Preparation method of a material for inhibiting cement autogenous shrinkage and application thereof

Abstract

The application relates to a preparation method of a cement self-shrinkage inhibiting material and application thereof, and relates to the technical field of cement-based composite materials. The application aims to solve the shortcomings that the traditional cement self-shrinkage inhibiting material cannot play the role of inhibiting cement self-shrinkage due to the reduction of water absorption in the cement-based material. The method comprises the preparation of a new cement self-shrinkage inhibiting material and the application of the material in cement. The hydrophilic carbon nanotube foam particles are obtained by hydrophilic treatment, cleaning and crushing of the carbon nanotube foam prepared by a chemical vapor deposition method. Finally, the H-CNTSPP is mixed with cement to obtain a cement-based material with low self-shrinkage. The material is composed of carbon nanotubes, can combine the advantages of the carbon nanotubes, does not need additional dispersion means, is not sensitive to the internal environment of the cement-based material, and solves the problem of cement-based material self-shrinkage by a new internal curing mechanism. The application is applied to the field of cement-based composite materials.

Description

Technical Field

[0001] This invention relates to the field of intelligent cement-based composite materials technology, and in particular to the preparation of a novel cement self-shrinkage inhibiting material (H-CNTSPP) and its application based on nano-modified cement-based materials. Background Technology

[0002] Cement-based materials are widely used and consumed in large quantities. With societal progress, modern cement-based materials are developing towards high strength and high performance, with a low water-cement ratio being one of their significant characteristics. However, a low water-cement ratio also leads to greater autogenous shrinkage, causing structural cracking, endangering structural safety, and reducing the service life of the structure. Autogenous shrinkage in cement-based materials is caused by cement hydration. Cement hydration consumes water in the pores, and the capillary pressure generated by capillary water loss further compresses the pore volume, ultimately resulting in a reduction in the overall volume of the cement-based material.

[0003] To address the self-shrinkage problem in cement-based materials, a common approach is to add super-adsorption polymers (SAPs). Through their three-dimensional network and hydrophilic polymer chain structure, SAPs absorb water and swell during the initial mixing stage of cement, and release the pre-absorbed water during the capillary drying stage, reducing self-shrinkage caused by capillary forces. Although SAPs can absorb hundreds of times their own mass in ultrapure water, their water absorption capacity in cement materials decreases by one to two orders of magnitude. SAP water absorption and release are driven by the osmotic pressure and humidity gradient of the solution, making them extremely sensitive to the application environment. Cement-based material systems are highly alkaline environments, containing a large number of divalent alkali metal ions (Ca...). 2+ Ions significantly reduce the water absorption capacity of SAP (Super Aerated Polymer), even leading to its failure. Simultaneously, the complex service environment of cement-based materials, such as high temperature and high pressure, also reduces the efficiency of SAP, preventing it from effectively inhibiting self-shrinkage. Therefore, there is an urgent need to develop a new type of environmentally insensitive, highly efficient material for inhibiting cement self-shrinkage.

[0004] Current research indicates that the addition of carbon nanotubes can reduce the self-shrinkage of cement-based materials by promoting cement hydration. However, these conclusions are all based on the premise of uniform dispersion of carbon nanotubes. Due to their hydrophobic surface properties, carbon nanotubes are extremely difficult to disperse effectively in water. Existing studies disperse carbon nanotubes using a combination of ultrasonication, stirring, and dispersants, which not only increases costs but also lacks standardized specifications, making the dispersion process difficult to apply to different cement-based material systems. These factors significantly limit the application of carbon nanotubes in cement-based materials. Therefore, there is an urgent need to develop a novel material to inhibit self-shrinkage. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of superabsorbent polymers (SAP) in inhibiting the self-shrinkage of cement-based materials, and to provide a method for preparing a novel cement self-shrinkage inhibiting material (H-CNTSPP) that is insensitive to environmental conditions. This material is hydrophilic carbon nanotube sponge powder (represented by H-CNTSPP). The micron-sized H-CNTSPP does not require additional dispersion methods and inhibits the self-shrinkage of cement-based materials with a novel internal curing mechanism.

[0006] The present invention discloses a method for preparing a cement self-shrinkage inhibiting material, which is carried out according to the following steps:

[0007] 1) Carbon nanotube foam was prepared by chemical vapor deposition.

[0008] 2) Take the carbon nanotube foam prepared in step 1) and perform acidification treatment: Immerse the carbon nanotube foam in nitric acid solution and place it in a water bath at 60-70°C and stir and heat for 1-4 hours to prepare acidified carbon nanotube foam.

[0009] 3) The acidified carbon nanotube foam prepared in step 2) is neutralized and dried for later use;

[0010] 4) Take the raw materials prepared in step 3), crush them, collect the undersize material, and prepare the material that inhibits cement self-shrinkage.

[0011] Furthermore, the specific process for preparing carbon nanotube foam by chemical vapor deposition as described in step 1) is as follows:

[0012] Carbon nanotube foams were prepared by using ferrocene and 1,2-dichlorobenzene as precursors and carbon sources, at a reaction temperature of 850-900℃, with a mixed gas of argon and hydrogen as the growth environment and quartz sheets as the growth substrate, and by continuous reaction for 4-5 hours.

[0013] Further, in step 1), carbon nanotube foam with a thickness of 8-10 mm is prepared.

[0014] Furthermore, the specific process of acidification treatment of carbon nanotube foam described in step 2) is as follows:

[0015] Carbon nanotube foam was immersed in 500 mL of nitric acid solution and placed in a water bath at 60 °C. The mixture was stirred and heated continuously for 4 h with a magnetic stirrer to prepare acidified carbon nanotube foam. The concentration of the nitric acid solution was 8-10 mol / L and the speed of the magnetic stirrer was 300-400 rpm.

[0016] Furthermore, the O / C ratio of the acidified carbon nanotube foam is greater than 5%.

[0017] Furthermore, the specific process of neutralizing the carbon nanotube foam described in step 3) is as follows:

[0018] The acidified carbon nanotube foam was soaked in 1L of deionized water and the water was changed every 12 hours until the solution became neutral. Then the acidified carbon nanotube foam was taken out and dried at 60-80℃ for 5-7 days to obtain dry neutral acidified carbon nanotube foam.

[0019] Furthermore, the specific process of breaking down the acidified carbon nanotube foam described in step 4) is as follows:

[0020] The neutralized carbon nanotube foam was artificially crushed using an 80-mesh sieve, and the sieve-underfill material was collected to obtain the aforementioned cement self-shrinkage inhibiting material H-CNTSPP (Hydrophilicity Carbon nanotube spongepowder, denoted as H-CNTSPP).

[0021] Furthermore, the particle size of the material used to inhibit cement self-shrinkage is less than 1 mm.

[0022] The present invention relates to an application of a material for inhibiting cement self-shrinkage, which is used to prepare low self-shrinkage cement-based composite materials.

[0023] Furthermore, the method for preparing cement-based composite materials is as follows:

[0024] The water-reducing agent is dispersed in the cement mixing water in advance for later use; the material that inhibits cement self-shrinkage is mixed and stirred with cement powder for later use; then the aqueous solution containing the water-reducing agent is mixed with cement containing the new material that inhibits cement self-shrinkage to prepare a cement-based composite material; finally, it is poured into a mold to prepare an H-CNTSPP cement-based composite material with low self-shrinkage.

[0025] The present invention has the following beneficial effects:

[0026] The material of this invention uses carbon nanotubes as its basic component, which not only combines the advantages of carbon nanotubes, but also does not require additional dispersion methods. At the same time, it is not sensitive to the internal environment of cement-based materials, and solves the problem of self-shrinkage of cement-based materials with a new internal curing mechanism.

[0027] This invention utilizes chemical vapor deposition to prepare carbon nanotube foam with a stable structure. The three-dimensional structure formed by high-modulus carbon nanotubes as a framework makes the carbon nanotube foam resistant to damage and exhibits excellent deformability. The carbon nanotube foam has a porosity of up to 99%, and its stable and uniformly distributed pore structure gives it the advantage of being a water-retaining material. Then, the carbon nanotube foam is hydrophilicated through acidification treatment, and oxygen-containing hydrophilic functional groups are modified on the surface of the carbon nanotubes to give it water absorption and retention properties. Finally, after neutralization treatment, a novel cement self-shrinkage inhibitor, H-CNTSPP, is prepared. Unlike the water absorption principle of the traditional internal curing agent SAP, H-CNTSPP adsorbs the surrounding solution through capillary forces. Therefore, its water absorption rate is not affected by the type of ions in the solution environment, and its water absorption rate in cement pore solutions is 200% higher than that of SAP. Meanwhile, the micron-sized H-CNTSPP does not require additional dispersion. Compared to the complex dispersion methods of traditional carbon nanotube-modified cementitious materials (including the use of dispersants, prolonged ultrasonic dispersion, and mechanical stirring), this significantly reduces costs and performance changes caused by dispersion effects. Furthermore, unlike the mechanism by which carbon nanotubes improve self-shrinkage properties by influencing cement hydration, the H-CNTSPP of this invention exerts its internal curing effect through a novel water absorption-release mechanism, while simultaneously generating calcium hydroxide with an expansion effect, synergistically reducing the self-shrinkage of cementitious materials. Attached Figure Description

[0028] Figure 1 The images show the physical sample and particle size distribution of H-CNTSPP provided in this embodiment of the invention; the left image is the physical sample, and the right image is the particle size distribution.

[0029] Figure 2 The above are XPS and O / C results of H-CNTSPP provided in this embodiment of the invention.

[0030] Figure 3 This is a comparison chart of the water absorption rates of H-CNTSPP and SAP in deionized water and cement pore solution provided in the embodiments of the present invention.

[0031] Figure 4 This is a graph showing the effect of different dosages of H-CNTSPP and SAP on the autogenous shrinkage of cement-based materials in an embodiment of the present invention.

[0032] Figure 5 The above is an H-NMR result diagram of H-CNTSPP provided in the embodiments of the present invention;

[0033] Figure 6 The images show CT scan results of H-CNTSPP in cement slurry at different times, as provided in the embodiments of the present invention.

[0034] Figure 7 The image shows a scanning electron microscope (SEM) image of H-CNTSPP and the calcium hydroxide generated inside it, as provided in the embodiments of the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the spirit of the contents disclosed in the present invention will be described in detail below. After understanding the embodiments of the present invention, any person skilled in the art can make changes and modifications based on the technology taught in the present invention without departing from the spirit and scope of the present invention.

[0036] The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0037] Example 1

[0038] This embodiment describes a method for preparing a novel cement self-shrinkage inhibiting material (H-CNTSPP) that is insensitive to environmental conditions. The method comprises the following steps:

[0039] 1. Carbon nanotube foam with a thickness of 8-10 mm was prepared by chemical vapor deposition, using ferrocene and 1,2-dichlorobenzene as precursors and carbon source, at a reaction temperature of 860℃, a mixed gas of argon and hydrogen as the growth environment, and a quartz sheet as the growth base, for a continuous reaction of 4 hours.

[0040] 2. Take the carbon nanotube foam prepared in step one and acidify it by immersing it in 500 mL of 8 mol / L nitric acid solution and placing it in a water bath at 60°C for 4 hours with continuous stirring and heating to prepare acidified carbon nanotube foam.

[0041] 3. Take the acidified carbon nanotube foam prepared in step 2 and clean it. Soak the acidified carbon nanotube foam in 1L of deionized water and change the water every 12 hours until the solution is neutral to prepare hydrophilic carbon nanotube foam. Dry it at 50℃ for 72 hours for later use.

[0042] IV. Take the raw materials prepared in step III, manually crush them using an 80-mesh sieve, collect the sieve material, and prepare a new type of cement self-shrinkage inhibiting material (H-CNTSPP).

[0043] Furthermore, the H-CNTSPP prepared by the above steps is mixed with cement to prepare a cement-based material with low autogenous shrinkage.

[0044] 1. Mix 0.13% of the water-reducing agent relative to the cement mass with 0.35% of the mixing water relative to the cement mass in advance; mix 0.05% to 0.2% of the new cement self-shrinkage inhibiting material relative to the cement mass with the cement dry powder in advance and stir for 10 minutes.

[0045] 2. Mix the raw materials from step one and stir continuously at 700-800 rpm for 4 minutes. Fill the mixture into a 20mm×20mm×20mm mold to obtain H-CNTSPP modified cement-based material with low auto-shrinkage.

[0046] The photograph and particle size distribution of the novel cement self-shrinkage inhibiting material (H-CNTSPP) prepared in this example are shown below. Figure 1 As shown, its XPS and O / C results are as follows: Figure 2 As shown. The water absorption rate in this embodiment is as follows: Figure 3 As shown, by Figure 3 As can be seen, the water absorption rate of the novel cement self-shrinkage inhibiting material in this embodiment is 65-70 g / g, and the difference in water absorption rate in different solution environments is less than 1%, indicating that it has extremely high stability and is not affected by the solution environment. At the same time, the water absorption rate of H-CNTSPP in the pore solution in this embodiment is 200% of that of traditional SAP materials, representing its extremely high water absorption efficiency.

[0047] The autogenous shrinkage test of H-CNTSPP modified cement-based materials yielded the following results: Figure 4 As shown in the figure, the novel cement self-shrinkage inhibiting material in this embodiment can effectively inhibit the self-shrinkage of cement-based materials. Its reduction in self-shrinkage rate and its comparison with traditional SAP are shown in the table below. The results in this embodiment indicate that the novel cement self-shrinkage inhibiting material can reduce the cement self-shrinkage rate by 63% to 109%, which is 200% higher than traditional SAP. Furthermore, at the same efficiency, the dosage of the novel cement self-shrinkage inhibiting material can be reduced by four times. These results demonstrate that, at the same dosage, the self-shrinkage inhibiting efficiency of H-CNTSPP far exceeds that of traditional SAP materials.

[0048] benchmark cement 0.3 0.00 benchmark cement 0.35 24.47 Baseline cement + novel cement autogenous shrinkage inhibitor (0.05%) 0.35 63.1 Baseline cement + novel cement autogenous shrinkage inhibitor (0.1%) 0.35 84.8 Baseline cement + novel cement autogenous shrinkage inhibitor (0.2%) 0.35 109.97 Baseline cement + SAP (0.05%) 0.35 16.94 Baseline cement + SAP (0.1%) 0.35 23.01 Baseline cement + SAP (0.2%) 0.35 55.76

[0049] The mechanism by which H-CNTSPP inhibits cement autogenous shrinkage was further elucidated using low-field nuclear magnetic resonance (H-NMR) testing. The results are as follows: Figure 5 As shown. Figure 5 (a)-(c) are the T2 relaxation time maps for different hydration times. Figure 5 (d)-(f) show the H-NMR analysis results. The peak intensity in the H-NMR spectrum represents the moisture content at that relaxation time. Comparison of the T2 relaxation time spectrum reveals that the addition of H-CNTSPP significantly reduces the peak intensity while broadening the T2 relaxation time range, indicating that H-CNTSPP affects the moisture distribution in the cement-based material system. The pore size range of H-CNTSPP was determined by measuring the H-NMR spectrum of a single H-CNTSPP in deionized water, as shown in the results. Figure 5 As shown in (e). Further according to Figure 5(e) The range of H-NMR signals extracted from H-CNTSPP cement paste represents the water content of H-CNTSPP, and the results are as follows: Figure 5 As shown in (f), it can be clearly observed that H-CNTSPP maintains a constant water absorption in the early stages, increases rapidly near the final setting stage, and then decreases again after final setting. The decrease in water absorption after final setting demonstrates the release of water from H-CNTSPP. This released water will compensate for the loss of capillary water due to hydration, inhibiting the generation of capillary pressure and thus reducing the autogenous shrinkage of cementitious materials. Unlike the traditional internal curing mechanism of SAP, H-CNTSPP does not immediately become saturated after addition, but rather undergoes a rapid water absorption-release phenomenon during final setting. This phenomenon is caused by the water absorption mechanism of H-CNTSPP. H-CNTSPP absorbs water through capillary pores. During final setting, the cement paste hardens, and the internal pressure increases rapidly, thus promoting water absorption by H-CNTSPP. After final setting, the loss of capillary water leads to the appearance of a humidity gradient, resulting in the release of water from H-CNTSPP, thus fulfilling its internal curing function. This unique water absorption-release phenomenon can be further demonstrated by CT image results, as shown in the figure. Figure 6 As shown, the CT images represent the distribution of H-CNTSPP in the cement paste. The depth of color represents its density, with darker colors indicating higher water content in the H-CNTSPP. It can be clearly observed that the density of H-CNTSPP increases before final setting and then rapidly decreases afterward. This phenomenon represents the process of H-CNTSPP rapidly absorbing water before final setting and then releasing it. Simultaneously, as... Figure 7 As shown, calcium hydroxide with an expansion effect will be rapidly generated inside H-CNTSPP, further inhibiting the occurrence of self-shrinkage. The novel cement self-shrinkage inhibiting material (H-CNTSPP) prepared by this patent is not affected by the environment in terms of water absorption. It can effectively reduce the self-shrinkage of cement-based materials at a low dosage. Moreover, it exerts its internal curing function with a water absorption-release mechanism different from SAP and carbon nanotubes, thereby reducing the self-shrinkage of cement-based materials.

[0050] The novel cement autogenous shrinkage-inhibiting material and its modified cement-based material prepared by the above-described preparation method in the embodiments of the present invention can be applied to construction sites such as bridges and dams that require low autogenous shrinkage.

Claims

1. A method for preparing a material to inhibit cement self-shrinkage, characterized in that, Follow these steps: 1) Carbon nanotube foam was prepared by chemical vapor deposition. 2) Acidification treatment of the carbon nanotube foam prepared in step 1): Immerse the carbon nanotube foam in nitric acid solution and place it in a water bath at 60-70 ℃ for continuous stirring and heating for 1-4 h to prepare acidified carbon nanotube foam; the O / C ratio of the acidified carbon nanotube foam is greater than 5%; 3) Take the acidified carbon nanotube foam prepared in step 2) and neutralize it, then dry it for later use; 4) Take the raw materials prepared in step 3), crush them, collect the undersize material, and prepare the cement self-shrinkage inhibiting material; the particle size of the cement self-shrinkage inhibiting material is less than 1 mm.

2. The method for preparing a cement self-shrinkage inhibiting material according to claim 1, characterized in that, The specific process for preparing carbon nanotube foam using chemical vapor deposition as described in step 1) is as follows: Carbon nanotube foams were prepared by using ferrocene and 1,2-dichlorobenzene as precursors and carbon sources, at a reaction temperature of 850-900℃, with a mixed gas of argon and hydrogen as the growth environment and quartz sheets as the growth substrate, and by continuous reaction for 4-5 hours.

3. The method for preparing a cement self-shrinkage inhibiting material according to claim 1, characterized in that, In step 1), prepare carbon nanotube foam with a thickness of 8-10 mm.

4. The method for preparing a cement self-shrinkage inhibiting material according to claim 1, characterized in that, The specific process of acidification treatment of carbon nanotube foam described in step 2) is as follows: Carbon nanotube foam was immersed in 500 mL of nitric acid solution and placed in a water bath at 60 °C. The mixture was continuously stirred and heated for 4 h with a magnetic stirrer to prepare acidified carbon nanotube foam. The concentration of the nitric acid solution was 8-10 mol / L and the speed of the magnetic stirrer was 300-400 rpm.

5. The method for preparing a cement self-shrinkage inhibiting material according to claim 1, characterized in that, The specific process of neutralizing carbon nanotube foam as described in step 3) is as follows: The acidified carbon nanotube foam was soaked in 1L of deionized water and the water was changed every 12 hours until the solution was neutral. Then the acidified carbon nanotube foam was taken out and dried at 60-80℃ for 5-7 days to obtain dry neutral acidified carbon nanotube foam.

6. The method for preparing a material to inhibit cement self-shrinkage according to claim 1, characterized in that, The specific process of step 4): The neutralized carbon nanotube foam was artificially crushed using an 80-mesh sieve, and the undersize material was collected to obtain the material for inhibiting cement self-shrinkage.

7. The application of a cement self-shrinkage inhibiting material prepared by the preparation method described in claim 1, characterized in that, Used to prepare low-self-shrinkage cement-based composite materials.

8. The application according to claim 7, characterized in that, The method for preparing cement-based composite materials is as follows: The water-reducing agent is dispersed in the cement mixing water in advance for later use; the cement self-shrinkage inhibitor is mixed and stirred with the cement powder for later use; then the aqueous solution containing the water-reducing agent is mixed with the cement containing the cement self-shrinkage inhibitor; finally, it is poured into a mold to prepare a cement-based composite material with low self-shrinkage.

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