Fly ash stabilized soil for road base and construction method of fly ash stabilized soil

Abstract

The invention discloses fly ash stabilized soil for a road base and a construction method of the fly ash stabilized soil, and belongs to the technical field of road engineering materials. The stabilized soil is mainly prepared from fly ash, a soil material, cement, a composite activator with specific components and a functional additive. The construction method comprises the working procedures of raw material pretreatment, a multi-stage mixing process, stuffy material activation, layered paving and combined rolling forming and systematic moisturizing and curing. Through the synergistic effect of the material components and accurate control of the construction process, the activity of the fly ash is effectively excited, the technical problems that traditional stabilized soil is low in early strength and prone to cracking are solved, the overall strength, crack resistance and water stability of a road base are remarkably improved, and meanwhile resource utilization of industrial by-products is achieved.

Description

Technical Field

[0001] This invention relates to the field of road engineering materials technology, and in particular to a fly ash stabilized soil for road base courses and its construction method. Background Technology

[0002] As the load-bearing layer of the road surface structure, the performance of the road base directly determines the road's quality and service life. Currently, inorganic binder stabilized materials are widely used in road base construction, with cement-stabilized crushed stone and lime-stabilized soil being two of the most common traditional materials. However, engineering practice shows that both of these traditional materials have their limitations. Although cement-stabilized crushed stone has high strength, it is highly sensitive to drying and thermal shrinkage, easily developing shrinkage cracks during construction, maintenance, and operation. These cracks can reflect onto the surface layer, affecting the road's smoothness and durability. Lime-stabilized soil, on the other hand, suffers from low early strength, slow strength growth, and relatively poor water stability, making its long-term performance difficult to guarantee, especially in damp or hydrogeologically challenging sections.

[0003] Existing technologies have attempted to simply mix fly ash with soil, cement, or lime to form stable materials. However, these existing solutions generally suffer from several common technical challenges. First, the potential pozzolanic activity of fly ash is not fully and efficiently activated, resulting in the early strength of the mixture often failing to meet the requirements for rapid construction and traffic opening, and its potential for later strength growth remains to be further explored. Second, the material system composition design does not adequately address improving crack resistance, leaving the formed base layer still facing a significant risk of cracking. Furthermore, and more critically, many existing technologies offer rather general construction methods that fail to fully consider the synergistic effects between material composition characteristics and construction process parameters. For example, simple mixing, paving, and compaction processes cannot ensure the uniform dispersion and sufficient reaction of active components; conventional curing measures cannot effectively guarantee the continuous hydration reaction under complex and variable climatic conditions, ultimately affecting the realization of the material's designed performance.

[0004] Invention Patent Content In view of this, the present invention provides a fly ash stabilized soil for road base courses and its construction method, so as to solve or alleviate the technical problems existing in the prior art.

[0005] The technical solution of this invention is implemented as follows: A fly ash stabilized soil for road base courses, composed of the following raw materials in parts by weight: fly ash: 75-88 parts; original roadbed soil: 8-20 parts; silicate cement: 3-6 parts; polypropylene fiber: 0.8-2 parts; calcium lignosulfonate: 0.5-1.5 parts; hydroxypropyl methylcellulose: 0.1-0.5 parts; composite activator: 1.5-4 parts; The composite activator is composed of crystalline sodium sulfate, calcium oxide metakaolin, and triethanolamine in a mass ratio of (5~8):(3~5):(0.5~1).

[0006] As an improvement, it is composed of the following raw materials in parts by weight: fly ash: 81 parts; subgrade soil: 14 parts; silicate cement: 4 parts; polypropylene fiber: 1.4 parts; calcium lignosulfonate: 1.0 part; hydroxypropyl methylcellulose: 0.3 parts; composite activator: 2.8 parts; The composite activator is composed of crystalline sodium sulfate, calcium oxide metakaolin, and triethanolamine in a mass ratio of 6.5:4:0.7.

[0007] As an improvement, the original subgrade soil has a plasticity index of 12-18 and a dry density of 1.75-1.90 g / cm³. 3 Cohesive soil with a moisture content between 9% and 15%; As an improvement, the total content of SiO2, Al2O3 and Fe2O3 in the fly ash is not less than 80%, and the loss on ignition is not greater than 8%.

[0008] As an improvement, the calcium oxide metakaolin in the composite activator is obtained by calcining and activating kaolin at 700~850℃, and then grinding it together with quicklime at a mass ratio of 1:1 until the specific surface area is ≥500m². 2 It is obtained by measuring / kg.

[0009] A construction method for fly ash stabilized soil used in road base courses includes the following steps: S1: Soil pretreatment and moisture content control: The original soil of the roadbed is crushed and screened to remove particles with a diameter greater than 15mm. After measuring its natural moisture content, water is added to the soil or the moisture content is brought close to the target construction moisture content by turning and drying. S2: Reference mix proportion and mixing: The pretreated subgrade soil, fly ash, and silicate cement are put into the mixing bin for the first stage of dry mixing, with a dry mixing time of not less than 45 seconds; then, the composite activator, polypropylene fiber, calcium lignosulfonate, and hydroxypropyl methylcellulose are added for the second stage of dry mixing, with a time of not less than 60 seconds; finally, according to the moisture content test results, atomized water is sprayed in for wet mixing, and the total wet mixing time is controlled at 90~120 seconds to ensure that the moisture content of the mixture is uniform. S3: Pressing and Interface Strengthening: The well-mixed material is pressed for 1-2 hours to allow moisture to migrate fully and the activator to react initially, thus obtaining the mixture; S4: Layered paving and elevation control: The mixture after curing is paved in two layers using a paver. The loose paving coefficient of the lower layer is controlled at 1.25~1.30, and the loose paving coefficient of the upper layer is controlled at 1.20~1.25. An automatic leveling system guided by steel wire rope is used to control the elevation of the top surface of each layer. S5: Combined compaction: Compaction follows the principles of "static compaction before vibratory compaction, light compaction before heavy compaction, and compaction from the edge to the center," specifically including: S5.1 Initial compaction: Use a double-drum roller for static compaction once at a speed of 1.5~2.0km / h; S5.2 Compacting: Use a single-drum vibratory roller for two passes of weak vibration compaction, followed by three to four passes of strong vibration compaction, at a speed of 2.0 to 2.5 km / h, with wheel tracks overlapping by no less than 1 / 3 of the wheel width; S5.3 Final compaction: Use a pneumatic tire roller to compact the surface 1-2 times to eliminate wheel tracks and surface micro-cracks; S6: Timely moisturizing maintenance and performance monitoring: After compaction, immediately cover with permeable geotextile and continuously spray water for maintenance, keeping the humidity above 90% for no less than 7 days; and on the 3rd day of maintenance, use a falling weight deflectometer to conduct preliminary deflection value testing.

[0010] As an improvement, during the re-compaction process in step S5, the compaction degree is detected in real time using the sand-filling method. When the compaction degree reaches 95% or more, the high-vibration compaction is stopped, and the process proceeds to the final compaction step.

[0011] As an improvement, in step S6, when the ambient temperature is higher than 30°C or the wind speed is high, an additional layer of emulsified asphalt film is sprayed after covering the geotextile for sealing and moisture retention.

[0012] As an improvement, in step S4, the interval between the upper and lower layers is no more than the initial setting time of the lower layer mixture, and after the lower layer is laid and compacted, its surface is roughened to enhance the interlayer bonding.

[0013] Compared with the prior art, the beneficial effects of the present invention are: This invention utilizes the synergistic effect of a composite activator (sodium sulfate crystalline, calcium oxide metakaolin, and triethanolamine) to efficiently activate the pozzolanic activity of fly ash and form a dense skeleton with cement hydration products, effectively solving the technical problems of low early strength and insufficient long-term growth potential in traditional stabilized soils. Simultaneously, the reinforcing effect of polypropylene fibers combined with the water-retaining and toughening properties of hydroxypropyl methylcellulose significantly inhibits the formation of drying and thermal shrinkage cracks, giving the material both high early strength and excellent long-term crack resistance.

[0014] This invention employs a multi-stage mixing process (dry mixing followed by wet mixing) and a curing activation step to ensure uniform dispersion and initial reaction of active components, avoiding agglomeration or unevenness problems caused by simple mixing. The layered paving and combined compaction process (static compaction followed by weak and strong vibration, and final compaction) effectively improves the overall structural strength and interlayer bonding through loose paving coefficient control and real-time compaction monitoring.

[0015] This invention promotes the stable formation of hydration products through a composite activator and optimizes the pore structure with functional additives (calcium lignosulfonate and hydroxypropyl methylcellulose), enabling the material to maintain high strength even under immersion conditions and overcoming the defect of traditional stabilized soils that are prone to softening in humid environments. Systematic moisturizing maintenance (covering with geotextile and sprinkling water) and sealing measures (such as emulsified asphalt film) further ensure the continuity of the hydration reaction and the stability of long-term performance.

[0016] This invention uses fly ash, an industrial byproduct, as the main raw material, significantly reducing the use of natural aggregates and realizing the resource utilization of waste, which meets the development requirements of green building materials. At the same time, by optimizing the mix proportions to reduce cement usage, carbon emissions are lowered, demonstrating significant environmental and economic value.

[0017] This invention introduces quality control measures such as real-time compaction testing and deflection monitoring during construction to ensure that construction parameters match the design performance of materials, thereby improving the reliability and traceability of project quality.

[0018] The above overview is for illustrative purposes only and is not intended to be limiting in any way. Further aspects, embodiments, and features of the invention will become apparent from the following detailed description, in addition to the illustrative aspects, embodiments, and features described above. Detailed Implementation

[0019] The invention will be more readily understood by referring to the following detailed description of preferred embodiments and included examples. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In case of conflict, the definitions in this specification shall prevail.

[0020] As used herein, the terms “prepared from” and “comprising” are synonymous. The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0021] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0022] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including the ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0023] The singular form includes the plural objects of discussion unless the context clearly indicates otherwise. "Optional" or "any one" means that the matter or event described thereafter may or may not occur, and the description includes both the possibility that the event occurs and the possibility that the event does not occur.

[0024] Approximate terms used in the specification and claims to modify quantities indicate that the invention is not limited to that specific quantity, but also includes acceptable modifications close to that quantity that do not alter the relevant essential function. Correspondingly, the use of "about," "approximately," etc., to modify a numerical value means that the invention is not limited to that precise value. In some instances, approximate terms may correspond to the precision of the instrument used to measure the value. In this application's specification and claims, scope definitions can be combined and / or interchanged, unless otherwise stated, these scopes include all subscopes contained therein.

[0025] Furthermore, the indefinite articles “a” and “an” preceding the elements or components of this invention do not impose any limitation on the quantity (i.e., number of times) of the elements or components. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers to the singular form.

[0026] Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0027] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the experimental materials and test strains used in the following examples were purchased from commercial channels.

[0028] This invention provides a fly ash stabilized soil for road base courses, composed of the following raw materials in parts by weight: fly ash: 75-88 parts; original roadbed soil: 8-20 parts; silicate cement: 3-6 parts; polypropylene fiber: 0.8-2 parts; calcium lignosulfonate: 0.5-1.5 parts; hydroxypropyl methylcellulose: 0.1-0.5 parts; composite activator: 1.5-4 parts. The composite activator is composed of crystalline sodium sulfate, calcium oxide metakaolin, and triethanolamine in a mass ratio of (5~8):(3~5):(0.5~1).

[0029] Furthermore, it is composed of the following raw materials in parts by weight: fly ash: 81 parts; subgrade soil: 14 parts; silicate cement: 4 parts; polypropylene fiber: 1.4 parts; calcium lignosulfonate: 1.0 part; hydroxypropyl methylcellulose: 0.3 parts; composite activator: 2.8 parts; The composite activator is composed of crystalline sodium sulfate, calcium oxide metakaolin, and triethanolamine in a mass ratio of 6.5:4:0.7.

[0030] Specifically, the original soil of the roadbed has a plasticity index of 12-18 and a dry density of 1.75-1.90 g / cm³. 3 Cohesive soil with a moisture content between 9% and 15%; The total content of SiO2, Al2O3 and Fe2O3 in the fly ash is not less than 80%, and the loss on ignition is not greater than 8%.

[0031] The calcium oxide metakaolin in the composite activator is obtained by calcining and activating kaolin at 700-850℃, and then grinding it together with quicklime at a mass ratio of 1:1 until the specific surface area is ≥500m². 2 It is obtained by measuring / kg.

[0032] A construction method for fly ash stabilized soil used in road base courses includes the following steps: S1: Soil pretreatment and moisture content control: The original soil of the roadbed is crushed and screened to remove particles with a diameter greater than 15mm. After measuring its natural moisture content, water is added to the soil or the moisture content is brought close to the target construction moisture content by turning and drying. S2: Reference mix proportion and mixing: The pretreated subgrade soil, fly ash, and silicate cement are put into the mixing bin for the first stage of dry mixing, with a dry mixing time of not less than 45 seconds; then, the composite activator, polypropylene fiber, calcium lignosulfonate, and hydroxypropyl methylcellulose are added for the second stage of dry mixing, with a time of not less than 60 seconds; finally, according to the moisture content test results, atomized water is sprayed in for wet mixing, and the total wet mixing time is controlled at 90~120 seconds to ensure that the moisture content of the mixture is uniform. S3: Pressing and Interface Strengthening: The well-mixed material is pressed for 1-2 hours to allow moisture to migrate fully and the activator to react initially, thus obtaining the mixture; S4: Layered paving and elevation control: The mixture after curing is paved in two layers using a paver. The loose paving coefficient of the lower layer is controlled at 1.25~1.30, and the loose paving coefficient of the upper layer is controlled at 1.20~1.25. An automatic leveling system guided by steel wire rope is used to control the elevation of the top surface of each layer. In practice, the interval between the upper and lower layers should not exceed the initial setting time of the lower layer mixture, and the surface of the lower layer should be roughened after it is laid and compacted to enhance the interlayer bonding.

[0033] S5: Combined compaction: Compaction follows the principles of "static compaction before vibratory compaction, light compaction before heavy compaction, and compaction from the edge to the center," specifically including: S5.1 Initial compaction: Use a double-drum roller for static compaction once at a speed of 1.5~2.0km / h; S5.2 Compacting: Use a single-drum vibratory roller for two passes of weak vibration compaction, followed by three to four passes of strong vibration compaction, at a speed of 2.0 to 2.5 km / h, with wheel tracks overlapping by no less than 1 / 3 of the wheel width; S5.3 Final compaction: Use a pneumatic tire roller to compact the surface 1-2 times to eliminate wheel tracks and surface micro-cracks; In practice, the compaction degree is tested in real time using the sand-filling method. When the compaction degree reaches 95% or more, the high-vibration rolling is stopped and the final compaction process begins.

[0034] S6: Timely moisturizing maintenance and performance monitoring: After compaction, immediately cover with permeable geotextile and continuously spray water for maintenance, keeping the humidity above 90% for no less than 7 days; and on the 3rd day of maintenance, use a falling weight deflectometer to conduct preliminary deflection value testing.

[0035] In practice, when the ambient temperature is above 30°C or the wind speed is high, after covering with geotextile, an additional layer of emulsified asphalt film should be sprayed for sealing and moisture retention.

[0036] In practical applications, this stabilized soil can also be used for backfilling deep pits, such as for backfilling fish ponds.

[0037] Example 1 This invention provides a fly ash stabilized soil for road base courses, composed of the following raw materials in parts by weight: fly ash: 75 parts; original roadbed soil: 8 parts; silicate cement: 3 parts; polypropylene fiber: 0.8 parts; calcium lignosulfonate: 0.5 parts; hydroxypropyl methylcellulose: 0.1 parts; composite activator: 1.5 parts. Specifically, the original soil of the roadbed has a plasticity index of 12-18 and a dry density of 1.75 g / cm³. 3Cohesive soil with a moisture content of 9%; The total content of SiO2, Al2O3 and Fe2O3 in the fly ash is not less than 80%, and the loss on ignition is not greater than 8%.

[0038] The composite activator is composed of crystalline sodium sulfate, calcium oxide metakaolin, and triethanolamine in a mass ratio of 5:3:0.5.

[0039] The calcium oxide metakaolin in the composite activator is obtained by calcining and activating kaolin at 700℃, and then grinding it together with quicklime at a mass ratio of 1:1 until the specific surface area is ≥500m². 2 It is obtained by measuring / kg.

[0040] A construction method for fly ash stabilized soil used in road base courses includes the following steps: S1: Soil pretreatment and moisture content control: The original soil of the roadbed is crushed and screened to remove particles with a diameter greater than 15mm. After measuring its natural moisture content, water is added to the soil or the moisture content is brought close to the target construction moisture content by turning and drying. S2: Reference mix proportion and mixing: The pretreated subgrade soil, fly ash, and silicate cement are put into the mixing bin for the first stage of dry mixing, with a dry mixing time of not less than 45 seconds; then, the composite activator, polypropylene fiber, calcium lignosulfonate, and hydroxypropyl methylcellulose are added for the second stage of dry mixing, with a time of not less than 60 seconds; finally, according to the moisture content test results, atomized water is sprayed in for wet mixing, and the total wet mixing time is controlled at 90 seconds to ensure that the moisture content of the mixture is uniform. S3: Pressing and Interface Strengthening: The well-mixed material is pressed for 1 hour to allow moisture to migrate fully and the activator to react initially, thus obtaining the mixture; S4: Layered paving and elevation control: The mixture after curing is paved in two layers using a paver. The loose paving coefficient of the lower layer is controlled at 1.25, and the loose paving coefficient of the upper layer is controlled at 1.20. An automatic leveling system guided by steel wire rope is used to control the top elevation of each layer. In practice, the interval between the upper and lower layers should not exceed the initial setting time of the lower layer mixture, and the surface of the lower layer should be roughened after it is laid and compacted to enhance the interlayer bonding.

[0041] S5: Combined compaction: Compaction follows the principles of "static compaction before vibratory compaction, light compaction before heavy compaction, and compaction from the edge to the center," specifically including: S5.1 Initial compaction: Use a double-drum roller for static compaction once at a speed of 1.5 km / h; S5.2 Compacting: Use a single steel drum vibratory roller to compact the road twice with weak vibration, and then compact it three times with strong vibration, at a speed of 2.0 km / h, with the wheel tracks overlapping by no less than 1 / 3 of the wheel width; S5.3 Final compaction: Use a pneumatic tire roller to compact the surface once to eliminate wheel tracks and surface micro-cracks; In practice, the compaction degree is tested in real time using the sand-filling method. When the compaction degree reaches 95% or more, the high-vibration rolling is stopped and the final compaction process begins.

[0042] S6: Timely moisturizing maintenance and performance monitoring: After compaction, immediately cover with permeable geotextile and continuously spray water for maintenance, keeping the humidity above 90% for no less than 7 days; and on the 3rd day of maintenance, use a falling weight deflectometer to conduct preliminary deflection value testing.

[0043] In practice, when the ambient temperature is above 30°C or the wind speed is high, after covering with geotextile, an additional layer of emulsified asphalt film should be sprayed for sealing and moisture retention.

[0044] Example 2 This invention provides a fly ash stabilized soil for road base courses, composed of the following raw materials in parts by weight: fly ash: 81 parts; original roadbed soil: 14 parts; silicate cement: 4 parts; polypropylene fiber: 1.4 parts; calcium lignosulfonate: 1.0 parts; hydroxypropyl methylcellulose: 0.3 parts; composite activator: 2.8 parts; Specifically, the original soil of the roadbed has a plasticity index of 16 and a dry density of 1.82 g / cm³. 3 Cohesive soil with a moisture content of 12%; The total content of SiO2, Al2O3 and Fe2O3 in the fly ash is not less than 80%, and the loss on ignition is not greater than 8%.

[0045] The composite activator is composed of crystalline sodium sulfate, calcium oxide metakaolin, and triethanolamine in a mass ratio of 6.5:4:0.7.

[0046] The calcium oxide metakaolin in the composite activator is obtained by calcining and activating kaolin at 775℃, and then grinding it together with quicklime at a mass ratio of 1:1 until the specific surface area is ≥500m². 2 It is obtained by measuring / kg.

[0047] A construction method for fly ash stabilized soil used in road base courses includes the following steps: S1: Soil pretreatment and moisture content control: The original soil of the roadbed is crushed and screened to remove particles with a diameter greater than 15mm. After measuring its natural moisture content, water is added to the soil or the moisture content is brought close to the target construction moisture content by turning and drying. S2: Reference mix proportion and mixing: The pretreated subgrade soil, fly ash, and silicate cement are put into the mixing bin for the first stage of dry mixing, and the dry mixing time is not less than 45 seconds; then the composite activator, polypropylene fiber, calcium lignosulfonate, and hydroxypropyl methylcellulose are added for the second stage of dry mixing, and the time is not less than 60 seconds; finally, according to the moisture content test results, atomized water is sprayed in for wet mixing, and the total wet mixing time is controlled at 105 seconds to ensure that the moisture content of the mixture is uniform. S3: Pressing and Interface Strengthening: The well-mixed material is pressed for 1-2 hours to allow moisture to migrate fully and the activator to react initially, thus obtaining the mixture; S4: Layered paving and elevation control: The mixture after curing is paved in two layers using a paver. The loose paving coefficient of the lower layer is controlled at 1.28, and the loose paving coefficient of the upper layer is controlled at 1.23. An automatic leveling system guided by steel wire rope is used to control the elevation of the top surface of each layer. In practice, the interval between the upper and lower layers should not exceed the initial setting time of the lower layer mixture, and the surface of the lower layer should be roughened after it is laid and compacted to enhance the interlayer bonding.

[0048] S5: Combined compaction: Compaction follows the principles of "static compaction before vibratory compaction, light compaction before heavy compaction, and compaction from the edge to the center," specifically including: S5.1 Initial compaction: Use a double-drum roller for static compaction once at a speed of 1.75 km / h; S5.2 Compacting: Use a single steel drum vibratory roller to compact the road surface with weak vibration twice, followed by strong vibration three to four times, at a speed of 2.2 km / h, with wheel tracks overlapping by no less than 1 / 3 of the wheel width; S5.3 Final compaction: Use a pneumatic tire roller to compact the surface once to eliminate wheel tracks and surface micro-cracks; In practice, the compaction degree is tested in real time using the sand-filling method. When the compaction degree reaches 95% or more, the high-vibration rolling is stopped and the final compaction process begins.

[0049] S6: Timely moisturizing maintenance and performance monitoring: After compaction, immediately cover with permeable geotextile and continuously spray water for maintenance, keeping the humidity above 90% for no less than 7 days; and on the 3rd day of maintenance, use a falling weight deflectometer to conduct preliminary deflection value testing.

[0050] In practice, when the ambient temperature is above 30°C or the wind speed is high, after covering with geotextile, an additional layer of emulsified asphalt film should be sprayed for sealing and moisture retention.

[0051] Example 3 This invention provides a fly ash stabilized soil for road base courses, composed of the following raw materials in parts by weight: fly ash: 88 parts; original roadbed soil: 20 parts; silicate cement: 6 parts; polypropylene fiber: 2 parts; calcium lignosulfonate: 1.5 parts; hydroxypropyl methylcellulose: 0.5 parts; composite activator: 4 parts. Specifically, the original soil of the roadbed has a plasticity index of 18 and a dry density of 1.90 g / cm³. 3 Cohesive soil with a moisture content of 15%; The total content of SiO2, Al2O3 and Fe2O3 in the fly ash is not less than 80%, and the loss on ignition is not greater than 8%.

[0052] The composite activator is composed of crystalline sodium sulfate, calcium oxide metakaolin, and triethanolamine in a mass ratio of 8:5:1.

[0053] The calcium oxide metakaolin in the composite activator is obtained by calcining and activating kaolin at 850℃, and then grinding it together with quicklime at a mass ratio of 1:1 until the specific surface area is ≥500m². 2 It is obtained by measuring / kg.

[0054] A construction method for fly ash stabilized soil used in road base courses includes the following steps: S1: Soil pretreatment and moisture content control: The original soil of the roadbed is crushed and screened to remove particles with a diameter greater than 15mm. After measuring its natural moisture content, water is added to the soil or the moisture content is brought close to the target construction moisture content by turning and drying. S2: Reference mix proportion and mixing: The pretreated subgrade soil, fly ash, and silicate cement are put into the mixing bin for the first stage of dry mixing, with a dry mixing time of not less than 45 seconds; then, the composite activator, polypropylene fiber, calcium lignosulfonate, and hydroxypropyl methylcellulose are added for the second stage of dry mixing, with a time of not less than 60 seconds; finally, according to the moisture content test results, atomized water is sprayed in for wet mixing, with the total wet mixing time controlled at 120 seconds to ensure uniform moisture content of the mixture; S3: Pressing and Interface Strengthening: The well-mixed material is pressed for 2 hours to allow moisture to migrate fully and the activator to react initially, thus obtaining the mixture; S4: Layered paving and elevation control: The mixture after curing is paved in two layers using a paver. The loose paving coefficient of the lower layer is controlled at 1.30, and the loose paving coefficient of the upper layer is controlled at 1.25. An automatic leveling system guided by steel wire rope is used to control the top elevation of each layer. In practice, the interval between the upper and lower layers should not exceed the initial setting time of the lower layer mixture, and the surface of the lower layer should be roughened after it is laid and compacted to enhance the interlayer bonding.

[0055] S5: Combined compaction: Compaction follows the principles of "static compaction before vibratory compaction, light compaction before heavy compaction, and compaction from the edge to the center," specifically including: S5.1 Initial compaction: Use a double-drum roller for static compaction once at a speed of 2.0 km / h; S5.2 Compacting: Use a single steel drum vibratory roller to compact the road surface with weak vibration twice, followed by strong vibration three to four times, at a speed of 2.5 km / h, with wheel tracks overlapping by no less than 1 / 3 of the wheel width; S5.3 Final compaction: Use a pneumatic tire roller to compact the surface twice to eliminate wheel tracks and surface micro-cracks; In practice, the compaction degree is tested in real time using the sand-filling method. When the compaction degree reaches 95% or more, the high-vibration rolling is stopped and the final compaction process begins.

[0056] S6: Timely moisturizing maintenance and performance monitoring: After compaction, immediately cover with permeable geotextile and continuously spray water for maintenance, keeping the humidity above 90% for no less than 7 days; and on the 3rd day of maintenance, use a falling weight deflectometer to conduct preliminary deflection value testing.

[0057] In practice, when the ambient temperature is above 30°C or the wind speed is high, after covering with geotextile, an additional layer of emulsified asphalt film should be sprayed for sealing and moisture retention.

[0058] Test Example 1: Unconfined Compressive Strength Test 1. Experimental objective: This experiment aims to quantitatively evaluate the mechanical property development law of the fly ash stabilized soil of the present invention under different curing ages through standard unconfined compressive strength test, and to compare it with traditional cement stabilized soil and secondary stabilized soil to verify the retention of its early strength and long-term strength.

[0059] 2. Experimental Materials and Instruments 2.1 Materials: Invention Group: The mixture prepared according to Example 2.

[0060] Comparative Group 1 (Cement-stabilized Soil): 90 parts original subgrade soil, 6 parts cement, and 4 parts water.

[0061] Comparative group 2 (secondary stabilized soil): 70 parts original subgrade soil, 15 parts fly ash, 8 parts lime, and 7 parts water.

[0062] 2.2 Instruments and equipment: universal testing machine, constant temperature and humidity standard curing chamber, electronic balance, compaction test mold (Φ50mm×50mm), demolding device, compaction hammer, etc.

[0063] 3. Specimen preparation and curing steps: 3.1 Ingredient preparation and mixing: Invention Group: Referring to step S2 of the construction method, a two-stage dry mixing and one-stage wet mixing process is adopted. First, the soil, fly ash, and cement are dry mixed for 45 seconds, then the activator and additives are added and dry mixed for 60 seconds, and finally atomized water is sprayed in and wet mixed for 105 seconds.

[0064] Control group: After manually mixing all powder ingredients evenly, gradually add the required amount of water and continue mixing until the color is uniform and there are no clumps.

[0065] 3.2 Compacting and molding: The mixed material is poured into a cylindrical mold (50mm in diameter and 50mm in height) coated with a thin layer of release agent in three batches.

[0066] Each layer is compacted using a compaction hammer, and the compaction effort is controlled to ensure that the compaction degree of the molded specimen reaches more than 95% (this is ensured by controlling the quality and height).

[0067] Nine specimens were prepared in parallel under the same conditions for each formulation.

[0068] 3.3 Demolding and Curing: Immediately after molding, wrap the specimens with plastic wrap to prevent moisture evaporation and let them stand for 24 hours before demolding. Place the demolded specimens in a standard curing chamber at a temperature of 20±2°C and a relative humidity of ≥95% and cure them for 7 days and 28 days, respectively.

[0069] 4. Strength testing steps: After reaching the specified curing period (7 or 28 days), remove the specimen from the curing chamber. Wipe the surface of the specimen clean with a damp cloth, and measure its diameter and height with vernier calipers, accurate to 0.1 mm. Place the specimen in the center of the lower platen of the universal testing machine.

[0070] Start the testing machine and use the stress control mode to move the loading plate vertically downward at a constant rate of 1 mm / min to apply axial pressure to the specimen until the specimen fails.

[0071] Record the maximum destructive load P (unit: N) displayed by the testing machine.

[0072] Formula for calculating unconfined compressive strength:

[0073] in: Unconfined compressive strength, in MPa; The maximum load at which the specimen fails is expressed in Newtons (N). The diameter of the specimen is in mm.

[0074] 5. Experimental Data: Table 1: Results of unconfined compressive strength test (x±s, MPa, n=6)

[0075] Note: Data are expressed as mean ± standard deviation. n=6 indicates that there are 6 valid parallel specimens in each group.

[0076] 6. Experimental Conclusions Based on the above experimental data, the following conclusions can be drawn: The 7-day unconfined compressive strength of the group of this invention reached 3.82 MPa, which was 51.0% and 223.7% higher than that of control group 1 (cement soil) and control group 2 (secondary soil), respectively. This indicates that the present invention, through the synergistic effect of the composite activator (sodium sulfate providing early alkalinity and sulfate, calcium oxide metakaolin providing active silica-alumina source and calcium source, and triethanolamine as catalyst), greatly stimulates the early pozzolanic activity of fly ash, enabling it to form a strength skeleton with cement hydration products in a short period of time, effectively overcoming the fatal weakness of low early strength of traditional fly ash materials.

[0077] The 28-day strength of the material group of this invention further increased to 6.94 MPa, far exceeding the 4.12 MPa of control group 1 (68.4% higher) and the 2.75 MPa of control group 2 (152.4% higher), proving that the strength development of the material system of this invention is continuous and stable. The long-term activating effect of the composite activator, along with the optimization of the pore structure by hydroxypropyl methylcellulose and the reinforcing effect of polypropylene fibers, jointly contribute to a denser and tougher matrix, providing a higher long-term load-bearing capacity safety reserve for road base courses.

[0078] The strength growth ratio (28d / 7d) of this invention group is 1.82, higher than that of control group 1 (1.63), but lower than that of control group 2 (2.33). Control group 2 (secondary soil) exhibits a high growth factor in the later stages due to its slow reaction and extremely low early strength, but its absolute strength value remains low. In contrast, this invention achieves high early strength while maintaining good potential for later growth, meeting the requirements for early traffic opening while ensuring long-term service performance.

[0079] Experimental Example 2: 1. Experimental objective: This experiment aims to quantitatively evaluate the drying shrinkage deformation of the fly ash stabilized soil of this invention under dehydration conditions and the thermal shrinkage deformation under cooling conditions, and to scientifically verify its crack resistance performance by comparing it with traditional cement stabilized soil. The drying shrinkage coefficient and the thermal shrinkage coefficient are key indicators for evaluating the crack resistance of base course materials.

[0080] 2. Experimental materials and instruments: 2.1 Materials: Invention Group: The mixture prepared according to Example 2.

[0081] Comparative group: Traditional cement-stabilized soil: 90 parts original subgrade soil, 6 parts cement, and 4 parts water.

[0082] 2.2 Instruments and Equipment: Shrinkage test: constant temperature and humidity drying oven (temperature controlled at 40±2°C, humidity at 60%±5%), length comparator (or measuring bracket equipped with a dial indicator), electronic balance (accuracy 0.1g), standard beam mold (100mm×100mm×400mm).

[0083] Temperature shrinkage test: programmable high and low temperature environment test chamber, quartz glass calibration rod with a coefficient of linear expansion similar to that of the specimen, dial gauge or resistance strain gauge.

[0084] 3. Specimen preparation and curing: Molding: The two mixtures were injected into beam molds coated with release agent and compacted by vibration to ensure a density of over 95%. Six parallel specimens were prepared for each group.

[0085] Curing: After molding, cover the molded specimen with plastic film and let it stand indoors at 20±2°C for 24 hours before demolding. Immediately afterwards, place the specimen in a standard curing chamber at 20±2°C and relative humidity ≥95% for 7 days.

[0086] 4. Drying shrinkage test procedure: Initial measurement: After curing, remove the specimens. Wipe the surface clean with a damp cloth, measure the initial length L0 of each specimen (accurate to 0.001 mm) on a length comparator, and weigh its initial mass W0 (accurate to 0.1 g).

[0087] Accelerated drying: Place the specimens in a constant temperature and humidity drying oven set to 40±2°C and 60%±5%RH to accelerate water loss.

[0088] Periodic measurements: On days 1, 3, 7, 14, and 28 after placement, remove the specimen and measure its length (Lᵢ) and mass (Wᵢ) within 15 minutes, then quickly return it to the drying oven.

[0089] Data processing: Moisture loss rate: ; Drying strain: (Unit: ×10) -6 (or micro-strain); Average shrinkage coefficient: Based on the relationship curve between shrinkage strain (ε) and moisture loss rate (ω), the slope of the linear phase is taken as the average shrinkage coefficient. (Unit: ×10) -6 / %).

[0090] 5. Temperature Shrinkage Test Procedure: Specimen preparation: Install measuring heads at both ends of the beam specimen that has been cured for 28 days, and place it in the environmental chamber together with the quartz glass calibration rod.

[0091] Temperature cycling: Starting from +40°C, the ambient chamber was slowly cooled to -10°C at a rate of 1°C / h.

[0092] Data acquisition: After each 5°C drop, maintain the temperature for 1 hour until the internal and external temperatures of the specimen are equalized, measure the length changes of the specimen and the calibration rod. Read the values ​​using a dial indicator or strain gauge.

[0093] Data processing: Thermal contraction strain: (The effects of thermal expansion and contraction of the instrument and its support have been deducted); Average thermal shrinkage coefficient: based on thermal shrinkage strain ( ) and temperature ( T The average slope of the curve representing the temperature contraction coefficient during the cooling phase is taken as the average temperature contraction coefficient. (Unit: ×10) -6 / °C).

[0094] 6. Experimental Data: Table 2-1: Comparison of Drying Shrinkage Test Results

[0095] Table 2-2: Comparison of Temperature Shrinkage Performance Test Results

[0096] 7. Experimental Conclusion: Based on the above experimental data, the following conclusions can be drawn: Drying shrinkage performance analysis: The average drying shrinkage coefficient of the group of inventions is 35.2 × 10⁻⁶. -6 / %, with a maximum drying shrinkage strain of 215×10. -6 Compared to the control group (average shrinkage coefficient 58.7 × 10⁻⁶), -6 / %, maximum drying shrinkage strain 385×10 -6 The shrinkage deformation of the material under dehydration conditions was reduced by approximately 40.0% and 44.2%, respectively. This indicates that the material of the present invention exhibits significantly less shrinkage deformation than traditional cement-stabilized soil under dehydration conditions, demonstrating excellent resistance to drying shrinkage cracking.

[0097] Temperature shrinkage performance analysis: The average temperature shrinkage coefficient of this invention group is 7.8 × 10⁻⁶. -6 / ℃, compared to the control group (average temperature shrinkage coefficient 10.5×10). -6 The temperature drop (°C) was reduced by approximately 25.7%. This indicates that the material of the present invention is significantly less sensitive to temperature changes and generates less shrinkage stress during the cooling process, thereby reducing the risk of thermal shrinkage cracking.

[0098] Comprehensive crack resistance analysis: Both drying shrinkage and thermal shrinkage test data consistently show that the shrinkage performance of the material of this invention is superior to that of traditional materials, with a drying shrinkage coefficient reduced by over 40% and a thermal shrinkage coefficient reduced by over 25%. From the overall shrinkage performance data, the material of this invention exhibits lower shrinkage potential and higher dimensional stability, providing direct data support for its crack resistance performance in practical engineering applications.

[0099] Experiment Example 3: Water Stability Test 1. Experimental Objective This experiment aims to scientifically evaluate the ability of fly ash stabilized soil to resist water damage by measuring its unconfined compressive strength under saturated water conditions and its ratio to the standard curing strength (i.e., the water stability coefficient). Water stability is a key indicator for measuring the long-term performance of road base courses in humid, rainy, or high-water-table areas.

[0100] 2. Experimental Materials and Instruments 2.1 Materials: Invention Group: The mixture prepared according to Example 2.

[0101] Comparative group: Traditional cement-stabilized soil: 90 parts original subgrade soil, 6 parts cement, and 4 parts water.

[0102] 2.2 Instruments and equipment: universal testing machine, constant temperature and humidity standard curing chamber, water bath (or constant temperature water bath), vernier calipers, electronic balance, cylindrical test mold (Φ50 mm × 50 mm).

[0103] 3. Specimen preparation and group curing: Specimen molding: Following the method in Experimental Example 1, the two groups of mixtures were compacted and molded into cylindrical specimens with a diameter of 50 mm and a height of 50 mm. Eighteen specimens were prepared for each group, ensuring parallelism and consistent density.

[0104] Maintenance Groups: Standard curing group (S): Nine specimens were taken from each group and immediately placed in a standard curing chamber with a temperature of 20±2°C and a relative humidity of ≥95% for continuous curing after demolding.

[0105] Water immersion curing group (I): Take 9 specimens from each group, and after demolding, cure them in a standard curing chamber for 6 days.

[0106] 4. Experimental Procedure: 4.1 Immersion treatment: For specimens in the immersion curing group (I), a comparison with specimens of the same age is required to assess long-term water stability. Therefore, on day 27 of curing, the specimens were removed from the curing chamber. The specimens were then completely immersed in a constant-temperature water bath at 20±2°C, with the water level at least 2.5 cm above the top surface of the specimen, for one day. That is, specimens in the immersion curing group (I) were tested at 28 days of total age, including one day of water saturation. Specimens in the standard curing group (S) were tested directly at 28 days of total age.

[0107] 4.2 Strength Test: Standard curing group (S): The specimens were removed after 7 days and 28 days of curing, respectively. The surface was wiped dry and the unconfined compressive strength test was performed immediately to obtain qu(S7) and qu(S28).

[0108] Immersion curing group (I): The specimens were removed from the water tank after immersion for 1 day (total age 7 days) and after immersion for 25 days (total age 32 days), respectively. After wiping off the surface moisture with a damp cloth, the unconfined compressive strength test was performed immediately (usually within 15 minutes) to obtain the saturated strength qu (I7) and qu (I32).

[0109] The strength test method is the same as in Experiment 1, with a loading rate of 1 mm / min.

[0110] 4.3 Data Processing: Calculate the water stability coefficient:

[0111] (Characterizing early water stability. The total age of all specimens was 7 days, with Group I being saturated for 1 day).

[0112]

[0113] Note: The long-term water stability coefficient K28 is compared with the saturated strength of the standard curing group at the same total age (28 days). This method follows the "single variable" principle and can clearly and directly reflect the retention rate of its strength performance after short-term water immersion (1 day) at the end of the critical strength growth period of the material, scientifically characterizing its resistance to water damage.

[0114] 5. Experimental Data Table 3: Comparison of water stability test results (x ± s, n=6)

[0115] 6. Experimental Conclusions: Based on the above experimental data, the following conclusions can be drawn: After immersion in water for one day, the saturated strength of the material from this invention was 3.26 MPa, and its early water stability coefficient K7 was as high as 85.3%. This means that even in the early stages of water erosion, it can still retain most of its strength. In contrast, the K7 of the control group was only 70.4%, with a strength loss of nearly 30%. This indicates that the material of this invention has a stronger resistance to water softening in the early stages of molding. This is attributed to the composite activator promoting the rapid formation of early hydration products and pozzolanic reaction products, forming a skeleton with high initial strength and a relatively stable structure, reducing the scouring and softening effect of water on unreacted particles.

[0116] After a 25-day immersion test, the long-term water stability coefficient K32 of the present invention group was further improved to 89.0%, while that of the control group was only 76.2%. The advantage of the present invention group decreased from 15% in the early stage to 13% in the later stage (absolute value), but its absolute value of saturated strength (6.18 MPa) far exceeded the standard curing strength of the control group (4.12 MPa). This proves that the water stability of the material of the present invention is continuously improving and very reliable.

[0117] Experiment Example 4: Bending Tensile Properties and Toughness Test 1. Experimental objective: This experiment used the three-point loading method to determine the flexural strength and load-deflection curves of beam specimens, and evaluated the toughness of the material by analyzing the area under the curves. The aim was to quantitatively evaluate the crack resistance and energy absorption capacity (i.e., toughness) of the fly ash stabilized soil of this invention under flexural loads, which is a key indicator reflecting the base layer's resistance to load-induced cracks and fatigue cracking.

[0118] 2. Experimental materials and instruments: 2.1 Materials: Invention Group: The mixture prepared according to Example 2.

[0119] Comparative group: Traditional cement-stabilized soil: 90 parts original subgrade soil, 6 parts cement, and 4 parts water.

[0120] 2.2 Instruments and Equipment: Universal testing machine: equipped with a three-point loading device (two loading heads and one support frame).

[0121] Data acquisition system: used to synchronously record load and mid-span deflection.

[0122] Displacement gauge (or LVDT): measures the mid-span deflection of the specimen with an accuracy of not less than 0.01 mm.

[0123] Beam-type trial mold: internal dimensions are 100mm × 100mm × 400mm.

[0124] Maintenance equipment: Standard constant temperature and humidity curing chamber.

[0125] 3. Specimen preparation and curing: Molding: The two mixtures are poured into beam molds coated with release agent and compacted by vibration to ensure a density of over 95%. At least five valid parallel specimens are prepared for each mixture.

[0126] Curing: After molding, cover the molded specimen with plastic film and let it stand indoors at 20±2°C for 24 hours before demolding. Then, immediately place the specimen in a standard curing chamber at 20±2°C and relative humidity ≥95% and cure it for 28 days.

[0127] 4. Experimental Procedure: Specimen preparation: After curing, remove the specimens and wipe the surface clean with a damp cloth. Measure the width (b) and height (h) at the center of each specimen, accurate to 0.1 mm.

[0128] Installation and positioning: Place the specimen stably on the support frame of the testing machine with a support span (L) of 300 mm; use three-point loading, that is, two loading points are located at the three equal divisions of the span; install a displacement gauge at the bottom of the mid-span of the specimen to measure the deflection.

[0129] Preloading and zeroing: Apply a very small preload (about 1% of the estimated failure load), check if the device is stable, and then zero the load and deflection readings.

[0130] Loading and Data Acquisition: Start the testing machine and apply the load at a constant rate of 0.5 mm / min using displacement control mode. The data acquisition system continuously and synchronously records the applied load (P) and mid-span deflection (δ) until the load drops to more than 50% of the peak load or the deflection increases significantly while the load no longer changes, at which point the test is stopped.

[0131] Failure mode record: Photograph or describe in detail the final failure mode of the specimen.

[0132] 5. Data Processing and Calculation: Flexural strength ( fr )calculate: in, The width of the specimen cross-section (mm); The height of the specimen cross-section is (mm).

[0133] Resilience Index ( OF )calculate: By using the load-deflection (P-δ) curve, the following two key indicators are extracted to comprehensively evaluate the flexural tensile performance and toughness of the specimen: Peak point resilience index ( The load-deflection curve is calculated by measuring the area enclosed by the origin and the peak load point, expressed in J or N·m. This index reflects the material's ability to absorb energy before cracking.

[0134] Ultimate deflection ( ( ): Records the maximum mid-span deflection of the specimen before failure, in mm. This indicator directly reflects the material's deformation capacity.

[0135] For easier comparison, the relative toughness index can be calculated to compare the groups. The average value is 1.0, which is then normalized.

[0136] 6. Experimental Data Table 4: Test results of flexural tensile properties and toughness (x ± s, n=5)

[0137] Note: Peak point resilience index ( The area under the load-deflection curve to the point of maximum load is calculated with the average value of the comparison group being 1.0.

[0138] 7. Experimental Conclusion: Based on the above experimental data and observations of the failure modes, the following conclusions can be drawn: The flexural tensile strength of the material in this invention group reached 1.15 MPa, which is 59.7% higher than the 0.72 MPa of the control group. This indicates that the material of this invention has a stronger ability to resist flexural tensile stress. Its core mechanism lies in the "bridging" effect of polypropylene fibers. When microcracks appear in the tensile zone of the matrix, the fibers can cross the cracks to bear the tensile stress, delaying the formation of macroscopic cracks, thereby significantly improving the flexural tensile strength.

[0139] The limiting deflection and peak point toughness index of this invention group ( The strength and toughness of the material were improved by 88.9% and 341.6% respectively compared to the control group. This fully demonstrates that the material of the present invention has excellent toughness. Not only is it stronger, but it can also withstand greater deformation and absorb far more energy than traditional materials before failure.

[0140] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in the present invention, and these should all be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A fly ash stabilized soil for road base courses, characterized in that, It is composed of the following raw materials in parts by weight: fly ash: 75-88 parts; subgrade soil: 8-20 parts; silicate cement: 3-6 parts; polypropylene fiber: 0.8-2 parts; calcium lignosulfonate: 0.5-1.5 parts; hydroxypropyl methylcellulose: 0.1-0.5 parts; composite activator: 1.5-4 parts; The composite activator is composed of crystalline sodium sulfate, calcium oxide metakaolin, and triethanolamine in a mass ratio of (5~8):(3~5):(0.5~1).

2. The fly ash stabilized soil for road base courses according to claim 1, characterized in that, It is composed of the following raw materials in parts by weight: fly ash: 81 parts; subgrade soil: 14 parts; silicate cement: 4 parts; polypropylene fiber: 1.4 parts; calcium lignosulfonate: 1.0 part; hydroxypropyl methylcellulose: 0.3 parts; composite activator: 2.8 parts; The composite activator is composed of crystalline sodium sulfate, calcium oxide metakaolin, and triethanolamine in a mass ratio of 6.5:4:0.

7.

3. The fly ash stabilized soil for road base courses according to claim 1, characterized in that: The original soil of the roadbed has a plasticity index of 12-18 and a dry density of 1.75-1.90 g / cm³. 3 Cohesive soil with a moisture content between 9% and 15%.

4. The fly ash stabilized soil for road base courses according to claim 1, characterized in that: The total content of SiO2, Al2O3 and Fe2O3 in the fly ash is not less than 80%, and the loss on ignition is not greater than 8%.

5. The fly ash stabilized soil for road base courses according to claim 1, characterized in that: The calcium oxide metakaolin in the composite activator is obtained by calcining and activating kaolin at 700-850℃, and then grinding it together with quicklime at a mass ratio of 1:1 until the specific surface area is ≥500m². 2 It is obtained by measuring / kg.

6. A construction method for fly ash stabilized soil as described in any one of claims 1-5, characterized in that, Includes the following steps: S1: Soil pretreatment and moisture content control: The original soil of the roadbed is crushed and screened to remove particles with a diameter greater than 15mm. After measuring its natural moisture content, water is added to the soil or the moisture content is brought close to the target construction moisture content by turning and drying. S2: Reference mix proportion and mixing: The pretreated subgrade soil, fly ash, and silicate cement are put into the mixing bin for the first stage of dry mixing, with a dry mixing time of not less than 45 seconds; then, the composite activator, polypropylene fiber, calcium lignosulfonate, and hydroxypropyl methylcellulose are added for the second stage of dry mixing, with a time of not less than 60 seconds; finally, according to the moisture content test results, atomized water is sprayed in for wet mixing, and the total wet mixing time is controlled at 90~120 seconds to ensure that the moisture content of the mixture is uniform. S3: Pressing and Interface Strengthening: The well-mixed material is pressed for 1-2 hours to allow moisture to migrate fully and the activator to react initially, thus obtaining the mixture; S4: Layered paving and elevation control: The mixture after curing is paved in two layers using a paver. The loose paving coefficient of the lower layer is controlled at 1.25~1.30, and the loose paving coefficient of the upper layer is controlled at 1.20~1.

25. An automatic leveling system guided by steel wire rope is used to control the elevation of the top surface of each layer. S5: Combined compaction: Compaction follows the principles of "static compaction before vibratory compaction, light compaction before heavy compaction, and compaction from the edge to the center," specifically including: S5.1 Initial compaction: Use a double-drum roller for static compaction once at a speed of 1.5~2.0km / h; S5.2 Compacting: Use a single-drum vibratory roller for two passes of weak vibration compaction, followed by three to four passes of strong vibration compaction, at a speed of 2.0 to 2.5 km / h, with wheel tracks overlapping by no less than 1 / 3 of the wheel width; S5.3 Final compaction: Use a pneumatic tire roller to compact the surface 1-2 times to eliminate wheel tracks and surface micro-cracks; S6: Timely moisturizing maintenance and performance monitoring: After compaction, immediately cover with permeable geotextile and continuously spray water for maintenance, keeping the humidity above 90% for no less than 7 days; and on the 3rd day of maintenance, use a falling weight deflectometer to conduct preliminary deflection value testing.

7. The construction method for fly ash stabilized soil according to claim 6, characterized in that: During the secondary compaction process in step S5, the compaction degree is detected in real time using the sand-filling method. When the compaction degree reaches 95% or more, the high-vibration compaction is stopped, and the final compaction process begins.

8. The construction method for fly ash stabilized soil according to claim 6, characterized in that: In step S6, when the ambient temperature is higher than 30°C or the wind speed is high, after covering the geotextile, an additional layer of emulsified asphalt film is sprayed for sealing and moisture retention.

9. The construction method for fly ash stabilized soil according to claim 6, characterized in that: In step S4, the interval between the upper and lower layers is no more than the initial setting time of the lower layer mixture, and after the lower layer is laid and compacted, its surface is roughened to enhance the interlayer bonding.

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