WO2000029504A1

WO2000029504A1 - Method for accelerated soil stabilisation

Info

Publication number: WO2000029504A1
Application number: PCT/EP1999/008387
Authority: WO
Inventors: Bettina Kopp-Holtwiesche; Doris Bell; Stephan Von Tapavicza; Sven Welper; Claus-Peter Herold
Original assignee: Cognis Deutschland Gmbh
Priority date: 1998-11-12
Filing date: 1999-11-03
Publication date: 2000-05-25
Also published as: AU1159500A; DE19852221A1

Abstract

Disclosed is a method for stabilising and hardening soil. According to said method, an aqueous PVAc dispersion combined with an aqueous alkaline metal silicate solution is brought into contact with said soil.

Description

Accelerated soil stabilization process

The present application relates to an improvement and extension of the teaching described in the older German patent application DE 43 24 474 for surface consolidation of sand and / or soil - hereinafter referred to as soil throughout. This earlier application describes a modification of the method known per se to form an at least temporary solidification by applying and introducing aqueous polymer dispersions onto or into the soil surface layers. The water of the applied impregnating agent dries up in a comparatively short time, the remaining polymer phase solidifies the granular structure of the treated soil without unreasonably affecting the water permeability of these layers. Such surface hardening is not limited to soil in the narrower sense. The corresponding stabilization of other surface areas that have to be protected against wind erosion, for example, also falls within the teaching of the inventive action. Examples include: landfills and / or spoil dumps with or without covering with topsoil or other protective layers.

For decades, development and practice have been concerned with the concept on which the invention is based, in which synthetic plastics which adhere particulate solids to one another in the form of their aqueous dispersions or emulsions are applied to the surfaces to be consolidated and dried there. In this context, aqueous polyvinyl acetate dispersions are of particular practical importance - hereinafter also referred to as PVAc dispersions. For example, reference is made to the following publications: A. Kulimann et al. in "Archives for Arable and Crops and Soil Science", 22nd Volume, No. 11 (1978), pages 713 to 719 (Chemical Abstracts 91 (5): 38081u). In addition to polyvinyl acetate, the following are described as useful binders: butadiene-styrene latex, a urea / formaldehyde polymer and a bitumen emulsion. The stabilization of dune sand in a corresponding manner against rainy weather is the subject of the publication D. Gabriels et al. in "Soil Science", Vol 118, No. 5 (1974), pages 332 to 338 (Chemical Abstracts 82 (15): 96945d). Here too, a binder system based on poly vinyl acetate base indicated among the preferred work equipment. From the further work carried out worldwide, reference is only made to a few patents by way of example, see in this connection US-A-4072020, US-A-3887506, Chemical Abstracts 85 (21): 158730c (= HU-A-11654) and ZA-A -7501787.

The list of requirements or tasks for such consolidation of the surface of the soil can be extremely varied. Without claiming to be complete, a number of the properties required in practice are enumerated: The material should at least be resistant to pedestrian traffic, it must not be impaired by the prevailing temperatures, air humidity and rain - for the intended period - it must be resistant to high wind speeds. The material to be applied should not be flammable and should not pose a fire or explosion hazard during storage, during and after use. No unusual protective measures or protective clothing should be worn during transport and processing. The hardened plastic impregnation should have no toxic effect on germinating plants, growing plants and animals and should be as colorless or transparent as possible.

The teaching of the older patent application DE 43 24 474 cited at the outset is based on the task of equipping PVAc homopolymer dispersions for the described application with plasticizers which on the one hand meet the varied technical requirements profile, but on the other hand are biocompatible and in particular are degraded on their part can. This is based on the specialist knowledge that PVAc homopolymers are generally biocompatible and degradable, even if the degradation of this polymer is comparatively slow. For the relevant literature, see, for example, H. Kastien et al. "The quantitative microbiological degradation of synthetic resins and polymer dispersions", färbe + lack, 98th year, 7/1992, 505-8. According to the teaching of the earlier application, the following selected substance classes are used as biologically acceptable plasticizers for PVAc dispersions: triesters of glycerol with lower aliphatic monocarboxylic acids, citric acid triesters with lower aliphatic monofunctional alcohols and / or epoxidized triglycerides, at least partially olefinically unsaturated fatty acids. For details of the technical teaching according to the older application DE 43 24 474, reference is made to its disclosure, which is hereby also made the subject of the present disclosure of the invention.

Using the consolidation agents described in the earlier application mentioned, it is possible to set optimized consolidations in the surface area of the treated soil, for example up to layer thicknesses in the range of a few centimeters, which, under normal conditions, meet the requirement profile set in practice. However, it has been shown that the curing or setting times of the setting agents described above do not always meet the requirements of practice in all cases. This applies in particular to the time that elapses before the soil is finally solidified by treatment with the PVAc dispersions. For example, when treating surfaces on airfields, a very fast curing time is required in order to limit the restrictions of air traffic - during the curing process there should be no load on the ground from take-off or landing aircraft - as short as possible. Soils which are treated with the agents according to the older application DE 43 24 474, however, generally require curing or consolidation times of 8 to 16 hours. For use e.g. At airports, this period should be reduced to significantly less than 3 hours, preferably less than 2 hours. In practice, it is also required that the solidification is retained to a sufficient extent even when re-moistened (rain).

The object on which the present invention is based was therefore to provide an accelerated method for the surface consolidation of sand or soil. The solidification should also be retained after rewetting.

It has been found that in the case of soil stabilization using polyvinyl acetate polymers, the use of certain alkali metal silicates leads to accelerated solidification of the treated soil, even when rewetted.

In a first embodiment, the present invention relates to a method for accelerating surface consolidation of soil, whereby that which is to be consolidated Soil both with an aqueous polyvinyl acetate dispersion, which contains, as biodegradable plasticizers, triesters of glycerol with lower aliphatic monocarboxylic acids, citric acid esters with lower aliphatic mono-functional alcohols and / or epoxidized triglycerides, partially or completely olefinically unsaturated fatty acids as well as, if appropriate, further additives, at the same time or with a time delay - brings the soil into contact with an aqueous alkali metal silicate solution.

The present method combines the known sole use of PVAc dispersions for soil stabilization with the use of a hardener in the form of an aqueous alkali metal silicate solution. The sole use of alkali silicates leads to a rapid and sufficient solidification of soil, but a soil treated in this way is largely impermeable to water. Surprisingly, however, it was found that in the process according to the invention, that is to say the combination of a treatment with PVAc dispersions in combination with a treatment with aqueous alkali metal silicate solutions, both the soil hardens rapidly and at the same time there is sufficient water permeability. In the sense of the method according to the invention, it is possible to bring the soil into contact with the PVAc dispersion and the aqueous alkali metal silicate solution at the same time, and to carry out the two steps with a time delay. If carried out at the same time, for example, a mixture of the PVAc dispersion and the alkali metal silicate solution can be prepared shortly before the actual application and this mixture can then be brought into contact with the ground. However, simultaneous application is also possible by simultaneously spraying a PVAc dispersion and an alkali metal silicate dispersion onto the same location on the ground.

The process can also be carried out in two stages, in a first step a) bringing the soil to be solidified into contact with the aqueous polyvinyl acetate dispersion and then with a time delay in step b) with the aqueous alkali metal silicate solution. Delayed means that there is a period of 1 to 30 minutes and preferably a period of 5 to 15 minutes between step a) and b).

The soil treated in this way solidifies quickly, ie at the latest 0.5 to 2 hours after the treatment according to the invention, the soil has developed a hard, solid surface. This applies in particular to high air humidity and / or low temperatures, which otherwise prevent the PVAc dispersion from hardening quickly due to evaporation.

Within the framework of the teaching according to the invention, the alkali metal silicate is used in the form of an aqueous solution following or simultaneously with the treatment with the aqueous polyvinyl acetate dispersions. The alkali metal silicates are sodium or potassium silicates with a molar ratio SiO ₂ : MO (modulus) of 2: 1 to 4: 1, where M stands for an alkali metal cation. Such silicates are sold in powder form, granule form or preferably as aqueous solutions which contain between 20 and 60% by weight of the silicate (based on dry substance). It is advantageous to select sodium silicates in the SiO ₂ : Na ₂ O molar ratio of 2: 1 to 3: 1. The solutions used in the process according to the invention preferably contain the alkali metal silicates in amounts of 1 to 25% by weight and preferably 1 to 10% by weight of dry substance. It has proven to be advantageous to use triacetion and / or propylene carbonate as auxiliaries together with the water glass. These substances are usually used in amounts of 1 to 10% by weight, based on the silicate solution.

In addition to the known polyvinyl compounds, the PVAc dispersions used in the process according to the invention also contain certain plasticizers. Three natural product-based, low molecular weight plasticizer types have proven to be suitable for fulfilling the requirements professional according to the invention. The first group includes triesters of glycerin with lower aliphatic monocarboxylic acids. Corresponding glycerol triesters of aliphatic monocarboxylic acids with 2 to 6 C atoms and in particular with 2 to 4 C atoms in the molecule are particularly suitable. A particularly important representative here is triacetin. The work on which the invention is based has shown that even a very small addition of the triacetin to the PVAc homopolymer can achieve a sufficient softening of the PVAc film for the application according to the invention, so that the mixture soaked in and mixed with the mixture originally dried with entered water solidified sand or soil formations do not become brittle and can therefore be walked on, for example. The second group of plasticizers suitable according to the invention is represented by citric acid triesters. The citric acid can be present as such, but also in the form of the variant acylated on its hydroxyl group. Suitable ester-forming alcohols for reaction with the carboxyl groups of citric acid are, in particular, monofunctional aliphatic alcohols with 2 to 6 carbon atoms and preferably corresponding alcohols with 2 to 4 carbon atoms. Both in this class of substances and in the class of glycerol triesters with aliphatic monocarboxylic acids given above, the choice of the chain length of the monofunctional constituent used for the esterification can influence the volatility and thus the boiling point of the plasticizer component. In the case of the citric acid esters concerned here, a further possibility of variation is possible via the chain length of the acyl radical which may be bonded to the hydroxyl group of citric acid. Corresponding residues of monofunctional, in particular saturated carboxylic acids having 2 to 10 carbon atoms, but possibly also residues of corresponding acids with an even higher carbon number are suitable. The teaching of the invention here opens up the possibility of limiting a possible loss of plasticizer under extreme conditions - for example in extreme sunlight - and thus embrittlement of the film layers formed.

The third class of plasticizer in the sense of the action according to the invention is represented by the epoxidized triglycerides of at least partially olefinically unsaturated fatty acids. The most important representatives of this class for practical and economic reasons are epoxidized rapeseed oil and epoxidized soybean oil, which have been put on the market and proposed as commercial products by the applicant for a wide variety of applications. It is precisely in this subclass of the plasticizers used according to the invention that the selection character of the teaching according to the invention can be recognized very clearly: triglyceride esters of saturated and / or unsaturated fatty acids, in particular corresponding triglycerides of natural origin present as oils under normal conditions, do not give an adequate plasticizer effect when mixed with PVAc homopolymers. In an unpredictable manner, the epoxidation of at least partially olefinically unsaturated triglycerides of this type and in particular by epoxidation of the rapeseed oil create a plasticizer which is complex The catalog of requirements corresponds to, fulfills the conditions set here and at the same time is subject to natural degradation processes as a natural product.

The amount of plasticizer required in the working materials used according to the invention to set the requirement profile is limited. In general, amounts of plasticizer of about 1 to 15% by weight and preferably of about 3 to 10% by weight, based in each case on the about 50% by weight PVAc homopolymer dispersion, give adequate results. Additional amounts in the range from about 5 to 8% by weight of plasticizer can be particularly important. An advantage of the teaching according to the invention that has already been mentioned can be seen here: partial discharge of plasticizer which occurs under extreme conditions, for example solar radiation, does not have a direct negative effect on the material properties of the dried PVAc film when mixed with the solidified soil mass. Even if the impregnation of plasticizer becomes comparatively poor, sufficient flexibility of the solidified layer is always guaranteed. Possibly the structural similarity of the plasticizer molecule with the structural unit of the PVAc homopolymer has a positive effect in the sense that a particularly intimate penetration of the plasticizer into the polymer molecule maintains the desired effect even in the range of low plasticizer concentrations.

The PVAc dispersions to be used in practice are the known aqueous preparations whose PVAc solids content can be, for example, in the range from 10 to 65% by weight and preferably in the range from 35 to 60% by weight. In the previous practice of applying aqueous PVAc dispersions, corresponding solid contents in the range from 50 to 60% by weight are often used. Basically, this can also be used in the sense of the teaching according to the invention.

In a particularly preferred embodiment, the invention provides that more

Additives of the aqueous impregnating and

Binder compositions are biodegradable and therefore biocompatible. Here's the

Invention in particular the use of biodegradable protective colloids for

Stabilization of the aqueous PVAc dispersions before. Suitable protective colloids are on the one hand

Polyvinyl alcohol, but also starch and / or water-soluble starch derivatives, the starch can also be subjected to a partial molecular weight reduction. In principle, however, especially in the case of starch and / or water-soluble starch derivatives as protective colloids, the use of too large amounts of these water-soluble components can endanger film stability against erosion due to irrigation and thus rapid film degradation. Accordingly, it is preferred according to the invention to limit the amounts of protective colloids or emulsifiers used in such a way that the PVAc coating is sufficiently resistant to the effects of weathering. The amounts of protective colloids or emulsifiers are usually at most about 5% by weight and in particular in the range from about 0.5 to 3% by weight, based in each case on PVAc solids.

Otherwise, the technical elements which have been developed in the relevant prior art for the formation of corresponding surface films can also be used in the course of the inventive action. Examples include the use of growth-promoting active ingredients, in particular auxiliaries with a fertilizer character, and / or the use of preferably finely divided particulate solid material in the flowable preparation. In the last-mentioned case, the state of the art, as is well known, particularly provides for the use of fine-particle solids based on natural substances such as wood flour, straw particles, cereal shells and the like, in order to enable the development of local breakthroughs for the further promotion of plant growth without reducing the overall cohesion endanger the solidified layer. In a manner known per se, the application of the soil-stabilizing aqueous active substance preparation can be carried out with the application of plant seeds. The appropriate finishing of the soil can also be carried out independently of the consolidation before or after the application of the aqueous preparation based on PVAc according to the invention. The applied amount of the aqueous active ingredient suspension is determined by a number of factors, for example the readiness for penetration of the upper layer of the earth, the intended goal, and in particular the duration of the consolidation, and the weather-related influences to be expected in the period in which the Sufficiently secure cohesion of the solidified surface layers of the soil should be guaranteed. It is preferred to apply components a) and b) in amounts of from 10 to 400 g / m ² , preferably from 10 to 250 g / m ^2, floor.

In general, the depth of entry of the aqueous PVAc dispersion into the soil will be in the range of a maximum of a few centimeters, with depths of entry in the range of approximately 0.5 to 3 cm and in particular approximately 1 to 2 cm being usually sufficient. In many applications, however, soil consolidation at a depth of less than 1 cm is sufficient.

Another embodiment of the present invention relates to the use of a combination of a) an aqueous polyvinyl acetate dispersion which, as biodegradable plasticizers, triesters of glycerol with lower aliphatic monocarboxylic acids, citric acid esters with lower aliphatic mono-functional alcohols and / or epoxidized triglycerides are partially or completely olefinically contains unsaturated fatty acids and optionally other additives, with b) an aqueous alkali metal silicate solution for the accelerated solidification of soil. It is advantageous to use the dispersion a) and the aqueous alkali metal silicate solution b) in a weight ratio of 2: 1 to 1: 2 and preferably in a weight ratio of about 1: 1.

example 1

Using a commercially available PVAc dispersion (approx. 50% by weight) - commercial product VP 4239/278 B (protective colloid polyvinyl alcohol) from Cordes - a dispersion (A) with 5% by weight triacetin as plasticizer and 8% by weight .-% sodium water glass (dry substance) from Henkel in the form of a 40% by weight aqueous solution, based in each case on the aqueous dispersion. For comparison, a dispersion (B) was prepared without the addition of water glass. The procedure is as follows: the plasticizer and the water glass solution are added to the dispersion with stirring at room temperature. The mixture is stirred for 10 minutes. Condition: IKA stirrer with paddle stirrer, U = 900 min ^"1

With the above-mentioned dispersions (A) and (B), tests for surface hardening of sand samples were carried out as follows: The surfaces of sand samples of the same type in each case with equal amounts of 10% by weight solutions of the dispersions (A) and (B) treated. The required curing time was then determined at ambient temperature (approx. 20 to 25 ° C) and a relative humidity of 75%. Result: The sand surface treated with the dispersion (A) according to the invention had formed a firm, hard surface after a period of about 120 minutes. In the case of the comparison dispersion (B), this result could only be observed after more than 16 hours.

Example 2

A 50% polyvinyl acetate dispersion with 5% by weight triacetin was used as test substance A, which is sold by the applicant under the trade name Terra-Control. Test substance B consisted of sodium water glass 37/40 with 6% triacetin plus 3% propylene carbonate as additional hardener component.

Laboratory disposable cups made of waxed cardboard that were filled with dry sand were chosen as the test system. The sand was compacted with a 1 kg weight and sprayed with the test solutions. The surface area was approximately 133 cm ² . The mixtures to be tested were each applied to the sand surfaces with 27 g of water. This corresponds to a quantity of water of approximately 2 l / m ² . The product quantities were 20-400 g / m ² (see Tab. 1) and were evenly distributed on the sand surface as 1-20% dilutions with commercially available spray pumps (Sidolin spray gun).

After 24 hours, the vessels had dried to constant weight. Now the compressive strength of the treated sand surfaces was measured with a hand penetrometer. 2 hours after rewetting with 2 l / m ² (water) in each case, the compressive strength was determined again with a hand penetrometer, a further 72 hours later (after drying again completely), a last measurement was carried out.

The aim of the experiment was to compare the compressive strength of sand surfaces which were pretreated with different concentrations of the mixture according to the invention. The compressive strength was determined both in the dry and in the moist state.

The concentration-dependent compressive strength of sand surfaces fixed with Terra-Control drops after rewetting and returns to their original values after drying (Tab. 1).

Sand surfaces attached with water glass are significantly more pressure-resistant when wet than when dry. Surfaces that have been moistened and dried again and treated with water glass no longer have any pressure resistance.

Sand surfaces secured with a mixture of Terra-Control and water glass achieve sufficient and lasting compressive strengths both in the dry and in the wet state.

Table 1:

It can be seen from the results in Table 1 that only the combination of terra control and water glass according to the invention leads to rapid and solidification of the soil which is insensitive to moisture. Neither water glass nor Terra Control alone can produce this effect.

Claims

claims

1. A method for accelerating the surface solidification of soil, whereby the soil to be solidified with an aqueous polyvinyl acetate dispersion, which as biodegradable plasticizer triesters of glycerol with lower aliphatic monocarboxylic acids, citric acid triesters with lower aliphatic monofunctional alcohols and / or epoxidized triglyceride partially or completely contains unsaturated fatty acids and, if appropriate, further additives, is brought into contact, characterized in that the soil is brought into contact with an aqueous alkali metal silicate solution at the same time or with a time delay.

2. The method according to claim 1, characterized in that in a first step a) the soil to be solidified is brought into contact with the aqueous polyvinyl acetate dispersion and then after a time delay in step b) with the aqueous alkali metal silicate solution.

3. The method according to claim 2, characterized in that between the implementation of step a) and step b) a waiting time of 1 minute to 30 minutes, preferably from 5 to 15 minutes, is observed.

4. The method according to claim 1, characterized in that the soil to be solidified is simultaneously brought into contact with the polyvinyl acetate dispersion and the alkali metal silicate solution.

5. Process according to Claims 1 to 4, characterized in that the aqueous polyvinyl acetate dispersion contains, as plasticizers, glycerol triesters of aliphatic monocarboxylic acids having 2 to 6, preferably 2 to 4, carbon atoms in the molecule, and in particular triacetin.

6. Process according to Claims 1 to 4, characterized in that the aqueous polyvinyl acetate dispersion contains, as a plasticizer, citric acid triesters with aliphatic monofunctional alcohols having 2 to 6 C atoms, preferably 2 to 4 C atoms.

7. The method according to claims 1 to 4, characterized in that the aqueous

Contains polyvinyl acetate dispersion as a plasticizer epoxidized beet oil and / or epoxidized soybean oil.

8. The method according to any one of claims 1 to 7, characterized in that the material to be solidified is brought into contact with an aqueous polyvinyl acetate dispersion, which, based on a 50 wt .-% aqueous polyvinyl acetate dispersion, plasticizer in amounts between Contains 1 and 15 wt .-%, preferably 3 to 10 wt .-%.

9. The method according to claims 1 to 8, characterized in that the solidified

Soil is brought into contact with an aqueous alkali metal silicate solution which, based on the solution, contains 1 to 25% by weight of alkali metal silicate, preferably 1 to 10% by weight (dry substance).

10. The method according to claims 1 to 9, characterized in that the alkali metal silicate solution contains a sodium silicate with the molar ratio SiO ₂ : Na ₂ O of 2: 1 to 3: 1.

11. The method according to claims 1 to 10, characterized in that the polyvinyl acetate dispersion and the alkali metal silicate solution are each sprayed onto the surface of the soil to be solidified.

12. The method according to claims 1 to 11, characterized in that components a) and b) are each applied in amounts of 10 to 400 g / m ^{2 of} soil.

13. Use of a combination of a) an aqueous polyvinyl acetate dispersion which, as a biodegradable plasticizer, triesters of glycerol with lower aliphatic monocarboxylic acids, citric acid triesters with lower aliphatic monofunctional alcohols and / or epoxidized triglycerides partially or contains completely olefinically unsaturated fatty acids and optionally further additives, with

b) an aqueous alkali metal silicate solution for the accelerated solidification of soil.

14. Use according to claim 13, characterized in that a) and b) in a weight ratio of 2: 1 to 1: 2 and preferably 1: 1 is used.