A crack-resistant c-(a)-s-h-based composite material, and a preparation method and application thereof

Abstract

This invention relates to a crack-resistant C-(A)-S-H based composite material, its preparation method, and its application. The composite material comprises the following raw materials: a calcium source, a silicon source, metakaolin, basalt fiber, and water. The calcium source is calcium oxide, and the silicon source is fumed silica. The mass of the basalt fiber is 0.55wt%~1.5wt% of the total mass of the composite material; the mass of the metakaolin is 30wt%~90wt% of the mass of the silicon source. Compared with the prior art, this invention is based on room-temperature volcanic ash reaction and achieves a comprehensive improvement in mechanical properties, crack resistance, carbonization resistance, and air permeability through the synergistic modification of basalt fiber and metakaolin. Its composition is compatible with the stone matrix and can be formed in situ at room temperature, making it particularly suitable for grouting reinforcement and surface repair of cracks in cultural relics such as sandstone and limestone.

Description

Technical Field

[0001] This invention relates to the field of inorganic cementitious materials technology, and in particular to a crack-resistant C-(A)-SH-based composite material, its preparation method, and its application. Background Technology

[0002] Stone artifacts, especially open-air sandstone artifacts, are prone to developing micro-cracks, hollowing, and surface peeling due to long-term exposure to wet-dry cycles, salt crystallization, freeze-thaw cycles, and carbonization. Traditional restoration materials, such as epoxy resin and other organic polymers, suffer from problems such as aging and yellowing, mismatched coefficients of thermal expansion, poor air permeability, and low reversibility. Ordinary cement-based materials, on the other hand, are prone to "secondary damage" due to their high alkalinity, high soluble salt content, and obvious tendency to crack due to drying shrinkage.

[0003] In recent years, biomimetic inorganic cementitious materials based on calcium silicate hydrate (CSH) have attracted attention due to their compatibility with stone components and their environmental friendliness and low carbon emissions. Calcium silicate hydrate (CSH) is a key cementing component in a variety of materials, from ancient mortar to modern cement, and has broad application prospects in the field of cultural heritage protection.

[0004] Previous research successfully prepared high-purity CSH grout through the pozzolanic reaction of gaseous SiO2 and Ca(OH)2. This material exhibits excellent workability in high-humidity, enclosed environments and is a potential candidate material for grouting and repairing cracks in stone cultural relics. However, the in-situ synthesized CSH grout material is inherently brittle, exhibiting significant drying shrinkage and carbonization shrinkage under ambient temperature curing in air, making it prone to obvious cracking. This greatly reduces the workability of the grout and restricts its practical application.

[0005] Common methods for modifying cement-based composite materials include incorporating fibers or mineral admixtures: polypropylene fibers have limited toughening effects and weak interfacial bonding; steel fibers have high density and are prone to corrosion; metakaolin can improve density and carbonization resistance, but when added alone, it often exacerbates the brittleness of the material.

[0006] Patent publication number CN110041007A discloses a permeability-resistant marble powder composite admixture, comprising modified marble powder, modified metakaolin, binder powder, and basalt fiber, used to improve the pore structure of concrete, increase its density, and enhance its permeability. Its primary application is in cement concrete, which contains organic binder powder at a significant content. If used for the protection of outdoor stone artifacts, it could affect their water and salt cycle, and the organic matter may deteriorate and decompose under prolonged exposure to sunlight and wind, causing secondary damage to the stone artifacts.

[0007] Patent CN121342393A discloses an alkali-reducing protective agent for basalt fibers. This agent effectively lowers the pH value of the pore solution through a composite system of active silica aerogel, metakaolin, and lithium slag powder, forming a protective layer on the fiber surface and delaying fiber performance degradation. Its main application is in building materials. However, lithium slag powder contains salt; if used for the preservation of stone cultural relics, it may cause salt precipitation, resulting in irreversible salt damage. Summary of the Invention

[0008] The purpose of this invention is to overcome the defects of existing technologies, such as cracking, instability, and salt damage, by providing a crack-resistant C-(A)-SH-based composite material, its preparation method, and its applications. Based on room-temperature volcanic ash reaction, and through the synergistic modification of basalt fiber and metakaolin, a comprehensive improvement in mechanical properties, crack resistance, carbonization resistance, and air permeability is achieved. Its composition is compatible with the stone matrix and can be formed in situ at room temperature, making it particularly suitable for grouting reinforcement and surface repair of cracks in cultural relics such as sandstone and limestone.

[0009] The objective of this invention can be achieved through the following technical solutions: One of the technical solutions of the present invention is to provide a crack-resistant C-(A)-SH-based composite material, which includes the following raw materials: calcium source, silicon source, metakaolin, basalt fiber and water.

[0010] Furthermore, the calcium source is calcium oxide (CaO) or calcium hydroxide (Ca(OH)2), preferably CaO; the silicon source is fumed silica (SiO2).

[0011] Furthermore, the mass of the basalt fiber is 0.55wt%~1.5wt% of the total mass of the composite material; The mass of the metakaolin is 30wt% to 90wt% of the mass of the silicon source.

[0012] Furthermore, the mass of the basalt fiber is 0.8wt%~1.2wt% of the total mass of the composite material; The mass of the metakaolin is 55wt% to 65wt% of the mass of the silicon source.

[0013] Furthermore, the molar ratio of calcium in the calcium source to silicon in the silicon source is 0.6 to 1:1.

[0014] Furthermore, the water-to-gel ratio of the total mass of the water and gel material is 1.5~2.5:1; The total mass of the gel material is the sum of the masses of the calcium source, silicon source, and metakaolin.

[0015] Furthermore, the composite material also includes a polycarboxylate superplasticizer (PCE), the mass of which is 4wt% to 7wt% of the total mass of the gel material, wherein the total mass of the gel material is the sum of the masses of the calcium source, the silicon source, and the metakaolin. The polycarboxylate superplasticizer includes one or more of the following types: methyl allyl ether, methyl allyl ether, or methacrylate.

[0016] Furthermore, the composite material also includes quartz sand, the mass of which is 2.5 to 3.5 times the total mass of the gel material (i.e., the sand-to-gel ratio is 2.5 to 3.5 times), wherein the total mass of the gel material is the sum of the masses of the calcium source, the silicon source, and the metakaolin.

[0017] The second technical solution of the present invention is to provide a method for preparing a crack-resistant C-(A)-SH-based composite material, wherein a calcium source, a silicon source, metakaolin, basalt fiber and water are mixed, and the composite material is obtained by stirring, molding and curing.

[0018] Furthermore, the curing process is as follows: first, cure at 20±2℃ and relative humidity ≥90% for 7 to 14 days, and then cure at 50% to 70% relative humidity for 21 to 28 days.

[0019] Furthermore, the mixing and molding temperature is room temperature.

[0020] Furthermore, the preparation method includes the following steps: S1. Dry mixing: The calcium source and silicon source are dry mixed to obtain a uniform dry mixture; S2, First wet mixing: Add water to the dry mixture obtained in step S1 and mix for the first time to obtain the basic slurry; S3. Secondary wet mixing: Add metakaolin and basalt fiber to the basic slurry obtained in step S2, and mix for the second time to obtain a uniform composite slurry. S4. Molding and curing: Inject the composite slurry obtained in step S3 into the mold, seal it and then cure it. When the composite material also includes a polycarboxylate superplasticizer, it is dissolved in deionized water and added in step S2; When the composite material also includes quartz sand, it is added together with metakaolin and basalt fiber in step S3.

[0021] Furthermore, in step S1, the rotational speed of the dry mixing is 40~60 r·min. -1 The duration is 30~120 seconds; In step S2, the rotation speed of the first stirring and mixing is 100~200 r·min. -1The duration is 30~120 seconds; In step S3, the second mixing is first performed by gentle stirring at a low speed of 40-60 r·min. -1 Stir for 30-120 seconds, then stir at medium speed for 100-200 rpm. -1 Stir for 120-180 seconds, then stir at high speed for 250-350 rpm. -1 Stir for 30~120s to obtain a uniform composite slurry.

[0022] The third technical solution of the present invention is to provide an application of crack-resistant C-(A)-SH-based composite material in the protection of stone cultural relics, wherein the application is to perform crack grouting, shallow layer reinforcement or surface protection on sandstone or limestone cultural relics.

[0023] Compared with the prior art, the present invention has the following advantages: (1) This invention optimizes the material structure at multiple scales from nanoscale to microscale to macroscale through the synergistic effect of basalt fiber and metakaolin, while achieving high toughness and high stability.

[0024] (2) The main hydration product of the composite material of the present invention is C-(A)-SH gel, which is compatible with the components of stone cultural relics, has low alkalinity and no harmful salts, thus avoiding secondary damage.

[0025] (3) The preparation process of this invention is simple, the entire process is carried out at room temperature, and there is no need for high-temperature calcination or external catalysts, making it suitable for on-site preparation and construction.

[0026] (4) The composite material of the present invention has a controllable pore structure and good air permeability, which is conducive to water vapor migration and avoids the accumulation of moisture and salt inside.

[0027] (5) The present invention can achieve directional design of mechanical properties by adjusting the amount of fiber and metakaolin according to the strength requirements of the repaired part, and has wide applicability.

[0028] In general, the crack resistance mechanism of basalt fiber (BF) mainly relies on physical bridging and crack deflection at the macroscale. The fiber significantly improves flexural strength and crack resistance by transferring stress across cracks and extending crack propagation paths. In contrast, the reinforcement mechanism of metakaolin (MK) operates at the nano- to micro-scale through chemical and physical mechanisms: its fine particles fill pores to refine the microstructure, while its pozzolanic reaction consumes calcium hydroxide to form additional CASH gel, thereby improving density, mechanical strength, and carbonization resistance. The BF / MK composite system exhibits a synergistic reinforcement mechanism: the MK-modified dense matrix provides stronger anchoring for the fibers, while the fibers compensate for the inherent brittleness of the MK-reinforced system. This multi-scale integration combines nano- to micro-scale densification with macro-scale fiber toughening, resulting in a composite material with balanced and excellent performance in terms of strength, crack resistance, and durability. Even after long-term storage in air, the modified mortar showed no signs of cracking or carbonization, demonstrating excellent durability under dry, air-exposed conditions. Its advantages, such as high durability due to its inorganic nature and lack of salt damage, highlight its enormous application potential in the protection and treatment of various stone cultural relics. Attached Figure Description

[0029] Figure 1 The XRD patterns (a, b) and infrared spectra (c, d) of the surface powder samples (sampling depth 0-5 mm) of mortar blocks after 28 days of curing in Examples 1-3 and Comparative Examples 1-9 of the present invention are shown. Figure 2 The flexural strength of specimens from Examples 1-3 and Comparative Examples 1-9 after curing for 28 days; Figure 3 The compressive strength of specimens from Examples 1-3 and Comparative Examples 1-9 after curing for 28 days; Figure 4 Surface (a) and cross-sectional (b) morphology images of specimens under different conditions; Figure 5 The microstructures obtained by sampling at a depth of 15–20 mm below the surface of each group of C-(A)-SH based mortar blocks after 28 days of curing are shown in (a) Comparative Example 2, (b) Comparative Example 3, (c) Comparative Example 7, and (d) Example 1. Figure 6 This is a TEM image of the microstructure obtained by sampling at a depth of 15-20 mm below the surface of the mortar block in Example 1; Figure 7 The macroscopic morphology of the specimen from Example 1 after curing in air for 28 days; Figure 8 On-site photos of the bonding and reinforcement operation of Kizil sandstone; Figure 9 This is a picture showing the effect after 28 days of bonding and curing of Kizil sandstone. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. All other embodiments obtained by those skilled in the art based on the given embodiments without creative effort are within the scope of protection of this application.

[0031] Unless otherwise specified, the reagents, methods, instruments and equipment used in this invention are conventional reagents, methods, instruments and equipment in the art.

[0032] Calcium oxide powder (analytical grade, purity ≥98%) was purchased from Tianjin Chemical Reagent Store (Tianjin, China). Calcium hydroxide powder (analytical grade, purity ≥95%) was supplied by Maclean's (Shanghai, China). Fumed silica (silica content ≥98%) was supplied by China State Construction Engineering Corporation (CSCEC) Building Materials & Chemicals Co., Ltd. (Henan, China). Quartz sand with an average particle size of approximately 58 μm was purchased from Huifeng New Materials Co., Ltd. (Henan, China). Basalt fiber (diameter 9-25 μm, length approximately 3 mm) and polypropylene (PP) fiber (diameter 9-25 μm, length approximately 3 mm) were purchased from Haining Anjie Composite Materials Co., Ltd. (Jiangsu, China) and Huixiang Fiber Direct Sales Co., Ltd. (Hunan, China), respectively. Powdered Sika polycarboxylate superplasticizer 540P (PCE, purity ≥98%) was purchased from Shanghai Chenqi Chemical Technology Co., Ltd. (Shanghai, China). High-purity metakaolin powder (purity ≥98%) is provided by Shanqishiyu Co., Ltd. (Xiangxi, Hunan, China). The metakaolin contains amorphous aluminum oxide (content ≥40%).

[0033] A crack-resistant C-(A)-SH-based composite material comprising the following raw materials: calcium source, silicon source, metakaolin, basalt fiber and water.

[0034] In some specific embodiments, the calcium source is calcium oxide (CaO) or calcium hydroxide (Ca(OH)2), preferably CaO; the silicon source is fumed silica (SiO2).

[0035] In some specific embodiments, the mass of the basalt fiber is 0.55wt% to 1.5wt% of the total mass of the composite material; The mass of the metakaolin is 30wt% to 90wt% of the mass of the silicon source.

[0036] In some specific embodiments, the mass of the basalt fiber is 0.8wt% to 1.2wt% of the total mass of the composite material; The mass of the metakaolin is 55wt% to 65wt% of the mass of the silicon source.

[0037] In some specific embodiments, the molar ratio of calcium in the calcium source to silicon in the silicon source is 0.6 to 1:1.

[0038] In some specific embodiments, the water-gel ratio of the total mass of the water and gel material is 1.5~2.5:1; The total mass of the gel material is the sum of the masses of the calcium source, silicon source, and metakaolin.

[0039] In some specific embodiments, the composite material further includes a polycarboxylate superplasticizer (PCE), the mass of which is 4wt% to 7wt% of the total mass of the gel material, wherein the total mass of the gel material is the sum of the masses of the calcium source, the silicon source, and the metakaolin. The polycarboxylate superplasticizer includes one or more of the following types: methyl allyl ether, methyl allyl ether, or methacrylate.

[0040] In some specific embodiments, the composite material further includes quartz sand, the mass of which is 2.5 to 3.5 times the total mass of the gel material (i.e., the sand-to-gel ratio is 2.5 to 3.5 times), wherein the total mass of the gel material is the sum of the masses of the calcium source, the silicon source, and the metakaolin.

[0041] A method for preparing a crack-resistant C-(A)-SH-based composite material involves mixing a calcium source, a silicon source, metakaolin, basalt fiber, and water, followed by stirring, molding, and curing to obtain the composite material.

[0042] In some specific embodiments, the curing process is as follows: first, curing at 20±2℃ and relative humidity ≥90% for 7 to 14 days, and then curing at 50% to 70% relative humidity for 21 to 28 days.

[0043] In some specific embodiments, the stirring and molding temperature is room temperature.

[0044] In some specific embodiments, the preparation method includes the following steps: S1. Dry mixing: The calcium source and silicon source are dry mixed to obtain a uniform dry mixture; S2, First wet mixing: Add water to the dry mixture obtained in step S1 and mix for the first time to obtain the basic slurry; S3. Secondary wet mixing: Add metakaolin and basalt fiber to the basic slurry obtained in step S2, and mix for the second time to obtain a uniform composite slurry. S4. Molding and curing: Inject the composite slurry obtained in step S3 into the mold, seal it and then cure it. When the composite material also includes a polycarboxylate superplasticizer, it is dissolved in deionized water and added in step S2; When the composite material also includes quartz sand, it is added together with metakaolin and basalt fiber in step S3.

[0045] In some specific embodiments, in step S1, the rotational speed of the dry mixing is 40~60 r·min. -1 The duration is 30~120 seconds; In step S2, the rotation speed of the first stirring and mixing is 100~200 r·min. -1 The duration is 30~120 seconds; In step S3, the second mixing is first performed by gentle stirring at a low speed of 40-60 r·min. -1 Stir for 30-120 seconds, then stir at medium speed for 100-200 rpm. -1 Stir for 120-180 seconds, then stir at high speed for 250-350 rpm. -1 Stir for 30~120s to obtain a uniform composite slurry.

[0046] The application of a crack-resistant C-(A)-SH-based composite material in the protection of stone cultural relics, wherein the application is to perform crack grouting, shallow layer reinforcement or surface protection on sandstone or limestone cultural relics.

[0047] Each of the above embodiments can be implemented individually or in any combination of two or more.

[0048] The following description uses specific examples to illustrate the point.

[0049] Example 1 A crack-resistant C-(A)-SH-based composite material comprising the following raw materials: calcium source, silicon source, metakaolin, basalt fiber, PCE, quartz sand and water.

[0050] In this embodiment, the calcium source is CaO powder, and the silicon source is fumed SiO2 powder. The mass of the basalt fiber is 1 wt% of the total mass of the composite material; the mass of the metakaolin is 60 wt% of the mass of the silicon source. The molar ratio of calcium in the calcium source to silicon in the silicon source is 0.8:1. The water-to-gel ratio of the total mass of the water and gel material is 2:1; the mass of the PCE is 6.3 wt% of the total mass of the gel material; and the mass of the quartz sand is 3 times the total mass of the gel material (sand-gel ratio is 3). The total mass of the gel material is the sum of the masses of the calcium source, silicon source, and metakaolin.

[0051] A method for preparing a crack-resistant C-(A)-SH-based composite material includes the following steps: (1) Sample preparation S1. Dry mixing: The calcium source (CaO powder) and silicon source (vaporized SiO2 powder) are added to a planetary mixer and gently stirred at low speed for 50 r·min. -1 60 s allows the dry components to be evenly dispersed, resulting in a homogeneous dry mixture.

[0052] S2, One-time wet mixing: Completely dissolve PCE in deionized water to obtain a PCE solution. Add the PCE solution to the dry mixture obtained in step S1 at 150 r·min. -1 The basic slurry was obtained by stirring at a certain speed for 60 seconds. After stopping the machine, the slurry adhering to the stirring paddle and the tank wall was scraped to the bottom, and then stirred at 300 r·min. -1 Continue stirring for 60 seconds.

[0053] S3. Secondary wet mixing: Add quartz sand powder, metakaolin, and basalt fiber to the base slurry obtained in step S2, and gently stir at low speed for 50 r·min. -1 Stir for 60 seconds, then stir at medium speed for 150 rpm. -1 Stir for 120 seconds, then stir at high speed for 300 rpm. -1 Stir for 60 seconds to obtain a uniform composite slurry; S4. Molding and curing: Inject the composite slurry obtained in step S3 into a 40 mm × 40 mm × 160 mm mold and immediately seal it with a plastic film to prevent atmospheric CO2 from carbonizing Ca(OH)2.

[0054] (2) Maintenance Three parallel specimens were prepared. After molding, the mold was placed in a constant temperature and humidity chamber (20℃, 75% RH) for curing for 7 days; then demolded and cured under the same conditions for another 28 days.

[0055] (3) Characterization After curing, the samples were characterized at both macroscopic and microscopic scales, including flexural strength, compressive strength, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS).

[0056] This embodiment is designated as S11.

[0057] Example 2 Compared with Example 1, except that the content of basalt fiber was adjusted to 0.5 wt% of the total mass of the composite material, all other aspects were the same. This example is designated as S10.

[0058] Example 3 Compared with Example 1, except that the content of basalt fiber was adjusted to 1.5 wt% of the total mass of the composite material, all other aspects were the same. This example is designated as S12.

[0059] Comparative Example 1 A crack-resistant CSH-based composite material comprising the following raw materials: calcium source, silicon source, PCE, quartz sand and water.

[0060] In this embodiment, the calcium source is Ca(OH)₂, and the silicon source is fumed SiO₂. The molar ratio of calcium in the calcium source to silicon in the silicon source is 0.8:1. The water-to-gel ratio of the total mass of the water and the gel material is 2:1; the mass of the quartz sand is three times the total mass of the gel material (sand-gel ratio of 3). The total mass of the gel material is the sum of the masses of the calcium source and the silicon source.

[0061] A method for preparing a crack-resistant CSH-based composite material includes the following steps: (1) Sample preparation S1. Dry mixing: The calcium source (Ca(OH)2 powder) and silicon source (vaporized SiO2 powder) are added to a planetary shaft mixer and mixed at 50 r·min. -1 Stir for 60 seconds to evenly disperse the dry components and obtain a homogeneous dry mixture.

[0062] S2, First wet mixing: Add deionized water to the dry mixture obtained in step S1 at 150 r·min -1 The basic slurry was obtained by stirring at a certain speed for 60 seconds. After stopping the machine, the slurry adhering to the stirring paddle and the tank wall was scraped to the bottom, and then stirred at 300 r·min. -1 Continue stirring for 60 seconds.

[0063] S3. Secondary wet mixing: First, add quartz sand powder, metakaolin, and basalt fiber to the base slurry obtained in step S2, and then gently stir at low speed for 50 r·min. -1 Stir for 60 seconds, then stir at medium speed for 150 rpm. -1 Stir for 120 seconds, then stir at high speed for 300 rpm. -1 Stir for 60 seconds to obtain a uniform composite slurry; S4. Molding and curing: Inject the composite slurry obtained in step S3 into a 40 mm × 40 mm × 160 mm mold and immediately seal it with a plastic film to prevent atmospheric CO2 from carbonizing Ca(OH)2.

[0064] (2) Maintenance Three parallel specimens were prepared. After molding, the mold was placed in a constant temperature and humidity chamber (20℃, 75% RH) for curing for 7 days; then demolded and cured under the same conditions for another 28 days.

[0065] (3) Characterization After curing, the samples were characterized at both macroscopic and microscopic scales, including flexural strength, compressive strength, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS).

[0066] This comparative example is labeled S1.

[0067] Comparative Example 2 Compared to Comparative Example 1, everything was the same except that the calcium source was changed to CaO powder. This comparative example is designated as S2.

[0068] Comparative Example 3 A crack-resistant CSH-based composite material comprising the following raw materials: calcium source, silicon source, basalt fiber, PCE, quartz sand and water.

[0069] In this embodiment, the calcium source is CaO powder, and the silicon source is fumed SiO2 powder. The mass of the basalt fiber is 1 wt% of the total mass of the composite material. The molar ratio of calcium in the calcium source to silicon in the silicon source is 0.8:1. The water-to-gel ratio of the total mass of the water and gel material is 2:1; the mass of the PCE is 6.3 wt% of the total mass of the gel material; and the mass of the quartz sand is 3 times the total mass of the gel material (sand-gel ratio is 3). The total mass of the gel material is the sum of the masses of the calcium source and the silicon source.

[0070] A method for preparing a crack-resistant C-(A)-SH-based composite material includes the following steps: (1) Sample preparation S1. Dry mixing: The calcium source (CaO powder) and silicon source (vaporized SiO2 powder) are added to a planetary shaft mixer and mixed at 50 r·min. -1 Stir for 60 seconds to evenly disperse the dry components and obtain a homogeneous dry mixture.

[0071] S2, One-time wet mixing: Completely dissolve PCE in deionized water to obtain a PCE solution. Add the PCE solution to the dry mixture obtained in step S1 at 150 r·min. -1 The basic slurry was obtained by stirring at a certain speed for 60 seconds. After stopping the machine, the slurry adhering to the stirring paddle and the tank wall was scraped to the bottom, and then stirred at 300 r·min. -1 Continue stirring for 60 seconds.

[0072] S3, Secondary wet mixing: Add quartz sand powder and basalt fiber to the base slurry obtained in step S2, and stir gently at low speed for 50 r·min. -1Stir for 60 seconds, then stir at medium speed for 150 rpm. -1 Stir for 120 seconds, then stir at high speed for 300 rpm. -1 Stir for 60 seconds to obtain a uniform composite slurry; S4. Molding and curing: Inject the composite slurry obtained in step S3 into a 40 mm × 40 mm × 160 mm mold and immediately seal it with a plastic film to prevent atmospheric CO2 from carbonizing Ca(OH)2.

[0073] (2) Maintenance Three parallel specimens were prepared. After molding, the mold was placed in a constant temperature and humidity chamber (20℃, 75% RH) for curing for 7 days; then demolded and cured under the same conditions for another 28 days.

[0074] (3) Characterization After curing, the samples were characterized at both macroscopic and microscopic scales, including flexural strength, compressive strength, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS).

[0075] This comparative example is labeled S5.

[0076] Comparative Example 4 Compared with Comparative Example 3, everything was the same except that the mass of the basalt fiber was adjusted to 0.5 wt% of the total mass of the composite material. This comparative example is designated as S4.

[0077] Comparative Example 5 Compared with Comparative Example 3, except that the mass of the basalt fiber was adjusted to 1.5 wt% of the total mass of the composite material, everything else was the same. This comparative example is designated as S6.

[0078] Comparative Example 6 Compared to Comparative Example 3, this example is identical except that the basalt fiber is replaced with polypropylene fiber. This comparative example is designated as S3.

[0079] Comparative Example 7 A crack-resistant C-(A)-SH-based composite material comprising the following raw materials: calcium source, silicon source, metakaolin, PCE, quartz sand and water.

[0080] In this embodiment, the calcium source is CaO powder, and the silicon source is fumed SiO2 powder. The mass of metakaolin is 60 wt% of the mass of the silicon source. The molar ratio of calcium in the calcium source to silicon in the silicon source is 0.8:1. The water-to-gel ratio of the total mass of the water and gel material is 2:1; the mass of PCE is 6.3 wt% of the total mass of the gel material; and the mass of quartz sand is 3 times the total mass of the gel material (sand-gel ratio is 3). The total mass of the gel material is the sum of the masses of the calcium source, silicon source, and metakaolin.

[0081] A method for preparing a crack-resistant C-(A)-SH-based composite material includes the following steps: (1) Sample preparation S1. Dry mixing: The calcium source (CaO powder) and silicon source (vaporized SiO2 powder) are added to a planetary shaft mixer and mixed at 50 r·min. -1 60 s allows the dry components to be evenly dispersed, resulting in a homogeneous dry mixture.

[0082] S2, First wet mixing: Add deionized water to the dry mixture obtained in step S1, and stir at 150 rpm for 60 seconds to obtain the basic slurry. After stopping the machine, scrape the slurry adhering to the stirring paddle and the barrel wall to the bottom, and continue stirring at 300 rpm for 60 seconds.

[0083] S3. Secondary wet mixing: Add metakaolin and basalt fiber to the base slurry obtained in step S2, and stir gently at low speed for 50 r·min. -1 Stir for 60 seconds, then stir at medium speed for 150 rpm. -1 Stir for 120 seconds, then stir at high speed for 300 rpm. -1 Stir for 60 seconds to obtain a uniform composite slurry; S4. Molding and curing: Inject the composite slurry obtained in step S3 into a 40 mm × 40 mm × 160 mm mold and immediately seal it with a plastic film to prevent atmospheric CO2 from carbonizing Ca(OH)2.

[0084] (2) Maintenance Three parallel specimens were prepared. After molding, the mold was placed in a constant temperature and humidity chamber (20℃, 75% RH) for curing for 7 days; then demolded and cured under the same conditions for another 28 days.

[0085] (3) Characterization After curing, the samples were characterized at both macroscopic and microscopic scales, including flexural strength, compressive strength, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS).

[0086] This comparative example is labeled S8.

[0087] Comparative Example 8 Compared to Comparative Example 7, the mass of the metakaolin was adjusted to 30 wt% of the mass of the silicon source, while all other parameters remained the same. This comparative example is designated as S7.

[0088] Comparative Example 9 Compared to Comparative Example 7, the mass of the metakaolin was adjusted to 90 wt% of the mass of the silicon source, while all other parameters remained the same. This comparative example is designated as S9.

[0089] Performance comparison: I. Selection of Calcium Source Comparative Examples 1 (S1) and 2 (S2) selected Ca(OH)2 powder and CaO powder as calcium sources, respectively, and prepared mortars according to the above method. After curing for 28 days, high-purity CSH was generated in both examples. Figure 1 The flexural strengths were 0.4 MPa and 0.6 MPa, respectively, and the compressive strengths were 7.1 MPa and 8.8 MPa, respectively. Figure 2 , Figure 3 Superior mechanical properties Figure 4 Therefore, this invention uses active CaO as the calcium source.

[0090] II. Selection of Fiber Types Comparative Examples 3 (S5) and 6 (S3) selected basalt fiber and polypropylene fiber as the source of reinforcing fibers, respectively, and prepared mortars according to the above method. After curing for 28 days, high-purity CSH was generated in both cases. Figure 1 The flexural strengths were 0.8 MPa and 2.0 MPa, respectively, and the compressive strengths were 9.5 MPa and 8.1 MPa, respectively. Figure 2 , Figure 3 No through-cracks were observed in either Comparative Examples 3 (S5) or 6 (S3) during the curing process. Figure 4 In contrast, the basalt fibers in Comparative Example 3 (S5) bonded more tightly to the mortar matrix, with no obvious fiber pull-out observed, and the effect on improving flexural strength was more significant. Therefore, basalt fibers were selected as the reinforcing fibers in this application.

[0091] III. Selection of Basalt Fiber Dosage The basalt fibers in Comparative Examples 3-5 (S5, S4, S6) were 1 wt%, 0.5 wt%, and 1.5 wt% of the total mass of the composite material, respectively. Mortar was prepared according to the above method, and after curing for 28 days, high-purity CSH (Chemical Silicates) was generated in each group. Figure 1The flexural strengths were 2.0 MPa, 0.8 MPa, and 2.8 MPa, respectively, and the compressive strengths were 8.1 MPa, 5.3 MPa, and 8.3 MPa, respectively. Figure 2 , Figure 3 No through-cracks appeared in Comparative Examples 3-5 (S5, S4, S6) during the curing process. However, the addition of 0.5 wt% basalt fiber in Comparative Example 4 (S4) resulted in a significant decrease in compressive strength compared to Comparative Example 2 (without basalt fiber), which may be related to the interfacial heterogeneity between the mortar matrix and the fiber. This effect gradually weakened with increasing basalt fiber content; when the basalt fiber content was 1%, the material had good fluidity and minimal impact on practical construction adaptability.

[0092] IV. Selection of Metakaolin Dosage The metakaolin masses in Comparative Examples 7-9 (S8, S7, S9) were 60wt%, 30wt%, and 90wt% of the silicon source, respectively. Mortars prepared according to the above method were cured for 28 days, and high-purity C-(A)-SH (…) were generated in each group. Figure 1 The flexural strengths were 1.4 MPa, 0.8 MPa, and 1.3 MPa, respectively, and the compressive strengths were 19.8 MPa, 16 MPa, and 18.1 MPa, respectively. Figure 2 , Figure 3 The introduction of metakaolin significantly improved the compressive strength of the mortar, which may be related to the formation of a dense three-dimensional network C-(A)-SH structure. Figure 5 ).

[0093] V. Synergistic Modification of Basalt Fibers and Metakaolin In Examples 1-3 (S11, S10, S12), the mass of the basalt fiber was fixed at 1 wt% of the total mass of the composite material, and the mass of the metakaolin was 60 wt%, 30 wt%, and 90 wt% of the silicon source, respectively. Mortar was prepared according to the above method, and after curing for 28 days, high-purity C-(A)-SH (…) was generated in each group. Figure 1 , Figure 6 The flexural strengths were 2.6 MPa, 1.9 MPa, and 5.2 MPa, respectively, and the compressive strengths were 18.6 MPa, 18.3 MPa, and 19.4 MPa, respectively. Figure 2 , Figure 3 In Examples 1-3 (S11, S10, S12), no observable cracks appeared during the entire curing process. Figure 7The slight decrease in compressive strength of Comparative Example 7 (S8) compared to Example 1 (S11) is due to the heterogeneity between the fiber and the mortar matrix. Under the condition of synergistic modification with 1 wt% basalt fiber and 60 wt% metakaolinite (Example 1 (S11)), a dense and tough composite structure was formed. The refined pore structure, the uniformly distributed C-(A)-SH hydration products, and the fiber network tightly bonded to the matrix work together to significantly improve the flexural strength, compressive strength, high stability, and crack resistance of the material. Figure 5 ).

[0094] In general, the crack resistance mechanism of basalt fiber (BF) mainly relies on macroscopic physical bridging and crack deflection. The fiber significantly improves flexural strength and crack resistance by transferring stress across cracks and extending crack propagation paths. In contrast, the reinforcement mechanism of metakaolin (MK) operates at the nano- to micro-scale through chemical and physical mechanisms: its fine particles fill pores to refine the microstructure, while its pozzolanic reaction consumes calcium hydroxide to form additional CASH gel, thereby improving density, mechanical strength, and carbonization resistance. The BF / MK composite system exhibits a synergistic reinforcement mechanism: the MK-modified dense matrix provides stronger anchoring for the fibers, while the fibers compensate for the inherent brittleness of the MK-reinforced system. This multi-scale integration of nano- to micro-scale densification with macroscopic fiber toughening enables the composite material to achieve a balanced and excellent performance in terms of strength, crack resistance, and durability. Even after long-term storage in air, the modified mortar showed no signs of cracking or carbonization, demonstrating excellent durability under dry, air-exposed conditions. Its advantages, such as high durability due to its inorganic nature and lack of salt damage, highlight its enormous application potential in the protection and treatment of various stone cultural relics.

[0095] VI. Sandstone Bonding and Repair of Kizil Caves The slurry obtained in Example 1 (S11) was used for in-situ bonding and repair of sandstone in the Kizil Grottoes. After curing under high humidity for 7 days, it was further cured at room temperature for 28 days. The results showed that the slurry was densely packed, no cracking was observed at the repair interface, the material had good air permeability, and the bonding performance was stable and reliable. Figure 8 , Figure 9 Therefore, the material of this invention can be considered suitable for grouting and reinforcing microcracks in stone cultural relics, repairing historical masonry structures, preparing protective layers for stone surfaces in humid environments, and other building repair projects that require highly compatible and durable inorganic materials.

[0096] Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A crack-resistant C-(A)-SH-based composite material, characterized in that, It includes the following raw materials: Calcium source, silicon source, metakaolin, basalt fiber and water.

2. The crack-resistant C-(A)-SH-based composite material according to claim 1, characterized in that, The calcium source is calcium oxide or calcium hydroxide, and the silicon source is fumed silicon dioxide.

3. The crack-resistant C-(A)-SH-based composite material according to claim 1, characterized in that, The basalt fiber accounts for 0.55wt% to 1.5wt% of the total mass of the composite material. The mass of the metakaolin is 30wt% to 90wt% of the mass of the silicon source.

4. The crack-resistant C-(A)-SH-based composite material according to claim 1, characterized in that, The molar ratio of calcium in the calcium source to silicon in the silicon source is 0.6 to 1:

1.

5. The crack-resistant C-(A)-SH-based composite material according to claim 1, characterized in that, The water-gel ratio of the total mass of the water and gel material is 1.5~2.5:1; The total mass of the gel material is the sum of the masses of the calcium source, silicon source, and metakaolin.

6. The crack-resistant C-(A)-SH-based composite material according to claim 1, characterized in that, The composite material also includes a polycarboxylate superplasticizer, the mass of which is 4wt% to 7wt% of the total mass of the gel material, wherein the total mass of the gel material is the sum of the masses of the calcium source, silicon source and metakaolin. The polycarboxylate superplasticizer includes one or more of the following: methyl allyl ether type, methyl allyl ether type, or methacrylate type.

7. The crack-resistant C-(A)-SH-based composite material according to claim 1, characterized in that, The composite material also includes quartz sand, the mass of which is 2.5 to 3.5 times the total mass of the gel material, wherein the total mass of the gel material is the sum of the masses of the calcium source, silicon source, and metakaolin.

8. A method for preparing a crack-resistant C-(A)-SH-based composite material as described in any one of claims 1 to 7, characterized in that, The composite material is obtained by mixing calcium source, silicon source, metakaolin, basalt fiber and water, followed by stirring, molding and curing.

9. The method for preparing a crack-resistant C-(A)-SH-based composite material according to claim 8, characterized in that, The preparation method includes the following steps: S1. Dry mixing: The calcium source and silicon source are dry mixed to obtain a uniform dry mixture; S2, First wet mixing: Add water to the dry mixture obtained in step S1 and mix for the first time to obtain the basic slurry; S3. Secondary wet mixing: Add metakaolin and basalt fiber to the basic slurry obtained in step S2, and mix for the second time to obtain a uniform composite slurry. S4. Molding and curing: Inject the composite slurry obtained in step S3 into the mold, seal it and then cure it. When the composite material also includes a polycarboxylate superplasticizer, it is dissolved in deionized water and added in step S2; When the composite material also includes quartz sand, it is added together with metakaolin and basalt fiber in step S3.

10. The application of a crack-resistant C-(A)-SH-based composite material as described in any one of claims 1 to 7 in the preservation of stone cultural relics, characterized in that, The application is for fissure grouting, shallow surface reinforcement, or surface protection of sandstone or limestone cultural relics.

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