JP2001058864A - Water absorption cement hardened body and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique that produces a water-absorbing cement hardened bodies produced by cold or steam aging not but autoclave aging with the durability to freezing and fusing increased and can build up the natural environment permitting algae and moss to grow up on the surface of the hardened body, as the waste soil occurring on the construction is effectively utilized. SOLUTION: Cement, soil and water are kneaded, formed to give the objective hardened body with 10-30% water absorption. In this case, the soil including 5-30 wt.% of fine particles with a particle size of <=44 μm under the absolute dryness is used at a weight ratio of the cement to the soil of 1/1-1/4 and at a weight ratio of water to cement of <=1.2. In a preferred embodiment, at least one selected from a fired powder of clay mineral, plaster and activated silica is formulated to the cement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hardened water-absorbing cement which easily grows algae and moss on the surface and provides a human-friendly touch, and a method for producing the same.

[0002]

^2. Description of the Related Art Conventionally, compressive strength is 10 to 60 N / mm ^2.
The water absorption of a hardened cement such as mortar and concrete is at most 4 to 6%, the water absorption rate is low, and it is basically an impermeable solid hardened body. Therefore, when concrete aesthetic measures are taken from the environmental aspect, as shown in vegetation blocks, concrete with a continuous space where plants can take root is made, and soil is put in that space, and plants and their seeds are put in place. Measures such as planting artificially were carried out. On the other hand, construction waste is a preferable material for landfill at the final disposal site, but it tends to be disliked because other waste that contaminates groundwater is discarded together at the final disposal site. Therefore, there is a problem that the construction of the final disposal site does not remain and it is difficult to dispose of a large amount of construction waste.

Japanese Patent Application No. 10-135106 proposed a solidifying material containing cement, gypsum, silica fume and the like, and a method for solidifying sludge having a particle diameter of 44 μm or less using the same. This proposal basically mixes the solidified material, sludge, fine aggregate and coarse aggregate using the water in the sludge.
The method is intended for use in roadbed materials and the like only for solidification methods of sludge of m or less, and no consideration is given to improvement of water absorption rate, growth of algae and moss, and vegetation effect. Also, Japanese Patent Application Laid-Open Nos. 9-142898 and 9-1324
No. 40 proposes an unsintered hardened body having a texture of soil, a high strength and a high water absorption, but this proposal is to mix clay with slaked lime and / or quick lime and to cure in an autoclave, Autoclave curing has the problem of poor freeze-thaw durability.

[0004]

Therefore, the freezing and thawing durability is improved by using normal room temperature or steam curing instead of autoclave curing, and an environment for naturally growing algae and moss is provided on the surface of the hardened cement. There has been a need for a technology capable of producing a hardened cement body that can be effectively used by using construction waste soil that has been poorly treated.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and the constitution of the present invention is to harden a mixture having a water absorption of 10 to 30% obtained by mixing and molding cement, soil and water. A soil having a content of 5 to 30% by weight of fine particles having a particle size of 44 μm or less in an absolutely dry state, wherein the weight ratio of cement: soil is 1: 1 to 1: 4 and water / The cement has a cement weight ratio of 1.2 or less, and is preferably characterized in that at least one of calcined clay mineral powder, gypsum, and activated silica is added to the cement.

[0006] The water-absorbing cement hardened body of the present invention absorbs water at a speed of several seconds to several minutes when water is applied, and retains the water as it is. Therefore, when used in place of conventional concrete, algae and moss grow naturally and also exhibit a vegetation effect to improve the environment. In addition, when the surface of the cured body of the water-absorbing cement of the present invention is touched, it gives a moist and gentle feel to human skin. Furthermore, although the temperature of the conventional concrete structure once heated by solar heat or the like is hardly cooled, the hardened water-absorbing cement of the present invention is hardly heated, so that the temperature and humidity may be controlled depending on the place of use in the building. It is effective and can maintain an excellent environment. Furthermore, the hardened water-absorbing cement of the present invention can be obtained by mixing a large amount of ordinary soil and construction soil with cement, so that the construction soil can be effectively used.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The cement used in the present invention is usually a variety of Portland cements such as high strength, ultra high strength, white, moderate heat, low heat generation and sulfate resistant cement; silica powder,
Various mixed cements mixed with fly ash, blast-furnace slag, etc .; rapid-hardening cements that harden rapidly due to the formation of ettringite, and alumina cement is not preferred.

[0008] The soil used in the present invention is a soil based on common general knowledge, and red soil, ocher, black soil, white earth, and the like can be used. Although construction-generated soil is basically desirable, even natural excavation can be used. The soil generated by construction includes soil excavated by various works such as construction of buildings such as buildings, tunnel construction, seawall protection of rivers and coasts, road construction and restoration. Soil having a content of fine particles of 44 μm or less of 5 to 30% by weight is preferred. 44m
The fine particles having a particle size of m or less are particles that are measured in an absolutely dry state where the soil is dried at 110 ° C. for 24 hours and pass through a JIS standard test sieve of 350 mesh and a nominal size of 44 μm. When the obtained soil is out of this range, it is possible to mix and adjust the soil having a large amount of fine particles and the soil having a small amount of fine particles before use.
If the fine particle content is less than 5% by weight, even if the compounding ratio of the soil is large,
It is difficult to obtain a hardened cement having a water absorption of 10% or more. If the fine particle content exceeds 30% by weight, practical strength cannot be obtained even if the mixing ratio of the soil is reduced, or the water absorption is 30% by weight. Even if an appropriate amount of air is entrained, the frost damage resistance decreases, which is not preferable.

[0009] The hardened cement of the present invention is basically a hardened mortar.
Up to 20% by weight, even if more than 30 grit (coarse aggregate) is mixed
There is no problem up to that point, but if the amount exceeds that, the water absorption is undesirably reduced. The maximum diameter of the coarse aggregate that can be used is 25 mm.

In the present invention, the water absorption of the cured product is 10 to 10.
It is 30%, preferably 15 to 25%. Here, the water absorption means that a columnar cured body having a diameter of 5 cm and a length of 10 cm is taken as 20 cm.
The weight (A) when immersed in water at 24 ° C. for 24 hours to obtain a saturated state was measured, and the weight (B) when dried at 105 ° C. for 24 hours was measured, and 100 (A−B) / B ( %). If the water absorption is less than 10%, it is difficult for algae and moss to grow,
If it exceeds 30%, it is difficult to obtain a practical strength of 10 N / mm ² or more, and the freeze-thaw durability decreases, which is not preferable.

In the present invention, cement is used as a binder. In order to enhance the strength of cement, components other than cement described later are blended, and this component is distinguished from cement as an admixture. Therefore, the binder refers to the cement alone or a mixture of the cement and the admixture. And the weight ratio of binder: soil is 1: 1 to 1: 4. In addition, the soil is calculated as a completely dry state. If the mixing ratio of the binder and the soil is less than 1: 1, it is difficult to obtain a hardened cement body having a water absorption of 10% by weight or more even if the fine particles passing through a sieve having a nominal diameter of 44 μm are 5% by weight or more. On the other hand, if the ratio exceeds 1: 4, a practical strength of 10 N / mm ² or more cannot be obtained, or even if a practical strength and an appropriate water absorption are obtained, the freeze-thaw durability deteriorates, which is not preferable.

In the present invention, the water / binder ratio is set to 1.2 or less, preferably 1.0 to 0.45. If it exceeds 1.2, a practical strength of 10 N / mm ² or more cannot be obtained when there are many fine particles. If it is less than 0.45, the strength becomes too large, the water absorption does not become 10% by weight or more, and the effect of naturally growing algae and moss cannot be obtained. The water / binder ratio in the present invention is a value obtained by converting the soil to a completely dry state or a completely dry state, and includes the amount of water absorbed by the soil.

Further, the softness is preferably 300 mm or less as a mortar flow value according to JIS R5201. Three
When the flow value exceeds 00 mm, the setting delay increases,
When manufactured by steam curing, cracks are likely to occur due to thermal expansion. In addition, the kneaded product of the present invention has a preferable flow value depending on the molding method because the adhesiveness becomes strong, and a more preferable flow value when molding by vibration molding is 120 to 250 mm.
It is. When it is less than 120 mm, it is preferable to perform extrusion molding or pressure molding.

In the present invention, one or more of calcined clay mineral, gypsum, and activated silica are used as the admixture component for increasing the strength without significantly changing the water absorption. These have the effect of increasing the strength when used alone, but higher strength can be obtained when used in combination.

The fired powder of the clay mineral is obtained by firing a clay mainly composed of alumina silicate at 600 to 1000 ° C. and is represented by metakaolin. When used alone or in combination with other admixtures, the amount is 20 parts by weight or less, preferably 5 to 15 parts by weight, based on 100 parts by weight of cement. If the amount is less than 5 parts by weight, the strength enhancement effect is small,
Even if it is used in excess of 0 parts by weight, the strength increasing effect is stagnant.

When used alone or in combination with other admixtures, gypsum is 15 parts by weight or less, preferably 2 to 10 parts by weight, based on 100 parts by weight of cement in terms of anhydride. If the amount is less than 2 parts by weight, the effect of increasing the strength is small, and if the amount exceeds 15 parts by weight, the effect of increasing the strength stagnates. The type of gypsum is not particularly limited, but is preferably type II anhydrous gypsum, which is called insoluble or hardly soluble anhydrous gypsum, and its fineness may be 3000 cm ² / g or more.

[0017] The active silica as a main component silica fume, silicified trees and paddy ash, amorphous SiO _2, such as Aerosil. The active silica is used alone or in combination with other admixtures in an amount of 30 parts by weight or less, preferably 3 to 25 parts by weight, per 100 parts by weight of cement. If the amount is less than 3 parts by weight, the effect of enhancing strength is small.
Even if it is used in excess of 0 parts by weight, the strength increasing effect is stagnant.

In the present invention, it is preferable to use a water reducing agent. As the type of water reducing agent, lignin sulfonate type, carboxylate type, polyol type and other general water reducing agents having a low water reducing rate, which reduce the water content to about 10% of the unit water in ordinary concrete; Compounded AE water reducing agent; For ordinary concrete, there are a high-performance water reducing agent and a high-performance AE water reducing agent that reduce the unit amount by 20 to 30%, and among them, a high-performance water reducing agent and a high-performance AE water reducing agent are preferable. General water reducing agents and AE water reducing agents are added up to about twice the amount specified by the manufacturer. High-performance water reducing agents include polyalkylallyl sulfonate and melamine resin sulfonate,
They have the property that even if they are added in relatively large amounts, there is no delay or air entrainment, and the water reduction rate improves according to the amount added. Representative brand names of commercially available products include “Mighty 150” manufactured by Kao Corporation and “FT-5” manufactured by Grace Chemicals, Inc.
00 "and" Sunflow PS "manufactured by Nippon Paper Industries.
These are added at most 3.0 parts by weight in terms of solid content based on 100 parts by weight of cement. Even if it is added in excess of 3.0 parts by weight, the elongation of the water reduction rate is small.

High performance water reducing agents do not have air entrainment,
Adds air entrainment to improve frost resistance. The high-performance AE water reducing agent is a so-called polycarboxylate-based water reducing agent, which has the property of improving the frost damage resistance due to its air entrainment property and improving the water reduction rate according to the amount added, but also has a delay property. growing. Therefore, in the case of a high-performance AE water reducing agent, the amount is at most twice the amount specified by the manufacturer for 100 parts by weight of the binder. If the addition exceeds twice, the retardation becomes too large, and when steam curing or the like is performed, cracks are likely to occur due to thermal expansion. Commercially available brand names of high-performance AE water reducing agents include MLE's "Leobuild PS8 Series", Fujisawa Pharmaceutical's "Palic Series", and Grace Chemicals'"Darlex Super Series". Can be

In the present invention, it is preferable to use an appropriate amount of various accelerators since the pre-curing time and the time required to obtain the demolding strength can be shortened. Examples of the accelerator include, but are not limited to, formic acid, calcium and magnesium nitrates, sodium and potassium salts, and calcium and magnesium thiocyanates.
Sodium, potassium salts, aluminum sulfate and the like are preferred. These accelerators are at most 2% by weight, preferably 0.2-1.5%, based on the binder (cement + admixture).
When the amount is small, the effect of accelerating the setting is small, and when the amount is too large, the elongation of the long-term strength is suppressed.

In the production of the hardened water-absorbing cement,
All components can be kneaded using a conventional mortar mixer or concrete mixer. More preferably,
Using a forced kneading mixer, add 70-80% of the total water as primary water to cement, soil, admixture and other additives, and after primary kneading for 1-3 minutes, remove the remaining 20-30% Add as secondary water and mix for a few minutes. The molding method may be extrusion molding, pressure molding, or vibration pressure molding, depending on the flow value of the mortar, as described above, in addition to vibration molding using a normal external or internal vibrator.

The curing method is not particularly limited, and may be room temperature. However, in the case of manufacturing as a precast product, normal pressure steam curing is preferable in terms of production efficiency. However, autoclave curing is not preferable because even if an appropriate amount of air is entrained, fine cracks are formed in the cured product upon cooling and the freeze-thaw durability is poor even at high strength. When normal pressure steam curing is performed, after the mixture is poured into a mold, 40 to 1 after a pre-curing time.
Cure at a temperature of 00 ° C.

[0023]

EXAMPLES Example 1 The following seven types of soil were collected. a Locally generated soil: Gray soil containing 3% by weight of fine particles of 44 μm or less b Locally generated soil: Black soil containing 7% by weight of fine particles of 44 μm or less c Locally generated soil: 13% by weight of fine particles of 44 μm or less
Red soil d Locally generated soil: contains 16% by weight of fine particles of 44 μm or less.
Loess e Locally generated soil: contains 24% by weight of fine particles of 44 μm or less,
Gray white f Locally generated soil: containing 32% by weight of fine particles of 44 μm or less,
Loess g Locally generated soil: containing 35% by weight of fine particles of 44 μm or less,
Gray-white The following seven types of test soils were prepared by blending these soils a to f so that the content of fine particles having a particle size of 44 μm or less became a sharp numerical value. A: Locally generated soil (3% by weight of fine particles of 44 μm or less, absolute dry weight 2.61) B: Mixture of locally generated soil and A (5% by weight of fine particles of 44 μm or less, absolute dry weight of 2.58) C) Mixture of locally generated soil and B (10% by weight of fine particles having a particle size of 44 μm or less, absolute specific gravity 2.40) D: Mixture of locally generated soil and C (15% by weight of fine particles having a particle size of 44 μm or less) Dry specific gravity 2.35) E: Mixture of e locally generated soil and D (20% by weight of fine particles of 44 μm or less, absolute dry specific gravity 2.13) F: f Mixture of locally generated soil and E (fine particles of 44 μm or less) 30% by weight, absolute dry density 2.01) G: g Locally generated soil (35% by weight of fine particles having a particle size of 44 μm or less,
Absolute specific gravity 2.01)

The types and amounts of soil (converted to absolute dry condition) shown in Tables 1 and 2 are kneaded with cement and water in the amounts shown in Tables 1 and 2 using a planetary forced kneading mixer, and the flow of the mortar. The values were measured according to JIS R 5201 and are shown in Tables 1 and 2. As the water reducing agent, a lignin sulfonic acid-based general AE water reducing agent was added to cement in a solid content of 0.1%.
25% (manufacturer-specified amount) was added. Mixing is usually done by adding 80% of the total water to Portland cement and soil.
The primary kneading was performed for 3 minutes, and then the remaining 20% of water was added, and the secondary kneading was performed for 3 minutes. Using the obtained mortar, three specimens having a diameter of 10 cm and a length of 20 cm for measuring the compressive strength, and a diameter of 5 cm and a length of 10 c for measuring the water absorption.
m specimens, 10 × 1 for measuring moss growth
Three specimens each having a size of 0 × 40 cm were formed on a shaking table,
After pre-curing for 5 hours, the temperature was raised from room temperature of 20 ° C. to 85 ° C. at a rate of 15 ° C./hour, kept for 4 hours, gradually cooled until the next day, and demolded. The compressive strength is 20 ° C and the relative humidity is 80%.
It was measured after indoor curing for a day. The moss was grown in a stream flowing through the forest. The moss formation and growth state were observed 6 months after arranging it on the edge of the river where water was not directly applied. The growing condition of moss was evaluated according to the following criteria. ×: No occurrence Δ: Growth on the side surface ○: Growth on a part of the side surface and the surface exposed to tree leakage ◎: Growth on the entire surface These results are also shown in Tables 1 and 2.

[0025]

[Table 1]

[Table 2]

The following facts can be understood from Tables 1 and 2. That is, when the fine particle content in the soil is less than 5% by weight, the water absorption is less than 10% by weight even if the mixing ratio of the soil to cement is 1: 4, and there is no natural growth of moss. For 5% by weight of fine particles, the mixing ratio is 1: 1 and the water / cement ratio is 0.1%.
By setting it to 45, the water absorption can exceed 10%. In order to obtain the same flow value, the water / cement ratio increases and the compressive strength decreases, but the water absorption increases, as the mixing ratio of the soil increases and the content of the fine particles increases. In the range of the present invention, in Experiment No. 1-23, which has the largest amount of fine particles and the highest mixing ratio of soil, practical strength, 1
The water / cement ratio for achieving 0 N / mm ² or more is 1.2
It was 0.

If the fine particle content exceeds 30% by weight, the mixing ratio is set to 1: 1, and even if the water / cement ratio is set to 1 or less, 10N
No compressive strength of / mm ² or more was obtained, indicating that the compressive strength is greatly affected not only by the water / cement ratio but also by the content of fine particles. The natural growth of moss has a water absorption of 10%
As described above, 15% or more is preferable, and the higher the water absorption, the better the growth. When the water absorption is 30%, the strength is also 10N / m
m ² or more, and the more preferable upper limit of the water absorption is considered to be about 25% in consideration of the balance of strength.

Example 2 Experiment Nos. 1-01 to 1-07 and 1-20 to 1 of Example 1
About 1-23, it shape | molded similarly to Example 1, steam-cured, and standard-cured for 14 days, and obtained the test specimen of 10 * 10 * 40cm. Using this, a freeze-thaw test is performed according to ASTM C 666 (rapid freezing in water, thawing in water).
The relative dynamic elastic modulus at 300 cycles was measured, and the results are shown in Table 3.

As is evident from Table 3, as the ratio of soil to cement increases, the kinetic elasticity coefficient also gradually decreases. However, when the mixing ratio of cement: soil exceeds 1: 4, it sharply drops to 60% or less. Frost damage resistance is expected to deteriorate. Further, even if the cement: soil ratio is the same, the soil with a large amount of fine particles tends to have a small relative elastic modulus, but up to 1: 4, it is 60% or more, and there is no problem.

[0030]

[Table 3]

Example 3 Natural anhydrous gypsum (type II, fineness of 450) was used as an admixture for 100 parts by weight of the ordinary portland cement of Example 1.
0 cm ² / g), silica fume (fineness: 22 m ² / g)
g) and metakaolin (fineness: 8500 cm ² / g) were blended in the proportions shown in Tables 4 and 5, and the blending ratio of the binder (cement + admixture) and soil was 1: 2.5, After kneading in the same manner, the flow value was measured. Specimens similar to those in Example 1 were prepared and cured by the same curing method, and the compressive strength and the water absorption were also shown in Tables 4 and 5. If the flow value is 120 mm or more, vibration molding using a shaking table is performed.
If it is less than 0 mm, it was press-formed at a pressure of 0.4 N / mm ² .

In Experiment No. 3-13, the implanted surface of the test piece expanded by several mm due to thermal expansion, and fine cracks were formed throughout. In Experiment No. 3-23, the cracked surface was not visible but the implanted surface was slightly swollen. (☆ in the table) As the water reducing agent, the following a and b were added in amounts shown in Tables 4 and 5 in terms of solid content. a ... 0.03-0.09% by weight based on the sum of the naphthalene sulfonate-based high-performance water reducing agent, cement and admixture
AE agent b (1 to 3 times the amount specified by the manufacturer) b: A polycarboxylate-based high-performance AE water reducing agent and an AE auxiliary agent that reduces the amount of air to 8 to 10% in Experiment No. 3-21 The amount of the high-performance AE water reducing agent used is the amount specified by the manufacturer. (★ in the table) Experiment No. 3-06 was performed by pressure molding (* in the table). Others are vibration molding.

[0033]

[Table 4]

[Table 5]

From Tables 4 and 5, the compressive strength gradually increases when the amount of anhydrous gypsum is increased while keeping other conditions constant, but the effect is recognized from 2 parts by weight per 100 parts by weight of cement. , More than 15 parts by weight, it is difficult to expect a further increase in strength. Similarly, when silica fume is blended as active silica, the effect is recognized from 3 parts by weight, and even if it is added in excess of 30 parts by weight, further increase in strength cannot be expected. In the case of metakaolin which is a fired product of an aluminosilicate clay, the effect is recognized at 5 parts by weight, and even if it exceeds 20 parts by weight, a further increase in strength cannot be expected. Further, when they are combined, a higher compressive strength is exhibited than when they are added alone.

Further, when the flow value is changed by adding the water reducing agent while keeping the water / binder (cement + admixture) ratio constant, when the flow value exceeds 300 mm, the water absorption becomes 30%.
Frost damage resistance is expected to decrease. Flow value is 11
In the case of 0 mm, there is no problem in pressure molding, but in vibration molding, the entrapped air does not escape and the strength is reduced. As described above, in the production of the hardened water-absorbing cement of the present invention, the mortar flow value is from 120 to 300 mm, and more preferably from 140 to 250 mm. It is also understood that when a high-performance AE water reducing agent is added, the effect of the delay property is not greatly affected up to about twice the upper limit specified by the manufacturer. (See Experiment Nos. 3-21 to 3-23)

Example 4 The amounts of calcium formate (reagent a) and calcium thiocyanate (reagent b) shown in Table 6 were added to the formulation of Experiment No. 3-11 in Table 4 in the same manner as in Example 1. Specimens for kneading, compression strength measurement and water absorption measurement were formed in the same manner. After curing 5 hours before, 20 ° C at a rate of 15 degrees / hour
Temperature from 85 ° C to 85 ° C, hold it for 4 hours, take it out of the curing tank, and remove it from the curing tank for 1 hour.
The compressive strength and the water absorption after curing in the room for 14 days were measured, and the results are shown in Table 6.

According to Table 6, the accelerator was (cement + admixture)
It is understood that when 0.2% by weight or more is added, the demolding strength is increased, but when it exceeds 2% by weight, the strength elongation after demolding is reduced.

[0038]

[Table 6]

[0039]

According to the present invention, it is possible to mix a large amount of soil into a cement composition, and the obtained water-absorbed cement hardened material absorbs water at a speed of several seconds to several minutes when water is applied. Algae and moss grow naturally when used instead of conventional concrete in specific places,
It also exerts vegetation effects to improve the environment. In addition, when the surface of the cured body of the water-absorbing cement of the present invention is touched, it gives a moist and gentle feel to human skin. Furthermore, the hardened water-absorbing cement of the present invention can be obtained by mixing a large amount of ordinary soil and construction soil with cement, so that the construction soil can be effectively used.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tetsuya Ando 1-4-1 Yurakucho, Chiyoda-ku, Tokyo Inside Denka Kagaku Kogyo Co., Ltd. (72) Inventor Kunio Shindo 385-36 Toiso, Isoba, Eniwa-shi, Hokkaido Kyowa Concrete Industry Inside R & D Co., Ltd.

Claims (7)

[Claims] 1. A hardened water-absorbing cement, which is obtained by kneading and mixing cement, soil and water, and has a water absorption of 10 to 30%. 2. A hardened water-absorbing cement according to claim 1, wherein soil having a content of fine particles having a particle size of 44 μm or less in an absolutely dry state is 5 to 30% by weight. 3. The total amount of cement or admixture added to cement: the weight ratio of soil is 1: 1 to 1: 4, and the water / cement weight ratio or the total amount of admixture added to water / cement. 3. The water-absorbing cement hardened product according to claim 1, wherein the weight ratio is 1.2 or less. 4. A hardened water-absorbent cement according to claim 3, wherein the admixture is at least one of calcined clay mineral powder, gypsum and activated silica. 5. A method for producing a hardened water-absorbing cement having a water absorption of 10 to 30% by adding water to kneaded cement and soil, kneading the mixture, and forming the fine particle content of 44 μm or less in a completely dry state. Using 5 to 30% by weight of soil. 6. The total amount of the cement or the admixture added to the cement: the weight ratio of the soil to 1: 1 to 1: 4, and the water / cement weight ratio or the total amount of the admixture added to the water / cement. The method according to claim 5, wherein the weight ratio is 1.2 or less. 7. The method of claim 6, wherein the admixture is at least one of calcined clay mineral powder, gypsum, and activated silica.