Lightweight aggregate, method for producing same, and mortar and concrete using same

Abstract

A lightweight aggregate according to an embodiment of the present disclosure is a granular material in which protrusions having an average diameter of less than 3.0 mm are scattered on a surface thereof and the arithmetic average roughness Ra of the surface excluding the protrusions falls within the range of 10 μm to 100 μm, and the density of which falls within the range of 0.9 g / cm3 to 1.3 g / cm3.

Description

Lightweight aggregate, its manufacturing method, and mortar and concrete using the same

[0001] The present disclosure relates to a lightweight aggregate, a method for producing the same, and a mortar and concrete using the same.

[0002] Lightweight aggregates containing plastic waste have been studied as aggregates for mortar and concrete. For example, composites containing plastic waste and waste other than plastic waste have been studied as lightweight aggregates (see, for example, Patent Documents 1 and 2).

[0003] Japanese Patent Laid-Open No. 11-147739 Japanese Patent Laid-Open No. 2006-169066

[0004] Lightweight aggregates made from plastic waste are desirable from the perspective of efficient resource utilization. However, the resins contained in plastic waste generally have low affinity for cement and water. As a result, lightweight aggregates containing resins are difficult to disperse uniformly in mortar or concrete, and mortars and concrete containing such aggregates tend to have reduced mechanical strength and durability. Furthermore, plastic waste sometimes contains aluminum-deposited film. When plastic waste contained in aluminum-deposited film is used as lightweight aggregate in mortar or concrete, the aluminum in the aluminum-deposited film reacts with the alkali derived from the cement to generate hydrogen, which can cause the mortar or concrete to expand.

[0005] The present disclosure aims to provide a lightweight aggregate that contains resin, particularly plastic waste, but has high affinity for cement and water and is easily dispersed uniformly in mortar or concrete, a method for producing the same, and mortar and concrete using the lightweight aggregate.

[0006] The present disclosure provides a surface having scattered protrusions with an average diameter of less than 3.0 mm, an arithmetic mean roughness Ra of the surface excluding the protrusions being in the range of 10 μm to 100 μm, and a density of 0.9 g / cm ３ 1.3g / cm or more ３ The present invention relates to a lightweight aggregate, which is a granular material within the following range:

[0007] 1 is a cross-sectional view showing a lightweight aggregate according to an embodiment of the present disclosure; 2 is a surface image of a lightweight fine aggregate obtained in this example; and 3 is a surface image of a lightweight coarse aggregate obtained in this example.

[0008] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0009] [Lightweight Aggregate] Fig. 1 is a cross-sectional view showing a lightweight aggregate according to one embodiment of the present disclosure. As shown in Fig. 1, the lightweight aggregate 1 is a granular body having a granular portion 10 and protrusions 20 scattered on the surface of the granular portion 10. The protrusions 20 have, for example, a diameter (D in Fig. 1) of 0.05 mm or more and a height (H in Fig. 1) of 0.2 mm or more. The height H of the protrusions 20 is the length relative to the surface 10a of the granular portion 10. The shape of the granular portion 10 is not particularly limited and may be, for example, spherical, elliptical, cylindrical, prismatic, conical, pyramidal, or irregular.

[0010] In the lightweight aggregate 1, the arithmetic mean roughness Ra of the surface 10a of the granular portion 10 excluding the protrusions 20 is in the range of 10 μm to 100 μm. The maximum height roughness Rz of the surface 10a of the granular portion 10 excluding the protrusions 20 may be, for example, in the range of 3 to 6 times the arithmetic mean roughness Ra. The arithmetic mean roughness Ra may be, for example, in the range of 20 μm to 70 μm. The maximum height roughness Rz may be, for example, in the range of 60 μm to 400 μm, or in the range of 60 μm to 180 μm. The arithmetic mean roughness Ra and the maximum height roughness Rz are the average values ​​of the arithmetic mean roughness Ra and the maximum height roughness Rz measured at three locations on the surface 10a of the granular portion 10 for each measurement sample, for example, using 10 lightweight aggregates 1 as measurement samples. The arithmetic mean roughness Ra and the maximum height roughness Rz can be measured using, for example, a shape measuring laser microscope.

[0011] The average diameter D (average diameter) of the protrusions 20 of the lightweight aggregate 1 is less than 3.0 mm. The average diameter of the protrusions 20 may be, for example, in the range of 0.1 mm or more and less than 2.0 mm. The average height H (average height) of the protrusions 20 of the lightweight aggregate 1 may be, for example, in the range of 0.4 mm or more and 2.0 mm or less. The average diameter and average height of the protrusions 20 are obtained by using, for example, 10 pieces of lightweight aggregate 1 as measurement samples and averaging the diameters and heights of the protrusions 20 measured for each measurement sample. The diameter and height of the protrusions 20 can be measured using, for example, a shape measurement laser microscope.

[0012] The number of protrusions 20 on the lightweight aggregate 1 is not particularly limited, but the average number of protrusions 20 per lightweight aggregate 1 may be, for example, in the range of 5 to 100, or in the range of 10 to 50.

[0013] The density of the lightweight aggregate 1 is 0.9 g / cm ３ 1.3g / cm or more ３ The water absorption rate of the lightweight aggregate 1 may be, for example, in the range of 5% by mass or more and 20% by mass or less. The density and water absorption rate of the lightweight aggregate 1 are values ​​measured in accordance with, for example, JIS A 1109:2020 (Test method for density and water absorption rate of fine aggregate) or JIS A 1110:2020 (Test method for density and water absorption rate of coarse aggregate). The unit volume mass (bone dry state) of the lightweight aggregate 1 may be in the range of 0.2 kg / L or more and 0.8 kg / L or less. The unit volume mass is a value measured in accordance with, for example, JIS A 1104:2019 (Test method for unit volume mass and actual volume rate of aggregate).

[0014] The particle size of the lightweight aggregate 1 is not particularly limited and can be adjusted depending on the application. For example, when used as fine aggregate, the 2.5 mm sieve residue measured using a sieve with a 2.5 mm mesh size may be 95 mass% or more, and the 5.0 mm sieve residue measured using a sieve with a 5.0 mm mesh size may be less than 15 mass%. When used as coarse aggregate, the 5.0 mm sieve residue measured using a sieve with a 5.0 mm mesh size may be 85 mass% or more. When used as coarse aggregate, the 25 mm sieve residue measured using a sieve with a 25 mm mesh size may be 5 mass% or less.

[0015] The lightweight aggregate 1 includes a low-melting point resin 11, non-low-melting point resin particles 12 dispersed in the low-melting point resin, and wood particles 13. The low-melting point resin 11 bonds the non-low-melting point resin particles 12 and the wood particles 13 to form granular portions 10. Some of the non-low-melting point resin particles 12 and the wood particles 13 protrude from the surface 10a of the granular portions 10 to form protrusions 20. The low-melting point resin 11 forms the unevenness of the surface 10a of the granular portions 10.

[0016] The low-melting-point resin 11 is, for example, a thermoplastic resin having a melting point in the range of 80°C or higher and lower than 190°C. Examples of the low-melting-point resin 11 include polystyrene (PS), acrylonitrile-butadiene-styrene resin (ABS), polyethylene (PE), polymethyl methacrylate (PMMA), polycarbonate (PC), polypropylene (PP), polyamide 12 (PA12), and polyacetal (POM). The non-low-melting-point resin particles 12 include, for example, at least one of a high-melting-point resin having a melting point of 190°C or higher and a thermosetting resin. The melting point of the high-melting-point resin may be 340°C or lower. Examples of high-melting-point resins include polyethylene terephthalate (PET), polyamide 6 (PA6), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), and polyether ether ketone (PEEK). The thermosetting resin is a resin after curing. Examples of the thermosetting resin include polyimide (PI), polyurethane (PU), and phenolic resin (PF). The average major axis of the non-low melting point resin particles 12 may be, for example, less than 3.0 mm, or may be in the range of 0.5 mm or more and less than 2.0 mm.

[0017] The low melting point resin 11 and non-low melting point resin particles 12 may be derived from plastic waste.

[0018] The average major axis of the wood particles 13 may be, for example, less than 3.0 mm, or may be in the range of 0.5 mm or more and less than 2.0 mm. The wood particles 13 may be, for example, crushed waste wood. Examples of waste wood that can be used include construction waste wood, thinned wood, and sawdust.

[0019] The content of the low-melting point resin 11 in the lightweight aggregate 1 may be, for example, in the range of 10% by mass to 80% by mass or in the range of 10% by mass to 50% by mass. The content of the non-low-melting point resin particles 12 in the lightweight aggregate 1 may be, for example, in the range of 10% by mass to 80% by mass or in the range of 15% by mass to 75% by mass. The content of the wood particles 13 in the lightweight aggregate 1 may be, for example, in the range of 10% by mass to 50% by mass or in the range of 20% by mass to 40% by mass. The ratio of the content of the wood particles 13 to the total content of the low-melting point resin 11 and the non-low-melting point resin particles 12 (total content of the low-melting point resin 11 and the non-low-melting point resin particles 12 / content of the wood particles 13) may be, for example, 3.0 or less by mass or 2.5 or less.

[0020] The lightweight aggregate 1 may further contain additives such as pigments, compatibilizers for improving the affinity between the low-melting point resin 11, the non-low-melting point resin particles 12, and the wood particles 13, fillers, lubricants, weather-resistant agents, heat stabilizers, foaming agents, and antistatic agents.

[0021] The lightweight aggregate 1 of this embodiment, configured as described above, is dotted with protrusions 20 having an average diameter within the above-mentioned range. The arithmetic mean roughness Ra and density of the surface 10a of the granular portion 10 excluding the protrusions 20 are within the above-mentioned ranges. This reduces the aggregation of the lightweight aggregate 1 and increases the contact area with cement and water. Therefore, even if the lightweight aggregate 1 of this embodiment contains a resin, it can be uniformly dispersed in mortar or concrete. This increases the contact area between the lightweight aggregate 1 and cement, thereby improving the mechanical strength of mortar or concrete. Furthermore, because the density is within the above-mentioned range, it is lower than the density of sand or gravel typically used as aggregate in mortar or concrete. Therefore, the lightweight aggregate 1 of this embodiment can be advantageously used as an aggregate in mortar or concrete.

[0022] In this embodiment, the lightweight aggregate 1 includes non-low-melting-point resin particles 12 and wood particles 13 dispersed in a low-melting-point resin 11, the melting point of the low-melting-point resin 11 being within the above-mentioned range, the non-low-melting-point resin particles 12 including at least one of the high-melting-point resin and the thermosetting resin, the granular portion 10 formed by the low-melting-point resin 11, and the protrusions 20 formed by at least one of the non-low-melting-point resin particles 12 and the wood particles 13. This results in a low density and more uniform dispersion in mortar or concrete. In particular, since the wood particles 13 have a high affinity for water, the lightweight aggregate 1 including the wood particles 13 can be more easily dispersed uniformly in mortar or concrete. Furthermore, since the wood particles 13 have a high affinity for cement, mortar or concrete using the lightweight aggregate 1 including the wood particles 13 is less likely to crack or break even if fracture occurs. Furthermore, if the low-melting-point resin 11 and the non-low-melting-point resin particles 12 are derived from plastic waste, resources can be effectively utilized. Plastic waste may contain aluminum-deposited film. Aluminum-deposited film is generally a low-melting-point resin film on which aluminum is vapor-deposited. Therefore, in the lightweight aggregate 1 of this embodiment, the aluminum of the aluminum-deposited film is dispersed in an oxidized state in the granular portion 10 together with the low-melting-point resin 11. Therefore, the lightweight aggregate 1 of this embodiment is less likely to generate hydrogen even when used as a lightweight aggregate for mortar or concrete.

[0023] In the lightweight aggregate 1 of this embodiment, when the average number of protrusions 20 per lightweight aggregate 1 is within the above range, the lightweight aggregates 1 are less likely to clump together and are more likely to be dispersed uniformly in mortar or concrete. Furthermore, when the height of the protrusions 20 is within the above range, the lightweight aggregates 1 are even less likely to clump together and are more likely to be dispersed uniformly in mortar or concrete.

[0024] In this embodiment, the lightweight aggregate 1 having a sieve residue of 95% by mass or more when measured using a sieve with a mesh size of 2.5 mm and less than 15% by mass when measured using a sieve with a mesh size of 5.0 mm can be used as a fine aggregate for mortar or concrete. Also, the lightweight aggregate 1 having a sieve residue of 85% by mass or more when measured using a sieve with a mesh size of 5.0 mm can be used as a coarse aggregate for concrete.

[0025] [Method for Producing Lightweight Aggregate] The lightweight aggregate 1 of this embodiment can be produced by a method including, for example, a molding step of extruding a mixture containing low-melting-point resin 11, non-low-melting-point resin particles 12, and wood particles 13 to form a molded body, a crushing step of crushing the obtained molded body to obtain a crushed product, and a classification step of classifying the obtained crushed product. Hereinafter, the method for producing lightweight aggregate will be described using, as an example, a case in which plastic waste is used as the material for the low-melting-point resin and non-low-melting-point resin particles, and waste wood is used as the material for the wood particles.

[0026] Plastic waste can include municipal solid waste, industrial waste, and marine plastic waste. Municipal waste is waste other than industrial waste and marine plastic waste, including household waste discarded from ordinary households. Plastic waste may contain substances other than synthetic resins. The substances other than synthetic resins may be inorganic or organic. Examples of inorganic substances include magnetic substances, non-magnetic metals, glass, pebbles, metals, shells, sand, desiccants such as silica gel, and iron-based oxygen absorbers. Examples of magnetic substances include iron, stainless steel, ferrite, cobalt, and nickel. Examples of non-magnetic metals include aluminum, copper, zinc, and brass. Examples of organic substances include oils and fats, food residues, and surfactants.

[0027] Examples of plastic waste derived from municipal waste include plastics used as product containers and packaging materials. Plastic waste derived from industrial waste is plastic waste generated as a result of business activities. Examples of plastic waste derived from industrial waste include substandard products and surplus production. Plastic waste derived from marine plastic waste is plastic waste that has accumulated in the ocean due to direct disposal of plastic in the ocean or plastic discarded on land flowing into the ocean via rivers and lakes. Plastic waste derived from marine plastic waste includes, for example, plastic discarded in the ocean (plastic pieces, PET bottles, fishing gear), and microplastics that are plastic products that have deteriorated due to the effects of waves and ultraviolet rays and are now 5 mm or smaller in size.

[0028] The content of low-melting-point resin in the synthetic resin contained in plastic waste may be, for example, in the range of 25% by mass to 95% by mass, or in the range of 35% by mass to 90% by mass. The total content of PP and PE in the low-melting-point resin of plastic-containing waste may be 90% by mass or less, or in the range of 20% by mass to 80% by mass. The content of non-low-melting-point resin in the synthetic resin contained in plastic waste may be, for example, in the range of 5% by mass to 75% by mass, or in the range of 10% by mass to 65% by mass. Furthermore, the ratio of the content of low-melting-point resin to non-low-melting-point resin contained in the low-melting-point resin (low-melting-point resin / non-low-melting-point resin) may be, for example, in the range of 1 / 3 to 5.00, or in the range of 0.71 to 3.00, in mass ratio. In addition, the ratio of the content of thermosetting resin to high-melting-point resin in the non-low-melting-point resin of the plastic-containing waste (thermosetting resin / high-melting-point resin) may be, for example, in the range of 0.01 or more and 100 or less in mass ratio, or may be in the range of 0.05 or more and 50 or less.

[0029] Methods for recovering low-melting-point resin and non-low-melting-point resin particles from plastic waste include, for example, a crushing process, a magnetic substance removal process, a non-magnetic metal removal process, a water washing process, a volume reduction process, and a pulverization process. The crushing process involves crushing plastic waste using a crusher to obtain plastic fragments. Examples of crushers that can be used include a uniaxial crusher. The magnetic substance removal process involves removing and recovering magnetic substances contained in the plastic fragments using a magnetic separator. Examples of magnetic separators that can be used include a suspended magnetic separator, a pulley magnetic separator, a drum magnetic separator, and a roll magnetic separator. The non-magnetic metal removal process involves removing and recovering non-magnetic metals contained in the plastic fragments using a non-magnetic metal separator. Examples of non-magnetic metal separators that can be used include an eddy current separator. The water washing process involves crushing the plastic fragments into coarse plastic particles using a wet crushing and washing machine equipped with a crushing function, while washing and removing any deposits adhering to the coarse plastic particles. The deposits include organic matter such as oils, fats, food residues, and surfactants, and inorganic matter such as glass, pebbles, metals, shells, sand, desiccants, and oxygen absorbers. The volume reduction process uses a compressor to remove moisture adhering to the coarse plastic particles and reduce their volume. A screw-type compressor equipped with a screw inside a barrel with a drainage hole can be used as the compressor. The pulverization process uses a pulverizer to pulverize the coarse plastic particles to obtain resin composition particles. A pulverizer can be a fine pulverizer (cutter mill) equipped with fixed and rotating blades that pulverizes plastic pieces by sandwiching them between the fixed and rotating blades. The coarse plastic particles are pulverized until they pass through a sieve with a specified mesh size. The sieve opening can be, for example, 3.0 mm. In this way, resin composition particles containing low-melting-point resin particles and non-low-melting-point resin particles with a specified average major axis can be obtained.

[0030] As a method for recovering wood particles from waste wood, for example, a method including a crushing step, a magnetic substance removal step, and a pulverization step can be used. The crushing step is a step of crushing waste wood using a crusher to obtain wood chips. As the crusher, for example, a uniaxial crusher can be used. The magnetic substance removal step is a step of removing and recovering magnetic substances contained in the wood chips using a magnetic separator. As the magnetic separator, the above-mentioned can be used. The crushing step is a step of crushing wood chips using a crusher to obtain wood particles. As the crusher, a cutter mill can be used. The crushing may be carried out simultaneously with the plastic coarse particles using the same equipment as that used to crush the plastic coarse particles described above.

[0031] In the molding step (3), the resin composition particles and wood particles obtained as described above are mixed in the above ratio to obtain a mixture. The resulting mixture is then extrusion-molded to form a molded body. By extrusion molding, the low-melting-point resin particles melt, resulting in a molded body in which non-low-melting-point resin particles and wood particles are dispersed in the low-melting-point resin. The shape of the molded body is not particularly limited, and it may be, for example, a plate-like shape. The molding temperature for the molded body is, for example, a temperature above the melting point of the low-melting-point resin particles and below the melting point of the non-low-melting-point resin particles. The molding temperature for the molded body varies depending on factors such as the type and content of the low-melting-point resin contained in the raw material mixture, but is, for example, 150°C or higher when PE is included. On the other hand, since wood particles decompose and gasify at temperatures above 190°C, which may cause bubbles to form in the resin composition molded body, the molding temperature is preferably below 190°C.

[0032] In the pulverization step, the obtained molded body is pulverized using a pulverizer to obtain a pulverized product. A uniaxial crusher, for example, can be used as the pulverizer for the molded body. The pulverization is carried out until the molded body passes through a sieve with a predetermined mesh size. The mesh size of the sieve may be, for example, 15.0 mm. By pulverizing the molded body, the molded body is pulverized starting from the wood particles or non-low-melting-point resin particles in the molded body. Therefore, protrusions are formed on the surface of the molded body, where the wood particles or non-low-melting-point resin particles protrude. Furthermore, irregularities with an arithmetic mean roughness Ra of 10 μm or more and 100 μm or less are formed on the surface of the low-melting-point resin between the wood particles or non-low-melting-point resin particles.

[0033] In the classification step, the resulting pulverized material is classified using a classifier, such as a vibrating sieve.

[0034] According to the method for producing the lightweight aggregate 1 of this embodiment configured as described above, the surface is dotted with protrusions 20 having an average diameter of less than 3.0 mm, the arithmetic mean roughness Ra of the surface 10 a of the granular portion 10 excluding the protrusions 20 is in the range of 10 μm or more and 100 μm or less, and the density is 0.9 g / cm ３ 1.3g / cm or more ３ Lightweight aggregate 1 within the following range can be produced industrially in an advantageous manner. Furthermore, if the plastic waste contains an aluminum-deposited film, the aluminum in the aluminum-deposited film is heated and oxidized during the molding process, and is dispersed in the molten low-melting-point resin. Therefore, lightweight aggregate 1 obtained by the production method of this embodiment is less likely to generate hydrogen even when used as a lightweight aggregate for mortar or concrete.

[0035] [Mortar] The mortar of this embodiment contains cement and the above-described lightweight aggregate 1. The content of the lightweight aggregate 1 in the mortar is, for example, in the range of 10% by mass to 30% by mass. The mortar of this embodiment can be used, for example, as an exterior wall material, an interior wall material, a tile base, and a joint material for bricks and blocks.

[0036] The mortar of this embodiment can be produced, for example, by mixing cement, lightweight aggregate 1, and water to prepare fresh mortar, and then applying and drying the resulting fresh mortar.

[0037] According to the mortar of this embodiment having the above-described configuration, since it contains the lightweight aggregate 1 described above, the lightweight aggregate 1 is easily dispersed uniformly and strength is easily developed.

[0038] [Concrete] The concrete of this embodiment contains cement, fine aggregate, and coarse aggregate. At least one of the fine aggregate and the coarse aggregate is the lightweight aggregate 1 described above. The content of the lightweight aggregate in the concrete is, for example, in the range of 10% by mass to 30% by mass. The concrete of this embodiment can be used as a material for various civil engineering works, such as foundation work and exterior construction, and as a paving material.

[0039] The concrete of this embodiment can be produced, for example, by a method including a fresh concrete preparation step, a pouring step, and a demolding step. The fresh concrete preparation step is a step of preparing fresh concrete by mixing cement, fine aggregate, coarse aggregate, and water. The pouring step is a step of pouring the obtained fresh concrete into a concrete forming form. The demolding step is a step of removing the concrete produced by hardening the fresh concrete from the form.

[0040] According to the concrete of this embodiment having the above-described configuration, since the concrete contains the lightweight aggregate 1 described above, the lightweight aggregate 1 is easily dispersed uniformly and strength is easily developed.

[0041] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited thereto and can be modified as appropriate. The lightweight aggregate 1 of the present embodiment includes a low-melting-point resin 11, non-low-melting-point resin particles 12 dispersed in the low-melting-point resin 11, and wood particles 13. However, the present disclosure is not limited thereto. For example, ceramic particles may be used in place of or in addition to the wood particles 13. Furthermore, in the lightweight aggregate 1 of the present embodiment, the low-melting-point resin 11 and the non-low-melting-point resin particles 12 are considered to be plastic waste. However, the present disclosure is not limited thereto. For example, resin products may be used as the low-melting-point resin 11 and the non-low-melting-point resin particles 12. Furthermore, in the method for producing the lightweight aggregate 1 of the present embodiment, the low-melting-point resin is crushed into particles. However, the low-melting-point resin does not have to be in the form of particles as long as it is melted during extrusion molding.

[0042] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to these examples.

[0043] Example 1: Preparation and Evaluation of Lightweight Fine Aggregate and Lightweight Coarse Aggregate Plastic waste derived from municipal waste, containing low-melting-point resins (PE, PP, PS) and non-low-melting-point resins (PA6, PET), was fed into a crusher and crushed. The resulting crushed material was passed through a high-magnetic pulley-type magnetic separator with a magnetic force of 20,000 gauss on the belt surface to remove magnetic materials. The crushed material from which the magnetic materials had been removed was then crushed in a uniaxial coarse crusher until it passed through a 50 mm mesh sieve, yielding plastic waste fragments. The magnetic materials contained in the resulting plastic waste fragments were removed and recovered using a hanging magnetic separator and a pulley-type magnetic separator. Next, non-magnetic metals contained in the plastic waste fragments were removed and recovered using a non-magnetic metal separator. The plastic waste fragments were then crushed and washed using a wet crusher and washer until they passed through a 12 mm mesh sieve, yielding coarse plastic waste particles. Next, the plastic waste coarse particles washed in the wet grinding and washing machine were compressed and dehydrated using a volume reduction and compression dehydrator to reduce their volume. The reduced plastic waste coarse particles were then pulverized using a cutter mill-type pulverizer until they passed through a sieve with 1 mm openings. In this way, plastic waste particles were obtained. The obtained plastic waste particles had a low-melting point resin content of 49% by mass and a non-low-melting point resin content of 50% by mass.

[0044] The waste wood was crushed in a crusher until it passed through a sieve with 50 mm openings, yielding waste wood chips. The magnetic material contained in the resulting waste wood chips was removed and recovered using a hanging magnetic separator and a pulley magnetic separator. The waste wood chips were then crushed using a cutter mill-type crusher until they passed through a sieve with 1 mm openings. In this way, waste wood particles were obtained.

[0045] A mixture was obtained by mixing plastic waste particles, waste wood particles, and additives (a mixture containing a pigment, a compatibilizer, an inorganic filler, a lubricant, and a weathering agent) in a mass ratio of 62:35:3. The mixture was molded using an extruder to obtain a plate-shaped molded product. The molded product was then crushed using a uniaxial crusher until it passed through a 15 mm mesh sieve, obtaining a crushed product.

[0046] The obtained pulverized material was classified using sieves with 2.5 mm and 5.0 mm openings. The pulverized material remaining on the 2.5 mm sieve was used as lightweight fine aggregate, and the pulverized material remaining on the 5.0 mm sieve was used as lightweight coarse aggregate.

[0047] The obtained lightweight coarse aggregate was measured for the mass fraction (passage rate) of the crushed material passing through each sieve using sieves with openings of 2.5 mm, 5.0 mm, 10 mm, 15 mm, 20 mm, and 25 mm in accordance with JIS A 1102:2014 (Sieving test method for aggregates). The results are shown in Table 1 below.

[0048]

[0049] The surfaces of the obtained lightweight fine aggregate and lightweight coarse aggregate were observed and the surface roughness, density, water absorption, and unit volume mass (in an oven-dry state) were measured by the following methods. The measurement results of surface roughness, density, water absorption, and unit volume mass (in an oven-dry state) are shown in Table 2 below.

[0050] (Surface Observation) Surface observation was performed using a digital microscope (Keyence Corporation, VHX-900F). Figure 2 shows a surface image of the lightweight fine aggregate, and Figure 3 shows a surface image of the lightweight coarse aggregate. From the observation images in Figures 2 and 3, it was confirmed that the lightweight fine aggregate and the lightweight coarse aggregate each had non-low melting point resin particles and wood particles exposed on the surface, and that some of the wood particles were scattered as protrusions.

[0051] (Surface Roughness) For each of the 10 lightweight fine aggregates and lightweight coarse aggregates, three regions (size: 500 × 725 μm) without protrusions were selected, and the arithmetic mean roughness Ra and maximum height roughness Rz on a straight line set within each region were measured using a shape measuring laser microscope (Keyence Corporation, VK-X100). The average values ​​of the obtained arithmetic mean roughness Ra and maximum height roughness Rz were calculated.

[0052] (Density, Water Absorption) The density and water absorption of the lightweight fine aggregate were measured in accordance with JIS A 1109:2020 (Testing method for density and water absorption of fine aggregate). The density and water absorption of the lightweight fine aggregate were measured in accordance with JIS A 1110:2020 (Testing method for density and water absorption of coarse aggregate).

[0053] (Unit volume mass) Measured in accordance with JIS A 1104:2019 (Test method for unit volume mass and actual volume ratio of aggregate).

[0054]

[0055] [Example 2, Comparative Example 1, Reference Example 1: Preparation and Evaluation of Fresh Mortar] The materials shown in Table 3 below were prepared. Plastic waste particles were prepared in the same manner as in Example 1, except that volume-reduced coarse particles of plastic waste were pulverized using a cutter mill-type pulverizer until they passed through a sieve with 5 mm openings.

[0056]

[0057] The above materials were mixed in the proportions shown in Table 4 below using a mortar mixer to prepare fresh mortar.

[0058] Using the obtained fresh mortar, specimens were prepared in accordance with JIS R 5201:2015 (Physical Testing Methods for Cement), and the unit volume mass and flexural strength of the obtained specimens were measured. The unit volume mass of the specimen was calculated by dividing the weight of the specimen by its volume. The volume of the specimen was calculated from the measured dimensions. In addition, the ratio of flexural strength to unit volume mass (flexural strength / unit volume mass) was calculated as specific strength. The results are shown in Table 4 below.

[0059]

[0060] The specific strength of the test specimen obtained from the fresh mortar of Example 2, which used the lightweight fine aggregate obtained in Example 1, was 1.55, which was equivalent to the specific strength of the test specimen obtained from the fresh mortar of Reference Example 1, which used conventional sand. This result confirmed that the use of the lightweight fine aggregate obtained in Example 1 allows the strength of the mortar to be developed. Furthermore, the test specimen obtained from the fresh mortar of Comparative Example 1, which used plastic waste particles, expanded during curing. This was because the aluminum in the aluminum-deposited film contained in the plastic waste particles reacted with the alkali derived from the cement, generating hydrogen gas.

[0061] [Examples 3 to 5, Reference Example 2: Preparation and Evaluation of Fresh Concrete] The materials shown in Table 5 below were prepared.

[0062]

[0063] Fresh concrete was prepared by mixing the above materials using a mortar mixer in the proportions shown in Table 6. In Examples 3 to 5, the water / cement ratio (W / C ratio) was adjusted so that the slump value of the fresh concrete was within the range of 5 to 15 cm.

[0064] Using the obtained fresh concrete, test specimens were prepared in accordance with JIS A 1106:2018 (Test method for bending strength of concrete), and the unit volume mass and bending strength of the obtained test specimens were measured. The results are shown in Table 6 below.

[0065]

[0066] It can be seen that by using the lightweight coarse aggregate obtained in this example, the unit volume mass of concrete can be significantly reduced. Also, by adjusting the blending ratio of the lightweight coarse aggregate, it is possible to obtain concrete having the same unit volume mass and bending strength as the fresh concrete obtained in Reference Example 2, which used conventional lightweight fine aggregate and lightweight coarse aggregate.

[0067] The following additional notes apply to aspects of the present disclosure: (Additional Note 1) A surface of a substrate is dotted with protrusions having an average diameter of less than 3.0 mm, the arithmetic mean roughness Ra of the surface excluding the protrusions is in the range of 10 μm to 100 μm, and the density is 0.9 g / cm ３ 1.3g / cm or more ３ Lightweight aggregate, which is a granular material within the following ranges:

[0068] (Appendix 2) A lightweight aggregate according to Appendix 1, comprising a low-melting resin, and non-low-melting resin particles and wood particles dispersed in the low-melting resin, wherein the low-melting resin has a melting point in the range of 80°C or higher and lower than 190°C, the non-low-melting resin particles comprise at least one of a high-melting resin and a thermosetting resin having a melting point of 190°C or higher, and the protrusions are formed by at least one of the non-low-melting resin particles and the wood particles.

[0069] (Supplementary Note 3) The lightweight aggregate according to Supplementary Note 1 or 2, wherein the average number of the protrusions per lightweight aggregate is within a range of 5 to 100.

[0070] (Appendix 4) The lightweight aggregate according to any one of Appendices 1 to 3, wherein the average height of the projections is in the range of 0.4 mm or more and 2.0 mm or less.

[0071] (Appendix 5) A lightweight aggregate according to any one of Appendices 1 to 4, wherein the sieve residue measured using a sieve with a mesh size of 2.5 mm is 95% by mass or more, and the sieve residue measured using a sieve with a mesh size of 5.0 mm is less than 15% by mass.

[0072] (Appendix 6) The lightweight aggregate according to any one of Appendices 1 to 5, wherein the sieve residue measured using a sieve with a mesh size of 5.0 mm is 85 mass% or more.

[0073] (Appendix 7) A lightweight aggregate which is a granular material having protrusions scattered on its surface, the protrusions having an average diameter of less than 3.0 mm, and which comprises a low-melting point resin, and non-low-melting point resin particles and wood particles dispersed in the low-melting point resin, wherein the low-melting point resin has a melting point in the range of 80°C or more and less than 190°C, the non-low-melting point resin particles comprise at least one of a high-melting point resin and a thermosetting resin having a melting point of 190°C or more, and the protrusions are formed by at least one of the non-low-melting point resin particles and the wood particles.

[0074] (Appendix 8) The lightweight aggregate according to Appendix 7, wherein the low melting point resin and the non-low melting point resin particles are derived from plastic waste.

[0075] (Appendix 9) A method for producing lightweight aggregate, comprising extrusion-molding a mixture containing a low-melting-point resin having a melting point in the range of 80°C or higher but lower than 190°C, and at least one of a high-melting-point resin and a thermosetting resin having a melting point of 190°C or higher, wherein the non-low-melting-point resin particles have an average major axis of less than 3.0 mm, and wood particles having an average major axis of less than 3.0 mm, to form a molded body, pulverizing the molded body to obtain a pulverized product, and classifying the pulverized product.

[0076] (Supplementary Note 10) A mortar comprising cement and the lightweight aggregate according to any one of Supplementary Notes 1 to 8.

[0077] (Supplementary Note 11) A concrete comprising cement and the lightweight aggregate according to any one of Supplementary Notes 1 to 8.

[0078] 1... lightweight aggregate, 10... granular portion, 10a... surface, 11... low melting point resin, 12... non-low melting point resin particle, 13... wood particle, 20... protrusion

Claims

1. The surface is dotted with protrusions having an average diameter of less than 3.0 mm, the arithmetic mean roughness Ra of the surface excluding the protrusions is in the range of 10 μm to 100 μm, and the density is 0.9 g / cm ３ 1.3g / cm or more ３ A lightweight aggregate which is a granular material within the following range:

2. A lightweight aggregate as described in claim 1, comprising a low melting point resin, and non-low melting point resin particles and wood particles dispersed in the low melting point resin, wherein the low melting point resin has a melting point in the range of 80°C or higher and lower than 190°C, the non-low melting point resin particles comprise at least one of a high melting point resin and a thermosetting resin having a melting point of 190°C or higher, and the protrusions are formed by at least one of the non-low melting point resin particles and the wood particles.

3. The lightweight aggregate according to claim 1 or 2, wherein the average number of said protrusions per said lightweight aggregate is within the range of 5 to 100.

4. A lightweight aggregate according to any one of claims 1 to 3, wherein the average height of the projections is within the range of 0.4 mm or more and 2.0 mm or less.

5. A lightweight aggregate described in any one of claims 1 to 4, in which the sieve residue measured using a sieve with a mesh size of 2.5 mm is 95 mass% or more, and the sieve residue measured using a sieve with a mesh size of 5.0 mm is less than 15 mass%.

6. A lightweight aggregate described in any one of claims 1 to 5, having a sieve residue measured using a sieve with a mesh size of 5.0 mm of 85 mass% or more.

7. A lightweight aggregate having a granular material with protrusions scattered on its surface having an average diameter of less than 3.0 mm, comprising a low melting point resin, and non-low melting point resin particles and wood particles dispersed in the low melting point resin, wherein the low melting point resin has a melting point in the range of 80°C or higher and lower than 190°C, the non-low melting point resin particles comprise at least one of a high melting point resin and a thermosetting resin having a melting point of 190°C or higher, and the protrusions are formed by at least one of the non-low melting point resin particles and the wood particles.

8. The lightweight aggregate according to claim 7, wherein the low melting point resin and the non-low melting point resin particles are derived from plastic waste.

9. A method for producing lightweight aggregate, comprising extruding a mixture containing a low-melting point resin having a melting point in the range of 80°C or higher but lower than 190°C, at least one of a high-melting point resin and a thermosetting resin having a melting point of 190°C or higher, wherein the non-low-melting point resin particles have an average major axis of less than 3.0 mm, and wood particles having an average major axis of less than 3.0 mm to form a molded body, pulverizing the molded body to obtain a pulverized material, and classifying the pulverized material.

10. A mortar comprising cement and the lightweight aggregate according to any one of claims 1 to 8.

11. A concrete comprising cement and the lightweight aggregate according to any one of claims 1 to 8.

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