Nano-kaolin modified hydraulic lime-based composite materials and their preparation and application

Abstract

This invention relates to a nano-metakaolin-modified hydraulic lime-based composite material and its preparation and application. The composite material comprises natural hydraulic lime and nano-metakaolin dispersed in the natural hydraulic lime, wherein the mass ratio of natural hydraulic lime to nano-metakaolin is (60-90):(10-40). The nano-metakaolin-modified hydraulic lime-based composite material of this invention exhibits controllable dispersibility and fluidity in the slurry after mixing with water. It also demonstrates good rock compatibility, low soluble salt content, controllable curing time, suitable post-curing strength, low permeability, and low shrinkage and expansion rate. The presence of a repair agent can specifically enhance the additional protective performance of the reinforcement material. It possesses high applicability, safety, and durability for the protection of stone cultural relics, without causing derivative damage.

Description

Technical Field

[0001] This invention belongs to the field of stone cultural relic protection technology, such as grottoes and temples, and relates to a nano-kaolin-modified hydraulic lime-based composite material and its preparation and application. Background Technology

[0002] The grotto temples, built against mountainsides and exposed to the natural environment for extended periods, have experienced varying degrees of weathering in some areas, such as rock pulverization, cracking, and flaking. This severely damages the artistic value of the artifacts. To improve their durability, it is necessary to develop protective materials that enhance the mechanical properties and impermeability of the artifacts. Currently, researchers primarily address cracking in stone artifacts by using repair and reinforcement materials to repair the cracked and damaged areas, reinforcing the damaged rock mass and preventing further expansion of the cracks that could compromise the safety of the artifacts.

[0003] Based on their composition, restoration and reinforcement materials can be divided into inorganic and organic materials. Organic materials (such as polyacrylic acid resin and epoxy resin) have good bonding properties and high fluidity, giving them an advantage in filling and reinforcing small cracks. However, their durability is low, and they can easily cause secondary damage to cultural relics. Inorganic materials, with similar composition and structure to the original cultural relic, have high compatibility and have attracted widespread attention from researchers in recent years.

[0004] Commonly used inorganic reinforcement materials include cement, lime, and water glass, all of which have been applied to the physical surfaces of cultural relics. However, inorganic materials also have certain drawbacks, such as large differences in strength, high soluble salt content, mismatched material properties, and poor permeability.

[0005] For example, Chinese patent CN114933461A describes a nano-silica ball-modified metakaolin-based composite material for fissure grouting, its preparation, and application. This composite material includes an inorganic cementitious material and porous silica microspheres dispersed within the inorganic cementitious material. The inorganic cementitious material is a composite of metakaolin and natural hydraulic lime. Chinese patent CN107935531A describes a grouting material for fissures in grouting rock masses and its preparation method. This grouting material includes hydraulic lime (a type of hydraulic lime), quartz sand, and metakaolin. Both patents use metakaolin as an active pozzolanic material to react with hydraulic lime, improving the various properties of the cementitious material after setting; however, the performance improvement effect is limited. Summary of the Invention

[0006] The purpose of this invention is to provide a nano-kaolin-modified hydraulic lime-based composite material and its preparation and application, for the restoration and reinforcement of weathered stone cultural relics such as grottoes and temples.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] One of the technical solutions of this invention provides a nano-metakaolin-modified hydraulic lime-based composite material, comprising natural hydraulic lime and nano-metakaolin dispersed in the hydraulic lime. The nano-metakaolin has the following properties: a white, flaky aluminosilicate clay mineral with a particle size of 2–200 nm and a specific surface area of ​​30–40 m². 2 / g, porosity 40-60%, activity index >125%.

[0009] Furthermore, the natural hydraulic lime is in the form of a white or light gray powder with an average particle size of <15μm and a density of 2.5–2.66 g / cm³. 3 .

[0010] Furthermore, the mass ratio of the natural hydraulic lime to nano-kaolin is (60-90):(10-40).

[0011] Furthermore, the composite material also incorporates a repair agent for surface functionalization and reinforcement protection.

[0012] Furthermore, the repair agent is selected from oxides, hydroxides or carbonates of Ca, Ti or Si, or one of antifreeze, defoamer or water-reducing agent.

[0013] Furthermore, the amount of the repair agent added is 0.5% to 1.5% of the total mass of the composite material.

[0014] The second technical solution of the present invention provides a method for preparing a nano-metakaolin-modified hydraulic lime-based composite material, wherein raw material components including natural hydraulic lime and nano-metakaolin are ground and mixed evenly to obtain the nano-metakaolin-modified hydraulic lime-based composite material.

[0015] The third technical solution of the present invention provides an application of a nano-kaolin-modified hydraulic lime-based composite material, which is used for the repair and reinforcement of damaged stone artifacts with cracks (especially large cracks).

[0016] Furthermore, when using this composite material, it is mixed evenly with water to obtain a composite slurry, which is then used to repair and reinforce damaged stone artifacts.

[0017] Furthermore, the amount of water used is 40-50 wt% of the composite material.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. The nano-metakaolin-modified natural hydraulic lime reinforcement material of the present invention combines the individual and composite characteristics of natural hydraulic lime and nano-metakaolin. The ratio of natural hydraulic lime to nano-metakaolin is adjustable, and it has high reactivity and fast hardening speed.

[0020] 2. The preparation method of the nano-kaolin-modified natural hydraulic lime reinforcement material of the present invention is simple, easy, fast and efficient, and has the prospect of large-scale application; the operation process is environmentally friendly and safe, with little impact on operators and the environment, and has good biocompatibility and is non-toxic and non-irritating.

[0021] 3. The nano-kaolin-modified natural hydraulic lime reinforcement material of the present invention has good compatibility with rocks, low soluble salt content, controllable curing time, high early strength, moderate final strength, and low shrinkage and expansion rate.

[0022] 4. The nano-kaolin-modified natural hydraulic lime reinforcement material of this invention is used to protect damaged stone cultural relics, mainly sandstone grottoes and temples. The effect is obvious and it has suitable mechanical strength. In addition, the inorganic reinforcement material has high durability and is more suitable for long-term protection of stone cultural relics. Attached Figure Description

[0023] Figure 1 This is a TEM scan of nano-kaolinite in this invention;

[0024] Figure 2 This is a SEM scan of the nano-kaolin-modified hydraulic lime composite reinforcement material of the present invention. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0026] In the following embodiments, natural hydraulic lime (NHL-5) was purchased from Shanghai Desaibao Building Materials Co., Ltd., nano-metakaolin was purchased from Inner Mongolia Chaopai New Materials Co., Ltd., nano-TiO2 and nano-SiO2 were purchased from Shanghai Naio Nanotechnology Co., Ltd., and water-reducing agent and defoamer were purchased from Guangzhou Zhongwan New Materials Co., Ltd.

[0027] Unless otherwise specified, the raw materials or processing techniques are conventional commercially available materials or conventional processing techniques in this field.

[0028] Example 1

[0029] (1) A nano-meta-kaolin modified hydraulic lime-based composite material for repairing and reinforcing damaged rock masses, the composite material comprising natural hydraulic lime and highly dispersed nano-meta-kaolin in the system, wherein the composite material is loaded with a repair agent for surface functionalization and reinforcement protection.

[0030] (2) The mass ratio of added natural hydraulic lime to nano-metakaolin is 10:1, and the average particle size of the natural hydraulic lime is <15μm. The nano-metakaolin is as follows: Figure 1 As shown, it exhibits a nanosheet structure with a particle size between 2-200 nm and good dispersibility.

[0031] (3) The repair agent is nano-TiO2 with an average particle size of 24 nm. First, natural hydraulic lime and nano-kaolin are ground and mixed evenly. Then, nano-TiO2 (accounting for 1% of the total solid mass) is added and mixed evenly. After mixing, it is added to water with a solid-liquid ratio of 2:1. After stirring in a mortar mixer, the sample is bonded to sandstone blocks at a temperature of 30°C and a humidity of 60°C and cured for 28 days.

[0032] (4) The uniaxial compressive strength of the specimen after curing was 16.35 MPa and the bond strength was 2.59 MPa. Compared with pure hydraulic lime, the impermeability of the composite specimen was improved by 10.65%. In addition, nano TiO2 can effectively reduce the ultraviolet light absorption of the specimen (20-30%), and improve the light stability and durability of the composite mortar.

[0033] Example 2

[0034] (1) A nano-meta-kaolin modified hydraulic lime-based composite material for repairing and reinforcing damaged rock masses, the composite material comprising natural hydraulic lime and highly dispersed nano-meta-kaolin in the system, wherein the composite material is loaded with a repair agent for surface functionalization and reinforcement protection.

[0035] (2) The mass ratio of added natural hydraulic lime to nano-metakaolin is 5:1, and the average particle size of the natural hydraulic lime is <15μm. The nano-metakaolin is in flake form, with a particle size of 2-200nm and a specific surface area of ​​30-40m². 2 / g, porosity 40-60%, activity index >125%.

[0036] (3) The repair agent is nano-SiO2 with an average particle size of 20nm. First, natural hydraulic lime and nano-kaolin are ground and mixed evenly. Then, nano-SiO2 (accounting for 1% of the total solid mass) is added and mixed evenly. After mixing, it is added to water with a solid-liquid ratio of 2:1. After stirring in a mortar mixer, the sample is bonded to sandstone blocks at a temperature of 30℃ and a humidity of 60℃ and cured for 28 days.

[0037] (4) Compared with pure hydraulic lime, the initial setting and final setting times of composite mortar were reduced from 300 minutes and 930 minutes to 262 minutes and 731 minutes, respectively, which were reduced by 12.67% and 21.40%. The uniaxial compressive strength of the cured sample was 20.32 MPa, the bond strength was 2.92 MPa, and the impermeability was improved by 13.32%.

[0038] Example 3

[0039] (1) A nano-meta-kaolin modified hydraulic lime-based composite material for repairing and reinforcing damaged rock masses, the composite material comprising natural hydraulic lime and highly dispersed nano-meta-kaolin in the system, wherein the composite material is loaded with a repair agent for surface functionalization and reinforcement protection.

[0040] (2) The mass ratio of added natural hydraulic lime to nano-metakaolin is 5:1, and the average particle size of the natural hydraulic lime is <15μm. The nano-metakaolin is in flake form, with a particle size of 2-200nm and a specific surface area of ​​30-40m². 2 / g, porosity 40-60%, activity index >125%.

[0041] (3) The repair agent is a superabsorbent resin containing hydrophilic groups and cross-linked polyacrylic acid macromolecules, spherical in shape with a particle size of approximately 6 mm. First, natural hydraulic lime and nano-kaolin are ground and mixed evenly. Then, the superabsorbent resin (0.3% of the total solid mass) is added and mixed evenly before being added to water at a solid-liquid ratio of 2:1. After mixing with a mortar mixer, the sample is bonded to sandstone blocks at a temperature of 30°C and a humidity of 60°C for 28 days.

[0042] (4) Compared with pure water-hardening lime, the uniaxial compressive strength of the cured sample is 19.35 MPa, the bond strength is 2.84 MPa, and the mass loss rate of the composite sample is <5% after 30 freeze-thaw cycles, indicating a significant improvement in freeze-thaw resistance.

[0043] Example 4

[0044] (1) A nano-meta-kaolin modified hydraulic lime-based composite material for repairing and reinforcing damaged rock masses, the composite material comprising natural hydraulic lime and highly dispersed nano-meta-kaolin in the system, the composite material being able to load a variety of repair agents and additives and to perform surface functionalization and reinforcement protection.

[0045] (2) The mass ratio of added natural hydraulic lime to nano-metakaolin is 10:1, and the average particle size of the natural hydraulic lime is <15μm. The nano-metakaolin is in flake form, with a particle size of 2-200nm and a specific surface area of ​​30-40m². 2 / g, porosity 40-60%, activity index >125%.

[0046] (3) The repair agent is an organosilicon defoamer, the main components of which are dimethyl silicone oil and silicon dioxide (mass ratio 9:1). First, natural hydraulic lime and nano-kaolin are ground and mixed evenly, then the organosilicon defoamer (accounting for 0.1% of the total solid mass) is added, mixed evenly, and then added to water with a solid-liquid ratio of 2:1. After being stirred in a mortar mixer, the sample is bonded to sandstone blocks at a temperature of 30°C and a humidity of 60°C, and cured for 28 days.

[0047] (4) The density of the sample increased after curing, and its internal structure was as follows: Figure 2 As shown, nano-metakaolin is uniformly dispersed in natural hydraulic lime, effectively improving the hydration degree of the composite sample. Compared to pure natural hydraulic lime, the ultrasonic velocity of the composite sample increased from 2.63 km / s to 2.77 km / s, the density (characterized by ultrasonic wave velocity) increased by 5.2%, and the porosity decreased from 50.38% to 42.03%. The saturated deformation of the composite sample was less than 0.5%, the uniaxial compressive strength was 16.03 MPa, and the bond strength was 2.65 MPa.

[0048] Example 5

[0049] (1) A nano-meta-kaolin modified hydraulic lime-based composite material for repairing and reinforcing damaged rock masses, the composite material comprising natural hydraulic lime and highly dispersed nano-meta-kaolin in the system, wherein the composite material is loaded with a repair agent for surface functionalization and reinforcement protection.

[0050] (2) The mass ratio of the added natural hydraulic lime to nano-metakaolin is 10:3, and the average particle size of the natural hydraulic lime is <15μm. The nano-metakaolin is in flake form, with a particle size of 2-200nm and a specific surface area of ​​30-40m². 2 / g, porosity 40-60%, activity index >125%.

[0051] (3) The repair agent is a polycarboxylate superplasticizer, a type of polyether with methacrylic acid as the main chain and grafted with different side chain lengths. First, natural hydraulic lime and nano-kaolin are ground and mixed evenly. Then, the polycarboxylate superplasticizer (accounting for 0.15% of the total solid mass) is added and mixed evenly. After mixing, it is added to water with a solid-liquid ratio of 2:1. After being stirred in a mortar mixer, the sample is bonded to sandstone blocks at a temperature of 30°C and a humidity of 60°C and cured for 28 days.

[0052] (4) The rheological properties of the composite mortar are improved. Compared with pure hydraulic lime, its fluidity increased from 170 mm to 213 mm, which is 25% higher; its viscosity decreased from 2.03 Pa·s to 1.42 Pa·s, which is 30% lower; its porosity decreased from 46.32% to 41.09%, which is 5.23% lower; and the uniaxial compressive strength of the composite sample after curing was 22.37 MPa and the bond strength was 3.55 MPa.

[0053] Example 6

[0054] In this embodiment, the repair agent is nano-calcium hydroxide, used to enhance the volcanic ash reaction and strengthen the bonding effect of inorganic gel materials. The rest is the same as in Example 1.

[0055] Example 7

[0056] In this embodiment, the repair agent is calcium carbonate nanocrystals, which can effectively improve the mechanical properties of the sample and enhance the bonding effect. The rest is the same as in Example 2.

[0057] Comparative Example 1:

[0058] Compared with Example 1, most of the results are the same, except that the nano-kaolin was replaced with an equal mass of ordinary cement. After curing, the strength of the cement-modified hydraulic lime cementitious material was improved to a certain extent, but the soluble salt content of the sample was significantly higher (>1wt%), which is not conducive to the protection of rock cultural relics and is prone to secondary damage.

[0059] Comparative Example 2:

[0060] Compared to Example 1, most aspects were the same, except that nano-kaolin was replaced with an equal mass of natural hydraulic lime. The mortar set slowly, the early strength of the set samples was low, and the uniaxial compressive strength of the samples after seven days of curing was less than 2 MPa.

[0061] Comparative Example 3:

[0062] Compared to Example 1, most aspects were the same, except that nano-metakaolin was replaced with an equal mass of metakaolin. The larger particle size of metakaolin (3–10 μm) resulted in a weaker pozzolanic reaction with hydraulic lime. The early strength of the metakaolin-modified hydraulic lime sample was significantly lower than that of the nano-metakaolin-modified sample. After 7 days of curing, the compressive strength of the nano-metakaolin-modified sample was 10.21 MPa, while that of the metakaolin-modified sample was only 5.12 MPa. Furthermore, after 28 days of curing, the compressive strength of the metakaolin-modified hydraulic lime sample was 9.94 MPa, also significantly lower than that of the nano-metakaolin-modified sample (compressive strength: 16.35 MPa).

[0063] Comparative Example 4:

[0064] Compared to Example 1, most aspects were the same, except that the TiO2 loading was omitted. The mechanical properties of the composite sample did not decrease significantly, but its resistance to photoaging was somewhat lower than that of the TiO2-loaded sample. Its ultraviolet light absorption capacity increased by 23.1%, and the sample durability decreased slightly. Specifically, the compressive strength of the sample without TiO2 loading was 14.45 MPa after 20 days of photoaging, while the compressive strength of the sample with TiO2 loading was 15.55 MPa after 20 days of photoaging.

[0065] Comparative Example 5:

[0066] Compared to Example 1, most aspects were the same, except that natural hydraulic lime was replaced with an equal mass of 3–10 μm hydraulic oyster shell lime. Hydraulic oyster shell lime contains less hydraulic components and more residual impurities such as calcium carbonate. The early strength of the natural hydraulic lime sample was significantly higher than that of the hydraulic oyster shell lime sample. After 7 days of curing, the compressive strength of the natural hydraulic lime sample was 10.21 MPa, while that of the hydraulic oyster shell lime sample was only 4.51 MPa. Furthermore, after 28 days of curing, the compressive strength of the hydraulic oyster shell lime sample was 6.94 MPa, which was also significantly lower than that of the natural hydraulic lime sample (compressive strength: 16.35 MPa).

[0067] Example 8:

[0068] Compared with Example 1, most of them are the same, except that the mass ratio of natural hydraulic lime to nano-kaolin in this example is as follows: 20% metakaolin, 78% natural hydraulic lime, and 2% nano-TiO2.

[0069] Example 9:

[0070] Compared with Example 4, most of the contents are the same, except that the mass ratio of natural hydraulic lime to nano-kaolin in this example is as follows: kaolin is 25%, natural hydraulic lime is 77.8%, and organosilicon defoamer is 0.2%.

[0071] Example 10:

[0072] Compared with Example 5, most of the components are the same, except that the mass ratio of natural hydraulic lime to nano-metakaolin in this example is as follows: nano-metakaolin is 25%, natural hydraulic lime is 74.9%, and polycarboxylate superplasticizer is 0.1%.

[0073] Example 11:

[0074] Compared with Example 5, most of them are the same, except that the weight ratio of natural hydraulic lime and nano-metakaolin in this example is as follows: nano-metakaolin is 40%, natural hydraulic lime is 59.8%, and polycarboxylate superplasticizer is 0.2%.

[0075] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A nano-metakaolin-modified hydraulic lime-based composite material, characterized in that, It includes natural hydraulic lime and nano-metakaolin dispersed in natural hydraulic lime. The nano-metakaolin has the following properties: a white, flaky aluminosilicate clay mineral with a particle size of 2-200 nm and a specific surface area of ​​30-40 m². 2 / g, porosity 40~60%, activity index >125%; The natural hydraulic lime is in the form of a white or light gray powder with an average particle size of <15μm and a density of 2.5~2.66 g / cm³. 3 ; The mass ratio of the natural hydraulic lime to the nano-meta-kaolin is (60~90):(10~40). The composite material also incorporates a repair agent for surface functionalization and reinforcement protection; The repair agent is an oxide, hydroxide, or carbonate of Ca, Ti, or Si, or the repair agent is one of an antifreeze agent, defoamer, or water-reducing agent.

2. The nano-metakaolin-modified hydraulic lime-based composite material according to claim 1, characterized in that, The amount of the repair agent added is 0.5 to 1.5% of the total mass of the composite material.

3. The preparation method of the nano-metakalin-modified hydraulic lime-based composite material as described in claim 1 or 2, characterized in that, The raw material components, including natural hydraulic lime and nano-metakaolin, are ground and mixed evenly to obtain nano-metakaolin-modified hydraulic lime-based composite material.

4. The application of the nano-metakalin-modified hydraulic lime-based composite material as described in claim 1 or 2, characterized in that, This composite material is used for the restoration and reinforcement of damaged stone artifacts with large cracks.

5. The application of the nano-kaolin-modified hydraulic lime-based composite material according to claim 4, characterized in that, When using this composite material, it is mixed evenly with water to obtain a composite slurry, which is then used to repair and reinforce damaged stone artifacts.

6. The application of the nano-kaolin-modified hydraulic lime-based composite material according to claim 5, characterized in that, The amount of water used is 40-50 wt% of the composite material.

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