Geopolymer-based low-thermal-disturbance low-temperature curing agent for active layer in permafrost region and application of low-thermal-disturbance low-temperature curing agent

Abstract

The invention relates to the technical field of soft soil curing, in particular to a low-temperature curing agent and application thereof. The invention provides a low-temperature curing agent which comprises a cementing material and water glass in a mass ratio of (3-5): 1, the cementing material comprises the following components in percentage by mass: 50%-65% of Portland cement, 20%-35% of fly ash, 5%-25% of superfine slag powder and 0.5%-2% of a flocculating agent. The low-temperature curing agent provided by the invention has excellent freeze-thaw resistance, impermeability and mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of soft soil solidification technology, and in particular to a low-temperature curing agent and its application. Background Technology

[0002] Soft soil consolidation technology aims to improve the engineering properties of soil by cementing soil particles or reacting with clay minerals at room temperature to generate cementitious substances. The effectiveness of this technology depends on the physicochemical interaction between the solidifying agent and the soil: on the one hand, the solidifying agent's own hydration and hydrolysis reactions and possible carbonation form cementitious products; on the other hand, because clay particles have a huge specific surface area and often contain active SiO2, Al2O3, and other components, these cementitious products can effectively encapsulate and bind soil particles, forming a stable structure.

[0003] Traditional low-temperature curing agents, such as silicate cement or lime (often with additives), are widely used in the treatment of soft soil in plains areas. However, when applied to frigid regions, especially in the curing of the active layer (seasonal thaw layer) in permafrost areas, traditional materials face severe challenges: 1. Frost heave in negative temperatures: During the freezing period (temperatures below 0°C), pore water in the soil freezes, causing volume expansion (frost heave). Simultaneously, moisture migration (accumulation towards the freezing front) exacerbates the formation of ice lenses, leading to significant frost heave deformation and threatening structural stability. 2. Thaw settlement in positive temperatures: During the thawing period (temperatures above 0°C), the melting of ice in the active layer leads to increased pore water and volume shrinkage in the soil, causing thaw settlement. This easily results in uneven subgrade settlement, road frost heave, slope instability, and a series of other engineering problems. 3. Poor adaptability to low-temperature environments: In low-temperature environments of 0-10℃, the hydration reaction rate of conventional silicate cement drops sharply, resulting in insufficient hydration. This leads to extremely slow strength development and a significant reduction in final strength, making it difficult to meet the timeliness and performance requirements of engineering projects. 4. Thermal disturbance of the underlying permafrost layer due to hydration heat release: The hydration process of traditional cement-based materials releases a large and concentrated amount of heat. When solidifying the active layer in permafrost regions, this heat of hydration is transferred downwards, significantly disturbing the thermal equilibrium of the underlying permafrost layer, whose temperature is close to the phase transition point (typically -0.5℃ to 0℃). This thermal disturbance may lead to: localized warming of the permafrost or even partial thawing, weakening its long-term bearing capacity and stability as a foundation ("thermal erosion" effect); altering the heat exchange process between the active layer and permafrost, exacerbating the interannual variation in the thickness of the active layer, and affecting the long-term thermal stability of engineering structures.

[0004] Therefore, there is an urgent need to develop new curing agents for the solidification of the active layer in permafrost regions. These curing agents must not only possess the ability to effectively activate and rapidly develop gelling activity at low temperatures of 0-10℃ to ensure sufficient strength, resistance to frost heave, and stability against thaw settlement in the solidified soil during freeze-thaw cycles; more importantly, their hydration heat release must be significantly lower than that of traditional cement to minimize heat input and thermal disturbance to the underlying temperature-sensitive permafrost layer, thus maintaining the long-term thermal stability and engineering safety of the permafrost foundation. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a low-temperature curing agent and its application, wherein the low-temperature curing agent has excellent resistance to freeze-thaw cycles, impermeability and mechanical properties.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a low-temperature curing agent, comprising a cementing material and water glass, wherein the mass ratio of the cementing material to the water glass is (3-5):1;

[0008] The cementitious material comprises the following components by mass percentage: 50%–65% silicate cement, 20%–35% fly ash, and 5%–25% slag powder. The cementitious material also includes a flocculant, the mass of which accounts for 0.5%–2% of the total mass of the silicate cement, fly ash, and slag powder.

[0009] Preferably, the modulus of the water glass is 2 to 3.

[0010] Preferably, the silicate cement is PO.42.5 silicate cement.

[0011] Preferably, the fly ash is grade F1 fly ash.

[0012] Preferably, the slag powder is S95 grade slag powder.

[0013] Preferably, the flocculant includes one or more of cellulose ether, polyacrylamide, polyethylene glycol diacrylate, and metakaolin.

[0014] The present invention also provides the application of the low-temperature curing agent described in the above technical solution in the solidification of soft soil.

[0015] Preferably, the method of application includes:

[0016] Excavation is carried out in the soft soil area to be solidified, with a depth of 3 to 4 meters;

[0017] The soft soil obtained after excavation is mixed with a low-temperature curing agent and then backfilled and cured in sequence.

[0018] Preferably, the moisture content of the soft soil is 30% to 50%;

[0019] The mass ratio of the cementitious material in the soft soil and the low-temperature curing agent is (6-7):(4-3).

[0020] Preferably, the ambient temperature of the area to be cured is 0 to 10°C.

[0021] This invention provides a low-temperature curing agent comprising a cementitious material and water glass, wherein the mass ratio of the cementitious material to the water glass is (3-5):1; the cementitious material comprises the following components by mass percentage: 50%-65% silicate cement, 20%-35% fly ash, and 5%-25% slag powder; the cementitious material further comprises a flocculant, wherein the mass of the flocculant accounts for 0.5%-2% of the total mass of the silicate cement, fly ash, and slag powder. In this invention, fly ash serves as the primary source of aluminosilicates, providing silica and alumina to participate in the reaction and generate gel. However, fly ash has relatively low reactivity. Therefore, in this invention, it is combined with slag powder to fully utilize the volcanic effect and micro-aggregate filling effect. Slag powder contains a high amount of calcium oxide, which participates in the formation of CSH gel and works synergistically with the active components of fly ash to influence the mechanical properties and setting time of the material. Simultaneously, the high reactivity of slag powder plays a crucial role in improving early strength. Combining fly ash and slag powder reduces the heat release during cement hydration, thereby minimizing disturbance to deep permafrost and protecting it. The flocculant ensures rapid solidification and facilitates construction. Water glass acts as an alkaline activator, promoting the dissolution and polymerization of silica and alumina components in the cementitious material, accelerating the hydration process, and simultaneously improving the early strength and impermeability of the solidified body. Detailed Implementation

[0022] This invention provides a low-temperature curing agent, comprising a cementing material and water glass, wherein the mass ratio of the cementing material to the water glass is (3-5):1;

[0023] The cementitious material comprises the following components by mass percentage: 50%–65% silicate cement, 10%–35% fly ash, and 5%–25% slag powder. The cementitious material also includes a flocculant, the mass of which accounts for 0.5%–2% of the total mass of the silicate cement, fly ash, and slag powder.

[0024] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0025] In this invention, the modulus of the water glass is preferably 2 to 3, more preferably 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3.0. In embodiments of this invention, the modulus of the water glass can be 2.5, 2.0, or 1.8.

[0026] In this invention, the mass ratio of the cementing material to water glass is (3-5):1, preferably 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1, 4:1, 4.2:1, 4.4:1, 4.6:1, 4.8:1, or 5:1. In embodiments of this invention, the mass ratio of the cementing material to water glass can be 3.8:1, 5:1, or 4:1.

[0027] In this invention, the water glass acts as an alkaline activator, promoting the dissolution and polymerization reaction of the silicon and aluminum components in the cementitious material, accelerating the hydration process, and improving the early strength and impermeability of the solidified body. The advantage of controlling the ratio of water glass to cementitious material within the above-mentioned range is that it matches the setting time with the construction window period.

[0028] The cementitious material of the present invention comprises 50% to 65% silicate cement by weight percentage, preferably 50%, 52%, 55%, 60%, 62%, or 65%. In embodiments of the present invention, the weight percentage of silicate cement in the cementitious material may be 60%, 65%, or 50%.

[0029] In this invention, the silicate cement is preferably PO.42.5 silicate cement.

[0030] In this invention, the rapid hydration characteristics of silicate cement provide high early strength, while the generated CSH gel effectively binds soil particles, enhancing the mechanical properties of the solidified body. As the main calcium source, it works synergistically with fly ash and slag powder to form more gel phases through pozzolanic reaction, further improving long-term strength and durability. Furthermore, silicate cement has wide adaptability; the setting time can be flexibly controlled by adjusting the dosage or adding admixtures such as water glass to meet different engineering needs. Compared to other cementing materials, it has comprehensive advantages in cost, performance stability, and ease of construction, making it an ideal base material for soft soil solidification formulations. Controlling the amount of silicate cement within the aforementioned range ensures the basic strength and rapid hardening ability of the solidified body, while leaving sufficient room for the addition of fly ash and slag powder. This formulation design fully utilizes the cementing properties of cement, enhances the long-term performance and environmental benefits of the material through the synergistic effect of industrial solid waste, and avoids the problem of hydration heat accumulation caused by excessive cement, making it particularly suitable for temperature-sensitive frozen soil environments. This dosage range achieves the best balance between strength, cost, and workability, and is a scientifically validated optimized ratio.

[0031] The cementitious material of the present invention comprises 20% to 35% fly ash by weight percentage, preferably 20%, 22%, 24%, 26%, 28%, 30%, 32%, or 35%. In embodiments of the present invention, the weight percentage of fly ash in the cementitious material may be 25%, 35%, or 30%.

[0032] In this invention, the fly ash is preferably classified as F1 fly ash according to its fineness.

[0033] In this invention, the fly ash provides active SiO2 and Al2O3 to participate in the pozzolanic reaction and react with the cement hydration product Ca(OH)2 to generate CSH and CAH gels. At the same time, it exerts a micro-aggregate effect to fill pores and improve the density of the solidified body. Controlling the amount of fly ash within the above range ensures that sufficient active components participate in the secondary hydration reaction, while avoiding excessive addition that would lead to slow early strength development. Controlling the grade of fly ash within the above range ensures that it has high activity and suitable fineness, which is beneficial to improving the reaction rate and the fluidity of the slurry, while ensuring the uniformity and stability of the solidification system.

[0034] The cementitious material of the present invention comprises 5% to 25% slag powder by weight percentage, preferably 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 24%, or 25%. In embodiments of the present invention, the weight percentage of slag powder in the cementitious material can be 10%, 5%, 20%, or 25%.

[0035] In this invention, the slag powder is preferably S95 grade slag powder.

[0036] In this invention, the slag powder serves to provide highly active CaO and a glassy structure, promoting the formation of CSH gel and reacting with SiO2 and Al2O3 in fly ash to undergo a pozzolanic reaction, thereby enhancing the later-stage strength and durability of the solidified body. Controlling the amount of slag powder within the aforementioned range significantly improves the reactivity of the cementitious system and enhances early strength development, while avoiding excessive addition that could lead to excessively high heat of hydration or excessively rapid setting time. Using the aforementioned types of slag powder ensures that it possesses a high specific surface area (≥400 m²). 2 The reaction efficiency is optimized and the overall performance of the cured material is improved by using the activity index (7d activity ≥75%, 28d activity ≥95%) and the activity index (7d activity ≥75%, 28d activity ≥95%).

[0037] The cementitious material of the present invention further includes a flocculant, wherein the mass percentage of the flocculant is 0.5% to 2% of the total mass of the silicate cement, fly ash, and slag powder, preferably 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0%. In embodiments of the present invention, the mass percentage of the flocculant in the cementitious material may be 1.5%, 2%, 0.8%, or 1%.

[0038] In this invention, the flocculant preferably includes one or more of cellulose ether, polyacrylamide, polyethylene glycol diacrylate, and metakaolin. When the flocculant is two or more of the above-mentioned specific selections, this invention does not impose any special limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio. In the embodiments of this invention, the flocculant is specifically cellulose ether, polyacrylamide, bentonite in a mass ratio of 1:1:1, cellulose ether and polyacrylamide, or bentonite and polyethylene glycol diacrylate in a mass ratio of 1:1.

[0039] In this invention, the flocculant functions by rapidly adsorbing soil particles to form a flocculated structure through the bridging effect of polymer chains and charge neutralization, significantly improving the initial shear strength of the slurry and ensuring that soft soil possesses good formability and erosion resistance in the early stages of solidification. Controlling the dosage of the flocculant within the aforementioned range achieves rapid consolidation (initial structure formation within 5-15 minutes) while avoiding excessive addition that could lead to excessive slurry viscosity, affecting pumpability or reducing final strength. The advantages of using the aforementioned type of flocculant include water solubility, pH adaptability, and environmental friendliness.

[0040] In this invention, the low-temperature curing agent is preferably mixed with its components before application. This invention does not impose any special limitations on the mixing process, and any process known to those skilled in the art can be used.

[0041] The present invention also provides the application of the low-temperature curing agent described in the above technical solution in the solidification of soft soil.

[0042] In this invention, the method of application preferably includes:

[0043] Excavation is carried out in the soft soil area to be solidified, with a depth of 3 to 4 meters;

[0044] The soft soil obtained after excavation is mixed with a low-temperature curing agent and then backfilled and cured in sequence.

[0045] The present invention involves excavation in the area of ​​soft soil to be solidified, with the excavation depth being 3 to 4 meters.

[0046] In this invention, the ambient temperature of the area to be cured is preferably 0 to 10°C.

[0047] The present invention does not impose any special limitations on the excavation process; any process known to those skilled in the art can be used.

[0048] After the excavation is completed, the present invention mixes the soft soil obtained after excavation with a low-temperature curing agent, and then backfills and cures it in sequence.

[0049] In this invention, the water content of the soft soil is preferably 30% to 50%, more preferably 35% to 45%.

[0050] In this invention, the preferred mass ratio of the cementitious material in the soft soil and the low-temperature curing agent is (6-7):(4-3), more preferably (6.3-6.7):(3.6-3.4). In embodiments of this invention, the mass ratio of the cementitious material in the soft soil and the low-temperature curing agent can be 6:4, 7:3, or 6.7:3.6.

[0051] The present invention does not impose any special limitations on the mixing process; any process known to those skilled in the art can be used.

[0052] In this invention, the backfilling and curing method is preferably sequential, layer by layer, with each layer being backfilled and cured sequentially. In this invention, the height of each backfilling and curing step is preferably 1 meter.

[0053] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0054] Example 1

[0055] Cementitious materials: 65% by weight of silicate cement (the type of silicate cement is PO.42.5 silicate cement), 25% by weight of fly ash (the grade of fly ash is F1 fly ash), 10% by weight of slag powder (the grade of slag powder is S95 slag powder), and also including 1% by weight of flocculant (the type of flocculant is cellulose ether) of the total mass of the silicate cement, fly ash and slag powder.

[0056] Low-temperature curing agent: cementitious material and water glass (modulus 2.5) in a mass ratio of 5:1;

[0057] Applications of low-temperature curing agents:

[0058] Excavation (4 meters deep) is carried out in the soft soil area to be solidified (ambient temperature range 0℃~10℃);

[0059] The soft soil (with a moisture content of 30%) obtained after excavation is mixed with the above-mentioned low-temperature curing agent at a mass ratio of 6:4. The mixture is then backfilled and cured layer by layer (each backfill and curing layer is 1 meter high) to obtain the cured soil.

[0060] Example 2

[0061] Cementitious materials: 60% by weight of silicate cement (silicate cement type PO.42.5), 35% by weight of fly ash (fly ash grade F1), 5% by weight of slag powder (S95 grade slag powder), and also including 1.5% by weight of flocculant (type of polyacrylamide) of the total mass of the silicate cement, fly ash and slag powder.

[0062] Low-temperature curing agent: cementitious material and water glass (modulus 2.0) in a mass ratio of 5:1;

[0063] Applications of low-temperature curing agents:

[0064] Excavation (4 meters deep) is carried out in the soft soil area to be solidified (ambient temperature range 0℃~10℃);

[0065] The soft soil (with a moisture content of 30%) obtained after excavation is mixed with the above-mentioned low-temperature curing agent at a mass ratio of 7:3. The mixture is then backfilled and cured layer by layer (each backfill and curing layer is 1 meter high) to obtain the cured soil.

[0066] Example 3

[0067] Cementitious materials: 50% by weight of silicate cement (silicate cement type PO.42.5), 30% by weight of fly ash (fly ash grade F1), 20% by weight of slag powder (S95 grade slag powder), and also including 2% by weight of flocculant (type of bentonite, cellulose ether, and polyacrylamide in a mass ratio of 1:1:1) of the total mass of the silicate cement, fly ash, and slag powder.

[0068] Low-temperature curing agent: cementitious material and water glass (modulus 2) in a mass ratio of 4:1;

[0069] Applications of low-temperature curing agents:

[0070] Excavation (4 meters deep) is carried out in the soft soil area to be solidified (ambient temperature range 0℃~5℃);

[0071] The soft soil (with a moisture content of 40%) obtained after excavation is mixed with the above-mentioned low-temperature curing agent at a mass ratio of 6.7:3.6. The mixture is then backfilled and cured layer by layer (each backfill and curing layer is 1 meter high) to obtain the cured soil.

[0072] Example 4

[0073] Cementitious materials: 50% by weight of silicate cement (silicate cement type PO.42.5), 25% by weight of fly ash (fly ash grade F1), 25% by weight of slag powder (S95 grade slag powder), and also including 1% by weight of flocculant (type of bentonite and polyethylene glycol diacrylate in a mass ratio of 1:1) of the total mass of the silicate cement, fly ash and slag powder;

[0074] Low-temperature curing agent: cementitious material and water glass (modulus 1.8) in a mass ratio of 4:1;

[0075] Applications of low-temperature curing agents:

[0076] Excavation (4 meters deep) is carried out in the soft soil area to be solidified (ambient temperature range 0℃~10℃);

[0077] The soft soil (with a moisture content of 40%) obtained after excavation is mixed with the above-mentioned low-temperature curing agent at a mass ratio of 6.3:3.4. The mixture is then backfilled and cured layer by layer (each backfill and curing layer is 1 meter high) to obtain the cured soil.

[0078] Test case

[0079] The unconfined compressive strength of the solidified soil described in Examples 1 to 4 was tested. The test standard was the "Unconfined Compressive Strength Test" method in GB / T50123-2019 Geotechnical Test Methods Standard. The results are shown in Table 1.

[0080] The freeze-thaw cycle resistance of the solidified soil described in Examples 1 to 4 was tested. The test standard was the "freeze-thaw cycle test" method in JTG E51-2009 "Test Procedure for Inorganic Binder Stabilized Materials for Highway Engineering" (using -20℃ to 20℃ cycles, and determining the mass loss rate and strength retention rate after 25 freeze-thaw cycles). The test results are shown in Table 1.

[0081] The water impermeability of the solidified soil described in Examples 1 to 4 was tested. The test standard was the "Impermeability Test" method in GB / T50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" (the permeability coefficient was determined by the stepwise pressure method). The test results are shown in Table 1.

[0082] Table 1 Performance parameters of the solidified soil described in Examples 1-4

[0083]

[0084] As shown in Table 1, the unconfined compressive strength of the solidified soil after this invention, after 24 hours, reaches 0.08–0.15 MPa, and after 28 days, it reaches 0.3–1.7 MPa. The mass loss after 10 freeze-thaw cycles is only 0.5%–2%, and the impermeability is 3.5 × 10⁻⁶ MPa. -3 ~7.6×10 -3 Therefore, the low-temperature curing agent described in this invention has excellent freeze-thaw resistance, impermeability, and mechanical properties.

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A low-temperature curing agent, characterized in that, It includes cementing materials and water glass, wherein the mass ratio of the cementing materials to water glass is (3-5):1; The cementitious material comprises the following components by mass percentage: 50%–65% silicate cement, 20%–35% fly ash, and 5%–25% slag powder. The cementitious material also includes a flocculant, the mass of which accounts for 0.5%–2% of the total mass of the silicate cement, fly ash, and slag powder.

2. The low-temperature curing agent as described in claim 1, characterized in that, The modulus of the water glass is 2 to 3.

3. The low-temperature curing agent as described in claim 1, characterized in that, The silicate cement is designated as PO.42.5 silicate cement.

4. The low-temperature curing agent as described in claim 1, characterized in that, The fly ash is classified as F1 fly ash.

5. The low-temperature curing agent as described in claim 1, characterized in that, The slag powder is S95 grade slag powder.

6. The low-temperature curing agent as described in claim 1, characterized in that, The flocculant includes one or more of cellulose ether, polyacrylamide, polyethylene glycol diacrylate, and metakaolin.

7. The application of the low-temperature curing agent according to any one of claims 1 to 6 in the solidification of soft soil.

8. The application as described in claim 7, characterized in that, The application method includes: Excavation is carried out in the soft soil area to be solidified, with a depth of 3 to 4 meters; The soft soil obtained after excavation is mixed with a low-temperature curing agent and then backfilled and cured in sequence.

9. The application as described in claim 8, characterized in that, The water content of the soft soil is 30% to 50%; The mass ratio of the cementitious material in the soft soil and the low-temperature curing agent is (6-7):(4-3).

10. The application as described in claim 8, characterized in that, The ambient temperature of the area to be cured is 0 to 10°C.

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