus of elasticity of HDPE decreases much faster than the dynamic modulus of elasticity in Example 2. The dynamic modulus of elasticity for the tape of Example 2 is almost three times higher than the dynamic modulus of elasticity for HDPE tape at 23 ° C. To obtain the same dynamic modulus of elasticity as HDPE tape has at 23 ° C, the tape of Example 2 must be heated to almost 60 ° C, i. the tape of Example 2 retains its dynamic modulus of elasticity better.

Tan Delta for HDPE tape increases exponentially, starting at about 75 ° C, meaning loss of elasticity (ie the material becomes too pliable and would not retain sufficient hardness and elasticity), so the tape is viscous and pliable. This is undesirable because geocells can heat up even when they are underground (like on a road). Tan Delta for the tape from Example 2 retains its properties at temperatures up to 100 ° C. This property is desirable because it provides an additional safety factor. Because performance at elevated temperatures is a way to predict long-term performance at moderate temperatures (as described in ASTM 6992), the fact that HDPE begins to lose its elasticity in seconds and thus its potential to carry a load at about 75 ° C, provides some understanding of its poor creep resistance and tendency to plastic deformation. Unlike HDPE, the composition according to the present disclosure retains its elasticity (low Tan Delta) at very high temperatures, whereby 2Q is assumed to have the potential to retain its properties for many years and many load cycles.

Example 5.

Three bands are tested according to procedure 25 PRS SIM to determine their long-term design voltage (LTDS). As a control, one HDPE tape was prepared according to Comparative Example 1. The first test strip 2Q was prepared according to Example 2. The second test strip was prepared according to Example 2, then oriented at 115 ° C to increase its initial length by 40 %. The results are shown in Table 6 below.

Table 6

Geocell Comparative Example 1 Example 2 Oriented Example 2 LTDS (MPa) 2.2 3 3

As can be seen, both Example 2 and Oriented Example 2 have an increased LTDS compared to Comparative Example 1.

Although specific embodiments, alternatives, modifications, variations, improvements, and significant equivalents that are or may be unforeseen in the present application are described, they may arise in applicants or other experts in the art. Accordingly, the appended claims, as filed and as they can be corrected, are intended to cover all such alternatives, modifications, variations, improvements, and essential equivalents.

Claims (21)

Geocell, characterized in that it is formed by a plurality of polymer strips, the adjacent strips being connected together by connections to form a honeycomb, the plurality of 45 strips extending in a direction perpendicular to the surfaces of the strips, at least a polymer strip has a dynamic modulus of elasticity of 500 MPa or more when measured in the longitudinal direction by Dynamic Mechanical Analysis (DMA) according to ASTM 04065 at 23 ° C and at a frequency of 1 Hz, where at least one polymer strip is made of polypropylene 2798 UI polymer, polyethylene polymer or polymer composition. Geocell according to claim 1, characterized in that the at least one polymer strip has a dynamic modulus of elasticity of 700 MPa or more. Geocell according to claim 1, characterized in that the at least one polymer strip has a dynamic modulus of elasticity of 1000 MPa or more. Geocell according to claim 1, characterized in that the at least one polymer strip has a stress at 12% strain of 14.5 MPa or more when measured according to the Izhar procedure at 23 ° C. Geocell according to claim 1, characterized in that the at least one polymer strip has a stress at 12% strain of 16 MPa or more when measured according to the Izhar procedure at 23 ° C. Geocell according to claim 1, characterized in that 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 ° C. Geocell according to claim 1, characterized in that the at least one polymer strip has a coefficient of thermal expansion of 120 x 10 ' ⁶ / ° C or less at 25 ° C according to ASTM 0696. 8. Geocell formed by a plurality of polymer strips, the adjacent strips being connected together by connections to form a honeycomb, the plurality of strips extending in a direction perpendicular to the surfaces of the strips, at least one polymer strip having a dynamic modulus of elasticity of 150 MPa or more when measured in the longitudinal direction by Dynamic Mechanical Analysis (DMA) according to ASTM 04065 at 63 ° C and at a frequency of 1 Hz, wherein at least one polymer strip is made of polypropylene polymer, polyethylene polymer or polymer composition. Geocell according to claim 8, characterized in that the at least one polymer strip has a dynamic modulus of elasticity of 250 MPa or more. Geocell according to claim 8, characterized in that at least one polymer strip has a dynamic modulus of elasticity 400 MPa or more. Geocell according to claim 8, characterized in that the at least one polymer strip has a stress at 12% strain of 14.5 MPa or more when measured according to the Izhar procedure at 23 ° C. Geocell according to claim 8, characterized in that the at least one polymer strip has a stress at 12% deformation of 16 MPa or more when measured according to the Izhar procedure at 23 ° C. Geocell according to claim 8, characterized in that 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 ° C. Geocell according to claim 8, characterized in that the at least one polymer strip has a coefficient of thermal expansion of 120 x 10 ⁶ / ° C or less at 25 ° C according to ASTM 0696. 15. A geocell formed of a plurality of polymer strips, the adjacent strips connected together to form a honeycomb with the plurality of strips extending in a direction perpendicular to the surfaces of the strips, at least one polymer strip having a long-term design stress of 2.6 MPa or more when measured according to a PRS SIM procedure, wherein at least one polymer strip is made of polypropylene polymer, polyethylene polymer or polymer composition. Geocell according to claim 15, characterized in that the at least one polymer strip has a long-term design voltage of 3 MPa or more when measured according to the PRS SIM procedure. Geocell according to claim 15, characterized in that the at least one polymer strip has a long-term design stress of 4 MPa or more when measured according to the PRS S1M procedure. Geocell according to claim 15, characterized in that the at least one polymer strip has a stress at 12% strain of 14.5 MPa or more when measured according to the Izhar procedure at 23 ° C. Geocell according to claim 15, characterized in that the at least one polymer strip has a stress at 12% deformation 2798 UI 16 MPa or more when measured according to the Izhar procedure at 23 ° C. Geocell according to claim 15, characterized in that 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 ° C. Geocell according to claim 15, characterized in that at least one polymer strip has a coefficient of thermal expansion of 120 x 10 ' ⁶ / ° C or less at 25 ° C according to ASTM 0696.