Preparation method and application of cement shrinkage-enhancement synergistic regulation material based on bacterial cellulose hydrogel

Abstract

The invention discloses a preparation method and application of a cement shrinkage-enhancement synergistic regulation material based on bacterial cellulose hydrogel, and relates to the technical field of low-water-binder-ratio cement-based composite materials. The invention aims to solve the contradiction between self-constriction inhibition and degradation of mechanical properties of the traditional internal curing material. The method comprises preparation of a novel cement shrinkage reducing material (BCH) and application of the novel cement shrinkage reducing material in cement, and bacterial cellulose synthesized by fermentation of acetobacter xylinum is purified and crushed to prepare bacterial cellulose hydrogel (BCH). And finally, mixing the BCH with cement with a low water-binder ratio to realize reduction-enhancement synergistic regulation and control of the cement-based material. According to the novel reduction material, the BCH self-assembly structure and the multi-scale pore characteristics of the BCH self-assembly structure are utilized, additional preparation means are not needed, meanwhile, the novel reduction material is not sensitive to the internal environment of the cement-based material, and the synergistic effect of internal maintenance and performance regulation and control is achieved. The method 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 shrinkage-reduction and reinforcement synergistic regulation material (bacterial cellulose hydrogel, BCH) and its application in cement-based materials modified based on BCH. Background Technology

[0002] Modern building materials are trending towards high strength and high toughness, and a low water-cement ratio is considered a key factor in refining the pore structure and improving the mechanical properties of cement-based materials. However, as the water-cement ratio decreases, the free water content in the matrix decreases during cement hydration, leading to a rapid drop in internal relative humidity. This increases capillary pressure and promotes the rapid development of autogenous shrinkage in cement-based materials. Simultaneously, the mechanical properties of cement-based materials are relatively low in the early stages of hydration. Under external or internal constraints, the shrinkage stress generated by autogenous shrinkage increases the risk of cracking, thereby accelerating the erosion and propagation of harmful external ions and reducing the service life of cement-based materials. Therefore, suppressing the development of autogenous shrinkage in cement-based materials is crucial for improving their durability.

[0003] A common method to reduce the autogenous shrinkage of cement is to add internal curing materials. Commonly used internal curing materials are super-adsorption polymers (SAPs). Through their three-dimensional network and polymer chain structure rich in hydrophilic groups, SAPs absorb water and swell in the early stages of cement mixing, and release the pre-absorbed water during the capillary drying stage, reducing autogenous 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 will decrease by one to two orders of magnitude. SAP water absorption and release are driven by the osmotic pressure of the solution ions and the humidity gradient, 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+ The release of ions (often referred to as "ions") will significantly reduce the water absorption capacity of SAP, and may even lead to its failure. Furthermore, after releasing water into the cement matrix, SAP leaves noticeable pores, increasing the matrix porosity and consequently reducing the mechanical properties of cement-based materials. Therefore, there is an urgent need to develop a new type of internal curing material that can achieve high internal curing efficiency while maintaining or even improving the mechanical properties of cement-based materials, thus realizing synergistic regulation of shrinkage reduction and strengthening in cement-based materials.

[0004] Current research indicates that the introduction of bacterial cellulose fibers can improve the mechanical properties of cement-based materials by promoting the cement hydration process, thereby inhibiting the development of autogenous shrinkage to some extent. However, existing studies often use bacterial cellulose prepared into granular or aerogel materials through complex processes such as freeze-drying. This preparation process is energy-intensive and costly, significantly limiting its engineering application potential. Furthermore, related research mainly focuses on the hydrophilic properties of bacterial cellulose components and their impact on cement autogenous shrinkage and mechanical properties, generally attributing performance improvements to the promoting effect of nanofiber materials on cement hydration, without considering the synergistic effect of bacterial cellulose self-assembly structure and its multi-scale porosity characteristics on internal curing and performance regulation. Therefore, there is an urgent need to redesign bacterial cellulose and fully utilize its structural characteristics to develop a novel shrinkage-reduction and reinforcement synergistic regulation material to achieve synergistic optimization of autogenous shrinkage inhibition and mechanical property improvement in low water-cement ratio cement-based materials. Summary of the Invention

[0005] The purpose of this invention is to address the contradictory problem that traditional internal curing materials reduce the autogenous shrinkage of cement-based materials but also degrade mechanical properties. Based on the unique structure of bacterial cellulose, a method for designing and preparing bacterial cellulose hydrogels (BCH) is proposed, providing a novel material that achieves synergistic regulation of shrinkage reduction and enhancement in cement-based materials. BCH does not require additional freeze-drying and dispersion treatments, fully utilizing its inherent moisture content and porous network structure to achieve both suppression of autogenous shrinkage and improvement of mechanical properties in low water-cement ratio cement-based materials through a novel shrinkage reduction-enhancing mechanism.

[0006] The present invention discloses a method for preparing a cement shrinkage-reduction and reinforcement synergistic regulating material based on bacterial cellulose hydrogel, which is carried out according to the following steps:

[0007] 1) Preparation of bacterial cellulose via bio-fermentation;

[0008] 2) Purify the bacterial cellulose prepared in step 1): Soak the bacterial cellulose in sodium hydroxide solution and keep it at room temperature for 12-24 h to prepare purified bacterial cellulose;

[0009] 3) The bacterial cellulose prepared in step 2) is neutralized and then soaked in deionized water for storage.

[0010] 4) Take the raw materials prepared in step 3) and subject them to high-speed shearing and crushing to prepare the material for inhibiting cement self-shrinkage - bacterial cellulose hydrogel.

[0011] Furthermore, the specific process for preparing bacterial cellulose by bio-fermentation as described in step 1) is as follows:

[0012] The activated Acetobacter xylinum was inoculated onto a solid agar plate and cultured in a 25°C incubator to obtain a stable strain.

[0013] Subsequently, the bacterial strain was transferred to a bioreactor for fermentation. During fermentation, liquid nutrient medium was evenly sprayed onto the upper part of the reactor. The liquid medium consisted of a buffer solution composed of 30-70 g / L glucose, 3-7 g / L yeast extract, 1-3 g / L citric acid, 2-6 g / L Na2HPO4, and 1-3 g / L KH2PO4. After 5-7 days of fermentation, a bacterial cellulose membrane formed on the surface of the solid substrate, which was then peeled off to obtain bacterial cellulose.

[0014] Further, in step 1), an 8-10 mm thick bacterial cellulose layer is prepared.

[0015] Furthermore, the specific process for purifying bacterial cellulose described in step 2) is as follows:

[0016] Bacterial cellulose was cut and then soaked in NaOH solution for 12 h at room temperature to prepare purified bacterial cellulose; wherein the concentration of NaOH solution was 0.1-0.5 mol / L.

[0017] Furthermore, the specific process of neutralization treatment to purify bacterial cellulose described in step 3) is as follows:

[0018] The purified bacterial cellulose was soaked in deionized water, and the water was changed every 8-12 hours until the solution became neutral. Then all the purified bacterial cellulose was soaked in deionized water and stored at 10°C for later use.

[0019] Furthermore, the specific process of the bacterial cellulose hydrogel described in step 4) is as follows:

[0020] The purified bacterial cellulose after neutralization treatment was placed in a high-speed mixer and crusher, and an equal mass of deionized water was added. After high-speed shearing and crushing, the cement self-shrinkage inhibitory material BCH was obtained.

[0021] Furthermore, the average particle size of the material used to inhibit cement self-shrinkage is 40~60 μm.

[0022] This invention relates to an application of a cement shrinkage-reduction and reinforcement synergistic regulation material based on bacterial cellulose hydrogel, 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 bacterial cellulose hydrogel was accurately weighed for later use; the high-efficiency polycarboxylate superplasticizer was dispersed in the mixing water for later use; the cement, the mixing water containing the superplasticizer and the bacterial cellulose hydrogel were mixed to prepare a cement-based composite material; finally, the cement slurry was poured into a mold to prepare a BCH cement-based composite material with low self-shrinkage.

[0025] Furthermore, the bacterial cellulose hydrogel accounts for 0.01%-0.05% of the mass of the cementitious material in the BCH cement-based composite material, the polycarboxylate superplasticizer accounts for 0.06-0.10% of the mass of the BCH cement-based composite material, and the total water-cement ratio is 0.3-0.354.

[0026] The present invention has the following beneficial effects:

[0027] The material of this invention uses bacterial cellulose nanofibers as its basic building blocks. It innovatively utilizes the structural advantages of bacterial cellulose to achieve water storage while remaining insensitive to the internal environment of cement. Simultaneously, it leverages the hydrophilic fiber skeleton to reinforce the cement matrix. Therefore, this material, utilizing its inherent advantages and without requiring additional dispersion methods, achieves synergistic regulation of shrinkage reduction and reinforcement in low water-cement ratio cementitious materials.

[0028] This invention utilizes a bio-fermentation method to prepare a bacterial cellulose hydrogel with a stable internal structure. The three-dimensional network structure formed by the interwoven high-modulus bacterial cellulose fibers makes it resistant to damage, and the strong hydrophilicity of individual fibers endows it with high water storage capacity. Purification removes proteins, citric acid, and residual nutrient solution from the bacterial cellulose to avoid their impact on cement hydration. Finally, the material is neutralized to obtain a novel cement self-shrinkage inhibitor, BCH. Compared to the osmotic pressure water absorption of traditional SAP, BCH absorbs water through capillary action, and its internal water molecules are fixed by hydrogen bonds, making its water absorption rate unaffected by the ionic strength of the liquid phase. Furthermore, its water absorption rate in cement pore solutions is 450% higher than that of SAP. Therefore, BCH has higher internal curing efficiency and can effectively inhibit the development of self-shrinkage in cement-based materials. Simultaneously, BCH's hydrophilic three-dimensional network structure and high structural stability promote the migration of liquid phase ions into its interior, further promoting the formation of hydration products within it. Compared to the pores formed after the release of water from SAP (superabsorbent polymer), bacterial cellulose hydrogel promotes the filling of these pores by hydration products, thereby effectively maintaining the development of mechanical properties. Therefore, the BCH 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 mitigating the self-shrinkage of low-water-cement ratio cementitious materials. Furthermore, the bacterial cellulose hydrogel, composed of hydrophilic nanofibers, exhibits good affinity with the cement matrix. Its internal interwoven three-dimensional network structure provides nucleation and growth space for cement hydration products, promoting their filling and thus improving the mechanical properties of the cement matrix. Ultimately, this material, with its inherent structural advantages, not only eliminates the need for complex drying processes but also achieves synergistic regulation of shrinkage reduction and reinforcement in low-water-cement ratio cementitious materials. Attached Figure Description

[0029] Figure 1 The images shown are physical images and particle size distribution diagrams of BCH provided in this embodiment of the invention; the left image is the physical image, and the right image is the particle size distribution diagram.

[0030] Figure 2 The above are schematic diagrams of BCH growth, FTIR, TGA, and BET results provided in the embodiments of the present invention.

[0031] Figure 3 This is a graph showing the water release rate of BCH in different humidity environments, as provided in this embodiment of the invention.

[0032] Figure 4 This is a diagram showing the effect of different dosages of BCH and SAP on the autogenous shrinkage of cementitious materials in an embodiment of the present invention.

[0033] Figure 5This is a graph showing the internal relative humidity results of cement-based materials with different BCH content provided in the embodiments of the present invention;

[0034] Figure 6 The images shown are SEM (Scanning Electron Microscopy) results of BCH in cement paste at different times provided in this embodiment of the invention.

[0035] Figure 7 The image shows a fluorescence microscope image of the BCH fluorescent labeling tracer used in this embodiment of the invention to study the release of water within the tissue. Detailed Implementation

[0036] 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.

[0037] 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.

[0038] Example 1

[0039] This embodiment discloses a method for preparing a novel cement self-shrinkage inhibiting material (BCH), which is carried out according to the following steps:

[0040] I. Activated *Acetobacter xylinum* was inoculated onto solid agar plates using a bio-fermentation method and cultured in a 25°C incubator to obtain a stable bacterial strain. The strain was then transferred to a bioreactor for fermentation. During fermentation, liquid nutrient medium was evenly sprayed onto the top of the reactor. The liquid medium consisted of glucose (50 g / L), yeast extract (5 g / L), citric acid (2 g / L), and a buffer solution composed of Na₂HPO₄ (4 g / L) and KH₂PO₄ (2 g / L). After 7 days of fermentation, a bacterial cellulose membrane formed on the surface of the solid substrate, which was then peeled off to obtain bacterial cellulose.

[0041] 2. The bacterial cellulose prepared in step one is purified by cutting it into 20cm×20cm pieces and soaking it in 1000 mL of 0.5 mol / L NaOH solution at room temperature for 12 h to prepare purified bacterial cellulose.

[0042] 3. Neutralize the purified bacterial cellulose prepared in step 2 by immersing it in 1L of deionized water and changing the water every 10 hours until the solution is neutral.

[0043] IV. Take the purified bacterial cellulose prepared in step 3, add the same mass of deionized water, and crush it for 5 minutes using a high-speed mixer to prepare a novel material for inhibiting cement self-shrinkage (BCH).

[0044] Furthermore, the BCH prepared by the above steps is mixed with cement to prepare a cement-based composite material with low self-shrinkage.

[0045] 1. Accurately weigh 0.01%-0.05% of BCH relative to the cement mass, and pre-mix 0.08% of polycarboxylate superplasticizer relative to the cement mass with 0.3-0.354% of mixing water relative to the cement mass to ensure that the total water-cement ratio is fixed at 0.354.

[0046] 2. Mix the raw materials from step one, stir continuously at 500-700 rpm for 5 minutes, and pour them into a 40 mm × 40 mm × 40 mm mold to prepare a BCH-modified cement-based composite material with low autogenous shrinkage.

[0047] This example demonstrates the preparation of bacterial cellulose hydrogels and their particle size distribution as follows: Figure 1 As shown, its internal morphology, FTIR, BET, and TGA results are as follows: Figure 2 As shown. In this embodiment, the water absorption rate of BCH in the cement pore solution is 118 g / g, and its water release capacity under different humidity environments is as follows. Figure 3 As shown. By Figure 3 As can be seen, BCH in this embodiment can stably release water in different humidity environments, proving that it has internal curing capabilities. Meanwhile, the water absorption rate of BCH in cement pore solution in this embodiment is 450% of that of traditional SAP materials, representing its extremely high water absorption efficiency.

[0048] The autogenous shrinkage test results of the BCH-modified cementitious material are as follows: Figure 4 As shown in the figure, the BCH material in this embodiment can effectively inhibit the autogenous shrinkage of cement-based materials. The reduction in autogenous shrinkage rate and its comparison with traditional SAP are shown in the table below. The results in this embodiment indicate that BCH can reduce the autogenous shrinkage rate of cement by 39%~82%, which is 30% higher than that of traditional SAP. Furthermore, at the same efficiency, the dosage of the new material for inhibiting cement autogenous shrinkage can be reduced by 20 times. These results demonstrate that the autogenous shrinkage inhibition efficiency of BCH far exceeds that of traditional SAP materials.

[0049]

[0050] The mechanism by which BCH inhibits cement autogenous shrinkage was further explored through internal relative humidity testing, and the results are as follows: Figure 5As shown in the figure. Internal humidity results indicate that the addition of BCH effectively suppresses the humidity reduction caused by moisture consumption. After incorporating 0.01% BCH, the internal relative humidity (IRH) of the system initially stabilized at 93.9%, subsequently decreasing to 89.2% at 7 days, but still significantly higher than that of the OPC-0.354 sample. This phenomenon is mainly attributed to the internal curing effect of BCH; the continuous release of its internally stored liquid effectively compensates for the humidity reduction caused by the self-drying process, thereby slowing down the decay of internal relative humidity and significantly inhibiting the development of self-shrinkage. When the BCH content increased from 0.02% to 0.05%, the IRH showed a gradual decreasing trend, mainly related to the decrease in the effective water-cement ratio from 0.30 to 0.23. Nevertheless, thanks to the internal curing effect of BCH, its slowly released stored water to some extent compensates for the reduction in internal moisture, allowing the IRH level at 7 days to remain within a range comparable to that of OPC-0.354. The above results further demonstrate that the self-shrinkage inhibition efficiency is significantly dependent on the BCH doping level. With increasing BCH doping, the material's internal curing ability is enhanced; however, simultaneously, a decrease in the effective water-cement ratio weakens its mitigation effect on self-shrinkage, leading to a decrease in the overall shrinkage inhibition efficiency. This unique water absorption-release phenomenon can be further demonstrated using fluorescent probe labeling, as shown in the results... Figure 6 As shown, the green fluorescent markers represent moisture in the BCH. As hydration progresses, the green fluorescent aggregation areas clearly diffuse into the cement matrix, demonstrating the internal curing process. Moisture is released from the BCH, compensating for the decrease in internal humidity and reducing capillary pressure, thereby inhibiting the development of cement autogenous shrinkage. The novel cement autogenous shrinkage inhibitor (BCH) prepared in this patent is unaffected by the environment in terms of water absorption. It can effectively reduce the autogenous shrinkage of cement-based materials at extremely low dosages, and it exerts its internal curing function through a water absorption-release mechanism different from SAP, thus reducing the autogenous shrinkage of cement-based materials.

[0051] Meanwhile, BCH also showed a significant improvement in the mechanical properties of low water-cement ratio cementitious materials. A comparison of 28-day strength clearly showed that the addition of traditional SAP (Small Acid-Based Polymer) curing materials significantly reduced mechanical properties. This phenomenon is attributed to the increased porosity of the cement matrix due to the pores left after SAP water release, thus reducing the mechanical properties of cementitious materials. This phenomenon is also the main limitation restricting the practical application of SAP in cementitious materials. However, the addition of BCH not only effectively reduced autogenous shrinkage but also improved mechanical properties. Compared to the control group, all BCH dosages showed a significant increase in strength. This phenomenon is mainly attributed to the excellent hydrophilicity of BCH, which promotes ion diffusion into its internal structure in the early stages of hydration. Simultaneously, the three-dimensional network structure of BCH provides nucleation space for the nucleation and growth of hydration products, promoting the formation of hydration products, thereby densifying the structure and ultimately improving mechanical properties. Therefore, BCH, relying on its own structural characteristics, achieves synergistic regulation of shrinkage reduction and strengthening in low water-cement ratio cementitious materials.

[0052]

[0053] The novel cement shrinkage-reduction and reinforcement synergistic control material and its modified low water-cement ratio cement-based material prepared by the above 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 and high mechanical properties.

Claims

1. A method for preparing a cement shrinkage-reduction and reinforcement synergistic regulation material based on bacterial cellulose hydrogel, characterized in that, The method is performed according to the following steps: 1) Preparation of bacterial cellulose via bio-fermentation; 2) Purify the bacterial cellulose prepared in step 1): Soak the bacterial cellulose in sodium hydroxide solution and keep it at room temperature for 12-24 h to prepare purified bacterial cellulose; 3) The bacterial cellulose prepared in step 2) is neutralized and then soaked in deionized water for storage. 4) Take the raw materials prepared in step 3) and subject them to high-speed shearing and crushing to prepare the bacterial cellulose hydrogel, which is the material for inhibiting cement self-shrinkage.

2. The preparation method of a cement shrinkage reduction-reinforcement synergistic regulation material based on bacterial cellulose hydrogel according to claim 1, characterized in that, The specific process for preparing bacterial cellulose by bio-fermentation as described in step 1) is as follows: The activated Acetobacter xylinum was inoculated onto a solid agar plate and placed in a constant temperature incubator for cultivation to obtain a strain with stable growth status. Subsequently, the bacterial strain was transferred to a bioreactor for fermentation. During fermentation, liquid nutrient medium was evenly sprayed onto the upper part of the reactor. The liquid medium consisted of a buffer solution composed of 30-70 g / L glucose, 3-7 g / L yeast extract, 1-3 g / L citric acid, 2-6 g / L Na2HPO4, and 1-3 g / L KH2PO4. After 5-7 days of fermentation, a bacterial cellulose membrane formed on the surface of the solid substrate, which was then peeled off to obtain bacterial cellulose.

3. The preparation method of a cement shrinkage reduction-reinforcement synergistic regulation material based on bacterial cellulose hydrogel according to claim 1, characterized in that, In step 1), prepare 8-10 mm thick bacterial cellulose.

4. The preparation method of a cement shrinkage reduction-reinforcement synergistic regulation material based on bacterial cellulose hydrogel according to claim 1, characterized in that, The specific process for purifying bacterial cellulose as described in step 2) is as follows: Bacterial cellulose was cut and then soaked in NaOH solution for 12 h at room temperature to prepare purified bacterial cellulose; wherein the concentration of NaOH solution was 0.1-0.5 mol / L.

5. The preparation method of a cement shrinkage reduction-reinforcement synergistic regulation material based on bacterial cellulose hydrogel according to claim 1, characterized in that, The specific process of neutralization treatment to purify bacterial cellulose described in step 3) is as follows: The purified bacterial cellulose was soaked in deionized water, and the water was changed every 8-12 hours until the solution became neutral. Then all the purified bacterial cellulose was soaked in deionized water and stored at 10°C for later use.

6. The preparation method of a cement shrinkage reduction-reinforcement synergistic regulation material based on bacterial cellulose hydrogel according to claim 1, characterized in that, The specific process of bacterial cellulose hydrogel formation described in step 4) is as follows: The purified bacterial cellulose after neutralization treatment was placed in a high-speed mixer and crusher, and an equal mass of deionized water was added. After high-speed shearing and crushing, the cement self-shrinkage inhibitory material BCH was obtained.

7. A method for preparing a cement shrinkage-reduction and reinforcement synergistic regulation material based on bacterial cellulose hydrogel according to claim 1 or 6, characterized in that, The average particle size of the material used to inhibit cement self-shrinkage is 40~60 μm.

8. The application of the cement shrinkage reduction-reinforcement synergistic regulation material based on bacterial cellulose hydrogel prepared as described in claim 1, characterized in that, It is used to prepare low-self-shrinkage cement-based composite materials.

9. The application according to claim 8, characterized in that, The method for preparing cement-based composite materials is as follows: The bacterial cellulose hydrogel was accurately weighed for later use; the polycarboxylate superplasticizer was dispersed in the mixing water for later use; the cement, the mixing water containing the superplasticizer, and the bacterial cellulose hydrogel were mixed to prepare the cement-based composite material; finally, the cement slurry was poured into a mold to prepare the BCH cement-based composite material.

10. The application according to claim 9, characterized in that, The bacterial cellulose hydrogel accounts for 0.01%-0.05% of the mass of the cementitious material in the BCH cement-based composite material, the polycarboxylate superplasticizer accounts for 0.06-0.10% of the mass of the BCH cement-based composite material, and the total water-cement ratio is 0.3-0.354.

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