Environment-friendly high-low-temperature-resistant anti-cracking cement-based solidified soil and preparation method thereof

Abstract

The invention discloses environment-friendly high-low-temperature-resistant anti-cracking cement-based solidified soil and a preparation method thereof. The solidified soil comprises the following raw materials: cement, solid waste steel slag powder, sodium sulfate, organic soil, a modified phase change material and water. The cement-based material curing agent is prepared from industrial wastes as raw materials, cement materials are replaced, the use amount of the cement materials in the cement-based curing agent is reduced, too fast consumption of limestone, clay and energy in cement production can be relieved, and the problems of high energy consumption and high pollution caused by cement production are solved; the problem of environmental pollution caused by industrial solid waste accumulation can be gradually eliminated; in addition, the characteristic that the solidified soil prepared from the organic soil is easy to crack is effectively inhibited by utilizing the characteristic of a solid waste steel slag powder excitation material; finally, the modified phase-change material is prepared from industrial waste residues, and solid waste utilization is achieved.

Description

Technical Field

[0001] This invention provides an environmentally friendly, high-temperature resistant, crack-resistant cement-based solidified soil and its preparation method, aiming to solve the shortcomings of soils with high plasticity index, such as clay, saline soil, and organic soil, which have poor solidification effect and are prone to cracking. It belongs to the field of building materials technology. Background Technology

[0002] Cement hardeners are mainly composed of cement, fly ash, and other raw materials, and are widely used in roadbeds, subbases, and other areas. Improving the strength of cement hardeners and expanding their practical applications in foundation reinforcement and aeolian sand stabilization are of great significance. Currently, improving the strength of cement hardeners mainly involves adding additives, such as slag powder, natural minerals, and high-strength fibers.

[0003] Steel slag is a major industrial solid waste generated during the steel smelting process. Approximately 100-150 kg of steel slag is produced for every ton of steel produced. Its main components are CaO, SiO2, FeO, MgO, Al2O3, free calcium oxide (f-CaO), and iron-phase minerals. The accumulation of large amounts of steel slag not only occupies land resources and damages the ecological environment, but also poses dust pollution, heavy metal leaching, and safety hazards caused by the hydration and expansion of f-CaO, becoming a prominent problem restricting the green and sustainable development of the steel industry.

[0004] Calcium chloride (CaCl2) is an important inorganic chemical product widely used in de-icing agents, desiccants, food additives, oilfield additives, and concrete accelerators. Its main production processes include the ammonia-soda process with byproduct recovery, the limestone-hydrochloric acid neutralization process, and the natural brine evaporation and crystallization process. In these production processes, especially those using industrial byproduct hydrochloric acid or natural brine as raw materials, a large amount of solid waste containing impurities—waste salt mud and tailings—is generated. The main components of this waste are unreacted calcium chloride and calcium sulfate (CaSO4), characterized by high alkalinity, high moisture content, and fine particles. According to incomplete statistics, approximately 0.15 to 0.3 tons of waste salt mud or tailings are generated for every ton of calcium chloride produced. For a long time, these wastes have been disposed of through stockpiling or landfilling, which not only occupies a large amount of land resources but also poses environmental risks such as leachate pollution of groundwater and dust pollution due to the presence of soluble salts and trace harmful elements. This has become a bottleneck restricting the green development of the calcium chloride industry.

[0005] Furthermore, soils with high plasticity indices, such as clay, saline soil, and organic soil, are highly prone to cracking during the hardening process. This is a common technical challenge in engineering, especially in applications such as foundations, roadbeds, diaphragm walls, and dam backfilling, where it is crucial to control cracking. Cracking not only affects the structural integrity and durability but also reduces impermeability, accelerates steel corrosion, and significantly increases subsequent maintenance costs. Particularly in winter, the extreme temperature difference between the inside and outside of large-volume solidified soil makes it highly susceptible to temperature cracks. Additionally, the low ambient temperature in winter will negatively impact the subsequent strength development of the solidified soil. Summary of the Invention

[0006] In view of the problems described above, the present invention provides a method for preparing a cementitious material with solid waste steel slag, sodium sulfate, modified phase change material and cement as the main components. It aims to solve the problems in the prior art, such as environmental pollution caused by industrial by-products such as solid waste steel slag and waste salt mud in the calcium chloride industrial production process, easy cracking of large-volume solidified soil in winter construction, slow hydration and low strength development, and further improves the strength and stability of solidified soil.

[0007] Given that solid waste steel slag contains highly active free calcium oxide (f-CaO), which expands in volume under the hydration reaction initiated by sodium sulfate, this effectively inhibits early plastic shrinkage in solidified soils with high plasticity indices, such as clay, saline soil, and organic soil, thus reducing the likelihood of cracking. It also supports the strength development of the solidified soil and reduces cement usage. Furthermore, sodium sulfate reacts with cement to promote early heat release; the addition of modified phase change materials can effectively absorb excess heat and then slowly release it later, maintaining the internal temperature of the solidified soil in winter and ensuring its strength development.

[0008] In light of the aforementioned problems of difficult utilization and serious waste of solid waste steel slag, as well as its inherent characteristics, this invention provides a method for preparing a cementitious material with solid waste steel slag, sodium sulfate, modified phase change materials, and cement as the main components. This method enables the resource utilization of solid waste steel slag, improves the crack resistance of solidified soil prepared from soil with a high plasticity index, effectively reduces cement usage, and finally solves the problem of insufficient strength development of solidified soil in winter.

[0009] To achieve the above objectives, the following technical solution is adopted: This invention provides an environmentally friendly, high-temperature resistant, crack-resistant solidified soil. The cement-based solidified soil comprises the following raw materials by weight: 150-300 parts cement, 20-125 parts solid waste steel slag powder, 4-12 parts sodium sulfate, 50-200 parts modified phase change material, 550-800 parts soil with a plasticity index of 20-25, and 110-130 parts water.

[0010] The modified phase change material is prepared by a method comprising the following steps: S1. Dry the diatomaceous earth to remove moisture. Pour the dried diatomaceous earth into a silane coupling agent modified solution and stir continuously to carry out a surface grafting reaction. After vacuum drying, silane modified diatomaceous earth is obtained. S2. The waste salt mud from the calcium chloride production process is mixed with the silane-modified diatomaceous earth in an aqueous solution and continuously stirred (so that CaCl2 is fully adsorbed into the porous structure of the silane-modified diatomaceous earth); the modified phase change material is obtained by drying. Preferably, the mass ratio of the modified phase change material to soil with a plasticity index of 20-25 is 7.5-28:100; more preferably, it is 15-20:100.

[0011] As one implementation scheme, the solid waste steel slag powder is obtained by calcining and grinding waste steel slag (industrial solid waste generated during the steel smelting process), and its particle size is ≤30% on a 45μm sieve.

[0012] As one implementation scheme, the chemical composition of the solid waste steel slag powder is as follows: CaO content is 45-52%, MgO content is 1-2%, SiO2 content is 30-35%, Fe2O3 content is 2%-4%, and Al2O3 content is 8%-15%.

[0013] As one embodiment, the silane coupling agent modified solution is prepared by adding KH-550 silane coupling agent to anhydrous ethanol and stirring, wherein the mass content of KH-550 silane coupling agent in the silane coupling agent modified solution is 5%-10%. Preferably, the silane coupling agent modified solution is formed by adding 5-10 parts of KH-550 silane coupling agent to 90-95 parts of anhydrous ethanol and stirring for 20-40 minutes.

[0014] As one implementation, in step S1, the drying temperature is 100 ℃-110 ℃ and the time is 1.5-2.5 hours.

[0015] As one implementation, in step S1, the continuous stirring is carried out at 20℃-30℃ for 40-90 minutes.

[0016] As one implementation scheme, in step S1, the vacuum drying temperature is 50℃-70℃ and the time is 10-14 hours.

[0017] As one implementation scheme, in step S1, the mass ratio of the dried diatomaceous earth to the silane coupling agent modified solution is 1:0.8-1.5.

[0018] As one implementation scheme, in step S2, the stirring time is 100-140 minutes.

[0019] As one implementation scheme, in step S2, the drying temperature is 90-105℃ and the time is 6-8h.

[0020] As one implementation method, the ratio of silane-modified diatomaceous earth to waste salt mud is 100g : 5-10g. In some implementation examples, the ratio of diatomaceous earth, silane coupling agent, and waste salt mud is 100g : 4-8g : 5-10g.

[0021] As one implementation scheme, the sodium sulfate is industrial-grade sodium sulfate with a purity of 99.5% or higher. Preferably, the mass ratio of sodium sulfate to solid waste steel slag powder is 6-25:90; more preferably, it is 8-24:90. According to the above scheme, the cement is (Conch) PO42.5 cement, 300m³. 2 / kg≤Specific Surface Area≤370m² 2 / kg.

[0022] As one implementation scheme, the soil with a plasticity index of 20-25 is selected from at least one of the following soil types: clay, saline soil, organic soil, etc., which have poor solidification effects and are prone to cracking.

[0023] The present invention also relates to a method for preparing the aforementioned environmentally friendly, high-temperature resistant, crack-resistant cement-based solidified soil, wherein the cement, solid waste steel slag powder, sodium sulfate, modified phase change material, and soil with a plasticity index of 20-25 are mixed to obtain raw materials; water is poured into the mixed raw materials and stirred to obtain environmentally friendly, high-temperature resistant, crack-resistant solidified soil.

[0024] During long-term research, the inventors discovered that using clay, saline soil, and organic soil—soils with high plasticity indices—to prepare solidified soil is prone to plastic cracking. Furthermore, the strength development of solidified soil is inhibited by ambient temperature after winter pouring. To address these issues, the inventors found that solid waste steel slag, with its high CaO content and highly active free calcium oxide (f-CaO), undergoes volume expansion under the hydration reaction activated by sodium sulfate. This effectively inhibits early plastic shrinkage in solidified soils with high plasticity indices, such as clay, saline soil, and organic soil, thereby suppressing cracking. Moreover, the activation effect of sodium sulfate on solid waste steel slag effectively supports the early strength development of solidified soil, shortening the construction progress in winter and effectively reducing cement usage and carbon emissions.

[0025] This invention prepares a modified phase change material and adds it to the solidified soil. Through early heat absorption, it can not only effectively absorb the large amount of heat generated by the reaction of sodium sulfate and cement, thus avoiding temperature cracks, but also slowly release heat during the subsequent strength development of the solidified soil. This avoids the inhibition of the strength development of the solidified soil by the influence of ambient temperature in winter, thus delaying the construction period.

[0026] This invention prepares a modified phase change material, a composite phase change material, which is prepared by modifying diatomaceous earth and waste salt mud from the calcium chloride production process. It combines the three-dimensional network porous structure of diatomaceous earth with the phase change characteristics of residual calcium chloride in the waste salt mud from the calcium chloride production process to achieve the endothermic and exothermic effects of the solidified soil during hydration. Utilizing the capillary adsorption and van der Waals forces of the porous structure of diatomaceous earth, liquid calcium chloride is firmly locked inside the pores. Simultaneously, the porous structure of diatomaceous earth provides sufficient space to absorb the volume expansion during the phase change of calcium chloride, preventing material cracking or structural damage. Finally, the diatomaceous earth uniformly disperses the calcium chloride particles in the pores, increasing the specific surface area and improving the phase change heat transfer efficiency. However, due to the difference in hydrophilicity and hydrophobicity between the hydroxyl groups on the surface of calcium chloride and diatomaceous earth, "desorption leakage" is prone to occur. Therefore, a silane coupling agent is used to modify the diatomaceous earth to solve the "desorption leakage" phenomenon. This modified phase change material is characterized by convenient material sourcing, simple preparation, and is also environmentally friendly, low-carbon, and utilizes solid waste.

[0027] This invention organically combines and utilizes the physical and chemical properties of industrial waste to achieve the goal of turning waste into treasure. First, by applying sodium sulfate to stimulate the micro-expansion effect of steel slag in solidified soil, the early shrinkage of solidified soil is effectively suppressed. In addition, sodium sulfate can react with cement to promote the early strength development of solidified soil. Finally, the application of phase change materials can not only effectively suppress the early cracking caused by the heat release of hydration in large-volume solidified soil, but also ensure the subsequent strength development in winter.

[0028] Compared with the prior art, the present invention has the following beneficial effects: 1) This invention combines the high CaO content and highly active free calcium oxide (f-CaO) in solid waste steel slag. Under the activation of the hydration reaction by sodium sulfate, it undergoes volume expansion, effectively inhibiting the early plastic shrinkage of solidified soils with high plasticity indices, such as clay, saline soil, and organic soil, thereby suppressing cracking. Furthermore, the activation effect of sodium sulfate effectively supports the early strength development of the solidified soil, which not only shortens the construction progress in winter but also effectively reduces cement usage and carbon emissions.

[0029] 2) Compared with existing cement-based solidified soil, this invention prepares modified phase change materials and adds them to the solidified soil. Through early heat absorption, it can not only effectively absorb the large amount of heat generated by the reaction of sodium sulfate and cement, avoiding temperature cracks, but also slowly release heat during the subsequent strength development of the solidified soil. This avoids the inhibition of the strength development of the solidified soil by the influence of ambient temperature in winter, thus delaying the construction period.

[0030] 3) Compared with existing cement-based solidified soil phase change materials, the modified phase change material of the present invention is prepared by modifying diatomaceous earth and waste salt mud from the calcium chloride production process. It has the characteristics of convenient material sourcing and simple preparation, and also has the advantages of environmental protection, low carbon emissions, and solid waste utilization. Detailed Implementation

[0031] The present invention will be described in detail below with reference to embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several adjustments and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0032] In the following embodiments and comparative examples, The chemical composition of solid waste steel slag powder is as follows: CaO content is 48%, MgO content is 1.5%, SiO2 content is 31%, Fe2O3 content is 3%, and Al2O3 content is 8.5%; its particle size is 45μm and the sieve residue is ≤30%.

[0033] The cement used is Conch PO42.5 cement.

[0034] The sodium sulfate used is industrial grade sodium sulfate with a purity of 99.5%.

[0035] Clay with a plasticity index of 24 was selected.

[0036] The modified phase change material was prepared as follows: 1) 100g of diatomaceous earth was dried at 105℃ for 2 hours to completely remove moisture; 2) A modification solution was then prepared: 5g of KH-550 silane coupling agent was added to 95g of anhydrous ethanol and stirred for 30 minutes; 3) The dried diatomaceous earth was slowly poured into the modification solution, and the mixture was stirred continuously at room temperature for 60 minutes to carry out a surface grafting reaction, and then vacuum dried at 60℃ for 12 hours to obtain silane-modified diatomaceous earth; 4) 6g of waste salt mud from the calcium chloride production process and 94g of silane-modified diatomaceous earth were mixed in an aqueous solution and stirred continuously for 120 minutes to allow CaCl2 to be fully adsorbed into the porous structure, and finally dried at 100℃ for 6 hours to obtain the diatomaceous earth / silane coupling agent / calcium chloride composite inorganic phase change material.

[0037] The chemical composition of the waste salt mud in the calcium chloride production process is CaCO3 52.3%, NaCl 18.6%, Mg(OH)2 8.6%, Ca(OH)2 9.2%, CaCl2 6.8%, and Fe2O3 4.5%.

[0038] Examples 1-11 Examples 1-11 provide environmentally friendly, high-temperature resistant, crack-resistant solidified soil, the specific components and dosages (parts) of which are shown in Table 1. During preparation, cement, solid waste steel slag powder, sodium sulfate, modified phase change material, and organic soil are mixed to obtain raw materials. Water is then poured into the mixed raw materials and stirred to obtain the environmentally friendly, high-temperature resistant, crack-resistant solidified soil.

[0039] Comparative Example 1 Mix 350 parts cement and 700 parts organic soil to obtain raw materials. Add 120 parts water to the mixed raw materials and stir to form ordinary solidified soil.

[0040] Table 1 Experimental proportions

[0041] Referring to the standard GB / T 17671-1999, the compressive strength and flexural strength of cement-based material samples were tested using a cement compressive strength testing machine and a cement electric flexural strength testing machine. The sample size was 50mm × 50mm × 200mm, with 5 samples per group. After demolding, the cement-based material samples were cured outdoors at 3-8℃ for 28 days before the compressive strength and flexural strength tests were conducted. The solidified soil crack resistance test was performed according to the plate cracking test method in the "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete" (test environment: 3-8℃ outdoors). Specific test results are shown in Table 2. Table 2 Mechanical Properties and Crack Resistance Test Table

[0042] Table 2 is a statistical analysis of the mechanical properties and crack resistance test results of the comparative examples and each group of embodiments. According to Comparative Example 1 and Examples 1-4, it can be seen that the compressive strength, flexural strength and early crack resistance of each group of embodiments at each age show a trend of first increasing and then decreasing as the ratio of finely ground steel slag powder to cement gradually increases. Among them, Example 1 has the best performance in all aspects. A comparative analysis of Comparative Example 1 and Example 4 shows that the performance indicators of the two are similar, and Example 4 can maximize the application of finely ground steel slag powder while ensuring performance. Regarding the application of sodium sulfate activator, according to the analysis of Comparative Example 1, Examples 3, and 5-7, it can be seen that as the amount of sodium sulfate activator applied gradually increases, the compressive strength, flexural strength, and early crack resistance at each age of each group of examples show a trend of first increasing and then decreasing. At the same time, according to the analysis of Comparative Example 1, Examples 3, and 8-11, it can be seen that as the dosage of modified phase change material increases, the initial appearance time of cracks in the solidified soil shows a trend of first delaying and then advancing, and the crack area shows a trend of first decreasing and then increasing. This indicates that the crack resistance of the solidified soil is effectively improved after incorporating an appropriate amount of phase change material.

[0043] In summary, the preparation process of this invention uses industrial waste as raw material to prepare cement-based material curing agents, thereby replacing cement materials and reducing the amount of cement materials used in cement-based curing agents. This not only alleviates the excessive consumption of limestone, clay, and energy in cement production, reducing the high energy consumption and high pollution problems caused by cement production, but also gradually eliminates the environmental pollution problems caused by the large accumulation of industrial solid waste. In addition, the characteristics of the material activated by solid waste steel slag powder are effectively used to suppress the tendency of organic soil to crack when preparing solidified soil. Finally, the use of industrial waste residue to prepare modified phase change materials also realizes the characteristic of solid waste utilization.

[0044] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An environmentally friendly, high-temperature resistant, crack-resistant cement-based solidified soil, characterized in that, The cement-based solidified soil comprises the following raw materials: 150-300 parts cement, 20-125 parts solid waste steel slag powder, 4-12 parts sodium sulfate, 50-200 parts modified phase change material, 550-800 parts soil with a plasticity index of 20-25, and 110-130 parts water. The modified phase change material is prepared by a method comprising the following steps: S1. The diatomaceous earth is dried to remove moisture. The dried diatomaceous earth is poured into a silane coupling agent modified solution and stirred continuously to carry out a surface grafting reaction. After vacuum drying, silane modified diatomaceous earth is obtained. S2. The waste salt mud from the calcium chloride production process is mixed with the silane-modified diatomaceous earth in an aqueous solution and continuously stirred; the modified phase change material is obtained by drying.

2. The environmentally friendly, high-temperature resistant, crack-resistant cement-based solidified soil according to claim 1, characterized in that, The cement used is P·O 42.5 cement, 300m 2 / kg≤Specific Surface Area≤370m² 2 / kg.

3. The environmentally friendly, high-temperature resistant, crack-resistant cement-based solidified soil according to claim 1, characterized in that, The solid waste steel slag powder is finely ground solid waste steel slag powder that has been calcined and ground to a particle size of 45μm and has a sieve residue of ≤30%.

4. The environmentally friendly, high-temperature resistant, crack-resistant cement-based solidified soil according to claim 1, characterized in that, The chemical composition of the solid waste steel slag powder is as follows: CaO content is 45-52%, MgO content is 1-2%, SiO2 content is 30-35%, Fe2O3 content is 2%-4%, and Al2O3 content is 8%-15%.

5. The environmentally friendly, high-temperature resistant, crack-resistant cement-based solidified soil according to claim 1, characterized in that, In step S1, the silane coupling agent modified solution is prepared by adding KH-550 silane coupling agent to anhydrous ethanol and stirring. The mass content of KH-550 silane coupling agent in the silane coupling agent modified solution is 5%-10%.

6. The environmentally friendly, high-temperature resistant, crack-resistant cement-based solidified soil according to claim 1, characterized in that, In step S1, the drying temperature is 100 ℃-110 ℃ and the time is 1.5-2.5 hours; the continuous stirring is carried out at 20 ℃-30 ℃ for 40-90 minutes; the vacuum drying temperature is 50 ℃-70 ℃ and the time is 10-14 hours. In step S2, the stirring time is 100-140 minutes; the drying temperature is 90-105℃, and the time is 6-8 hours. The ratio of silane-modified diatomaceous earth to waste salt mud is 100g : 5-10g.

7. The environmentally friendly, high-temperature resistant, crack-resistant cement-based solidified soil according to claim 1, characterized in that, The sodium sulfate mentioned is industrial grade sodium sulfate with a purity of 99.5% or higher.

8. The environmentally friendly, high-temperature resistant, crack-resistant cement-based solidified soil according to claim 1, characterized in that, The soil with a plasticity index of 20-25 is selected from at least one of clay, saline soil, and organic soil.

9. The environmentally friendly, high-temperature resistant, crack-resistant cement-based solidified soil according to claim 1, characterized in that, The mass ratio of the modified phase change material to soil with a plasticity index of 20-25 is 7.5-28:100; the mass ratio of sodium sulfate to solid waste steel slag powder is 6-25:

90.

10. A method for preparing environmentally friendly, high-temperature resistant, crack-resistant cement-based solidified soil according to any one of claims 1-9, characterized in that, The raw materials are obtained by mixing the cement, solid waste steel slag powder, sodium sulfate, modified phase change material, and soil with a plasticity index of 20-25; water is poured into the mixed raw materials and stirred to obtain the environmentally friendly, high-temperature resistant, crack-resistant solidified soil.

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