Method for constructing lightweight embankment, synthetic resin foam block for lightweight embankment, and lightweight embankment structure

Abstract

To provide a construction method of lightweight banking using a synthetic resin foam block for lightweight banking using polylactic acid which is a plant-derived raw material as a raw material and suppressing deterioration of physical properties in soil.SOLUTION: In the construction method of the lightweight banking including the construction of the lightweight banking structure by stacking synthetic resin foamed blocks, polylactic acid-based resin foamed blocks composed of a polylactic acid-based resin subjected to terminal blocking treatment are used as at least a part of the synthetic resin foamed blocks constituting the lightweight banking structure, and the closed cell ratio of the polylactic acid-based resin foamed blocks is set to 50% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a lightweight embankment construction method, a synthetic resin foam block for lightweight embankments, and a lightweight embankment structure. [Background technology]

[0002] Lightweight embankment construction methods, which use synthetic resin foam as an embankment material, have been known for some time as a construction method for widening sloped embankments or embankments behind bridge abutments. Lightweight embankment construction methods involve building an embankment structure by stacking block-shaped synthetic resin foam, which has properties such as light weight, shock absorption, and ease of processing, according to a set pattern, and then covering the outer surface with soil or sand. Lightweight embankment construction methods can reduce the weight of the embankment structure and earth pressure, thereby shortening construction time and reducing costs compared to embankment construction methods that use soil. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-118039 Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, from the viewpoint of reducing the environmental impact, there is a demand to construct lightweight embankment structures using foam blocks made from resins derived from plant-derived materials.

[0005] For example, polylactic acid resins are examples of plant-derived resins. In addition to having excellent mechanical properties, polylactic acid is made from starch and corn, making it possible to mass-produce it, which is thought to help reduce costs.

[0006] However, because polylactic acid resins are degradable, when foam blocks made from polylactic acid resins are buried in the ground to form lightweight embankments, they are susceptible to degradation due to the temperature and moisture in the soil, resulting in a deterioration in their physical properties. For this reason, polylactic acid resins have traditionally been considered unsuitable as a material for foam blocks that form lightweight embankments.

[0007] The present invention was made in consideration of the above circumstances, and aims to provide a synthetic resin foam block for lightweight embankments that uses polylactic acid resin, a plant-derived raw material, and that suppresses the deterioration of physical properties in the soil, as well as a lightweight embankment structure and a lightweight embankment construction method that use this block. [Means for solving the problem]

[0008] In order to solve the above problems, the following lightweight embankment construction method, synthetic resin foam blocks for lightweight embankments, and lightweight embankment structure are provided. [1] A lightweight embankment construction method that includes stacking synthetic resin foam blocks to construct a lightweight embankment structure, As at least a part of the synthetic resin foam blocks constituting the lightweight embankment structure, polylactic acid resin foam blocks made of end-blocked polylactic acid resin are used, A method for constructing lightweight embankments, wherein the polylactic acid resin foam block has a closed cell rate of 50% or more. [2] The method for constructing lightweight embankments according to [1], wherein the polylactic acid resin is end-blocked with one or more compounds selected from the group consisting of carbodiimide compounds, epoxy compounds, oxazoline compounds, and isocyanate compounds. [3] The lightweight embankment construction method according to [2], wherein the compound is mixed in an amount of 0.1 to 5 parts by mass with respect to 100 parts by mass of the polylactic acid resin. [4] The compressive stress at 10% strain of the polylactic acid resin foam block is 10 N / cm 2 The above-mentioned lightweight embankment construction method according to any one of [1] to [3]. [5] The density of the molded product of the polylactic acid-based resin foam block is 10 to 60 kg / m3 A construction method for lightweight embankment according to any one of [1] to [4] above. [6] A synthetic resin foam block for a lightweight embankment structure, the synthetic resin foam block is a polylactic acid-based resin foam block made of a polylactic acid-based resin that has been end-blocked; The polylactic acid-based resin foam block has a closed cell rate of 50% or more. [7] A lightweight embankment structure constructed by stacking synthetic resin foam blocks, The synthetic resin foam block is a lightweight embankment structure including the synthetic resin foam block of [6]. [Effects of the Invention]

[0009] According to the lightweight embankment construction method of the present invention, it is possible to construct lightweight embankments using plant-derived materials to construct lightweight embankment structures in which the deterioration of physical properties in the soil is suppressed more than conventional methods. Furthermore, the polylactic acid resin foam blocks for lightweight embankments and the lightweight embankment structures of the present invention can be used for lightweight embankments because they use plant-derived materials and the deterioration of physical properties in the soil is suppressed. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, one embodiment of the lightweight embankment construction method, synthetic resin foam block, and lightweight embankment structure of the present invention will be described.

[0011] In the lightweight embankment construction method of the present invention, a lightweight embankment structure is constructed by stacking synthetic resin foam blocks. The synthetic resin foam blocks used in the lightweight embankment construction method of the present invention are polylactic acid resin foam blocks (hereinafter, polylactic acid resin foam blocks may be simply referred to as "foam blocks") made of end-blocked polylactic acid resin, and have a closed cell rate of 50% or more.

[0012] The lightweight embankment structure of the present invention is constructed by stacking synthetic resin foam blocks, and is constructed by including the polylactic acid resin foam block of the present invention as the synthetic resin foam block that constitutes the lightweight embankment structure. In other words, in the lightweight embankment construction method and lightweight embankment structure of the present invention, the polylactic acid resin foam block of the present invention may be used alone or in combination with other synthetic resin foam blocks.

[0013] As the synthetic resin foam block, for example, a block obtained by foaming a thermoplastic resin such as polystyrene, polyethylene, polypropylene, polyurethane, or polyvinyl chloride can be used. Furthermore, from the viewpoints of excellent water resistance and high strength even at low density, extruded foams and molded articles made from expanded beads can also be used. Among these, it is preferable to use molded articles made from expanded polylactic acid resin beads (hereinafter, molded articles made from expanded beads may be referred to as "molded articles made from expanded beads") as the polylactic acid resin foam block of the present invention. As the other synthetic resin foam block, preferably, a polystyrene resin foam bead molded product obtained by in-mold molding or a polystyrene resin foam obtained by extrusion can be used.

[0014] The polylactic acid resin constituting the foamed block is preferably a polymer containing 50 mol% or more of component units derived from lactic acid. Examples of polylactic acid resins include (a) polymers of lactic acid, (b) copolymers of lactic acid and other aliphatic hydroxycarboxylic acids, (c) copolymers of lactic acid, aliphatic polyhydric alcohols, and aliphatic polycarboxylic acids, (d) copolymers of lactic acid and aliphatic polycarboxylic acids, (e) copolymers of lactic acid and aliphatic polyhydric alcohols, and (f) mixtures of any of (a) to (e). Polylactic acid also includes what are called stereocomplex polylactic acid and stereoblock polylactic acid. Specific examples of lactic acid include L-lactic acid, D-lactic acid, DL-lactic acid, or their cyclic dimers, L-lactide, D-lactide, DL-lactide, or mixtures thereof.

[0015] The polylactic acid resin is end-capping treated. Here, "end-capping treatment" refers to a process in which the end groups (-COOH) of polylactic acid are reacted with an end-capping agent to give the polylactic acid an end-capping structure, thereby suppressing hydrolysis of the end groups. Furthermore, it is not necessary for all of the end groups (-COOH) of the polylactic acid resin used in the present invention to react with the end-capping agent; unreacted end groups (-COOH) may remain.

[0016] In the lightweight embankment construction method of the present invention, the polylactic acid resin constituting the foamed block is end-blocked, which reduces the decomposition of the polylactic acid resin foamed block, thereby preventing the deterioration of the physical properties of the polylactic acid resin foamed block in the soil.

[0017] An end-capping agent is a compound capable of reacting with the terminal group (—COOH) of polylactic acid to block the end group. Examples of the end-capping agent include carbodiimide compounds, oxazoline compounds, isocyanate compounds, and epoxy compounds. Among these, carbodiimide compounds are preferred. Specific examples include aromatic monocarbodiimides such as bis(dipropylphenyl)carbodiimide (e.g., Stabaxol 1-LF manufactured by Rhein Chemie), aromatic polycarbodiimides (e.g., Stabaxol P manufactured by Rhein Chemie, Stabaxol P400 manufactured by Rhein Chemie), and aliphatic polycarbodiimides such as poly(4-4′-dicyclohexylmethanecarbodiimide) (e.g., Carbodilite LA-1 manufactured by Nisshinbo Chemical Inc.). These end-capping agents may be used alone or in combination of two or more.

[0018] The amount of end-capping agent is preferably 0.1 to 5 parts by weight, more preferably 0.5 to 3 parts by weight, per 100 parts by weight of polylactic acid. When multiple end-capping agents are used, the amount refers to the total amount. When the amount of end-capping agent is within this range, the polylactic acid resin is end-capping-treated, reducing the decomposition potential of the foamed block and stably preventing the deterioration of the foamed block's physical properties in soil.

[0019] Furthermore, the end-capping agent blended into the polylactic acid resin not only reacts with the polylactic acid resin to block the ends, but also leaves unreacted residue in the resin, which reacts with functional groups generated by hydrolysis of the polylactic acid resin, thereby contributing to suppressing decomposition.

[0020] Whether or not the polylactic acid in the polylactic acid resin constituting the foam block is end-blocked can be analyzed by a known method. Specifically, for example, the sample is extracted with chloroform, the soluble matter is concentrated, and then the insoluble matter (separated matter) is extracted with methanol, and the insoluble matter is analyzed by IR, 1 The end-blocking structure of polylactic acid can be confirmed by measurements such as 1H NMR, pyrolysis GC / MS, and reactive pyrolysis GC / MS.

[0021] Furthermore, other resins can be mixed with polylactic acid-based resins as long as the objects and effects of the present invention are not impaired. The mixed resin of polylactic acid and other resins contains 50% by weight or more of polylactic acid, preferably 70% by weight or more, and more preferably 90% by weight or more. Examples of other resins that can be mixed with polylactic acid include polyethylene-based resins, polypropylene-based resins, polystyrene-based resins, and polyester-based resins other than polylactic acid-based resins.

[0022] In the lightweight embankment construction method of the present invention, the closed cell ratio of the foamed block is 50% or more. If the closed cell ratio of the foamed block is within this range, the foamed block will have excellent strength properties when used as lightweight embankment. From this perspective, the closed cell ratio of the foamed block is preferably 60% or more, and more preferably 70% or more.

[0023] The closed cell ratio of the foamed block is measured, for example, as follows. A 25 x 25 x 30 mm sample is cut from the center of the foam block (all skin removed) to serve as the measurement sample, and its apparent volume Va is accurately measured using the submersion method as described below. After measuring the apparent volume Va, the measurement sample is thoroughly dried, and then its true volume Vx is measured using a Toshiba Beckman Corporation air comparison hydrometer 930 in accordance with procedure C described in ASTM-D2856-70. Based on these volumes Va and Vx, the closed cell ratio is calculated using equation (2) below, and the average value for N=5 is taken as the closed cell ratio of the foam particles. Closed cell ratio (%)=(Vx-W / ρ)×100 / (Va-W / ρ) (2) however, Vx: The true volume of the expanded beads measured by the above method, i.e., the sum of the volume of the resin constituting the expanded beads and the total volume of the closed cells in the expanded beads (cm 3 ) Va: The apparent volume (cm) of the foamed particles measured by submerging the foamed particles in a measuring cylinder containing water and measuring the rise in the water level. 3 ) W: Weight of the measurement sample (g) ρ: Density of the resin that makes up the foam block (g / cm 3 ) When the foamed block is a foamed bead molding or when the foamed beads are used to form a foamed bead molding, the closed cell content can be measured in the same manner.

[0024] In the lightweight embankment construction method of the present invention, from the viewpoint of workability, the compressive stress of the foam block at 10% strain is 10N / cm 2 It is preferable that the resistance is 15N / cm or more. 2 More preferably, it is 20 N / cm or more. 2 There is no particular upper limit to the compressive stress, but it is generally 100 N / cm 2The compressive stress of the foamed block at 10% strain can be determined, for example, by cutting ten test pieces, 100 mm long x 100 mm wide x 50 mm thick, at equal intervals from the foamed block, excluding the skin, and conducting a compression test based on JIS K7220 (2006). The test can be conducted, for example, on a plurality of test pieces, and the arithmetic mean value of the obtained values ​​can be used as the compressive stress at 10% strain.

[0025] The weight-average molecular weight (MW) of the polylactic acid resin constituting the foamed block is preferably 150,000 to 300,000. When the weight-average molecular weight (MW) of the polylactic acid resin is within this range, the foamed block can more stably exhibit its physical properties in the soil.

[0026] The density of the foam block is 10 to 60 kg / m 3 is preferably 20 to 50 kg / m 3 When the molding density of the foamed block is within this range, the foamed block has excellent mechanical properties as a foamed block for lightweight embankment, and is also lightweight.

[0027] When the foamed block is an expanded bead molding, the fusion rate of the expanded bead molding is preferably 50% or more, more preferably 60% or more, and even more preferably 80% or more. When the fusion rate of the expanded bead molding is within this range, the expanded bead molding will have superior mechanical properties as a foamed block for lightweight embankments. The fusion rate of the expanded bead molding refers to the material failure rate based on the number of foamed beads on the fracture surface when the expanded bead molding is broken; unfused portions do not break, but peel at the interface between the expanded beads. The method for measuring the fusion rate will be described later.

[0028] From the viewpoint of workability and handling, the flexural strength of the foamed block is preferably 350 kPa or more, and more preferably 380 kPa or more. The flexural strength is a value obtained according to JIS K7221-1 (2006).

[0029] Furthermore, when the foamed block is an expanded bead molding, the expanded beads constituting the expanded bead molding preferably have a core layer and a coating layer (a fusion-improving layer) formed around the core layer. By providing the coating layer to the expanded beads, the expanded beads are sufficiently fused together, and the expanded beads are formed into an expanded polylactic acid resin bead molding with few voids between them.

[0030] The coating layer is preferably composed of a resin having a lower melting point or softening temperature than the crystalline polylactic acid resin constituting the expanded beads. Specific examples of the resin constituting the coating layer include polyvinyl acetate, polyvinyl alcohol, polyester, polyesteramide, and low-crystalline polylactic acid. Of these, the resin constituting the coating layer is preferably low-crystalline polylactic acid. The low-crystalline polylactic acid preferably has a ratio of crystalline polylactic acid to amorphous polylactic acid (crystalline polylactic acid / amorphous polylactic acid) of 10 / 90 to 30 / 70. The method for forming the coating layer on the expanded beads is not particularly limited. For example, the surface of the expanded beads may be coated with the coating layer, or the surface of the resin particles before expansion may be coated with the coating layer, and the resin particles may be expanded to form the coating layer on the surface of the expanded beads.

[0031] Next, expanded beads having a core layer and a coating layer (multi-layer expanded beads) will be described.

[0032] In these expanded beads, the softening point (B) [°C] of the polylactic acid resin constituting the coating layer is preferably lower than the softening point (A) [°C] of the polylactic acid resin constituting the core layer of the expanded beads. Specifically, the difference between the softening points (A) and (B) [(A) - (B)] is preferably greater than 0°C and not greater than 105°C, more preferably 15 to 105°C, and even more preferably 20 to 105°C. Expanded beads having a difference within this range can be obtained by, for example, co-extrusion of the polylactic acid resins constituting the coating layer and the core layer, each having a softening point (B) and a softening point (A). This method allows for efficient production of expanded beads, which exhibit excellent heat-sealing properties during in-mold molding more stably, facilitating in-mold molding of a foamed block made of expanded beads.

[0033] From the viewpoint of the ease of handling the expanded beads and the mechanical strength of the resulting expanded bead molding at high temperatures, the softening point (B) of the polylactic acid resin constituting the coating layer is in the above-mentioned range relative to the softening point (A) of the polylactic acid resin constituting the core layer, and is preferably 50°C or higher, more preferably 55°C or higher, and particularly preferably 65°C or higher.

[0034] The softening point in this specification refers to the Vicat softening temperature measured by the A50 method based on JIS K7206 (1999). For the measurement specimen, a polylactic acid resin is thoroughly dried in a vacuum oven, and then pressurized under conditions of 200°C and 20 MPa, with air removal as necessary to prevent air bubbles from being mixed in, to prepare a test specimen measuring 20 mm long x 20 mm wide x 4 mm thick. The test specimen is then annealed in an oven at 80°C for 24 hours before use in the measurement. A measuring device such as the "HDT / VSPT Tester Model TM-4123" manufactured by Ueshima Seisakusho Co., Ltd. can be used.

[0035] In expanded beads comprising a core layer and a coating layer, the weight ratio of the resin forming the core layer to the resin forming the coating layer is preferably 99.9:0.1 to 80:20, more preferably 99.7:0.3 to 90:10, and even more preferably 99.5:0.5 to 92:8. When the weight ratio of the resin forming the core layer to the resin forming the coating layer of the expanded beads is within this range, the fusion strength between the expanded beads is increased, resulting in an expanded bead molding having particularly excellent mechanical properties, and further excellent mechanical properties due to the increased proportion of the core layer, which contributes to improving the physical properties of the expanded beads.

[0036] In the expanded bead molding used in the present invention, the end-capping agent is preferably added to at least the core layer of the expanded beads, and more preferably to both the core layer and the coating layer.

[0037] Next, a method for producing a foamed block made of a foamed bead molding suitable for use as the foamed block of the present invention will be described. The method for producing the foamed block of the present invention may be a conventionally known method, and for example, the method described in JP 2016-222807 A can be taken into consideration.

[0038] The expanded beads used in the expanded bead molding can be produced by a conventionally known expansion method, such as a conventionally known method for producing extruded expanded beads, a method in which resin beads are produced and then impregnated with a blowing agent to form expandable resin beads, and the expandable resin beads containing the blowing agent are released from a pressurizable sealed container to expand, or a method in which expandable resin beads containing a blowing agent are heated, softened, and expanded. Among the above-mentioned production methods, the expanded beads used in the present invention are preferably obtained by dispersing composite resin particles consisting of a core layer and a coating layer in an aqueous medium (usually water) in a pressurizable sealed container (e.g., an autoclave), adding a dispersant, injecting a required amount of blowing agent, pressurizing the mixture, and stirring under heat for a required time to impregnate the composite resin particles with the blowing agent, and then releasing the contents together with the aqueous medium into a pressure region lower than the pressure inside the container, thereby foaming the particles.

[0039] Specifically, a polylactic acid resin and a terminal blocking agent are heated and melt-kneaded in an extruder to perform a terminal blocking treatment, and then extruded into strands and cut to produce resin particles (pellets).These resin particles are dispersed in an aqueous medium in a sealed container, heated, and impregnated with a physical foaming agent to form expandable resin particles.These expandable resin particles are then released from the sealed container together with the aqueous medium at a temperature suitable for foaming, thereby producing expanded particles (expanded polylactic acid particles). The polylactic acid foam particles include, for example, polylactic acid resin foams under the trade name "LACTIF (registered trademark)" manufactured by JSP Co., Ltd., which have a bulk density of 15 to 200 kg / m 3 In addition, expanded particles can also be obtained by referring to JP-B-53-1313, WO 2012 / 086305, JP-A-2012-025869, etc.

[0040] The physical foaming agent may be, for example, an organic physical foaming agent such as hydrocarbons such as butane, pentane, or hexane, or a halogenated hydrocarbon such as trichlorofluoromethane, dichlorofluoromethane, tetrachlorodifluoroethane, or dichloromethane, or an inorganic physical foaming agent such as inorganic gases such as carbon dioxide, nitrogen, or air, or water, which may be used alone or in combination of two or more. The amount of physical foaming agent added can be adjusted as appropriate, but for example, the amount of inorganic physical foaming agent added is preferably 0.1 to 30 parts by weight, more preferably 0.5 to 15 parts by weight, and even more preferably 1 to 10 parts by weight, per 100 parts by weight of the base resin (polylactic acid-based resin).

[0041] The resulting expanded beads can be used to obtain an expanded bead molded article by a known in-mold molding method. Specific examples of the in-mold molding method include compression molding, cracking molding, pressure molding, compression filling molding, and atmospheric pressure filling molding, which use a conventionally known expanded bead molding die (see, for example, JP-B Nos. 46-38359, 51-22951, 4-46217, 6-22919, and 6-49795).

[0042] Furthermore, the foamed bead molding can be appropriately processed into a desired shape and size to obtain a foamed block. Specifically, the foamed block is a rectangular parallelepiped block and may be of various sizes. A block may be formed by combining a plurality of foams by adhesive or other means. When the foamed block is made of a foamed bead molding, the foamed block preferably has a rectangular parallelepiped shape with a thickness of 400 mm or more, and more preferably has a height of 2000 mm or more, a width of 1000 mm or more, and a thickness of 500 mm or more. It is preferable to form a foamed block made of a foamed bead molding as a single molded product by in-mold molding using a mold having the shape of the foamed bead molding to obtain a foamed block of the desired rectangular parallelepiped shape.

[0043] The lightweight embankment construction method, foam block, and lightweight embankment structure of the present invention are not limited to the above-described embodiments. [Example]

[0044] The present invention will be described below with reference to examples, but the lightweight embankment construction method, foamed block, and lightweight embankment structure of the present invention are not limited to the following examples. Although foamed blocks are used in the lightweight embankment construction method and lightweight embankment structure, in the examples, foamed bead moldings were used as the foamed blocks to evaluate their performance. The foamed bead moldings that form the foamed blocks can be formed using the foamed beads obtained in the following examples, by changing the size of the mold as appropriate.

[0045] The apparatus used for producing the multilayer resin particles was an extruder equipped with a co-extrusion die for forming a multilayer strand at the outlet side of an extruder for forming a core layer having an inner diameter of 65 mm and an extruder for forming a coating layer having an inner diameter of 30 mm.

[0046] The base resins for forming the core layer and the coating layer shown in Table 1 and a carbodiimide (Bioamide 100, manufactured by Rhein Chemie) as an end-capping agent were fed to the extruder for forming the core layer and the extruder for forming the coating layer, respectively, in the proportions shown in Table 1, and melt-kneaded at 200 to 220°C. The molten mixture was introduced into the co-extrusion die, merged inside the die, and co-extruded from the holes in the nozzle attached to the tip of the extruder as a multilayer strand with the coating layer formed on the side of the core layer. The co-extruded strand was water-cooled, cut into pieces weighing approximately 1 mg using a pelletizer, and dried to obtain multilayer resin particles.

[0047] The polylactic acid resin of the core layer was supplied with a masterbatch of polytetrafluoroethylene powder (product name: TFW-1000, manufactured by Seishin Enterprise Co., Ltd.) as a cell control agent to a content of 1000 ppm by weight, and the polylactic acid resin of the coating layer was supplied with a masterbatch of phthalocyanine green pigment to a content of 100 ppm by weight.

[0048] Next, expanded polylactic acid resin particles were prepared using the multilayer resin particles. First, 1 kg of the resin particles obtained as described above was placed in a 5-L autoclave equipped with a stirrer along with 3 L of water as a dispersion medium. Furthermore, 0.45 parts by weight of aluminum oxide as a dispersant and 0.01 parts by weight of a surfactant (product name: Neogen S-20F, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., sodium alkylbenzene sulfonate) were added to the dispersion medium. Carbon dioxide was then injected into the autoclave until the pressure inside the autoclave reached 1.0 MPa (G). The temperature was then raised to the foaming temperature shown in Table 1 while stirring, and carbon dioxide was further injected until the pressure shown in Table 1 was reached. The temperature was maintained at the foaming temperature shown in Table 1 for 15 minutes. The contents of the autoclave were then released to atmospheric pressure while applying back pressure with nitrogen, yielding expanded beads with the apparent density shown in Table 1. The amounts (parts by weight) of dispersant and surfactant added are based on 100 parts by weight of polylactic acid resin particles.

[0049] Next, a foamed bead molding was produced using the foamed beads. The resulting foamed beads were filled into a mold for molding a body having dimensions of 200 mm wide x 250 mm long x 50 mm thick, and in-mold molding was carried out by steam heating to obtain one foamed bead molding, which was used as a foam block. Therefore, the physical properties of the foamed bead molding measured in this example were equivalent to those of the foam block.

[0050] Various physical properties of the expanded beads and the expanded bead moldings were measured by the following methods.

[0051] [Apparent density of foamed particles] The expanded particles are left to cure for 10 days in a temperature-controlled room under atmospheric pressure, a relative humidity of 50%, and a temperature of 23°C. Next, in the same temperature-controlled room, the weight W1 (g) of the expanded particles after curing (approximately 500 ml) is measured, and the weighted expanded particles are submerged in a measuring cylinder containing water at 23°C using a tool such as a wire mesh. Next, the volume V1 (L) of the expanded particles is measured from the rise in the water level after subtracting the volume of the tool such as a wire mesh below the water surface. The weight W1 of the expanded particles placed in the measuring cylinder is divided by the volume V1 (W1 / V1) to determine the apparent density (kg / cm 3 ) was sought.

[0052] [Average bubble diameter of expanded particles] The average cell diameter can be determined as follows based on an enlarged microscope photograph of a cross section of an expanded bead divided into approximately two equal parts. In the enlarged photograph of the cross section of the expanded bead, four line segments are drawn from one surface of the expanded bead to the other, passing through approximately the center of the cross section of the cell. The line segments are drawn so as to form radial straight lines extending in eight equally spaced directions from approximately the center of the cross section of the cell to the surface of the cut particle. Next, the total number N (cells) of cells intersecting with the four line segments is determined. The sum L (μm) of the lengths of the four line segments is calculated, and the value (L / N) obtained by dividing the sum L by the sum N is taken as the average cell diameter of one expanded bead. This process is performed on 10 expanded beads, and the arithmetic mean of the average cell diameters of each expanded bead is taken as the average cell diameter of the expanded beads.

[0053] [Closed cell ratio of expanded beads and expanded bead molded products] Measurement was carried out by the method described above.

[0054] [Mold density of foamed bead molded body] The weight of the expanded bead molding was measured and divided by the volume of the expanded bead molding determined from the external dimensions.

[0055] [Fusion rate of foamed bead molding] The fusion rate was measured and evaluated by the following method. The expanded bead molding was bent and broken, and the number of expanded beads present on the fracture surface (C1) and the number of broken expanded beads (C2) were determined. The ratio of broken expanded beads to the total number of expanded beads (C2 / C1 × 100) was calculated as the material failure rate. The above measurement was performed five times using different test pieces, and the material failure rate was determined for each test piece. The arithmetic average of these values ​​was taken as the fusion rate.

[0056] [Number average molecular weight Mn, weight average molecular weight Mw and polydispersity Mw / Mn] The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of polyethylene wax were measured by gel permeation chromatography (GPC) using polystyrene as a standard. Chromatograms were obtained using a Tosoh HLC-8321GPC / HT. The polyethylene wax sample was dissolved in o-dichlorobenzene (o-DCB) at 145°C and filtered to prepare a 1 g / L sample solution. Next, the sample was separated by gel permeation chromatography (GPC) using one TSKguardcolumn SuperH-H and two TSK-GEL GMHHR-H(S)HT columns connected in series under the following separation conditions: o-dichlorobenzene (o-DCB) as the eluent, o-dichlorobenzene (o-DCB), flow rate: 1.0 mL / min, column temperature: 145°C. Chromatograms were obtained. The retention times in the chromatogram were converted into molecular weights using a calibration curve prepared using standard polystyrene to obtain a differential molecular weight distribution curve, from which the weight-average molecular weight of the sample was calculated.

[0057] [Durability of foamed bead moldings] (1) Degradability Test samples were cut out from the obtained expanded bead moldings and buried in the soil. After 9 months, the shape changes of the expanded bead molding samples, as well as the changes over time in various physical properties and molecular weight (number average molecular weight (Mn), weight average molecular weight (Mw)) were measured. ○: The shape of the sample (0.15m wide x 0.15m long x 0.06m thick) was maintained during the underground test. ×: In the soil test, the polylactic acid resin was decomposed, and the sample was disintegrated.

[0058] (2) Physical properties Based on JIS K7220 (2006), the 10% compressive stress was measured and evaluated according to the following criteria. 〇;10N / cm 2 It has a compressive stress of 10% or more. × 10N / cm 2 has a compressive stress of less than 10%.

[0059] Table 1 shows the physical properties of the expanded bead moldings.

[0060] [Table 1]

[0061] As shown in Table 1, the foam block samples of Examples 1 and 2, which are made of end-blocked polylactic acid resin and foamed bead moldings with a closed cell rate of 50% or more, have sufficient physical properties for use as lightweight embankment structures and are confirmed to be inhibited from decomposing in the soil.

[0062] On the other hand, it was confirmed that it was difficult to prevent decomposition in soil and deterioration of physical properties in the foamed block sample of Comparative Example 1, which was made of expanded bead moldings composed of polylactic acid resin that had not been end-capped.Furthermore, it was confirmed that the foamed block of Comparative Example 2, which was made of expanded bead moldings composed of end-capped polylactic acid resin and had a closed cell ratio of less than 50%, was prevented from decomposing in soil, but was not suitable for use as lightweight embankment.

[0063] The compressive stress at 10% strain of the foamed bead molding of Example 1 was 21 N / cm 2 The compressive stress at 10% strain of the foamed bead molding of Example 2 was 22 N / cm 2 The bending strength of Example 1 was 406 kPa, and the bending strength of Example 2 was 400 kPa.

[0064] Furthermore, the change in molecular weight with time before and after the soil test was measured for the expanded bead molding of Example 1. The molecular weight of the sample before the soil test was Mn=10×10 4 , Mw=20×10 4 The molecular weight of the sample after the soil test was Mn = 11 × 10 for the "low embankment" in which the foamed bead molding was buried at a distance of 0.1 m from the embankment surface. 4 , Mw=20×10 4 , Mw / Mn=1.8, and Mn=11×10 for the "high embankment" in which the foamed bead molding was buried at a distance of 0.85 m from the embankment surface. 4 , Mw=20×10 4 , Mw / Mn=1.8, and no change was observed in either example.

[0065] Therefore, it was confirmed that the expanded bead molding of Example 1 that was kept in the embankment maintained its molecular weight even after 9 months had passed, and decomposition was suppressed.

Claims

1. A lightweight embankment construction method that includes stacking synthetic resin foam blocks to construct a lightweight embankment structure, As at least a part of the synthetic resin foam blocks constituting the lightweight embankment structure, polylactic acid resin foam blocks made of end-blocked polylactic acid resin are used, A method for constructing lightweight embankments, wherein the polylactic acid resin foam block has a closed cell rate of 50% or more.

2. A lightweight embankment construction method as described in claim 1, wherein the polylactic acid resin is end-blocked with one or more compounds selected from carbodiimide compounds, epoxy compounds, oxazoline compounds and isocyanate compounds.

3. 3. The lightweight embankment construction method according to claim 2, wherein the compound is mixed in an amount of 0.1 to 5 parts by mass per 100 parts by mass of the polylactic acid resin.

4. The polylactic acid resin foam block has a compressive stress of 10 N / cm at 10% strain. ２ 3. The lightweight embankment construction method according to claim 1 or 2.

5. The density of the molded product of the polylactic acid resin foam block is 10 to 60 kg / m ３ 3. The method for constructing lightweight embankments according to claim 1 or 2,

6. A synthetic resin foam block for a lightweight embankment structure, the synthetic resin foam block is a polylactic acid-based resin foam block made of a polylactic acid-based resin that has been end-blocked; The synthetic resin foam block has a closed cell rate of 50% or more.

7. A lightweight embankment structure constructed by stacking synthetic resin foam blocks, A lightweight embankment structure, wherein the synthetic resin foam block comprises the synthetic resin foam block according to claim 6.

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