A quaternary solid waste-based soil stabilizer for base layer, and a preparation method and application thereof

Abstract

The application discloses a quaternary solid waste-based soil stabilizer (GSCP) for a base layer, which is composed of slag (GGBFS), steel slag (SSA), calcium carbide slag (CS) and phosphogypsum (PG) and has a weight ratio of GGBFS:SSA:CS:PG=56:24:12:8. The stabilizer forms C-S-H colloid and ettringite (AFt) through alkaline activation and sulfate activation, does not need to add cement or chemical activator, is used for stabilizing silty clay and steel slag mixed soil, and significantly improves the unconfined compressive strength, splitting tensile strength, water stability and freeze-thaw resistance. Compared with a traditional cement-based stabilizer, the application reduces carbon emission by 82% and cost by 31.25%, provides a low-carbon and economical solution for road engineering, and is suitable for the base layer and the subbase layer of a secondary road or above.

Description

Technical Field

[0001] This invention relates to the field of road engineering and building materials, specifically to a quaternary solid waste-based soil stabilizer for base courses without cement or chemical activators, its preparation method, and its application in highway base / subbase courses and soft soil foundation reinforcement. Background Technology

[0002] Traditional soil stabilization methods primarily use materials such as cement and lime, but their production process is energy-intensive. Each ton of cement clinker requires 110–120 kg of standard coal to produce and emits a large amount of CO2, accounting for 8% of global carbon emissions. Furthermore, cement prices have increased by approximately 65% ​​since 2015, further increasing project costs. In addition, cement-based solidifiers have poor compatibility with silty clay, often resulting in insufficient early strength and poor durability.

[0003] At the same time, my country's annual industrial solid waste production exceeds 4 billion tons, with steel slag and phosphogypsum accounting for a significant proportion. Steel slag production is approximately 150 million tons annually, with a comprehensive utilization rate of less than 30%; carbide slag production exceeds 24 million tons annually, and phosphogypsum production exceeds 70 million tons annually, with a stockpile exceeding 800 million tons, resulting in resource waste and environmental pollution.

[0004] Although some studies have attempted to use industrial solid waste (such as slag and fly ash) to replace part of the cement, it usually still needs to be combined with cement or alkali activators, and the synergistic utilization of all solid waste has not been achieved. There are still problems such as high carbon emissions, high costs and complex processes. Patent content

[0005] The purpose of this invention is to provide a quaternary solid waste-based curing agent (GSCP) and its preparation and application methods to address the problems of high carbon emissions, high costs, and low solid waste utilization rates associated with traditional cement-based materials. This curing agent, through the synergistic effect of steel slag, mineral slag, carbide slag, and phosphogypsum, significantly improves the mechanical properties and durability of silty clay and steel slag mixed soils, providing a low-carbon and economical solution for road engineering.

[0006] GSCP curing agent contains the following components in parts by weight:

[0007] 14 parts slag powder; 6 parts steel slag powder; 3 parts calcium carbide slag; 2 parts phosphogypsum.

[0008] The slag provides an aluminosilicate phase, with the main components being 46.05% CaO, 27.84% SiO2, and 13.2% Al2O3.

[0009] Steel slag (SSA): The main components are CaO content of 48.89%, Fe2O3 content of 17.89%, SiO2 content of 17.8%, and Al2O3 content of 9.26%.

[0010] The main component of carbide slag is calcium oxide, accounting for 87%, which provides an alkaline environment.

[0011] The main component of phosphogypsum is CaSO4·2H2O, which provides SO4. 2- It promotes the formation of ettringite (AFt).

[0012] The optimal ratio was determined through orthogonal experiments.

[0013] GSCP curing agent has the following properties: standard consistency water requirement 158mm, initial setting time 310 minutes, final setting time 510 minutes, 28-day compressive strength 20.6MPa, and flexural strength 7.0MPa.

[0014] Microscopic analysis (X-ray diffraction XRD and scanning electron microscopy SEM) showed that GSCP generates CSH colloids and ettringite (AFt) through alkaline excitation of calcium carbide slag (providing Ca(OH)2) and sulfate excitation of phosphogypsum (providing CaSO4·2H2O), which provide the source of its strength.

[0015] The preparation method of GSCP curing agent includes the following steps:

[0016] (1) Raw material processing: The slag is grade S95, with an activity index of ≥70% after 7 days. After aging for 1 year, the steel slag is screened to separate components smaller than 2mm, ball-milled, and passed through a 200-mesh sieve. The carbide slag is cleaned of impurities, dried, ball-milled, and passed through a 200-mesh sieve. The phosphogypsum is dried, ball-milled, and passed through a 200-mesh sieve.

[0017] (2) Mixing: Mechanically mix according to the mass ratio of 56:24:12:8 to ensure uniformity.

[0018] (3) Quality control: The consistency, setting time and strength are tested in accordance with GB / T1346-2011 "Test Method for Standard Consistency Water Requirement, Setting Time and Soundness of Cement" and GB / T17671-2021 "Test Method for Strength of Cement Mortar (S0 Method)" to ensure that the performance meets the standards.

[0019] This invention provides two curing methods.

[0020] GSCP solidification method:

[0021] (1) Dry the original soil, crush it, and screen it to a particle size ≤2mm;

[0022] (2) Add water to the soil obtained in step (1) at a rate 3% lower than the optimum moisture content, mix well, place in a plastic bag and seal, and let it sit for 24 hours;

[0023] (3) The soil obtained in step (2) is mixed with the GSCP solidifying agent described in claim 1 or 2 at a dosage of 4 to 12% (by mass), and water is added to the optimal moisture content and mixed evenly.

[0024] (4) Conduct a compaction test on the mixed soil obtained in step (3) to obtain the optimum moisture content and maximum dry density.

[0025] (5) Mold unconfined compressive strength specimens according to the optimal moisture content and maximum dry density obtained in step (4), and cure them according to standard until the required age for strength testing.

[0026] GSCP-Steel Slag Solidification Soil Method:

[0027] (1) Dry the original soil, crush it, and screen it to a particle size ≤2mm;

[0028] (2) Add 0-60% steel slag aggregate (SSA) to the soil obtained in step (1) according to the engineering requirements, add water at a rate 3% lower than the optimum moisture content, mix evenly, place in a plastic bag and seal, and let it sit for 24 hours;

[0029] (3) The soil obtained in step (2) is mixed with the GSCP solidifying agent described in claim 1 or 2 at an admixture ratio of 8% (by mass), and water is added to the optimal moisture content and mixed evenly.

[0030] (4) Conduct a compaction test on the mixed soil obtained in step (3) to obtain the optimum moisture content and maximum dry density.

[0031] (5) Mold unconfined compressive strength specimens according to the optimal moisture content and maximum dry density obtained in step (4), and cure them according to standard until the required age for strength testing.

[0032] The present invention has the following beneficial effects:

[0033] Efficiently utilize steel slag, mineral slag, carbide slag, and phosphogypsum to reduce solid waste accumulation and promote resource recycling. Utilize solid waste synergistic mechanisms to prepare high-performance all-solid-waste solidifying agents to replace traditional cement-based materials for use in building materials and soil solidification.

[0034] GSCP-SSA solidified soil possesses high strength, high durability, and good environmental adaptability. Different mix proportions can meet the requirements of various levels and light, medium, and heavy traffic loads. For example, the 7-day strength of a mixture of 8% solidifier and 40% steel slag reaches 5.63 MPa, making it suitable for heavy traffic on highways. It also has great potential for soft soil foundation reinforcement, and is particularly suitable for high-humidity, high-salt, and cold regions.

[0035] Significantly reduces carbon emissions and environmental pollution, meeting carbon peaking and carbon neutrality goals. It substantially reduces material and construction costs, making it suitable for large-scale engineering applications. The carbon emissions of solidified soil with 8% GSCP and 40% steel slag are 10.7 kg CO2 / ton, an 82% reduction compared to cement (61.14 kg CO2 / ton). The cost is 52.48 yuan / ton, a 31.25% reduction compared to cement (76.80 yuan / ton). Each kilometer of road (12m wide, 0.18m thick) saves 340 tons of cement, 219 tons of CO2, and 106,000 yuan. Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below with the aid of embodiments. Obviously, the described embodiments are only some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort are within the scope of protection of this application.

[0037] The present application will be further described in detail below with reference to the embodiments.

[0038] Example 1: Preparation of GSCP curing agent

[0039] (1) Raw material processing: The slag powder grade is S95, and the 7-day activity index is not less than 70%. The CaO content is 46.05%, SiO2 is 27.84%, and Al2O3 is 13.2%. After aging for one year, the steel slag with a diameter of less than 2 mm is screened and then ground by XU-XQM-12 planetary ball mill to prepare steel slag powder with a diameter of less than 0.075 mm. The calcium carbide slag is dried outdoors to remove impurities. The calcium carbide slag is dried at 45℃ for no less than 24 hours. The moisture content is measured every 12 hours. The drying is stopped when the moisture content change does not exceed 0.1%. The dried calcium carbide slag raw material is ground by QM-30L light ball mill and screened by 0.075 mm. The main component is calcium oxide, accounting for 87%. The phosphogypsum powder is dried at 45℃ and then screened by 0.075 mm.

[0040] Table 1 Chemical composition of raw materials

[0041]

[0042] (2) Design of curing agent mixing ratio

[0043] Table 2 Curing agent mix design and results

[0044]

[0045] The ratio of slag to steel slag has the most significant impact on compressive strength, with the best effect observed when the ratio exceeds 7:3. The total content of slag and steel slag has the most significant impact on flexural strength, with a particularly noticeable increase in strength when the total content exceeds 70%. Maintaining a moderate ratio of calcium carbide slag to phosphogypsum (6:4) can effectively balance the hydration reaction rate and strength development of the system.

[0046] (3) Verification

[0047] Based on the analysis results of the orthogonal experiment, the optimal mix ratio (slag:steel slag powder:carbide slag:phosphogypsum = 14:6:3:2) yielded the best compressive and flexural strengths, along with relatively good standard consistency water requirements and setting time. Regarding the GSCP solidifier used in this study, since this combination was not directly included in the initial orthogonal experiment, further experiments were conducted to verify its effectiveness. Table 3.21 compares the workability of GSCP solid waste solidifier and cement.

[0048] Table 3 Comparison of workability of GSCP curing agent and cement

[0049]

[0050] GSCP solid waste curing agent has lower early strength than ordinary Portland cement, but has significant potential for later strength growth. Its 28-day compressive strength reaches 20.6 MPa, which is 62% of that of cement; its flexural strength reaches 7.0 MPa, which is 99% of that of cement. Its long setting time, high standard consistency and low fluidity make it suitable for low-flowability filler materials, cement-stabilized soil and foundation reinforcement.

[0051] Example 2: Solidified Silty Clay

[0052] (1) The original soil is dried, crushed and screened to a particle size ≤2mm;

[0053] (2) Add water to a moisture content 3% below the optimum moisture content, mix well, and seal for 24 hours;

[0054] (3) Add different amounts of GSCP curing agent (4%, 6%, 8%, 10%, 12%), add water to the optimal moisture content, and mix evenly;

[0055] (4) Mold unconfined compressive strength specimens according to the optimum moisture content and maximum dry density, and cure them according to standard until the required age for strength testing.

[0056] Table 4 Relationship between curing agent dosage and solidified soil strength

[0057]

[0058] Example 3: Solidified steel slag mixed soil

[0059] (1) The original soil is dried, crushed and screened to a particle size ≤2mm;

[0060] (2) Add 0%, 20%, 40%, 50% and 60% of steel slag aggregate, add water to a moisture content 3% below the optimum moisture content, mix evenly, and seal and let it sit for 24 hours;

[0061] (3) Add 8% of the curing agent, add water to the optimal moisture content, and mix well;

[0062] (4) Mold unconfined compressive strength specimens according to the optimum moisture content and maximum dry density, and cure them according to standard until the required age for strength and durability testing.

[0063] Table 5 Effect of Steel Slag Addition on Compressive Strength

[0064]

[0065] Table 6 Effect of steel slag content on splitting strength

[0066]

[0067] Table 7. Effect of steel slag content on water stability performance

[0068]

[0069] Table 8 Effect of Steel Slag Addition on Freeze-Thaw Performance

[0070]

[0071] in conclusion:

[0072] (1) When solidifying silty clay, the GSCP content is positively correlated with the strength. 8% is the optimal content - which satisfies the mechanical performance requirements and controls the material cost. The strength improvement is limited after the content exceeds 10%, and it does not have an economic advantage.

[0073] (2) When the steel slag content is 0%-50%, the strength continues to rise in 7 days / 28 days, reaching the peak at 50% content (5.78 MPa in 7 days and 6.96 MPa in 28 days); when the steel slag content exceeds 50% (60%), the strength decreases slightly (5.26 MPa in 7 days and 6.53 MPa in 28 days).

[0074] (3) The splitting strength gradually increases with the increase of steel slag content. The strength reaches 1.52 MPa after 28 days with 50% content and only 1.51 MPa with 60% content, which is basically the same. Compared with the group without steel slag (0.82 MPa after 28 days), the splitting strength is increased by 85.4% with 50% steel slag content, which significantly improves toughness.

[0075] (4) The water immersion strength increases significantly with the increase of steel slag content. The water immersion strength after 28 days is 6.03 MPa when the steel slag content is 40%, which is 2.4 times that of the group without steel slag (2.51 MPa). The higher the steel slag content, the better the water stability, which reflects the skeleton support role of steel slag aggregate.

[0076] (5) The strength of the group without steel slag (S0) after 11 freeze-thaw cycles was only 1.05 MPa, with a decrease of 58.2%; the strength of the group with 50% steel slag content (S50) after 11 freeze-thaw cycles was 4.65 MPa, with a decrease of 30.9%, and the freeze-thaw resistance was significantly improved; the group with 60% steel slag content experienced accelerated decay in the later stage of freeze-thaw (3.44 MPa after 11 cycles), and its performance was not as good as that of the 50% content group.

[0077] (6) When solidifying steel slag mixed soil, the optimal content of steel slag aggregate is 50%. At this time, the mechanical properties (compression resistance, splitting crack resistance) and durability properties (water stability, freeze-thaw resistance) reach their peak, which is suitable for the needs of heavy traffic roads (such as 7-day strength of 5.78MPa to meet the requirements of highway base course).

[0078] This invention provides an innovative quaternary solid waste-based stabilizer that significantly improves the mechanical properties and durability of silty clay through the synergistic effect of solid wastes such as steel slag, while reducing carbon emissions and costs. This stabilizer offers a feasible technical solution for low-carbon road engineering and has broad application prospects.

[0079] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0080] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A quaternary solid waste-based soil stabilizer for base courses, characterized in that, It is a compound of the following components in a mass ratio of 56:24:12:8: S95 grade slag powder, steel slag powder aged for more than one year, calcium carbide slag powder, and phosphogypsum powder. The S95 grade slag powder has a 7-day activity index ≥70% and a CaO content of 45~47%; the steel slag powder has a particle size ≤0.075mm and a CaO content of 48~50%; the calcium carbide slag powder has a particle size ≤0.075mm and a CaO content ≥85%; and the phosphogypsum powder has a particle size ≤0.075mm and a CaSO4·2H2O content ≥90%.

2. The preparation method of the quaternary solid waste-based soil stabilizer for base courses according to claim 1, characterized in that, Includes the following steps: 1) Raw material processing: S95 grade slag powder can be used directly; steel slag is aged in a natural environment for more than 1 year, screened to a particle size of ≤2mm, and then ball-milled to a particle size of ≤0.075mm to obtain steel slag powder; calcium carbide slag is dried at 45℃ for more than 24 hours and ball-milled to a particle size of ≤0.075mm to obtain calcium carbide slag powder; phosphogypsum is dried at 45℃ for more than 24 hours and ball-milled to a particle size of ≤0.075mm to obtain phosphogypsum powder; 2) Mechanical mixing: The slag powder, steel slag powder, calcium carbide slag powder and phosphogypsum powder processed in step 1) are put into a horizontal mixer at a mass ratio of 56:24:12:8 and mixed at a speed of 300~400r / min for 10~15min until the components are evenly dispersed. 3) Quality Inspection: Refer to GB / T1346-2011 for consistency water consumption and setting time, and refer to GB / T17671-2021 for 3-day and 28-day compressive / flexural strength. The initial setting time should be ≥300min, the final setting time ≤550min, the 28-day compressive strength ≥20MPa, and the 28-day flexural strength ≥6.8MPa. If the test is qualified, it is a finished product.

3. A method for curing powdery clay using the GSCP curing agent according to claim 1, characterized in that, Includes the following steps: 1) Soil pretreatment: Dry, crush, and sieve the original silty clay to a particle size ≤2mm; 2) Curing: Add water to the pretreated soil to a moisture content 3% below the optimum moisture content, mix well, place in a plastic bag and seal, and cure for 24 hours at 20±2℃. 3) Mixing and solidification: Add 4-12% by mass of the solidifying agent described in claim 1 to the soil after curing, add water to the optimum moisture content and mix evenly; 4) Compaction molding: Conduct a compaction test on the mixed soil to obtain the optimum moisture content and maximum dry density, and mold unconfined compressive strength specimens according to these parameters; 5) Standard curing: Place the specimens in an environment with a temperature of 20±2℃ and a relative humidity of ≥95% for curing until the specified age for performance testing.

4. The curing method according to claim 3, characterized in that, The curing agent is added at a mass ratio of 8%, at which point the 28-day unconfined compressive strength of the cured silty clay is ≥3.75MPa, taking into account both mechanical properties and economy.

5. A method for curing steel slag mixed soil using the curing agent according to claim 1, characterized in that, Includes the following steps: 1) Soil pretreatment: Dry, crush, and sieve the undisturbed soil to a particle size ≤2mm; 2) Steel slag aggregate blending: Add steel slag aggregate (particle size ≤20mm) at a mass ratio of 0~60% to the pretreated soil, add water to a moisture content 3% below the optimum moisture content, mix evenly, place in a plastic bag and seal, and let it sit at 20±2℃ for 24 hours. 3) Mixing and curing: Add 8% by mass of the curing agent described in claim 1 to the steel slag mixture after curing, add water to the optimum moisture content and mix evenly; 4) Compaction molding: Conduct a compaction test on the mixed soil to obtain the optimum moisture content and maximum dry density, and mold unconfined compressive strength specimens according to these parameters; 5) Standard curing: Place the specimens in an environment with a temperature of 20±2℃ and a relative humidity of ≥95% for curing until the specified age for performance testing.

6. The curing method according to claim 5, characterized in that, The steel slag aggregate content is 50% by mass. At this point, the solidified steel slag mixed soil has an unconfined compressive strength of ≥6.96MPa and a splitting tensile strength of ≥1.52MPa after 28 days, exhibiting optimal mechanical properties and durability.

7. The application of the quaternary solid waste-based soil stabilizer for base courses according to claim 1, characterized in that, The curing agent is used for soil solidification in the base / subbase of secondary and above highways, soft soil foundation reinforcement, and road engineering in high-humidity, high-salt / cold regions, without the need to add cement or chemical activators.

Images