JPH0860152A - Method for hardening soil - Google Patents

Abstract

PURPOSE: To provide a method for inexpensively and surely hardening soil using steel slag and/or molten pretreated slag, gypsum and an alumina-based substance. CONSTITUTION: This method for hardening soil is to blend soil with 15-50-wt.% of steel slag and/or molten retreated slag, 0.5-20wt.% of gypsum and 0.5-20wt.% of an alumina-based substance based on total weight after blending. Soil can inexpensively and surely be hardened and further, can be modified without using expensive cement, coal, blast water-granulated slag by the method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reliably and inexpensively hardening soil by using steelmaking, hot metal pretreatment slag and the like.

[0002]

2. Description of the Related Art Generally, steelmaking and hot metal pretreatment slag (hereinafter abbreviated as slag) has lime remaining in the slag in a free form (hereinafter referred to as free CaO). When used as a civil engineering material, it is known that swelling occurs due to hydroxylation and carbonation of free CaO.

Therefore, at present, the slag is generally cooled naturally,
After crushing, free CaO is stabilized by stacking outdoors or artificially contacting with steam. On the other hand, free CaO in slag is also utilized to develop curability. For example, JP-A-58-58
As disclosed in Japanese Patent No. 189409, it is a method in which a slurry containing steelmaking slag, coal ash, and gypsum is filled in a depression and solidified. In addition, JP-A-4-16534
There is also a method in which one or more kinds of blast furnace slag, gypsum and lime are mixed with steelmaking slag and coal ash as shown in Japanese Patent Publication.

[0004]

Although soil cement is sometimes used at present as a method for hardening soft soil having a high water content, soil cement is generally expensive. Therefore, the present inventor has proposed an inexpensive method as disclosed in Japanese Patent Application Laid-Open No. 58-58.
When the method of Japanese Patent No. 189409 was carried out, sufficient curability was not obtained. This is Ca for hardening
It is necessary that O, Al ₂ O ₃ and CaSO ₄ dissolve in water to form a compound consisting of these three and water,
It is considered that sufficient curability was not obtained because the amount of Al ₂ O ₃ in the coal ash was small.

Next, the inventor implemented the method disclosed in Japanese Patent Laid-Open No. 4-16534. That is, it was attempted to harden the soil using steelmaking slag, coal ash, blast furnace slag and gypsum, but in this case good reproducibility of hardening was not obtained. It is considered that this is because the elution behavior of blast furnace slag when it comes into contact with soil is complicated, and the curability of the blast furnace slag fluctuates greatly due to the influence of the trace components of both.

An object of the present invention is to solve these problems and to solidify the soil inexpensively and reliably by using slag or the like.

[0007]

Means for Solving the Problems The present invention is to solve the above problems, and the gist thereof is to mix steel-making slag and / or hot metal pretreatment slag, gypsum and an alumina-based substance with water-containing soil and to cure it. It is characterized by That is, the feature of the present invention is that, in the soil, 15 to 50% by weight of steelmaking slag and / or hot metal pretreatment slag, 0.5 to 20% by weight of gypsum, and an alumina-based substance relative to the total weight after mixing. Is mixed in an amount of 0.5 to 20% by weight to cure the soil. Here, the alumina-based material refers to an alumina-based refractory after-use product, red mud, bauxite, shale shale, and the like. That is, of the metal oxides contained, alumina is the most abundant substance.

[0008]

The present invention will be described in detail below. Steelmaking slag and / or hot metal pretreatment slag generated in a converter or a hot metal wheel are cooled, solidified and crushed. Next, steelmaking slag and / or hot metal pretreatment slag is added to soft soil with high water content such as mud and dredging sludge in an amount of 15 to 50 relative to the total weight after mixing.
% By weight, 0.5-20% by weight of gypsum, and 0.5-20% by weight of an alumina-based substance are mixed and cured. At this time, CaO is eluted from the slag, CaSO _{4 is} extracted from the gypsum, and Al ₂ O ₃ is eluted from the alumina-based substance, and they react in water to form a compound called ettringite. That is, it is generated by the following reaction formula.

3CaO + Al ₂ O ₃ + 3CaSO ₄ +3
2H ₂ O → 3CaO ・ Al ₂ O ₃ / 3CaSO ₄・ 32
H ₂ O This reaction product, ettringite, is insoluble, and this compound precipitates as a solid while taking in water as crystal water, and the curability is exhibited by increasing the proportion of the solid in the space.

In order to positively generate ettringite, it is necessary to supply Al ₂ O ₃ together with CaO, CaSO ₄ , and H ₂ O. When SiO ₂ is supplied from a silica-based material instead of Al ₂ O ₃ , calcium silicate hydrate is produced, but since the number of water of crystallization per molecule is smaller than that of ettringite, it is free in the soil. The ability to fix water is small. Therefore, an alumina-based substance is desirable as a substance to be mixed with soil.

The blending amount of slag is set to 15 to 50% by weight.
Is less than 15% by weight CaO is deficient
Do not generate enough. Etrin over 50% by weight
Unreacted free C due to lack of other substances required for gite formation
This is because aO remains. Add 0.5 to 2 gypsum
0% by weight means that CaSO is less than 0.5% by weight. _Four
Is insufficient to generate enough ettringite. 20 weight
%, Ettringite is excessively formed, and its crystals
This is because the tissue is destroyed by the growth pressure.

When the amount of the alumina-based substance is 0.5 to 20% by weight, if the amount is less than 0.5% by weight, the amount of alumina is insufficient and ettringite is not sufficiently formed. This is because if the amount exceeds 20% by weight, ettringite is excessively formed and the crystal growth pressure destroys the structure. In the prior art, coal ash also contains about 25% Al ₂ O ₃ . However, it is generally present as mullite or 3Al ₂ O ₃ .2SiO ₂ . Therefore, Al ₂
The activity of O ₃ becomes small, which is disadvantageous for elution. Also in this respect, an alumina-based material having a large activity is more advantageous. The water content in the soil is generally 30 to 90% by weight, but the present invention can be applied even when the water content is higher or lower, and the soil containing the slag, gypsum, and alumina-based material is included in the soil. It cures due to the water content.

[0013]

EXAMPLES The present invention will now be described in more detail based on examples. Table 1 shows the chemical compositions of the slag and the alumina-based material of this example.

[0014]

[Table 1]

After the steelmaking slag was cooled and solidified, it was crushed to a size of 6 mm or less and magnetically separated. This steelmaking slag was mixed with an alumina-based material and soil with a water content of 32% at the ratio shown in Table 2, and
The test piece was cast into a test piece according to the method for measuring the compressive strength in the physical test method for SR5201 cement, and the compressive strength on the 28th day of the casting material was measured. The measured values are shown in Table 2.

[0016]

[Table 2]

The alumina-based material used this time is an alumina-based refractory waste material in a molten steel ladle. As a comparative example, comparative example No.
Comparative Example No. 1 is a case where only the slag is mixed in the soil, and Comparative Example No. 2 is a case where the steelmaking slag, coal ash, and gypsum are mixed in the soil, as shown in JP-A-58-189409. As disclosed in JP-A-4-16534, the steel is mixed with steelmaking slag, coal ash, granulated blast furnace slag and gypsum. Table 1 shows the chemical composition of coal ash and granulated blast furnace slag. From Table 2, all the examples showed higher strength than the comparative examples.

[0018]

Industrial Applicability According to the present invention, soil can be hardened inexpensively and reliably. Therefore, expensive cement, lime,
It became possible to modify the soil without using granulated blast furnace slag.

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Claims (1)

[Claims] 1. A steelmaking slag and / or a hot metal pretreatment slag is added to the soil containing water in an amount of 15 to 15 with respect to the total weight after the addition.
50% by weight, 0.5 to 20% by weight of gypsum, and 0.5 to 20% by weight of an alumina-based substance are mixed and cured to cure the soil.