Application of industrial waste modified cement in soft soil stabilization

Abstract

The invention relates to the technical field of modified cement, in particular to application of industrial waste modified cement in soft soil stabilization. The modified cement comprises P.O 42.5 sulfate cement, slag, steel slag, coal gangue and high-purity Al2O3 powder, the ratio of Al < 3 + > to Fe < 3 + > to Si < 4 + > in the modified cement is 2: 1: 1, and the modified cement is applied to soft soil stabilization. According to the application of the industrial waste modified cement in soft soil stabilization, the industrial waste rich in Al < 3 + >, Fe < 3 + > and Si < 4 + > is adopted as a modification material and is mixed with the cement to prepare the modified cement stabilizer. Through action mechanisms of ion exchange, hydration reaction and the like, the modified cement stabilizer can effectively improve the strength and stability of soft soil, a compact structure is formed, and the porosity is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of modified cement, in particular to the application of industrial waste modified cement in soft soil stabilization. BACKGROUND

[0002] Coastal plains, aeolian plateaus, arid regions and numerous earthen sites are all composed of soft soil, but the potential hazards in construction engineering and ecological fields are significant, becoming a key geological problem restricting the sustainable development of cities. Soft soil has poor bearing capacity and is prone to settlement, often causing foundation instability, leading to building tilting and collapse, threatening the safety of residents. Its high water content characteristics are prone to liquefaction in strong earthquakes, exacerbating ground subsidence, damaging underground pipe networks, and polluting soil and water sources. Frequent geological hazards force projects to invest high reinforcement costs, delay construction schedules, and exacerbate regional economic burdens, affecting the allocation of public resources. Frequent road collapse accidents in coastal soft soil areas have long restricted urban development and disaster response efficiency. Therefore, soft soil needs to be stabilized to improve its strength and stability to address environmental hazards.

[0003] There are many solution systems for soft soil problems. Using microorganisms to optimize soft soil contaminated with bulk solid waste into an organic-microorganism-inorganic framework for soil reuse. Jute fibers change the soil microstructure, enhance the cohesion of the solidified soil, and reduce the deformation capacity, solving the swelling problem in engineering applications. Electrochemical methods not only can evenly strengthen the positive and negative electrodes, but also can produce gel materials through electrochemical reactions to fill pores. However, among the many stabilization methods, microbial remediation is not suitable for practical engineering, and organic materials, fibers, and other reinforcing materials are relatively high in cost. In contrast, using cement to stabilize silt is an economical and efficient method.

[0004] Cement stabilized soil is a technique that improves the volume stability, strength, impermeability, and durability of soil by incorporating cement. In the treatment of heavy metal contaminated soil, cement stabilizer is a commonly used method that can effectively reduce the mobility and bioavailability of heavy metals, thereby improving the stability and engineering performance of the soil. In addition, cement can effectively stabilize kaolin clay contaminated with crude oil, significantly improving its geological environmental performance. Through cement stabilization treatment, the performance indicators of the soil are improved, and it can be used for roadbed construction, pavement repair, and retaining wall reinforcement engineering. However, due to differences in geological and environmental conditions, the types of soft soil vary in different regions, and the stabilization effect of cement cannot meet the requirements, and the huge carbon footprint of cement causes irreversible harm to the environment. In addition, industrial solid waste has always been a research difficulty due to its low utilization rate, so solid waste modified cement has become a research hotspot.

[0005] Modified cement prepared by industrial solid waste instead of part of cement not only can improve construction quality, prolong the service life of buildings, but also can better adapt to complex and changeable application environment. Metakaolin modified cement can significantly improve the compactness and strength performance of soft clay. Diatom modified cement can improve the cohesion and internal friction angle of cement soil in coastal areas. Nano-MgO modified cement can significantly enhance the compressive strength, stiffness and toughness of expansive soil. Nano-silicon dioxide modified cement can significantly improve the CBR value and compressive strength when used in silt soil road construction. In addition, graphene oxide (GO) and silica fume (SF) modified cement-based composite materials can effectively solidify loose silt sand, reduce permeability and improve mechanical strength. However, most of the current research focuses on the development of cement replacement materials, and this repetitive innovation does not solve the problem of soil stabilization.

[0006] Therefore, it is of great practical significance to develop low-carbon and environmentally friendly soft soil stabilization materials with excellent performance.

[0007] Therefore, the application of industrial waste modified cement in soft soil stabilization is designed to provide a technical solution to the above technical problems. SUMMARY

[0008] Therefore, it is necessary to provide an application of industrial waste modified cement in soft soil stabilization to solve the technical problems raised in the background art.

[0009] In order to solve the above technical problems, the application adopts the following technical solutions:

[0010] A modified cement, the modified cement comprising P.O 42.5 Portland cement, slag, steel slag, coal gangue, high-purity Al2O3 powder.

[0011] As a preferred embodiment of the modified cement provided by the application, the ratio of Al 3+ , Fe 3+ and Si 4+ in the modified cement is 2:1:1.

[0012] The modified cement is applied in soft soil stabilization.

[0013] As a preferred embodiment of the application of the modified cement in soft soil stabilization provided by the application, the application method is as follows:

[0014] Mixing soft soil with modified cement to form a cement soil mixture;

[0015] Pouring the cement soil mixture into the required shape and curing.

[0016] As a preferred embodiment of the application of the modified cement in soft soil stabilization, the liquid-solid ratio of the soft soil is 0.36-0.39.

[0017] As a preferred embodiment of the application of the modified cement in soft soil stabilization, the curing age is 7 days or 28 days or 56 days.

[0018] The modified cement is prepared from industrial solid waste raw materials.

[0019] A preparation method of a modified cement, the steps of the preparation method are as follows:

[0020] A. High-purity Al2O3 powder is mixed with slag in proportion, and the total Al2O3 content is adjusted to obtain an aluminum modified raw material;

[0021] B. Fe2O3 refined from industrial hematite is mixed with steel slag to obtain an iron modified raw material;

[0022] C. Si2O is mixed with coal gangue to obtain a silicon modified raw material;

[0023] D. The aluminum modified raw material obtained in step A, the iron modified raw material obtained in step B, and the silicon modified raw material obtained in step C are compounded and proportioned with P.O 42.5 sulfate cement to prepare a soil stabilizer.

[0024] It can be seen without doubt that the above technical solutions of the present application can certainly solve the technical problems to be solved by the present application.

[0025] At the same time, through the above technical solutions, the present application at least has the following beneficial effects:

[0026] The application of the industrial waste modified cement in soft soil stabilization provided by the present application uses industrial waste (such as slag, steel slag, coal gangue, etc.) rich in Al 3+ , Fe 3+ and Si 4+ as a modified material, which is mixed with cement to prepare a modified cement stabilizer. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0028] Figure 1A schematic diagram of soil XRD component analysis of the present application;

[0029] Figure 2 A schematic diagram of XRD test results of raw materials of the present application;

[0030] Figure 3 A schematic diagram of material model of the present application;

[0031] Figure 4 A schematic diagram of establishment of soil stabilizer model of the present application;

[0032] Figure 5 A schematic diagram of unconfined compressive strength of the present application;

[0033] Figure 6 A schematic diagram of analysis and calculation of RDF of the present application;

[0034] Figure 7 A schematic diagram of analysis and calculation of MSD of the present application;

[0035] Figure 8 A schematic diagram of Fourier transform infrared spectroscopy analysis of stabilized soil of the present application;

[0036] Figure 9 A schematic diagram of specific surface area analysis of stabilized soil of the present application;

[0037] Figure 10 A schematic diagram of SEM microstructure analysis of stabilized soil of the present application;

[0038] Figure 11 A schematic diagram of XRD analysis of stabilized soil of the present application;

[0039] Figure 12 A schematic diagram of EDS analysis of stabilized soil of the present application;

[0040] Figure 13 A schematic diagram of interaction energy of four kinds of stabilized soil of the present application;

[0041] Figure 14 A schematic diagram of image-based stabilized soil pore analysis of the present application;

[0042] Figure 15 A schematic diagram of stabilized soil pore analysis results of the present application. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0044] In order for those skilled in the art to better understand the technical scheme of the present application, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings.

[0045] It should be noted that the embodiments in the present application and the features and technical solutions in the embodiments can be combined with each other without conflict.

[0046] It should be noted that: similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0047] Reference Figures 1-15 , the application of industrial waste modified cement in soft soil stabilization, comprising

[0048] 1. Preparation of soil stabilizer

[0049] Three kinds of industrial solid waste raw materials developed by Beijing Construction Engineering Group Co., Ltd. were studied, which were slag, steel slag and coal gangue. High-purity Al2O3 powder was physically mixed with slag in proportion, and the total Al2O3 was adjusted to the target value to obtain aluminum modified raw material. The iron modified raw material used industrial hematite to refine Fe2O3, and then mixed with steel slag. The silicon modified raw material used Si2O and coal gangue to perform the same operation. The preparation of modified raw materials was completed by Beijing Construction Engineering Group, and the research purchased the prepared raw materials. After obtaining the modified raw materials, P.O42.5 Portland cement and industrial solid waste containing different components were used as modified raw materials for composite ratio experiment research to prepare soil stabilizer.

[0050] The laboratory designed the molar mass of all the raw materials obtained, and each part of the cement was placed as the main solidifying agent, and the modified materials were treated without impurities affecting the experimental results. The ion content of the stabilizer was adjusted by calculating the molar mass, and the soil stabilizer obtained by adjusting was labeled, the a group stabilizer contains: 18.3% of slag, 12.5% of steel slag and 9.2% of coal gangue powder and 60% of cement; the b group is composed of 7.2% of slag, 22.6% of steel slag, 10.2% of fly ash and 60% of cement; the c group adds 8.3% of slag, 12.8% of steel slag, 18.9% of coal gangue and 60% of cement; the d group is configured with 60% of cement plus 12.8% of slag, 16.5% of steel slag, 10.7% of coal gangue, and each group contains 100%, which is not related to the content of the soil. Then the results are tested by XRF Figure 1), and finally four kinds of soil stabilizers were obtained. The four groups of stabilizers were (a) Al3+ / Fe3+ / Si4+= 2 / 1 / 1, (b) Al3+ / Fe3+ / Si4+= 1 / 2 / 1, (c) Al3+ / Fe3+ / Si4+= 1 / 1 / 2, (d) Al3+ / Fe3+ / Si4+= 1 / 1 / 1 Figure 1 ). In the paper, a, b, c, d are used to represent the stabilizer. The four groups of stabilizers were analyzed by XRD mineral composition and observed by SEM, and the results are as follows Figure 2 .

[0051] 2、Method

[0052] 2.1. Stirring experiment

[0053] The stabilized soil was mixed with a planetary cement mortar mixer. The mixing amount was preferably 1 / 3 of the total volume of the mixing container. The actual amount of silt, soil stabilizer, and water was calculated according to the size of the mixing volume and filled into the pot. The pot was placed on the fixed frame and raised to the fixed position, then the machine was immediately started. The dry soil was mixed for 60 s, and then distilled water was added for wet mixing for 280 s. The waste soil stabilizer for performance test was obtained. According to the technical standard of Technical Standard for Backfilling Project by Using Premixed Fluidized Solidified Soil (T / BGEA001-2019) released by Beijing Geotechnical Engineering Association in 2019, the compressive strength of the solidified soil should be prepared as a cube specimen of 100mm*100mm*100mm. The research was designed according to the formula of 4.4,6-1 to 4.4,6-3 in T / BGEA 001-2019. Five gradients of solidified agent content of 8%-15% were set for the experiment. It was found that when the solidified agent content exceeded 12%, the engineering cost was high and could not be used as a reasonable application method. When the content was less than 10%, the stabilized soil specimen could not be solidified in a short period of time, which delayed the construction period. The liquid-solid ratio was adjusted according to the solidified agent content. It was found that between 0.36-0.39 could meet the requirements of molding and early solidification. In order to save cost, the ash-soil ratio was 0.1 and the liquid-solid ratio was 0.36.

[0054] 2.2 Compressive strength experiment and results

[0055] Before the compression test, the surface of the test piece with the curing age is cleaned, and the size is measured to 1 mm. If the difference between the actual size and the nominal size is not more than 1 mm, the calculation is carried out according to the nominal size. The test piece is placed on the lower pressing plate or lower cushion plate of the testing machine, ensuring that the bearing surface of the test piece is perpendicular to the top surface during molding, and the center of the test piece is aligned with the center of the lower pressing plate or lower cushion plate of the testing machine. Start the testing machine, and when the upper pressing plate approaches the test piece or the upper cushion plate, adjust the ball seat to ensure that the contact surface is evenly stressed. The compression test should be continuously and uniformly loaded at a rate of 1 mm / min until the test piece is destroyed, and the failure load is recorded. The curing experiment also follows the T / BGEA 001-2019 standard, and tests are conducted at 7d, 28d, and 56d ages. The curing age is the same as the cement soil mixture design (JGJ / T 233-2011). The strength of the stabilized soil test piece at three days is also studied to inspire the development of early strength stabilized agent in the future.

[0056] 2.3 X-ray diffraction (XRD)

[0057] The study used a D8 Advance X-ray diffractometer (XRD) produced by Bruker Company in Germany. In the test, a Cu target was used as the X-ray source, operating at 40 kV and 40 mA, with a measurement range of 5° to 70° and a scanning speed of 2° / min. Rietveld refinement was performed on the soil sample, with 5% wt Si added as an internal standard. The soil sample was refined by TOPAS-Academic V5, and the experiment referred to Santini's scheme (Santini 2015). The crystal structure model of all mineral phases was from ICDD.

[0058] 2.4 X-ray fluorescence spectrometer (XRF)

[0059] The study used a PANALYTICAL AXIOS X-ray fluorescence spectrometer. The stabilized soil sample was treated as a powder with a particle size not exceeding 74 μm. The working conditions of XRF were ambient temperature 10-35℃. The power supply voltage was 220V±10%, with an output fluctuation control within ±0.005%. The sample used a split-cycle cooling water system with a maximum refrigeration capacity of 8kW, a maximum water pressure of 5Kg / cm 2 , and a water flow of 20L / min.

[0060] 2.5 Scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS)

[0061] The study used a Gemini SEM 300 field emission scanning electron microscope produced by Germany Zeiss Company, combined with EDS test analysis. The X / Y axis stroke was 130 mm, the Z axis stroke was 50 mm, and the inclination range was 20°. In terms of micro-area component analysis, EDS was used for qualitative and semi-quantitative analysis, the half-height width of Mn Kα peak was better than 127 eV, and the half-height width of C Kα peak was better than 56 eV.

[0062] 2.6 Fourier transform infrared spectrometer (FTIR)

[0063] The FTIR spectrum test was analyzed by AXIOS X-ray fluorescence spectrometer of PANALYTICAL company. The particle size of the powder sample was 200 meshes, and the sample amount was 10 mg. The experiment used KBr tabletting method, 1 mg of powder sample was mixed with 200 mg of optical pure KBr under a heating lamp, and then ground into a uniform powder, and then pressed into a translucent round sheet sample using a hydraulic press. During testing, the background scan was 32 times, the sample scan was 16 times, the spectral analysis range was 4000-400 cm -1 , and the resolution was 4 cm -1 .

[0064] 2.7 BET surface area

[0065] The study used ASAP 2020HD88 full-automatic physical adsorption analyzer of American Micromeritics Company. N2 was used as the adsorbate for testing. The powder particle size was less than 3 mm, and was poured into a 100 ml closed bottle and shaken for 2 minutes, and the possible clumps were crushed to make the sample fully loose. The degassing temperature was controlled at about 300°C, and the degassing time was 8 hours. BJH method was used for pore size distribution analysis.

[0066] 2.8 Image J calculates the porosity of stable soil

[0067] The open source software Image J was used to analyze the porosity, first the SEM image was preprocessed, after the detection image was imported into the Image J software, the filter tool was used to remove the noise in the image. Then, the image was converted to a binary image by the global threshold method, so that the pores and solid parts were effectively segmented, and the pore part was black and the rest was white. Next, the Analyze Particles in ImageJ was used to quantitatively analyze the pores in the binary image.

[0068] 3. Molecular simulation

[0069] The study wants to verify the degree of influence of different ion contents on the process of soil stabilization through simulation methods, adding comprehensiveness to the research from a molecular point of view. Although molecular simulations can provide valuable insights into atomic-scale interactions and dynamic behavior, we should also recognize some inherent limitations. First, the accuracy of simulations depends largely on the chosen force field and empirical parameters, which may not fully capture complex quantum effects or special bonding environments. Second, the spatial and temporal scales achievable by traditional simulations limit their direct correspondence to macroscopic experimental conditions. Third, simplifications in system setup, such as fixed boundary conditions, idealized solvent models, or neglecting defect dynamics, can alter predictions of real-world phenomena.

[0070] 3.1 Material model establishment

[0071] 3.1.1 sandy silt soils model

[0072] According to the XRD-Rietveld and XRF experiments of soft soil, the sandy silt soils model is constructed, and four mineral components are filled according to 58.76% of Quartz, 14.35% of Kaolinite, 18.89% of Illite and 8% of Calcite. The quartz model selects the model made by Ikuta et al. (Ikuta et al. 2007), the chemical formula is O6Si3, and the supercell of 3*2*2 is made for the model and filled into the soil material simulation box. The Calcite model selects the model made by Pippiner et al. (Pippinger et al. 2014), the chemical formula is C 10 O 30 Ca 10 , and the supercell of 2*2*1 is made for the model and filled into the box. The Illite model selects the model made by Drits et al. (Drits et al. 2010), the chemical formula is O 24 Na 0.06 Mg 0.44 Al 4.68 Si 6.86 K 1.32 Ca 0.06 Fe 0.02 , and the supercell of 2*2*1 is made for the model and filled into the box. The Kaolinite model selects the model made by Cora et al. (Cora et al. 2014), the chemical formula is Al4Si4H8O 18, the simulation box is set as O: 130.422, Si: 36.42, Al: 14.58, H: 11.48, Ca: 21.134, and the atomic percentage of each kind of atom is consistent with the detection result. The simulation box is set as The force field uses the Clayff force field more suitable for the cement model. All the following models use the Clayff force field. The structure is optimized using the Forcite-Geometry Optimization task for the material box, and the energy convergence standard is set as ΔE < 1e-5 kcal / mol, and the step size is 5000 steps. All the following optimization processes use the Forcite-Geometry Optimization task. The optimization result shows that the structure is stable, the model is reasonable, and the material model is executable. Figure 3 ).

[0073] 3.1.2 Establishment of cement model

[0074] The research combines the XRD detection results and finds that there are C-S-H gel, ettringite and gypsum, and C-S-H gel is the key determinant of the performance of cement-based materials, ettringite affects the setting and hardening of cement and the key of expansion characteristics, and gypsum can adjust the setting time of cement, so the three materials are selected as the cement model. The research does not add calcium hydroxide, which is a defect of the simulation, because the research initially found that too many components reduce the credibility of the model, and Ca 2+ (OH)2 is not the focus of the research, so it is abandoned. In the following research, the author will conduct in-depth analysis and thinking. C-S-H gel is an amorphous structure, and the theoretical model of C-S-H has been repeatedly modified. The research uses the Tobermorite crystal structure established by Battocchio as the initial structure of simulation study, and uses the Build Crystal instruction in MS software to modify the Ca / Si structure of the structure from 0.68-0.83 to 1.1-1.3, and converts the monoclinic box to an orthogonal box. The model is filled into the cement simulation box with a 3*2*1 supercell. The ettringite crystal model uses the model established by Norman et al., and the model is filled into the cement model with a 2*1*1 supercell. The gypsum crystal model uses the model made by Nazzareni et al., and the model is filled into the model with a 2*1*1 supercell. The Geometry Optimization instruction is used to optimize the cement material box, and the cement material model is obtained. ​Figure 3 ). Based on the cement model, the study needs to introduce four different groups of ion components and use the Modules-Amorphous Cell module in MS to establish an ion solution model. The mass fraction of the ion solution is 13.6% and the density is 1g / mL. The first group performs ion configuration on group d and fills in Al 3+ / Fe 3+ / Si 4+ =1 / 1 / 1, then repeat the establishment of group d model, and do Al for groups a, b, and c respectively. 3+ , Fe 3+ , Si 4+ 2 times the filling. (a) Al 3+ / Fe 3+ / Si 4+ =2 / 1 / 1,(b)Al 3+ / Fe 3+ / Si 4+ =1 / 2 / 1,(c)Al 3+ / Fe 3+ / Si 4+ =1 / 1 / 2,(d)Al 3+ / Fe 3+ / Si 4+ = 1 / 1 / 1 ionic solution model. Use Build-Build Layers to fix the cement model, introduce the ionic solution model, and then perform Geometry Optimization to obtain the modified stabilizer model.

[0075] 3.2 Model analysis method.

[0076] 3.2.1 Interaction energy

[0077] The study is based on molecular dynamics analysis and interaction energy calculation to evaluate the stabilization strength of four material models on silt. The soil stabilizer model is injected into the soil material model and optimized using the Geometry Optimization command to obtain the stabilized soil model. The lowest energy value in the spectrum is selected as the indicator of the most stable configuration of the system in the energy channel output by the model. The specific frame corresponding to the lowest energy state is selected through the ballistic panel. Based on this frame, the Energy task in Forcite-Calculation is used to obtain the overall energy of the simulation box (denoted as E t ) and soil materials (E 1,t ) and soil stabilizer (E 2,t )'s individual energy ( Figure 12 ), calculate them separately in the simulation box, and then calculate the interaction energy according to the formula.

[0078] Eat =E t -E 1,t -E 2,t (1)

[0079] 3.2.2 MSD curve and ion diffusion coefficient

[0080] The study used the Forcite-Dynamics module to perform molecular dynamics simulations of heavy metal ions in four stabilized soil models. The relaxation task was set in the NVT ensemble system with a time step of 1 fs and a temperature control of 298K. The soil model and the soil stabilizer model were independently relaxed for 3 ns, followed by a 2 ns equilibrium process between the matrix and the solution, and continued for 2 ns to reach steady state. The dynamic simulation time was 300 ns. After obtaining the results, the MSD task in the Module-Force Analysis Module was used to analyze the Al in the four models. 3+ , Fe 3+ , Si 4+ The mean square displacement curve ( Figure 6 After obtaining the trend equation of each curve, the diffusion coefficients of different ions were calculated using Einstein's expression (Formula 2).

[0081]

[0082] 3.2.3 RDF Radial Distribution Function

[0083] Study uses Edit-Edit sets to mark Al 3+ , Fe 3+ , Si 4+ , calculated by Modules-ForciteAnalysis-Radial distribution function command, Trajectory is 21 frames-End, Sets are three research ions and O - The radial distribution of the cutoff should not exceed one times the radius of the van der Waals force used and should not exceed 1 / 2 of the minimum side length of the simulation box. Get Al 3+ -O - , Fe 3+ -O - and Si 4+ -O - RDF curve ( Figure 5 ).

[0084] 4. Results and Discussion

[0085] 4.1 Compressive strength results

[0086] The experiment was conducted on five groups of compressive strength and the average value was taken as the result value ( Figure 2 The compressive strength results for the five groups were within an error range of 0.2 MPa. The test results show that Group A exhibited significantly higher compressive strength than the other two groups, reaching 2-3 times that of the other groups at 54 days. Group B exhibited similar strength to Group A, meeting most construction requirements. Groups C and D exhibited lower strength. These strength performances are attributed to the stabilizer.

[0087] 4.2 Modified ions reduce the thickness of the double electrical layer on the surface of silt minerals

[0088] 4.2.1 Modified ions destroy the double layer structure

[0089] Soil particles dissociate in the water medium. After dissociation, cations diffuse into the free water, while anions remain on the surface of the soil particles. Therefore, soil particles not only adsorb charged cations, but also replace cations with low surface charges, which will cause an unbalanced negative charge on the crystal surface. Under the action of electrostatic attraction, negative charges will form a double layer structure with water molecules on the surface of the surrounding silt particles. The double layer on the surface of soil particles is a key factor affecting the structural strength of soil particles. The study used MS software for ion analysis and calculated the modified cations to O - RDF to compare Al 3+ , Fe 3+ , Si 4+ Short-range enrichment of soil particles and local structural order ( Figure 6 ) to verify and compare the ability of modified ions to change the double layer structure of soil particles. Figure 6 Al in B 3+ The RDF peak values ​​of different stabilizers showed significant differences, and the peak value of stabilizer a reached 17.65. This shows that Al 3+ The presence of helps to enrich the stabilizer in a short distance and enhances the Al 3+ Order in the local structure. Compared with Al 3+ , Fe 3+ The RDF results in different stabilizers showed similar peaks. Figure 6 In C, the highest RDF peak is 19.8, indicating that at high concentrations of Fe 3+ In this case, Fe 3+ -O - The short-range ordered structure is more significant. This peak value is due to the double electrical layer of the soil particles 3+ The complexation effect of Fe 3+ Adsorption is embedded in the surface of soil particles. In contrast, Figure 6 D in Si 4+The RDF curves under different stabilizer conditions all show relatively low characteristics, with peak positions concentrated between 3.51 and 3.84, and Si 4+ The effect of different modified stabilizers is not obvious, Si 4+ The effect on soil particles is weak. This is because Si 4+ is mostly in the form of silicate or silicon dioxide in soil, which has strong covalent bonding ability, making it not easily affected by external chemical environment. Therefore, Si 4+ plays a more important role in the skeleton support in the soil solidification process.

[0090] The short-range order and enrichment shown by the RDF analysis results are due to the ionization reaction of the soil stabilizer after water (formula 3), which dissociates strong cations H3O + , free Al 3+ , Fe 3+ and Si 4+ , etc. These high-valent cations can replace the original low-valent cations (such as Na + , K + ) in the double electric layer by the attraction between positive and negative charges, and are more easily adsorbed on the surface of soil particles. This adsorption mode releases polar water molecules in the double electric layer, thereby reducing the strongly bound water on the surface of soil particles. However, it does not change the double electric layer structure of clay particles and cannot completely remove the bound water in clay. In addition, high-valent cations neutralize the surface vacancy anions of soil particles, thinning the thickness of the bound water layer caused by soil pore suction, surface tension and capillary force, etc. Thus, the repulsive force between particles is reduced. The high-valent cations on the damaged double electron layer, due to the strong charge density, thin the adsorbed water film and ion region on the surface of soil particles, making the extended layer of the double electric layer thinner. With the thinning of the double electric layer, the repulsive force between particles becomes smaller, and particles will produce two phenomena of aggregation and attraction through electrostatic attraction. Aggregation promotes the "flocculation" of particles, and the particles change from point-plane contact to plane-plane contact, forming more stable particle aggregates. "Attraction" pulls adjacent particles closer, so that particles form a molecular chain-like lapping structure through electrostatic static force.

[0091] H + +H2O→H3O + (3)

[0092] 4.2.2 Ion exchange of modified ions reduces ζ potential

[0093] Zeta potential is the main reason for repelling soil particles and affecting the formation of soil particle skeleton. The study uses MSD to compare the modification of zeta potential by modified ions. Higher zeta potential means stronger repulsive force between particles, resulting in stronger particle diffusion, i.e. more dispersed particle movement. Through MSD and ion diffusion coefficient, the diffusion rate of modified ions in different stable soils can be observed. Figure 6 MSD results of Al 3+ , Fe 3+ and Si 4+ in four soil stabilizer models are shown. a In the calculation of three ions, the curve is the slowest and the diffusion coefficient is the smallest, about 0.025A 2 / ps to 0.03A 2 / ps, the particle diffusion is most inhibited, which reflects the optimal stabilizing effect. The inhibition of particle diffusion by Fe 3+ is between Al 3+ and Si 4+ , with an ion diffusion coefficient of about 0.06A 2 / ps, indicating weak ion stability and less improvement in soil structure compactness than Al 3+ . In the presence of Si 4+ , the growth trend of MSD curves a, b, c, d of the four stabilized soils is more significant, indicating that the particle mobility is the strongest and the diffusion coefficient is the largest, all above 0.07A 2 / ps. This means that under the condition of Si 4+ , the repulsive force between soil particles cannot be effectively reduced, and the particle aggregation is poor.

[0094] The MSD analysis results are due to the fact that the valence of cations in the electrolyte solution around the soil particles and the degree of hydration affect the zeta potential of the soil particles. Using external modified ions to reduce zeta potential is a very important means to improve the strength of stabilized soil. The hydration radius of Al 3+ is 0.48 nm, smaller than that of Fe 3+ and Si 4+ , and cations with smaller hydration radius have greater exchange potential. Al 3+ changes the type and concentration of ions on the surface of soil particles by strong ion exchange and ion exchange reaction with weakly bonded polar water molecules, thereby reducing the thickness of the double electric layer, reducing the zeta potential, increasing the interparticle attraction, promoting soil particle aggregation and cohesion, and making the soil show relative inertia and stability. In addition, clay particles contain Ca 2+ , Mg 2+ and other cations on their surfaces, and form a bound water layer with the surrounding polar water molecules. The thickness of the bound water layer affects the formation of a dense structure of soil particles. After adding the stabilizer, the soil stabilizer dissociates many cations, among which Al 3+ , Fe3+ The high concentration of cations, high osmotic pressure, small molecules, strong hydration potential, and the ability to easily enter the counterion layer from the free solution, and further ion exchange reaction with Ca 2+ , Mg 2+ , and other cations on the surface of the soil particles. Further reducing the thickness of the bound water layer, reducing the zeta potential of clay particles, and reducing the distance between particles to arrange more densely. At the same time, the replaced Ca 2+ , Mg 2+ , and other cations into the free liquid state, and further form precipitates with OH - , enhancing the strength of the stabilized soil. This ion exchange reaction is irreversible, that is, when the silt is solidified by the stabilizer, the soil will not return to its original ion imbalance state.

[0095] 4.2.3 FTIR test of the effect of modified ions on soil particles

[0096] The FTIR experiment was used to verify the effect of modified ions on the double electric layer, Figure 7 The FTIR analysis results of the stabilized soil samples are shown. In group a, the infrared spectrum shows an absorption peak at 532.549 cm -1 , corresponding to the bending vibration of Si-O bond, the peak at 594.743 cm -1 corresponds to the characteristic vibration of Al-O bond. The peak at 1119.349 cm -1 is related to the asymmetric stretching vibration of SiO4 tetrahedron, indicating that the SiO4 unit is orderly distributed in the system and interacts with Al 3+ , forming a stable framework structure. In the high-frequency region, the absorption peak at 3427.18 cm -1 corresponds to the O-H stretching vibration, representing the stretching frequency of adsorbed water, and the absorption peak at 1636.486 cm -1 represents the structural water, which side evidences the role of Al 3+ in increasing the adsorption sites of the double electric layer, enhancing the structural stability and the role in water molecule binding. The FTIR spectrum of group b shows that the absorption peak at 595.101 cm -1 is attributed to the bending vibration of Fe-O bond, and the peak at 670.788 cm -1 corresponds to the bending vibration of Si-O bond. The peak at 1119.223 cm -1 indicates that the stability of the silicon-oxygen network is similar to that of group a. In group c, the increase in the proportion of Si 4+ does not result in the appearance of new peaks, and the only significant absorption peak is at 526.127 cm -1corresponding to the bending vibration of Al-O bond. Overall, the spectral features of group c are relatively flat, reflecting the lower reactivity and weaker adsorption capacity, and the orderliness of mineral structure and adsorption capacity are not significantly enhanced compared with groups a and b. In the FTIR spectrum of group d, the ratio of Al 3+ , Fe 3+ and Si 4+ is 1:1:1, and the absorption features are more balanced. The absorption peak at 529.514 cm -1 corresponds to the bending vibration of Al-O bond, while the peak at 645.419 cm -1 is related to the bending vibration of Fe-O bond, indicating that the equal ratio helps to form a more stable and coordinated lattice structure. The broad O-H stretching vibration peak at high frequency of 3443 cm -1 indicates that the system has strong water absorption capacity. The comprehensive analysis of the spectral features of the four groups shows that the high proportion of Al 3+ significantly enhances the binding capacity of adsorbed water, indicating its role in strengthening the anion adsorption sites on the double electric layer. At the same time, the increase of Fe 3+ improves the local lattice symmetry and enhances the diversity of adsorbed water, especially through stabilizing the Fe-O bond. The high proportion of Si 4+ in general improves the soil stabilization and modification effect. The chemical bonds obtained by FTIR detection analysis further verify the model results, proving that the modified ions have reacted with the soil particles and the ions have affected the double electric layer structure of the soil particle surface.

[0097] 4.2.4 Thin double electric layer compact soil skeleton

[0098] The BET adsorption-desorption isotherms and pore size distribution curves were used to study the contribution of different modified ions to the regulation of the soil skeleton structure. Figure 9 The isotherms of the four groups of stabilized soil presented in the study are typical type IV characteristics, forming a clear hysteresis loop between the relative pressure range of 0.4 to 0.9, indicating that the material is mainly mesoporous structure. By analyzing the adsorption and desorption isotherms of the four groups, the adsorption capacity reaches the maximum value when the pressure value is close to 1, and the maximum values of group a, group b, group c and group d are 24 cm 3 / g, 22 cm 3 / g, 30 cm 3 / g and 70 cm 3nm, b group 3-4 nm, c group 4-6 nm, d group 20-30 nm. BET experimental results show that the pore volume of group a is relatively small, the pore size distribution is narrow and uniform, and there is a lack of macropores and adsorptive bandwidth network. The structural properties of group a make the material more dense, while providing some resistance to the penetration of external ions, and the overall strength of the soil is higher. Compared with group a, the specific surface area and pore volume of group b are relatively small, and the pore size of the stable soil is highly uniform, and the pore formation process has good controllability. There are very few macropores in group b, and the pore structure is relatively tight, without significant macropores and coherent macro-pores. Group c shows obvious differences in pore structure and adsorption behavior. The adsorption capacity increases rapidly in the high relative pressure region (P / P0>0.9), which is due to the presence of some large pores or wider inter-particle pores in the stable soil. The pore size distribution obtained by BJH analysis shows that the pore size distribution range of this material is wider than the first two materials. The double peak distribution of group c indicates that the sample has a higher pore volume and a wider pore size distribution, and the connectivity of the sample is stronger and the stability is weaker. Group d has greater pore connectivity and more macropores, and the wide pore size distribution indicates that the stable soil has both mesoporous and macroporous structures, and its significant hierarchical pore structure reduces the density and strength of the stable soil. In summary, the stable soil with Al 3+ as the main modification has the least pores, the highest density, the best overall strength, and the most closed pore network with the lowest connectivity. Fe 3+ The pore structure of the modified cement stable soil increases slightly, but the connectivity of the pore formation is relatively small, and the structure has a certain stability. However, Si 4+ As a modified ion, the stabilizer shows more macropores and certain connectivity of the pore formation, and the strength is not high

[0099] 4.3 Modified ions promote the generation of hydration products of stabilizers

[0100] 4.3.1 Hydration products of soil stabilizers enhance the strength of stable soil

[0101] Another important mechanism of cement stabilizers to solidify silt is to cement loose silt particles through cement hydration products, and to fill the pores between silt particles with hydration products. Cement hydration products are the key factor to improve strength, and increasing the degree of hydration reaction and the amount of hydration products by using modified ions is an important way to enhance the stability of soil. Figure 11 The hydration products formed after the reaction of cement clinker with water, such as calcium silicate hydrate (C-S-H), calcium hydroxide (CH), monosulfate type calcium aluminate hydrate (AFm) and ettringite (AFt), are shown. Through SEM microstructure comparative analysis, the influence of different modified ions on hydration products can be clearly observed. Combined with the results of XRD and FTIR, it can be found that the hydration products of different modified ions are different. Figure 11The amount of ettringite generated in group a is significantly more than other groups, and its needle-like and columnar crystals are uniformly distributed in the matrix. At the same time, Ca(OH)2 exists in the form of large block crystals, forming a closely intertwined structure with AFt, while the proportion of AFm and C-S-H is relatively low, mainly filling in the form of amorphous gel between other hydration products. In contrast, the amount of ettringite in group b is significantly reduced, and AFm is distributed in the form of sheet aggregates in the matrix, with reduced Ca(OH)2 content. This occurs because there is a lack of sufficient aluminum ions to promote the conversion of AFm to AFt, which is one of the reasons why the strength of group b is lower than that of group a. The amount of ettringite in group c is further reduced and is only distributed in a few local areas. AFm is mainly in the form of sheets and clusters, filling most of the matrix space. At the same time, Ca(OH)2 is more dispersed, and the content of C-S-H is extremely low. The micro-morphology of group d is similar to that of group c, with less ettringite generated and smaller morphology. In contrast, AFm is more widely distributed, and the content of Ca(OH)2 is lower. This is due to the presence of high concentrations of Si 4+ ions, which inhibit the generation of AFt, resulting in a significant reduction in the overall content of hydration products. The SEM observation results directly show that modified ions significantly affect the hydration kinetics and the stability of each phase. According to the SEM results, the C-S-H gel, which is the main contributor to the strength of cement, fails to generate in large quantities, and is instead dominated by CH and AFt, which may be one of the reasons why the strength of the stabilized soil does not exceed 20 MPa. Future research can improve the performance of soil stabilizer by promoting the generation of more C-S-H gel.

[0102] 4.3.2 Modified ions affect the degree of uniform hydration reaction

[0103] Hydration is the most effective way for soil stabilizer to work, and by adding modified ions, the hydration reaction can be more uniform and complete, thereby enhancing the strength of the stabilized soil. Figure 12 EDS shows the distribution of different elements in the stabilized soil sample, and the degree of reaction is studied by observing the uniform distribution of elements and local enrichment. By comparing the Al distribution of the four groups of stabilized soil, it can be clearly seen that the Al 3+ distribution in group a is very uniform on the surface of the soil particles. The distribution of Ca and Si in the sample is uniform, and the high Al 3+ proportion may promote the formation of silicate structures in the soil, making the hydration reaction more uniform. Figure 12 (3) Ca and Si are close in proportion, combined Figure 7 with the FTIR detection in group a, 3427.18 cm -1of C-S-H gel in group a. The loose distribution of Ca and Si and the local increase of Fe in group b may be due to the high concentration of Fe 3+ which leads to the preferential precipitation of iron oxides in the reaction and may interact with Al 3+ and Si 4+ to form iron-aluminum-silicate network, which is manifested as the increase of particle cluster and surface compactness. Group c shows the enrichment of Si in local area and the loose and uneven distribution of Ca. This may be due to the high Si 4+ ratio which helps to form silicate hydrates but its diffusion may be limited by the preferential precipitation of Ca 2+ , leading to incomplete reaction and poor local uniformity. The incomplete reaction may result in large pores and loose structure between particles, reducing the overall mechanical properties of the sample. The loose distribution of Al, Fe, and Si in group d and the local concentration of hydration products weaken the uniformity of the stabilized soil. The uniform distribution of reaction products in group a reflects the high reaction efficiency and excellent stability performance. Group b shows enhanced cohesiveness and the tendency to form iron-based minerals due to the increase of Fe 3+ , while group c shows incomplete reaction due to the limited diffusion of high Si 4+ ratio in the reaction. Optimizing the ratio of Al 3+ , Fe 3+ , and Si 4+ will be the key to further improving the uniformity and mechanical properties of stabilized soil. Optimizing the ratio of curing agent and reaction conditions to reduce the local enrichment of hydration products and enhance the uniform and complete reaction of hydration are important strategies to improve the uniformity and mechanical properties of stabilized soil.

[0104] 4.3.3 Strength comparison of stabilized soil with modified cement raw materials

[0105] The study compares the strength performance of modified cement stabilized soil by calculating the interaction energy to verify the influence of modified ions on cement hydration products and thus on the strength of stabilized soil. Figure 12 is the calculation result of the interaction energy of a, b, c, and d groups, which directly reveals the influence of different modified cements on the system energy and structural stability. The results show that when the Al 3+ ratio is the highest, the total interaction energy of the system reaches the lowest value of -22903.81 kJ / mol, indicating the strongest combination between ions and the most stable overall structure. Al 3+ has a significant electrostatic attraction ability due to its high charge density and small ionic radius, which dominates the structure and promotes the formation of highly stable combination state. When Fe 3+The proportion of Si 4+ increased to 1:1:2, the total interaction energy increased significantly to -16645.90 kJ / mol, showing a higher internal energy, indicating a decrease in structural stability. A high proportion of Si 4+ may cause distortion of the local structure, further reducing the strength of electrostatic attraction and increasing the heterogeneity of the system. In contrast, when the proportions of the three ions are all 1:1:1, the total energy is -18703.93 kJ / mol, showing a relatively high internal energy. Based on the above analysis, it can be seen that in the molecular simulation system of hydration products and soil structure, Al 3+ and Fe 3+ significantly contribute to structural stability, while Si 4+ does not reduce the stability of the stabilizer. The results of the molecular simulation are consistent with the experimental results.

[0106] 4.3.4 Hydration products cement the silt particles and fill the pore space of the framework

[0107] The gel material generated during the hydration of cement can form a cement paste film on the surface of the mineral soil, wrapping the soil particles and allowing them to contact each other. Figure 14 The pore distribution analysis results after processing by Image J software are shown, verifying the denseness of the stabilized soil structure by hydration products. The pore distribution of sample a is sparse and uniform, the pore of sample b increases significantly, the coverage is larger and the distribution is uneven. The pore distribution of sample c has a unique feature, mainly concentrated in the edge area, while the core area is relatively dense. The pores of sample d are widely distributed in the entire structure, with large pores and interconnected.

[0108] Figure 15 The pore-related data of different stabilized soil samples are shown. In Figure 14 A, the average pore size of sample a is the smallest. Figure 14 B shows the comparison results of the porosity and average pore area of the four stabilized soil samples. The porosity of sample c is the highest, close to 0.25, and the porosity of sample a is the lowest, only 0.05, with an average pore area of 17.257 nm. The porosity and average pore area of sample b are similar to those of sample a, and the porosity of sample d is slightly lower than that of sample c, and the average pore area is similar to that of sample b, showing different pore distribution characteristics. The analysis of the average size of the particles and the porosity shows that sample a and sample d achieve fine and uniform particle distribution and low porosity through optimized stabilizer ratio, thus showing the best performance in soil stabilization.

[0109] 5. SUMMARY

[0110] The present invention discusses the incorporation of Al3+ , Fe 3+ and Si 4+ industrial waste-modified cement on the stabilization mechanism of soft soil, the following main conclusions are drawn:

[0111] (1) Al 3+ modified cement showed the highest compressive strength, reaching 15 MPa, significantly better than Fe 3+ or Si 4+ modified cement. The strength improvement is closely related to the superior ability of Al 3+ to reduce the thickness of the double electric layer and promote hydration reactions. Fe 3+ produces moderate strength improvement by enhancing lattice symmetry and bonding efficiency, while Si 4+ mainly improves soil structure through skeletal support, but its stabilization effect is limited.

[0112] (2) FTIR and RDF analysis shows that Al 3+ and Fe 3+ destroy the double electric layer structure around the soil particles through ion exchange, forming Al-O and Fe-O bonds, thereby reducing the ζ potential and weakening the interparticle repulsion. BET analysis further shows that Al 3+ and Fe 3+ significantly reduce the mesopore volume, enhancing the compactness of the soil, demonstrating the effectiveness of both in modifying the double electric layer and improving soil particle cohesion, thereby forming a dense structure and increasing the compressive strength.

[0113] (3) SEM images verify the role of Al 3+ in promoting the formation of hydration products, especially ettringite, significantly filling soil pores and improving the compactness of the soil structure. Interaction energy analysis shows that the total energy of the Al 3+ and Fe 3+ modified system is about -22000 kJ / mol, indicating that this stabilized soil system has high structural stability. Image J analysis further shows that Al 3+ promotes hydration reactions, enhances the cementation of soil particles and effectively fills pores, significantly improving the strength and stability of the soil.

[0114] The preferred embodiments of the invention disclosed above are only used to help illustrate the invention. The preferred embodiments do not describe all the details, nor limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of the present specification. The present specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the invention, so that those skilled in the art can well understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A modified cement, characterized in that: The modified cement comprises sulfate cement with PO 42.5, slag, steel slag, coal gangue and high-purity Al2O3 powder.

2. A modified cement according to claim 1, characterized in that: The Al in the modified cement 3+ 、Fe 3+ and Si 4+ The ratio is 2:1:

1.

3. Use the modified cement according to any one of claims 1 to 2 in soft soil stabilization.

4. The modified cement according to claim 3 is used in soft soil stabilization, characterized in that: The application method is as follows: Mixing soft soil with modified cement to form a cement-soil mixture; The cement soil mixture is poured into the desired shape and cured.

5. The modified cement according to claim 4 is used in soft soil stabilization, characterized in that: The liquid-to-solid ratio of the soft soil is 0.36-0.

39.

6. The modified cement according to claim 4 is used in soft soil stabilization, characterized in that: The curing age is 7 days, 28 days or 56 days.

7. The modified cement according to any one of claims 1 to 2 is prepared from industrial solid waste raw materials.

8. A method for preparing modified cement, for use in the modified cement according to any one of claims 1 to 2, characterized in that: The preparation method comprises the following steps: A. Mixing high-purity Al2O3 powder and slag in proportion and adjusting the total Al2O3 content to obtain aluminum modified raw materials; B. Mixing Fe2O3 extracted from industrial hematite with steel slag to obtain iron modified raw materials; C. Mixing SiO with coal gangue to obtain a siliceous modified raw material; D. Compounding the aluminum modified raw material obtained in step A, the iron modified raw material obtained in step B, and the silicon modified raw material obtained in step C with sulfate cement having a PO 42.5 content to prepare a soil stabilizer.

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