Production method of soil cement

Abstract

To provide a production method of soil cement with deformation follow-up ability allowing re-excavation to be easily carried out and capable of expanding its application and usability.SOLUTION: The present invention pertains to a production method of soil cement including at least the following (A) to (D) processes. (A) a production process of a mixture for producing the mixture by adding, to sediment, at least 50 to 400 kg of solidification material per 1 m3 of soil cement, (B) a temporary curing process of the mixture to temporarily cure the mixture for a period where the mixture is allowed to be broken out, (C) a breaking-out process of the mixture for getting a broken-out product by breaking out the temporally-left and cured mixture to the one with particle diameters of 200 mm or less, (D) a rolling process of the broken-out product for getting the soil cement through rolling the broken-out product.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention provides a method for producing soil cement that has high deformation compliance, is easy to re-excavate, and can expand its applications and uses. [Background technology]

[0002] In a broad sense, soil cement refers to a mixture (fresh state) of soil and sand mixed with a solidifying agent and water, etc., as well as the solidified body that hardens due to hydration of the solidifying agent. Recently, in consideration of environmental issues, soil cement made from soil and sand generated during various construction works is widely used. This allows the generated soil to be effectively used at the same construction site or at a different construction site, extending the life of the soil and sand disposal site and reducing the costs required for the transportation, disposal, and procurement of the soil, as well as environmental problems such as noise and vibration when the soil is transported. Therefore, soil cement is economical and has the advantage of being less likely to cause the environmental problems mentioned above.

[0003] Conventionally, methods for adding solidification materials to soil and sand in the production of soil cement include the lump-sum addition method, in which the entire amount of solidification material is added to the soil and sand at once (Patent Document 1 and Patent Document 2), and the divided addition method, in which the solidification material is added to the soil and sand in two separate additions, the first and second additions (Patent Document 3). However, when the soil and sand is difficult to solidify, such as volcanic ash clayey soil and organic soil, or highly viscous soil such as heavy clay, the amount of solidification material required to achieve the target strength with the above-mentioned lump-sum addition method is greater than that required for other soil and sand, such as coarse-grained soil or low moisture content soil.

[0004] The divided addition method has the advantage that it can obtain the same strength as the one-time addition method with a smaller amount of solidification material than the one-time addition method, but because the strength is relatively high, it can be difficult to re-excavate in construction work that requires re-filling, such as backfilling underground buried pipes, making it unsuitable for such applications. Furthermore, soil cement produced by the divided addition method has the disadvantage that it has a small fracture strain and is poorly responsive to strain (deformation) caused by earthquakes, etc. Therefore, with the divided addition method, the applications and uses are limited, and it is difficult to optimize the amount of solidification material added, which can result in an excess or deficiency of solidification material in the soil cement. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-15022 A [Patent Document 2] JP 2018-21303 A [Patent Document 3] Patent No. 704216 Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, an object of the present invention is to provide a method for producing soil cement that has high deformation followability, is easy to re-excavate, and can expand its applications and uses. [Means for solving the problem]

[0007] Therefore, the inventors conducted intensive research to achieve the above-mentioned object, and discovered that a method for producing soil cement having the following configuration can achieve the above-mentioned object, thereby completing the present invention.

[0008] [1] A method for producing soil cement, comprising at least the following steps (A) to (D): (A) Add at least 1 m of soil cement to the soil. 3 Mix 50 to 400 kg per unit and mix to create a mixture. (B) a temporary curing step of temporarily curing the mixture for a period during which the mixture can be crushed. (C) A process of crushing the mixture after the temporary curing to obtain crushed material having a particle size of 200 mm or less. (D) A step of compacting the crushed material to obtain soil cement. [2] The method for producing soil cement according to [1] above, wherein in the step (B), the temporary curing period is within a range of 3 to 365 days. [3] A method for producing soil cement according to [1] or [2], wherein in step (C), the crushed material is stored until use. [4] The method for producing soil cement according to [1] or [2] above, wherein in step (D), the compacted soil cement is further cured. Effect of the Invention

[0009] The soil cement produced according to the present invention has high adaptability to deformation and is strong enough to be re-excavated. In addition, since the mixture prepared in step (A) is temporarily placed and cured for a certain period of time, and the crushed material from step (C) is stored until it is used, it is possible to ensure a long usage period, thereby expanding the applications and uses of soil cement. [Brief description of the drawings]

[0010] [Figure 1] (C) Photographs showing the state of the mixture after temporary curing in the process. The photograph on the left shows the mixture in a state where it is too strong to be crushed, the photograph in the middle shows the mixture in a state where it is easy to crush and has been crushed, and the photograph on the right shows the mixture in a state where it has become muddy and cannot be crushed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] As described above, the present invention is a method for producing soil cement, which includes at least the steps of (A) preparing a mixture, (B) temporarily curing the mixture, (C) crushing the mixture, and (D) compacting the crushed material. The present invention will be described in detail below with respect to the steps (A) to (D).

[0012] (A) Mixture preparation process The step (A) is a step of adding at least a solidification material to soil and sand and mixing them to prepare a mixture. Next, the soil and sand, the solidification material, the mixing device, and the addition of water will be described in this order. (i) Soil The soil and sand may be one or more selected from soil and sand generated at construction sites such as building sites and road construction sites, surplus soil, waste soil, and other soil and sand generated at construction sites such as excavation sites, and soil and sand that can be collected near construction sites, etc. The type of soil and sand is not particularly limited, and may be one or more selected from difficult-to-solidify soils such as coarse-grained soil, fine-grained soil, volcanic ash clayey soil, organic soil, and highly organic soil, and highly clayey soil.

[0013] (ii) Solidifying agent The solidification material is at least one selected from blast furnace cement type B, blast furnace cement type A, blast furnace cement type C, Portland cement, silica cement, fly ash cement, ecocement, and cement-based solidification materials. Here, the cement-based solidification material is a composite material with cement as a base material, and may be selected according to the purpose of solidification, such as for general soft soil, for special soil (general purpose type), and for highly organic soil, and the conditions of the solidification site. As examples of the cement-based solidification material, commercially available examples include Geoset 200 (registered trademark, manufactured by Taiheiyo Cement Corporation) for general-purpose use, and Geoset 225 (registered trademark, manufactured by Taiheiyo Cement Corporation) for high organic soil. Considering low cost and high solidification performance, the solidification material is preferably blast-furnace cement type B and a cement-based solidification material.

[0014] The amount of the solidification material added is 1 m of the soil cement. 3 The amount of addition is 50 to 400 kg per 1 m of soil cement. 3 If the amount of the solidification material is less than 50 kg per m of soil cement, the strength of the soil cement is insufficient, as shown in Comparative Example 1 in Table 1 and Comparative Example 10 in Table 3 below, and if the amount of the solidification material is more than 400 kg, the strength of the soil cement becomes too high, as shown in Comparative Example 6 in Table 1 and Comparative Example 13 in Table 3 below, and crushing in the step (C) may not be easy. 3 The amount is preferably 80 to 300 kg per unit. The appropriate amount of the additive may be determined in advance by an indoor blending test or the like.

[0015] (iii) Mixing device The device for mixing the soil and the solidifying agent is not particularly limited, and may be a mixer generally used for mixing concrete or mortar, such as a tilting mixer, a forced mixing mixer, a drum mixer, a gravity mixer, a hand mixer, etc. In addition, at construction sites, the mixing device may be a backhoe, a bucket mixer, or a batch or continuous mixer dedicated to soil cement. Incidentally, the effects of adding solidifying material to soil and sand include the following: (a) The apparent moisture content decreases. (b) The soil particles in the soil are aggregated, improving the soil texture. (c) Workability, such as compaction, is improved. (d) The calcium ions in the solidification material react with humic acids and other corrosive acids in the soil and sand, fixing the corrosive acids that inhibit the solidification of soil cement, thereby further promoting the solidification reaction.

[0016] (iv) Addition of water In step (A), if the soil or sand has a high viscosity making it difficult or impossible to stir and mix the solidification agent, or if the soil or sand has a low moisture content and there is insufficient water to hydrate the solidification agent, it is preferable to add water when kneading the mixture. Here, when we say that the soil and sand has such a high viscosity that it is difficult or impossible to stir and mix the solidification material, this cannot be stated unequivocally because the stirring and mixing depends on the performance of the mixing equipment, but it means, for example, that stirring and mixing is not possible or that the mixture is not uniformly mixed. The water used for the water addition may be tap water, river water, lake water, seawater, treated sewage water, etc. The amount of water to be added may be determined by actually preparing a mixture using the water to be used. In this case, when using water other than tap water, it is preferable to confirm in advance that it does not adversely affect the solidification performance.

[0017] (B) Temporary curing process of the mixture The step (B) is a step of temporarily storing and curing the mixture for a period during which the mixture can be disintegrated. The "period during which the mixture can be crushed" depends on the performance of the tools and equipment used for crushing, but in terms of the compressive strength of the mixture, it is, for example, 0.03 to 1.5 N / mm 2 The compressive strength is 0.03N / mm 2 If the strength of the mixture is less than 1.5N / mm, the mixture will not have enough strength to be crushed, and may become muddy when force is applied. 2 If the compressive strength exceeds 0.08 to 1.0 N / mm, the crushing may not be easy or the rolling compaction after crushing may be difficult. 2 Incidentally, based on Tables 1 to 3 shown below, the period of temporary curing is within the range of 3 to 365 days. In principle, the more solidifying material is used and the longer the curing period, the higher the strength will be, making crushing more difficult. However, even if the amount of solidifying material is large, if the curing period is short, the increase in strength will be small and crushing may be easy. On the other hand, even if the amount of solidifying material is small, if the curing period is long, the increase in strength will be large and crushing may be difficult. In other words, since [strength (mainly dependent on the amount of solidifying material) / curing period / difficulty of crushing] are interrelated, it is important to determine each of them taking into consideration the purpose and destination of utilization. Therefore, it is preferable to conduct preliminary mix tests using actual soil and sand. The method of temporary curing is not particularly limited, and examples thereof include covering with a sheet, sealed curing, and sealed curing.

[0018] (C) Crushing process of the mixture This step is a step of crushing the mixture after the temporary curing to obtain a crushed material having a particle size of 200 mm or less. If the particle size exceeds 200 mm, it may be difficult to perform rolling compaction. The particle size is preferably 150 mm or less, more preferably 100 mm or less, even more preferably 50 mm or less, and even more preferably 10 mm or less. In addition, the crushing method used in the present invention is not particularly limited, but examples thereof include a method in which the mixture that has been temporarily placed and cured is crushed using a crusher equipped with a sieve, and a method in which the mixture is crushed using the bucket or caterpillar of a backhoe.

[0019] The compressive strength of the mixture during crushing is 1.0 N / mm 2 If the water content exceeds this value, it is preferable to add water to the crushed material, as this will increase the compaction ability (filling ability) of the crushed material and thereby improve the strength of the soil cement. The water used for the water addition can be tap water, river water, lake water, seawater, treated sewage water, etc. The amount of water to be added can be determined by actually preparing a mixture using the water to be used. In this case, when using water other than tap water, it is preferable to confirm that it does not adversely affect the solidification performance. It is convenient to store the crushed material until it is time to use it. The stored crushed material can be used by performing compaction or the like as needed, thereby expanding the uses and applications of the soil cement in the future.

[0020] (D) Compaction process of crushed material This step involves compacting the crushed material to obtain soil cement. The rolling method used in the present invention is not particularly limited, and examples of the rolling method include rolling with a vibrating roller or a vibration damper. For applications requiring higher strength, it is preferable to add a solidifying material to the crushed material before rolling. In addition, if the strength of the soil cement is insufficient, a solidifying agent can be added to the crushed material in the compaction step to obtain soil cement. In this process, it is preferable to carry out curing to prevent freezing after construction in winter and drying of the pouring surface after construction in summer. Examples of the curing include the use of curing sheets or mats, and the combination of these with water spraying or heat absorption curing. EXAMPLES

[0021] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. 1.Materials used (1) Sample soil The sample soils used were soil from Kanagawa Prefecture (Table 1), Shizuoka Prefecture (A in Table 2), Hiroshima Prefecture (B in Table 2), Hokkaido (C in Table 2), and Kumamoto Prefecture (Table 3).

[0022] (2)Solidification material The solidification materials used were Geoset 225 [registered trademark, manufactured by Taiheiyo Cement Corporation] (Tables 1 and 3) and blast-furnace cement type B [manufactured by Taiheiyo Cement Corporation] (Table 2).

[0023] 2. Determining the degree of difficulty of disintegration The sample soil and the solidification material for the first addition were mixed in a Hobart mixer to prepare a mixture according to the formulations shown in Tables 1 to 3. However, when mixing was difficult, water was added until the mixture could be mixed. Next, the mixture is placed in a plastic bag, and the compressive strength of the mixture is measured to see if it is 0.02 (Comparative Example 1, etc.) to 2.07 (Comparative Example 6) N / mm 2 After the mixture was temporarily stored under sealed curing until it reached a temperature of 100° C., it was passed through a sieve with 9.5 mm openings to crush the mixture having the material ages shown in Tables 1 to 3. The degree of difficulty of crushing was judged based on the condition of each mixture when it was crushed. 2 Comparative Example 10, which is 0.02 N / mm 2 In Comparative Examples 1 and 11, when pressure was applied to pass the material through a sieve, the material became muddy and could not be disintegrated.

[0024] 3. Preparation of specimen Next, according to the formulations shown in Tables 1 to 3, the crushed material alone (Examples) or the crushed material and a secondary solidification material (Comparative Examples) were mixed using a Hobart mixer, and the mixture was compacted into a mold with an inner diameter of 50 mm and a height of 100 mm according to the Cement Association Standard Test Method (JCAS L-01) to prepare test specimens for the Examples and Comparative Examples. Moreover, the specimens of Reference Examples 1 to 3 were prepared by rolling only, without adding any solidifying agent.

[0025] 4.Water resistance test The water resistance of the test specimens (referred to as solidified bodies in Tables 1 to 3) was evaluated by visually checking for muddying or collapse in order to evaluate the water resistance of the soil cement due to rainfall, etc., and the water resistance was judged to be good or bad. Note that, in Tables 1 and 2, test specimens 28 days after molding were used, which were made by rolling compaction of the crushed material obtained by crushing a 7-day-old mixture, and in Table 3, test specimens 28 days after molding were used, which were made by rolling compaction of the crushed material obtained by crushing a 28-day-old mixture.

[0026] 5.Compressive strength test and breaking strain test The compressive strength of the specimens (represented as "strength" in the table) and the fracture strain of the specimens 28 days after molding using crushed material from a 7-day-old mixture were measured in accordance with JIS A 1216 "Unconfined compression test method for soil." In addition, in Comparative Example 13 in Table 3, the solidification material was added for the first time, and immediately after that, the solidification material was compacted and molded, and the compressive strength, fracture strain, and water resistance of the molded body (specimen used in a normal compressive strength test) were measured 28 days and 91 days after molding. The degree of difficulty of disintegration in Comparative Example 13 was judged based on the measured strength. The above results are shown in Tables 1 to 3, and the evaluation of the test results is discussed below, mainly comparing the examples and comparative examples that have the same type of soil (origin) and the same type and amount of solidification agent, which affect the physical properties of the soil cement.

[0027] [Table 1]

[0028] (1) About Table 1 (i) Comparison of Example 5 with Comparative Examples 2 and 3 The total amount of solidification material added is 250 kg / m 3Although the strength ratios (numbers in parentheses) of Example 5 / Comparative Example 2 and Example 5 / Comparative Example 3 after 28 and 91 days from molding were low at 0.10 to 0.20 for the crushed material with an age of 7 days and the crushed material with an age of 28 days. Note that the numbers in parentheses in Table 1, for example, "0.20" for the crushed material with an age of 7 days in Comparative Example 2, indicates the strength ratio of Example 5 / Comparative Example 2. The same applies to the other values ​​in Table 1. In addition, the fracture strain of both the 7-day-old crushed material and the 28-day-old crushed material was about four times higher in Example 5 than in Comparative Examples 2 and 3, and the deformation followability was excellent. Furthermore, the water resistance of the Example and Comparative Example was good.

[0029] (ii) Comparison of Example 7 with Comparative Examples 4 and 5 The total amount of solidification material added is 350 kg / m 3 Despite being the same as above, the strength ratios (numbers in parentheses) of Example 7 / Comparative Example 4 and Example 7 / Comparative Example 5 28 and 91 days after molding were low at 0.11 to 0.22 for the crushed material with an age of 7 days and the crushed material with an age of 28 days. In addition, the fracture strain of both the 7-day-old crushed material and the 28-day-old crushed material was about 5 times higher in Example 7 than in Comparative Examples 4 and 5, and the deformation followability was excellent. Furthermore, the water resistance of the Example and Comparative Example was good. Although the compressive strength and fracture strain of Reference Example 1 (no solidification material added) were similar to those of Comparative Example 1 (solidification material added) which used the same soil and sand, the water resistance was poor because it was not modified with a solidification material.

[0030] (iii) Comparative Example 1 In Comparative Example 1, soil cement 1 m 3 The amount of solidification material added per unit is 40 kg / m 3 Therefore, in this invention, the amount of solidification material is set to 1 / m of soil cement to reduce the strength. 3 50kg / m 3 If it is less than this, disintegration becomes difficult.

[0031] [Table 2]

[0032] (3) About Table 2 Comparison of Example 11 and Comparative Example 7 The total amount of solidification material added is 240 kg / m 3 Although the strength ratios (numbers in parentheses) of Example 11 / Comparative Example 7 were low, ranging from 0.43 to 0.86, for the crushed material aged 7 days and the crushed material aged 28 days. Note that the numbers in parentheses in Table 2, for example, "0.86" for the crushed material aged 7 days in Example 11, indicates the strength ratio of Example 11 / Comparative Example 7. The same applies to the other values ​​in Table 2. Moreover, the breaking strain in Example 11 was about 1.3 times higher than that in Comparative Example 7, and the deformation followability was excellent. Furthermore, the water resistance in both Example 11 and Comparative Example 7 was good. Furthermore, even if the type of soil sample changes, such as from Hiroshima (Example 12, Comparative Example 8) or Hokkaido (Example 13, Comparative Example 9), the same can be said as for the Shizuoka sample (Example 11, Comparative Example 7). Although the compressive strength and fracture strain of Reference Example 2 (no solidification material added) were similar to those of Example 9 (solidification material added) which used the same soil and sand, the water resistance was poor because it was not modified with a solidification material.

[0033] [Table 3]

[0034] (4) About Table 3 (i) Comparison of Example 14 and Comparative Example 11 The total amount of solidification material added is 150 kg / m 3 Although the strength ratios (numbers in parentheses) of Example 14 / Comparative Example 11 were low, ranging from 0.38 to 0.76, for the 28-day-old crushed material and the 365-day-old crushed material. Note that the numbers in parentheses in Table 3, for example, "0.76" for the 28-day-old crushed material of Example 14, indicate the strength ratio of Example 14 / Comparative Example 11. The same applies to the other values ​​in Table 3. Moreover, the breaking strain in Example 14 was about 1.1 times higher than that in Comparative Example 11, and the deformation followability was high. Furthermore, the water resistance in both Example 14 and Comparative Example 11 was good. These findings show that even when using crushed material that has been temporarily cured for 365 days, it is possible to produce soil cement that has appropriate strength, high deformation compliance and water resistance. Although the compressive strength and fracture strain of Reference Example 3 (no solidification material added) were similar to those of Comparison Example 10 (solidification material added) which used the same soil and sand, the water resistance was poor because it was not modified with a solidification material.

[0035] (ii) Comparison of Example 16 and Comparative Example 12 The total amount of solidification material added is 250 kg / m 3 Although the strength ratios (values ​​in parentheses) of Example 16 / Comparative Example 12 were the same as those of the 28-day-old crushed material and the 365-day-old crushed material, the ratios were as low as 0.34 to 0.88. Moreover, the breaking strain in Example 16 was 1.8 times higher than that in Comparative Example 12, and the deformation followability was excellent. Furthermore, the water resistance in both Example 16 and Comparative Example 12 was good. These findings show that even when using crushed material that has been temporarily cured for 365 days, it is possible to produce soil cement that has appropriate strength, high deformation compliance and water resistance. (iii) Comparative Example 10 In Comparative Example 10, soil cement 1 m 3 The amount of solidification material added per unit is 30 kg / m 3 Because the amount of material was so small, the material turned into mud during crushing, making crushing difficult. (iv) Comparative Example 13 As described above, Comparative Example 13 is a compact (a specimen used in ordinary compressive strength tests) that was compacted and molded immediately after the initial addition of the solidification material. However, compared to the soil cement of the present invention, it has a high compressive strength, is difficult to crush, and has a low fracture strain, resulting in poor deformation compliance.

Claims

1. A method for producing soil cement comprising at least the following steps (A) to (D). (A) Add at least 1 m of soil cement to the soil. ３ A process for preparing a mixture in which 50 to 400 kg per unit is added and mixed to prepare a mixture. (B) a step of temporarily curing the mixture, in which the mixture is temporarily cured for a period during which the mixture can be crushed. (C) A crushing step of crushing the mixture after the temporary curing to obtain crushed material having a particle size of 200 mm or less. (D) A step of compressing the crushed material to obtain soil cement.

2. The method for producing soil cement according to claim 1, wherein in the step (B), the period of temporary curing is within the range of 3 to 365 days.

3. The method for producing soil cement according to claim 1 or 2, wherein in step (C), the crushed material is stored until use.

4. The method for producing soil cement according to claim 1 or 2, wherein in the step (D), the compacted soil cement is further cured.

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