Soil conditioner and soil containing the same

Abstract

To provide a soil conditioner that tends not to form lumps, and soil containing the same.SOLUTION: The soil conditioner of the present invention is a soil conditioner comprising aggregate and asphalt. The aggregate contains 20 mass% or less of aggregate having a particle size of 0.250 mm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a soil conditioner and soil containing the same. [Background technology]

[0002] Soil is used as the surface layer in various outdoor athletic fields such as baseball fields, schoolyards, and parks. The surface soil can generate dust due to the effects of wind and the impact of athletes' shoes.

[0003] Therefore, dust suppressants are sometimes used for such soils. For example, Patent Document 1 discloses a dust suppressant for outdoor playgrounds that contains a polybutene emulsion.

[0004] Furthermore, Patent Document 2 discloses a soil conditioner for outdoor playgrounds, which contains aggregate, asphalt, and polybutene. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-67841 [Patent Document 2] Patent Publication No. 2021-88871 Summary of the Invention [Problem to be solved by the invention]

[0006] Soil conditioners are used by mixing them with soil base materials, but when the soil base material and soil conditioner are mixed, clumps of asphalt mortar may occur. The occurrence of such clumps means that the soil base material and soil conditioner are not mixed uniformly, and the soil may generate dust.

[0007] Therefore, the present invention provides a soil conditioner that is less likely to form lumps, and soil containing the same. [Means for solving the problem]

[0008] The present inventors have found that a soil conditioner having the following features and soil containing the same can reduce freezing in outdoor playgrounds and the resulting generation of dust.

[0009] That is, the present invention has the following aspects: <<Aspect 1>> A soil conditioner comprising aggregate and asphalt, wherein the proportion of aggregate having a particle size of 0.250 mm or less is 20 mass % or less. <<Aspect 2>> 2. The soil conditioner according to aspect 1, wherein the proportion of aggregates having particle sizes of 2.00 mm or more in the aggregates is 10 mass % or more. Aspect 3 2. The soil conditioner of claim 1, further comprising a plasticizer. Aspect 4 4. The soil conditioner of claim 3, wherein the plasticizer comprises a fatty acid-based compound. Aspect 5 5. The soil conditioner according to claim 4, wherein the fatty acid compound is a fatty acid alkyl ester compound. Aspect 6 The soil conditioner according to aspect 3, wherein the aggregate content is 90 to 99% by mass, the total content of the asphalt and the plasticizer is 1 to 10% by mass, and the plasticizer content is 5 to 50 parts by mass per 100 parts by mass of the asphalt. Aspect 7 Soil comprising a soil base material and the soil improver according to any one of aspects 1 to 6. Aspect 8 8. The soil of claim 7, wherein the soil base material comprises red soil and mountain sand. Aspect 9 9. The soil according to aspect 8, wherein the soil base material is contained in an amount of 50 to 90% by volume, and the soil improver is contained in an amount of 10 to 50% by volume. Aspect 10 An outdoor playground comprising the soil according to embodiment 8 in a surface layer. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a soil conditioner that is less likely to form lumps, and soil containing the same. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 shows the results of the freeze-thaw test in Experiment 2. [Figure 2] Figure 2 shows the results of Experiment 3 regarding clump formation. DETAILED DESCRIPTION OF THE INVENTION

[0012] <Soil conditioner> In one embodiment, the soil conditioner of the present invention is a soil conditioner containing aggregate and asphalt, wherein the aggregate has a particle size of 0.250 mm or less and a proportion of aggregate with a particle size of 0.250 mm or less is 20% by mass or less. The inventors have discovered that when the soil conditioner contains a large amount of small particle size aggregate, particularly aggregate with a particle size of 0.250 mm or less or 0.425 mm or less, lumps of asphalt mortar tend to form when the aggregate is mixed with asphalt, and the lumps cannot be eliminated by a typical mixing method for the soil conditioner and soil base material. This is thought to be because small particle size aggregates tend to form aggregates when mixed with asphalt, and once formed, the aggregates are difficult to break down using normal mixing, so even if the soil conditioner containing lumps is mixed with the soil base material, the lumps remain.

[0013] <aggregate> The aggregate is not particularly limited as long as the proportion of aggregate with a particle size of 0.250 mm or less is 20 mass% or less, as long as the advantageous effects of the present invention are obtained. In this specification, the particle size of the aggregate refers to a value measured in accordance with JIS A1102:2014. In this specification, even if there is a particle size not specified in the JIS standard, the particle size can be specified in the same manner as in the JIS standard.

[0014] The proportion of aggregate with a particle size of 0.075 mm or less may be 15% by mass or less, 10% by mass or less, 5% by mass or less, or 3% by mass or less, or may be 0.1% by mass or more, 1% by mass or more, 3% by mass or more, or 5% by mass or more.

[0015] The proportion of aggregate with a particle size of 0.106 mm or less may be 15% by mass or less, 10% by mass or less, 5% by mass or less, or 3% by mass or less, or may be 0.1% by mass or more, 1% by mass or more, 3% by mass or more, or 5% by mass or more.

[0016] The proportion of aggregate with a particle size of 0.250 mm or less may be 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, or 10% by mass or less, or may be 3% by mass or more, 5% by mass or more, 10% by mass or more, or 15% by mass or more.

[0017] The proportion of aggregate with a particle size of 0.425 mm or less may be 60% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less, or 20% by mass or less, or may be 5% by mass or more, 10% by mass or more, 15% by mass or more, or 20% by mass or more.

[0018] The proportion of aggregate with a particle size of 2.00 mm or less may be 95% by mass or less, 90% by mass or less, or 85% by mass or less, or may be 60% by mass or more, 70% by mass or more, or 80% by mass or more.

[0019] The proportion of aggregate with a particle size of 0.075 mm or more and 0.250 mm or less may be 3% by mass or more, 5% by mass or more, or 7% by mass or more, or 20% by mass or less, 15% by mass or less, or 10% by mass or less.

[0020] The proportion of aggregate with a particle size of 0.250 mm or more and 0.425 mm or less may be 5% by mass or more, 7% by mass or more, or 10% by mass or more, or may be 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, or 10% by mass or less.

[0021] The proportion of aggregate with a particle size of 0.250 mm or more and 2.00 mm or less may be 50% by mass or more, 60% by mass or more, 65% by mass or more, or 70% by mass or more, or may be 80% by mass or less, 75% by mass or less, or 70% by mass or less.

[0022] The proportion of aggregate with a particle size of 0.425 mm or more and 2.00 mm or less may be 40% by mass or more, 50% by mass or more, or 60% by mass or more, or 80% by mass or less, 75% by mass or less, or 70% by mass or less.

[0023] The type of aggregate is not particularly limited as long as it has the particle size described above, and examples that can be used include river sand, dune sand, mountain sand, sea sand, crushed sand, fine sand, screenings, crushed stone dust, silica sand, artificial sand, glass cullet, and foundry sand.

[0024] The aggregate content in the soil conditioner may be 80% by mass or more, 85% by mass or more, 90% by mass or more, 92% by mass or more, 94% by mass or more, or 96% by mass or more, or 99% by mass or less, 97% by mass or less, 95% by mass or less, 93% by mass or less, or 90% by mass or less. The aggregate content in the soil conditioner can be, for example, 90% by mass or more and 99% by mass or less, or 94% by mass or more and 97% by mass or less.

[0025] <asphalt> Soil modifiers include asphalt, which can impart adhesion to aggregates and prevent dust generation. The type of asphalt is not particularly limited, but ordinary petroleum asphalt can be used. Examples of asphalt include straight asphalt, which is petroleum asphalt for paving, as well as modified asphalt. Examples of modified asphalt include blown asphalt and asphalt modified with polymeric materials such as thermoplastic elastomers and thermoplastic resins.

[0026] The total content of asphalt and plasticizer in the soil conditioner may be 1.0% by mass or more, 2.0% by mass or more, 3.0% by mass or more, 4.0% by mass or more, or 5.0% by mass or more, or 10.0% by mass or less, 8.0% by mass or less, 6.0% by mass or less, 5.0% by mass or less, or 4.0% by mass or less. The total content of asphalt and plasticizer in the soil conditioner can be, for example, 1.0% by mass or more and 10.0% by mass or less, or 3.0% by mass or more and 6.0% by mass or less.

[0027] <Plasticizer> The soil conditioner may contain a plasticizer, which plasticizes the asphalt and improves its mixability with aggregate. Such plasticizers are not particularly limited as long as they are compatible with asphalt, but examples include resin-based plasticizers, wax-based plasticizers, petroleum-based plasticizers, mineral-based plasticizers, animal oil-based plasticizers, and vegetable oil-based plasticizers.

[0028] The plasticizer may contain a fatty acid compound. The inventors have discovered that using a fatty acid compound as a plasticizer for asphalt in a soil conditioner can reduce freezing and dust generation in outdoor athletic fields. This is thought to be because the plasticizer effectively plasticizes the asphalt, firmly adhering it to the aggregate, making it difficult for water to penetrate between the aggregates, thereby suppressing freezing. It is also thought that the asphalt binds soil particles together, thereby suppressing dust generation. On the other hand, since the use of a fatty acid compound can increase the likelihood of clumping, it is thought that the advantageous effects of the present invention are particularly easily achieved when a fatty acid compound is used as a plasticizer.

[0029] The fatty acid compound may be, for example, a fatty acid compound having an iodine value of 50 to 110. The plasticizer may be a combination of multiple fatty acid compounds, in which case the iodine value refers to the value of the fatty acid compound in which multiple compounds are combined. The iodine value of the fatty acid compound is measured in accordance with JIS K0070-1992.

[0030] Examples of fatty acid compounds include fatty acids and fatty acid alkyl esters, fatty acid polyoxyalkylene alkyl esters, and polyoxyalkylene fatty acid esters, and these can be used alone or in combination of two or more selected from these.

[0031] Specifically, the fatty acid compound can be a compound represented by the following general formula (1): R1-CO-(AO)m-OR2...General formula (1) (In the formula, R1 represents a linear or branched hydrocarbon group having 15 to 19 carbon atoms; R2 represents either hydrogen or a linear or branched hydrocarbon group having 1 to 18 carbon atoms; AO represents a linear or branched alkylene oxide unit having 2 to 4 carbon atoms; and m represents the average number of moles added, which is a number from 0 to 30.)

[0032] The molecular weight (g / mol) of the fatty acid compound may be, for example, 100 or more, 150 or more, 200 or more, 250 or more, 270 or more, or 280 or more, or 500 or less, 450 or less, 400 or less, 350 or less, 330 or less, or 320 or less. When a fatty acid compound is used in combination with multiple compounds, the molecular weights may be weight-average molecular weights.

[0033] Here, R1 can be a linear or branched alkyl group having 15 to 17 carbon atoms or a linear or branched alkenyl group having 15 to 17 carbon atoms. R2 can be hydrogen or a methyl group. AO can be an ethylene oxide unit. m can be 0 to 15. The iodine value of the fatty acid compound can be 60 to 100 (g / 100 mg) or 70 to 85 (g / 100 mg). In the present invention, the term "alkenyl group" refers to a hydrocarbon group containing 1 to 3 double bonds.

[0034] The fatty acid compounds (b) represented by the general formula (1) include fatty acids: R1COOH, fatty acid methyl esters: R1COOCH3, and fatty acid (poly)oxyethylene methyl esters: R1COO(CH2CH2O). m CH3, (poly)oxyethylene fatty acid ester: R1COO(CH2CH2O) m Specific examples include palmitic acid, palmitic acid methyl ester, palmitic acid (poly)oxyethylene methyl ester (average number of moles added: 1 to 15), (poly)oxyethylene palmitic acid ester (average number of moles added: 1 to 15), stearic acid, stearic acid methyl ester, stearic acid (poly)oxyethylene methyl ester (average number of moles added: 1 to 15), (poly)oxyethylene stearate ester (average number of moles added: 1 to 15), oleic acid, oleic acid methyl ester, oleic acid (poly)oxyethylene methyl oleic acid esters (average number of moles added: 1 to 15), (poly)oxyethylene oleic acid esters (average number of moles added: 1 to 15), linoleic acid, linoleic acid methyl ester, linoleic acid (poly)oxyethylene methyl ester (average number of moles added: 1 to 15), (poly)oxyethylene linoleic acid esters (average number of moles added: 1 to 15), linolenic acid, linolenic acid methyl ester, linolenic acid (poly)oxyethylene methyl ester (average number of moles added: 1 to 15), (poly)oxyethylene linolenic acid esters (average number of moles added: 1 to 15).

[0035] Among these, a fatty acid methyl ester mixture containing 75 to 95 mass% of oleic acid methyl ester and having an iodine value of 50 to 110 (g / 100 mg) or a polyoxyethylene fatty acid ester having 16 to 18 carbon atoms (average number of added moles: 3 to 15) can be used.

[0036] The content of the plasticizer in the soil conditioner may be 5 parts by mass or more, 10 parts by mass or more, 15 parts by mass or more, 20 parts by mass or more, 25 parts by mass or more, or 30 parts by mass or more, relative to 100 parts by mass of asphalt, and 70 parts by mass or less, 60 parts by mass or less, 50 parts by mass or less, 40 parts by mass or less, 35 parts by mass or less, 30 parts by mass or less, or 25 parts by mass or less. For example, the content of the plasticizer in the soil conditioner may be 5 parts by mass or more and 50 parts by mass or less, or 10 parts by mass or more and 30 parts by mass or less, relative to 100 parts by mass of asphalt. Within this range, even when the soil conditioner is mixed with the soil base material, the advantageous effects of the present invention can be obtained, and stickiness and the like are reduced.

[0037] The content of the plasticizer in the soil conditioner may be 0.1% by mass or more, 0.3% by mass or more, 0.5% by mass or more, 1.0% by mass or more, or 1.5% by mass or more, or 5.0% by mass or less, 3.0% by mass or less, 2.0% by mass or less, 1.5% by mass or less, 1.0% by mass or less, or 0.8% by mass or less. For example, the content of the plasticizer in the soil conditioner may be 0.1% by mass or more and 5.0% by mass or less, or 0.5% by mass or more and 1.5% by mass or less.

[0038] <others> The soil conditioner may contain no other components than aggregate, asphalt, and plasticizer. For example, the soil conditioner may contain no more than 50% by mass, 40% by mass, 30% by mass, 20% by mass, 10% by mass, 5% by mass, 1% by mass, or 0.1% by mass of other components.

[0039] "soil" The soil of the present invention includes a soil base material and the soil improver described above. This soil can be used as the surface layer of an outdoor sports field.

[0040] <Base material for soil> The soil base material is not particularly limited, but examples thereof include the above-mentioned aggregate, mountain sand, red soil, and pitted clay.

[0041] The soil base material may contain, for example, 5 to 45 mass%, 10 to 40 mass%, or 15 to 35 mass% of soil particles with a particle size of 0.075 mm or less, 50 to 95 mass%, 55 to 90 mass%, or 60 to 85 mass% of soil particles with a particle size of more than 0.075 mm and less than 2.0 mm, and 0 to 30 mass%, 0 to 20 mass%, or 5 to 15 mass% of soil particles with a particle size of more than 2.0 mm and less than 4.75 mm. The occurrence of lumps is affected by the particle size of the aggregate contained in the soil conditioner, but not by the particle size of the soil base material. This is thought to be because the lumps occur during the production of the soil conditioner, and the lumpy state remains intact even when the soil conditioner is subsequently mixed with the soil base material.

[0042] The content of the soil base material in the soil may be 10% by volume or more, 20% by volume or more, 30% by volume or more, 40% by volume or more, 50% by volume or more, or 60% by volume or more, or 90% by volume or less, 85% by volume or less, 80% by volume or less, 75% by volume or less, or 70% by volume or less. The content of the soil base material in the soil can be, for example, 10% by volume or more and 90% by volume or less, or 40% by volume or more and 80% by volume or less.

[0043] The content of the soil modifier in the soil may be 10% by volume or more, 20% by volume or more, 30% by volume or more, 40% by volume or more, or 50% by volume or more, or 80% by volume or less, 70% by volume or less, 60% by volume or less, 50% by volume or less, or 40% by volume or less. The content of the soil modifier in the soil can be, for example, 10% by volume or more and 80% by volume or less, or 20% by volume or more and 60% by volume or less.

[0044] The soil may contain no other components than the soil base material and the soil conditioner. For example, the soil may contain no more than 50% by mass, no more than 40% by mass, no more than 30% by mass, no more than 20% by mass, no more than 10% by mass, no more than 5% by mass, no more than 1% by mass, or no more than 0.1% by mass of other components.

[0045] <<Soil conditioner and soil manufacturing method>> The method for producing a soil conditioner includes mixing asphalt and aggregate. For each component of the method for producing a soil conditioner, reference can be made to the components described above. For the types and amounts of asphalt, aggregate, plasticizer, etc., the above-described types and contents can be referenced.

[0046] The method for producing the soil conditioner can include the steps of mixing asphalt and aggregate to obtain a first mixture, and adding and mixing a plasticizer to the first mixture to obtain the soil conditioner. Here, the aggregate can be dried by heating it to, for example, about 180°C before mixing, and can be heated to about 150°C to 170°C before mixing.

[0047] The soil conditioner thus obtained can be cured to cool it down and then mixed with the soil base material. If the soil base material contains a lot of water, the water content can be reduced by aeration or the like before mixing the soil base material with the soil conditioner.

[0048] The present invention will be explained in more detail in the following examples, but the present invention is not limited thereto. [Example]

[0049] Experiment 1: Experiment on the mixing ratio of soil conditioner and soil base material <Production example> The following seven types of plasticizers were prepared: [Table 1]

[0050] The fine sand aggregate was heated to 185°C and mixed with asphalt (straight asphalt 60 / 80) heated to 160°C. Twenty seconds after mixing the fine sand and asphalt, plasticizer 1 was added and mixed to obtain a soil conditioner. The fine sand and asphalt were mixed in a mass ratio of 94:6, and 22 parts by mass of plasticizer was mixed per 100 parts by mass of asphalt. In other words, this soil conditioner contained 92.8% by mass of fine sand, 5.9% by mass of asphalt, and 1.3% by mass of plasticizer. This soil conditioner was cured overnight and, once its temperature had dropped to approximately 60°C, it was loosened with a shovel.

[0051] The soil conditioner was then transported to a test site in a cold region, where it was mixed with the soil base materials of red soil and mountain sand using a backhoe for approximately one hour. For the soil of Reference Example 1, the red soil, mountain sand, and soil conditioner were mixed at 40 vol%, 30 vol%, and 30 vol%, respectively, while for the soil of Reference Example 2, they were mixed at 40 vol%, 10 vol%, and 50 vol%, respectively. For the soil of Comparative Example 1, red soil and mountain sand were mixed at 40 vol% and 60 vol%, respectively. These soils were then spread and compacted as surface layers in three adjacent construction areas of an outdoor playground.

[0052] The particle size distribution, unit volume mass, and water content of the soil conditioner, red soil, and mountain sand used are as shown in the table below. [Table 2]

[0053] The particle size distribution of the soil obtained for each example was as follows: [Table 3]

[0054] Test Method <Permeability test> A permeability test was conducted to evaluate the drainage of the soil of the playground. The test was conducted in accordance with the method described in F010 of the "Pavement Survey and Testing Methods Handbook."

[0055] <Proctor needle penetration test> Proctor needle penetration tests were conducted to evaluate the cushioning properties of the soil in the playground. The tests were conducted in accordance with the method described in the "Guidelines for the Construction of Outdoor Sports Facilities."

[0056] <Freeze-thaw test> A freeze-thaw test was conducted to evaluate the effects of freezing on the playground soil. The test was conducted in accordance with the method described in the "Construction Sludge Recycling Manual" for the wet-dry cycle test. The test specimens were prepared using the method described in Method F007-A of the "Pavement Survey and Test Methods Handbook." The specimens were placed in a freezer at -10°C for one day, and then the frozen specimens were immersed in water at 20°C for one day. This cycle was repeated three times, and the dry mass was measured before and after the test to confirm the survival rate.

[0057] <Dust generation test> After winter, in early spring, a dust generation test was conducted in the above playground. The test was conducted by enclosing the playground in a hemispherical container with soil underneath, blowing air into the container from the top, and measuring the generated dust inside the container with a digital dust meter.

[0058] "result" The test results are shown in the table below: [Table 4]

[0059] The permeability of the soils of Reference Examples 1 and 2 was lower than that of the soil of Comparative Example 1, but was still sufficient for use as a playground. Furthermore, a Proctor needle penetration test revealed that the soils of Reference Examples 1 and 2 had increased cushioning properties and were moderately hard. Furthermore, it was found that the soil of Comparative Example 1 completely lost its pre-freezing shape when thawed after freezing, whereas the soils of Reference Examples 1 and 2 were significantly less affected by freezing. Furthermore, it was found that the dust generation of the soils of Reference Examples 1 and 2 was significantly reduced compared to the soil of Comparative Example 1 after wintering.

[0060] It should be noted that clumps of asphalt mortar were observed in the soil of Reference Example 2 compared to the soil of Reference Example 1. Furthermore, when tests were conducted in Reference Example 1 by changing Plasticizer 1 to Plasticizers 2 to 7, roughly the same results were obtained.

[0061] Experiment 2: Experiment on the amount of plasticizer in soil conditioner The soil conditioners of Reference Examples 3 to 5 were produced in the same manner as in Experiment 1, except that the amount of plasticizer per 100 parts by mass of asphalt was changed to 10 parts by mass, 20 parts by mass, and 30 parts by mass. Each soil was obtained by mixing 30% by volume of these soil conditioners with 70% by volume of the same soil base material. Test specimens were also produced using the soil conditioner of Reference Example 4, with the amount of soil base material varied from 0% by volume to 100% by volume.

[0062] A freeze-thaw test was carried out on each soil in the same manner as in Experiment 1. The results are shown in Figure 1.

[0063] A comparison of Reference Examples 3 and 4 shows that reducing the amount of plasticizer worsens the freeze-thaw resistance. On the other hand, a comparison of Reference Examples 4 and 5 shows that increasing the amount of plasticizer slightly worsens the freeze-thaw resistance. The soil of Reference Example 5 felt slightly sticky when touched with the hand.

[0064] Experiment 3: Experiment on particle size and clump formation of soil conditioner The aggregate for each example listed in Table 5 below was heated to 185°C and mixed with asphalt (straight asphalt 60 / 80, As) heated to 160°C. Twenty seconds after mixing the aggregate and asphalt, plasticizer 1 was added and mixed to obtain the soil conditioner for each example. Fine sand and asphalt were mixed in a mass ratio of 94:6, and 22 parts by mass of plasticizer was mixed per 100 parts by mass of asphalt. This soil conditioner was cured overnight, and when the temperature had dropped to approximately 60°C, it was loosened with a shovel.

[0065] Then, the red soil and mountain sand in Table 2 above were mixed with the soil conditioner of each example at 40 volume%, 30 volume%, and 30 volume%, respectively, using a backhoe for about an hour to produce soil for a playground.

[0066] The lump formation rate for each example was measured by sieving using a 4.75 mm sieve, and the results are shown in Table 5. The soil produced in each example was sieved using a 4.75 mm sieve, and the material remaining on the sieve was treated as lumps. The lump formation rate was calculated by dividing the mass of the lumps by the total mass of the soil. Figure 2 shows a photograph of the soil after the lumps were removed. The upper right corner of the photograph for each example in Figure 2 is the lumps, and for Example 1, the lumps are shown surrounded by a dashed line.

[0067] [Table 5]

[0068] As is clear from the results of the clump occurrence rate, clump occurrence was significantly reduced in Examples 1 and 2, which used soil conditioners containing a large amount of relatively large aggregates. Also, looking at the photograph in Figure 2, it can be seen that there were very few large clumps containing a large amount of black asphalt in Examples 1 and 2.

Claims

1. A soil conditioner comprising aggregate and asphalt, wherein the proportion of aggregate having a particle size of 0.250 mm or less is 20 mass % or less.

2. The soil conditioner according to claim 1, wherein the proportion of aggregates having a particle size of 2.00 mm or more is 10% by mass or more.

3. The soil conditioner according to claim 1 , further comprising a plasticizer.

4. The soil conditioner according to claim 3 , wherein the plasticizer comprises a fatty acid-based compound.

5. The soil conditioner according to claim 4, wherein the fatty acid compound is a fatty acid alkyl ester compound.

6. The content of the aggregate is 90 to 99% by mass, the total content of the asphalt and the plasticizer is 1 to 10% by mass, and the content of the plasticizer is 5 to 50 parts by mass relative to 100 parts by mass of the asphalt. The soil conditioner according to claim 3, wherein the soil conditioner is 5 to 50 parts by mass.

7. Soil comprising a soil base material and the soil improver according to any one of claims 1 to 6.

8. The soil according to claim 7, wherein the soil base material comprises red soil and mountain sand.

9. The soil according to claim 8, wherein the content of the soil base material is 50 to 90% by volume and the content of the soil modifier is 10 to 50% by volume.

10. An outdoor playground comprising the soil according to claim 8 in its surface layer.

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