Polymer cement-based repairing material for stone sculptures and stone sculptures and repairing method of polymer cement-based repairing material

Abstract

The invention discloses a polymer cement-based repairing material for stone sculptures and a repairing method of the polymer cement-based repairing material, and belongs to the technical field of cultural relic repairing. The repairing material is prepared from the following components in parts by mass: 50 to 70 parts of PO.42.5 ordinary Portland cement, 20 to 30 parts of water, 5 to 15 parts of calcined kaolin, 0.03 to 1 part of nano silicon oxide, 1 to 3 parts of nano calcium carbonate, 0.01 to 0.03 part of organic silicon defoaming agent, 0.01 to 0.04 part of surfactant and 2 to 10 parts of vinyl acetate-ethylene copolymer. The polymer cement-based repairing material prepared by the invention can realize high bonding strength on a stone matrix and reversible removal at the same time. The polymer repairing material is simple in preparation process and green and environment-friendly in production, and has a wide application prospect in the field of repairing of cultural relics such as stone sculptures and the like.

Description

Technical Field

[0001] This invention belongs to the field of cultural relic repair technology, specifically relating to a polymer cement-based repair material for stone carvings and a repair method thereof. Background Technology

[0002] Stone carvings and sculptures possess significant historical and artistic value; however, due to long-term natural weathering and environmental erosion, many stone artifacts have suffered varying degrees of damage, including surface powdering, cracking, and peeling. Using repair materials with physicochemical properties similar to the original materials for structural restoration and surface protection is a widely recognized and effective technical approach in the current preservation of stone artifacts. Polymer-modified cement-based repair materials have gradually become an effective supplement and an important development direction for the restoration of stone artifacts. This technological development is mainly reflected in the application of high-performance polymer modifiers and the refined design of composite system formulations. Currently, commonly used technical approaches include: using polymer emulsions such as acrylates, epoxy resins, and polyurethanes to composite modify silicate cement matrices. The polymer phase can form a film and a three-dimensional network structure within the cement hydration products, thereby achieving a synergistic enhancement effect between the flexibility of organic polymers and the rigidity of the inorganic cement matrix, significantly improving the bond strength, flexural strength, and impermeability between the repair material and the stone matrix. In addition, by incorporating active mineral admixtures such as silica fume and ultrafine fly ash, the micropore structure of the composite system can be further optimized, thereby improving its anti-aging and environmental erosion resistance.

[0003] Nevertheless, these materials still face several key technical challenges in practical applications of cultural relic restoration. The primary issue lies in their conflict with the "reversibility" requirement in cultural relic protection principles. Existing cement-based materials exhibit high mechanical strength but poor volume stability after hydration, making them highly susceptible to secondary damage to the relic when removal or replacement is necessary. On the other hand, while polymer modification can improve the durability of cement-based materials to some extent, their performance deteriorates under complex natural environments, subject to the combined effects of freeze-thaw cycles, alternating wet and dry conditions, salt crystallization pressure, and biological erosion. This degradation leading to poor repair results remains a pressing issue. Therefore, developing novel stone cultural relic repair materials that combine excellent long-term durability with reversible construction performance remains a crucial scientific and technological challenge that urgently needs to be addressed in this field. Summary of the Invention

[0004] Based on the aforementioned shortcomings of the prior art, the purpose of this invention is to provide a polymer cement-based repair material for stone carvings, which has the characteristics of weather resistance, environmental friendliness, and reversible removal. It realizes the reversible removal of the repair material on the stone carving substrate, while further improving the mechanical properties and durability of the polymer cement-based material, enabling efficient repair of stone carvings.

[0005] The technical solution adopted in this invention is as follows: A polymer cement-based repair material for stone carvings, the formula of which is as follows by mass: 50-70 parts of PO·42.5 ordinary silicate cement, 20-30 parts of water, 5-15 parts of calcined kaolin, 0.3-1 parts of nano-silica, 1-3 parts of nano-calcium carbonate, 0.01-0.03 parts of organosilicon defoamer, 0.01-0.04 parts of surfactant, and 2-10 parts of vinyl acetate-ethylene copolymer.

[0006] Furthermore, the PO·42.5 ordinary silicate cement contains 60 parts, water 24 parts, calcined kaolin 7.5 parts, nano-silica 0.3 parts, nano-calcium carbonate 1 part, organosilicon defoamer 0.02 parts, surfactant 0.015 parts, and vinyl acetate-ethylene copolymer 4.8 parts.

[0007] Furthermore, the nano-silica has a particle size of 20-50 nm, wherein particles with a particle size of less than 30 nm account for more than 95%; the nano-calcium carbonate has a particle size of 100-500 nm, wherein particles with a particle size of less than 300 nm account for more than 95%; and the nano-calcium carbonate has a particle size of 100-500 nm, wherein particles with a particle size of less than 300 nm account for more than 95%.

[0008] Furthermore, the silicone defoamer is a water-emulsion silicone defoamer or a solid powder silicone defoamer.

[0009] Furthermore, the surfactant is sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, or sodium polyacrylate.

[0010] The principle of this invention is as follows: During the setting and hardening process, the -CC- long chains of the vinyl acetate-ethylene copolymer continuously polymerize in situ in the cement stone matrix to form a network structure, which interpenetrates with the -Si-O-Si- tetrahedral three-dimensional structure of the cement stone to form a three-dimensional flexible rigid two-phase homogeneous structure, thereby improving the mechanical properties of the polymer cement matrix. At the same time, the two nanomaterials play a filler effect and a pozzolanic activity effect, thereby improving the durability of the composite material.

[0011] Another objective of this invention is to provide a method for repairing stone carvings, using the polymer cement-based repair material described above, which features weather resistance, environmental friendliness, and reversible removal. The method steps are as follows:

[0012] S1. Preparation of nanomaterial dispersion

[0013] The surfactant was added to water and completely dissolved. Then, while stirring, nano-silica powder and nano-calcium carbonate powder were added separately to obtain a nanomaterial solution. The solution was then subjected to high-speed shearing and ultrasonic dispersion to obtain a uniformly mixed nanomaterial dispersion.

[0014] S2. Preparation of polymer cement-based repair paste

[0015] PO·42.5 ordinary silicate cement and calcined kaolin dry powder are mixed evenly, and the nanomaterial dispersion liquid obtained in step S1 is added and mechanically stirred to obtain a paste-like solid. Water, vinyl acetate-ethylene copolymer and organosilicon defoamer are added and mechanically stirred to mix evenly to obtain a cement-based material for stone carving repair.

[0016] S3, Repair materials for stone carvings and their reversible removal

[0017] Apply a thin film of vinyl acetate-ethylene copolymer to the cleaned stone carving substrate. After air drying and curing for 6 hours, apply cement-based material to the film substrate surface. Once it has solidified and hardened, the repair is complete. For reversible removal, drill a hole in the cement-based material to the depth of the vinyl acetate-ethylene copolymer film on the substrate surface and inject acetone. This allows for reversible removal of the cement-based material.

[0018] Furthermore, in step S1, during the preparation of the nanomaterial dispersion, the mass ratio of water to solid nanopowder is 10:1; the high-speed shearing rate is 3000-7000 rpm, the shearing time is 3-6 minutes, the ultrasonic power is 750W, and the ultrasonic time is 5-10 minutes. In step S2, during the preparation of the polymer cement-based repair paste, the mechanical stirring speed is 100-180 rpm, and the stirring time is 5-10 minutes.

[0019] Furthermore, in step S2, the vinyl acetate-ethylene copolymer is added in the form of a vinyl acetate-ethylene copolymer emulsion with a solid content of 54.5%.

[0020] Furthermore, in step S2, all the water includes water in the nanomaterial dispersion, water in the water-emulsion silicone defoamer, water in the vinyl acetate-ethylene copolymer emulsion, and added water, and the water:cement mass ratio is always maintained at 0.4:1.

[0021] Furthermore, in step S3, during the reversible removal process: an injection port is set every 10cm, 20cm, and 50cm, and the injection ports are arranged in a grid pattern. After injecting acetone, it is left to stand for 6-12 hours to repair the substrate detachment and achieve reversible removal.

[0022] The principle of this invention: The repair material of this invention is composed of a vinyl acetate-ethylene copolymer emulsion and cement. The polymer emulsion is uniformly dispersed in the cement paste to form a continuous phase, while the cement hydration products constitute an inorganic framework. These two components interpenetrate to form a three-dimensional organic-inorganic interpenetrating network structure. Furthermore, by incorporating nano-inorganic materials that exhibit both pozzolanic and microfiller effects, the structural density and weathering resistance of the composite material are further enhanced, resulting in a strong, tough, and highly durable repair material. Simultaneously, the vinyl acetate-ethylene copolymer is used to pretreat the interface with the repair substrate, effectively enhancing the bond strength between the repair material and the substrate. Based on the principle of "like dissolves like," this provides a basis for the reversible removal of the repair material using acetone when necessary. This design meets the requirements for high bond strength while adhering to the principle of minimal intervention in cultural relic restoration.

[0023] Advantages and benefits of the present invention:

[0024] 1. Excellent environmental friendliness and economy: The vinyl acetate-ethylene copolymer emulsion used does not contain volatile organic compounds (VOCs), making it environmentally friendly; at the same time, the raw material cost is low, the production process is simple, and it is in line with the concept of sustainable development.

[0025] 2. Significant Improvement in Mechanical Properties and Structural Toughness: By introducing polymer emulsions into cement paste, the synergistic process of cement hydration (active components such as C3S and C2S) and polymer crosslinking film formation is achieved. This process promotes the mutual induction and in-situ symbiosis of inorganic hydration products (such as CSH gel) and organic polymer carbon chains, forming a dense three-dimensional network structure that interpenetrates between organic and inorganic components. This structure fundamentally improves the toughness of cement paste, and its strengthening and toughening effect is superior to traditional fiber reinforcement methods, resulting in a significant improvement in the overall mechanical properties of the material.

[0026] 3. Excellent durability and resistance to environmental erosion: The continuous, dense three-dimensional organic film structure formed by the polymer in the system effectively blocks the transmission of moisture and corrosive media. In addition, the micro-filling and secondary hydration effects of nanomaterials significantly improve the water resistance, density and weathering resistance of the repair material, enabling it to adapt to more demanding long-term service environments.

[0027] 4. Reliable interfacial bonding and reversible repair process: Pre-treatment of the repair substrate interface with a homologous polymer emulsion greatly improves the compatibility and bonding strength between the new and old materials. More importantly, this design provides a prerequisite for the safe and non-destructive removal of the repair layer using solvents such as acetone when necessary in the future, thus simultaneously meeting the engineering requirements of high bonding strength and the principle of minimal intervention in cultural relic restoration. Attached Figure Description

[0028] Figure 1This describes the preparation process of polymer cement-based repair materials;

[0029] Figure 2 Optical morphology images of the prepared square and plate-shaped samples;

[0030] Figure 3 A schematic diagram of the three-dimensional network structure formed by polymer and cement stone;

[0031] Figure 4 The image shows the test process of the shear bond strength of the sample and the cross-sectional morphology after failure.

[0032] Figure 5 This is a schematic diagram of the microstructure of the sample. Detailed Implementation

[0033] The technical solutions of this invention are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on this invention are within the scope of protection of this invention. Unless otherwise specified in the specific circumstances, the numerical ranges listed herein include upper and lower limits, as well as all integers and fractions within that range, but are not limited to the specific values ​​listed when the range is defined.

[0034] Example 1: This example provides a method for repairing stone carvings. The polymer cement-based repair material used has the following formula: 1440g of PO·42.5 ordinary Portland cement, 648g of water, 180g of calcined kaolin, 19.2g of nano-silica, 24g of nano-calcium carbonate, 0.48g of solid powdered organosilicon defoamer, 0.36g of sodium dodecyl sulfate, and 115.2g of vinyl acetate-ethylene copolymer. Figure 1 As shown, the method includes the following steps:

[0035] 1) Sodium dodecyl sulfate was added to water and completely dissolved. While stirring, nano-silica powder and nano-calcium carbonate powder were added separately to obtain a nanomaterial solution. The solution was sheared at a high speed of 5000 rpm for 3 minutes. The resulting solution was then ultrasonically dispersed at 20% power for 5 minutes to obtain a uniformly mixed nanomaterial dispersion.

[0036] 2) Mix PO·42.5 ordinary silicate cement and calcined kaolin dry powder evenly, add the nanomaterial dispersion prepared in step 1), and mechanically stir at a speed of 120 rpm for 5 minutes to obtain a paste-like solid. Add water, vinyl acetate-ethylene copolymer and organosilicon defoamer, and mechanically stir at a speed of 120 rpm for 5 minutes to mix evenly to obtain a cement-based material for stone carving repair.

[0037] 3) Apply a thin film of vinyl acetate-ethylene copolymer to the cleaned stone carving substrate, with a thickness controlled at 400μm±100μm. After air drying and curing for 6 hours, apply cement-based material to the film substrate surface. Allow it to solidify and harden to complete the repair. For reversible removal, install an injection port every 20cm in a grid pattern on the polymer cement-based repair material, drilling to the depth of the vinyl acetate-ethylene copolymer film on the substrate surface. Inject acetone, let stand for 6 hours, and the repaired substrate will detach, allowing for reversible removal.

[0038] Example 2: The only difference between Example 2 and Example 1 is the raw materials and proportions of the aerogel as follows: 1260g of PO 42.5 ordinary silicate cement, 648g of water, 360g of calcined kaolin, 14.4g of nano-silica, 36g of nano-calcium carbonate, 0.24g of solid powder organosilicon defoamer, 0.36g of hexadecyltrimethylammonium bromide, and 115.2g of vinyl acetate-ethylene copolymer.

[0039] Example 3: The only difference between Example 3 and Example 1 is the raw materials and the proportions as follows: PO 42.5 ordinary silicate cement 1440g, water 648g, calcined kaolin 180g, nano silica 7.2g, nano calcium carbonate 24g, water-emulsion type silicone defoamer 0.48g, sodium polyacrylate 0.36g, and vinyl acetate-ethylene copolymer 230.4g.

[0040] Example 4: The only difference between Example 4 and Example 1 is the raw materials and the proportions as follows: 1560g of PO·42.5 ordinary silicate cement, 648g of water, 60g of calcined kaolin, 7.2g of nano-silica, 24g of nano-calcium carbonate, 0.36g of water-emulsion type silicone defoamer, 0.48g of sodium polyacrylate, and 60g of vinyl acetate-ethylene copolymer.

[0041] Comparative Example 1: This example is an adjustment based on Example 1, except that nano-silica and nano-calcium carbonate are not added. The amounts of other raw materials and the preparation method are the same as in Example 1.

[0042] Comparative Example 2: This example is an adjustment to Example 1, except that vinyl acetate-ethylene copolymer is not added. The amounts of other raw materials and the preparation method are the same as in Example 1.

[0043] Comparative Example 3: Comparative Example 2 and Example 1 have the same raw materials and proportions, but differ in that the preparation steps of the reversible polymer cement-based repair material are as follows:

[0044] 1) Mix nano-silica, nano-calcium carbonate, sodium dodecyl sulfate, cement and kaolin by mechanical stirring at 150 rpm for 10 minutes until homogeneous;

[0045] 2) Add vinyl acetate-ethylene copolymer and organosilicon defoamer to the uniformly mixed dry powder and then mechanically stir at a speed of 180 rpm for 10 minutes to mix evenly, to obtain a cement-based material for stone carving repair.

[0046] 3) Apply a thin film of vinyl acetate-ethylene copolymer to the cleaned stone carving substrate, with a thickness controlled at 400μm±100μm. After air drying and curing for 10 hours, apply cement-based material to the film substrate surface. Allow it to solidify and harden to complete the repair. For reversible removal, install an injection port every 50cm in the polymer cement-based repair material, arranged in a grid pattern. Drill holes to the depth of the vinyl acetate-ethylene copolymer film on the substrate surface, inject acetone, and let stand for 6 hours. The repaired substrate will then detach, allowing for reversible removal.

[0047] Testing and Experiment

[0048] Experiment 1: Flowability and setting time tests were conducted on Examples 1-4 and Comparative Examples 1-3 according to standards GB / T 2419-2005 and GB / T 1346-2011. The test results are shown in Table 1.

[0049] Table 1 Performance of Polymer Cementitious Repair Materials

[0050] category Liquidity (mm) Initial setting time (min) Final setting time (min) Example 1 145 221 283 Example 2 93 264 377 Example 3 115 281 413 Example 4 193 169 223 Comparative Example 1 171 198 256 Comparative Example 2 208 171 225 Comparative Example 3 106 261 347

[0051] The results show that the workability of Examples 1-4 varies significantly with different material ratios. On the one hand, increasing the content of nanomaterials and calcined kaolin reduces the free water in the system. Secondly, increasing the content of vinyl acetate-ethylene copolymer increases the viscosity of the polymer cementitious material, thus reducing the system's fluidity. On the other hand, calcined kaolin, nano-calcium carbonate, and nano-silica have low early hydration activity. Furthermore, the incorporation of polymer polymers reduces the crystal nucleation process of CSH, which severely hinders the cement hydration reaction, leading to prolonged setting time. The workability test results of Examples 1-4 and Comparative Examples 1 and 2 indicate that the fluidity of the polymer cementitious material is directly related to the nanomaterials and vinyl acetate-ethylene copolymer, especially the latter. Comparative Example 3 shows that directly incorporating nanomaterials into the cement matrix without dispersion treatment severely affects its fluidity and setting time. For repair materials, excessive fluidity leads to sagging, while insufficient fluidity makes smoothing difficult. The fluidity of Examples 1 and 3 indicates a workability state conducive to construction.

[0052] Experiment 2: The compressive and flexural strengths of the polymer cementitious repair materials of Examples 1-4 and Comparative Examples 1-3, as well as the shear bond strength of the corresponding materials on concrete substrates, were tested at 28 days according to the standard GB / T 17671-2021. The results are shown in Table 2 (test samples are shown in Table 2). Figure 2 (As shown).

[0053] Table 2 Mechanical properties of polymer cementitious repair materials

[0054] category Compressive strength (MPa) Flexural strength (MPa) Shear bond strength (MPa) Example 1 54.01 7.21 2.77 Example 2 48.63 6.13 2.68 Example 3 42.36 8.56 3.45 Example 4 58.83 4.77 1.87 Comparative Example 1 45.15 6.11 2.73 Comparative Example 2 51.34 5.63 1.42 Comparative Example 3 37.69 4.25 2.15

[0055] The results showed that nano-silica and nano-calcium carbonate significantly improved the compressive strength of polymer cementitious materials, while vinyl acetate-ethylene copolymer significantly improved the flexural strength. Compared with Example 3, doubling the vinyl acetate-ethylene copolymer content in Example 1 increased the flexural strength by 17.8%. The addition of polymer emulsion also increased the porosity of the material, leading to a decrease in flexural strength. The nanopowder could act as a filler, increasing the density of the composite material and thus improving the compressive strength, compensating for the strength reduction caused by the addition of polymer emulsion. The shear bond strength test results of Examples 1-4 and Comparative Examples 1-3 indicate that the higher the vinyl acetate-ethylene copolymer content in the composite material, the greater the shear bond strength of the polymer cementitious material (the shear bond test process and the fracture morphology after failure are shown in Figure 1-3). Figure 4 (As shown). This is because the more vinyl acetate-ethylene copolymer in the composite material, the better its compatibility with the interface, the fewer defects in the interface transition zone, and the higher the strength (microstructure as shown). Figure 5 (As shown).

[0056] Experiment 3: The samples prepared in Example 1 and Comparative Examples 1-2 were subjected to a sodium sulfate robustness test according to the length measurement method in standard GB / T 749-2008 to evaluate the materials' resistance to salt crystallization weathering. The specimens were subjected to wet-dry cycles with a 5% sodium sulfate solution. The expansion rate was tested after 15 and 30 cycles, each lasting 24 hours. The test results are shown in Table 3. The samples prepared in Example 1 and Comparative Examples 1-2 were subjected to a neutral salt spray test to accelerate the evaluation of the materials' corrosion resistance. The test method was based on national standard GB / T 10125-2021. The test solution was a 5% sodium chloride solution, the chamber temperature was maintained at 35℃, and the specimens were sprayed continuously for 720 hours. The surface morphology was observed, and the compressive strength retention rate was measured. The test results are shown in Table 4. The samples prepared in Example 1 and Comparative Examples 1-2 were subjected to a chloride ion penetration resistance test according to GB / T 50082-2009. The specimens, cured to the specified age, were processed into cylinders with a diameter of 100 mm and a height of 50 mm. After being vacuum-saturated with water, they were installed in an electrical flux testing device. 3.0% NaCl solution and 0.3 mol / L NaOH solution were injected into both sides of the specimen, respectively, and a constant DC voltage of 60 V was applied. The test was conducted continuously for 6 hours, and the total electrical charge passing through the specimen was recorded. The test results are shown in Table 5.

[0057] Table 3 Results of the Sodium Sulfate Robustness Test

[0058] category Expansion rate (%) after 15 cycles Expansion rate (%) after 30 cycles Example 1 0.012 0.025 Comparative Example 1 0.085 0.183 Comparative Example 2 0.035 0.065

[0059] The results show that after 30 cycles of wet and dry sodium sulfate, the expansion rate of Example 1 provided by the present invention is only 0.025%, which is much lower than that of Comparative Example B (without polymer, 0.182%) and Comparative Example C (without nanomaterials, 0.068%). This indicates that there is a significant synergistic enhancement effect between polymers and nanomaterials, and the combined effect of the two is what makes the material achieve the best durability.

[0060] Table 4. Salt spray test results

[0061] category Appearance Strength retention rate (%) Example 1 The surface is intact and shows no obvious changes. 97 Comparative Example 1 Indicates the presence of white crystals 61 Comparative Example 2 The surface is rough, with a small amount of salt precipitated. 82

[0062] Table 5 Results of Electricity Flux Test

[0063] category The electrical flux Q(C) passing through in 6 hours Example 1 385.7 Comparative Example 1 1337.4 Comparative Example 2 1641.6

[0064] The results show that the filling effect of nanomaterials has a significant effect on improving the density of composite materials and thus enhancing their resistance to salt spray erosion. Example 1 exhibits the highest strength retention rate, with only 3% strength loss, and the electrical flux passing through it after 6 hours is only 385.7C, far lower than that of Comparative Examples 1 and 2. This indicates that the combination of organic polymers and inorganic nanomaterials achieves synergistic reinforcement, improving the durability of polymer cement-based materials.

[0065] Experiment 4: The samples of Example 1 and Comparative Example 3 were drilled to the bonding interface, acetone was injected, and the shear bond strength of the samples after soaking for different times was tested. The results are shown in Table 6.

[0066] Table 6 Shear bond strength after acetone immersion for different times

[0067] category 1h (MPa) 3h (MPa) 6h (MPa) 9h (MPa) Example 1 1.12 0.47 0.12 0.04 Comparative Example 3 1.45 1.10 0.64 0.36

[0068] The results show that the shear bond strength of Example 1 decreases rapidly with increasing acetone soaking time, and almost completely loses its adhesiveness after 9 hours of soaking, enabling reversible removal. In contrast, Comparative Example 3, after 9 hours of soaking, still maintains a bond strength of 0.36 MPa, indicating incomplete detachment. This demonstrates that achieving reversible removal requires careful spacing of the acetone injection ports; too large a spacing leads to insufficient acetone dissolution, while too small a spacing increases acetone consumption, potentially causing environmental pollution.

[0069] As can be seen from the above examples and comparative examples, the entire repair process of the present invention is simple and the raw material cost is low, which can well solve the technical requirements of good bonding performance and reversible removal in cultural relic restoration.

Claims

1. A polymer cement-based repair material for stone carvings and engravings, characterized in that, The formula, by weight parts, is as follows: 50-70 parts of PO·42.5 ordinary silicate cement, 20-30 parts of water, 5-15 parts of calcined kaolin, 0.3-1 parts of nano-silica, 1-3 parts of nano-calcium carbonate, 0.01-0.03 parts of organosilicon defoamer, 0.01-0.04 parts of surfactant, and 2-10 parts of vinyl acetate-ethylene copolymer.

2. The polymer cement-based repair material for stone carvings and engravings according to claim 1, characterized in that, The PO·42.5 ordinary silicate cement consists of 60 parts, water 24 parts, calcined kaolin 7.5 parts, nano-silica 0.3 parts, nano-calcium carbonate 1 part, organosilicon defoamer 0.02 parts, surfactant 0.015 parts, and vinyl acetate-ethylene copolymer 4.8 parts.

3. The polymer cement-based repair material for stone carvings and engravings according to claim 1, characterized in that, The nano-silica has a particle size of 20-50 nm, of which particles with a particle size of less than 30 nm account for more than 95%; the nano-calcium carbonate has a particle size of 100-500 nm, of which particles with a particle size of less than 300 nm account for more than 95%; the nano-calcium carbonate has a particle size of 100-500 nm, of which particles with a particle size of less than 300 nm account for more than 95%.

4. The polymer cement-based repair material for stone carvings and engravings according to claim 1, characterized in that, The silicone defoamer is a water-emulsion type silicone defoamer or a solid powder silicone defoamer.

5. A polymer cement-based repair material for stone carvings and engravings according to claim 1, characterized in that, The surfactant is sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, or sodium polyacrylate.

6. A method for repairing stone carvings, using a polymer cement-based repair material for stone carvings as described in any one of claims 1-5, the method comprising the following steps: S1. Preparation of nanomaterial dispersion The surfactant was added to water and completely dissolved. Then, while stirring, nano-silica powder and nano-calcium carbonate powder were added separately to obtain a nanomaterial solution. The solution was then subjected to high-speed shearing and ultrasonic dispersion to obtain a uniformly mixed nanomaterial dispersion. S2. Preparation of polymer cement-based repair paste PO·42.5 ordinary silicate cement and calcined kaolin dry powder are mixed evenly, and the nanomaterial dispersion liquid obtained in step S1 is added and mechanically stirred to obtain a paste-like solid. Water, vinyl acetate-ethylene copolymer and organosilicon defoamer are added and mechanically stirred to mix evenly to obtain a cement-based material for stone carving repair. S3, Repair materials for stone carvings and their reversible removal Apply a thin film of vinyl acetate-ethylene copolymer to the cleaned stone carving substrate. After it has air-dried and cured for 6 hours, apply cement-based material to the film substrate surface. Once it has solidified and hardened, the repair is complete. To achieve reversible removal, drill a hole in the cement-based material to the depth of the vinyl acetate-ethylene copolymer film on the substrate surface and inject acetone. This allows for reversible removal of the cement-based material.

7. A method for repairing stone carvings according to claim 6, characterized in that, In step S1, during the preparation of the nanomaterial dispersion, the mass ratio of water to solid nanopowder is 10:1; the high-speed shearing rate is 3000-7000 rpm, the shearing time is 3-6 minutes, the ultrasonic power is 750W, and the ultrasonic time is 5-10 minutes. In step S2, during the preparation of the polymer cement-based repair paste, the mechanical stirring speed is 100-180 rpm, and the stirring time is 5-10 minutes.

8. A method for repairing stone carvings according to claim 6, characterized in that, In step S2, the vinyl acetate-ethylene copolymer is added in the form of a vinyl acetate-ethylene copolymer emulsion with a solid content of 54.5%.

9. A method for repairing stone carvings according to claim 6, characterized in that, In step S2, all the water includes water in the nanomaterial dispersion, water in the water-emulsion silicone defoamer, water in the vinyl acetate-ethylene copolymer emulsion, and added water, and the water:cement mass ratio is always maintained at 0.4:

1.

10. A method for repairing stone carvings according to claim 6, characterized in that, Step S3, during the reversible removal process: an injection port is set every 10cm, 20cm, and 50cm, and the injection ports are arranged in a grid pattern. After injecting acetone, let it stand for 6-12 hours to repair the substrate detachment and achieve reversible removal.

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