Self-repairing filler additive material for cooling tower body and preparation method thereof
Patent Information
- Application Number
- CN202610906178.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-06-23
- Publication Date
- 2026-09-15
Smart Images
Figure CN122749075A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of concrete repair materials technology, specifically to a self-healing filler additive for cooling tower bodies and its preparation method. Background Technology
[0002] Currently, research on self-healing concrete materials mainly focuses on technologies such as microcapsule-encapsulated repair agents, hollow fiber-loaded repair fluids, and microbial mineralization-induced calcium carbonate precipitation. However, microcapsules and hollow fibers are prone to breakage and failure during concrete mixing, and have poor interfacial compatibility with the cement matrix. Microbial mineralization, on the other hand, is limited by the low bacterial activity and slow repair response in high-alkaline environments.
[0003] To address these issues, CN121851694A discloses a highly interfacially compatible flexible self-healing material grafted with silanized waterborne polyurethane and cellulose nanocrystals. By embedding reversible disulfide bonds into the waterborne polyurethane backbone and using the silane coupling agent APTES to bridge the cellulose nanocrystals as reinforcing fillers, a balance between tensile strength and self-healing efficiency is achieved. However, the repair process relies on external heating to trigger it. Although the self-healing efficiency increases with heating time, it cannot respond autonomously to cracks without human intervention. Furthermore, the cellulose nanocrystals only serve as a reinforcing phase and do not participate in the repair reaction. The self-healing relies solely on the breaking and recombination of disulfide bonds, resulting in a single repair mechanism. CN121494408B discloses a method for preparing lightweight self-healing concrete. It utilizes hollow glass microspheres to encapsulate calcium nitrate solution and grows a porous zeolite coating on the surface of the microspheres to form a core-shell-pore structure filler. Simultaneously, polydopamine-coated carboxymethyl cellulose hydrogel is prepared to achieve photothermal response repair. However, its self-healing relies on external near-infrared light irradiation to trigger the hydrogel's temperature rise and coordination bond dissociation, lacking passive self-repair capability. Furthermore, the hollow glass microspheres are easily broken during concrete mixing, leading to premature leakage of the repair agent. Although the chemical bonding between the zeolite coating and the cement matrix can improve interfacial strength, the release rate of calcium ions is limited by water molecule penetration, resulting in a slow repair response.
[0004] In summary, existing self-healing technologies lack passive, long-term, and highly compatible self-healing solutions for micro-cracks in cooling tower concrete under long-term wet-dry cycle conditions. Therefore, there is an urgent need to develop a self-healing filler additive material based on natural plant fibers and utilizing the calcium source of the cement matrix itself to achieve autonomous crack filling. Summary of the Invention
[0005] To address the shortcomings of existing technologies, this invention proposes a self-healing filler material for cooling tower bodies and its preparation method. This invention uses short flax fibers as a micro-reinforced substrate, depositing aluminum silicate gel in situ on its surface and within its pores. This gel is then regulated with triethanolamine and sealed with a hydrophobic outer layer of potassium methylsilicate. Finally, it is compounded with cement-compatible inorganic dispersion powder to form a dry granular filler. When the filler is incorporated into concrete, the flax fibers limit the crack width, and the aluminum silicate gel releases silicate, aluminum ions, and a small amount of sulfate ions upon contact with water in the cracks. These react with calcium ions in the cement pore liquid to generate CSH gel and ettringite, achieving chemical bonding and expansion compaction. The hydrophobic potassium methylsilicate layer, the alkali-resistant aluminum silicate gel layer, and the triethanolamine complexing layer collectively slow down the early erosion of the fibers and gel by alkali solutions. This solves the technical problems caused by traditional SAP self-healing methods, such as concrete strength loss, degradation of natural plant fibers in high-alkali concrete environments, premature dissolution of the silicate gel coating in alkaline environments, and fiber clumping and uneven dispersion during concrete mixing.
[0006] This invention proposes a self-healing filler additive for cooling tower bodies, comprising the following raw materials in parts by weight: 100 parts of flax short fiber, 120-200 parts of sodium silicate with effective solid content, 30-80 parts of aluminum sulfate octadecylhydrate, 3-18 parts of potassium methylsilicate with effective solid content, 0.5-6 parts of early strength agent, 30-140 parts of cement-based compatible inorganic dispersing powder, and 1-10 parts of polycarboxylate dispersant.
[0007] This invention also proposes a method for preparing a self-healing filler additive for cooling tower bodies, the specific technical solution of which is as follows: Step 1: Wash and filter the flax short fibers with an organic solvent aqueous solution, then dry them in an oven. Open the dried fibers and then soak the opened flax short fibers in a sodium silicate solution.
[0008] Step 2: Add aluminum sulfate solution to the impregnation system and stir. After filtration, wash with deionized water and dry to obtain gel-loaded fibers. Spray early strength agent onto the surface of the gel-loaded fibers and then place them.
[0009] Step 3: Use a peristaltic pump to spray potassium methylsilicate solution onto the surface of the gel-supported fiber treated with early strength agent, and then place it in a sealable curing chamber for humid heat curing, with CO2-containing air introduced into the curing chamber.
[0010] Step 4: The cured fiber, cement-compatible inorganic dispersant powder, and polycarboxylate dispersant are put into a drum mixer for mixing, then heated, dried and sieved to obtain dry granular self-healing filler additive.
[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Using flax short fibers to replace superabsorbent resin to prepare self-healing fillers, since the fibers themselves have a micro-reinforcing effect, they can effectively inhibit plastic shrinkage cracks. At the same time, the slow-release products of aluminum silicate gel, CSH and ettringite, can fill the tiny pores around the fibers, further densifying the interface transition zone, so that the self-healing function will not come at the expense of mechanical properties.
[0012] 2. The aluminum silicate gel coating is chemically stable, and the potassium methyl silicate hydrophobic layer provides physical isolation, which greatly reduces the alkali degradation rate of the fiber. This allows the fiber to maintain its micro-reinforcing function and gel slow-release capacity during long-term concrete service, avoiding the seepage channels caused by fiber decay.
[0013] 3. When water enters through cracks in the tower body, the aluminum silicate gel will hydrolyze to produce aluminum ions and sulfate ions, which react with calcium ions and hydroxide ions in the cement to form ettringite. During the crystallization process, it expands and actively compresses the crack wall, causing the crack to tend to close. At the same time, CSH gel provides chemical bonding that is homogeneous with concrete, ensuring the long-term durability of the repair interface. Attached Figure Description
[0014] Figure 1 The images are optical microscope images comparing the crack morphology of concrete samples before and after repair in the examples and comparative examples. In the images, a is the crack morphology of the unrepaired sample, b is the crack morphology of the sample after repair in Example 1, c is the crack morphology of the sample after repair in Comparative Example 2, d is the crack morphology of the sample after repair in Comparative Example 3, e is the crack morphology of the sample after repair in Comparative Example 6, and f is the crack morphology of the sample after repair in Comparative Example 7. Figure 2 The images shown are low-magnification SEM images of the crack sections of concrete samples from the examples and comparative examples. In the images, a is the crack section of sample 1 from Example 1, b is the crack section of sample 2 from Comparative Example 2, c is the crack section of sample 3 from Comparative Example 3, d is the crack section of sample 6 from Comparative Example 4, and e is the crack section of sample 7 from Comparative Example 5. Figure 3 The images shown are high-magnification SEM images of the crack filling products of concrete samples from the examples and comparative examples. In the images, a represents the crack filling morphology of Example 1, b represents the crack filling morphology of Comparative Example 2, c represents the crack filling morphology of Comparative Example 3, d represents the crack filling morphology of Comparative Example 6, and e represents the crack filling morphology of Comparative Example 7. Figure 4 The images shown are EDS surface scans of the crack filling products of concrete samples from the examples and comparative examples. In the examples, a is the surface scan of Example 1, b is the surface scan of Comparative Example 2, c is the surface scan of Comparative Example 3, d is the surface scan of Comparative Example 6, and e is the surface scan of Comparative Example 7. Detailed Implementation
[0015] The self-healing filler material for cooling tower bodies described in this application is further described in detail below. This does not limit the scope of protection of this application, which is defined by the claims. Certain specific details disclosed provide a comprehensive understanding of the various disclosed embodiments. However, those skilled in the art will recognize that embodiments can be implemented using other materials, etc., without employing one or more of these specific details.
[0016] This invention proposes a method for preparing a self-healing filler additive for cooling tower bodies, the specific technical solution of which is as follows: 1. Fiber cleaning and sodium silicate impregnation After being washed and dried in an aqueous organic solvent solution, the opened flax staple fibers are immersed in a sodium silicate solution. Washing with the aqueous organic solvent solution removes waxes, greases, fine dust particles, and some hemicellulose adhering to the fiber surface. The presence of these substances hinders the subsequent penetration of the solution into the fiber. The washing solution is then separated from the fiber by filtration, and the fibers are dried in an oven to remove any free water that entered the fibers during the washing process, restoring the fibers to a dry state. The opening process uses mechanical action to separate potentially sticky or tangled fiber bundles into individual fibers, increasing the contact area between each fiber and the external environment, eliminating mechanical entanglement between fibers, and providing a uniform dispersion for subsequent impregnation.
[0017] After being opened, the short flax fibers are completely immersed in a sodium silicate solution. The sodium silicate solution is then used to migrate into the fiber along the longitudinal grooves, surface microcracks, and natural pores on the cross-section of the fiber by the action of capillary force and external pressure difference. The liquid phase transport allows silicate ions with active groups to be pre-distributed on all available surfaces of the fiber, providing a spatially uniform silicon source distribution for the subsequent reaction with aluminum ions.
[0018] 2. Aluminosilicate reaction and early strength agent treatment Aluminum sulfate solution was added to the impregnation system and stirred. After filtration, washing, drying, and spraying with an early-strength agent solution, the mixture was allowed to stand. In a system containing sodium silicate impregnation solution and fibers, aluminum sulfate solution was added directly. Stirring allowed aluminum ions to rapidly diffuse in the liquid phase and contact the silicate ions already attached to the fibers. The resulting insoluble aluminum silicate gel was deposited in situ on the fiber surface and pore walls, forming a continuous or semi-continuous covering layer. Filtration then separated the fibers from the remaining reaction liquid, removing unreacted aluminum ions, sodium ions, sulfate ions, and byproducts. Drying was then performed to restore the gel-loaded fibers to dryness while simultaneously promoting further gel adhesion to the fibers.
[0019] The accelerator solution is sprayed using atomization or dripping to uniformly cover the dried gel-supporting fiber surface. Utilizing the fiber's adsorption capacity and the liquid's spreading properties, the accelerator molecules form a uniform adsorption film on the gel layer surface. After a period of time, the accelerator has sufficient time to penetrate and diffuse into the gel layer, completing contact with aluminum ions on the gel surface and within. Because the nitrogen and oxygen atoms in the accelerator molecules possess lone pairs of electrons, they can form stable water-soluble complexes with aluminum ions. These free aluminum ions then form insoluble hydroxide precipitates during subsequent drying or storage, clogging the micropores on the fiber surface or affecting the uniformity of the gel layer. Furthermore, when filler additives are finally incorporated into concrete, the accelerator can accelerate the hydration reaction of the aluminate and silicate phases in the cement clinker, thereby improving the early strength of the concrete.
[0020] 3. Apply potassium methylsilicate spray and cure with moist heat. After spraying potassium methylsilicate solution onto the fiber surface using a peristaltic pump, the fiber is placed in a sealed curing chamber and humidified with CO2-containing air. The peristaltic pump precisely controls the flow rate of the potassium methylsilicate solution, spraying the liquid onto the fiber surface in the form of fine droplets or a continuous stream. This spraying method avoids immersing the fibers in large amounts of liquid, thus reducing fiber adhesion, while ensuring that the outer surface of each fiber is covered with the liquid. A potassium methylsilicate liquid film forms on the sprayed fiber surface. The sprayed fibers are then placed in a sealable curing chamber, the door is closed to create a sealed space, and CO2-containing air is introduced into the chamber. The temperature and humidity inside the chamber are maintained at a high water vapor content and above room temperature, thus preventing the liquid film on the fiber surface from cracking due to excessive drying, while also providing the necessary heat and moisture for the curing reaction of the film. The introduction of CO2 gas alters the composition of the atmosphere inside the chamber, placing the liquid film on the fiber surface in an atmosphere containing CO2. This causes potassium methylsilicate to complete a hydrophobic film-forming reaction on the fiber surface, transforming it into an insoluble polymethylsilicate resin film, thereby forming a dense hydrophobic sealing layer on the outer layer of the fiber.
[0021] 4. Inorganic powder mixing, drying and sieving The cured fibers are mixed with inorganic dispersing powder and a dispersant, then dried and sieved. The three solid materials are placed together in the sealed chamber of a drum mixer. The rotation of the mixer drum causes relative displacement and collisions between the fibers and powder. During repeated tumbling, the inorganic dispersing powder particles gradually adhere to the outer surface of the fibers under the action of friction, electrostatic adsorption, and mechanical extrusion, thus forming a powdery isolation shell. The polycarboxylate dispersant also participates in the mixing, partially adsorbing on the fiber surface or dispersing within the powder shell, to improve its dispersion behavior in concrete.
[0022] After the materials are mixed, they are removed and sent to a heating and drying equipment. Heating evaporates the trace amounts of moisture remaining inside and on the surface of the fibers, while promoting further fixation between the dispersant and the fiber surface. Subsequently, agglomerates exceeding the screen aperture, excessively long fibers, or undispersed fiber bundles are intercepted and reprocessed through sieving, thereby ensuring the uniformity of the product particle size and facilitating its uniform incorporation into concrete.
[0023] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Table 1 shows the information on the raw materials used in the embodiments.
[0024] Table 1 Raw Material Information Table ; Example 1 S1: Take 100 parts by weight of flax short fiber, stir and wash it in 50wt% ethanol aqueous solution for 10 min, then filter it and put it in an oven to dry at 60℃ for 2 h. Put the dried fiber into an opening machine for opening treatment, put the opened fiber into a reaction vessel, add 430 parts by weight of 40wt% sodium silicate solution (containing 172 parts of effective sodium silicate content) into the reaction vessel, and add deionized water until the fiber is completely submerged. Evacuate the reaction vessel to -0.09MPa and maintain the vacuum to impregnate the fiber for 30 min.
[0025] S2: Release the vacuum in the reactor, dissolve 52 parts by weight of aluminum sulfate octadechydrate in 320 parts by weight of deionized water, stir until completely dissolved, and then add the entire solution to the reactor. Stir at 200 rpm for 20 minutes at 25°C. Then filter the solution through a 200-mesh filter cloth to collect the fibers, and then rinse three times with deionized water. Spread the washed fibers flat on a stainless steel tray and dry them in a 45°C forced-air drying oven for 40 minutes. Dissolve 3.0 parts by weight of triethanolamine in 20 parts by weight of deionized water, and spray the entire solution onto the surface of the dried fibers using a spray bottle. Let stand for 15 minutes.
[0026] S3: Use a peristaltic pump to spray 50 parts by weight of 30wt% potassium methylsilicate solution onto the fiber surface at a flow rate of 5mL / min (containing 15 parts of effective potassium methylsilicate). Keep the fiber loose during the spraying process. Transfer the sprayed fiber to a sealable carbonization curing chamber. After closing the chamber door, introduce air containing 3% CO2 into the curing chamber at a flow rate of 2L / min. Set the chamber temperature to 40℃ and the relative humidity to 95%. Curing time is 30min.
[0027] S4: The cured fiber, along with 130 parts by weight of inorganic dispersion powder and 6 parts by weight of sodium polyacrylate, is put into a V-type drum mixer and mixed at 30 rpm for 8 minutes. Then, the mixture is transferred to a forced-air drying oven and dried at 55°C for 4 hours. After drying, it is sieved through a 4 mm square hole sieve and the sieve material is collected to obtain dry granular self-healing filler additive.
[0028] Example 2 The difference from the preparation method in Example 1 is as follows: S1: Sodium silicate solution concentration is 35wt%, and soaking time is 20min; S2: Stirring temperature is 20℃, stirring time is 15min, and standing time is 10min; S3: Potassium methylsilicate solution concentration is 25wt%, curing temperature is 35℃, curing humidity is 90%, and curing time is 20min; S4: The mixing speed is 20 rpm and the mixing time is 5 min. All other steps are the same.
[0029] Example 3 The difference from the preparation method in Example 1 is as follows: S1: Sodium silicate solution concentration is 45wt%, and soaking time is 45min; S2: Stirring temperature is 30℃, stirring time is 30min, and standing time is 30min; S3: Potassium methylsilicate solution concentration is 35wt%, curing temperature is 45℃, curing humidity is 98%, and curing time is 45min; S4: Mixing speed is 40 rpm, mixing time is 12 min, all other steps are the same. Example 4 The difference from the preparation method in Example 1 is as follows: S1: Add 300 parts by weight of 40wt% sodium silicate solution, which contains 120 parts of effective sodium silicate content; S2: Take 30 parts by weight of aluminum sulfate octadechydrate and 0.5 parts by weight of triethanolamine; S3: Take 10 parts by weight of 30wt% potassium methylsilicate solution, which contains 3 parts of effective potassium methylsilicate content; S4: Take 30 parts by weight of inorganic dispersible powder and 1 part by weight of sodium polyacrylate. The remaining steps are the same.
[0030] Example 5 The difference from the preparation method in Example 1 is as follows: S1: Add 500 parts by weight of 40wt% sodium silicate solution, which contains 200 parts of effective sodium silicate content; S2: Take 80 parts by weight of aluminum sulfate octadechydrate and 6 parts by weight of triethanolamine; S3: Take 60 parts by weight of 30wt% potassium methylsilicate solution, which contains 18 parts of effective potassium methylsilicate content; S4: Take 140 parts by weight of inorganic dispersible powder and 10 parts by weight of sodium polyacrylate. The remaining steps are the same.
[0031] Example 6 The difference from the preparation method in Example 1 is as follows: S1: Replace the ethanol aqueous solution with the methanol aqueous solution, and the rest of the steps are the same.
[0032] Example 7 The difference from the preparation method in Example 1 is as follows: S1: Replace the ethanol aqueous solution with the acetone aqueous solution, and the rest of the steps are the same.
[0033] Example 8 The difference from the preparation method in Example 1 is as follows: S2: Triethanolamine is replaced with triisopropanolamine, and the remaining steps are the same.
[0034] Example 9 The difference from the preparation method in Example 1 is as follows: S2: Triethanolamine is replaced with diethanol monoisopropanolamine, and the remaining steps are the same.
[0035] Example 10 The difference from the preparation method in Example 1 is as follows: S4: Replace sodium polyacrylate with sodium salt of acrylic acid-maleic acid copolymer, and the remaining steps are the same.
[0036] Example 11 The difference from the preparation method in Example 1 is as follows: S4: Sodium polyacrylate is replaced with sodium methacrylate sulfonate, and the remaining steps are the same.
[0037] Comparative Example 1 The difference from the preparation method in Example 1 is as follows: S2: Cancel step S2; all other steps remain the same.
[0038] This comparative example prepares fillers lacking aluminum silicate gel filling.
[0039] Comparative Example 2 The difference from the preparation method in Example 1 is as follows: S2: Replace aluminum sulfate octahydrate with an equimolar amount of aluminum chloride hexahydrate, and the rest of the steps are the same.
[0040] This comparative preparation of fillers lacking the expansion and compaction effect of calcite.
[0041] Comparative Example 3 The difference from the preparation method in Example 1 is as follows: S3: No spraying with potassium methylsilicate solution is performed; all other steps are the same.
[0042] This comparative example prepared a filler lacking a potassium methylsilicate hydrophobic sealing layer.
[0043] Comparative Example 4 The difference from the preparation method in Example 1 is as follows: S2: Skip the spraying of triethanolamine solution and the standing process; all other steps remain the same.
[0044] This comparative example prepared fillers without early strength agent treatment.
[0045] Comparative Example 5 The difference from the preparation method in Example 1 is as follows: S2: Replace the aluminum sulfate solution with a dilute sulfuric acid solution; the remaining steps are the same.
[0046] This comparative preparation produced fillers that did not form aluminum silicate gel, but only ordinary silicate gel.
[0047] Comparative Example 6 The difference from the preparation method in Example 1 is as follows: S3: Do not introduce CO2 during humid heat curing; all other steps are the same.
[0048] This comparative example prepares potassium methylsilicate fillers that do not form dense hydrophobic films.
[0049] Comparative Example 7 The difference from the preparation method in Example 1 is as follows: The filler is obtained by mixing commercially available sodium polyacrylate superabsorbent resin particles with cement-based compatible inorganic dispersant powder and polycarboxylate dispersant.
[0050] This comparison uses conventional SAP self-healing filler.
[0051] Experimental Example 1 According to GB / T 50344-2019 "Technical Standard for Testing Building Structures", the self-healing fillers prepared in Examples 1-11 and Comparative Examples 1-7 were made into prism specimens of 100mm×100mm×400mm. The concrete mix proportion was: P·O 42.5 cement 330kg / m³. 3 Grade I fly ash 60kg / m³ 3 S95 slag powder 50kg / m 3Medium sand with a fineness modulus of 2.6: 720 kg / m³ 3 5~20mm continuously graded crushed stone 1050kg / m 3 Mixing water 160kg / m 3 Polycarboxylate superplasticizer 6.0 kg / m 3 Self-healing filler 3.5kg / m 3 (The flax fiber volume fraction is 25%~35%, the effective gel content is 18%~25%, the sulfate residue is 0.3%~1.5%, and the alkali content is 0.5%~2.5%). After the prepared specimens are cured for 28 days, a three-point bending loading method is used to pre-create cracks in the mid-span: the support spacing is 300mm, the load is applied at a displacement rate of 0.05mm / min, and the crack is monitored with a crack observation instrument with an accuracy of 0.01mm. When the crack width on the tension surface reaches 0.3~0.5mm, the load is immediately unloaded. Three measuring points are marked in the crack area, and the initial width is measured and the average value W0 is taken. The specimens are placed in a wet-dry cycle chamber, and the conditions are: soaking in tap water at 20℃ for 12h, followed by drying in hot air at 40℃ for 12h, and the cycle is repeated for 14 days. After the end, the width W1 after repair is measured at the same measuring point. The crack closure rate is calculated according to the formula = (W0-W1) / W0×100%.
[0052] According to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", the self-healing fillers prepared in Examples 1-11 and Comparative Examples 1-7 were made into 100mm×100mm×100mm cubic specimens with the same mix proportions. After 28 days of standard curing, three specimens were taken for compressive strength testing: the loading rate was 0.5MPa / s, the failure load was recorded, and the average value was taken as the reference strength σ0. Three more specimens were taken for pre-cracking: axial compression was applied to 75% of the reference strength σ0, and the displacement rate was controlled at 0.05mm / min to induce longitudinal cracks of 0.2~0.4mm in the specimens. After unloading, the crack width was confirmed, and the pre-cracked specimens were placed in a wet-dry cycle chamber for 14 days. After repair, the compressive strength was tested under the same conditions, and the average value σ1 was obtained. The compressive strength recovery rate was calculated according to the formula = σ1 / σ0×100%.
[0053] Table 2 Self-healing effects of the examples and comparative samples ; As shown in Table 2, the samples in the examples all exhibited high crack closure rates and compressive strength recovery rates, indicating that the synergistic modification process, which involves in-situ generation of aluminosilicate gel on the surface of flax fibers, hydrophobic sealing with potassium methylsilicate, and isolation by inorganic dispersion powder, effectively endows concrete with self-healing capabilities. Comparative Example 1, lacking both aluminosilicate gel and triethanolamine, showed a significant decrease in crack closure rate and compressive strength recovery rate, indicating that aluminosilicate gel is key to providing chemical repair components. Comparative Example 2, replacing aluminum sulfate with aluminum chloride hexahydrate, lacked sulfate ions and could not generate ettringite, relying solely on CSH gel for filling; both indicators were significantly lower than in the examples. Comparative Example 3, without potassium methylsilicate spraying, lost its hydrophobic protection, leading to premature gel dissolution and fiber degradation, resulting in low repair performance; this demonstrates that the hydrophobic sealing layer is crucial for maintaining long-term repair performance. Comparative Example 4, without triethanolamine spraying, lacked aluminum ion complexation and early strength effects; both indicators were significantly lower, indicating that triethanolamine has… It is beneficial to optimize gel release kinetics and early strength recovery; Comparative Example 5, which replaced aluminum sulfate with dilute sulfuric acid, only formed ordinary silica gel, which had poor alkali resistance and significantly reduced repair performance, indicating that the introduction of aluminum into the aluminum silicate gel is the core to improve alkali stability; Comparative Example 6, which did not introduce carbon dioxide during humid heat curing, could not form a dense hydrophobic film with potassium methylsilicate, and both indicators were poor; Comparative Example 7 used conventional superabsorbent resin self-healing filler, which had a certain crack closing ability, but the large pores left by water absorption caused strength loss, and the compressive strength recovery rate was significantly lower than all examples, highlighting the superiority of the fiber-alumina silicate gel system of the present invention in terms of mechanical property maintenance.
[0054] Experiment Example 2 According to GB / T 35378-2017 "Test Method for Tensile Mechanical Properties of Plant Single Short Fibers", self-healing fillers prepared in Examples 1-11 and Comparative Examples 1-6 were used. Flax single fibers with a length of about 5 mm were separated by washing and filtration. 30 fibers were randomly selected and the initial breaking strength was tested using a single fiber strength tester: the gauge length of the clamp was 2 mm, the tensile speed was 0.5 mm / min, the breaking load was recorded, and the fiber diameter was measured with a micrometer. The breaking strength was calculated and the average value F0 was taken. Another 30 fibers were randomly selected and immersed in simulated concrete pore liquid: 1.18 g of calcium hydroxide, 4.76 g of potassium hydroxide, and 2.26 g of sodium hydroxide were dissolved in 1 L of deionized water, the pH was adjusted to 13.0-13.5, the liquid-solid ratio was 20:1, and the fibers were placed in a 40℃ constant temperature water bath and sealed for 28 days. The liquid was changed every 7 days. After being taken out, the fibers were washed and dried, and the breaking strength F1 was tested. The fiber tensile strength retention rate was calculated according to the formula = F1 / F0 × 100%.
[0055] According to the electrical flux method in GB / T 50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Concrete", cylindrical specimens with a diameter of 100 mm and a height of 50 mm were prepared from Examples 1-11 and Comparative Examples 1-7, with the same mix proportions. After standard curing for 28 days, the specimens were divided into two groups: a control group without cracking and a pre-cracked repair group. In the repair group, longitudinal cracks with a depth of 2 mm and a width of 0.3-0.5 mm were pre-introduced along the axial direction on the side using the splitting method. After curing in a wet-dry cycle chamber for 14 days, the specimens were then subjected to further treatment before testing. The specimens were subjected to vacuum saturation: vacuum was applied to -0.09 MPa and maintained for 3 hours, then deionized water was injected and vacuum was continued for 1 hour, followed by immersion in normal pressure for 18 hours. The saturated specimens were then installed in an electrical flux fixture, with 3.0% sodium chloride solution injected on one side and 0.3 mol / L sodium hydroxide solution injected on the other side. A DC voltage of 60 V was applied, and the current was recorded every 30 minutes for 6 hours. The total electrical flux was calculated using the trapezoidal integral method. The effect of crack repair on chloride ion penetration was evaluated based on the electrical flux of the uncracked specimens.
[0056] Table 3 Durability of the Examples and Comparative Samples ; As shown in Table 3, the fiber tensile strength retention rate of the example samples was higher, and the electrical flux after cracking and repair was lower, indicating that the process of the present invention can simultaneously protect the fiber from alkali corrosion and reduce the risk of chloride ion penetration at the cracks. Comparative Example 1, lacking aluminosilicate gel protection, resulted in a decrease in tensile strength retention and an increase in chloride ion penetration, indicating that the absence of aluminosilicate gel led to insufficient fiber protection and inadequate crack sealing. Comparative Example 2, replacing aluminum sulfate with aluminum chloride hexahydrate, resulted in the inability to form ettringite without sulfate ions, leading to increased chloride ion penetration, indicating that the absence of ettringite reduced the crack sealing effect. Comparative Example 3, without spraying with potassium methylsilicate, lacked a hydrophobic barrier, resulting in a decrease in tensile strength retention and an increase in chloride ion penetration, indicating that the absence of a hydrophobic layer reduced the fiber's alkali resistance and resulted in incomplete crack sealing. Comparative Example 4, omitting triethanolamine, resulted in a slight decrease in tensile strength retention and an increase in chloride ion penetration. The increase indicates that the lack of triethanolamine leads to a decrease in fiber protection and repair density; Comparative Example 5 only generates ordinary silica gel, which does not contain aluminum, resulting in a low tensile strength retention rate and high chloride ion permeability, indicating that the lack of aluminum-containing gel leads to a decrease in alkali resistance and crack sealing effect; Comparative Example 6 does not introduce carbon dioxide, and the potassium methylsilicate film is incomplete, resulting in a decrease in tensile strength retention rate and high chloride ion permeability, which is due to the lack of carbon dioxide leading to an incomplete hydrophobic film; Comparative Example 7 uses conventional superabsorbent resin self-healing filler without fiber, and its chloride ion permeability is higher than that of the examples, indicating that the effect of this system in reducing chloride ion permeability is lower than that of the chemical filling system of the present invention.
[0057] Experimental Example 3 According to GB / T 176-2025 "Chemical Analysis Methods for Cement", the total soluble alkali equivalent (calculated as Na2O equivalent) in concrete after incorporating the self-healing fillers prepared in Examples 1-11 and Comparative Examples 1-7 was determined. Three 150mm cube specimens were formed for each batch, with the mix proportions as above. Immediately after mixing, 2kg of sample was taken from the mixer, and the mortar portion was sieved through a 5mm square-hole sieve. The mortar was then placed into a 50mm diameter, 100mm high steel extrusion cylinder and extruded under a pressure of 30MPa on a press. 10mL of the extruded pore fluid was collected, and the Na2O content was determined using a flame photometer. + and K + Concentration, calculated using the formula Na₂O equivalent concentration = C(Na + )×1.348+C(K + )×1.205×0.658, where C(Na) + ) and C(K + ) is Na + and K + Concentration, then calculate the total alkali amount according to the formula = (C Na2O ×0.08) / 1000, where C Na2O This represents the equivalent concentration of Na₂O in the pore fluid.
[0058] According to GB / T 749-2008 "Test Method for Sulfate Attack Resistance of Cement" and JGJ / T 70-2009 "Standard for Test Methods of Basic Performance of Building Mortar", prism specimens of 25mm×25mm×280mm were used. Coarse aggregate was removed from the mix design. Three specimens were formed for each batch. Stainless steel probes were pre-embedded at both ends of the mold during molding, with a gauge length of 250mm. After curing in the mold at 20℃ and 95% relative humidity for 24 hours, the specimens were demolded and the initial length L0 was immediately measured with a length comparator. The specimens were then placed in a 20℃ water curing chamber and cured for 28 days. The length L1 was measured after curing. The expansion rate was calculated as (L1-L0) / 250×100%. At the same time, a reference specimen without filler was prepared, and its expansion rate was measured as the reference expansion rate. The net expansion rate was calculated as: expansion rate with filler - expansion rate of reference specimen.
[0059] Table 4. Mixing performance of the examples and comparative samples ; As shown in Table 4, the total alkali content and net expansion rate of the example samples were lower than those of the comparative examples, indicating that the process of the present invention can reduce the total alkali content and net expansion rate. Comparative Example 1 omitted step S2, resulting in no aluminum silicate gel and triethanolamine treatment on the fiber surface. During the extraction of the pore liquid, ions were not adsorbed, leading to the highest total alkali content. The absence of gel filling in the cracks resulted in sulfate intrusion and the formation of expansion products, leading to the highest net expansion rate. Comparative Example 2 replaced aluminum sulfate with aluminum chloride hexahydrate. Without sulfate ions, ettringite could not be formed. The cracks were filled solely by CSH, resulting in insufficient compactness. Sulfate was more likely to intrude and generate secondary expansion products within the cement stone, leading to an increased net expansion rate. The Cl- introduced by aluminum chloride hexahydrate... - Interference with ion adsorption resulted in a higher total alkali content compared to the examples; Comparative Example 3, without potassium methylsilicate spraying, lacked a hydrophobic film on the outer fiber layer, making it easier for ions to be released during extrusion, leading to an increase in total alkali content. The absence of the hydrophobic film resulted in erosion of the gel in an alkaline environment, leading to decreased integrity of the crack-filling layer and increased sulfate intrusion, resulting in a higher net expansion rate; Comparative Example 4, without triethanolamine spraying, lacked Al during gel formation. 3+ Complexing agents lead to a less dense gel network and reduced ion adsorption capacity, resulting in an increase in total alkali content. Decreased gel density leads to insufficient crack filling, increasing the net expansion rate. Comparative Example 5 replaces aluminum sulfate with dilute sulfuric acid to generate ordinary silica gel. Silica gel has poor stability and is easily dissolved in alkaline environments, and its fiber protection and crack filling effects are weaker than aluminum-containing gels, resulting in higher total alkali content and net expansion rate than the examples. Comparative Example 6 does not introduce carbon dioxide, and potassium methylsilicate cannot be completely converted into an insoluble hydrophobic film, resulting in insufficient hydrophobic effect; both total alkali content and net expansion rate are higher than the examples. Comparative Example 7 uses conventional SAP self-healing filler. SAP absorbs water and expands to form large pores; crack sealing relies solely on physical plugging, which is less dense than chemical filling. Sulfate can slowly penetrate, resulting in a higher net expansion rate than most examples. SAP does not adsorb alkali metal ions and introduces Na+. + This results in a slightly higher total alkali content compared to some examples.
[0060] Experiment Example 4 The self-healing fillers prepared in the examples and comparative examples were formulated into 100mm×100mm×400mm prism concrete specimens with the same mix proportions as above. After mixing, the specimens were molded and compacted, covered and kept moist for 24 hours, then demolded and placed in a standard curing room for 28 hours. After standard curing, pre-cracking and repair cycles were performed, with the pre-cracking and wet-drying cycles performed as above. Another specimen that had been pre-cracking but not repaired was taken as a blank specimen. The same crack section in the middle of each group of specimens was selected, avoiding the edge damage area. The surface water was gently wiped away with lint-free paper. The specimens were then placed in a constant temperature chamber for 45 minutes to equilibrate until there was no obvious reflective water film on the surface. The cracks of the specimens were observed using an optical microscope. The results are as follows. Figure 1 As shown.
[0061] After the wet-dry cycle, a 10mm × 10mm × 10mm cubic block was cut from the middle section of the crack in the specimen, with the cutting direction perpendicular to the crack direction. The cut piece was immediately immersed in anhydrous ethanol for 24 hours, with the solution changed 2-3 times during this period to terminate hydration and reduce further changes in CSH and ettringite. After removing the sample, it was vacuum dried at 35℃ for 24 hours. Subsequently, a Pt film was sprayed onto the sample surface, and the sample was scanned using a field emission scanning electron microscope at low and high magnification. The scanning results are shown below. Figures 2-3 As shown.
[0062] A 10mm × 10mm × 5mm sample was taken from the middle section of the crack. Hydration was terminated with anhydrous ethanol for 24 hours, followed by vacuum drying at 35℃. The sample was then vacuum impregnated with low-viscosity epoxy resin for 30 minutes, and subsequently subjected to non-aqueous polishing. The sample was ground progressively with 400#, 800#, 1200#, and 2000# sandpaper, and polished with a 1μm diamond suspension. A C-film was then sprayed onto the sample, and an EDS surface scan was performed at a 15kV accelerating voltage. The scanning results are as follows: Figure 4 As shown.
[0063] Figure 1 In the first example, sample a is the sample before repair. It can be seen that there are through cracks with clear boundaries in the sample. Sample b is the sample of Example 1 after repair. It can be seen that after 14 days of wet-dry cycles, continuous grayish-white or light-white filling products appeared inside the concrete cracks of the sample of Example 1, and the crack width was significantly reduced, with some areas approaching closure. Sample c is the sample of Comparative Example 2 after repair. It can be seen that because aluminum sulfate was replaced with aluminum chloride, the system lacked sulfate ions, and the formation of ettringite was insufficient. Therefore, there were some precipitates in the cracks, but the continuity and fullness were weaker than those of Example 1. Samples d and e are the samples of Comparative Example 3 and Comparative Example 6 after repair, respectively. It can be seen that because Comparative Example 3 lacked a potassium methylsilicate hydrophobic layer, and Comparative Example 6 did not introduce CO2, the hydrophobic film was not dense. Both showed discontinuous filling and large residual crack width. Sample f is the sample of Comparative Example 7 after repair. It can be seen that there was apparent blockage in the test block, but the cracks were accompanied by pores or shrinkage marks.
[0064] Figure 2 The images show SEM cross-sections of the cracks in the test blocks. Image a is an SEM cross-section of Example 1, showing a continuous filling band within the crack channel. The filling product adheres tightly to the crack wall, and fiber-bridged cracks can be observed locally. Image b is a sample from Comparative Example 2, showing gel-like products but insufficient needle-like crystals, resulting in a thin crack filling layer. Images c and d are from Comparative Examples 3 and 6, respectively. Due to the lack of a protective layer or insufficient film formation, the gel dissolves prematurely, leading to a more dispersed distribution of products within the cracks. Image e is from Comparative Example 7, showing numerous large pores, collapsed pores, or shrinkage pores in the sample, corresponding to pore structure defects caused by the expansion of SAP after water absorption.
[0065] Figure 3The images show high-magnification SEM scans of the crack-filling products of the samples. Image a is a high-magnification SEM image of the sample from Example 1, showing two types of repair products: flocculent CSH gel and needle-like or rod-shaped ettringite (Aft) crystals. CSH coats the crack walls and fiber surfaces, forming a continuous cemented phase between particles. The ettringite crystals appear as slender needle bundles, interwoven within the cracks to form a spatial network and embedded in the CSH gel. Images b and c are samples from Comparative Examples 2 and 3, respectively. These samples lack needle-like ettringite and CSH gel, thus failing to form a continuous three-dimensional framework and filler, resulting in ineffective crack sealing. Image d is sample from Comparative Example 6, showing a certain amount of needle-like ettringite, but the crystal arrangement is disordered, and the CSH gel is unevenly distributed, resulting in poor overall density. Image e is sample from Comparative Example 7, showing numerous interconnected pores. This is due to the polymer film formed by the shrinkage of SAP after water absorption and expansion, leaving numerous permanent pores and resulting in poor repair durability.
[0066] Figure 4 Figure a shows the EDS surface scan of the sample from Example 1. It can be seen that Ca is clearly distributed in the crack walls and filling products in Example 1, corresponding to cement pore liquid and hydration products. Si and Ca are co-located in the gel region, corresponding to CSH gel. Al is enriched near needle-like crystals or fibers, originating from the release of aluminosilicate gel. S is co-located with Al and Ca in the needle-like crystal region, originating from ettringite Aft crystals. Figure b corresponds to the sample from Comparative Example 2. Due to the lack of sulfate, the S signal is significantly weakened, and the Ca-Al-S co-location region is small. Figures c and d are the samples from Comparative Example 3 and Comparative Example 6. It can be seen that the distribution of Si, Al, and S is more dispersed, and the continuous filling band inside the crack is not obvious. Figure e is the sample from Comparative Example 7. Although Ca enrichment is observed, the synergistic distribution of Ca-Si-Al-S is not as clear as in Example 1.
Claims
1. A self-healing filler additive for cooling tower bodies, characterized in that, The self-healing filler additive is composed of the following raw materials in parts by weight: 100 parts of flax short fiber, 120-200 parts of sodium silicate with effective solid content, 30-80 parts of aluminum sulfate octadecylhydrate, 3-18 parts of potassium methylsilicate with effective solid content, 0.5-6 parts of early strength agent, 30-140 parts of cement-based compatible inorganic dispersing powder, and 1-10 parts of polycarboxylate dispersant.
2. The self-healing filler material for cooling tower bodies according to claim 1, characterized in that: The self-healing filler additive uses the flax short fiber as a base, with aluminum silicate gel deposited in situ on the fiber surface and in the pores. The gel is coated with a hydrophobic layer of potassium methyl silicate. The aluminum silicate gel is generated in situ on the fiber surface and in the pores by sodium silicate and aluminum sulfate octadecylhydrate. The cement-based compatible inorganic dispersion powder is a compound of silica fume, metakaolin, and limestone powder.
3. A method for preparing a self-healing filler additive for a cooling tower body according to any one of claims 1 to 2, characterized in that, The preparation steps include the following: S1: Wash and filter the flax short fibers with an organic solvent aqueous solution and dry them in an oven. Then, open the dried fibers and soak the opened flax short fibers in sodium silicate solution. S2: Add aluminum sulfate solution to the impregnation system and stir. After filtration, wash with deionized water and dry to obtain gel-loaded fibers. Spray early strength agent on the surface of the gel-loaded fibers and then place them. S3: Use a peristaltic pump to spray potassium methylsilicate solution onto the surface of the gel-supporting fiber treated with early strength agent, and then place it in a sealable curing chamber for humid heat curing, with CO2-containing air introduced into the curing chamber; S4: The cured fiber is mixed with cement-based compatible inorganic dispersant powder and polycarboxylate dispersant in a drum mixer, then heated, dried and sieved to obtain dry granular self-healing filler additive.
4. The method for preparing a self-healing filler additive for a cooling tower body according to claim 3, characterized in that: The organic solvent mentioned in S1 is one or more of ethanol, methanol, and acetone.
5. The method for preparing a self-healing filler additive for a cooling tower body according to claim 3, characterized in that: The concentration of the sodium silicate solution in S1 is 35wt%~45wt%; the immersion time is 20~45min.
6. The method for preparing a self-healing filler additive for a cooling tower body according to claim 3, characterized in that: The early strength agent mentioned in S2 is one or more of triethanolamine, triisopropanolamine, and diethanol monoisopropanolamine.
7. The method for preparing a self-healing filler additive for a cooling tower body according to claim 3, characterized in that: The stirring temperature in S2 is 20~30℃, the stirring time is 15~30min, and the settling time is 10~30min.
8. The method for preparing a self-healing filler additive for a cooling tower body according to claim 3, characterized in that: The concentration of the potassium methylsilicate solution in S3 is 25wt%~35wt%; the temperature of the moist heat curing is 35~45℃, the humidity is 90%~98%, and the curing time is 20~45min.
9. The method for preparing a self-healing filler additive for a cooling tower body according to claim 3, characterized in that: The polycarboxylic acid dispersant mentioned in S4 is one or more of sodium polyacrylate, sodium salt of acrylic acid-maleic acid copolymer, and sodium methacrylate sulfonate.
10. The method for preparing a self-healing filler additive for a cooling tower body according to claim 3, characterized in that: The mixing speed in S4 is 20~40 rpm, and the mixing time is 5~12 min.
Citation Information
Patent Citations
A method for preparing a lightweight self-healing concrete
CN121494408B