CN114409355B

CN114409355B - Low-water-to-gel ratio vertical barrier material and preparation method and application thereof

Info

Publication number: CN114409355B
Application number: CN202210036869.6A
Authority: CN
Inventors: 黎璇; 杜延军; 王敏; 姜哲元; 傅贤雷
Original assignee: Southeast University
Current assignee: Southeast University
Priority date: 2022-01-13
Filing date: 2022-01-13
Publication date: 2023-02-10
Anticipated expiration: 2042-01-13
Also published as: CN114409355A

Abstract

The invention discloses a low-water-to-gel ratio vertical barrier material and a preparation method and application thereof. The paint comprises the following components in parts by mass: 33-67% of sodium modified bentonite, and the balance of granulated blast furnace slag micro powder, active magnesium oxide and sodium hexametaphosphate; wherein, the granulated blast furnace slag micro powder: the mass ratio of the active magnesium oxide is 4-11:1, the addition amount of the sodium hexametaphosphate is 0.5 to 4 percent of the dry mass of the sodium modified bentonite. On the premise of ensuring that the seepage-proofing performance is not reduced, the low-water-cement-ratio vertical barrier material reduces the water-cement ratio from more than 4 to 1.8-2.5, can keep the slurry return amount in a lower state under a high-pressure triaxial, biaxial and high-pressure rotary spraying method, and can provide certain strength. The low slurry return amount can ensure that the barrier material is smoothly and fully mixed with the in-situ soil, and the function of the vertical barrier is fully exerted; the preparation method is simple and clear, has low requirements on production construction equipment and sites, and has wide application market.

Description

Low-water-to-gel ratio vertical barrier material and preparation method and application thereof

Technical Field

The invention relates to a low-water-to-gel ratio vertical barrier material and a preparation method and application thereof, belonging to the technical field of barrier control of polluted sites.

Background

The main reasons for frequent water and soil safety accidents are as follows: on one hand, the adjustment of economic structure and industrial layout, the shutdown and the removal from urban areas of a large number of industrial enterprises, and the leaving of a large number of industrial polluted sites; on the other hand, as the progress of urban industrialization is continuously promoted, intensive production and living modes generate a large amount of solid wastes such as industrial wastes and household garbage. The industrial pollution site and the solid waste and the disposal site thereof are existing or potential centralized pollution sources of underground environment, and seriously threaten public health and the safety of the surrounding underground environment.

As one of the technologies for dealing with environmental pollution, the barrier has been developed in the four and fifty years of the twentieth century by european and us mud excavation technologies, bentonite mud is used for trench retaining walls, and two different kinds of anti-seepage barrier technologies are gradually developed. At the end of the 20 th century, the cement-bentonite vertical cut-off wall technology was developed in europe and widely applied to dams, dam foundations and underground anti-seepage facilities of power plants. The technology is introduced into China at the beginning of the century, and the bentonite vertical barrier is mainly a soil-bentonite barrier at present; a cement-bentonite barrier; a soil-cement-bentonite barrier; magnesium oxide excites novel vertical barrier walls such as slag-bentonite and the like.

However, the vertical barrier has the problem that a high water-to-gel ratio is required in the preparation process of the slurry sample of the vertical barrier of the bentonite system due to the ultrahigh water absorption capacity of the bentonite in the construction process, which causes three substantial disadvantages: one is that a higher water-to-gel ratio will severely limit the material properties and reduce the strength of the rigid or semi-rigid barrier wall. If the bentonite vertical barrier is to obtain a lower permeability coefficient, a higher proportion of bentonite needs to be added, and the higher the bentonite mixing amount is, the higher the water-gel ratio needed by mixing is, and the water-gel ratio needed by the traditional bentonite slurry sample is more than 4. The higher the water-gel ratio is, the lower the strength is, so that the situation that the permeability coefficient and the strength cannot meet the requirements at the same time exists; secondly, because of the cost problem, the domestic vertical separation barrier construction generally adopts a three-shaft stirring or high-pressure rotary spraying method, and in the construction process, a higher water-to-glue ratio can cause a larger slurry return amount, which not only seriously causes material waste and field pollution, but also seriously causes that the material of the vertical separation barrier cannot be sufficiently and fully mixed with in-situ soil, thereby seriously affecting the separation performance; thirdly, the high water-cement ratio leads to higher water content of the wall body, after the construction is completed, the wall body cracks due to the evaporation of the water in the wall body, and further a permeable advantage channel is formed, so that the function of the barrier wall is seriously affected and even loses efficacy.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a vertical barrier material with a low water-to-adhesive ratio, a preparation method and an application thereof, which can realize that: (1) Simultaneously, the strength and the permeability coefficient are considered, and the permeability coefficient is ensured to be lower than 1 x 10 x ^-9 m/s and the unconfined compressive strength of more than 100kPa; (2) Water to glue ratioReducing the slurry content to 1.8-2.5, and generating lower slurry return amount in the construction process; (3) The water content of the vertical barrier is reduced, and the vertical barrier can resist cracking; (4) The used materials contain a large amount of industrial byproducts, so that the waste and pollution of the materials in the construction process are effectively reduced, and carbon neutralization is responded.

In order to solve the technical problems, the invention adopts the technical scheme that:

a low water-to-gel ratio vertical barrier material comprising the following components in parts by mass: 50% of sodium modified bentonite, 50% of granulated blast furnace slag micro powder, 50% of active magnesium oxide and 50% of sodium hexametaphosphate; wherein, the granulated blast furnace slag micro powder: the mass ratio of the active magnesium oxide is 4-11:1, the addition amount of the sodium hexametaphosphate is 0.5 to 4 percent of the dry mass of the sodium modified bentonite.

The improvement is that the sodium hexametaphosphate is industrial sodium hexametaphosphate, white crystals, the content of pure sodium hexametaphosphate is more than or equal to 40 percent, the inactive sulfate is less than or equal to 7.5 percent, the pH value is 5.8 to 7.3, and the water-insoluble substance is less than or equal to 0.05 percent.

The improvement is that the water-to-gel ratio of the material is determined according to the mixture ratio of the granulated blast furnace slag micro powder, the active magnesium oxide and the sodium hexametaphosphate, and the water-to-gel ratio ranges from 1.8 to 2.5.

The preparation method of the vertical barrier material with the low water-gel ratio comprises the following steps:

step 1), dissolving sodium hexametaphosphate in distilled water, and stirring to ensure that the sodium hexametaphosphate is fully dissolved to obtain a sodium hexametaphosphate solution;

step 2), uniformly mixing the sodium modified bentonite, the granulated blast furnace slag micro powder and the active magnesium oxide according to a dry mass ratio of 100;

and 3) selecting a water-gel ratio according to the material ratio, adding the MSB dry powder into the sodium hexametaphosphate solution obtained in the step 1), and continuously stirring the MSB dry powder to obtain a modified MSB slurry sample, namely the low water-gel ratio vertical barrier material.

Compared with the traditional mixing mode of mixing and stirring after sodium hexametaphosphate and MSB dry powder are mixed, the water-gel ratio can be reduced by more than 20%.

Further, the stirring speed in the step 1) is 710-2880r/min, and the stirring time is 1-2 minutes.

Further, the stirring time in the step 3) is 10-15min, and the stirring speed is 710-2880r/min.

The application of any one of the materials for the vertical barrier with the low water-gel ratio in the vertical barrier is characterized in that the vertical barrier is formed after the materials for the vertical barrier with the low water-gel ratio are mixed with in-situ soil and maintained.

As an improvement, the low-water-gel ratio vertical barrier material can be applied to vertical barriers in the air or in complex polluted sites of buildings.

Has the advantages that:

compared with the prior art, the vertical barrier material with low water-cement ratio and the preparation method and application thereof provided by the invention have the following specific advantages that the water-cement ratio can be reduced to 1.8-2.5 from more than 4 required by the traditional bentonite material while the construction workability is met:

1. the low-water-gel ratio vertical barrier material has the capability of giving consideration to both strength and low permeability coefficient. The low water-gel ratio vertical barrier material meets the condition that the permeability coefficient is lower than 1 x 10 ^-9 The water-gel ratio is reduced under the premise of m/s, so that higher strength can be provided;

2. the low water-gel ratio vertical blocking barrier material can reduce the slurry return amount from more than 50% of the traditional bentonite material to 20% under a triaxial construction method under the pressure of 2-4MPa or a high-pressure rotary spraying method under the pressure of 20-40 MPa, and the blocking material can be fully mixed with in-situ soil to ensure the integrity of the vertical blocking barrier;

3. the low-water-gel-ratio vertical barrier material has good anti-cracking capability. By reducing the water-to-glue ratio of the material of the vertical blocking barrier, the water content of the wall is reduced by 20%, the possibility of cracking is reduced, the anti-seepage performance of the material during use is enhanced, and the service life of the vertical blocking barrier is prolonged;

4. the low water-gel ratio vertical barrier material belongs to green and resource recycling materials, wherein a main material belongs to a non-toxic and harmless state and belongs to a green material no matter in the production or use process; the granulated blast furnace slag micro powder belongs to industrial byproducts/waste materials, has the functions of carbon fixation and carbon reduction, and belongs to an environment-friendly low-carbon material;

5. the low-water-gel-ratio vertical barrier material has simple and clear preparation method, low requirements on production and construction equipment and sites, and easy popularization and application.

Detailed Description

The following examples and engineering examples are intended to further illustrate the present invention and are not intended to limit the scope of the invention in any way.

Examples

Step 1) weighing sodium hexametaphosphate 2% of the dry mass of sodium modified bentonite, adding the sodium hexametaphosphate into distilled water, stirring by using an electric stirrer, setting the rotation speed to be 710r/min, and fully stirring to completely dissolve the sodium hexametaphosphate;

step 2), mixing the sodium modified bentonite (produced from Weifang remote bentonite Limited, the free expansion amount is 16ml/2 g), the granulated blast furnace slag micro powder and the active magnesium oxide according to a dry mass ratio of 10;

step 3) after respectively preparing the sodium hexametaphosphate solution and the MSB dry powder, setting the rotating speed of an electric stirrer to be 710r/min and the water-to-glue ratio to be 2.5, continuously stirring the sodium hexametaphosphate solution while adding the MSB dry powder, and continuously stirring after the MSB dry powder is completely added;

step 4) adding a proper amount of water according to the viscosity state of the slurry observed in the stirring process, wherein the stirring time is 10min, and obtaining a modified MSB slurry sample, namely the low water-gel ratio vertical barrier material; the material obtained this time is named "low water".

Comparative example

In order to visually compare various indexes of the traditional vertical separation barrier and the low-water-gel-ratio vertical separation barrier, and clearly determine the advantages of the low-water-gel-ratio vertical separation barrier, a traditional soil-bentonite vertical separation barrier material is set as a comparison group, and the composition material is sodium modified bentonite (produced from Zhenjiang Mufeng bentonite factory, the free expansion is 16ml/2 g), and the fluidity is measured at the same time.

The preparation method of the sodium modified bentonite slurry vertical barrier material of the control group comprises the following steps:

step 1) setting the rotating speed of an electric stirrer to be 710r/min and the water-to-glue ratio to be 4, continuously stirring distilled water while adding the sodium modified bentonite, and continuously stirring after the sodium modified bentonite is completely added;

step 2) adding a proper amount of water according to the viscosity state of the slurry observed in the stirring process, wherein the stirring time is 10min, so as to obtain the traditional bentonite slurry vertical barrier material; the material obtained at this time is named as 'traditional'.

Performance test

The fluidity test is improved by referring to the 12 th cement paste fluidity test in GB/T8077-2000 concrete admixture homogeneity test method, and the test instrument is as follows: a. an electric mixer; b. a truncated cone circular die, wherein the diameter of an upper opening is 36 mm, the diameter of a lower opening is 60 mm, the height is 60 mm, and the inner wall of the truncated cone circular die is smooth and seamless; c. a glass plate; d. a stopwatch; e. a rigid ruler; f. a scraper; g. medicine balance, division value 0.1g.

Further, the fluidity test procedure is as follows:

step 1) placing the glass plate in a horizontal position, and wiping the glass plate, the truncated cone circular mold, the stirrer and the stirring pot by using wet cloth to enable the surface of the glass plate to be wet without water stains. Placing the truncated cone round die in the center of the glass plate, and covering the truncated cone round die with wet cloth for later use;

step 2), quickly injecting the mixed slurry sample into a truncated cone round die, and leveling by using a scraper;

and 3) lifting the truncated cone circular mold in the vertical direction, starting a stopwatch to time at the same time, allowing the clean cement paste to flow on the glass plate for 30s, measuring the maximum diameter of the flowing part in two mutually vertical directions by using a ruler, and taking the average value as the fluidity of the clean cement paste.

The permeability coefficient test was performed using a fluid loss test. Wherein, according to the technical Specification of geotechnical engineering of sanitary landfill of domestic garbage and the technical catalog of repairing contaminated site in China (the first one)Batch) presented that the permeability coefficient of vertical baffle walls needs to be less than 1 x 10 ^-9 m/s requirement.

The advantages of the vertical barrier material with low water-gel ratio can be seen by comparing the four aspects of water-gel ratio, fluidity, 28-day age unconfined compressive strength and permeability coefficient. As can be seen from table 1, at lower water-to-gel ratios, the "low water" achieved higher fluidity and lower permeability coefficient, while having some strength at 28 days of age.

TABLE 1 indoor test results for each material

Examples of the applications

In a certain plot in Guangxong county in Shandong, the plot was reported to be buried in 2013-2014 with industrial waste oil residues with unknown sources. The length of the south and north of the land is 140m, the length of the east and west is 45-65m, and the area is about 7338m ² The surface of the land is flat, and the upper part of the land is covered with a layer of backfill soil and construction waste, so that the vegetation is luxuriant. The industrial waste oil residue in the land is mixed with the backfill soil to form industrial solid waste.

The conditions of the land formation are as follows: in the depth range of 25m, the fourth series stratum around the land is composed of miscellaneous fill, silty clay, silty soil, silty sand, silty clay, silty sand, silt and the like from top to bottom. The upper part in the ground block is back filled with construction waste, miscellaneous filling soil and the like.

TABLE 2 Permeability coefficient of each soil layer

The construction method of the vertical blocking barrier with the low water-cement ratio comprises the following steps:

step 1) preparing a vertical barrier material with a low water-to-glue ratio in a stirring and stirring pool according to an embodiment;

step 2) pumping the MSB slurry sample in the first stirring and stirring tank into a second stirring and stirring tank, and continuously stirring for standby application to prevent solid-liquid separation of the slurry sample;

and 3) setting the pressure of an air compressor to be 20MPa, pumping the MSB slurry in the secondary stirring and stirring tank into a high-pressure rotary spraying machine, starting construction, and repeating the process of the step 1) in the primary stirring and stirring tank.

Engineering comparison example:

in order to visually compare various indexes of the traditional vertical separation barrier and the low-water-gel-ratio vertical separation barrier, and clearly determine the advantages of the low-water-gel-ratio vertical separation barrier, a comparison case of the traditional soil-bentonite vertical separation barrier is set.

In 2018, a central fourth environmental protection supervision group is connected to a fertilizer plant in Jiangsu Zhenjiang, the plant has the problem of environmental pollution, according to the result of investigation and treatment, the plant continuously closes all production lines in 6 months in the current year, removes all production equipment from 2019, and decommissions land parcels.

The conditions of the land stratum are as follows: within the depth range of 44m, the soil layer of the land can be divided into 4 layers from top to bottom, and the soil layer comprises: miscellaneous fill, plain fill, silt, clay-intercalated silty clay, strongly weathered granite. The water level is higher, and the burial depth of the stable water level is 0.96-5.58 m.

The construction steps of the traditional soil-bentonite vertical barrier wall are as follows:

step 1) preparing bentonite slurry according to the proportion of comparative example materials by stirring;

step 2) pumping the slurry sample in the first stirring pool into the second stirring pool, and continuously stirring for standby so as to prevent solid-liquid separation of the slurry sample;

and 3) setting the pressure of an air compressor to be 20MPa, sending the prepared slurry sample to a high-pressure jet grouting pile machine, starting construction, and repeating the process of the step 1) in a stirring and stirring pool.

In order to quantitatively compare the two materials, the four aspects of slurry return amount, permeability coefficient, unconfined compressive strength and wall forming integrity are considered.

Wherein, the stock return amount = stock return volume/pumped stock volume.

The permeability coefficient test method adopts an improved fluid loss experiment for testing. Wherein, according to the technical Specification of geotechnical engineering of sanitary landfill for domestic garbage and the technical catalog of remediation of polluted sites (the first place)Batch), the permeability coefficient of the vertical barrier walls needs to be less than 1 x 10 ^-9 m/s。

The strength test adopts the unconfined compressive strength test of 28-day maintenance of the embodiment. The comparison example is a flexible wall, and the unconfined compressive strength cannot be measured.

TABLE 3 comparison of two materials engineering data

In conclusion, the low water-gel ratio vertical barrier material can reduce the slurry return amount from more than 50% of the traditional bentonite material to 20% under a triaxial construction method under the pressure of 2-4MPa or a high-pressure jet grouting method under the pressure of 20-40 MPa, the barrier material can be fully mixed with in-situ soil, the integrity of the vertical barrier is ensured, and the barrier material belongs to a green and resource recycling material, wherein a main material belongs to a non-toxic and harmless state and belongs to a green material no matter in the production or use process; the granulated blast furnace slag micro powder belongs to industrial byproducts/waste materials, has the functions of carbon fixation and carbon reduction, belongs to an environment-friendly low-carbon material, has a simple and clear preparation method, has low requirements on production construction equipment and sites, and is easy to popularize and apply.

The above description is only a preferred embodiment of the present invention, and the scope of the present invention is not limited thereto, and any simple modifications or equivalent substitutions of the technical solutions that can be obviously obtained by those skilled in the art within the technical scope of the present invention are within the scope of the present invention.

Claims

1. The vertical barrier material with the low water-binder ratio is characterized by comprising 50% of sodium modified bentonite, 50% of granulated blast furnace slag micro powder and 50% of active magnesium oxide in percentage by mass; wherein, the granulated blast furnace slag micro powder: the mass ratio of the active magnesium oxide is 4-11:1, the addition amount of the sodium hexametaphosphate is 0.5 to 4 percent of the dry mass of the sodium modified bentonite; the sodium hexametaphosphate is industrial grade sodium hexametaphosphate and white crystal, the content of pure sodium hexametaphosphate is more than or equal to 40 percent, the content of inactive sulfate is less than or equal to 7.5 percent, the pH value is 5.8-7.3, and the content of water insoluble substances is less than or equal to 0.05 percent; the water-to-gel ratio of the material is determined according to the proportion of the granulated blast furnace slag micro powder, the active magnesium oxide and the sodium hexametaphosphate, and the water-to-gel ratio range is 1.8-2.5; the preparation method of the low water-gel ratio vertical barrier material comprises the following steps: step 1), dissolving sodium hexametaphosphate in distilled water, and stirring to ensure that the sodium hexametaphosphate is fully dissolved to obtain a sodium hexametaphosphate solution; step 2), uniformly mixing the sodium modified bentonite, the granulated blast furnace slag micro powder and the active magnesium oxide according to a dry mass ratio of 100; and 3) selecting a water-gel ratio according to the material ratio, adding the MSB dry powder into the sodium hexametaphosphate solution obtained in the step 1), and continuously stirring the MSB dry powder to obtain a modified MSB slurry sample, namely the low water-gel ratio vertical barrier material.

2. The low water-to-gel ratio vertical barrier material of claim 1, wherein: in the step 1), the stirring speed is 710-2880r/min, and the stirring time is 1-2 minutes.

3. The low water-to-gel ratio vertical barrier material of claim 1, wherein: and 3) stirring for 10-15min at the stirring speed of 710-2880r/min.

4. The use of a low water-gel ratio vertical barrier material in a vertical barrier in accordance with claim 1, wherein the low water-gel ratio vertical barrier material is mixed with in situ soil and cured to form a vertical barrier.

5. The use of claim 4, wherein the low water gel ratio vertical barrier material is used for vertical barriers in the vicinity of an empty or complex contaminated site in a building.