Cellulose nanocrystal enhanced alkali-activated cementing material and preparation method thereof

Abstract

The invention relates to the technical field of building materials, and relates to a cellulose nanocrystal reinforced alkali-activated cementing material and a preparation method thereof, the material is prepared from the following raw materials by weight: 0.05%-0.5% of cellulose nanocrystal, 0.05%-0.5% of sodium silicate, 0.05%-0.5% of sodium silicate, and the balance of water. 4%-8% of an alkali activator; 10%-60% of fly ash; 10%-60% of slag; 15%-45% of water; the sum of the weight percentages of the raw materials is 100%. The prepared cementing material has excellent compressive strength, bending strength and low shrinkage, is suitable for civil engineering fields of buildings, roads, bridges and the like, and provides reliable guarantee for long-term stability and safety of engineering structures.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and more particularly, to a cellulose nanocrystal reinforced alkali-activated cementitious material and a preparation method thereof. Background Art

[0002] For more than a century, ordinary Portland cement has been the backbone of the construction industry and is widely used due to its good durability, strength, and adaptability. It is estimated that its production process is accompanied by high energy consumption and a large amount of CO 2 emissions (accounting for 8%-10% of the global CO 2 emissions), which imposes a great burden on the environment. Therefore, it is necessary to find new sustainable building materials. The raw materials of alkali-activated cementitious materials are derived from industrial by-products such as fly ash and slag, which can provide mechanical strength comparable to ordinary Portland cement while having a lower carbon footprint and are viable alternatives to ordinary Portland cement. However, alkali-activated cementitious materials also face some challenges, such as low flexural strength and easy shrinkage, which limit their wide application in the construction field. Summary of the Invention

[0003] The purpose of the present invention is to provide a cellulose nanocrystal reinforced alkali-activated cementitious material and a preparation method thereof to improve the above problems. To achieve the above purpose, the technical solutions adopted by the present invention are as follows:

[0004] On the one hand, the present application provides a cellulose nanocrystal reinforced alkali-activated cementitious material, including: cellulose nanocrystals: 0.05%-0.5%; alkali activator: 4%-8%; fly ash: 10%-60%; slag: 10%-60%; water: 15%-45%; the sum of the weight percentages of the above raw materials is 100%.

[0005] Further, the weight ratio of the fly ash to the slag includes 3:7-7:3.

[0006] Further, the water-cement ratio ranges from 0.35 to 0.5.

[0007] Further, the particle size range of the fly ash is 0.3-224 μm.

[0008] Further, the particle size range of the slag is 0.3-158 μm.

[0009] Further, the alkali activator is anhydrous sodium metasilicate.

[0010] Further, the modulus of the anhydrous sodium metasilicate is 0.9-1.1.

[0011] Further, the crystallinity index of the cellulose nanocrystals is 70.80%.

[0012] In a second aspect, the present application provides a method for preparing a cellulose nanocrystal-reinforced alkali-activated cementitious material, the method comprising:

[0013] S1: Prepare a cellulose nanocrystal solution;

[0014] S2: Mix fly ash, slag, and an alkali activator in a stirrer for 3 minutes to obtain a mixed dry material;

[0015] S3: Slowly add the cellulose nanocrystal solution to the above-mentioned mixed dry material and stir for 5 minutes to obtain a cementitious material.

[0016] The beneficial effects of the present invention are as follows:

[0017] 1. By adding cellulose nanocrystals, the present invention can not only improve the mechanical properties of the alkali-activated cementitious material, but also solve the problem of large shrinkage.

[0018] 2. The present invention uses industrial waste such as fly ash and slag as the main raw materials, reducing the occupation and pollution of the environment by waste, providing a new way and method for the resource utilization of industrial waste, conforming to the concept of sustainable development. At the same time, the energy consumption is lower than that of traditional cementitious materials during the preparation process, and the carbon dioxide emissions are reduced.

[0019] Other features and advantages of the present invention will be described in the subsequent specification, and part of them will become obvious from the specification, or can be understood by implementing the embodiments of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the structures specifically pointed out in the written specification, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0021] Figure 1 is a flowchart of the method for preparing a cellulose nanocrystal-reinforced alkali-activated cementitious material described in the embodiments of the present invention.

[0022] Figure 2 is a graph showing the test results of the compressive strength of the cementitious material paste.

[0023] Figure 3 is a graph showing the test results of the flexural strength of the cementitious material paste.

[0024] Figure 4is the drying shrinkage rate of the cementitious material paste.

[0025] Figure 5 is the autogenous shrinkage test result of the cementitious material paste.

[0026] Figure 6 is the XRD pattern of the cementitious material paste.

[0027] Figure 7 is the Fourier transform infrared spectrum of the cementitious material paste.

[0028] Figure 8 is the SEM image of the cementitious material paste at 28 days of age.

[0029] Figure 9 is the schematic diagram of the nucleation of cellulose nanocrystals within 8A0.3C. Detailed implementation manners

[0030] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0031] Unless otherwise specified, the raw materials in the embodiments of this application are all purchased through commercial channels. Unless otherwise specified, the test methods are all conventional methods, and the instruments all adopt the configurations recommended by the manufacturers.

[0032] Ordinary Portland cement has always been the pillar of the construction industry and is widely used because of its good durability, strength, adaptability and other advantages. However, the high energy consumption and a large amount of CO 2 emissions (accounting for 8%-10% of the global CO 2 emissions) during its production process impose a great burden on the environment. Therefore, it is necessary to find new sustainable building materials. The raw materials of alkali-activated cementitious materials are derived from industrial by-products. Because they have a low carbon footprint and can also provide mechanical strength comparable to that of ordinary Portland cement, they are viable alternatives to ordinary Portland cement. However, alkali-activated cementitious materials also face some challenges, such as low flexural strength and easy shrinkage, etc. These defects limit their wide application in the construction field. Therefore, it is urgent to propose a cellulose nanocrystal-reinforced alkali-activated cementitious material, which can solve the problems of low flexural strength and high shrinkage faced by existing materials.

[0033] The above-mentioned cellulose nanocrystal-reinforced alkali-activated cementitious material is prepared from the following raw materials in weight percentages:

[0034] Cellulose nanocrystals: 0.05%-0.5%;

[0035] Alkali activator: 4%-8%;

[0036] Fly ash: 10%-60%;

[0037] Slag: 10%-60%;

[0038] Water: 15%-45%;

[0039] The sum of the weight percentages of the above raw materials is 100%.

[0040] In order to further enhance the mechanical strength and stability of the alkali-activated cementitious material, the components of the above formula are further selected as the following types:

[0041] Further, the weight ratio of the fly ash to the slag is in the range of 3:7 - 7:3.

[0042] Further, the range of the water-binder ratio is 0.35 - 0.5.

[0043] Further, the particle size range of the fly ash is 0.3 - 224 μm.

[0044] Further, the particle size range of the slag is 0.3 - 158 μm.

[0045] Further, the alkali activator is anhydrous sodium metasilicate.

[0046] Further, the modulus of the anhydrous sodium metasilicate is 0.9 - 1.1.

[0047] Further, the crystallinity index of the cellulose nanocrystals is 70.80%.

[0048] In the present application, the preparation method of the cellulose nanocrystal-reinforced alkali-activated cementitious material includes the following steps:

[0049] S1: Prepare a cellulose nanocrystal solution;

[0050] S2: Mix the fly ash, slag, and alkali activator in a stirrer for 3 minutes to obtain a mixed dry material;

[0051] S3: Slowly add the cellulose nanocrystal solution to the above mixed dry material and stir for 5 minutes to obtain a cementitious material.

[0052] In step S1, the preparation of the cellulose nanocrystal solution includes:

[0053] Pour the cellulose nanocrystals into water and stir with a glass rod until there are no visible cellulose nanocrystal aggregates in the water;

[0054] Use an ultrasonic disperser to perform ultrasonic treatment on the cellulose nanocrystal solution for 30 min to obtain a well-dispersed cellulose nanocrystal solution.

[0055] The above method only involves simple physical mixing, so it is easy to operate, does not require harsh reaction conditions, has a lower cost, and is more likely to be promoted. The present invention uses industrial wastes such as fly ash and slag as the main raw materials, reducing the occupation and pollution of the environment by the wastes, providing a new way and method for the resource utilization of industrial wastes, and conforming to the concept of sustainable development; at the same time, compared with traditional cementitious materials, the present invention can reduce energy consumption and carbon dioxide emissions during the preparation process, which has a positive significance for environmental protection. This cementitious material solves the problems of low flexural strength and high shrinkage faced by existing materials, can be widely applied in multiple fields, and its good performance and environmental protection characteristics make it have broad application prospects in various projects.

[0056] In the naming of the following examples, A refers to anhydrous sodium metasilicate, and C refers to cellulose nanocrystals; the meanings of the numbers are as follows: the dosage of anhydrous sodium metasilicate is 4% and 8% of the total weight of fly ash and ground granulated blast furnace slag, and the dosages of cellulose nanocrystals are 0.05%, 0.1%, 0.2%, and 0.3% of the total weight of fly ash and ground granulated blast furnace slag for preparation.

[0057] Example 1: Preparation of 1# (4A0C) alkali-activated cementitious material

[0058] It can be understood that the slag selected in the preparation method of the present invention is ground granulated blast furnace slag. The alkali-activated cementitious material in this example is prepared from the following raw materials by weight: 500 g of fly ash, 500 g of ground granulated blast furnace slag, 40 g of anhydrous sodium metasilicate. The weight of water is based on the total weight of fly ash, ground granulated blast furnace slag and anhydrous sodium metasilicate. When the water-cement ratio is maintained at 0.35, the water is 364 g. The preparation process is as follows: Weigh fly ash, ground granulated blast furnace slag, anhydrous sodium metasilicate and water according to weight. First, put fly ash, ground granulated blast furnace slag and anhydrous sodium metasilicate into a mixer and stir for 3 minutes to obtain a mixed dry material; add mixing water to the mixed dry material and stir for 5 minutes to obtain a uniform alkali-activated cementitious material.

[0059] Example 2: Preparation of 2# (4A0.05C) cellulose nanocrystal-reinforced alkali-activated cementitious material

[0060] The cellulose nanocrystal-reinforced alkali-activated cementitious material in this embodiment is prepared from raw materials with the following weights: 500 g of fly ash, 500 g of ground granulated blast furnace slag, 40 g of anhydrous sodium metasilicate, and 0.5 g of cellulose nanocrystals. The weight of water is based on the total weight of fly ash, ground granulated blast furnace slag, and anhydrous sodium metasilicate. When the water-binder ratio is maintained at 0.35, the water is 364 g. The preparation process is as follows: Weigh fly ash, ground granulated blast furnace slag, anhydrous sodium metasilicate, cellulose nanocrystals, and water according to weight; First, add the cellulose nanocrystal powder to the mixing water and stir until there are no visibly obvious cellulose nanocrystal aggregates, and then perform ultrasonic dispersion treatment on it, ultrasonically treating it in pulse mode for 30 minutes to obtain a uniformly dispersed cellulose nanocrystal solution; Put fly ash, ground granulated blast furnace slag, and anhydrous sodium metasilicate into a mixer and stir for 3 minutes to obtain a mixed dry material; Add the cellulose nanocrystal solution to the mixed dry material and stir for 5 minutes to obtain a uniform cellulose nanocrystal-reinforced alkali-activated cementitious material.

[0061] Example 3: Preparation of 3# (4A0.1C) cellulose nanocrystal-reinforced alkali-activated cementitious material

[0062] The difference from Example 2 is that the dosage of cellulose nanocrystals is 1 g, and the others are the same as in Example 2, which will not be elaborated here.

[0063] Example 4: Preparation of 4# (4A0.2C) cellulose nanocrystal-reinforced alkali-activated cementitious material

[0064] The difference from Example 2 is that the dosage of cellulose nanocrystals is 2 g, and the others are the same as in Example 2, which will not be elaborated here.

[0065] Example 5: Preparation of 5# (4A0.3C) cellulose nanocrystal-reinforced alkali-activated cementitious material

[0066] The difference from Example 2 is that the dosage of cellulose nanocrystals is 3 g, and the others are the same as in Example 2, which will not be elaborated here.

[0067] Example 6: Preparation of 6# (8A0C) alkali-activated cementitious material

[0068] The difference from Example 1 is that the dosage of anhydrous sodium metasilicate is 80 g, and the weight of water is based on the total weight of fly ash, ground granulated blast furnace slag, and anhydrous sodium metasilicate. When the water-binder ratio is maintained at 0.35, the water is 378 g, and the others are the same as in Example 1, which will not be elaborated here.

[0069] Example 7: Preparation of 7# (8A0.05C) cellulose nanocrystal-reinforced alkali-activated cementitious material

[0070] The cellulose nanocrystal reinforced alkali-activated cementitious material in this embodiment is prepared from the following raw materials by weight: 500 g of fly ash, 500 g of ground granulated blast furnace slag, 80 g of anhydrous sodium metasilicate, and 0.5 g of cellulose nanocrystals. The weight of water is based on the total weight of fly ash, ground granulated blast furnace slag, and anhydrous sodium metasilicate. When the water-binder ratio is maintained at 0.35, the water is 378 g. The preparation process is as follows: Weigh fly ash, ground granulated blast furnace slag, anhydrous sodium metasilicate, cellulose nanocrystals, and water according to weight; First, add the cellulose nanocrystal powder to the mixing water and stir until there are no obvious visible aggregates of cellulose nanocrystals, and then perform ultrasonic dispersion treatment on it, with ultrasonic treatment in pulse mode for 30 minutes to obtain a uniformly dispersed cellulose nanocrystal solution; Put fly ash, ground granulated blast furnace slag, and anhydrous sodium metasilicate into a mixer and stir for 3 minutes to obtain a mixed dry material; Add the cellulose nanocrystal solution to the mixed dry material and stir for 5 minutes to obtain a uniform cellulose nanocrystal reinforced alkali-activated cementitious material.

[0071] Example 8: Preparation of 8# (8A0.1C) cellulose nanocrystal reinforced alkali-activated cementitious material

[0072] The difference from Example 7 is that the dosage of cellulose nanocrystals is 1 g, and the others are the same as in Example 7, which will not be elaborated here.

[0073] Example 9: Preparation of 9# (8A0.2C) cellulose nanocrystal reinforced alkali-activated cementitious material

[0074] The difference from Example 7 is that the dosage of cellulose nanocrystals is 2 g, and the others are the same as in Example 7, which will not be elaborated here.

[0075] Example 10: Preparation of 10# (8A0.3C) cellulose nanocrystal reinforced alkali-activated cementitious material

[0076] The difference from Example 7 is that the dosage of cellulose nanocrystals is 3 g, and the others are the same as in Example 7, which will not be elaborated here.

[0077] In this application, the beneficial effects of the present invention are illustrated by testing the properties of the materials in Examples 1-10 of this application.

[0078] Compressive strength test: According to the ASTM C109 standard, use samples of 50×50×50 mm 3 to conduct compressive strength tests at 3 days, 7 days, and 28 days of age, as Figure 2As shown in the compressive strength test results of the cementitious material paste, the 28-day compressive strength of the cementitious material paste with 0.3% cellulose nanocrystals increased by 18.54% under 8% alkali activator and by 16.99% under 4% alkali activator. The overall compressive strength of the mixture with 8% alkali activator content is higher than that of the mixture with 4% alkali activator content.

[0079] Flexural strength test: According to ASTM C348 standard, samples with dimensions of 40×40×160 mm 3 were used for flexural strength tests at 3 days, 7 days and 28 days of age, as Figure 3 shown in the flexural strength test results of the cementitious material paste. The 28-day flexural strength of the cementitious material paste with 0.3% cellulose nanocrystals increased by 60.87% under 8% alkali activator and by 50.12% under 4% alkali activator. The overall flexural strength of the mixture with 8% alkali activator content is higher than that of the mixture with 4% alkali activator content.

[0080] Drying shrinkage test: According to ASTM C157 standard, samples with dimensions of 25×25×280 mm 3 were used for drying shrinkage tests at 1 day, 2 days, 3 days, 4 days, 14 days, 28 days, 56 days and 90 days of age, as Figure 4 shown in the drying shrinkage rate of the cementitious material paste. The drying shrinkage of the cementitious material paste with 0.3% cellulose nanocrystals decreased by 50.32% under 8% alkali activator and by 22.05% under 4% alkali activator.

[0081] Autogenous shrinkage test: According to ASTM C1698 standard, corrugated pipe samples with a diameter of 30 mm and a length of 450 mm were used, and autogenous shrinkage data were recorded every 15 minutes within 7 days, as Figure 5 shown in the autogenous shrinkage test results of the cementitious material paste. The autogenous shrinkage of the cementitious material paste with 0.3% cellulose nanocrystals decreased by 26.42% under 8% alkali activator and by 11.74% under 4% alkali activator.

[0082] Microstructural analysis: X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to analyze the microstructure of the samples at 28 days of age, and the formation of hydration products and the changes in microtopography were observed, as Figure 6 shown in the XRD pattern of the cementitious material paste, Figure 6XRD patterns of cementitious material pastes with different contents of alkali activators and different contents of cellulose nanocrystals. By comparing the curves of 4A0C (4% alkali activator, 0% cellulose nanocrystals) and 8A0C (8% alkali activator, 0% cellulose nanocrystals), it can be found that the intensity of some diffraction peaks changes with the increase in the content of alkali activator, indicating that the content of alkali activator affects the formation and crystallization degree of hydration products. After adding cellulose nanocrystals (such as samples 4A0.1C, 4A0.3C, 8A0.1C, 8A0.3, etc.), the intensity and position of some diffraction peaks also change compared with the control group, which also reflects the influence of cellulose nanocrystals on the hydration products of cementitious material pastes such as calcium aluminosilicate hydrate (C-A-S-H), calcium silicate hydrate (C-S-H), etc. By comparing the XRD patterns, it is innovatively found that cellulose nanocrystals have a regulatory effect on the composition and structure of hydration products.

[0083] As Figure 7 shown in the Fourier transform infrared spectrum of the cementitious material paste, it can be seen that the broad band at about 3441 - 3474 cm -1 is attributed to the stretching vibration of the H-O-H bond and hydroxyl groups; the peak observed at 1631 - 1649 cm -1 is related to the bending vibration of the -OH group, which is a typical characteristic of the hydration reaction products. The peak intensity observed in the range of 2977 - 2989 cm -1 indicates the presence of the C-H bond, which is a characteristic of cellulose. In the FTIR analysis of the cementitious material paste, the peak observed in the range of 1419 - 1527 cm -1 indicates that carbonation occurs during the hardening process. The stretching vibrations of the Si-O-Si and Si-O-Al bonds are observed in the range of 945 - 981 cm -1 . In the amorphous structures of N-A-S-H gels and C-A-S-H gels, the antisymmetric stretching vibrations of these bonds occur between 1100 cm -1 and 950 cm -1 . The regulatory effect of cellulose nanocrystals on the chemical structure of the cementitious material paste is confirmed by the FTIR spectrum. It is found that cellulose nanocrystals can participate in the chemical reactions of the system, change the vibration characteristics and distribution of relevant functional groups, and affect the chemical composition and structure of the hydration products. This discovery provides a key basis for understanding the internal chemical mechanism of cellulose nanocrystals enhancing the performance of cementitious material pastes, opens up new research perspectives and directions for the development of high-performance alkali-activated cementitious materials, and helps to optimize the material performance by reasonably regulating the content of cellulose nanocrystals.

[0084] As Figure 8 shown, Figure 8SEM images showing the 28-day-old cementitious material pastes. After adding 0.3% cellulose nanocrystals, the macropore and microcrack sizes in 4A0.3C and 8A0.3C are reduced compared to their respective control groups, and the structure is relatively denser. These phenomena indicate that cellulose nanocrystals have a positive effect on improving the microstructure of the paste.

[0085] The specific observation characteristics are shown in Table 1:

[0086]

[0087] As Figure 9 shown, Figure 9 It represents the nucleation effect of cellulose nanocrystals in 8A0.3C. The special structure formed by cellulose nanocrystals and their bridging effect indicate that cellulose nanocrystals are not simply dispersed in the paste but actively participate in constructing the microstructure. Their bridging effect can connect different particles to enhance the interaction between particles; the deposition of alkali-activated reaction products on the surface of cellulose nanocrystals shows that cellulose nanocrystals provide attachment sites for reaction products, promoting the progress of the hydration reaction and the growth of products. The specific observation characteristics are shown in Table 2:

[0088]

[0089] Figures 8 to 9 Together, they explain from a microscopic perspective the internal reasons for cellulose nanocrystals to improve the strength and reduce the shrinkage of cementitious material pastes, providing a new way to optimize the microstructure. It provides an important basis for developing high-performance and low-shrinkage cellulose nanocrystal-reinforced alkali-activated cementitious materials, and helps to promote the development of building materials towards a more high-quality and durable direction. The above is only the preferred embodiment of the present invention and is not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0090] As mentioned above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope

[0091] disclosed by the present invention can easily think of changes or replacements, which should all be covered within the protection scope of the present invention.

[0092] Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A cellulose nanocrystal-enhanced alkali-activated gelling material, characterized in that: It is prepared from the following raw materials in weight percentage: Cellulose nanocrystals: 0.05%-0.5%; Alkali activator: 4%-8%; Fly ash: 10%-60%; Slag: 10%-60%; Water: 15%-45%; The sum of the weight percentages of the above raw materials is 100%.

2. The cellulose nanocrystal-enhanced alkali-activated gelling material according to claim 1, characterized in that: The weight ratio of the fly ash to the slag is 3:7-7:

3.

3. The cellulose nanocrystal-enhanced alkali-activated gelling material according to claim 1, characterized in that: The water-to-cement ratio ranges from 0.35 to 0.

5.

4. The cellulose nanocrystal-enhanced alkali-activated gelling material according to claim 1, characterized in that: The particle size of the fly ash ranges from 0.3 to 224 μm.

5. The cellulose nanocrystal-enhanced alkali-activated gelling material according to claim 1, characterized in that: The particle size of the slag is in the range of 0.3-158 μm.

6. The cellulose nanocrystal-enhanced alkali-activated gelling material according to claim 1, characterized in that: The alkaline activator is anhydrous sodium metasilicate.

7. The cellulose nanocrystal-enhanced alkali-activated gelling material according to claim 6, characterized in that: The modulus of the anhydrous sodium metasilicate is 0.9-1.

1.

8. The cellulose nanocrystal-enhanced alkali-activated gelling material according to claim 1, characterized in that: The crystallinity index of the cellulose nanocrystals is 70.80%.

9. A method for preparing a cellulose nanocrystal-enhanced alkali-activated gelling material, characterized in that: Here are the steps: S1: preparation of cellulose nanocrystal solution; S2: Mix fly ash, slag and alkali activator in a mixer for 3 minutes to obtain a mixed dry material; S3: slowly adding the cellulose nanocrystal solution into the mixed dry materials and stirring for 5 minutes to obtain the cellulose nanocrystal enhanced alkali-activated gelling material.

10. The method for preparing the cellulose nanocrystal-enhanced alkali-activated gelling material according to claim 9, characterized in that: The method for preparing the cellulose nanocrystal solution comprises: Pour cellulose nanocrystals into water and stir with a glass rod until there are no visible cellulose nanocrystal aggregates in the water; The cellulose nanocrystal solution was ultrasonically treated for 30 min using an ultrasonic disperser to obtain a well-dispersed cellulose nanocrystal solution.

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