Improvement method for improving strength of red clay by using bagasse biochar

Abstract

The invention belongs to the technical field of geotechnical engineering, and particularly relates to an improvement method for improving the strength of red clay by using bagasse biochar. The preparation method comprises the following steps: performing heat treatment on bagasse in an oxygen-limited environment to prepare bagasse biochar; adjusting the water content of the red clay to 13-18%, then adding the bagasse biochar, and uniformly mixing to obtain the improved red clay. The geotechnical engineering material prepared from the improved red clay is used in geotechnical engineering construction processes of red clay roadbeds, retaining walls and the like. The bagasse biochar is added into the red clay, so that the strength of the red clay can be remarkably improved, the construction requirements are met, and the red clay is good in chemical stability, good in improvement durability and easy for mechanical construction.

Description

Technical Field

[0001] The present invention belongs to the technical field of geotechnical engineering, and more specifically relates to a method for improving the strength of red clay by using bagasse biochar. Background Art

[0002] Red clay is a kind of cohesive soil formed by the physicochemical weathering of carbonate rocks in a humid and hot environment. Generally, the fine-grained content of red clay is very high, and the clay minerals are mainly kaolinite and illite. The structure presents a honeycomb shape, and at the same time, a cotton-like structure also appears. Due to the inclusion of a large amount of iron oxide, the soil mass shows a reddish-brown color, and there is also corresponding iron oxide cementation between the particles. Red clay is often used as a subgrade filler, so the strength characteristics of red clay are directly related to the stability of the subgrade.

[0003] Biochar is pyrolyzed from biomass materials at a certain temperature under an oxygen-limited condition, and has a rich pore structure, surface area, high cation exchange capacity, and a stable chemical state. In the field of agricultural ecology, biochar has been widely used as an additive to improve the field water holding capacity, fertilizer fixation and other capabilities of the soil, and promote agricultural development. This is mainly because the incorporation of biochar can change the internal structure of the soil mass, and its porous structure can change the water adsorption property, thereby affecting the corresponding physical properties.

[0004] The development of the sugar industry has led to an increasing amount of industrial waste bagasse, which has become a difficult-to-consume waste. The previous incineration treatment method causes serious environmental pollution. Recycling bagasse by making it into biochar is a new development direction. Therefore, it is of great significance to develop a method for improving the strength of red clay by adding biochar. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for improving the strength of red clay by using bagasse biochar, which can consume bagasse waste while improving the strength of red clay.

[0006] To achieve the above purpose, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention: provides a method for improving the strength of red clay by using bagasse biochar, and the steps include:

[0008] Preparing bagasse biochar from bagasse through heat treatment in an oxygen-limited environment;

[0009] Adjusting the moisture content of the red clay to 13-18%, and then adding the bagasse biochar and mixing evenly to obtain the improved red clay.

[0010] The particle size range of the biochar prepared from bagasse is very wide, and biochars of various particle sizes may have different filling effects on pores of different sizes. Under the optimal moisture content condition, when compacting the red clay, the soil particles will first form an aggregate structure; when incorporating the biochar, small biochar particles will enter the interior of the aggregates during the mixing process and form aggregates together with the soil particles, which will reduce the pores inside the aggregates and make the aggregates denser. In addition, the larger-sized biochar will also be stored in the space between the aggregates, making the soil sample denser, increasing the contact area between the aggregates - biochar - aggregates, and thus improving the strength of the specimen. In addition, the aggregates will also be overlapped through the biochar, and this overlap will increase the connection force between the aggregates, thus providing the strength of the specimen.

[0011] The oxygen-limited environment in the present invention is provided by vacuum or inert atmosphere.

[0012] Further, the size of the bagasse is not higher than 1 cm.

[0013] Further, the temperature of the heat treatment is 300 - 500 °C, and the time is 2 - 3 h.

[0014] Optionally, the temperature of the heat treatment is 300 °C, and the time is 2 h.

[0015] Further, the red clay is the red clay passed through a 2-mm sieve.

[0016] Optionally, the particle size distribution of the red clay is as follows: the proportion of particles larger than 0.075 mm is 20.4 wt.%, the proportion of particles between 0.05 mm and 0.075 mm is 6.81 wt.%, and the proportion of particles smaller than 0.05 mm is 72.79 wt.%.

[0017] Further, the moisture content is 15.3%.

[0018] Further, the dosage of the bagasse biochar is 0 - 10% of the mass of the red clay, and it is not 0.

[0019] Optionally, the dosage of the bagasse biochar is 2 - 10% of the mass of the red clay.

[0020] The second technical solution of the present invention: provides an improved red clay prepared by the above improvement method.

[0021] The third technical solution of the present invention: provides an application of the above improved red clay in the preparation of geotechnical engineering materials.

[0022] According to the water content, the content of red clay is adjusted, and bagasse biochar is added according to the corresponding mass ratio. Generally, the higher the content of biochar, the more obvious the strength enhancement. Then, relevant mechanical equipment is used to mix water, bagasse biochar and red clay to ensure the uniform distribution of water and bagasse biochar in the red clay. Finally, when compacting the red clay subgrade, mechanical equipment is used to roll it to the maximum dry density. In order to avoid the reduction of water caused by water evaporation during the rolling process, the water content can be increased by 2% when preparing the soil sample.

[0023] Technical solution four of the present invention: Provide a geotechnical engineering material, which is obtained by compacting the above-mentioned improved red clay.

[0024] The improvement method provided by the present invention can significantly improve the shear strength of red clay. Especially when compacting red clay with the optimal water content as the subgrade filler, the addition of bagasse biochar can more significantly improve the shear strength of red clay; due to the better chemical stability of biochar, the durability of strength improvement is stronger. In addition, the resource utilization of bagasse biochar provides a new way for carbon sequestration, which is of great significance to environmental protection.

[0025] Technical solution five of the present invention: Provide an application of bagasse biochar in enhancing the cohesion of red clay.

[0026] Technical solution six of the present invention: Provide an application of bagasse biochar in enhancing the strength of red clay under confining pressure.

[0027] Technical solution seven of the present invention: Provide an application of bagasse biochar in enhancing the shear strength of red clay.

[0028] The present invention discloses the following technical effects:

[0029] By adding bagasse biochar into red clay, the present invention can significantly improve the strength of red clay, meet the construction requirements, and has good chemical stability and good improvement persistence, and is easy for mechanical construction; bagasse belongs to the agricultural waste of the sugar industry, with a large quantity and low price. The improvement method of the present invention utilizes waste resources, turning waste into treasure, and bagasse does not belong to chemical additives. Using it for red clay improvement is non-toxic, harmless, green and environmentally friendly, and will not cause damage to the surrounding environment and personnel. With the support of the improvement method, a large amount of bagasse can be consumed, further achieving the purpose of carbon sequestration and making a certain contribution to environmental protection.

[0030] The geotechnical engineering material prepared by compacting the improved red clay prepared by the present invention has excellent cohesion and shear strength.

[0031] The geotechnical engineering material prepared by the present invention can be applied to the construction of geotechnical engineering such as red clay subgrade and retaining wall, and the strength of red clay is improved by adding different contents of bagasse biochar. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0033] Figure 1 are the strengths of the specimens prepared from Comparative Example 1 and Examples 1-4 of the biochar-improved red clay under different confining pressure conditions.

[0034] Figure 2 is the variation relationship of the internal friction angle with the incorporation amount of bagasse biochar.

[0035] Figure 3 is the variation relationship of the cohesion with the incorporation amount of bagasse biochar.

[0036] Figure 4 are the compaction curves of red clay under different water contents.

[0037] Figure 5 is the schematic diagram of the microstructure of red clay after incorporating bagasse biochar. DETAILED DESCRIPTION OF THE INVENTION

[0038] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation to the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0039] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0040] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0041] Without departing from the scope or spirit of the present invention, various modifications and variations can be made to the specific embodiments of the present invention's specification, which will be obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention will be obvious to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0042] Regarding "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0043] The red clay used in the specific embodiments of the present invention is taken from Guilin, Guangxi, dried and crushed. To prevent the broken particle structure, it is hammered with a wooden mallet and then passed through a 2 mm sieve. The red clay under the sieve is collected for use in the examples and comparative examples. The specific gravity of this red clay is 2.76, the liquid and plastic limits are 45.91% and 18.42% respectively, and the maximum dry density is 1.86 g / cm 3 。

[0044] Example 1

[0045] The preparation steps of the geotechnical engineering material include:

[0046] S1. Prepare red clay, and the particle size distribution is: the proportion of particles larger than 0.075 mm is 20.4 wt.%, the proportion between 0.05 mm and 0.075 mm is 6.81 wt.%, and the proportion of particles smaller than 0.05 mm is 72.79 wt.%;

[0047] S2. Crush the bagasse and pass it through a 2 mm sieve, set the calcination temperature at 300 °C, and calcine it for 2 h under oxygen-limited conditions to obtain bagasse biochar;

[0048] Among them, the pH value of the above bagasse biochar is 7.42, and the density is 0.99 g / cm 3 ;

[0049] Test the ash content of the above bagasse biochar according to the method provided by ASTM D1762-84 standard, and it is 12.42%.

[0050] S3. Adjust the moisture content of the red clay in step S1 to 15.3%, add the bagasse biochar prepared in step S2 accounting for 2% of the mass of the red clay, and stir evenly to obtain improved red clay;

[0051] S4. Compact the above improved red clay to the maximum dry density to obtain the geotechnical engineering material.

[0052] Example 2

[0053] Compared with Example 1, the difference is only that the addition amount of bagasse biochar in step S3 is 5% of the mass of the red clay.

[0054] Example 3

[0055] Compared with Example 1, the only difference is that the addition amount of bagasse biochar in step S3 is 7% of the mass of red clay.

[0056] Example 4

[0057] Compared with Example 1, the only difference is that the addition amount of bagasse biochar in step S3 is 10% of the mass of red clay.

[0058] Example 5

[0059] Compared with Example 1, the only difference is that the moisture content in step S3 is adjusted to 14.03%.

[0060] Example 6

[0061] Compared with Example 1, the only difference is that the moisture content in step S3 is adjusted to 17.66%.

[0062] Comparative Example 1

[0063] The preparation steps of the geotechnical engineering material include:

[0064] S1. Prepare red clay, and the particle size distribution is: the proportion of particles larger than 0.075 mm is 20.4 wt.%, the proportion of particles between 0.05 mm and 0.075 mm is 6.81 wt.%, and the proportion of particles smaller than 0.05 mm is 72.79 wt.%;

[0065] S2. Adjust the moisture content of the red clay in step S1 to 15.3%, stir evenly, and compact it to the maximum dry density to obtain the geotechnical engineering material.

[0066] Comparative Example 2

[0067] Compared with Example 4, the only difference is that the calcination temperature in step S2 is 600 °C.

[0068] Comparative Example 3

[0069] Compared with Example 4, the only difference is that the calcination temperature in step S2 is 200 °C.

[0070] Comparative Example 4

[0071] Compared with Example 4, the only difference is that the moisture content of the red clay in step S3 is adjusted to 12.07%.

[0072] Comparative Example 5

[0073] Compared with Example 4, the only difference is that the moisture content of the red clay in step S3 is adjusted to 19.15%.

[0074] Test Example

[0075] Using the methods of Examples 1-6 and Comparative Examples 1-5, the compaction was carried out in three layers in the mold to obtain a triaxial cylindrical specimen, and the cylindrical specimen had a diameter of 39.1 mm and a length of 80 mm.

[0076] Using the triaxial shear test, the triaxial shear process mainly complied with the "Standard for Geotechnical Test Methods (GB / T 50123-2019)", and the confining pressure was controlled at σ 3 = 100 kPa, 200 kPa, 300 kPa and 400 kPa, and the shear rate was controlled at 0.08 mm / min.

[0077] According to the above tests, the stress-strain curves of biochar-improved red clay under different confining pressures can be obtained, and the strength under different confining pressures can be obtained according to the "Standard for Geotechnical Test Methods (GB / T 50123-2019)".

[0078] Figure 1 For the strength of biochar-improved red clay of the specimens prepared in Comparative Example 1 and Examples 1-4 under different confining pressure conditions. From Figure 1 It can be seen that under the confining pressure conditions of 100 kPa, 200 kPa, 300 kPa and 400 kPa, the addition of bagasse biochar can significantly improve the strength of red clay. When the confining pressure is 100 kPa, the addition of biochar ranges from 0 to 10%, and the strength increases from 883.1 kPa to 1821.7 kPa, with an enhancement amplitude of 106.3%; when the confining pressure is 400 kPa, when the incorporation amount changes from 0 to 10%, the strength increases from 1446 kPa to 2403.4 kPa, with an increase amplitude of 66.2%.

[0079] According to the method provided by the "Standard for Geotechnical Test Methods (GB / T 50123-2019)", the internal friction angle and cohesion of bagasse biochar-improved red clay are obtained.

[0080] Figure 2 For the variation relationship of the internal friction angle with the incorporation amount of bagasse biochar. From Figure 2 It can be seen that with the increase of the biochar incorporation amount, the internal friction angle varies between 27.5° and 29°, indicating that the addition of bagasse biochar has little effect on the internal friction angle.

[0081] Figure 3 For the variation relationship of the cohesion with the incorporation amount of bagasse biochar. From Figure 3 It can be seen that with the increase of the incorporation amount of bagasse biochar, the cohesion shows an obvious increase. When the mass ratio of bagasse biochar increases from 0 to 10%, the cohesion increases from 215 kPa to 485 kPa, with an increase amplitude of 125.6%.

[0082] It can be described by the following formula:

[0083] c = 215 + 80×θ 0.52

[0084] Wherein, c is the cohesion and θ is the mass ratio of bagasse biochar.

[0085] The main mechanism of the present invention is that the red clay is compacted under the condition of the optimal water content. First, the soil particles will form an aggregate structure, and then the aggregates will be piled up together to form a red clay sample. With the incorporation of bagasse biochar, the bagasse biochar will enter the interior of the aggregates during the sample preparation process and form aggregates together with the soil particles, which will reduce the pores inside the aggregates and make the aggregates more dense. In addition, the bagasse biochar will also exist in the space between the aggregates, making the soil sample more dense and increasing the contact area between the aggregates - bagasse biochar - aggregates, thereby improving the strength of the sample. In addition, the aggregates will also be lapped through the bagasse biochar, and this lap will increase the connection force between the aggregates, thereby enhancing the strength of the sample.

[0086] Figure 4 are the compaction curves of red clay at different water contents (Example 1, Examples 5 - 6 and Comparative Examples 4 - 5). As can be seen from the figure, under the condition of the same compaction work at different water contents, the best compaction effect can be produced at a water content of 15.30%, that is, the most dense state is reached, which is called the optimal water content and the maximum dry density. Generally, in specific projects, the compaction effect will be preferably compacted to the maximum dry density state at the optimal water content.

[0087] Figure 5 is the schematic diagram of the microstructure of red clay after incorporating bagasse biochar.

[0088] The strengths of the biochar - improved red clay under different confining pressures in Examples 1 - 4 and Comparative Example 1 are shown in Table 1.

[0089] Table 1

[0090] <![CDATA[σ 3 = 100 kPa]]> <![CDATA[σ 3 = 200 kPa]]> <![CDATA[σ 3 = 300 kPa]]> <![CDATA[σ 3 = 400 kPa]]> Comparative Example 1 883.1 1142.1 1294.9 1446 Example 1 1269.1 1400.5 1593.4 1748.8 Example 2 1468.9 1632.6 1819.6 1998.3 Example 3 1625.7 1833 2021.3 2177.2 Example 4 1821.7 2007.8 2181.3 2403.4

[0091] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same and similar parts among the embodiments, reference can be made to each other.

[0092] The foregoing description of the disclosed embodiments enables those skilled in the art to practice or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An improved method for improving the strength of red clay using bagasse biochar, characterized in that the steps include: The sugarcane bagasse is thermally treated to prepare sugarcane bagasse biochar in an oxygen-limited environment; The moisture content of the red clay is adjusted to 13-18%, and then the bagasse biochar is added and mixed evenly to obtain improved red clay.

2. The improved method according to claim 1, characterized in that: The size of the bagasse is not higher than 1 cm; and / or the temperature of the heat treatment is 300-500° C. and the time is 2-3 hours; and / or the red clay is red clay sieved through a 2 mm sieve.

3. The improved method according to claim 2, characterized in that: The heat treatment temperature is 300° C. and the time is 1 h; and / or the particle gradation distribution of the red clay is: particles larger than 0.075 mm account for 20.4 wt.%, particles between 0.05 mm and 0.075 mm account for 6.81 wt.%, and particles smaller than 0.05 mm account for 72.79 wt.%.

4. The improved method according to claim 1, characterized in that: The moisture content is 15.3%; and / or, the amount of the bagasse biochar is 0-10% of the mass of the red clay, and is not 0.

5. Improved red clay prepared by the improvement method according to any one of claims 1 to 4.

6. Use of the improved red clay according to claim 5 in preparing geotechnical engineering materials.

7. A geotechnical engineering material, characterized in that: The geotechnical engineering material is obtained by compacting the improved red clay described in claim 5.

8. Application of bagasse biochar in improving the cohesion of red clay.

9. Application of bagasse biochar in improving the strength of red clay under confining pressure.

10. Application of bagasse biochar in improving the shear strength of red clay.

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