JPS5824469B2 - Doshitsu Antei Kahou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for stabilizing soil quality by mixing a urea-formaldehyde grouting agent with soil or permeating it into the soil to solidify soil particles. This invention relates to a method for stabilizing soft ground into a solid one using a non-polluting urea-formaldehyde grouting agent that does not have an irritating odor.

Conventionally, methods of injecting various chemical solutions into the soil have been known as a method of solidifying and stabilizing soft ground, but in recent years in particular, as a grouting agent, an aqueous solution containing urea-formaldehyde condensation resin as the main ingredient and curing consisting of a drug,
So-called urea-formaldehyde grouting agents are attracting attention because of their low cost and the high strength of hardened soil.

Urea-formaldehyde condensation resin (hereinafter simply referred to as urea-formaldehyde condensation resin)
An aqueous solution of formaldehyde resin (formaldehyde resin) is usually produced by condensing an aqueous solution of urea and formaldehyde at about 40 to 100°C under weakly alkaline to weakly acidic conditions. A resin solution containing a large amount of water-insoluble resin (white turbidity) and extremely poor storage stability is produced.On the other hand, when a large amount of formaldehyde is used, a resin solution with no turbidity and sufficiently good storage stability is produced. Therefore, the condensation reaction is usually carried out at a ratio of 2 to 3 moles of formaldehyde per 1 mole of urea.

However, a considerable amount of unreacted formaldehyde usually remains in the urea-formaldehyde resin aqueous solution obtained by reacting urea and formaldehyde in such proportions, and its irritating odor makes it difficult to inject the grouting agent into the soil. Not only is this not easy, but it also causes various problems when excavating soil that has been stabilized after treatment.

Conventionally, as a method to eliminate the formaldehyde odor of urea-formaldehyde grouting agents, the main ingredient, urea-
A method of adding various chemicals to a formaldehyde resin aqueous solution and causing a reaction, such as a method of adding urea to a urea-formaldehyde resin aqueous solution and causing a reaction (Japanese Patent Publication No. 45-2
4951) or a method of adding an ammonium salt and an alkaline substance to the resin aqueous solution and reacting it (Japanese Patent Publication No. 4951)
8-9336) and the like have been proposed.

However, all of these methods require that urea-
After producing an aqueous formaldehyde resin solution, various chemicals are added to the aqueous resin solution and reacted with the remaining formaldehyde in the aqueous resin solution.In order to obtain an aqueous resin solution without formaldehyde odor, the formaldehyde reaction is carried out in at least two stages. This is accompanied by the annoyance of having to let it go.

The present inventors have attempted to produce an aqueous solution of urea-formaldehyde resin that originally has no odor of formaldehyde, that is, an aqueous solution of urea-formaldehyde resin that does not have an odor of formaldehyde, by a one-step reaction between urea and formalin, which is completely different from such conventional methods. As a result of research,
Surprisingly, when urea and formalin are subjected to a conventional condensation reaction in the presence of water-soluble salts of alkaline earth metals such as calcium, magnesium, and barium, the amount of formaldehyde is significantly reduced compared to conventional methods. It was discovered that an aqueous urea-formaldehyde resin solution that produced a small amount of white turbidity and had good storage stability could be easily obtained even when the reaction was carried out in the presence of the above-mentioned salts. The aqueous resin solution obtained by reacting at near molar concentrations has no cloudiness or formaldehyde odor, has sufficiently good storage stability, and can be suitably used as a non-polluting urea-formaldehyde grouting agent. Heading, we arrived at the present invention.

That is, the present invention provides an aqueous formaldehyde solution containing a water-soluble salt of an alkaline earth metal selected from the group consisting of (1) urea and (2) calcium, magnesium, and barium at a molar ratio of urea to formaldehyde of 1. 0.9 to 1.2, a urea-formaldehyde resin aqueous solution with no formaldehyde odor, which is obtained by carrying out a condensation reaction according to a known method and then adjusting the resulting reaction solution to be neutral to weakly alkaline, is added to the soil together with a hardening agent. This is a soil stabilization method characterized by mixing or infiltrating into the soil and hardening it.

The urea-formaldehyde resin aqueous solution used in the present invention is
It is produced by subjecting urea to a condensation reaction in a conventional manner with an aqueous formaldehyde solution to which a water-soluble salt of an alkaline earth metal selected from the group consisting of calcium, magnesium, and barium has been added.

It is appropriate to use a commercially available formaldehyde aqueous solution having a formaldehyde concentration of 36 to 40% by weight.

Regarding the reaction ratio of urea and formaldehyde, the molar ratio of urea to formaldehyde is usually set at 1:0.0. 9-1.
It is preferable to set it to 2.

Typical alkaline earth metal salts added to the formaldehyde aqueous solution include calcium chloride, calcium nitrate, magnesium chloride, barium chloride, etc., and two or more of these may be used in combination.

Irrespective of the type of these salts, adding 2 to 3% by weight of these salts to an aqueous formaldehyde solution is sufficient to obtain an aqueous resin solution that meets the objectives of the present invention, but the more they are used, the greater the strength of the soil after treatment. Since it is advantageous that 10% of the formaldehyde aqueous solution is
Add ~70% by weight.

Any known method can be applied to the condensation reaction of urea and formaldehyde aqueous solution.

For example, a mixture of the above-mentioned components (urea, formaldehyde aqueous solution, and alkaline earth metal salt) is adjusted to a weakly alkaline to weakly acidic range with an alkaline substance such as sodium hydroxide or an amine such as triethanolamine, and the temperature is React at 50-70°C for 0.5-4 hours.

Usually, if the pH is made weakly alkaline at about 7.5 to 8.0 at the beginning of the reaction, the pH gradually decreases to weakly acidic during the reaction.

At the initial stage of the reaction, a methylolated product of urea is produced, which is then condensed to produce a urea-formaldehyde resin.

The end point of the reaction is suitably set at a point at which a slight cloudiness occurs when 1 to 2 ml of the resin aqueous solution is mixed with 1000% water (20°C).

If the reaction is allowed to proceed too much, a water-insoluble resin will be produced, which is not preferable.

After the reaction is completed, the reaction solution is adjusted to be neutral to weakly alkaline in order to improve storage stability, especially at pH 7.0 to 8.
It is preferable to adjust it to 5.

The urea-formaldehyde resin aqueous solution obtained in this way is a colorless, transparent or translucent aqueous solution with a viscosity of 15 to 45 centipoise (20°C), and there is no formaldehyde stimulant at all, and even when stored at room temperature for one month, the viscosity does not change. pH
There is no change.

The hardening agent used in the present invention is a substance that hardens the above-mentioned urea-formaldehyde resin aqueous solution in soil, and includes acids such as sulfuric acid, phosphoric acid, and hydrochloric acid, or acid salts such as acidic ammonium sulfate and acidic sodium sulfate. It will be done.

If a large amount of hardening agent is used, the gel time will be fast, but the strength of hardened soil will be weak.On the other hand, if a small amount of hardening agent is used, the gel time will be slow, but the strength of hardened soil can be increased.

Therefore, the amount of curing agent used can be changed as appropriate depending on the desired gel time or soil strength, but it is usually 1 to 20% by weight of an aqueous solution based on the resin aqueous solution.
It is appropriately selected and used within the range of 50% by weight.

The soil stabilization process uses a chemical solution in which each component of a urea-formaldehyde resin solution and a hardening agent are dissolved in water.

It is appropriate that the chemical solution be of a two-component type, that is, an aqueous resin solution and a curing agent are prepared separately.

The two liquids are mixed with the soil or injected into the soil at the same time,
It hardens in the soil and stabilizes soft ground.

Next, the advantages of the present invention will be described.

The conventional method for deodorizing formaldehyde odors from urea-formaldehyde-based grouting agents involves first producing an aqueous urea-formaldehyde resin solution containing free formaldehyde, and then adding various chemicals to the solution to react with the free formaldehyde. However, since the aqueous resin solution after deodorization has poor storage stability, deodorization treatment often has to be carried out at the construction site, but in such cases, especially heat sources and labor are required. Furthermore, since an aqueous resin solution containing harmful free formaldehyde is brought to the construction site, there are problems in its transportation and storage.

On the other hand, the formaldehyde odor-free resin aqueous solution used in the present invention is obtained by a one-step reaction between urea and formalin, and is always manufactured at a resin aqueous solution manufacturing factory, so it is not as described above in the prior art. It is advantageous because it does not have the disadvantages of

In addition, the urea-formaldehyde resin aqueous solution of the present invention is
It can also be used for applications other than grouting agents, such as adhesives and coating agents.

Next, the present invention will be explained in detail with reference to Examples. In each of the following Examples, all parts and percentages refer to weights.

Examples 1 to 8 and Comparative Examples (a) Production of urea-formaldehyde resin aqueous solution 438 parts of commercially available 37% formalin (formaldehyde content: 54 mol) was heated to about 54°C, and calcium chloride (Examples 1 to 3) was added to the mixture. , calcium nitrate (Examples 4 to 6), magnesium chloride (Example 7), and barium chloride (Example 8) were added in the proportions shown in Table 1 and completely dissolved.

Next, urea was added to the above mixture in the proportions listed in Table 1, and the pH was adjusted to 5.5 to 8.0 with sodium hydroxide.
The reaction was carried out for 60 minutes at a temperature of 50 to 70°C while adjusting the temperature within the range of .

After the reaction was completed, the pI of the reaction solution was finally adjusted to 7.8 to obtain an aqueous urea-formaldehyde resin solution of the present invention.

On the other hand, for comparison, a urea-formaldehyde resin aqueous solution was prepared in the same manner as above without adding an alkaline earth metal salt.

(This is taken as a comparative example) Table 1 shows the amount of urea used in Examples and Comparative Examples, the amount of alkaline earth metal salt used, and the properties of the resulting resin liquid.

As is clear from Table 1, the urea-formaldehyde resin aqueous solutions obtained in each example have little residual formaldehyde, are colorless and transparent, and have sufficiently good storage stability. The urea-formaldehyde resin aqueous solution has a lot of white turbidity and has extremely poor storage stability.
Not suitable as a grouting agent.

(b) Soil stabilization Aqueous urea-formaldehyde resin solution obtained in (a) 180
One part was diluted with water to make 200 parts, and this was used as Solution A.

On the other hand, as a hardening agent, 20 parts of 70% sulfuric acid was diluted with water.
00 parts, and this was designated as Solution B.

Both solutions A and B were thoroughly mixed and poured into standard sand, and after gelation, they were left for one week and their unconfined compressive strength was measured.

The results obtained are shown in Table 2. As is clear from Table 2, the strength of the sand gel produced by the aqueous resin solution produced without using an alkaline earth metal salt is only weak.

Claims (1)

[Scope of Claims] 1. A soil stabilization method, which comprises mixing a urea-formaldehyde resin aqueous solution produced as described below with soil together with a hardening agent, or allowing it to penetrate into the soil and harden it. (1) urea and (2) a formaldehyde aqueous solution containing a water-soluble salt of an alkaline earth metal selected from the group consisting of calcium, magnesium, and barium at a molar ratio of urea to formaldehyde of 1 to 0.9. 1.2, a urea-formaldehyde resin aqueous solution free of formaldehyde odor, which is obtained by carrying out a condensation reaction according to a known method, and then adjusting the resulting reaction solution to be neutral to weakly alkaline.