Roadbed filler based on calcium carbonate industrial solid waste and red clay collaborative improvement and construction method thereof

Abstract

This invention discloses a roadbed filler material based on the synergistic improvement of calcium carbonate industrial solid waste and red clay, and its construction method, belonging to the technical field of roadbed filler materials. The raw materials of the roadbed filler material based on the synergistic improvement of calcium carbonate industrial solid waste and red clay, by weight, include: 40-65 parts calcium carbonate industrial solid waste, 30-55 parts red clay, 0.2-0.6 parts citric acid, 2-5 parts alkali-modified sugarcane bagasse, 0.5-1 parts sodium-based bentonite, and 1-2 parts silica fume. This invention, by replacing purchased sand and gravel with calcium carbonate industrial solid waste, can efficiently dispose of solid waste and reduce carbon emissions. The synergistic effect of citric acid and medium-temperature roasting further promotes the CaO reduction of calcium carbonate industrial solid waste. 2+ The dissociation process, combined with sodium-based bentonite, further reduces the shrinkage rate and liquid limit of red clay. The addition of alkali-modified bagasse strengthens the interface and improves long-term road performance. The construction method of this invention is simple, balances environmental protection, performance, and economy, and is suitable for transportation infrastructure needs, demonstrating significant application value.

Description

Technical Field

[0001] This invention relates to the field of roadbed fill technology, and in particular to a roadbed fill material based on the synergistic improvement of calcium carbonate industrial solid waste and red clay, and its construction method. Background Technology

[0002] In the field of transportation infrastructure construction, the subgrade, as the basic structural layer of the pavement, directly determines the overall stability and durability of the road project through the performance of its filler material. Subgrade filler mainly refers to the engineering materials used in the main filling layer of the subgrade. Its core functions include transferring the superstructure load to the foundation, restraining subgrade deformation, and maintaining the overall structural stability. The performance of subgrade filler mainly relies on the dual mechanism of "dense particle size distribution + small amount of cementing": by optimizing the particle size distribution to form a dense skeleton structure, and by using the cementing effect of low-volume (usually ≤5%) cementing materials to improve the overall integrity. However, traditional subgrade filler has two major contradictions: first, the performance defects of natural materials lead to poor engineering adaptability; second, the level of industrial solid waste resource utilization still needs to be further improved.

[0003] Red clay, due to its wide distribution and abundant reserves, has promising applications in the field of filler soil. However, due to its inherent defects such as high liquid limit (≥50%), high plasticity index, easy softening upon contact with water, and easy shrinkage upon water loss, it is prone to inducing settlement cracking and insufficient impermeability when directly used as roadbed filler soil. Therefore, it is not suitable for direct use as roadbed filler soil. To improve its performance, the traditional improvement method usually involves adding 30-40% purchased sand and gravel aggregate to suppress its wet expansion and dry shrinkage deformation. However, this treatment method is costly and violates the concept of resource sustainability. At the same time, the addition of excessive aggregate will dilute the fine-grained components in the soil, weaken the cohesion between particles and the overall structure, especially under long-term dynamic loads and wet-dry cycles, leading to an increased risk of segregation, strength reduction, and uneven settlement within the filler layer.

[0004] Currently, the marble and limestone processing industries generate a large amount of calcium carbonate industrial solid waste, which is traditionally disposed of primarily through landfill. Although some studies have attempted to use it for soil stabilization, existing technological approaches have significant limitations: when using calcium carbonate industrial solid waste alone, approximately 5% cement needs to be added as an activator, increasing the overall cost by more than 35%; furthermore, the utilization of calcium carbonate industrial solid waste in current technologies remains at a preliminary stage. Therefore, when using this material as a raw material for roadbed filler, the product performance is usually limited without the addition of a high proportion of silicate cement for chemical activation.

[0005] In the existing technology, there is no technical solution that can efficiently, cost-effectively, and on a large scale dispose of calcium carbonate industrial solid waste, thoroughly improve the road performance of red clay, and meet the environmental protection requirements of the entire life cycle of roadbed filling. This hinders the advancement of resource-saving and environmentally friendly transportation infrastructure construction. Summary of the Invention

[0006] The purpose of this invention is to provide a roadbed fill material and its construction method based on the synergistic improvement of calcium carbonate industrial solid waste and red clay, thereby solving the aforementioned problems in the background art. This invention, by replacing purchased sand and gravel with calcium carbonate industrial solid waste, can efficiently dispose of solid waste and reduce carbon emissions. The synergistic effect of citric acid and medium-temperature roasting further promotes the Ca2+ oxidation of the calcium carbonate industrial solid waste. 2+ The dissociation process, combined with sodium-based bentonite, further reduces the shrinkage rate and liquid limit of red clay. The addition of alkali-modified bagasse strengthens the interface and improves long-term road performance. The construction method of this invention is simple, balances environmental protection, performance, and economy, and is suitable for transportation infrastructure needs, demonstrating significant application value.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] One of the technical solutions of this invention is to provide a roadbed filler material based on the synergistic improvement of calcium carbonate industrial solid waste and red clay, wherein the raw materials, by mass parts, include:

[0009] The mixture consists of 40-65 parts calcium carbonate industrial solid waste, 30-55 parts red clay, 0.2-0.6 parts citric acid, 2-5 parts alkali-modified sugarcane bagasse, 0.5-1 parts sodium bentonite, and 1-2 parts silica fume.

[0010] Preferably, the calcium carbonate industrial solid waste is a processing byproduct of marble, limestone, or calcite.

[0011] Preferably, the calcium carbonate industrial solid waste contains powder with an average particle size of less than 0.075 mm and coarse aggregate with an average particle size of 5-10 mm, and the mass ratio of the powder to the coarse aggregate is 45-60:40-55.

[0012] Calcium carbonate industrial solid waste powder within the particle size and proportion range defined in this invention can effectively fill the pores between aggregates.

[0013] Preferably, the calcium carbonate industrial solid waste powder is subjected to medium-temperature roasting treatment before use; the temperature of the medium-temperature roasting treatment is 300-400℃, and the time is 1-2h.

[0014] Preferably, the method for preparing the alkali-modified bagasse includes the following steps: crushing the bagasse to an average particle size of 3-6 mm, and then soaking it in a 5-8 wt% NaOH aqueous solution for 2-3 hours to obtain the alkali-modified bagasse.

[0015] Preferably, the silica fume has an average particle size of 0.1-0.3 μm and a specific surface area of ​​15-30 m². 2 / g.

[0016] Preferably, the average particle size of the sodium-based bentonite is 10-50 μm.

[0017] The second technical solution of this invention provides a construction method for the above-mentioned roadbed fill material based on the synergistic improvement of calcium carbonate industrial solid waste and red clay, comprising the following steps:

[0018] All raw materials except citric acid are mixed according to their mass proportions to obtain a dry mixture;

[0019] Dissolve citric acid in water to obtain a mixed water solution;

[0020] Mix the mixing water with the dry materials to obtain the mixture;

[0021] The mixture is laid on the road surface to be constructed using a layered filling method, compacted, and cured to complete the preparation.

[0022] Preferably, the moisture content of the mixture is 12-15 wt%.

[0023] Preferably, the maintenance period is 7 days.

[0024] The technical principle of this invention is as follows:

[0025] The microparticles in the calcium carbonate industrial solid waste powder added in this invention can fill the pore structure inside the matrix material (red clay often forms many pores due to its agglomeration) through their particle morphology characteristics, achieving physical compaction; at the same time, the calcium carbonate (CaCO3) contained in these microparticles can dissociate into Ca 2+ Ca 2+ As an active activator, it reacts with clay minerals in red clay (mainly kaolinite and illite, with a small amount of montmorillonite) through ion exchange, hydration, or pozzolanic reactions, improving product properties. Specifically, the dissociated Ca... 2+ On the one hand, it can replace the weakly bound water between the mineral layers of red clay through ion exchange, thereby reducing the dispersibility and swelling of clay particles; on the other hand, Ca... 2+ It can promote the slow hydration reaction of aluminosilicate components in red clay, generating low-crystallinity cementitious substances (hydrated calcium silicate, hydrated calcium aluminate, etc.), thereby stimulating the potential activity of red clay and further improving its mechanical strength (resistance to compressive density, cohesion, etc.) and water stability (resistance to impermeability, resistance to softening, etc.).

[0026] However, while limiting the particle size of calcium carbonate industrial solid waste powder to a lower level can increase the specific surface area and improve the Ca content per unit mass, it is not the only method that can achieve this.2+ The dissociation rate is high, but its dissolution-dissociation equilibrium in roadbed fillers is still severely biased towards the undissociated state, resulting in a limited amount of Ca that can actually participate in the reaction. 2+ The proportion of Ca in the total Ca content of solid waste is still extremely low. Therefore, how to further promote Ca... 2+ Deconvolution is the key to overcoming performance bottlenecks.

[0027] The addition of citric acid can consume Ca. 2+ CO3 produced by dissociation 2- This promotes Ca 2+ Continued dissociation; and the citrate produced by the reaction can react with Ca 2+ Synergistically improve the bonding strength of roadbed filler.

[0028] However, the amount of citric acid added should not be too high, otherwise it will corrode the hydroxyl groups (-OH) on the surface of red clay particles, destroying the interlayer bonding force of mineral components such as kaolinite and illite. This will cause the plasticity of the subgrade filler to fail to meet the subgrade requirements, making it more prone to stability problems such as drying shrinkage cracking and wet swelling deformation. The pH drop caused by excessive citric acid will also directly inhibit the gelation reaction rate, preventing the formation of an effective cementitious structure.

[0029] To further promote Ca 2+ In addition to dissociation, the present invention also subjected calcium carbonate industrial solid waste powder to medium-temperature roasting treatment, so as to remove adsorbed water and crystal water on the surface of the particles, forming a porous and loose structure, increasing the specific surface area and reactivity.

[0030] Sodium-based bentonite releases Na + K can be found between red clay layers + / H + Ion exchange occurs, further compressing the clay double layer and reacting with Ca. 2+ Together, they reduce the expansibility of red clay.

[0031] Through actual testing, this invention revealed that when only calcium carbonate industrial solid waste powder with a particle size of less than 0.075 mm is used, it is difficult to form an effective skeleton, leading to compressive deformation of the roadbed after long-term load bearing. However, the use of coarse aggregate from calcium carbonate industrial solid waste can form a rigid skeleton, improve aggregate support, and thus further improve the compaction and compressive strength of the roadbed.

[0032] The red clay and calcium carbonate industrial solid waste used in this invention have a weak interfacial bonding: red clay is hydrophilic clay, while the solid waste is a hydrophobic mineral. A water film gap easily forms at the interface, leading to easy delamination after long-term wet-dry cycles, causing roadbed cracking and insufficient long-term crack resistance. However, the alkali-modified sugarcane bagasse introduced in this invention can act as an interfacial enhancer, strengthening the interfacial bonding. After alkali modification, hydroxyl (-OH) and carboxyl (-COOH) groups are generated on the surface of the alkali-modified sugarcane bagasse, changing it from hydrophobic to amphiphilic. It can form hydrogen bonds with the hydroxyl groups on the surface of red clay and with the Ca groups on the surface of calcium carbonate solid waste. 2+ It forms coordination bonds and eliminates gaps in the water film. Alkali-modified bagasse is distributed in a network in the raw material and can form a bridging structure at the interface. When the roadbed is subjected to micro-stress caused by wet-dry cycles, the joints can absorb the stress and inhibit crack propagation.

[0033] The beneficial technical effects of the present invention are as follows:

[0034] This invention utilizes industrial solid waste from the calcium carbonate industry to replace purchased sand and gravel, achieving efficient solid waste disposal and reducing carbon emissions. The synergistic effect of citric acid and medium-temperature roasting further promotes the CaO reduction of the industrial solid waste. 2+ Dissociation, in conjunction with sodium-based bentonite, further reduces the swelling rate and liquid limit of red clay. The addition of alkali-modified bagasse strengthens the interface and improves long-term road performance.

[0035] This invention does not require the addition of cement; it achieves improvement solely through the synergistic effect between solid waste, citric acid, silica fume, and other materials, resulting in lower costs compared to traditional cement-based solidification solutions.

[0036] This invention eliminates the need for additional aggregates, which is beneficial for achieving the dual goals of solid waste resource utilization and low-cost improvement.

[0037] This invention is simple to construct, takes into account environmental protection, performance and economy, and is suitable for the needs of transportation infrastructure, and has great application value. Detailed Implementation

[0038] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0039] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0040] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. It should be noted that any aspects of this invention not described in detail are conventional practices in the art and are not the focus of this invention.

[0041] The terms “comprising,” “including,” “having,” “containing,” etc., used in this invention are all open-ended terms, meaning that they include but are not limited to.

[0042] The calcium carbonate industrial solid waste used in the following embodiments and comparative examples of this invention are all by-products of marble processing. The average particle size of the calcium carbonate industrial solid waste powder is 0.053 mm, and the average particle size of the calcium carbonate industrial solid waste coarse aggregate is 7.6 mm. The calcium carbonate industrial solid waste used was subjected to the following medium-temperature calcination treatment before use: the calcium carbonate industrial solid waste was placed in a heating furnace and heated at 380°C for 2 hours.

[0043] The average particle size of the silica fume used in the following embodiments and comparative examples of the present invention is 0.21 μm, and the specific surface area is 24.7 m². 2 / g. The average particle size of the sodium-based bentonite used is 30.6μm.

[0044] The preparation method of alkali-modified bagasse used in the following embodiments and comparative examples of the present invention is as follows: the bagasse is crushed to an average particle size of 4-5 mm, then soaked in 7 wt% NaOH aqueous solution for 3 h, rinsed with water until neutral, and dried at 105 °C for later use to obtain alkali-modified bagasse.

[0045] All raw materials used in the following embodiments and comparative examples of the present invention are commercially available products.

[0046] Example 1

[0047] A roadbed filler based on the synergistic improvement of calcium carbonate industrial solid waste and red clay, wherein the raw materials, by mass parts, are:

[0048] The mixture consists of 53 parts calcium carbonate industrial solid waste (in which the mass ratio of powder to coarse aggregate is 52:48), 45 parts red clay, 0.5 parts citric acid, 4.5 parts alkali-modified sugarcane bagasse, 0.7 parts sodium-based bentonite, and 1.5 parts silica fume.

[0049] Example 2

[0050] A roadbed filler based on the synergistic improvement of calcium carbonate industrial solid waste and red clay, wherein the raw materials, by mass parts, are:

[0051] The mixture consists of 40 parts of calcium carbonate industrial solid waste (in which the mass ratio of powder to coarse aggregate is 52:48), 55 parts of red clay, 0.2 parts of citric acid, 2 parts of alkali-modified sugarcane bagasse, 0.5 parts of sodium-based bentonite, and 1 part of silica fume.

[0052] Example 3

[0053] A roadbed filler based on the synergistic improvement of calcium carbonate industrial solid waste and red clay, wherein the raw materials, by mass parts, are:

[0054] The mixture consists of 65 parts of calcium carbonate industrial solid waste (in which the mass ratio of powder to coarse aggregate is 52:48), 30 parts of red clay, 0.6 parts of citric acid, 3 parts of alkali-modified sugarcane bagasse, 1 part of sodium-based bentonite, and 2 parts of silica fume.

[0055] Comparative Example 1

[0056] The only difference from Example 1 is that the calcium carbonate industrial solid waste powder is replaced with an equal mass of mineral powder (average particle size of 0.05 mm), and the calcium carbonate industrial solid waste coarse aggregate is replaced with an equal mass of mineral powder (average particle size of 7 mm).

[0057] Comparative Example 2

[0058] The only difference from Example 1 is that the addition of calcium carbonate industrial solid waste powder is omitted and an equal mass of calcium carbonate industrial solid waste coarse aggregate is added.

[0059] Comparative Example 3

[0060] The only difference from Example 1 is that the addition of coarse aggregate from calcium carbonate industrial solid waste is omitted and an equal mass of calcium carbonate industrial solid waste powder is added.

[0061] Comparative Example 4

[0062] The only difference from Example 1 is that the addition of citric acid is omitted.

[0063] Comparative Example 5

[0064] The only difference from Example 1 is that the addition of alkali-modified sugarcane bagasse is omitted.

[0065] Example 2

[0066] A construction method for the above-mentioned roadbed fill material (Examples 1-3 and Comparative Examples 1-5) includes the following steps:

[0067] (1) Before construction, the subgrade (plain soil cushion layer) is inspected and compacted to a degree of ≥93% and a flatness deviation of ≤5mm / 3m. High-pressure water guns are used to clean the loose soil and debris on the surface of the subgrade to ensure that there are no loose particles on the surface.

[0068] (2) Add all raw materials except citric acid into the mixer according to the mass proportions, dry mix for 8 minutes to obtain a dry mixture with uniform color and no lumps;

[0069] Dissolve citric acid in water to obtain a mixed water solution;

[0070] Slowly inject the mixing water into the dry mixture and wet mix for 5 minutes to obtain a mixture with a moisture content of 12-15 wt%.

[0071] (3) The mixture is laid on the subgrade layer by layer filling, with each layer having a loose thickness of ≤30cm; water is sprinkled between layers to prevent interface peeling; a vibratory roller is used to compact the mixture under the same conditions; after compaction, the mixture is covered with geotextile and naturally cured for 7 days; water is sprinkled daily during the curing period to keep the moisture content at 10-12%.

[0072] Effect verification

[0073] The performance of the products from each embodiment and comparative example after construction according to the construction method of Example 2 was tested as follows. The test results are shown in Table 1.

[0074] 1. Mechanical properties and deformation control (refer to JTG E40-2007)

[0075]

[0076] 2. Refer to the "Specifications for Design of Highway Subgrade" (JTG D30-2015) to test the water-immersed CBR / dry CBR and permeability coefficient.

[0077]

[0078] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A roadbed filler based on the synergistic improvement of calcium carbonate industrial solid waste and red clay, characterized in that, Raw materials, by mass parts, include: 40-65 parts of calcium carbonate industrial solid waste, 30-55 parts of red clay, 0.2-0.6 parts of citric acid, 2-5 parts of alkali-modified sugarcane bagasse, 0.5-1 parts of sodium-based bentonite, and 1-2 parts of silica fume; The solid waste from the calcium carbonate industry is a processing byproduct of marble, limestone, or calcite. The calcium carbonate industrial solid waste contains powder with an average particle size of less than 0.075 mm and coarse aggregate with an average particle size of 5-10 mm, and the mass ratio of the powder to the coarse aggregate is 45-60:40-55. The preparation method of the alkali-modified bagasse includes the following steps: crushing the bagasse to an average particle size of 3-6 mm, and then soaking it in a 5-8 wt% NaOH aqueous solution for 2-3 hours to obtain the alkali-modified bagasse.

2. The roadbed filler material based on the synergistic improvement of calcium carbonate industrial solid waste and red clay according to claim 1, characterized in that, The calcium carbonate industrial solid waste powder was subjected to medium-temperature roasting treatment before use; the temperature of the medium-temperature roasting treatment was 300-400℃, and the time was 1-2h.

3. The roadbed filler material based on the synergistic improvement of calcium carbonate industrial solid waste and red clay according to claim 1, characterized in that, The silica fume has an average particle size of 0.1-0.3 μm and a specific surface area of ​​15-30 m². 2 / g.

4. The roadbed filler material based on the synergistic improvement of calcium carbonate industrial solid waste and red clay according to claim 1, characterized in that, The average particle size of the sodium-based bentonite is 10-50 μm.

5. A construction method for roadbed fill material based on the synergistic improvement of calcium carbonate industrial solid waste and red clay as described in any one of claims 1-4, characterized in that, Includes the following steps: All raw materials except citric acid are mixed according to their mass proportions to obtain a dry mixture; Dissolve citric acid in water to obtain a mixed water solution; Mix the mixing water with the dry materials to obtain the mixture; The mixture is laid on the road surface to be constructed using a layered filling method, compacted, and cured to complete the preparation.

6. The construction method according to claim 5, characterized in that, The moisture content of the mixture is 12-15 wt%.

7. The construction method according to claim 5, characterized in that, The maintenance period is 7 days.

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