NZ231743A - Increasing the strength and impermeability of soils and engineering structures by in-situ formation of silica gels - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £31 743 231743 Priority Date(s): Complete Specification Filed: l^". Class: Publication Date: 2.6. MAR .1991 P.O. Journal. No: .. . K3x Patents Form No. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION METHOD FOR IMPROVING THE STRENGTH AND IMPERMEABILITY OF SOILS AND ENGINEERING STRUCTURES WE, ALTALANOS IPARFEJLESZTESI RT., of 1033 Budapest, Tavasz u. 3., HUNGARY ex. company ori^aniseci Under laws oj? HUNGARY hereby declare the invention, for which We pray that a patent may be granted to us, and the method by which it 231743 i METHOD FOR IMPROVING THE STRENGTH AND IMPERMEABILITY OP SOILS AND ENGINEERING STRUCTURES The invention relates to a method for improving the strength and impermeability of soils and engineering structures particularly ducts and pipelines» In tha specification and claims the terms "soil" and. "engineering structure" are interpreted in the broadest sense; these teras also covering various storage tanks, tunnels, natural and artificial cavities rocks, etc., and soils surrounding them.

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 -1 a- (followed by page 2) -2- ? 31 743 i part, to the inappropriate quality of the construction materials and, in part, to defects in the impermeability of pipe connections, or because of damages in the engineering structures upon the effect of ageing, traffic, etc. It is also well known 5 that the repair of engineering structures, particularly underground ducts and pipelines, requires enormously high investments and labour, and in most cases the result is insufficient.

^ Hungarian patent No. 153,975 describes a simple and rapid method for improving the strength and impermeability of 10 soils and engineering structures. According to this method, water glass or a water glass-containing mediua is applied into or onto the article to be treated, and then the water glass is exposed to the effect o? hydrogen fluoride, silicon tetra-fluoride and/or hydrogen silicofluoride. Water glass, when 15 contacted with a gaseous fluoride, rapidly gellifies and completely plugs the leakages, cracks and cavities. '.Yhen this method is utilized to render underground engineering structures (such as ducts or storage tanks) water-tight, it is an addi-tional advantage that water glass which enters the soil through 20 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 if ^ <fa only a very narrow application in practice* The widespread C-9 MAR 1990 application of this method is considerably restricted by the \ f> <>./ \ -*\^, V! v' ffict that hydrogen fluoride and silicon tetrafluoride are strongly poisonous, thus their use is prohibited in most of the 30 countries due to environmental protection reasons. It is a 231743 - "3 - 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 swellability of silicic acid gels is inappropriate, they cannot plug the new cracks formed in the gel upon movement.

In order to avoid the above disadvantages methods have been elaborated in which aqueous acids are utilized to gellify water glass instead of the poisonous acidic fluoride gases, and, to ensure the required elasticity and swellability of the gel, synthetic organic polymers are formed in the gel structure in parallel with the gel formation. Such methods are disclosed in Hungarian patents Nos. 186,586 and 189,250, in the published Hungarian patent application No. 1095/84, as well as in the published international patent application No. PCT/HU-85/00027. A common feature of the techniques disclosed therein is that the gel is formed by admixing two liquids with one another: one of the liquids comprises water glass and organic polymer-forming components, such as polymerizable monomers or a linear polymer to be cross-linked, which are compatible with water glass, whereas the other liquid is an aqueous solution of the acid required to gellify water glass and of the substances required to perform polymerization or cross-linking, such as catalyst, initiator, cross-linking agent, etc.

When the appropriate mixing of the two liquids is ,i: provided for, hydrogels of good quality, possessing appropriate ^-9 MAR 1990 'II // strength, elasticity and swellability can be formed. However, A *■ wijth the so-called "filling-up" techniques generally applied in^soil strenghening and in the water-tight plugging of the defects of engineering structures (particularly underground ?3 1743 ducts, pipelines and tunnels) the appropriate mixing of the t-»o liquids generally cannot be ensured throughout the whole section of the soil or engineering structure to be treated. The essence of filling-up technique is that first one of the two liquids, generally the water glass-containing solution, ia applied onto the area to be treated e.g. in such a way that the liquid is filled into the duct section to be repaired, and then, after an appropriate waiting time, the excess of the first liquid is optionally removed, and the second liquid, generally the aqueous solution comprising the acid and the 3ubstance required for polymerization, is introduced. Through the defect sites of uneven dimensions the liquids enter the soil at an uneven rate, and, as a consequence of the uneven pore and cavity structure of the soil, their movement rate in the soil is uneven, too. This involves that there are considerable local variations between the mixing ratios of the two liquids. This means that at certain sites gel cannot be formed at all in the first filling-up cycle, whereas at other sites, depending on the actual mixing ratio, considerable local variations in gel quality can be observed. Thus e.g. when a i?ater glass solution is introduced first and then an aqueous solution which cannot form gel per se upon neutralization (such' as an aqueous solution comprising an acid other than id additional non-gelling components, is applied onto the water glass solution, no gel is formed from the portions of the acidic solution which are in excess or which cannot be mixed with the water glass solution. These pprtions of the acidic solution flow through the soil' section, more or less impregnated with water glass, without utilization, polymerization catalysts, etc.) 231743 * . 5 - 1 cutting channel-like passages through the soil. These channel-lika passages render the gel structure more or less open to water exfiltration, thus the water tightness of the gel formed in the first filling-up cycle is inappropriate. A gel with the required water tightness can be obtained only by repeating the filling-up cycle two or more times, which decreases the efficiency of the process and involves a consider-able increase in operation costs.

When each of the two liquids comprises a component 10 which gellifies upon neutralization (such as one of the liquids comprises water glass and the other comprises a monomer or oligomer which polymerizes when contacting it with an alkali), uneven mixing of the two liquids has the consequence that, instead of obtaining a gel with homogeneous microstruc-15 ture in whioh ghe organic and mineral parts are amalgamated, a gel consisting of easily distinguishable discrete mineral (silicate) and organic (polymer) blocks, i.e. a gel with in-homogeneous microstructure is formed. The strength and swelling characteristics of the organic and mineral blocks greatly 20 differ from one another. These gels with inhomogeneous micro-structure combine essentially all the disadvantages of the completely mineral and completely organic gels: at the mineral blocks the gel is non-elastic, rigid, and cracks upon soil movements, whereas at the organic blocks the gel is too soft an<* cannot withstand the damaging effects of higher strains. j|"Y o| - Uneven mixing outlined above is a necessary con- ^ -9 .;;/COmitant of all filling-up techniques which apply two liquids.

In order to avoid the disadvantageous consequences of uneven mixing a pair of gel-forming liquids is required, in which 30 - gel can be formed from both liquids upon a chemical reac- ^31743 » tioa, and - the properties of the gela formed separately from the two liquids are highly similar.

Furthermore, in order to decrease the rigidity of 5 the gel and to ensure an appropriate swellability, a substance Is required which does not polymerize and gellify per se, but is able to be built into the gel structure wherein it exerts a plasticizing effect. In order to decrease the disadvantageous consequences of uneven mixing it is desirable that this sub-10 stance should be able to reach by diffusion even those liquid . portions which do not mix with one another.

Now it has been found that the above requirements can be fulfilled by using a pair of liquids in which one of the liquids is an aqueous solution of water glass optionally 15 also comprising one or more natural or synthetic oligomer or polymer, and the other liquid is a silicic acid sol in which the dispersion medium consists, at least in part, of a water-miscible organic liquid which is able to react with the alkali content of the water glass solution, gellifying thereby the water glass.

- E N j ^ ^ o. The gels formed from the water glass solution upon •*\\ i^jitralizing its alkali content and from the silicic acid sol 9 MAR l99Q1p'on reacting the organic dispersion medium are equally silicate V gels with very close physical properties. Both the alkali 25 present in the water glass solution and the reactive organic dispersion medium present in the silicic acid sol are able to move by diffusion, thus, after a certain period of time, the reaction proceeds even in those liquid portions which have not been mixed with one another or in which mixing has been in-30 appropriate. It has also been found that the organic dispersion 231743 ;<**•- - 7 - median of the eilicic acid sol Immediately builds into the gel structure in parallel with gel formation and exerts there a plaaticizing effect, i.e. leada to the formation of a more swelling and more deforsable gel. As a net result, upon the 5 reaction of the alkali present in the water glass solution and the organic dispersion medium present in the silicic acid sol, which proceeds immediately in the well-mixed liquid portions and within a diffusion-controlled period in the less or non-nixed liquid portions, a silicate gel is formed from both 10 liquids which contains the organic dispersion medium or its reaction product entrapped into the gel structure. Gel formation proceeds even at those sites where the mixing of the two liquids is inappropriate or the mixing ratio differs from the pre-adjusted value, and the properties of the gel blocks 15 foraed at the sites of inhomogsneous mixing well approach to those of the gel blocks foraed from homogeneous mixtures.

Based on the above, the invention relates to a method for improving the strength and impermeability of soils or engineering structures, which comprises the steps of: (a) applying to the side of the soil or of the engineering structure an alkaline water glass solution comprising water glass in an amount of 15 to 40% by weight calculated as dry substance; (b) allowing a time period to pass sufficient to permit the alkali present in the water glass solution to move by diffusion; (c) applying to the same site as in step (a), a silicic acid sol comprising SiC^ in an amount of 5-50% by weight, calculated as dry substance, and an organic dispersion medium in which 10-100% by volume of the dispersion medium consists of a water-miscible organic solvent capable of reacting with the alkali content of the water glass solution applied during step (followed by page 7a) ViTi'JT OFFICE 18 DEL iyyu rece!\'*:d 231743 - 7a - (a), thereby gellifying the water glass so that the reaction product of the water-miscible organic solvent and the alkali content of the water glass is trapped within the gelled water glass; and (d) allowing a time period to pass sufficient to permit the respective organic dispersion medium present in the silicic acid sol to move by diffusion, so that gellification of the water glass takes place evenly when mixing of the water glass solution applied during step (a) and the silicic acid sol. applied during step (c) to the soils or to the engineering structures takes place to effect a plasticizing effect on the resulting water glass gel. (followed by page 8) N.Z. PAi EisJT OFFICE 18 DEC 1980 231743 The term "water glass" as used in the specification and claims covers alkali metal (Na, K) and ammonium water glasses and mixtures thereof.

The aqueous solution of water glass may comprise natural and/or synthetic oligomers and/or polymers. Of the natural oligomers and polymers hydrolysed proteins and natural latex, whereas of the synthetic oligomers and polymers polyvinyl alcohol and butadiene latex are mentioned. Obviously, the oligo-» mers or polymers applied should be alkali-resist ant and coapat-ible with the aqueous water glass solution. These polymers are entrapped into the gel structure either physically or chemically upon gel formation, and increase the deformation and swelling ability of the gel.

The silicic acid sols (so-called "organosols") applied in the method of the Invention are known or can be prepared by known methods Z5 ,K. Her: Colloid Chemistry of Silica and Silicates; Cornell University Press, Ithaca, 31.Y., pp. 90-95 (1955) and R.2. Iler: The Chemistry of Silica; John Wiley and Sons, J.Y., pp. 331-343 and 415-4-19 (197917* These aols comprise disperse silicic acid particles 'with a particle size of 3-200 nm, preferably 10-50 run. The disperse silicic acid particles may be optionally pre-treated on their surface; mono- or polyvalent alcohols, alkylene oxide oligomers or polymers or Al^+ or ?e^+ ions can be attached, through the surface hydroxy groups, to the surface of these pre-treated silicic acid particles. The silicic acid sols comprising silicic acid particles ore-treated on their surface are known or can be oreoared by known methods, e.g. as 'fTif 1 Qir-it 1n tr 1 nhn-f taxt- i 18DEC1U9 0 231743 booka. According to our experiences silicic aold sola comprising silicic acid particles pre-treated on their surface provide better results than those comprising untreated 9ilicic acid particles. The term "silicic acid sol" as used in the specification and claims covers sols comprising such pre-treated silicic acid particles as well.

At least 10 % by volume of the dispersion medium of the silicic acid sol should consist of a water-miscible organic liquid capable of reacting with alkaline agents. The term "water-miscibleM refers to liquids with unrestricted rater miscibility, i.e. which form stable mixtures with water at any ratio. Such organic liquids are e.g. esters, amides, acetals, etc., examples of -which are the following: diethylene glycol diacetate, glycerol diacetate, ethylene carbonate, ethyl urethane and formamide. The remainder of the dispersion medium, if any, may consist of any organic liquid unrestrictedly miscible with both water and the organic liquids mentioned. above and being indifferent towards alkaline agents; of them alcohols and ketones are to be mentioned. The dispersion medium may also contain water in an amount not exceeding 80 % by volume. losses in water glass solution are supplemented in such a way that the height of the liquid does not drop belovr 1.5 m. After 30 minutes the liquid is pumped from the duct with a high A defective duct section witL _ 3 bordered by two shafts, is filled up first with 10 m of a concentrated aqueous water glass solution (Component A). The The invention is elucidated the following non-limiting Example. Example ({ 5 I f 3 performance pump within 5 seconds, and then 10 nr of Component B with the composition given below are filled into the duct section: 3 Glucose diacetate 2 tar ludox CL-I (a silicic acid sol comprising 46 % by weight of SiC^f pH = 9»1» sold by E.I.

DuPont de Semours and Co., Wilmington, Delaware, USA) 3 oa? Diethylene glycol aonomethyl ether 1 V7ater 4 m? The liquid height is maintained at 1.5 m in the duot by supplementing Component B until exfiltration stops (for about 60 ninutes). Thereafter the excess of Component B is pumped from the duct.

The quality of repair was checked by water pressure, test. No reduction in water level could be observed, which means that the repair was perfect. 231743 - ii -

Claims (4)

WHAT WE CLAIM IS:

1. A method for improving the strength and impermeability of soils or engineering structures, which comprises the steps of: (a) applying to the side of the soil or of the engineering structure an alkaline water glass solution comprising water glass in an amount of 15-40% by weight calculated as dry substance; (b) allowing a time period to pass sufficient to permit the alkali present in the water glass solution to move by diffusion; (c) applying to the same site as in step (a), a silicic acid sol comprising SiC>2 in an amount of 5-50% by weight, calculated as dry substance, and an organic dispersion medium in which 10-100% by volume of the dispersion medium consists of a water-miscible organic solvent capable of reacting with the alkali content of the water glass solution applied during step (a), thereby gellifying the water glass so that the reaction product of the water-miscible organic solvent and the alkali content of the water glass is trapped within the gelled water glass; and (d) allowing a time period to pass sufficient to permit the respective organic dispersion medium present in the silicic acid sol to move by diffusion, so that gellification of the water glass takes place evenly when mixing of the water glass solution applied during step (a) and the silicic acid sol. applied during step (c) to the soils or to the engineering structures takes place to effect a plasticizing effect on the resulting water glass gel.

2. A method as claimed in claim 1, wherein according to step (c) the silicic acid sol comprises silicic acid particles with mono- or polyvalent alcohols, alkylene oxide oligomers or 3+ 3+ polymers or A1 or Fe ions bound to their surface's^. 231743 12

3. A method as claimed in claim 1 or 2, wherein according to step (c) the silicic acid sol comprises as the water-miscible organic solvent diethylene glycol diacetate, glycerol diacetate, ethylene carbonate, ethyl urethane or forroamide .

4. A method as claimed in claim 1 and substantially as described in this specification with reference to the example. ALTALANOS IPARFEJLESZTESI RT "By their Attorneys BALDWIN SON & CAREY N.Z. PATEMT OFFICE 18 DEC 1380 n f— <-\r-1 \ ' -•