Modified limestone powder and preparation method thereof

Abstract

The present invention provides a modified limestone powder and a preparation method thereof, which belongs to the technical field of building materials, and comprises the following steps: step S1, ball-milling the limestone powder, adding the ball-milled limestone powder to a prepared 2-(perfluorooctyl)ethyl methacrylate emulsion, adding an initiator, heating and stirring, filtering and washing, and obtaining pretreated limestone powder; step S2, adding fly ash after surface activation to a sodium erythrose solution with a pH condition of 7-9, heating and stirring, filtering and washing, and drying to obtain modified fly ash; step S3, mixing and stirring the pretreated limestone powder, modified fly ash, a dispersant, a binder, and an anti-caking agent to obtain modified limestone powder; the ratio of the pretreated limestone powder to the modified fly ash is (7-8): (2-3). The modified limestone powder provided by the present invention can achieve the purpose of concrete being impermeable, durable, and having good mechanical properties.

Description

Technical Field

[0001] The invention relates to the technical field of building materials, and in particular to modified limestone powder and a preparation method thereof. Background Art

[0002] In existing technologies, limestone powder, due to its low inherent reactivity, can improve concrete's early strength and fluidity to a certain extent when used as a mineral admixture, but its later strength is significantly insufficient. Furthermore, limestone powder, like other common mineral admixtures, suffers from a range of shortcomings, including poor resistance to chloride ion permeability and insufficient frost resistance. These performance shortcomings make it difficult for limestone powder to meet the high durability requirements of concrete in specialized engineering environments, thus limiting its potential for application.

[0003] Application document CN110563369A discloses a modified limestone powder, its preparation method, and concrete. The modified limestone powder is composed of 94%-97% limestone powder, 1% physical modifier, and 2%-5% chemical modifier by mass. The chemical modifier is a mixture of oxalic acid, phosphate tailings, and polyferrosilicon flocculant. This solution addresses the sulfate attack issue of limestone powder concrete in the prior art by physically and chemically modifying the limestone powder. The resulting modified limestone powder has high density, low porosity, and excellent sulfate resistance. However, it fails to address the concrete's tendency to crack during freeze-thaw cycles, resulting in insufficient overall concrete durability. Application document CN112745050A discloses a method for preparing modified limestone powder for mass concrete. The method comprises the following steps: heating and stirring limestone powder and a silane coupling agent in an ethanol solution for 1-2 hours; cooling the solution to 60-70°C, adding polyoxyethylene ether and ammonium persulfate, stirring for 1-2 hours, and cooling; adding a high-molecular-weight polymer and stirring at high speed for 1-2 hours; and drying and removing the ethanol to obtain the modified limestone powder. This method grafts a phase-change material onto the surface of the limestone powder, enabling it to melt into a liquid state within a temperature range of 40-60°C and absorb the heat of hydration from the concrete, slowing the temperature rise. When the concrete temperature falls below 40°C, it cools and solidifies, releasing heat, reducing the temperature difference between the inside and outside of the concrete structure and minimizing surface cracking. However, this method fails to improve the concrete's durability, such as its permeability and frost resistance.

[0004] Therefore, it is necessary to provide a modified limestone powder and a preparation method thereof to solve the problems existing in the above-mentioned prior art. Summary of the Invention

[0005] In view of this, the present invention provides a modified limestone powder and a preparation method thereof, which can achieve the purpose of making concrete anti-penetration, durable and having good mechanical properties.

[0006] The specific scheme of the present invention is as follows: a method for preparing modified limestone powder, comprising the following steps:

[0007] Step S1, pretreatment of limestone powder:

[0008] The limestone powder is ball-milled, and then the ball-milled limestone powder is added to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion, an initiator is added, the mixture is heated and stirred, and the mixture is filtered and washed to obtain pretreated limestone powder;

[0009] Step S2, modification of fly ash:

[0010] The surface activated fly ash is added to a sodium erythrosetate solution at a pH of 7-9, heated and stirred, filtered, washed, and dried to obtain modified fly ash;

[0011] Step S3, preparation of modified limestone powder:

[0012] The pretreated limestone powder, modified fly ash, dispersant, binder and anti-caking agent are mixed and stirred to obtain modified limestone powder;

[0013] The ratio of the pretreated limestone powder to the modified fly ash is (7-8): (2-3).

[0014] 2-(Perfluorooctyl)ethyl methacrylate is a functional monomer containing long-chain perfluorinated groups. The acrylate groups in 2-(Perfluorooctyl)ethyl methacrylate can form copolymers through free radical polymerization. These copolymers adhere to the surface of limestone powder through adsorption, forming a stable structure. Furthermore, the high symmetry and strong C-H bonds of the perfluorooctyl groups in 2-(Perfluorooctyl)ethyl methacrylate impart low surface energy to the limestone powder, making it hydrophobic. This prevents water and chloride ion penetration, improving erosion resistance and thus enhancing the concrete's permeability. Furthermore, this hydrophobicity reduces water retention in the concrete, preventing damage caused by water expansion during freeze-thaw cycles, improving the concrete's durability and extending its service life. Pretreatment of the limestone powder reduces its surface energy, minimizing electrostatic adsorption and agglomeration, and enhancing its dispersibility. During concrete preparation, the modified limestone powder's fine particles effectively fill micropores in the cement matrix, increasing the concrete's density and ultimately improving the mechanical properties of the final concrete.

[0015] Sodium erythroalginate molecules contain carboxyl and hydroxyl groups. These carboxyl groups chelate with metal ions in the glassy structure on the fly ash surface, forming a complex. This extracts the metal ions from the glassy structure, causing it to become unstable and partially break up, exposing unreacted active components within it, such as alumina and silica. These components then participate in the pozzolanic reaction, reducing the heat of hydration of concrete and delaying the onset of the hydration exotherm. This results in the formation of a gel-like CSH gel, which acts as a retarding agent and improves the later strength and overall performance of concrete. Sodium erythroalginate molecules carry a negative charge and adsorb on the surface of fly ash particles, generating electrostatic repulsion between the particles. This reduces agglomeration between fly ash particles, improves the uniformity and dispersibility of the modified limestone powder, and contributes to enhancing the workability of the modified limestone powder and the mechanical properties of concrete.

[0016] Pretreated limestone powder has fine particles that can fill concrete micropores, reducing porosity, increasing early concrete density, and improving early strength. The reactive silica and alumina in fly ash react with calcium hydroxide produced by cement hydration to form additional CSH gel, which enhances concrete's later strength. The resulting modified limestone powder can create a favorable strength development curve for concrete, meeting early construction requirements while ensuring stable performance later in the construction process. Furthermore, modified limestone powder improves concrete's durability and crack resistance by filling pores and can partially replace cement, reducing production costs.

[0017] Preferably, in step S1, the pretreatment comprises the following steps: ball milling the limestone powder, sieving, washing and drying the limestone powder to obtain pretreated limestone powder.

[0018] Preferably, the ball milling process is carried out at a speed of 200-400 r / min and for a time of 0.5-2 h; and the screening mesh size is 225-325.

[0019] Preferably, in step S1, the preparation of the 2-(perfluorooctyl)ethyl methacrylate emulsion comprises the following steps: slowly adding 2-(perfluorooctyl)ethyl methacrylate monomer to deionized water, then adding an emulsifier, stirring at room temperature, and performing ultrasonic treatment for 5-10 minutes to obtain the 2-(perfluorooctyl)ethyl methacrylate emulsion.

[0020] The emulsion obtained by ultrasonic treatment is beneficial to the subsequent modification process, so that the copolymer can be evenly covered on the surface of the limestone powder particles, thereby improving its dispersibility and reducing agglomeration.

[0021] Preferably, the emulsifier is one of sodium lauryl sulfate, Span80 and Tween80; the initiator is one of ammonium persulfate, potassium persulfate and sodium persulfate.

[0022] Preferably, in step S1, the temperature of the heating and stirring is 65-75° C., the speed is 300-400 r / min, and the time is 2-3 h.

[0023] Preferably, in step S2, the surface activation comprises the following steps: washing and drying the fly ash, adding it into a 5-10wt% sodium hydroxide solution and soaking it for 1-3h, filtering and washing it, and drying it to obtain surface-activated fly ash.

[0024] Alkali treatment promotes the destruction of the glass phase in the shell of fly ash particles, releases the internal active components, and improves its reaction performance.

[0025] Preferably, in step S2, the heating and stirring temperature is 50-60° C., the speed is 300-400 r / min, and the time is 2-4 h.

[0026] Preferably, in step S3, the mixing speed is 400-600 r / min and the time is 1-2 h.

[0027] To achieve the above object, the present invention further provides modified limestone powder prepared by the above-mentioned method for preparing modified limestone powder, comprising the following components in parts by weight:

[0028] 70-80 parts of pretreated limestone powder, 20-30 parts of modified fly ash, 0.5-2 parts of dispersant, 1-2 parts of binder and 0.5-1 part of anti-caking agent;

[0029] The raw materials for pre-treating limestone powder include: 90-100 parts of limestone powder, 10-15 parts of 2-(perfluorooctyl)ethyl methacrylate, 0.5-1 part of emulsifier, 70-80 parts of deionized water and 0.5-1 part of initiator;

[0030] The raw materials of the modified fly ash include: 40-50 parts of fly ash and 5-10 parts of sodium erythroalginate solution.

[0031] The above technical solution of the present invention includes at least the following beneficial effects:

[0032] (1) The perfluorooctyl group in 2-(perfluorooctyl)ethyl methacrylate has a high degree of symmetry and a strong CF bond, which can give the limestone powder a low surface energy, making it hydrophobic and preventing the penetration of water and chloride ions, thereby improving the durability of concrete and extending its service life. The surface energy between the pretreated limestone powder particles is reduced, and it has better dispersibility, which can effectively fill the micropores in the cement matrix and improve the mechanical properties of concrete.

[0033] (2) The carboxyl groups in the sodium erythrosetate molecule can chelate with the metal ions in the glassy phase structure on the surface of fly ash to form a complex, which causes the glassy phase structure to break up and allows the internal active components, alumina and silica, to participate in the pozzolanic reaction to generate CSH gel, which can improve the mechanical properties of concrete.

[0034] (3) Modified limestone powder can make concrete form a good strength development curve, which can not only meet the early construction requirements but also ensure the stability of the later performance. At the same time, it can also replace part of the cement and reduce production costs. DETAILED DESCRIPTION

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention. All other embodiments obtained by ordinary technicians in this field based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0036] Example 1

[0037] Slowly add 10 parts of 2-(perfluorooctyl)ethyl methacrylate monomer to 75 parts of deionized water, and then add 0.5 parts of emulsifier sodium lauryl sulfate. Stir at room temperature and perform ultrasonic treatment for 10 minutes to obtain a 2-(perfluorooctyl)ethyl methacrylate emulsion for later use.

[0038] 100 parts of limestone powder were selected for ball milling at a ball milling speed of 300 r / min for 1 hour. After sieving, 225-325 mesh limestone powder was selected and added to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion. Then, 1 part of initiator ammonium persulfate was added, and the mixture was heated to 70°C and stirred at a speed of 400 r / min for 2 hours. After the reaction was completed, the mixture was filtered, washed and dried to obtain pretreated limestone powder.

[0039] 50 parts of fly ash after washing and drying were added to a 10wt% sodium hydroxide solution and soaked for 2 hours for surface activation. The fly ash after surface activation was added to 8 parts of sodium erythrosebate solution and stirred at a speed of 300r / min for 4 hours at a temperature of 50°C and a pH of 7-9. After the stirring was completed, it was filtered, washed and dried to obtain modified fly ash.

[0040] Mix 75 parts of pretreated limestone powder, 25 parts of modified fly ash, 1 part of dispersant, 1 part of binder and 0.5 part of anti-caking agent, stir at a speed of 500 r / min for 1.5 hours to ensure uniform mixing, and dry the mixed material to constant weight to obtain modified limestone powder.

[0041] Example 2

[0042] Slowly add 15 parts of 2-(perfluorooctyl)ethyl methacrylate monomer to 80 parts of deionized water, and then add 1 part of emulsifier Span80. Stir at room temperature and perform ultrasonic treatment for 5 minutes to obtain a 2-(perfluorooctyl)ethyl methacrylate emulsion for later use.

[0043] 90 parts of limestone powder were selected for ball milling at a ball milling speed of 200 r / min for 2 hours. After sieving, 225-325 mesh limestone powder was selected and added to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion. Then, 0.5 parts of initiator potassium persulfate were added, and the mixture was heated to 75° C. and stirred at a speed of 300 r / min for 3 hours. After the reaction was completed, the mixture was filtered, washed and dried to obtain pretreated limestone powder.

[0044] 40 parts of fly ash after washing and drying were added to a 5wt% sodium hydroxide solution and soaked for 3 hours for surface activation. The fly ash after surface activation was added to 5 parts of sodium erythrosebate solution and stirred at a speed of 400r / min for 3 hours at a temperature of 60°C and a pH of 7-9. After the stirring was completed, it was filtered, washed and dried to obtain modified fly ash.

[0045] Mix 70 parts of pretreated limestone powder, 30 parts of modified fly ash, 0.5 parts of dispersant, 2 parts of binder and 1 part of anti-caking agent, stir at a speed of 400 r / min for 2 hours to ensure uniform mixing, and dry the mixed material to constant weight to obtain modified limestone powder.

[0046] Example 3

[0047] Slowly add 12 parts of 2-(perfluorooctyl)ethyl methacrylate monomer to 80 parts of deionized water, then add 0.5 parts of emulsifier Tween 80, stir at room temperature and perform ultrasonic treatment for 10 minutes to obtain a 2-(perfluorooctyl)ethyl methacrylate emulsion for later use.

[0048] 90 parts of limestone powder were selected for ball milling at a ball milling speed of 400 r / min for 0.5 h. After sieving, 225-325 mesh limestone powder was selected and added to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion. Then, 1 part of initiator sodium persulfate was added, and the mixture was heated to 65° C. and stirred at a speed of 350 r / min for 2.5 h. After the reaction was completed, the mixture was filtered, washed and dried to obtain pretreated limestone powder.

[0049] 45 parts of fly ash after washing and drying were added to a 7wt% sodium hydroxide solution and soaked for 2 hours for surface activation. The fly ash after surface activation was added to 10 parts of sodium erythrosebate solution and stirred at a speed of 300 r / min for 3 hours at a temperature of 55°C and a pH of 7-9. After the stirring was completed, it was filtered, washed and dried to obtain modified fly ash.

[0050] 80 parts of pretreated limestone powder, 20 parts of modified fly ash, 2 parts of dispersant, 1 part of binder and 0.5 parts of anti-caking agent were mixed, stirred at a speed of 600 r / min for 1 hour to ensure uniform mixing, and the mixed material was dried to constant weight to obtain modified limestone powder.

[0051] Example 4

[0052] Slowly add 10 parts of 2-(perfluorooctyl)ethyl methacrylate monomer to 80 parts of deionized water, then add 1 part of emulsifier Span80, stir at room temperature and perform ultrasonic treatment for 10 minutes to obtain a 2-(perfluorooctyl)ethyl methacrylate emulsion for later use.

[0053] 100 parts of limestone powder were selected for ball milling at a ball milling speed of 200 r / min for 2 hours. After sieving, 225-325 mesh limestone powder was selected and added to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion. Then, 1 part of initiator sodium persulfate was added, and the mixture was heated to 65° C. and stirred at a speed of 300 r / min for 2.5 hours. After the reaction was completed, the mixture was filtered, washed and dried to obtain pretreated limestone powder.

[0054] 50 parts of fly ash after washing and drying were added to a 10wt% sodium hydroxide solution and soaked for 2 hours for surface activation. The fly ash after surface activation was added to 5 parts of sodium erythrosebate solution and stirred at a speed of 400r / min for 2.5 hours at a temperature of 50°C and a pH of 7-9. After the stirring was completed, it was filtered, washed and dried to obtain modified fly ash.

[0055] 80 parts of pretreated limestone powder, 30 parts of modified fly ash, 1.5 parts of dispersant, 1 part of binder and 1 part of anti-caking agent were mixed, stirred at a speed of 450 r / min for 1.5 hours to ensure uniform mixing, and the mixed material was dried to constant weight to obtain modified limestone powder.

[0056] Example 5

[0057] Slowly add 12 parts of 2-(perfluorooctyl)ethyl methacrylate monomer to 75 parts of deionized water, and then add 0.5 parts of emulsifier Tween 80. Stir at room temperature and perform ultrasonic treatment for 10 minutes to obtain a 2-(perfluorooctyl)ethyl methacrylate emulsion for later use.

[0058] 90 parts of limestone powder were selected for ball milling at a ball milling speed of 400 r / min for 0.5 h. After sieving, 225-325 mesh limestone powder was selected and added to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion. Then, 1 part of initiator ammonium persulfate was added, and the mixture was heated to 75° C. and stirred at a speed of 350 r / min for 2 h. After the reaction was completed, the mixture was filtered, washed and dried to obtain pretreated limestone powder.

[0059] 40 parts of fly ash after washing and drying were added to a 5wt% sodium hydroxide solution and soaked for 2.5 hours for surface activation. The fly ash after surface activation was added to 10 parts of sodium erythrosebate solution and stirred at a speed of 300 r / min for 4 hours at a temperature of 50°C and a pH of 7-9. After the stirring was completed, it was filtered, washed and dried to obtain modified fly ash.

[0060] Mix 70 parts of pretreated limestone powder, 20 parts of modified fly ash, 1 part of dispersant, 1.5 parts of binder and 1 part of anti-caking agent, stir at a speed of 400 r / min for 1.5 hours to ensure uniform mixing, and dry the mixed material to constant weight to obtain modified limestone powder.

[0061] Example 6

[0062] Slowly add 10 parts of 2-(perfluorooctyl)ethyl methacrylate monomer to 80 parts of deionized water, and then add 1 part of emulsifier Tween 80. Stir at room temperature and perform ultrasonic treatment for 5 minutes to obtain a 2-(perfluorooctyl)ethyl methacrylate emulsion for later use.

[0063] 90 parts of limestone powder were ball-milled at a speed of 400 r / min for 1 h. After sieving, 225-325 mesh limestone powder was selected and added to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion. 0.5 parts of initiator potassium persulfate were added, and the mixture was heated to 75° C. and stirred at a speed of 400 r / min for 2 h. After the reaction was completed, the mixture was filtered, washed and dried to obtain pretreated limestone powder.

[0064] 50 parts of fly ash after washing and drying were added to a 10wt% sodium hydroxide solution and soaked for 1.5 hours for surface activation. The fly ash after surface activation was added to 5 parts of sodium erythrosebate solution and stirred at a speed of 350r / min for 2 hours at a temperature of 55°C and a pH of 7-9. After the stirring was completed, the mixture was filtered, washed and dried to obtain modified fly ash.

[0065] 70 parts of pretreated limestone powder, 25 parts of modified fly ash, 2 parts of dispersant, 1 part of binder and 0.5 parts of anti-caking agent were mixed, stirred at a speed of 600 r / min for 1 hour to ensure uniform mixing, and the mixed material was dried to constant weight to obtain modified limestone powder.

[0066] Example 7

[0067] Slowly add 15 parts of 2-(perfluorooctyl)ethyl methacrylate monomer to 70 parts of deionized water, and then add 0.5 parts of emulsifier sodium lauryl sulfate. Stir at room temperature and perform ultrasonic treatment for 10 minutes to obtain a 2-(perfluorooctyl)ethyl methacrylate emulsion for later use.

[0068] 90 parts of limestone powder were selected for ball milling at a ball milling speed of 200 r / min for 2 hours. After sieving, 225-325 mesh limestone powder was selected and added to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion. Then, 1 part of initiator sodium persulfate was added, and the mixture was heated to 70°C and stirred at a speed of 350 r / min for 3 hours. After the reaction was completed, the mixture was filtered, washed and dried to obtain pretreated limestone powder.

[0069] 45 parts of fly ash after washing and drying were added to 8wt% sodium hydroxide solution and soaked for 2.5 hours for surface activation. The fly ash after surface activation was added to 8 parts of sodium erythrosebate solution and stirred at a speed of 400r / min for 2 hours at a temperature of 55°C and a pH of 7-9. After the stirring was completed, it was filtered, washed and dried to obtain modified fly ash.

[0070] Mix 75 parts of pretreated limestone powder, 30 parts of modified fly ash, 1.5 parts of dispersant, 1 part of binder and 1 part of anti-caking agent, stir at a speed of 550 r / min for 1 hour to ensure uniform mixing, and dry the mixed material to constant weight to obtain modified limestone powder.

[0071] Example 8

[0072] Slowly add 15 parts of 2-(perfluorooctyl)ethyl methacrylate monomer to 80 parts of deionized water, and then add 1 part of emulsifier sodium lauryl sulfate. Stir at room temperature and perform ultrasonic treatment for 10 minutes to obtain a 2-(perfluorooctyl)ethyl methacrylate emulsion for later use.

[0073] 95 parts of limestone powder were ball-milled at a speed of 350 r / min for 1 h. After sieving, 225-325 mesh limestone powder was selected and added to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion. Then, 1 part of initiator potassium persulfate was added. The mixture was heated to 75° C. and stirred at a speed of 400 r / min for 2.5 h. After the reaction was completed, the mixture was filtered, washed and dried to obtain pretreated limestone powder.

[0074] 45 parts of fly ash after washing and drying were added to a 5wt% sodium hydroxide solution and soaked for 2.5 hours for surface activation. The fly ash after surface activation was added to 10 parts of sodium erythrosebate solution and stirred at a speed of 350r / min for 2 hours at a temperature of 50°C and a pH of 7-9. After the stirring was completed, the mixture was filtered, washed and dried to obtain modified fly ash.

[0075] 80 parts of pretreated limestone powder, 25 parts of modified fly ash, 1.5 parts of dispersant, 1.5 parts of binder and 0.5 parts of anti-caking agent were mixed, stirred at a speed of 450 r / min for 2 hours to ensure uniform mixing, and the mixed material was dried to constant weight to obtain modified limestone powder.

[0076] The present invention also carried out comparative examples and related tests.

[0077] Comparative Example 1

[0078] The only difference between Comparative Example 1 and Example 1 is that 2-(perfluorooctyl)ethyl methacrylate is not used to pretreat the limestone powder in Comparative Example 1. Other compositions and preparation methods are the same as those in Example 1 to prepare modified limestone powder.

[0079] Comparative Example 2

[0080] The only difference between Comparative Example 2 and Example 1 is that sodium erythrocyanate is not used to modify the fly ash in Comparative Example 2. Other compositions and preparation methods are the same as those in Example 1, and modified limestone powder is prepared.

[0081] Comparative Example 3

[0082] Comparative Example 3 is modified limestone powder prepared by the method for preparing modified limestone powder for mass concrete disclosed in Publication No. CN112745050B.

[0083] Performance testing

[0084] The modified limestone powder prepared in Examples 1-8 and Comparative Examples 1-3 was used to prepare concrete, and the obtained concrete was subjected to performance test according to the following standards.

[0085] Mechanical properties were measured according to the national standard GB / T50081-2019, "Test Methods for Physical and Mechanical Properties of Concrete." Frost resistance and water penetration resistance (expressed as water seepage height) were measured according to the national standard GB / T50082-2009, "Test Methods for Long-Term Properties and Durability of Ordinary Concrete." The test results are shown in Table 1 below.

[0086] Table 1

[0087]

[0088] According to the data in Table 1, compared with Examples 1-8, the frost resistance and water permeability of the concrete prepared by the modified limestone powder obtained in Comparative Example 1 decreased significantly, indicating that the pretreatment of the limestone powder with 2-(perfluorooctyl)ethyl methacrylate can improve the hydrophobicity of the limestone powder, which helps to improve the frost resistance and water permeability of the concrete; compared with Examples 1-8, the mechanical properties of the concrete prepared by the modified limestone powder obtained in Comparative Example 2 decreased significantly, indicating that the modification of fly ash by sodium erythroalginate can promote the release of fly ash pozzolanic activity, further promote the formation of CSH gel, and help improve the mechanical properties of the concrete; compared with Examples 1-8, the performance of the concrete prepared by the modified limestone powder used in Comparative Example 3 decreased in all aspects, indicating that the limestone powder prepared by the embodiment of the present invention has better performance.

[0089] The above is a preferred embodiment of the present invention. Those skilled in the art may make several improvements and modifications without departing from the principles of the present invention. These improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing modified limestone powder, characterized in that: The following steps are involved: Step S1, pretreatment of limestone powder: The limestone powder is ball-milled, and then the ball-milled limestone powder is added to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion, an initiator is added, the mixture is heated and stirred, and the mixture is filtered and washed to obtain pretreated limestone powder; Step S2, modification of fly ash: The surface activated fly ash is added to a sodium erythrosetate solution at a pH of 7-9, heated and stirred, filtered, washed, and dried to obtain modified fly ash; Step S3, preparation of modified limestone powder: The pretreated limestone powder, modified fly ash, dispersant, binder and anti-caking agent are mixed and stirred to obtain modified limestone powder; The ratio of the pretreated limestone powder to the modified fly ash is (7-8): (2-3).

2. The method for preparing modified limestone powder according to claim 1, wherein In step S1, the ball milling treatment includes the following steps: ball milling the limestone powder, sieving, washing, and drying to obtain the ball milled limestone powder.

3. The method for preparing modified limestone powder according to claim 2, wherein The ball milling process is carried out at a speed of 200-400 r / min and a time of 0.5-2 h; and the screening mesh size is 225-325.

4. The method for preparing modified limestone powder according to claim 1, wherein In step S1, the preparation of the 2-(perfluorooctyl)ethyl methacrylate emulsion includes the following steps: slowly adding 2-(perfluorooctyl)ethyl methacrylate monomer to deionized water, then adding an emulsifier, stirring at room temperature, and performing ultrasonic treatment for 5-10 minutes to obtain the 2-(perfluorooctyl)ethyl methacrylate emulsion.

5. The method for preparing modified limestone powder according to claim 4, wherein The emulsifier is one of sodium lauryl sulfate, Span80 and Tween80; the initiator is one of ammonium persulfate, potassium persulfate and sodium persulfate.

6. The method for preparing modified limestone powder according to claim 1, wherein In the step S1, the temperature of the heating and stirring is 65-75° C., the speed is 300-400 r / min, and the time is 2-3 h.

7. The method for preparing modified limestone powder according to claim 1, wherein In step S2, the surface activation comprises the following steps: washing and drying the fly ash, adding it into a 5-10wt% sodium hydroxide solution and soaking it for 1-3h, filtering and washing it, and drying it to obtain surface-activated fly ash.

8. The method for preparing modified limestone powder according to claim 1, wherein In step S2, the heating and stirring temperature is 50-60° C., the speed is 300-400 r / min, and the time is 2-4 h.

9. The method for preparing modified limestone powder according to claim 1, wherein In step S3, the mixing and stirring speed is 400-600 r / min and the time is 1-2 h.

10. A limestone powder prepared by the method for preparing a modified limestone powder according to any one of claims 1 to 9, characterized in that: The composition comprises the following components in parts by weight: 70-80 parts of pretreated limestone powder, 20-30 parts of modified fly ash, 0.5-2 parts of dispersant, 1-2 parts of binder and 0.5-1 part of anti-caking agent; The raw materials for pre-treating limestone powder include: 90-100 parts of limestone powder, 10-15 parts of 2-(perfluorooctyl)ethyl methacrylate, 0.5-1 part of emulsifier, 70-80 parts of deionized water and 0.5-1 part of initiator; The raw materials of the modified fly ash include: 40-50 parts of fly ash and 5-10 parts of sodium erythroalginate solution.

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