Titanium gypsum composite roadbed applied to expressway and construction method

Abstract

The invention relates to the technical field of building materials, in particular to a titanium gypsum composite roadbed applied to an expressway and a construction method. The titanium gypsum composite roadbed comprises a base material and a curing agent, the base material comprises titanium gypsum, pulverized coal, a curing agent and water; the base material comprises titanium gypsum, pulverized coal, a curing agent and water; the curing agent is prepared from the following components in parts by weight: 5 to 11 parts of lime, 10 to 20 parts of mineral powder, 15 to 25 parts of cement clinker, 20 to 30 parts of fly ash, 0.5 to 1.5 parts of sodium silicate, 14 to 47 parts of titanium gypsum and 2.5 to 4.5 parts of additive. By optimizing material components and introducing a ternary synergistic curing system, the mechanical property and durability of the material are improved, and efficient and standard application of titanium gypsum in roadbed engineering is realized.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a titanium-gypsum composite roadbed for highways and its construction method. Background Technology

[0002] The subgrade of a highway is the supporting foundation of the pavement structure, and its strength, stability, and durability directly determine the service life of the road and driving safety. Titanium gypsum composite subgrade is a type of composite subgrade for highways that uses titanium gypsum and fly ash subgrade filler. Titanium gypsum and fly ash subgrade filler is a highway subgrade filling material formed by uniformly mixing titanium gypsum, fly ash, and other materials with a special modified curing agent and water in the required proportions.

[0003] Existing technology discloses a titanium-gypsum composite roadbed material, which uses titanium gypsum, titanium extraction tailings powder, fly ash, and an alkaline activator as base materials, and adds additives such as early-strength agents, retarders, water-reducing agents, and water-repellent agents. This material uses an alkaline activator to promote hydration reactions, generating products such as ettringite, thereby improving the strength and erosion resistance of the roadbed material.

[0004] However, this existing technology still has the following problems: First, the curing system it uses is mainly alkaline activation and relies on traditional cementing materials such as cement. This has limited activation efficiency for the active components in titanium gypsum, resulting in insufficient strength development in the later stages of the material and making it difficult to meet the strength requirements of high-grade highway subgrades. Secondly, the material does not effectively control the content of easily soluble salts, which may pose a risk of salt leaching and expansion during long-term use, affecting the long-term stability and durability of the roadbed. In addition, the titanium gypsum in this technology needs to undergo high-temperature calcination pretreatment to change its crystal structure, which increases the complexity of the production process and energy consumption, making it unfavorable for large-scale promotion and application. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a titanium-gypsum composite subgrade and its construction method for highways, solving problems such as insufficient strength development, high soluble salt content, complex pretreatment processes, and lack of supporting construction techniques in the prior art. By optimizing material composition and introducing a ternary synergistic curing system, the mechanical properties and durability of the material are improved. Simultaneously, by clarifying construction process parameters and quality control requirements, the efficient and standardized application of titanium-gypsum in subgrade engineering is achieved.

[0006] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions: A titanium gypsum composite subgrade for highways includes a base material and a curing agent; the base material includes titanium gypsum, fly ash, curing agent and water; the curing agent, by weight, includes 5-11 parts lime, 10-20 parts mineral powder, 15-25 parts cement clinker, 20-30 parts fly ash, 0.5-1.5 parts sodium silicate, 14-47 parts titanium gypsum and 2.5-4.5 parts admixtures.

[0007] Furthermore, by weight, the composition is 50-70 parts titanium gypsum, 25-40 parts fly ash, and 3-8 parts curing agent.

[0008] Furthermore, when the moisture content of titanium gypsum in the base material is ≤40%, the proportion of titanium gypsum is 60-65 parts, fly ash is 30-35 parts, and curing agent is 4-5 parts.

[0009] Furthermore, the curing agent, by weight, comprises 5-11 parts lime, 10-20 parts mineral powder, 15-25 parts cement clinker, 20-30 parts fly ash, 0.5-1.5 parts sodium silicate, 14-47 parts titanium gypsum, and 2.5-4.5 parts admixtures.

[0010] Furthermore, the ingredients are: 8 parts lime, 15 parts mineral powder, 20 parts cement clinker, 25 parts fly ash, 1 part sodium silicate, 27.5 parts titanium gypsum, and 3.5 parts admixtures.

[0011] Furthermore, the moisture content of the fly ash does not exceed 15%.

[0012] Furthermore, the particle size distribution of pulverized coal ranges from 0.001 mm to 1.18 mm, with particles smaller than 0.075 mm accounting for more than 45%.

[0013] Furthermore, the additives include at least two of the following: an active activator, a nano-activator, a crystallizing anti-shrinkage agent, a water-reducing dispersant, and a surfactant.

[0014] This invention also provides a construction method for titanium gypsum composite subgrade applied to highways as described above, including the following steps: spreading titanium gypsum on the subgrade base, sprinkling fly ash, sprinkling curing agent, mixing at least three times with a road mixer to ensure uniform mixing of materials, leveling the mixture, controlling the moisture content between 26% and 30%, and compacting with a road roller.

[0015] Furthermore, the compaction process includes first using a vibratory roller for static compaction once, then two passes of weak vibration compaction, two passes of strong vibration compaction, and finally one pass of static compaction to finish the surface.

[0016] Furthermore, after leveling, a level instrument is used to check the elevation control points, and a test section is set at a set interval. The compaction degree is tested by sand filling method to ensure that the compaction degree meets the design requirements.

[0017] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages: The titanium gypsum composite roadbed of this invention comprises a base material and a curing agent. The base material includes titanium gypsum, fly ash, a curing agent, and water. The curing agent comprises lime, mineral powder, cement clinker, fly ash, sodium silicate, titanium gypsum, and admixtures. By using bulk industrial solid wastes such as titanium gypsum and fly ash as the main base material, combined with a specially designed composite curing agent, large-scale utilization of solid waste resources is achieved. In the curing agent, lime provides an alkaline environment, mineral powder and cement clinker provide cementitious properties, sodium silicate acts as an activator to promote the reaction, and admixtures improve construction performance and long-term durability. Compared with existing single alkaline activation or cement curing systems, this invention constructs a multi-component composite curing system. Through the synergistic effect of multiple components, it effectively overcomes the defects of limited activation efficiency and insufficient later strength of single systems, comprehensively improving the efficiency of the cementation reaction and the quality of the product. Moreover, it stabilizes and solidifies harmful ions and controls the leaching of easily soluble salts through a dual mechanism of chemical bonding and physical encapsulation. At the same time, instead of changing the crystal structure of titanium gypsum itself to meet curing requirements, the original state of titanium gypsum is directly treated and stabilized through an external curing system. This avoids the high-temperature calcination pretreatment step, reduces the complexity of the production process and energy consumption, and enables the efficient and standardized application of titanium gypsum in roadbed engineering.

[0018] Advantages of additional aspects of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0019] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0020] This embodiment proposes a titanium gypsum composite subgrade for highways, comprising a base material and a curing agent; the base material includes titanium gypsum, fly ash, curing agent and water; the curing agent includes lime, mineral powder, cement clinker, fly ash, sodium silicate, titanium gypsum and admixtures.

[0021] By using lime and sodium silicate to provide dual alkaline activation, cement clinker, mineral powder, and fly ash to provide multiple sources of cementitious components, and supplemented by the filling effect of the matrix, a composite and synergistic hydration hardening system is formed, effectively overcoming the shortcomings of single systems in terms of limited activation efficiency and insufficient later strength. Multiple sources of active components: The curing agent not only contains cement clinker that provides traditional silicate cementitious binders, but also mineral powders and fly ash with potential pozzolanic activity. These materials are activated in an alkaline environment and react with the calcium and sulfur components in titanium gypsum to generate more diverse and stable hydration products, such as various forms of CSH gel and ettringite, which contribute to strength in multiple ways.

[0022] Establishing an efficient activating environment: The addition of lime provides a continuous and stable strongly alkaline environment. Sodium silicate, as a highly efficient alkali activator and accelerator, can rapidly increase the pH value of the system, accelerate the hydration reaction rate of cementitious materials (including cement clinker, mineral powder, and fly ash), not only improving early strength but also laying a solid foundation for later strength development.

[0023] Synergistic and compacting effects of components: Titanium gypsum and fly ash not only act as the solidified material in the system but also as functional fillers. The fine particles have a good filling effect, which can optimize the particle size distribution of the system, fill the pores, and make the solidified body structure more compact, thereby improving strength and durability.

[0024] By fixing free ions through chemical reactions and sealing them within a dense solidified body through physical means, the risk of salt leaching and accompanying volume expansion is reduced at the source, thereby improving the long-term stability of the roadbed. Chemical bonding and solidification: The abundant CSH gel, ettringite, and other hydration products generated under strongly alkaline conditions possess enormous specific surface area and gelling properties. These products can adsorb, complex, or chemically bond potentially leaching metal ions (such as Mn) from titanium gypsum. 2+ Zn 2+ Cr 3+ (etc.) are fixed in their grid-like structure, transforming them into insoluble compounds, thereby greatly reducing the freeness and leaching of these ions.

[0025] Physical encapsulation and sealing: The large amount of hydration products generated in a multi-component system form a dense microstructure. This structure can physically encapsulate soluble salts, preventing them from contacting external moisture, thereby inhibiting salt dissolution and blocking the channels for outward migration.

[0026] By designing a curing system with sufficiently high activity, the necessity of crystal transformation of titanium gypsum raw materials is bypassed, and the raw titanium gypsum is directly processed, thus solving the problems of complex pretreatment processes and high energy consumption. Direct use of dihydrate gypsum: This involves using uncalcined titanium gypsum, primarily composed of calcium sulfate dihydrate. The strongly alkaline components and active cementitious components in the curing agent can react with the dihydrate gypsum, for example, to form more stable ettringite, without first converting it to hemihydrate or anhydrous gypsum.

[0027] Embracing the original state: The pretreatment requirements for titanium gypsum are extremely low, only requiring its moisture content to meet the construction requirements. Therefore, it only requires simple spreading and drying to reduce moisture, without the need for high-temperature calcination equipment that consumes a lot of energy. This simplifies the early process, reduces energy consumption and production costs, and makes large-scale application possible.

[0028] Specifically, by weight, the composition is 50-70 parts titanium gypsum, 25-40 parts fly ash, and 3-8 parts curing agent. The 50-70 parts of titanium gypsum effectively utilize industrial solid waste, reducing storage pressure; the 25-40 parts of fly ash provide both filling and activation without reducing the overall strength of the roadbed due to excessive dosage; and the 3-8 parts of curing agent precisely control the curing reaction, avoiding insufficient curing and strength due to insufficient dosage, or increased costs and potential roadbed shrinkage cracking due to excessive dosage. The synergistic effect of these three components achieves a balance between strength, solid waste utilization, and economy in the composite roadbed, resolving the challenge of balancing solid waste usage with roadbed performance.

[0029] When the moisture content of titanium gypsum in the base material is ≤40%, the proportion of titanium gypsum is 60-65 parts, fly ash is 30-35 parts, and curing agent is 4-5 parts.

[0030] When the moisture content of titanium gypsum is ≤40%, its own moisture can participate well in the curing reaction. At this point, the ratio of 60-65 parts titanium gypsum, 30-35 parts fly ash, and 4-5 parts curing agent can achieve the optimal synergistic effect of each component. The amount of titanium gypsum used can ensure the utilization rate of solid waste without causing the mixture to be too wet due to excessive moisture. The amount of fly ash can fill the gaps between titanium gypsum particles and improve the gradation. The amount of curing agent can just activate the activity of titanium gypsum and fly ash to generate sufficient strength substances, avoiding insufficient strength or cost waste caused by suitable moisture content but improper component ratio.

[0031] The curing agent, by weight, comprises 5-11 parts lime, 10-20 parts mineral powder, 15-25 parts cement clinker, 20-30 parts fly ash, 0.5-1.5 parts sodium silicate, 14-47 parts titanium gypsum, and 2.5-4.5 parts admixtures.

[0032] The amount of lime (5-11 parts) can be adjusted according to the required alkalinity of the system to ensure a suitable alkaline environment for the activation of active materials. Mineral powder (10-20 parts) plays a dual role in filling gaps and activating the material, participating in the hydration reaction while filling voids. Cement clinker (15-25 parts) serves as the main cementitious material, and its amount determines the early strength development. Fly ash (20-30 parts) synergizes with the fly ash in the base material, supplementing the pozzolanic activity. Sodium silicate (0.5-1.5 parts) regulates the reaction rate, ensuring coordinated development of early and later strength. Titanium gypsum (14-47 parts) further improves the utilization rate of solid waste, and its active components participate in the solidification reaction. Admixtures (2.5-4.5 parts) specifically improve various properties of the solidified material. Within this range, the synergistic effect of each component forms a ternary synergistic activation system that is superior to traditional systems in terms of strength, water resistance, and salinization control.

[0033] Based on the test results and considering various performance aspects and costs, the optimal mix proportion was determined to be: 8 parts lime, 15 parts mineral powder, 20 parts cement clinker, 25 parts fly ash, 1 part sodium silicate, 27.5 parts titanium gypsum, and 3.5 parts admixtures. Under this mix proportion, the modified titanium gypsum cured material exhibits good mechanical and road performance, meeting the requirements of road engineering, while also demonstrating good economic efficiency.

[0034] The fly ash has a moisture content of no more than 15% and a particle size distribution between 0.001 mm and 1.18 mm, of which the content of particles smaller than 0.075 mm is greater than 45%.

[0035] The moisture content of fly ash should not exceed 15% to avoid excessive moisture affecting the overall moisture content of the mixture. If the moisture content is too high, drying or other dehydration measures are necessary; otherwise, the mixture will be too wet, leading to wheel sticking during compaction. The fly ash particle size should be between 0.001mm and 1.18mm, with particles smaller than 0.075mm accounting for more than 45%. This particle size distribution allows the fly ash to better fill the voids between titanium gypsum particles, improving the gradation of the mixture. Smaller fly ash particles have a larger specific surface area, allowing them to participate more fully in the hydration reaction and synergistically generate more strength-enhancing substances with the curing agent components, improving the density and strength of the subgrade. If the particle size is too large or the content of small particles is insufficient, it will lead to insufficient void filling, decreased density, and consequently affect the bearing capacity and durability of the subgrade.

[0036] The admixtures include at least two of the following: an active activator, a nano-activator, a crystallizing anti-shrinkage agent, a water-reducing dispersant, and a surfactant. The active activator further activates the titanium gypsum and fly ash; the nano-activator promotes the hydration reaction to generate more high-strength hydration products; the crystallizing anti-shrinkage agent reduces shrinkage cracking during the curing process; the water-reducing dispersant improves the workability of the mixture and reduces water consumption; and the surfactant enhances the interfacial bonding between the components. The combination of admixtures can be tailored to specific needs to improve the strength, shrinkage resistance, and workability of the roadbed, ensuring that the roadbed meets the various requirements of highways.

[0037] Specifically: 1. Titanium plaster: The titanium gypsum material should be general industrial solid waste as specified in the national standard GB18599-2020. The concentration of any characteristic pollutant in the leachate obtained according to the method specified in the national environmental protection standard HJ557-2010 should not exceed the maximum allowable discharge concentration of the national standard "Integrated Wastewater Discharge Standard" (GB8978-1996) (the maximum allowable discharge concentration of Class II pollutants shall be implemented in accordance with the Class I standard), and the pH value should be within the range of 6 to 9.

[0038] 2. Fly ash: Wet fly ash should be used, with a moisture content not exceeding 15%. If the moisture content is high, measures such as drying should be taken to reduce moisture. Fly ash must not contain lumps, humus, or other impurities. The particle size should be between 0.001 mm and 1.18 mm, the content of particles smaller than 0.075 mm should be greater than 45%, the SO3 content should not exceed 3%, and the loss on ignition should be less than 20%.

[0039] 3. Special curing agent for titanium plaster; Using a special curing agent for titanium gypsum, the titanium gypsum fly ash mixture meets the technical specifications for roadbed filler after curing.

[0040] (1) Lime: Lime primarily functions as an alkaline activator in titanium gypsum modified curing agents. Its main component is calcium oxide (CaO). When lime comes into contact with water, a vigorous hydration reaction occurs, producing calcium hydroxide (Ca(OH)2), creating a strongly alkaline environment. This alkaline environment is crucial for activating the activity of materials such as mineral powder and fly ash.

[0041] (2) Mineral powder: Mineral powder, also known as finely ground blast furnace slag powder, is an ultrafine powder obtained by grinding blast furnace slag. In titanium gypsum modified curing agents, mineral powder has a dual function of filling and activating activity.

[0042] (3) Cement clinker: Cement clinker is an important cementing material in titanium gypsum modified curing agents, and its main mineral composition includes tricalcium silicate (3CaO•SiO2). 2） dicalcium silicate (2CaO•SiO) 2） Tricalcium aluminate (3CaO•Al2O) 3） and tetracalcium aluminoferrite (4CaO•Al2O3•Fe2O) 3） wait.

[0043] Cement clinker undergoes a hydration reaction with water, producing hydration products such as CSH gel, calcium hydroxide, and ettringite. Among these, CSH gel is the main source of strength in cement stone, calcium hydroxide provides an alkaline environment for the system, promoting the activation of active materials such as mineral powder and fly ash, and ettringite, formed by the reaction of tricalcium aluminate and titanium gypsum, further enhances the strength and durability of the cured material.

[0044] (4) Fly ash: Fly ash is an industrial waste emitted by coal-fired power plants. It possesses pozzolanic activity and plays a crucial role in titanium gypsum modification and curing agents. Its chemical activity primarily depends on the content of the vitreous phase and the content of amorphous SiO2 and Al2O3.

[0045] (5) Sodium silicate: Sodium silicate (Na2O•nSiO2) is mainly used as an accelerator and activator in titanium gypsum modified curing agents. Its aqueous solution is highly alkaline, which can rapidly increase the pH value of the system, accelerate the hydration reaction of cement clinker and the activation of mineral powder and fly ash, thereby improving the early strength of the cured material.

[0046] Meanwhile, the SiO2 component in sodium silicate can react with the Ca in the system. 2+ The reaction generates CSH gel, increasing the amount of hydration products and further enhancing the strength and density of the cured material. In addition, sodium silicate can improve the impermeability and corrosion resistance of the cured material, thus improving its durability.

[0047] (6) Titanium plaster: Titanium gypsum in the curing agent plays a triple synergistic role: First, as a sulfate activator, its provided sulfate ions can rapidly react with components such as calcium aluminate in the curing agent to form ettringite, providing early strength to the system and accelerating subsequent hydration reactions. Second, as a micro-aggregate, its fine particles can optimize the particle size distribution of the curing agent, fill pores, and improve density. Third, as a fixing component, it ensures the uniformity of the chemical composition of each batch of curing agent and the stability of the reaction effect. Titanium gypsum makes the curing agent a highly efficient reaction initiator, solving the problems of insufficient activation efficiency and slow early strength development of titanium gypsum in traditional systems.

[0048] (7) Admixtures: Although additives are used in small quantities in titanium gypsum modified curing agents, they can significantly affect the performance of the cured material. The additives used in this curing agent are composed of several components, including active activators, nano-activators, crystallization anti-shrinkage agents, water-reducing dispersants, and surfactants.

[0049] 4. Water: Not lower than the standard for irrigation water.

[0050] Fill material mix proportions, optimum moisture content, and wet density: 5. Recommended optimal mixing ratio: When the moisture content of titanium gypsum is ≤40%, the proportion of titanium gypsum is 60-65 parts, fly ash is 30-35 parts, and curing agent is 4-5 parts; when the moisture content of titanium gypsum exceeds 40%, the amount of fly ash should be increased.

[0051] Tests showed that the optimum moisture content of the fill material was 28%, and the moisture content during compaction should ideally be ±2% of the optimum moisture content; the measured wet density was approximately 17.0 kN / m³. 3 .

[0052] For each cubic meter of fill material, it is recommended to use 1000 kg of titanium gypsum, 600 kg of fly ash, and 60-100 kg of special curing agent. The amount of curing agent should be determined based on experiments.

[0053] Through orthogonal experiments, using 7-day and 28-day unconfined compressive strength as the main evaluation indicators, and combining other properties of the cured material (such as frost resistance, water resistance, shrinkage, etc.) and economy, the mix proportion was optimized and determined, as shown in Table 1 below: Table 1. Selection of Raw Materials and Mix Proportion Design for Curing Agent

[0054] This curing agent is mainly composed of raw materials such as lime, mineral powder, cement clinker, fly ash, sodium silicate, titanium gypsum, and additives. The curing mechanism is a ternary synergistic activation system of lime-fly ash-slag. The curing performance of this curing agent is compared with that of commonly used single and binary curing agents on the market. The test results are shown in the table below.

[0055] Table 2 Comparison of Experiments

[0056] As can be seen from Table 2 above, the ternary synergistic system is significantly better than the single or binary system in terms of strength, water resistance, and salinization control. In particular, the soluble salt content is reduced to 0.14%, which meets the requirements of non-saline soil subgrade (<0.3%).

[0057] This embodiment also provides a construction method for titanium gypsum composite subgrade applied to highways as described above, including: spreading titanium gypsum on the subgrade base, spreading fly ash, spreading a curing agent, mixing at least three times with a road mixer to ensure uniform mixing of materials, leveling the mixture, controlling the moisture content between 26% and 30%, and compacting with a road roller.

[0058] After spreading the titanium plaster, fly ash and hardener are sprinkled in sequence, and then mixed at least three times with a road mixer. This ensures that all materials are evenly mixed and avoids insufficient curing or poor strength caused by uneven local components. Leveling the mixture ensures the smoothness of the subgrade surface, laying the foundation for subsequent compaction. Controlling the moisture content to 26%–30% ensures that the mixture is in optimal condition during compaction, improving compaction degree. Using a road roller for compaction creates a dense structure in the mixture, enhancing the subgrade strength and stability, ensuring controllable subgrade construction quality, and meeting the construction requirements of highway subgrades.

[0059] Furthermore, the compaction process includes first using a vibratory roller for static compaction once, then two passes of weak vibration compaction, two passes of strong vibration compaction, and finally one pass of static compaction to finish the surface.

[0060] First, a static compaction pass allows the mixture to initially take shape, preventing it from shifting during subsequent vibratory compaction. Two passes of weak vibratory compaction gradually increase the mixture's density while minimizing damage to the initially formed structure. Two subsequent passes of strong vibratory compaction further enhance density, ensuring the roadbed meets design strength requirements. Finally, a static compaction pass finishes the surface, improving its smoothness and eliminating wheel tracks left by vibratory compaction. This compaction combination ensures thorough compaction of the roadbed from the surface to the deeper layers, preventing localized undercompaction and guaranteeing consistent overall strength and stability.

[0061] After leveling, use a level to check the elevation control points, and set up a test section at a set distance. Use the sand cone method to check the compaction degree to ensure that the compaction degree meets the design requirements.

[0062] Using a level to check elevation control points ensures that the roadbed elevation meets design requirements, preventing excessive elevation deviations that could affect subsequent pavement construction. By setting up test sections at predetermined intervals and using the sand cone method to test compaction, the compaction quality of all parts of the roadbed can be comprehensively monitored, allowing for the timely detection and remediation of areas with insufficient compaction. Through these tests, effective control over roadbed construction quality can be achieved, ensuring that the roadbed compaction meets design requirements, thereby guaranteeing the roadbed's strength and stability and meeting the long-term service requirements of the highway.

[0063] Construction process requirements: 1. Titanium gypsum fly ash roadbed fill material should be filled and compacted in layers, with the compacted thickness of each layer preferably controlled between 20 and 30 cm. When filling in different work sections, steps should be reserved in the first section, and each compacted layer should overlap each other with an overlap length of not less than 150 cm. The compaction degree within the joint area of ​​adjacent work sections should meet the specified requirements.

[0064] 2. During construction, attention should be paid to monitoring the moisture content changes of the fill material. The moisture content during compaction should ideally be within ±2% of the optimum moisture content. After paving, it should be compacted promptly at the optimum moisture content, ensuring that paving and compaction are completed on the same day. The edging soil should be compacted simultaneously with the fly ash fill.

[0065] 3. It is advisable to use a 22t or larger single-drum vibratory roller for compaction.

[0066] 4. Mixing: The titanium gypsum-fly ash roadbed fill material is mixed on-site using a road mixer. The spread fill material is crushed and mixed using a road mixer. Three mixing processes are performed during construction: the first mixing is done after spreading the titanium gypsum material; the second mixing is done after spreading the fly ash material; and the third mixing is done after the curing agent is applied using a concrete placing boom. After mixing, the fill material should have a uniform color, be free of ash streaks and spots, and have a uniform overall layer size, with particle size meeting compaction requirements. During the mixing process, a designated person should accompany the machine to continuously check the mixing depth. If the mixing depth is too deep or too shallow, the road mixer operator should be contacted immediately to adjust the mixing depth. The mixing machine's travel speed should be controlled during the mixing process, generally requiring 3–6 m / min.

[0067] 5. Leveling: Use a bulldozer for rough leveling, followed by a grader for fine leveling. Leveling should proceed from the center outwards, ensuring the smoothness after leveling is ≤20mm. Repeat this process three times. On-site personnel should be present to address any small potholes and remove debris. During leveling, a slight cross slope should be created in the roadbed to facilitate drainage. After leveling, manual string lines should be used to remove any protruding parts.

[0068] To ensure the compaction and stability of the roadbed edges, the paving width of the fill material is 50cm wider on each side than the design width. Considering the pre-compaction effect of the bulldozer's own weight on the fill material during paving, the loose paving thickness is controlled by the bulldozer's paving thickness. After the bulldozer paving, elevation control points are set out with a level, their elevations are measured, and the loose paving thickness of the fill material after the bulldozer has roughly leveled the surface is calculated.

[0069] 6. Compaction: (1) Inspection before compaction: The moisture content must be controlled to meet the compaction requirements. If the moisture content is too high, it needs to be dried. The moisture content of the filling material should be controlled within ±2% of the optimum moisture content.

[0070] (2) Compaction: The compaction combination for the roadbed is tentatively set as follows: the first pass of the 22t roller is a static compaction using a vibratory roller, followed by two passes of weak vibration compaction and two passes of strong vibration compaction using the vibratory roller. Finally, the surface is compacted once using a roller.

[0071] Before compaction, the loose thickness and flatness of the fill layer must be checked, and compaction can only proceed if they meet the requirements. Static compaction should be performed first, followed by vibratory compaction. The offset width between the rollers on the vibratory roller should not be less than 1 / 3 of the compaction wheel width. For straight sections of the roadbed, compaction should be carried out from both sides towards the middle, while for curved sections, compaction should be carried out from the lower side towards the higher side. The roller's travel speed should not exceed 4 km / h, and compaction should be carried out to ensure no missed areas or dead zones, and to ensure uniform compaction. Uneven areas should be leveled manually. During compaction, the roller must not stop, turn, or brake midway.

[0072] Compaction should proceed from the edges to the center to form a road crown; start with lighter compaction and gradually increase the weight to accommodate the gradually increasing subgrade strength; start slowly and gradually increase the speed to prevent loose soil from being pushed away by machinery. Simultaneously, the road surface should be leveled before compaction, forming a 2%–4% cross slope from the centerline towards both sides of the embankment. When compacting on curves, compaction should proceed from the lower edge to the higher edge to create a unidirectional superelevation. The wheel tracks should overlap by 12cm–20cm. Special attention should be paid to controlling the uniformity of compaction to avoid uneven settlement.

[0073] (3) Compaction degree test: Each test point of the cross section is set up in 20-meter intervals and all tests are carried out. Starting from the first pass of strong vibration, the density (using the sand cone method) and elevation measurement are carried out on the set test points after each pass of rolling to determine the loose thickness and compaction thickness when the qualified requirements are met, and record the process parameter data such as the number of passes of the road roller.

[0074] 7. Inspection and Acceptance (1) Loose paving thickness inspection and control: Before the embankment is filled, left, middle and right stakes are laid out every 20m and the elevation of the point is measured with a level. Bamboo poles are nailed at the stake positions and red paint is marked at the loose paving thickness elevation position to effectively control the loose paving thickness and facilitate construction. If any frost heave or rebound is found, it is dug out with an excavator, repaved and re-compacted.

[0075] (2) Acceptance: After the embankment is compacted to a qualified standard, it is compacted once with a 22T vibratory roller. During the acceptance, the surface of the roadbed working surface is required to be flat and dense, without pits, frost heave, soft elasticity, obvious wheel tracks, etc. After the acceptance is qualified, the next step of construction can be carried out.

[0076] In summary, this embodiment proposes a titanium gypsum composite subgrade for highways based on titanium gypsum modification and curing. Titanium gypsum, fly ash, and other materials are uniformly mixed with a special modifying and curing agent and water in the required proportions to form a highway subgrade filling material. This material is then layered and compacted to form a composite subgrade. After testing and acceptance, the next construction step can proceed. This method offers the following technical advantages: (1) Strength improvement: Density after curing ≥ 17.0 kN / m 3 (13% improvement over traditional materials); (2) Waste utilization: Titanium gypsum utilization rate > 60%, fly ash utilization rate > 30%; (3) Construction efficiency: Layered compaction reduces rework rate and shortens construction period by 15%; (4) Environmental protection: Reduces pollution from titanium gypsum stockpiling and conforms to solid waste resource utilization.

[0077] While the specific embodiments of the present invention have been described above, they are not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A titanium-gypsum composite subgrade for highways, characterized in that, Includes base material and curing agent; The base material includes titanium gypsum, fly ash, curing agent and water; The curing agent, by weight, comprises 5-11 parts lime, 10-20 parts mineral powder, 15-25 parts cement clinker, 20-30 parts fly ash, 0.5-1.5 parts sodium silicate, 14-47 parts titanium gypsum, and 2.5-4.5 parts admixtures.

2. The titanium-gypsum composite subgrade for highways as described in claim 1, characterized in that, By weight, 50-70 parts titanium gypsum, 25-40 parts fly ash, and 3-8 parts curing agent.

3. The titanium-gypsum composite subgrade for highways as described in claim 2, characterized in that, When the moisture content of titanium gypsum in the base material is ≤40%, the proportion of titanium gypsum is 60-65 parts, fly ash is 30-35 parts, and curing agent is 4-5 parts.

4. The titanium-gypsum composite subgrade for highways as described in claim 1, characterized in that, The ingredients are: 8 parts lime, 15 parts mineral powder, 20 parts cement clinker, 25 parts fly ash, 1 part sodium silicate, 27.5 parts titanium gypsum, and 3.5 parts admixtures.

5. The titanium-gypsum composite subgrade for highways as described in claim 1, characterized in that, The moisture content of the fly ash shall not exceed 15%.

6. The titanium-gypsum composite subgrade for highways as described in claim 1, characterized in that, The particle size distribution of pulverized coal ranges from 0.001 mm to 1.18 mm, with particles smaller than 0.075 mm accounting for more than 45%.

7. The titanium-gypsum composite subgrade for highways as described in claim 1, characterized in that, The additives include at least two of the following: active activators, nano-activators, crystallizing anti-shrinkage agents, water-reducing dispersants, and surfactants.

8. A construction method for titanium-gypsum composite subgrade for highways as described in any one of claims 1-7, characterized in that, Includes the following steps: Spread titanium gypsum on the roadbed, sprinkle fly ash and hardener, and use a road mixer to mix at least three times to ensure the materials are evenly mixed. Level the mixture, control the moisture content between 26% and 30%, and use a road roller to compact it.

9. The construction method as described in claim 8, characterized in that, The compaction process includes first using a vibratory roller for static compaction once, then two passes of weak vibration compaction, two passes of strong vibration compaction, and finally one pass of static compaction to finish the surface.

10. The construction method as described in claim 8, characterized in that, After leveling, use a level to check the elevation control points, and set up a test section at a set distance. Use the sand cone method to check the compaction degree to ensure that the compaction degree meets the design requirements.

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