JPS6043389B2 - Method for increasing the strength of hydrated soft soil using sulfuric acid modified blast furnace slag - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for economically and efficiently increasing the strength of hydrous soft soil by using finely quenched blast furnace slag modified with sulfuric acid and Boltland cement as strength increasing agents. .

Traditionally, it has been used to improve soft, water-containing soil deposited in the sea, ports, rivers, lakes, etc., or to dredge and bury it.
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It is generally known that water-containing soft soil can be strengthened to increase its strength.

Among such methods for increasing the strength of weak athletes, a method using a strength increasing agent or a solidifying agent is used as a method that can achieve a large increase in strength in a relatively short period of time. in this case,
Cement, quicklime, water glass, asphalt, organic polymer substances, etc. have been proposed as strength increasing agents.
All of them have drawbacks such as being inferior in terms of strength increase and being unprofitable in terms of economic efficiency, so they are not satisfactory.Especially in the treatment of soft materials with a high water content such as sludge. In this case, since the amount of treatment per process reaches tens of thousands to hundreds of thousands of units, the amount of strength-increasing agent to be applied is necessarily large, and therefore, this strength-increasing agent must be used as cheaply as possible. The present inventors have previously proposed an inexpensive and effective method for increasing the strength of water-containing soft and weak materials (Japanese Patent Application No. 8915/1989, No. 55-4395 (hereinafter referred to as the prior art).

These prior art technologies succeeded in increasing the strength of hydrated soft soil by reducing the amount of additives used compared to conventional methods and shortening the time it takes to reach the required strength of hydrated soft soil. It is. In other words, these methods divide boltland cement, blast furnace slag, and gypsum-based strength-increasing agents into two types of additives, and specify the addition order ratio and additive particle size of these additives. As a result, reactions involved in increasing the strength of hydrated soft soil, such as mutual reactions between each added component and reactions between these components and soil components, occur efficiently and smoothly. As a result of further research into a series of these techniques, the present inventors have arrived at the present invention, which effectively utilizes industrial waste as a resource and is even more superior from an ecological and economic perspective. That is, the present invention consists of adding and mixing Bortland cement with finely quenched blast furnace slag having a particle size of 300 μm or less, which has been modified with sulfuric acid, into hydrous soft soil. The present invention provides a method for increasing the strength of hydrous soft soil, characterized in that the soil is modified using 3 to 5 parts of sulfuric acid per 10 parts of soil.

In the present invention, as one of the components of the strength increasing agent, finely quenched blast furnace slag modified with sulfuric acid is used as a special acid.

According to the research conducted by the present inventors, it has been found that this sulfuric acid modified quenched blast furnace slag exhibits a very remarkable effect as a strength increasing component. That is, when finely quenched blast furnace slag is brought into contact with sulfuric acid and reacted, (a) the blast furnace slag is decomposed by the acid, and at the same time, the silica and alumina components on its surface are activated;
The specific surface area of blast furnace slag increases significantly. (b) Sulfuric acid finally acts with the calcium component contained in the blast furnace slag, and
It remains in the metamorphosed blast furnace slag as crystals of suiseki ko. Therefore, due to the effect of the sulfuric acid treatment as described above, this sulfuric acid modified blast furnace slag exhibits significantly enhanced reactivity as a strength enhancer component as a whole. The sulfuric acid modified blast furnace slag in the present invention can be obtained by reacting finely quenched blast furnace slag with sulfuric acid while stirring it in a reactor. In this case, the fine quenched blast furnace slag is obtained by rapidly cooling the blast furnace slag (slag) produced as a by-product from a steelmaking blast furnace, and is further reduced to a particle size of 300p or less! It is crushed. Blast furnace slag is rapidly cooled by a wet method in which it is granulated and rapidly cooled with water, a semi-dry method in which a small amount of water and air is used, and a dry method in which only air is used. Generally, so-called blast furnace slag produced by a wet method is suitable as a raw material. This slag is made by quenching slag, a byproduct of iron-making blast furnaces, with water and crushing it into sand or granules of about 1 to 57 nm in size. This composition varies slightly depending on the composition of the iron ore, the blast furnace used, and the operating policy, but it is approximately as follows. SlO23O~35%, Al2O3l3~18%, C
aO38-45%, Fe2O3O. 5-1.0%, Mg
O3-6%, SO. 5-1.0%, MnOO. 5-1.
5%, TiO2O. 5-1.5%. The finely quenched blast furnace slag used in the present invention has latent hydraulic properties that can exhibit hydraulic properties when stimulated by alkali or the like.

Such latent hydraulic properties can be obtained by rapidly cooling the blast furnace slag, avoiding its crystallization, and making it amorphous (glass-like) in which crystallization energy is stored internally. The crystalline material obtained by slowly cooling blast furnace slag is a dense crystalline material whose main constituents are melilite (Gehlenite Ca2Al, SlO7/okermanite Ca2MgSi2O7 solid solution) and calcium orthosilicate, and has no latent hydraulic properties. Therefore, it is inappropriate. Moreover, since this rapidly cooled blast furnace slag is used as a reactant, it is necessary to use it in as fine a state as possible. Normal 1-5? Coarse particles are unsuitable because the surface area that contributes to the reaction with sulfuric acid during sulfuric acid modification and the reaction with the soil and cement L of the transformed blast furnace slag is too small, resulting in a marked decrease in reactivity. In the case of the present invention, it is preferable to use finely quenched blast furnace slag of 300 p or less, especially 100 to 1 p. The industrially preferable sulfuric acid treatment method for finely quenched blast furnace slag applied to the present invention is roughly divided into the following two types.

(1) Sulfuric acid is applied directly to the finely quenched blast furnace slag. (2
) In the flue gas desulfurization treatment, the sulfuric acid content obtained by absorbing and oxidizing SOO in the flue gas is made to act on the finely quenched blast furnace slag. (1
The sulfuric acid used in the method (2) may be commercially available sulfuric acid, but from the economic and ecological standpoints, it is preferable to use waste sulfuric acid discharged from various chemical factories.

This sulfuric acid treatment can be carried out in various ways, for example,
(a) Adding and mixing blast furnace slag to an aqueous sulfuric acid solution, (b)
Blast furnace slag is dispersed in the separated mother liquor of sulfuric acid-treated blast furnace slag,
Adding and mixing a specified amount of sulfuric acid to this, (c) adding and mixing sulfuric acid to the blast furnace slag once or in multiple batches, or
(d) There is a method of adding and mixing an excess of sulfuric acid to blast furnace slag, and adding and mixing the blast furnace slag to this in one time or in multiple batches. In this case, the amount of sulfuric acid to be added is not particularly limited, but in order to obtain modified blast furnace slag that is preferable as a strength increasing agent, 3 to 5 parts of sulfuric acid (in terms of 100% sulfuric acid) should be added to 10 parts by weight of blast furnace slag.
It is applied in a proportion of 1 part by weight, preferably 5 to 3 parts by weight.
The concentration of sulfuric acid to be added may be such that a predetermined amount of sulfuric acid is uniformly dispersed and mixed in the blast furnace slag. When sulfuric acid is brought into contact with blast furnace slag, the silica and alumina components are activated as described above, and most of the sulfuric acid eventually becomes dihydrate.

In this case, a portion of the alkaline component of the blast furnace slag reacts with sulfuric acid and dissolves, but since the solubility of calcium sulfate is lower than other sulfates, it ultimately turns into dihydrate crystals and remains in the transformed blast furnace slag. Therefore, in producing this sulfuric acid modified blast furnace slag, it is preferable to repeatedly use the mother liquor from which the product is separated as a dilute solution of sulfuric acid. By using this generatrix, the elution of MgO and AI2O3 from the blast furnace slag can be suppressed, and the loss due to the dissolution of dihydrate (C
(asO4 equivalent amount dissolved in water at approximately 0.2%) can be prevented. In the present invention, agent B (Boltland cement) may be added to and mixed with the hydrated soft soil together with the slurry solution of sulfuric acid modified blast furnace slag. At this time, care is taken so that the final concentration of the slurry solution becomes a predetermined value. Further, there are the following two specific methods for implementing the method (2) above. (a) Dilute sulfuric acid obtained in the flue gas desulfurization process is added to blast furnace slag and reacted.

(b) P of the suspension is added to the suspension of blast furnace slag in water.
While adding blast furnace slag from the outside so as to maintain H in the range of 1.5 to 4.0, it is brought into contact with SOO-containing flue gas, the resulting suspension is passed through the mouth, and the transformed blast furnace slag is recovered. .

In either method (a) or (b), the amount of sulfuric acid reacted with the blast furnace slag is adjusted to an appropriate range, as in the case of (1) above.

The other component of the strength increasing agent used in the present invention is Bortland cement (hereinafter referred to as agent B).

The commonly used one is Japanese Industrial Standard JISR5.
It is equivalent to ordinary cement in 2l Or Portland cement, but depending on the conditions of treating soft soil with water, it can be used alone as boltland cement that conforms to standards such as moderate heat cement, early strength cement, and ultra early strength cement. Or a mixture of these may be used. The method of the present invention involves adding and mixing the above-mentioned agents A and B as essential components of a strength increasing agent to water-containing soft soil.

In this case, other suitable additives may be added as auxiliary components in order to further enhance deodorizing properties, affinity, and early strength. In the present invention, the addition weight ratio A/B of agent A and agent B is 7.
It is in the range of 0/30 to 35/65.

The weight ratio A/B of Additive A and Additive B used in the present invention to the hydrated soft soil should be maintained in the range of 7V30 to 3V65 in order to efficiently and smoothly increase the strength of the hydrated soft soil. is important.

That is, when the addition weight ratio A/B ratio is larger than 70/30, various reactions in the water-containing soft soil are insufficiently induced;
If it is smaller than 5/65, it will be out of the balance ratio of the overall optimum composition, and the effect of increasing the strength of the hydrated soft soil will be small. Furthermore, if the ratio of the amount added of agent B is too large, that is, if A/B is too small, the following problems (a) to (d) will occur in addition to the disadvantage that the strength increasing effect becomes small. (a) During strength-increasing treatment, heat generation increases and problems such as internal distortions occur in the treated soil. (b) Since the treated soil contains a large amount of calcium hydroxide, the treated soil becomes highly alkaline. (c) Easily eroded by sewage and seawater. (d) The cost of additives is high. In order to preferably implement the present invention, first,
Add and mix agent A to the moist soft soil.

This additive mixture improves the workability of soft soil containing water.
The subsequent mixing of agent B can be performed uniformly and easily. In addition, since the gypsum in agent A dissolves approximately 0.2 g in terms of anhydrous CasO4 per 100V of water, when agent B is added, agent A and agent B and soil components are dissolved. Etrin guide (3Ca0-Al.O3・3Ca
S04/32H20) is a condition that makes it easy to generate. Next, agent B is added and mixed to such water-containing soft soil with increased reactivity.

When the hydration reaction starts due to the addition of agent B, reactions between agent B and each component in agent A, and reactions between each component of additives A and B and the components of fine soil are induced. , the strength of water-containing soft soil is increased. In this case, as mentioned above,
The hydrated soft soil to which Additive A has been added has been modified into a soil base that makes it easier for the various reactions to occur, and workability has also been improved, so subsequent addition and mixing of Additive B can be done uniformly. It is easy to carry out, and the strength-increasing reaction in hydrated soft soil proceeds extremely efficiently. In the present invention, as mentioned above, when carrying out a treatment to increase the strength of hydrated soft soil, various reactions such as cation exchange reaction, ettrin guide production reaction, pozzolan reaction, etc., occur between the components of agents A and B and the soil. However, in the first addition treatment, the A agent and the water-containing soft soil are uniformly mixed, so by the addition of the B agent in the second addition treatment, the various reactions involved in these strength increasing reactions are The process progresses uniformly and smoothly over the entire soft soil containing water, and a rapid increase in the strength of the soft soil containing water is achieved.

As mentioned above, when performing strength increasing treatment on hydrated soft soil,
It is most desirable to add and mix the B agent after adding and mixing the A agent, but the second most desirable is to add and mix the A agent and the B agent to the water-containing soft soil at the same time. In order to increase the strength of water-containing soft soil, if agent A is added and mixed after agent B is added and mixed, the workability is poor, so it is necessary to use a special construction machine for this process. When Agent B is first added to hydrated soft soil, it has a significant negative effect on the viscosity, gel strength, and pH value of hydrated soft soil. Due to this, the workability of the operation treatment inevitably deteriorates, and it becomes difficult to uniformly mix the hydrated soft soil. This adversely affects the subsequent uniform dispersion of agent A and its reaction, making it difficult to increase the strength of the hydrated soft soil. Viscosity, gel strength and PH of hydrous soft soil by adding agent B
The cause of the negative effect on the value is Ca2+ and 0 in cement.
It is H-. As mentioned above, the adverse effects caused by Ca2+ and 0H- can be overcome by specifying the order of addition of Part A and Part B. The workability of strength-increasing operations is improved, and its chemical properties can be effectively utilized. A major feature of the present invention, as described above, is that fine quenched blast furnace slag modified with sulfuric acid is used as one of the essential components of the strength enhancer.

In this sulfuric acid modified blast furnace slag, the calcium content in the blast furnace slag is converted to gypsum content by the reaction with sulfuric acid, and at the same time, the silica content and alumina content in the blast furnace slag are converted to an active state, and furthermore, the silica content and alumina content in the blast furnace slag are converted into active state. Trace components temporarily become sulfates and elute from the surface, and then undergo complex chemical changes such as being solidified and attached to the surface by the action of calcium in the blast furnace slag. The reactivity of soft soil to the strength increase reaction is extremely large, and its strength increase effect is significantly greater than that obtained by simply mixing blast furnace slag and gypsum. This sulfuric acid-converted blast furnace slag does not exhibit exceptional hydraulic properties by itself, but it exhibits hydraulic properties when it is effectively stimulated by slaked lime content produced by the hydration reaction of Boltland cement in soft, water-containing soil. In the treatment for increasing the strength of hydrated soft soil according to the present invention, due to the excellent reactivity of the applied sulfuric acid modified blast furnace slag, cation exchange reactions, ettringite formation reactions, and pozzolanic reactions of the soil, which are involved in increasing the strength of hydrated soft soil, can be carried out. occurs efficiently, and a rapid and efficient increase in strength of hydrated soft soil is achieved. When carrying out the present invention, both Part A and Part B can be added in the form of powder or slurry. The soil to be treated is generally
The reactivity varies depending on the type of clay mineral, the content of fine particles, the content of organic components, and the pH value, and is further influenced by the initial moisture content. However, the amount of the strength/durability increasing agent according to the present invention used to achieve the purpose of normal required strength is usually about 50 to 100 k9 in dry total amount of A and B agents per 1 d of soft soil. In addition, when a large amount of organic matter is contained in the hydrated soft soil, the conventional method suffers from the effect of increasing the strength of the hydrated soft soil, but the method of the present invention has relatively few such disadvantages. When treating soft, water-containing soil containing a large amount of organic matter, the method of the present invention increases the total amount of Agents A and B by approximately 5% compared to the usual case.
If it increases by about 0%, the objective can be achieved. However, if the hydrated soft soil contains a large amount of highly reactive clay minerals and is suitable for strength-increasing reactions, even if a large amount of organic matter is included, the increase in the total amount of organic matter added will be small. The method of the present invention is not limited by the water content ratio of the water-containing soft soil, and can be used not only for soft soil with a water content of 50 to 200%, but also to
It can also be applied to soft soils with an extremely high water content of 50%. When the present invention is applied to soft soil with a high water content ratio, water in excess of a certain amount is separated from the treated soil by pleating and floats to the surface. According to the present invention, as described above, it is possible to efficiently increase the strength of hydrous soft soil, but in this case, since the amount of cement used as agent B is relatively small, The heat generated by the hydration reaction is significantly suppressed, and no distortion occurs in the treated soil.Furthermore, because the amount of residual alkali in the treated soil is small, no increase in alkalinity in the treated soil is observed. The treated soil will not be eroded by sewage or seawater.

In addition, in the case of the present invention, the total amount of additives used is small, the amount of cement added is small, and the A agent is used as sulfuric acid converted blast furnace slag consisting of waste, so it is economically superior. It is. Next, the present invention will be explained in detail using examples.

In the examples described below, commercially available fine blast furnace water slag treated with sulfuric acid was used as the strength increasing agent A, and ordinary cement in Bortland cement (specific surface area 3300 a1/y by plane method measurement) was used as the B agent. was used. The composition and particle size of commercially available fine blast furnace water slag are shown in Tables 1 and 2. Furthermore, it was confirmed by observation using a polarizing microscope that most of this commercially available fine blast furnace water slag was glassy. In addition, the raw material water-containing soft soil has a water content ratio of 26
0%, particle size composition is O~2μ14%, 2~5μ42%, 5
~10μ19%, 10~20p25%, water content 260%
Osaka Nanko dredging bottom mud with a density of 1.21 g/d was used.

In addition, the mixed sample containing the specified strength increasing agent was poured into a cylindrical mold with an inner diameter of 50 TWL and a height of 100 gourds, and kept at a saturation level of 20 ± 1°C in a constant temperature and humidity incubator for a specified period of time. After curing, the mold is removed and its uniaxial strength is determined by JISA.
It was measured according to l2l6T, l976 (uniaxial compression test method for soil).

Example 1 26.8 kg of sulfuric acid was dissolved in 400 y of water (mother liquor), and 100 kg of fine blast furnace water slag was added to the solution at room temperature and mixed for 2 hours.

This slurry solution is centrifuged to separate it from the mother liquor,
Sulfuric acid modified blast furnace slag 195k containing 32.5% by weight of mother liquor
9 (131.7 kg on air-dry basis). The water used in the preparation was obtained by adding water to the mother liquor obtained by filtering the sulfuric acid modified blast furnace slag, and then adding water to the mother liquor recovered after being used repeatedly for the sulfuric acid treatment of the fine blast furnace slag. This product 5
4.4k9 (36.7k9 on an air-dried basis) was added as agent A to 1 TrI of raw soft mud and mixed uniformly in a kneader, and then 30.5 kg of agent B was added and thoroughly mixed in a kneader.

This sample was subjected to measurement of its uniaxial strength. For comparison, a test was conducted in the same manner except that the fine blast furnace water slag was used as the A agent without sulfuric acid treatment. The results are shown in Table 1. In addition, for reference comparison, the proportion of dihydrite contained in agent A is similar to that above, that is, dihydrite 3
A test similar to the above was conducted using a mixture consisting of 6k9 fine blast furnace water slag and 64k9 fine blast furnace water slag instead of agent A.

As a result, the unconfined compressive strength of the treated soil at 14 days of age was 1.3.
It was k9/d. Example 2 Various types A with different sulfuric acid treatment conditions for 1 d of raw material soft soil
The test was conducted in the same manner as in Example 1 except that 30.6k9 of Agent B and 36.6 kg of Agent B were used.

Regarding the obtained treated soil, on the 14th day (14th day of material age)
The unconfined compressive strength of is shown in Table 2. Example 3 A test was carried out in the same manner as in Example 1, except that the weight ratio of Part A and Part B was changed.

Table 3 shows the unconfined compressive strength of the obtained treated soil on the 14th and 28th days. Example 4 9% sulfuric acid aqueous solution 83.3k9 and fine blast furnace slag 27.9k
After adding 9 and stirring for 2 hours, the mixture was cooled to room temperature, and then 30.5k9 of agent B was added and mixed uniformly to prepare a slurry solution.

Claims (1)

[Claims] 1. It consists of adding and mixing finely quenched blast furnace slag with a particle size of 300 μm or less and Portland cement that has been modified with sulfuric acid to hydrous soft soil, and the finely quenched blast furnace slag that has been modified with sulfuric acid is A method for increasing the strength of hydrous soft soil, characterized in that the soil is modified using 3 to 50 parts by weight of sulfuric acid per 100 parts by weight. 2. The method according to claim 1, in which finely quenched blast furnace slag modified with sulfuric acid is added to hydrated soft soil, and then Portland cement is added and mixed. 3. The method according to claim 1, which comprises adding and mixing a mixture of finely quenched blast furnace slag modified with sulfuric acid and Portland cement to hydrated soft soil. 4 The weight ratio A/B of finely quenched blast furnace slag A modified with sulfuric acid and Portland cement B is 70/30 to 35/6
5. The method according to any one of claims 1 to 3.