Solid waste-based soil stabilizer for expansive soil as well as preparation method and application of solid waste-based soil stabilizer

Abstract

The invention discloses a solid-waste-based soil stabilizer for expansive soil as well as a preparation method and application of the solid-waste-based soil stabilizer. The solid-waste-based soil stabilizer comprises the following components in percentage by mass: 10-30% of waste concrete recycled micro powder, 10-30% of a curing agent and the balance of water, 5% to 10% of high belite sulphoaluminate cement; 1%-2% of phosphogypsum; 2%-4% of slaked lime; and 1%-3% of nano silicon dioxide. The two solid waste materials of the waste concrete recycled micro powder and the ardealite are effectively utilized, the problem that the volume stability is difficult to regulate and control in the expansive soil solidification process is solved, and resource utilization of all the solid wastes is promoted.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials and relates to a solid waste-based soil curing agent for expansive soil and a preparation method and application thereof. Background Art

[0002] Expansive soil is a type of soil that undergoes significant volume changes under wet or dry conditions, usually showing the characteristics of swelling when wet and shrinking when dry. This characteristic poses a serious threat to the stability of building foundations, roads and other civil engineering facilities. The shrinkage and expansion phenomenon of expansive soil not only affects the safety of engineering structures, but also increases the maintenance cost of the project. Therefore, improving the shrinkage performance of expansive soil and enhancing its mechanical properties have always been the focus of research in the field of civil engineering.

[0003] Existing improvement methods mainly include physical improvement and chemical solidification. Although physical improvement methods such as compaction and reinforcement can improve the mechanical properties of expansive soil, they have limited effects on long-term stability and shrinkage inhibition. Chemical solidification methods usually use curing agents such as cement and lime. Although these curing agents can effectively improve the performance of expansive soil, they have disadvantages such as environmental issues, high costs and limited effects.

[0004] In recent years, the resource utilization of solid waste has become an important environmental protection trend. Solid waste-based soil stabilizers, as a new type of improvement material, have received widespread attention. By converting solid waste resources such as industrial waste and agricultural waste into soil improvers, it can not only reduce costs but also help protect the environment. However, existing solid waste-based soil stabilizers still have certain shortcomings in improving the shrinkage performance of expansive soil and improving its long-term stability.

[0005] Therefore, developing an efficient and environmentally friendly solid waste-based soil solidifier that can effectively improve the shrinkage properties of expansive soil and enhance its mechanical properties is a technical problem that needs to be solved urgently. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology, and provide a solid waste-based soil solidifier for improving the shrinkage performance of solidified expansive soil, and a preparation method and application thereof, so as to solve the problems of severe shrinkage and unstable strength of existing solidified expansive soil.

[0007] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0008] A solid waste-based soil solidifier for expansive soil, comprising the following components in percentage by mass based on the mass of the dry expansive soil:

[0009] Waste concrete recycled powder 10%-30%;

[0010] High belite sulphoaluminate cement: 5%-10%;

[0011] Phosphogypsum: 1%-2%;

[0012] Hydrated lime: 2%-4%;

[0013] Nano-silica: 1%-3%.

[0014] As a further improvement, the particle size range of the waste concrete recycled fine powder is 10-100 μm, and the specific surface area is 700-800 m 2 / kg.

[0015] As a further improvement, the specific surface area of the high belite sulphoaluminate cement is 300-400 m 2 / kg.

[0016] As a further improvement, the average particle size of the phosphogypsum is 30-40 μm, the pH value is 2-3, and the mass percentage of calcium sulfate dihydrate is 90%-95%.

[0017] As a further improvement, the particle size range of the hydrated lime is 30-60 μm.

[0018] As a further improvement, the particle size range of the nano-silica is 15-25 nm.

[0019] The present invention also provides a preparation method of the solid waste-based soil stabilizer as described above, comprising the following steps:

[0020] 1) Stir and mix the phosphogypsum and the high belite sulphoaluminate cement evenly to obtain product ①;

[0021] 2) Add the waste concrete recycled fine powder to product ① and continue stirring to obtain product ②;

[0022] 3) Add the hydrated lime and the nano-silica to product ② and continue stirring until uniform to obtain the solid waste-based soil stabilizer.

[0023] As a further improvement, stir for 2-5 minutes after adding each new raw material.

[0024] The present invention also provides an application of the solid waste-based soil stabilizer as described above, comprising: mixing the solid waste-based soil stabilizer with the expansive soil, adding water and stirring, and then curing.

[0025] As a further improvement, the amount of water added for stirring is 65%-75% of the mass of the expansive soil.

[0026] By reasonably selecting the solid waste materials and their components and optimizing and modifying them, the present invention significantly improves the stability and shrinkage performance of the expansive soil. Compared with the prior art, the beneficial effects of the present invention are:

[0027] 1) The present invention uses recycled fine powder of waste concrete as one of the key components, and modifies it by using solid waste resources. This not only effectively solves the problem of the disposal of waste concrete, but also provides raw materials with good hydration activity and filler function. The introduction of recycled fine powder of waste concrete not only reduces the cost of the curing agent, but also has environmental protection significance, which is in line with the development trend of green building materials.

[0028] 2) The present invention forms a curing agent with a synergistic effect by reasonably proportioning a variety of active materials (recycled fine powder of waste concrete, high belite sulphoaluminate cement, phosphogypsum, slaked lime, nano-silica). Each component plays a different role in improving the shrinkage, strength and stability of expansive soil: the recycled fine powder of waste concrete restricts the shrinkage of expansive soil by providing a filler function and forming a gel network structure; high belite sulphoaluminate cement forms a gel network structure with stable strength through its hydration reaction, while reducing the shrinkage of expansive soil; phosphogypsum promotes the hydration of the cement aluminate phase and further strengthens the gel network; slaked lime promotes the reaction of the silica-alumina phase by providing an alkaline environment, generating CSH gel and further controlling shrinkage; nano-silica serves as a hydration reaction site, helps to form a microscopic skeleton structure and improves the curing effect. The synergistic effect of these multi-components can improve the performance of the cured expansive soil at multiple levels.

[0029] 3) Compared with the curing agents using a single component (such as single cement or lime) in the prior art, the curing agent of the present invention has multiple functions and can effectively improve the long-term stability of expansive soil. The interaction of different components not only enhances the compressive strength of expansive soil, but also significantly inhibits its shrinkage behavior, which is crucial for the long-term use of expansive soil. Detailed implementation manners

[0030] To facilitate the understanding of the present invention, the following will describe the present invention in a more comprehensive and detailed manner in combination with preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0031] Unless otherwise defined, all the professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0032] Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments and equipment used in the present invention can be obtained through market purchase or can be prepared by existing methods.

[0033] In some specific implementation manners, for the solid waste-based soil curing agent of the present invention, compared with dry expansive soil (with a mass of 100%), the curing agent includes the following components and mass percentage contents:

[0034] 10%-30% recycled fine powder of waste concrete;

[0035] 5%-10% high belite sulphoaluminate cement;

[0036] 1%-2% phosphogypsum;

[0037] 2%-4% slaked lime;

[0038] 1%-3% nano-silica.

[0039] In some embodiments, the recycled fine powder of waste concrete is generated when waste concrete is peeled and crushed, and the particle size range of the prepared recycled fine powder of waste concrete is (10-100) μm. The specific surface area of the recycled fine powder of waste concrete is (700-800) m 2 / kg, the loss on ignition is ≤2.5%, and the 28-day activity index is >115%. The recycled fine powder of waste concrete can exhibit a good filling effect and has a certain degree of hydration activity, which can form a gel network structure for solidifying expansive soil and effectively limit the shrinkage of solidified expansive soil.

[0040] In some embodiments, the main mineral components of the high belite sulphoaluminate cement are 30%-50% calcium sulfoaluminate, 40%-60% dicalcium silicate, 5%-10% tetracalcium aluminoferrite and 5%-10% calcium sulfate, and the specific surface area is (300-400) m 2 / kg. The aluminate phase in the high belite sulphoaluminate cement can react rapidly in the early stage of hydration to form a gel network structure with strength. Dicalcium silicate can ensure the stable development of later strength. At the same time, the calcium ions and aluminum ions generated during the hydration process can effectively reduce the thickness of the water film layer of soil particles, reduce the water consumption, and thus reduce the shrinkage of solidified expansive soil.

[0041] In some embodiments, the average particle size of the phosphogypsum is (30-40) μm, the pH value is 2-3, and the content of dihydrate calcium sulfate is 90%-95%. The phosphogypsum can effectively promote the hydration of the aluminum phase of the high belite sulphoaluminate cement and form sufficient ettringite to further reinforce the gel network structure.

[0042] In some embodiments, the particle size range of the slaked lime is (30-60) μm. The slaked lime can provide an alkaline environment, promote the dissolution of the silicon-aluminum phase in the solidified soil system to a certain extent, and undergo a pozzolanic reaction with it to produce CSH gel, thereby controlling shrinkage and providing strength.

[0043] In some embodiments, the particle size range of the nano-silica is (15 - 25) nm. The silica with this particle size can provide sites for the initial hydration of high belite sulphoaluminate cement in the system, thus ensuring the necessary conditions for the crystallization, cementation, filling of hydration products and hardening into a microscopic framework structure.

[0044] Preferably, except for nano-silica, the particle sizes of the remaining powders should be distributed between (10 - 100) μm to ensure the uniform mixing and reaction of each powder.

[0045] In some specific embodiments, the preparation method of the solid waste-based soil stabilizer of the present invention includes the following steps:

[0046] 1) Add phosphogypsum and high belite sulphoaluminate cement to the mixing tank according to weight percentages, start the mixing equipment to mix evenly, and obtain product ①;

[0047] 2) Add the waste concrete recycled fine powder with the corresponding weight percentage to product ① and continue to stir to obtain product ②;

[0048] 3) Add the corresponding weight percentages of slaked lime and nano-silica to product ②, and continue to stir until uniform to obtain the stabilizer product.

[0049] In some embodiments, it is recommended to control the stirring speed of each raw material between 100 - 200 rpm / min. After all the raw materials are mixed evenly, continue to stir for 2 - 5 minutes. If a large amount of accumulation occurs during the stirring process, the rotation speed should be reduced to 50 - 100 rpm / min. After adding each new raw material, stir for 2 - 5 minutes.

[0050] In some specific embodiments, the application of the solid waste-based soil stabilizer of the present invention includes: mixing the solid waste-based soil stabilizer and expansive soil according to the corresponding weight percentages, adding water for mixing, and the water consumption for mixing is 65 - 75% of the soil mass, and then curing.

[0051] The soil stabilizer of the present invention ensures a high hydration rate in the early stage and a stable increase in strength in the later stage of the stabilizer by adding high belite sulphoaluminate cement. At the same time, the calcium ions and aluminum ions released during the hydration process of high belite sulphoaluminate cement can effectively reduce the thickness of the water film layer of clay particles in the expansive soil and reduce the water demand. In addition, the filling effect of the waste concrete recycled fine powder and the synergistic hydration effect of phosphogypsum, slaked lime and nano-silica ensure the strength and volume stability of the cured expansive soil. The present invention effectively utilizes two solid waste materials, namely waste concrete recycled fine powder and phosphogypsum, solves the problem that the volume stability in the process of expansive soil curing is difficult to control, and promotes the resource utilization of the above-mentioned solid wastes.

[0052] In the following Examples 1 - 3 and Comparative Examples 1 - 4:

[0053] All raw materials are from the same batch to ensure comparability;

[0054] Among them, the particle size of recycled waste concrete powder is (10 - 100) μm, the average particle size of phosphogypsum is (30 - 40) μm, the particle size range of hydrated lime is (30 - 60) μm, and the particle size range of nano-silica is (15 - 25) nm;

[0055] The preparation method is as follows:

[0056] 1) Add phosphogypsum and high belite sulphoaluminate cement to the mixing tank according to the weight percentage, start the mixing equipment to mix evenly to obtain Product ①; if no phosphogypsum or high belite sulphoaluminate cement is added, directly proceed to the next step; if aluminate cement is used, it will replace the high belite sulphoaluminate cement;

[0057] 2) Add the corresponding weight percentage of recycled waste concrete powder to Product ① and continue mixing to obtain Product ②;

[0058] 3) Add the corresponding weight percentage of hydrated lime and nano-silica to Product ②, and continue mixing until uniform to obtain the curing agent product; if no nano-silica is added, it will be omitted.

[0059] Example 1:

[0060] A solid waste-based soil curing agent for improving the shrinkage performance of solidified expansive soil. Based on the amount used to solidify 1 kg of dry expansive soil, it includes the following components: 300 g of recycled waste concrete powder, 100 g of high belite sulphoaluminate cement, 15 g of phosphogypsum, 40 g of hydrated lime, and 25 g of nano-silica.

[0061] Example 2:

[0062] A solid waste-based soil curing agent for improving the shrinkage performance of solidified expansive soil. Based on the amount used to solidify 1 kg of dry expansive soil, it includes the following components: 200 g of recycled waste concrete powder, 100 g of high belite sulphoaluminate cement, 10 g of phosphogypsum, 30 g of hydrated lime, and 20 g of nano-silica.

[0063] Example 3:

[0064] A solid waste-based soil curing agent for improving the shrinkage performance of solidified expansive soil. Based on the amount used to solidify 1 kg of dry expansive soil, it includes the following components: 100 g of recycled waste concrete powder, 100 g of high belite sulphoaluminate cement, 15 g of phosphogypsum, 40 g of hydrated lime, and 25 g of nano-silica.

[0065] Comparative Example 1:

[0066] A solid waste-based soil stabilizer for improving the shrinkage performance of solidified expansive soil. Based on the amount used to solidify 1 kg of dry expansive soil, it includes the following components: 300 g of waste concrete recycled powder, 15 g of phosphogypsum, 40 g of slaked lime, and 25 g of nano-silica.

[0067] Comparative Example 2:

[0068] A solid waste-based soil stabilizer for improving the shrinkage performance of solidified expansive soil. Based on the amount used to solidify 1 kg of dry expansive soil, it includes the following components: 300 g of waste concrete recycled powder, 100 g of high belite sulphoaluminate cement, 40 g of slaked lime, and 25 g of nano-silica.

[0069] Comparative Example 3:

[0070] A solid waste-based soil stabilizer for improving the shrinkage performance of solidified expansive soil. Based on the amount used to solidify 1 kg of dry expansive soil, it includes the following components: 300 g of waste concrete recycled powder, 100 g of high belite sulphoaluminate cement, 15 g of phosphogypsum, and 40 g of slaked lime.

[0071] Comparative Example 4:

[0072] A solid waste-based soil stabilizer for improving the shrinkage performance of solidified expansive soil. Based on the amount used to solidify 1 kg of dry expansive soil, it includes the following components: 300 g of waste concrete recycled powder, 100 g of aluminate cement, 15 g of phosphogypsum, 40 g of slaked lime, and 25 g of nano-silica.

[0073] Comparative Example 5:

[0074] Commercially available stabilizer, with the main component being portland cement. Based on the amount used to solidify 1 kg of dry expansive soil, 100 g is added.

[0075] Mix the stabilizers in the above examples and comparative examples with soil (expansive soil) in proportion. The mixing water consumption is 70% of the soil mass, and specimens of 40 mm×40 mm×40 mm are prepared. Place the specimens in a standard curing room at a temperature of 20±2 °C, and measure the compressive strength after 28 days of curing. At the same time, prepare specimens of 40 mm×40 mm×160 mm, place them for indoor curing, control the room temperature at 20±2 °C, and to accelerate drying, control the humidity between 40% - 50%, and use a dilatometer to measure the drying shrinkage rate at 28 days.

[0076] The following table shows the results of 28-day compressive strength / 28-day drying shrinkage rate examples:

[0077] Specimen 28-day compressive strength (MPa) 28-day drying shrinkage rate (%) Example 1 3.5 0.22 Example 2 3.0 0.29 Example 3 2.6 0.54 Comparative Example 1 0.5 2.83 Comparative Example 2 3.1 0.29 Comparative Example 3 3.2 0.32 Comparative Example 4 3.0 0.35 Comparative Example 5 1.8 1.31

[0078] From the compressive strength test results and drying shrinkage test results in the table, it can be seen that the compressive strength of Examples 1-3 is significantly higher than that of Comparative Example 5, and the drying shrinkage rates are all significantly lower than that of Comparative Example 5. From Example 3 to Example 1, with the increase in the dosage of recycled waste concrete powder, the compressive strength of the examples is effectively improved and the drying shrinkage rate is reduced. High belite sulphoaluminate cement was not added in Comparative Example 1, indicating that high belite sulphoaluminate cement is the key component for the curing agent to exert its effect. The reduction of its dosage will significantly reduce the curing effect. At the same time, Comparative Examples 2-3 show that phosphogypsum and nano-silica can also optimize the curing effect. Comparative Example 4 shows that replacing high belite sulphoaluminate cement with ordinary aluminate cement will significantly increase the shrinkage rate. The reason is that its early shrinkage is large, resulting in a large amount of shrinkage before the strength structure of the solidified soil is completely formed. The results show that the soil curing agent with waste concrete and other solid waste-based materials as fillers, supplemented by high belite sulphoaluminate cement and other admixtures, can effectively improve the volume shrinkage problem of solidified expansive soil.

[0079] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Therefore, any simple modifications, equivalent changes and decorations made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention shall fall within the scope of protection of the technical solution of the present invention.

Claims

1. A solid waste-based soil stabilizer for expansive soil, characterized in that, Based on the quality of the dried expansive soil, the curing agent comprises the following components by mass percentage: Recycled fine powder of waste concrete: 10%-30%; High belite sulphoaluminate cement: 5%-10%; Phosphogypsum: 1%-2%; Slaked lime: 2%-4%; Nano-silica: 1%-3%.

2. The solid waste-based soil stabilizer according to claim 1, wherein The particle size range of the waste concrete recycled fine powder is 10 - 100 μm, and the specific surface area is 700 - 800 m 2 / kg.

3. The solid waste-based soil stabilizer according to claim 1, characterized in that, The specific surface area of the high belite sulphoaluminate cement is 300 - 400 m 2 / kg.

4. The solid waste-based soil stabilizer according to claim 1, characterized in that, The average particle size of the phosphogypsum is 30-40 μm, the pH value is 2-3, and the mass percentage content of calcium sulfate dihydrate is 90%-95%.

5. The solid waste-based soil stabilizer according to claim 1, wherein The particle size range of the slaked lime is 30-60 μm.

6. The solid waste-based soil stabilizer according to claim 1, wherein The particle size range of the nano-silica is 15-25 nm.

7. The preparation method of the solid waste-based soil stabilizer according to any one of claims 1 to 6, characterized in that, It includes the following steps: 1) Stir and mix the phosphogypsum and the high belite sulphoaluminate cement evenly to obtain Product ①; 2) Add the recycled fine powder of waste concrete to Product ① and continue to stir to obtain Product ②; 3) Add the slaked lime and the nano-silica to Product ② and continue to stir until evenly mixed to obtain the solid waste-based soil curing agent.

8. The preparation method according to claim 7, characterized in that, Stir for 2-5 minutes each time after adding new raw materials.

9. Application of the solid waste-based soil stabilizer according to any one of claims 1 to 6, characterized in that, It includes: Mix the solid waste-based soil curing agent with the expansive soil, mix with water, and then carry out curing.

10. The application according to claim 9, wherein The amount of water for mixing is 65%-75% of the mass of the expansive soil.