Microbial improvement of red clay and method of preparation thereof

Abstract

The application discloses a kind of microbial improved red clay and preparation method thereof, belong to roadbed material technical field.Microbial improved red clay includes the following mass fraction of raw materials: red clay 100 parts, gypsum 1~1.2 parts, sodium aluminate 0.3~0.5 parts, microbial composite particle 0.3~0.5 parts, urease solution 5~8 parts, urea 1~1.5 parts, calcium chloride 1~1.5 parts, alkaline external admixture 1~2 parts and straw biochar 4~5 parts.The unconfined compressive strength of the microbial improved red clay of the application reaches 1.27~1.29MPa, which can be used as roadbed material, overcoming the technical prejudice that red clay cannot be applied to highway engineering.

Description

Technical Field

[0001] This invention relates to the field of roadbed material technology, and in particular to a microbially modified red clay and its preparation method. Background Technology

[0002] Subgrade materials refer to road construction materials located below the pavement base course, which bear the vehicle loads transmitted from the pavement during application and resist the erosion caused by various environmental factors (freeze-thaw cycles, drying, and aqueous solution infiltration). Subgrade materials should possess good strength, water stability, and durability. Traditional subgrade materials include crushed stone, river sand, and cement. However, with the large-scale development of transportation infrastructure construction, natural resources such as crushed stone are nearing depletion; using river sand and cement involves significant expenditures on machinery, manpower, and costs. Continuing to use large quantities of crushed stone, river sand, and cement as subgrade materials is clearly no longer suitable for the rapid development of transportation infrastructure construction. Therefore, finding a material that can partially replace crushed stone, sand, or cement as a subgrade material has become a pressing technical problem that needs to be solved by those skilled in the art.

[0003] Red clay refers to the residual, colluvial, or residual-colluvial brownish-red, reddish-brown, or yellowish-brown highly plastic clay formed by the weathering of carbonate rocks (limestone, dolomite, argillaceous mudstone, etc.) under subtropical warm and humid climate conditions. It is widely distributed in southern my country, with varying thicknesses across different regions, and its reserves are abundant. However, red clay has a high liquid limit; its bearing capacity decreases rapidly after absorbing water and expanding, and it easily shrinks and cracks after drying. It is significantly affected by climate, therefore, it is rarely used as a roadbed material. Summary of the Invention

[0004] The purpose of this invention is to provide a microbially modified red clay and its preparation method to solve the problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] One of the technical solutions of the present invention is a microbial-modified red clay, comprising the following raw materials in parts by weight: 100 parts red clay, 1-1.2 parts gypsum, 0.3-0.5 parts sodium aluminate, 0.3-0.5 parts microbial composite particles, 5-8 parts urease solution, 1-1.5 parts urea, 1-1.5 parts calcium chloride, 1-2 parts alkaline admixture, and 4-5 parts straw biochar.

[0007] Furthermore, the alkaline admixture includes magnesium oxide and / or lignin fibers.

[0008] Furthermore, the microbial composite particles comprise the following components in parts by weight: 3-4 parts of Pseudomonas aeruginosa, 10-12 parts of starch, and 13-15 parts of peanut cake powder.

[0009] Furthermore, the method for preparing the microbial composite particles includes the following steps:

[0010] After mixing Pseudomonas aeruginosa, starch and peanut cake powder evenly, the mixture was granulated at low temperature to obtain the microbial contents.

[0011] The microbial composite particles are obtained by spraying a carboxymethyl cellulose solution onto the contents of the microorganisms and then drying them.

[0012] Furthermore, the particle size of the granulation is 0.8–1.0 mm; and the concentration of the carboxymethyl cellulose solution is 4–6 wt.%.

[0013] Furthermore, the method for preparing the urease solution includes the following steps:

[0014] After crushing soybeans, add them to water, stir, let stand, centrifuge, and filter to obtain the urease solution.

[0015] Furthermore, the method for preparing the straw biochar includes the following steps:

[0016] Rice straw is crushed, calcined, and ground to obtain straw biochar (nanoscale).

[0017] The second technical solution of the present invention: a method for preparing the above-mentioned microbially modified red clay, comprising the following steps:

[0018] After mixing red clay, gypsum, microbial composite particles, alkaline admixtures and straw biochar evenly, a mixture of urea, calcium chloride, sodium aluminate and urease solution is sprayed on, and the mixture is stirred evenly and then cured to obtain microbially improved red clay.

[0019] Furthermore, the curing temperature is 18–22°C, and the curing time is 6–8 days.

[0020] Urease solution can decompose urea to produce free CO3. 2- The role of free CO3 2- It reacts with calcium ions to form calcite-type calcium carbonate crystals (EICP reaction), which can improve the unconfined compressive strength of soil.

[0021] Magnesium oxide possesses characteristics such as large surface area and excellent dispersibility. When added to soil, it rapidly undergoes physical and chemical reactions with soil particles, forming strong polycrystalline aggregates at the soil particle interface, thereby enhancing the unconfined compressive strength of the soil. Furthermore, magnesium oxide can provide nucleation sites for the EICP reaction, solving the problem that the lack of nucleation sites in the EICP reaction leads to a large portion of calcium carbonate crystals forming independently in the interstitial space without fully binding with soil particles.

[0022] Magnesium oxide (MgO) is an octahedron with uniform and small inter-radii of cations and anions, giving it strong adsorption properties. Upon entering the soil, free water is rapidly adsorbed, becoming adsorbed water on the surface of the MgO particles. This causes a rapid decrease in soil moisture content, significantly increasing the soil's unconfined compressive strength. Secondly, at room temperature, MgO reacts with carbon dioxide and water to form basic magnesium carbonate, creating a slightly alkaline environment in the soil. This slightly alkaline environment is conducive to EICP (enzyme-induced calcium carbonate) reactions, further enhancing the soil's unconfined compressive strength. Simultaneously, free magnesium ions have the ability to replace sodium ions or other low-valent cations in soil particles (ion exchange reactions promote the aggregation of smaller soil particles into larger aggregates, reducing small voids and making the connections between soil particles tighter, thus limiting particle porosity). This limitation of inter-particle porosity is beneficial for the improvement of red clay. Furthermore, the microbial method for improving red clay generates a large number of carbonate ions during the mineralization process, which preferentially react with free divalent cations in the soil to form carbonate precipitates. Furthermore, due to the presence of biochar and mineral products, some free sodium ions and other low-valence cations will also be adsorbed and fixed, thereby further enhancing the unconfined compressive strength of the soil.

[0023] Soils are generally slightly acidic, and the pH changes resulting from a series of reactions within the soil affect the degree of hydroxyl dissociation in clay. As pH increases, the degree of hydroxyl dissociation increases, leading to a higher net negative charge, a thicker electrical double layer on soil particle surfaces, and enhanced stability of soil aggregates. This results in the formation of strong polycrystalline aggregates within soil particles, and the increased interparticle bonding strength leads to increased unconfined compressive strength. Magnesium oxide can create a slightly alkaline environment, raising the soil pH and thus increasing its unconfined compressive strength.

[0024] Lignin fiber has stable physicochemical properties and can be solidified into a whole with soil. At the same time, the surface of lignin fiber contains many micropores, which can provide calcium carbonate with sufficient nucleation sites. After solidification, it will gradually polymerize to form cross-linked network polymer chains, which will wrap and connect soil particles and fill the gaps between the particles, thereby improving the unconfined compressive strength of the soil.

[0025] Urease solution rapidly acidifies at room temperature, leading to a decline in activity. Therefore, it is not conducive to providing free CO3 for sustained reactions. 2- Adding microbial composite particles that can produce urease at the same time as urease can continue to provide urease after the activity of urease solution decays, thereby increasing the amount of calcium carbonate crystals generated and thus improving the unconfined compressive strength of the soil.

[0026] Microorganisms can be made into microbial composite particles to improve their survival rate and vitality in the soil, thereby enhancing their ability to produce urease.

[0027] The reaction between gypsum and sodium aluminate can produce ettringite needle-like crystals. These crystals interpenetrate, embed, and interweave with soil particles, reducing the average pore size and enhancing the connection between particles. This results in a denser soil structure, reduced porosity, and impeded water entry, thus avoiding the adverse effects of high soil water sensitivity (improving soil water stability) and enhancing the unconfined compressive strength of the soil.

[0028] Straw biochar has impermeability. When mixed into the soil, it can not only reduce soil porosity and make the soil structure more compact, but also reduce soil moisture content, thus preventing cracking caused by the soil absorbing and losing a lot of water.

[0029] The third technical solution of the present invention: an application of the above-mentioned microbially modified red clay as a roadbed material.

[0030] The present invention discloses the following technical effects:

[0031] The unconfined compressive strength of the microbially modified red clay of this invention reaches 1.27-1.29 MPa, which can be used as a roadbed material, overcoming the technical prejudice that red clay cannot be used in highway engineering.

[0032] The method of the present invention can improve the structure of red clay, reduce pores, fill the pores of red clay, further reduce the liquid limit index and plasticity of red clay, improve the unconfined compressive strength of red clay, and significantly improve the road performance of the soil. Detailed Implementation

[0033] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0034] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0035] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0036] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0037] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0038] In the following examples, "parts" refers to "parts by weight".

[0039] The red clay used in this invention was taken from the construction site of the Yanshan Campus of Guilin University of Technology in Guilin City. After being dried, it was sieved through a 2mm sieve and its basic physical properties were measured (see Table 1).

[0040] Table 1 Basic physical properties of red clay

[0041]

[0042] The magnesium oxide used in this invention is light magnesium oxide, which is a white, loose, amorphous powder. Compared with heavy magnesium oxide, it has more active chemical properties and is resistant to high temperatures. Its basic physical properties are shown in Table 2.

[0043] Table 2 Basic physical properties of magnesium oxide

[0044] 95.12％ 10.3 Slightly soluble in water <![CDATA[56.72m 2 / g]]>

[0045] The lignin fiber used in this invention is M-2 type pure poplar wood fiber, which is beige and has certain high temperature resistance, acid and alkali resistance and frost resistance. It is chemically inert and is a green material. Its basic physical properties are shown in Table 3.

[0046] Table 3 Basic physical properties of lignin fibers

[0047] ≥98％ 7～9 Slightly soluble in water 60 mesh 98％

[0048] The method for preparing urease solution used in this invention is as follows:

[0049] Commercially available white-navel soybeans were pulverized using a multi-purpose mill (Naio AQ-180E) and passed through a 100-mesh sieve to obtain soybean flour. The soybean flour was added to distilled water to prepare a soybean flour solution with a concentration of 70 g / L. The soybean flour solution was then placed on an electromagnetic stirrer and stirred for 30 minutes. It was then left to stand in a refrigerator at 4°C for 2 hours. Next, it was centrifuged in a high-speed centrifuge at a speed of 4000 r / min for 30 minutes. Finally, it was passed through an 80-mesh geotextile to obtain a soybean urease solution.

[0050] The *Pseudomonas aeruginosa* and *Actinomyces* used in this invention were commercially available, and the bacterial count of *Pseudomonas aeruginosa* was 1.0 × 10⁻⁶. 9 The cfu / g concentration of actinomycetes was 1.0 × 10⁻⁶. 9 cfu / g.

[0051] Urease activity assay: According to Whiffin's research, the change in conductivity is linearly positively correlated with urease activity. Urease activity can be expressed as the amount of urea hydrolyzed per unit time, and the unit of urease activity is also the amount of urea hydrolyzed per unit time (mmol·min). -1 This invention involves mixing soybean urease solution with 27 mL of 1 mol / L urea solution to test conductivity. The conductivity of the mixed solution is recorded at the 1st and 8th minutes, and the urease activity is calculated using the following formula (average of three measurements):

[0052] U=(t8-t1)×11.11×10 / (7×1000)

[0053] Where U represents urease activity, in mmol·min -1 1 μS·min -1 The change in conductivity corresponds to 11.11 μmol·min. -1 ; 10 represents the dilution factor; t8 is the conductivity after 8 minutes of reaction, and t1 is the conductivity after 1 minute of reaction; 7 represents the time interval difference, i.e., t8-t1. The calculated urease activity of the soybean urease solution prepared according to this invention is 11.96 mmol·min⁻¹. -1 (Reference value for urease activity extracted from 70g / L soybean).

[0054] The method for preparing straw biochar used in this invention is as follows:

[0055] Rice straw was crushed to 100 mesh and then calcined at 500℃ for 3 hours to obtain biochar particles. The biochar particles were then added to water and wet-milled until the particle size was ≤100nm. After drying, straw biochar was obtained.

[0056] Example 1

[0057] A method for preparing microbially modified red clay:

[0058] The improved red clay is composed of the following raw materials in parts by weight: 100 parts red clay, 1.2 parts gypsum, 0.5 parts sodium aluminate, 0.4 parts microbial composite particles, 6 parts urease solution, 1.5 parts urea, 1.5 parts calcium chloride, 2 parts alkaline admixture (magnesium oxide), and 5 parts straw biochar.

[0059] Preparation of microbial composite particles: 4 parts of Pseudomonas aeruginosa, 10 parts of starch and 15 parts of peanut cake powder were mixed evenly and granulated at low temperature (around 30℃) (particle size of 0.8 mm) to obtain microbial contents; a 6 wt.% carboxymethyl cellulose solution (mass / volume ratio of microbial contents to carboxymethyl cellulose solution of 15 g: 2 mL) was sprayed onto the microbial contents and dried at low temperature to obtain microbial composite particles.

[0060] Preparation of improved red clay:

[0061] (1) Mix red clay, gypsum, microbial composite particles, alkaline admixture and straw biochar evenly to obtain a mixed soil sample.

[0062] (2) Add urea, calcium chloride and sodium aluminate to 15 parts of water and mix evenly. Then add urease solution and mix evenly to obtain cement solution.

[0063] (3) Spray the cementing liquid evenly onto the mixed soil sample, mix evenly, and then press it statically with a compaction degree of 96% to obtain a sample with a diameter of 39.1 mm and a height of 80 mm. Place it in a curing box for curing (curing temperature set at 20±2℃, humidity ≥95%) for 7 days to obtain the improved red clay sample.

[0064] Example 2

[0065] A method for preparing microbially modified red clay:

[0066] The improved red clay is composed of the following raw materials in parts by weight: 100 parts red clay, 1 part gypsum, 0.4 parts sodium aluminate, 0.5 parts microbial composite particles, 5 parts urease solution, 1 part urea, 1 part calcium chloride, 1 part alkaline admixture (lignin fiber), and 4 parts straw biochar.

[0067] Preparation of microbial composite particles: 3 parts of Pseudomonas aeruginosa, 12 parts of starch and 13 parts of peanut cake powder were mixed evenly and granulated at low temperature (around 30℃) (particle size of 1.0 mm) to obtain microbial contents; a 4 wt.% carboxymethyl cellulose solution (mass / volume ratio of microbial contents to carboxymethyl cellulose solution of 15 g: 2 mL) was sprayed onto the microbial contents and dried at low temperature to obtain microbial composite particles.

[0068] Preparation of improved red clay: Same as in Example 1.

[0069] Example 3

[0070] Same as Example 1, except that the alkaline admixture is composed of magnesium oxide and lignin fiber in a mass ratio of 1:1.

[0071] Preparation of improved red clay: Same as in Example 1.

[0072] Comparative Example 1

[0073] Same as Example 1, except that the addition of gypsum, sodium aluminate, microbial composite particles and straw biochar is omitted.

[0074] Improved red clay is composed of the following raw materials in parts by weight: 100 parts red clay, 6 parts urease solution, 1.5 parts urea, 1.5 parts calcium chloride, and 2 parts alkaline admixture (magnesium oxide).

[0075] Preparation of improved red clay:

[0076] (1) After mixing the red clay and alkaline admixture evenly, a mixed soil sample is obtained.

[0077] (2) Add urea and calcium chloride to 15 parts of water and mix well. Then add urease solution and mix well to obtain cemented liquid.

[0078] (3) Spray the cementing liquid evenly onto the mixed soil sample, mix evenly, and then press it statically with a compaction degree of 96% to obtain a sample with a diameter of 39.1 mm and a height of 80 mm. Place it in a curing box for curing (curing temperature set at 20±2℃, humidity ≥95%) for 7 days to obtain the improved red clay sample.

[0079] Comparative Example 2

[0080] Same as Example 1, except that the addition of gypsum, sodium aluminate, microbial composite particles and straw biochar is omitted, and magnesium oxide is replaced with lignin fiber.

[0081] Improved red clay is composed of the following raw materials in parts by weight: 100 parts red clay, 6 parts urease solution, 1.5 parts urea, 1.5 parts calcium chloride, and 2 parts alkaline admixture (lignin fiber).

[0082] Preparation of improved red clay:

[0083] (1) After mixing the red clay and alkaline admixture evenly, a mixed soil sample is obtained.

[0084] (2) Add urea and calcium chloride to 15 parts of water and mix well. Then add urease solution and mix well to obtain cemented liquid.

[0085] (3) Spray the cementing liquid evenly onto the mixed soil sample, mix evenly, and then press it statically with a compaction degree of 96% to obtain a sample with a diameter of 39.1 mm and a height of 80 mm. Place it in a curing box for curing (curing temperature set at 20±2℃, humidity ≥95%) for 7 days to obtain the improved red clay sample.

[0086] Comparative Example 3

[0087] Same as Example 1, except that the addition of gypsum, sodium aluminate, microbial composite particles, straw biochar and alkaline admixture is omitted.

[0088] Improved red clay is composed of the following raw materials in parts by weight: 100 parts red clay, 6 parts urease solution, 1.5 parts urea, and 1.5 parts calcium chloride.

[0089] Preparation of improved red clay:

[0090] (1) Add urea and calcium chloride to 15 parts of water and mix evenly. Then add urease solution and mix evenly to obtain a cementing solution.

[0091] (2) The cementing liquid was sprayed evenly onto the mixed soil sample. After mixing evenly, it was statically pressed with a compaction degree of 96% to obtain a sample with a diameter of 39.1 mm and a height of 80 mm. The sample was placed in a curing box for curing (curing temperature set at 20±2℃, humidity ≥95%) for 7 days to obtain the improved red clay sample.

[0092] Comparative Example 4

[0093] Same as Example 1, except that the addition of straw biochar is omitted and the amount of gypsum is increased to 6.2 parts.

[0094] Improved red clay is composed of the following raw materials in parts by weight: 100 parts red clay, 6.2 parts gypsum, 0.5 parts sodium aluminate, 0.4 parts microbial composite particles, 6 parts urease solution, 1.5 parts urea, 1.5 parts calcium chloride, and 2 parts alkaline admixture (magnesium oxide).

[0095] Preparation of improved red clay:

[0096] (1) Mix red clay, gypsum, microbial composite particles and alkaline admixture evenly to obtain a mixed soil sample.

[0097] (2) Add urea, calcium chloride and sodium aluminate to 15 parts of water and mix evenly. Then add urease solution and mix evenly to obtain cement solution.

[0098] (3) Spray the cementing liquid evenly onto the mixed soil sample, mix evenly, and then press it statically with a compaction degree of 96% to obtain a sample with a diameter of 39.1 mm and a height of 80 mm. Place it in a curing box for curing (curing temperature set at 20±2℃, humidity ≥95%) for 7 days to obtain the improved red clay sample.

[0099] Comparative Example 5

[0100] Same as Example 1, except that the addition of gypsum and sodium aluminate is omitted.

[0101] The improved red clay is composed of the following raw materials in parts by weight: 100 parts red clay, 0.4 parts microbial composite particles, 6 parts urease solution, 1.5 parts urea, 1.5 parts calcium chloride, 2 parts alkaline admixture (magnesium oxide), and 5 parts straw biochar.

[0102] Preparation of improved red clay:

[0103] (1) Mix red clay, microbial composite particles, alkaline admixture and straw biochar evenly to obtain a mixed soil sample.

[0104] (2) Add urea and calcium chloride to 15 parts of water and mix well. Then add urease solution and mix well to obtain cemented liquid.

[0105] (3) Spray the cementing liquid evenly onto the mixed soil sample, mix evenly, and then press it statically with a compaction degree of 96% to obtain a sample with a diameter of 39.1 mm and a height of 80 mm. Place it in a curing box for curing (curing temperature set at 20±2℃, humidity ≥95%) for 7 days to obtain the improved red clay sample.

[0106] Comparative Example 6

[0107] Same as Example 1, except that the addition of microbial composite particles is omitted.

[0108] The improved red clay is composed of the following raw materials in parts by weight: 100 parts red clay, 1.2 parts gypsum, 0.5 parts sodium aluminate, 6 parts urease solution, 1.5 parts urea, 1.5 parts calcium chloride, 2 parts alkaline admixture (magnesium oxide), and 5 parts straw biochar.

[0109] Preparation of improved red clay:

[0110] (1) Mix red clay, gypsum, alkaline admixture and straw biochar evenly to obtain a mixed soil sample.

[0111] (2) Add urea, calcium chloride and sodium aluminate to 15 parts of water and mix evenly. Then add urease solution and mix evenly to obtain cement solution.

[0112] (3) Spray the cementing liquid evenly onto the mixed soil sample, mix evenly, and then press it statically with a compaction degree of 96% to obtain a sample with a diameter of 39.1 mm and a height of 80 mm. Place it in a curing box for curing (curing temperature set at 20±2℃, humidity ≥95%) for 7 days to obtain the improved red clay sample.

[0113] Comparative Example 7

[0114] Same as Example 1, except that the Pseudomonas aeruginosa in the microbial composite particles is replaced with an equal amount of actinomycetes.

[0115] Comparative Example 8

[0116] Same as Example 1, except that the addition of urease solution is omitted.

[0117] The improved red clay is composed of the following raw materials in parts by weight: 100 parts red clay, 1.2 parts gypsum, 0.5 parts sodium aluminate, 0.4 parts microbial composite particles, 1.5 parts urea, 1.5 parts calcium chloride, 2 parts alkaline admixture (magnesium oxide), and 5 parts straw biochar.

[0118] (1) Mix red clay, gypsum, microbial composite particles, alkaline admixture and straw biochar evenly to obtain a mixed soil sample.

[0119] (2) Add urea, calcium chloride and sodium aluminate to 15 parts of water and mix evenly to obtain a cementing solution.

[0120] (3) Spray the cementing liquid evenly onto the mixed soil sample, mix evenly, and then press it statically with a compaction degree of 96% to obtain a sample with a diameter of 39.1 mm and a height of 80 mm. Place it in a curing box for curing (curing temperature set at 20±2℃, humidity ≥95%) for 7 days to obtain the improved red clay sample.

[0121] Example 1

[0122] The unconfined compressive strength of the modified red clay prepared in Examples 1-3 and Comparisons 1-8 and cured for 7 days was determined, and the results are shown in Table 4.

[0123] The method for determining unconfined compressive strength is as follows:

[0124] Unconfined compressive strength tests were conducted using a laboratory universal testing machine. Axial pressure was applied to the prepared soil sample at a loading rate of 1 mm / min until the peak stress was reached. The test ended when the stress decreased steadily or the sample completely broke, and the data were exported. This experiment was used to determine the compressive strength characteristics of the soil sample under vertical pressure only, simulating the ideal condition of modified red clay as a foundation.

[0125] Table 4 Unconfined compressive strength

[0126] Example 1 1.28 Example 2 1.26 Example 3 1.27 Comparative Example 1 0.55 Comparative Example 2 0.50 Comparative Example 3 0.36 Comparative Example 4 1.22 Comparative Example 5 1.18 Comparative Example 6 1.15 Comparative Example 7 1.22 Comparative Example 8 1.01

[0127] The above data are the average values ​​of three repeated experiments.

[0128] Example 2

[0129] The liquid limit and plasticity index of the improved red clay prepared in Examples 1-3 and Comparative Examples 1-8 and cured for 7 days were determined according to the geotechnical testing standard GBT50123-2019. The results are shown in Table 5.

[0130] Table 5 Liquid Limit and Plasticity Index

[0131]

[0132]

[0133] As can be seen from Tables 4 and 5, the method of the present invention can reduce the liquid limit and plasticity index of red clay, improve the unconfined compressive strength of red clay, and enable red clay to be used as a roadbed material.

[0134] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A microbial-modified red clay, characterized in that, The raw materials include the following parts by weight: 100 parts red clay, 1-1.2 parts gypsum, 0.3-0.5 parts sodium aluminate, 0.3-0.5 parts microbial composite granules, 5-8 parts urease solution, 1-1.5 parts urea, 1-1.5 parts calcium chloride, 1-2 parts alkaline admixture, and 4-5 parts straw biochar; The alkaline admixture includes magnesium oxide and / or lignin fibers; The microbial composite particles comprise the following components in parts by weight: 3-4 parts of Pseudomonas aeruginosa, 10-12 parts of starch, and 13-15 parts of peanut cake powder; The method for preparing the microbial composite particles includes the following steps: After mixing Pseudomonas aeruginosa, starch and peanut cake powder evenly, the mixture is granulated at about 30°C to obtain the microbial contents. The microbial composite particles are obtained by spraying carboxymethyl cellulose solution onto the contents of the microorganisms and then drying them. The method for preparing the urease solution includes the following steps: After crushing soybeans, add them to water, stir, let stand, centrifuge, and filter to obtain the urease solution. The method for preparing the straw biochar includes the following steps: Rice straw is crushed, calcined, and ground to obtain straw biochar.

2. The microbially modified red clay according to claim 1, characterized in that, The granulation process produces particles with a diameter of 0.8–1.0 mm; the concentration of the carboxymethyl cellulose solution is 4–6 wt.%.

3. A method for preparing microbially modified red clay according to any one of claims 1 to 2, characterized in that, Includes the following steps: After mixing red clay, gypsum, microbial composite particles, alkaline admixtures and straw biochar evenly, a mixture of urea, calcium chloride, sodium aluminate and urease solution is sprayed on, and the mixture is stirred evenly and then cured to obtain microbially improved red clay.

4. The preparation method according to claim 3, characterized in that, The curing temperature is 18–22℃, and the time is 6–8 days.

5. The application of the microbially modified red clay as described in any one of claims 1 to 2 as a roadbed material.

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