A sulfate saline soil road base improvement material and a preparation method thereof

Abstract

The application provides a kind of improved sulphate saline soil road base road building material and preparation method, the improved sulphate saline soil road base road building material includes the following raw material components: by mass percentage, steel slag 1~3.45%, fly ash 1~3.45%, cement 0.55~1.77%, sodium hydroxide 0.54~1.7%, water 1.68~6.38% and sulphate saline soil 83.25~95.23%, the mass percentage of each component is 100%, and the preparation method includes: step 1, the formula amount of steel slag, fly ash, cement is dried and then ground and mixed, then mixed with the formula amount of water and stirred uniformly to prepare mixed liquor A; the formula amount of NaOH is prepared to obtain 10mol / L NaOH solution; step 2, mixed liquor A and the NaOH solution prepared in step 1 are mixed to prepare geopolymer; step 3, the geopolymer is mixed with the formula amount of sulphate saline soil to obtain the product. The improved material provided by the application has the characteristics of good low-temperature resistance, strong anti-freeze-thaw cycle ability, good impermeability, small expansion, good volume stability, and high mechanical properties of the reinforced soil body.

Description

Technical Field

[0001] This invention belongs to the field of materials and relates to a road base improvement material for sulfate saline soil and its preparation method. Background Technology

[0002] In sulfate-saline soil areas, the soluble salts in sulfate soils dissolve under the influence of external water bodies such as rainfall and groundwater seepage in summer, leading to significant changes in soil properties. In winter, the frequent freeze-thaw cycles cause continuous changes in the internal moisture, salt, and temperature fields, making the soil structure increasingly unstable. Sulfate soils also have unique physical and mechanical characteristics such as high porosity, strong collapsibility, high soluble salt content, and strong water sensitivity. In addition, sulfate soils also have defects such as surface heave and cracking caused by frost heave and salt heave, which greatly reduces the stability of roadbed and pavement structures. Therefore, when constructing roads in sulfate-saline soil areas, the main building materials used are loose soil and rock materials. However, in the existing technology, due to the remoteness of the project site or the high price of raw materials, local sulfate soil can only be used as the road base construction material in certain areas or under certain working conditions in order to solve the problem of raw material supply in emergency situations. Before use, the sulfate soil must be improved. The existing improvement methods mainly include lime reinforcement and cement reinforcement. The shortcomings of the existing methods are: the strength adjustment range of sulfate soil is small, the improved material has poor resistance to freeze-thaw cycles, obvious drying shrinkage and thermal shrinkage characteristics, poor shear strength, large expansion deformation, poor water stability and low temperature resistance, which urgently need to be improved. Summary of the Invention

[0003] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a sulfate-saline soil road base improvement material and its preparation method, so as to solve the technical problem of poor performance of sulfate-saline soil improvement materials in the existing technology.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] A road base construction material for improved sulfate-saline soil comprises the following raw material components by mass percentage: 1-3.45% steel slag, 1-3.45% fly ash, 0.55-1.77% cement, 0.54-1.7% sodium hydroxide, 1.68-6.38% water, and 83.25-95.23% sulfate-saline soil, with the total mass percentage of each component being 100%.

[0006] The present invention also has the following technical features:

[0007] Specifically, it includes the following raw material components by mass percentage: 1% steel slag, 1% fly ash, 0.55% cement, 0.54% sodium hydroxide, 1.68% water, and 95.23% sulfated soil.

[0008] Specifically, the steel slag has a particle size of 400 mesh.

[0009] Furthermore, the sulfated soil has a sulfate content of 3% to 5%, a plastic limit index of 19.2%, a liquid limit of 32.1%, a clay content of less than 5 μm of soil particle size of 21.4%, a silt content of 5 μm to 75 μm of particle size of 74.2%, and a sand and gravel content of 75 μm to 2000 μm of particle size of 4.4%.

[0010] This invention also protects a method for preparing a modified sulfate-saline soil road base material as described above, comprising the following steps:

[0011] Step 1: Take the prescribed amounts of steel slag, fly ash, and cement, dry them, grind and mix them, then mix them with the prescribed amount of water and stir evenly to obtain mixture A; take the prescribed amount of NaOH to prepare a 10mol / L NaOH solution;

[0012] Step 1: Mix the mixture A with the NaOH solution obtained in Step 1 to obtain the geopolymer;

[0013] Step 3: Mix the geopolymer with the prescribed amount of sulfated soil to obtain the final product;

[0014] The composition, by mass percentage, consists of 7–39% sulfated soil, 38–70% steel slag, 20–25% fly ash, 0.1–0.5% silicate cement, and 0.05–0.1% carbide slag and water, 7–39% water and 7–39% sodium hydroxide, with the total mass percentage of each component being 100%.

[0015] Furthermore, the steel slag, fly ash, and cement of the formula amount are dried, ground, and mixed, and then mixed with the water of the formula amount and stirred evenly to obtain mixed liquid A; a 10 mol / L NaOH solution is prepared by taking the NaOH of the formula amount.

[0016] Step 2: Mix the mixture A with the NaOH solution obtained in Step 1 to obtain the geopolymer;

[0017] Step 3: Mix the geopolymer with the prescribed amount of sulfated soil to obtain the final product;

[0018] The composition, by mass percentage, is as follows: steel slag 1%, fly ash 1%, cement 0.55%, sodium hydroxide 0.54%, water 1.68%, and sulfated soil 95.23%.

[0019] Compared with the prior art, the present invention has the following technical effects:

[0020] (1) The improved material provided by the present invention achieves solidification of sulfated soil by adding geopolymer to sulfated soil. The improved material has many advantages such as strong resistance to dryness and wetness and freeze-thaw, fast setting time, high early strength, low expansion deformation, strong bonding ability and good low temperature resistance.

[0021] (2) The 400-mesh steel slag and secondary fly ash used in the method of this invention to prepare oligomers are both industrial emissions or waste materials, which are inexpensive and help reduce engineering costs, increase the utilization rate of industrial solid waste, and achieve the effect of green, low-carbon and environmentally friendly. The method of this invention is simple to operate and easy to promote. Attached Figure Description

[0022] Figure 1 Electron micrographs of the materials prepared for the examples, wherein (a) corresponds to Example 1, (b) corresponds to Example 3, and (c) corresponds to Example 4;

[0023] Figure 2 Triaxial shear strength diagrams of the materials prepared in the examples and comparative examples;

[0024] Figure 3 The triaxial shear strength of the materials prepared in the examples and comparative examples after undergoing wet and dry cycles is shown in (a) as 50 kPa, (b) as 10050 kPa, and (c) as 15050 kPa.

[0025] Figure 4 The triaxial shear strength of the materials prepared in the examples and comparative examples after undergoing freeze-thaw cycles is shown in (a) 50 kPa, (b) 10050 kPa, and (c) 15050 kPa.

[0026] The specific content of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, any other embodiments obtained by those skilled in the art are within the scope of protection of the present invention.

[0028] It should be noted that, unless otherwise specified, all raw materials used in this invention are those known in the art.

[0029] Steel slag originates from the production waste of steel mills and other enterprises. It is inexpensive and has advantages such as high density, high strength, good stability, good durability, and rough surface. Its main components are oxides such as silicon dioxide and ferric oxide, and it contains active minerals such as tricalcium silicate, dicalcium silicate, and aluminoferrite. It has hydraulic cementitious properties similar to cement.

[0030] Fly ash originates from industrial waste generated by thermal power plants. Fly ash particles are small, spherical granules with a small specific surface area, resulting in cementitious materials with good flowability and minimal capillary action on water. Under alkaline conditions induced by caustic soda, fly ash undergoes an erosion-hydration reaction from the surface to the interior, generating compounds with hydraulic cementing properties, exhibiting good strength and workability. The hydration products produced by fly ash in an alkaline environment can fill the pores in sulfate-saline soils, solidify the sulfates within the loess, significantly reduce porosity, and refine the pore size and particle size, thereby improving the pore structure and interfacial characteristics of the solidified loess.

[0031] Cement's main components are tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite. It is a material with a high calcium content. The calcium ions released during its hydration reaction help promote the condensation reaction of steel slag, forming a composite gel of hydrated calcium aluminosilicate gel and hydrated sodium aluminosilicate gel. The hydration reaction of cement clinker precedes the pozzolanic reaction of fly ash; therefore, adding a certain amount of silicate cement can, to some extent, improve the early strength of solidified loess.

[0032] Under alkaline conditions, the surfaces of raw materials such as steel slag, fly ash, and cement are continuously eroded by hydroxide ions (OH-) released by caustic soda, causing the covalent breakdown of Si-O-Si and Si-O-Al in the steel slag, fly ash, and cement, producing silica-alumina monomers. In an alkaline solution environment, when the content of silica-alumina monomers in the slurry is high, a polymerization reaction occurs to generate oligomeric silica-alumina gel. These oligomeric silica-alumina gels interact and rearrange to form a three-dimensional network polymer structure, continuously densifying and strengthening the slurry, thus increasing its strength. After adding geopolymers to sulfate-saline soils, the resulting composite gel fills the pores between soil particles and between soil particles and sulfate crystals, improving its density and strength. Furthermore, the composite gel also enhances the absorption of calcium ions (Ca). 2+ Aluminum ions Al 3+ Alkali metal ions have an adsorption effect, which can further form water-resistant alkali metal compounds CaO-Al2O3-SiO2-H2O, thereby improving the water stability and impermeability of sulfate saline soil subgrade materials.

[0033] The improved sulfate-alkali soil road base material provided by this invention is used as a base and subbase filling material during road construction, and is used after mixing with water. Intermittent paving is employed; the upper structure is paved and compacted only after the lower layer of solidified soil has gained strength, to prevent vibrations from the equipment during operation from damaging the structure of the unstrengthened improved sulfate-alkali soil road base material. After paving, the improved sulfate-alkali soil road base material is repeatedly compacted approximately three times with a smooth-drum roller, followed by compaction with a vibratory roller, and finally finished with a double-drum roller to eliminate wheel tracks. The setting time of the improved sulfate-alkali soil road base material is within the range of 37–58 minutes, and paving and compaction are completed within 2 hours after mixing.

[0034] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0035] Example 1

[0036] This embodiment provides an improved sulfate-saline soil road base material, comprising the following raw material components: by mass percentage, 1% steel slag, 1% fly ash, 0.55% cement, 0.54% sodium hydroxide, 1.68% water, and 95.23% sulfate-saline soil.

[0037] The material is prepared using the following method:

[0038] Step 1: Take the prescribed amounts of steel slag, fly ash, and cement, dry them, grind and mix them, then mix them with the prescribed amount of water and stir evenly to obtain mixture A; take the prescribed amount of NaOH to prepare a 10mol / L NaOH solution;

[0039] Step 2: Mix the mixture A with the NaOH solution obtained in Step 1 at a volume ratio of 3:1 to obtain the geopolymer.

[0040] Step 3: Mix the geopolymer with the prescribed amount of sulfated soil to obtain the final product.

[0041] When the modified material prepared in this embodiment is used to improve roads in sulfate-saline soil:

[0042] Add an appropriate amount of water to the prepared modified sulfated soil road base material to produce a modified sulfated soil road base material with a moisture content of 14.5% to 15.5%.

[0043] Example 2

[0044] The improved sulfate-saline soil road base material given in this embodiment is prepared in the same way as in Example 1, except that it includes the following raw material components: by mass percentage, steel slag 2.08%, fly ash 2.08%, cement 1.27%, sodium hydroxide 1.13%, water 2.54%, and sulfate-saline soil 90.9%.

[0045] When the modified material prepared in this embodiment is used to improve roads in sulfate-saline soil:

[0046] Add an appropriate amount of water to the prepared modified sulfated soil road base material to make a modified sulfated soil road base material with a moisture content of 15.0% to 16.0%.

[0047] Example 3

[0048] The improved sulfate-saline soil road base material given in this embodiment is prepared in the same way as in Example 1. By mass percentage, it contains 3.02% steel slag, 3.02% fly ash, 1.7% cement, 1.64% sodium hydroxide, 3.72% water, and 86.9% sulfate-saline soil.

[0049] When the modified material prepared in this embodiment is used to improve roads in sulfate-saline soil:

[0050] Add an appropriate amount of water to the prepared modified sulfated soil road base material to produce a modified sulfated soil road base material with a moisture content of 15.7% to 16.3%.

[0051] Example 4

[0052] This embodiment provides an improved sulfate-saline soil road base material, comprising the following raw material components: by mass percentage, steel slag 3.45%, fly ash 3.45%, cement 1.77%, sodium hydroxide 1.7%, water 6.38%, and sulfate-saline soil 83.25%.

[0053] In this embodiment, when the prepared modified sulfated soil road base material is used to improve sulfated soil roads, an appropriate amount of water is added to the material to prepare a modified sulfated soil road base material with a moisture content of 16.6% to 17.3%.

[0054] Comparative Example 1

[0055] This comparative example provides a sulfated soil road base material without the addition of geopolymer. When used, the optimal moisture content of the sulfated soil road base material is 14.0% to 15.0%.

[0056] Comparative Example 2

[0057] This comparative example provides a lime-modified sulfate-saline soil road base material. The raw material components of the material include lime, water and sulfate-saline soil, and the material is prepared with an optimal moisture content of 17.8% to 18.3%.

[0058] Scanning electron microscope (SEM) images of the modified sulfate-saline soil road base material prepared by this method are shown below. Figure 1 As shown.

[0059] Performance testing:

[0060] The materials prepared in Examples 1-4 and Comparative Examples 1-2 were made into standard-sized cylindrical specimens (39.1 mm in diameter and 80 mm in height) and placed in a curing chamber for 28 days of standard curing (curing temperature 20 ± 2℃, relative humidity ≥ 95%). The triaxial shear strength of the specimens after curing was tested under confining pressures of 50 kPa, 100 kPa, and 150 kPa. The test results are shown in Table 1.

[0061]

[0062]

[0063] Table 1. Triaxial shear strength test results of materials prepared in Examples 1-4 and Comparative Examples 1-2

[0064] As can be seen from the table above, with the increase of confining pressure and geopolymer content, the triaxial shear strength of the improved sulfate soil road base materials in Examples 1-4 gradually increased after 28 days, indicating that the addition of geopolymer can significantly improve the shear strength of sulfate soil road base.

[0065] The sulfate-saline soil road base reinforcement materials prepared in the above four examples and two comparative examples were subjected to alternating wet and dry cycles and freeze-thaw cycles, and their triaxial shear strength was measured under confining pressures of 50 kPa, 100 kPa, and 150 kPa.

[0066] The test results are shown in Tables 2, 3, 4, and 5. Figure 3 and Figure 4 As shown.

[0067]

[0068]

[0069] Table 2 shows the triaxial shear strength (MPa) of the materials obtained after wet-dry cycles in the examples.

[0070]

[0071] Table 3 shows the triaxial shear strength (MPa) of the materials obtained after freeze-thaw cycles in the examples.

[0072]

[0073] Table 4 shows the triaxial shear strength (MPa) of the materials after wet-dry cycling in comparative examples.

[0074]

[0075]

[0076] Table 5 shows the triaxial shear strength (MPa) of the materials after freeze-thaw cycles, obtained in comparative examples.

[0077] The data above show that the sulfate-treated road base course, after being cured with geopolymer, exhibits good resistance to wet-drying and freeze-thaw cycles, and the higher the admixture content, the more significant the resistance to wet-drying and freeze-thaw cycles. The method of this invention is simple to operate, increases the utilization rate of industrial solid waste, and achieves a green, low-carbon, and environmentally friendly effect.

[0078] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0079] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A road base construction material for improved sulfate-saline soil, characterized in that, The raw material components include the following by mass percentage: steel slag 1~3.45%, fly ash 1~3.45%, cement 0.55~1.77%, sodium hydroxide 0.54~1.7%, water 1.68~6.38%, and sulfated soil 83.25~95.23%, with the total mass percentage of each component being 100%. The sulfated soil has a sulfate content of 3% to 5%, a plastic limit index of 19.2%, a liquid limit of 32.1%, a clay content of less than 5 μm of soil particle size of 21.4%, a silt content of 5 μm to 75 μm of particle size of 74.2%, and a sand and gravel content of 75 μm to 2000 μm of particle size of 4.4%. The steel slag has a particle size of 400 mesh.

2. The road construction material for improved sulfate-saline soil road base as described in claim 1, characterized in that, The raw material components include the following by mass percentage: 1% steel slag, 1% fly ash, 0.55% cement, 0.54% sodium hydroxide, 1.68% water, and 95.23% sulfated soil.

3. The road construction material for improved sulfate-saline soil road base as described in claim 1, characterized in that, The fly ash is grade II fly ash.

4. The method for preparing the improved sulfate-saline soil road base construction material as described in claim 1, characterized in that, Includes the following steps: Step 1: Take the prescribed amounts of steel slag, fly ash, and cement, dry them, grind and mix them, then mix them with the prescribed amounts of water and stir evenly to obtain mixture A; take the prescribed amounts of NaOH to prepare a 10 mol / L NaOH solution; Step 2: Mix the mixture A with the NaOH solution obtained in Step 1 to obtain the geopolymer; Step 3: Mix the geopolymer with the prescribed amount of sulfated soil to obtain the final product; The composition, by mass percentage, is as follows: steel slag 1%, fly ash 1%, cement 0.55%, sodium hydroxide 0.54%, water 1.68%, and sulfated soil 95.23%.

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