Magnetic field-microorganism reinforcing method for steel slag gravel road base, reinforcing strength model and construction method of reinforcing strength model

Abstract

The invention belongs to the field of road engineering, and particularly relates to a magnetic field-microorganism reinforcing method for a steel slag gravel road base, a reinforcing strength model and a construction method of the reinforcing strength model. The reinforcement method comprises the following steps: firstly, soaking the steel slag broken stones by using a solution containing bacillus alcalophilus, then paving the steel slag broken stones on a roadbed, and applying a constant magnetic field; the reinforcement strength model comprises a prediction model of a vertical rebound modulus E1 and a prediction model of anisotropy coefficients gamma 1 and gamma 2; the construction method of the reinforcement strength model comprises the following steps: according to a variable confining pressure dynamic triaxial test result, then analyzing the result, obtaining fitting results of fitting parameters k1 and k2 and anisotropy coefficients gamma 1 and gamma 2 under different bacterial liquid concentrations and magnetic field intensities, and constructing a prediction model. The invention provides a novel treatment method for free calcium oxide and free magnesium oxide in steel slag macadam. The reinforcement strength model provides a tool which is high in cost benefit, simple and convenient to operate and accurate in prediction, so that the design and application of the steel slag gravel as a road base material are supported.

Description

Technical Field

[0001] The invention belongs to the technical field of road materials, and in particular relates to a magnetic field-microorganism reinforcement method for a steel slag and gravel road base, a reinforcement strength model and a construction method thereof. Background Art

[0002] In the field of road engineering, the selection of base materials is crucial to ensure the bearing capacity and durability of road structures. Granular bases such as graded crushed stone and graded gravel without any binder are flexible bases. Studies have shown that steel slag crushed stone can be used as an unbonded granular base material and a substitute for general mineral graded crushed stone for the subbase of roads due to its high strength and good angularity. However, untreated steel slag crushed stone has significant volume stability problems, which limits its direct application in road engineering. The main reason is that the free calcium oxide (f-CaO) and free magnesium oxide (f-MgO) contained in the steel slag will undergo hydration reaction when exposed to water, causing volume expansion, resulting in structural cracking or even damage.

[0003] At present, the main methods for treating steel slag include aging, hydrothermal pretreatment, digestion with additives, etc. Aging is the process of carbonation reaction between carbon dioxide and steel slag, but if natural aging is carried out by stacking, it takes a long time; if hydrothermal method is used to accelerate aging, special steel slag hot stewing equipment is required; and the additives used in the digestion with additives in the prior art are mostly complex in composition, which increases the cost of steel slag treatment to a certain extent.

[0004] In addition, the dynamic behavior of steel slag crushed stone also plays a very important role in the stability and durability of the pavement structure. Existing studies have shown that the mechanical response of steel slag crushed stone under cyclic loads exhibits nonlinear elastic characteristics, and its dynamic rebound modulus has significant differences in different directions, making the pavement stress calculation results in the specifications unsafe. At present, the dynamic rebound modulus of crushed stone materials is mainly obtained by dynamic triaxial testing. The equipment is expensive, complex to operate, and time-consuming, which brings inconvenience to the evaluation of base performance and pavement structure design.

[0005] In terms of the strength prediction of crushed stone materials, existing technologies often fail to fully consider the orthotropic characteristics of materials when evaluating crushed stone pavement bases, that is, the mechanical properties of materials in different directions are different. This neglect limits the accurate prediction of material properties and the precision of engineering design, which may lead to improper design and underutilization of material properties. Summary of the invention

[0006] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a magnetic field-microorganism reinforcement method for steel slag crushed stone road base, a reinforcement strength model and a construction method thereof. The present invention is proposed based on an in-depth analysis of the prior art and a comprehensive understanding of the characteristics of steel slag crushed stone materials, and aims to fully utilize the potential of microorganisms to induce calcium carbonate precipitation through a new method, and at the same time, through the application of a magnetic field, to achieve precise control of the reinforcement process, and at the same time, to construct a prediction model; it not only improves the mechanical properties of steel slag crushed stone, but also provides a more accurate and economical solution for road engineering design, and opens up a new technical approach for the application of steel slag crushed stone in road engineering.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention proposes a magnetic field-microorganism reinforcement method for a steel slag and gravel road base, comprising the following steps:

[0009] Step (i) Material preparation: prepare steel slag and crushed stone according to the road base grading requirements; prepare alkaliphilic Bacillus liquid;

[0010] Step (ii) carbonization pretreatment of steel slag gravel by soaking method: steel slag gravel, sodium bicarbonate, urea, bacterial solution and water are mixed according to the designed proportion and put into the curing tank, so that the bacterial solution fully soaks the steel slag gravel to obtain pretreated steel slag gravel, which is recorded as steel slag S;

[0011] Step (iii) drying the steel slag S to an optimum moisture content, and then spreading it on the roadbed to form a cushion layer; rolling the cushion layer flat until the compaction, flatness and deflection values ​​reach the set standards; applying a constant magnetic field to the cushion layer while rolling; the intensity of the constant magnetic field is 0.02T to 0.08T, and the application time of the constant magnetic field is 0.5 to 1.0h; and curing for more than 7 days after the constant magnetic field treatment.

[0012] Furthermore, in step (ii), the concentration of sodium bicarbonate is 0.8-1.2 mol / L, the concentration of urea is 1.8-2.2 mol / L, and the amount of bacterial solution is 10 mg / L-25 mg / L; the steel slag gravel is completely immersed in the mixture of sodium bicarbonate, urea, bacterial solution and water for more than 24 hours.

[0013] Furthermore, the preparation process of the alkaliphilic bacillus bacterial liquid is as follows: peptone, beef extract and agar powder are added in proportion to 0.85 volume parts of deionized water, the mixture is stirred evenly and then sterilized to obtain liquid A; deionized water is added to 3-cyclohexylaminopropanesulfonic acid to dilute the mixture to 0.15 volume parts, the mixture is stirred evenly and then sterilized to obtain liquid B, wherein the concentration of 3-cyclohexylaminopropanesulfonic acid in the liquid B is 39-45 g / L; the liquid A and the liquid B are fully mixed and then poured into a culture dish, 2.0-2.2 volume percent of alkaliphilic bacillus H4 and 2.0-2.2 mol / L of urea are added in sequence, the mixture is cultured at a constant temperature of 35°C for 48 hours and then used for standby use, to obtain an alkaliphilic bacillus bacterial liquid with an OD600 value of 0.8-1.2.

[0014] The magnetic field-microorganism reinforcement method for the steel slag gravel base proposed in the present invention has no previous experience, and there is no ready-made strength estimation model or empirical value for reference. This results in the need for road designers and construction personnel to make and test steel slag gravel road base specimens many times when optimizing the reinforcement parameters of the steel slag gravel base in actual construction, which is inconvenient. Therefore, the present invention also proposes a magnetic field-microorganism reinforcement strength model construction method and the constructed model that are compatible with the above-mentioned magnetic field-microorganism reinforcement method, so as to facilitate designers and construction personnel to quickly learn the strength index of the current modified steel slag graded gravel base.

[0015] A method for constructing a magnetic field-microorganism reinforcement strength model for a steel slag and gravel road base comprises the following steps:

[0016] Step 1: Material preparation: prepare steel slag and crushed stone according to the road base grading requirements; prepare alkaliphilic Bacillus liquid;

[0017] Step 2: Carbonization pretreatment of steel slag gravel is performed by soaking method: steel slag gravel, sodium bicarbonate, urea, bacterial solution and water are mixed according to the experimental design ratio and placed in different curing tanks for mixing, so that the steel slag gravel is fully soaked in bacterial solution of different concentrations, and several groups of pretreated steel slag gravel are obtained, which are recorded as steel slag A;

[0018] Step 3: according to the optimum moisture content and the maximum dry density, the pre-treated steel slag graded gravel is poured into the curing mold, and statically pressed in three layers to obtain the specimen A; the specimen A is treated with constant magnetic fields of different intensities, and the constant magnetic field treatment is applied for 0.5 to 1.0 hours. The specimen A is cured for more than 48 hours to obtain several groups of specimens B;

[0019] Step 4: Perform variable confining pressure dynamic triaxial test on specimen B, and obtain the test results of different groups of specimens B respectively; perform linear fitting on the variable confining pressure dynamic triaxial test to establish the vertical rebound modulus E 1 prediction models;

[0020] Step 5: In order to quantify the strength anisotropy of slag-graded crushed stone, define the anisotropy coefficient γ1 is the horizontal modulus E 3 The vertical elastic modulus E 1 The ratio of ; define the anisotropy coefficient γ 2 is the shear modulus G and the vertical elastic modulus E 1 The ratio of

[0021]

[0022]

[0023] In the formula, E 1 is the vertical elastic modulus; E 3 is the horizontal modulus, which can be obtained by linear programming by using the dynamic triaxial test results and the orthogonal anisotropic characteristic model; G is the shear modulus, μ 13 is the Poisson's ratio of the vertical to the horizontal direction;

[0024] According to the results of the variable confining pressure dynamic triaxial test, the anisotropy coefficient γ of specimen B under different bacterial solution concentrations and magnetic field intensities was obtained. 1 and γ 2 ; Then, the anisotropy coefficient γ is obtained through linear fitting 1 and γ 2 prediction models;

[0025] The magnetic field-microbial reinforcement strength model of steel slag gravel road base includes the vertical rebound modulus E 1 The prediction model and anisotropy coefficient γ 1 and the anisotropy coefficient γ 2 prediction model.

[0026] Furthermore, in step 4, the vertical rebound modulus E is established 1 The prediction model is:

[0027] E 1 =k 1 σ d +k 2 ;

[0028]

[0029] k 2 =3.8911×C B +426.92;

[0030] In the formula, k 1 is the fitting parameter, representing the vertical elastic modulus E 1 The rate of change of the fitting parameter k 2 , whose value mainly reflects the initial vertical rebound modulus of the steel slag crushed stone reinforced by magnetic field accelerated microorganisms; σ drepresents the deviatoric stress amplitude, C B is the bacterial solution concentration, in mg / L; S M is the magnetic field strength, unit is T.

[0031] Furthermore, it is characterized in that: in step 5, the steel slag crushed stone strength model obtained is:

[0032]

[0033] In the formula, C B is the bacterial solution concentration, in mg / L; S M is the magnetic field strength of the steady magnetic field, in T.

[0034] Furthermore, the fitting parameter k 1 , anisotropy coefficient γ 1 and γ 2 All were fitted by Poly12 linear model of Matlab software.

[0035] Furthermore, in step 4, the variable confining pressure dynamic triaxial test includes conventional triaxial compression, triaxial shear and triaxial tension, and 10 stress loading sequences are set for each test mode;

[0036] The variation law of vertical rebound modulus strength of specimen B under different bacterial solution dosages, constant magnetic field with different magnetic field strengths and deviatoric stress was analyzed; the bacterial solution dosage was 0-25 mg / L, the magnetic field strength of the constant magnetic field was 0-0.08 T, and the deviatoric stress was 60-80 kPa.

[0037] Furthermore, the maintenance mold includes a base with a cavity inside, a main mold matching the base, a permeable stone placed at the bottom of the main mold, and an upper hoop ring and a lower hoop ring tightly fixed to the outer periphery of the main mold; a plurality of drainage holes are opened on the top of the base, and the drainage holes are connected to the cavity inside the base, and a drainage pipe connecting the outside and the cavity is also arranged on the outer periphery of the base; the main mold includes 2-6 sub-molds assembled together; and a plurality of ventilation holes are opened on the main mold.

[0038] The working principle of the present invention is that in order to solve the problem of steel slag gravel swelling when exposed to water, the present invention applies the microbial induced calcium carbonate precipitation (MICP) technology to the carbonization treatment of steel slag to promote the formation of a calcium carbonate protective film on the surface of the steel slag, and help fill the gaps between the steel slag gravel, thereby improving its volume stability and structural layer strength. At the same time, the present invention introduces a magnetic field as an external physical stimulus to achieve precise control of the precipitation position and improve the reinforcement efficiency. Since the steel slag itself has certain electrical conductivity and magnetization characteristics, after applying a constant magnetic field, the intensity at the contact position of the steel slag gravel is relatively large, which helps to promote the attachment of microorganisms and the generation of calcium carbonate precipitation. The calcium carbonate crystals formed under the stimulation of this magnetic field gather at the contact position between the steel slag gravel to form a strong bond, thereby significantly improving the strength and stability of the steel slag gravel.

[0039] The beneficial effects of the present invention are:

[0040] (1) The present invention proposes a new method for treating free calcium oxide and free magnesium oxide in steel slag gravel. The steel slag gravel is treated by biologically induced calcium carbonate precipitation (MICP) technology, so that free calcium oxide and free magnesium oxide are combined with carbonate to form a coating layer on the surface of the steel slag gravel, thereby inhibiting the activity of free calcium oxide and free magnesium oxide. At the same time, the method utilizes the regulatory effect of the magnetic field on the metabolic activity of microorganisms and the calcium carbonate precipitation process, and can effectively regulate the degree of calcium carbonate precipitation in the steel slag gravel, promote the strength reinforcement of the steel slag gravel, enhance the bonding force between the gravel, improve its dynamic rebound modulus and structural strength, improve the overall mechanical properties of the material, and meet the bearing capacity requirements of the base material for road engineering; solve the hydration reaction and volume expansion problems caused by the free calcium oxide and magnesium oxide in the steel slag gravel when encountering water, significantly improve the volume stability of the material, and thus reduce the risk of engineering structure damage caused by material expansion.

[0041] (2) The magnetic field-microorganism reinforcement strength model of the steel slag gravel road base and its construction method of the present invention are intended to provide a cost-effective, easy-to-operate, and accurate prediction tool to support the design and application of steel slag gravel as a road base material. The reinforcement strength model is a strength prediction model for steel slag gravel road base. Aiming at the nonlinear modulus and orthogonal anisotropy characteristics of steel slag gravel, the present invention establishes the model, comprehensively considering the magnetic field intensity, microbial reinforcement conditions, and stress state, and is used to predict the dynamic rebound modulus and shear modulus of the steel slag gravel road base in the vertical and horizontal directions, so as to facilitate designers and construction personnel to quickly know the strength index of the current modified steel slag graded gravel base. Without conducting dynamic triaxial tests, it can provide road designers and construction personnel with a fast steel slag gravel road base strength estimation method, and can reversely determine the bacterial liquid concentration and magnetic field intensity suitable for road structure performance, greatly reducing the optimization cost of steel slag gravel materials and improving construction efficiency.

[0042] The strength model established in the present invention takes into account the microbial reinforcement conditions of the material and its orthogonal anisotropic characteristics, and can more accurately predict the mechanical properties of the steel slag crushed stone base in different directions. The existence of this model reduces the dependence on professional equipment and operators during actual construction, simplifies the test process, reduces costs, and helps to improve the reliability and safety of engineering design.

[0043] (3) The present invention improves the engineering application value of steel slag crushed stone, promotes the resource utilization and environmentally friendly utilization of industrial by-products, and conforms to the current development trend of sustainable development and circular economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. Among them:

[0045] Figure 1 It is a schematic structural diagram of a curing mold in an embodiment of the present invention.

[0046] Figure 2 It is a structural schematic diagram of the main mold in an embodiment of the present invention.

[0047] Figure 3 Schematic diagram of the structure of the vent hole in the embodiment of the present invention.

[0048] Figure 4 4 is a gradation curve diagram of steel slag crushed stone in an embodiment of the present invention.

[0049] Figure 5 This is a graph showing the results of the water swelling rate test in Example 1 of the present invention.

[0050] Figure 6 This is the relationship between the vertical rebound modulus and the deviatoric stress in Example 2 of the present invention.

[0051] Figure 7 is the fitting parameter k in Example 2 of the present invention 1 The prediction model fitting results.

[0052] Figure 8 is the fitting parameter k in Example 2 of the present invention 2 The prediction model fitting results.

[0053] Fig. 9 is the anisotropy coefficient γ in Example 2 of the present invention 1 Results vary with magnetic field strength.

[0054] Fig.10 is the anisotropy coefficient γ in Example 2 of the present invention 2 Results vary with magnetic field strength.

[0055] In the figure: 1-main mold, 2-upper hoop, 3-copper core enameled coil, 4-sample, 5-permeable stone, 6-drain pipe, 7-anchor bolt, 8-lower hoop, 9-base, 10-vent. DETAILED DESCRIPTION

[0056] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0057] A magnetic field-microorganism reinforcement method for a steel slag and gravel road base comprises the following steps:

[0058] Step (i) Material preparation: prepare steel slag and crushed stone according to the road base grading requirements; prepare alkaliphilic Bacillus liquid;

[0059] Step (ii) carbonization pretreatment of steel slag gravel by soaking method: steel slag gravel, sodium bicarbonate, urea, bacterial solution and water are mixed according to the designed proportion and put into the curing tank, so that the bacterial solution fully soaks the steel slag gravel to obtain pretreated steel slag gravel, which is recorded as steel slag S;

[0060] Step (iii) Dry the steel slag S to an optimum moisture content (or air dry or air dry the steel slag S, then add water to adjust it to an optimum moisture content), then spread it on the roadbed to form a cushion layer; roll the cushion layer flat until the compaction, flatness and deflection values ​​reach the set standards; apply a constant magnetic field with magnetic lines downward to the cushion layer while rolling; the intensity of the constant magnetic field is 0.02T to 0.08T, and the application time of the constant magnetic field is 0.5 to 1.0h; maintain for more than 7 days after the constant magnetic field treatment. In actual construction, a constant magnetic field is applied by hanging electromagnets or permanent magnets on the construction vehicle, or a special frame structure equipped with electromagnets or permanent magnets can be made to apply a constant magnetic field.

[0061] Furthermore, in step (ii), the concentration of sodium bicarbonate is 0.8-1.2 mol / L, the concentration of urea is 1.8-2.2 mol / L, and the amount of bacterial solution is 10 mg / L-25 mg / L; the steel slag and gravel are completely immersed in the mixed solution consisting of sodium bicarbonate, urea, bacterial solution and water, and the steel slag and gravel are soaked for more than 24 hours.

[0062] The preparation process of the alkaliphilic bacillus liquid is as follows: 3g of peptone, 10g of beef extract and agar powder are added in proportion to 0.85L of deionized water, the mixture is stirred evenly and then sterilized to obtain liquid A; deionized water is added to 3-cyclohexylaminopropanesulfonic acid to dilute the mixture to 0.15 volume parts, the mixture is stirred evenly and then sterilized to obtain liquid B, wherein the concentration of 3-cyclohexylaminopropanesulfonic acid CAPS in the liquid B is 44.3g / L or 0.2mol / L; the liquid A and the liquid B are fully mixed and then poured into a culture dish, 2.0-2.2% volume fraction of alkaliphilic bacillus H4 and 2.0-2.2mol / L of urea are added in sequence, the mixture is cultured at a constant temperature of 35°C for 48h and then used for standby, to obtain an alkaliphilic bacillus liquid with an OD600 value of 0.8-1.2;

[0063] There are two processes in the preparation of the alkaliphilic Bacillus liquid. One process is the expansion culture process of alkaliphilic Bacillus H4 to increase the number of alkaliphilic Bacillus H4. Studies have shown that in the high alkaline environment of steel slag, the enzyme activity of microorganisms will be maintained at a very low level and cannot grow and reproduce, which significantly reduces the amount of calcium carbonate generated; the alkaliphilic Bacillus H4 used in the present invention can survive in the high alkaline environment of steel slag, and the alkaliphilic Bacillus H4 is deposited in CGMCC NO.9629. The other process is to use urease reaction to decompose urea into carbonate, thereby accelerating the carbonization process of steel slag.

[0064] The base of the road structure provides a solid foundation for the entire pavement structure, and therefore requires high strength. Before actual construction, tests such as compaction degree and 7d unconfined compressive strength will be conducted to obtain the strength of the slag gravel base. However, the magnetic field-microorganism reinforcement method for the slag gravel base proposed in the present invention has no previous experience, and there is no ready-made strength estimation model or empirical value for reference. This results in the need for road designers and construction personnel to repeatedly make and test and compare slag gravel road base specimens when optimizing the reinforcement parameters of the slag gravel base in actual construction, which slows down the construction efficiency of the slag gravel road base. The existing repeated loading / variable confining pressure dynamic triaxial test equipment is costly, complicated to operate, and requires professional personnel to carry out, which limits its widespread use in engineering design and engineering applications.

[0065] In order to solve the above problems, the present invention also proposes a magnetic field-microbial reinforcement model of a steel slag gravel road base and its construction method that are compatible with the above reinforcement method, so as to facilitate designers and construction personnel to quickly obtain the strength index of the current modified steel slag graded gravel base.

[0066] A method for constructing a magnetic field-microorganism reinforcement strength model for a steel slag and gravel road base comprises the following steps:

[0067] Step 1: Material preparation: prepare steel slag and crushed stone according to the road base grading requirements; prepare alkaliphilic Bacillus liquid;

[0068] Step 2: Carbonization pretreatment of steel slag gravel is performed by soaking method: steel slag gravel, sodium bicarbonate, urea, bacterial solution and water are mixed according to the experimental design ratio and placed in different curing pools for mixing, so that the steel slag gravel is fully soaked in bacterial solution of different concentrations to obtain several groups of pretreated steel slag gravel, which are recorded as steel slag A; in order to ensure the accuracy of the model, the pretreated steel slag gravel needs to be naturally air-dried / air-dried until the quality does not change;

[0069] Step 3: Determine the optimum moisture content and maximum dry density of steel slag graded gravel through heavy compaction test; pour the pretreated steel slag graded gravel into the curing mold according to the optimum moisture content and maximum dry density, and statically press the pretreated gravel into three layers to obtain specimen A; treat specimen A with constant magnetic fields of different intensities, apply constant magnetic field treatment for 0.5 to 1.0 h, and cure specimen A for more than 48 h to obtain several groups of specimens B; the compaction of specimen A is displacement controlled in accordance with the Highway Geotechnical Test Code JTG3430-2020;

[0070] Step 4: Perform variable confining pressure dynamic triaxial test on specimen B, and obtain the test results of different groups of specimens B respectively; perform linear fitting on the variable confining pressure dynamic triaxial test to establish the vertical rebound modulus E 1 prediction models;

[0071] Step 5: In order to quantify the strength anisotropy of slag-graded crushed stone, define the anisotropy coefficient γ 1 is the horizontal modulus E 3 The vertical elastic modulus E 1 The ratio of; define the anisotropy coefficient γ 2 is the shear modulus G and the vertical elastic modulus E 1 The ratio of

[0072]

[0073] In the formula, E 1 is the vertical elastic modulus; E 3 is the horizontal modulus, which can be obtained by linear programming by using the dynamic triaxial test results and the orthogonal anisotropic characteristic model; G is the shear modulus, μ 13 is the Poisson's ratio of the vertical to the horizontal direction;

[0074] According to the results of the variable confining pressure dynamic triaxial test, the anisotropy coefficient γ of steel slag crushed stone under different bacterial liquid concentrations and magnetic field intensities was obtained. 1 and γ 2 ; Then, the anisotropy coefficient γ is obtained through linear fitting 1 and γ 2The dynamic rebound modulus reflects the elastic recovery ability of the material under dynamic load, and the anisotropy coefficient describes the difference in plastic behavior of the material in different directions. These two parameters together constitute a comprehensive description of the mechanical properties of the material. Therefore, the present invention uses the rebound modulus E 1 The prediction model and anisotropy coefficient γ 1 and γ 2 The prediction models are collectively referred to as the magnetic field-microbial reinforcement strength model of steel slag gravel road base.

[0075] like Figures 1 to 3 As shown, the curing mold includes a base 9 with a cavity inside, a main mold 1 matched with the base 9, a permeable stone 5 placed at the bottom of the main mold 1, an upper hoop ring 2 and a lower hoop ring 8 tightly fixed to the outer periphery of the main mold 1, and the upper hoop ring 2 and the lower hoop ring 8 are respectively locked by anchor bolts 7 and nuts matched therewith; a plurality of drainage holes are provided on the top of the base 9, and the drainage holes are connected to the cavity inside the base 9. A drainage pipe 6 connecting the outside and the cavity is also provided on the outer periphery of the base 9; the main mold 1 includes 2-6 sub-molds that are spliced ​​together; and a plurality of ventilation holes 10 are provided on the main mold 1. In this embodiment, the main mold 1 includes 2 sub-molds, that is, the main mold 1 adopts a split mold design for easy disassembly. The curing mold can be made of cast iron or stainless steel, etc., and the mold strength is relatively high. At the same time, in order to facilitate demolding and promote the growth of microorganisms and the formation of calcium carbonate precipitation, taking into account the structural strength of the mold, ventilation holes 10 are provided on the surface of the mold, such as Figure 2 , Figure 3 As shown, the diameter of the vent hole 10 is 2 cm and the spacing is 50 cm. When in use, first assemble the curing mold, put the permeable stone 5 at the bottom, pour the pre-treated steel slag graded crushed stone into the curing mold according to the optimal water content and maximum dry density, and statically press the mold in three layers to obtain the sample 4.

[0076] Example 1

[0077] This embodiment will refer to the accompanying drawings and combine with the embodiments to explain in detail the technical effect of the magnetic field-microorganism reinforcement method for steel slag and gravel road base of the present invention, specifically through a water immersion expansion rate test.

[0078] The water expansion rate test of the magnetic field-microorganism reinforcement method of the steel slag crushed stone road base is carried out indoors and includes the following steps:

[0079] Step 1: Material preparation:

[0080] The steel slag used in the present invention comes from the cold steel slag produced by a steel plant in Henan Province, and its chemical composition is shown in Table 1. The collected steel slag crushed stone has been placed in the open air for about one month without aging treatment. The steel slag crushed stone is brown-gray in color and has obvious holes on the surface. The particle size is between 0 and 26.5 mm. Among them, the average apparent density of the steel slag crushed stone is about 3.246 g / cm 3 In addition, the particle size distribution of slag graded crushed stone is as follows Figure 1 As shown, it meets the specification limit requirements of "Steel Slag Stability Test Method" GB / T 24175-2009.

[0081] Table 1 Chemical composition of steel slag crushed stone in the embodiment

[0082] <![CDATA[Fe 2 THE 3 ]]> CaO <![CDATA[SiO 2 ]]> MgO MnO <![CDATA[Al 2 THE 3 ]]> <![CDATA[P 2 THE 5 ]]> <![CDATA[Na 2 The]]> other Alkalinity 22.15％ 38.75％ 16.44％ 7.51％ 5.60％ 3.76％ 1.82％ 1.23％ 2.74％ 2.36

[0083] Prepare alkaliphilic Bacillus liquid: add 3g peptone, 10g beef extract and appropriate amount of agar powder (liquid A) to 0.85L deionized water, stir evenly and sterilize; similarly, add deionized water to 3-cyclohexylaminopropanesulfonic acid CAPS and dilute to 0.15L (liquid B), and sterilize; mix liquid A and liquid B thoroughly and pour into a culture dish, add 2% volume fraction of alkaliphilic Bacillus H4 and 2mol / L urea in sequence, and culture at a constant temperature of 35°C for 48h for standby use. According to experimental determination, the OD600 value of the bacterial liquid concentration used in this embodiment is about 1.0. Peptone and beef extract provide nutrients for the growth of bacteria; 3-cyclohexylaminopropanesulfonic acid is mainly used to adjust the pH value of the culture medium in microbial culture to ensure that microorganisms reproduce in an ideal growth environment.

[0084] Step ② uses the immersion method to carbonize the steel slag and gravel:

[0085] Steel slag gravel, sodium bicarbonate, urea, bacterial solution and water are mixed according to the designed proportion and put into the curing tank, so that the bacterial solution can fully soak the steel slag gravel to obtain pretreated steel slag gravel, which is recorded as steel slag S. In this embodiment, 1 mol / L of sodium bicarbonate and 2 mol / L of urea are added to the reaction solution, and the bacterial solution dosage is designed to be 5 kinds, namely 0 mg / L, 10 mg / L, 15 mg / L, 20 mg / L and 25 mg / L.

[0086] Step 3: Compaction and maintenance of slag graded gravel specimens:

[0087] Through heavy compaction tests, the optimum moisture content and maximum dry density of slag graded crushed stone were determined to be 7.7% and 2.593 g / cm 3; Adjust the moisture content of steel slag S, pour the pre-treated steel slag graded crushed stone into the curing mold according to the optimum moisture content and maximum dry density, and statically press the pre-treated steel slag into three layers to obtain specimens A; the specimen size is 100 mm × 200 mm; use constant magnetic field treatments of different intensities to treat the specimens A, apply constant magnetic field treatment for 0.5 h, and the magnetic field intensities are 0 T, 0.02 T, 0.04 T, 0.06 T and 0.08 T, respectively, and then these specimens A are cured for more than 48 h to obtain several groups of specimens B;

[0088] Step ④ Evaluation of carbonization effect of steel slag graded crushed stone:

[0089] With reference to the "Steel Slag Stability Test Method" GB / T 24175-2009, the curing specimen was removed from the copper core enameled coil, and a porous plate and a load top plate were installed at the bottom and top of the specimen; the displacement percentage indicator was placed on the load top plate, and the displacement change of the expansion of specimens B in different groups was tested respectively; the specimen B was immersed in a water bath, maintained at 90°C for 6 hours, and then naturally cooled for 18 hours, and the test results were continuously tested and recorded for 10 days; the water expansion rate (ER) was calculated as shown in formula (1);

[0090]

[0091] Where, d 0 and d 10 They are the initial and final readings of the dial indicator for the load top plate test of specimen B, respectively.

[0092] like Figure 5 As shown in the figure, based on the results of the water expansion rate test, the carbonization effect of steel slag gravel under different bacterial liquid concentrations and magnetic field strengths is compared and analyzed. The smaller the expansion rate, the better the carbonization effect and the more stable the volume of steel slag gravel. Figure 5 It can be seen that with the increase of bacterial solution concentration, the water expansion rate of the steel slag gravel sample after curing is significantly reduced, which shows that the addition of microorganisms improves the carbonization efficiency of steel slag gravel and enhances its volume stability. When the bacterial solution concentration is 0 mg / L, the effect of magnetic field intensity on the expansion rate of steel slag gravel is not obvious, but when microorganisms are added, for example, when the bacterial solution concentration is increased to 10 mg / L, the water expansion rate decreases significantly with the increase of magnetic field intensity. This shows that the stimulation of the magnetic field mainly acts on the growth and enzyme activity of microorganisms, and the carbonization efficiency of steel slag gravel can only be improved with the participation of microorganisms. In addition, when the bacterial solution concentration is 20 mg / L and 25 mg / L, the difference in the water expansion rate of the steel slag gravel sample is only 0.06%, and the beneficial effect of the magnetic field is also relatively close. Therefore, considering the actual construction cost and specification requirements, the bacterial solution concentration recommended in this embodiment is 20 mg / L and the magnetic field intensity is 0.04T.

[0093] Example 2

[0094] The strength model building method of the present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0095] A method for constructing a magnetic field-microorganism reinforcement strength model for a steel slag and gravel road base comprises the following steps:

[0096] Step 1: Material preparation:

[0097] The steel slag used in the present invention comes from the cold steel slag produced by a steel plant in Henan Province, and its chemical composition is shown in Table 1. The collected steel slag gravel has been placed in the open air for about one month without aging treatment. The steel slag gravel is brown-gray in color and has obvious holes on the surface. The particle size is between 0 and 26.5 mm. Among them, the average apparent density of the steel slag gravel is about 3.246 g / cm 3 In addition, the particle size distribution of slag graded crushed stone is as follows Figure 1 As shown, the specification limit requirements of "Steel Slag Stability Test Method" GB / T 24175-2009 are met; the alkaliphilic Bacillus bacterial solution is prepared according to the method in Example 1.

[0098] Step 2: Carbonization pretreatment of steel slag and crushed stone by immersion method:

[0099] According to the experimental design ratio, steel slag gravel, sodium bicarbonate, urea, bacterial solution and water are mixed and placed in different curing pools to make the steel slag gravel fully soaked with bacterial solution of different concentrations, and several groups of pretreated steel slag gravel are obtained, which are recorded as steel slag A. In order to ensure the accuracy of the model, the pretreated steel slag gravel needs to be naturally air-dried / air-dried until the quality does not change;

[0100] In order to simulate the microbial carbonization effect, in this embodiment, 1 mol / L sodium bicarbonate and 2 mol / L urea were added to the reaction solution, and the bacterial solution dosages were 0 mg / L, 10 mg / L, 15 mg / L, 20 mg / L, and 25 mg / L, respectively.

[0101] Step 3: Make the test piece and process it in magnetic field:

[0102] Through heavy compaction tests, the optimum moisture content and maximum dry density of slag graded crushed stone were determined to be 7.7% and 2.593 g / cm 3 ; According to the optimum moisture content and maximum dry density, the pre-treated steel slag graded crushed stone was poured into the curing mold and statically pressed in three layers to obtain the specimen A; the specimen size was 100mm×200mm; the specimen A was treated with constant magnetic fields of different intensities, and the constant magnetic field was applied for 0.5h, and then the specimen A was cured for 48h to obtain several groups of specimens B; according to the preliminary test results, the ambient temperature was controlled at 25℃±2℃;

[0103] In this embodiment, a copper core enameled coil 3 is arranged on the periphery of the curing mold to apply a vertical downward / upward constant magnetic field to the steel slag A sample in the main mold. The magnetic field strengths are 0 T, 0.02 T, 0.04 T, 0.06 T and 0.08 T. In other embodiments, a permanent magnet or an electromagnet can be placed above / below or on the side of the main mold to apply a constant magnetic field.

[0104] Step 4: Perform variable confining pressure dynamic triaxial test on specimen B, and obtain the test results of different groups of specimens B respectively; perform linear fitting on the variable confining pressure dynamic triaxial test to establish the vertical rebound modulus E 1 prediction models;

[0105] In this embodiment, the variable confining pressure dynamic triaxial test developed by the International Aggregate Research Center (ICAR) of the United States is used to characterize the nonlinear and anisotropic behavior of steel slag graded crushed stone. In this embodiment, the triaxial test scheme is used to achieve three net stress test modes of graded crushed stone through static stress + small dynamic pulse stress, namely conventional triaxial compression, triaxial shear and triaxial tension. Each test mode sets 10 sets of stress loading sequences to obtain the stress sensitivity and anisotropy of graded crushed stone. The variable confining pressure dynamic triaxial test test scheme is shown in Table 2.

[0106] Table 2 Static + dynamic loading sequence of the dynamic triaxial test scheme

[0107]

[0108] By performing dynamic triaxial tests with variable confining pressure under the above loading sequence, the axial and radial strain peaks of triaxial compression and triaxial shear under small dynamic stress can be obtained. Combining equations (2) to (4), the vertical elastic modulus E can be calculated. 1 , Poisson's ratio of vertical to horizontal μ 13 and shear modulus G;

[0109]

[0110]

[0111]

[0112] In the above formula, Δσ 1 c is the vertical cyclic stress increment applied under triaxial compression mode; Δε 1 c is the vertical strain increment of the specimen under triaxial compression mode; Δε 3 c is the horizontal strain increment of the specimen under triaxial compression mode.

[0113] Step 5: In order to quantify the strength anisotropy of slag-graded crushed stone, define the anisotropy coefficient γ 1 is the horizontal modulus E 3 The vertical elastic modulus E 1 The ratio of ; define the anisotropy coefficient γ 2 is the shear modulus G and the vertical elastic modulus E 1 The ratio of; see equations (5) and (6);

[0114]

[0115]

[0116] In the formula, E 1 is the vertical elastic modulus; E 3 is the horizontal modulus, which can be obtained by linear programming by using the dynamic triaxial test results and the orthogonal anisotropic characteristic model; G is the shear modulus, μ 13 is the Poisson's ratio of the vertical to the horizontal direction;

[0117] According to the structural layer and stress state of the road base, the vertical modulus under a confining pressure of 40 kPa was selected as the representative value, and the dynamic triaxial test results were analyzed. The strength variation law of the magnetic field accelerated microbial reinforcement of steel slag crushed stone under different bacterial liquid dosages (0 mg / L, 10 mg / L, 15 mg / L, 20 mg / L, 25 mg / L) and magnetic field intensities (0 T, 0.02 T, 0.04 T, 0.06 T and 0.08 T) was analyzed. The vertical rebound modulus test results of specimen B are shown in Table 3. Figure 6 shown.

[0118] Table 3 Vertical rebound modulus of specimen B (MPa)

[0119]

[0120]

[0121] like Figure 6 As shown in Figure 3, the vertical rebound modulus and deviatoric stress of specimen B at each bacterial solution dosage are linearly related. By linearly fitting the test data in Table 3, a prediction model for the vertical rebound modulus can be established in the form of formula (7), where the main fitting parameter k is 1 The results are shown in Table 4. Fitting parameter k 1 It reflects the stress hardening characteristics of steel slag crushed stone, that is, with the increase of deviatoric stress, the vertical rebound modulus gradually increases, and its change rate can be expressed by the fitting parameter k 1 The size of

[0122] E 1 =k 1 σ d +k2 (7);

[0123] Table 4 Parameter results of linear fitting between vertical rebound modulus and deviatoric stress of specimen B

[0124]

[0125]

[0126] Then, according to the results in Table 4, the fitting parameter k under different bacterial concentrations and magnetic field intensities was established. 1 , fitting parameter k 1 The fitting regression equation is obtained by using the Poly12 linear model of Matlab software to determine the fitting parameter k. 1 The prediction model is shown in formula (8), and the comparison between the prediction result and the true value is shown in Figure 7 As shown, the goodness of fit R 2 Up to 97.68%; for the fitting parameter k 2 , whose value mainly reflects the initial vertical rebound modulus of the steel slag crushed stone reinforced by magnetic field accelerated microorganisms. As shown in Table 4, the fitting parameter k 2 It increases with the increase of bacterial concentration, but there is no obvious linear relationship between it and the magnetic field strength, and its value has a small relative change rate with the magnetic field strength. Therefore, this scheme recommends only establishing the fitting parameter k 2 The prediction model that changes with the bacterial solution concentration is shown in formula (9), and the fitting results are shown in Figure 8 The results show that the model's goodness of fit is 93.5%, which meets the needs of general road engineering.

[0127]

[0128] k 2 =3.8911×C B +426.92 (9);

[0129] In formula (8), C B is the bacterial solution concentration, in mg / L; S M is the magnetic field strength, unit is T.

[0130] Substituting equations (8) and (9) into equation (7), the vertical elastic modulus E of slag graded gravel under different bacterial liquid concentrations, magnetic field strengths and deviatoric stress conditions is established: 1 The prediction model is developed to facilitate the design and construction personnel to quickly learn the strength index of the current modified steel slag graded crushed stone base.

[0131] Table 5 Anisotropy coefficient results at different bacterial concentrations and magnetic field intensities

[0132] Bacterial liquid concentration (mg / L) Magnetic field strength (T) <![CDATA[Anisotropy coefficient γ 1 > <![CDATA[Anisotropy coefficient γ 2 > 0 0 0.5163 0.3245 0 0.02 0.5214 0.3253 0 0.04 0.5168 0.3251 0 0.06 0.5240 0.3258 0 0.08 0.5185 0.3241 10 0 0.4532 0.3634 10 0.02 0.4803 0.3657 10 0.04 0.4874 0.3683 10 0.06 0.4894 0.3739 10 0.08 0.4906 0.3823 15 0 0.4346 0.3953 15 0.02 0.4382 0.4017 15 0.04 0.4450 0.4078 15 0.06 0.4487 0.4098 15 0.08 0.4580 0.4110 20 0 0.4204 0.4001 20 0.02 0.4234 0.4085 20 0.04 0.4328 0.4185 20 0.06 0.4388 0.4207 20 0.08 0.4427 0.4239 25 0 0.4215 0.4146 25 0.02 0.4228 0.4177 25 0.04 0.4285 0.4214 25 0.06 0.4304 0.4341 25 0.08 0.4318 0.4375

[0133] At the same time, according to the results of the variable confining pressure dynamic triaxial test, the anisotropy coefficient γ 1 and the anisotropy coefficient γ 2 The anisotropy coefficient under different bacterial concentrations and magnetic field intensities can be calculated by using the definitions of (5) and (6), as shown in Table 5. The influence of different magnetic field intensities on the anisotropy coefficient is shown in Fig. 9 and Fig.10 .

[0134] Depend on Fig. 9 It can be seen that the anisotropy coefficient γ of steel slag crushed stone without microbial treatment is 1 The value of is large and is not significantly affected by the magnetic field intensity. With the increase of bacterial liquid concentration, the anisotropy coefficient γ of microbial reinforced steel slag crushed stone 1 This indicates that the main effect of microbial reinforcement of steel slag crushed stone is to increase the vertical dynamic rebound modulus of steel slag crushed stone, and the effect on the horizontal modulus is small or has a certain negative impact, which leads to the anisotropy coefficient γ of steel slag crushed stone. 1 However, with the increase of magnetic field intensity, the adhesion between slag and gravel is enhanced, thereby increasing the horizontal modulus of slag and gravel, and the anisotropy coefficient γ 1 Therefore, the anisotropy coefficient γ is established by using the Poly12 linear model of Matlab software. 1 The prediction model is shown in formula (10), and the goodness of fit is 95.45%.

[0135]

[0136] In formula (10), C B is the bacterial solution concentration, in mg / L; S M is the magnetic field strength, unit is T.

[0137] Depend on Fig.10 It can be seen that the anisotropy coefficient γ of microbial reinforced steel slag crushed stone is 2 It increases with the increase of bacterial liquid concentration and magnetic field strength. This shows that the microbial reinforcement significantly improves the shear modulus of steel slag gravel, and its ability to resist deformation is further enhanced under the stimulation of the magnetic field. The anisotropy coefficient γ is established through the Poly12 linear model of Matlab software. 2 The prediction model is shown in formula (11), and the goodness of fit is 98.20%.

[0138]

[0139] In formula (11), C B is the bacterial solution concentration, in mg / L; S Mis the magnetic field strength, unit is T.

[0140] Through the construction method of the magnetic field-microorganism reinforcement strength model of the steel slag gravel road base, the influence of the bacterial solution concentration and magnetic field strength on the dynamic rebound modulus and anisotropy coefficient of the microbial reinforced steel slag gravel can be accurately known, and the mathematical function relationship between each strength parameter and the bacterial solution concentration and magnetic field strength (reinforcement strength model) is established. Based on the obtained reinforcement strength model, a rapid estimation method for the strength of the magnetic field-microorganism reinforced steel slag gravel road base is provided to road designers and construction personnel. It can reversely determine the bacterial solution concentration and magnetic field strength suitable for road structure performance without conducting dynamic triaxial tests, greatly reducing the optimization cost of materials and improving construction efficiency.

[0141] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A method for constructing a magnetic field-microorganism reinforcement strength model for a steel slag and gravel road base, characterized in that: The following steps are involved: Step 1: Material preparation: prepare steel slag and crushed stone according to the road base grading requirements; prepare alkaliphilic Bacillus liquid; Step 2: Carbonization pretreatment of steel slag gravel is performed by soaking method: steel slag gravel, sodium bicarbonate, urea, bacterial solution and water are mixed according to the experimental design ratio and placed in different curing tanks for mixing, so that the steel slag gravel is fully soaked in bacterial solution of different concentrations, and several groups of pretreated steel slag gravel are obtained, which are recorded as steel slag A; Step 3: according to the optimum moisture content and the maximum dry density, the pre-treated steel slag graded gravel is poured into the curing mold, and statically pressed in three layers to obtain the specimen A; the specimen A is treated with constant magnetic fields of different intensities, and the constant magnetic field treatment is applied for 0.5 to 1.0 hours. The specimen A is cured for more than 48 hours to obtain several groups of specimens B; Step 4: Perform a variable confining pressure dynamic triaxial test on specimen B to obtain test results of different groups of specimens B; Linear fitting was performed on the variable confining pressure dynamic triaxial test to establish a prediction model for the vertical rebound modulus E1. Step 5: In order to quantify the strength anisotropy of slag graded crushed stone, the anisotropy coefficient γ1 is defined as the ratio of the horizontal modulus E3 to the vertical elastic modulus E1; the anisotropy coefficient γ2 is defined as the ratio of the shear modulus G to the vertical elastic modulus E1; Where, E1 is the vertical elastic modulus; E3 is the horizontal modulus, which can be obtained by linear programming by using the dynamic triaxial test results and the orthogonal anisotropic characteristic model; G is the shear modulus, μ 13 is the Poisson's ratio of the vertical to the horizontal; According to the results of the variable confining pressure dynamic triaxial test, the anisotropy coefficients γ1 and γ2 of specimen B under different bacterial solution concentrations and magnetic field intensities were obtained; then, the prediction models of the anisotropy coefficients γ1 and γ2 were obtained through linear fitting; the magnetic field-microbial reinforcement strength model of the steel slag gravel road base includes the prediction model of the vertical rebound modulus E1, the anisotropy coefficient γ1 and the anisotropy coefficient γ2.

2. The method for constructing a magnetic field-microorganism reinforcement strength model for a steel slag and gravel road base according to claim 1, characterized in that: In step 4, the prediction model of the vertical rebound modulus E1 is established as: E1=k1σ d +k2; k2=3.8911×C B +426.92; Where, k1 is the fitting parameter, which indicates the change rate of the vertical elastic modulus E1; the fitting parameter k2, whose value mainly reflects the initial vertical rebound modulus of the steel slag gravel reinforced by magnetic field accelerated microorganisms; σ d represents the deviatoric stress amplitude, C B is the bacterial solution concentration, in mg / L; S M is the magnetic field strength, unit is T.

3. The method for constructing a magnetic field-microorganism reinforcement strength model for a steel slag and gravel road base according to claim 2 is characterized in that: In step 5, the steel slag crushed stone strength model is obtained as follows: γ1=0.5143-0.006×C B +0.1808×S M +0.0001×C B 2 +0.004×C B ×S M ; γ2=0.3221+0.0058×C B +0.0364×S M -0.0001×C B 2 +0.0122×C B ×S M ; In the formula, C B is the bacterial solution concentration, in mg / L; S M is the magnetic field strength of the steady magnetic field, unit is T.

4. The method for constructing a magnetic field-microorganism reinforcement strength model for a steel slag and gravel road base according to claim 3 is characterized in that: The fitting parameters k1, anisotropy coefficients γ1 and γ2 were fitted by the Poly12 linear model of Matlab software.

5. The method for constructing a magnetic field-microorganism reinforcement strength model for a steel slag and gravel road base according to claim 1, characterized in that: In step 4, the variable confining pressure dynamic triaxial test includes conventional triaxial compression, triaxial shear and triaxial tension, and 10 sets of stress loading sequences are set for each test mode; The variation law of vertical rebound modulus strength of specimen B under different bacterial solution dosages, constant magnetic field with different magnetic field strengths and deviatoric stress was analyzed; the bacterial solution dosage was 0-25 mg / L, the magnetic field strength of the constant magnetic field was 0-0.08 T, and the deviatoric stress was 60-80 kPa.

6. The method for constructing a magnetic field-microorganism reinforcement strength model for a steel slag and gravel road base according to claim 1, characterized in that: The maintenance mold includes a base with a cavity inside, a main mold matching the base, a permeable stone placed at the bottom of the main mold, and an upper hoop ring and a lower hoop ring tightly fixed to the outer periphery of the main mold; a plurality of drainage holes are opened on the top of the base, and the drainage holes are connected to the cavity in the base. A drainage pipe connecting the outside and the cavity is also arranged on the outer periphery of the base; the main mold includes 2-6 sub-molds assembled together; and a plurality of ventilation holes are opened on the main mold.

7. A magnetic field-microorganism reinforcement strength model for steel slag and gravel road base, characterized by: The magnetic field-microorganism reinforcement strength model of the steel slag and gravel road base is constructed using the method for constructing the magnetic field-microorganism reinforcement strength model of the steel slag and gravel road base as described in any one of claims 1 to 6.

8. A magnetic field-microorganism reinforcement method for steel slag and gravel road base, characterized in that: The following steps are involved: Step (i) Material preparation: prepare steel slag and crushed stone according to the road base grading requirements; prepare alkaliphilic Bacillus liquid; Step (ii) carbonization pretreatment of steel slag gravel by soaking method: steel slag gravel, sodium bicarbonate, urea, bacterial solution and water are mixed according to the designed proportion and put into the curing tank, so that the bacterial solution fully soaks the steel slag gravel to obtain pretreated steel slag gravel, which is recorded as steel slag S; Step (iii) drying the steel slag S to an optimum moisture content, and then spreading it on the roadbed to form a cushion layer; rolling the cushion layer flat until the compaction, flatness and deflection values ​​reach the set standards; applying a constant magnetic field to the cushion layer while rolling; the intensity of the constant magnetic field is 0.02T to 0.08T, and the application time of the constant magnetic field is 0.5 to 1.0h; and curing for more than 7 days after the constant magnetic field treatment.

9. The magnetic field-microorganism reinforcement method for steel slag and gravel road base according to claim 8 is characterized in that: In step (ii), the concentration of sodium bicarbonate is 0.8-1.2 mol / L, the concentration of urea is 1.8-2.2 mol / L, and the amount of bacterial solution is 10 mg / L-25 mg / L; the steel slag gravel is completely immersed in the mixed solution consisting of sodium bicarbonate, urea, bacterial solution and water for more than 24 hours.

10. The magnetic field-microorganism reinforcement method for steel slag and gravel road base according to claim 8, characterized in that: The preparation process of the alkaliphilic bacillus bacterial liquid is as follows: peptone, beef extract and agar powder are added in proportion to 0.85 volume parts of deionized water, the mixture is stirred evenly and then sterilized to obtain liquid A; deionized water is added to 3-cyclohexylaminopropanesulfonic acid to dilute the mixture to 0.15 volume parts, the mixture is stirred evenly and then sterilized to obtain liquid B, wherein the concentration of 3-cyclohexylaminopropanesulfonic acid in the liquid B is 39-45 g / L; the liquid A and the liquid B are fully mixed and then poured into a culture dish, 2.0-2.2 volume percent of alkaliphilic bacillus H4 and 2.0-2.2 mol / L of urea are added in sequence, the mixture is cultured at a constant temperature of 35 DEG C for 48 hours and then used for standby, to obtain the alkaliphilic bacillus bacterial liquid with an OD600 value of 0.8-1.2.

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