Salinized soil conditioner based on solid waste and proportion design method

Abstract

The invention particularly relates to a salted soil conditioner based on solid waste and a proportion design method. On the basis of a response surface method, the optimal mixing amount combination of mineral powder, lime and an alkali activator is determined, namely 20.51 wt.% of mineral powder, 4.04 wt.% of lime and 3.99 wt.% of NaOH, the unconfined compressive strength and the dynamic elastic modulus can be improved, and the permeability coefficient can be reduced. According to the method, the engineering property of the salinized soil is improved, and the raw materials are all industrial solid wastes. According to the method for improving the salinized soil through the industrial solid waste, an efficient, environment-friendly and economical solution is provided for solidification treatment of the salinized soil, and wide application value and popularization potential are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of saline soil improvement, and particularly relates to a saline soil improver based on solid waste and a proportion design method thereof. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and it is not necessarily regarded as an admission or any form of implication that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Saline soil is a type of soil that is extremely sensitive to changes in environmental conditions. When moisture and temperature fluctuate, the salts inside the soil, especially those easily soluble salts, will undergo phase changes and concentration changes accordingly. This dynamic change characteristic of salts causes saline soil to exhibit significant instability in engineering applications, easily leading to many soil disease problems, such as pavement pumping, settlement, secondary salinization, etc., seriously affecting the engineering quality and service life. To improve the engineering properties of saline soil, domestic and foreign scholars have recommended using mineral powder as this industrial solidifying agent through a large number of studies.

[0004] Response surface methodology (RSM) is a statistical method that, through experimental design, uses a multiple quadratic regression equation to fit the functional relationship between various factors and the response value. This method can analyze the regression equation, find the optimal condition parameters, and thus effectively solve multi-variable problems. Design-Expert is a test design software system developed by Stat-Ease, Inc. in the United States. It has powerful statistical analysis functions, can fit curves to test data, establish mathematical models, and provide two-dimensional contour graphs of different factors to predict test results and three-dimensional solid graphs to observe the response surface, thereby obtaining the optimal values of various factors in the test. Currently, this software has been widely used in the design and analysis of various multi-factor tests. In the field of saline soil improvement, response surface analysis method can be used to explore the relationship between the dosage of industrial solid waste and the strength of the soil body. However, there are complex interactions between these factors, and this interaction is often non-linear, making the optimization process of the sintering process relatively difficult. Traditional optimization methods, such as the trial-and-error method or single-factor experiments, although they can also optimize the sintering process parameters to a certain extent, require a large number of tests, data collection, and demonstration analysis. This not only consumes a large amount of manpower and material resources and is costly, but also it is difficult to comprehensively consider the interactions and non-linear relationships between various parameters. The optimization results may not be the global optimal solution and only show better responses within a certain interval.

[0005] Ordinary Portland cement has many deficiencies when solidifying saline soil. Its corrosion resistance is poor and it is easily eroded by soft water, acids, and salts, resulting in a decline in the performance of the solidified soil mass; its heat resistance is also not good, and performance changes are likely to occur in a high-temperature environment. In addition, in terms of anti-salt expansion, the formation of ettringite may occur during the cement solidification process, which may cause soil mass expansion and strength loss. These factors may all have an adverse impact on the engineering properties and long-term stability of the solidified saline soil. Therefore, there is an urgent need for a green and environmentally friendly solid waste method to deeply explore the relationship between the dosage of industrial solid waste and the strength of the soil mass, with a view to achieving the efficient improvement of saline soil. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides the following technical solutions: In the first aspect of the present invention, a solid waste-based saline soil improver is provided. The improver is composed of mineral powder, lime, and an alkaline activator; wherein, the mass ratio of mineral powder: lime: alkaline activator is 16-24: 2-6: 2-6.

[0007] In the above improver, the mineral powder is blast furnace slag powder, the main component of which is calcium oxide and is in a vitreous state. The vitreous components rich in the mineral powder contain a large amount of active silicate and aluminate. Under appropriate activation conditions, such as in an alkaline environment or in the presence of sulfate, these active components can undergo a hydration reaction with water to generate hydration products with gelling properties, thereby enhancing the strength and durability of the material. In addition, the fine particles and large specific surface area of the mineral powder also promote its full contact with water and other activators, further improving the effect of active activation. As the matrix component of the improver, the principle of improving saline soil mainly includes the following aspects: 1. Saline soil contains a large amount of salts, such as sulfates and chlorides, and these salts will affect the stability of the soil mass. The active components (such as Ca(OH)2) in the mineral powder can react with sulfate ions (SO4 2- ), carbonate ions (CO3 2- ) in the saline soil to generate insoluble products such as calcium sulfate and calcium carbonate. The main reactions involved are as follows: Ca(OH)2 + SO4 2- →CaSO4↓ + 2OH − Ca(OH)2 + CO3 2- →CaCO3↓ + 2OH − Thereby reducing the salt content in the soil mass and reducing soil settlement and damage.

[0008] 2. Combined reaction of mineral powder and lime (pozzolanic reaction): Components such as reactive silica and alumina in the mineral powder can undergo a hydration reaction with calcium hydroxide in the soil in the presence of water and alkaline substances (such as lime) to form hydration products such as calcium silicate hydrate (C-S-H) gel. The main reactions involved are as follows: Formation of calcium silicate hydrate: SiO2 + Ca(OH)2 + H2O → C3S2H3 Formation of calcium aluminate hydrate: Al2O3 + Ca(OH)2 + H2O → C3AH6 The above products can fill the pores in the soil, significantly improve the unconfined compressive strength (UCS) and dynamic elastic modulus (DEM), and at the same time reduce the permeability coefficient (k).

[0009] The lime is an air-hardening inorganic binder mainly composed of calcium oxide, also known as quicklime. Lime (CaO) hydrolyzes to generate Ca²⁺ and OH⁻, providing an alkaline environment and activating the reactive components in the mineral powder. An appropriate amount of lime can fully promote the pozzolanic reaction and optimize the formation of cementitious products.

[0010] The alkaline activator is an inorganic base. Further, it is sodium hydroxide or calcium hydroxide. In a more preferred embodiment, it is sodium hydroxide. Among the above modifiers, the alkaline activator destroys the surface structure of the slag through high-concentration OH⁻, accelerates the dissolution of reactive components, and promotes the formation of Ca(OH)2. An appropriate amount of alkaline activator can optimize the quality of hydration products, form a dense microstructure, synchronously improve UCS and DEM, and reduce the permeability coefficient to the lowest level. In a more preferred embodiment of the present invention, the more preferred components and ratios of the modifier are as follows: the mass ratio of mineral powder: lime: sodium hydroxide is 20-22:4-6:3-6; further, it is 20-22:4-6:3-6; specifically, it is 20.51:4.04:3.99.

[0011] In the second aspect of the present invention, a method for designing the ratio of the saline soil modifier in the first aspect is provided, including the following steps: (1) Taking the mineral powder content, lime content, and alkaline activator content as key factors, and taking the unconfined compressive strength, dynamic elastic modulus, and permeability coefficient of the soil as evaluation indicators: Set variables X1, X2, and X3, which are independent of each other. Variable X1 represents the mineral powder content, variable X2 represents the lime content, and variable X3 represents the alkaline activator content; (2) Construct samples and conduct single-factor experimental studies on the key factors and evaluation indicators; (3) Adopt the Box-Behnken design response surface experimental scheme, generate the experimental design scheme through Design Expert, and add a center point in the experimental design scheme to estimate the model fitting error and help estimate the quadratic term coefficient; (4) Establish a response surface model based on the test data in step (2) to obtain a multiple regression equation; conduct variance analysis and significance analysis on the regression equation to verify the model fitting degree; (5) Establish contour maps and surface plots according to the response surface model, and determine the location of the optimal point in combination with the graphs; based on the maximum value of the objective function, establish a response optimization graph to determine the optimal curing plan, that is, the admixture ratio to achieve the maximum unconfined compressive strength.

[0012] In the above step (1), the value range of X1 is 16 - 24%, the value range of X2 is 2 - 6%, and the value range of X3 is 2 - 6%.

[0013] In the above step (2), the construction method of the specimen is as follows: Select a barrel with a diameter - height ratio of 3 - 4:7 - 9, and use the method of layered static pressure to mix lime, mineral powder, alkaline activator and saline - alkali soil and compact them in a mold to form a specimen. After curing, detect the unconfined compressive strength, dynamic elastic modulus and permeability coefficient respectively.

[0014] In the above step (3), the variables X1, X2, X 3， Each variable takes three levels, and a full - factorial experimental design scheme with 3 factors, 3 levels and 3 center points is generated by Design Expert.

[0015] In the above step (4), regression models of unconfined compressive strength, dynamic elastic modulus and permeability coefficient with the three variables are constructed respectively according to the test data in step (2). Further, in step (5), according to the three regression models obtained in step (4), the MINITAB software is used to set the unconfined compressive strength and dynamic elastic modulus to be the maximum, while the permeability coefficient is the minimum, so as to obtain the admixture ratio of the modifier.

[0016] In the third aspect of the present invention, a method for improving saline - alkali soil is provided, and the method includes treating the saline - alkali soil based on the modifier described in the first aspect.

[0017] The weight ratio of the modifier described in the above first aspect to the saline - alkali soil to be treated is 27 - 34%:66 - 73%.

[0018] The application method of the modifier is as follows: (1) Take samples from the saline - alkali soil area to be improved and measure the physical and chemical properties, and the physical and chemical properties include unconfined compressive strength, dynamic elastic modulus and permeability coefficient, and obtain the corresponding mineral powder content, lime content and alkaline activator content according to the ratio design method described in the second aspect above; (2) Sun-dry and control the particle size of the improved saline soil area, with the particle size preferably 2 mm or less; premix the mineral powder, lime and alkaline activator in step (1) to obtain an improver, and divide the improver into three equal parts and mix it progressively with the saline soil area to be improved to obtain an improved soil mass. (3) Cure the improved soil mass for 7 - 28 days. During the curing period, monitor the humidity and temperature of the improved soil mass, and turn and toss it regularly to improve the curing uniformity.

[0019] Preferably, in the above step (1), the sampling method is as follows: Set a grid sampling point with a side length of 10 m × 10 m, and the sampling depth is 0 - 30 cm.

[0020] Preferably, in the above step (2), the progressive mixing method is as follows: Divide the saline soil to be improved into bottom soil, middle soil and surface soil from bottom to top on average. After mixing the improver evenly with each layer of soil, add 8 - 12% of the soil mass of water and mix evenly again. Among them, the bottom soil is premixed by spreading the improver, and the middle soil is sprayed with the improver to promote penetration; after the improved soil mass is spread and shaped, it is double-compacted by static pressing 2 times and vibrating pressing 4 times.

[0021] Preferably, in the above step (3), the appropriate humidity is RH≥90%, and the appropriate temperature is 20±5℃.

[0022] Compared with the prior art, the beneficial effects of the present invention are: 1. Based on the response surface research method, the present invention provides a formulation design method for an improver, constructs a regression equation of mineral powder, lime, sodium hydroxide and the unconfined compressive strength, dynamic elastic modulus and permeability coefficient of the soil body, and conducts variance analysis according to the response surface model. The total effect main effect and 3-factor interaction effect terms of the above regression equation are all significant. The correlation parameter P value of the model is 0.0009, which is less than 0.05, indicating that there is no lack of fit in the test data and the model fitting is significant. Based on the above response surface model, the present invention first confirms the synergistic optimization interval between the above components, and further obtains an optimal formulation, 20.51 wt.% of mineral powder, 4.04 wt.% of lime, 3.99 wt.% of NaOH, and the unconfined compressive strength can reach 9.38 MPa, and the permeability coefficient is only k = 2.44×10⁻ 6 cm / s. Applying the above optimal formulation to the improvement of saline soil, the present invention observes that the anti-disintegration characteristics and unconfined compressive strength of the saline soil have been significantly improved, and at the same time, the permeability coefficient is reduced to the lowest. This shows that the industrial solid waste formulation optimized by the response surface method can effectively improve the engineering properties of saline soil, providing an efficient, environmentally friendly and economical solution for the engineering application of saline soil.

[0023] 2. The present invention also provides a solid waste-based saline soil conditioner, which uses industrial solid wastes such as mineral powder and lime as raw materials. Lime is inexpensive and easily available, and can effectively neutralize the acidic substances in saline soil, reduce the dispersibility of the soil mass, and enhance its cohesion. The mineral powder undergoes a pozzolanic reaction in the alkaline environment of lime to generate hydrated products such as calcium silicate hydrate (C-S-H) gel, further improving the strength and density of the soil mass. At the same time, under the alkaline activation of water glass, the mineral powder reacts with the salts in the soil to generate stable hydrated products, consuming the salts in the soil and reducing the soil mass damage caused by salt expansion. The conditioner provided by the present invention has simple composition and low cost, realizing the reuse of waste. This combined solidification method not only improves the engineering properties of saline soil, but also has good economy and environmental friendliness, with high innovation. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0025] Figure 1 Flow chart of the proportion design method of the saline soil conditioner in the present invention; Figure 2 Response results of the dosages of mineral powder (A) and lime (B) on the unconfined compressive strength (UCS); Figure 3 Response results of the dosages of mineral powder (A) and lime (B) on the dynamic elastic modulus (DEM); Figure 4 Response results of the dosages of mineral powder (A) and lime (B) on the permeability coefficient (k); Figure 5 Response results of the dosages of lime (B) and NaOH (C) on the unconfined compressive strength (UCS); Figure 6 Response results of the dosages of lime (B) and NaOH (C) on the dynamic elastic modulus (DEM); Figure 7 Response results of the dosages of lime (B) and NaOH (C) on the permeability coefficient (k); Figure 8 Response results of the dosages of mineral powder (A) and NaOH (C) on the unconfined compressive strength (UCS); Figure 9 Response results of the dosages of mineral powder (A) and NaOH (C) on the dynamic elastic modulus (DEM); Figure 10 Response results of the dosages of mineral powder (A) and NaOH (C) on the permeability coefficient (k); The aboveFigures 2 - 10 Among them, a) is a two-dimensional contour map and b) is a three-dimensional response surface map. Specific implementation manners

[0026] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0027] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0028] Term explanation: C3S2H3: Abbreviation of calcium silicate hydrate, i.e., calcium-silicon ratio Ca / Si = 1.5, water-silicon ratio H / Si = 1.5; C3AH6: Abbreviation of tricalcium aluminate hexahydrate.

[0029] In the research process of optimizing the above-mentioned formulation of the saline soil improver by the present invention, the interaction effects of two components of mineral powder, lime, and alkaline activator on the unconfined compressive strength (UCS), dynamic elastic modulus (DEM), and permeability (k) were studied. The research methods are as follows: I. Research on the interaction between mineral powder (A) and lime (B) The content of mineral powder (A: 18.96% - 26.96%, wt.), the content of lime (B: 2% - 6%, wt.), and the alkaline activator is sodium hydroxide (the content is fixed at 4 wt.%). The surface response of UCS, DEM, and k to the changes of A and B within the above ranges was explored respectively. The results are as Figures 2 - 4 shown; among them, the interaction of the response curves of the contents of mineral powder and lime has a synergistic optimization effect on the unconfined compressive strength performance.

[0030] As Figure 2 shown, when in the range of A = 20.5 - 22.5 wt.% and B = 4.2 - 4.8 wt.%, UCS is in the red high-strength core area in the figure, ≥9.0 MPa, and the peak value is 9.44 MPa (corresponding to A = 21.96 wt.% and B = 4.5 wt.%); on the contrary, when A > 24% and B < 3%, at this ratio, the unreacted mineral powder particles accumulate, and UCS is in the blue low-strength edge area in the figure, ≤5.0 MPa, and the lowest reaches 3.5 MPa.

[0031] II. Research on the Interaction between Lime (B) and Sodium Hydroxide (C) When the lime content (B: 2 - 6 wt.%), sodium hydroxide content (C: 2 - 6 wt.%), and mineral powder content are fixed at 20 wt.%, the surface response of UCS, DEM, and k to the changes of B and C contents within the above ranges is explored respectively. The results are as Figures 5 - 7 shown. Among them, there is a synergistic optimization of the interaction between lime and NaOH contents on the permeability coefficient.

[0032] As Figure 7 shown, when in the range of B = 4.2 - 4.8 wt.% and C = 3.8 - 4.2 wt.%, the permeability (k) is in the blue low - permeability core area, and the lowest value reaches 2.3×10⁻ 6 cm / s (corresponding to B = 4.5 wt.% and C = 4 wt.%). On the contrary, when B > 4% or C > 4%, the permeability (k) is in the red high - permeability marginal area, k≥5.0×10⁻ 6 cm / s. At this time, excessive lime (B) causes CaO expansion cracks, and NaOH (C) generates loose sodium - based gels (N - A - S - H), resulting in insufficient gel products, loose particle packing, and a significant increase in gel deterioration.

[0033] III. Research on the Interaction between Mineral Powder (A) and Sodium Hydroxide (C) When the mineral powder content (A: 16 - 24 wt.%), NaOH content (C: 2 - 6 wt.%), and lime content are fixed at 4 wt.%, the surface response of UCS, DEM, and k to the changes of A and C contents within the above ranges is explored respectively. The results are as Figures 8 - 9 shown. According to the above results, the mineral powder and NaOH contents have a coupling effect on the dynamic elastic modulus (DEM).

[0034] As Figure 9 shown, when in the range of A = 20 - 22 wt.% and C = 4.2 - 4.8 wt.%, the DEM is in the red high - modulus core area in the figure, DEM≥2.2 GPa, and the peak value is 2.35 GPa (corresponding to A = 21 wt.% and C = 4.5 wt.%). On the contrary, when A > 24% and C < 4%: excessive mineral powder leads to the accumulation of unreacted particles (porosity≥25%), insufficient generation of C - S - H gels (quantitative XRD ratio < 30%), and the DEM drops sharply to 1.2 GPa; or when C > 5% and A < 20%: high - concentration NaOH causes alkaline erosion, generates loose sodium - based gels, and the pore connectivity index CI > 0.8, DEM≤1.4 GPa.

[0035] According to the above research on the interaction of pairwise components, the more preferred dosage ranges of the three components in the saline soil conditioner are as follows: A = 16 - 24 wt.%, B = 2 - 6 wt.%, C = 2 - 6 wt.%.

[0036] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with specific embodiments.

[0037] In the following examples, the saline soil was collected from the coastal area of Weifang Economic Development Zone (36.7°N, 119.1°E). Through particle size distribution analysis, the soil was classified as silt, of which 65% were fine particles (silt and clay), and the liquid limit and plastic limit were 30.5% and 21.8% respectively. The contents of various ions and the pH value of the saline-alkali soil are shown in Table 1 below: Table 1 Contents of various ions and pH value in saline-alkali soil In the following examples, the mineral powder used was high-quality S105 grade granulated blast furnace slag powder produced by Qingdao Building Materials Company, and its chemical composition and physical properties are shown in Table 2: Table 2 Core physical indicators of S105 grade slag powder In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with specific embodiments.

[0038] Example 1 In this example, using lime, mineral powder, and sodium hydroxide as raw materials, according to the dosage ranges obtained from the above research, a design method for the optimal ratio of saline soil conditioner is provided, and the specific steps are as follows: This example adopts the Box-Behnken design response surface test scheme, and a full factor test design scheme with 3 factors, 3 levels, and 5 center points is generated through Design Expert 13.0 software. There are 3 factors, 3 levels, and 3 center points, a total of 15 groups of tests. The three levels of the mineral powder are 16, 20, and 24 wt.%, and the three levels of lime and NaOH are 2, 4, and 6 wt.%.

[0039] The test method is as follows: Mix mineral powder, lime, sodium hydroxide with saline soil, add water at the optimal water content, and then use the layered static pressure method to form cylindrical specimens with a diameter of 39.1 mm and a height of 80 mm. Apply a static pressure of 5 kN in three layers and keep it stable for 30 seconds. After demolding, place the specimens in a standard curing box at a temperature of (20±2) °C and a humidity of ≥90% for 28 days. The unconfined compressive strength test is carried out using a YAW-3000 type pressure testing machine, loading at a constant rate of 2.4 mm / min until the specimen fails, recording the peak load and calculating the strength value. Take the average value of three parallel tests for each mixture ratio; conduct a reference test through a DT-20 type dynamic elastic modulus tester: Fix the specimen horizontally on the support platform, apply a swept-frequency excitation in the range of 0.1 - 10 kHz, collect the resonance frequency using the built-in piezoelectric sensor, and calculate the initial dynamic elastic modulus based on the ASTM C215 specification (take the average value of 3 repetitions for each specimen); The permeability coefficient is measured using a TST-55 type variable-head permeameter. After the specimen is pre-treated by vacuum saturation, it is placed in a permeation container with an inner diameter of 50 mm, fixed with permeable stones at both ends and sealed with silica gel. Set the initial water head to 150 cm and record the time required for the water level to drop to 50 cm, and calculate the permeability coefficient according to the ASTM D5084 standard. Take the geometric mean of the three test results.

[0040] Determine the test variables and variable levels. Variables X1, X2, and X3 are independent of each other. Variable X1 represents the content of mineral powder, variable X2 represents the content of lime, and variable X3 represents the content of alkaline activator; The three-level content of mineral powder X1 is 24%, 24%, and 16%, the content of lime X2 is 6%, 4%, and 2%, and the content of alkali activator X3 is 6%, 4%, and 2%. Each variable and variable level are listed in Table 1.

[0041] Through the transformation of test parameters, convert the free variables and mechanical properties of each test factor into matrix form, and then use the least squares method regression to obtain the coefficients of equations (1), (2), and (3) (as shown in the following equations (1), (2), and (3)), so as to establish the multiple regression empirical formulas of unconfined compressive strength, dynamic elastic modulus and permeability coefficient with different two-ash ratios containing salt.

[0042] Y1 = 9.18 + 1.51625*A + 0.37375*B - 0.085*C - 0.19*AB + 0.5125*AC + 0.4425*BC - 2.095*A² - 1.8*B² - 2.0425*C² (1) Y2 = 2.29 + 0.29*A + 0.035*B + 0.0075*C - 0.0275*AB + 0.0925*AC + 0.1475*BC - 0.34625*A² - 0.33125B² - 0.45125*C² (2) Y3 = 3.433333 + 1.8137*A + 3.775*B + 5.625*C - 3.075*AB + 6.95*AC + 3.225*BC + 2.57333*A + 2.93583*B + 2.44333*C² (3) Table 1 Results of Unconfined Compressive Strength Response Surface Test Table 2 Results of Dynamic Elastic Modulus Response Surface Test Table 3 Results of Permeability Coefficient Response Surface Test Model Fitting Verification: The second-order regression models shown in equations (1), (2), and (3) were fitted using software for variance analysis of the equations. The results are shown in Tables 4 - 6. It can be seen that the p-value of the established second-order regression model equation after variance analysis is < 0.05, meeting the test requirements, indicating that the established model is reasonable.

[0043] Table 4 Variance Analysis of 28d Unconfined Compressive Strength Regression Model Table 5 Variance Analysis of 28d Unconfined Compressive Strength Regression Model Table 6 Variance Analysis of 28d Permeability Regression Model Set the unconfined compressive strength and dynamic elastic modulus to the maximum values, and the permeability coefficient to the minimum value. According to the above equations (1), (2), and (3), the optimal formula of the saline soil conditioner is calculated as follows: mineral powder 20.51 wt.%, lime 4.04 wt.%, NaOH 3.99 wt.%.

[0044] After incorporating the conditioner into the saline soil according to the above ratio, the soil properties were tested. The measured results are as follows: UCS = 9.38 MPa (error +0.43%, i.e., the difference from the simulation result of equation (1)), k = 2.44×10⁻ 6 cm / s (error +4.27%, i.e., the difference from the simulation result of equation (3)).

[0045] The above results show that: First, the model constructed in this embodiment has good prediction accuracy and meets the engineering requirements; Second, the modifier provided according to the optimal ratio of the present invention can effectively improve the soil properties of saline soil. According to Section 4.2 (Material Composition Design) and Chapter 5 (Construction Quality Control) of the "Technical Rules for the Construction of Highway Pavement Subbase" (JTG / T F20-2015), for the cement stabilized subbase: the unconfined compressive strength at 7 days ≥ 3 - 5 MPa (generally 4 - 5 MPa for the subbase of expressways / first-class highways). The unconfined compressive strength of the soil treated with the modifier of the present invention ≥ 9.0 MPa, meeting the requirements of the above highway pavement subbase. Therefore, the saline soil treated with the modifier of the present invention is expected to be used as the matrix material for highway pavements.

[0046] Example 2 In this embodiment, another solid waste-based saline soil modifier is provided. The doping ratio of the modifier to the saline soil is as follows: 16 wt.% mineral powder, 2 wt.% lime, 2 wt.% sodium hydroxide, and 80 wt.% saline soil.

[0047] Example 3 In this embodiment, another solid waste-based saline soil modifier is provided. The doping ratio of the modifier to the saline soil is as follows: 24 wt.% mineral powder, 6 wt.% lime, 6 wt.% sodium hydroxide, and 64 wt.% saline soil.

[0048] Example 4 In this embodiment, another solid waste-based saline soil modifier is provided. The doping ratio of the modifier to the saline soil is as follows: 20 wt.% mineral powder, 4 wt.% lime, 3 wt.% sodium hydroxide, and 73 wt.% saline soil.

[0049] Example 5 In this embodiment, another solid waste-based saline soil modifier is provided. The doping ratio of the modifier to the saline soil is as follows: 22 wt.% mineral powder, 6 wt.% lime, 6 wt.% sodium hydroxide, and 66 wt.% saline soil.

[0050] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A solid waste-based saline soil conditioner, characterized in that, The modifier is composed of mineral powder, lime and alkaline activator; among them, the mass ratio of mineral powder:lime:alkaline activator is 16-24:2-6:2-6; the alkaline activator is sodium hydroxide; the mineral powder is blast furnace slag powder.

2. The saline soil conditioner according to claim 1, characterized in that, The components and proportions of the modifier are as follows, the mass ratio of mineral powder:lime:sodium hydroxide is 20-22:4-6:3-6.

3. The saline soil conditioner according to claim 2, characterized in that, The mass ratio of the mineral powder:lime:sodium hydroxide is 20-22:4-6:3-6.

4. A method for designing the proportion of a saline soil conditioner, characterized in that, It includes the following steps: (1) Taking the mineral powder content, lime content, and alkaline activator content as key factors, and the unconfined compressive strength, dynamic elastic modulus, and permeability coefficient of the soil mass as evaluation indicators: Set variables X1, X2, and X3, which are independent of each other. Variable X1 represents the mineral powder content, X2 represents the lime content, and variable X3 represents the alkaline activator content; the value range of X1 is 16-24%, the value range of X2 is 2-6%, and the value range of X3 is 2-6%; (2) Construct specimens and conduct single-factor experimental studies on the key factors and evaluation indicators; (3) Adopt the Box-Behnken design response surface test scheme, generate the test design scheme through Design Expert, and add a central point in the test design scheme to estimate the model fitting error and help estimate the quadratic term coefficient; (4) Establish a response surface model based on the test data in step (2) to obtain a multiple regression equation; Conduct variance analysis and significance analysis on the regression equation to verify the model fitting degree; (5) Establish contour maps and surface maps based on the response surface model, determine the position of the optimal point in combination with the graphs; based on the maximum value of the objective function, establish a response optimization graph to determine the optimal curing scheme, that is, the modifier ratio to achieve the maximum unconfined compressive strength.

5. The formulation design method of the saline soil conditioner according to claim 4, characterized in that, In step (2), the method for constructing the specimen is as follows: Select a barrel with a diameter-height ratio of 3-4:7-9, and use the method of layered static pressure to mix lime, mineral powder, alkaline activator and saline soil and then compact them in a mold to form a specimen. After curing, detect the unconfined compressive strength, dynamic elastic modulus and permeability coefficient respectively.

6. The formulation design method of the saline soil conditioner according to claim 4, characterized in that, In step (4), regression models of the unconfined compressive strength, dynamic elastic modulus and permeability coefficient with the three variables are constructed respectively according to the test data in step (2); in step (5), according to the three regression models obtained in step (4), set the unconfined compressive strength and dynamic elastic modulus to be the maximum and the permeability coefficient to be the minimum through MINITAB software, so as to obtain the modifier ratio.

7. A method for improving saline soil, characterized in that, The method includes treating saline soil with the modifier according to any one of claims 1-3.

8. The improved method according to claim 7, wherein, The weight ratio of the modifier to the saline soil to be treated is 27-34%:66-73%.

9. The improved method according to claim 7, wherein The application method of the modifier is as follows: (1) Take samples from the saline soil area to be improved and measure the physical and chemical properties, and the physical and chemical properties include unconfined compressive strength, dynamic elastic modulus and permeability coefficient, and obtain the corresponding mineral powder content, lime content, and alkaline activator content according to the ratio design method according to any one of claims 4-6; (2)Turn over and sun-dry the area of the improved saline soil and control the particle size to 2 mm or less; premix the mineral powder, lime, and alkaline activator in step (1) to obtain a modifier, and divide the modifier into three equal parts and mix it progressively with the area of the saline soil to be improved to obtain an improved soil mass; (3)Cure the improved soil mass for 7 - 28 days. During the curing period, monitor the humidity and temperature of the improved soil mass, and turn it over regularly to improve the curing uniformity.

10. The improved method according to claim 9, wherein In step (1), the sampling method is as follows: set a grid sampling point with a side length of 10 m × 10 m, and the sampling depth is 0 - 30 cm; In step (2), the progressive mixing method is as follows: divide the saline soil to be improved into bottom soil, middle soil, and surface soil from bottom to top on average. After mixing the modifier evenly with each layer of soil, add 8 - 12% of the soil mass of water and mix evenly again. Among them, the bottom soil is premixed by spreading the modifier, and the middle soil is sprayed with the modifier to promote penetration; after the improved soil mass is spread and shaped, it is double-compacted by static pressing 2 times and vibrating pressing 4 times; In step (3), the humidity is RH≥90%, and the temperature is 20 ± 5℃.

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