Method for curing surface of mass concrete based on electric field regulation

Abstract

The application discloses a large-volume concrete surface maintenance method based on electric field regulation, and comprises the following steps: preparing a polymer gel containing a nano-silica aqueous solution; coating the polymer gel on a concrete surface to be maintained, and standing for 2-5 hours to form a 2-5 cm polymer gel film; applying an electric field to the polymer gel film according to needs, controlling the voltage at 5-20 V, and controlling the time at 20-40 minutes to promote the nano-silica aqueous solution to be released to the concrete surface; and further comprising the steps of removing the electric field, supplementing the nano-silica aqueous solution to the polymer gel film until the original state is restored; the application coats a layer of 'absorbing solution-releasing solution' reversible maintenance film on the concrete surface, the absorbing solution provides good moisturizing effect in the initial maintenance stage, and the waste of water resources is reduced; in the maintenance process, the aqueous solution containing nano-silica and other substances is released through external electric field stimulation response, internal cracks of the concrete are filled and repaired, and the overall strength and compactness of the concrete are improved.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a method for curing concrete surfaces. Background Technology

[0002] With the vigorous development of modern concrete, various concrete structures are widely used in various super high-rise buildings, long-span bridges, and industrial buildings. After the concrete is poured, if the moisture on the concrete surface evaporates too quickly, the cement particles that have formed a gel will not be fully hydrated, resulting in flaking or powdering on the concrete surface. At the same time, premature evaporation of moisture will also cause significant shrinkage deformation and drying shrinkage cracks. Therefore, surface curing of concrete after pouring is very important.

[0003] The common maintenance methods in construction projects include the following: water spraying, covering, curing agent, shed erection, and heat storage.

[0004] Watering is difficult to maintain a consistently moist concrete surface in practical engineering applications, resulting in poor curing effectiveness and wasting water resources. Covering is the most common method for moisturizing and insulating concrete, but it is easily affected by environmental climate, prone to damage and incomplete sealing during use, and is not suitable for non-planar structures.

[0005] Curing agents can be categorized into internal and external curing. External curing agents involve spraying a polymer solution onto the concrete surface. After the moisture evaporates, a continuous, waterproof polymer film forms on the surface, preventing the evaporation of free moisture from the concrete's internal pores and ensuring proper curing. However, this method requires precise application and is susceptible to issues such as missed areas, uneven application, and damage to the bond between new and old concrete. Internal curing agents are made of highly absorbent resins and can be poured along with the concrete. As cement hydration leads to an increase in pH or ion concentration, the superabsorbent resin releases water, providing a moisturizing effect. However, due to its strong absorption capacity, it absorbs a significant amount of mixing water during concrete mixing, which can negatively impact the concrete's workability and reduce its strength.

[0006] Tent curing, heated shed curing, and heat storage curing are all types of heating curing, which are suitable for concrete curing that requires wind protection, heat insulation, and sun shading or in low-temperature environments. However, they have high construction costs and require strict construction measures.

[0007] The above-mentioned curing methods each have their own characteristics and shortcomings. They cannot effectively control the relative humidity of the concrete surface in the long term, and the construction is relatively complicated, costly, and consumes a lot of manpower and freshwater resources. Therefore, it is necessary to further improve the surface curing methods of concrete, simplify the construction, and reduce the waste of costs and resources. Summary of the Invention

[0008] The purpose of this invention is to provide a method for curing large-volume concrete surfaces. A reversible curing film consisting of an adsorption solution and a release solution is coated on the concrete surface. In the early stages of curing, the adsorption solution provides good moisturizing effect and reduces water waste. During the curing process, an aqueous solution containing nano-silica and other substances is released in response to external electric field stimulation, filling and repairing internal cracks in the concrete and improving the overall strength and density of the concrete.

[0009] To achieve the above objectives, the following technical solution is adopted:

[0010] The method for curing large-volume concrete surfaces based on electric field control includes the following steps:

[0011] (1) Preparation of polymer gel containing aqueous solution of nano-silica;

[0012] (2) The polymer gel is coated on the concrete surface to be cured and left to stand for 2-5 hours to form a 2-5cm polymer gel film;

[0013] (3) Apply an electric field to the polymer gel membrane as needed, with the voltage controlled at 5-20V and the time controlled at 20-40 minutes, to promote the release of nano-silica aqueous solution to the concrete surface.

[0014] According to the above scheme, step 3 includes inserting two thin electrode plates into the polymer gel membrane and applying a DC voltage. By controlling the voltage intensity and the distance between the electrode plates, the release rate of the nano-silica aqueous solution is adjusted.

[0015] According to the above plan, in step 3, when curing a large area of ​​concrete surface, the electric field is applied in sections.

[0016] According to the above scheme, step 3 also includes removing the electric field and replenishing the polymer gel membrane with nano-silica aqueous solution until it returns to its original state.

[0017] According to the above scheme, the polymer gel containing nano-silica aqueous solution is prepared by the following method:

[0018] Mix the monomer containing double bonds, chitosan, crosslinking agent, initiator and water, heat to 60-70℃ under an inert atmosphere and stir for 20-50 min, then add 5-10 wt% of nano silica aqueous solution and continue stirring at a constant temperature for 1-1.5 h to obtain a polymer gel containing nano silica aqueous solution.

[0019] According to the above scheme, the monomer containing double bonds is one or a mixture of acrylic acid, acrylamide, 2-(acrylamido)-2-methylpropanesulfonic acid, 2-hydroxyethyl methacrylate, N-vinylpyrrolidone, 2-acrylamido-2-methyl-1-propanesulfonic acid, and N-isopropylacrylamide.

[0020] According to the above scheme, the chitosan is carboxymethyl chitosan.

[0021] According to the above scheme, the initiator is one of ammonium persulfate or potassium persulfate.

[0022] According to the above scheme, the crosslinking agent is one of N,N-methylenebisacrylamide, bisvinylimidazolium salt, and polyethylene glycol dimethacrylate.

[0023] According to the above plan, the raw materials are calculated in parts by weight as follows:

[0024] 20-25 parts of monomers containing double bonds; 5-8 parts of chitosan; 1.2-1.5 parts of crosslinking agent; 1-1.2 parts of initiator; 90-100 parts of water; 6-14 parts of nano-silica aqueous solution.

[0025] According to the above scheme, the nano-silica aqueous solution is prepared by the following method:

[0026] Nano-silica and silane coupling agent were added to an ethanol / water solution with a volume ratio of 1:1 and ultrasonically treated; then an ether / acetone solution with a volume ratio of 1:1 was added, and the mixture was stirred at high speed and centrifuged; the precipitate was redispersed in pure water to obtain an aqueous solution of nano-silica.

[0027] According to the above scheme, the particle size of the nano-silica is 500-800nm.

[0028] This invention provides an electrically responsive mesh polymer gel, which is prepared by using double-bonded monomers with polar groups under the action of an initiator and a crosslinking agent to obtain a mesh polymer, and then adsorbing an aqueous solution containing nano-silica to form a gel substance, which is then coated on the concrete surface.

[0029] The polar groups introduced into the mesh-like polymer gel effectively enhance its adsorption performance for sodium aqueous solutions, providing excellent moisture retention on concrete surfaces. The presence of nano-silica in the mesh-like polymer gel effectively improves overall mechanical properties and structural strength, maintaining structural stability under wind and rain conditions. Simultaneously, the chitosan segments in the mesh-like polymer exhibit temperature insensitivity, effectively improving overall temperature resistance and preventing structural damage due to the heat of hydration on the concrete surface.

[0030] The chain segments of the network polymer gel contain polar groups, which attract and reach equilibrium with opposite ions in the aqueous solution. When stimulated by an external electric field, the ions in the aqueous solution move towards the electrode, while the polar groups in the network polymer do not move accordingly. This causes the network structure to deform and shrink, releasing the aqueous solution containing nano-silica from within the polymer. By controlling the application time and intensity of the electric field, the "adsorption-release" process can be controlled. After the aqueous solution containing nano-silica is released, it penetrates into the micro-cracks inside the concrete, participates in the hydration reaction to repair the cracks, and improves the overall strength and durability of the concrete.

[0031] Compared with existing technologies, the novel surface maintenance technology used in this invention has the following advantages:

[0032] (1) The coating of the curing film is convenient to construct; the reversible effect of the curing film in "adsorbing solution - releasing solution" can be used to recycle and reduce costs; the amount of curing water used is reduced, thus saving water resources.

[0033] (2) It has a good moisturizing effect in the early stage of curing; the curing film has excellent temperature resistance and strong adaptability to the external environment, and is especially suitable for large and irregular concrete components.

[0034] (3) During the curing process, the nano-silica aqueous solution adsorbed in the curing film is released in a controlled manner to fill and repair the internal cracks of the concrete, effectively improving the strength and density of the concrete surface. Detailed Implementation

[0035] The following embodiments further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0036] Example 1

[0037] Preparation of nano-silica aqueous solution: Take an appropriate amount of nano-silica (average particle size 600nm) and silane coupling agent, add them to an ethanol / water mixture (volume ratio 1:1) and sonicate. Then add an ether / acetone mixture (volume ratio 1:1), stir at high speed and centrifuge. Take the precipitate and redisperse it in pure water to obtain nano-silica aqueous solution.

[0038] Preparation of the network polymer gel: Acrylamide monomer (20g), carboxymethyl chitosan monomer (5g), crosslinking agent N,N-methylenebisacrylamide (1.2g), initiator ammonium persulfate (1g) and water (90ml) were added to a container in proportion. After stirring with nitrogen gas for 30min, the temperature was raised to 60℃ and stirred for 30min. Then, nano-silica aqueous solution (8wt%) was added and the mixture was stirred at a constant temperature for 1h to obtain a pre-gelled network polymer.

[0039] A pre-gelled, grid-like polymer is coated onto the concrete surface and allowed to stand at room temperature for 3 hours to form a gel film with a thickness controlled at 3 cm. During curing, an electric field is applied to the grid-like polymer gel film as needed. Two thin electrode plates with the same cross-sectional dimensions as the gel are inserted into the gel, and a DC voltage (10V, for 30 minutes) is applied. By controlling the voltage intensity and the distance between the electrode plates, the release of nano-silica aqueous solution is induced. The electric field is then removed, and nano-silica aqueous solution is replenished until the curing film returns to its original state.

[0040] Example 2

[0041] Preparation of nano-silica aqueous solution: Take an appropriate amount of nano-silica (average particle size 700nm) and silane coupling agent, add them to an ethanol / water mixture (volume ratio 1:1) and sonicate. Then add an ether / acetone mixture (volume ratio 1:1), stir at high speed and centrifuge. Take the precipitate and redisperse it in pure water to obtain nano-silica aqueous solution.

[0042] Preparation of the network polymer gel: N-isopropylacrylamide monomer (25g), carboxymethyl chitosan monomer (6g), polyethylene glycol dimethacrylate crosslinking agent (1.5g), potassium persulfate initiator (1.1g), and water (95ml) were added to a container in proportion. After stirring under nitrogen for 30min, the temperature was raised to 70℃ and stirred for 40min. Then, nano-silica aqueous solution (10wt%) was added and the mixture was stirred at a constant temperature for 1.5h to obtain a pre-gelled network polymer.

[0043] A pre-gelled, mesh-like polymer is coated onto the concrete surface and allowed to stand at room temperature for 4 hours to form a gel film with a thickness controlled at 4 cm. During curing, an electric field is applied to the mesh-like polymer gel film as needed. Two thin electrode plates with the same cross-sectional dimensions as the gel are inserted into the gel, and a DC voltage (15V, for 35 minutes) is applied. By controlling the voltage intensity and the distance between the electrode plates, the release of nano-silica aqueous solution is induced. The electric field is then removed, and nano-silica aqueous solution is replenished until the curing film returns to its original state.

[0044] Example 3

[0045] Preparation of nano silica aqueous solution: Take an appropriate amount of nano silica (average particle size 750nm) and silane coupling agent, add them to an ethanol / water mixture (volume ratio 1:1) solution and sonicate. Then add an ether / acetone mixture (volume ratio 1:1), stir at high speed and centrifuge. Take the precipitate and redisperse it in pure water to obtain nano silica aqueous solution.

[0046] Preparation of the mesh-like polymer gel: 22 g of monomer 2-(acrylamido)-2-methylpropanesulfonic acid, 6 g of monomer carboxymethyl chitosan, 1.3 g of crosslinking agent N,N-methylenebisacrylamide, 1.2 g of initiator potassium persulfate, and 100 ml of water were added to a container in proportion. After stirring under nitrogen for 30 min, the mixture was heated to 65 °C and stirred at a constant temperature for 50 min. Then, 9 wt% of nano-silica aqueous solution was added, and the mixture was stirred at a constant temperature for 1.5 h to obtain a pre-gelled mesh-like polymer.

[0047] A pre-gelled, grid-like polymer is coated onto the concrete surface and allowed to stand at room temperature for 5 hours to form a gel film with a thickness controlled at 5 cm. During curing, an electric field is applied to the grid-like polymer gel film as needed. Two thin electrode plates with the same cross-sectional dimensions as the gel are inserted into the gel, and a DC voltage (20V, for 30 minutes) is applied. By controlling the voltage intensity and the distance between the electrode plates, the release of nano-silica aqueous solution is induced. The electric field is then removed, and nano-silica aqueous solution is replenished until the curing film returns to its original state.

[0048] Comparative Example

[0049] According to the patent CN202211404843.9, "A long-lasting, highly dispersed, self-reinforcing concrete internal curing agent and its preparation method", a conventional concrete internal curing agent is prepared and added to the concrete at 10% of the cementitious material for molding.

[0050] Experimental control:

[0051] Four sets of concrete blocks, each 150mm × 150mm × 150mm in size, were prepared according to Examples 1-3 and the control example (conventional curing). The mix proportions are shown in Table 1. Compressive strength tests were conducted according to GB / T50081-2002 "Standard for Test Methods of Mechanical Properties of Concrete", and the test results are shown in Table 2.

[0052] Table 1 Concrete Mix Proportions

[0053] cement Mineral powder fine sand coarse sand fine stones Zhongshi water admixtures 160 240 220 600 300 630 160 6

[0054] Table 2 Comparison of compressive strength

[0055] 7-day compressive strength (MPa) 28-day compressive strength (MPa) Example 1 33.5 54.1 Example 2 35.7 55.7 Example 3 37.2 57.3 Comparison Example 33.5 52.4

[0056] The polymer gel obtained in Example 1 was cut into shapes of 2.5cm × 2.5cm × 2.0cm. After applying a set voltage of 15V to a DC power supply for 30 minutes, the weight of the sample before and after dehydration was measured.

[0057] Original weight (g) Weight (g) after energization Weight (g) after power-on and water replenishment are completed Example 1 6.5 3.1 6.0 Example 2 7.7 4.7 7.0 Example 3 7.2 3.8 7.0

[0058] The results showed that the sample released nearly 50% of the solution after being energized, and its weight recovered to 90% after water replenishment, meeting the requirements for concrete surface curing and recycling.

Claims

1. A method for curing large-volume concrete surfaces based on electric field control, characterized in that... Includes the following steps: (1) Preparation of polymer gel containing nano-silica aqueous solution; specifically including: mixing monomers containing double bonds, carboxymethyl chitosan, crosslinking agent, initiator and water, heating to 60-70℃ under an inert atmosphere and stirring at a constant temperature for 20-50 min, then adding 5-10wt% nano-silica aqueous solution, and continuing to stir at a constant temperature for 1-1.5 h to obtain polymer gel containing nano-silica aqueous solution; the raw materials are as follows by weight: monomers containing double bonds 20-25 parts; carboxymethyl chitosan 5-8 parts; crosslinking agent 1.2-1.5 parts; initiator 1-1.2 parts; water 90-100 parts; nano-silica aqueous solution 6-14 parts; (2) Apply the polymer gel to the surface of the concrete to be cured and let it stand for 2-5 hours to form a 2-5 cm polymer gel film; (3) Apply an electric field to the polymer gel film as needed, with the voltage controlled at 5-20V and the time controlled at 20-40 minutes, to promote the release of nano-silica aqueous solution to the concrete surface; The nano-silica aqueous solution was prepared by the following method: Nano-silica and silane coupling agent were added to an ethanol / water solution with a volume ratio of 1:1 and ultrasonically treated; then an ether / acetone solution with a volume ratio of 1:1 was added, and the mixture was stirred at high speed and centrifuged; the precipitate was redispersed in pure water to obtain an aqueous solution of nano-silica.

2. The method for curing large-volume concrete surfaces based on electric field control as described in claim 1, characterized in that... Step (3) involves inserting two thin electrode plates into the polymer gel membrane and applying a DC voltage. The release rate of the nano-silica aqueous solution is adjusted by controlling the voltage intensity and the distance between the electrode plates.

3. The method for curing large-volume concrete surfaces based on electric field control as described in claim 1, characterized in that... Step (3) also includes removing the electric field and replenishing the polymer gel membrane with an aqueous solution of nano-silica until it returns to its original state.

4. The method for curing large-volume concrete surfaces based on electric field control as described in claim 1, characterized in that... The monomer containing the double bond is one of acrylic acid, acrylamide, 2-hydroxyethyl methacrylate, N-vinylpyrrolidone, 2-acrylamido-2-methyl-1-propanesulfonic acid, and N-isopropylacrylamide.

5. The method for curing large-volume concrete surfaces based on electric field control as described in claim 1, characterized in that... The initiator is one of ammonium persulfate or potassium persulfate; the crosslinking agent is one of N,N-methylenebisacrylamide, bisvinylimidazolium salt, or polyethylene glycol dimethacrylate.

6. The method for curing large-volume concrete surfaces based on electric field control as described in claim 1, characterized in that... The nano-silica particles have a diameter of 500-800 nm.