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Article

Development of Self-Sustaining Improvement Material for a Mud Film of the Weathered Soil of Red Beds

by
Zhen Liu
,
Jingqi Wang
,
Yi Gao
,
Jin Liao
,
Chunhui Lan
and
Cuiying Zhou
*
School of Civil Engineering, Sun Yat-sen University, Zhuhai 519082, China
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(21), 15284; https://doi.org/10.3390/su152115284
Submission received: 18 September 2023 / Revised: 14 October 2023 / Accepted: 23 October 2023 / Published: 25 October 2023
(This article belongs to the Special Issue Development and Application of Functional Materials in Disaster Prevention and Sustainable Restoration)
Browse Figures
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Abstract

:
Red beds are widely distributed in various regions of China. Adapting measures to adjust to local conditions and using nearby materials to ecologically protect slopes, mines, and other engineering projects are methods advocated by environmental protection. A mud film of the weathered soil of red beds with improved materials for insulation and entropy preservation is commonly used in engineering ecological protection, and its self-sustainability is an important indicator with which to measure the protective effect; however, most of the commonly used improvement materials in production have high concentrations of chemical substances and high costs, causing environmental pollution. In response to this issue, this study has developed four new composite improved materials using waste paper as raw material. The low temperature resistance (−20 °C, 0 °C), high temperature resistance (40 °C, 60 °C, and 80 °C), and recyclability (dry and wet cycle: zero, one, two, and three times) of the four materials were tested. Under the conditions of changing the addition amounts of four new self-developed composite materials (0 g, 10 g, 20 g, 30 g, 40 g, 50 g, 60 g, 70 g, 80 g, 90 g, and 100 g), experiments were conducted on the thin-layer property, corrosion resistance, and flexibility of the mud film of weathered soil of red beds, and they were compared with conventional materials studied by the team in the early stage. At the same time, outdoor on-site testing was conducted. The experimental results indicate that the self-developed new composite improvement material has a good improvement effect on the self-sustainability and ecological protection effect of the mud film of weathered soil of red beds. This article summarizes the improvement mechanism and control factors of self-developed new composite materials in the self-sustainability of the mud film of the weathered soil of red beds, improves the suitability of engineering ecological protection, and develops green and low-cost engineering ecological protection technology.

1. Introduction

The naturally formed weathered soil of red beds is widely distributed and rich in a large number of substances [1], with the advantages of low cost, no pollution, and good compatibility with the environment [2,3]. The preparation of a mud film by using the naturally weathered soil of red beds as raw material can address the shortcomings of natural geotechnical materials in film formation and engineering ecological protection. The mud film formed by the weathered soil of red beds with improved materials can be used for engineering ecological protection [4]; however, the most commonly used materials for improving the weathered soil of red beds in production are chemically rich [5], expensive, and environmentally unfriendly. A mud film system with ecological functions is constructed by improving the flexibility, thinness, and corrosion resistance of the mud film [6,7]; endowing the mud film with self-regulation, self-supporting, and self-healing ecological improvement effects; achieving the goal of ecological diversity [8] and environmental beautification [9] of the mud film; and reducing the amounts of plastic film and non-woven fabric used [10]. Therefore, developing improved materials with low cost, a suitable environment, abundant sources, and significant effects to prepare a mud film of the weathered soil of red beds is of great significance for the development of green and low-cost engineering ecological protection technologies.
The research on materials for improving mud films mainly focuses on two aspects: traditional improved materials and polymer-improved materials [11]. In terms of traditional improvement materials, cement or lime is used as an additive to improve mud films [12]. The method of mixing lime and fly ash can prevent the shrinkage and dehiscence of cementitious soil [13]. Cement can maintain the stable compressive strength of the mixtures of the mud film and fly ash [12]. The type of mud film can affect the stability of dust in cement kilns [14]. Researchers have also considered special types of soil as research objects and discussed the strengthening effect of traditional mud film reinforcement materials on them [15,16,17]. Fly ash and lime can improve the strength of calcareous expansive clay [18]. Marine clay added to with lime has good compressibility [11]. Lime, cement, and artificial volcanic ash can be used for the improvement of expansive soil [19]. The use of rice husk ash cement can improve the properties of residual soil [20]. The stabilization effect of high-calcium fly ash and cement is compared to improve cohesive soil [21]. Fly ash can improve soft soil [22], and lime and cement can improve muddy soil [23]. The combined application of biochar and fly ash can further improve soil quality and crop productivity [24]. Polymers, such as fly ash and carbide slag, have an improved effect on marine soft clay [25]. Domestic scholars focus on conducting material research and development based on existing traditional mud film improvement materials; however, the above research has many flaws. It is difficult to control the cement setting time when cement is used as the main modifier for mud film improvement materials. The mixing uniformity of mud film improvement materials makes it difficult to distinguish between the colour differences of cement and mud film, and its mixing effect will affect the actual construction quality [14,26]. Lime- and fly ash-improved soil have poor early strength, significant shrinkage, easy softening, and poor water stability [20,21,23]. In terms of polymer-modified materials, it is mainly achieved by exploring a type of multifunctional material that can achieve natural degradation. Acrylic acid and other vinyl monomers can be used for the main reaction to synthesize a new soil improvement material [3]. The structure of polymer mud films has a significant impact on the improvement effect. STW-type materials are organic materials that can be used as improved materials. Inorganic binder, terrazyme, and lotion polymer have good improvement effects. Researchers have conducted various studies from the perspectives of mud film types, mud film improvement effects, and improvement mechanisms. Polymer material SH can be applied to enhance loess; PVA-improved mud films have an anti-raindrop erosion effect [27]. Ecological mud film improvement materials have an improvement effect on the stability of soil slopes. STW-type ecological mud films are improved materials that can enhance the hydraulic properties and strength of cohesive soil. Water-soluble polymer substances can improve the stability of aggregates in water [28]. The higher the concentration of acrylamide solution, the lower the conductivity of a mud film. Organic polymer substances have a certain impact on the long-term fertility of a mud film [29]. A previous study used an organic polymer to reinforce the surface soil of the slope [30]. Polymers have a long-term effect on strengthening clay [31]. A polymer composed of clay and fly ash has outstanding strength properties [32]. Non-traditional additives can improve the characteristics and microstructure of the red layer [33]. Currently, research on polymer-modified materials focuses on the preparation and innovation of materials, with insufficient emphasis on cost and environmental protection. Further research can be conducted to develop pollution-free waste into mud film-modified materials.
The combined capacity of jute fibres (JFs) and ground-granulated blast furnace slag (GBFS) can ameliorate the inferior engineering properties of micaceous clays as a sustainable solution [34]. Rubber waste powders (RWPs) offer a promising solution with which to enhance the consolidation and deformation properties of low-plasticity clay soil (CS) while promoting environmental sustainability [35]. Cellulose(C6H10O5)n exhibits excellent improvement performance in conventional materials and is a good material for improvement [36,37]; however, the cost of cellulose is considerably high and is not suitable for large-scale applications in engineering ecological protection. Therefore, based on the experimental results of cellulose, suitable improved materials can be further explored in low-cost cellulose materials to explore low-cost and effective improved materials. Waste paper is a common pollutant with strong recycling value and low cost. It contains a large amount of cellulose and is easy to extract. Therefore, based on the principles of waste utilization and environmental protection, waste paper is selected as the raw material for new composite materials.
Based on waste paper, a new type of self-made composite material for the mud film formation of the weathered soil of red beds is developed and tested. We have tested the self-developed new composite materials in three aspects: low-temperature resistance, high-temperature resistance, and recyclability. Based on self-developed new composite materials, membrane formation tests, outdoor and on-site testing, as well as the verification of the weathered soil of red beds are conducted. The advantages and disadvantages of self-developed new composite materials in improving the self-sustainability of the mud film formation of the natural weathered soil of red beds, as well as the improvement mechanism and control elements, are summarized.

2. Research Content and Methods

2.1. Development of Improved Materials

The red beds in China are mainly red continental clastic rock, and their weathered products are formed by mesozoic cenozoic sedimentation. The red beds in this era have the same sedimentary background; thus, their properties are similar. Our team has completed the testing of the mechanical properties of red beds in more than 20 provinces in China, and the results are similar [36,37], as shown in Figure 1.
By classifying and treating waste newspapers, waste envelope paper, waste oily magazines, and waste non-oily magazines as raw materials, and focusing on the idea of waste reuse, four types of improved materials are manufactured, mainly consisting of wood fibres (F), thin fibres (G), colloidal fibres (H), and lightweight fibres (I). The four fibres have similar molecular structures to that of cellulose [37]. The weathered soil of red beds is supplemented with improved materials to produce a mud film of the weathered soil of red beds for ecological protection, and to develop green and low-cost engineering ecological protection technology.
Take 100 g of newspapers, envelope paper, oily magazines, and non-oily magazines (waste paper from the East Campus Laboratory of Sun Yat-sen University Guangzhou Campus). Cut the waste paper into 1–20 mm fragments for easy heating and stirring treatment. Put the fragmented waste paper into a heating instrument pre-filled with 800 mL of water, and heat the fragmented waste paper at a temperature of 60–100 °C for about 5 to 20 min until it becomes soft and viscous. Put the soft and viscous waste paper that has been heated and boiled into a mixer (Subor SP902S grinder), and add 200 mL of water. Stir for about 15 min until it is sticky and elastic to the touch. The production process diagram of improved materials is shown in Figure 2.
The elemental compositions of four self-developed new composite materials, obtained through an energy spectrum analysis, are shown in Figure 3.
The elemental compositions of four self-developed new composite materials are made up of C, H, O, and Na. The distribution of elements in colloidal fibres is the most balanced, with a large proportion of C in wood fibres, a large proportion of O in thin fibres, and a large proportion of H and O in light fibres.
The viscosity and density parameters of four self-developed new composite materials are shown in Table 1.

2.2. Testing the Self-Sustainability of a Mud Film of the Weathered Soil of Red Beds Based on Improved Materials

Comparative experiments on the formation of mud films from the weathered soil of red beds were conducted, and the self-sustaining properties of mud films from the weathered soil of red beds with the addition of self-developed new composite materials were investigated. According to the types of self-developed new composite materials, self-developed new composite materials were divided into four types. Four experimental groups with self-developed new composite materials added and one control group without materials added were set up.
For the same self-developed new composite material, starting from 10 g, it gradually increases to 100 g based on a mass gradient of 10 g. It is then mixed with 200 g of the natural weathered soil of red beds and 1000 g of water each time to study the optimal solution of the effect of self-developed new composite material on the natural weathered soil of red beds. The control group adds 10 g of the natural weathered soil of red beds each time. Different-quality self-developed new composite materials with the weathered soil of red beds and water are mixed to create mud films.
After the production of mud films of the natural weathered soil of red beds is completed, the properties of each group of mud films of the natural weathered soil of red beds are tested. The self-sustainability of the mud films is reflected through their thin-layer property, corrosion resistance, and flexibility.
  • Thin-layer property (overall anti-skid): The thickness of the mud film of the naturally weathered soil of red beds in each group is measured. The thicker the mud film of the natural weathered soil of red beds, the stronger the self-developed new composite material improves the thin-layer properties of the weathered soil of red beds.
  • Corrosion resistance: A dropper is used to continuously add hydrochloric acid solution and sodium hydroxide solution to the mud film of the weathered soil of red beds of different groups. The concentrations of hydrochloric acid solution and sodium hydroxide solution are 0.01, 0.1, and 1 mol/L. They are dripped once every 5 s until the mud film of the weathered soil of red beds ruptures. The pH value is then recorded at this time to obtain the corrosion resistance of the mud film.
  • Flexibility (local compression resistance): Pressure is applied to different groups of the mud film of the weathered soil of red beds, starting from 100 N and increasing by 10 N each time, until the mud film of the weathered soil of red beds ruptures. The pressure value is recorded at this time to obtain the flexibility of the mud film.
The self-developed new composite material of the weathered soil of red beds is taken and placed in a constant-temperature box. The temperature is set to −20 °C, 0 °C, 20 °C, 40 °C, 60 °C, and 80 °C for 6, 12, and 24 h. The self-developed new composite material is then mixed with the weathered soil of red beds to create a mud film of the weathered soil of red beds, and the self-sustainability of the mud film of the weathered soil of red beds is tested similarly.
After this, 50 mL of water is added to the newly developed composite material. It is allowed to sit in sunlight for 12 h for a cycle. Each material is cycled 0–3 times. The self-developed new composite material is then mixed with the weathered soil of red beds to create a mud film of the weathered soil of red beds, and the self-sustainability of mud films of the weathered soil of red beds is tested similarly.

2.3. Application Test of Engineering Ecological Protection Based on Improved Materials

At present, only indoor experiments have been conducted on the formation of red weathered soil films, but most of the working conditions of mud films of the weathered soil of red beds are in the natural environment on-site. To verify that the film formation law based on self-developed new composite materials can be carried out smoothly on-site, a small piece of land without vegetation was selected on-site, and pigeon pea was planted in experimental areas 1 and B, as well as the control area, to verify whether the results of the indoor planting experiment can be applied on-site. An open area with sparse vegetation and insufficient sunlight on-site is selected, with an area of approximately 9 m2. The pigeon pea is a sun-loving plant. The improvement of the growth of pigeon pea by materials under extreme environmental conditions was explored.
The specific test steps are as follows:
① Clean the test area. A hoe is used to remove weeds from the experimental area, and debris, such as fallen leaves, is removed.
② Digging the soil. A hoe and a shovel are used to turn the soil in the test area to a depth of approximately 8 cm to ensure that the pigeon pea seeds can take root.
③ Define the scope of the experiment. The experimental area is divided into experimental area A, experimental area B, and control area.
④ Sowing. The prepared pigeon pea seeds are soaked in water for 1–2 days and are evenly placed in experimental areas A and B, as well as control areas, with a spacing of 100 seeds per area.
⑤ Produce self-developed new composite materials. Five hundred grams of thin fibres are cut into small pieces, and the fragmented waste paper is heated and boiled until it becomes soft and viscous.
⑥ Make mud film and apply it. On-site, two sets of mud films of the naturally weathered soil of red beds are produced, one with the addition of self-developed new composite materials and the other without any additional materials. Mud films of the weathered soil of red beds with the addition of self-developed new composite materials on the A test area are spread. Notable, materials on the B test area are not added, as shown in Figure 4.
⑦ Curing. Water each group with 35 L daily for the first five days, and water them with 35 L every three to five days for the next 15 days.
The on-site verification monitoring plan is as follows:
① Before the experiment begins, 5 g of planting soil is taken, and a sample for the energy spectrum analysis experiments is prepared.
② Measurement of soil moisture and conductivity. During the experiment, daily measurements of soil moisture and conductivity are conducted via the use of a soil environmental detector in experimental areas A and B, as well as control areas. The instrument is connected, and the probe of the soil environment detector is inserted into the soil by approximately 3 cm. Ten points are measured each time, and the average value is recorded.
③ Measurement of soil compaction. During the experiment, the soil compactness of test areas A and B, as well as the control area, is measured daily via the use of a soil compactness meter. The soil compactness meter is inserted into the soil by approximately 10 cm, and the average value is measured at 10 points each time and recorded.
④ Measurement of soil oxygen and carbon dioxide content. During the experiment, soil oxygen and carbon dioxide concentrations are measured daily using a soil gas analyser in test areas A and B, as well as the control area. The soil gas analyser pipeline is connected. First, the air inside the pipeline is removed, and the probe is inserted into the soil by approximately 10 cm. Then, 10 points are measured each time, and the average value is recorded.
⑤ Measurement of the germination rate and height of pigeon pea. The germination of seeds is measured every day after germination, and only seeds with a germination height exceeding 1 cm can be recorded as germinated. The height of plant growth is measured and recorded for 20 days.

3. Research Results and Discussion

3.1. Analysis of Self-Sustaining Improvement Effect of Red Layer Weathered Soil Mud Films

3.1.1. The Effect of Self-Developed New Composite Materials on the Self-Sustainability of Mud Films of the Weathered Soil of Red Beds

The effect of the additional amount of self-developed new composite materials on the thin-layer properties, corrosion resistance, and flexibility of natural red weathered soil films is shown in Figure 5.
The orange curve serves as the control group, and, without the addition of other self-developed new composite materials, the increase in the use of red weathered soil does not affect the thin-layer properties of the natural red weathered soil mud films. Among them, compared with the control group, wood fibres, thin-slice fibres, colloidal fibres, and light fibres all improved the thin-layer properties of the mud films of the weathered soil of red beds. The use of wood fibres has a linear effect on the thin-layer properties of the mud film of weathered soil of red beds, with a thickness range of 55 to 190 mm; the use of thin fibres has a linear effect on the thinness of natural red weathered soil films with a thickness range of 54 to 215 mm; the use of colloidal fibres has a linear effect on the thin-layer properties of weathered soil films in the natural red layer with a thickness range of 72 to 230 mm; and the use of lightweight fibres has a linear effect on the thin-layer properties of natural red weathered soil films with a thickness range of 58 to 205 mm.
The orange curve serves as the control group, and without the addition of other self-developed new composite materials, the increase in the use of the weathered soil of red beds does not affect the corrosion resistance of mud films of the weathered soil of red beds. Compared with the control group, wood fibres, thin-sheet fibres, colloidal fibres, and lightweight fibres all improved the corrosion resistance of natural red weathered soil mud films. The use of wood fibres has a linear effect on the corrosion resistance of natural red weathered soil films with a pH range of 0.6 to 12; the use of thin fibres has a linear effect on the corrosion resistance of natural red weathered soil films with a pH range of 1.2 to 11.3; the use of colloidal fibres has a linear effect on the corrosion resistance of natural red weathered soil films with a pH range of 0.7 to 12.3; the use of lightweight fibres has a linear effect on the corrosion resistance of natural red weathered soil films with a pH range of 1.5 to 13.6.
The orange curve serves as the control group. Without the addition of other self-developed new composite materials, the increase in the use of the weathered soil of red beds does not affect the flexibility of mud films of the weathered soil of red beds. Compared with the control group, wood fibres, thin-sheet fibres, colloidal fibres, and lightweight fibres improved the flexibility of the natural red weathered soil membrane. The use of wood fibres, thin fibres, colloidal fibres, and lightweight fibres has a linear effect on the flexibility enhancement of natural red weathered soil films, with pressure ranges of 1600 to 2800, 2100 to 3400, 1900 to 3600, and 1800 to 3200 N, respectively.

3.1.2. The Effect of Self-Developed New Composite Materials after Constant Temperature Tests on the Self-Sustainability of Mud Films of the Weathered Soil of Red Beds

The self-sustainability of mud films of the weathered soil of red beds with the addition of self-developed new composite materials after constant temperature tests is shown in Figure 6.
The normal temperature is set to 20 °C, as shown in Figure 6a. Wood fibres and light fibres have good resistance to high and low temperatures. After a constant temperature for 6, 12, and 24 h, the thin-layer properties of mud films of the weathered soil of red beds with the addition of wood fibres and light fibres remain unchanged. Moreover, the thin-layer properties of mud films of the weathered soil of red beds formed by the thin fibres under low temperatures remain unchanged, while the thin-layer properties of mud films of the weathered soil of red beds formed by high temperatures are enhanced. Additionally, the constant temperature time increases and the effect remains unchanged. After being subjected to low and high temperatures, the thin-layer properties of mud films of the weathered soil of red beds formed by colloidal fibres remain unchanged, while the thin-layer properties of the red weathered soil mud films formed by high temperatures are enhanced. The thin-layer properties of the mud films are enhanced as the constant temperature time increases.
As shown in Figure 6b, the colloidal fibres have good high-temperature and low-temperature resistance. After 6, 12, and 24 h of constant temperature, the corrosion resistance of red weathered soil films with the addition of colloidal fibres remains basically unchanged. The corrosion resistance of mud films of the weathered soil of red beds formed by wood fibres under high temperature remains basically unchanged, while the corrosion resistance of mud films of the weathered soil of red beds formed by low temperature decreases. The corrosion resistance of mud films of the weathered soil of red beds formed by wood fibres is less affected by the duration of constant temperature. The corrosion resistance of mud films of the weathered soil of red beds formed by light fibres at high temperatures is enhanced, while the corrosion resistance of mud films of the weathered soil of red beds formed by light fibres at low temperatures is weakened, and the corrosion resistance of mud film of the weathered soil of red beds with the addition of light fibres decreases with an increase in constant temperature time. The corrosion resistance of mud films of the weathered soil of red beds formed by the thin fibres at high temperatures is enhanced, while the corrosion resistance of mud films of the weathered soil of red beds formed by low temperatures remains basically unchanged, and the corrosion resistance of mud films of the weathered soil of red beds after adding thin fibres is basically not affected by the constant temperature duration.
The wood fibre magazine has good resistance to high and low temperatures, as shown in Figure 6c. After a constant temperature of 6, 12, and 24 h, the flexibility of mud films of the weathered soil of red beds with the addition of wood fibres remains unchanged. The flexibility of mud films of the weathered soil of red beds formed by thin fibres under low temperature decreases, while the flexibility of mud films of the weathered soil of red beds formed under high temperature remains unchanged. The constant temperature time increases, and the flexibility of mud films of the weathered soil of red beds remains unchanged. The flexibility of mud films of the weathered soil of red beds formed by colloidal fibres under low temperature remains unchanged, while the flexibility of mud films of the weathered soil of red beds formed under high temperature increases. The constant temperature time increases, and the flexibility of mud films of the weathered soil of red beds increases. The flexibility of mud films of the weathered soil of red beds formed by light fibres under low temperature decreases, while the flexibility of mud films of the weathered soil of red beds formed by high temperature increases. The constant temperature time increases and the flexibility of mud films of the weathered soil of red beds remains unchanged.

3.1.3. The Effect of Self-Developed New Composite Materials after Cyclic Testing on the Self-Sustainability of Mud Films of the Weathered Soil of Red Beds

Figure 7 shows the self-sustainability of mud films of the weathered soil of red beds with the addition of self-developed new composite materials after cyclic testing.
As shown in Figure 7a, the thin-layer properties of mud films of the weathered soil of red beds with the addition of wood fibres, flake fibres, colloidal fibres, and light fibres gradually weaken as the number of cycles for various self-developed new composite materials after zero–three cycles increases.
As shown in Figure 7b, the corrosion resistance of the added wood fibres, sheet fibres, colloidal fibres, and lightweight fibres gradually weakens as the number of cycles of various self-developed new composite materials increases after zero–three cycles of testing.
The flexibility of mud films of the weathered soil of red beds with the addition of wood fibres and colloidal fibres gradually weakens as the number of cycles of various self-developed new composite materials increases after conducting 0–3 cycles, as shown in Figure 7c. The flexibility of the mud film of weathered soil of red beds with thin and lightweight fibres remains unchanged.
No matter how many cycles of testing have been conducted on self-developed new composite materials, the thin-layer properties of mud films of the weathered soil of red beds with the addition of thin fibres are the best, while those with the addition of colloidal fibres are the worst; the addition of wood fibres has the best corrosion resistance, the addition of light fibres has the worst alkali resistance, and the addition of colloidal fibres has the worst acid resistance; the flexibility of mud films of the weathered soil of red beds with the addition of wooden fibres is the best, while those with the addition of thin fibres have the worst.

3.1.4. Comparison of Self-Developed New Composite Materials and Conventional Materials for Improving the Self-Sustainability of Mud Films of the Naturally Weathered Soil of Red Beds

Based on the previous research results of our team [36,37], we will compare and analyse the improvement effect of self-developed new composite materials on the self-sustainability of mud films of the weathered soil of red beds with previous research on conventional materials, as shown in Table 2.
Compared with conventional materials, self-developed new composite materials significantly increase the thin-layer properties, flexibility, and minimum flexibility of mud films of the weathered soil of red beds. The maximum improvement in corrosion resistance (acid resistance), the minimum improvement in corrosion resistance (acid resistance), and the maximum improvement in mud film corrosion resistance (alkali resistance) slightly increase. The minimum improvement in thin-layer properties and the minimum improvement in mud film corrosion resistance (alkali resistance) remain unchanged. Compared with conventional materials, self-developed new composite materials have better improvement effects on the self-sustainability of mud films of the naturally weathered soil of red beds.

3.2. Analysis and Evaluation of Engineering Ecological Protection in Mud Films of the Naturally Weathered Soil of Red Beds

During the experiment (in March), the stable temperature was approximately 21 °C and the stable humidity was approximately 38%. There was no rain during this period. The external environment was stable, and the impact of the environment on the growth of pigeon pea was relatively small.
During the experiment, the changes in soil moisture and conductivity in the three regions are shown in Figure 8a,b. The soil conductivity in experimental areas A and B, as well as the control area, are stable at 40, 27, and 4 μs/cm, and the values of the soil moisture are stable at 13%, 8%, and 5%, respectively. The better the growth of pigeon pea, the more intense their life activities and the higher the soil conductivity as well as moisture content. The area covered with mud films of the naturally weathered soil of red beds without adding materials showed better growth of pigeon peas compared to the control area. The area covered with mud films of the naturally weathered soil of red beds with the addition of a newly developed composite material has a higher growth rate of dal compared to the area covered with mud films of the natural weathered soil of red beds without the addition of material.
During the experiment, the changes in oxygen and carbon dioxide levels in the three regions are shown in Figure 8c,d. The higher the content of oxygen and carbon dioxide in the soil, the stronger the growth activity of pigeon pea and the better its growth. The content of oxygen and carbon dioxide in the soil of test area A is greater than that of test area B, as well as that of the control area. The area covered with mud films of the naturally weathered soil of red beds without adding materials has better growth of pigeon pea than that of the control area. The area covered with mud films of the naturally weathered soil of red beds with adding a new self-developed composite material has better growth potential than the area covered with mud films of the natural weathered soil of red beds without adding materials.
During the experiment, the changes in soil compaction in the three regions are shown in Figure 8e. Pigeon pea begins to take root on the fifth day, and the soil compactness will increase after it takes root. The better the growth of pigeon pea, the greater the soil compactness. After approximately 18 days, the growth cycle of pigeon pea was completed, and the roots no longer grew downwards. The compactness reached its maximum value and then stabilized. Starting from the fifth day, in experiment A the soil compaction was greater than that in experiment B, and the growth of pigeon pea was better in the area covered with mud films of the naturally weathered soil of red beds without adding materials than in the control area. The area covered with mud films of the naturally weathered soil of red beds with adding a new self-developed composite material has better growth potential than the area covered with mud films of the naturally weathered soil of red beds without adding materials.
The growth status of the plant after planting is shown in Figure 9.
After 10 days of planting pigeon pea, the number of sprouted pigeon pea in experimental area A was significantly greater than that in experimental area B, as well as that in the control area. The height of sprouted pigeon pea in experimental area A was significantly higher than that in experimental area B, and greater than that in the control area. The addition of new self-developed composite materials in mud films of the naturally weathered soil of red beds and the absence of materials in mud films of the naturally weathered soil of red beds improved the germination rate and height of pigeon pea, and the effect of adding new self-developed composite materials to mud films of the natural weathered soil of red beds was better.
The germination rate of pigeon pea in experimental areas A and B, as well as the control area, was 72%, 53%, and 36%, respectively. Compared to the control group, the germination rate of pigeon pea in experimental areas A and B increased by 100% and 47.2%, respectively. The germination rate of pigeon pea in the area covered with mud films of the naturally weathered soil of red beds without adding materials is higher than that in the control area. The germination rate of pigeon pea in the area covered with mud films of the naturally weathered soil of red beds with adding a new self-developed composite material is higher than that in the area covered with mud films of the naturally weathered soil of red beds without adding materials. The addition of new self-developed composite materials to mud films of the naturally weathered soil of red beds and the absence of materials to mud films of the naturally weathered soil of red beds improved the germination rate of pigeon pea, and the effect of adding new self-developed composite materials to mud films of the naturally weathered soil of red beds was better.
Pigeon pea sprouted from the fifth day, reaching stability when growing to 36.3, 31.5, and 29.2 mm in experimental zones A and B as well as the control zone, respectively. Compared to the control group, the height of pigeon pea in experimental areas A and increased by 23.8% and 7%, respectively. The final growth height of pigeon pea in the area covered with mud films of the naturally weathered soil of red beds without adding materials is higher than that in the control area. The final growth height of pigeon pea in the area covered with mud films of the natural weathered soil of red beds with adding a new self-developed composite material is higher than that in the area covered with mud films of the natural weathered soil of red beds without adding materials. The addition of new self-developed composite materials to mud films of the natural weathered soil of red beds and the absence of materials to mud films of the natural weathered soil of red beds improved the final growth height of pigeon pea, and the effect of adding new self-developed composite materials to mud films of the natural weathered soil of red beds was better.
The porosity of mud films of the weathered soil of red beds is an important parameter, reflecting their ecological protection effect, and has a very important impact on plant growth. Appropriate aeration porosity and water-holding porosity are beneficial for the exchange of water, heat, air, nutrients, and other substances, thereby promoting plant growth. Conversely, they will inhibit plant growth. During the formation process of mud films of the weathered soil of red beds, with the addition of improved materials, the porosity of mud films will gradually decrease, and the aeration porosity as well as water-holding porosity will undergo corresponding changes. The water content of the control area, experimental area B, and experimental area A will stabilize at 5%, 8%, and 13%, respectively. The gas activity in experimental area A will also become more intense, and the growth of plants will also be better.

3.3. Improvement Principles and Control Elements of Mud Films of the Weathered Soil of Red Beds

3.3.1. The Film-Forming Principle of Mud Films of the Naturally Weathered Soil of Red Beds

During the filtration of mud films of the weathered soil of red beds under external pressure, only the viscous filtrate flows into the porous medium channel of red weathered soil particles, and larger particles of material cannot enter the pores of the ground layer in a timely manner when the particle diameter of self-developed new composite materials is larger than the surface pore size of the particles of the weathered soil of red beds. The larger particles of material gradually accumulate and block the larger pores on the surface of the weathered soil of red beds. A layer of porous medium with a slightly smaller pore size is then formed on the surface of the formation, and the pores with smaller particle diameters in the weathered soil of red beds are further blocked by small particles of material in the mud, resulting in the continuous accumulation and blockage of the surface skeleton of the weathered soil of the red layer and forming a dense membrane structure of material particles. A physical accumulation of mud film can be easily formed due to surface accumulation and blockage form (Figure 10).

3.3.2. Control Elements of Mud Films of the Natural Weathered Soil of Red Beds Based on Self-Developed New Composite Materials

The control factors for the formation of mud films of the natural weathered soil of red beds based on self-developed new composite materials include the types of self-developed new composite materials and the percentage of added self-developed new composite materials in the total mass of mud films of the natural weathered soil of red beds. A total of four self-developed new composite materials were used in this experiment, such as thin fibre, wood fibre, lightweight fibre, and colloidal fibre. For the same self-developed new composite material, the percentage of the mass of the self-developed new composite material added to the total mass of mud films of the naturally weathered soil of red beds is changed, and the amount of addition is listed in Table 3.
The influence of self-developed new composite material types on the self-sustainability of naturally weathered red soil mud films is shown in Figure 11.
Under the condition of uniformly adding a self-developed new composite material with a mass of 50% of the total mass of mud films of the naturally weathered soil of red beds, the thicknesses of mud films of the naturally weathered soil of red beds made of thin fibres, wood fibres, lightweight fibres, and colloidal fibres are 36, 44, 58, and 77 mm, respectively. The thickness of mud films of the natural weathered soil of red beds that can be formed by thin fibres, wood fibres, lightweight fibres, and colloidal fibres gradually increases, and the thin-layer properties of mud films of the natural weathered soil of red beds are better.
The corrosion resistance (acid resistance) range of mud films of the weathered soil of red beds with added thin fibres is pH 6.2 to 7, and the corrosion resistance (alkali resistance) range is pH 6 to 8.6. The corrosion resistance (acid resistance) range of mud films of the weathered soil of red beds with the addition of wood fibres is pH 5.5 to 7, and the corrosion resistance (alkali resistance) range is pH 6 to 8.9. The corrosion resistance (acid resistance) range of mud films of the weathered soil of red beds with the addition of light fibres is pH 5.1 to 7, and the corrosion resistance (alkali resistance) range is pH 6 to 9.3. The corrosion resistance (acid resistance) range of mud films of the weathered soil of red beds with added colloidal fibres is pH 3.8 to 7, and the corrosion resistance (alkali resistance) range is pH 6 to 9.8. Under the condition of adding the same quality of self-developed new composite materials, thin fibre, wood fibre, lightweight fibre, and colloidal fibre gradually enhance the corrosion resistance effect of mud films of the weathered soil of red beds.
Under the condition of uniformly adding a self-developed new composite material with a mass of 50% of the total mass of mud films of the weathered soil of red beds, mud films of the weathered soil of red beds made of thin fibres, wood fibres, lightweight fibres, and colloidal fibres are subjected to pressures of 520, 610, 700, and 780 N, respectively, when they rupture. Thin fibres, wood fibres, lightweight fibres, and colloidal fibres gradually increase the pressure on mud films of the weathered soil of red beds when they rupture, resulting in better flexibility of mud films of the weathered soil of red beds.
For the same self-developed new composite material, the percentage of the added self-developed new composite material to the total mass of mud films of the natural weathered soil of red beds was changed. The self-sustainability of mud films of the weathered soil of red beds is shown in Figure 12.
For the same type of self-developed new composite material, while the total mass of mud films of the weathered soil of red beds remains unchanged, the more the self-developed new composite material is added, the thicker the mud films of the weathered soil of red beds, and the better the thin-layer properties of mud films of the weathered soil of red beds.
For the same self-developed new composite material, the more self-developed new composite material added, the better the corrosion resistance of mud films of the weathered soil of red beds, while the total mass of mud films of the weathered soil of red beds remains unchanged.
For the same self-developed new composite material, the more building materials added, the better the flexibility of mud films of the weathered soil of red beds, while the total mass of mud films of the weathered soil of red beds remains unchanged.

4. Conclusions

The conclusions of this study are as follows:
(1)
The self-developed new composite material has a good improvement effect on the self-sustainability of mud films of the natural weathered soil of red beds. After undergoing constant temperature and cyclic tests on self-made new composite materials, mud films of the naturally weathered soil of red beds with the addition of wood fibres have the best high-temperature resistance effect, while mud films of the naturally weathered soil of red beds with the addition of thin fibres have the weakest high-temperature resistance effect. Mud films of the natural weathered soil of red beds with the addition of thin fibres have the best low-temperature resistance effect, while mud films of the natural weathered soil of red beds with the addition of colloidal fibres have the weakest low-temperature resistance effect. Research has shown that self-developed new composite materials have good improvement effects on mud films of the naturally weathered soil of red beds, promoting research on the self-sustaining green environmental improvement methods of mud films of the natural weathered soil of red beds.
(2)
Through on-site testing, the addition of self-developed new composite materials to mud films of the naturally weathered soil of red beds and the absence of materials to mud films of the naturally weathered soil of red beds promote vegetation growth. The addition of self-developed new composite materials to mud films of the naturally weathered soil of red beds has a better effect, verifying the ecological protection effect of mud films of the naturally weathered soil of red beds based on the new composite material.
(3)
The control factors for the self-sustainability of mud films of the naturally weathered soil of red beds based on self-developed new composite materials are the type and quality proportion of materials, which can be promoted and applied to ecological protection projects, such as slopes and mines.

Author Contributions

Data curation, J.W., Y.G. and C.L.; formal analysis, J.W. and Y.G.; funding acquisition, C.Z. and Z.L.; investigation, J.W. and Y.G.; methodology, Z.L., J.W., Y.G., J.L. and C.L.; project administration, Z.L., J.W., Y.G., J.L. and C.L.; writing—original draft, Z.L., J.W., Y.G., J.L. and C.L.; writing—review and editing, Z.L., J.W., Y.G., J.L., C.L. and C.Z. All authors have read and agreed to the published version of the manuscript.

Funding

The research is supported by the National Natural Science Foundation of China (NSFC) (grant numbers: 42293354, 42293355, 42293351, 42277131, and 41977230).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

All relevant data are contained within the manuscript.

Acknowledgments

The authors would like to thank the anonymous reviewers for their very constructive and helpful comments.

Conflicts of Interest

The authors declare that they have no known competing financial interest or personal relationships that could have appeared to influence the work reported in this paper.

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Figure 1. Natural weathered soil sample of red beds.
Figure 1. Natural weathered soil sample of red beds.
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Figure 2. Schematic diagram of the production process of improved materials.
Figure 2. Schematic diagram of the production process of improved materials.
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Figure 3. Element distributions of self-developed new composite materials.
Figure 3. Element distributions of self-developed new composite materials.
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Figure 4. Production and construction of mud films.
Figure 4. Production and construction of mud films.
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Figure 5. The self-sustainability of mud films of the weathered soil of red beds with the addition of self-developed new composite materials. (a) Thin-layer property, (b) corrosion resistance, and (c) flexibility.
Figure 5. The self-sustainability of mud films of the weathered soil of red beds with the addition of self-developed new composite materials. (a) Thin-layer property, (b) corrosion resistance, and (c) flexibility.
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Figure 6. The self-sustainability of mud films of the weathered soil of red beds with the addition of self-developed new composite materials after constant temperature tests. (a) Thin-layer property, (b) corrosion resistance, and (c) flexibility.
Figure 6. The self-sustainability of mud films of the weathered soil of red beds with the addition of self-developed new composite materials after constant temperature tests. (a) Thin-layer property, (b) corrosion resistance, and (c) flexibility.
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Figure 7. The self-sustainability of mud films of the weathered soil of red beds with the addition of self-developed new composite materials after cyclic testing. (a) Thin-layer property, (b) corrosion resistance, and (c) flexibility.
Figure 7. The self-sustainability of mud films of the weathered soil of red beds with the addition of self-developed new composite materials after cyclic testing. (a) Thin-layer property, (b) corrosion resistance, and (c) flexibility.
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Figure 8. Monitoring of the experimental area. (a) Conductivity, (b) moisture content, (c) oxygen, (d) carbon dioxide, and (e) compactness.
Figure 8. Monitoring of the experimental area. (a) Conductivity, (b) moisture content, (c) oxygen, (d) carbon dioxide, and (e) compactness.
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Figure 9. The state of plant growth.
Figure 9. The state of plant growth.
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Figure 10. Film-forming principle.
Figure 10. Film-forming principle.
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Figure 11. The influence of self-developed new composite material types on the self-sustainability of natural weathered red soil mud films.
Figure 11. The influence of self-developed new composite material types on the self-sustainability of natural weathered red soil mud films.
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Figure 12. Quality control diagram of the self-sustainability of self-developed new composite materials. (a) Thin-layer property, (b) corrosion resistance, and (c) flexibility.
Figure 12. Quality control diagram of the self-sustainability of self-developed new composite materials. (a) Thin-layer property, (b) corrosion resistance, and (c) flexibility.
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Table 1. Self-developed new composite materials.
Table 1. Self-developed new composite materials.
Self-Developed New Composite MaterialsViscosity (Pa s)Density (g/cm3)
Wood fibre70.21.3
Flake fibre65.31.5
Colloidal fibre61.81.8
Lightweight fibre62.61.1
Table 2. Comparison of self-developed new composite materials and conventional materials for improving the self-sustainability of mud films of the natural weathered soil of red beds.
Table 2. Comparison of self-developed new composite materials and conventional materials for improving the self-sustainability of mud films of the natural weathered soil of red beds.
Material TypeAdhesiveMineral MaterialsConstruction MaterialPlant MaterialsCelluloseSelf-Developed New Composite Materials
Maximum improvement in thin-layer properties (%)No. 1 (780)Albite (579)Environmentally friendly adhesive (640)Wheat straw (495)HBR cellulose (690)Wood fibre (850)Flake fibre (975)Colloidal fibre (1050)Lightweight fibre (925)
Minimal improvement in thin-layer properties (%)No. 4 (190)Feldspar (166)Air-entraining agents (81.5)Corn straw (31.5)HHBR cellulose (150)Wood fibre (175)Flake fibre (170)Colloidal fibre (260)Lightweight fibre (195)
Maximum improvement in corrosion resistance (acid resistance) (%)No. 2 (91.7)Feldspar (86.7)Thickener (91.7)Wormwood straw (55)HBR cellulose (68.3)Wood fibre (90)Flake fibre (80)Colloidal fibre (88.3)Lightweight fibre (75)
Minimal improvement in corrosion resistance (acid resistance) (%)No. 1 (20)Albite (13.3)Environmentally friendly adhesive (20)Rice straw
(−13.3)		HHBR cellulose
(−3.3)		Wood fibre (21.7)Flake fibre (11.7)Colloidal fibre (6.6)Lightweight fibre (16.7)
Maximum improvement in corrosion resistance (alkali resistance) (%)No. 1 (68.8) Nano-silica (65)Drought strengthening agent (45)Yangmei Tannin Extract (65)HHR cellulose (52.1)Wood fibre (50)Flake fibre (41.25)Colloidal fibre (53.8)Lightweight fibre (70)
Minimal improvement in corrosion resistance (alkali resistance) (%)No. 6 (15)Nano-silica (10)Putty (9.8)Potato straw (10)HHBR cellulose
(−2.5)		Wood fibre
(−6.2)		Flake fibre (3.75)Colloidal fibre (5)Lightweight fibre (2.5)
Maximum improvement in flexibility (%)No. 7 (187.5)Feldspar (150)Putty (225)Sweet potato straw (112.5)HHR cellulose (187.5)Wood fibre (250)Flake fibre (325)Colloidal fibre (350)Lightweight fibre (300)
Minimal improvement in flexibility (%)No. 5 (125)Albite (50)Water-reducing agent (100)Pine straw (25)HBR cellulose (75)Wood fibre (100)Flake fibre (162.5)Colloidal fibre (137.5)Lightweight fibre (125)
Table 3. Quality control table for self-developed new composite materials.
Table 3. Quality control table for self-developed new composite materials.
NameThe Percentage of the Added Self-Developed New Composite Material in the Total Mass of Mud Films of the Natural Weathered Soil of Red Beds (%)
Flake fibre0, 20, 40, 60, 80
Wood fibre0, 20, 40, 60, 80
Lightweight fibre0, 20, 40, 60, 80
Colloidal fibre0, 20, 40, 60, 80
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Liu, Z.; Wang, J.; Gao, Y.; Liao, J.; Lan, C.; Zhou, C. Development of Self-Sustaining Improvement Material for a Mud Film of the Weathered Soil of Red Beds. Sustainability 2023, 15, 15284. https://doi.org/10.3390/su152115284

AMA Style

Liu Z, Wang J, Gao Y, Liao J, Lan C, Zhou C. Development of Self-Sustaining Improvement Material for a Mud Film of the Weathered Soil of Red Beds. Sustainability. 2023; 15(21):15284. https://doi.org/10.3390/su152115284

Chicago/Turabian Style

Liu, Zhen, Jingqi Wang, Yi Gao, Jin Liao, Chunhui Lan, and Cuiying Zhou. 2023. "Development of Self-Sustaining Improvement Material for a Mud Film of the Weathered Soil of Red Beds" Sustainability 15, no. 21: 15284. https://doi.org/10.3390/su152115284

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