Composite curing agent and method for improving sulfate salinized soil by using composite curing agent

Abstract

The invention relates to the technical field of soil improvement and remediation, and discloses application of a composite curing agent, and the composite curing agent is used for improving sulfate saline soil. The invention further provides an application method of the composite curing agent. The application method comprises the following steps: pretreating a soil sample of the sulfate saline soil; before a test, a soil sample is firstly pretreated, the soil sample is firstly air-dried to ensure that moisture in the soil sample is fully volatilized so as to avoid influence on a subsequent test, then the air-dried soil sample is crushed into fine particles, and the fine particles are screened by a 2mm screen so as to ensure that the granularity of the soil sample is uniform and consistent and facilitate subsequent mixing and preparation. The composite curing agent provided by the invention can improve the sulfate salinized soil, and the salinized soil improved by the composite curing agent has the advantages that the salt expansion deformation is reduced, the early strength is high, the water stability is good, the treated solidified soil meets the engineering use standard, the industrial waste is fully utilized, and the like.

Description

Technical Field

[0001] The invention relates to the technical field of soil improvement and restoration, and in particular to a composite curing agent and a method for improving sulfate-affected soil. Background Art

[0002] Saline soil is a special soil with a salt content greater than 0.5%. It has special engineering properties such as salt swelling, dissolution and corrosion, and is widely distributed in Xinjiang, my country. Common saline soils can be mainly divided into sulfate saline soils, chloride saline soils and carbonate saline soils according to the types of soluble salts they contain. Among them, Xinjiang is mainly sulfate saline soil. The special properties of saline soil often cause harm to road projects and seriously hinder highway construction in Xinjiang. Therefore, solidifying and modifying typical saline soils in Xinjiang, making full use of saline soils along the project and reducing construction costs are of great engineering significance to road traffic construction in Xinjiang.

[0003] Previous studies have shown that the modification of curing materials is an effective method for treating saline soil. At present, the modification of saline soil is mainly divided into inorganic modification, organic modification, combined modification of curing materials, biological modification, etc. The traditional modification method is inorganic modification, and the main methods include common lime, fly ash, slag, cement or inorganic curing materials. The addition of inorganic curing materials can significantly improve the mechanical properties of the soil; inorganic curing materials generate a variety of cementitious materials through chemical reactions, which solidify and harden, connect with each other, fill pores and improve density. For organic modified saline soil, common organic curing materials mainly include acrylamide, desulfurized lignin, polyacrylamide, modified polyvinyl alcohol, etc. The modification of organic curing materials is mainly through the polymerization, adsorption and wrapping of polymer chains to bond soil particles into a whole, thereby forming a spatial elastic network structure, improving the overall strength of soil particles, and improving the water stability and durability of soil. Organic matter is often combined with inorganic matter for joint modification. The effect of joint modification of multiple solidifying materials is better than that of a single solidifying material. The individual advantages of each solidifying material can be comprehensively utilized. The joint solidification effect of organic and inorganic matter is more obvious, and all of them are modified by methods with a larger proportion of inorganic matter and a smaller proportion of organic matter. At present, the overall research on the joint solidification of saline soil using organic matter as a solidifying material is still in its initial stage, and there are relatively few experimental studies using salt swelling as an evaluation indicator. Considering that solid waste inorganic cementitious materials are mainly used to improve the mechanical properties of soil and meet the strength requirements, organic matter is used to improve the physical and chemical properties of soil.

[0004] Sulfate soil, as a special type of soil widely distributed around the world, often brings many challenges in engineering construction because it contains soluble sulfate. This type of soil is very likely to cause geotechnical disasters when it comes into contact with water, such as dissolution, expansion, and corrosion of foundations, which seriously affects the construction and operation of public infrastructure.

[0005] Current technological development status:

[0006] Traditional solidification methods: At present, traditional sulfate soil solidification methods mostly rely on single materials such as cement. However, this method has obvious problems. Cement easily reacts with sulfate ions in sulfate soil to produce a large amount of calcium aluminate, which leads to poor expansion, strength loss and reduced durability of the reinforced body. Especially in western my country and coastal areas, where the sulfate soil content is high, the effect of traditional solidification methods is particularly limited.

[0007] Composite curing agent attempts: In order to overcome the limitations of traditional curing methods, researchers began to try to use composite curing agents.

[0008] Problems:

[0009] Unstable curing effect: Although the composite curing agent improves the curing effect to a certain extent, it is often difficult to maintain a stable curing effect due to the complexity and diversity of sulfate saline soil. Sulfate saline soils in different regions have great differences in composition, structure, salt content, etc., which makes the same composite curing agent have different application effects in different regions.

[0010] Higher cost: The preparation cost of composite curing agent is usually high, which increases the cost of project construction.

[0011] Environmental issues: Some composite curing agents may cause environmental pollution during preparation and use. For example, some curing agents may contain heavy metals or other harmful substances, posing a potential threat to the environment and human health. Summary of the invention

[0012] In order to solve the technical problems raised in the background technology, the present invention provides a composite curing agent and a method for improving sulfate saline soil.

[0013] The present invention is implemented by the following technical scheme: a composite curing agent, wherein the dosage of each component of the curing agent is:

[0014] Fly ash 10%~15%; slag 5%~7.5%; polyacrylamide 2%; water reducing agent: 0.1%~0.25%; sodium hydroxide 0.5%.

[0015] Preferably, the fly ash is primary fly ash.

[0016] Preferably, the slag particle size is mainly distributed in the range of 1 to 35 μm, and the specific surface area is 430 m 2 / kg.

[0017] Preferably, the polyacrylamide is produced by Sinopharm and has a molecular weight of 10 million.

[0018] Preferably, the water reducer is a composite polyhydroxy acid high-efficiency water reducer.

[0019] Preferably, the alkaline activator sodium hydroxide is produced by Chinese medicine.

[0020] A preparation method of a composite curing agent comprises the following steps: mixing fly ash, slag, polyacrylamide, sodium hydroxide dry materials and soil dry materials, stirring them evenly, adding water mixed with a water reducing agent into the dry materials, and stirring them evenly to obtain the composite curing agent.

[0021] An application of a composite curing agent, using the composite curing agent to improve sulfate-saline soil.

[0022] The present invention also proposes an application method of the composite curing agent, comprising the following steps:

[0023] Pretreatment of sulfate soil samples: Before the test, the soil samples were first pretreated by air-drying them to ensure that the water inside them was fully volatilized to avoid affecting the subsequent tests. The air-dried soil samples were then crushed into fine particles and screened through a 2 mm sieve to ensure that the particle size of the soil samples was uniform and consistent, which was convenient for subsequent mixing and preparation.

[0024] Mixing: Mix the pre-treated soil with polyacrylamide, slag and fly ash; during the mixing process, ensure that the mixture is fully stirred so that the polyacrylamide can be evenly distributed in the soil, thereby playing its due role;

[0025] Inject water; then, add an appropriate amount of distilled water to the mixture according to the predetermined optimal moisture content, and mix again; the purpose of this step is to make the soil sample reach the optimal moisture content to simulate the soil environment in actual engineering;

[0026] Bag and let stand; put the mixed soil sample into a plastic bag and perform a stuffing treatment; during this process, the soil sample is sealed in the plastic bag and left to stand, so that it can fully absorb water and reach a stable state; preferably, the stuffing time is 1 day to ensure that the soil sample reaches the expected moisture content and uniformity;

[0027] Compacting: Compacting the soil samples to form a roadbed.

[0028] During the process of roadbed filling in sulfate saline soil areas, the composite curing agent is added and subjected to manual or mechanical mixing and compaction treatment to form a composite roadbed that meets the requirements of engineering performance indicators, or the composite curing agent is added to a saline soil site through a deep mixing method to generate a composite foundation.

[0029] Based on the salt swelling characteristics of saline soil, curing materials are selected from the perspectives of improving early strength, reducing soluble salt content in soil, and improving water stability, so as to give full play to the action and combination effects of composite materials and achieve the improvement of saline soil.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The composite curing agent proposed in the present invention can improve sulfate saline soil. The saline soil improved by the composite curing agent has the advantages of reduced salt expansion deformation, high early strength, good water stability, and the treated solidified soil meets the engineering use standards and fully utilizes industrial waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a salt expansion variation curve diagram under the dosage of the composite curing agent proposed by the present invention;

[0033] Figure 2 for Figure 1 The maximum salt expansion rate bar graph;

[0034] Figure 3 The compressive strength variation curve of saline soil under different composite curing agent dosages;

[0035] Figure 4 This is a graph showing the relationship between the residual weight of natural soil and the solidified soil doped with composite solidifying agent and the immersion time;

[0036] Figure 5 This is a graph showing the relationship between the sample mass loss rate and the content of the composite curing agent. DETAILED DESCRIPTION

[0037] The present invention is further described below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form a new embodiment.

[0038] Embodiment 1:

[0039] This scheme proposes a composite curing agent, the dosage of each component of the curing agent is:

[0040] Fly ash 10%~15%; slag 5%~7.5%; polyacrylamide 2%; water reducing agent: 0.1%~0.25%; sodium hydroxide 0.5%.

[0041] As an optional implementation mode of the present invention, the fly ash is primary fly ash.

[0042] As an optional embodiment of the present invention, the slag particle size is mainly distributed in the range of 1 to 35 μm, and the specific surface area is 430 m 2 / kg.

[0043] As an optional implementation mode of the present invention, the polyacrylamide is produced by Sinopharm and has a molecular weight of 10 million.

[0044] As an optional embodiment of the present invention, the water reducer is a composite polyhydroxy acid high-efficiency water reducer.

[0045] As an optional embodiment of the present invention, the alkaline activator sodium hydroxide is produced by Chinese medicine.

[0046] A preparation method of a composite curing agent comprises the following steps: mixing fly ash, slag, polyacrylamide, sodium hydroxide dry materials and soil dry materials, stirring them evenly, adding water mixed with a water reducing agent into the dry materials, and stirring them evenly to obtain the composite curing agent.

[0047] An application of a composite curing agent, using the composite curing agent to improve sulfate-saline soil.

[0048] The present invention also proposes an application method of the composite curing agent, comprising the following steps:

[0049] Pretreatment of sulfate soil samples: Before the test, the soil samples were first pretreated. The soil samples were air-dried to ensure that the moisture inside was fully evaporated to avoid affecting subsequent tests. The air-dried soil samples were then crushed into fine particles and screened through a 2 mm sieve to ensure that the particle size of the soil samples was uniform and consistent, which was convenient for subsequent mixing and preparation.

[0050] Mixing: Mix the pretreated soil with polyacrylamide, slag and fly ash; during the mixing process, ensure that it is fully stirred so that the polyacrylamide can be evenly distributed in the soil to play its due role.

[0051] Inject water; then, add an appropriate amount of distilled water to the mixture according to the predetermined optimal moisture content, and mix again; the purpose of this step is to make the soil sample reach the optimal moisture content to simulate the soil environment in actual engineering;

[0052] Bag and let stand; put the mixed soil sample into a plastic bag and perform a stuffing treatment; during this process, the soil sample is sealed in the plastic bag and left to stand, so that it can fully absorb water and reach a stable state; preferably, the stuffing time is 1 day to ensure that the soil sample reaches the expected moisture content and uniformity;

[0053] Compacting: Compacting the soil samples to form a roadbed.

[0054] During the process of roadbed filling in sulfate saline soil areas, the composite curing agent is added and subjected to manual or mechanical mixing and compaction treatment to form a composite roadbed that meets the requirements of engineering performance indicators, or the composite curing agent is added to a saline soil site through a deep mixing method to generate a composite foundation.

[0055] Based on the salt swelling characteristics of saline soil, curing materials are selected from the perspectives of improving early strength, reducing soluble salt content in soil, and improving water stability, so as to give full play to the action and combination effects of composite materials and achieve the improvement of saline soil.

[0056] The saline soil improved and treated with the composite solidifying agent proposed in this scheme has the advantages of reduced salt expansion deformation, high early strength, good water stability, and the treated solidified soil meets the engineering use standards and makes full use of industrial waste.

[0057] like Figure 1-5 As shown in the figure, when the dosage of composite curing agent is between 9% and 15%, the salt expansion of saline soil is reduced as the dosage of curing agent increases. When the dosage is between 15% and 19%, the salt expansion increases slightly. When the dosage of composite curing agent is 15%, the effect of inhibiting salt expansion is most obvious. Fly ash and slag react with the more active minerals in the oxides in saline soil to generate hydration products such as hydrated calcium silicate and hydrated calcium aluminate, which improve the strength of the soil and achieve the effect of inhibiting salt expansion through "forced deformation".

[0058] Improve strength. Adding curing agent can significantly improve its mechanical strength. When the curing agent dosage is between 9% and 15%, the mechanical properties of the soil sample are greatly enhanced with the increase of dosage. When the dosage is between 15% and 19%, the strength decreases slightly. When the dosage of composite curing agent reaches 15%, the 7d compressive strength of the sample reaches 993.02kPa, which is 3 times higher than the strength of uncured soil.

[0059] Increase water stability: Natural soil quickly disintegrates before 4 hours. When the content of composite curing agent exceeds 9%, the mass loss rate of stabilized soil samples remains below 6.47%. The addition of composite curing agent has a strong inhibitory effect on the disintegration of stabilized soil.

[0060] The effect of the dosage of composite curing agent and triple curing agent on salt swelling of saline soil was studied. 2% PAM was added quantitatively. According to the relationship between the total dosage of composite curing agent of 9%, 11%, 13%, 15%, 17% and 19% and the mass ratio of slag to fly ash of 1:2, the specific dosage of slag and fly ash under each level was calculated. For example, at the total dosage of 17%, 5% slag + 10% fly ash + 2% PAM were added. The law of salt swelling change is shown in Figure 1 and Figure 2. As can be seen from the figure, when the dosage is between 9% and 15%, the salt expansion of saline soil is reduced as the dosage of composite curing agent increases. When the dosage is between 15% and 19%, the salt expansion increases slightly. When the dosage of composite curing agent is 15%, the effect of inhibiting salt expansion is most obvious. Fly ash and slag react with the more active minerals in the oxides in the saline soil to generate hydration products such as hydrated calcium silicate and hydrated calcium aluminate, which improve the strength of the soil and achieve the effect of inhibiting salt expansion through "forced deformation".

[0061] Figure 3 The unconfined compressive strength of saline soil at different composite curing agent dosages after curing for 7 days. Figure 3 It can be seen that the curing agent can significantly improve its mechanical strength. When the curing agent dosage is between 9% and 15%, the mechanical properties of the soil sample are greatly enhanced with the increase of the amount of composite curing agent. When the dosage is between 15% and 19%, the strength decreases slightly. When the dosage of the composite curing agent reaches 15%, the 7d compressive strength of the sample reaches 993.02kPa, which is more than 3 times higher than the strength of the uncured soil. The possible reason is that when the curing agent dosage is not large, the fly ash and slag react with volcanic ash to generate hydrated gel material, the strength is improved, and the improvement effect is significant; when the curing agent dosage is greater than 15%, the excessive fly ash and slag cause the strength to decrease.

[0062] It is a commonly used evaluation method to characterize the water stability of samples by disintegration rate and immersion test. Disintegration rate refers to the mass loss of a sample under specific conditions, usually expressed as weight loss within a certain period of time. The immersion test is to completely immerse the sample in water and observe its morphological changes and mass changes within a certain period of time. In highway engineering, water stability tests can be used to evaluate the durability and water erosion resistance of pavement materials to ensure the safety and reliability of roads. Disintegration rate and immersion tests can be used to obtain the changes of the sample in water and then evaluate its water stability. Figure 4 (Changes in the residual weight of natural soil and composite curing agent cured soil with immersion time) and Figure 5 (Variation of sample mass loss rate with composite curing agent content) is the disintegration rate test result of the sample, Figure 4 , 5 It can be seen that the natural soil disintegrated rapidly before 4 hours of immersion, and the tensile force of the sample dropped to below 0.1N after 4 hours. In comparison, the composite curing agent plays an important role in maintaining the stability of the soil after immersion. Figure 4 It can be clearly seen that the solidified soil sample hardly disintegrated, and even the curves corresponding to soil samples with different composite solidifying agent contents almost overlap. Figure 5It can be seen that the effect of the composite curing agent content on the water stability of the sample is relatively small. In this study, the ratio of the tensile loss in the final state to the tensile force in the initial state is defined as the mass loss rate. When the composite curing agent content exceeds 9%, the mass loss rate of the stabilized soil sample remains below 6.47%. In addition, with the increase of the composite curing agent content, although there is a trend to reduce the mass loss, the change is not significant, indicating that the composite curing agent has a strong inhibitory effect on the disintegration of the stabilized soil, while the excessive composite curing agent has no significant improvement on the water stability of the stabilized soil. The lower disintegration rate and smaller mass change indicate that the sample has better water stability and can withstand the erosion and influence of water. However, the higher disintegration rate and larger mass change indicate that the water stability of the sample is poor, and it may lose structural stability in a water environment, causing structural damage or performance degradation.

[0063] The above-mentioned embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A composite curing agent, characterized in that: The dosage of each component of the curing agent: Fly ash 10%~15%; slag 5%~7.5%; polyacrylamide 2%; Water reducing agent: 0.1%~0.25%; sodium hydroxide 0.5%.

2. A composite curing agent according to claim 1, characterized in that: The fly ash is primary fly ash.

3. A composite curing agent as claimed in claim 1, characterized in that: The slag particle size is mainly distributed in the range of 1 to 35 μm, and the specific surface area is 430 m 2 / kg.

4. A composite curing agent as claimed in claim 1, characterized in that: The polyacrylamide is produced by Sinopharm and has a molecular weight of 10 million.

5. A composite curing agent as claimed in claim 1, characterized in that: The water reducer is a composite polyhydroxy acid high-efficiency water reducer.

6. A method for preparing a composite curing agent according to any one of claims 1 to 5, characterized in that: Fly ash, slag, polyacrylamide, sodium hydroxide dry materials and soil dry materials are mixed and evenly mixed, and then water mixed with a water reducing agent is added to the dry materials and then evenly mixed to obtain the product.

7. Use of a composite curing agent as described in any one of claims 1 to 5, using the composite curing agent to improve sulfate saline soil.

8. The method for applying a composite curing agent according to claim 7, characterized in that: The steps include: Pretreatment of sulfate soil samples: Before the test, the soil samples were first pretreated by air-drying them to ensure that the water inside them was fully volatilized to avoid affecting the subsequent tests. The air-dried soil samples were then crushed into fine particles and screened through a 2 mm sieve to ensure that the particle size of the soil samples was uniform and consistent, which was convenient for subsequent mixing and preparation. Mixing: Mix the pre-treated soil with polyacrylamide, slag and fly ash; during the mixing process, ensure that the mixture is fully stirred so that the polyacrylamide can be evenly distributed in the soil, thereby playing its due role; Inject water; then, according to the predetermined optimal moisture content, add an appropriate amount of distilled water mixed with a water reducer into the mixture, and mix it again; the purpose of this step is to make the soil sample reach the optimal moisture content to simulate the soil environment in the actual project; Bag and let stand; put the mixed soil sample into a plastic bag and carry out stuffing treatment; during this process, the soil sample is sealed in the plastic bag and left to stand, so that it can fully absorb moisture and reach a stable state; Compacting: Compact the above soil samples.

9. The method for applying a composite curing agent according to claim 7, characterized in that: The soaking time is 1 day to ensure that the soil sample reaches the expected moisture content and uniformity.

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