Loess roadbed material based on nano-silicon powder improvement and preparation method thereof

Abstract

The application discloses a loess roadbed material improved based on nano silicon powder and a preparation method thereof, and belongs to the technical field of road engineering.The loess roadbed material improved based on the nano silicon powder comprises the following raw materials: loess and nano silicon powder; wherein the mass of the nano silicon powder is 0-1.0% of the mass of the loess, and 0% is excluded.The loess roadbed material improved based on the nano silicon powder is not prone to damage when meeting water, and can improve the stability and sustainability of an engineering project; and the loess roadbed material improved based on the nano silicon powder does not cause problems such as energy consumption and environmental pollution in the production and maintenance process.

Description

Technical Field

[0001] This invention relates to the field of road engineering technology, and in particular to a loess subgrade material based on nano-silica powder and its preparation method. Background Technology

[0002] Loess ranges in color from light yellow to brown, and its porous structure is primarily composed of powdery particles. Loess possesses important characteristics such as porosity, water sensitivity, high soluble salt content, high permeability, and well-developed vertical structure. These characteristics make the internal structure of loess easily damaged by water, potentially leading to engineering accidents. Therefore, physical methods such as compaction, layer replacement, and reinforcement are commonly used in engineering projects, along with the addition of highly reactive additives such as cement, fly ash, and lime to strengthen the soil. However, traditional soil conditioners can generate energy consumption and environmental pollution during production and maintenance. Therefore, there is an urgent need to find a method for improving loess to enhance the stability and sustainability of engineering projects. Summary of the Invention

[0003] The purpose of this invention is to provide a loess roadbed material based on nano-silicon powder and its preparation method, so as to solve the problems existing in the prior art.

[0004] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of the present invention is a loess roadbed material based on nano-silica powder, the raw materials of which include loess and nano-silica powder; The mass of the nano-silicon powder is 0 to 1.0% of the mass of the loess, excluding 0%.

[0005] Preferably, the mass of particles with a diameter ≥ 0.075 mm in the loess accounts for 30-50% of the total mass.

[0006] Preferably, the particle size distribution of the loess is as follows: Particle size < 0.005 mm, mass percentage 1.86%; Particle size ≤ 0.005 mm, mass percentage 35.56%; Particle size ≤ 0.05mm < 0.075mm, mass percentage 24.26%; Particle size ≤ 0.075 < 0.1 mm, mass percentage 24.21%; Particle size ≤ 0.1mm < 0.25mm, mass percentage 11.80%; Particle size ≥ 0.25 mm, mass percentage 2.31%.

[0007] Preferably, the plastic limit ω of the loess p It is 19.9%, liquid limit ω L It is 29.9%, and the plasticity index Ip The maximum dry density ρ is 10.0. dmax It is 1.89 g / cm³ 3 Optimal moisture content ω op It is 14.64%.

[0008] Preferably, the nano-silicon powder has a particle size of 15 nm and a purity of ≥99.5%.

[0009] Preferably, the density of the nano-silicon powder (nano-silica) is 0.13~0.15 g / cm³. 3 Specific surface area is 290~300g / m² 2 .

[0010] Nano-silica is an environmentally friendly material with a wide range of applications.

[0011] The size effect and high specific surface area of ​​nano-silica can fill the pores between particles to form a granular structure, thereby improving the mechanical properties of loess. Moreover, the porosity is minimized when the nano-silica content is 0.2%.

[0012] The second technical solution of the present invention: a method for preparing the above-mentioned loess roadbed material based on nano-silica powder, comprising the following steps: Dry soil is obtained by drying loess. The dry soil is sieved and then sprayed with a mixed solution of nano-silica powder and water, and mixed evenly to obtain the loess roadbed material.

[0013] Preferably, the sieve used for sieving has an aperture of 2mm.

[0014] Preferably, the mass ratio of the dry soil to water is 83:17.

[0015] The third technical solution of the present invention: the application of the above-mentioned loess subgrade material based on nano-silica powder in subgrade preparation.

[0016] The present invention discloses the following technical effects: (1) The loess roadbed material based on nano-silica powder of the present invention is not easily damaged when exposed to water, which can improve the stability and sustainability of engineering projects; and the loess roadbed material based on nano-silica powder of the present invention will not generate energy consumption and environmental pollution during production and maintenance.

[0017] (2) The method of the present invention can improve the strength of loess. Under different conditions, the strength is proportional to the confining pressure. The effect of 0.2% nano silica powder is the best (strength is 456 kPa). The addition of nano silica powder has the most significant effect on the cohesion of the soil. The maximum value is reached at 0.2% (cohesion is 54.7 kPa). Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 The particle size distribution curve of the loess used in Example 1; Figure 2 The image shows the actual nano-silica powder used in Example 1. Figure 3 The cylindrical sample prepared by triaxial compaction in Example 1; Figure 4 Stress-strain curves of cylindrical samples with different nano-silica doping contents prepared in Example 1 under a confining pressure of 100 kPa; Figure 5 Stress-strain curves of cylindrical samples with different nano-silica doping contents prepared in Example 1 under a confining pressure of 200 kPa; Figure 6 Stress-strain curves of cylindrical samples with different nano-silica doping contents prepared in Example 1 under a confining pressure of 300 kPa; Figure 7 Stress-strain curves of a cylindrical sample with 0% nano-silica doping prepared in Example 1 under different confining pressures; Figure 8 Stress-strain curves of a cylindrical sample with 0.2% nano-silica doping prepared in Example 1 under different confining pressures; Figure 9 Stress-strain curves of a cylindrical sample with 0.4% nano-silica doping prepared in Example 1 under different confining pressures; Figure 10 Stress-strain curves of a cylindrical sample with 0.6% nano-silica doping prepared in Example 1 under different confining pressures; Figure 11 Stress-strain curves of a cylindrical sample with 0.8% nano-silica doping prepared in Example 1 under different confining pressures; Figure 12 Stress-strain curves of a cylindrical sample with 1.0% nano-silica doping prepared in Example 1 under different confining pressures; Figure 13 Stress-strain curves of a cylindrical sample with 1.5% nano-silica doping prepared in Example 1 under different confining pressures; Figure 14 Stress-strain curves of a cylindrical sample with 2.0% nano-silica doping prepared in Example 1 under different confining pressures; Figure 15 The molar stress circle and strength envelope of the cylindrical sample with a nano-silica doping content of 0.2% prepared in Example 1; Figure 16 The internal friction angles of cylindrical samples with different nano-silica doping levels prepared in Example 1; Figure 17 The cohesive strength of cylindrical samples with different nano-silica doping levels prepared in Example 1; Figure 18 The images show the morphology of the cylindrical sample with 0.2% nano-silica doping prepared in Example 1 before the confining pressure test, after the low confining pressure treatment of 100 kPa, and after the high confining pressure treatment of 300 kPa. (a) is before the test, (b) is after the low confining pressure treatment of 100 kPa, and (c) is after the high confining pressure treatment of 300 kPa. Figure 19 Nuclear magnetic resonance T2 spectrum distribution of cylindrical samples with different nano-silica doping amounts prepared in Example 1; Figure 20 Hyperbolic fitting of the stress-strain relationship of cylindrical samples with different nano-silica doping contents prepared in Example 1 under a confining pressure of 100 kPa. Figure 21 Hyperbolic fitting of the stress-strain relationship of cylindrical samples with different nano-silica doping contents prepared in Example 1 under a confining pressure of 200 kPa. Figure 22 The stress-strain relationship of cylindrical samples with different nano-silica doping levels prepared in Example 1 under a confining pressure of 300 kPa is shown by hyperbolic fitting. Detailed Implementation

[0020] 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.

[0021] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to 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. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0022] 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. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0023] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0024] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0025] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0026] Example 1 A method for preparing loess roadbed material based on nano-silica powder: (1) Loess: The sampling site is located in the Jingyangling section of the Bianmen Expressway in the loess distribution area of ​​eastern Qinghai Province. The route generally runs from northwest to southeast. The sampling station is K42+650, located in Haibei Tibetan Autonomous Prefecture, Qinghai Province.

[0027] According to the test methods specified in the "Specifications for Geotechnical Testing of Highways" (JTG 3430-2020), particle size analysis tests were conducted on loess. The results are shown in Table 1 and... Figure 1 .

[0028] Table 1. Particle composition of loess As can be seen from Table 1, particles with a diameter ≥ 0.075 mm account for 30-50% of the total mass of the soil sample, indicating that the soil sample belongs to silty clay.

[0029] In accordance with the "Specifications for Testing Soil in Highway Engineering" (JTG 3430-2020), the soil samples were subjected to indoor compaction tests, liquid limit tests, plastic limit tests, and density tests. The basic physical properties of the soil samples are shown in Table 2.

[0030] Table 2 Basic physical properties of soil samples (2) The physical properties of the nano-silica powder are shown in Table 3, and the actual object is shown in [the table]. Figure 2 .

[0031] Table 3. Basic physical properties of nano-silica powder (3) Preparation method After passing the loess sample through a 2mm sieve, it was placed in an oven to dry. After being removed and cooled to room temperature, the dry soil was obtained.

[0032] Water and nano-silica powder were mixed at a mass ratio of 10:1 and stirred evenly. The mixture was then sprayed onto dry soil (dry soil to water mass ratio of 83:17) (the amount of nano-silica powder was 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.5%, or 2.0% of the dry soil mass). The mixture was stirred multiple times to prepare wet soil, which was then stored in a sealed environment for 24 hours to obtain loess roadbed material with nano-silica powder content of 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.5%, or 2.0%.

[0033] Using loess subgrade materials with nano-silica powder content of 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.5%, or 2.0% as raw materials (i.e., plain soil and modified loess with nano-silica powder content of 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.5%, or 2.0%), samples were prepared in five layers using a three-lobe-type sample preparation tool and a layered sample preparation method. To ensure that the samples were not disturbed by external factors, after the samples were prepared, they were sealed with plastic wrap and placed in self-sealing bags for curing for 24 hours. The triaxially compacted samples were cylindrical samples with a height of 80 mm and a diameter of 39.1 mm. See [link to documentation]. Figure 3 .

[0034] Example 1 Triaxial compression test (UU): Triaxial compression tests were conducted on cylindrical samples prepared in Example 1 with different nano-silica powder contents using a servo motor-controlled dynamic triaxial testing system, DYNTTS. The triaxial test method was unconsolidated and undrained, with a shear rate of 0.8 mm / min. The test was stopped when the axial strain reached 15%. Three parallel samples were set for each nano-silica content, and the tests were conducted under confining pressures of 100 kPa, 200 kPa, or 300 kPa. The specific test scheme is shown in Table 4.

[0035] Table 4 Triaxial Test Scheme (1) Stress-strain curve Stress-strain curves of cylindrical samples with different nano-silica contents (i.e., plain soil and modified loess with nano-silica powder contents of 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.5%, or 2.0%) under different confining pressures are shown in [Figure 1]. Figure 4 (100kPa) Figure 5 (200kPa) and Figure 6 (300kPa).

[0036] from Figures 4-6 As can be seen, the stress-strain curve of the raw loess is basically a weak strain softening type. With the increase of confining pressure, the stress-strain curve gradually changes to a strain hardening type. This is because the presence of confining pressure causes the sample to bear circumferential compressive stress. The higher the confining pressure, the greater the stress, reducing the possibility of weak sliding surfaces appearing. Moreover, the stress-strain characteristics of the modified loess with nano-silica powder content of 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.5%, or 2.0% are basically strain hardening type, and the higher the confining pressure, the more obvious the effect.

[0037] from Figures 4-6 As can be seen, under all working conditions, the modified loess with a 0.2% admixture exhibits the highest strength. Furthermore, the strength difference between loess with different admixtures gradually decreases with increasing confining pressure. This is because the soil density under high confining pressure is higher than that under low confining pressure. Under low confining pressure conditions, nano-silica powder fills the internal pore structure of the soil, making it denser. However, as the confining pressure gradually increases, the increase in soil density caused by the confining pressure weakens the increase in density brought about by the nano-silica powder filling, thus gradually narrowing the strength difference between the seven admixtures. Therefore, the compressibility coefficient and compressibility index of the modified loess both show a decreasing trend, while the compressibility modulus shows an increasing trend. This indicates that when nano-silica is added, due to the size effect and high specific surface area of ​​nanomaterials, it can fill the interparticle pores to form a granular structure, thereby reducing the compressible space of the soil and significantly improving the compressibility of the loess.

[0038] from Figures 4-6 It can also be seen that the modified loess with nano-silica powder content of 0.4%, 0.6%, 0.8%, 1.0%, 1.5% and 2.0% has a weaker strength than that with a content of 0.2%, but is significantly better than that of plain loess.

[0039] The stress-strain curves of cylindrical samples with the same nano-silica doping content under different confining pressures are shown below. Figure 7 , Figure 8 , Figure 9 , Figure 10 , Figure 11 , Figure 12 , Figure 13 and Figure 14 .

[0040] from Figures 7-14 As can be seen, under the same dosage, the ultimate strength of the soil increases with the increase of confining pressure, and the stress-strain relationship curve gradually changes to strain hardening type.

[0041] from Figures 7-14 The results show that modified loess with nano-silica powder content ranging from 0.2% to 2.0% exhibits enhanced strength compared to plain loess. For soils with the same powder content, under the same axial strain, the deviatoric stress increases with increasing confining pressure. Compared to soils incorporating nano-silica powder, the peak deviatoric stress is smaller in plain loess. This is because the incorporation of nano-silica powder increases the specific surface area and clay particles, resulting in better macroscopic performance of the soil under axial force. The results indicate that strain hardening is the dominant process in the soil samples. Under low confining pressure, soil exhibits a significant peak strength followed by a weak strain softening trend. Under high confining pressure, soil generally shows a strain hardening trend with no obvious peak strength. This is mainly because under high confining pressure, the soil experiences greater lateral confinement forces, leading to further compaction. This increases the friction between soil particles and between nano-silica powder particles, resulting in a denser internal structure. Furthermore, the uniform distribution of nano-silica powder within the soil increases the amount of clay particles formed by adsorbed water molecules, further enhancing the soil's density and strengthening its potential weak points, thus delaying failure. Conversely, under low confining pressure, the effective friction within the soil is less than under high confining pressure, leading to weak strain softening.

[0042] (2) Shear strength index The molar stress circle and strength envelope of the modified loess sample with 0.2% nano-silica powder were plotted on the τ-σ stress plane at failure. The shear strength index was obtained, and the results are shown in [Figure number missing]. Figure 15 The internal friction angle and cohesion of modified loess samples with different nano-silica powder content were obtained using the same method, and the results are shown in [see figure]. Figure 16 and Figure 17 .

[0043] from Figure 16 As can be seen, the internal friction angle of the modified loess samples with different amounts of nano-silica powder showed a trend of first increasing and then decreasing, with an overall decreasing trend. This is because nano-silica powder is insoluble in water and its content incorporated into the soil is relatively small, so it does not have a significant impact on the arrangement of soil particles, and therefore has a small impact on the internal friction angle of the soil. Figure 17It can be seen that the cohesion of modified loess (0.2~1.0% admixture) is improved compared with that of plain loess, with the most significant improvement at 0.2% admixture. As the admixture increases, the cohesion of the soil shows a downward trend. This indicates that the admixture of 0.2~1.0% nano silica powder can effectively improve the cohesion of the soil.

[0044] (3) Analysis of failure modes The morphological images of cylindrical samples with a nano-silica powder content of 0.2% before the confining pressure test, after the low confining pressure treatment of 100 kPa and the high confining pressure treatment of 300 kPa are shown in Figure 18. Among them, (a) is the sample before the test, (b) is the sample after the low confining pressure treatment of 100 kPa and (c) is the sample after the high confining pressure treatment of 300 kPa.

[0045] from Figure 18 As can be seen, when the confining pressure is low, all specimens undergo shear deformation to varying degrees. The specimen as a whole is compressed, and oblique shear bands are generated on the outer surface of the specimen. The main failure mode is "shear-like" (Figure (b)), which affects the strength of the specimen and reduces its load-bearing capacity. When the confining pressure is high, the main failure mode is "waist-drum-like", that is, obvious axial compression occurs (Figure (c)), and it presents a shape of "small at both ends and bulging in the middle".

[0046] Example 2 Nuclear magnetic resonance experiment: To investigate the microstructural changes of loess samples under saturation, the experiment used nuclear magnetic resonance (NMR) technology to monitor the microstructural information of samples with different nano-silica powder contents in real time. Cylindrical samples (i.e., triaxial test samples) prepared in Example 1 with different nano-silica powder contents were placed in a saturation apparatus and saturated at room temperature for 24 hours. Three parallel samples were prepared for each nano-silica powder content, and then immediately placed in an NMR spectrometer for NMR testing.

[0047] The T2 spectrum distribution of nuclear magnetic resonance (NMR) can reflect the distribution of pore size within a sample, and the area integral of the T2 spectrum curve can reflect the change in pore volume within the sample. Therefore, the change in the area of ​​the NMR T2 spectrum curve of a sample can reflect the evolution of the pore structure within the sample. NMR measurements were performed on saturated cylindrical samples with different concentrations of nano-silica powder to obtain their T2 spectra (see the NMR T2 spectrum distribution diagram). Figure 19 The samples were processed to obtain the area of ​​the nuclear magnetic resonance T2 spectrum curve. The results are shown in Table 5.

[0048] Table 5 Peak percentage and total area of ​​samples with different doping concentrations As shown in Table 5, when the dosage of nano-silica powder increases from 0% to 2%, the area ratio of the first peak changes little, with the largest being in the plain soil. At a dosage of 0.2%, the area ratio of the sample's peak is the smallest. Conversely, the change in the area ratio of the second peak indicates that the pores inside the sample gradually expand and connect, transitioning from small pores to medium and large pores. The total area is smallest at a dosage of 0.2%, indicating that the soil sample with a 0.2% dosage has the lowest porosity.

[0049] Example 3 Mathematical model of stress-strain curve: Based on the characteristics of the stress-strain relationship curve in Example 1, a hyperbolic model is used for fitting, i.e., formula (1): In the formula: σ1 is the first principal stress; σ3 is the third principal stress; ε1 is the strain; a and b are fitting parameters.

[0050] After mathematical transformation, equation (1) can be written as equation (2): With ε1 as the x-axis, Using the vertical axis as the ordinate, a hyperbola fit of the stress-strain relationship can be obtained for cylindrical samples with different nano-silica doping amounts, see [reference]. Figure 20 (100kPa) Figure 21 (200kPa) Figure 22 (300kPa).

[0051] from Figures 20-22 As can be seen, the stress-strain relationship of cylindrical samples with different nano-silica doping contents can be fitted using a hyperbolic model, and the fitting effect is good. Under the same confining pressure and doping content, the slope of the 0.2% doping content is the smallest, and the intercept is relatively large under low confining pressure. Under different confining pressures, the higher the confining pressure, the more dispersed the distribution of the curves. Under high confining pressure, the strength difference of cylindrical samples with different nano-silica doping contents gradually decreases because the density under high confining pressure is higher than that under low confining pressure, and the change in elastic modulus is smaller.

[0052] The above results demonstrate that incorporating nano-silica powder into loess significantly improves its mechanical strength; it also significantly reduces the porosity of the samples, particularly at a dosage of 0.2%, where the porosity reaches its lowest point, indicating an extremely compact soil structure. Furthermore, the samples at a dosage of 0.2% exhibit optimal shear resistance and cohesion, demonstrating that 0.2% nano-silica powder has a significant effect on improving the mechanical properties of the soil.

[0053] Nano-silica powder has a large specific surface area, small particle size, and size effect, which can effectively fill the interior of soil fissures, reduce soil porosity, and improve soil shear resistance and cohesion.

[0054] At higher confining pressures, modified loess exhibits greater initial compressive strength, but the rate of increase in compressive strength slows down with increasing strain.

[0055] 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 loess roadbed material based on nano-silica powder, characterized in that, The raw materials include loess and nano-silica powder; The mass of the nano-silicon powder is 0 to 1.0% of the mass of the loess, excluding 0%.

2. The loess roadbed material according to claim 1, characterized in that, The mass of particles with a diameter ≥ 0.075 mm in the loess accounts for 30-50% of the total mass.

3. The loess roadbed material according to claim 1, characterized in that, The particle size distribution of the loess is as follows: Particle size < 0.005 mm, mass percentage 1.86%; Particle size ≤ 0.005 mm, mass percentage 35.56%; Particle size ≤ 0.05mm < 0.075mm, mass percentage 24.26%; Particle size ≤ 0.075 < 0.1 mm, mass percentage 24.21%; Particle size ≤ 0.1mm < 0.25mm, mass percentage 11.80%; Particle size ≥ 0.25 mm, mass percentage 2.31%.

4. The loess roadbed material according to claim 1, characterized in that, The plastic limit ω of the loess p It is 19.9%, liquid limit ω L It is 29.9%, and the plasticity index I p The maximum dry density ρ is 10.

0. dmax It is 1.89 g / cm³ 3 Optimal moisture content ω op It is 14.64%.

5. The loess roadbed material according to claim 1, characterized in that, The nano-silicon powder has a particle size of 15 nm and a purity of ≥99.5%.

6. The loess roadbed material according to claim 1, characterized in that, The density of the nano-silicon powder is 0.13 g ~ 0.15 g / cm³. 3 Specific surface area is 290~300g / m² 2 .

7. A method for preparing loess roadbed material based on nano-silicon powder as described in any one of claims 1 to 6, characterized in that, Includes the following steps: Dry soil is obtained by drying loess. The dry soil is sieved and then sprayed with a mixed solution of nano-silica powder and water, and mixed evenly to obtain the loess roadbed material.

8. The preparation method according to claim 7, characterized in that, The sieve used for sieving has an aperture of 2mm.

9. The preparation method according to claim 7, characterized in that, The mass ratio of the dry soil to water is 83:

17.

10. The application of the loess subgrade material based on nano-silica powder modified according to any one of claims 1 to 6 in subgrade preparation.

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