Freeze-thaw resistant modified material of solidified soil water-blocking layer

Abstract

The freeze-thaw-resistant modified material comprises 100 parts of pretreated engineering in-situ soil or a selected soil material, 25-35 parts of a gelling component, 8-12 parts of an alkali activator, 50-60 parts of a water-permeable skeleton adjusting material and 25-55 parts of water, wherein the content of silicon-aluminum oxide in the pretreated engineering in-situ soil or the selected soil material is greater than or equal to 50%; the gelling component comprises low-calcium fly ash and superfine slag powder; the alkali activator is a sodium silicate solution which is formed by compounding solid sodium silicate, solid sodium hydroxide and water; and the water-permeable framework adjusting material is coal gangue crushed fine material. The material constructs a special solidified soil body with stability and high water permeability, and the solidified soil body can quickly gather and guide moisture at the lower part of a roadbed through an internal communicated pore network, so that the moisture content of the soil body is always controlled below an initial frost heaving critical value, and the possibility of frost heaving damage caused by moisture accumulation and icing is completely eradicated from the source.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and more specifically, to a freeze-thaw resistant modified material for a water-blocking layer of solidified soil. Background Technology

[0002] In the field of construction engineering, soil consolidation technology is a traditional technique that improves the engineering properties of soil by incorporating specific cementing materials into it, causing a physicochemical reaction to meet the requirements of engineering structures for foundations or fill materials. Conventional consolidation materials typically include cement and lime. These materials react with water and soil particles to form gel substances such as hydrated calcium silicate, which binds loose soil particles into a whole, forming a slab structure with high load-bearing capacity. This technology is widely used in treating soft soil foundations and roadbed improvement, and its advantages lie in utilizing in-situ soil materials, reducing the cost of transporting materials from elsewhere, and improving the overall performance of the foundation. However, traditional soil consolidation technology mainly pursues the density and unconfined compressive strength of the material. Its hydration products tend to fill the pores inside the soil, resulting in very low permeability of the solidified soil, or even near-impermeability. This characteristic may be beneficial in general engineering environments, but it reveals serious inadequacies in specific harsh environments.

[0003] When engineering environments involve seasonal freeze-thaw cycles, such as in road engineering in cold regions, the fundamental mechanism of freeze-thaw damage lies in moisture. When the subgrade soil freezes at low temperatures, the internal pore water expands as it freezes, generating frost heave stress, which causes the pavement to bulge and deform. As temperatures rise and the ice melts, the soil structure softens due to previous damage, and its bearing capacity drops sharply. Repeated cycles eventually lead to the complete destruction of the road structure. Traditional soil stabilization technology creates low-permeability or even impermeable structures. In such environments, the dense structure hinders the timely drainage of moisture. Once moisture enters the subgrade through capillary action or lateral seepage and is trapped inside or beneath the stabilized soil layer, it accumulates and freezes during the freezing period, generating enormous frost heave stress. This stress usually exceeds the tensile strength of the material itself, leading to cracking. Moreover, these cracks provide channels for more moisture to penetrate, accelerating the damage process. In addition, when using traditional cementitious materials such as cement, the chemical and volume stability of their hydration products, such as CSH gel, is relatively insufficient under freeze-thaw cycles. Repeated freeze-thaw cycles and thaw stress can easily lead to fatigue damage at the cementation interface, causing the overall structure to disintegrate. Summary of the Invention

[0004] This invention provides a freeze-thaw resistant modified material for a water-blocking layer of solidified soil. This material constructs a special solidified soil with stable and high permeability. The solidified soil can quickly collect and guide water from the lower part of the subgrade through an internal interconnected pore network, thereby keeping the soil moisture content below the critical value of initial frost heave, thus eliminating the possibility of water accumulation, freezing, and frost heave damage from the source.

[0005] The technical solution of this invention is as follows: A freeze-thaw resistant modified material for a solidified soil water barrier layer comprises 100 parts of pretreated in-situ engineering soil or selected soil, 25-35 parts of cementitious components, 8-12 parts of alkaline activator, 50-60 parts of permeable skeleton modifier, and 25-55 parts of water. Among them, the total content of silicon and aluminum oxides in the pretreated in-situ soil or selected soil material is greater than or equal to 50%, and is neutral or weakly alkaline. The cementing components include low-calcium fly ash and slag powder, with a mass ratio of low-calcium fly ash to slag powder of 1:(0.5~1.5). The alkaline activator is a sodium silicate solution, which is composed of solid sodium silicate, solid sodium hydroxide, and water. The permeable skeleton regulating material is finely crushed coal gangue.

[0006] The above-mentioned antifreeze-thaw modified material for solidified soil water-blocking layer, Methods for preparing pretreated in-situ soil or selected soil materials include: Spread out the in-situ soil or selected soil material to air dry naturally or place it in an oven to dry, so that the moisture content of the in-situ soil or selected soil material does not exceed the specified value. After drying, crush the in-situ soil or selected soil material and screen it through a vibrating screen. Keep the powder that passes through the vibrating screen and remove the particles that cannot pass through the vibrating screen. The powder passing through the vibrating screen is calcined at low temperature, and the calcined powder is then checked for organic matter content, so that the organic matter content is reduced to below the specified value.

[0007] In-situ soil or selected soil material usually refers to soil material that can be obtained in the project, such as soil material directly generated by excavating the roadbed at the road construction site where a water-blocking layer is planned to be laid, or silt, low-plasticity clay, or engineering waste soil such as shield tunneling slag, dewatered silt, and construction trench soil.

[0008] The goal of pretreatment is to transform the original, heterogeneous soil material into soil powder with relatively stable and uniform composition and particle size, so as to ensure accurate subsequent mixing and consistent reaction results.

[0009] The total organic matter content of the pretreated in-situ soil or selected soil material should be less than 5%, preferably less than or equal to 0.5%, and the sulfate content should be less than 0.5%.

[0010] The freeze-thaw resistant modified material for the above-mentioned solidified soil water-blocking layer uses low-calcium fly ash of type F, with a calcium oxide content of no more than 10% and a loss on ignition of no more than 8%.

[0011] The synergistic effect of low-calcium fly ash and slag powder in the cementing components is that fly ash provides the main source of silica and alumina, while slag powder provides additional active silica and alumina sources and calcium sources. Under alkaline activation, the two together form a geopolymer gel with cementing properties.

[0012] The curing agent of this invention cannot be added to cement; instead, low-calcium fly ash and slag powder are used as the cementing agent for the solidified soil. The low-calcium fly ash (low-calcium aluminosilicate glass, with a calcium oxide content of less than 10%) in the material undergoes a geopolymer reaction under alkaline activation, forming a three-dimensional network of amorphous aluminosilicate gel (NASH). If high-calcium fly ash is used, the reaction in the solidified soil tends towards cement hydration due to the presence of a large amount of free calcium oxide and dicalcium silicate crystalline phases, thus generating CSH and ettringite. The geopolymer gel (NASH) has a denser microstructure and stronger chemical resistance than cement hydration products (CSH). The geopolymer gel encapsulates and binds the coal gangue aggregate to form a porous but strong whole, while cement hydration tends to fill pores and cannot form a permeable, interconnected pore structure.

[0013] In the above-mentioned antifreeze-thaw modified material for solidified soil water-blocking layer, when solid sodium silicate and solid sodium hydroxide are used as the alkaline activator, the mass ratio of solid sodium silicate to solid sodium hydroxide is sodium silicate:sodium hydroxide = (2.0~3.5):1.

[0014] The amount of activator added maintains the initial pH of the system at 12.5–13.5. This alkaline environment can effectively activate the activity of fly ash and slag powder, and initiate the depolymerization and recombination of the aluminosilicate network structure.

[0015] The freeze-thaw resistant modified material for the above-mentioned solidified soil water-blocking layer has a sodium silicate modulus of 1.2 to 1.8 in the activator.

[0016] When the modulus is near the lower limit of 1.2, it means that the concentration of free sodium hydroxide in the solution is high, the system is extremely alkaline, and the highly alkaline environment can rapidly destroy the silica-alumina glass network on the surface of fly ash and slag particles, quickly releasing a large amount of silica-alumina monomers, causing the reaction to proceed violently in a short time and releasing a large amount of heat. Conversely, when the modulus is close to the upper limit of 1.8, the proportion of polymerized silicate ions in the solution increases, the alkalinity is relatively mild, the reaction initiation becomes more gradual, and the hydration exothermic curve is also more gradual.

[0017] Sodium silicate not only provides the alkaline activator, but its own silicate groups are also an important component of the final gel network. Within a suitable modulus range, the activated active silica-alumina species undergo polymerization reactions with the silicate and hydroxide groups provided in the solution to generate aluminosilicate gels with a three-dimensional network structure. At lower moduli, the system has a high sodium ion content, tending to generate gels with more sodium ions participating in charge balance, which may result in a looser structure. At higher moduli, more silicate groups are provided, which helps to form a gel network with tighter silicon-oxygen tetrahedral connections and a higher degree of polymerization, resulting in a denser structure and greater potential for strength development. However, excessively high moduli will significantly increase the solution viscosity, which is not conducive to mixing and uniform distribution at low water-to-gel ratios, and may also lead to incomplete activation due to insufficient initial alkalinity. Therefore, the selected range of 1.2–1.8 ensures sufficient activation strength, promotes the formation of a dense gel, maintains good workability, and guides the reaction to produce a geopolymer gel with high chemical stability, low shrinkage, and a dense internal structure.

[0018] Geopolymer gels obtained through modulus control possess better chemical resistance and volume stability than traditional cement hydration products. The uniform and dense gel phase formed under appropriate modulus can more completely and firmly encapsulate and bond coal gangue aggregate particles, creating a robust interfacial transition zone around the aggregate. This bonding structure not only imparts overall strength to the material but also stabilizes the permeable pore network formed by aggregate accumulation, preventing particle debonding or skeleton collapse under freeze-thaw cycle stress, thus ensuring the long-term continuity and functional stability of drainage channels. Simultaneously, the uniform gel structure helps refine and evenly distribute micropores, reducing the presence of harmful macropores and lowering the risk of damage caused by localized water accumulation and freezing.

[0019] The above-mentioned antifreeze-thaw modified material for a solidified soil water barrier layer uses a permeable skeleton regulating material that is a continuously graded fine material obtained by crushing and screening non-self-combusting coal gangue.

[0020] Furthermore, the particle size distribution of the permeable skeleton regulating material meets the following conditions: particles with a diameter of 5mm to 2.5mm account for 15% to 30%, particles with a diameter of 2.5mm to 0.6mm account for 40% to 60%, and particles with a diameter less than 0.6mm account for 20% to 35%.

[0021] The aggregate used in this invention is coal gangue. Firstly, coal gangue is one of the largest industrial solid wastes emitted in China, making it relatively easy to obtain. Secondly, coal gangue itself has a porous and rough surface; after crushing, the particles have rough surfaces and sharp edges, resulting in strong mechanical interlocking force when they overlap, forming a mechanically stable skeleton. The pores are not prone to collapse, and its hardness is higher than ordinary soil, enabling it to bear loads and serve as a durable load-bearing skeleton. Furthermore, the main component of coal gangue is aluminosilicate, which is inert in alkaline environments and does not react harmfully with geopolymer gels, ensuring the long-term chemical stability of the skeleton and preventing structural damage due to self-reaction expansion. The lack of spontaneous combustion means that coal gangue does not contain harmful substances such as free calcium oxide, providing the absolute volume stability necessary for freeze-thaw resistance.

[0022] The particle size distribution of the permeable skeleton modifier is expressed as a percentage by mass.

[0023] The purpose of the particle size distribution of permeable aggregate is to form a stable skeleton structure with a large number of interconnected pores, while ensuring that fine particles can fully contact and be encapsulated by the cementitious slurry. This creates numerous interconnected pores for rapid drainage and ensures that the skeleton structure is sufficiently robust and does not collapse under load and freeze-thaw cycles. Its continuity ensures the construction of a stable mechanical structure within the aggregate mass, with progressively filling and mutual support from coarse to fine particles, thus forming a pore network that is both high-strength and highly permeable. Permeable aggregate with a particle size of 5mm to 2.5mm serves as the framework structure of the permeable interconnected pore structure, forming large pore channels (relatively). Permeable aggregate with a particle size of 2.5mm to 0.6mm serves as the filling and stabilizing layer of the permeable interconnected pore structure, ensuring pore connectivity and structural density. Permeable aggregate with a particle size less than 0.6mm serves as a fine-tuning and cementing medium for the permeable interconnected pore structure, optimizing porosity and increasing overall integrity.

[0024] If the particle size distribution of the aforementioned permeable skeleton material is unbalanced, such as having too many particles in the 5mm-2.5mm range, the initial permeability will be high but unstable, making it prone to instability under mechanical compaction or frost heave, and the drainage function will rapidly decline. If there are too few particles in the 5mm-2.5mm range, the permeability coefficient of the water barrier layer will be too low, resulting in poor drainage efficiency and an inability to remove water in time, thus losing the function of active drainage. If there are too few particles in the 2.5mm-0.6mm range, the structural strength of the water barrier layer will be low, the permeability will be uneven, and local water accumulation will easily occur. If the proportion of particles smaller than 0.6mm is too large, the permeability will drop sharply, the material will tend to be impermeable, and the risk of frost heave will increase. If the proportion of particles smaller than 0.6mm is too small, the overall strength of the material will be low and the material will be brittle, making it prone to disintegration under freeze-thaw cycles.

[0025] The aforementioned antifreeze-thaw modified material for a water-blocking solidified soil layer also contains 3 to 5 parts of an antifreeze reinforcing agent, which is power plant desulfurization gypsum or phosphogypsum.

[0026] The antifreeze enhancer introduces small amounts of calcium and sulfate ions (as an antifreeze auxiliary material, rather than as the main cementing agent for the solidified soil), which promotes the early formation of ettringite in an alkaline environment. The resulting moderate micro-expansion helps to establish micro-prestress within the solidified soil and refine the pores, thereby improving the material's ability to resist fatigue damage caused by freeze-thaw cycles.

[0027] The above-mentioned antifreeze-thaw modified material for a soil-stabilized water-blocking layer, the construction process of the soil-stabilized water-blocking layer includes: Step S1. Dry mixing: The pretreated in-situ soil or selected soil, cementitious components, permeable skeleton modifier and antifreeze enhancer (if added) are put into a forced mixer according to the proportion and dry mixed for a time not less than the set time until the color is uniform and there are no lumps. Step S2. Preparation of activator solution: Dissolve solid sodium silicate and solid sodium hydroxide in part of the mixing water, stir until completely dissolved, and prepare a homogeneous activator solution; Step S3. Wet mixing: Spray the activator solution evenly into the dry mixture, while adding the remaining mixing water, and continue mixing for a set time until all solid particles are evenly coated with slurry, forming a moist, loose but cohesive mixture. Step S4. Spreading and compaction: Spread the mixture to the construction section and use a road roller for static and vibratory compaction. The degree of compaction shall not be lower than the set value. Step S5. Curing: Immediately after compaction, cover with geotextile or plastic film for heat preservation and moisture retention. The curing temperature should not be lower than the set temperature, and the curing period should not be less than the set time. Keep the surface moist during the curing period to allow the geopolymer reaction to proceed fully.

[0028] The aforementioned antifreeze-thaw modified material for solidified soil water-blocking layer is used to form an active drainage water-blocking layer in road structures. The water-blocking layer is set at a specific depth below the top surface of the roadbed or above the groundwater level inside the roadbed.

[0029] The freeze-thaw resistant modified material of the solidified soil water-blocking layer of the present invention utilizes its own stable high permeability to quickly accumulate and discharge water that rises from the roadbed by capillary action or infiltrates laterally during the freeze-thaw season, thereby significantly reducing the moisture content of the roadbed soil and eliminating or mitigating frost heave caused by water accumulation from the source.

[0030] The freeze-thaw modified material of the solidified soil water-blocking layer of this invention constructs a robust and porous skeleton. This skeleton is composed of non-self-burning coal gangue particles with a specific continuous gradation. These hard and rough non-self-burning coal gangue particles overlap and interlock, forming preliminary channels through which water can pass quickly. To prevent the aggregate from becoming unstable under load, a geopolymer reaction between low-calcium fly ash and an alkaline activator is utilized. The resulting aluminosilicate gel can coat and anchor the surface and contact points of the coal gangue particles, thereby giving the skeleton overall strength. Because the aluminosilicate gel binds the particles rather than filling the pores, the connectivity of the pores is preserved, and the formed pore channels are not blocked.

[0031] According to the above-described solution, the beneficial effects of this invention are as follows: 1. It provides dynamic drainage and controls subgrade moisture content to prevent frost heave: By constructing a stable, highly permeable solidified soil body, the interconnected pore network rapidly collects and guides moisture from the subgrade, keeping the soil moisture content consistently below the critical value for initial frost heave. This eliminates the possibility of moisture accumulation, freezing, and frost heave damage at the source. The permeable skeleton modifier in the material (such as fine coal gangue) forms a continuously graded pore structure. These pores act as drainage channels, promptly removing water that rises capillarily or seeps laterally into the subgrade during freeze-thaw seasons. This not only reduces localized water accumulation but also maintains the long-term stability of the subgrade through continuous moisture regulation.

[0032] 2. High freeze-thaw resistance and durability, preventing structural damage: Utilizing low-calcium fly ash and slag powder under alkaline activation, a geopolymer gel (NASH) is generated. This gel has a denser microstructure and stronger chemical resistance than traditional cement hydration products (CSH), resulting in better volume stability of the solidified soil material. In freeze-thaw environments, this invention reduces the space for ice crystal formation (water freezing causes volume expansion) by controlling moisture content and refining pores. The stability of the permeable skeleton is ensured by the rough surface of the coal gangue particles and the anchoring effect of the geopolymer gel, preventing particle debonding or skeleton collapse under freeze-thaw stress. Under optimized conditions, a small amount of antifreeze reinforcing agent (such as power plant desulfurization gypsum) is introduced to promote the formation of ettringite, producing moderate micro-expansion to refine pores and enhance resistance to freeze-thaw fatigue damage. Multiple protective mechanisms ensure that the material does not disintegrate or experience strength degradation under repeated freeze-thaw cycles, thereby extending road service life and reducing maintenance requirements.

[0033] 3. Environmental protection and resource utilization, reducing environmental burden: The permeable skeleton regulating material uses coal gangue (one of the largest industrial solid wastes in China), and the cementing components use low-calcium fly ash and slag powder, all of which are common industrial by-products. The pretreatment and reuse of in-situ soil or selected soil materials (such as shield tunneling slag and dewatered sludge) reduces the consumption of natural aggregates, cement and soil materials, reduces carbon emissions and waste storage problems, and also reduces project costs. Detailed Implementation

[0034] To make the technical problems, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0035] A freeze-thaw resistant modified material for a solidified soil water-blocking layer comprises 100 parts of pretreated in-situ engineering soil or selected soil material, 25-35 parts of cementitious component, 8-12 parts of alkaline activator, 50-60 parts of permeable skeleton modifier, and 25-55 parts of water; wherein, the total content of silicon and aluminum oxides in the pretreated in-situ engineering soil or selected soil material is greater than or equal to 50%, and is neutral or weakly alkaline; the cementitious component includes low-calcium fly ash and slag powder, with a mass ratio of low-calcium fly ash: slag powder = 1:(0.5-1.5); the alkaline activator is sodium silicate solution, which is composed of solid sodium silicate, solid sodium hydroxide, and water; the permeable skeleton modifier is crushed coal gangue fines.

[0036] For in-situ soil or selected soil materials, priority should be given to soil materials, silt, low-plasticity clay generated from roadbed excavation at the road construction site, or engineering waste soil such as shield tunnel slag, dewatered silt, and construction trench soil. The total content of silicon and aluminum oxides should not be less than 50%, and the soil should be neutral or weakly alkaline, with a sulfate content of less than 0.5% and an organic matter content controlled below 5%, preferably not greater than 0.5%.

[0037] The low-calcium fly ash in the cementitious component is selected from Class F fly ash, with a calcium oxide content of no more than 10% and a loss on ignition of no more than 8%, which meets the requirements of "Fly Ash for Cement and Concrete" (GB / T1596-2017).

[0038] The slag powder uses S95 grade granulated blast furnace slag powder with a specific surface area of ​​not less than 400 m² / kg and an activity index of not less than 95% after 28 days, meeting the standard of "Granulated Blast Furnace Slag Powder for Cement and Concrete" (GB / T18046-2017).

[0039] The alkaline activator is industrial-grade solid sodium silicate and flake sodium hydroxide. The sodium silicate has a sodium oxide content of not less than 28% and a silicon dioxide content of not less than 32%. The sodium hydroxide has a purity of not less than 96% and a moisture content of not more than 1%.

[0040] The permeable skeleton regulating material is made of non-self-combusting coal gangue, which is crushed and screened to form a continuous graded fine material. Among them, the mass proportion of particles with a diameter of 5mm to 2.5mm is 15% to 30%, the mass proportion of particles with a diameter of 2.5mm to 0.6mm is 40% to 60%, and the mass proportion of particles with a diameter of less than 0.6mm is 20% to 35%. The particle surface must be rough without obvious weathering, and the hardness must meet the requirements of the load-bearing skeleton.

[0041] The antifreeze enhancer is selected from power plant desulfurization gypsum or phosphogypsum, with a purity of not less than 90%, a moisture content of not more than 5%, and no obvious clumping.

[0042] The mixing water is tap water or natural clean water that meets the "Standard for Water Used in Concrete" (JGJ63-2006), with a pH value between 6 and 8, a chloride ion content not exceeding 200 mg / L, and free from oil, organic matter, and other harmful impurities.

[0043] The in-situ soil or selected soil material is first spread out to air dry naturally. If the construction period is tight, it can be dried in an oven at a temperature controlled at 105±5℃ for 4-6 hours to ensure that the final moisture content of the soil material does not exceed 5%. After drying, the soil material is crushed to a particle size of no more than 10mm using a jaw crusher. During the crushing process, it is important to avoid introducing impurities such as gravel and debris. The crushed particles must be promptly transported to the screening process to prevent moisture absorption and clumping. The crushed particles are then screened using a single-layer vibrating screen with a screen aperture of 2mm. Powder that passes through the screen is retained, while larger particles that do not pass through are returned to the crusher for re-crushing to ensure uniform particle size. The screened powder is then fed into a low-temperature calcination furnace at a temperature controlled at 500±50℃ for 3-4 hours, with a heating rate controlled at 5℃ / min to avoid sudden temperature increases that could damage the powder structure. The organic matter in the soil material is removed through high-temperature decomposition. After calcination, the powder is cooled to room temperature, and the organic matter content is determined using the potassium dichromate titration method. The organic matter content must be reduced to below 5%, preferably below 0.5%. If this is not met, the calcination time should be extended by 0.5–1 hour. Simultaneously, the pretreated soil is subjected to chemical composition testing to confirm that the total content of silicon and aluminum oxides is not less than 50% and the sulfate content is less than 0.5%. The qualified soil is stored in a sealed silo equipped with a dehumidifier to control the relative humidity to no more than 60%, and the storage time is no more than 3 months.

[0044] Non-self-igniting coal gangue is crushed, graded, and screened. After crushing, large particles are first removed by passing through a 5mm screen, and then sieved through 2.5mm and 0.6mm grading screens. Particles of different particle size ranges are collected according to the gradation requirements, mixed evenly, and then sealed and stored to avoid particle segregation.

[0045] The materials are measured by mass proportions, with the following base: 100 parts of pretreated in-situ soil or selected soil, 25-35 parts of cementitious component (low-calcium fly ash to slag powder mass ratio 1:(0.5-1.5)), 8-12 parts of alkaline activator (solid sodium silicate to solid sodium hydroxide mass ratio 2.0-3.5:1), 50-60 parts of permeable skeleton modifier, 25-55 parts of mixing water, and 3-5 parts of antifreeze enhancer (if added). Electronic weighing scales with an accuracy of no less than ±0.5% are used. The weighing equipment must be calibrated before batching to ensure that the weighing error is within the allowable range. The amount of mixing water needs to be adjusted according to the ambient temperature. In low-temperature environments (5-10℃), the water volume can be appropriately increased but not exceeding 5% of the total water volume. In high-temperature and dry environments (temperature ≥30℃, humidity ≤60%), the water volume can be reduced but not less than 25 parts to avoid affecting the construction performance of the mixture.

[0046] Pretreated in-situ soil or selected soil material, cementitious components (low-calcium fly ash and slag powder pre-mixed evenly), permeable skeleton modifier, and antifreeze reinforcing agent (if added) are sequentially added to a forced mixer. The mixing speed is set to 300-400 r / min, and the dry mixing time is not less than 5 minutes, preferably 5-8 minutes, until the material has a uniform color and no obvious lumps. During the dry mixing process, the mixing uniformity needs to be checked periodically by sieving. Samples from different parts are sieved, and the passing rate deviation should not exceed 3%. If the mixing is not uniform, the mixing time should be extended by 1-2 minutes. During the mixing process, the state of the material should be observed. If local agglomeration occurs, the mixing speed can be appropriately reduced by 30-50 r / min, and mixing can continue until the agglomerates are dispersed to ensure that all solid particles can be fully contacted, avoiding insufficient subsequent reaction due to uneven mixing, which would affect the strength and permeability of the material.

[0047] The preparation of the alkaline activator solution requires strict control of its modulus and concentration to ensure effective activation of the gelling components. Take 60%–70% of the total mixing water as solvent and pour it into a mixing tank. First, add the measured amount of solid sodium silicate to the solvent, turn on the stirrer, and control the stirring speed at 200–250 r / min for 10–15 min until the sodium silicate is completely dissolved. Then, slowly add the measured amount of solid sodium hydroxide and continue stirring for 5–8 min to prepare a homogeneous activator solution. During stirring, control the solution temperature at 20–30℃ to avoid high temperatures causing sodium hydroxide volatilization, which would affect the alkalinity of the solution. After the solution is prepared, use a modulus meter to test the modulus of sodium silicate, ensuring it is within the range of 1.2–1.8. If the modulus deviation exceeds ±0.1, it needs to be corrected by adjusting the ratio of solid sodium silicate to sodium hydroxide; increase the amount of sodium silicate if the modulus is too low, and increase the amount of sodium hydroxide if the modulus is too high. The activator solution should be used within 30 minutes after preparation to avoid concentration changes due to prolonged storage. If temporary storage is required, it should be sealed and stirred thoroughly before use.

[0048] The prepared activator solution is evenly sprayed into the dry mix, while the remaining mixing water is slowly added. A forced mixer is then turned on and stirred at high speed, with the stirring speed increased to 500-600 rpm. The stirring time is no less than 3 minutes, preferably 3-5 minutes, until all solid particles are evenly coated with the slurry, forming a moist, loose, and cohesive mixture. During the wet mixing process, the state of the mixture needs to be observed. If the mixture is too dry and the particles are dispersed and lack cohesion, a small amount of mixing water can be added, but not exceeding 5% of the total water volume. If the mixture is too wet and slurry seeps out, a small amount of dry mix (prioritizing permeable skeleton modifier) ​​can be added to adjust the mixture, ensuring that it is easy to spread and compact while guaranteeing sufficient subsequent reactions. After the mixture is prepared, a permeability coefficient prediction test is used for preliminary testing to ensure it has the expected permeability. Simultaneously, the air content of the mixture is tested, controlling it to not exceed 5% to avoid excessive air bubbles affecting the material's density and strength.

[0049] Before construction, the subgrade base layer needs to be treated, removing loose slag, dust, water, and loose soil from the surface. The base layer should be leveled, with a flatness deviation not exceeding 5mm. If there are low-lying areas, they should be filled with the same material and compacted. The ambient temperature during construction should be controlled between 5 and 35℃. Construction should be avoided in rainy, snowy, or windy weather. In low-temperature environments, insulation measures should be taken, and in high-temperature environments, direct sunlight should be avoided to prevent the mixture from evaporating too quickly. The prepared mixture should be spread to the construction section using a paver or manually. The paving thickness should be determined according to design requirements, generally 20-40cm. The paving sequence should proceed continuously from one end of the road to the other. Segregation should be avoided during paving. If particles accumulate, they should be manually dispersed evenly. After paving, compaction should be carried out immediately with a road roller. Static compaction should be performed 2-3 times at a speed of 2-3 km / h, followed by vibratory compaction 3-4 times at a vibration frequency of 25-30Hz, with a compaction degree of not less than 95%. During compaction, the compaction should proceed from both sides of the road towards the center, with the overlap width being 1 / 3 to 1 / 2 of the roller wheel width to avoid missed areas. After compaction, the compaction degree should be tested using the ring cutter method, with each test point spaced no more than 50m apart. If the compaction degree does not meet the standard, it needs to be compacted 1 to 2 more times until the requirements are met. The surface of the compacted water-blocking layer should be smooth, without obvious wheel tracks, cracks, or potholes.

[0050] The curing phase aims to promote the full reaction of the geopolymer, ensuring the strength development and freeze-thaw resistance of the material. Immediately after compaction, cover with geotextile or plastic film for insulation and moisture retention. During curing, control the ambient temperature to be no lower than 5℃ and the relative humidity to be no lower than 90%. The curing period should be no less than 7 days in normal environments (temperature 15–25℃, humidity 60%–80%), no less than 14 days in low-temperature environments (5–10℃), and no less than 10 days in high-temperature, dry environments (temperature ≥30℃, humidity ≤60%). Regular watering is required during curing, 2–3 times daily, to ensure the geotextile or plastic film remains moist and prevent the surface of the water-blocking layer from drying and cracking. During curing, it is strictly forbidden to collide with, roll over, or disturb the water-blocking layer. Heavy objects should not be piled on top, and vehicles should not drive on it to avoid damaging the formed pore structure and overall strength. When curing in low-temperature environments, the geotextile must be covered with an insulating blanket. Open flame heating is prohibited to prevent excessively high local temperatures from causing thermal stress within the material and leading to cracks. After the curing period, the performance of the water-blocking layer must be tested, including unconfined compressive strength, permeability coefficient, and freeze-thaw cycle resistance (strength loss not exceeding 15% after 20 freeze-thaw cycles). Subsequent construction can only proceed after the tests are passed.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A freeze-thaw resistant modified material for a water-blocking layer of solidified soil, characterized in that, It includes 100 parts of pretreated in-situ soil or selected soil, 25-35 parts of cementitious components, 8-12 parts of alkaline activator, 50-60 parts of permeable skeleton modifier, and 25-55 parts of water. Among them, the total content of silicon and aluminum oxides in the pretreated in-situ soil or selected soil material is greater than or equal to 50%, and is neutral or weakly alkaline. The cementing components include low-calcium fly ash and slag powder, with a mass ratio of low-calcium fly ash to slag powder of 1:(0.5~1.5). The alkaline activator is a sodium silicate solution, which is composed of solid sodium silicate, solid sodium hydroxide, and water. The permeable skeleton regulating material is finely crushed coal gangue.

2. The freeze-thaw resistant modified material for a water-blocking layer of solidified soil according to claim 1, characterized in that, Methods for preparing pretreated in-situ soil or selected soil materials include: Spread out the in-situ soil or selected soil material to air dry naturally or place it in an oven to dry, so that the moisture content of the in-situ soil or selected soil material does not exceed the specified value. After drying, crush the in-situ soil or selected soil material and screen it through a vibrating screen. Keep the powder that passes through the vibrating screen and remove the particles that cannot pass through the vibrating screen. The powder passing through the vibrating screen is calcined at low temperature, and the calcined powder is then checked for organic matter content, so that the organic matter content is reduced to below the specified value.

3. The freeze-thaw resistant modified material for a water-blocking layer of solidified soil according to claim 1, characterized in that, Low-calcium fly ash is classified as Class F fly ash, with a calcium oxide content of no more than 10% and a loss on ignition of no more than 8%.

4. The freeze-thaw resistant modified material for a water-blocking layer of solidified soil according to claim 1, characterized in that, In alkaline activators, when solid sodium silicate and solid sodium hydroxide are used in combination, the mass ratio of solid sodium silicate to solid sodium hydroxide is sodium silicate:sodium hydroxide = (2.0~3.5):

1.

5. The freeze-thaw resistant modified material for a water-blocking layer of solidified soil according to claim 1, characterized in that, The modulus of sodium silicate in the activator is 1.2 to 1.

8.

6. The freeze-thaw resistant modified material for a water-blocking layer of solidified soil according to claim 1, characterized in that, The permeable skeleton conditioning material is a continuously graded fine material obtained by crushing and screening non-self-combusting coal gangue.

7. The freeze-thaw resistant modified material for a water-blocking layer of solidified soil according to claim 6, characterized in that, The particle size distribution of the permeable skeleton material should meet the following conditions: particles with a diameter of 5mm to 2.5mm account for 15% to 30%, particles with a diameter of 2.5mm to 0.6mm account for 40% to 60%, and particles with a diameter less than 0.6mm account for 20% to 35%.

8. The freeze-thaw resistant modified material for a water-blocking layer of solidified soil according to claim 1, characterized in that, The raw materials also contain 3 to 5 parts of antifreeze enhancer, which is power plant desulfurization gypsum or phosphogypsum.

9. The freeze-thaw resistant modified material for a water-blocking layer of solidified soil according to claim 1, characterized in that, The construction process of the solidified soil water-blocking layer includes: Step S1. Dry mixing: The pretreated in-situ soil or selected soil, cementitious components, permeable skeleton modifier and antifreeze enhancer (if added) are put into a forced mixer according to the proportion and dry mixed for a time not less than the set time until the color is uniform and there are no lumps. Step S2. Preparation of activator solution: Dissolve solid sodium silicate and solid sodium hydroxide in part of the mixing water, stir until completely dissolved, and prepare a homogeneous activator solution; Step S3. Wet mixing: Spray the activator solution evenly into the dry mixture, while adding the remaining mixing water, and continue mixing for a set time until all solid particles are evenly coated with slurry, forming a moist, loose but cohesive mixture. Step S4. Spreading and compaction: Spread the mixture to the construction section and use a road roller for static and vibratory compaction. The degree of compaction shall not be lower than the set value. Step S5. Curing: Immediately after compaction, cover with geotextile or plastic film for heat preservation and moisture retention. The curing temperature should not be lower than the set temperature, and the curing period should not be less than the set time. Keep the surface moist during the curing period to allow the geopolymer reaction to proceed fully.

10. The freeze-thaw resistant modified material for a water-blocking layer of solidified soil according to claim 1, characterized in that, Used to form an active drainage water-blocking layer in road structures, the water-blocking layer is set at a specific depth below the top surface of the roadbed or above the groundwater level inside the roadbed.