Sulphoaluminate cement ecological soil for slope regreening and preparation method of sulphoaluminate cement ecological soil

Abstract

The invention discloses sulphoaluminate cement ecological soil for slope greening, and belongs to the technical field of slope ecological restoration. The ecological soil is composed of a base layer and a surface layer, wherein the base layer is prepared from the following raw materials: 950-1250 parts of a soil sample, 60-100 parts of quick-hardening sulphoaluminate cement, 45-95 parts of flue gas desulfurization gypsum, 20-65 parts of limestone powder, 5-18 parts of fly ash and 300-500 parts of water; the surface layer is prepared from the following raw materials in parts by weight: 1000-1200 parts of a soil sample, 20-90 parts of quick-hardening sulphoaluminate cement, 10-42 parts of flue gas desulfurization gypsum, 6-25 parts of limestone powder, 2-5 parts of fly ash and 200-400 parts of water; all the components are in parts by weight. According to the ecological soil, quick-hardening sulphoaluminate cement with low alkalinity is particularly selected as a raw material, and the pH value of a system is greatly reduced while the energy consumption and the consumption of non-renewable resources are effectively reduced by virtue of the synergistic effect of flue gas desulfurization gypsum, limestone powder and fly ash. In addition, the invention further discloses an ecological soil preparation method which is simple in preparation and high in operability, the construction time can be greatly shortened, the labor intensity can be greatly reduced, and the engineering efficiency can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of slope ecological restoration, and in particular relates to sulphoaluminate cement ecological soil for slope greening and a preparation method thereof. Background Art

[0002] Slope ecological restoration technology relies on the water-retention and soil-stabilizing properties of plants to stabilize slopes. By introducing pioneer plant species, it gradually achieves community replacement, aiming to gradually restore natural ecological balance. While large-scale engineering construction has boosted local and regional economic growth, its environmental impacts are also becoming increasingly prominent. Hydropower projects, in particular, not only create numerous exposed slopes but also create the risk of geological disasters, further exacerbating ecological conditions and leading to ecosystem decline. These issues limit the sustainable development of engineering construction, making slope ecological restoration a pressing issue.

[0003] Currently, traditional Portland cement is commonly used for slope protection in my country. Slope reinforcement methods include frame anchors, frame anchor cables, herringbone frame slope protection, diamond frame slope protection, and arch frame slope protection. Frame beams offer excellent protection for soil, gravel, and rock slopes. If necessary, anchors can be installed on frame beams to further enhance slope stability. Concrete frame protection is suitable for soil or gravel slopes with slope ratios between 1:0.75 and 1:1.25. However, this method presents a number of ecological challenges. First, the pH value of conventional slope protection concrete is generally high, which is unfavorable for plant growth and can easily lead to degradation of the slope's ecological environment and instability of plant communities. Second, while concrete slope protection and anchor frame beam slope protection can effectively prevent surface and rockfall hazards, they completely seal the slope surface, blocking material exchange between the slope and the natural environment. Third, the production of conventional concrete slope protection materials consumes significant amounts of energy and non-renewable resources, placing a significant burden on the ecological environment.

[0004] At the same time, existing ecological restoration technologies focus solely on either solidification or greening, lacking an integrated solution that addresses both. Therefore, to address these issues, it is necessary to propose a solution that combines environmentally friendly raw materials with excellent mechanical properties, plant growth performance, and ecological restoration capabilities. Summary of the Invention

[0005] The present invention provides a sulphoaluminate cement eco-soil for slope regreening. The formula specifically selects low-alkalinity, fast-hardening sulphoaluminate cement as the raw material. Through the synergistic effect of flue gas desulfurization gypsum, limestone powder, and fly ash, the system improves its mechanical properties while significantly reducing its pH, thereby meeting the needs of plant growth. By designing a double-layer (base layer and surface layer) structure and rationally configuring the material components and strength of the double-layer structure, cement usage is further reduced, while ensuring the overall stability of the slope, enhancing the slope's ability to resist rainwater erosion, reducing soil erosion, and maintaining the retention of water, soil, and organic matter, thereby achieving integrated slope solidification and greening. The eco-soil of the present invention uses industrial byproducts and organic waste as raw materials and has advantages such as environmental friendliness, ease of construction, and low cost. It is suitable for large-scale slope ecological restoration projects, integrating engineering reinforcement with ecological restoration. Furthermore, the eco-soil of the present invention has the characteristics of rapid setting and hardening, making it suitable for the field of slope ecological restoration. Through its inherent fluidity and self-compacting properties, the eco-soil can fully cover and solidify the slope, creating the necessary conditions for plant seed growth.

[0006] The present invention also provides a method for preparing sulphoaluminate cement ecological soil for slope regreening. The method has a simple preparation process, strong operability, and a convenient construction process, which greatly reduces construction time and labor intensity and improves engineering efficiency.

[0007] Unless otherwise specified, all raw materials in the present invention are calculated by weight.

[0008] The technical solutions of the present invention are as follows: A sulphoaluminate cement ecological soil for slope greening, comprising a base layer and a surface layer, wherein the base layer comprises: 950-1250 parts of soil sample, 60-100 parts of rapid-hardening sulphoaluminate cement, 45-95 parts of flue gas desulfurization gypsum, 20-65 parts of limestone powder, 5-18 parts of fly ash, and 300-500 parts of water; The surface layer raw materials include: 1000~1200 parts of soil sample, 20~90 parts of fast-hardening sulphoaluminate cement, 10~42 parts of flue gas desulfurization gypsum, 6~25 parts of limestone powder, 2~5 parts of fly ash, and 200~400 parts of water.

[0009] Preferably, the soil samples in the base layer are 1000 to 1200 parts.

[0010] In order to enable the seeds to fully absorb moisture in the soil and improve their germination rate, the surface layer further contains 20 to 300 parts of plant seeds; preferably, the plant seeds are one or more of Amorpha fruticosa seeds, tall fescue seeds, Alopecurus purpurogenus seeds, Magnolia multiflora seeds or Cynodon dactylon seeds; more preferably, the plant seeds are one or more of 40 to 60 parts of Amorpha fruticosa seeds, 40 to 60 parts of tall fescue seeds, 40 to 60 parts of Alopecurus purpurogenus seeds, 20 to 30 parts of Magnolia multiflora seeds or 20 to 30 parts of Cynodon dactylon seeds; further preferably, the plant seeds are 200 to 300 parts.

[0011] In order to provide plant seeds with rich nutrients and a suitable growth environment and promote rapid germination and growth of seeds, the surface soil sample further contains 700~840 parts of nutrient soil. Preferably, the organic matter mass content in the nutrient soil is ≥70%; more preferably, the organic matter mass content in the nutrient soil is 72%, and the mass content of total nutrients (N+P2O5+K2O) is 1.86%. Among them, total nutrients (N+P2O5+K2O) represents the total content of the three main nutrients of nitrogen, phosphorus and potassium in the fertilizer. It is an important parameter for measuring fertilizer quality and fertilizer efficiency.

[0012] In order to improve the structure of ecological soil samples, enhance the water retention and air permeability of cement ecological soil, and at the same time, consider that the organic matter in humus can provide necessary nutrients for plant seeds and promote plant growth; the organic acid therein can also react with Ca(OH)2 in the system to further reduce the pH value of the system.

[0013] Furthermore, the base layer further comprises 30-100 parts of humus, and the surface layer further comprises 100-120 parts of humus. Preferably, the humus is one or more of sugarcane bagasse, rice husks, straw, sawdust, mushroom residue, and coconut husks; more preferably, the humus is rice husks.

[0014] In this invention, rapid-hardening sulphoaluminate cement, used as the primary cementitious material, exhibits rapid setting and high early strength. Its hydration reaction produces ettringite (AFt) and calcium silicate hydrate (CSH), significantly enhancing the early strength of the cement eco-soil.

[0015] Preferably, the rapid hardening sulphoaluminate cement in the base layer is 60 to 85 parts.

[0016] Preferably, the Blaine specific surface area of ​​the rapid hardening sulphoaluminate cement is 350 m 2 / kg or more, the strength grade is 42.5 or more, and more preferably, the Blaine specific surface area of ​​hard sulphoaluminate cement is 350~520m 2 / kg; Further preferably, the Blaine specific surface area of ​​the rapid hardening sulphoaluminate cement is 410~520m 2 / kg.

[0017] In the present invention, CaSO4·2H2O in the flue gas desulfurization gypsum reacts with the aluminate in the cement to form ettringite (AFt), which enhances the early strength of the cement eco-soil. At the same time, the addition of gypsum can consume Ca(OH)2 in the system, effectively lowering the pH value of the cement eco-soil and reducing the negative impact of the alkaline environment on plant growth.

[0018] Preferably, the flue gas desulfurization gypsum in the base layer is 45 to 85 parts, more preferably, the flue gas desulfurization gypsum is 60 to 85 parts; further preferably, the flue gas desulfurization gypsum is 65 to 85 parts.

[0019] Preferably, the mass content of CaSO4·2H2O in the flue gas desulfurization gypsum is ≥85%; more preferably, the mass content of CaSO4·2H2O in the flue gas desulfurization gypsum is 92%.

[0020] In this invention, the CaCO₃ in the limestone powder provides nucleation sites during cement hydration, promoting the formation of ettringite (AFt) and producing semi-carbonic calcium aluminate carbonate hydrate, significantly increasing the density and later strength of the cement eco-soil. Furthermore, the limestone powder optimizes the structure of the cement eco-soil through its physical filling effect, reducing porosity and increasing compressive strength.

[0021] Preferably, the limestone powder in the base layer is 20 to 30 parts.

[0022] Preferably, the mass content of CaCO3 in the limestone powder is ≥75%, and the fineness of the limestone powder is ≥300 mesh; more preferably, the mass content of CaCO3 in the limestone powder is 88%, and the fineness of the limestone powder is 325 mesh.

[0023] In this method, the active SiO2 and Al2O3 in fly ash react with C4A3S in cement to form hydrated calcite and ettringite (AFt), which can improve the strength and durability of cement-based eco-soil. The addition of fly ash also produces a pozzolanic effect, consuming Ca(OH)2, lowering the pH of the cement-based eco-soil and reducing the inhibitory effects of alkalinity on plant growth.

[0024] Preferably, the fly ash in the base layer is 5 to 15 parts.

[0025] Preferably, the fly ash is one of Class I fly ash or Class II fly ash, with a fineness of ≥300 mesh and a SiO2 mass content of ≥40%; more preferably, the fly ash is Class II fly ash; further preferably, the fly ash is Class II fly ash with a fineness (45µm square hole sieve residue) of 26.6% and a SiO2 mass content of 44.6%.

[0026] Preferably, the soil sample is one or more of sandy soil, silty clay, clay, and humus with a pH value of 7.50 to 8.50; the soil sample particle size is less than 5 mm; more preferably, the soil sample is silty clay with a pH value of 8.0, and the soil sample particle size is less than 5 mm.

[0027] The present invention also relates to a method for preparing sulphoaluminate cement ecological soil for slope greening, comprising the following steps: weighing raw materials for both the base layer and the surface layer according to a proportion, mixing the raw materials without water and soil samples, adding water and stirring into a slurry, and then fully mixing with the soil sample and discharging the material.

[0028] Plant seeds can be added during the preparation of the surface layer, or they can be sprinkled on the surface after the surface layer is prepared (see plant growth test). In order to allow the seeds to fully absorb moisture from the soil and increase the germination rate, it is preferred that the plant seeds be added during the preparation of the surface layer. The specific preparation method is as follows: A method for preparing sulphoaluminate cement ecological soil for slope greening comprises the following steps: Preparation of base layer: weigh all raw materials according to the proportion, first mix all raw materials except water and soil sample evenly; then add water and continue stirring until uniform to form a mixed slurry; finally, mix the mixed slurry with the soil sample thoroughly to complete the discharge; Preparation of the surface layer: weigh the raw materials according to the ratio, first mix the raw materials except water, soil samples, and plant seeds evenly, then add water and mix well to obtain a mixed slurry; then mix the soil samples and plant seeds to obtain a mixture, and finally fully mix the mixed slurry and the mixture and discharge the material.

[0029] More preferably, both the base layer and the surface layer of the ecological soil contain humus, and the surface layer soil sample contains nutrient soil. The specific preparation method is as follows: A method for preparing sulphoaluminate cement ecological soil for slope greening comprises the following steps: Preparation of the base layer: weigh the raw materials according to the proportion, first mix the rapid hardening sulphoaluminate cement, flue gas desulfurization gypsum, limestone powder, fly ash and humus, then add water and mix to obtain a mixed slurry, finally fully mix the mixed slurry with the soil sample and discharge the material; Preparation of the surface layer: weigh the raw materials according to the ratio, first mix the fast-hardening sulphoaluminate cement, flue gas desulfurization gypsum, limestone powder, fly ash and humus, then add water and mix to obtain a mixed slurry; then add nutrient soil and plant seeds and mix to obtain a mixture, finally fully mix the mixture with the remaining soil samples without nutrient soil, and discharge the material.

[0030] In terms of material design, the formula of the double-layer structure of ecological soil contains common ingredients such as fast-hardening sulphoaluminate cement, which forms chemical bonds through the hydration reaction of cement to ensure interfacial bonding strength; in terms of strength design, the double-layer structure adopts a gradient design - the base layer strength is 0.5~1.2MPa, and the surface layer strength is 0.3~0.5MPa. This design ensures the overall stability of the slope, that is, the base layer provides higher strength and density to support the entire slope structure and prevent slope collapse and landslides; the surface layer provides moderate strength and a good plant growth environment, and realizes ecological restoration through vegetation cover, prevents soil erosion, improves the ecological environment, and avoids stiffness mutations to ensure overall collaborative deformation capacity.

[0031] According to the vegetation concrete (CBS) slope protection technology, through the numerical simulation verification of the two-dimensional finite element analysis software (PLAXIS 2D) for geotechnical engineering and rock mechanics, when the compressive strength of the base layer and the surface layer is 0.3MPa, the overall safety factor of the slope is greater than the standard factor of 1.25, which meets the overall stability requirements of the slope and can still maintain reliable bearing capacity in extreme weather (level 6 wind and daily rainfall of 77.5mm). When the strength is increased to 0.5MPa, the displacement increment is only 10 -1 The impact on stability is negligible at the mm level, so from an engineering economics perspective, a strength index of 0.3 MPa is more feasible. When applied to a steep slope with a gradient of 1:0.75, the displacement of the slope structure increased by 5% to 8% compared to the baseline condition; while on a gentle slope of 1:1.25, the displacement decreased by 8% to 12%. These displacement changes remain within a reasonable range and have no impact on the overall stability of the slope. Therefore, this technology is widely applicable within the slope gradient range of 1:0.75 to 1:1.25, meeting the technical requirements of various typical engineering scenarios, including steep slopes, standard slopes, and gentle slopes.

[0032] During application, the mixed base layer slurry can be evenly spread on the slope surface to ensure uniform thickness (the base layer thickness can be set to 8-12 cm depending on the height, gradient, and geological conditions of the slope). After spreading, the base layer should be initially compacted and then initially cured for 2-4 hours. After the base layer has basically solidified, the surface layer slurry should be evenly sprayed or spread on the base layer surface to ensure uniform surface layer thickness (the surface layer thickness should be 2-5 cm to meet the needs of plant growth and development. If the thickness is less than 2 cm, it may affect seed germination; if it exceeds 5 cm, it may increase the risk of slippage). The paved surface layer should be lightly compacted to enhance mechanical bite. After compaction, water should be sprayed regularly to maintain moisture.

[0033] In this invention, the synergistic effect of rapid-hardening sulphoaluminate cement and flue gas desulfurization gypsum produces a large amount of ettringite (AFt), providing early strength support. The addition of limestone powder and fly ash further enhances the density and later strength of the cement eco-soil. The synergistic effect with the flue gas desulfurization gypsum significantly lowers the pH of the system, reducing the negative impact of alkalinity on plant growth. The addition of humus not only provides nutrients for plants but also improves the structure of the eco-soil sample, enhancing its water retention and air permeability.

[0034] In addition, in the surface layer, the nutrient soil and humus work together to effectively enhance the water retention and air permeability of the soil, and provide rich nutrients and a suitable growth environment for plant seeds, promoting the rapid germination and growth of seeds and extending to the base layer ( Figure 8 Plant seeds rely on the nutrients and environmental support of the surface layer to germinate and grow quickly, forming vegetation cover, further stabilizing the slope surface and preventing soil erosion.

[0035] The ability of surface plant roots to penetrate the base layer depends primarily on the base layer's pore structure, strength gradient design, the effects of humus and nutrient soil, and the cement hydration reaction. During the preparation process, the base layer develops a dense structure with a certain porosity, providing space for root growth. During the hydration process, rapid-hardening sulfoaluminate cement forms ettringite (AFt) and calcium silicate hydrate (CSH), creating a microporous structure that further provides channels for root growth.

[0036] Plant roots extend through the substrate ( Figure 8 ), forming a structure similar to a "biological anchor," enhancing the mechanical stability of the slope, preventing soil erosion, improving soil structure, promoting ecosystem recovery, and enhancing the long-term stability of the slope. The network of roots in the base effectively stabilizes the soil, reducing soil erosion caused by rainwater erosion. Furthermore, root activity improves the microstructure of the base, enhancing its water retention and air permeability, providing an optimal environment for long-term plant growth.

[0037] The beneficial effects of the present invention are: (1) Eco-soil specifically uses fast-hardening sulphoaluminate cement with low alkalinity. Through the synergistic effect of various industrial by-products and solid wastes, such as flue gas desulfurization gypsum, limestone powder, and fly ash, the active ingredients in solid waste are fully utilized while ensuring the mechanical properties of the system. This not only significantly reduces the pH value of the material system, reduces the amount of sulphoaluminate cement, energy consumption, and the consumption of non-renewable resources, but also effectively solves the environmental pollution problem caused by solid waste storage.

[0038] (2) Ecological soil adopts a double-layer structure design: the base layer provides high strength and density to ensure the stability of the slope; the surface layer, through vegetation coverage and pH adjustment, creates a good plant growth environment, prevents soil erosion, and improves the ecological environment. By rationally configuring the material components and strength of the ecological soil double-layer structure, while further reducing the amount of cement in the system, the slope's ability to resist rainwater erosion is significantly improved, biodiversity is enhanced, and the integration of engineering reinforcement and ecological restoration is achieved.

[0039] (3) Ecological soil has the advantages of being environmentally friendly, easy to construct, and low cost. At the same time, its preparation process is simple and highly operable. It is suitable for large-scale slope ecological restoration projects and has both engineering and ecological benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 For grassroots photos; Figure 2 The unconfined compressive strength (USC) graphs of the specimens of Examples 1 to 5 were measured after curing to the corresponding ages (3d, 7d, and 28d); Figure 3 The pH values ​​of the specimens of Examples 1 to 5 were measured after curing to the corresponding ages (3d, 7d, and 28d); Figure 4 The unconfined compressive strength graph of the specimens of Example 1 and Comparative Examples 1 to 14 measured after 28 days of curing; Figure 5 The pH values ​​of the specimens of Example 1 and Comparative Examples 1 to 14 were measured after curing for 28 days. Figure 6 This is a diagram showing the vegetation effect of the mixed plant seeds 3 days after sowing in Examples 6 to 9; Figure 7 This is a diagram showing the vegetation effect of the mixed plant seeds 21 days after sowing in Examples 6 to 9; Figure 8 This is a cross-sectional view of tall fescue growing in sulphoaluminate cement ecological soil (I); Figure 9 This is the cross-section of tall fescue growing in sulphoaluminate cement ecological soil (II); Figure 10 This is a cross-sectional view of tall fescue growing in sulphoaluminate cement ecological soil (3).

[0041] Reference numerals a. Example 6; b. Example 7; c. Example 8; d. Example 9; 1. Amorpha fruticosa; 2. Tall fescue; 3. Medicago sativa; 4. Bermuda grass. DETAILED DESCRIPTION

[0042] The specific embodiments listed in the present invention are only examples of the present invention, and the present invention is not limited to the specific embodiments described below. For those skilled in the art, any equivalent modifications and substitutions to the embodiments described below are also within the scope of the present invention. Therefore, equivalent transformations and modifications made without departing from the spirit and scope of the present invention should be included within the scope of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. All reagents or instruments without the manufacturer specified are conventional products that can be purchased commercially. In order to better illustrate the present invention, numerous specific details are given in the specific embodiments below. Those skilled in the art should understand that the present invention can also be implemented without certain specific details. In other embodiments, methods, means, equipment and steps well known to those skilled in the art are not described in detail in order to highlight the main purpose of the present invention.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art. Unless otherwise specified, the units used in this specification are International Standard Units, and the numerical values ​​and numerical ranges appearing in this invention should be understood to include the inevitable systematic errors in industrial production.

[0044] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0045] Soil sample: silty clay with pH value = 8.0 and particle size < 5 mm.

[0046] Rapid-hardening sulphoaluminate cement: The Blaine surface area of ​​42.5 strength grade rapid-hardening sulphoaluminate cement is 410m 2 / kg; the Blaine specific surface area of ​​52.5 strength grade rapid hardening sulphoaluminate cement is 450m 2 / kg; the Blaine specific surface area of ​​62.5 strength grade rapid hardening sulphoaluminate cement is 480m 2 / kg; the Blaine specific surface area of ​​72.5 strength grade rapid hardening sulphoaluminate cement is 520m 2 / kg.

[0047] The mass content of CaSO4·2H2O in flue gas desulfurization gypsum is 92%.

[0048] The mass content of CaCO3 in the limestone powder is 88%, and the fineness of the limestone powder is 325 mesh.

[0049] The mass content of SiO2 in Class II fly ash is 44.6%, and the fineness of Class II fly ash (residue on a 45µm square sieve) is 26.6%.

[0050] The mass content of organic matter in the surface nutrient soil is 72%, and the mass content of total nutrients (N+P2O5+K2O) is 1.86%.

[0051] Example 1 The base layer of sulphoaluminate cement ecological soil for slope regreening of the present invention is prepared from the following raw materials in parts by weight: 1000 parts of soil sample, 60 parts of 62.5 strength grade fast-hardening sulphoaluminate cement, 85 parts of flue gas desulfurization gypsum, 25 parts of limestone powder, 5 parts of grade II fly ash, 50 parts of rice husks and 500 parts of water.

[0052] The preparation method is as follows: weigh the raw materials according to the proportion, first mix the rapid hardening sulphoaluminate cement, flue gas desulfurization gypsum, limestone powder and fly ash, then add water and mix to obtain a mixed slurry, and finally mix the mixed slurry with the soil sample to prepare an ecological soil cube specimen with a size of 70.7 mm × 70.7 mm × 70.7 mm ( Figure 1 ).

[0053] Example 2 The base layer of sulphoaluminate cement ecological soil for slope regreening of the present invention is prepared from the following raw materials in parts by weight: 1200 parts of soil sample, 60 parts of 62.5 strength grade fast-hardening sulphoaluminate cement, 45 parts of flue gas desulfurization gypsum, 65 parts of limestone powder, 10 parts of grade II fly ash, 30 parts of rice husks and 300 parts of water.

[0054] The preparation method is as follows: weigh the raw materials according to the ratio, first mix the fast-hardening sulphoaluminate cement, flue gas desulfurization gypsum, limestone powder and fly ash, then add water and mix to obtain a mixed slurry, and finally mix the mixed slurry with the soil sample to finally prepare an ecological soil cube specimen with a size of 70.7 mm × 70.7 mm × 70.7 mm.

[0055] Example 3 The base layer of sulphoaluminate cement ecological soil for slope regreening of the present invention is prepared from the following raw materials in parts by weight: 1000 parts of soil sample, 80 parts of 62.5 strength grade fast-hardening sulphoaluminate cement, 65 parts of flue gas desulfurization gypsum, 25 parts of limestone powder, 15 parts of grade II fly ash, 100 parts of rice husks and 500 parts of water.

[0056] The preparation method is as follows: weigh the raw materials according to the ratio, first mix the fast-hardening sulphoaluminate cement, flue gas desulfurization gypsum, limestone powder and fly ash, then add water and mix to obtain a mixed slurry, and finally mix the mixed slurry with the soil sample to finally prepare an ecological soil cube specimen with a size of 70.7 mm × 70.7 mm × 70.7 mm.

[0057] Example 4 The base layer of sulphoaluminate cement ecological soil for slope regreening of the present invention is prepared from the following raw materials in parts by weight: 1200 parts of soil sample, 80 parts of 52.5 strength grade fast-hardening sulphoaluminate cement, 45 parts of flue gas desulfurization gypsum, 45 parts of limestone powder, 8 parts of grade II fly ash, 50 parts of rice husks and 500 parts of water.

[0058] The preparation method is as follows: weigh the raw materials according to the ratio, first mix the fast-hardening sulphoaluminate cement, flue gas desulfurization gypsum, limestone powder and fly ash, then add water and mix to obtain a mixed slurry, and finally mix the mixed slurry with the soil sample to finally prepare an ecological soil cube specimen with a size of 70.7 mm × 70.7 mm × 70.7 mm.

[0059] Example 5 The base layer of sulphoaluminate cement ecological soil for slope regreening of the present invention is prepared from the following raw materials in parts by weight: 1000 parts of soil sample, 100 parts of 72.5 strength grade fast-hardening sulphoaluminate cement, 45 parts of flue gas desulfurization gypsum, 25 parts of limestone powder, 12 parts of fly ash, 100 parts of rice husks and 500 parts of water.

[0060] The preparation method is as follows: weigh the raw materials according to the ratio, first mix the fast-hardening sulphoaluminate cement, flue gas desulfurization gypsum, limestone powder and fly ash, then add water and mix to obtain a mixed slurry, and finally mix the mixed slurry with the soil sample to finally prepare an ecological soil cube specimen with a size of 70.7 mm × 70.7 mm × 70.7 mm.

[0061] Example 6 The surface layer of sulphoaluminate cement ecological soil for slope regreening of the present invention is prepared from the following raw materials in parts by weight: 1000 parts of soil sample (including 700 parts of nutrient soil), 20 parts of 42.5 strength grade fast-hardening sulphoaluminate cement, 10 parts of flue gas desulfurization gypsum, 6 parts of limestone powder, 2 parts of grade II fly ash, 100 parts of rice husks and 200 parts of water.

[0062] The preparation method is as follows: weigh the raw materials according to the ratio, first mix the fast-hardening sulphoaluminate cement, flue gas desulfurization gypsum, limestone powder, fly ash and humus, then add water and mix to obtain a mixed slurry, then add nutrient soil and mix to obtain a mixture, and finally mix the mixture with the remaining soil samples without nutrient soil, and finally prepare an ecological soil cube specimen with a size of 70.7 mm × 70.7 mm × 70.7 mm.

[0063] Example 7 The surface layer of sulphoaluminate cement ecological soil for slope regreening of the present invention is prepared from the following raw materials in parts by weight: 1200 parts of soil sample (including 840 parts of nutrient soil), 40 parts of 52.5 strength grade fast-hardening sulphoaluminate cement, 19 parts of flue gas desulfurization gypsum, 11 parts of limestone, 3 parts of grade II fly ash, 110 parts of rice husks and 300 parts of water.

[0064] The preparation method is as follows: weigh the raw materials according to the ratio, first mix the fast-hardening sulphoaluminate cement, flue gas desulfurization gypsum, limestone powder, fly ash and humus, then add water and mix to obtain a mixed slurry, then add nutrient soil and mix to obtain a mixture, and finally mix the mixture with the remaining soil samples without nutrient soil, and finally prepare an ecological soil cube specimen with a size of 70.7 mm × 70.7 mm × 70.7 mm.

[0065] Example 8 The surface layer of sulphoaluminate cement ecological soil for slope regreening of the present invention is prepared from the following raw materials in parts by weight: 1060 parts of soil sample (including 700 parts of nutrient soil), 60 parts of 62.5 strength grade fast-hardening sulphoaluminate cement, 28 parts of flue gas desulfurization gypsum, 17 parts of limestone, 4 parts of grade II fly ash, 120 parts of rice husks and 400 parts of water.

[0066] The preparation method is as follows: weigh the raw materials according to the ratio, first mix the fast-hardening sulphoaluminate cement, flue gas desulfurization gypsum, limestone powder, fly ash and humus, then add water and mix to obtain a mixed slurry, then add nutrient soil and mix to obtain a mixture, and finally mix the mixture with the remaining soil samples without nutrient soil, and finally prepare an ecological soil cube specimen with a size of 70.7 mm × 70.7 mm × 70.7 mm.

[0067] Example 9 The surface layer of sulphoaluminate cement ecological soil for slope regreening of the present invention is prepared from the following raw materials in parts by weight: 1140 parts of soil sample (including 840 parts of nutrient soil), 90 parts of 72.5 strength grade fast-hardening sulphoaluminate cement, 42 parts of flue gas desulfurization gypsum, 25 parts of limestone, 5 parts of grade II fly ash, 100 parts of rice husks and 200 parts of water.

[0068] The preparation method is as follows: weigh the raw materials according to the ratio, first mix the fast-hardening sulphoaluminate cement, flue gas desulfurization gypsum, limestone powder, fly ash and humus, then add water and mix to obtain a mixed slurry, then add nutrient soil and mix to obtain a mixture, and finally mix the mixture with the remaining soil samples without nutrient soil, and finally prepare an ecological soil cube specimen with a size of 70.7 mm × 70.7 mm × 70.7 mm.

[0069] Comparative Example 1 On the basis of Example 1, no flue gas desulfurization gypsum was added, and other conditions remained unchanged.

[0070] Comparative Example 2 On the basis of Example 1, the amount of flue gas desulfurization gypsum was changed to 30 parts, and the other conditions remained unchanged.

[0071] Comparative Example 3 On the basis of Example 1, the amount of flue gas desulfurization gypsum was changed to 120 parts, and the other conditions remained unchanged.

[0072] Comparative Example 4 On the basis of Example 1, no limestone powder was added and other conditions remained unchanged.

[0073] Comparative Example 5 On the basis of Example 1, the amount of limestone powder was changed to 10 parts, and the other conditions remained unchanged.

[0074] Comparative Example 6 On the basis of Example 1, the amount of limestone powder was changed to 80 parts, and the other conditions remained unchanged.

[0075] Comparative Example 7 On the basis of Example 1, fly ash was not added and other conditions remained unchanged.

[0076] Comparative Example 8 Based on Example 1, the amount of fly ash was changed to 2 parts, and the other conditions remained unchanged.

[0077] Comparative Example 9 On the basis of Example 1, the amount of fly ash was changed to 20 parts, and the other conditions remained unchanged.

[0078] Comparative Example 10 On the basis of Example 1, no flue gas desulfurization gypsum and limestone powder were added, and other conditions remained unchanged.

[0079] Comparative Example 11 On the basis of Example 1, no flue gas desulfurization gypsum and fly ash were added, and other conditions remained unchanged.

[0080] Comparative Example 12 On the basis of Example 1, limestone powder and fly ash were not added, and other conditions remained unchanged.

[0081] Comparative Example 13 On the basis of Example 1, the amount of rapid-hardening sulphoaluminate cement was changed to 40 parts, and the other conditions remained unchanged.

[0082] Comparative Example 14 On the basis of Example 1, the amount of rapid-hardening sulphoaluminate cement was changed to 120 parts, and the other conditions remained unchanged.

[0083] Strength and pH testing After demolding the molded specimens of Examples 1 to 9 and Comparative Examples 1 to 14 at room temperature, the surfaces were covered with felt and watered and cured to the corresponding ages for unconfined compressive strength tests and pH value tests.

[0084] The unconfined compressive strength of the specimens of Examples 1 to 5 after curing to the corresponding ages (3d, 7d, 28d) is as follows: Figure 2 and as shown in Table 1.

[0085] The pH values ​​of the samples of Examples 1 to 5 after curing to the corresponding ages (3d, 7d, 28d) are as follows: Figure 3 and as shown in Table 2.

[0086] Table 1 Unconfined compressive strength of specimens from Examples 1 to 5

[0087] Table 2 pH values ​​of specimens from Examples 1 to 5

[0088] According to the regulations of CJJT 292-2018 "Technical Standard for Slope Spraying Greening Engineering", DB 42 / T 1355-2018 "Technical Specification for Slope Ecological Protection", and JTG D30-2015 "Highway Roadbed Design Specification", the 28d unconfined compressive strength of the base layer should be controlled between 0.3 and 1.5 MPa. If the base layer strength is too high, the roots will have difficulty penetrating, affecting the growth of plants and the ecological restoration effect of the slope. Figure 2 As can be seen from Table 1, the 28d unconfined compressive strength of the ecological soil bases of Examples 1 to 5 all meet the requirements, and the strength is lower than 1.5 MPa, which meets the requirements of plant root growth for base strength.

[0089] Depend on Figure 3 As shown in Table 2, although the pH value of the ecological soil base of Examples 1 to 5 at 28 days is slightly higher than the ideal range for plant growth, the pH value is effectively controlled by adding flue gas desulfurization gypsum, limestone powder, fly ash and humus. The 3d pH value is around 10, and the 28d pH value does not exceed 10, avoiding the serious inhibition of plant growth by excessive alkalinity. These pH values ​​are within the controllable range and can be further optimized and reduced through reasonable formulation design. In addition, as the curing time increases, the pH value shows a trend of gradual decline, indicating that the alkalinity of the system gradually stabilizes and is suitable for plant growth. It also shows that the materials such as fast-hardening sulphoaluminate cement, flue gas desulfurization gypsum, limestone powder and fly ash used in the present invention play an important role in reducing the pH value of the system, ensuring the plant growth performance of the ecological soil.

[0090] The unconfined compressive strengths of the specimens of Example 1 and Comparative Examples 1 to 14 after curing to the corresponding ages (3d, 7d, 28d) are shown in Table 3. The unconfined compressive strengths measured after 28d are shown in Table 3. Figure 4 shown.

[0091] The pH values ​​of the test specimens of Example 1 and Comparative Examples 1 to 14 after curing to the corresponding ages (3d, 7d, 28d) are shown in Table 4. The pH values ​​measured after 28d are shown in Table 4. Figure 5 shown.

[0092] Table 3 Unconfined compressive strength of Example 1 and Comparative Examples 1 to 14

[0093] Table 4 pH values ​​of Example 1 and Comparative Examples 1 to 14

[0094] As can be seen from Tables 3 and 4, the 28d unconfined compressive strength (0.54 MPa) of Comparative Example 1 (without FGD gypsum) is 23.9% lower than that of Example 1 (full components). At the same time, its 28d pH value (10.44) is also significantly lower than 8.48 of Example 1 (full components), which exceeds the suitable growth range of plants. This result verifies the synergistic effect of the three components of FGD gypsum, limestone powder, and fly ash. The synergistic effect of limestone powder and fly ash is evident. This difference is primarily due to the lack of desulfurization gypsum, which leads to insufficient formation of ettringite, slow early strength development, and ineffective consumption of Ca(OH)2 in the system, exacerbating the alkaline environment. The 28-day strength of Comparative Example 2 (containing 30 parts of flue gas desulfurization gypsum) was 0.61 MPa, a 14.1% decrease compared to Example 1. Furthermore, the 28-day pH value of Comparative Example 2 (10.32) was significantly higher. Test results indicate that when the desulfurization gypsum dosage is less than 45 parts, it is difficult to meet the dual strength and pH requirements of cement eco-soil. While the 28-day pH value of Comparative Example 3 (containing 120 parts of flue gas desulfurization gypsum) was lower than that of Comparative Examples 1 and 2, its early strength development was also suppressed. This suggests that excessive addition of desulfurization gypsum (120 parts) can lead to a retarding effect, making it unsuitable for engineering applications.

[0095] The 28d strength of Comparative Example 4 (without limestone powder) is 0.60 MPa, which is 15.5% lower than that of Example 1 (full components). Its 28d pH value of 10.37 is also high, significantly lower than that of 8.48 in Example 1 (full components). This result verifies the synergistic effect of the three components of flue gas desulfurization gypsum, limestone powder and fly ash. The flue gas desulfurization gypsum and fly ash components exhibit a synergistic effect. This difference is primarily due to the lack of nucleation sites in the system due to the absence of limestone powder, resulting in a loose structure and insufficient density in the hydration product. Comparative Example 5 (containing 10 parts limestone powder) achieved a 28-day strength of 0.65 MPa and a 28-day pH of 10.29. Comparative Example 6 (containing 80 parts limestone powder) exhibited comparable strength to Example 1, but the 28-day pH still differed significantly. Furthermore, excessive addition of limestone powder not only increases costs but also impairs the hydration reaction due to overfilling.

[0096] The 28d strength of Comparative Example 7 (without fly ash) is 0.57 MPa, which is 19.7% lower than that of Example 1 (full components). The 28d pH value is as high as 10.59, which is significantly worse than 8.48 of Example 1 (full components). This result verifies the synergistic effect of the three components of flue gas desulfurization gypsum, limestone powder and fly ash. The flue gas desulfurization gypsum and limestone powder exhibit a synergistic effect. This discrepancy is primarily due to the lack of fly ash, which deprives the system of its pozzolanic effect and prevents effective Ca(OH)2 consumption. The pH value of Comparative Example 8 (containing 2 parts fly ash) at 28 days (10.25) remains high. Experimental results indicate that a fly ash dosage of 5 parts is required to effectively control the alkalinity of the system. The early strength development of Comparative Example 9 (containing 20 parts fly ash) is significantly hindered. This indicates that excessive fly ash slows the hydration process, hindering engineering applications.

[0097] Comparative Example 10 (which lacks flue gas desulfurization gypsum and limestone powder) exhibited poor performance (last-lowest pH value and second-lowest strength), with a 28-day strength of only 0.46 MPa and a 28-day pH value of 10.66. This fully demonstrates the critical impact of the synergistic effect of desulfurization gypsum and limestone powder on the performance of cement eco-soil. Comparative Example 11 (which lacks flue gas desulfurization gypsum and fly ash) exhibited a 28-day strength of 0.50 MPa and a 28-day pH value of 10.47, significantly inferior to Example 1. This further validates the synergistic effect of desulfurization gypsum and fly ash in pH control. Comparative Example 12 (which lacks limestone powder and fly ash) exhibited a 28-day strength (0.62 MPa) close to that of Example 1, but its 28-day pH value (10.13) was still relatively high, and its later-stage density was insufficient. Comparative Example 13 (which contained 40 parts of rapid-hardening sulphoaluminate cement) exhibited a 28-day strength of only 0.35 MPa, failing to meet engineering requirements. While comparative example 14 (containing 120 parts by weight of rapid-hardening sulphoaluminate cement) achieved the required strength (0.90 MPa), the pH rose to 10.39, and the material cost increased significantly. Extensive experiments have shown that while maintaining performance, the cement dosage should not be less than 60 parts by weight.

[0098] From Comparative Examples 1 to 14, it can be seen that the rapid-hardening sulphoaluminate cement, flue gas desulfurization gypsum, limestone powder, and fly ash fully exert the synergistic effect among the components: rapid-hardening sulphoaluminate cement ensures early strength development; flue gas desulfurization gypsum promotes the formation of ettringite and regulates the pH value; limestone powder optimizes the microstructure and participates in alkalinity regulation; and fly ash improves long-term performance through the pozzolanic effect. At the same time, it also fully demonstrates the synergistic effect of the three components of flue gas desulfurization gypsum, limestone powder, and fly ash. Any two components of flue gas desulfurization gypsum, limestone powder, and fly ash exhibit synergistic effects; the absence or excess of any single component disrupts this synergistic balance, leading to a decrease in the performance of sulphoaluminate cement eco-soil. The mix ratio of this invention optimizes material usage and minimizes costs while ensuring engineering performance.

[0099] Vegetation test The sulphoaluminate cement ecological soil surface layer prepared in Examples 6 to 9 was subjected to a vegetation test with Amorpha fruticosa, tall fescue, truncatum purpurogenum and bermudagrass. The order of sowing seeds in each surface layer from left to right was Amorpha fruticosa, tall fescue, truncatum purpurogenum and bermudagrass. Each seed was sown 100 cm 2 , the test results are as follows Figure 6 、 Figure 7 As shown in the two figures, the planting order of areas a to d is exactly the same, namely, Amorpha fruticosa, tall fescue, alfalfa and Bermuda grass from left to right.

[0100] from Figure 6 、 Figure 7 It can be seen that tall fescue has the fastest germination speed and the most rapid growth. The plant height is 5-8 cm 3 days after sowing, and the plant height can reach 15-21 cm after 21 days of growth. Amorpha fruticosa also germinates relatively quickly. Amorpha fruticosa has germinated 3 days after sowing, and the plant height is 4-6 mm. 15 days after sowing, the seedling height reaches 40-55 mm. 21 days after sowing, the growth is even better. Alfalfa germination and growth are slow. Not many sprouts appear 3 days after sowing, and the plant height is only 1-2 mm. 21 days after sowing, the seedling height reaches 20-30 mm. Bermuda grass basically does not germinate, which may be affected by the season. Tall fescue has better adaptability to sulphoaluminate cement ecological soil than Amorpha fruticosa, alfalfa, and bermuda grass. Therefore, tall fescue can be used as the preferred plant for sulphoaluminate cement ecological soil.

[0101] from Figures 8 to 10As the tall fescue plants grew, their roots gradually extended into the sulfoaluminate cement eco-soil, penetrating significantly into the concrete. The roots became more developed and complex, and their bond with the soil became even closer. This root-substrate synergy not only optimized the plant's growth environment but also enhanced the overall stability of the sulfoaluminate cement eco-soil through biomechanical interactions, achieving the dual benefits of ecological protection and engineering reinforcement. The results showed that after 21 days of cultivation, the tall fescue plant root network had effectively penetrated the surface layer of the sulfoaluminate cement eco-soil, forming a stable three-dimensional support system.

[0102] The above-described embodiments merely represent specific implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of protection of the present application. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the technical concept of the present application, all of which fall within the scope of protection of the present application.

Claims

1. A sulphoaluminate cement ecological soil for slope greening, characterized in that: The ecological soil is composed of a base layer and a surface layer, wherein the base layer raw materials include: 950-1250 parts of soil sample, 60-100 parts of rapid hardening sulphoaluminate cement, 45-95 parts of flue gas desulfurization gypsum, 20-65 parts of limestone powder, 5-18 parts of fly ash, and 300-500 parts of water; The surface layer materials include: 1000-1200 parts of soil sample, 20-90 parts of rapid hardening sulphoaluminate cement, 10-42 parts of flue gas desulfurization gypsum, 6-25 parts of limestone powder, 2-5 parts of fly ash, and 200-400 parts of water; The raw materials are all calculated by weight.

2. The sulphoaluminate cement ecological soil for slope greening according to claim 1, characterized in that: The surface layer contains 20 to 300 parts of plant seeds.

3. The sulphoaluminate cement ecological soil for slope greening according to claim 2, characterized in that: The surface soil sample contains 700 to 840 parts of nutrient soil.

4. The sulphoaluminate cement ecological soil for slope greening according to claim 3, characterized in that: The base layer also contains 30 to 100 parts of humus; and the surface layer also contains 100 to 120 parts of humus.

5. The sulphoaluminate cement ecological soil for slope regreening according to any one of claims 1 to 4, characterized in that: The rapid hardening sulphoaluminate cement in the base layer is 60 to 85 parts.

6. The sulphoaluminate cement ecological soil for slope regreening according to any one of claims 1 to 4, characterized in that: The flue gas desulfurization gypsum in the base layer is 45 to 85 parts.

7. The sulphoaluminate cement ecological soil for slope regreening according to any one of claims 1 to 4, characterized in that: The limestone powder in the base layer is 20 to 30 parts.

8. The sulphoaluminate cement ecological soil for slope regreening according to any one of claims 1 to 4, characterized in that: The fly ash in the base layer is 5 to 15 parts.

9. The sulphoaluminate cement ecological soil for slope regreening according to any one of claims 1 to 4, characterized in that: The soil sample is one or more of sandy soil, silty clay, clay, and humus soil with a pH value of 7.50 to 8.50; and the particle size of the soil sample is less than 5 mm.

10. A method for preparing the sulphoaluminate cement ecological soil for slope greening according to any one of claims 2 to 4, characterized in that: The steps include: Preparation of base layer: weigh all raw materials according to the proportion, first mix all raw materials except water and soil sample evenly; then add water and continue stirring until uniform to form a mixed slurry; finally, mix the mixed slurry with the soil sample thoroughly to complete the discharge; Preparation of the surface layer: weigh the raw materials according to the ratio, first mix the raw materials except water, soil samples, and plant seeds evenly, then add water and mix well to obtain a mixed slurry; then mix the soil samples and plant seeds to obtain a mixture, and finally fully mix the mixed slurry and the mixture and discharge the material.

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