Modified limestone powder and preparation method thereof

Abstract

The invention provides modified limestone powder and a preparation method thereof, and belongs to the technical field of building materials, and the preparation method comprises the following steps: S1, carrying out ball milling treatment on limestone powder, adding the limestone powder subjected to ball milling treatment into a prepared 2-(perfluorooctyl) ethyl methacrylate emulsion, adding an initiator, heating, stirring, filtering, washing, and drying to obtain modified limestone powder; pre-treated limestone powder is obtained; s2, adding the fly ash subjected to surface activation into a sodium erythorbate solution under the pH condition of 7-9, heating, stirring, filtering, washing and drying to obtain modified fly ash; s3, mixing and stirring the pretreated limestone powder, the modified fly ash, a dispersing agent, a binder and an anti-blocking 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 invention can realize the purposes of permeation resistance, durability and good mechanical properties of concrete.

Description

Technical Field

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

[0002] In the prior art, due to the low self-activity of limestone powder, although using it as a mineral admixture can improve the early strength and fluidity of concrete to a certain extent, there are obvious deficiencies in the later strength. In addition, like other common mineral admixtures, limestone powder has a series of similar defects, including poor chloride ion penetration resistance and insufficient frost resistance. These performance shortboards make it difficult for limestone powder to meet the high requirements for the durability of concrete in special engineering environments, thus limiting its application potential.

[0003] The application document with the publication number of CN110563369A discloses a modified limestone powder, a preparation method thereof and concrete, which are made of 94%-97% of limestone powder, 1% of physical modifier and 2%-5% of chemical modifier by mass percentage. Among them, the chemical modifier is a mixture of oxalic acid, phosphorus tailings and polyferrosilicon flocculant. This scheme solves the problem of sulfate erosion of limestone powder concrete in the prior art through physical and chemical double modification of limestone powder. The obtained modified limestone powder has high density, low porosity and excellent sulfate erosion resistance, but fails to solve the problem that concrete is prone to cracking during freeze-thaw cycles, resulting in insufficient overall durability of concrete. The application document with the publication number of CN112745050A discloses a preparation method of modified limestone powder for mass concrete, including the following steps: heating and stirring limestone powder and silane coupling agent in an ethanol solution for 1-2 h; cooling to 60-70 °C, adding polyoxyethylene ether and ammonium persulfate, and stirring for 1-2 h to cool; adding a high molecular polymer and stirring at high speed for 1-2 h; drying to remove ethanol to obtain modified limestone powder. This scheme grafts a phase change material on the surface of limestone powder, so that it can melt into a liquid state and adsorb the hydration heat of concrete within the range of 40-60 °C, delaying the temperature rise rate. When the temperature of the concrete is lower than 40 °C, it cools and solidifies and releases heat, reducing the temperature difference between the inside and the surface of the concrete structure and reducing the surface cracking phenomenon, but fails to improve the durability performance such as the impermeability and frost resistance of the concrete.

[0004] Therefore, it is necessary to provide a modified limestone powder and a preparation method thereof to solve the problems existing in the above 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 good impermeability, durability and mechanical properties of concrete.

[0006] The specific solution of the present invention is as follows. A preparation method of modified limestone powder includes the following steps: Step S1, pretreatment of limestone powder: The limestone powder is subjected to ball milling treatment, and then the ball-milled limestone powder is added to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion. An initiator is added, the temperature is raised and stirred, and then filtered and washed to obtain pretreated limestone powder; Step S2, modification of fly ash: The surface-activated fly ash is added to the sodium erythrobate solution under the pH condition of 7-9, heated and stirred, filtered and washed, and then 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).

[0007] 2-(Perfluorooctyl)ethyl methacrylate is a functional monomer containing a long-chain perfluoro group. The acrylate group carried by 2-(perfluorooctyl)ethyl methacrylate can form a copolymer through free radical polymerization. The copolymer adheres to the surface of limestone powder through adsorption to form a stable structure. In addition, the perfluorooctyl group in 2-(perfluorooctyl)ethyl methacrylate has high symmetry and strong C-F bonds, which can endow the limestone powder with low surface energy, making the limestone powder have good hydrophobicity, preventing the penetration of moisture and chloride ions, improving the anti-corrosion ability, and thus enhancing the impermeability of concrete. At the same time, the hydrophobicity can reduce the retention of moisture in the concrete, avoid the damage caused by the expansion of moisture during freeze-thaw cycles, improve the durability of the concrete, and extend the service life. The surface energy of the pretreated limestone powder is reduced, reducing electrostatic adsorption and agglomeration phenomena, and having better dispersibility. During the preparation of concrete, the particles of the modified limestone powder are fine, which can effectively fill the micropores in the cement matrix, improve the compactness of the concrete, and thus enhance the mechanical properties of the final concrete.

[0008] Sodium erythrobate has carboxyl and hydroxyl groups in its molecule. The carboxyl groups chelate with metal ions in the glassy phase structure on the surface of fly ash to form a complex, extracting the metal ions from the glassy phase structure, resulting in the instability of the glassy phase structure. It begins to break partially, exposing the unreacted active ingredients inside, such as alumina and silica, enabling them to participate in the pozzolanic reaction, reducing the heat of hydration of concrete, delaying the appearance of the hydration heat release peak, generating gel-like C-S-H gel, which can play a retarding role and improve the late strength and overall performance of concrete. The sodium erythrobate molecule carries a negative charge and adsorbs on the surface of fly ash particles, generating electrostatic repulsion between the particles, reducing the agglomeration phenomenon between fly ash particles, improving the uniformity and dispersibility of the modified limestone powder, and contributing to enhancing the workability of the modified limestone powder and the mechanical properties of concrete.

[0009] The pretreated limestone powder particles are relatively fine, which can fill the micro-pores of concrete, reduce the porosity, increase the density of early concrete, and improve the early strength. The active silica and alumina in fly ash react with calcium hydroxide generated by cement hydration to form additional C-S-H gel, enhancing the late strength of concrete. The modified limestone powder prepared from the two can enable concrete to form a good strength development curve, which can not only meet the early construction requirements but also ensure the stability of late performance. In addition, the modified limestone powder can improve the durability and crack resistance of concrete by filling the pores, and can replace part of the cement to reduce the production cost.

[0010] Preferably, in the step S1, the pretreatment includes the following steps: ball-milling the limestone powder, sieving it, and then washing and drying it to obtain the pretreated limestone powder.

[0011] Preferably, the speed of the ball-milling treatment is 200 - 400 r / min, the time is 0.5 - 2 h; the mesh number for sieving is 225 - 325.

[0012] Preferably, in the step S1, the preparation of 2-(perfluorooctyl)ethyl methacrylate emulsion includes the following steps: slowly adding 2-(perfluorooctyl)ethyl methacrylate monomer into deionized water, then adding an emulsifier, stirring at room temperature, and performing ultrasonic treatment for 5 - 10 min to obtain 2-(perfluorooctyl)ethyl methacrylate emulsion.

[0013] Obtaining the emulsion through ultrasonic treatment is beneficial for the subsequent modification process, enabling the copolymer to uniformly cover the surface of limestone powder particles, enhancing its dispersibility, and reducing the agglomeration phenomenon.

[0014] Preferably, the emulsifier is one of sodium dodecyl sulfate, Span80, and Tween80; the initiator is one of ammonium persulfate, potassium persulfate, and sodium persulfate.

[0015] Preferably, in the step S1, the temperature for heating and stirring is 65 - 75 °C, the speed is 300 - 400 r / min, and the time is 2 - 3 h.

[0016] Preferably, in the step S2, the surface activation includes the following steps: After washing and drying the fly ash, it is added to a 5 - 10 wt% sodium hydroxide solution and soaked for 1 - 3 h, then filtered, washed, and dried to obtain surface-activated fly ash.

[0017] Through alkali treatment, the destruction of the glass phase in the fly ash particle shell layer is promoted, the internal active components are released, and its reaction performance is improved.

[0018] Preferably, in the step S2, the temperature for heating and stirring is 50 - 60 °C, the speed is 300 - 400 r / min, and the time is 2 - 4 h.

[0019] Preferably, in the step S3, the speed of mixing and stirring is 400 - 600 r / min, and the time is 1 - 2 h.

[0020] To achieve the above object, the present invention also provides modified limestone powder prepared by the above preparation method of modified limestone powder, which includes 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 of the pretreated 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 erythrobate solution.

[0021] The above technical solutions of the present invention at least include the following beneficial effects: (1) The perfluorooctyl group in 2-(perfluorooctyl)ethyl methacrylate has high symmetry and strong C-F bonds, which can endow the limestone powder with low surface energy, make the limestone powder have good hydrophobicity, prevent the penetration of moisture and chloride ions, improve the durability of concrete, and extend the service life. After pretreatment, the surface energy between the 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.

[0022] (2) The carboxyl group in the sodium erythrobate molecule can chelate with metal ions in the glass phase structure on the surface of fly ash to form a complex, resulting in the fragmentation of the glass phase structure, enabling the internal active components alumina and silica to participate in the pozzolanic reaction to generate C-S-H gel, which can improve the mechanical properties of concrete.

[0023] (3) The modified limestone powder can enable concrete to form a good strength development curve, which can not only meet the early construction requirements but also ensure the stability of later performance. At the same time, it can also replace part of the cement to reduce production costs. Specific implementation manners

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 part of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention belong to the scope of protection of the present invention.

[0025] Example 1 In 75 parts of deionized water, 10 parts of 2-(perfluorooctyl)ethyl methacrylate monomer was slowly added, and then 0.5 part of emulsifier sodium dodecyl sulfate was added. Stir at room temperature and perform ultrasonic treatment for 10 min to obtain 2-(perfluorooctyl)ethyl methacrylate emulsion for standby.

[0026] 100 parts of limestone powder was selected for ball milling treatment. The ball milling speed was 300 r / min and the time was 1 h. After sieving, the limestone powder with a mesh size of 225-325 was added to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion, and then 1 part of initiator ammonium persulfate was added. Heat to 70 °C and stir at a speed of 400 r / min for 2 h. After the reaction is completed, filter, wash, and dry to obtain pretreated limestone powder.

[0027] 50 parts of fly ash after cleaning and drying was added to 10 wt% sodium hydroxide solution and soaked for 2 h for surface activation. The surface-activated fly ash was added to 8 parts of sodium erythrobate solution. Under the conditions of a temperature of 50 °C and a pH of 7-9, stir at a speed of 300 r / min for 4 h. After stirring, filter, wash, and dry to obtain modified fly ash.

[0028] 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 were mixed and stirred at a speed of 500 r / min for 1.5 h to ensure uniform mixing. The mixed material was dried to a constant weight to obtain modified limestone powder.

[0029] Example 2 In 80 parts of deionized water, slowly add 15 parts of 2-(perfluorooctyl)ethyl methacrylate monomer, then add 1 part of emulsifier Span80, stir at room temperature and perform ultrasonic treatment for 5 min to obtain 2-(perfluorooctyl)ethyl methacrylate emulsion for standby.

[0030] Select 90 parts of limestone powder for ball milling treatment at a ball milling speed of 200 r / min for 2 h. After sieving, select limestone powder with a mesh size of 225 - 325 meshes and add it to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion. Then add 0.5 part of initiator potassium persulfate, heat to 75 °C, and stir at a speed of 300 r / min for 3 h. After the reaction is completed, filter, wash and dry to obtain pretreated limestone powder.

[0031] Soak 40 parts of fly ash after cleaning and drying in 5 wt% sodium hydroxide solution for 3 h for surface activation. Add the surface-activated fly ash to 5 parts of sodium erythrobate solution, and stir at a speed of 400 r / min for 3 h at a temperature of 60 °C and a pH of 7 - 9. After stirring, filter, wash and dry to obtain modified fly ash.

[0032] Mix 70 parts of pretreated limestone powder, 30 parts of modified fly ash, 0.5 part of dispersant, 2 parts of binder and 1 part of anti-caking agent, and stir at a speed of 400 r / min for 2 h to ensure uniform mixing. Dry the mixed material to a constant weight to obtain modified limestone powder.

[0033] Example 3 In 80 parts of deionized water, slowly add 12 parts of 2-(perfluorooctyl)ethyl methacrylate monomer, then add 0.5 part of emulsifier Tween80, stir at room temperature and perform ultrasonic treatment for 10 min to obtain 2-(perfluorooctyl)ethyl methacrylate emulsion for standby.

[0034] Select 90 parts of limestone powder for ball milling treatment at a ball milling speed of 400 r / min for 0.5 h. After sieving, select limestone powder with a mesh size of 225 - 325 meshes and add it to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion. Then add 1 part of initiator sodium persulfate, heat to 65 °C, and stir at a speed of 350 r / min for 2.5 h. After the reaction is completed, filter, wash and dry to obtain pretreated limestone powder.

[0035] Soak 45 parts of fly ash after cleaning and drying in 7 wt% sodium hydroxide solution for 2 h for surface activation. Add the surface-activated fly ash to 10 parts of sodium erythrobate solution, and stir at a speed of 300 r / min for 3 h at a temperature of 55 °C and a pH of 7 - 9. After stirring, filter, wash and dry to obtain modified fly ash.

[0036] Mix 80 parts of pretreated limestone powder, 20 parts of modified fly ash, 2 parts of dispersant, 1 part of binder, and 0.5 part of anti-caking agent, and stir at a speed of 600 r / min for 1 h to ensure uniform mixing. Dry the mixed material to a constant weight to obtain modified limestone powder.

[0037] Example 4 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 min to obtain 2-(perfluorooctyl)ethyl methacrylate emulsion for standby.

[0038] Select 100 parts of limestone powder for ball milling at a speed of 200 r / min for 2 h. After sieving, select 225-325 mesh limestone powder and add it to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion. Then add 1 part of initiator sodium persulfate, heat to 65 °C, and stir at a speed of 300 r / min for 2.5 h. After the reaction is completed, filter, wash, and dry to obtain pretreated limestone powder.

[0039] Add 50 parts of fly ash after cleaning and drying to 10 wt% sodium hydroxide solution and soak for 2 h for surface activation. Add the surface-activated fly ash to 5 parts of sodium erythrobate solution, and stir at a speed of 400 r / min for 2.5 h at a temperature of 50 °C and a pH of 7-9. After stirring, filter, wash, and dry to obtain modified fly ash.

[0040] Mix 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, and stir at a speed of 450 r / min for 1.5 h to ensure uniform mixing. Dry the mixed material to a constant weight to obtain modified limestone powder.

[0041] Example 5 Slowly add 12 parts of 2-(perfluorooctyl)ethyl methacrylate monomer to 75 parts of deionized water, then add 0.5 part of emulsifier Tween80, stir at room temperature and perform ultrasonic treatment for 10 min to obtain 2-(perfluorooctyl)ethyl methacrylate emulsion for standby.

[0042] Select 90 parts of limestone powder for ball milling at a speed of 400 r / min for 0.5 h. After sieving, select 225-325 mesh limestone powder and add it to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion. Then add 1 part of initiator ammonium persulfate, heat to 75 °C, and stir at a speed of 350 r / min for 2 h. After the reaction is completed, filter, wash, and dry to obtain pretreated limestone powder.

[0043] Add 40 parts of fly ash after cleaning and drying to a 5wt% sodium hydroxide solution and soak for 2.5 h for surface activation. Add the surface-activated fly ash to 10 parts of sodium erythrobate solution, and stir at a speed of 300 r / min for 4 h at a temperature of 50 °C and a pH of 7 - 9. After stirring, filter, wash and dry to obtain modified fly ash.

[0044] 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, and stir at a speed of 400 r / min for 1.5 h to ensure uniform mixing. Dry the mixed material to constant weight to obtain modified limestone powder.

[0045] Example 6 Slowly add 10 parts of 2-(perfluorooctyl)ethyl methacrylate monomer to 80 parts of deionized water, then add 1 part of emulsifier Tween 80, stir at room temperature and perform ultrasonic treatment for 5 min to obtain 2-(perfluorooctyl)ethyl methacrylate emulsion for standby.

[0046] Select 90 parts of limestone powder for ball milling at a speed of 400 r / min for 1 h. After sieving, select limestone powder with a mesh size of 225 - 325 meshes and add it to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion. Then add 0.5 part of initiator potassium persulfate, heat to 75 °C, and stir at a speed of 400 r / min for 2 h. After the reaction is completed, filter, wash and dry to obtain pretreated limestone powder.

[0047] Add 50 parts of fly ash after cleaning and drying to a 10wt% sodium hydroxide solution and soak for 1.5 h for surface activation. Add the surface-activated fly ash to 5 parts of sodium erythrobate solution, and stir at a speed of 350 r / min for 2 h at a temperature of 55 °C and a pH of 7 - 9. After stirring, filter, wash and dry to obtain modified fly ash.

[0048] Mix 70 parts of pretreated limestone powder, 25 parts of modified fly ash, 2 parts of dispersant, 1 part of binder and 0.5 part of anti-caking agent, and stir at a speed of 600 r / min for 1 h to ensure uniform mixing. Dry the mixed material to constant weight to obtain modified limestone powder.

[0049] Example 7 Slowly add 15 parts of 2-(perfluorooctyl)ethyl methacrylate monomer to 70 parts of deionized water, then add 0.5 part of emulsifier sodium dodecyl sulfate, stir at room temperature and perform ultrasonic treatment for 10 min to obtain 2-(perfluorooctyl)ethyl methacrylate emulsion for standby.

[0050] 90 portions of limestone powder were selected for ball milling at a speed of 200 r / min for 2 h. After sieving, the limestone powder with a mesh size of 225 - 325 was added to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion, and then 1 portion of initiator sodium persulfate was added. It was heated to 70 °C and stirred at a speed of 350 r / min for 3 h. After the reaction was completed, it was filtered, washed and dried to obtain pretreated limestone powder.

[0051] 45 portions of fly ash after cleaning and drying were added to an 8 wt% sodium hydroxide solution and soaked for 2.5 h for surface activation. The surface-activated fly ash was added to 8 portions of sodium erythrobate solution and stirred at a speed of 400 r / min for 2 h at a temperature of 55 °C and a pH of 7 - 9. After stirring, it was filtered, washed and dried to obtain modified fly ash.

[0052] 75 portions of pretreated limestone powder, 30 portions of modified fly ash, 1.5 portions of dispersant, 1 portion of binder and 1 portion of anti-caking agent were mixed and stirred at a speed of 550 r / min for 1 h to ensure uniform mixing. The mixed material was dried to a constant weight to obtain modified limestone powder.

[0053] Example 8 In 80 portions of deionized water, 15 portions of 2-(perfluorooctyl)ethyl methacrylate monomer were slowly added, and then 1 portion of emulsifier sodium dodecyl sulfate was added. It was stirred at room temperature and subjected to ultrasonic treatment for 10 min to obtain 2-(perfluorooctyl)ethyl methacrylate emulsion for standby.

[0054] 95 portions of limestone powder were selected for ball milling at a speed of 350 r / min for 1 h. After sieving, the limestone powder with a mesh size of 225 - 325 was added to the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion, and then 1 portion of initiator potassium persulfate was added. It was heated to 75 °C and stirred at a speed of 400 r / min for 2.5 h. After the reaction was completed, it was filtered, washed and dried to obtain pretreated limestone powder.

[0055] 45 portions of fly ash after cleaning and drying were added to a 5 wt% sodium hydroxide solution and soaked for 2.5 h for surface activation. The surface-activated fly ash was added to 10 portions of sodium erythrobate solution and stirred at a speed of 350 r / min for 2 h at a temperature of 50 °C and a pH of 7 - 9. After stirring, it was filtered, washed and dried to obtain modified fly ash.

[0056] 80 portions of pretreated limestone powder, 25 portions of modified fly ash, 1.5 portions of dispersant, 1.5 portions of binder and 0.5 portion of anti-caking agent were mixed and stirred at a speed of 450 r / min for 2 h to ensure uniform mixing. The mixed material was dried to a constant weight to obtain modified limestone powder.

[0057] The present invention also carried out comparative examples and related tests.

[0058] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is only that 2-(perfluorooctyl)ethyl methacrylate was not used for the pretreatment of limestone powder in Comparative Example 1, and the other components and preparation methods are the same as those in Example 1, and the modified limestone powder was prepared.

[0059] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is only that sodium erythrobate was not used for the modification of fly ash in Comparative Example 2, and the other components and preparation methods are the same as those in Example 1, and the modified limestone powder was prepared.

[0060] Comparative Example 3 Comparative Example 3 is the modified limestone powder prepared by the preparation method of a modified limestone powder for mass concrete disclosed in the publication number CN112745050B.

[0061] Performance detection test The modified limestone powders prepared in Examples 1-8 and Comparative Examples 1-3 were used for concrete preparation, and the performance test of the obtained concrete was carried out according to the following standards.

[0062] The mechanical properties were measured according to the national standard GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". The frost resistance and impermeability (expressed by the height of water seepage) were measured according to the national standard GB / T50082-2009 "Standard for Test Methods of Long-Term Properties and Durability of Ordinary Concrete". The test results are shown in Table 1 below.

[0063] Table 1

[0064] It can be seen from the data in Table 1 that, compared with Examples 1-8, the frost resistance and water seepage performance of the concrete prepared with the modified limestone powder obtained in Comparative Example 1 decreased significantly, indicating that the pretreatment of limestone powder with 2-(perfluorooctyl)ethyl methacrylate can improve the hydrophobicity of limestone powder and contribute to the improvement of the frost resistance and impermeability of concrete; compared with Examples 1-8, the mechanical properties of the concrete prepared with the modified limestone powder obtained in Comparative Example 2 decreased significantly, indicating that the modification of fly ash with sodium erythrobate can promote the release of the pozzolanic activity of fly ash and further promote the formation of C-S-H gel, which is helpful to improve the mechanical properties of concrete; compared with Examples 1-8, the performance of the concrete prepared with the modified limestone powder used in Comparative Example 3 decreased in all aspects, indicating that the performance of the limestone powder prepared in the examples of the present invention is better.

[0065] The above are the preferred embodiments of the present invention. Without departing from the principle of the present invention, those of ordinary skill in the art can also make several improvements and modifications, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of modified limestone powder, characterized in that, It includes the following steps: Step S1, pretreatment of limestone powder: Perform ball milling on the limestone powder, then add the ball-milled limestone powder into the prepared 2-(perfluorooctyl)ethyl methacrylate emulsion, add an initiator, raise the temperature and stir, filter and wash to obtain pretreated limestone powder; Step S2, modification of fly ash: Add the surface-activated fly ash into the sodium erythrobate solution, with the pH condition being 7-9, heat and stir, filter and wash, and obtain modified fly ash after drying; Step S3, preparation of modified limestone powder: Mix and stir the pretreated limestone powder, modified fly ash, dispersant, binder and 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).

2. The preparation method of a modified limestone powder according to claim 1, wherein, In the said step S1, the ball milling treatment includes the following steps: perform ball milling on the limestone powder, sieve it, and then wash and dry it to obtain the ball-milled limestone powder.

3. The preparation method of a modified limestone powder according to claim 2, characterized in that, The speed of the ball milling treatment is 200-400 r / min, the time is 0.5-2 h; the mesh number for screening is 225-325.

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

5. The preparation method of a modified limestone powder according to claim 4, characterized in that, The emulsifier is one of sodium dodecyl sulfate, Span80 and Tween80; the initiator is one of ammonium persulfate, potassium persulfate and sodium persulfate.

6. The preparation method of a modified limestone powder according to claim 1, characterized in that, In the said step S1, the temperature for raising the temperature and stirring is 65-75 °C, the speed is 300-400 r / min, and the time is 2-3 h.

7. A method for preparing modified limestone powder according to claim 1, characterized in that, In the said step S2, the surface activation includes the following steps: after washing and drying the fly ash, add it into a 5-10 wt% sodium hydroxide solution and soak for 1-3 h, then filter and wash, and obtain the surface-activated fly ash after drying.

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

9. The preparation method of a modified limestone powder according to claim 1, wherein, In the said step S3, the speed of mixing and stirring 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 1-9, characterized in that, It includes components in the following weight parts: 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 of the pretreated 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 erythrobate solution.

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