Coal ash-slag-coal gangue geopolymer-based soft soil curing agent as well as preparation method and application thereof

Abstract

The invention discloses a coal ash-slag-coal gangue geopolymer-based soft soil curing agent which takes coal ash, slag and uncalcined coal gangue as ternary precursors according to a mass ratio of (5-10%): (80-90%): (5-10%). The preparation method comprises the following steps: firstly, uniformly mixing ternary precursor powder, and then stirring with an alkali activator formed by a mixed solution of NaOH and Na2SiO3; during application, the soft soil and the curing agent are uniformly mixed according to the proportion that the mixing amount of the ternary precursor is 20% of the mass of the soft soil, and the mixture is subjected to compaction molding and standard curing to form a high-strength cured soil body. According to the method disclosed by the invention, the uncalcined coal gangue is activated in a calcium-rich strong alkali environment by utilizing the synergistic enhancement effect of the ternary precursor, the silica-alumina ratio of the system is regulated and controlled, and the generation of a large amount of N-A-S-H and C-A-S-H gel is promoted, so that the unconfined compressive strength of the soft soil is remarkably improved. The method has the advantages of being environmentally friendly, economical, simple and convenient in process, remarkable in strength improvement and the like, and a new technical support is provided for resource utilization of the uncalcined coal gangue and soft soil foundation improvement.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation and application of a civil engineering material for soft foundation treatment, in particular, a geopolymer-based soft soil stabilizer taking fly ash, slag and uncalcined coal gangue as precursors, a preparation method thereof and an application in soft soil stabilization engineering. BACKGROUND

[0002] Soft soil is a kind of cohesive soil with high water content (usually more than the liquid limit) and large void ratio (usually greater than 1.0) formed by natural deposition, which is widely distributed in coastal, lake and river areas. In addition, dredging engineering and underground engineering construction also produce a large amount of similar soft soil. Soft soil has poor engineering properties such as high compressibility, low strength and poor permeability, so it must be reinforced before engineering construction on soft soil foundation.

[0003] The commonly used soft soil stabilization methods at present include mechanical method, physical method and chemical method, among which the chemical method mainly adds cement and other stabilizers into the soil to promote the formation of cementation between soil particles, thereby improving the engineering properties of the soil.

[0004] However, the production process of cement has high energy consumption and large carbon emissions, which is contrary to the requirement of environmental sustainable development. Although traditional cement stabilization is widely used, its high energy consumption and high carbon emission problems are increasingly prominent. Geopolymer (geopolymer for short) is a new type of cementing material generated by the polymerization of precursors rich in silicon and aluminum under alkaline activation. Its production energy consumption is only about 30% of that of cement, and it is superior to cement in many properties and is considered as the green cementing material with the greatest potential to replace cement in the 21st century.

[0005] The commonly used aluminosilicate precursors at present mainly include fly ash, blast furnace slag, metakaolin and red mud, etc. Among them, fly ash has become one of the most commonly used precursors in geopolymer preparation due to its high content of active silicon and aluminum components and wide sources. However, the microstructure and strength development of fly ash-based geopolymer are significantly affected by temperature, and a high dosage of alkali activator is often needed to obtain ideal strength under normal temperature curing conditions. In order to reduce the dosage of alkali under normal temperature conditions and maintain the strength, the existing researches mostly use fly ash and blast furnace slag rich in calcium to form a binary precursor system.

[0006] Coal gangue is the main solid waste generated in the process of coal mining, washing and processing, accounting for about 10% to 25% of the original coal output. Since 2010, the annual output of coal gangue in China has been about 750 million tons, accounting for nearly one fourth of the total amount of industrial solid waste. The main chemical components of coal gangue are silicon dioxide and aluminum oxide, which theoretically have the potential to be used as geopolymer precursors. However, uncalcined coal gangue has stable crystal structure and low reactivity, which is difficult to be directly used for geopolymer preparation. Studies have shown that a small amount of uncalcined coal gangue can be effectively activated and involved in the reaction in a calcium-rich system.

[0007] At present, the research of geopolymer taking fly ash and slag as precursor is relatively mature, but the utilization of large solid waste such as coal gangue still mainly depends on the mechanical or thermal activation pretreatment with high energy consumption, and its application in geopolymer-based soft soil curing is still insufficient. SUMMARY

[0008] In view of the above prior art, the present application provides a fly ash-slag-coal gangue geopolymer-based soft soil curing agent and its preparation method and application, the optimal ratio of the three precursors of the fly ash-slag-coal gangue geopolymer-based soft soil curing agent is determined, and the preparation method of the geopolymer-based curing agent is clear. The geopolymer soft soil curing agent is a green cementitious material, and it is successfully applied to soft soil curing, which provides a new technical approach for efficient resource utilization of uncalcined coal gangue and green soft soil curing. In the present application, by accurately designing the ratio of fly ash-slag-coal gangue ternary precursor, under the calcium-rich environment provided by slag and the alkaline conditions provided by alkali activator, the potential activity of uncalcined coal gangue is effectively stimulated, and a synergistic effect is produced with fly ash and slag, so that excellent soft soil curing effect is achieved without pre-activation, and environmental and economic benefits are achieved.

[0009] In order to solve the above technical problems, the present application provides a fly ash-slag-coal gangue geopolymer-based soft soil curing agent, which comprises a ternary precursor mixture and an alkali activator, the ternary precursor mixture is composed of fly ash, slag and coal gangue, wherein the mass percentage of fly ash, slag and coal gangue is 5-10%:80-90%:5-10%, and the mass percentage of fly ash and coal gangue is ≥5%; the mass ratio of alkali activator to ternary precursor mixture is 4:5.

[0010] Further, the soft soil curing agent provided by the present application, wherein: Preferably, the mass percentage of fly ash, slag and coal gangue is 10%:80%:10%.

[0011] The fly ash is F-class fly ash, the slag is S95-grade blast furnace slag, and the coal gangue is uncalcined and unground coal gangue.

[0012] The chemical components of the F-class fly ash mainly include SiO2 and Al2O3, wherein the mass percentage of SiO2 is 52% to 56%, and the mass percentage of Al2O3 is 32% to 36%; the chemical components of the S95-grade blast furnace slag mainly include CaO, SiO2 and Al2O3, wherein the mass percentage of CaO is 34% to 36%, the mass percentage of SiO2 is 30% to 34%, and the mass percentage of Al2O3 is 16% to 18%; and the main chemical components of the coal gangue without calcination and grinding treatment mainly include SiO2 and Al2O3, wherein the mass percentage of SiO2 is 60% to 64%, and the mass percentage of Al2O3 is 23% to 27%.

[0013] The coal gangue is a powder of original coal gangue without any mechanical grinding or calcination activation treatment and passes through a 200-mesh screen.

[0014] The preparation method of the soft soil stabilizer includes the following steps: preparing a ternary precursor mixture: taking the fly ash, the blast furnace slag and the coal gangue according to the mass percentage of 5% to 10%: 80% to 90%: 5% to 10%, and the mass percentage of the fly ash and the coal gangue is greater than or equal to 5%, and then uniformly mixing and stirring to obtain the ternary precursor mixture; mixing NaOH solution and Na2SiO3 solution according to the mass ratio of 1:2 to prepare an alkali activator; and uniformly stirring the alkali activator and the ternary precursor mixture according to the mass ratio of 4:5 to prepare the soft soil stabilizer.

[0015] Further, the preparation method of the present application has the following characteristics: In the step 1, the mixing and stirring is performed in a stirring machine at a rotating speed of 50 to 60 r / min for 3 to 5 minutes.

[0016] In the step 2, after the NaOH solution and the Na2SiO3 solution are mixed, the obtained alkali activator is cooled and placed.

[0017] In the step 3, the cooled and placed alkali activator is slowly and uniformly poured into the ternary precursor mixture at a rate of 0.5 to 2.0 mL / s according to the mass ratio of 4:5, and then stirred at a rotating speed of 50 to 60 r / min for 3 to 5 minutes.

[0018] The application of the soft soil stabilizer prepared by the preparation method in soft soil stabilization is as follows: 20% of the soft soil stabilizer is weighed according to the mass percentage of the ternary precursor mixture and the powdery soft soil, the soft soil stabilizer and the powdery soft soil are uniformly mixed, water is added and stirred uniformly, wherein the mass ratio of the water to the ternary precursor mixture is 50%, and the cured soil body is formed after compaction and curing; through testing, the unconfined compressive strength of the cured soil body cured for 14 days is 536.1~802.4 kPa, the unconfined compressive strength of the cured soil body cured for 28 days is 724.5~848.5 kPa, and the unconfined compressive strength of the cured soil body cured for 90 days is 887.1~901.4 kPa.

[0019] In the process of soft soil stabilization, in the alkaline environment provided by the alkali activator, the slag provides a calcium source, and the fly ash provides a silicon-aluminum source; in the alkaline environment, the calcium source and the silicon-aluminum source jointly react to generate N-A-S-H and C-A-S-H gels; the coal gangue is activated under the condition of calcium-rich strong alkali, releases aluminum ions to adjust the silicon-aluminum ratio of the system, and promotes the generation of more gels; the gels fill the pores of the soft soil and cement the soil particles, forming a dense microstructure, thereby significantly improving the strength of the soft soil.

[0020] Compared with the prior art, the application has the following beneficial effects: (1) System innovation and synergistic effect: for the first time, uncalcined coal gangue is introduced into the geopolymer system to build a fly ash-slag-coal gangue ternary synergistic system. Through the optimized ratio of 1:8:1, the activity of each component is fully stimulated in a high-calcium and strong-alkali environment, the chemical complementary and synergistic effect of multiple sources of solid waste is achieved, and the microstructure is optimized and the strength is significantly improved under normal temperature conditions.

[0021] (2) Solid waste utilization and green economy: direct and efficient utilization of uncalcined coal gangue is achieved, high-energy consumption activation pretreatment is saved, cost and carbon emissions are reduced from the source, solid waste disposal and economic benefits are combined, and the sustainable development concept of green and low carbon is met.

[0022] (3) Simple process, easy to promote: the standardized process of "dry mixing-wet mixing" is adopted, the process is simple, the conditions are controllable, and no special equipment is needed, which has good site adaptability and engineering promotion prospects.

[0023] (4) Excellent performance, wide applicability: mechanical tests prove that the method can significantly improve the macro-mechanical and engineering properties of soft soil, and is especially suitable for the reinforcement of typical soft soil such as silt soft soil, and the curing effect is stable, and the application prospect is broad.

[0024] In summary, the present application proposes a fly ash-slag-gangue ternary geopolymer-based soft soil solidifying agent, by optimizing the precursor ratio, a ternary synergistic system composed of fly ash, slag and uncalcined gangue is constructed, the amount of alkali activator is reduced in the preparation process, and the technical bottlenecks such as insufficient strength development, large amount of alkali activator, low cost-effectiveness, and difficulty in direct and efficient resource utilization of uncalcined gangue in the existing fly ash-slag binary geopolymer system in soft soil reinforcement are overcome. The soft soil solidifying agent described in the present application is suitable for reinforcement of natural soft soil such as marine, lacustrine and fluvial deposits, and the strength of the solidified soil is improved by 50%-4000%, as shown in the test results of experimental examples numbered 23 and 43, 22 and 40 in Tables 2 and 3, and the soft soil solidifying agent can be widely used in soft soil foundation treatment in the fields of building, transportation, water conservancy and the like. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The photos of soft soil and precursor components, wherein: (a) is the photo of Tianjin soft soil; (b) is the photo of fly ash, (c) is the photo of slag, and (d) is the photo of gangue; Figure 2 The SEM images of soft soil before and after geopolymer solidification, wherein: (a) is the SEM image of soft soil before reinforcement, (b) is the SEM image of soft soil after fly ash-slag geopolymer reinforcement, and (c) is the SEM image of soft soil after fly ash-slag-gangue geopolymer reinforcement; Figure 3 The schematic diagram of the solidification mechanism of the fly ash-slag-gangue geopolymer reinforced soft soil prepared by the present application. DETAILED DESCRIPTION

[0026] The application provides a fly ash-slag-gangue ternary geopolymer-based soft soil curing agent, and the design concept is: based on the chemical complementation principle of multi-source aluminosilicate materials, a ternary synergistic system is formed by optimizing the ratio of the soft soil curing agent precursor, the synergistic reinforcing effect of each component is fully played, the amount of alkali activator required in the preparation is small, the soft soil curing strength and macro mechanical properties are significantly improved, the material cost is reduced, and a new technical approach is provided for the green and efficient utilization of uncalcined gangue and the improvement of soft soil foundation. The soft soil curing agent comprises a ternary precursor mixture and an alkali activator, the ternary precursor mixture is composed of fly ash, slag and gangue, wherein the mass percentage of fly ash, slag and gangue is 5-10%: 80-90%: 5-10%, and the mass percentage of the fly ash and the gangue is greater than or equal to 5%, and the preferred ratio is 10%: 80%: 10%; the mass ratio of the alkali activator to the ternary precursor mixed powder is 4:5; the preparation method adopts a dry mixing-wet mixing process, and the main steps include: a ternary precursor mixture is prepared by using a dry mixing process; fly ash, slag and gangue are weighed according to the designed mass percentage, and are uniformly mixed and stirred to obtain the ternary precursor mixture; an alkali activator is obtained by mixing NaOH solution and Na2SiO3 solution; the alkali activator and the ternary precursor mixture are uniformly stirred by using a wet mixing process to obtain the soft soil curing agent. The activity of uncalcined gangue is successfully activated at room temperature, a large amount of C-A-S-H and N-A-S-H gel is generated by using the synergistic effect, and the microstructure and macro mechanical properties of the soft soil are significantly improved. The method is simple, low in cost, green and environmentally friendly, the fly ash-slag-gangue ternary geopolymer-based soft soil curing agent is used for soft soil reinforcement, and in the application, the soft soil curing agent is weighed according to the mass percentage of 20% of the ternary precursor mixture and the powdered soft soil, the soft soil curing agent and the powdered soft soil are uniformly mixed, water is added according to the mass ratio of 50% and is uniformly stirred, and after compaction and curing, a cured soil body is formed. In the soft soil curing process, the uncalcined gangue is activated in the calcium-rich strong alkali environment, the silicon-aluminum ratio of the system is regulated, a large amount of N-A-S-H and C-A-S-H gel is generated, the unconfined compressive strength of the soft soil is significantly improved, and a high-strength cured soil body is formed. The application process has the advantages of green economy and simple process, the strength of the cured soil body is significantly improved, the unconfined compressive strength test is conducted on the cured soil samples cured for 14 days, 28 days and 90 days, the mechanical property development is evaluated, and test results show that the unconfined compressive strength of the cured soil body cured for 14 days is 536.1-802.4 kPa, the unconfined compressive strength of the cured soil body cured for 28 days is 724.5-848.5 kPa, and the unconfined compressive strength of the cured soil body cured for 90 days is 887.1-901.4 kPa. Meanwhile, a new technical support is provided for the resource utilization of uncalcined gangue and the improvement of soft soil foundation.

[0027] The application will be further described in conjunction with the accompanying drawings and specific embodiments, but the following embodiments are by no means any limitation on the application.

[0028] Embodiment Preparation of a fly ash-slag-gangue ternary geopolymer-based soft soil stabilizer and its application in soft soil stabilization.

[0029] 1. Basis for determining the mass of each component of the ternary precursor mixture in the soft soil stabilizer and the alkali activator In this embodiment, the soft soil sample is Tianjin soft soil, such as Figure 1 As shown in (a), the plasticity index is 22.4, and the The mass is determined according to formula (1).

[0030] (1) In formula (1), is the mass of the soft soil sample, e is the void ratio of the soft soil sample, which is obtained by converting the soil particle specific gravity, density and water content measured by indoor soil test; is the density of water; V is the volume of the soft soil sample; , , , are the specific gravities of the soft soil sample, fly ash, slag and gangue, respectively, which are obtained by converting the densities of each component measured by indoor soil test; is the mass ratio of the ternary precursor mixture to the soft soil sample, and in this embodiment, the value of is 0.2; , , are the mass fractions of fly ash, slag and gangue in the ternary precursor powder, respectively. The photos of F-class fly ash, S95-grade slag and uncalcined gangue in the ternary precursor mixture are shown in Figure 1 Among them, (b) is the photo of fly ash, (c) is the photo of slag, and (d) is the photo of gangue, and the mass of each component and the mass of the alkali activator are determined according to formula (2).

[0031] (2) In formula (2), , , , are the masses of fly ash, slag, gangue and alkali activator, respectively; is the mass ratio of the alkali activator to the ternary precursor mixture, the value of is 0.8.

[0032] 2. Preparing a ternary precursor mixture, comprising: Preparation of raw materials: F-class fly ash, the main components of which are SiO2(52%~56%) and Al2O3(32%~36%). S95-grade blast furnace slag, the main components of which are CaO(34%~36%), SiO2(30%~34%) and Al2O3(16%~18%). Raw coal gangue without any mechanical grinding or calcination activation treatment, the main components of which are SiO2(60%~64%) and Al2O3(23%~27%), which is crushed, classified and sieved through a 200-mesh sieve for standby use.

[0033] Preparation of the precursor mixture: the mass of the soft soil sample is , and the mass of the ternary precursor mixture is =10%, =80%, =10% The amounts of fly ash, slag and coal gangue are weighed according to formula (2) , , , and then the three are physically mixed. The mixture is stirred in a blender at a speed of 50~60 r / min for 3~5 minutes to obtain a uniformly mixed ternary precursor powder mixture with a mass of + + for standby use.

[0034] 3. Preparation of an alkali activator: mix NaOH solution and Na2SiO3 solution according to a mass ratio of 1:2, wherein the concentration of the NaOH solution is 1.47 g / ml, and the concentration of the Na2SiO3 solution is 0.412 g / ml. The mixed solution is the alkali activator. After preparation, it is left to cool to room temperature for standby use.

[0035] 4. Preparation of a soft soil solidifier: weigh the alkali activator left to cool with a mass of , and slowly and uniformly pour it into the ternary precursor mixture at a rate of 1.5 mL / s. Stir at a speed of 60 r / min for 5 minutes to obtain a uniformly mixed soft soil solidifier with a mass of + + + =0.2 .

[0036] 5. Preparation of a geopolymer solidified soil sample: first, weigh the powdered soft soil sample with a predetermined mass of . In this embodiment, the soft soil sample is Tianjin soft soil, as shown in (a) of the accompanying drawings, with a plasticity index of 22.4. In this embodiment, Figure 1 ​=100g. Then, 36g of the soft soil stabilizer prepared in step 4 and 100g of the Tianjin soft soil are mixed uniformly, and 10g of water is added. After stirring, the mixture is the geopolymer stabilized soft soil sample. Next, the mixture is loaded into a mold by using a layered compaction method, and is evenly divided into four layers for compaction. The environmental temperature is controlled to be 20-30°C. After demolding, the sample is cured under standard curing conditions (constant temperature of 20°C±2°C and constant humidity of 95%±3%) for 14 days, 28 days and 90 days, respectively. After curing, the unconfined compressive strength test is performed according to the relevant standards to evaluate the development of the mechanical properties.

[0037] The soft soil stabilization mechanism of the stabilizer The core mechanism of the present application is to utilize the synergistic enhancement effect among fly ash-slag-unburned coal gangue ternary precursor, as shown in the following formula: Figure 3 As shown in the formula, first, when the alkali activator is uniformly mixed with the ternary precursor material and the soil, the OH - begins to dissolve and destroy the siliceous and aluminous substances in the ternary precursor. With the increase of OH - , the network structure of silicon / aluminum oxides in the ternary precursor is gradually destroyed, so that part of the active silicon / aluminum substances form oligomers such as silicon oxide tetrahedron or aluminum oxide tetrahedron. Then, due to the existence of metal cations (Na + and Ca 2+ ) in the system, the unstable silicon oxide tetrahedron and aluminum oxide tetrahedron undergo polycondensation reaction to form new silicate and aluminate polymer gels (N–A–S–H, C–A–S–H) with high degree of polymerization and three-dimensional network structure. With the increase of the amount of the gels, the soil is stabilized through the cementation between soil particles and the filling of soil pores.

[0038] The soft soil stabilization mechanism in the present application is summarized as follows: 1) Dominant reaction: slag provides calcium source as a calcium-rich component; fly ash provides active silicon / aluminum substances as a high-quality silicon / aluminum source. In the alkaline environment provided by the alkali activator, the two react together to generate sodium silicate and aluminate (N–A–S–H) gel and calcium silicate and aluminate (C–A–S–H) gel.

[0039] 2) Synergistic regulation: unburned coal gangue is activated under the high-calcium environment and alkaline condition created by slag, and releases Al 3+ , which is mutually regulated with the silicon source of fly ash to accurately balance the Si / Al ratio in the system, so as to promote the generation of more and more stable N–A–S–H and C–A–S–H gels.

[0040] 3) Structure reinforcement: The ternary system promotes the formation of gel phase through chemical complementation and synergistic effect. A large amount of gel product effectively fills the soft soil pores and cements the soil particles, making the microstructure more dense and uniform, and significantly reducing the pore volume (especially the proportion of macropores >1 μm), which is reflected in the significant improvement of the unconfined compressive strength.

[0041] Experimental examples and effect verification The steps 2-5 of the above examples were repeated, except that the components and proportions of the precursor powder were changed, as shown in Tables 1-3, to prepare 43 groups of solidified soil samples for effect verification.

[0042] The unconfined compressive strength of the 43 groups of solidified soil samples listed in Tables 1-3 was tested after 14 days, 28 days and 90 days of curing, respectively, with the solidified agent precursor including a single system (fly ash or slag or coal gangue), a binary system without coal gangue (including fly ash and slag), a binary system without fly ash (slag and coal gangue), a binary system without slag (fly ash and coal gangue), and a ternary system (fly ash, slag and coal gangue).

[0043] The results show that, compared with the solidified soil samples of the fly ash and slag binary system without coal gangue (Nos. 4-9), the unconfined compressive strength of some ternary geopolymer solidified soil samples (Nos. 22, 40) is significantly improved at each age, and the microstructure observation also shows that the pores are more dense and uniform, as shown in Figure 2 The synergistic reinforcement effect of the ternary system is fully verified. As shown in Table 2, when the proportion is fly ash 10%, slag 80%, and coal gangue 10% (No. 22 solidified soil sample), the 14-day unconfined compressive strength is 536.1 kPa, the 28-day unconfined compressive strength is 724.5 kPa, and the 90-day unconfined compressive strength is as high as 901.4 kPa. When the proportion is fly ash 5%, slag 90%, and coal gangue 5% (No. 40 solidified soil sample), the 14-day unconfined compressive strength is 802.4 kPa, the 28-day unconfined compressive strength is 848.5 kPa, and the 90-day unconfined compressive strength is as high as 887.1 kPa. The test results prove that the fly ash-slag-unfired coal gangue ternary precursor material provided by the present application effectively adjusts the Si / Al ratio through synergistic effect, promotes the formation of N-A-S-H and C-A-S-H gel, fully fills the soft soil pores and cements the soil particles, and forms a dense and uniform microstructure (as shown in Figure 2 The unconfined compressive strength and overall mechanical properties of the soft soil are significantly improved.

[0044] In Table 1, the data of the experimental example No. 2 shows that the monomial slag system solidified soil sample also has relatively high unconfined compressive strength, but from the data in Table 1, it can be concluded that the strength of the solidified soil sample is reversed at 90 days, which indicates that the long-term strength growth is limited and has limitations.

[0045] The data of the experimental examples No. 4 and No. 5 shows that the unconfined compressive strength of the binary fly ash and slag system solidified soil sample is relatively high, but from the data in Table 1, it can be concluded that the strength development is uneven and the long-term strength is not ideal, and the use of coal gangue cannot be reflected.

[0046] The data of the experimental examples No. 14 and No. 15 shows that the unconfined compressive strength of the binary slag and coal gangue system solidified soil sample is also relatively high, but from the data in Table 2, it can be concluded that the strength is not ideal compared to the experimental examples No. 4 and No. 5, and the unactivated coal gangue cannot be fully activated.

[0047] Even in the ternary fly ash, slag and coal gangue system solidified soil sample (No. 23, No. 24, No. 28, No. 32, No. 33 and No. 43), due to the low content of slag (≤20%) or the high content of unactivated coal gangue (≥40%) in these experimental examples, the corresponding solidified soil is difficult to ensure high basic strength, and a large number of precursors in the system do not participate in the reaction, and the amount of generated gel is not enough to ensure high solidification strength. Therefore, the ratio of the three must be controlled to ensure that the unactivated coal gangue is fully activated while significantly improving the unconfined compressive strength of the solidified soil sample. Therefore, in the present application, the ratio of the three is controlled to be 5-10%:80-90%:5-10% of fly ash, slag and coal gangue, and the mass percentage of the fly ash and the coal gangue is ≥5%.

[0048] Table 1 Tianjin soft soil solidification experimental example data-1

[0049] Table 2 Tianjin soft soil solidification experimental example data-2

[0050] Table 3 Tianjin soft soil solidification experimental example data-3

[0051] The application provides a fly ash-slag-gangue geopolymer-based soft soil curing agent and a preparation method and application thereof, and the core lies in realizing direct and efficient resource utilization of industrial solid wastes such as fly ash, slag and uncalcined gangue. The slag is a solid waste generated in the blast furnace ironmaking process; the fly ash is fine ash and furnace bottom slag collected in the flue gas of a coal-fired power plant boiler; and the gangue is associated waste in the process of coal mining and washing, and accounts for about 15% to 20% of the raw coal output, and the application realizes full utilization of resources.

[0052] In summary, in the application, by optimizing the ratio (1:8:1 or 0.5:9:0.5) and the dry mixing-wet mixing process, the uncalcined gangue activity is successfully excited under normal temperature conditions, a large amount of C-A-S-H and N-A-S-H gel is generated by using the synergistic effect, and the microstructure and macroscopic mechanical properties of the soft soil are significantly improved. The method has simple process, low cost and green environmental protection, and provides a promising solution for soft soil foundation treatment and resource utilization of bulk solid waste.

[0053] Although the application is described above in combination with the drawings, the application is not limited to the specific embodiments described above, and the specific embodiments described above are only illustrative but not restrictive, and many improvements and changes can be made by those skilled in the art without departing from the purpose of the application under the inspiration of the application, and these all belong to the protection of the application.

Claims

1. A fly ash - slag - coal gangue geopolymer based soft soil stabilizer characterized in that, The soft soil solidifying agent comprises a ternary precursor mixture and an alkali activator, the ternary precursor mixture is composed of fly ash, slag and coal gangue, the mass percentage of the fly ash, the slag and the coal gangue is 5-10%:80-90%:5-10%, and the mass percentage of the fly ash and the coal gangue is greater than or equal to 5%; the mass ratio of the alkali activator to the ternary precursor mixture is 4:

5.

2. The soft soil stabilizer according to claim 1, characterized in that: The fly ash is F-class fly ash, the slag is S95-grade blast furnace slag, and the coal gangue is coal gangue without calcination and grinding treatment.

3. The soft ground stabilizer according to claim 2, characterized in that: The chemical components of the F-class fly ash mainly include SiO2 and Al2O3, wherein the mass percentage of SiO2 is 52%-56%, and the mass percentage of Al2O3 is 32%-36%. The chemical components of the S95-grade blast furnace slag mainly include CaO, SiO2 and Al2O3, wherein the mass percentage of CaO is 34%-36%, the mass percentage of SiO2 is 30%-34%, and the mass percentage of Al2O3 is 16%-18%. The main chemical components of the coal gangue without calcination and grinding treatment mainly include SiO2 and Al2O3, wherein the mass percentage of SiO2 is 60%-64%, and the mass percentage of Al2O3 is 23%-27%.

4. The soft soil stabilizer according to claim 3, characterized by, The coal gangue is a powder of original coal gangue without any mechanical grinding or calcination activation treatment and passes through a 200-mesh screen.

5. A method for producing the soft soil solidifying agent as claimed in any one of claims 1 to 4, characterized by, The method comprises the following steps: Step 1, the fly ash, the slag and the coal gangue are weighed according to the mass percentage of 5-10%:80-90%:5-10%, and the mass percentage of the fly ash and the coal gangue is greater than or equal to 5%, and then the ternary precursor mixture is prepared by mixing and stirring uniformly; Step 2, NaOH solution and Na2SiO3 solution are mixed according to the mass ratio of 1:2, and the obtained mixture is the alkali activator; Step 3, the alkali activator is added into the ternary precursor mixture according to the mass ratio of 4:5, and then the soft soil solidifying agent is obtained by stirring uniformly.

6. The production method according to claim 5, wherein In step 1, the mixing and stirring is carried out in a stirring machine at a stirring speed of 50-60 r / min for 3-5 minutes.

7. The preparation method according to claim 5, characterized in that, In step 2, after the NaOH solution and the Na2SiO3 solution are mixed, the obtained alkali activator is cooled and placed.

8. The preparation method according to claim 5, characterized in that, In step 3, the cooled and placed alkali activator is slowly and uniformly poured into the ternary precursor mixture at a rate of 0.5-2.0 mL / s, and then the soft soil solidifying agent is obtained by stirring at a stirring speed of 50-60 r / min for 3-5 minutes.

9. Use of a soft soil stabilizer in the stabilization of soft soil, characterized in that, According to the mass percentage of the ternary precursor mixture and the powdery soft soil, 20% of the soft soil curing agent prepared by the preparation method in any one of claims 5 to 8 is weighed, the soft soil curing agent and the powdery soft soil are uniformly mixed, water is added and stirred uniformly, wherein the mass ratio of water to the ternary precursor mixture is 50%, after compaction and curing, the cured soil body is formed; through testing, the unconfined compressive strength of the cured soil body cured for 14 days is 536.1~802.4 kPa, the unconfined compressive strength of the cured soil body cured for 28 days is 724.5~848.5 kPa, and the unconfined compressive strength of the cured soil body cured for 90 days is 887.1~901.4 kPa.

10. Use according to claim 9, characterized in that, In the process of soft soil curing, in the alkaline environment provided by the alkali activator, the slag provides a calcium source, and the fly ash provides a silicon-aluminum source, and the calcium source and the silicon-aluminum source jointly react to generate N-A-S-H and C-A-S-H gels in the alkaline environment; the coal gangue is activated under the condition of calcium-rich strong alkali to release aluminum ions to adjust the silicon-aluminum ratio of the system, promote the generation of more gels, and fill the pores of the soft soil and cement the soil particles to form a dense microstructure, thereby significantly improving the strength of the soft soil, and the strength of the cured soil is improved by 50%~4000%.

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