Construction method of powder coal cinder-based marine silt flow-state solidified soil

Abstract

The invention discloses a powder coal cinder-based marine silt flow-state solidified soil construction method, which fully utilizes active components in powder coal cinder, and determines the content of the active components of the powder coal cinder according to the free water consumption of the hydration reaction of the powder coal cinder under the excitation condition of an alkaline triggering agent. The mixing amount of the alkaline triggering agent is determined according to the content of active ingredients of the pulverized coal cinder. By adjusting the water cement ratio, the plastic-flow conversion of the solidified soil is realized, an organic polymerization dispersant or other composite dispersants are not needed, the solidified material is simple in component, local materials are used, the field preparation process is simple, the cost is low, and the method is suitable for industrial production. And resource recycling of the powder coal cinder and the silt soft soil can be realized.

Description

Technical Field

[0001] This invention relates to the technical field of civil engineering construction, and in particular to a construction method for solidified marine silt fluidized soil based on fly ash. Background Technology

[0002] Fly slag from thermal power plants contains numerous harmful heavy metals and non-metallic elements. These harmful elements seep into the surrounding area via leachate from the fly slag stockpile, polluting groundwater and even potentially entering the ocean. This paper proposes a technical system for producing fluidized solidified soil based on fly slag and dredged silt, leveraging the physical and mechanical properties of both materials. This system will provide casting materials for off-site construction of anti-seepage walls and off-site injection of cement-soil mixing pile foundations at thermal power plant stockpiles. Fly slag particles from thermal power plants exhibit varying sizes and unstable activity, while silty soft soil has high water content and strong viscosity. Achieving thorough mixing of fly slag and silty soft soil under appropriate water-cement ratio conditions to obtain stable and economically viable fluidized solidified soil remains a significant technical challenge.

[0003] Chinese patent CN114753346A discloses a method for preparing premixed fluidized solidified soil using in-situ silty clay. This method achieves the preparation of fluidized solidified soil by adding a composite clay dispersant and a composite soft soil solidifier to the silty clay. The composite dispersant significantly affects the age-appropriate strength of the fluidized solidified soil, and its addition also increases the preparation cost. Chinese patent CN112030940B discloses a marine soft soil solidifier and an in-situ premixed cement-soil cast-in-place pile construction process. This process requires a solidifier made from slag, cement, fly ash, alkaline triggering agent, water-reducing agent, retarder, and expanding agent, resulting in complex components, high cost, and hindering the widespread application of the process. Chinese patent CN111908855B discloses a composite pile premixed fluidized solidified soil slurry and its preparation method. Using clay as the main raw material, it requires adding a certain weight of fine sand to the clay to improve its gradation and thus enhance the fluidity of the fluidized solidified soil. Summary of the Invention To address the shortcomings of existing technologies, this invention provides a method for preparing fly ash-based silt fluidized solidified soil. The method utilizes coarse-grained fly ash from a thermal power plant as the base solidifying material. By measuring the activity of the fly ash, an appropriate alkaline trigger is introduced to induce a hydration reaction of the active components in the fly ash. This hydration is then thoroughly mixed with silty soft soil to form solidified soil. By adjusting the water-cement ratio, the plastic-to-fluid transition of the solidified soil is achieved. The unreacted coarse-grained fly ash acts as coarse aggregate in the entire solidified soil system, thereby improving the age strength and impermeability of the solidified soil.

[0004] To address the aforementioned technical problems, this invention provides a method for detecting the activity of fly ash, characterized by determining the content of active silica and alumina in the fly ash, with the following detection steps: (1) Take a certain mass of fly ash, dry it, and weigh it as M1; (2) Add a certain mass of water to the fly ash, the mass of which is M2; (3) Stir the fly ash and add ordinary silicate cement as an alkaline trigger, the mass of which is M3; (4) Mix thoroughly and pour into fly ash test blocks. Weigh the mass of the curing test block as M4. Theoretically, M4 = M1 + M2 + M3. (5) Place the test block in a standard curing room for curing. After 28 days, take it out and weigh it as M5. (6) Place the test block in room temperature for curing and drying for 7 days, and weigh it as M6. The mass of free water consumed in the entire hydration reaction is M0 = M6 - M1 - M3. (7) Based on the amount of alkaline triggering agent in ordinary Portland cement, the free water consumption under complete reaction conditions is calculated to be M. 01 Therefore, the amount of free water consumed in the hydration reaction of the active components in fly ash is M. 02 =M0-M 01 ; (8) According to M 02 Based on the molecular weight ratio of water of crystallization after the hydration reaction, the mass of active silica and aluminum oxide participating in the hydration reaction can be calculated. (9) By repeating steps (1) to (8) above, the mass ratio of active ingredients in pulverized coal slag can be accurately determined.

[0005] The above method abandons the traditional indirect measurement method of the activity index using the age-strength ratio. Instead, it calculates the amount of active silica and alumina participating in the hydration reaction by the amount of free water consumed, thereby obtaining the mass ratio of active ingredients in fly ash. This parameter is the key parameter for determining the dosage of alkaline trigger and the water-ash ratio.

[0006] This invention also provides a construction method for solidified marine silt based on fly ash, comprising the following steps: Step 1) Conduct an activity test on the fly ash to determine the content of active silica and aluminum oxide in the fly ash; the test method is as described above.

[0007] Step 2) Determine the amount of alkaline trigger agent to be used based on the amount of active silica and alumina in the fly ash, and prepare the alkaline trigger agent slurry. Step 3) Excavate a temporary mixing tank at the construction site, and install partition steel plates at the bottom and on the surrounding side walls of the mixing tank; Step 4) Pour fly ash into the mixing tank and use a full-section solidification mixing device to stir the fly ash while spraying the triggering agent slurry. Step 5) Adjust the water-cement ratio to 1:1.5 and add an air-entraining agent. Use an excavator to excavate the silty soft soil and pour it into the mixing tank. Continue to use a full-section solidification mixing device to mix and solidify the soil while spraying water. After mixing evenly, measure the fluidity of the solidified soil. If the fluidity does not meet the requirements, continue to adjust the water-cement ratio to 1:2 and continue mixing. After mixing evenly, continue to measure the fluidity of the solidified soil. If the fluidity does not meet the requirements, continue to adjust the water-cement ratio and increase the amount of water until the fluidity reaches more than 160mm. Then stop mixing. Generally, the water-cement ratio should not exceed 3. Step 6) Using a mud pump, the solidified soil slurry is poured into pre-set trenches and holes to form structural layers with specific functions, such as off-site cast-in-place anti-seepage walls and cast-in-place piles. As a preferred embodiment of the above technical solution, the construction method for solidified coal-fired marine silt based on fly ash provided by the present invention further includes some or all of the following technical features: As an improvement to the above technical solution, in step 2), the initial water-cement ratio is 0.6-0.8, determined based on the total amount of active silica, alumina, and alkaline triggering agent in the fly ash. The dosage of alkaline triggering agent is determined based on the mass of the active components silica and alumina in the fly ash. The alkaline triggering agent accounts for 10%-15% of the mass of the active components in the fly ash.

[0008] As an improvement to the above technical solution, the triggering agent slurry is characterized in that: the triggering agent slurry is one or a mixture of two of carbide slag and 42.5 ordinary Portland cement, and if mixed, the mass ratio of the two components is 1:1.

[0009] As an improvement to the above technical solution, the mass fraction of each component in the method is as follows: silty soft soil: 60-70 parts, fly ash: 20-30 parts, alkaline trigger: 5-10 parts, air-entraining agent: 0.5-1.0 parts, initial water ratio: 0.6-0.8, and adjusted water-cement ratio: 2.5-3.0.

[0010] As an improvement to the above technical solution, the silty soft soil includes silt, dredged silt, silty clayey soil, peat, silty silty clay, and silty sandy soil.

[0011] As an improvement to the above technical solution, the pulverized coal slag is untreated pulverized coal slag from the stockpile during the production process of thermal power plants; in the solidified soil system, the active component acts as the main body of the solidified material, and the inactive component acts as coarse aggregate.

[0012] As an improvement to the above technical solution, the mass of the fly ash is 30%-60% of the mass of the silt and soft soil.

[0013] As an improvement to the above technical solution, the alkaline triggering agent is one or a combination of two of carbide slag and ordinary silicate cement.

[0014] As an improvement to the above technical solution, the air-entraining agent is AOS powder air-entraining agent.

[0015] This invention fully utilizes the active components in fly ash, and initiates the hydration reaction of the active components through an alkaline trigger, thereby realizing the preparation of solidified soil. By adjusting the water-cement ratio, the plastic-fluid transition of the solidified soil is achieved. No organic polymer dispersant or other composite dispersant is required. The solidified material has a simple composition, uses locally sourced materials, and has a simple on-site preparation process with low cost. It can realize the resource recycling of fly ash and silty soft soil in a timely manner.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention uses coal slag from thermal power plants and marine silt as the main materials for cohesive fluidized solidified soil. This technology fully utilizes the active components within the coal slag, promoting hydration reactions of these active components under the action of an alkaline trigger, thus solidifying the marine silt. Then, by adjusting the water-cement ratio of the solidified soil, a plastic-to-fluid transition is achieved, forming fluidized solidified soil. This invention fully utilizes the coarse particles of coal slag as coarse aggregate in the solidified soil, improving its mixability and age-appropriate strength. Furthermore, this invention creatively proposes calculating the mass of the active components in the coal slag based on the mass of bound water formed during the hydration reaction, abandoning the traditional indirect measurement method using the age-appropriate strength ratio. This method is more intuitive and allows for the calculation of the mass of coal slag, alkaline trigger, and other additives using this key parameter.

[0017] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, the following detailed description is provided in conjunction with preferred embodiments. Detailed Implementation

[0018] The following detailed description of specific embodiments of the present invention is part of this specification. The principles of the present invention are illustrated through examples, and other aspects, features and advantages of the present invention will become apparent from this detailed description.

[0019] In the following embodiments, fluidity is used to reflect the fluidity of the solidified soil. The method of measurement is as follows: a cylinder with openings at both ends and a diameter and height of 8 cm is placed on a clean, horizontal glass surface, solidified soil is poured in, compacted, smoothed, and then the cylinder is lifted. The solidified soil collapses. The minimum and maximum diameters of the collapsed body are measured, and the arithmetic mean of the two is the fluidity.

[0020] In the following embodiments, the solidification strength of the fluidized solidified soil is expressed by its unconfined compressive strength. The determination method is as follows: a cubic mold with dimensions of 70.5mm × 70.5mm × 70.5mm is selected, and the fluidized solidified soil is poured into the mold. After 48 hours, the mold is removed and placed in a standard curing room with a temperature of 20±2℃ and a relative humidity of >95% for 14 days and 28 days. The compressive strength of the specimen is tested using an unconfined uniaxial compression tester.

[0021] In the following embodiments, the fly ash used is fly ash from Linhai Thermal Power Plant and its nearby thermal power plants in Taizhou City, Zhejiang Province. The general indicators of fly ash are shown in Table 1.

[0022] Table 1. Characteristic parameters of fly ash in the embodiments

[0023] The marine silt used in the following embodiments is marine silty clay surrounding the thermal power plant, and the soil properties are shown in Table 2.

[0024] Table 2 Physical and mechanical parameters of marine dredged silty clay

[0025] Examples 1-4 The composition and dosage of the fly ash-based marine silt fluidized solidified soil in Examples 1-4 are shown in Table 3. The active components of fly ash were tested using the method provided by this invention, and the results of the calculation of the mass percentage of fly ash were used to ensure that the mass dosage of active components in fly ash was 8%-14%. The alkaline triggering agent was calcium carbide slag, and the modulus and performance of calcium carbide slag met the performance requirements of the alkaline triggering agent. The AOS air-entraining agent accounted for 0.1% of the total mass of the active components of fly ash and calcium carbide slag. The final water-cement ratio of each group of experiments was not greater than 3.

[0026] Table 3 Components of Fly Slag-Based Marine Silt Fluidized Solidified Soil (Examples 1-4)

[0027] The specific steps involved in the solidified marine silt-based fluidized bed soil based on fly ash in Examples 1-4 are as follows: 1) Determine the amount of alkaline trigger agent to be used based on the amount of active silica and alumina in the fly slag, and prepare the alkaline trigger agent slurry. The initial water-cement ratio is 0.6-0.8. The amount of water added to the trigger agent slurry is determined based on the total amount of active silica, alumina and alkaline trigger agent in the fly slag.

[0028] 2) A temporary mixing tank is excavated at the construction site, and partition steel plates are installed at the bottom and on the surrounding side walls of the mixing tank.

[0029] 3) Pour fly ash into the mixing tank and use a full-section solidification mixing device to stir the fly ash while spraying the triggering agent slurry.

[0030] 4) Adjust the water-cement ratio to 1:1.5, and use an excavator to excavate the silty soft soil and pour it into the mixing tank. Continue to use the full-section solidification mixing equipment to mix the solidified soil, spraying water while mixing. After mixing evenly, measure the fluidity of the solidified soil. If the fluidity does not meet the requirements, continue to adjust the water-cement ratio to 1:2 and continue mixing. After mixing evenly, continue to measure the fluidity of the solidified soil. If the fluidity does not meet the requirements, continue to adjust the water-cement ratio and increase the amount of water until the fluidity reaches more than 160mm. Then stop mixing. Generally, the water-cement ratio should not exceed 3.

[0031] Step 5) Molding, hardening, demolding, and curing of fluidized solidified soil test blocks.

[0032] The flowability and 14-day and 28-day unconfined compressive strength of the above four groups of fluidized solidified soil were tested, and the results are shown in Table 3. The flowability was between 165-182 mm, indicating that the fluidized solidified soil has good fluidity, which is beneficial for construction. The strength of the solidified soil after 14 days of curing was 0.65-0.94 MPa, and the unconfined compressive strength after 28 days reached 0.88-1.04 MPa. The solidified soil has the properties of being suitable for both soil improvement and structural layer with specific functional requirements.

[0033] Table 4. Main performance tests of four groups of solidified soil

[0034] All the raw materials listed in this invention, as well as the upper and lower limits and ranges of the raw materials and the upper and lower limits and ranges of the process parameters (such as temperature, time, etc.), can realize this invention. Examples are not listed one by one here.

[0035] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for detecting the activity of fly ash, characterized in that, The following are the steps to determine the content of active silica and aluminum oxide in fly ash: (1) Take a certain mass of fly ash, dry it, and weigh it as M1; (2) Add a certain mass of water to the fly ash, the mass of which is M2; (3) Stir the fly ash and add ordinary silicate cement as an alkaline trigger, the mass of which is M3; (4) Mix thoroughly and pour into fly ash test blocks. Weigh the mass of the curing test block as M4. Theoretically, M4 = M1 + M2 + M3. (5) Place the test block in a standard curing room for curing. After 28 days, take it out and weigh it as M5. (6) Place the test block in room temperature for curing and drying for 7 days, and weigh it as M6. The mass of free water consumed in the entire hydration reaction is M0 = M6 - M1 - M3. (7) Based on the amount of alkaline triggering agent in ordinary Portland cement, the free water consumption under complete reaction conditions is calculated to be M. 01 Therefore, the amount of free water consumed in the hydration reaction of the active components in fly ash is M. 02 =M0-M 01 ; (8) According to M 02 Based on the molecular weight ratio of water of crystallization after the hydration reaction, the mass of active silica and aluminum oxide participating in the hydration reaction can be calculated. (9) By repeating steps (1) to (8) above, the mass ratio of active ingredients in pulverized coal slag can be accurately determined.

2. A construction method for solidified marine silt based on fly ash, characterized in that, It includes the following steps: Step 1) Perform activity testing on the fly ash to determine the content of active silica and alumina in the fly ash; the testing method is as described in claim 1; Step 2) Determine the amount of alkaline trigger agent to be used based on the amount of active silica and alumina in the fly ash, and prepare the alkaline trigger agent slurry. Step 3) Excavate a temporary mixing tank at the construction site, and install partition steel plates at the bottom and on the surrounding side walls of the mixing tank; Step 4) Pour fly ash into the mixing tank and use a full-section solidification mixing device to stir the fly ash while spraying the triggering agent slurry. Step 5) Adjust the water-cement ratio to 1:1.5 and add an air-entraining agent. Use an excavator to excavate the silty soft soil and pour it into the mixing tank. Continue to use the full-section solidification mixing equipment to mix and solidify the soil while spraying water. After mixing evenly, measure the fluidity of the solidified soil. If the fluidity does not meet the requirements, continue to adjust the water-cement ratio to 1:2 and continue mixing. After mixing evenly, continue to measure the fluidity of the solidified soil. If the fluidity does not meet the requirements, continue to adjust the water-cement ratio and increase the amount of water until the fluidity reaches more than 160 mm. Stop mixing. Generally, the water-cement ratio should not be greater than 3. Step 6) Using a mud pump, the solidified soil slurry is poured into pre-set trenches and holes to form structural layers with specific functions, such as off-site cast-in-place anti-seepage walls and cast-in-place piles.

3. The construction method for solidified marine silt based on fly ash as described in claim 2, characterized in that: In step 2), the initial water-cement ratio is 0.6-0.8, and the amount of triggering agent is determined according to the total amount of active silica and alumina in the fly ash. The amount of triggering agent accounts for 10%-15% of the mass of active components in the fly ash.

4. The construction method for solidified marine silt based on fly ash as described in claim 3, characterized in that: The triggering agent slurry is one or a mixture of two of the following: carbide slag and 42.5 ordinary Portland cement. If mixed, the mass ratio of the two components is 1:

1.

5. The construction method for solidified marine silt based on fly ash as described in claim 2, characterized in that, The mass fractions of each component in the method are as follows: silty soft soil: 60-70 parts, fly ash: 20-30 parts, alkaline trigger: 5-10 parts, air-entraining agent: 0.5-1.0 parts, initial water ratio: 0.6-0.8, and adjusted water-cement ratio: 2.5-3.

0.

6. The construction method for solidified marine silt based on fly ash as described in claim 2, characterized in that: The silty soft soil includes silt, dredged silt, silty clay, peat, silty silty clay, and silty sandy soil.

7. The construction method for solidified marine silt based on fly ash as described in claim 5, characterized in that: The pulverized coal slag is untreated pulverized coal slag from the stockpile during the production process of thermal power plants; in the solidified soil system, the active component acts as the main body of the solidified material, and the inactive component acts as the coarse aggregate.

8. The construction method for solidified marine silt based on fly ash as described in claim 5, characterized in that: The mass of the fly ash is 30%-60% of the mass of the silt and soft soil.

9. The construction method for solidified marine silt based on fly ash as described in claim 5, characterized in that: The alkaline triggering agent is one or a combination of two of carbide slag and ordinary silicate cement.

10. The construction method for solidified marine silt based on fly ash as described in claim 2, characterized in that: The air-entraining agent is AOS powder air-entraining agent.

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