High-liquid-limit silty soil modified material for construction backfill and preparation method of high-liquid-limit silty soil modified material

Abstract

The invention discloses a high-liquid-limit silt modifying material for construction backfilling and a preparation method, and relates to the technical field of high-liquid-limit silt improvement. The material comprises high liquid limit silt, and further comprises a substrate gel system, a polymeric lightweight aggregate; and a biopolymer organic modifier. Wherein the substrate gelling system is selected from a multi-component solid waste gelling system which comprises fly ash, furnace bottom slag, desulfurized gypsum and cement and has a specific cement-gelling ratio of 0.20 to 0.26 and a water-gelling ratio of 0.60 to 0.75; or a one-pack dry alkali-activated geopolymer gel system which contains a silicon-aluminum precursor and solid anhydrous sodium metasilicate and satisfies the specific equivalent weight of 4-8% and the molar ratio of 3.5-5.5; the polymer lightweight aggregate is EPS particles, the particle size is 3-4 mm, and the volume fraction is 15-25%; the biopolymer organic modifier is guar gum, and the doping amount of the biopolymer organic modifier is 0.2-0.6% of the total dry weight. The modified material has the fluidity of 220 to 260 mm, the bleeding rate, the 28-day strength of 1 to 8 MPa and the water stability coefficient.

Description

Technical Field

[0001] This invention relates to the field of high liquid limit silt improvement technology, and in particular to a high liquid limit silt modification material and its preparation method for construction backfilling. Background Technology

[0002] High liquid limit silt is frequently encountered in backfilling projects for highways, railway subgrades, and building foundations. High liquid limit silt (such as silty mud or some red clay) typically exhibits undesirable engineering characteristics, including high natural water content, large void ratio, high compressibility, low strength, and poor water stability. If such soils are used directly as backfill material, they are prone to significant settlement under load or their own weight. Especially in rainy areas or when groundwater levels fluctuate, the backfill is susceptible to significant strength reduction or even collapse after immersion in water, threatening project safety and long-term durability.

[0003] To improve the engineering performance of high liquid limit silt, existing technologies typically employ chemical solidification methods. Traditional methods mainly rely on ordinary silicate cement for stabilization, but cement production is energy-intensive and generates significant carbon emissions, contradicting the requirements of sustainable development. Therefore, the preparation of controlled low-strength materials (CLSM) from industrial solid waste (such as fly ash, bottom ash, and desulfurized gypsum) has become a research hotspot. However, how to rationally proportion various solid wastes to simultaneously meet the requirements of high fluidity, low bleeding rate, controllable later-stage strength (facilitating future excavation), and environmental protection requirements (such as compliance with heavy metal leaching standards) for backfill construction remains a challenge for existing technologies.

[0004] As a low-carbon alternative to cement, alkali-activated geopolymer technology is increasingly being applied to soil and rock solidification. This technology utilizes silica-alumina materials such as slag, fly ash, or agricultural waste ash (e.g., rice husk ash, coconut shell ash) as precursors. However, most existing geopolymer technologies rely on liquid strong alkalis (such as...) Liquid activators (such as solutions and water glass) are used as activators. These liquid activators are highly corrosive and require precise on-site preparation, which not only increases the complexity and safety risks of construction but also hinders the standardized premixed production and convenient application of materials. Furthermore, to reduce the weight of the backfill, existing technologies often incorporate lightweight polymer aggregates, such as expanded polystyrene (EPS) particles, into the modified materials. However, while the addition of lightweight aggregates reduces density, it also easily leads to severe segregation and bleeding (high bleeding rate) in the freshly mixed slurry, resulting in uneven internal structure and poor integrity after hardening, further reducing its strength and resistance to water erosion.

[0005] In summary, there is currently a lack of a technical solution that can systematically solve the above problems, i.e., on the basis of using high liquid limit silt and industrial solid waste, to provide a backfill modified material that can realize lightweight, ensure high fluidity and anti-segregation of the slurry, and ensure that the solidified body meets the controllable strength and high water stability (such as high water immersion strength retention rate). SUMMARY

[0006] The purpose of the present application is to provide a high liquid limit silt modified material for construction backfill and a preparation method, aiming to solve the technical problems of existing lightweight backfill materials, such as easy segregation, high bleeding rate, and poor water stability.

[0007] In a first aspect, the embodiments of the present application propose a high liquid limit silt modified material for construction backfill, comprising high liquid limit silt, and the modified material further comprises a base cementitious system, wherein the base cementitious system is:

[0008] A multi-component solid waste cementitious system comprising fly ash, bottom slag, desulfurization gypsum, and cement, wherein the mass ratio of cement to the total mass of fly ash, bottom slag, desulfurization gypsum, and cement is 0.20-0.26, and the mass ratio of water to the total mass of fly ash, bottom slag, desulfurization gypsum, and cement is 0.60-0.75; or, a one-package dry-method alkali-activated geopolymer cementitious system, the one-package dry-method alkali-activated geopolymer cementitious system comprises at least one siliceous precursor selected from slag, fly ash, rice husk ash, and coconut shell ash, and anhydrous sodium metasilicate as a solid alkali activator, and satisfies an equivalent of 4-8% of the mass of the precursor and a molar ratio of 3.5-5.5;

[0009] The modified material further comprises:

[0010] An EPS particle as a polymer lightweight aggregate, the particle size of the EPS particle is 3-4 mm, and the volume fraction of the EPS particle is 15-25%; and,

[0011] Guar gum as a biopolymer organic modifier, the dosage of the guar gum is 0.2-0.6% of the total dry weight of the modified material;

[0012] And the fluidity of the modified material after being mixed into a slurry is 220-260 mm, the bleeding rate The unconfined compressive strength of the modified material cured for 28d is 1-8MPa, the 24h water immersion strength retention rate The water stability coefficient , and the heavy metal leaching is lower than the corresponding limit value of GB 5085.3-2007.

[0013] Preferably, when the base cementitious system is a multi-component solid waste cementitious system comprising fly ash, bottom ash, desulfurization gypsum and cement, wherein the mass ratio of cement to the total mass of fly ash, bottom ash, desulfurization gypsum and cement is 0.20-0.26, and the mass ratio of water to the total mass of fly ash, bottom ash, desulfurization gypsum and cement is 0.60-0.75, the multi-component solid waste cementitious system is composed of the following components in mass percentage: fly ash 20-60%, bottom ash 10-30%, desulfurization gypsum 5-20%, and the balance being cement.

[0014] Preferably, the modified material has a fresh density of 1840-2100 kg / m3, a dry density of 1760-1890 kg / m3, and a porosity of 20-30%. 3 .

[0015] Preferably, the modified material further comprises inert aggregates, and the inert aggregates are selected from coal gangue and / or gasification coarse slag, and the total amount of the inert aggregates accounts for 10-40% of the total volume of the aggregates.

[0016] Preferably, the modified material has a permeability coefficient of 1.0-2.0x10-10 m2 under a confining pressure of 100 kPa. , and a 30-minute water immersion disintegration amount of 0.5-1.5%. .

[0017] Preferably, when the base cementitious system is a one-bag dry-method alkali-activated geopolymer cementitious system, the one-bag dry-method alkali-activated geopolymer cementitious system comprises at least one siliceous and aluminous precursor selected from slag, fly ash, rice husk ash, and coconut shell ash, and anhydrous sodium metasilicate as a solid alkali activator, and satisfies an equivalent amount of 4-8% based on the mass of the precursor, and a molar ratio of 3.5-5.5, the base cementitious system is a mixture of the siliceous and aluminous precursor and the anhydrous sodium metasilicate as a solid alkali activator.

[0018] Preferably, the combination of the EPS volume fraction and the particle size of 3-4 mm exhibits higher yield or structural strength at the same volume fraction compared with the particle size of 0-3 mm.

[0019] In a second aspect, the embodiments of the present application also propose a preparation method of the modified material proposed in the foregoing embodiments, comprising:

[0020] dry-premixing the high liquid limit silt and the base cementitious system;

[0021] adding water and stirring to form a slurry;

[0022] end-mixing EPS particles as polymer lightweight aggregates into the slurry, and performing low-shear stirring for a duration not shorter than 10 minutes;

[0023] Guar gum as a biopolymer organic modifier is added to the slurry, and secondary low shear stirring is performed;

[0024] and the prepared modified material is subjected to standard curing under conditions of temperature , relative humidity .

[0025] Preferably, when the base cementitious system is a one-bag dry-activated alkali-activated geopolymer cementitious system, the one-bag dry-activated alkali-activated geopolymer cementitious system comprises a siliceous-alumina precursor selected from at least one of slag, fly ash, rice husk ash, and coconut shell ash, and anhydrous sodium metasilicate as a solid alkali activator, and satisfies an equivalent of 4-8% of the mass of the precursor and a molar ratio of 3.5-5.5, the base cementitious system is a mixture of the siliceous-alumina precursor and the anhydrous sodium metasilicate as a solid alkali activator, and the dry pre-mixing step is a dry mixing pre-mixing step of the high-plasticity clay and the mixture, and the step of adding water and stirring to form a slurry is a step of adding water on site to achieve mixing.

[0026] Preferably, the shear rate of the step of performing low shear stirring and the step of performing secondary low shear stirring is controlled at 50-150 rpm.

[0027] Beneficial effects: The present application systematically solves the technical problems of easy segregation, high bleeding rate, and poor uniformity of the existing lightweight backfill material by synergistically compounding a specific base cementitious system, a specific particle size and volume fraction of polymer lightweight aggregate, and a trace amount of biopolymer organic modifier. The thickening, water retention, and cementing properties of biopolymers (guar gum) significantly improve the cohesiveness of the slurry, effectively inhibit the floating of lightweight aggregate and the exudation of water, thereby ensuring the high uniformity of the hardened material structure and excellent water erosion resistance (high water stability coefficient and immersion strength retention rate). In addition, the one-bag dry-activated alkali-activated geopolymer cementitious system provided by the present application uses a solid alkali activator (anhydrous sodium metasilicate) instead of traditional liquid alkali with high corrosion, greatly simplifying the on-site construction process, reducing the operation safety risk, and making large-scale application of low-carbon geopolymer materials possible. The large-scale resource utilization of high-plasticity clay and industrial solid waste is realized, and the modified material can simultaneously meet the multiple engineering performance requirements of high flowability, low bleeding rate, controllable strength (re-excavation), high durability, and environmentally friendly leaching standards. BRIEF DESCRIPTION OF DRAWINGS

[0028] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0029] Figure 1 This is a schematic flowchart of a method for preparing a high liquid limit silt modified material for construction backfilling, as described in Embodiment 2 of the present invention. Detailed Implementation

[0030] To more clearly illustrate the technical solutions in the embodiments of the invention or the prior art, the invention will be briefly introduced below in conjunction with the accompanying drawings and descriptions of the embodiments or the prior art. Obviously, the following description of the structure of the drawings is only some embodiments of the invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. It should be noted that the description of these embodiments is for the purpose of helping to understand the invention, but does not constitute a limitation on the invention.

[0031] Example 1

[0032] This embodiment provides a high liquid limit silt modified material for construction backfilling. This embodiment aims to illustrate the specific preparation process and performance verification of two preferred base cementing systems of the modified material (Type A-1: ​​multi-component solid waste cementing system; Type A-2: one-pack dry alkali-activated geopolymer cementing system).

[0033] Experimental raw materials: High liquid limit silt. The high liquid limit silt used in this example was taken from dredged silt from a certain project. Its physical properties were determined by indoor geotechnical testing as follows: Liquid limit: (Above 50%, meets the definition of high liquid limit), plastic limit is The plasticity index is 21.7. The natural moisture content is... Soil particle density The value was 2.70. Before the test, all high liquid limit silt was placed... Dry in an oven for 24 hours until constant weight, then crush and pass through. Use the sieve for later use.

[0034] Base cementitious system (Type A-1): A multi-component solid waste cementitious system. In this embodiment, the following industrial solid waste and cement are used as components of the Type A-1 cementitious system:

[0035] Cement: PI 42.5 Portland cement, conforming to GB 175-2007 standard. Fly ash: Grade II fly ash, its chemical composition analyzed by XRF (X-ray fluorescence spectroscopy), mainly consisting of... (51.8%) (28.2%) (6.5%) and (5.1%). Bottom ash: Bottom ash from power plant boilers was used, ground in a ball mill for 30 minutes. Its chemical composition was analyzed by XRF, and the main components were... (55.1%) (25.9%) (6.8%) and (3.9%). Desulfurization gypsum: Power plant flue gas desulfurization gypsum is used; its main chemical components are... .

[0036] Base gelling system (Type A-2): A one-pack dry-process alkali-activated geopolymer gelling system. In this embodiment, the following precursors and solid activators are used as components of the Type A-2 gelling system:

[0037] The silica-alumina precursor is blast furnace slag, specifically S95 grade granulated blast furnace slag powder with a density of 2.90 g / cm³. Its main chemical components are... (33.5%) (34.2%) and (14.1%). Fly ash, using Grade II fly ash (same as Type A-1). Rice husk ash, selected after... Rice husk ash calcined for 2 hours is used as a supplementary material for highly active amorphous silica.

[0038] Solid alkali activator: Industrial grade powdered anhydrous sodium metasilicate ( ). It was determined that its The mass fraction is approximately 51.0%. This solid activator replaces the highly corrosive liquid activator used in traditional geopolymer processes, which requires on-site preparation. By combining water glass, we have achieved "one-package" dry premixing and "on-site water-only" construction.

[0039] The polymer lightweight aggregate (B) uses expanded polystyrene (EPS) particles. To achieve the technical effects of this invention, the particle size of the EPS particles needs to be strictly controlled. The inventors discovered that the structural strength of lightweight soil is negatively correlated with the size of the EPS; when the EPS volume ratio and the cementitious material mixing ratio are constant, the structural strength increases with the increase of the EPS size (e.g., ...). This significantly reduces [the weight / weight]. Therefore, to balance the lightweight effect with structural strength, this embodiment preferably uses spherical EPS particles, with the particle size strictly controlled within [specific range]. to Between, the average particle size is selected The particles have a bulk density of approximately .

[0040] The biopolymer organic modifier (C) uses industrial-grade guar gum powder. Guar gum, as a non-ionic galactomannan, hydrates readily in cold water to form a high-viscosity colloidal solution. Its mechanism of action in this invention is multifaceted: 1) As a highly efficient thickener and water-retaining agent, it significantly improves the cohesiveness of freshly mixed slurry and inhibits water exudation from the slurry (i.e., reduces the bleeding rate); 2) Through the bridging and encapsulation effects of its polymer chains, it achieves an effectively very low suspension density (…). ) EPS particles overcome gravity differences and fundamentally inhibit the floating and segregation of EPS particles; 3) At the micro level, guar gum hydrogel can fill the pores between soil particles and form a polymer film on the particle surface, which plays a good cementing role and improves the integrity and water erosion resistance of hardened soil.

[0041] Ordinary tap water is used for mixing.

[0042] Preparation of modified materials

[0043] Example 1-A: Using A-1 type gelling system

[0044] Preparation in this embodiment The modified material was designed to validate the A-1 type gelling system. The specific formulation is shown in the table below:

[0045] Component Class Material Unit amount Soil High liquid limit silt (oven dried) 1000 kg Cementitious system A-1 (total amount ) Cement (P.I 42.5) 98.4 kg Fly ash 180.4 kg Bottom ash 81.6 kg Desulfurization gypsum 49.6 kg Total mass of cementitious system 410.0 kg Lightweight aggregate B EPS granules (3-4 mm) 0.22m³ Organic modifier C Guar gum 6.36 kg Mixing water Water 258.3 kg

[0046] Verification of proportioning parameters:

[0047] The ratio of cement to the total mass of cementitious components: .

[0048] The ratio of water to the total mass of the cementitious components: .

[0049] EPS particle volume fraction: .

[0050] Guar gum content (percentage of total dry weight): Total dry weight = (silt + cementing system + EPS + guar gum) = . .

[0051] Preparation steps (using a specific process sequence to prevent EPS segregation):

[0052] 1) Dry mixing: The dried... High liquid limit silt, cement, fly ash, Bottom slag and The desulfurized gypsum was placed in a horizontal forced mixer and dry-mixed for 4 minutes to ensure that the cementitious material and the silt particles were mixed evenly.

[0053] 2) Dissolving the modifier: [The text abruptly ends here, likely due to an incomplete sentence or a formatting error.] Guar gum powder added slowly In the mixing water, a high-speed disperser (speed) is used simultaneously. Disperse and stir for 4 minutes until the guar gum is completely hydrated and dissolved to form a homogeneous, high-viscosity colloidal solution.

[0054] 3) Wet mixing to form a slurry: Slowly pour the guar gum solution prepared in step (2) into the dry mixture in step (1), and wet mix at medium speed for 4 minutes to form a uniform slurry with high cohesiveness.

[0055] 4) End-stage addition of lightweight aggregate: ... EPS particles (particle size) Pour it into the slurry.

[0056] 5) Low-shear mixing (critical step): To prevent EPS particles from breaking and segregation due to excessive shear force, the mixer speed is reduced to a low speed (controlled at...). Stir slowly for 12 minutes. Observation shows that the EPS particles are uniformly suspended in the slurry, without floating or segregation.

[0057] 6) Discharge and Curing: Pour the prepared modified material slurry into the... Cube trial mold and The cylindrical mold was placed in a standard curing chamber (temperature). relative humidity ) and maintain until the specified age (3d, 7d, 28d).

[0058] Example 1-B: Using Type A-2 geopolymer cementing system

[0059] Preparation in this embodiment The modified material was designed to validate the A-2 type one-pack gelling system. The specific formulation is shown in the table below:

[0060] Component Class Material Unit amount Soil High liquid limit silt (oven dried) 1000 kg Cementitious system A-2 (total amount B_2) [precursor] Slag (S95) 336.0 kg [precursor] Fly ash 84.0 kg [Solid excitation agent] 53.5 kg Total mass of cementitious system 473.5 kg Lightweight aggregate B EPS granules (3-4 mm) 0.18m³ Organic modifier C Guar gum 7.38 kg Mixing water Water 280.0 kg

[0061] Equivalent (percentage of precursor mass):

[0062] Total mass of precursor .

[0063] Activator quality , including quality .

[0064] Equivalent = .

[0065] Mole ratio:

[0066] After calculation, by S95 slag, Class II fly ash and The system composed of anhydrous sodium metasilicate, The molar ratio is within this range and meets the requirements. Requirements.

[0067] EPS volume fraction: .

[0068] Guar gum content:

[0069] Total dry weight = . .

[0070] Preparation steps:

[0071] 1) Preparation of a single-pack cementitious material: ... slag, fly ash and Solid anhydrous sodium metasilicate powder was placed together in a dry V-type mixer and thoroughly dry-mixed for 12 minutes to prepare a homogeneous one-pack dry alkali-activated geopolymer gelation system. This system is a premixed mixture and can be bagged and transported to the construction site.

[0072] 2) Dry mixing: [The text abruptly ends here, likely due to an incomplete sentence or a formatting error.] dried high liquid limit silt and of The gelling material is placed in a horizontal forced mixer and dry-mixed for 4 minutes.

[0073] 3) Dissolving the modifier: [The text abruptly ends here, likely due to an incomplete sentence or a formatting Guar gum powder added slowly Disperse and stir at high speed in water for 4 minutes to prepare a homogeneous colloidal solution.

[0074] 4) Wet mixing with "water only": Slowly pour the guar gum solution (i.e., the water used for mixing) from step (3) into the dry mixture from step (2) (this is the process of "water only added on site"), and wet mix at medium speed for 4 minutes to form a geopolymer slurry.

[0075] 5) End-stage addition of lightweight aggregate: ... EPS particles (particle size) Pour it into the slurry.

[0076] 6) Low-shear mixing: Also using low speed ( Stir slowly for 12 minutes to prevent EPS particles from breaking.

[0077] 7) Discharge and curing: Same as in Example 1-A, pour the test mold and cure in a standard curing room.

[0078] Performance Tests and Results:

[0079] The samples prepared in Examples 1-A and 1-B were tested according to the defined performance indicators.

[0080] Flowability test method: Refer to ASTM D6103-17 and GB / T 50080-2016 standards, using a flowability cylinder (inner diameter...) ,high Test the spread diameter of the slurry on a horizontal plate.

[0081] Test Results: Example 1-A (CLSM): The measured flowability was [value missing]. Example 1-B (geopolymer): The measured flowability was... .

[0082] Conclusion: The flowability of both embodiments is within [specific range]. Within the range.

[0083] Bleeding rate, test method: refer to GB / T 50080-2016 standard, put the slurry into a standard container and let it stand, measure the surface bleeding volume at regular intervals, and calculate the bleeding rate.

[0084] Test Results: Example 1-A (CLSM): The measured bleeding rate was... Example 1-B (geomer): The measured bleeding rate was... .

[0085] Conclusion: The bleeding rate was similar in both embodiments. This is thanks to the strong water-retention and thickening effect of guar gum, which effectively inhibits the bleeding of the slurry and solves the problem of easy segregation and bleeding of lightweight EPS soil.

[0086] 28-day unconfined compressive strength (28dUCS), test method: according to GB / T 50081-2019 standard, test the unconfined compressive strength of cubic specimens cured for 28 days.

[0087] Test Results: Example 1-A (CLSM): The measured 28dUCS was [value missing]. Example 1-B (geopolymer): The measured 28 dUCS was [value missing]. .

[0088] Conclusion: Both embodiments of the 28dUCS are in Within the specified range, the controllable strength (allowing for further excavation) requirement is met.

[0089] 24-hour water immersion strength retention rate, test method: The sample, after standard curing for 28 days, is immersed in room temperature water for 24 hours, removed and dried, and its unconfined compressive strength after immersion is immediately tested. Strength retention rate = ( / ) .

[0090] Test Results: Example 1-A (CLSM): Strength after immersion in water for Retention rate = ( ) Example 1-B (Geopolymer): Strength after immersion in water for Retention rate = ( ) .

[0091] Conclusion: Both embodiments showed good retention of water immersion strength. .

[0092] Water stability coefficient, test method: The softening coefficient K (K = strength after immersion / strength before immersion) is used as the evaluation index of water stability coefficient.

[0093] Test Results: Example 1-A (CLSM): Water stability coefficient K = Example 1-B (Geopolymer): Water stability coefficient K = .

[0094] Conclusion: The water stability coefficients of both embodiments are... This indicates that the material of the present invention has extremely high water stability, which is significantly better than traditional high liquid limit clay (which disintegrates upon immersion in water) and ordinary EPS lightweight soil (which easily absorbs water, leading to strength reduction).

[0095] Heavy metal leaching test method: The leaching test was carried out on the samples cured for 28 days according to HJ 557-2010 (horizontal oscillation method), and the evaluation was carried out according to GB 5085.3-2007 standard.

[0096] Test results: Eight heavy metal elements, including Cr, Mn, Cu, Zn, As, Pb, Cd, and Hg, were detected.

[0097] Example 1-A (CLSM): The leaching values ​​of all heavy metals were far below the limits specified in GB 5085.3-2007.

[0098] Example 1-B (Geopolymer): Geopolymer gels (such as CASH or NASH) have excellent physical adsorption and chemical complexation effects on heavy metal ions, and the leaching values ​​of all heavy metals are far below the limit.

[0099] Conclusion: Both embodiments meet environmental protection requirements.

[0100] Permeability and resistance to collapse, permeability coefficient: The permeability coefficient was tested under a confining pressure of 100 kPa, according to the "Standard for Geotechnical Testing Methods" GB / T 50123-2019. Example 1-A yielded a permeability coefficient of [missing value]. The permeability coefficient measured in Example 1-B was: All satisfy Requirements. Disintegration resistance: A disintegration test was conducted. Uncured silty clay completely disintegrated within 300 seconds (5 minutes). However, the samples 1-A and 1-B in this example, after immersion in water for 30 minutes, showed the following disintegration amounts: and All satisfy It meets the requirements and exhibits excellent resistance to disintegration.

[0101] To verify the inclusion of inert aggregate in the preferred formulation, density was determined by adding an additional agent to the formulation of Example 1-A. The volume of coal gangue replaces part of the silt.

[0102] Test results: The freshness density of this formula is The dry density is .

[0103] Conclusion: This density value falls within the fresh density specified by the preferred scheme ( ) and dry density ( Within the range.

[0104] Microstructure analysis, SEM analysis: Scanning electron microscopy (SEM) analysis was performed on the samples after 28 days of curing.

[0105] Example 1-A (CLSM): A large amount of hydrated calcium silicate (CSH) gel and needle-like ettringite (AFt) were observed. Simultaneously, a film-like substance formed by guar gum polymer was observed to coat the soil particles and EPS balls, tightly connecting the EPS balls to the cementitious matrix and effectively preventing interfacial separation.

[0106] Example 1-B (Geopolymer): Abundant dense CASH (calcium aluminosilicate hydrate) gel and NASH (sodium aluminosilicate hydrate) gel were observed. These geopolymer gels filled the pores, forming a high-strength three-dimensional network structure. Similarly, the guar gum polymer film interweaves with the geopolymer gel network, further enhancing the adhesion between EPS particles and the matrix and filling the micropores.

[0107] Conclusion: Microscopic analysis confirms that the present invention achieves a macroscopic balance of high fluidity, anti-segregation, high strength and high water stability through the synergistic effect of (A) inorganic gelling agent, (B) EPS lightweight aggregate and (C) guar gum organic modifier.

[0108] This embodiment prepared modified materials with specific ratios of two gelling systems, specific EPS particles, specific guar gum content, and all performance indicators (flowability, bleeding rate, 28-day strength, water retention rate, water stability coefficient, and heavy metal leaching) through two approaches, A-1 and A-2 (geopolymer). The density, permeability, and anti-disintegration characteristics of the preferred scheme were verified. The technical solution of this invention is detailed and specific, with reliable and authentic data, demonstrating full feasibility.

[0109] Example 2

[0110] This embodiment describes in detail a method for preparing a high liquid limit silt modified material for construction backfilling, as proposed in the second aspect of the present invention. This method aims to prepare the modified material as described in Example 1 and systematically solves the technical challenge of uniformly mixing extremely low density polymer lightweight aggregate (B) with a high-density base cementing system (A) and high liquid limit silt.

[0111] The core of the preparation method of this invention lies in the control of the mixing sequence and stirring energy, especially the synergistic application of the "end-incorporation" process and the "double low-shear" step, which ensures the integrity of (B) EPS particles and their uniform suspension in the slurry. At the same time, through the viscosity control effect of (C) biopolymer organic modifier, a uniform, stable, non-segregating, and performance-compliant lightweight modified material is finally obtained.

[0112] The raw materials used in this embodiment are the same as those described in Example 1, and are briefly described below:

[0113] High liquid limit silt: taken from dredged silt of a certain project, dried, crushed and processed. Use the sieve for later use. Its liquid limit is... The plasticity index is .

[0114] The base cementitious system (Type A-1) includes PI 42.5 cement, Class II fly ash, ground bottom ash, and desulfurized gypsum.

[0115] The base cementing system (Type A-2) includes S95 grade granulated blast furnace slag powder (Slag 1), Grade II fly ash, and powdered anhydrous sodium metasilicate as a solid alkali activator. ).

[0116] Polymer lightweight aggregate (B): Made of expanded polystyrene (EPS) granules, with particle size strictly controlled. The bulk density is approximately .

[0117] Biopolymer organic modifier (C): Industrial-grade guar gum powder.

[0118] Water used for mixing: Ordinary tap water.

[0119] Preparation method A (corresponding to type A-1 CLSM system):

[0120] This section details the method and steps for preparing modified materials using a multi-component solid waste gelling system (Type A-1). This example focuses on the preparation of... Taking the modified material as an example, the formulation in Example 1-A is used:

[0121] High liquid limit silt: Base cementing system ( ): (Among them, cement) fly ash Bottom slag Desulfurized gypsum EPS particles (3-4mm): Guar gum: Water for mixing: The detailed preparation steps are as follows:

[0122] Step S1: Dry premix the high liquid limit silt with the base cementing system;

[0123] Dry premixing, High liquid limit silt dried and crushed and The base cementitious system (Type A-1, i.e., a mixture of cement, fly ash, bottom ash, and desulfurization gypsum) is added together to a horizontal forced mixer (e.g., HJW-150 type). The mixer is started at medium speed (e.g., approximately...). Perform dry premixing for 4 minutes.

[0124] Process objective: The purpose of this step is to break up the clumps of high liquid limit silt by utilizing the friction and shearing between solid particles before adding water, and to uniformly coat the surface of the silt particles with tiny particles of cementing materials such as fly ash and bottom ash. This lays a uniform material foundation for subsequent hydration reactions and slurry formation.

[0125] Step S2: Add water and stir to form a slurry;

[0126] Add water and stir to form a slurry, while keeping the mixer running at medium speed. The mixing water (excluding guar gum) is slowly and evenly added to the dry mix using a spray device. After the water is added, continue stirring at medium speed for 4 minutes.

[0127] This step initiates the hydration of the cementitious materials (especially cement) and fully wets the silt particles, forming a homogeneous slurry with a certain degree of fluidity but low viscosity (guar gum has not been added at this point).

[0128] Step S3: Add the EPS particles, which serve as polymer lightweight aggregate, to the end of the slurry and perform low-shear stirring for a duration of not less than 10 minutes.

[0129] EPS particles are incorporated at the end and subjected to low-shear mixing. The mixer speed is reduced to a low speed (e.g., ...). The rotational speed falls within (within the range). EPS particles (particle size) Pour all of it into the slowly stirring slurry. Keep it warm. With a low shear rate, continue stirring for 12 minutes.

[0130] Process objective: End-stage incorporation to increase the density of EPS particles ( ) much lower than the slurry (approximately EPS particles are fragile and easily broken. If added in step S1 or S2, they will be ground and crushed under high shear force, causing the lightweighting effect to fail and reducing the final strength. Therefore, they must be added only after the slurry has formed. Low-shear mixing is necessary. The low-speed stirring provides sufficient power for the EPS particles to overcome buoyancy and disperse into the slurry, but its shear force is lower than the compressive strength of the EPS particles, ensuring the integrity of the particles. Duration ( Due to the significant difference in density between EPS and slurry, sufficient mixing time (12 minutes in this example) is required to achieve the desired result. EPS particles in The space within the slurry is uniformly distributed.

[0131] Step S4: Add guar gum, which serves as an organic modifier for biopolymers, to the slurry and perform a second low-shear stirring.

[0132] Add guar gum and perform a second low-shear mixing; while maintaining While stirring at low speed, Evenly sprinkle the dry powdered guar gum into the bubbling slurry. Continue "secondary low-shear mixing" for 4 minutes.

[0133] Process Objective: Timing: This invention innovatively adds guar gum after the EPS particles. This allows the EPS particles (step S3) to be preferentially dispersed in the low-viscosity slurry, reducing the difficulty of dispersion. Function: Guar gum powder rapidly hydrates upon contact with water in step S4, and the viscosity and yield stress of the entire slurry are dramatically increased during the 4-minute secondary stirring. Effect: This "post-viscosity enhancement" method, like a "locking" mechanism, "freezes" the uniformly dispersed EPS particles in step S3 in place, preventing them from floating. This fundamentally solves the problem of vertical segregation and stratification that easily occurs in lightweight soil during the settling and pouring process (i.e., after stirring stops).

[0134] Step S5: and the temperature of the prepared modified material. relative humidity Standard maintenance shall be carried out under the following conditions.

[0135] After standard curing, stop stirring and pour the uniform, segregated modified material slurry into the mold. Place the mold in the standard curing chamber (temperature...). relative humidity After curing for 24 hours, the sample is demolded and cured under standard conditions until 28 days of age, ready for performance testing.

[0136] Preparation method B (corresponding to type A-2 geopolymer system)

[0137] This section details the method and steps for preparing modified materials using a "one-package" dry alkali-activated geopolymer gelation system (Type A-2). This example focuses on the preparation of... Taking the modified material as an example, the formulation in Example 1-B is used:

[0138] High liquid limit silt: Base cementing system ( ): (This is a premix), EPS granules (3-4mm): Guar gum: Water for mixing: .

[0139] The detailed preparation steps are as follows:

[0140] Step S-Pre: Preparation of "One-Pack" Mixture. This step is a factory prefabrication step, not a construction site step. Slag (S95) fly ash and Powdered solid alkali activator (anhydrous sodium metasilicate) Place it in a large, dry V-type mixer. Dry premix thoroughly for 12 minutes to ensure uniform particle size distribution of the solid activator and the aluminosilicate precursor. The mixture of materials is sealed in packaging, which is the defined "base gelling system" (Type A-2).

[0141] Process objective: This is key to achieving "one-package" geopolymers. It uses highly corrosive, high-viscosity liquid alkali activators (such as those used in traditional processes). The replacement of water glass solution with a stable solid activator greatly improves the material's ease of transportation, storage stability, and construction safety.

[0142] Step S1': Dry premixing; at the construction site, [the following steps are taken] dried high liquid limit silt and "One-pack" mixture ( Add the ingredients together to the horizontal forced mixer. Start the mixer and run it at medium speed (approximately...). Dry premix for 4 minutes.

[0143] Process objective: To uniformly mix high liquid limit silt with "one-pack" cementitious powder.

[0144] Step S2': Add water and stir to form a slurry; while keeping the mixer running at medium speed, Slowly and evenly add the water (excluding guar gum) to the dry mix. This step is called "mixing by adding water only on-site". After adding the water, continue mixing at medium speed for 4 minutes.

[0145] Process objective: Water dissolves the solid activator in the mixture ( This forms a highly alkaline solution, which immediately begins to dissolve and activate the silica-alumina precursors (slag and fly ash), resulting in a geopolymer reaction and the formation of a homogeneous slurry.

[0146] Step S3': Incorporate EPS particles at the end and perform low-shear mixing (same as S3); reduce the mixer speed to a low speed (e.g., , falling (within the range). EPS particles (particle size) Pour into the slurry. Keep At a low shear rate, continue stirring for 12 minutes (meeting the requirement of "not less than 10 minutes").

[0147] Process objective: Same as step S3, to ensure that EPS is uniformly dispersed in the geopolymer slurry without breaking.

[0148] Step S4': Add guar gum and perform a second low-shear mixing (same as S40); while maintaining... While stirring at low speed, Evenly sprinkle the dry powdered guar gum into the slurry. Continue "secondary low-shear mixing" for 4 minutes.

[0149] Process objective: Similar to step S4, guar gum rapidly hydrates and thickens in the geopolymer slurry, "locking" the dispersed EPS particles in a suspended state to prevent segregation.

[0150] Step S5': Standard curing (same as S5) Stop mixing, pour the test mold, and cure in a standard curing chamber (temperature). relative humidity Keep them in the environment until they reach 28 days old.

[0151] Comparative Example 2-1: Incorrect Mixing Sequence (“Integrated Feeding Method”)

[0152] Method: The formulation of Example 1-A was used. silt, gelling system ( ), EPS particles Guar gum and Add all the water to the blender at once and try mixing it.

[0153] Result: Stirring failed. Guar gum powder rapidly formed high-viscosity gel clumps ("fish eyes") upon contact with water in localized areas, making it impossible to disperse. EPS particles (density) Because of buoyancy, it immediately floats on the water surface and the upper layer of the slurry, and cannot be carried by the agitator into the heavy materials (silt and cementitious material) below.

[0154] Conclusion: The "integrated feeding method" cannot be used to prepare the modified material of this invention. The specific sequence of "dry premixing", "adding water to form a slurry", "terminal addition of EPS", and "post-addition of guar gum" is a necessary condition for achieving uniform mixing.

[0155] Comparative Example 2-2: Incorrect stirring rate (high shear stirring)

[0156] Method: The formulation and mixing sequence of Example 1-A were used. However, in step S3 (incorporation of EPS particles), a medium-high speed (e.g., Approaching the upper limit The stirring rate is set to 1000 rpm (or higher), while the rest of the steps remain unchanged.

[0157] Results: After 12 minutes of stirring, visual inspection of the slurry revealed that a large number of EPS particles had been broken and abraded by the stirring impeller. A large amount of white debris floated on the surface of the slurry. Performance testing was conducted after 28 days of curing; its 28-day unconfined compressive strength was only [missing data]. .

[0158] Conclusion: High-shear mixing severely damages the structure of EPS particles. The broken EPS particles not only lose the integrity of the lightweight aggregate but also become structural defects within the material, leading to a decrease in strength. (lower than) The lower limit of the range. Therefore, the defined range is... (Preferred) A low shear rate is a necessary condition for ensuring material properties.

[0159] Comparative Examples 2-3: Incorrect timing of guar gum addition (added before EPS)

[0160] Method: The formulation of Example 1-A was used, but the order of steps S3 and S4 was changed.

[0161] (S1) Dry premixing (silt + cementitious material).

[0162] (S2) Add water to form a slurry.

[0163] (New S3) Add to the slurry Guar gum, mix on low speed for 4 minutes.

[0164] (New S4) is added to the end of the slurry (which has now been thickened). EPS granules, stir at low speed for 12 minutes.

[0165] Results: In (New S3), guar gum significantly increased the viscosity of the paste. In (New S4), when EPS particles (density) When added to a high-viscosity slurry, the mixer requires extremely high torque to "press" these very light particles into the viscous slurry. After mixing for 12 minutes, it was found that the EPS particles were distributed very unevenly, with a large number of particles agglomerated near the mixing shaft or forming "clumps," making it impossible to achieve uniform dispersion.

[0166] Conclusion: Premature addition of guar gum leads to excessively high slurry viscosity, hindering the dispersion of lightweight EPS particles. Therefore, the predetermined order of first adding EPS (for dispersion at low viscosity) and then adding guar gum (for locking at high viscosity) is a non-obvious technical solution to resolve this technical contradiction and achieve uniform dispersion.

[0167] Comparative Examples 2-4: Traditional Geopolymer Process (Liquid Alkali Method)

[0168] Method: The formulation of Example 1-B was used, but the solid activator was replaced with a traditional liquid alkali.

[0169] (S-Pre) At the construction site, will of The equivalent (6.5%) required liquid water glass and NaOH solution (corrosion-resistant equipment must be worn) and Mix with water to produce a highly corrosive liquid alkali activator.

[0170] (S1') Dry mix (silt + precursor).

[0171] (S2') Spray the liquid alkali prepared in S-Pre into the dry mixture.

[0172] (S3' / S4' / S5') Same as Example 1-B.

[0173] Results: The preparation process generated a strong, pungent odor and alkaline mist, posing a significant corrosion risk to operators and equipment (mixer). Although the material can eventually be molded (28-day strength is...), the corrosion risk is still significant. (within the range of 1-8MPa), but the safety, convenience and environmental friendliness of the process are extremely poor.

[0174] Conclusion: By using a "pre-dry mixed mixture" and "on-site mixing with only water," the safety and operational difficulties caused by liquid alkali are completely avoided while achieving the same material properties, representing a significant improvement.

[0175] This embodiment details the process for preparing the modified material, including specific operational steps for the CLSM system (A-1) and the "one-pack" geopolymer system (A-2). Through comparison with Comparative Examples 2-1 to 2-4, the specific mixing sequence (dry mixing first, then slurry formation, followed by EPS addition, and finally guar gum addition) and specific process parameters (low shear stirring rate) defined by the method of this invention are fully demonstrated. Duration This is the key to overcoming the technical challenges of segregation, breakage, and uneven dispersion of lightweight EPS particles, as well as solving the alkali hazards of traditional geopolymers.

[0176] Finally, it should be noted that the above are merely preferred embodiments of the invention and are not intended to limit the scope of protection of the invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A modified material for high liquid limit silt used in construction backfilling, comprising high liquid limit silt, characterized in that, The modified material further includes a base cementing system, wherein the base cementing system is: A multi-component solid waste cementitious system comprising fly ash, bottom ash, desulfurization gypsum, and cement, wherein the mass ratio of cement to the total mass of fly ash, bottom ash, desulfurization gypsum, and cement is 0.20–0.26, and the mass ratio of water to the total mass of fly ash, bottom ash, desulfurization gypsum, and cement is 0.60–0.75; or, a one-pack dry-process alkali-activated geopolymer cementitious system comprising a silica-alumina precursor selected from at least one of slag, fly ash, rice husk ash, and coconut shell ash, and anhydrous sodium metasilicate as a solid alkali activator, and satisfying the following conditions: The equivalent content is 4–8% of the precursor mass and The molar ratio is 3.5–5.5; The modified material also includes: An EPS (expanded polystyrene) particle as a polymeric lightweight aggregate, wherein the EPS particle has a particle size of 3–4 mm and a volume fraction of 15–25%; and, Guar gum as an organic modifier for biopolymers, wherein the amount of guar gum is 0.2–0.6% of the total dry weight of the modified material; Furthermore, the modified material, after being mixed into a slurry, has a flowability of 220–260 mm and a bleeding rate of [missing information]. The unconfined compressive strength after 28 days of curing is 1–8 MPa, and the strength retention rate after 24 hours of immersion in water is [not specified]. Water stability coefficient Furthermore, the leaching of heavy metals is below the corresponding limit in GB 5085.3-2007.

2. The modified material according to claim 1, characterized in that, When the base cementing system is a multi-component solid waste cementing system comprising fly ash, bottom ash, desulfurization gypsum, and cement, wherein the mass ratio of cement to the total mass of fly ash, bottom ash, desulfurization gypsum, and cement is 0.20–0.26, and the mass ratio of water to the total mass of fly ash, bottom ash, desulfurization gypsum, and cement is 0.60–0.75, the multi-component solid waste cementing system is composed of the following components by mass percentage: 20–60% fly ash, 10–30% bottom ash, 5–20% desulfurization gypsum, with the balance being cement.

3. The modified material according to claim 1, characterized in that, The modified material has a fresh density of 1840–2100 kg / m³ and a dry density of 1760–1890 kg / m³. 3 .

4. The modified material according to claim 1, characterized in that, The modified material also includes inert aggregates selected from coal gangue and / or gasification slag, wherein the total amount of inert aggregates accounts for 10–40% of the total aggregate volume.

5. The modified material according to claim 1, characterized in that, The permeability coefficient of the modified material under a confining pressure of 100 kPa And the amount of material that disintegrates after 30 minutes of immersion in water .

6. The modified material according to claim 1, characterized in that, When the base cementing system is a one-package dry alkali-activated geopolymer cementing system, the one-package dry alkali-activated geopolymer cementing system comprises a silica-alumina precursor selected from at least one of slag, fly ash, rice husk ash, and coconut shell ash, and anhydrous sodium metasilicate as a solid alkali activator, and satisfies the following conditions: The equivalent content is 4–8% of the precursor mass and When the molar ratio is 3.5–5.5, the substrate gelling system is a mixture formed by pre-dry mixing of the silica-alumina precursor and the anhydrous sodium metasilicate as a solid alkali activator.

7. The modified material according to claim 1, characterized in that, The combination of EPS volume fraction and 3–4 mm particle size is relative to At the same volume fraction, the particle size exhibits higher yield or structural strength.

8. A method for preparing the modified material as described in claim 1, characterized in that, include: The high liquid limit silt is dry-premixed with the base cementing system; Add water and stir to form a slurry; EPS particles, which serve as polymer lightweight aggregate, are incorporated into the end of the slurry and subjected to low-shear stirring for a duration of not less than 10 minutes. Guar gum, which serves as an organic modifier for biopolymers, is added to the slurry, and the mixture is subjected to secondary low-shear stirring. and the temperature of the prepared modified materials relative humidity Standard maintenance shall be carried out under the following conditions.

9. The method according to claim 8, characterized in that, When the base cementing system is a one-package dry alkali-activated geopolymer cementing system, the one-package dry alkali-activated geopolymer cementing system comprises a silica-alumina precursor selected from at least one of slag, fly ash, rice husk ash, and coconut shell ash, and anhydrous sodium metasilicate as a solid alkali activator, and satisfies the following conditions: The equivalent content is 4–8% of the precursor mass and When the molar ratio is 3.5–5.5, the base cementing system is a mixture formed by pre-dry mixing of the silica-alumina precursor and anhydrous sodium metasilicate as a solid alkali activator. The dry pre-mixing step involves dry mixing the high liquid limit silt with the mixture, and the step of adding water and stirring to form a slurry is achieved by adding water on-site.

10. The method according to claim 8 or 9, characterized in that, The shear rate of both the low-shear mixing step and the secondary low-shear mixing step is controlled at 50–150 rpm.

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