Natural hydraulic lime-based mortar for cultural and insurance building restoration and preparation method of natural hydraulic lime-based mortar

Abstract

The invention discloses natural hydraulic lime-based mortar for cultural and cultural conservation building repair and a preparation method thereof, and belongs to the technical field of building materials, the mortar contains a microcapsule structure, is applied to cultural and cultural conservation building repair and has a water absorption swelling effect, and when the mortar is washed by rainwater, microcapsules can absorb water and swell to promote core layer substances to be released, so that the water absorption swelling effect is achieved; when the repairing layer is in contact with urea, urea is decomposed through urease to generate carbonate, and the carbonate is combined with calcium ions to form calcium carbonate precipitates, so that the cultural and cultural conservation building is reinforced under rain wash, and the situation that the repairing layer falls off due to long-term rain wash is avoided; the stripped calcium-based diatomite can be used as a silicon source to enhance the hydration effect of the natural hydraulic lime, the hydration effect can generate calcium silicate gel and ettringite on the surface of the cultural and cultural protection building, the ettringite is a needle-like substance, has expansibility and can be inserted into the gel to serve as an early reinforcing phase, and the expansion effect can extrude the microcapsules to promote the release of the microcapsules, so that the microcapsule release is promoted; the deposition of calcium carbonate is synergistically promoted.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically a natural hydraulic lime-based mortar for the restoration of cultural heritage buildings and its preparation method. Background Technology

[0002] my country boasts a diverse array of ancient buildings, representing a precious cultural heritage that embodies rich history and tradition. However, years of natural erosion, coupled with human-caused damage, have led to varying degrees of aging and damage in many ancient structures, including cracks, peeling, and even collapse. While traditional methods of restoring ancient buildings are effective, they are typically time-consuming, complex, and require a high level of expertise. Furthermore, conventional cement-based materials often present serious compatibility issues with the inherent properties of ancient architecture.

[0003] Traditional air-hardening lime has good compatibility with ancient building substrates and is widely used in the restoration of ancient buildings. However, traditional air-hardening lime has slow strength development, large drying shrinkage, and high water demand, making it difficult to meet the requirements of rapid molding. In contrast, natural hydraulic lime combines the advantages of both hydraulic and air-hardening properties, exhibiting faster strength development, smaller drying shrinkage, and excellent air permeability. It also has better compatibility with ancient building substrates and holds promise for use in the restoration of ancient buildings.

[0004] After the restoration of ancient buildings, rainwater erosion has become one of the core natural causes of the detachment of the restoration layer. The erosion of the restoration layer by rainwater is not a simple surface erosion, but rather a progressive process of physical impact, water penetration, and interface damage. During rainfall, the impact force of raindrops directly wears down the hydration products on the surface of the restoration mortar. Especially for materials with insufficient strength development or loose structure, the surface is easily washed away and becomes sandy, gradually losing its integrity. At the same time, rainwater can penetrate through the capillary pores of the mortar and the interface gaps between the restoration layer and the ancient building substrate, diluting the internal cementitious system, leading to the loss of hydration products and weakening the strength of the mortar itself. Summary of the Invention

[0005] The purpose of this invention is to provide a natural hydraulic lime-based mortar for the restoration of cultural heritage buildings and its preparation method. The mortar contains a self-synthesized multifunctional composite aerogel with a microcapsule structure. When applied to the restoration of cultural heritage buildings, it has a water-absorbing and swelling effect. When exposed to rainwater, the microcapsules can absorb water and swell, causing the core material to be released. When in contact with urea, urease decomposes the urea to produce carbonate ions, which combine with calcium ions to form calcium carbonate precipitate. This achieves reinforcement of cultural heritage buildings under rainwater erosion and avoids the peeling of the repair layer caused by long-term rainwater erosion.

[0006] The objective of this invention can be achieved through the following technical solutions: A method for preparing natural hydraulic lime-based mortar for the restoration of cultural heritage buildings includes the following steps: Step 1: By vacuum impregnation, sodium bicarbonate solution is fully introduced into the pores of diatomaceous earth, reacting with calcium chloride to generate calcium carbonate which is deposited in the pores and on the surface of the diatomaceous earth to obtain calcium-based diatomaceous earth.

[0007] Step 2: The diatomaceous earth aggregates are broken down by the combined action of microwave heating and mechanical stirring, and the diatomaceous earth sheets are then dispersed and exfoliated by ultrasonication to prepare exfoliated calcium-based diatomaceous earth.

[0008] Step 3: Using exfoliated calcium-based diatomaceous earth as a carrier, a high-molecular matrix with adhesive properties is formed by sodium alginate and polyvinyl alcohol. After encapsulating the microbial agent, the cross-linking effect of calcium ions is used to form gel microspheres, thus obtaining the diatomaceous earth composite microbial agent.

[0009] Step 4: Using polyvinyl alcohol as a binder, carboxylated cellulose nanofibers are dispersed in water to form a carboxylated cellulose nanofiber precursor suspension, which is then combined with diatomaceous earth composite microbial agent to prepare a multifunctional composite aerogel.

[0010] Step 5: Mix NHL5 type natural hydraulic lime, quartz sand, limestone powder, polycarboxylate superplasticizer, multifunctional composite aerogel, urea and water, and stir at 50-52 r / min for 10-15 min to obtain natural hydraulic lime-based mortar for cultural heritage building restoration.

[0011] Furthermore, the dosage ratio of NHL5 type natural hydraulic lime, quartz sand, limestone powder, polycarboxylate superplasticizer, multifunctional composite aerogel, urea and water is 600-700g: 150-200g: 50-70g: 1-2g: 20-30g: 4-5g: 100-120g.

[0012] Furthermore, the specific preparation steps for calcium-based diatomaceous earth are as follows: Diatomaceous earth and a sodium bicarbonate solution with a mass fraction of 10-12% were added to a reaction vessel and impregnated under vacuum at 20-25℃ and 500-600 r / min for 2-3 hours. Then, a calcium chloride solution with a mass fraction of 30-40% was added and the reaction was continued for 1-2 hours. The mixture was then filtered, and the filter cake was washed 2-4 times with deionized water and anhydrous ethanol, respectively. The mixture was then dried under vacuum at 60-70℃ for 1-2 hours to obtain calcium-based diatomaceous earth.

[0013] Furthermore, the ratio of diatomaceous earth, sodium bicarbonate solution, and calcium chloride solution is 100-120g: 300-400mL: 120-130mL.

[0014] Furthermore, the specific preparation steps for exfoliated calcium-based diatomaceous earth are as follows: Calcium-based diatomaceous earth, deionized water, and anhydrous ethanol were added to a reaction vessel and stirred for 10-12 minutes at 20-25℃ and 500-600 r / min. Then, the mixture was heated to 60-65℃, microwaved at 600W for 1-2 hours, ultrasonically dispersed for 1-1.5 hours, and vacuum dried at 60-70℃ for 1-2 hours to obtain exfoliated calcium-based diatomaceous earth.

[0015] Furthermore, the ratio of calcium-based diatomaceous earth, deionized water, and anhydrous ethanol is 80-82g: 1-1.5L: 3-4L.

[0016] Furthermore, the specific preparation steps of the microbial inoculant are as follows: The culture medium was prepared using the formula ATCC 1376 NH4-YE recommended by the American Culture Collection Center. The culture medium was then sterilized at 120-122℃ for 20-22 minutes, followed by UV sterilization on a clean bench with ventilation. Once the culture medium cooled to room temperature, it was transferred to a container, and *Bacillus pasteurellii* was added using a sterile pipette to obtain the bacterial suspension. The volume ratio of *Bacillus pasteurellii* to the culture medium was 1:100. The bacterial suspension was then placed in a constant temperature shaking incubator at 28-30℃ for 48-50 hours to obtain the microbial inoculum.

[0017] Furthermore, the specific preparation steps of the diatomaceous earth composite microbial agent are as follows: Sodium alginate, polyvinyl alcohol, and deionized water were added to a reaction vessel and stirred for 10-12 minutes at 20-25℃ and 500-600 r / min. Then, microbial inoculants were added, and stirring was continued for 30-40 minutes to obtain a mixed solution. The mixed solution was then added dropwise to a crosslinking solution containing 3-4% calcium chloride solution and 5-6% boric acid solution. Then, calcium-based diatomaceous earth was added, and stirring was continued for 1-2 hours. The mixture was filtered, and the filter cake was washed 2-4 times with deionized water and anhydrous ethanol, respectively. The cake was then vacuum dried at -20℃ for 1-2 hours to obtain a diatomaceous earth composite microbial inoculant.

[0018] Furthermore, the ratio of sodium alginate, polyvinyl alcohol, deionized water, and microbial agent is 50-60g: 40-50g: 700-800mL: 5-10g.

[0019] Furthermore, the ratio of the mixed solution, cross-linking solution, and exfoliated calcium-based diatomaceous earth is 200-300 mL: 800-900 mL: 70-72 g.

[0020] Furthermore, the specific preparation steps of the multifunctional composite aerogel are as follows: Carboxylated cellulose nanofiber powder and deionized water were stirred and mixed to obtain a carboxylated cellulose nanofiber precursor suspension. The carboxylated cellulose nanofiber precursor suspension was placed in a reaction vessel and stirred for 30-40 min at 70-75℃ and 500-600 r / min. Then, diatomaceous earth composite microbial agent and polyvinyl alcohol were added, and stirring was continued for 4-5 h. The mixture was then ultrasonically dispersed in an ultrasonic disperser with an ultrasonic intensity of 600 W for 1-1.2 h, frozen at -5℃ for 30-40 min, and vacuum dried at -20℃ for 22-24 h to obtain a multifunctional composite aerogel.

[0021] Furthermore, the ratio of carboxylated cellulose nanofiber precursor suspension, diatomaceous earth composite microbial agent, and polyvinyl alcohol is 800-900g: 30-40g: 10-20g.

[0022] The beneficial effects of this invention are: 1. The natural hydraulic lime-based mortar for the restoration of cultural heritage buildings prepared in this invention contains a self-synthesized multifunctional composite aerogel. The multifunctional composite aerogel contains a microcapsule structure. When applied to the restoration of cultural heritage buildings, it has a water-absorbing and swelling effect. When exposed to rainwater, the microcapsules can absorb water and swell, causing the core material to be released. When in contact with urea, urease decomposes the urea to produce carbonate ions, which combine with calcium ions to form calcium carbonate precipitate. This achieves reinforcement of cultural heritage buildings under rainwater erosion and avoids the peeling of the repair layer caused by long-term rainwater erosion.

[0023] 2. The multifunctional composite aerogel of the present invention uses exfoliated calcium-based diatomaceous earth as a carrier, with Bacillus pasteurella as the core layer and polyvinyl alcohol-modified sodium alginate microcapsules as the shell layer. The large specific surface area of ​​the exfoliated calcium-based diatomaceous earth can provide abundant sites for the loading of microcapsules, preventing them from falling off. In addition, the surface contains abundant calcium ion sites, which can promote the cross-linking degree of polyvinyl alcohol and sodium alginate, and improve the overall strength of the microcapsules.

[0024] 3. The multifunctional composite aerogel of the present invention is a composite of carboxylated cellulose nanofibers and diatomaceous earth composite microbial agents bonded together with polyvinyl alcohol. The surface contains a rough, porous structure with interwoven fibers, giving it good structural compatibility. It is suitable for the repair of ancient building components with complex shapes. Since the shell of the diatomaceous earth composite microbial agent is pre-modified with polyvinyl alcohol, the microcapsules can serve as secondary bonding nodes rather than isolated dispersed particles, ensuring the uniform dispersion of the microcapsules. At this time, the microcapsules also play a bridging role, improving the compatibility of the diatomaceous earth composite microbial agent.

[0025] 4. The exfoliated calcium-based diatomaceous earth of the present invention can be used as a silicon source to enhance the hydration of natural hydraulic lime. The hydration process can generate calcium silicate gel and ettringite on the surface of cultural heritage buildings. ettringite is a needle-like substance with expansibility, which can be inserted into the gel as an early reinforcing phase. The expansibility will squeeze the microcapsules, promote the release of the microcapsules, and synergistically promote the deposition of calcium carbonate. Attached Figure Description

[0026] Figure 1 This is a SEM image of the calcium-based diatomite in Example 3.

[0027] Figure 2 This is a SEM image of the calcium-based diatomaceous earth stripped in Example 3.

[0028] Figure 3 This is a SEM image of the multifunctional composite aerogel in Example 3. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1: A method for preparing natural hydraulic lime-based mortar for the restoration of cultural heritage buildings, comprising the following steps: S1: Add 100g of diatomaceous earth and 300mL of 10% sodium bicarbonate solution to a reaction vessel, and impregnate under vacuum at 20℃ and 500r / min for 2h. Then add 120mL of 30% calcium chloride solution and continue the reaction for 1h. Filter the mixture and wash the filter cake twice with deionized water and anhydrous ethanol, respectively. Dry it under vacuum at 60℃ for 1h to obtain calcium-based diatomaceous earth.

[0031] S2: Add 80g of calcium-based diatomaceous earth, 1L of deionized water and 3L of anhydrous ethanol to a reaction vessel, stir for 10min at 20℃ and 500r / min, then heat to 60℃, microwave stir at 600W for 1h, ultrasonically disperse for 1h, and vacuum dry at 60℃ for 1h to obtain exfoliated calcium-based diatomaceous earth.

[0032] S3: The culture medium was prepared using the formula ATCC 1376 NH4-YE recommended by the American Culture Collection Center. The culture medium was then sterilized at 120℃ for 20 minutes, and then placed on a clean bench for UV sterilization and ventilation. When the temperature of the culture medium dropped to room temperature, the culture medium was taken into a container, and Bacillus pasteurellii was added to the culture medium using a sterile pipette to obtain the bacterial solution. The volume ratio of Bacillus pasteurellii to culture medium was 1:100. The bacterial solution was placed in a constant temperature shaking incubator for incubation at 28℃ for 48 hours to obtain the microbial inoculum.

[0033] S4: Add 50g sodium alginate, 40g polyvinyl alcohol and 700mL deionized water to a reaction vessel and stir for 10min at 20℃ and 500r / min. Then add 5g microbial agent and continue stirring for 30min to obtain a mixed solution. Add 200mL of the mixed solution dropwise to 800mL of a crosslinking solution containing 3% calcium chloride solution and 5% boric acid solution. Then add 70g of calcium-based diatomaceous earth and continue stirring for 1h. Filter and wash the filter cake twice with deionized water and anhydrous ethanol, respectively. Dry under vacuum at -20℃ for 1h to obtain diatomaceous earth composite microbial agent.

[0034] S5: Carboxylated cellulose nanofiber powder and deionized water were stirred and mixed to obtain a carboxylated cellulose nanofiber precursor suspension; 800g of the carboxylated cellulose nanofiber precursor suspension was placed in a reaction vessel and stirred for 30min at 70℃ and 500r / min; then 30g of diatomaceous earth composite microbial agent and 10g of polyvinyl alcohol were added and stirred for 4h; ultrasonic dispersion was performed in an ultrasonic disperser with an ultrasonic intensity of 600W for 1h; freezing was performed at -5℃ for 30min; and vacuum drying was performed at -20℃ for 22h to obtain a multifunctional composite aerogel.

[0035] S6: Mix 600g NHL5 type natural hydraulic lime, 150g quartz sand, 50g limestone powder, 1g polycarboxylate superplasticizer, 20g multifunctional composite aerogel, 4g urea and 100g water, and stir at 50r / min for 10min to obtain natural hydraulic lime-based mortar for cultural heritage building restoration.

[0036] Example 2: A method for preparing natural hydraulic lime-based mortar for the restoration of cultural heritage buildings, comprising the following steps: S1: Add 110g of diatomaceous earth and 350mL of 11% sodium bicarbonate solution to the reaction vessel, and impregnate under vacuum at 22.5℃ and 550r / min for 2.5h. Then add 125mL of 35% calcium chloride solution and continue the reaction for 1.5h. Filter the mixture, wash the filter cake three times with deionized water and anhydrous ethanol respectively, and dry it under vacuum at 65℃ for 1.5h to obtain calcium-based diatomaceous earth.

[0037] S2: Add 81g of calcium-based diatomaceous earth, 1.25L of deionized water and 3.5L of anhydrous ethanol to a reaction vessel, stir for 11min at 22.5℃ and 550r / min, then heat to 62.5℃, microwave stir at 600W for 1.5h, ultrasonically disperse for 1.25h, and vacuum dry at 65℃ for 1.5h to obtain exfoliated calcium-based diatomaceous earth.

[0038] S3: The culture medium was prepared using the formula ATCC 1376 NH4-YE recommended by the American Culture Collection Center. The culture medium was then sterilized at 121°C for 21 min, and then placed on a clean bench for UV sterilization and ventilation. When the temperature of the culture medium dropped to room temperature, the culture medium was taken into a container, and Bacillus pasteurellii was added to the culture medium using a sterile pipette to obtain the bacterial solution. The volume ratio of Bacillus pasteurellii to culture medium was 1:100. The bacterial solution was placed in a constant temperature shaking incubator at 29°C for 49 h to obtain the microbial inoculum.

[0039] S4: Add 55g sodium alginate, 45g polyvinyl alcohol and 750mL deionized water to a reaction vessel and stir for 11min at 22.5℃ and 550r / min. Then add 7.5g microbial agent and continue stirring for 35min to obtain a mixed solution. Add 250mL of the mixed solution dropwise to 850mL of a crosslinking solution containing 3.5% calcium chloride solution and 5.5% boric acid solution. Then add 71g of calcium-based diatomaceous earth and continue stirring for 1.5h. Filter and wash the filter cake three times with deionized water and anhydrous ethanol respectively. Dry under vacuum at -20℃ for 1.5h to obtain diatomaceous earth composite microbial agent.

[0040] S5: Carboxylated cellulose nanofiber powder and deionized water were stirred and mixed to obtain a carboxylated cellulose nanofiber precursor suspension; 850g of the carboxylated cellulose nanofiber precursor suspension was placed in a reaction vessel and stirred for 35min at 72.5℃ and 550r / min. Then, 35g of diatomaceous earth composite microbial agent and 15g of polyvinyl alcohol were added and stirred for 4.5h. The mixture was then ultrasonically dispersed in an ultrasonic disperser with an ultrasonic intensity of 600W for 1.1h, frozen at -5℃ for 35min, and vacuum dried at -20℃ for 23h to obtain a multifunctional composite aerogel.

[0041] S6: Mix 650g NHL5 type natural hydraulic lime, 175g quartz sand, 60g limestone powder, 1.5g polycarboxylate superplasticizer, 25g multifunctional composite aerogel, 4.5g urea and 110g water, and stir at 51r / min for 12.5min to obtain natural hydraulic lime-based mortar for cultural heritage building restoration.

[0042] Example 3: A method for preparing natural hydraulic lime-based mortar for the restoration of cultural heritage buildings, comprising the following steps: S1: Add 120g of diatomaceous earth and 400mL of 12% sodium bicarbonate solution to the reaction vessel, and impregnate under vacuum at 25℃ and 600r / min for 3h. Then add 130mL of 40% calcium chloride solution and continue the reaction for 2h. Filter the mixture and wash the filter cake four times with deionized water and anhydrous ethanol, respectively. Dry it under vacuum at 70℃ for 2h to obtain calcium-based diatomaceous earth.

[0043] S2: Add 82g of calcium-based diatomaceous earth, 1.5L of deionized water and 4L of anhydrous ethanol to a reaction vessel, stir for 12min at 25℃ and 600r / min, then heat to 65℃, microwave stir at 600W for 2h, ultrasonically disperse for 1.5h, and vacuum dry at 70℃ for 2h to obtain exfoliated calcium-based diatomaceous earth.

[0044] S3: The culture medium was prepared using the formula ATCC 1376 NH4-YE recommended by the American Culture Collection Center. The culture medium was then sterilized at 122℃ for 22 minutes, and then placed on a clean bench for UV sterilization and ventilation. When the temperature of the culture medium dropped to room temperature, the culture medium was taken into a container, and Bacillus pasteurellii was added to the culture medium using a sterile pipette to obtain the bacterial solution. The volume ratio of Bacillus pasteurellii to culture medium was 1:100. The bacterial solution was placed in a constant temperature shaking incubator at 30℃ for 50 hours to obtain the microbial inoculum.

[0045] S4: Add 60g sodium alginate, 50g polyvinyl alcohol and 800mL deionized water to a reaction vessel and stir for 12min at 25℃ and 600r / min. Then add 10g microbial agent and continue stirring for 40min to obtain a mixed solution. Add 300mL of the mixed solution dropwise to 900mL of a crosslinking solution containing 4% calcium chloride solution and 6% boric acid solution. Then add 72g of calcium-based diatomaceous earth and continue stirring for 2h. Filter and wash the filter cake 4 times with deionized water and anhydrous ethanol respectively. Dry under vacuum at -20℃ for 2h to obtain diatomaceous earth composite microbial agent.

[0046] S5: Carboxylated cellulose nanofiber powder and deionized water were stirred and mixed to obtain a carboxylated cellulose nanofiber precursor suspension; 900g of the carboxylated cellulose nanofiber precursor suspension was placed in a reaction vessel and stirred for 40min at 75℃ and 600r / min; then 40g of diatomaceous earth composite microbial agent and 20g of polyvinyl alcohol were added, and stirring was continued for 5h; ultrasonic dispersion was performed in an ultrasonic disperser with an ultrasonic intensity of 600W for 1.2h; freezing was performed at -5℃ for 40min; and vacuum drying was performed at -20℃ for 24h to obtain a multifunctional composite aerogel.

[0047] S6: Mix 700g NHL5 type natural hydraulic lime, 200g quartz sand, 70g limestone powder, 2g polycarboxylate superplasticizer, 30g multifunctional composite aerogel, 5g urea and 120g water, and stir at 52r / min for 15min to obtain natural hydraulic lime-based mortar for cultural heritage building restoration.

[0048] Comparative Example 1: Compared with Example 3, the calcium-based diatomaceous earth in step S4 was replaced with the calcium-based diatomaceous earth prepared in step S1.

[0049] Comparative Example 2: Compared with Example 3, the diatomaceous earth composite microbial agent in step S5 was replaced with a mixture of stripped calcium-based diatomaceous earth and microbial agent at a mass ratio of 72:5.

[0050] Comparative Example 3: Compared with Example 3, the polyvinyl alcohol in step S4 was omitted.

[0051] The performance of the natural hydraulic lime-based mortars for cultural relic restoration prepared in Examples 1-3 and Comparative Examples 1-3 was tested. The compressive strength of the mortar was tested according to BS EN 459-2:2021 "Building lime - Part 2: Test methods"; the flexural strength of the mortar was tested according to GB / T 17671-2021 "Cement mortar strength test method (ISO method)"; and the bond strength of the mortar was tested according to JC / T 2381-2016 "Repair mortar". The specimens were fixed on the test bench and continuously sprayed and washed for 72 hours at a spray pressure of 0.1 MPa and a rainfall of 10 mm / h. The mass of the specimens was weighed and the mass loss rate was tested.

[0052] The results are shown in Table 1: Table 1

[0053] As shown in Table 1, the calcium-based diatomaceous earth in Comparative Example 1 was not subjected to microwave and ultrasonic exfoliation treatment, and the aggregates were not broken up. Its specific surface area was much smaller than that of the exfoliated calcium-based diatomaceous earth, which could not provide abundant loading sites for the microcapsules. As a result, the microcapsules were prone to agglomeration and detachment during the subsequent composite process, and could not be uniformly dispersed in the mortar system. The calcium ion sites on the surface of the calcium-based diatomaceous earth were not sufficiently exposed, which made it difficult to promote the cross-linking reaction between polyvinyl alcohol and sodium alginate. The overall strength of the microcapsules was weak, and they were easily damaged during rain or mortar mixing. They could not achieve the reinforcement function of water absorption, swelling and release of bacterial agents. Due to the failure of the microcapsule loading, there was a lack of reinforcement effect from calcium carbonate deposition. In addition, the calcium-based diatomaceous earth itself had poor dispersibility and insufficient interfacial compatibility with the mortar substrate. The repair layer was prone to sanding and peeling.

[0054] In Comparative Example 2, the microorganisms were easily inactivated and could not be released in a controlled manner. Without being encapsulated in sodium alginate and polyvinyl alcohol microcapsules, *Bacillus pasteurellii* was directly exposed to the mortar mixing and curing environment, making it susceptible to inactivation due to pH and temperature variations. Furthermore, the lack of a shell-based water absorption and swelling triggering mechanism prevented targeted release of the microbial agent during rainwater runoff, resulting in the complete failure of the reinforcement effect of urease decomposing urea to generate calcium carbonate. The stripped calcium-based diatomaceous earth and microbial agent were merely physically mixed, lacking the polyvinyl alcohol modification of the microcapsule shell, thus failing to form secondary bonding nodes. The particles were easily isolated and dispersed, resulting in weak interfacial bonding with carboxylated cellulose nanofibers and the mortar substrate, leading to decreased interlayer adhesion strength. Due to the absence of calcium carbonate deposition reinforcement and uneven system dispersion, the internal porosity was too high, making it susceptible to rainwater penetration and erosion, increasing the mass loss rate, and leading to hollowing and detachment of the repair layer with long-term use.

[0055] In Comparative Example 3, the microcapsules exhibited extremely low strength. Polyvinyl alcohol (PVA) acts as a modifier for the sodium alginate shell, enhancing its density and mechanical strength through hydrogen bonding with sodium alginate. However, without PVA, the microcapsule shell relies solely on calcium chloride and boric acid for cross-linking, resulting in a loose and fragile shell that is prone to breakage during mortar mixing and ultrasonic dispersion. This leads to premature leakage of the bacterial agent and the inability to withstand the physical impact of rainwater erosion. Furthermore, the lack of PVA modification prevents the microcapsules from serving as secondary bonding nodes, resulting in poor interfacial compatibility with carboxylated cellulose nanofibers and exfoliated calcium-based diatomaceous earth. Consequently, the internal structure of the multifunctional composite aerogel becomes loose, failing to form a rough and porous compatible structure, thus rendering it ineffective in repairing complex-shaped ancient architectural components.

[0056] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a natural hydraulic lime-based mortar for the restoration of cultural heritage buildings, characterized by, Comprising the following steps: Step one: through vacuum impregnation, sodium bicarbonate solution fully enters the pores of diatomite, reacts with calcium chloride to generate calcium carbonate deposited in the pores and surface of diatomite to obtain calcium-based diatomite; Step two: through the synergistic effect of microwave heating and mechanical stirring, diatomite agglomerates are destroyed, and diatomite layers are ultrasonically dispersed and peeled off to prepare exfoliated calcium-based diatomite; Step three: taking exfoliated calcium-based diatomite as a carrier, by forming a high-molecular matrix with adhesion through sodium alginate and polyvinyl alcohol, the microbial agent is wrapped, and a gel microsphere is formed by the cross-linking effect of calcium ions to obtain a diatomite composite microbial agent; Step four: taking polyvinyl alcohol as a binder, after dispersing carboxylated cellulose nanofiber in water to form a carboxylated cellulose nanofiber precursor suspension, the diatomite composite microbial agent is compounded to prepare a multifunctional composite aerogel; Step five: mixing NHL5 type natural hydraulic lime, quartz sand, limestone powder, polycarboxylic acid water reducing agent, multifunctional composite aerogel, urea and water, stirring at 50-52 r / min for 10-15 min to obtain a natural hydraulic lime-based mortar for cultural heritage building repair.

2. The method for preparing natural hydraulic lime-based mortar for the restoration of cultural heritage buildings according to claim 1, characterized in that, The amount ratio of the NHL5 type natural hydraulic lime, quartz sand, limestone powder, polycarboxylic acid water reducing agent, multifunctional composite aerogel, urea and water is 600-700 g:150-200 g:50-70 g:1-2 g:20-30 g:4-5 g:100-120 g.

3. The method for preparing natural hydraulic lime-based mortar for the restoration of cultural heritage buildings according to claim 1, characterized in that, The calcium-based diatomite is specifically prepared as follows: The diatomite and sodium bicarbonate solution with a mass fraction of 10-12% are added to a reaction kettle, vacuum impregnated at 20-25 DEG C and 500-600 r / min for 2-3 h, then calcium chloride solution with a mass fraction of 30-40% is added, and the reaction is continued for 1-2 h, the filter cake is washed with deionized water and anhydrous ethanol for 2-4 times respectively, and vacuum dried at 60-70 DEG C for 1-2 h to obtain calcium-based diatomite.

4. The method for preparing natural hydraulic lime-based mortar for the restoration of cultural heritage buildings according to claim 3, characterized in that, The amount ratio of the diatomite, sodium bicarbonate solution and calcium chloride solution is 100-120 g:300-400 mL:120-130 mL.

5. The method for preparing natural hydraulic lime-based mortar for the restoration of cultural heritage buildings according to claim 1, characterized in that, The exfoliated calcium-based diatomite is specifically prepared as follows: The calcium-based diatomite, deionized water and anhydrous ethanol are added to a reaction kettle, stirred at 20-25 DEG C and 500-600 r / min for 10-12 min, then heated to 60-65 DEG C, microwave stirring at 600 W for 1-2 h, ultrasonic dispersion for 1-1.5 h, and vacuum drying at 60-70 DEG C for 1-2 h to obtain exfoliated calcium-based diatomite; The amount ratio of the calcium-based diatomite, deionized water and anhydrous ethanol is 80-82 g:1-1.5 L:3-4 L.

6. The method for preparing natural hydraulic lime-based mortar for the restoration of cultural heritage buildings according to claim 1, characterized in that, The diatomite composite microbial agent is specifically prepared as follows: Sodium alginate, polyvinyl alcohol and deionized water are added into a reaction kettle, stirred at 20-25 DEG C and 500-600 r / min for 10-12 min, then microbial inoculum is added, and stirring is continued for 30-40 min to obtain a mixed solution; the mixed solution is dropped into a crosslinking solution containing 3-4% by mass calcium chloride solution and 5-6% by mass boric acid solution, then stripping calcium-based diatomite is added, and stirring is continued for 1-2 h, then the filter cake is washed with deionized water and anhydrous ethanol for 2-4 times respectively, and vacuum dried at -20 DEG C for 1-2 h to obtain diatomite composite microbial inoculum.

7. The method for preparing natural hydraulic lime-based mortar for the restoration of cultural heritage buildings according to claim 6, characterized in that, The amount ratio of sodium alginate, polyvinyl alcohol, deionized water and microbial inoculum is 50-60 g:40-50 g:700-800 mL:5-10 g; the amount ratio of mixed solution, crosslinking solution and stripping calcium-based diatomite is 200-300 mL:800-900 mL:70-72 g.

8. The method for preparing natural hydraulic lime-based mortar for the restoration of cultural heritage buildings according to claim 1, characterized in that, The specific preparation steps of the multifunctional composite aerogel are as follows: Carboxylated cellulose nanofiber powder and deionized water are stirred and mixed to obtain a carboxylated cellulose nanofiber precursor suspension; the carboxylated cellulose nanofiber precursor suspension is placed in a reaction kettle, stirred at 70-75 DEG C and 500-600 r / min for 30-40 min, then diatomite composite microbial inoculum and polyvinyl alcohol are added, and stirring is continued for 4-5 h, then ultrasonic dispersion is carried out in an ultrasonic disperser with an ultrasonic intensity of 600 W for 1-1.2 h, then freezing is carried out at -5 DEG C for 30-40 min, and vacuum drying is carried out at -20 DEG C for 22-24 h to obtain a multifunctional composite aerogel.

9. A method for preparing natural hydraulic lime-based mortar for the restoration of cultural heritage buildings according to claim 8, characterized in that, The amount ratio of carboxylated cellulose nanofiber precursor suspension, diatomite composite microbial inoculum and polyvinyl alcohol is 800-900 g:30-40 g:10-20 g.

10. A natural hydraulic lime-based mortar for restoration of cultural heritage buildings, characterized by, Prepared by the preparation method of any one of claims 1-9.

Images