INI) ENGINEERING STRUCTURES

{Technical Field

The invention relates to a method for improving the strength and impermeability of soils and engineering structures particularly ducts and pipelines. In the specification and claims the terms "soil" and "engineering structure" are inter- prated in the broadest sense; these terms also covering various storage tanks, tunnels, natural and artificial -cavities, rocks, etc., and soils surrounding them _*

Background Art

It is well known that most of the engineering structures, such as underground ducts,' pipelines and storage tanks, do not possess the required impermeability characteristics, owing, in part, to the inappropriate quality of the construction material and, in part, to defects in the impermeability of pipe connec¬ tions, or because of damages in the engineering structures upon the effect of ageing, traffic, etc. It is also well known that the repair of engineering structures, particularly under¬ ground ducts and pipelines, requires enormously high invest¬ ments and labour, and in most cases the result is insufficient.

Hungarian patent No _* 15 *975 describes a simple end rapid method for improving the strength and impermeability of soils and engineering structures. According to this method, water glass or a water glass-containing medium is applied into or onto the article to be treated, and then the water glass is exposed to the effect of hydrogen fluoride, silicon tβtrafluor- ide and/or hydrogen silicofluoridθ. Water glass, when contacted with a gaseous fluoride, rapidly gellifies and completely plugs the leakages, cracks and cavities. When this method is utilized

to render underground engineering structures ( such as ducts or storage tanks) water-tight, it is an additional advantage that water glass which enters the soil through the cracks solidifies as well, improving thereby the embedding of the structure and strengthening the surrounding soil. Fluoride gases have the additional advantage that they improve the corrosion resistance of concrete and reinforced concrete elements _*

Despite of its numerous advantages, this method has had only a very narrow application in practice. (The wide¬ spread application of this method is considerably restricted by the fact that hydrogen fluoride and silicon te traf luoride are strongly poisonous, thus their use is prohibited in most of the countries due to environmental protection reasons. It is a further disadvantage that the resulting silicic acid gel is not elastic, thus it cannot follow the movements of the article or soil treated. Since the SWΘ liability of silicic acid gels is inappropriate, they cannot plug the new cracks formed in the gel upon movement. Hungarian pa tents Nos. 177 _» 3 -3 _» 181,056, 181,775 and

181,573 describe the use of various polymerizsble organic monomers, primarily acrylic acid and acryla ide monomers, as starting substances for gel-forming reactions. The gels formed from such compounds are sufficiently elastic and have good swβllability in water, they are , however, relatively soft and cannot withstand the damaging effects of higher strains. As an additional disadvantage, most of the monomers to be used as gel-forming agents is very expensive, and the gel- forming technology sometimes requires special training and equipment*

The above disadvantages are avoided by the method dis¬ closed in Hungarian patent applications Nos. 12482 and 967/85 in such a way the water glass is applied in combine-

tion with various gel-forming, water-soluble organic poly¬ mers and cross-linking agents for the polymers. In these instances a silicic .acid gel is precipitated in parallel wit the cross-linking of the polymer, and gels composed of miner end organic blocks are formed, which combine the favourable properties of the completely organic and completely mineral gels. Under large-scale conditions it appeared, however, - that the method is very difficult to perform. Owing to the ir high average molecular weight, gel-forming polymers, even in small amounts, increase the viscosity of the starting water glass solution to such an extent that the resulting mixture is very difficult to handle, its application and the removal of the excess involves numerous technical problems. Sometime the required amount of polymer cannot be introduced into the water glass solution, since a very thick, honey-like mixture is formed, which cannot be applied onto the article to be treated with the injecting apparatuses available. Gel-formi mixtures with appropriately low viscosity contain generally a rather small amount of polymer, thus the elasticity and ε el lability of the resulting gels still remain insufficient

Disclosure of the Invention

Now it has been found that all of the difficulties and disadvantages outlined above can be avoided when, instea of the pre - ormed polymer, the monomers which build up the gel-forming polymer are βdded to water glass, and polymeriza tion and cross-linking of the polymer are performed simul¬ taneously with the formation of the silicic acid gel.

Based on the above, the invention relates to a metho for improving the strength and impermeability of soils and engineering structures by forming a hydrogel composed of silicic acid and a cross-linked swellable organic polymer in or on the soil or structure treated. According to the in¬ vention one proceeds in such a way that an aqueous solution

of a silicic acid gel precursor is contacted with a water- soluble gel-forming vinyl monomer in the presence of

- a redox polymerization catalyst system,

- a cross-linking agent for the polymer obtained, - an organic polycarboxylic acid,

- optionally an additive which modifies the properties of the gel matrix formed, and.

- optionally a filling agent.

When contacting the aqueous solution of a precursor of silicic acid gel (e.g. an aqueous solution of water glass with a water-soluble gel-forming vinyl monomer in the pres¬ ence of the components described above, the following chemical processes proceed simultaneously:

- the monomers polymerize upon the effect of the redox catalyst system,

- the resulting linear polymer reacts with the cross- linking agent to form a cross-linked polymer gel, end

- a silicic acid gel forms from.its precursor upon the effect of the polycarboxylic acid. Since these chemical processes take place in parallel, and all of the intermediates formed in the process interact with one another, a gel is formed in which the organic and mineral parts are amalgamated. She visual appearance of the resulting gel clearly differs from that of the gels ob- tained according to Hungarian patent applications Nos.

3124/82 and 967/83. These letter gels are opaque, and the organic and mineral blocks can be distinguished easily in their structure, i.e. β gel with inhomogeneous microstructure is obtained. On the other hand, the -gels prepared according to the invention are transparent, which indicates a homo¬ geneous microstructure. On this basis it can be assumed that an organo-mineral copolymer is formed in.contrast to a blend of organic and mineral polymer blocks _*

In the process of the invention any substance whic forms silicic acid gel when contacted with an acid can be utilized as silicic acid gel precursor. The most preferred representatives of silicic acid gel precursors ere the various water glasses (sodium silicate , potassium silicate , etc.) , but water-soluble siliconβs and poly silicates, such as those commonly utilized for preparing moulds, can also be applied.

Of the water-soluble gel-forming vinyl monomers the following are to be mentioned: acrylic acid, me the cry lie acid, itaconic acid, maleic acid, fumaric acid, water-solub salts and esters of these acids, acryl amide, me t ha cr 1 amide, etc _* These monomers can be . used either alone or as a mixture of two or more monomers. As cross-linking agents for the organic . polymer e.g. aldehydes (such as glyoxal, glu araldehyde, etc.) or di viny or trivinyl compounds (such as me hylene-bis-βcrylsmide , ethylene-bis-acrylamide , triacryl triazine etc.) can be use The cross-linking agents should be sufficiently water-solub their solubility in water should be at least 1 %•

The redox catalyst system utilized according to the . invention consists of an oxidizing and a reducing component. Any of the known redox type free radical initiator systems utilized conventionally in the production of vinyl . polymers can be applied. The oxidizing component may be e.g. hydroge peroxide, an alkali persulfate or a water-soluble organic peraoid, whereas the reducing component may be e .g. a water- soluble organic amine , a water-soluble salt of a metal with varying valencies, a thiosulfate , a bisulfite , etc. Polycarboxylic acids (i.e. orgenic carboxylic acids with at least two earboxy groups) which can be utilized in the process of the invention are e .g. tartario acid, sucoini acid, citric acid, malic acid, ascorbic acid, etc _*

The silicic acid gel precursor to vinyl monomer weight ratio, calculated for the dry substances, may vary over a wide range, e.g. 10:1 to 1:10, preferably 5:1 to 1:1, most preferably 4:1 to 2:1. Due to economical reasons it is pre- ferred to utilize the vinyl monomers in low amounts. It has been observed that the elasticity and the swelling properties of the gel remain essentially the same as those of the completely organic gel even with a high mineral : ortanic ratio, furthermore the higher the silicic acid content of . the gel, the greater its strength and resistance to stress.

The silicic acid gel precursor to polycarboxylic acid weight ratio, calculated for the dry substances, may vary within 1:0.5 to 1:0.06, preferably 1:0.2 to 1:0.08, most preferably about 1:0.1. The amount of the cross-linking agent, calculated for the. eight of the vinyl monomer.present, may be 1:0.01 to 1*0.3, preferably 1:0.05 to 1:0.2.

The amount of the redox catalyst system, calculated for the weight of the vinyl monomer present, may be 1:0.01 to 1:0.5, preferably 1:0.05 to 1:0.3» Within this range, the cβtalyst system contains the oxidizing and the reducing components preferably in about equimolar amounts.

If desired, the gel-forming mixture may also contain one or more additives which modify the properties of the gel formed. These additives may be the commonly known addi¬ tives of cross-linked vinyl polymers, such as plasticizers, stabilizers, decomposition inhibitors, etc., of which melaminβ, urea, monomethylol urea and thiourea are mentioned. The amounts of such additives, if present, may reach the amount of the vinyl monomer*

If desired, the gel-forming mixture may contain one or more filling agent(s) generally applied in such.compositions, such as βsbestos, sand, fly ^' ash, bβntonite, etc. The amount

of such filling agents is not critical and is restricted essentially by technological factors (e.g. stirrebility end viscosity of the mixture, _, ease of application, etc.) _*

When applying the method of the invention for the treatment of soil or engineering structures, one may proceed in such a way that the individual components of the gel-form¬ ing mixture are admixed with one another in an appropriate sequence, determined by compatibility factors, directly on the field of treatment (e.g. in the defective duct to be rβ- paired). It is more preferred, however, to start with two pre- o med βqueous solutions and to admix them on the field of treatment. The compositions of the two aqueous solutions should be chosen so that both solutions remain stable and storable for a prolonged period, and no premature gel forma- tion occurs. To select the appropriate composition of the solutions, the following compatibility factors should be kept in mind:

- the silicic acid gel precursor must not be in a common solution with the polycarboxylic acid; - the two components of the redox catalyst system must not be in a common solution; and

- the aqueous solution of the vinyl monomer must not contain the oxidizing component of the redox catalyst system in free state (it may contain, however, the oxidizing com- ponent in masked, such as in complβxed, form) •

Considering the above compatibility factors, the two aqueous solutions to be admixed on the field of treatment may have e.g. the following compositions: Solution "A": silicic acid gel precursor (e.g. water glass), ~ ^~ oxidizing component of the redox catalyst system, water;

Solution "B ^M : water-soluble vinyl monomer, a cross-linking agent for the organic polymer, a polycarboxylic acid, reducing component of the redox catalyst system water; or Solution "A": a silicic acid gel precursor,

" ^' . reducing component of the redox catalyst system water; Solution "B ^M : water-soluble vinyl monomer, a cross-linking agent for the organic polymer, a polycarboxylic acid, oxidizing component of the redex catalyst syste in masked form (e.g. complexed with uree), water.

The optional additives and filling agents can be added to any of solutions "A" and ⁿ B", βs far as the compatibility requirements are.provided for. Thus, for instance, an acidic filling agent (e.g. acidic ly ash) must not be added to the solution of the silicic acid gel precursor.

Industrial Applicability

As mentioned above, the method of the invention can be applied in the building industry for improving the strength and impermeability of soils and engineering structures. For this purpose, the individual components of the gel-forming mixture - presented preferably in two pre-formed aqueous solutions - are admixed with one another at the place of the treatment, e.g. in or on the soil or in or on the engineer¬ ing structure _* When soil is to be solidified by the method of the invention, it is preferred to fill the two aqueous solutions into the tanks of a two-tank injector provided with a mixing head, end to inject the mixture of the two solutions into the soil to be treated. When a duct is to be repaired

by the method of the invention, it is preferred to use the so-celled "filling up" technique, where the two solutions are introduced after one another into the duct to be repaired.

The method of the invention retains all the major ad- vantages of the known methods disclosed in the cited patents and patent applications. Like these known methods, it provides a quick, safe and economical way for rendering soils or engineering structures strong and water-tight. Compared to the known methods, the method of the invention has the following additional advantages:

- it does not require chemicals detrimental to health or environment;

- it provides a strong gel which is sufficiently elastic and swellable to.counterbalance the damages occurring after repair due e.g. to soil movements, traffic wear, etc.;

- the gel-forming mixtures are easy to handle, the treatment requires no specific equipment end no specific technological precaution;

- the method is fβr less expensive than the known ones which utilize fully organic gels;

- the life span of the gel produced far exceeds that of the gels produced by the known methods, which can be attributed to the homogeneous organo-mineral copoly er structure of the gel.

Ways of Carrying out the Invention

Further details of the invention are elucidated by the aid of the following non-limiting Examples.

Example 1

Two aqueous solutions with the following compositions are prepared:

Solution ".A" : water 40. ml potassium persulfatβ 1.8 S thiourea 14 S concentrated aqueous water glass solution (dry substance : 37 w/w %) 50 ml

Solution "B" : water 80 ml methacrylic acid 16 ml tartaric acid 10. ε me thylene-bis-acrylamidβ 0.5 s ferrous sύlfatβ 0.5 g

The two solutions are admixed with one another under intense stirring. A homogeneous, transparent gel is formed in 7 _* 5 minutes _*

Comparative Tejst_A .

Two aqueous solutions with the following compositions are prepared:

Solution "A": water ^* 90. ml potassium persulfatβ 1 _* 8 g thiourea 14 g

Solution "B": wβter ^* 80 ml acrylic acid 16 ml tartaric acid 10. g methylenβ-bis-acrylamide 0.5 g ferrous sulfate 0.5 C

None of the solutions contains water glass. The two solutions are admixed with one another under intense stirring _* A homogeneous, transparent, completely organic gel is obtained in 12 minutes*

Comparative Tβs.t B.2.

Two aqueous solutions with the following compositions are prepared:

Solution "A": water 40 ml thiourea 14 g concentrated aqueous water glass solution (dry substance: 37 w/w %) 50 ml

Solution "B": water ^{" "} 80 ml acrylic acid 16 S tartaric βcid 10. S methylene-bis-acrylamide 0.5 c

Since no redox catalyst system is present, no vinyl polymer can be produced. The two solutions ere admixed with one another under intense stirring. An opaque mineral gel is formed within one minute. The gel shows strong syneresis.

Example 2

Two aqueous solutions with the following compositions are prepared:

Solution "A": water 40. ml potassium persulfate 1.8 S thiourea 14 c concentrated aqueous water glass solution (dry substance: 37 w/w %) 50 ml

Solution "B": water 80 ml acrylic acid 16 C succinic acid 10 c methylene-bis-acryl8mide 2 ε ferrous sulfate 1 c

The two solutions are admixed with one another under intense stirring..A homogeneous, transparent gel is formed within one minute.

Example 3

Two aqueous solutions with the following compositions are prepared:

Solution "A": water 70. ml potassium persulfatβ 0.9 e melamine 7 ε concentrated aqueous water glass solu- tion (dry substance: 37 w/w %) 25 ml

Solution "B": water 80 ml met acr lie acid 16 ml tartaric acid 10 S methylβne-biB-acrylamidβ 0.5 g ferrous sulfate 0.5 ε

The two solutions are admixed with one another under intense stirring. A homogeneous, transparent gel is formed in 120 minutes.

Example 4

Two aqueous solutions with the following compositions are prepared: Solution "A": water 16. ml potassium persulfate 0.8 g elamine 6 g concentrated aqueous water glass solu- tion (dry substance: 37 w/w %) 20 ml

Solution "B": water ~ 50 ml itaconic acid 4. g ferrous sulfate 0,5 g methylene-biβ-acrylamide 0.5 g citric acid 2 g

The two solutions are admixed with one another under intense stirring. A homogeneous, transparent gel is formed in 15 minutes. Example 5

Two aqueous solutions with the following compositions are prepared:

Solution "A? ¹ : water 19 ml concentrated aqueous water glass solution (dry substance: 37 w/w %) 80 ml triethanol a ine 1 ml

Solution "B": water 85 ml acrylic acid 15 ml citric acid 10 ml hydrogen peroxide complexed with urea 4. ε methylene-bis-acrylamide 0.5 g

The two solutions are admixed with one another under intense stirring. A homogeneous, transparent gel is formed in 18 minutes.

The compressive strength and deformstion of the gels prepared according to the above Examples end Comparative Tests are measured by _, standard procedures. The results are summarized in Table 1 _* It appears from the data of the table that the gels prepared according to the invention are superior in quality to those prepared by known methods _*

Table 1

Example No _* Cόmprβssive ₂ Deforma¬ strength, kg/ tion, %

1 21 48 2 23 55

3 15 60 4 19 64

5 17 51

Comparative Test A 13 67 Comparative Test B 2 5

Example 6

Solutions "A" and "B" with the compositions given in Example 1 are used for duct repair as follows:

The duct section to be treated is shown in Fig. 1. The duct section bordered by shafts 2 and 3 is cleaned appro¬ priately and then blocked at the shafts with tube stoppers 1 _* Thereafter the closed duct section is filled up with solu-. tion "A" through shaft 2. Solution "A" is stored in tank 4 _* The pre sure required to inject the ^' solution into the leak¬ ages, cracks and cavities is provided by fillint up the shaft to the appropriate height. Depending on the defects of the duct, through which solution "A.T exfiltrates, a solution height of about 1-2 a is maintained in.shaft 2 _* The solution in the shaft is refilled, if necessary. After an appropriate period, generally about 10-20 minutes, the remainder of the liquid is pumped back from the duct section into tank 4 through sha _f

Thereafter, as shown in Fig. 2, solution "B" is intro¬ duced from tank 6 into the duct section through shaft 2 _* Again, the pressure required to inject the solution into the leakages, cracks and cavities is ensured by filling up the shaft to the appropriate height _* The solution is refilled,

if necessary. After an appropriate period, preferably when exfiltration ceases, the remainder of the liquid is pumped back into tank 6 through shaft 2, εad the tube stoppers are removed. Thus repair is finished. If the results are to be checked by water-tightness tests using water.or air, this can b e done before removing the tube stoppers. However, this quality control can be avoided by leaving solution "B" in shaft 2 for an appropriate period _* When the level of the solution in shaft 2 is not lowered within 15 minutes (or the extent of lowering is with¬ in the prescribed, tolerable limits),,this indicates that the duct is appropriately water tight.

Solutions "A" and "B" βxfiltratβd through the defects, inappropriate joints or cracks of the duct form stable gel 5 inside and/or in the surroundings of the duct treated. This enables not only the seepage lines of the duct to be blocked perfectly, but also the soil surroundi ng the duct to solidi¬ fy and become water-tight. Consequently, the embedding con¬ ditions of the duct als@ improve to a great extent, which is a decisive factor in view of the stability and life span of duct networks _* a