In-situ carbonization reinforcement method for solid waste improvement project muck and three-dimensional ventilation device

Abstract

The invention discloses an in-situ carbonization reinforcement method for solid waste improved project muck and a three-dimensional ventilation device. The method comprises the steps that S1, improved project muck is prepared; s2, a containing groove is excavated, and a three-dimensional ventilation device is pre-buried in the bottom of the groove; s3, the improved engineering muck is transported to the containing groove for first construction layer filling; s4, the surface of the first construction layer is covered with a sealing film, an air pressure detector is installed on the sealing film, and COO is introduced into the improvement engineering muck in the first construction layer through a three-dimensional ventilation device for carbonization; and S5, the steps from S2 to S4 are repeated till filling of the whole subgrade is completed. According to the method, the roadbed subjected to rolling and filling construction does not need to be excavated or punched again, damage to the structure and strength of the roadbed is avoided, meanwhile, the construction technology is greatly simplified, and efficient in-situ solidification of solid waste is achieved with low cost.

Description

Technical Field

[0001] This invention belongs to the field of soil improvement technology in geotechnical engineering, specifically relating to an in-situ carbonization reinforcement method for soil in solid waste improvement projects. Background Technology

[0002] Urban construction projects generate large quantities of construction waste, including earthwork and sludge. Currently, the common disposal method for various types of construction waste in China, especially clay and silt with poor engineering properties, is landfill. The treatment cost of construction waste generated in urban construction is high, and it impacts the urban environment. The disposal of this waste not only consumes significant resources but can also lead to hazardous accidents if not handled properly. Domestic and international research and practice have proven that after solidification and stabilization, construction waste can be widely used in road filling, pipe gallery backfilling, and new building materials, demonstrating high potential and value for resource utilization.

[0003] With the continuous deepening of scientific research and engineering applications, applying bulk solid waste, such as blast furnace slag, carbide slag, phosphogypsum, and alkali slag, to soil improvement and building material research and development to reduce cement usage is an efficient and environmentally friendly method for the resource utilization of solid waste. The principle is generally that the solidified material acts as a cementing material and undergoes a hydration reaction with water, or the solidified material acts as an activator to stimulate the original mineral substances in the soil to undergo volcanic ash reaction and ion exchange reaction with the solidified material to generate a cementing substance mainly composed of hydrated calcium silicate. While encapsulating and binding soil particles, it continues to harden, forming a skeleton in the soil, which is interconnected to form a spatial network structure, thereby improving the soil strength.

[0004] However, existing slag carbonization reinforcement technologies are mostly limited to laboratory scale or non-in-situ applications. For example, "wet carbonization" requires preparing the slag into a fluid state, which does not meet the requirements of actual engineering compaction; "in-situ ex-situ carbonization" requires excavation, treatment, and backfilling of the slag, resulting in a complex process and high costs; while "carbonization treatment followed by pumping" is not applicable to typical scenarios such as roadbed filling. None of these methods have solved the core problem of how to effectively and uniformly carbonize slag after compaction according to construction methods on actual engineering sites. The technical bottleneck lies in the fact that the compacted slag has high density, making it difficult for CO2 to effectively penetrate from the surface to the deeper layers; if drilling followed by aeration is used, it will damage the integrity and structural strength of the already formed roadbed. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide an in-situ carbonization reinforcement method for solid waste improvement engineering slag. This invention eliminates the need for re-excavation or drilling of the roadbed after compaction and filling, thus avoiding damage to the roadbed structure and strength. At the same time, it greatly simplifies the construction process and achieves efficient in-situ solidification of solid waste at a lower cost.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: An in-situ carbonization reinforcement method for slag from solid waste improvement projects includes the following steps: S1. Preparation of improved engineering slag: The raw material composition of each cubic meter of the improved engineering slag includes, by weight, 10-100 parts of blast furnace slag, 10-100 parts of calcium carbide slag, 50-500 parts of filler, and 10-100 parts of water. S2. Excavate a placement trench, and pre-embed a three-dimensional ventilation device in the bottom of the placement trench. The three-dimensional ventilation device has multiple levels of independently controllable gas diffusion channels. S3. Rolling and compacting construction: The improved engineering waste soil prepared in step S1 is transported to the placement trench described in step S2 for the first construction layer filling. After filling, it is loosely laid and rolled. S4. Aeration and Carbonation: After compaction, a sealing film is applied to the surface of the first construction layer and sealed. A pressure gauge is installed on the sealing film. CO2 gas is then introduced from bottom to top into the improved engineering waste soil within the first construction layer through the three-dimensional aeration device for carbonization. During the aeration process, the pressure value between the sealing film and the surface of the first construction layer is monitored using the pressure gauge. When the pressure value displayed by the pressure gauge reaches the pressure threshold A, aeration is stopped, and the soil is left to stand for the CO2 gas to fully diffuse until the pressure gauge reading returns to zero. At this point, a non-destructive test of the subgrade is performed. If the subgrade meets the test qualification standard, the aeration and carbonation process ends. After the aeration and carbonation process is completed, the sealing film is kept sealed, and the soil continues to be cured normally until the next construction phase. S5. Repeat steps S2 to S4 according to the subgrade filling layer design requirements, and carry out the filling construction of each layer from bottom to top until the entire subgrade filling is completed.

[0007] Beneficial Effects: Based on the research idea of ​​using industrial solid waste as a solidifying agent to improve engineering slag soil to reduce cement consumption and realize the resource utilization of slag soil, this invention proposes a novel in-situ carbonization and solidification method for improving engineering slag soil by combining CO2 carbonization technology. It is innovatively applied to the field of roadbed filling, realizing the transformation of slag soil solidification technology into carbon reduction and emission reduction, solid waste resource utilization, and CO2 recovery and recycling. It integrates CO2 aeration carbonization technology into the on-site roadbed filling construction process, promoting the mineralization and storage of carbon dioxide without significantly increasing the complexity of construction and engineering costs.

[0008] Secondly, the CO2 ventilation pipe in this invention is pre-buried below the soil layer, eliminating the need to excavate or drill holes in the roadbed after compaction and filling, thus avoiding damage to the roadbed structure and strength. It can also be carried out in conjunction with pre-construction preparations, without significantly affecting the construction period. After construction, it does not need to be recycled and can be left directly underground. The material is inexpensive and easy to process, greatly simplifying the construction process. It solves the problem of how to introduce CO2 at a low cost, providing a new approach for in-situ CO2 carbonization and solidification construction.

[0009] As a preferred embodiment of the above reinforcement method, in step S4, the duration of a single ventilation is controlled at 20-25 minutes. If the roadbed does not meet the inspection qualification standard after a single ventilation, a second ventilation is performed. The ventilation pressure of the second ventilation is greater than that of the previous ventilation and increases in a stepwise manner until the roadbed meets the inspection qualification standard.

[0010] Beneficial effects: This invention takes into account that as carbonization and aeration proceed, the gas permeability of the solidified soil decreases, which hinders the diffusion of CO2 gas in the later stage. The invention effectively improves the gas diffusion rate by using a pulsed progressive aeration method that increases the aeration pressure in stages.

[0011] As a preferred embodiment of the above reinforcement method, the filler is at least one of engineering waste soil, silt, silty clay or cohesive soil, and the filler is dried, crushed and sieved through a 2mm sieve; in step S4, the amount of CO2 gas introduced is 10-100 parts.

[0012] As a preferred embodiment of the above-mentioned reinforcement method, the mass ratio of blast furnace slag to carbide slag is 2:3.

[0013] As a preferred embodiment of the above-mentioned reinforcement method, the blast furnace slag is granulated blast furnace slag powder of grade S95 or above; and / or, the carbide slag is powder that has been pretreated by sun drying and crushing.

[0014] As a preferred embodiment of the above reinforcement method, the subgrade meets the inspection qualification standard when the deflection value decreases by less than 10% or the dynamic rebound modulus increases by more than 10%.

[0015] This invention further discloses a three-dimensional ventilation device applied to the in-situ carbonization reinforcement method for the aforementioned solid waste improvement project slag, comprising: The CO2 supply unit, CO2 gas pressure reducing valve, and multiple vent pipes include, The length of a single vent pipe is the same as the length of the placement groove. Multiple vent pipes are arranged parallel to each other and evenly spaced along the width of the placement groove. Ventilation holes are evenly spaced on the upper surface of each vent pipe along the length of the vent pipe. CO2 gas discharged from the ventilation holes is discharged vertically upward. A diffusion column is connected to the vent hole. The same number of vent holes are spaced between adjacent diffusion columns on each vent pipe. The diffusion column has diffusion holes with gradually decreasing diameters along the column wall from bottom to top. The CO2 gas discharged from the diffusion hole diffuses horizontally into the interior of the improved engineering slag. One end of each vent pipe is connected to the CO2 supply unit via a gas supply hose and a CO2 gas pressure reducing valve.

[0016] Beneficial effects: This invention innovatively proposes a diffusion column and a pulsed progressive ventilation method, which effectively expands the ventilation influence range of the CO2 ventilation pipeline described in this invention. At the same time, in response to the problem of poor soil permeability and difficulty in effective CO2 gas diffusion after solidification, a second ventilation hole with a decreasing diameter from bottom to top is set on the diffusion column.

[0017] As a further preferred embodiment of the above-mentioned three-dimensional ventilation device, the height of the diffusion column is 1 / 2 of the thickness of the construction layer.

[0018] As a further preferred embodiment of the above-mentioned three-dimensional ventilation device, the ventilation pipe includes: The inner ventilation hose has a first ventilation hole on its wall for CO2 gas diffusion. An outer protective sleeve is fitted over the inner ventilation hose. Multiple second ventilation holes are evenly spaced along the pipe axis on the upper part of the sleeve wall. Sealing caps are provided at both ends of the outer protective sleeve. A buffer layer is installed between the inner ventilation hose and the outer protective sleeve. The diffusion column is connected to the inside of the outer protective sleeve through the second vent hole, and the same number of second vent holes are arranged between adjacent diffusion columns on the outer protective sleeve.

[0019] Beneficial effects: The buffer layer between the outer protective sleeve and the inner ventilation hose can be made of crushed stone with a larger particle size or other materials that will not block the ventilation holes. Its function is to form a relatively stable skeleton structure between the inner and outer pipes, which can support the outer protective sleeve against the pressure of the overlying soil. If the outer protective sleeve is crushed under pressure, a coarse aggregate buffer layer can be formed to prevent the soil from directly blocking the ventilation holes of the inner ventilation hose.

[0020] As a further preferred embodiment of the above-mentioned three-dimensional ventilation device, the first ventilation hole of the inner ventilation hose, the second ventilation hole of the outer protective sleeve, and the diffusion hole of the diffusion column are all wrapped with breathable geotextile.

[0021] Beneficial effects: This invention uses breathable fine mesh or breathable geotextile to wrap and secure the air pipe vents, preventing them from becoming clogged. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the CO2 ventilation carbonization system of the present invention; Figure 2 This is a diagram illustrating the zoning of the field test site for this invention. Figure 3 This is the load pressure-penetration curve of Embodiment 1 of the present invention, a comparative example. Detailed Implementation

[0023] To better understand the present invention, the following embodiments further illustrate the content of the invention, but the present invention is not limited to the embodiments described below. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0024] An in-situ carbonization-reinforced solid waste improvement engineering slag soil, the raw material composition by weight ratio includes: 10-100 parts blast furnace slag, 10-100 parts calcium carbide slag, 50-500 parts filler, 10-100 parts CO2 gas and 10-100 parts water.

[0025] Preferably, the blast furnace slag is S95 grade or higher superior granulated blast furnace slag powder.

[0026] Preferably, the carbide slag is a powder that has undergone sun-drying, pulverizing, and pretreatment.

[0027] Preferably, the filler material includes raw soil, which can be engineering waste soil, silt, silty clay, or cohesive soil. More preferably, the raw soil is dried, crushed, and sieved through a 2mm sieve. Raw soil that does not meet the requirements can be further screened.

[0028] The water is tap water, purified water, or distilled water.

[0029] A ventilation device for in-situ carbonization and reinforcement of solid waste in engineering projects includes a CO2 cylinder (gas tank), a CO2 gas pressure reducing valve, and a double-layer ventilation sleeve, such as... Figure 1 As shown.

[0030] CO2 cylinders (gas tanks) include a vent valve.

[0031] The CO2 gas pressure reducing valve includes a pressure reducing valve and a gas pressure gauge.

[0032] The double-layer ventilation sleeve includes a CO2 ventilation hose, an outer protective sleeve, and a buffer layer between the outer protective sleeve and the inner ventilation hose.

[0033] CO2 ventilation hoses are divided into connection sections and ventilation sections. The ventilation section needs to be protected by an outer protective sleeve, and has single or multiple rows of small holes with a diameter of 1-2 cm spaced 5-10 cm apart for CO2 gas diffusion. The hose with holes needs to be wrapped and secured with breathable fine mesh or breathable geotextile to prevent the ventilation holes from being blocked.

[0034] The outer protective sleeve needs to have single or multiple rows of small holes spaced 20-30cm apart and 3-5cm in diameter on the horizontal upward side to provide a channel for CO2 gas diffusion and constrain its diffusion direction. It also needs to be wrapped and tied securely with breathable fine mesh or breathable geotextile to prevent the air vents of the gas pipe from being blocked.

[0035] Finally, after inserting the CO2 ventilation hose into the ventilation section, sealing caps should be installed at both ends of the protective sleeve and sealed with anti-leakage mud to reduce unnecessary air leakage and loss.

[0036] Diffusion columns with a length of 1 / 2 the thickness of a single layer are added at 1m intervals on the outer protective sleeve. The diffusion columns have omnidirectional diffusion holes with a gradually decreasing diameter from 5cm to 2cm from bottom to top. They also need to be wrapped and tied securely with breathable fine mesh or breathable geotextile to prevent the air pipe ventilation holes from being blocked. Its function is to change the ventilation area of ​​the diffusion holes by using physical structural design, and to physically enhance the gas ventilation pressure under the condition of fixed gas output. Combined with the pulsed progressive ventilation method, it prevents the gas permeability of the solidified soil from decreasing as carbonization ventilation progresses, which would hinder the diffusion of CO2 gas in the later stage.

[0037] As a preferred embodiment of the above-mentioned technical means of the present invention, the buffer layer between the outer protective sleeve and the inner ventilation hose can be made of gravel with a larger particle size or other materials that will not block the ventilation holes. Its function is to form a relatively stable skeleton structure between the inner and outer pipes, which can support the outer protective sleeve against the pressure of the overlying soil. If the outer protective sleeve is crushed under pressure, a coarse aggregate buffer layer can be formed to prevent the soil from directly blocking the ventilation holes of the inner ventilation hose.

[0038] An in-situ carbonization reinforcement method for slag from solid waste improvement projects includes the following steps: S1. Preparation of solid waste improvement engineering slag, including preparing the proportion of each material according to the design ratio, turning over and drying the engineering waste slag to control the moisture content, and directly mixing the blast furnace slag and carbide slag into the original engineering waste slag in the stockpile according to the design ratio in a uniform and dispersed manner. During the mixing process, larger clods and agglomerates are picked out, crushed in time, and added back into the mixture to continue mixing. The mixing is completed after ensuring that the engineering slag and solid waste solidifying agent are mixed evenly and there are no large lumps that affect the quality of compaction construction. S2. Installation of the carbonized ventilation system, including the burial and backfilling of ventilation pipes and the connection of the ventilation system. On the existing lower foundation layer, use an excavator and shovel to dig a trench for the ventilation pipe. The size of the trench should match the double-layer ventilation sleeve, with a spacing of 1-1.5m between the trenches. Bury the pre-prepared double-layer ventilation sleeve into the trench. Turn the perforated surface of the outer protective sleeve so that it is horizontal and facing upward. Extend the connection section of the inner ventilation hose to the CO2 cylinder (gas tank) storage area and connect it to it through the CO2 pressure reducing valve. Take care to prevent breakage throughout the process. Then, backfill and flatten the area where the pipe is buried.

[0039] S3. Roller compaction construction includes the transportation, loosening, and compaction of the waste soil from the solid waste improvement project. Excavators and construction waste trucks are used to transport the waste soil from the stockpile to the construction area. Then, excavators are used to loosen the soil according to the construction area and plan, and stabilization measures such as edge sealing and slope sealing are carried out. Finally, vibratory rollers are used for compaction, using a compaction process of first static compaction, then two vibratory compaction passes, and finally static compaction to make the surface smooth. The offset width during compaction is 1 / 4 of the width of the iron wheel.

[0040] S4. Ventilation, carbonization, and curing, including sealing the edges of the sealing membrane, ventilation, carbonization, and normal curing. After the compaction and filling construction is completed, the site will be completely covered with the sealing membrane. At the overlaps and edges of the site, soil or waste building materials will be used for edge pressing and sealing. A pressure gauge will be installed on the sealing membrane. After the sealing membrane is sealed, the CO2 cylinder ventilation valve will be opened for pulsed, gradual ventilation.

[0041] During the ventilation process, the air pressure between the sealing membrane and the surface of the first construction layer is monitored. When the air pressure reading on the pressure gauge reaches the air pressure threshold A, ventilation is stopped, and the area is left to stand for the CO2 gas to diffuse fully. The value of A ranges from 0.05 to 0.15 MPa. The purpose of setting the A value is to accurately determine whether the roadbed is filled with CO2 gas and to stop the inflation. Non-destructive testing of the roadbed is carried out when the reading on the pressure gauge returns to zero. If the decrease in the roadbed deflection value is less than 10% or the increase in the dynamic rebound modulus is greater than 10%, the ventilation carbonization is terminated. After the ventilation carbonization is completed, the sealing membrane is kept sealed, and the soil continues to be cured normally until the next construction phase. In this embodiment, the initial CO2 gas pressure is set to 100 kPa. During the ventilation process, the gas pressure valve is manually controlled to keep the sealing film on the soil surface slightly bulging. The duration of each ventilation cycle is controlled to be 20-25 minutes. After the ventilation is completed, the gas is left to stand for 5-10 minutes to allow the CO2 gas to fully diffuse. Then, non-destructive testing of the subgrade is performed. If the subgrade deflection value decreases by more than 10% or the dynamic rebound modulus increases by more than 10%, the next ventilation cycle begins, and the ventilation pressure is adjusted to 200 kPa. Other operations are the same as the previous ventilation process. In multiple consecutive ventilation cycles, only the ventilation pressure is adjusted, ensuring that the ventilation pressure of each subsequent cycle is higher than that of the previous cycle and maintaining a stepwise increase. Each cycle lasts approximately 30 minutes, with the total ventilation time controlled at 2-3 hours. The maximum ventilation pressure throughout the entire carbonation and ventilation curing process should not exceed 600 kPa; otherwise, excessive pressure may cause soil erosion, affecting subsequent strength development. The reason for ensuring that the ventilation pressure is higher each time is to prevent CO2 gas from being blocked by the carbonized area and unable to diffuse effectively. 24 hours after ventilation, a portable falling weight deflectometer can be used for non-destructive testing. Carbonation ends when the roadbed deflection value decreases by less than 10% or the dynamic rebound modulus increases by more than 10%. After CO2 ventilation and carbonization, the sealing membrane should be kept sealed, allowing the soil to continue normal curing until the next construction phase.

[0042] S5. After completing the current layer of carbonized and solidified soil subgrade filling, repeat steps S2-S4 to continue filling the next layer of carbonized and solidified soil subgrade until the entire subgrade filling construction is completed. Example

[0043] The following examples are all from the test section of a road construction project in Nanjing. The silty clay used was taken from the same construction site. The basic indicators are shown in Table 1, and the chemical composition is shown in Table 2. The carbide slag and blast furnace slag used were purchased from Nanjing Jinjiali New Material Technology Co., Ltd. The carbide slag was crushed and ground by a ball mill, and the blast furnace slag was S95 grade superior granulated blast furnace slag powder. The composition is shown in Table 2.

[0044] Table 1 Basic property indicators of raw soil from the site

[0045] Table 2. Main chemical components of carbide slag, blast furnace slag and on-site raw material soil

[0046] This invention conducted an on-site filling test at a road construction project site in Nanjing, setting up two construction areas with different engineering conditions: a carbonization maintenance area and a normal maintenance area. The materials used for the on-site roadbed filling in both areas were the solid waste modified engineering slag soil described in this invention. Each cubic meter of the solid waste modified engineering slag soil contains: 40 parts of calcium carbide slag, 60 parts of blast furnace slag, 400 parts of engineering waste slag soil, 75 parts of water, and 50 parts of CO2 gas. The engineering waste slag soil needs to be turned over and dried in advance to control the overall moisture content.

[0047] Considering the actual construction situation, due to the location of the test section, artificial slope protection could not be carried out on the surface of the carbonation curing test section. Therefore, during the roadbed compaction and filling stage, the compaction effect was poor in some areas near the side of the carbonation curing section. The carbonation curing area and the ordinary curing area were divided into four zones, such as... Figure 2 As shown, these are carbonization region I, carbonization region II, ordinary region I, and ordinary region II, respectively. To explain the practical application effect of the present invention in more detail, carbonization region I is used as Example 1, carbonization region II is used as Example 2, and ordinary region I and ordinary region II are used as comparative examples.

[0048] Example 1 Both Example 1 and Example 2 were carried out using CO2 aeration carbonization, and the construction was carried out using the following steps: S1. Preparation of solid waste improvement engineering slag: Prepare the proportions of each material according to the design ratio, turn over and dry the engineering waste slag to control the moisture content, and directly mix the blast furnace slag and carbide slag into the original engineering waste slag in the stockpile according to the design ratio in a uniform and dispersed manner. During the mixing process, pick out the larger soil clods and lumps, crush them in time, and add them back into the mixture to continue mixing. Ensure that the engineering slag and solid waste solidifying agent are mixed evenly and there are no large lumps that affect the quality of compaction construction before completing the mixing. S2. Carbonized Ventilation System Layout: On the existing lower foundation layer, use an excavator and shovel to dig trenches for ventilation pipes, with trenches spaced 1-1.5m apart. Bury the pre-prepared double-layer ventilation sleeves into the trenches, turn the perforated surface of the outer protective sleeve to face horizontally upwards, extend the connecting section of the inner ventilation hose to the CO2 cylinder (gas tank) storage area and connect it to it through the CO2 pressure reducing valve. Take precautions to prevent breakage throughout the process, and then backfill and flatten the area where the pipes are buried.

[0049] S3. Roller compaction construction: Excavators and construction waste trucks are used to transport the improved construction waste from the stockpile to the construction area. Then, excavators are used to loosely spread the waste according to the construction area and plan, and stabilization measures such as edge sealing and slope sealing are carried out. Finally, vibratory rollers are used for compaction. The compaction process is to first perform one pass of static compaction, then two passes of vibratory compaction, and finally static compaction to make the surface smooth. The offset width during compaction is 1 / 4 of the width of the roller.

[0050] S4. Ventilation, Carbonation, and Curing: After the compaction and filling construction is completed, the site is completely covered with a sealing membrane. At the overlaps and edges of the site, soil or waste building materials are used to press and seal the edges. This step aims to minimize the rate at which CO2 escapes into the air from the gaps in the plastic membrane and the edges of the site during carbonation ventilation, ensuring effective carbonation and curing. After sealing the edges with the sealing membrane, open the CO2 cylinder ventilation valve. The initial CO2 gas pressure is set to 100 kPa. During ventilation, the pressure valve is manually controlled to keep the sealing membrane on the soil surface slightly bulging. Each ventilation cycle should last 20-25 minutes. After each ventilation cycle, allow the site to stand for 5-10 minutes to allow the CO2 gas to fully diffuse before starting the next ventilation cycle. Adjust the ventilation pressure to 200 kPa, and perform the same operations as the previous ventilation cycle. In multiple consecutive ventilation cycles, only the ventilation pressure is adjusted so that the ventilation pressure of the next cycle is greater than that of the previous cycle and increases in a stepwise manner. Each cycle lasts about 30 minutes, and the total ventilation time is controlled at 2-3 hours. The maximum ventilation pressure in the entire carbonization ventilation curing process should not exceed 600 kPa, otherwise the soil will be broken due to excessive air pressure, which will affect the later strength development. The reason why the ventilation pressure should be greater than the previous one is to prevent CO2 gas from being blocked by the carbonized area and unable to diffuse effectively.

[0051] After a single ventilation is completed, a portable falling weight deflectometer is used for non-destructive testing. Ventilation is terminated when the subgrade deflection value decreases by less than 10% or the dynamic rebound modulus increases by more than 10%. After CO2 ventilation and carbonization are completed, the sealing membrane is kept sealed, and the soil continues to be cured normally until the next construction.

[0052] S5. Repeat steps S2-S4 to continue filling the next layer of carbonized and solidified soil subgrade on the already filled subgrade until the filling construction of the entire subgrade is completed.

[0053] S6. Solidification effect test: Conduct on-site tests on the compacted roadbed of the improved project solid waste soil after filling to verify the effect of ventilation and carbonization curing and the filling effect of solid waste improvement project soil.

[0054] During the field test of the slag compaction subgrade of this solid waste improvement project, due to the influence of the field test area and construction equipment, artificial slope protection could not be carried out on the outside of the carbonization curing site. When the road roller carried out compaction, accidents such as collapse and landslide were likely to occur. Therefore, the compaction effect in the area of ​​Example 1 (the area near the carbonization curing site without soil support) was worse than that in other areas, and the compaction degree was lower.

[0055] Example 2 The construction steps and maintenance methods of Example 2 are the same as those of Example 1. The difference between Example 2 and Example 1 is that the area where Example 2 is located is closer to the middle of the test area, so the compaction is more thorough and the degree of compaction is higher than that of the area in Example 1. The CO2 aeration carbonization method is the same as that in Example 1.

[0056] Comparative Example The solid waste used in the comparative example is the same as that in Examples 1 and 2, but the construction steps and curing methods are different, as detailed below: S1. Preparation of solid waste improvement engineering slag: Prepare the proportions of each material according to the design ratio, turn over and dry the engineering waste slag to control the moisture content, and directly mix the blast furnace slag and carbide slag into the original engineering waste slag in the stockpile according to the design ratio in a uniform and dispersed manner. During the mixing process, pick out the larger soil clods and lumps, crush them in time, and add them back into the mixture to continue mixing. Ensure that the engineering slag and solid waste solidifying agent are mixed evenly and there are no large lumps that affect the quality of compaction construction before completing the mixing. S2. Roller compaction construction: Excavators and construction waste trucks are used to transport the improved construction waste from the stockpile to the construction area. Then, excavators are used to loosely spread the waste according to the construction area and plan, and stabilization measures such as edge sealing and slope sealing are carried out. Finally, vibratory rollers are used for compaction. The compaction process is to first perform one pass of static compaction, then two passes of vibratory compaction, and finally static compaction to make the surface smooth. The offset width during compaction is 1 / 4 of the width of the roller.

[0057] S3. General Curing: After the compaction and filling construction is completed, the comparative site and the sites of Examples 1 and 2 will be covered together with a sealing membrane. At the overlaps and edges of the site, soil or waste building materials will be used for edge pressing and sealing. The purpose of this step is to minimize the rate at which CO2 escapes into the air from the gaps in the plastic membrane and the edges of the site during carbonization ventilation, ensuring the effectiveness of carbonization curing in the ventilated carbonized areas. In this example, CO2 ventilation carbonization is not required; general curing begins immediately after the sealing membrane is completed.

[0058] S4. Repeat steps S2-S3 to continue filling the next layer of ordinary solidified soil subgrade on the already filled subgrade until the filling construction of the entire subgrade is completed.

[0059] S5. Solidification effect test: Conduct on-site tests on the compacted subgrade of the improved project solid waste soil after filling to verify the effect of ordinary maintenance and the filling effect of solid waste improved project soil, and provide a reference for the carbonization maintenance implementation example.

[0060] The solid waste improvement project slag used in the comparative example is the same as that in the above two examples. The main purpose of setting up this comparative example is to compare it with Example 1 and Example 2, to verify the curing effect of CO2 ventilation carbonization technology, and to further highlight its characteristics.

[0061] The following describes the deflection value test and the roadbed CBR test conducted on the above embodiments.

[0062] I. Deflection Value Testing Deflection tests were conducted on Examples 1 and 2 and the comparative example after the subjects reached 0, 9, and 15 days of age. The deflection tests were performed using a portable falling weight deflectometer (FWD) in accordance with the "Specifications for Field Testing of Highway Subgrade and Pavement" (JTG 3450-2019), "Standards for Quality Inspection and Evaluation of Highway Engineering" (JTG F80 / 1-2017), "Specifications for Geotechnical Testing of Railway Engineering" (TB 10102-2023), and "Specifications for Field Testing of Dynamic Resilient Modulus of Highway Subgrade" (DB 34 / T 3704-2020).

[0063] Deflection test results: Table 3 Results of deflection test on slag and soil from solid waste improvement project

[0064] As shown in Table 3, the deflection values ​​before aeration and carbonization in Examples 1, 2, and the comparative example were 0.89, 0.69, and 0.55, respectively, and the dynamic resilient modulus was 25.34, 32.91, and 40.27, respectively. It can be seen that the compaction effect from poor to good is Example 1, Example 2, and the comparative example. The main reason is that slope protection and sealing measures cannot be carried out on the side of the carbonization curing area, and the effect of roller compaction is poor. The compaction degree of the subgrade after compaction in the carbonization curing area is lower than that in the ordinary curing area, resulting in the road performance of Examples 1 and 2 being worse than that of the comparative example before CO2 carbonization curing.

[0065] Comparing Example 1 and the comparative example, when the curing age was 9 days, the deflection values ​​of Example 1 and the comparative example were 0.55 and 0.31, respectively, and the dynamic resilient modulus were 41.85 and 67.17, respectively. The deflection value of Example 1 decreased rapidly, and the dynamic resilient modulus increased rapidly, further narrowing the gap with the comparative example. This indicates that the performance improvement effect of the area after CO2 carbonization curing was more obvious. That is, carbonization curing promoted the occurrence of hydration reaction, volcanic ash reaction, ion exchange reaction, etc. of the slag soil in the solid waste improvement project, and at the same time added the occurrence of carbonization reaction, which made the bearing capacity of Example 1 increase rapidly, specifically manifested as a decrease in deflection value and an increase in dynamic resilient modulus.

[0066] By comparing Example 2 and the comparative example, when the curing age was 9 days, the deflection values ​​of Example 2 and the comparative example were 0.35 and 0.31, respectively, and the dynamic resilient modulus were 65.04 and 67.17, respectively. The values ​​were very close, which means that CO2 carbonization curing effectively narrowed the performance gap between Example 2 and the comparative example. Through carbonization curing, Example 2 was prompted to undergo a carbonization reaction, generating carbonized products with higher strength. At the same time, the volume expanded, filling the pores, forming a skeleton and compacting the soil, so that Example 2 achieved road performance similar to that of the comparative example under the early conditions of lower compaction.

[0067] Through Examples 1, 2, and the comparative example, when the curing age reached 15 days, the deflection values ​​of Examples 1, 2, and the comparative example were 0.36, 0.26, and 0.32, respectively, and the dynamic resilient modulus were 64.03, 83.96, and 74.24, respectively. Among them, the test results of Example 1 were close to those of the comparative example, while the test results of Example 2 exceeded those of the comparative example, with a lower deflection value and a higher dynamic resilient modulus. This indicates that the curing effect of CO2 aeration carbonization technology is better. The result of Example 1, with the lowest compaction degree, was almost the same as that of the comparative example with the highest compaction degree. The result of Example 2, with a slightly lower compaction degree than the comparative example, exceeded that of the comparative example. This shows that the method proposed in this invention can effectively improve early strength in actual engineering, and can achieve the purpose of carbon sequestration and emission reduction while meeting engineering requirements.

[0068] II. Subgrade CBR Testing For Example 1 and the comparative example, the CBR test of the subgrade was carried out at a curing age of 15 days. The LCB-2 type field CBR measuring instrument was used and the test was performed in accordance with the "Field Test Procedure for Highway Subgrade and Pavement" (JTG 3450-2019). According to the requirements of the "Specification for Design of Highway Subgrade" (JTG D30-2015), the CBR of the upper embankment and lower embankment of expressways and first-class highways should not be less than 4% and 3%, respectively. The higher the CBR value, the better the bearing capacity and road performance of the subgrade.

[0069] Figure 3 The load pressure-penetration curves for Example 1 and the comparative example are used to calculate the CBR. 2.5 CBR 5.0 Ultimately, according to the specifications, the CBR value of the solid waste improvement project excavated soil was determined by the test value at a penetration depth of 2.5 mm, i.e., CBR. 2.5The CBR values ​​of Example 1 and the comparative example are 90.9% and 108.4%, respectively, far exceeding the requirements for roadbed CBR values ​​in relevant specifications. Referring to the deflection measurement test results of Example 2, which are better than those of the comparative example, the reason why the CBR value of Example 1 is slightly lower than that of the comparative example has been explained above. That is, the compaction degree of the area in Example 1 is the lowest due to the influence of rolling construction, which is significantly different from that of the comparative example area. At the same time, due to the influence of site conditions and on-site construction conditions, it is not possible to conduct CBR tests in the area of ​​Example 2. Based on the deflection test results, statistical mathematical methods are used for correction. When the curing age is 15 days, the theoretical CBR value of the area of ​​Example 2 should be around 125.73%, which exceeds that of the comparative example area.

[0070] Considering that Example 1 had the lowest compaction degree due to the influence of rolling construction, and referring to the deflection value measurement test, the final CBR value obtained by the CO2 carbonization curing reinforcement method proposed in this invention should be greater than 90.9%, reaching a level close to that of the comparative example. Finally, the method described in this application is merely a preferred embodiment and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for in-situ carbonization reinforcement of slag from solid waste improvement projects, characterized in that, Includes the following steps: S1. Preparation of improved engineering slag: The raw material composition of each cubic meter of the improved engineering slag includes, by weight, 10-100 parts of blast furnace slag, 10-100 parts of calcium carbide slag, 50-500 parts of filler, and 10-100 parts of water. S2. Excavate a placement trench, and pre-embed a three-dimensional ventilation device in the bottom of the placement trench. The three-dimensional ventilation device has multiple levels of independently controllable gas diffusion channels. S3. Rolling and compacting construction: The improved engineering waste soil prepared in step S1 is transported to the placement trench described in step S2 for the first construction layer filling. After filling, it is loosely laid and rolled. S4. Aeration and Carbonation: After compaction, a sealing film is applied to the surface of the first construction layer and sealed. A pressure gauge is installed on the sealing film. CO2 gas is then introduced from bottom to top into the improved engineering waste soil within the first construction layer through the three-dimensional aeration device for carbonization. During the aeration process, the pressure value between the sealing film and the surface of the first construction layer is monitored using the pressure gauge. When the pressure value displayed by the pressure gauge reaches the pressure threshold A, aeration is stopped, and the soil is left to stand for the CO2 gas to fully diffuse until the pressure gauge reading returns to zero. At this point, a non-destructive test of the subgrade is performed. If the subgrade meets the test qualification standard, the aeration and carbonation process ends. After the aeration and carbonation process is completed, the sealing film is kept sealed, and the soil continues to be cured normally until the next construction phase. S5. Repeat steps S2 to S4 according to the subgrade filling layer design requirements, and carry out the filling construction of each layer from bottom to top until the entire subgrade filling is completed.

2. The in-situ carbonization reinforcement method for solid waste improvement engineering slag as described in claim 1, characterized in that, In step S4, the duration of a single ventilation session is controlled at 20-25 minutes. If the roadbed does not meet the inspection standards after a single ventilation session, a second ventilation session is conducted. The ventilation pressure of the second session is greater than that of the previous session and increases in a stepwise manner until the roadbed meets the inspection standards.

3. The in-situ carbonization reinforcement method for solid waste improvement engineering slag as described in claim 1, characterized in that, In step S1, the filler is at least one of engineering waste soil, silt, silty clay or cohesive soil, and the filler is dried, crushed and sieved through a 2mm sieve; in step S4, the amount of CO2 gas introduced is 10-100 parts.

4. The in-situ carbonization reinforcement method for solid waste improvement engineering slag as described in claim 1, characterized in that, In step S1, the mass ratio of blast furnace slag to carbide slag is 2:

3.

5. The in-situ carbonization reinforcement method for solid waste improvement engineering slag as described in claim 1, characterized in that, In step S1, the blast furnace slag is granulated blast furnace slag powder of grade S95 or above; and / or, the calcium carbide slag is powder that has been pretreated by sun drying and crushing.

6. The in-situ carbonization reinforcement method for solid waste improvement engineering slag as described in claim 1, characterized in that, In step S4, the subgrade meets the inspection qualification standard when the deflection value of the subgrade decreases by less than 10% or the dynamic rebound modulus increases by more than 10%.

7. A three-dimensional ventilation device, applied to the in-situ carbonization reinforcement method for solid waste improvement engineering slag as described in any one of claims 1 to 6, characterized in that, include: The CO2 supply unit, CO2 gas pressure reducing valve, and multiple vent pipes include, among which, The length of a single vent pipe is the same as the length of the placement groove. Multiple vent pipes are arranged parallel to each other and evenly spaced along the width of the placement groove. Ventilation holes are evenly spaced on the upper surface of each vent pipe along the length of the vent pipe. CO2 gas discharged from the ventilation holes is discharged vertically upward. A diffusion column is connected to the vent hole. The same number of vent holes are spaced between adjacent diffusion columns on each vent pipe. The diffusion column has diffusion holes with gradually decreasing diameters along the column wall from bottom to top. The CO2 gas discharged from the diffusion hole diffuses horizontally into the interior of the improved engineering slag. One end of each vent pipe is connected to the CO2 supply unit via a gas supply hose and a CO2 gas pressure reducing valve.

8. The three-dimensional ventilation device according to claim 7, characterized in that, The height of the diffusion column is 1 / 2 of the thickness of the construction layer.

9. The three-dimensional ventilation device according to claim 7, characterized in that, The ventilation tube includes: The inner ventilation hose has a first ventilation hole on its wall for CO2 gas diffusion. An outer protective sleeve is fitted over the inner ventilation hose. Multiple second ventilation holes are evenly spaced along the pipe axis on the upper part of the sleeve wall. Sealing caps are provided at both ends of the outer protective sleeve. A buffer layer is installed between the inner ventilation hose and the outer protective sleeve. The diffusion column is connected to the inside of the outer protective sleeve through the second vent hole, and the same number of second vent holes are arranged between adjacent diffusion columns on the outer protective sleeve.

10. The three-dimensional ventilation device according to claim 9, characterized in that, The first vent hole of the inner ventilated hose, the second vent hole of the outer protective sleeve, and the diffusion hole of the diffusion column are all wrapped with breathable geotextile.

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