Soil-stabilising composition comprising <i>Azobacter vinelandii</i>, <i>Acidithiobacillus ferrooxidans</i>, alginase, and calcium chloride; method for stabilising soils; method for preparing stabilised paths; use of the soil-stabilising composition

Abstract

A formulation for stabilizing soils is described comprising bacteria, enzymes and cations, wherein the bacteria preferably correspond to Azotobacter vinelandii and Acidithiobacillus ferrooxidans, the enzyme preferably corresponds to an alginase and the cations are preferably provided in the form of calcium chloride. A method for stabilizing soils; a method for preparing stabilized paths; and use of the soil-stabilizing composition are also described.

Claims

1. A soil-stabilizing composition comprising: (i) a solution A comprising Azotobacter vinelandii, Acidithiobacillus ferrooxidans and a Pseudomonas aeruginosa alginase; wherein solution A comprises from 8% to 15% Azotobacter vinelandii as a percentage by weight based on the total weight of solution A, from 11% to 19% Acidithiobacillus ferrooxidans as a percentage by volume based on the total volume of solution A, and from greater than 0% to 5% of alginase as a percentage by weight based on the total weight of solution A; and (ii) a solution B comprising cations in the form of calcium chloride; wherein solution B contains from 20% to 35% calcium chloride as a percentage by weight based on the total weight of solution B.

2. The soil-stabilizing composition of claim 1 wherein (i) solution A comprises 8% Azotobacter vinelandii, as a percentage by weight based on the total weight of solution A, 15% Acidithiobacillus ferrooxidans as a percentage by volume based on the total volume of solution A, and 5% alginase as a percentage by weight based on the total weight of solution A; and (ii) solution B contains 20% calcium chloride, as a percentage by weight based on the total weight of solution B.

3. A method of soil stabilization, comprising: (a) adding the solution A of claim 1 to a water tank of a first cistern truck; (b) adding the solution B of claim 1 to a water tank of a second cistern truck; (c) pouring a diluted solution A from step (a) into a soil; and (d) pouring a diluted solution B from step (b) into the soil, wherein the diluted solution from step (a) had previously been poured into said soil, as specified in step (c); and (e) obtaining a stabilized soil.

4. The method of claim 3, comprising independently adding 1 litre of solution A to 1000 litres of water contained in the water tank of the first cistern truck from step (a) to form diluted solution A, and independently adding 1 litre of solution B to 1000 litres of water contained in the water tank of the second cistern truck from step (b) to form diluted solution B.

5. The method of claim 4 comprising compacting the soil after step (d).

6. The method of claim 5, wherein the compacting is accomplished with a roller.

7. A method to prepare a stabilized road, comprising: (a) reconditioning the soil by the incorporation of filler or structural material, approximately at a depth of about 10 to 15 cm; (b) homogeneously incorporating the soil-stabilizing composition of claim 1; (c) mixing the homogeneous soil-stabilizing composition from step (b) with the filler material or with reconditioned soil from step (a); (d) spreading the homogenized material from step (c) on the road to be constructed; (e) wetting; and (f) mechanically compacting an area of the road to be constructed.

8. The method of claim 7, wherein the mechanically compacting of stage (f) is accomplished by means of a roller.

9. The method of claim 8 comprising forming a stabilized road having a California bearing ratio (CBR) value of at least approximately 136%.

10. The method of claim 8 comprising forming a soil that is stabilized for 1 to 1.5 years.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) A composition comprising at least Azotobacter vinelandii, Acidithiobacillus ferrooxidans, alginase and calcium chloride is provided, which stabilizes soils when making contact with said soil.

(2) In a preferred embodiment, the soil-stabilizing composition is a bi-component formulation that comprises solution A and solution B.

(3) In a preferred embodiment, solution A comprises as a percentage by weight based on the total weight of solution A, approximately 8% to 15% Azotobacter vinelandii, a percentage by volume based on the total volume of solution A of 11-19% Acidithiobacillus ferrooxidans, and an approximate concentration of alginase up to approximately 5% by weight based on the total weight of solution A.

(4) In said preferred embodiment, solution B comprises, as a percentage by weight based on the total weight of solution B, approximately 20% to 35% calcium chloride. Such preferred proportions are understood as illustrative by an expert in the art, and do not correspond in any way to limitations of the present invention, since said conditions may be varied depending on the characteristics of the soil, or on the weather conditions.

(5) In an even more preferred embodiment, solution A comprises as a percentage by weight based on the total weight of solution A, approximately 8% Azotobacter vinelandii, a percentage by volume based on the total volume of solution A of 15% Acidithiobacillus ferrooxidans, and an approximate concentration of alginase of about 5% by weight based on the total weight of solution A.

(6) In said even more preferred embodiment, solution B comprises approximately 20% of calcium chloride as a percentage by weight based on the total weight of solution B.

(7) In some preferred embodiments, the alginase enzyme is a non-purified native or recombinant enzyme. In yet another preferred embodiment, the alginase enzyme is a purified native or recombinant enzyme. In an even more preferred embodiment, the alginase is a Pseudomonas aeruginosa alginase. An expert in the art will understand that said Pseudomonas aeruginosa alginase is one of multiple options, and can indiscriminately be exchanged for another alginase with the activity and required reaction conditions similar to those of Pseudomonas aeruginosa alginase.

(8) In another aspect of the invention, a method of road stabilization is provided which comprises adding the soil-stabilizing composition of the invention to a soil, obtaining as a result a stabilized soil.

(9) In a preferred embodiment, the method of soil stabilization of the present invention comprises the stages of: a) adding solution A of the present invention to the water tank of a first cistern truck; b) adding solution B of the present invention to the water tank of a second cistern truck; c) pouring the diluted solution from stage (a) into a soil; and then d) pouring the diluted solution from stage (b) into a soil, wherein the diluted solution from stage (a) had previously been poured into that soil, as specified in stage (c).

(10) Preferably, to obtain the diluted solutions from stages (a) and (b) of the method of the present invention, the above described solutions A and B of the present invention are diluted at a ratio of approximately 1 litre of solution per 1000 litres of water, wherein said diluted solutions from stages (a) and (b) are entirely poured into the soil. An expert in the art will understand that other ratios are possible for the method object of the present invention obtaining similar results.

(11) Preferably, the soil to be stabilized is additionally compacted after stage (d) by methods known in the art, for instance, with a roller, in order to compress the soil particles even further, improving the stabilizing effect of the soil-stabilizing composition, object of the present invention.

(12) In another embodiment that is even more preferred, a method is provided to prepare a stabilized road that comprises the stages of: a) depending on the granulometric analysis, reconditioning the soil by incorporating filler or structural material, to a depth of approximately 10 to 15 cm; b) homogeneously incorporating the soil-stabilizing composition of the invention; c) mixing the soil stabilizer with filler material or with the same already extracted soil; d) spreading the previously homogenized material on the road to be constructed; e) wetting, where the amount of water required for wetting will depend on the result of the modified Proctor test; and f) mechanically compacting the area of the road to be built, where mechanical compaction is preferably accomplished with a roller.

(13) Preferably, the surface must be free from potholes and longitudinal distortions (pitting and material accumulation), and transversal distortions (undulations and calamines), leaving longitudinal side indentations to allow drainage of rainwater in order to prevent damaging the rolling surface, before applying the soil-stabilizing composition of the invention.

(14) Preferably, compaction of the soil to be treated with the stabilizing composition of the invention should be at least 95%.

(15) In general, the soil-stabilizing composition of the present invention, the method of soil stabilization and the method for preparing a stabilized road of the present invention, improve at least one property of the soil, such as its volumetric stability, resistance, permeability, compressibility and durability. Said improved properties correspond to only one group of those identified, and do not limit the positive effects of the present invention for soil stabilization.

(16) In a preferred aspect, the composition of the present invention and the method of soil stabilization improve CBR, resulting in a value of approximately 136%.

(17) In yet another preferred aspect, the composition and method of the invention produce a soil stabilized for approximately 1 to 1.5 years.

(18) The term improving volumetric stability used is defined as maintaining the soil volume relatively constant for the purpose of using it for road construction; the increase of which is desirable for soils susceptible to liquefaction, expansive and collapsible, such as clayey soils.

(19) Soil resistance, which is significantly improved by the application of the composition of the invention, is defined on the basis of the parameters known for the technique in the field of soil stabilization, among them, California Bearing Ratio or CBR.

(20) Permeability is understood as the capability of a medium to transfer water or other substances. In soils, permeability is due to the existence of interconnected pores. Said factor is improved by applying the composition of the invention, since soil compaction generally generates a sealing of the surface layer of the roads, making water permeability impossible. The composition of the invention does not affect permeability in a negative way, allowing water to flow and preventing water from forming puddles on the road surface.

(21) Compressibility is defined as the degree in which the volume of the soil body decreases under the effect of a load. It is a property that in itself affects others, such as permeability, modifying soil resistance to shear or causing landslides. Compressibility is proportional to the plasticity index, so the higher the plasticity index, the higher the compressibility of the soil.

(22) Durability is associated to resistance to weather conditions, such as the erosion or abrasion caused by traffic, which is improved when applying the composition object of this invention, since the higher the compaction percentage, the greater the particle cohesion generated, increasing road support (CBR), impacting on durability of the road.

(23) The composition and method object of the present invention can be applied to roads and soils of multiple natures. Non-limiting examples of such roads are rural tracks, working paths, tunnels, parking lots, landing strips, internal farm paths, secondary roads, agricultural tracks, beaches and esplanades, and highway shoulders.

(24) Ways to Implement the Invention

(25) Preferred ways to implement the invention are described below, in addition to illustrative experimental results related to the invention. Notwithstanding the above, an expert in the field should understand that these examples are illustrative, and in no way correspond to limitations of the scope of the present invention.

Example 1

Method to Prepare the Soil-Stabilizing Composition

(26) The culture of A. vinelandii is carried out under standard conditions known in the art. Particularly for this example, bacteria were grown at 30 C. for two days, in standard culture media for A. vinelandii that contained the components described in Table 1 per 1000 millilitres of the total medium. at a pH of approximately 7.3 (Table 1)

(27) Table 1: Culture Medium for A. vinelandii.

(28) TABLE-US-00001 TABLE 1 Culture medium for A. vinelandii. Amount per 1000 litres Component of total culture medium Glucose 5.00 g Manitol 5.00 g CaCl.sub.2 x2H.sub.2O 0.10 g MgSO.sub.4 x7H.sub.2O 0.10 g Na.sub.2MoO.sub.4 x2H.sub.2O .sup.5.00 mg K.sub.2HPO.sub.4 0.90 g KH.sub.2PO.sub.4 0.10 g FeSO.sub.4 x7H.sub.2O 0.01 g CaCO.sub.3 5.00 g Agar 15.00 g

(29) The culture of A. ferrooxidans is also carried out under standard conditions known in the art. Particularly for this example, said culture of A. ferrooxidans was carried out growing the bacteria at 25 C. from three to seven days in standard culture media for A. ferrooxidans at a pH of approximately 1.8, which is obtained by mixing 950 mL of Solution 1, with 50 mL of Solution 2, and 1 mL of Solution 3, according to Table 2

(30) TABLE-US-00002 TABLE 2 Culture medium for A. ferrooxidans. Solution 1 Component of Solution 1 Amount (NH.sub.4).sub.2SO.sub.4 132.0 mg MgCl.sub.2 x6H.sub.2O 53.0 mg KH.sub.2PO.sub.4 27.0 mg CaCl.sub.2 x2H.sub.2O 147.0 mg Solution 2 Component of Solution 2 Amount FeSO.sub.4 x7H.sub.2O 20.0 g.sup. H.sub.2SO.sub.4 0.25N 50.0 mL Solution 3 Component of Solution 3 Amount MnCl.sub.2 x2H.sub.2O 62.0 mg ZnCl.sub.2 68.0 mg CoCl.sub.2 x6H.sub.2O 64.0 mg H.sub.3BO.sub.3 31.0 mg Na.sub.2MoO.sub.4 10.0 mg CuCl.sub.2 x2H.sub.2O 67.0 mg

(31) In turn, alginase is prepared as it is known in the art. For illustrative purposes, alginase preparation is described as follows: a) adding 50 mL of filtered distilled water to a 100 mL beaker; b) adding approximately 20 to 50 mg of alginase to the 50 mL of water, and agitating at least for 5 minutes; c) adding the alginase solution from stage (b) to 2 litres of distilled water, while maintaining constant agitation; d) adding 100 ml of a mixture with a volume ratio of the culture of A. vinelandii to the volume of the culture of A. ferrooxidans of approximately 4:1, ensuring that it is vigorously agitated; e) allowing to stand at least for 3 hours and ideally overnight, and confirming that the solution loses viscosity by conventional methods known in the art; and f) starting agitation again for an additional 30 minutes, and stopping agitation afterwards.

(32) The solution obtained by mixing the bacterial cultures with the reconstituted alginase corresponds to undiluted solution A.

(33) The concentrated solution B of the present invention is prepared by means known to an expert in the art, and corresponds to a 70% weight/weight calcium chloride solution, in distilled water.

Example 2

Method to Apply the Soil-Stabilizing Composition

(34) Generally, to apply this stabilizer, approximately 1 litre of solution A or solution B was diluted in approximately 1,000 litres of water. In general, 1 litre of each concentrated solution A and B allows stabilizing approximately 200 m2 of compacted soil.

(35) The stabilization results of the composition of the invention, obtained by the method of stabilization that is also an object of the invention, are illustrated in Table 3, below:

(36) TABLE-US-00003 TABLE 3 Results of soil stabilization by the composition of the invention, with respect to other stabilizers. Salts in Composition of the Properties Bischofite Asphalt Lime Cement general invention Compacting 106% 102% 98% 97% 105% 136% capacity (CBR) Economic High economic High economic High economic High economic High Low economic cost costs values values values values economic (60% compared to values Bischofita) Toxicity Possible Possible Possible Possible Possible Non- contaminant (Environment) contamination contamination contamination contamination contamination of crops of crops of crops of crops of crops adjoining the adjoining the adjoining the adjoining the adjoining the road road road road road Applicability Climatic Not applicable Climatic conditions of Climatic Can be applied at conditions of temperature and rainfall should conditions of any time temperature be considered in terms of their temperature and rainfall application and rainfall should be should be considered in considered in terms of their terms of their application application Operating High operating High operating High operating High operating High Very low operating costs costs costs costs costs operating costs (70% (Machinery, costs compared to Transport, Bischofite) Labour, etc.) Safety Slippery Not applicable Slippery surfaces in the Slippery Does not affect surfaces in the presence of fog, rain, surface surfaces in the traffic safety presence of moisture, among others presence of fog, rain, fog, rain, surface surface moisture, moisture, among others among others

(37) Bearing ratio or CBR is measured as a percentage (%) and at 0.2 penetration in a saturated sample and pre-compacted to a density equal to or over 95% of the M.C.D.D. obtained in the Modified Proctor test (NCh1534/2).

(38) In areas where the average annual precipitation is less than 50 mm, CBR test is conducted on non-saturated samples, provided that it is previously authorized by the Supervisor.

(39) With regard to compaction to the sub-base, it is compacted until the density obtained is not less than 95% of the M.C.D.D. obtained in the Modified Proctor test (NCh1534/2).