Expressway roadbed filler, preparation method and construction process thereof

Abstract

The invention discloses an expressway roadbed filler, a preparation method and a construction process thereof, and belongs to the technical field of road engineering materials. Industrial solid waste ardealite and phosphate tailings are used as main raw materials of the roadbed filler, the mass ratio of the ardealite to the phosphate tailings is 3: 2-4: 1, fly ash and blast furnace slag are doped as curing agents, the mass ratio of the fly ash to the blast furnace slag is 7: 3-8: 2, and the total doping amount is 8%-10%. The exciting agent is calcium formate, a water glass solution or a sulfonate solution, and the doping amount is 0.5%-1.5%; admixtures such as hydroxyl or carboxyl long-molecular-chain polymers rich in double bonds, polysaccharides, nano-scale water-soluble fibers, water-retaining agents, flocculants, coupling agents and nano-silicon dioxide composite particles can be added according to performance requirements. According to the invention, industrial solid wastes are fully utilized, and the prepared roadbed filler has good compaction performance, high CBR value and excellent anti-scouring and anti-cracking performance, meets the technical requirements of highway roadbed fillers, and has both environmental protection and economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of road engineering materials technology, and relates to a roadbed construction technology, specifically a highway roadbed filler, its preparation method and construction process. Background Technology

[0002] Phosphogypsum (PG) is a major byproduct of the extraction of phosphoric acid and phosphate fertilizer from phosphate rock using sulfuric acid. Phosphogypsum is chemically acidic, and its composition is identical to natural gypsum, both being calcium sulfate dihydrate (CaSO4·2H2O). It also contains small amounts of fluorides (NaF, Na2SiF6, Na3AlF6, Na3FeF6, CaF2), sulfate ions (such as chromium, copper, zinc, and cadmium), and organic matter (aliphatic compounds like carbonic acid, amines, and ketones). These impurities adhere to the surface of the gypsum crystals, making phosphogypsum a highly polluting and land-consuming solid waste. Tailings, generated during phosphate ore beneficiation, also suffer from difficulties in storage and low utilization rates. Similar to phosphogypsum, phosphate tailings, as a byproduct of phosphate ore beneficiation, also suffer from low comprehensive utilization rates and large-scale storage. my country has abundant phosphate rock resources, but mining is difficult, with few high-grade and easily beneficiated ores and many low-grade and difficult-to-beneficiate ores. In recent years, the rapid growth in phosphate fertilizer production capacity and the increasing demand for phosphate chemical products have accelerated the development and utilization of phosphate rock resources. During the phosphate ore beneficiation process, approximately 41% of the ore becomes tailings and fails to be utilized in a timely manner, resulting in large-scale stockpiling on-site, causing resource waste and environmental pollution. Therefore, the efficient and comprehensive utilization of phosphate tailings is a crucial step in achieving green mining.

[0003] Currently, the resource utilization of phosphogypsum and tailings slag is mostly limited to building materials and landfill, and a large-scale technical system for highway subgrade filling has not yet been formed.

[0004] Traditional roadbed fillers rely heavily on natural sand and gravel resources, which are costly and unsustainable. However, utilizing phosphogypsum and tailings slag to prepare high-performance roadbed fillers can achieve the resource utilization of solid waste and reduce road construction costs, resulting in significant economic and environmental benefits. Summary of the Invention

[0005] This invention aims to solve the dual problems of pollution from phosphogypsum and phosphate tailings stockpiles and resource dependence on traditional roadbed fillers. It provides a highway roadbed filler, its preparation method, and its construction process. Using phosphogypsum and phosphate tailings as the main raw materials, through precise proportioning design, scientific mixing process, and standardized construction procedures, the filler possesses excellent mechanical properties, water stability, and environmental safety, fully meeting the technical requirements of highway roadbed fillers. To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a low-cost highway subgrade filler, composed of the following raw materials in the following weight proportions: The main ingredient consists of phosphogypsum and phosphorus tailings, with a mass ratio of phosphogypsum to phosphorus tailings of 5:5 to 9:1. The curing agent is composed of fly ash and blast furnace slag in a mass ratio of 6:4 to 9:1, and the total amount of the curing agent is 5% to 15% of the total weight of the main materials. The activator is at least two of the following: calcium formate, water glass solution, and lignosulfonate solution, with a total dosage of 1% to 3% of the total weight of the main material; Water; and Additives.

[0006] Preferably, the phosphogypsum is a byproduct of industrial wet-process phosphoric acid production.

[0007] More preferably, the phosphogypsum contains more than 80% gypsum, has been aged for no less than 2 years, has a pH value of no less than 3.0, and contains no less than 30% particles with a fineness of no less than 0.42 mm and less than 4.75 mm.

[0008] Preferably, the phosphorus tailings contain more than 30% silica by mass and more than 50% magnesium carbonate and calcium carbonate by mass.

[0009] More preferably, the phosphorus tailings are waste products generated during the beneficiation process of phosphate rock, and the aggregate particle size meets the requirements for aggregate specifications in the "Technical Specifications for Construction of Highway Pavement Base Course" (JTGTF20-2015).

[0010] Preferably, the ratio of selected phosphogypsum to phosphate tailings in the main material is 3:2-4:1.

[0011] Preferably, the fly ash is grade I fly ash, the blast furnace slag is granulated blast furnace slag, and the mass ratio of fly ash to blast furnace slag is 7:3-8:2 for optimal effect.

[0012] Preferably, the total content of the curing agent and the activator accounts for 8-10% of the total weight of the main material.

[0013] Preferably, the moisture content of the highway subgrade filler is 11.1%-15.1%, with an optimal moisture content of 13.1%.

[0014] Preferably, the activator comprises at least a water glass solution.

[0015] Preferably, the additive is at least one of toughening agent, water-retaining agent, flocculant, coupling agent and nano-active filler.

[0016] More preferably, the toughening agent is at least one of the following: a long-chain polymer rich in double-bonded hydroxyl or carboxyl groups, a polysaccharide, or a nanoscale water-soluble fiber.

[0017] More preferably, the long-chain polymer is a polyacryl alcohol emulsion; the polysaccharide is starch; the water-retaining agent is polyacrylamide; the flocculant is aluminum sulfate; the coupling agent is DL602 silane coupling agent; and the nano-active filler is nano-silica composite particles.

[0018] Secondly, the present invention provides a low-cost method for preparing highway subgrade filler, wherein the mixing is carried out using a forced twin-shaft mixer for two-stage continuous mixing, including the following steps: S1. Feed phosphogypsum, phosphate tailings, fly ash, and blast furnace slag into a primary mixer and mix them evenly. S2. Add the activator aqueous solution, mix well, and then continue stirring in a secondary mixer; S3. Add admixtures as needed and adjust the moisture content with water to the optimal level to obtain highway subgrade filler material suitable for construction.

[0019] Furthermore, in step S3, the optimal moisture content is 12.1%-14.1% (by mass).

[0020] After adjusting the moisture content, mix thoroughly to ensure the materials have a uniform color and are free of obvious lumps and stratification. During the mixing process, adjust the mixing time and speed as needed to ensure mixing quality.

[0021] Thirdly, the present invention provides a construction process for highway subgrade fill material, comprising the following steps: M1. In-situ surface treatment: Remove surface debris and vegetation, and compact the original ground surface; M2, Construction of cohesive soil sub-sealing layer: Cohesive soil is laid in layers and compacted. M3. Composite geotextile laying: The geotextile is laid and fixed on the compacted cohesive soil sub-seal layer; M4. Filling layer construction: The edging soil and highway subgrade fill material are filled in layers simultaneously and compacted layer by layer until the filling layer reaches the target thickness. M5. Upper sealing layer construction: The filling layer is compacted again.

[0022] Furthermore, in step M1, the compaction degree is not less than 90%, and the foundation bearing capacity is not less than 100 kPa.

[0023] Furthermore, in step M2, when spreading cohesive soil in layers, the loose layer thickness is ≤30cm, and the loose layer coefficient is controlled between 1.2 and 1.5; during compaction, a bulldozer is used for initial leveling and a grader for fine leveling, and the moisture content is controlled within the range of the optimum moisture content ±2%; the compaction sequence is: static pressure → weak vibration → strong vibration → static pressure, and the compaction degree is not less than 93%.

[0024] Furthermore, in step M3, the integrity of the geotextile should be checked before laying, and the cross-sectional and longitudinal overlap width should be ≥15cm, and it should be fixed with soil nails; after laying, the filling layer should be constructed in a timely manner to avoid prolonged exposure.

[0025] Furthermore, in step M4, during the construction of each layer, the edging soil and the highway subgrade fill material are filled simultaneously, and the contact area should be compacted 2-3 times more to ensure a tight bond.

[0026] Furthermore, in step M4, the moisture content of the highway subgrade filler needs to be tested before it is laid. If the moisture content exceeds the optimal range, watering or sun-drying is carried out to bring the moisture content within the range of ±2% (11.1%-15.1%) of the optimal moisture content.

[0027] Furthermore, in step M4, the highway subgrade fill material is produced using a centralized plant mixing method, and paving and compaction are completed within 48 hours after mixing. During compaction, a roller of 26t or more is used, and the compaction sequence is: 1 pass of static compaction → 1 pass of weak vibration → 4-6 passes of strong vibration → 1 pass of static compaction. The compaction speed is controlled at 1.5-2.0 km / h, the wheel track overlap is ≥40cm, and the longitudinal overlap is ≥2.0m.

[0028] Furthermore, in step M4, when the filling height of the filling layer is greater than 4m, a geogrid reinforcement layer is set between two adjacent layers; the geogrid should be taut and flat, and the overlap width should meet the requirements of the highway construction design specifications.

[0029] Furthermore, in step M4, during the layered synchronous filling process, the thickness of each loose layer is ≤30cm, and the loose layer coefficient is controlled between 1.2 and 1.5.

[0030] Furthermore, in step M4, after each layer of compaction is completed, compaction degree, deflection value, and CBR must be tested. Only after passing the tests can the next layer be laid. Otherwise, compaction is required again until it passes the tests.

[0031] Furthermore, in steps M2, M4, and M5, during the compaction process, the compaction degree is controlled at 93%~96%, preferably 95%, the CBR (California Bearing Ratio) is not less than 4%, and the deflection value is not greater than 150 (0.01mm).

[0032] Furthermore, in step M4, during the layered synchronous filling process, the joint treatment during layered paving is as follows: the joints between work sections should be stepped, with a step width of not less than 1m and a height equal to the compacted thickness, or an overlapping method should be used to ensure good overlap and avoid weak zones. Sections constructed on the same day should be continuously compacted to avoid the formation of longitudinal cold joints. Paving direction: paving should preferably proceed from the lower side of the roadbed to the higher side.

[0033] Furthermore, in step M4, during the compaction process of layered synchronous filling, the overlap width is as follows: the roller tracks should overlap; for vibratory compaction, the overlap is typically 1 / 3 to 1 / 2 of the roller width, and for static compaction, the overlap is 1 / 4 to 1 / 3 of the roller width. The driving route follows the principle of "light to heavy, slow to fast, static to vibratory, from the edge to the center, and from low to high."

[0034] The principle of this invention is as follows: Unlike pavement materials, subgrade materials, due to their inherent characteristics, have specific requirements, such as shear strength and rigidity, i.e., overall shear strength (CBR) and stiffness (resilience modulus) under large-scale, thick-layer filling. Strict control of total deformation and cumulative plastic deformation (settlement, rutting) is crucial. Compaction degree, CBR, and deflection value are key control indicators. Water stability and temperature stability (frost resistance) are paramount. The material must not experience significant strength reduction after water immersion or freeze-thaw cycles. It must be easily paved and compacted on a large scale in the field to achieve the required degree of compaction.

[0035] Common types of alkali activators in existing technologies include traditional calcium-based solidifying agents (carbide slag, quicklime, hydrated lime, calcium oxide, calcium hydroxide), strong alkali activators (sodium hydroxide, potassium hydroxide), and neutral salt activators (calcium chloride, sodium sulfate, sodium carbonate, aluminum sulfate). Traditional calcium-based solidifying agents mainly function by providing Ca(OH)₂, resulting in two effects: ion exchange-flocculation and pozzolanic reaction. Ion exchange-flocculation involves Ca… 2+ Replace the low-valent cations (such as Na) on the surface of soil particles + K + This process reduces the thickness of the electric double layer, causing particle flocculation and improving early strength. The pozzolanic reaction involves the reaction of Ca(OH)₂ with active SiO₂ and Al₂O₃ in fly ash and slag to form hydrated calcium silicate (CSH) gel. This is the main source of its long-term strength. For low-calcium, high-silica and high-alumina fly ash and slag, the alkalinity of Ca(OH)₂ (pH ~ 12.4) alone is insufficient to fully activate its activity; the reaction is slow and incomplete. Therefore, traditional calcium-based solidifying agents require large amounts to provide sufficient Ca. 2+ It is not economical in alkaline environments and may cause volume instability due to expansion; traditional calcium-based curing agents mainly generate CSH gel, which does not fully utilize the sulfate and aluminum phases in phosphogypsum. The generated CSH is easily decomposed in acidic environments (such as residual phosphoric acid and hydrofluoric acid in phosphogypsum), and its water stability is relatively poor.

[0036] The water glass in this invention provides an extremely high pH value (>13), which can rapidly and thoroughly disrupt the vitreous structure of fly ash / slag, releasing active silica and alumina. This invention not only generates CSH gel (calcium from slag), but also primarily generates a three-dimensional network geopolymer (NASH gel), which is denser, stronger, and more acid-resistant. In a high-alkali, high-calcium environment, the Ca of phosphogypsum... 2+ and SO4 2- It can effectively participate in the formation of ettringite, contributing early strength and micro-expansion, making the system denser.

[0037] Compared to strong base activators (sodium hydroxide, potassium hydroxide), strong base activators only provide alkalinity (OH-). - The reaction system does not provide soluble silicon (SiO2), and the source of silicon in the reaction system depends entirely on the dissolution of solid raw materials. This may result in an excessively low silicon-to-aluminum ratio in the initial liquid phase, leading to a large number of low-polymerization products that affect the strength and durability in the later stages. The reaction products also shrink significantly, which can easily cause cracking.

[0038] The water glass (Na2O·nSiO2) of this invention provides both high alkalinity (OH-) - It also directly provides soluble silicate ions (SiO3). 2- This allows for precise control of the silicon-to-aluminum ratio (n(SiO2) / n(Al2O3)) in the reaction system, which is key to forming a high-strength, high-stability geopolymer network.

[0039] Compared with neutral salt activators (calcium chloride, sodium sulfate, sodium carbonate, aluminum sulfate), neutral salt activators have insufficient or no alkalinity, and cannot effectively activate the potential activity of fly ash and slag.

[0040] Furthermore, polymer modifiers such as long-chain polymers rich in double-bonded hydroxyl or carboxyl groups, polysaccharides, nano-scale water-soluble fibers, water-retaining agents, flocculants, coupling agents, and nano-silica composite particles can encapsulate phosphogypsum, altering its crystal growth pattern and inhibiting crystal growth along the long axis. This causes calcium sulfate crystals to transform from slender to short and thick, allowing the growing heterogeneous crystals to produce a superimposed boron intercalation effect. Simultaneously, this polymer modifier interacts with the hydration products after alkali activation, and a unique three-dimensional nanofiber structure is embedded within the structure, resulting in a stable and dense structure of cement phosphogypsum hydrate. Moreover, the crystals generated by this system exhibit excellent water stability, avoiding the strong water absorption and looseness characteristic of pure phosphogypsum, which would lead to a decrease in the softening coefficient and mechanical strength of the phosphogypsum.

[0041] The formate ions in calcium formate can interfere with the formation of Ca(OH)2, promoting the formation of homogeneous C. S H-gel, simultaneously optimizing the formation rate of ettringite. Nanoscale water-soluble fibers can disperse well in the matrix and connect microcracks and micropores, thus limiting lateral deformation of the sample. The flocculant can reduce the Ca in the matrix... 2+ Mg 2+ F - SO4 2- ,PO4 3- Or charged particles approach each other, thus forming flocculent coagulation sediment.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Solid waste resource utilization: Large-scale utilization of phosphogypsum and phosphate tailings reduces environmental pressure. According to calculations, approximately 200,000 tons of a mixture of phosphogypsum and phosphate tailings will be consumed per kilometer. 2. Excellent performance: Through the synergistic effect of curing agent and activator, a stable structure is formed, with high CBR value and good water stability; 3. Convenient construction: The materials are readily available and the preparation process is simple, making it suitable for large-scale roadbed filling; 4. Environmental protection and safety: The solidification system can effectively fix harmful elements such as phosphorus and fluorine, and the leaching toxicity is lower than the national standard.

[0043] This invention effectively activates the potential activity of industrial solid waste through the synergistic effect of curing agents and activators, forming a stable gel structure. It not only solves the environmental pollution problems of phosphogypsum and phosphate tailings, but also produces high-performance roadbed fillers, taking into account both environmental protection value and engineering practicality. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0045] Figure 1 This is a process flow diagram of the preparation of roadbed filler in an embodiment of the present invention. Detailed Implementation

[0046] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0047] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can more clearly understand the present invention.

[0048] Example 1: The main material sources for the following examples are as follows: phosphogypsum and phosphate tailings are provided by Yidu Xingfa Chemical Co., Ltd., slag is provided by an ironmaking plant in Wuhan, fly ash is provided by Hubei Jiaotong Construction Group Co., Ltd., water glass solution and sulfonate solution are purchased from the market, and the admixtures are toughening agent polyacryl alcohol emulsion, water-retaining agent polyacrylamide, flocculant aluminum sulfate, and coupling agent KH550 silane coupling agent, all of which are purchased from the market.

[0049] A highway subgrade filler based on phosphogypsum and phosphate tailings is prepared from the following raw material components by weight ratio: phosphogypsum:phosphate tailings = 78:22 (mass ratio), solidifying agent: fly ash: blast furnace slag = 7:3, with a total admixture content of 10%. Activator: 1% water glass + 1% lignin sulfonate; water: controlled moisture content of 13.1%; toughening agent: 0.2% polyacryl alcohol emulsion; water-retaining agent: 0.2% polyacrylamide; flocculant: 0.2% aluminum sulfate; coupling agent: 0.2% KH550 silane coupling agent.

[0050] Example 2: The main material sources for the following examples are as follows: phosphogypsum and phosphate tailings were provided by Yidu Xingfa Chemical Co., Ltd., slag was provided by an ironworks in Wuhan, fly ash was provided by Hubei Jiaotong Construction Group Co., Ltd., calcium formate, water glass solution, and sulfonate solution were all purchased from the market, toughening agent: xanthan gum polysaccharide, water retention agent: polyacrylamide, flocculant: ferric sulfate, coupling agent: KH550 silane coupling agent, toughening agent: nano-sized water-soluble fiber, all of which were purchased from the market.

[0051] A highway subgrade filler based on phosphogypsum and phosphate tailings is prepared from the following raw material components by weight ratio: phosphogypsum:phosphate tailings = 7:3 (mass ratio), solidifying agent: fly ash: blast furnace slag = 8:2, with a total admixture of 10%. Activator: 1% water glass + 1% lignosulfonate + 1% calcium formate; Water: moisture content controlled at 13.1%; Toughening agent: xanthan gum polysaccharide 0.2%; Water retention agent: polyacrylamide 0.2%; Flocculant: ferric sulfate 0.2%; Coupling agent: KH550 silane coupling agent 0.2%; Toughening agent: nano-sized water-soluble fiber 0.2%.

[0052] Example 3: The main material sources for the following examples are as follows: phosphogypsum and phosphate tailings were provided by Yidu Xingfa Chemical Co., Ltd., slag was provided by an ironworks in Wuhan, fly ash was provided by Hubei Jiaotong Construction Group Co., Ltd., calcium formate, water glass solution, and sulfonate solution were all purchased from the market, and the admixtures were toughening agent: polyacryl alcohol emulsion, polysaccharide starch, water-retaining agent: polyacrylamide, flocculant: aluminum sulfate, coupling agent: DL602 silane coupling agent, and nano-active filler: nano-silica composite particles, all of which were purchased from the market.

[0053] A highway subgrade filler based on phosphogypsum and phosphate tailings is prepared from the following raw material components by weight ratio: phosphogypsum:phosphate tailings = 8:2 (mass ratio), solidifying agent: fly ash: blast furnace slag = 8:2, with a total admixture amount of 8%. Activator: 1% water glass + 1% lignosulfonate + 1% calcium formate; Water: moisture content controlled at 13.1%; Toughening agent: 0.2% polyacryl alcohol emulsion, 0.2% polysaccharide starch; Water retention agent: 0.2% polyacrylamide; Flocculant: 0.2% aluminum sulfate; Coupling agent: 0.2% DL602 silane coupling agent; Nano-active filler: 0.2% nano-silica composite particles.

[0054] The specific construction process of the above embodiments of the present invention includes the following steps: W1. Primary mixing: Phosphogypsum, phosphorus tailings, fly ash and blast furnace slag are fed into the primary mixer in proportion and mixed initially until the materials are evenly distributed. W2. Secondary mixing: Add an activator aqueous solution to the mixture after primary mixing, mix evenly, and then send it to a secondary mixer for continuous mixing to improve the material binding degree; W3. Conditioning and mixing: Add admixtures according to performance requirements, and add water to adjust to the optimal moisture content of 13.1%±1%. Mix thoroughly until the material color is uniform and there are no obvious lumps or stratification. During the mixing process, the mixing time and speed can be adjusted according to the material state to ensure the mixing quality and obtain a mixture for use as a filler in highway subgrade. W4. The material transport vehicle is responsible for transporting the mixed asphalt to the site to provide materials for base course paving. The asphalt should be loaded and transported immediately after mixing, with the time from mixing completion to delivery to the site not exceeding 3 hours; otherwise, the asphalt will easily begin to set. Simultaneously, a transport capacity control standard of 1.2 times the theoretical calculation value is used. Coordinate the operations of mixing, transportation, and paving to avoid downtime due to insufficient asphalt supply and waste caused by excessive supply.

[0055] W5. Original surface treatment: Remove surface debris and vegetation, compact the original ground, with a compaction degree of not less than 90% and a foundation bearing capacity of not less than 100kPa; W6. Construction of the cohesive soil sub-sealing layer: The cohesive soil is laid in layers with a loose layer thickness of ≤30cm; bulldozer is used for initial leveling and grader for fine leveling, and the moisture content is controlled within the range of optimum moisture content ±2%; the rolling sequence is: static pressure → weak vibration → strong vibration → static pressure, and the compaction degree is not less than 93%.

[0056] W7. Composite geotextile laying: Before laying, check the integrity of the geotextile, and the overlap width in both the horizontal and longitudinal directions should be ≥15cm. It should be fixed with soil nails. After laying, the upper layer of filling material should be constructed in a timely manner to avoid prolonged exposure.

[0057] W8. Filling layer construction: The edging soil and the highway subgrade fill material are filled in layers simultaneously and compacted layer by layer until the filling layer reaches the target thickness; the contact area should be compacted 2-3 more times to ensure a tight bond.

[0058] During the filling construction, the highway subgrade fill material is produced by centralized plant mixing, and paving and compaction are completed within 48 hours after mixing. Rollers of 26t or above are used, and the compaction sequence is: 1 pass of static compaction → 1 pass of weak vibration → 4-6 passes of strong vibration → 1 pass of static compaction. The compaction speed is controlled at 1.5-2.0km / h, the wheel track overlap is ≥40cm, and the longitudinal overlap is ≥2.0m.

[0059] When the height of the fill layer is greater than 4m, a geogrid reinforcement layer shall be set between the two adjacent layers; the geogrid shall be taut and flat, and the overlap width shall meet the requirements of the highway construction design specifications.

[0060] W9. Top sealing layer construction: The top sealing layer adopts an innovative construction process that follows the principle of excavator pressure stabilization + single steel wheel static pressure and vibration pressure + rubber wheel kneading + double steel wheel finishing; After the roadbed is filled and compacted, measurement and testing should be carried out in a timely manner. According to the "Specifications for Design of Highway Subgrade" (JTG D30-2015), the main quality control items are compaction degree, CBR and deflection value. The test results are shown in Table 1.

[0061] Table 1 Measurement Results After Subgrade Filling and Compaction

[0062] In Table 1, 0.01 mm is the unit of deflection value, and the tested deflection value is a multiple of this unit. The test results show that the filler has a high CBR value under different compaction degrees, which is much greater than the standard requirement. The deflection value does not exceed 30, which is much lower than the standard requirement of 150, thus meeting the strength requirements of highway subgrade filler.

[0063] For the subgrade filling during the construction of a highway using the technology of Example 1, the leachate of the highway subgrade filler at the filling point was tested in accordance with "HJ 1147-2020, GB 7484-1987, GB 8978-1996 Appendix D3". The test results are shown in Table 2 below.

[0064] Table 2 shows the test results of leachate from highway subgrade filler in the example.

[0065] It can be seen that the environmental protection requirements of the technology of this invention meet the national standards.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-cost highway subgrade filler, characterized in that, Composed of the following raw materials in the following weight proportions: The main ingredient consists of phosphogypsum and phosphorus tailings, with a mass ratio of phosphogypsum to phosphorus tailings of 5:5 to 9:

1. The curing agent is composed of fly ash and blast furnace slag in a mass ratio of 6:4 to 9:1, and the total amount of the curing agent is 5% to 15% of the total weight of the main materials. The activator is at least two of calcium formate, water glass solution, and sulfonate solution, with a total dosage of 1% to 3% of the total weight of the main material; Water; and Additives.

2. The low-cost highway subgrade filler according to claim 1, characterized in that, The phosphogypsum is a byproduct of industrial wet-process phosphoric acid production.

3. The low-cost highway subgrade filler according to claim 1, characterized in that, The phosphorus tailings contain more than 30% silica by mass and more than 50% magnesium carbonate and calcium carbonate by total mass.

4. The low-cost highway subgrade filler according to claim 1, characterized in that, The total content of the curing agent and activator accounts for 8-10% of the total weight of the main material.

5. The low-cost highway subgrade filler according to claim 1, characterized in that, The moisture content of the roadbed fill material for the highway is 11.1%-15.1%.

6. The low-cost highway subgrade filler according to claim 1, characterized in that, The additive is at least one of toughening agent, water-retaining agent, flocculant, coupling agent and nano-active filler.

7. The low-cost highway subgrade filler according to claim 6, characterized in that, The toughening agent is at least one of the following: a long-chain polymer rich in double-bonded hydroxyl or carboxyl groups, a polysaccharide, or a nanoscale water-soluble fiber.

8. A method for preparing low-cost highway subgrade filler according to any one of claims 1-7, characterized in that, Includes the following steps: The phosphogypsum, phosphate tailings, fly ash, and blast furnace slag are fed into a primary mixer and mixed evenly. Add the activator aqueous solution, mix well, and then transfer to a secondary mixer for further stirring. Add admixtures as needed and adjust the moisture content with water to the optimal level to obtain highway subgrade filler material suitable for construction.

9. A construction process for highway subgrade filler prepared by the method of claim 8, characterized in that, Includes the following steps: In-situ surface treatment: Remove surface debris and vegetation, and compact the original ground surface; Construction of cohesive soil sub-sealing layer: Cohesive soil is laid in layers and compacted. Composite geotextile laying: The geotextile is laid and fixed on the compacted cohesive soil sub-seal layer; Filling layer construction: The edging soil and highway subgrade fill material are filled in layers simultaneously and compacted layer by layer until the filling layer reaches the target thickness. Upper sealing layer construction: The filling layer is compacted again.

10. The construction process for highway subgrade fill material according to claim 9, characterized in that, During the construction of the cohesive soil lower sealing layer, the filling layer, and the upper sealing layer, the compaction degree of the rolling construction shall be controlled at 93%~96%, the CBR shall not be less than 4%, and the deflection value shall not be greater than 150mm.

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