Maintenance construction method for protective layer on concrete surface of small box girder

Abstract

The invention relates to the technical field of road and bridge construction materials and engineering, discloses a maintenance construction method of a small box girder concrete surface protective layer, and relates to a special composition composed of a polyvinyl alcohol-based component A and a component B containing borate and lithium silicate. During construction, the two components are atomized and sprayed to the surface of wet concrete by adopting double-channel equipment, and a thixotropic gel layer is formed in situ under the catalysis of a base plane alkaline environment, so that the sagging problem of a facade is solved; and during the standing period, the syneresis inducer is utilized to initiate gel slurry separation shrinkage, a micro-pumping effect is generated to actively press lithium silicate into the deep positions of capillary pores, and the lithium silicate reacts with a hydration product to generate C-S-H gel. And after the curing period, the gel can be removed through high-pressure water flushing by utilizing the chemical reversibility of the gel structure. According to the invention, synergism of thick film water retention and deep densification is realized, the surface hardness and impermeability of concrete are improved, the surface is clean and residue-free, and construction is efficient and convenient.

Description

Technical Field

[0001] This invention relates to the field of road and bridge construction materials and engineering technology, specifically a method for the maintenance and construction of a protective layer on the concrete surface of a small box girder. Background Technology

[0002] Precast small box girders are widely used in modern highway bridge construction due to their lightweight structure and high torsional stiffness. As a key component of the concrete structure, the web and flanges of the small box girder typically have a large vertical or inclined surface area. Early curing after concrete pouring is crucial for preventing surface shrinkage cracks and ensuring structural strength and durability. Simultaneously, surface densification treatment is often required in engineering projects to improve the wear resistance, carbonation resistance, and impermeability of the concrete surface.

[0003] Currently, conventional curing and protection methods have significant limitations for concrete components with large vertical surfaces, such as small box girders. Traditional methods like water spraying or covering with geotextiles are difficult to maintain continuous moisture on vertical surfaces, as moisture is easily lost under gravity. Furthermore, fixing and covering with geotextiles is cumbersome and can leave textures or color variations on the concrete surface, affecting appearance quality. To overcome the drawbacks of physical curing, liquid chemical curing agents and penetrating liquid hardeners are increasingly being used. However, existing single-component liquid curing agents mainly rely on film formation to seal moisture, but their permeability is poor, failing to provide deep reinforcement to the concrete surface. Moreover, the residual organic film layer after curing is often difficult to remove, severely affecting the adhesion of subsequent waterproofing or decorative coatings.

[0004] While penetrating liquid hardeners can improve surface hardness, their viscosity is typically low, making them prone to severe sagging when sprayed on vertical surfaces. This results in significant material loss and uneven distribution, making it difficult to ensure sufficient effective coverage. Adding thickeners to increase viscosity and prevent sagging significantly sacrifices the material's penetrating ability, causing the active ingredients to remain only on the surface of the substrate and unable to penetrate deep into the pores to form an effective, dense layer. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a curing and construction method for the protective layer on the concrete surface of small box girders. This method resolves the contradiction between high viscosity anti-sagging and low viscosity deep penetration when using existing liquid curing agents and densifiers on the vertical surfaces of small box girders. It also solves the problem that traditional film-forming curing agents leave a residual film layer that is difficult to remove completely after curing, affecting the adhesion of subsequent coatings.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a composition for the curing of a protective layer on the concrete surface of a small box girder, employing the following technical solution:

[0008] A composition for the curing of a protective layer on the concrete surface of a small box girder, the composition comprising separately packaged component A and component B;

[0009] Component A is made from raw materials comprising the following weight percentages: 5.0%-8.0% polyvinyl alcohol, 2.0%-4.0% moisturizing plasticizer, 0.05%-0.15% wetting and defoaming agent, and water as the balance; the sum of the weight percentages of all raw materials is 100%.

[0010] Component B is made from raw materials comprising the following weight percentages: 3.0%-5.0% borate crosslinking agent, 30.0%-40.0% lithium silicate aqueous solution, 4.0%-6.0% polyether or inorganic salt dehydration shrinkage inducer, and water as the balance; the sum of the weight percentages of the various raw materials is 100%.

[0011] By employing the above technical solution, this invention constructs a chemical curing and densification system with dual functions of in-situ gelation and controlled pulp shrinkage. The mechanism of action is analyzed as follows:

[0012] Thixotropic shaping mechanism: Polyvinyl alcohol (PVA) in component A serves as the film-forming matrix, maintaining a low-viscosity liquid state with the borate crosslinking agent in component B during the initial mixing stage, facilitating atomization and initial spreading on the concrete surface. When the mixture contacts the concrete surface, utilizing the high pH value (alkaline environment) of the concrete pore solution, borate ions rapidly complex with the hydroxyl groups on the PVA molecular chains, forming a diol-boron ester crosslinking network. This network imparts low shear viscosity and yield stress to the material, thereby forming a stable gel layer on the vertical substrate, effectively overcoming the sagging and loss problem of conventional liquid densifiers under gravity.

[0013] Active penetration mechanism: Conventional gel systems tend to bind solutes, hindering the migration of active ingredients to the substrate. By introducing polyether or inorganic salt dehydration shrinkage inducers, a thermodynamically unstable state is created within the gel network.

[0014] When the inducing agent is an inorganic salt (such as sodium sulfate), the salting-out effect is used to destroy the hydration layer of the PVA molecular chain, reduce the affinity between the polymer chain segments and the solvent, and drive the polymer chain to undergo conformational contraction.

[0015] When the inducing agent is a polyether (such as PEG), it utilizes the phase separation tendency and osmotic pressure difference between it and PVA in aqueous solution to repel the free aqueous phase within the gel network. Both of these induction mechanisms lead to spontaneous macroscopic shrinkage of the gel volume (separation), and the resulting shrinkage stress extrudes the lithium silicate-rich liquid phase encased within the gel network. Because the outer surface of the gel loses water quickly when exposed to air, forming a dense skin, while the interface between the gel and concrete remains moist, the extruded active liquid phase, under the combined action of shrinkage stress and capillary force, is directionally pressed deep into the capillary pores of the concrete.

[0016] Preferably, in component A: the polyvinyl alcohol is partially hydrolyzed, with an average degree of polymerization of 1700-2400 and a degree of hydrolysis of 87.0 mol%-89.0 mol%; the moisturizing plasticizer is selected from glycerol or sorbitol; the wetting and defoaming agent is selected from tributyl phosphate or fatty alcohol polyoxyethylene ether. In component B: the borate crosslinking agent is selected from sodium tetraborate or sodium metaborate; the lithium silicate aqueous solution has a modulus of 2.8-3.2 and a solid content of 21.0 wt%-23.0 wt%; the polyether or inorganic salt dehydration shrinkage inducer is polyethylene glycol with an average molecular weight (Mw) between 380-600, or anhydrous sodium sulfate.

[0017] By employing the above technical solutions, PVA with specific degrees of polymerization and hydrolysis can provide a suitable crosslinking point density while ensuring water solubility. This allows the formed gel to possess sufficient mechanical strength to resist sagging while maintaining a certain degree of flexibility to adapt to the shrinkage process. Using medium- to low-molecular-weight polyethylene glycol or inorganic salts as inducing agents allows for precise control of the time window for gelation, ensuring that significant liquid phase migration only begins after the gel layer has fully adhered to and sealed the substrate, thus avoiding premature delamination that could affect film quality. Lithium silicate, as a densifying agent, has lower viscosity and a smaller ionic radius compared to sodium- or potassium-based silicates. Combined with the pumping effect generated by gel shrinkage, it can penetrate more than 3 mm into the concrete surface, reacting with the hydration product calcium hydroxide to form CSH gel, thereby improving surface hardness and impermeability.

[0018] Secondly, the present invention provides a method for preparing the above-mentioned composition, which adopts the following technical solution:

[0019] A method for preparing a composition, comprising the following steps:

[0020] Preparation of component A: Polyvinyl alcohol is dispersed in water at room temperature, heated to 90℃-95℃ and stirred until it is transparent, cooled to 50℃-60℃ and then moisturizing plasticizer and wetting defoamer are added, mixed evenly and then cooled and filtered.

[0021] Preparation of component B: Dissolve the borate crosslinking agent in water at 40℃-50℃, add a polyether or inorganic salt dehydration shrinkage inducer and stir until homogeneous, then slowly add an aqueous solution of lithium silicate while stirring, and mix and homogenize to obtain a homogeneous liquid.

[0022] By adopting the above technical solutions, the problem of easy agglomeration during PVA dissolution is addressed by employing a low-temperature dispersion and high-temperature dissolution process. This ensures the full extension of the polymer chains, reduces the generation of microscopic gel particles, and guarantees the uniformity and transparency of the film-forming solution. Regarding the stability issues arising from the coexistence of high concentrations of lithium silicate, borates, and inducers in component B, a specific feeding sequence and temperature control strategy are employed: first, a homogeneous system of borates and inducers is established, and then lithium silicate is introduced. This avoids silicate gelation or salting-out precipitation caused by excessively high local concentrations, ensuring the rheological stability of component B during storage and making it suitable for industrial two-component spraying equipment.

[0023] Thirdly, this invention provides a method for the maintenance and construction of a protective layer on the concrete surface of a small box girder, employing the following technical solution:

[0024] A method for curing a protective layer on the concrete surface of a small box girder includes the following steps:

[0025] S1. Base surface preparation: Ensure that the concrete surface of the small box girder to be treated is moist but without standing water;

[0026] S2, Two-component atomized spraying: Using a dual-channel spraying device, component A and component B are sprayed out simultaneously, so that the two liquid streams mix before or at the moment of contact with the concrete surface.

[0027] S3, In-situ gelation: The mixed liquid is sprayed onto the concrete surface, and the alkaline environment of the concrete surface is used to catalyze the cross-linking reaction, so that the liquid is transformed into a thixotropic gel layer in situ on the surface.

[0028] S4. Kinetic shrinkage and penetration: The thixotropic gel layer is left to stand, causing the dehydration shrinkage inducer in it to disrupt the gel swelling balance, triggering the separation shrinkage effect, squeezing out the liquid phase in the gel network and pressing it into the capillary pores of the concrete.

[0029] S5. Maintenance and Cleaning: Keep the gel layer covered for maintenance. After the maintenance period, remove the gel layer by water rinsing.

[0030] By adopting the above technical solution, this invention resolves the contradiction between water retention and curing and penetration densification during facade construction through the spatiotemporal coupling control of physicochemical reactions. The specific reaction and action process are as follows:

[0031] Mixing and Adhesion Stage: The two components are mixed at the nozzle outlet. Due to the pH sensitivity of the cross-linking reaction between PVA and borate, the reaction rate is slower under neutral or weakly alkaline conditions (the pH of the components themselves). The mixture maintains a low viscosity atomization state during flight and has good wetting ability when it comes into contact with the substrate.

[0032] Interfacial catalytic gelation stage: Once the mixture comes into contact with the strongly alkaline surface of freshly poured concrete, OH- ions at the interface rapidly diffuse into the liquid film, catalyzing the complexation reaction between borate and PVA. This causes the system viscosity to increase exponentially within seconds, quickly crossing the liquid-gel transition point. This in-situ formed gel layer has yield stress, resisting gravity and achieving single-coat thick application without sagging. Simultaneously, it seals the moisture evaporation channels on the concrete surface, providing excellent physical curing.

[0033] Induced shrinkage and penetration stage: As the gel network matures, the dissolved inducers (PEG or sodium sulfate) begin to function. Due to the thermodynamic incompatibility between the inducers and the cross-linked PVA network, osmotic pressure or repulsive force is generated within the gel network, forcing the gel skeleton to shrink. This volume shrinkage generates positive pressure at the gel-concrete interface, squeezing out the unbound, small-molecule lithium silicate-rich liquid phase from the network and pressing it into the concrete capillaries.

[0034] Reaction and Degradation Stage: The lithium silicate extruded into the pores reacts with calcium hydroxide in the concrete to form CSH gel, filling the pores and achieving surface densification. Simultaneously, as curing time progresses, carbonization of the concrete surface leads to a slight decrease in pH. Combined with external environmental factors, the PVA-boronate bonds undergo partial reversible dissociation, reducing the adhesion between the gel film and the substrate. This makes it easy to remove after curing by high-pressure water rinsing, without leaving a release layer that could affect subsequent coating applications.

[0035] Preferably, in step S2, the nozzle of the dual-channel spraying equipment is set to external mixing mode, and the volumetric flow rate ratio of component A to component B is controlled to be 1.5:1-3:1; during spraying, the wet film coverage of the mixture on the concrete surface is controlled to be 200g / m². 2 -300g / m 2 More preferably, the volumetric flow rate ratio of component A to component B is 2:1 to 2.5:1.

[0036] By employing the above technical solution and controlling the volumetric flow ratio of the two components within a specific range, the stoichiometric ratio of crosslinking points to polymer segments in the system can be adjusted. Within this ratio range, the formed gel network has a suitable crosslinking density, ensuring sufficient anti-sagging strength without completely locking the liquid phase migration channels due to excessive crosslinking, thus ensuring the smooth progress of the slurry shrinkage effect. Simultaneously, this formulation ensures an effective supply of lithium silicate, meeting the reaction requirements of C50 and higher grade concrete surfaces.

[0037] Preferably, in S4, the specific process of the slurry shrinkage effect is as follows: within 5-60 minutes after the gel layer is formed, the gel network undergoes volume shrinkage, and a liquid phase rich in lithium silicate migrates at the interface between the gel layer and the concrete substrate.

[0038] By adopting the above technical solution, the time window for the occurrence of slurry shrinkage is controlled within 5-60 minutes. If the shrinkage occurs too quickly (<5 minutes), the gel layer has not yet completely flowed and covered, which will lead to the film layer cracking or uneven thickness. If the shrinkage occurs too slowly (>60 minutes), the pores of the concrete surface will be partially blocked by early hydration products, or the surface will have begun to dry, which is not conducive to the deep penetration of the densifying agent.

[0039] Preferably, in S5, the curing period is at least 7 days; the hydraulic rinsing is carried out using a high-pressure water gun with a pressure ≥0.5MPa, and no polymer residue remains on the concrete surface after rinsing.

[0040] This invention provides a method for curing a protective layer on the concrete surface of a small box girder. It has the following beneficial effects:

[0041] 1. This invention employs a two-component in-situ gelation technology, utilizing the alkaline environment of the concrete surface to catalyze the instantaneous cross-linking of PVA and borate. This allows the low-viscosity spray coating liquid to immediately transform into a thixotropic gel with high yield stress upon contact with the substrate. This in-situ curing mechanism ensures that a uniform, non-flowing, closed film layer can be formed on the vertical web surface of the small box girder in one go, effectively blocking the moisture evaporation channels, improving the water retention and curing quality of the facade structure, and avoiding the curing failure caused by gravity loss of traditional liquid curing agents.

[0042] 2. This invention introduces specific polyether or inorganic salt dehydration shrinkage inducers into the gel network, utilizing the salting-out effect or osmotic pressure difference to induce controlled slurry shrinkage of the gel layer. This shrinkage process generates hydrostatic pressure inside the gel, forming a micro-pumping effect, which actively squeezes out and presses the nano-sized lithium silicate dense component wrapped in the network into the depth of the concrete capillary pores. This improves the shortcomings of traditional densifiers that only penetrate shallowly through capillary action, allowing the dense component to react with the hydration products in the deep layers of concrete to generate CSH gel, thereby improving the surface hardness and impermeability.

[0043] 3. Based on the chemically reversible properties of PVA-boron ester bonds, the protective film formed undergoes partial dissociation of its cross-linked structure and natural attenuation of interfacial adhesion after a 7-day curing period of hydration and carbonization. After construction, the film layer can be completely broken and peeled off simply by using a conventional high-pressure water gun, without the need for chemical paint removers or tedious mechanical grinding. The washed concrete surface is clean and free of organic polymer residue, providing a rough base for subsequent waterproofing layer construction or surface coating, achieving integrated operation of curing, densification, and surface cleaning. Detailed Implementation

[0044] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0045] Preparation Example A-1:

[0046] This preparation example demonstrates the preparation of a matrix film-forming solution (component A). 90.9 kg of deionized water was weighed and added to a reactor equipped with a heating mantle and a mechanical stirrer. Stirring was started (400 rpm), and 6.0 kg of polyvinyl alcohol (PVA, degree of polymerization 1799, degree of hydrolysis 88%) was slowly added. After dispersing at room temperature for 20 minutes, the temperature was raised to 92°C and stirred at a constant temperature for 60 minutes until the solution was completely transparent. Subsequently, the reactor temperature was lowered to 55°C, and 3.0 kg of glycerol and 0.1 kg of tributyl phosphate were added sequentially. Stirring was continued for 20 minutes to mix thoroughly. After naturally cooling to room temperature, the mixture was filtered through a 100-mesh filter to obtain matrix film-forming solution A-1 with a viscosity of approximately 550 mPa·s.

[0047] Preparation Example A-2:

[0048] This preparation example prepares a high-solids-content matrix film-forming solution (component A). 87.85 kg of deionized water was weighed, and following the same process steps as in Preparation Example A-1, 8.0 kg of polyvinyl alcohol (PVA, degree of polymerization 2488, degree of hydrolysis 88%), 4.0 kg of glycerol, and 0.15 kg of tributyl phosphate were added sequentially. The dissolution temperature was maintained at 95°C, and the dissolution time was extended to 90 minutes, yielding a matrix film-forming solution A-2 with a viscosity of approximately 780 mPa·s.

[0049] Preparation Example A-3:

[0050] This preparation example prepares a low-solids-content matrix film-forming solution (component A). 92.95 kg of deionized water was weighed, and following the same process steps as in preparation example A-1, 5.0 kg of polyvinyl alcohol (PVA, degree of polymerization 1788, degree of hydrolysis 88%), 2.0 kg of glycerol, and 0.05 kg of tributyl phosphate were added sequentially to obtain matrix film-forming solution A-3 with a viscosity of approximately 420 mPa·s.

[0051] Preparation Example B-1:

[0052] This preparation example prepares a functional initiator solution (component B) containing a polymer inducer. 56.0 kg of deionized water was weighed and added to a stirred tank, heated to 45°C, and 4.0 kg of sodium tetraborate decahydrate was added. The mixture was stirred until completely dissolved, followed by the addition of 5.0 kg of polyethylene glycol (PEG-400). The mixture was stirred for 10 minutes, and finally, 35.0 kg of lithium silicate aqueous solution (22% solid content) was slowly added dropwise at 200 rpm. After the addition was complete, the mixture was stirred for another 15 minutes to obtain a homogeneous and transparent functional initiator solution B-1.

[0053] Preparation Example B-2:

[0054] This preparation example prepares a high-concentration functional initiator solution (component B). 49.0 kg of deionized water was weighed, heated to 45°C, and 5.0 kg of sodium tetraborate decahydrate was dissolved. Then, 6.0 kg of polyethylene glycol (PEG-400) was added and mixed thoroughly. Finally, 40.0 kg of lithium silicate aqueous solution (solid content 22%) was slowly added dropwise, and the mixture was stirred until homogeneous to obtain functional initiator solution B-2.

[0055] Preparation Example B-3:

[0056] This preparation example prepares a functional initiator solution (component B) containing an inorganic salt inducer. 56.0 kg of deionized water was weighed and heated to 45°C to dissolve 4.0 kg of sodium tetraborate decahydrate. Then, 5.0 kg of anhydrous sodium sulfate was added as a dehydration shrinkage inducer, and the mixture was stirred until completely dissolved. Finally, 35.0 kg of lithium silicate aqueous solution (solid content 22%) was slowly added dropwise, and the mixture was stirred until homogeneous to obtain functional initiator solution B-3.

[0057] Preparation Example B-4:

[0058] This preparation example demonstrates the preparation of a functional initiator solution without a dehydration shrinkage inducer for comparative experiments. 61.0 kg of deionized water was weighed, heated to 45°C, and 4.0 kg of sodium tetraborate decahydrate was dissolved. Without adding polyethylene glycol or sodium sulfate, 35.0 kg of lithium silicate aqueous solution (22% solid content) was slowly added dropwise. After stirring until homogeneous, the comparative initiator solution B-4 was obtained.

[0059] Preparation Example B-5:

[0060] This preparation example demonstrates the preparation of a functional initiator solution without a penetrating densifying agent for comparative experiments. 91.0 kg of deionized water was weighed, heated to 45°C, and 4.0 kg of sodium tetraborate decahydrate was dissolved. Then, 5.0 kg of polyethylene glycol (PEG-400) was added, and the mixture was stirred until homogeneous. No lithium silicate aqueous solution was added, resulting in the comparative initiator solution B-5.

[0061] Example 1:

[0062] This embodiment provides a method for curing the protective layer on the concrete surface of a small box girder, specifically including the following steps:

[0063] (1) Base surface preparation: Select a C50 concrete box girder that has just completed steam curing and removed the side formwork, and confirm that its vertical surface of the web is wet and without standing water, the surface temperature is 25℃ and the pH value is about 12.5.

[0064] (2) Preparation of spraying equipment: Select a dual-channel high-pressure airless sprayer. Connect channel A to the storage tank containing the substrate film-forming liquid obtained in preparation example A-1, and connect channel B to the storage tank containing the functional initiator liquid obtained in preparation example B-1. Adjust the spray gun to the dual-nozzle external mixing mode, set the nozzle angle to 35°, and adjust the pump pressure to make the volume flow ratio (VA:VB) of the two channels at the nozzle outlet stable at 2:1.

[0065] (3) Construction operation: Hold the spray gun 40cm away from the concrete surface and spray evenly. The mixed liquid will undergo thixotropic gelation upon contact with the concrete surface, forming a non-sagging transparent gel film. Control the wet film coverage to be about 250g / m. 2 After spraying, the gel layer was left to stand for observation. After about 15 minutes, a trace amount of liquid phase precipitation appeared on the surface of the gel layer, indicating that the gel network was undergoing dehydration and shrinkage and was squeezing the liquid phase towards the inside of the substrate.

[0066] (4) Curing and cleaning: Keep the gel layer covered for 7 days. No additional watering is required during the curing period. After the curing period, use a high-pressure water gun with a pressure of 0.6MPa to rinse the surface. The gel film will break down quickly and fall off with the water flow, exposing the dense concrete surface.

[0067] Example 2:

[0068] This embodiment provides a method for curing the protective layer on the concrete surface of a small box girder, specifically including the following steps:

[0069] (1) Base preparation: Select the C50 concrete box girder after demolding and keep the surface moist.

[0070] (2) Preparation of spraying equipment: A dual-channel pneumatic spray gun is selected. Channel A is filled with the high solids content matrix film-forming liquid obtained in preparation example A-2, and channel B is filled with the high concentration functional initiator liquid obtained in preparation example B-2. The spraying air pressure and flow valve are adjusted so that the volume flow ratio (VA:VB) is controlled at 2.5:1.

[0071] (3) Construction operation: Spraying is carried out on the surface of the vertical web of concrete at a distance of 35cm. Due to the high viscosity of component A, the moving speed is appropriately reduced to ensure coverage. The wet film dosage is controlled at 280g / m. 2 After the mixed liquid is applied to the wall, it quickly builds up strength without flowing. After standing for 20 minutes, the gel layer shrinks.

[0072] (4) Maintenance and cleaning: After 7 days of natural maintenance, use a mechanical brush with low-pressure water flow to clean and remove the residual gel film on the surface.

[0073] Example 3:

[0074] This embodiment provides a method for curing the protective layer on the concrete surface of a small box girder, specifically including the following steps:

[0075] (1) Base preparation: Same as in Example 1.

[0076] (2) Preparation of spraying equipment: A two-component spraying system was used. Channel A was connected to the low-viscosity substrate film-forming liquid obtained in Preparation Example A-3, and channel B was connected to the functional initiator liquid containing inorganic salt inducer obtained in Preparation Example B-3. The volume flow ratio (VA:VB) of the two channels was set to 2:1.

[0077] (3) Construction operation: Spray the web of the box girder with a wet film coverage of 220g / m 2 This system utilizes the salting-out effect of inorganic salts to induce PVA gel shrinkage. About 10 minutes after spraying, the shrinkage of the gel layer and the migration of the interfacial liquid phase can be observed. Due to the low viscosity of the matrix liquid A-3, the initial flowability of the mixture is slightly better than that of Example 1, which is more conducive to spreading on rough surfaces. Subsequently, it is rapidly shaped under the action of borate.

[0078] (4) Maintenance and cleaning: After 7 days of maintenance, remove the surface film by natural rainwater or manual rinsing.

[0079] Example 4:

[0080] This embodiment provides a method for curing the protective layer on the concrete surface of a small box girder, specifically including the following steps:

[0081] (1) Base preparation: Same as in Example 1.

[0082] (2) Preparation of spraying equipment: Use a dual-channel sprayer. The raw materials are selected from Preparation Example A-1 and Preparation Example B-1, respectively. Adjust the flow control valve to adjust the volume flow ratio (VA:VB) to 1.5:1. At this time, the relative proportion of crosslinking agent and inducing agent in the system is relatively high.

[0083] (3) Construction operation: according to 300g / m 2 When spraying with the appropriate amount of component B, the gelation speed is extremely fast due to the increased proportion of component B. The resulting gel network is more rigid and has a significant shrinkage effect, which is beneficial for pressing more lithium silicate components into the matrix. However, it is important to note that the spraying operation should be continuous to avoid premature gelation at the nozzle.

[0084] (4) Maintenance and cleaning: After 7 days of maintenance, rinse with a water gun to remove.

[0085] Example 5:

[0086] This embodiment provides a method for curing the protective layer on the concrete surface of a small box girder, specifically including the following steps:

[0087] (1) Base preparation: Same as in Example 1.

[0088] (2) Preparation of spraying equipment: Use a dual-channel sprayer. The raw materials are selected from Preparation Example A-1 and Preparation Example B-1 respectively. Adjust the flow control valve to adjust the volume flow ratio (VA:VB) to 3:1. At this time, the proportion of PVA matrix in the system is relatively high.

[0089] (3) Construction operation: according to 240g / m 2 The amount of product used for spraying results in a relatively flexible gel layer with good water retention and sealing properties. The shrinkage process after separation of the slurry is more gradual than that in Example 1 and lasts for a longer period of time, making it suitable for construction scenarios with low ambient humidity and requiring longer-lasting physical sealing.

[0090] (4) Maintenance and cleaning: After 7 days of maintenance, rinse with a water gun to remove.

[0091] Comparative Example 1:

[0092] Compared with Example 1, the difference is that the two-component chemical curing system of the present invention is not used. Instead, the traditional manual watering curing method is adopted, in which the concrete surface is sprayed with water every 4 hours to keep the surface moist for 7 days. The other base preparation and subsequent test conditions are the same.

[0093] Comparative Example 2:

[0094] Compared to Example 1, the difference is that component A (matrix film-forming liquid) was not used during construction; instead, a single-channel spraying device was used to spray Preparation Example B-4 (lithium silicate borate solution without inducing agent, simulating conventional liquid thickener), and the spraying amount was controlled at 250 g / m³.2 Everything else is the same. This comparative example is used to simulate the application of conventional densifiers on vertical planes without the use of a gel carrier.

[0095] Comparative Example 3:

[0096] Compared to Example 1, the difference is that component B (functional initiator) used in the construction was replaced with Preparation Example B-5 (containing only borate crosslinking agent and PEG inducer, without lithium silicate), while the rest of the raw material formulation and process parameters were the same. This comparative example is used to simulate the case where only gel sealing curing is performed but chemical densification components are lacking.

[0097] Comparative Example 4:

[0098] Compared to Example 1, the difference lies in that component B (functional initiator) used in construction was replaced with Preparation Example B-4 (which does not contain dehydration shrinkage inducers such as polyethylene glycol or sodium sulfate), while the rest of the raw material formulation and process parameters remained the same. This comparative example was used to verify the effect on the densifier penetration performance when there is a lack of active slurry induction mechanism in the gel network.

[0099] Comparative Example 5:

[0100] Compared with Example 1, the difference is that sodium tetraborate decahydrate (crosslinking agent) is not added during the preparation of component B, so that the system cannot undergo in-situ crosslinking reaction after spraying and mixing, and only relies on the physical viscosity of the PVA solution and lithium silicate mixture for adhesion. Everything else is the same.

[0101] Test Example 1: Process adaptability and gel kinetics test

[0102] This test case aims to verify the feasibility of the composition and construction method of the present invention on a vertical base surface, focusing on the anti-sagging performance, gelation response speed, and the occurrence of slurry shrinkage effect.

[0103] 1. Test subject:

[0104] The composition systems prepared in Examples 1-5 and Comparative Examples 2, 4, and 5 were selected as test subjects. Comparative Example 1 was cured in pure water and did not have film-forming characteristics, so it was not included in this test; Comparative Example 3 only changed the functional components without changing the film-forming matrix, and its rheological behavior was similar to that of Example 1, so it was not repeated.

[0105] 2. Testing Method:

[0106] (1) Vertical sag resistance test: A standard C50 concrete test slab (500mm×500mm) was vertically fixed. A high-pressure airless sprayer was used for spraying, keeping the nozzle 30cm away from the substrate. The number of spray passes was gradually increased to increase the wet film thickness. When the first run of more than 5cm appeared on the coating surface, spraying was stopped immediately. The wet film thickness was measured and recorded using a wet film thickness gauge, which was recorded as the maximum sag resistance thickness.

[0107] (2) In-situ gelation time test: Spray the designed thickness (approximately 250 g / m) onto the concrete surface. 2 The coating was applied. Timing began the moment spraying ended, and every 2 seconds, a 2mm diameter glass rod was used to lightly touch the coating surface. The time required for the coating to change from a liquid to a gel-like state, and for the glass rod to be lifted without stringing, was recorded.

[0108] (3) Test for grout bleeding: A quantitative coating (300g / m³) is sprayed onto the surface of a horizontally placed concrete specimen. 2 Immediately seal the surrounding area with plastic wrap to prevent natural evaporation of moisture. After standing for 30 minutes, cover the coated surface with a known mass of quantitative filter paper (11 cm in diameter), and place a 500 g weight on the filter paper and apply pressure for 30 seconds to adsorb the liquid phase precipitated from the gel shrinkage. Weigh the increase in weight of the filter paper and calculate the amount of liquid exuded per unit area (mg / cm²). 2 This indicator reflects the degree of phase separation and shrinkage / discharge of the gel network.

[0109] 3. Test results: The specific data obtained from each group of experiments are shown in Table 1.

[0110] Table 1 shows the process adaptability and rheological behavior test data for each embodiment and comparative example.

[0111] Test group Maximum anti-sagging thickness (μm) In-situ gelation time (s) <![CDATA[30-min bleeding volume (mg / cm 2 )]]> Remark Example 1 2150 14 12.4 The gel layer is uniform and the surface is slightly moist. Example 2 3240 11 8.7 High viscosity matrix, large shrinkage resistance Example 3 1680 9 18.2 Significant salting-out effect, large volume of liquid excretion Example 4 2210 5 15.1 High cross-linking density, rapid shrinkage Example 5 1850 22 10.3 The gel is relatively soft and the reaction is relatively mild. Comparative Example 2 <60 N / A N / A It flows directly in liquid form and does not form a film. Comparative Example 4 2280 13 1.2 The gel layer dried with almost no drainage. Comparative Example 5 340 ＞600 0.4 Physical thickening, obvious sagging

[0112] Regarding vertical application performance: Both the examples and Comparative Example 4 showed anti-sagging thicknesses greater than 1600 μm, with gelation times controlled within 25 seconds. This indicates that utilizing the alkaline environment of the concrete surface to induce a complexation reaction between PVA and borate can effectively achieve a liquid-gel phase transition, giving the material excellent adhesion on vertical surfaces. In contrast, Comparative Example 2, containing only lithium silicate solution with extremely low viscosity, could not remain on vertical surfaces, resulting in a sagging thickness of less than 60 μm, confirming that a simple liquid densifier cannot meet the requirements for vertical surface application. Although Comparative Example 5 contained high-molecular-weight PVA, it lacked a crosslinking agent and could not form a chemical gel. Physical viscosity alone could not support thick film application, and the drying time was extremely long.

[0113] Example 3 used low-viscosity PVA in combination with an inorganic salt inducer and measured the highest amount of exudate, indicating that the salting-out effect has a stronger driving force on the shrinkage of the gel network than the difference in polymer compatibility.

[0114] Both Example 1 and Comparative Example 4 formed stable gel layers, but the secretion volume of Comparative Example 4 was only 1.2 mg / cm³. 2 The values ​​are close to the margin of measurement error. This confirms that in the absence of an inducing agent, the PVA-boric acid gel network tends to bind water and solute through hydrogen bonds, causing the lithium silicate solution to be locked inside the gel and unable to migrate to the interface. This data directly supports the necessity of dehydration shrinkage inducers for disrupting gel swelling equilibrium and constructing an active pumping mechanism.

[0115] Test Example 2: Curing effect, surface densification performance and interlayer adhesion performance test.

[0116] This test case mainly focuses on the comprehensive evaluation of the hardened performance indicators of concrete test blocks treated by the methods of the examples and comparative examples, covering water retention and curing efficiency, the enhancement effect of surface physical and mechanical properties, and the compatibility with subsequent processes.

[0117] 1. Sample preparation:

[0118] Standard C50 concrete test blocks with dimensions of 150mm × 150mm × 150mm were prepared, and the test surfaces were placed vertically immediately after demolding. Spraying treatment was performed according to the schemes of Examples 1-5 and Comparative Examples 1-5 (Comparative Example 1 used covering and water spraying). The treated test blocks were placed in a standard curing room (temperature 20±2℃, relative humidity 60±5%) and left to stand for 7 days. After 7 days, the residual curing layer was removed (washed with water), and the blocks were allowed to air dry naturally until 28 days of age for subsequent testing.

[0119] 2. Testing Method:

[0120] (1) 72-hour moisture retention rate test:

[0121] The procedure was carried out in accordance with the standard "Concrete Curing Agent" (JC901). 300mm × 300mm × 100mm concrete reference specimens were prepared. Immediately after demolding, the molded surfaces were treated according to the processes of each embodiment and comparative example (Comparative Example 1 involved spraying water every 4 hours). The specimens were placed in a standard environment (temperature 38±2℃, relative humidity 35±5%, wind speed 0.5m / s). The immediate mass after treatment and the mass after 72 hours were weighed, and the moisture retention rate was calculated.

[0122] (2) 28-day surface resilience test:

[0123] After 28 days of curing, the test blocks were vertically fixed, and a ZC3-A type rebound hammer was used to conduct a rebound test on the treated surface. Each test block was divided into 10 test areas, and 16 points were impacted in each test area. After removing the three maximum and three minimum values, the average value was taken, and the converted value of the surface concrete strength (MPa) was calculated according to the relevant specifications of JGJ / T23. This index reflects the degree of surface densification and hardening.

[0124] (3) Surface water absorption coefficient test (Karsten tube method):

[0125] After 28 days of curing and drying, the Karsten tube (Rilem tube) is sealed and fixed to the vertical concrete surface using putty. Water is poured into the tube to the "0" mark, and the volume (mL) of liquid level drop over 60 minutes is recorded. The lower the water absorption, the better the surface pore sealing and the stronger the impermeability.

[0126] (4) Determination of the thickness of the permeable dense layer:

[0127] After the test, the specimen was split open perpendicular to the treated surface, and water mist was sprayed onto the cut surface. Due to the reduced capillary water absorption in the densified region, a different wetting color difference will be observed compared to the substrate. The average thickness (mm) of the dry / low-wetting area on the surface was measured using vernier calipers.

[0128] (5) Subsequent interlayer bond strength test (pull-out test):

[0129] After the curing period (7 days) and cleaning process, a 40mm thick layer of cement paste (C40 mix) was poured directly onto the treated surface of each test block. After 28 days of standard curing, a pull-out test was conducted using the rebar anchoring method, and the failure load and failure mode (interfacial failure or cohesive failure) were recorded. This test was used to evaluate whether the residue in the curing layer had an adverse effect on interlayer bonding.

[0130] 3. Test Results: See Table 2 for detailed data obtained from each group of tests.

[0131] Table 2 Summary of comprehensive test data on concrete surface curing, densification and bonding performance.

[0132] Test group 72h moisture retention rate (%) 28-day surface resilience (MPa) Surface water absorption (mL) over 60 minutes Thickness of the permeable dense layer (mm) Interlayer pull-out bond strength (MPa) Forms of destruction Example 1 92.4 43.8 0.12 2.85 2.14 Cohesive failure of concrete Example 2 94.1 42.6 0.18 2.10 2.08 Cohesive failure of concrete Example 3 89.5 44.5 0.09 3.45 2.21 Cohesive failure of concrete Example 4 91.8 44.1 0.11 3.10 2.15 Cohesive failure of concrete Example 5 93.6 41.2 0.22 1.85 1.95 Cohesive failure of concrete Comparative Example 1 68.2 34.5 0.85 0.00 1.88 Cohesive failure of concrete Comparative Example 2 71.5 36.2 0.68 0.35 1.92 Cohesive failure of concrete Comparative Example 3 92.1 35.8 0.81 N / A 0.65 Interface destruction Comparative Example 4 93.2 36.9 0.58 0.45 2.05 Cohesive failure of concrete Comparative Example 5 78.4 35.1 0.76 0.15 1.98 Cohesive failure of concrete

[0133] (1) Driving effect of gel shrinkage on densifier migration: Both Example 1 and Comparative Example 4 have extremely high water retention rates (>90%), indicating that the PVA-boric acid gel system effectively blocks water evaporation. However, there are significant differences between the two in terms of densification index. The thickness of the penetrated densified layer in Example 1 reaches 2.85 mm, and the surface resilience strength is increased to 43.8 MPa; while Comparative Example 4, which lacks a dehydration shrinkage inducer, has a penetration depth of only 0.45 mm, and its resilience strength (36.9 MPa) is only slightly higher than that of the water curing group. This indicates that in the static gel network, active substances such as lithium silicate are easily bound by polymer chains and retained on the surface. Only by introducing an inducer to trigger the gel's separation shrinkage can sufficient microscopic pumping force be generated to push the active substances into the deep layers of the matrix. Although Comparative Example 4 has a good curing effect, it loses the deep modification function.

[0134] (2) The necessity of the carrier for vertical surface construction: In Comparative Example 2, the liquid densifier was directly sprayed, and it was severely lost due to gravity. The water retention rate (71.5%) and penetration depth (0.35mm) were both low, and effective curing could not be achieved. Example 1 solved the carrier adhesion problem by in-situ gelation, and achieved the dual effects of curing and densification.

[0135] (3) Removability and interlayer compatibility of the curing layer: Comparative Example 3 only used PVA gel for curing. Although the water retention rate met the standard, its interlayer pull-out strength was only 0.65 MPa, and interface failure occurred. This indicates that the unmodified PVA film is difficult to completely remove in the later stage and becomes an isolation layer. In contrast, the pull-out strength of Example 1 reached 2.14 MPa, which is comparable to the reference concrete.

[0136] (4) High efficiency of salting out effect: In Example 3, the maximum penetration depth and the highest rebound strength were obtained by using inorganic salt to induce contraction, which shows that the strong osmotic pressure difference generated by inorganic salt has extremely high efficiency in driving liquid phase migration, and verifies the broad spectrum and effectiveness of the selection of inducing agent.

Claims

1. A composition for the curing of a protective layer on the concrete surface of small box girders, characterized in that, The composition consists of separately packaged component A and component B; Component A is made from raw materials comprising the following weight percentages: Polyvinyl alcohol: 5.0%-8.0%; Moisturizing plasticizer: 2.0%-4.0%; Wetting and defoaming agent: 0.05%-0.15%; Water: Balance; The sum of the weight percentages of all raw materials is 100%; Component B is made from raw materials comprising the following weight percentages: Borate crosslinking agent: 3.0%-5.0%; Lithium silicate aqueous solution: 30.0%-40.0%; Polyether-based or inorganic salt-based dehydration shrinkage inducers: 4.0%-6.0%; Water: Balance; The sum of the weight percentages of all raw materials is 100%.

2. The composition for curing a protective layer on the concrete surface of a small box girder according to claim 1, characterized in that, The weight percentage of the raw materials is: Component A contains: 5.0%-6.0% polyvinyl alcohol, 2.0%-3.0% moisturizing plasticizer, 0.05%-0.10% wetting and defoaming agent, and water as the balance. Alternatively, component A may contain: 6.0%-8.0% polyvinyl alcohol, 3.0%-4.0% moisturizing plasticizer, 0.10%-0.15% wetting defoamer, and water as the remainder. Component B contains: 4.0%-5.0% borate crosslinking agent, 35.0%-40.0% lithium silicate aqueous solution, 5.0%-6.0% dehydration shrinkage inducer, and water as the balance.

3. The composition for curing a protective layer on the concrete surface of a small box girder according to claim 1, characterized in that, In component A: The polyvinyl alcohol is a partially alcoholyzed form with an average degree of polymerization of 1700-2400 and a degree of alcoholysis of 87.0 mol%-89.0 mol%. The moisturizing plasticizer is selected from glycerol or sorbitol; The wetting and defoaming agent is selected from tributyl phosphate or fatty alcohol polyoxyethylene ether.

4. The composition for curing a protective layer on the concrete surface of a small box girder according to claim 1, characterized in that, In component B: The borate crosslinking agent is selected from sodium tetraborate or sodium metaborate; The lithium silicate aqueous solution has a modulus of 2.8-3.2 and a solid content of 21.0wt%-23.0wt%. The polyether or inorganic salt dehydration shrinkage inducer is polyethylene glycol with an average molecular weight (Mw) between 380 and 600, or anhydrous sodium sulfate.

5. A method for preparing a composition for curing a protective layer on the surface of concrete of a small box girder, applied to the composition for curing a protective layer on the surface of concrete of a small box girder as described in any one of claims 1-4, characterized in that, Includes the following steps: Preparation of component A: Polyvinyl alcohol is dispersed in water at room temperature, heated to 90℃-95℃ and stirred until it is transparent, cooled to 50℃-60℃ and then moisturizing plasticizer and wetting defoamer are added, mixed evenly and then cooled and filtered. Preparation of component B: Dissolve the borate crosslinking agent in water at 40℃-50℃, add the dehydration shrinkage inducer and stir until homogeneous, then slowly add lithium silicate aqueous solution dropwise while stirring, and mix and homogenize to obtain a homogeneous liquid.

6. A method for curing a protective layer on the concrete surface of a small box girder, applied to the composition for curing a protective layer on the concrete surface of a small box girder as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Base surface preparation: Ensure that the concrete surface of the small box girder to be treated is moist but without standing water; S2, Two-component atomized spraying: Using a dual-channel spraying device, component A and component B are sprayed out simultaneously, so that the two liquid streams mix before or at the moment of contact with the concrete surface. S3, In-situ gelation: The mixed liquid is sprayed onto the concrete surface, and the alkaline environment of the concrete surface is used to catalyze the cross-linking reaction, so that the liquid is transformed into a thixotropic gel layer in situ on the surface. S4. Kinetic shrinkage and penetration: The thixotropic gel layer is left to stand, causing the dehydration shrinkage inducer in it to disrupt the gel swelling balance, triggering the separation shrinkage effect, squeezing out the liquid phase in the gel network and pressing it into the capillary pores of the concrete. S5. Maintenance and Cleaning: Keep the gel layer covered for maintenance. After the maintenance period, remove the gel layer by water rinsing.

7. The curing construction method for the concrete surface protective layer of a small box girder according to claim 6, characterized in that, In S2, the nozzle of the dual-channel spraying equipment is set to external mixing mode, and the volume flow ratio of component A to component B is controlled to be 1.5:1-3:

1. During spraying, control the wet film coverage of the mixture on the concrete surface to be 200g / m². 2 -300g / m 2 .

8. The curing construction method for the concrete surface protective layer of a small box girder according to claim 7, characterized in that, The volumetric flow rate ratio of component A to component B is 2:1 to 2.5:

1.

9. The method for curing and constructing a protective layer on the concrete surface of a small box girder according to claim 6, characterized in that, In S4, the specific process of the slurry shrinkage effect is as follows: within 5-60 minutes after the gel layer is formed, the gel network undergoes volume shrinkage, and a liquid phase rich in lithium silicate migrates at the interface between the gel layer and the concrete substrate.

10. A method for curing and constructing a protective layer on the concrete surface of a small box girder according to claim 6, characterized in that, In S5, the curing period is at least 7 days; the hydraulic flushing is carried out using a high-pressure water gun with a pressure ≥0.5MPa, and there is no polymer residue on the concrete surface after flushing.