Method for preventing weathering of high-thick brick city wall surface layer

Abstract

The application discloses a high-thick-brick city wall surface layer weathering prevention method and belongs to the field of historical building protection. The weathering prevention method controls the chemical reaction of a hydrophobic material, reduces the mass of hydrophobic substances generated by the chemical reaction in the penetration process, avoids the influence of the penetration process of weak hydrophobic substances on the penetration coefficient of the city wall surface layer bricks, prolongs the penetration time of the hydrophobic material, improves the penetration depth of the hydrophobic material in the city wall surface layer, weakens the dry shrinkage reciprocating change, realizes the deformation and stress coordination of the waterproof layer of the city wall surface layer and the internal wall body, avoids the stress concentration phenomenon of the waterproof layer shell, further achieves the purpose of preventing the weathering effect of external rain and snow immersion into the city wall surface layer and limiting the salt accumulation caused by the evaporation of the water in the city wall, realizes the purpose of deeper penetration of the hydrophobic material into the city wall, and solves the weathering diseases of the high-thick-brick city wall.

Description

Technical Field

[0001] This invention relates to a method for preventing weathering of the surface layer of a thick brick city wall, belonging to the field of historical building protection. Background Technology

[0002] Prevention and control of surface defects in brick city walls is a key task for cultural relics departments. Compared with the protection of earthen city walls, the protection of brick city walls tends to be a passive strategy of "letting nature take its course." When the outer surface bricks become severely efflorescent, a large-scale brick replacement method is used for repairs. This causes stress redistribution inside the city wall, leading to safety hazards to the wall itself, damage to its original historical appearance, and loss of cultural information.

[0003] With the development of interdisciplinary integration, in order to prevent rain and snow from affecting the surface bricks of city walls, the protection of city wall bricks also adopts the method of surface spraying with hydrophobic materials, and many patents have been applied for (201610115783.7, 201510639789.X, 200610007879.8, 200810059775.0, 201010173702.1, 201310523281.4). The surface spraying method is suitable for treating thinner materials, such as clothing and umbrellas, and can be completely penetrated. For thicker materials such as city walls, the penetration process of hydrophobic materials follows Darcy's law of liquid flow. The penetration depth is greatly affected by the penetration resistance of the brick. The penetration process of hydrophobic materials is both a chemical reaction process of hydrophobic materials and a process in which the penetration resistance of the brick itself increases rapidly. The increase in penetration resistance hinders the penetration of hydrophobic materials and determines that the penetration depth of hydrophobic materials is limited. While surface spraying can mitigate the adverse effects of rain and snow on the city wall, water in the foundation continues to rise along the wall's interior due to capillary action, leading to a further increase in internal salt content. Simultaneously, due to external temperature changes, water vapor gradually condenses at the interface between the hydrophobic surface layer and the untreated sections, increasing the moisture content and accelerating material deterioration. Therefore, spraying cannot completely prevent water-induced deterioration of the city wall. Furthermore, spraying causes a shell-like phenomenon on the wall's surface, where the material properties of the hydrophobic layer differ significantly from the untreated interior. Under sunlight, this generates internal stress, which, repeated day after day, causes cracking and large-scale peeling of the hydrophobic layer. Thus, spraying leads to an unreasonable stress accumulation phenomenon.

[0004] To address the issue of insufficient penetration depth in waterproofing materials, patent 201810121349.9 provides a permeable damp-proofing system for the foundation and bottom walls of historical buildings. This system uses vacuum negative pressure to apply external force, accelerating the wetting process and allowing the hydrophobic material solution to fully penetrate and fill the foundation and bottom walls, thus improving their waterproofing. However, this method is only suitable for thin, conventional brick walls and is not applicable to thick, brick-clad city walls. Summary of the Invention

[0005] In view of this, the present invention provides a method for preventing weathering of the surface of a thick brick city wall. In view of the characteristics of the large size and severe weathering of the thick brick city wall, the present invention solves the problem that the existing weathering prevention technology only has the protection method of spraying. The method relies on the principle of natural penetration of hydrophobic materials to form a thin rain and snow waterproof layer on the surface of the city wall, which cannot resist the secondary damage to the city wall caused by stress accumulation in the shell of the waterproof layer due to factors such as temperature.

[0006] By controlling the chemical reaction of hydrophobic materials, reducing the amount of hydrophobic substances produced during the infiltration process, and avoiding the significant impact of weaker hydrophobic substances on the permeability coefficient of the surface bricks of the city wall, the infiltration time of hydrophobic materials is extended, the penetration depth of hydrophobic materials on the surface of the city wall is increased, and the occurrence of drying shrinkage is reduced. This achieves the coordination of deformation and stress between the surface waterproof layer and the internal wall, avoids the occurrence of stress concentration in the waterproof layer shell, and thus prevents external rain and snow from seeping into the weathering effect of the city wall surface and limits the salt accumulation caused by the evaporation of moisture inside the city wall. This allows the hydrophobic materials to penetrate deeper into the city wall, thereby solving the weathering problems of high and thick brick-clad city walls.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preventing weathering of the surface layer of a thick brick city wall, comprising the following steps:

[0009] (1) Determine the penetration depth, penetration time, and size and arrangement of the air membrane based on the current condition of the city wall;

[0010] (2) Desalinate the city wall and install an air-insulating membrane on the outside of the city wall;

[0011] (3) Add hydrophobic material to the cavity between the air barrier membrane and the city wall, and extract the air in the cavity so that the hydrophobic material can penetrate into the city wall bricks. The hydrophobic material is a mixture of polyvinyl alcohol and sodium methylsilicate or potassium methylsilicate.

[0012] (4) After draining the excess hydrophobic material, carbon dioxide is introduced into the cavity to carbonize the hydrophobic material in the city wall bricks.

[0013] (5) Clean the outer surface of the city wall.

[0014] Based on the above technical solution, the present invention can be further improved as follows:

[0015] Furthermore, the current status of the city wall in step (1) includes the temperature of the environment in which the city wall is located, the depth of the groundwater level, the mechanical properties of the city wall bricks, the degree of weathering of the city wall bricks, the salt content of the city wall bricks, and the permeability coefficient of the city wall bricks.

[0016] Furthermore, the determination method in step (1) is based on the shell model, with the tensile stress generated by the outer surface layer being less than the tensile stress of the material as the basis for calculating the penetration depth, and the permeability resistance of the hydrophobic layer being greater than the water pressure inside the city wall caused by the rise of the groundwater level.

[0017] Furthermore, the hydrophobic material is a mixture of polyvinyl alcohol and sodium methylsilicate, with a polyvinyl alcohol concentration of 1%-4% and a sodium methylsilicate concentration of 0.7-1.5%. The volume ratio of polyvinyl alcohol to sodium methylsilicate is 1:1. Polyvinyl alcohol has good permeability and forms a thick film on the particle surface after drying, exhibiting hydrophobic properties, but its durability is poor. Sodium methylsilicate has poor permeability and produces sodium ions after the reaction. It forms a thin film on the particle surface after drying, exhibiting good hydrophobic properties, but its film uniformity is poor and it cannot effectively confine sodium ions. The methylsilanol generated by the reaction of sodium methylsilicate can be more uniformly dispersed with the help of polyvinyl alcohol, allowing it to react better with the compounds in the brick. Polyvinyl alcohol can also effectively adsorb sodium ions.

[0018] Furthermore, the desalination process in step (2) is electroosmosis or water washing to avoid the accumulation of salt crystallization swelling force.

[0019] Furthermore, the air-isolation membrane in step (2) is mainly dark in color and includes an impermeable geomembrane. The impermeable geomembrane has sealing rubber rings around its perimeter and in the middle. The cross-section of the sealing rubber ring is a hollow square or circle. Water is injected into the hollow tube inside. Pressure is applied to the outside of the rubber ring to fix the air membrane and to prevent the hydrophobic material from leaking and air from entering.

[0020] Furthermore, the wall thickness of the rubber ring is at least greater than 30 mm.

[0021] Furthermore, the air-insulating membrane is installed by fixing a reaction frame on the outside of the city wall and pressing the rubber ring tightly with external force. The water inside the rubber ring will bulge out adaptively under the action of external force, so that the rubber ring is tightly bonded to the city wall.

[0022] Furthermore, the purpose of extracting air from the cavity is to allow the hydrophobic material to come into contact with more of the wall through atmospheric pressure, thereby increasing the penetration speed and depth of the hydrophobic material, enhancing the penetration effect, reducing the application of hydrophobic material, and increasing the construction speed. The degree of air extraction should be terminated when the hydrophobic material is evenly distributed, and should not be too great.

[0023] Furthermore, the carbon dioxide concentration in step (4) is 1%-5%, and the specific concentration value is adjusted according to the depth of the hydrophobic material. The deeper the depth, the higher the concentration, so as to accelerate the carbonization reaction rate of the hydrophobic material.

[0024] Hydrophobic materials can form a waterproof membrane after reacting with carbon dioxide. At the same time, filling the cavity with carbon dioxide can increase the air pressure and increase the penetration depth.

[0025] Furthermore, step (1) also includes setting up a humidity sensor and / or a salinity sensor.

[0026] Furthermore, the cleaning operation described in step (5) involves soaking the surface of the city wall in clean water or spraying it with high-pressure water according to the salinity sensor value. Specifically, when the salinity of the city wall surface is high, it should be soaked in clean water before the surface of the city wall dries and forms a hydrophobic film; when the salinity of the city wall surface meets the standard requirements, it should be sprayed with clean water under certain pressure after the surface of the city wall dries and forms a hydrophobic film. This cleaning operation can also test the effectiveness of the protective treatment on the surface of the city wall.

[0027] The beneficial effects of this invention are as follows:

[0028] (1) Hydrophobic materials are used to form a hydrophobic film in the micropores. Based on the principle of surface tension, the reverse surface tension is generated on the water to form a "thrust" and achieve the purpose of preventing rainwater and groundwater from penetrating into the brick wall.

[0029] (2) Based on the chemical reaction characteristics of hydrophobic materials, by setting up an air-barrier membrane, the chemical reaction rate of hydrophobic materials can be controlled, the chemical reaction of hydrophobic materials on the outer surface of the city wall bricks can be slowed down, the permeation resistance can be reduced, and the permeation depth of hydrophobic materials can be increased.

[0030] (3) Based on the chemical reaction characteristics of hydrophobic materials, carbon dioxide is introduced into the gas barrier membrane to accelerate the chemical reaction of hydrophobic materials, thereby improving the construction speed and the weathering resistance of the city wall bricks.

[0031] (4) The increase in the penetration depth of the hydrophobic material not only improves the water-blocking effect of the city wall bricks, but also, according to the principle of the component resisting external forces, the increase in the hydrophobic material layer increases the stiffness of the hydrophobic material layer, reduces the stress of the hydrophobic material layer, avoids the "thin shell effect", prolongs the durability of the city wall brick protective layer, and improves the weathering resistance of the city wall bricks.

[0032] In summary, the weathering prevention method for the surface of thick brick city walls of this invention solves the protection problems such as shallow penetration depth of the bricks and surface peeling after permeable rain and moisture protection treatment of the city walls. It improves the penetration depth of the hydrophobic material, effectively prevents rainwater from seeping into the city walls and groundwater from wetting the wall, avoids freeze-thaw damage, salt and biological damage to the surface of the city walls, and extends the life of the city walls. Attached Figure Description

[0033] Figure 1 This is a flowchart of the weathering prevention method of the present invention;

[0034] Figure 2 This is a schematic diagram showing the positional relationship between the city wall and the air-insulating membrane of the present invention;

[0035] Figure 3 This is a cross-sectional view showing the positional relationship between the city wall and the air-insulating membrane of the present invention.

[0036] The attached diagram lists the components represented by each number as follows:

[0037] 1. City wall, 2. Air-isolated membrane, 21. Rubber ring, 22. Cavity, 3. Permeation depth, 4. Salinity sensor, 5. Reaction frame. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Example 1

[0040] like Figure 1-3 As shown, the method for preventing weathering on the surface of a thick brick city wall works by using the following reaction formula to carry out a chemical reaction of hydrophobic materials, forming a protective layer on the city wall. This avoids the reaction products of hydrophobic substances affecting the permeability coefficient of the surface bricks of the city wall, thus achieving the goal of allowing hydrophobic liquids to penetrate deeper into the city wall.

[0041] 2CH3Si(OH)2ONa+CO2+H2O→2CH3Si(OH)3+Na2CO3

[0042] n[CH3Si(OH3)]→[CH3SiO( 3 / 2 )]n+3 / 2H2O

[0043] The steps are as follows:

[0044] (1) Based on the temperature of the environment where the city wall 1 is located, the depth of the groundwater level, the mechanical properties of the city wall bricks, the weathering degree of the city wall bricks, the salt content of the city wall bricks and the permeability coefficient of the city wall bricks, based on the shell model, the tensile stress generated by the outer surface layer is less than the tensile stress of the material as the basis for calculating the permeation depth, and the permeation resistance of the hydrophobic layer is greater than the water pressure inside the city wall caused by the rise of the groundwater level, the permeation depth, permeation time and the size and arrangement of the air film are determined. The temperature, humidity and salt sensors 4 are fixed in the gaps of the city wall bricks.

[0045] (2) When chloride ions are greater than 0.5%, nitrate ions are greater than 0.3% or sulfate ions are greater than 1.5%, the city wall is desalinated and a reaction frame 5 is erected on the outside of the city wall 1. The air-isolated membrane 2 is fixed on the reaction frame 5. A water pump is used to inject clean water into the cavity inside the rubber ring 21 to apply external force to the reaction frame 5, so that the rubber ring 21 is in close contact with the city wall and sealed, thereby preventing the hydrophobic material from leaking and air from entering.

[0046] (3) A mixture of polyvinyl alcohol and sodium methylsilicate is selected as the hydrophobic material. The concentration of polyvinyl alcohol is 1%-4%, the concentration of sodium methylsilicate is 0.7-1.5%, and the volume ratio of polyvinyl alcohol to sodium methylsilicate is 1:1. The hydrophobic material is added to the cavity between the air barrier membrane 2 and the city wall 1, and the air in the cavity is extracted to prevent the hydrophobic material from reacting. This is equivalent to sealing and storing the hydrophobic material to avoid changes in its properties. Relying on the capillary action of the city wall bricks and the pressure of the hydrophobic material, it continuously penetrates into the interior of the city wall bricks until the required penetration depth 3 is reached, so that the hydrophobic material penetrates into the city wall bricks.

[0047] (4) After draining the excess hydrophobic material, carbon dioxide is introduced into the cavity to carbonize the hydrophobic material in the city wall bricks.

[0048] (5) Clean the outer surface of the city wall.

[0049] In another embodiment of the present invention, step (2) desalination treatment is carried out by electroosmosis or water washing depending on the humidity of the environment where the city wall is located, so as to avoid the accumulation of salt crystallization swelling force.

[0050] In another embodiment of the present invention, the air-isolation membrane 2 in step (2) is mainly dark in color and includes an impermeable geomembrane. The impermeable geomembrane has a sealing rubber ring around its perimeter and in the middle. The cross-section of the sealing rubber ring is a hollow square or circle. Water is injected into the hollow tube inside. Pressure is applied to the outside of the rubber ring to fix the air membrane and to prevent the hydrophobic material from leaking and air from entering.

[0051] The wall thickness of the rubber ring should be at least 30mm.

[0052] In another embodiment of the present invention, the carbon dioxide concentration in step (4) is 1%-5%, and the specific concentration value is adjusted according to the depth of the hydrophobic material. The deeper the depth, the higher the concentration, so as to accelerate the carbonization reaction rate of the hydrophobic material.

[0053] In another embodiment of the present invention, step (5) cleaning involves soaking the surface of the city wall in clean water or cleaning it with high-pressure water jets based on the value of the salinity sensor 4. Specifically, when the salt content of the surface layer of the city wall is higher than 10 mS / cm... -1When the surface of the city wall is not yet dry and a hydrophobic film has formed, it should be soaked in clean water; when the salt content of the surface of the city wall is less than or equal to 10 ms / cm... -1 At that time, after the surface of the city wall has dried and formed a hydrophobic film, it should be sprayed with clean water under certain pressure for cleaning; this cleaning operation can also test the effectiveness of the protective treatment on the surface of the city wall.

Claims

1. A method for preventing weathering of the surface layer of a high-thickness brick city wall, characterized in that, The steps are as follows: (1) Determine the penetration depth, penetration time, and size and arrangement of the air film of the hydrophobic material based on the current status of the city wall. The current status of the city wall includes the temperature of the environment where the city wall is located, the depth of the groundwater level, the mechanical properties of the city wall bricks, the weathering degree of the city wall bricks, the salt content of the city wall bricks, and the permeability coefficient of the city wall bricks. The determination method is based on the shell model, with the tensile stress generated by the outer surface layer being less than the tensile stress of the material as the basis for calculating the penetration depth, and satisfying that the permeability resistance of the hydrophobic layer is greater than the water pressure inside the city wall caused by the rise of the groundwater level. (2) Desalination treatment of the city wall and installation of an air-isolation membrane on the outside of the city wall. The air-isolation membrane includes an impermeable geomembrane. The impermeable geomembrane has sealing rubber rings around its perimeter and in the middle. The cross-section of the sealing rubber ring is a hollow square or circle. Water is injected into the hollow tube inside. The wall thickness of the rubber ring is at least greater than 30 mm. (3) Add hydrophobic material to the cavity between the air-barrier membrane and the city wall, and extract the air in the cavity so that the hydrophobic material can penetrate into the city wall bricks. The hydrophobic material is a mixture of polyvinyl alcohol and sodium methylsilicate. The concentration of polyvinyl alcohol is 1%-4%, the concentration of sodium methylsilicate is 0.7-1.5%, and the volume ratio of polyvinyl alcohol to sodium methylsilicate is 1:

1. (4) After draining the excess hydrophobic material, carbon dioxide is introduced into the cavity to carbonize the hydrophobic material inside the city wall bricks. (5) Clean the outer surface of the city wall.

2. The method for preventing weathering of the surface layer of a thick brick city wall according to claim 1, characterized in that, The desalination process in step (2) is electroosmosis or water rinsing.

3. The method for preventing weathering of the surface layer of a thick brick city wall according to claim 1, characterized in that, The air-insulating membrane is installed by fixing a reaction frame on the outside of the city wall and pressing the rubber ring tightly with external force. The water inside the rubber ring will bulge out adaptively under the action of external force, so that the rubber ring is tightly bonded to the city wall.

4. The method for preventing weathering of the surface layer of a high-thickness brick city wall according to claim 1, characterized in that, The carbon dioxide concentration in step (4) is 1%-5%.

5. The method for preventing weathering of the surface layer of a thick brick city wall according to claim 1, characterized in that, Step (1) also includes setting up a humidity sensor and / or a salinity sensor.

6. The method for preventing weathering of the surface layer of a high-thickness brick city wall according to claim 5, characterized in that, The cleaning operation described in step (5) involves soaking the surface of the city wall in clean water or cleaning it with high-pressure water jets based on the salinity sensor values.

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