Modified fly ash as well as preparation method and application thereof
By wrapping halloysite nanotubes loaded with rust inhibitors on the surface of fly ash, the problems of insufficient early strength and decreased alkalinity of fly ash concrete were solved, the microstructure of concrete and the durability of steel bars were improved, and low-carbon and environmentally friendly resource utilization was achieved.
Patent Information
- Application Number
- CN202511010326.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-22
- Publication Date
- 2025-09-19
AI Technical Summary
The insufficient early strength and decreased internal alkalinity of fly ash concrete lead to the degradation of early mechanical properties of concrete and accelerated corrosion of steel bars, especially the durability problems of infrastructure serving in marine environments.
Halloysite nanotubes loaded with rust inhibitors are encapsulated on the surface of fly ash to form modified fly ash through electrostatic adsorption, thereby increasing the specific surface area and surface roughness of the fly ash, and enhancing the passivation ability of the steel bars through the controlled-release function of the rust inhibitor.
It improves the microstructure and early mechanical properties of concrete, enhances its impermeability and resistance to chloride ion corrosion, prolongs the durability of steel bars, and alleviates environmental pollution and greenhouse gas emissions.
Smart Images
Figure CN120664805A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the field of concrete, and in particular relates to modified fly ash and a preparation method and application thereof. Background Art
[0002] Fly ash is the primary solid waste discharged from coal-fired power plants. With the development of the power industry, fly ash emissions have increased annually, becoming one of the largest industrial waste streams in my country and posing a significant environmental risk. Through long-term development and utilization, fly ash has been used as a low-carbon cementitious material in engineering construction, replacing some cement. This resource not only significantly addresses environmental pollution but also effectively mitigates greenhouse gas emissions.
[0003] However, the replacement of cement with fly ash is also accompanied by negative impacts on concrete performance, such as insufficient early strength and decreased internal alkalinity. The addition of fly ash slows down the early hydration process of cement, resulting in more pores and cracks within the concrete. This not only leads to a decrease in the early mechanical properties of concrete, but also provides a convenient channel for the penetration and diffusion of harmful ions, accelerating the corrosion process of the steel bars. At the same time, the reduction in cement usage leads to a decrease in the pH value of the pore fluid within the concrete, deteriorating the high alkaline environment that forms a passivation film on the surface of the steel bars. In particular, low-carbon reinforced concrete infrastructure serving in marine environments is exposed to the harsh conditions of high chloride salts, high humidity, and high temperatures for a long time, and the internal steel bars are prone to severe corrosion, which in turn leads to a series of durability problems.
[0004] In the existing technology, the measures to deal with the insufficient early strength of fly ash concrete are mainly to modify the fly ash, including physical, biological modification, chemical modification, etc. The main principle is to increase the specific surface area and roughness of the fly ash particle surface, or to improve the surface activity of the fly ash particles through modification methods. Among the many fly ash modification technologies, the use of micro-nano materials to modify the fly ash surface is a current research hotspot. In addition, the method to reduce the alkalinity inside fly ash concrete is mainly steel bar rust inhibitors. The steel bar rust inhibitors added during the concrete mixing stage can be adsorbed on the steel bar surface during the steel bar passivation period to form a denser passivation protective film, thereby coping with the internal environment of the concrete pore fluid with a low pH value. Although rust inhibitors are effective in improving the corrosion resistance of steel bars, they still face problems such as "affecting concrete performance" and "poor long-term effectiveness" during their application. Summary of the Invention
[0005] Purpose of the invention: The first purpose of the present invention is to provide a modified fly ash that solves the problems of insufficient early strength and decreased internal alkalinity of fly ash concrete; the second purpose of the present invention is to provide a method for preparing the modified fly ash; the third purpose of the present invention is to provide the application of the modified fly ash in concrete.
[0006] Technical solution: The modified fly ash of the present invention is formed by encapsulating halloysite nanotubes loaded with a rust inhibitor on the surface of the fly ash.
[0007] Preferably, the mass ratio of the rust inhibitor-loaded halloysite nanotubes to fly ash is 1:10 to 1:20. The amount of halloysite may affect the thickness of the fly ash coating, thereby affecting the basic properties of the fly ash (the improved mechanical properties are different).
[0008] Preferably, the halloysite is nano-scale tubular halloysite.
[0009] Preferably, the preparation method of the halloysite nanotubes loaded with rust inhibitor is: adding the rust inhibitor to a solvent to prepare a solution of the rust inhibitor, immersing the halloysite nanotubes in the rust inhibitor solution, ultrasonically dispersing for 5 to 30 minutes, standing under negative pressure conditions at 20 to 40° C. for 12 to 48 hours, repeating 3 to 5 times, taking out, washing, and drying to obtain the halloysite nanotubes loaded with rust inhibitor.
[0010] Preferably, the solvent is water.
[0011] Preferably, the concentration of the rust inhibitor in the rust inhibitor solution is 0.1-1M.
[0012] Preferably, the negative pressure condition is 0.5-0.8 MPa.
[0013] Preferably, the rust inhibitor is one or more of nitrite, molybdate, benzotriazole, calcium lignin sulfonate, sodium citrate, and sodium dodecylbenzene sulfonate.
[0014] The method for preparing the modified fly ash of the present invention comprises the following steps:
[0015] (1) mixing the halloysite nanotubes loaded with the rust inhibitor and the fly ash powder uniformly, adding an activator and mixing uniformly, so that the halloysite nanotubes loaded with the rust inhibitor are coated on the surface of the fly ash under the action of electrostatic adsorption;
[0016] (2) washing the mixed solution until the pH value of the solution reaches a range of 6 to 7, and drying to obtain chemically modified fly ash;
[0017] The activator plays an alkali activating role, making the surface of fly ash positively charged and the outer surface of halloysite negatively charged, so the positive and negative charges will produce electrostatic adsorption.
[0018] Preferably, the mass ratio of water glass solution to sodium hydroxide solution in the activator solution is 5:1 to 1:1; the mass fraction of the water glass solution is 30 to 50%; and the concentration of the sodium hydroxide solution is 10 to 14 M. The concentration ratio of the activator to the sodium hydroxide solution affects the alkaline excitation reaction on the surface of the fly ash coated with halloysite nanotubes loaded with the rust inhibitor. The higher the sodium hydroxide concentration, the faster the alkaline excitation reaction on the fly ash surface, and the faster the adsorption of the halloysite nanotubes loaded with the rust inhibitor.
[0019] Preferably, the mass ratio of the activator solution to fly ash is in the range of 10:1 to 1:1. The activator mass ratio affects the amount of rust inhibitor-loaded halloysite nanotubes coated on the fly ash surface. A higher mass ratio results in a faster alkaline activation reaction on the fly ash surface, resulting in more halloysite nanotubes adsorbing the rust inhibitor.
[0020] Preferably, in step (2), the washing comprises: repeatedly centrifuging, filtering, and washing the mixed solution with ionized water; and the drying comprises: centrifuging, filtering, and drying.
[0021] Application of the modified fly ash of the present invention in concrete.
[0022] Invention mechanism: The modified fly ash of the present invention, on the one hand, uses halloysite loaded with rust inhibitor to modify the surface of fly ash particles, and stimulates the pozzolanic activity of fly ash by increasing the specific surface area and surface roughness of fly ash, so that the number of hydration products is increased during the hydration process. A large number of hydration products are intertwined, filling the pores between particles, and the matrix microstructure is gradually densified, thereby improving the concrete's impermeability and resistance to chloride ion corrosion. On the other hand, the halloysite loaded with rust inhibitor plays a control-release function, which not only reduces the risk of rust inhibitor participation in the hydration process and ensures the long-term effectiveness of the rust inhibitor performance, but also enhances the passivation ability and chloride ion corrosion resistance of steel bars in low-alkali environments through the release and adsorption of rust inhibitors. The rust inhibitor is released from the halloysite nanotubes and adsorbed onto the surface of the steel bar matrix, forming a corresponding rust inhibitor ion oxidation protective layer, which not only improves the passivation ability of steel bars in low-alkali environments, but also enhances the steel bars' resistance to chloride ion corrosion. Therefore, modified fly ash coordinately improves the durability of reinforced concrete from two aspects: concrete microstructure and steel bar passivation performance.
[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The modified fly ash of the present invention adopts the surface of the fly ash particles modified by halloysite loaded with rust inhibitor, thereby increasing the specific surface area and surface roughness of the fly ash, and the halloysite loaded with rust inhibitor has a control-release function; (2) The fly ash incorporated in the present invention is industrial solid waste, which alleviates environmental pollution and waste of resources while reducing greenhouse gas emissions, thereby achieving a low-carbon effect; (3) The preparation method is simple and easy to industrialize; (4) The modified fly ash of the present invention is used in concrete, which improves the microstructure and early mechanical properties of concrete, and improves the concrete's impermeability and resistance to chloride ion corrosion. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1 TEM images of the halloysite before and after loading the rust inhibitor in Example 1;
[0025] Figure 2 The SEM images of fly ash before and after modification in Example 1;
[0026] Figure 3 This is a Nyquist comparison diagram of electrochemical impedance spectroscopy of pure slurry samples of modified fly ash used for pre-embedded steel bars in Comparative Example 1 and Examples 1 to 4, which were immersed in a 3.5 wt % sodium chloride solution for 180 days. DETAILED DESCRIPTION
[0027] The technical solution of the present invention will be further described below in conjunction with embodiments.
[0028] Example 1
[0029] The preparation method of the modified fly ash of the present invention comprises the following steps:
[0030] (1) Benzotriazole (BTA) was added to 100 mL of deionized water to prepare a 0.5 M aqueous solution of rust inhibitor. Halloysite nanotubes were immersed in the aqueous solution of rust inhibitor and ultrasonically dispersed for 10 min. The solution was allowed to stand at a negative pressure of 0.8 MPa at 30 °C for 24 h. This process was repeated three times. The solution was washed and dried at room temperature to obtain halloysite nanotubes loaded with rust inhibitor (named HNT@BTA) for later use.
[0031] (2) Weigh 40 g of water glass solution (37 wt.%, mass ratio of SiO2 to Na2O is 3:2) and 10 ml of sodium hydroxide solution (10 M) to prepare an activator solution.
[0032] (3) Weigh 1 g of the rust inhibitor-loaded halloysite prepared in step (1) and 20 g of fly ash powder and place them in a beaker and mix them evenly; then add the activator solution prepared in step (2) to the beaker containing the mixed powder, and stir at a constant speed of 300 r / min, a stirring time of 60 s, and a stirring temperature of 25°C.
[0033] (4) Repeat the centrifugation, filtration, and ionized water washing process of the mixed solution in step (3) until the pH value of the solution reaches a range of 6 to 7; centrifuge, filter, and dry again to obtain chemically modified fly ash (named FA-HNT@BTA).
[0034] like Figure 1 This is a TEM comparison of the halloysite before and after loading the rust inhibitor in step (1). Figure 1 (a) is halloysite, Figure 1 (b) is the halloysite after loading the rust inhibitor. It can be seen that there is an obvious black shadow in the inner cavity of the halloysite, indicating that the rust inhibitor is successfully loaded.
[0035] like Figure 2 This is the SEM comparison of fly ash before and after modification. It can be clearly seen that the untreated fly ash particles are spherical particles with smooth surfaces. Figure 2 (a), from Figure 2 (b) It can be observed that the halloysite loaded with rust inhibitor is successfully coated on the surface of fly ash particles, indicating that the modification is successful.
[0036] Example 2
[0037] The preparation method of the modified fly ash of the present invention comprises the following steps:
[0038] (1) Molybdate was added to 100 mL of deionized water to prepare a 0.5 M aqueous solution of a rust inhibitor, and the halloysite nanotubes were immersed in the aqueous solution of the rust inhibitor, ultrasonically dispersed for 10 min, and allowed to stand for 24 h under a negative pressure of 0.8 MPa at 30 ° C. This was repeated three times, and the solution was taken out, washed, and dried at room temperature to obtain the halloysite nanotubes loaded with the rust inhibitor for later use.
[0039] (2) Weigh 40 g of water glass solution (37 wt.%, mass ratio of SiO2 to Na2O is 3:2) and 10 ml of sodium hydroxide solution (10 M) to prepare an activator solution.
[0040] (3) Weigh 2 g of the rust inhibitor-loaded halloysite prepared in step (1) and 20 g of fly ash powder, place them in a beaker and mix them evenly. Then add the activator solution prepared in step (2) to the beaker containing the mixed powder, and stir at a constant speed of 300 r / min for 60 s at a temperature of 25°C.
[0041] (4) Repeat the centrifugation, filtration, and ionized water washing process on the mixed solution until the pH value of the solution reaches 6 to 7. Centrifuge, filter, and dry again to obtain chemically modified fly ash.
[0042] Example 3
[0043] The preparation method of the modified fly ash of the present invention comprises the following steps:
[0044] (1) Nitrite was added to 100 mL of deionized water to prepare a 0.5 M aqueous solution of a rust inhibitor, and the halloysite nanotubes were immersed in the aqueous solution of the rust inhibitor, ultrasonically dispersed for 10 min, and allowed to stand for 24 h under a negative pressure of 0.8 MPa at 30 ° C. This was repeated three times, and the tubes were taken out, washed, and dried at room temperature to obtain the halloysite nanotubes loaded with the rust inhibitor for later use.
[0045] (2) Weigh 40 g of water glass solution (37 wt.%, mass ratio of SiO2 to Na2O is 3:2) and 10 ml of sodium hydroxide solution (14 M) to prepare an activator solution.
[0046] (3) Weigh 1 g of the rust inhibitor-loaded halloysite prepared in step (1) and 20 g of fly ash powder, place them in a beaker and mix them evenly. Then add the activator solution prepared in step (2) to the beaker containing the mixed powder, and stir at a constant speed of 300 r / min for 60 s at a temperature of 25°C.
[0047] (4) Repeat the centrifugation, filtration, and ionized water washing process on the mixed solution until the pH value of the solution reaches 6 to 7. Centrifuge, filter, and dry again to obtain chemically modified fly ash.
[0048] Example 4
[0049] The preparation method of the modified fly ash of the present invention comprises the following steps:
[0050] (1) Sodium citrate was added to 100 mL of deionized water to prepare a 0.5 M aqueous solution of a rust inhibitor. The halloysite nanotubes were immersed in the aqueous solution of the rust inhibitor and ultrasonically dispersed for 10 min. The solution was allowed to stand for 24 h under a negative pressure of 0.8 MPa at 30 ° C. This was repeated three times. The solution was taken out, washed, and dried at room temperature to obtain the halloysite nanotubes loaded with the rust inhibitor for later use.
[0051] (2) Weigh 20 g of water glass solution (37 wt.%, mass ratio of SiO2 to Na2O is 3:2) and 10 ml of sodium hydroxide solution (10 M) to prepare an activator solution.
[0052] (3) Weigh 1 g of the rust inhibitor-loaded halloysite prepared in step (1) and 20 g of fly ash powder, place them in a beaker and mix them evenly. Then add the activator solution prepared in step (2) to the beaker containing the mixed powder, and stir at a constant speed of 300 r / min for 60 s at a temperature of 25°C.
[0053] (4) Repeat the process of centrifuging, filtering, and washing with ionized water on the mixed solution until the pH value of the solution reaches 6-7, and then centrifuge, filter, and dry again to obtain chemically modified fly ash.
[0054] Comparative Example 1
[0055] Comparative Example Group A: Test blocks without embedded steel bars were prepared using a grout containing cement, unmodified fly ash, and mixing water in a mass ratio of 4:1:2. Ordinary Portland cement with a P·O 42.5 rating was used. Mechanical and porosity tests were performed after 28 days of curing under standard conditions.
[0056] Comparative Example Group B: Test blocks with pre-embedded rebar were prepared using a grout consisting of cement, unmodified fly ash, and mixing water in a mass ratio of 4:1:2. The cement used was ordinary Portland cement with a P·O 42.5 ratio. After 28 days of standard curing, the blocks were immersed in a 3.5wt% sodium chloride solution for 180 days. Electrochemical impedance spectroscopy (EIS) testing was then performed.
[0057] Performance Testing
[0058] Test method: The modified fly ash prepared in Examples 1 to 4 was mixed with cement to form a slurry test block. The slurry test blocks were divided into two groups: Group A had no embedded steel bars and was used to test the mechanical properties and pore structure of the test blocks; Group B had embedded steel bars and was used to test the corrosion resistance of the steel bars. The slurry test blocks were composed of cement, modified fly ash, and mixing water, with a mass fraction ratio of cement: modified fly ash: water = 4:1:2; the cement was ordinary Portland cement with a P·O 42.5 ratio; the slurry test blocks in Group A were subjected to mechanical and porosity tests after 28 days under standard curing conditions, and the slurry test blocks in Group B were subjected to characterization curing conditions for 28 days and then immersed in a 3.5wt% sodium chloride solution for 180 days. After the immersion, electrochemical impedance spectroscopy tests were performed.
[0059] Table 1 Compressive strength and porosity of comparative examples and examples
[0060] Pure slurry test block Compressive strength / (MPa) Porosity / (%) Comparative Example 1A 40.3 33.6 Example 1 52.4 27.5 Example 2 51.0 28.4 Example 3 51.6 29.3 Example 4 49.5 29.5
[0061] Table 1 shows the compressive strength and porosity test results for Examples 1-4 and Comparative Example 1. The modified fly ash-cement paste samples from Examples 1-4 exhibit a significant increase in compressive strength and a significant decrease in porosity. This is because the fly ash surface is coated with halloysite nanotubes loaded with rust inhibitors, increasing the specific surface area and surface roughness. This facilitates the pozzolanic reaction of fly ash particles during the fly ash-cement hydration reaction, thereby gradually increasing the production of hydration products. These hydration products interweave and fill the inter-particle pores, gradually densifying the microstructure and ultimately improving the early mechanical properties and porosity of the concrete matrix.
[0062] In Example 2, the mass ratio of the rust inhibitor-loaded halloysite nanotubes to fly ash was increased compared to Example 1, resulting in a slight decrease in the compressive strength and a further increase in porosity. This is because the increased rust inhibitor-loaded halloysite nanotubes aggregated on the fly ash surface, promoting the entrapment of moisture and air, leading to stress concentration and reducing the increase in mechanical strength.
[0063] In Example 3, the concentration of sodium hydroxide in the activator composition was increased compared to Example 1, resulting in a slight decrease in the compressive strength of the sample and a further increase in porosity. This is because the increased rate of the fly ash pozzolanic reaction caused some of the hydration products generated during the hydration process to agglomerate.
[0064] Compared to Example 1, Example 4 exhibits a slight decrease in compressive strength and a further increase in porosity due to the reduced mass of the activator. This is because the fly ash surface is not fully coated with the halloysite nanotubes loaded with the rust inhibitor, reducing the fly ash's specific surface area, inhibiting its pozzolanic reaction, and lowering the hydrate content in the sample.
[0065] Figure 3 The EIS graphs for Examples 1-4 and Comparative Example 1B show that, compared to Comparative Example 1B, over the 180-day corrosion period, Examples 1-4 exhibited a significant improvement in corrosion resistance due to the release of the rust inhibitor from the halloysite nanotubes, which acted on the surface of the embedded rebar. This promoted the formation of a passive film on the rebar surface, improved the density and composition of the passive film, and enhanced the corrosion resistance of the rebar. Consequently, the capacitive reactance arc radius in the EIS results was significantly larger, indicating that the modified fly ash significantly improved the corrosion resistance of the rebar in the clean slurry test piece during long-term corrosion.
Claims
1. A modified fly ash, characterized in that: The modified fly ash is formed by encapsulating the halloysite nanotubes loaded with the rust inhibitor on the surface of the fly ash.
2. The modified fly ash according to claim 1, characterized in that The mass ratio of the halloysite nanotubes loaded with the rust inhibitor to the fly ash is 1:10 to 1:
20.
3. The modified fly ash according to claim 1, characterized in that The halloysite is nano-scale tubular halloysite.
4. The modified fly ash according to claim 1, characterized in that The preparation method of the rust inhibitor-loaded halloysite nanotubes comprises the following steps: adding a rust inhibitor to a solvent to prepare a rust inhibitor solution, immersing the halloysite nanotubes in the rust inhibitor aqueous solution, ultrasonically dispersing the halloysite nanotubes for 5 to 30 minutes, allowing the nanotubes to stand under negative pressure at 20 to 40° C. for 12 to 48 hours, repeating the steps 3 to 5 times, taking out the nanotubes, washing them, and drying them to obtain the rust inhibitor-loaded halloysite nanotubes.
5. The modified fly ash according to claim 4, characterized in that: The concentration of the rust inhibitor in the rust inhibitor solution is 0.1-1M.
6. The modified fly ash according to claim 1, characterized in that: The rust inhibitor is one or more of nitrite, molybdate, benzotriazole, calcium lignin sulfonate, sodium citrate, and sodium dodecylbenzene sulfonate.
7. A method for preparing the modified fly ash according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) mixing the halloysite nanotubes loaded with the rust inhibitor and the fly ash powder uniformly, adding an activator and mixing uniformly, so that the halloysite nanotubes loaded with the rust inhibitor are coated on the surface of the fly ash under the action of electrostatic adsorption; (2) washing the mixed solution until the pH value of the solution reaches a range of 6 to 7, and drying to obtain chemically modified fly ash; The activator solution is a mixture of water glass solution and sodium hydroxide solution.
8. The method for preparing modified fly ash according to claim 7, characterized in that: The mass ratio of the water glass solution to the sodium hydroxide solution in the activator solution is 5:1 to 1:1; the mass fraction of the water glass solution is 30 to 50%, and the concentration range of the sodium hydroxide solution is 10 to 14M.
9. The method for preparing modified fly ash according to claim 7, wherein: The mass ratio of the activator solution to fly ash is in the range of 10:1 to 1:
1.
10. Use of the modified fly ash according to any one of claims 1 to 6 in concrete.