A soil stabilizing material and method of use thereof

Abstract

The application discloses a kind of soil solidification material and its using method, the solidification material is composed of magnesium oxide, magnesium sulfate and silica ash, wherein, the mass ratio of magnesium sulfate and magnesium oxide is (0.05-0.3):1.0, and the mass ratio of silica ash and magnesium oxide is (0.05-0.3):1.0.The solidified soil ecology is close to rock and soil under natural conditions, not only has good water stability, but also has good ecology, has no harm to the environment, is conducive to plant growth, and can realize the dual purpose of soil solidification and ecological environmental protection.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soil solidification, in particular to a soil solidification material and a method for using the same. BACKGROUND

[0002] With the rapid development of social economy in China, various production and construction projects are growing rapidly. Human production and construction activities are increasingly damaging the earth's surface, destroying the original vegetation on the surface of the soil, and further leading to a series of environmental problems, such as soil erosion, land desertification, dust, etc. In order to fix the soil, such as to reinforce soft soil foundation and road subgrade, people often use solidification components to solidify the soil to improve the stability and bearing capacity of the soil. By using solidification components to solidify the soil, it is more effective than methods such as compaction and replacement with concrete and other materials to improve the bearing capacity of the soil, and it can also significantly reduce the cost of soil treatment. In addition, solidification components or solidification agents can be used for temporary floor hardening, temporary or low-grade roads, roadbed engineering, etc., which can improve the soil to meet complex construction requirements, thereby speeding up the construction speed and saving construction costs.

[0003] At present, the commonly used soil solidification materials in engineering mainly include inorganic solidification materials such as Portland cement and lime. However, there are many problems in the use of inorganic solidification materials: for example, the soil solidification technology based on Portland cement is relatively mature, and the solidified soil can obtain high strength, but due to the high solubility of the hydration product calcium hydroxide and the high alkalinity (pH value of 12-13), it has poor ecological properties, which can cause the hydration product calcium hydroxide to enter the surrounding water, thereby affecting the surrounding water and making the plants grow slowly or even unable to recover, and also harming the growth of fish and other aquatic life in the surrounding environment, so the use of Portland cement-based materials to solidify the soil will be limited from the ecological point of view; secondly, the existing cement-based solidification materials have poor resistance to dry-wet cycle, and the soil is prone to collapse under the repeated dry-wet cycle in nature, affecting the solidification effect; in addition, the cement-based solidification agent has poor compatibility with the soil matrix and large drying shrinkage. Lime-based solidification materials are less used alone and need to be used in combination with Portland cement, fly ash, and slag and other materials with certain activity. Due to the strong alkalinity, lime-based solidification materials also have poor ecological properties, and their effect on soil solidification is very limited compared to Portland cement.

[0004] At present, there have been many reports on the application of organic solidification agents. Compared with inorganic solidification materials, organic solidification agents have the advantages of small dosage and some of them can be dissolved in water, so they are convenient to use. However, organic solidification agents are expensive and have poor water resistance, and their long-term stability cannot be guaranteed when used to solidify soil, especially since many organic solidification agents have certain toxicity, so organic solidification agents have not been widely accepted from the ecological point of view. SUMMARY

[0005] In view of the above problems existing in the prior art, the present application aims to provide a soil solidification material and a use method thereof, so as to solve the problems of poor ecological property, harm to the growth of surrounding organisms, easy to collapse under the action of repeated dry-wet cycles and influence on the solidification effect of the inorganic solidification material in the prior art.

[0006] In order to solve the above technical problems, the present application adopts the following technical solutions:

[0007] The soil solidification material is composed of magnesium oxide, magnesium sulfate and silica fume, wherein the mass ratio of magnesium sulfate to magnesium oxide is (0.05-0.3):1.0, and the mass ratio of silica fume to magnesium oxide is (0.05-0.3):1.0.

[0008] In the present application, it is found through in-depth research on the solidification material that the commonly used inorganic solidification material has high alkalinity while obtaining high strength, the pH value can reach 12-13, and even after long time in the natural environment, the pH value is still as high as 12. Therefore, the raw materials of the solidification material are selected, and it is found that magnesium oxide can be well used as the main component of the solidification material, and is combined with composite magnesium sulfate and silica fume. When the magnesium oxide-based soil solidification material is used, the magnesium oxide and the magnesium sulfate react rapidly in advance to form a certain strength and combine the soil into a whole, and then the reaction between the magnesium oxide and the silica fume can form high strength within 3-14 days. The amount of the magnesium oxide is in an excessive state compared with the amounts of the magnesium sulfate and the silica fume, and then there is excessive magnesium oxide which does not participate in the reaction of the magnesium sulfate and the silica fume. The excessive magnesium oxide can contact air, underground water, carbon dioxide and moisture in the soil, continuously generate carbonization reaction, and cement the soil into a whole. Moreover, since the natural environment is often dry and wet alternately, the carbonization process can be continuously enhanced in the dry-wet cycle, which can not only continuously improve the water resistance and strength of the solidified soil, but also control the final pH value of the solidified soil in the range close to 7, so as to not bring adverse effects on the growth of surrounding organisms, and has very good ecological property.

[0009] In the present application, the composition ratio of the soil solidification material can be adjusted according to the properties of the soil, environmental conditions and different engineering requirements, so that the strength, water resistance, ecological property and the like of the solidified soil can meet the requirements of different regions, and the solidification material can be truly and effectively applied to the fields of mine ecological restoration, road subgrade and foundation treatment, and can also be used in other places for preventing water and soil loss, and can also be used in the ecological restoration of waterfronts.

[0010] Preferably, the magnesium oxide is dead-burned magnesium oxide, light-burned magnesium oxide or a mixture of dead-burned magnesium oxide and light-burned magnesium oxide, and the particle size of the magnesium oxide is less than 80 μm. If the particle size is smaller, the amount of water used can be increased, but in the present application, the amount of magnesium oxide used is small, so the effect of the particle size is not obvious.

[0011] Preferably, the particle size of the magnesium sulfate is less than 1.0 mm.

[0012] The present application also provides a method for using the soil solidification material, comprising the following steps:

[0013] Step 1: Prepare the raw materials.

[0014] Step 2: Mix the solidification material, the soil to be solidified and water to obtain a mixture; wherein the mass percentage of the solidification material in the soil to be solidified is less than 20%, and the total mass of water and water contained in the soil to be solidified accounts for less than 70% of the total mass of the solidification material and the soil to be solidified.

[0015] Step 3: Apply the mixture obtained in step 2 to the site where the soil to be solidified is needed by spraying, pouring and vibrating or by paving and compacting, and the strength of the solidified soil increases with the age. In specific implementation, the fluidity of the mixture is related to the amount of water used, and the mixture with a certain plasticity can be paved to the application site and then compacted, the mixture with good fluidity when a large amount of water is used can be poured to the application site, or the mixture can be pumped and sprayed to the application site. The solidified soil of the solidification material is usually used at an ambient temperature of 5-40°C, and can be naturally cured without other curing. Early watering is beneficial to the stability and water resistance of the solidified soil, and when plant seeds are mixed, regular watering is needed to ensure seed germination and plant growth. Regular watering does not reduce the solidification effect of the soil, but rather improves the solidification effect. When the ambient temperature is low, the strength of the solidified soil develops slowly, and watering can be appropriately delayed. When the ambient temperature is higher than 0°C and lower than 5°C, the solidification material of the present application can still be used, but the ratio of the solidification material to the soil should be appropriately increased to 15-20%; when the ambient temperature is higher than 40°C, watering needs to be strengthened.

[0016] Preferably, in step 3, when the mixture obtained in step 2 is applied to vegetation restoration, within the first week, a 0.001% to 0.01% citric acid solution is sprayed on the surface of the soil to surface wetting, and no less than 2 times. The specific spraying times are determined according to the pH monitoring results and the specific construction conditions, the citric acid solution can be sprayed at the same time as watering, and the concentration of the citric acid solution needs to be adjusted according to the amount of water, the citric acid solution is usually sprayed in the early stage of soil solidification, and the role is to reduce the early pH value of the soil, when there is no water stain on the surface of the solidified body, the citric acid solution can be sprayed.

[0017] Preferably, the mass ratio of the solidified material to the soil to be solidified is 1:(5-25).

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] 1. The solidified soil of the present application has ecological properties close to rock-soil under natural conditions, not only has good ecological properties, is harmless to the environment, and is beneficial to plant growth, but also has good water stability, and can realize the dual purposes of ecological protection and soil solidification.

[0020] 2. The solidified material of the present application uses several composite cementing systems, and through hydration and carbonation reactions of different composite cementing systems at different periods, the strength development of the system is first low and then high. After being used to solidify soil, although the early strength development is slow and relatively low, it will not affect the normal germination and rooting of plant seeds, and is especially suitable for vegetation restoration. Although the softening coefficient of the early solidified soil is only 10%-20%, the solidified soil will not collapse when it meets water, so that the solidified soil will not cause water and soil loss, and plants can grow normally. After 12 dry-wet cycles, the compressive strength of the solidified soil not only does not decrease but also increases by up to 20%, and the softening coefficient also increases with the increase of the number of dry-wet cycles, and can reach up to 69% in the test time. Therefore, when the soil solidification material of the present application is used in nature, although the early strength development is slow, the strength continues to grow under the action of long-term repeated rain-dry cycles, which shows that the solidified material of the present application has excellent dry-wet cycle resistance, and is suitable for use in natural environment. Unlike existing solidified materials which are prone to collapse after drying and rainwater immersion, the use of the solidified material of the present application can avoid the hidden dangers such as collapse of existing engineering foundation and collapse of roadbed.

[0021] 3、The solidified material has low alkalinity and solubility, and the early pH value is about 9, which is far lower than that of cement-based and lime-based solidified materials, and is about 2-4 lower than that of the two; during the curing process, after being treated by spraying with a citric acid solution, the pH value can be reduced to about 7, which is close to neutral, and is more close to the natural environment; the solubility of the reaction product of the solidified material is 2.9 mg / 100 ml, which is far lower than that of 165 mg / 100 ml of calcium hydroxide generated by hydration of cement-based materials; therefore, the use of the soil solidified material has no adverse effect on the surrounding environment, and the low alkalinity can make it possible to simultaneously realize soil solidification and vegetation restoration.

[0022] 4、The soil solidified material is simple to use, and can be used after the solidified material, soil and additional water are uniformly mixed; the obtained mixture has adjustable fluidity, and can be constructed by means of paving and compacting, pouring or spraying, and can be watered or naturally cured. DETAILED DESCRIPTION

[0023] The application will be further described below in combination with examples.

[0024] I. Examples and Comparative Examples

[0025] Example 1

[0026] According to the mass mixing ratio, 60 g of magnesium oxide, 15 g of magnesium sulfate, 6 g of silica fume, 1000 g of soil and 500 g of water are weighed and poured into a mixer to be stirred into a uniform slurry mixture. The mixture is injected into a mold, tamped and leveled, and cured at room temperature for 1 day, then demolded and cured to the specified age to test the strength and pH value, and the demolded test piece is subjected to a dry-wet cycle test to test the softening coefficient and observe the collapse.

[0027] Example 2

[0028] According to the mass mixing ratio, 60 g of magnesium oxide, 6 g of magnesium sulfate, 6 g of silica fume, 1200 g of soil and 250 g of water are weighed and poured into a mixer to be stirred into a uniform mixture. The mixture is injected into a mold, and is formed by pressure molding with a pressure of 15 MPa, and is cured at room temperature for 1 day, then demolded and cured to the specified age to test the strength and pH value, and the test piece is subjected to a dry-wet cycle test to test the softening coefficient and observe the collapse.

[0029] Example 3

[0030] According to the mass mixing ratio, 100 g of magnesium oxide, 10 g of magnesium sulfate, 10 g of silica fume, 1000 g of soil and 500 g of water are weighed and poured into a blender to stir into a uniform slurry mixture. The mixture is injected into the mold, tamped and leveled, and cured at room temperature for 1 d, then demolded and cured to the specified age to test strength and pH value. At the same time, the demolded test piece is subjected to dry-wet cycle test to test softening coefficient and observe the collapse.

[0031] Example 4

[0032] According to the mass mixing ratio, 100 g of magnesium oxide, 10 g of magnesium sulfate, 10 g of silica fume, 1000 g of soil and 500 g of water are weighed and poured into a blender to stir into a uniform slurry mixture. The mixture is injected into the mold, tamped and leveled, and cured at room temperature for 1 d, then demolded and cured to the specified age to test strength and pH value. At the same time, the demolded test piece is subjected to dry-wet cycle test to test softening coefficient and observe the collapse.

[0033] Example 5

[0034] According to the mass mixing ratio, 100 g of magnesium oxide, 10 g of magnesium sulfate, 10 g of silica fume, 1000 g of soil and 500 g of water are weighed and poured into a blender to stir into a uniform slurry mixture. The mixture is injected into the mold, tamped and leveled, and cured at room temperature for 1 d, then demolded and cured to the specified age to test strength and pH value. At the same time, the demolded test piece is subjected to dry-wet cycle test to test softening coefficient and observe the collapse.

[0035] Example 6

[0036] According to the mass mixing ratio, 100 g of magnesium oxide, 10 g of magnesium sulfate, 10 g of silica fume, 1000 g of soil and 500 g of water are weighed and poured into a blender to stir into a uniform slurry mixture. The mixture is injected into the mold, tamped and leveled, and cured at room temperature for 1 d, then demolded and cured to the specified age to test strength and pH value. At the same time, the demolded test piece is subjected to dry-wet cycle test to test softening coefficient and observe the collapse.

[0037] Example 7

[0038] According to the mass mixing ratio, 100 g of magnesium oxide, 10 g of magnesium sulfate, 10 g of silica fume, 1000 g of soil and 500 g of water are weighed and poured into a blender to stir into a uniform slurry mixture. The mixture is injected into the mold, tamped and leveled, and cured at room temperature for 1 d, then demolded and cured to the specified age to test strength and pH value. At the same time, the demolded test piece is subjected to dry-wet cycle test to test softening coefficient and observe the collapse.

[0039] Comparative Example 1

[0040] According to the mass mixing ratio, 80 g of Portland cement, 1000 g of soil and 500 g of water are weighed and poured into a blender to stir into a uniform slurry mixture. The mixture is injected into the mold, tamped and leveled, and cured at room temperature for 1 d, then removed from the mold and cured to the specified age for testing pH value.

[0041] Comparative Example 2

[0042] According to the mass mixing ratio, 140 g of magnesium oxide, 20 g of magnesium sulfate, 20 g of silica fume, 1000 g of soil and 550 g of water are weighed and poured into a blender to stir into a uniform slurry mixture. The mixture is injected into the mold, tamped and leveled, and cured in a 6℃ curing box for 3 d, then removed from the mold and cured to the specified age for testing strength.

[0043] II. Performance Analysis

[0044] The soil solidification materials obtained in Examples 1-7 above were tested for performance, and the results are shown in Tables 1-4. The unconfined compressive strength test used a 50KN universal testing machine at a rate of 1mm / min to test the compressive strength value of the solidified soil, and the test process and method referred to the "Highway Soil Test Procedures"; the water resistance was evaluated using the softening coefficient, and the test piece was completely immersed in water to saturation, the surface water was wiped off to measure the compressive strength in the saturated state and compared with the compressive strength in the dry state; the dry-wet cycle performance was determined according to GB / T 11975-1997 "Aerated Concrete Dry-wet Cycle Test Method", and 4h of immersion and 2d of standard curing was one dry-wet cycle; the pH value test was determined according to YS / T 5225-2016 "Soil Test Procedures".

[0045] Table 1 Unconfined compressive strength of soil solidification material of example

[0046]

[0047] Table 2 Softening coefficient of soil solidification material of the above examples

[0048]

[0049] Table 3 Dry-wet cycle performance of soil solidification material of example

[0050]

[0051] Table 4 pH value of soil solidification material of example

[0052]

[0053] Through analysis of the above test results, it can be concluded that:

[0054] (1) Magnesium oxide-based solidified soil has low early compressive strength, but the strength continues to grow with the extension of curing age, and increasing the amount of solidified material can also increase the strength of solidified soil, so the strength of solidified soil can be adjusted by adjusting the amount of solidified material to meet different engineering needs;

[0055] (2) The amount of water and the molding method have great influence on the compressive strength of solidified soil, and the strength of solidified soil by pressing molding is about 8 times higher than that by pouring molding, and high strength can be obtained at an early stage, so the magnesium oxide-based solidified material can be used for road and building foundation reinforcement by pressure molding;

[0056] (3) Magnesium oxide-based solidified soil has good water resistance, and the solidified soil of Examples 1-7 does not collapse after soaking for 3 days, and the softening coefficient of solidified soil increases with the extension of curing age, and as can be seen from Comparative Examples 3 and 5, appropriately increasing the proportion of magnesium sulfate in the solidified material can increase the strength and water resistance of the solidified soil;

[0057] (4) Magnesium oxide-based solidified soil has excellent dry-wet cycle resistance, and the compressive strength of the pouring molded test piece increases after 12 dry-wet cycles, with a maximum increase of about 20% compared to the initial strength, so this performance is the biggest advantage of magnesium oxide-based solidified material over other soil solidified materials;

[0058] (5) The pH value of magnesium oxide-based solidified soil gradually decreases with the extension of age, and is about 9 at 90 days, while the pH value of Portland cement solidified soil with the same amount is still greater than 12, indicating that the ecological property of magnesium oxide-based solidified soil is better; as can be seen from Comparative Examples 3 and 5, appropriately increasing the proportion of magnesium sulfate in the solidified material can reduce the pH value of the solidified soil; as can be seen from Comparative Examples 3 and 4, and Examples 6 and 7, spraying 0.002% and 0.005% citric acid solution on the surface of the solidified soil can reduce the pH value of the magnesium oxide-based solidified soil, and the minimum can be reduced to 7.5, and after a longer time, when the excess magnesium oxide is completely carbonized, the pH value will approach neutral;

[0059] (6) As can be seen from Comparative Example 6 and Comparative Example 2, the performance of magnesium oxide-based solidified soil is related to the curing temperature, and at a lower curing temperature, the early strength development of magnesium oxide-based solidified soil is slow, the early water resistance is poor, the late strength development is fast, and the final strength is about 87% of the normal temperature curing strength;

[0060] (7) In actual engineering applications, the amount, proportion and preparation method of the solidified material can be adjusted as needed to obtain appropriate compressive strength, water resistance and alkalinity.

[0061] Finally, it needs to be explained that the above examples are only used to illustrate the technical solutions of the present application but not to limit the technical solutions, and those of ordinary skill in the art should understand that the technical solutions of the present application are modified or equivalently replaced without departing from the purpose and scope of the technical solutions, which should be covered in the scope of claims of the present application.

Claims

1. A soil solidification material, characterized by, The solidified material is composed of magnesium oxide, magnesium sulfate and silica fume, wherein the mass ratio of magnesium sulfate to magnesium oxide is (0.05-0.3):1.0, and the mass ratio of silica fume to magnesium oxide is (0.05-0.3):1.

0.

2. The soil stabilizing material of claim 1, wherein, The magnesium oxide is heavy-burned magnesium oxide, light-burned magnesium oxide or a mixture of heavy-burned magnesium oxide and light-burned magnesium oxide, and the particle size of the magnesium oxide is less than 80 μm.

3. The soil stabilizing material of claim 1, wherein, The particle size of the magnesium sulfate is less than 1.0 mm.

4. A method of using a soil stabilizing material, comprising: The method comprises the following steps: Step 1: preparing the soil solidified material according to any one of claims 1-3; Step 2: mixing the solidified material, the soil to be solidified and water to obtain a mixture; Step 3: applying the mixture obtained in step 2 to a site where the soil to be solidified is located, and the strength of the solidified soil increases with the age.

5. The method of using the soil stabilizing material of claim 4, wherein, In step 3, when the mixture obtained in step 2 is applied to vegetation recovery, within the first week, a 0.001%-0.01% citric acid solution is sprayed on the surface of the soil to wet the surface, and the spraying is performed no less than 2 times.

6. The method of using the soil stabilizing material of claim 4, wherein, The mass ratio of the solidified material to the soil to be solidified is 1:(5-30).

7. The method of using the soil stabilizing material of claim 4, wherein, The water-solid ratio of the solidified material is 0.10-0.70.

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