Method for preparing gel material by compounding phosphoric acid-based geopolymer with plant fiber

Abstract

The invention relates to a method for preparing a gel material from phosphoric acid-based geopolymer composite plant fiber, which comprises the following steps: (1) reacting phosphoric acid serving as an acid activator with metakaolin, and adding phosphoric acid, water and metakaolin into a mixing stirrer to react for 30 minutes; (2) adding the Chinese fir fibers into the geopolymer gel, uniformly stirring for a certain time, putting the mixed slurry into a rectangular mold of 220 * 50 * 20mm, putting the rectangular mold on a hot press for compression molding, and setting the temperature of the hot press to be 60 DEG C and the pressure of the hot press to be 45MPa; and (3) putting the composite material obtained by pressing and the mold into a drying oven at 60 DEG C for curing, demolding after 1 day, putting the demolded sample into a sample bag for sealing, continuously curing in the drying oven at 60 DEG C for 3 days, removing the sample bag, then curing for 3 days, and then testing the performance of the sample. When the molar ratio of H2O to Al2O3 is 10, the molar ratio of H3PO4 to Al2O3 is 2.0 and the fiber content is 10%, the static bending intensity of the prepared geopolymer composite material reaches the optimal value of 13.75 MPa, and the internal bonding strength also reaches the optimal value of 2.17 MPa. The static bending intensity of the sample after freezing and thawing cycle can still reach 10.87 MPa to the maximum, and the frozen and thawed sample does not have edge missing, corner missing and cracking.

Description

Technical Field

[0001] The present invention relates to the field of material preparation, and particularly relates to a method for preparing a high-performance geopolymer. Technical Background

[0002] As a new type of cementitious material, phosphate-based geopolymer has only gradually developed in the past ten years or so. Phosphate-based geopolymer has many advantages. It has the advantages of alkali-based geopolymer, such as high compressive strength, low shrinkage, water impermeability, fire resistance, frost resistance, corrosion resistance, etc. It also has the advantages that alkali-based geopolymer does not have, such as more excellent thermal stability and compressive strength under high temperature conditions. Although phosphate-based geopolymer has many advantages, as an inorganic cementitious material, it also has the inherent disadvantages of inorganic materials, such as brittleness and easy fracture.

[0003] On the other hand, plant fibers are one of the most abundant natural resources, and the economically effective materials mainly include agricultural and forestry product residues such as straw, rice husk, corn straw, bagasse, cotton straw, wood chips, bamboo chips, etc. Existing research has shown that adding fibers to geopolymer can not only overcome the brittleness of geopolymer, but also improve its flexural strength and fracture toughness. However, current related research mainly uses non-plant fibers to enhance the related properties of geopolymer, and there is less research on using plant fibers to enhance the properties of geopolymer. There is no report on the research of adding plant fibers to phosphate-based geopolymer as the matrix. The compressive strength of phosphate-based geopolymer is generally higher than that of alkali-based geopolymer. Therefore, by compounding phosphate-based geopolymer with plant fibers, the performance of the prepared phosphate-based geopolymer composite material is expected to make a breakthrough.

[0004] To prepare high-performance geopolymers composites, relevant scholars in the industry have carried out a large amount of R & D work. For example, in the "Preparation method and application of a phosphoric acid-based geopolymer - clinoptilolite foam CO2 adsorbent" invented by Qiao Qiancheng et al., with the publication number: CN117463286A, clinoptilolite powder and metakaolin are mixed to obtain a solid-phase raw material, and then the solid-phase raw material is added to an acidic activator. After stirring evenly, a foaming agent and a foam stabilizer are added for foaming. Finally, it is cast into a mold and cured to obtain a phosphoric acid-based geopolymer - clinoptilolite foam material. This preparation method uses natural clinoptilolite and metakaolin as raw materials, and the obtained foam material can effectively adsorb CO2. In the "A phosphoric acid-based geopolymer porous material and its preparation method, and a method for extracting xylan from bagasse" invented by Cui Xuemin et al., with the publication number: CN117510142A, the rich acidic sites of the phosphoric acid-based geopolymer porous material have high selectivity for extracting xylan. At the same time, introducing sodium ions can solubilize the fibers and help hydrogen ions penetrate into the fibers better, which helps to improve the xylan yield. In the "Geopolymer concrete mix ratio and its preparation method for enhancing the mechanical properties of fiber-reinforced concrete" invented by Sun Qingwei et al., with the publication number: CN116477880A, the alkali activation technology is used to replace most of the cement with fly ash, and polypropylene fibers are incorporated to enhance the mechanical properties of geopolymer concrete, enhance the toughness of geopolymer concrete, and reduce the cracking of geopolymer concrete and other phenomena.

[0005] The present invention uses a phosphoric acid-based geopolymer as the matrix, and the prepared phosphoric acid-based geopolymer - plant fiber composite material not only has good flexural strength and excellent durability, but also is non-toxic, green and environmentally friendly, and has very high potential application value. Summary of the Invention

[0006] In order to prepare high-performance geopolymer materials, the present invention provides a method for preparing a gel material from a phosphoric acid-based geopolymer composite plant fiber, that is, using a phosphoric acid-based geopolymer as the matrix to prepare a phosphoric acid-based geopolymer - plant fiber composite material.

[0007] The technical solution of the present invention is as follows:

[0008] (1) Phosphoric acid, water and metakaolin are added to a mixing stirrer at a molar ratio of H3PO4 / Al2O3 of 1 - 2 and a molar ratio of H2O / Al2O3 of 9 - 12 and reacted for 30 min;

[0009] (2) Chinese fir fibers are added to the geopolymer gel. After stirring evenly, the mixed slurry is placed into a rectangular mold of 220 * 50 * 20 mm and pressed into shape on a hot press.

[0010] (3) The composite material obtained by pressing and the mold are placed in an oven at 60 °C for curing. After 1 day, demolding is carried out. The demolded sample is sealed in a sample bag and continues to be cured in the oven at 60 °C for 3 days. Then, the sample bag is removed and curing is continued for 3 days;

[0011] Further, the particle size of the Chinese fir fiber is 10 - 60 mesh;

[0012] Further, in step (1), the molar ratios of H3PO4 / Al2O3 and H2O / Al2O3 need to be controlled within the effective ranges of 1 - 2 and 9 - 12 respectively to prepare an effective phosphate-based geopolymer;

[0013] Further, in step (2), the effective range of the addition amount of the Chinese fir fiber is 5% - 25%, the stirring time is 15 min, the temperature of the hot press during pressing is 60 °C, and the pressure is 45 MPa;

[0014] Further, in step (3), during the curing process of the composite material, the curing regime is 1 - 3 - 3, and the demolded sample needs to be cured in a sealed bag for 3 days first.

[0015] Compared with the prior art, the features and beneficial effects of the present invention are:

[0016] (1) Using Chinese fir fiber as a material for enhancing the properties of geopolymer can not only overcome the brittleness of geopolymer, but also improve its flexural strength and fracture toughness. At the same time, Chinese fir fiber itself is also a green resource with excellent characteristics such as renewable, biodegradable and thermally stable.

[0017] (2) For the composite material prepared by the present invention, static bending strength test, internal bond strength test, screw holding force test, 24-hour water absorption and thickness swelling rate measurement, high temperature resistance and durability measurement, and frost resistance measurement are carried out. The static bending strength can reach 13.75 MPa, the internal bond strength reaches 2.17 MPa. After 25 freeze-thaw cycles, the static bending strength of the sample can still reach 10.87 MPa, and there are no edge defects, corner defects or cracks in the sample after freeze-thaw. Geopolymer

[0018] Specific embodiments

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] Example 1

[0021] (1) Phosphoric acid, water, and metakaolin were added to a mixing stirrer at an H3PO4 / Al2O3 molar ratio of 1.4 and an H2O / Al2O3 molar ratio of 8 and reacted for 30 min;

[0022] (2) 5% Chinese fir fiber was added to the geopolymer gel. After stirring evenly for a certain period of time, the mixed slurry was placed into a rectangular mold of 220*50*20 mm, and then put on a hot press for compression molding. The temperature of the hot press was set at 60 °C and the pressure was 45 MPa;

[0023] (3) The obtained composite material and the mold were placed in an oven at 60 °C for curing. After demolding after 1 day, the demolded sample was sealed in a sample bag and continued to be cured in an oven at 60 °C for 3 days. Then the sample bag was removed and cured for another 3 days. The flexural strength of the obtained geopolymer composite was 10.75 MPa, the internal bond strength was 1.68 MPa, and the flexural strength after freeze-thaw cycles was 7.23 MPa.

[0024] Example 2

[0025] (1) Phosphoric acid, water, and metakaolin were added to a mixing stirrer at an H3PO4 / Al2O3 molar ratio of 1.8 and an H2O / Al2O3 molar ratio of 10 and reacted for 30 min;

[0026] (2) 15% Chinese fir fiber was added to the geopolymer gel. After stirring evenly for a certain period of time, the mixed slurry was placed into a rectangular mold of 220*50*20 mm, and then put on a hot press for compression molding. The temperature of the hot press was set at 60 °C and the pressure was 45 MPa;

[0027] (3) The obtained composite material and the mold were placed in an oven at 60 °C for curing. After demolding after 1 day, the demolded sample was sealed in a sample bag and continued to be cured in an oven at 60 °C for 3 days. Then the sample bag was removed and cured for another 3 days. The flexural strength of the obtained geopolymer composite was 13.75 MPa, the internal bond strength was 2.17 MPa, and the flexural strength after freeze-thaw cycles was 10.87 MPa.

[0028] Example 3

[0029] (1) Phosphoric acid, water, and metakaolin were added to a mixing stirrer at an H3PO4 / Al2O3 molar ratio of 2.0 and an H2O / Al2O3 molar ratio of 12 and reacted for 30 min;

[0030] (2) 25% Chinese fir fiber was added to the geopolymer gel. After stirring evenly for a certain period of time, the mixed slurry was placed into a rectangular mold of 220*50*20 mm, and then put on a hot press for compression molding. The temperature of the hot press was set at 60 °C and the pressure was 45 MPa;

[0031] (3) The composite material obtained by pressing and the mold are put into an oven at 60°C for curing. After 1 day, demolding is carried out. The demolded sample is sealed in a sample bag and continues to be cured in the oven at 60°C for 3 days. Then, the sample bag is removed and cured for another 3 days. The flexural strength of the prepared geopolymer composite material is 5.45 MPa, the internal bond strength is 1.17 MPa, and the flexural strength after freeze-thaw cycles is 6.33 MPa.

[0032] The above description is a detailed description of the preferred and feasible embodiments of the present invention. However, the embodiments are not intended to limit the scope of the patent application of the present invention. Any equivalent changes or modifications made under the technical spirit disclosed by the present invention shall fall within the scope of the patent covered by the present invention.

Claims

1. A method for preparing a gel material from a phosphate-based geopolymer composite plant fiber, which relates to the preparation of a composite gelling material, comprising the following steps: (1) Phosphoric acid, water and metakaolin are added into a mixing agitator at a molar ratio of H3PO4 / Al2O3 of 1 to 2 and a molar ratio of H2O / Al2O3 of 9 to 12, and reacted for 30 minutes; (2) Adding fir fiber to geopolymer gel, stirring evenly, placing the mixed slurry into a rectangular mold of 220*50*20 mm, and placing it on a hot press for pressing and molding; (3) The pressed composite material and the mold are placed in an oven at 60°C for curing. The mold is demolded after 1 day. The demolded sample is placed in a sample bag and sealed. The sample is further cured in an oven at 60°C for 3 days. The sample bag is removed and cured for another 3 days.

2. The method for preparing a gel material from a phosphate-based geopolymer composite plant fiber according to claim 1, characterized in that The particle size of fir fiber is 10-60 mesh.

3. The method for preparing a gel material from a phosphate-based geopolymer composite plant fiber according to claim 1, characterized in that In step (1), the molar ratio of H3PO4 / Al2O3 and the molar ratio of H2O / Al2O3 need to be controlled within the effective ranges of 1 to 2 and 9 to 12, respectively, to produce an effective phosphate-based geopolymer.

4. The method for preparing a gel material from a phosphate-based geopolymer composite plant fiber according to claim 1, characterized in that In step (2), the effective range of the added amount of the fir fiber is 5% to 25%, the stirring time is 15 minutes, and the temperature of the hot press during pressing is 60° C. and the pressure is 45 MPa.

5. The method for preparing a gel material from a phosphate-based geopolymer composite plant fiber according to claim 1, characterized in that In step (3), the composite material curing system is 1-3-3, and the sample after demoulding needs to be sealed in a sealed bag and cured for 3 days.