A method for improving the performance of cement paste using plasma

Abstract

The application belongs to the technical field of material preparation, and particularly relates to a method for improving the performance of cement net slurry by using plasma. The method uses normal pressure plasma to treat cement powder, and changes the hydrophobicity, electrical performance and compressive strength of the cement by screening gas and optimizing the parameters of glow discharge treatment. The cement treated by the plasma shows hydrophobicity in the interface performance and the mechanical compressive strength is improved.

Description

[0001] Priority application

[0002] This application claims priority to Chinese invention patent application No. [202311454431.0] "A method for improving the performance of cement paste using plasma", filed on November 3, 2023, which is incorporated herein by reference in its entirety. Technical Field

[0003] This invention belongs to the field of materials preparation technology, specifically relating to a method for improving the performance of cement paste using plasma. Background Technology

[0004] Cement is one of the most widely used building materials in modern times. Compared with other commonly used building materials such as steel, wood, and plastics, cement production has low energy consumption, abundant raw materials, and a simple preparation process. Furthermore, cement has the characteristics of high durability, good fire resistance, and strong adaptability. Therefore, cement will continue to be the most widely used building material for a long time to come. However, with the development of building technology and the diversified requirements of building structures, the requirements for cement performance in this field are also increasing, including the need to improve its strength and shorten the maintenance cycle. Currently, two common methods are used to improve cement performance: one is the chemical method by adding admixtures, and the other is the physical method by changing the properties of water (electrochemical or magnetized water) or directly changing the properties of cement powder. In the chemical method, because it requires the addition of admixtures or various fiber and mineral active materials to improve the strength and curing time of cement, this strategy not only increases material costs but also complicates the construction process and places higher demands on construction equipment. In comparison, using physical methods to directly improve the properties of cement powder is easier to industrialize.

[0005] Plasma modification technology refers to the process by which the surface of a material is activated, oxidized, or functionalized due to changes in surface functional groups and morphology after being subjected to plasma. However, plasma modification technology is currently widely used in the semiconductor, textile, and biomedical fields, but its application in civil engineering is relatively limited.

[0006] Patent CN112548089A (20210326), entitled "Application of a Discharge Plasma Modification Method in Treating Spherical / Near-Spherical Metal Powders Prepared by Atomization," discloses a method of sealing metal powder in a container and then performing plasma modification treatment using high-voltage equipment. This patented method primarily targets the plasma modification of hollow metal spherical powders. Its principle involves using a high-current-density current filament to generate a cold-field plasma that bombards the surface of the metal spherical powder, creating instantaneous high temperatures and causing localized thermal melting. However, this method is not suitable for modifying cement powder. The purpose of modifying the surface of cement powder is to functionalize it and improve certain properties; if thermal melting occurs on the surface, it can actually damage the cement powder.

[0007] Patent CN115140958A (20221004), entitled "A Multifunctional Smart Cement and Its Preparation Method," discloses a method for modifying cement powder materials at room temperature using rotating, low-pressure (10-80 Pa) plasma technology. In this method, nitrogen-containing particles act on the surface of the cement powder, forming a uniform nitrogen-doped structure. The doped nitrogen replaces the oxygen in the cement, forming calcium nitrate and calcium nitrite during cement hydration. The cement material modified by this method exhibits higher electrical conductivity, electromagnetic properties, and mechanical properties; however, this method does not improve the hydrophilic / hydrophobic properties of the cement material.

[0008] In conclusion, it is necessary to propose a new methodology to address the shortcomings of existing technologies. Summary of the Invention

[0009] In view of this, the purpose of the present invention is to provide a method for improving cement performance and preparing cement paste using plasma, the specific technical solution of which is as follows.

[0010] A method for modifying cement powder using atmospheric pressure plasma includes the following steps:

[0011] S01: The cement powder is evenly spread in a transparent container, and then the transparent container is placed in the sample chamber of the static dielectric barrier plasma discharge device. The static dielectric barrier plasma discharge device uses a quartz plate as a dielectric barrier layer, and the thickness of the cement powder spread in the transparent container is no more than 1 cm.

[0012] S02: Inject gas into the sample chamber of the static dielectric barrier plasma discharge device, and perform glow discharge after the gas fills the sample chamber. The sample chamber is at standard atmospheric pressure.

[0013] S03: The glow discharge treatment time is 5-30 min, and the discharge power is 200-400W. After treatment, modified cement powder is obtained.

[0014] Furthermore, the discharge power of the glow discharge treatment is 300-400W.

[0015] Furthermore, the voltage applied to the upper and lower positive and negative electrodes of the static dielectric barrier plasma discharge device is 100-140V.

[0016] Furthermore, the cement powder includes silicates, phosphates, or aluminosilicates.

[0017] Furthermore, the gas injected into the sample chamber includes nitrogen or oxygen.

[0018] The modified cement powder prepared by the above method.

[0019] A hydrophobic, antifouling cement block is prepared from the modified cement powder described above. The surface of the hydrophobic cement block has needle-like ettringite and gel-like or gelatinous calcium silicate hydrate. In some embodiments, the calcium silicate hydrate is Ca5(SiO4)2(OH)2.

[0020] A method for preparing hydrophobic and antifouling cement blocks, wherein the modified cement powder is prepared by adding water to the above-mentioned modified cement powder and undergoing a hydration reaction, wherein the modified cement powder is mixed with tap water at a ratio of 1:0.4.

[0021] Furthermore, the mixture of the modified cement powder and the tap water is poured into a container in batches and vibrated, and finally the surface of the mixture in the container is smoothed.

[0022] Furthermore, the mixture is cured in an environment with a temperature of 20±2℃ and a humidity of ≥95% to obtain a hydrophobic and antifouling cement block.

[0023] Beneficial technical effects

[0024] This invention provides a method for modifying cement powder using plasma generated by glow discharge under standard atmospheric pressure. By selecting the glow discharge power, time, and gas filling the sample chamber, the functional groups on the surface of the cement powder modified by this plasma are changed, and a layer of hydrophobic material is deposited, making the surface of the cement prepared subsequently more hydrophobic. This improved performance can be applied to the research and use of building waterproofing materials in industry.

[0025] The static plasma equipment used in this invention is a semi-automatic plasma device (samples are statically treated, and manual inspection is required after filling with gas), which has a low cost. However, our team has developed a simple and feasible method based on this semi-automatic equipment, which can effectively modify cement powder. Therefore, this method is suitable for industrial application and can effectively reduce production costs.

[0026] The improved overall performance of the cement block (cement paste) finally prepared by the method of this invention includes enhanced hydrophobicity and stable improvement in compressive strength. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. The elements or parts in the drawings are not necessarily drawn to scale. Obviously, the drawings described below are some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0028] Figure 1 This is a schematic diagram of the static dielectric barrier discharge plasma equipment and process operation of the present invention (a is a schematic diagram of the equipment, b is a schematic diagram of the operation);

[0029] Figure 2 The image shows a comparison of the changes in hydrophilicity and hydrophobicity of untreated cement and cement treated with DBD plasma for different durations after 28 days of cement hydration (a is the front of cement treated for 0 minutes, b is the front of cement treated for 5 minutes, c is the front of cement treated for 30 minutes, d is the side of cement treated for 0 minutes, e is the side of cement treated for 5 minutes, and f is the side of cement treated for 30 minutes).

[0030] Figure 3 A comparison chart showing the changes in electrical properties of untreated cement and cement treated with DBD plasma for different durations after 28 days of cement hydration.

[0031] Figure 4 A comparison chart showing the changes in compressive properties of untreated cement and cement treated with DBD plasma for different durations after 28 days of cement hydration;

[0032] Figure 5 Scanning electron microscope (SEM) images of untreated cement and cement treated with DBD plasma for different durations (a: 0 minutes of treatment, b: 5 minutes of treatment, c: 30 minutes of treatment);

[0033] Figure 6X-ray diffraction (XRD) images of untreated cement and cement treated with DBD plasma for different durations;

[0034] Figure 7 Fourier transform infrared (FTIR) spectra of untreated cement and cement treated with DBD plasma for different durations. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0036] In this document, "and / or" includes any and all combinations of one or more of the listed related items.

[0037] In this article, "multiple" means two or more, that is, it includes two, three, four, five, etc.

[0038] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0039] As used in this specification, the term "about" typically means + / - 5% of the value, more typically + / - 4%, more typically + / - 3%, more typically + / - 2%, even more typically + / - 1%, even more typically + / - 0.5% of the value.

[0040] In this specification, certain embodiments may be disclosed in a range-bound format. It should be understood that this "range-bound" description is merely for convenience and brevity and should not be construed as a rigid limitation on the disclosed range. Therefore, the description of the range should be considered as having specifically disclosed all possible subranges and independent numerical values ​​within those ranges. For example, range The description should be considered as having specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numbers within this range, such as 1, 2, 3, 4, 5, and 6. The above rules apply regardless of the breadth of the range.

[0041] Glossary

[0042] The "cement paste" described in this invention refers to a cement block obtained by mixing cement powder and water and then molding it. This invention uses modified cement powder to prepare the cement paste, thus yielding a modified cement paste.

[0043] Example 1

[0044] This embodiment provides an example of a method for modifying cement powder (powder).

[0045] This embodiment uses a static dielectric barrier plasma discharge device, model DBD50, purchased from Nanjing Perspett Electronic Technology Co., Ltd. The cement powder used in this embodiment is PO42.5.

[0046] Static dielectric barrier discharge (DBD) devices for generating plasma, such as Figure 1 As shown in Figure a. The cement powder to be modified is evenly spread in a transparent container, with a thickness not exceeding 1 cm. The transparent container is then placed inside the sample chamber of a static dielectric barrier discharge device that generates plasma, with a quartz plate serving as the dielectric barrier layer. The sample chamber is at normal atmospheric pressure (atmospheric pressure is 1 atmosphere, 1 standard atmosphere is 101325 Pa). Gas is injected into the sample chamber until it is full, then the gas cylinder is closed. As an example, a gas cylinder can be connected to one end of the device, and a balloon can be attached to the other end. When the balloon begins to inflate, it indicates that the device is full of gas. The discharge parameters of the device are adjusted. Once the gas in the sample chamber between the two quartz plates is ionized to a certain degree, plasma discharge is generated. The generated plasma acts on the cement powder placed in the sample chamber, modifying the powder surface. During the discharge process, the cement powder is turned over every few minutes (e.g., 2-3 minutes) to ensure uniform plasma treatment. The device discharge is then turned off, the sample chamber is opened, and the modified cement powder sample is removed. The cement powder is then subjected to a hydration reaction to obtain modified cement blocks, also known as cement paste. For detailed operating procedures, please refer to [link to relevant documentation]. Figure 1 b.

[0047] The cement powder used in this embodiment is any one of silicate, phosphate, and aluminosilicate cement powder.

[0048] In this embodiment, the plasma modification time ranges from 1 to 30 minutes.

[0049] The discharge power range of this embodiment is 200-400W.

[0050] In this embodiment, the voltage applied to the upper and lower positive and negative electrodes of the plasma device is 100V-140V.

[0051] In this embodiment, the gas injected into the sample chamber includes nitrogen or oxygen.

[0052] The following is a screening and verification process using different discharge times, powers, and gases introduced into the sample chamber.

[0053] Table 1 Nitrogen filling

[0054] DBD parameters Contact angle 0min 11.84° 200W, 5min 27.16° 200W, 30min 48.03° 325W, 5min 44.66° 325W, 30min 125.76° 400W, 5min 57.17° 400W, 30min 82.01°

[0055] Table 2 Oxygen Filling

[0056] DBD parameters 0min 325W, 5min 325W, 30min Contact angle 11.84° 95.16° 44.5°

[0057] Example 2

[0058] This embodiment provides an example of a method for hydrating the modified cement powder from Example 1.

[0059] Modified cement powder was mixed with tap water at a water-cement ratio of 0.4. Half of the mixture was poured into a test module and vibrated for 60 seconds using a ZS-15 vibration table. The other half of the mixture was then poured into the same module and vibrated for another 60 seconds. Finally, the surface of the mixture in the module was smoothed (e.g., by scraping with a scraper). The sample was then placed in a curing chamber for standard curing (temperature 20±2℃; humidity ≥95%) for one day, resulting in a cement block (i.e., cement paste). The silicone mold on the outside of the cement block was then removed (i.e., demolding), and curing continued for 28 days before performance testing. It is understood that the module size varies depending on the specific test (compression specimen size: 40×40×40mm; electrical specimen size: 20×20×80mm).

[0060] The hydration reaction equation is as follows:

[0061] 3CaO·2SiO2+6H2O→3CaO·2SiO2·3H2O

[0062] CaO + H₂O → Ca(OH)₂

[0063] 2C3S + 6H → C3S2H3 + 3CH

[0064] C3AH6 + 12H → 3AH6 + 6CH

[0065] Example 3

[0066] This embodiment provides performance verification of modified cement.

[0067] In Example 1, the hydrophilicity and hydrophobicity of the interface of the plasma-modified cement powder changed, and the hydrophilicity and hydrophobicity of the cement block prepared from it also changed. Figure 2 ac is an image of the contact angle of the front of the cement block; Figure 2 df is an image of the contact angle on the side of the cement block; DBD 0min indicates no plasma treatment; DBD 5min or DBD 30min represents the plasma treatment time, with a power of 325W. Figure 2 As can be seen from AC, the surface contact angle of the front side of all cement block samples is close to zero, indicating hydrophilicity. After plasma modification, the surface contact angle of the side surface of the cement block samples increases with the increase of plasma treatment time, from... Figure 2 As can be seen from the datasheet, the contact angle of the sample side surface after 5 minutes of DBD treatment is larger than that of the sample without plasma treatment, indicating a gradual shift from hydrophilicity to hydrophobicity. A higher contact angle means a smaller contact area between the water droplet and the cement surface, causing the droplet to tend to remain round rather than penetrate the cement. This suggests that the method in Example 1 increases the hydrophobicity of the cement powder, and the hydrophobic cement powder, when prepared into cement blocks, can effectively achieve waterproofing and stain resistance.

[0068] Figure 3 The electrical properties of the cement blocks prepared after plasma modification in Example 2 also changed. The resistivity trend shows that the resistivity at DBD 5min is greater than that at DBD 30min, and greater than that at DBD 0min (i.e., without plasma modification). Cement hydration reaction refers to the process in which cement powder and water react chemically to form cement colloid. Plasma modification of cement powder accelerates the hydration reaction, resulting in increased resistivity. Higher resistivity indicates less solution in the pores of the cement block and lower liquid-filled porosity. However, increased resistivity is an undesirable effect of this invention; the aim is to improve the conductivity of cement, i.e., reduce resistivity.

[0069] Figure 4 The figure shows the change in compressive strength of cement blocks prepared after plasma modification in Example 2. The longer the DBD treatment time, the higher the compressive strength of the cement blocks.

[0070] Figure 5The image shown is a scanning electron microscope (SEM) image of cement blocks prepared from plasma-modified cement powder in Example 2. The image reveals that with increasing DBD treatment time, the surface roughness of the cement blocks increases, along with the increase in needle-like structures (ettringite AFt) and colloidal or cementitious substances CSH (Ca5(SiO4)2(OH)2). The increased surface roughness leads to a reduced contact area between water droplets and the solid surface, a larger contact angle, and enhanced hydrophobicity. Furthermore, the formation of AFt can increase the early strength of the cement because AFt is an early hydration product that forms high-strength crystals in the early stages of cement hydration, resulting in better compressive strength. CSH typically exhibits a colloidal or cementitious structure, which appears as a continuous, irregular network or texture in the SEM image; its formation also contributes to improving the compressive strength of the cement.

[0071] Figure 6 As shown, the peak CSH intensity at 23.2° and 47.7° increases with increasing plasma treatment time. Higher intensity indicates better CSH formation and crystallization. This explains why the compressive strength of the cement blocks prepared by the method of this invention increases with prolonged plasma treatment time.

[0072] Figure 7 As shown, the peak value is 2350 cm⁻¹ as the DBD processing time increases. -1 substance CO3 - The decrease in peak intensity indicates a reduction in the carbide content in the cement (at 0 min, there is a small downward peak at 2350 nm, but this peak does not appear at 5 min and 30 min, indicating a decrease in peak intensity). Carbides are compounds formed by the reaction of cement and carbon dioxide. CO3 - The presence of carbides interferes with the cement hydration process, affecting the formation of cement hydration products (i.e., AFt and CSH). This impacts the early strength and long-term strength stability of cement. Carbide formation can also affect the pore structure of cement. Lower carbide content means less cement porosity, which is one of the main reasons for the increased compressive strength of cement samples treated with DBD.

[0073] In summary, the improved overall performance of the cement blocks prepared by this invention includes enhanced hydrophobicity and compressive strength. However, increased resistivity is an undesirable effect. Therefore, the optimal solution is DBD treatment for 30 minutes.

[0074] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A hydrophobic and stain-resistant cement block, characterized in that, The hydrophobic antifouling cement block is prepared by adding water to modified cement powder and undergoing a hydration reaction. The surface of the hydrophobic antifouling cement block has needle-like ettringite and colloidal or gelatinous hydrated calcium silicate. The modified cement powder is prepared using an atmospheric pressure plasma method, including the following steps: S01: The cement powder is evenly spread in a transparent container, and then the transparent container is placed in the sample chamber of the static dielectric barrier plasma discharge device. The static dielectric barrier plasma discharge device uses a quartz plate as a dielectric barrier layer, and the thickness of the cement powder spread in the transparent container is no more than 1 cm. S02: Inject gas into the sample chamber of the static dielectric barrier plasma discharge device, and perform glow discharge after the gas fills the sample chamber. The sample chamber is at standard atmospheric pressure. S03: The glow discharge treatment time is 5-30 min, and the discharge power is 200-400W. After treatment, modified cement powder is obtained.

2. The hydrophobic and antifouling cement block as described in claim 1, characterized in that, The discharge power of the glow discharge treatment is 300-400W.

3. The hydrophobic and antifouling cement block as described in claim 1, characterized in that, The voltage applied to the upper and lower positive and negative electrodes of the static dielectric barrier plasma discharge device is 100-140V.

4. The hydrophobic and antifouling cement block as described in claim 1, characterized in that, The cement powder includes silicates, phosphates, or aluminosilicates.

5. The hydrophobic and antifouling cement block as described in claim 1, characterized in that, The gas injected into the sample chamber includes nitrogen or oxygen.

6. The hydrophobic and antifouling cement block as described in claim 1, characterized in that, The modified cement powder was mixed with tap water at a ratio of 1:0.

4.

7. A hydrophobic and antifouling cement block as described in claim 6, characterized in that, The mixture of the modified cement powder and the tap water is poured into a container in batches and vibrated. Finally, the surface of the mixture in the container is smoothed.

8. The hydrophobic and antifouling cement block as described in claim 7, characterized in that, The mixture was cured in an environment with a temperature of 20±2℃ and a humidity of ≥95% to obtain a hydrophobic and stain-resistant cement block.

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