Modified fly ash, high-performance concrete containing the modified fly ash, and preparation method

Abstract

The invention discloses modified fly ash, high-performance concrete containing the modified fly ash, and a preparation method thereof, and relates to the technical field of concrete. The preparation method of the high-performance concrete is as follows: slag powder is soaked in water until saturated with water to obtain pre-wetted slag powder, which is then mixed evenly with cement and modified fly ash, and then a water reducer, water, coarse aggregate, and fine aggregate are added and mixed evenly, the obtained mixture is molded, vibrated, and formed, and the mold is removed after film curing, and steam-cured to a specified age to obtain the obtained mixture; the modified fly ash and slag powder are used to perform step-by-step dense filling of a cementitious material system, thereby effectively improving the mechanical properties and durability of the concrete; the modified fly ash can improve the pore structure of the concrete, reduce the autogenous shrinkage during the hydration process, and impart excellent flexural and crack resistance to the concrete.

Description

Technical Field

[0001] The invention relates to the technical field of concrete, and in particular to modified fly ash, high-performance concrete containing the modified fly ash, and a preparation method thereof. Background Art

[0002] The continuous development of modern construction technology places higher demands on cement concrete, which is developing towards high strength, high toughness, high crack resistance, high durability, high volume stability, and excellent workability. High-performance concrete, a new type of high-tech concrete, combines high durability, high strength, and high workability, and is widely considered by the engineering community to be a key development direction for concrete materials. However, while possessing these many excellent properties, its high cementitious material content and low water-cement ratio also make it more brittle and prone to cracking.

[0003] Research has shown that concrete is rich in microcracks, and the process of concrete failure is a process in which cracks develop and expand until they become unstable. To overcome concrete's brittleness, long fibers such as asbestos fibers, steel fibers, carbon fibers, polyvinyl alcohol fibers, polypropylene fibers, and basalt fibers have been used in concrete to enhance its toughness. However, the large-scale use of these long fibers tends to cause them to clump together in the concrete, hindering the uniform dispersion of aggregates and limiting their application in concrete containing coarse aggregates.

[0004] In concrete, aggregates account for more than 60% of the volume. Aggregates are important components in concrete that bear loads, resist erosion, and enhance the volume stability of concrete. Studies have shown that the performance of concrete in construction is affected by the size of aggregates, such as the initial slump, slump retention, and slump loss of concrete; and the agglomeration of soil or its coating on the surface of aggregates will hinder the bonding between aggregates and cement, forming structural weak areas and reducing the strength of concrete; the presence of mud will also affect the concrete's resistance to carbonation and reduce the concrete's weather resistance; and if the mud agglomerates, it will reduce the local strength of the concrete, posing a safety hazard.

[0005] Fly ash is the primary solid waste emitted by coal-fired power plants. Its production is gradually increasing. It's inexpensive and a reactive powder material. Currently, fly ash emissions exceed 300 million tons annually. Since coal accounts for approximately 70% of China's primary energy consumption, and coal-fired power generation will remain the primary source for a long time to come, significant fly ash production will continue. Currently, the comprehensive utilization rate of fly ash in China is only around 30%. This significant amount of fly ash is not effectively utilized, and its disposal in piles not only occupies significant land but also pollutes the environment. Therefore, the task of resource utilization of solid waste is daunting.

[0006] Chinese patent document CN114873970A discloses a high-performance machine-made sand concrete and its preparation method. The high-performance machine-made sand concrete is composed of crushed stone, machine-made sand, cement, fly ash, limestone powder, silica fume, mineral powder, a water reducer, and a gel reducer. By optimizing the raw material ratio, lower-grade machine-made sand can be used to produce concrete with the same properties as higher-grade raw materials. Furthermore, the addition of an optimized gel reducer significantly improves the concrete's strength, dispersibility, and workability. However, the concrete's flexural and crack resistance still needs to be improved. Summary of the Invention

[0007] In order to address the deficiencies in the prior art, the present invention aims to provide a modified fly ash, a high-performance concrete containing the modified fly ash, and a preparation method. The modified fly ash and slag powder are used to densely fill the cementitious material system step by step, thereby effectively improving the mechanical properties and durability of the concrete. The modified fly ash can improve the pore structure of the concrete, reduce the autogenous shrinkage during the hydration process, and give the concrete excellent flexural and crack resistance.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for preparing modified fly ash comprises the following steps:

[0010] (1) adding fly ash to anhydrous ethanol, ultrasonically treating, centrifuging, washing, and drying, then adding the mixture to a NaOH solution, stirring evenly, centrifuging, washing, and drying the product to obtain hydroxylated fly ash;

[0011] (2) dispersing the hydroxylated fly ash in dimethyl sulfoxide, then adding allyl succinic anhydride, stirring to react, centrifuging, washing, and drying the product to obtain carboxylated fly ash;

[0012] (3) adding the carboxylated fly ash into deionized water to prepare a fly ash suspension, then adding methyl allyl alcohol polyoxyethylene ether, stirring and mixing, adding ammonium persulfate dropwise, heating to react, cooling, filtering, washing, and drying the product to obtain modified fly ash.

[0013] Preferably, in step (1), the ultrasonic treatment time is 10 to 30 minutes, the concentration of the NaOH solution is 15 to 30 wt%, and the stirring condition is 50 to 100 r / min for 30 to 90 minutes.

[0014] Preferably, in step (1), the usage ratio of fly ash to anhydrous ethanol is 10 g: 100-150 mL; the usage ratio of fly ash to NaOH solution is 10 g: 30-50 mL.

[0015] Preferably, in step (2), the mass ratio of hydroxylated fly ash, dimethyl sulfoxide, and allyl succinic anhydride is 10:50-80:0.5-3.

[0016] Preferably, in step (2), the stirring reaction condition is 40-60° C. for 3-6 hours.

[0017] Preferably, in step (3), the usage ratio of carboxylated fly ash, methyl allyl alcohol polyoxyethylene ether, and ammonium persulfate is 10g:1.5-2.3:0.005-0.03; and the solid content of the fly ash suspension is 30-45wt%.

[0018] Preferably, in step (3), the temperature-raising reaction condition is to raise the temperature to 60-70° C. and keep the reaction for 3-6 hours.

[0019] The present invention also claims protection for modified fly ash prepared by the preparation method.

[0020] The present invention also claims a high performance concrete containing the modified fly ash, which is made of the following components in cubic dosage: cement 200-350 kg / m 3 , coarse aggregate 600~720kg / m 3 , fine aggregate 400~500kg / m 3 , modified fly ash 60~120kg / m 3 , slag powder 40~100kg / m 3 , water reducing agent 6~10kg / m 3 , water 150~300kg / m 3 .

[0021] Preferably, the cement is PO 42.5 ordinary Portland cement.

[0022] Preferably, the coarse aggregate is limestone crushed stone with a particle size of 5 to 25 mm, a mud content of less than 0.5 wt%, and a needle-like content of less than 1.7 wt%.

[0023] Preferably, the fine aggregate is natural river sand with a fineness modulus of 2.3 to 3.0 and a particle size of 0.25 to 0.5 mm.

[0024] Preferably, the slag powder is S95 slag powder, with a 28d activity index greater than 100% and a specific surface area greater than 350m 2 / kg.

[0025] Preferably, the water reducer is a polycarboxylic acid water reducer with a water reduction rate greater than 20% and an air content less than 2%.

[0026] The present invention also claims protection for a method for preparing high-performance concrete containing the modified fly ash, comprising the following steps: soaking slag powder in water until saturated with water to obtain pre-wet slag powder, mixing the pre-wet slag powder with cement and modified fly ash, then adding a water reducer, water, coarse aggregate, and fine aggregate, and mixing them evenly, molding, vibrating, and shaping the resulting mixture, removing the mold after film curing, and steam curing to a specified age to obtain the high-performance concrete containing modified fly ash.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) The present invention provides a modified fly ash. First, the fly ash is pretreated with anhydrous ethanol, and then the fly ash is hydroxylated with a NaOH solution, so that the micropores on the fly ash surface become rough, the specific surface area is increased, and the closed pores of the fly ash are opened to increase its porosity. Then, allyl succinic anhydride is used to react with the hydroxyl groups on the surface of the hydroxylated fly ash to introduce a large number of carboxyl groups and unsaturated double bonds into the fly ash surface. The hydrophilic carboxylic acid groups can be adsorbed on the surface of cement particles to play an anchoring role, so that the cement particles are evenly dispersed under the action of electrostatic repulsion, the contact area between the cement particle surface and water is increased, and the cement hydration rate is accelerated. , the cement hydration products fill the interior of the dense concrete, reduce internal cracks, and enhance the concrete's crack resistance and impermeability; finally, methyl allyl alcohol polyoxyethylene ether is adsorbed on the surface of the carboxylated fly ash, and a polymer is formed on its surface through a polymerization reaction, so that the modified fly ash can absorb and accommodate a part of the bound water. As the concrete solidifies, the side chains of the comb-like polymer molecules will gradually hydrolyze under alkaline conditions, continuously releasing small molecules and bound water. On the one hand, it can improve the dispersibility of the concrete slurry, and on the other hand, it can continuously reduce the capillary pressure in the concrete during the curing stage, improve the self-shrinkage phenomenon of the concrete, and improve the strength and crack resistance of the concrete.

[0029] 2) The present invention provides a high-performance concrete containing modified fly ash, wherein coarse aggregate and fine aggregate serve as the basic overlap skeleton of the concrete, and continuously graded crushed stone and river sand are filled in the skeleton to further enhance the strength of the overlap skeleton. Cement and slag powder form a slurry when in contact with water and wrap around the outside of the skeleton to further increase the density and cohesion of the concrete. Fly ash and slag powder have an active effect, an interface effect, a micro-filling effect, and a water-reducing effect, which can not only improve the rheological properties of the concrete slurry, reduce the hydration heat, reduce the slump loss, and reduce segregation and bleeding, but also improve the mechanical properties of the concrete and enhance the mechanical properties and durability of the concrete. The spherical glass in the fly ash can act as a ball bearing to improve the workability of the concrete mixture. After modification, the fly ash can also improve the self-shrinkage and pore structure of the concrete, reduce microcracks in the concrete, and enhance the flexural and crack resistance of the concrete. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the embodiments. Of course, the specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0031] Unless otherwise specified, the chemical reagents and materials in the present invention are purchased from commercial sources or synthesized from commercially purchased raw materials.

[0032] The fly ash was Class II fly ash with a 45 μm sieve residue of 15%, and was purchased from Wuhan Qingshan Power Plant.

[0033] A method for preparing high-performance concrete containing modified fly ash comprises the following steps:

[0034] (1) 10 g of fly ash was added to 100-150 mL of anhydrous ethanol, ultrasonically treated for 10-30 min, centrifuged, washed, and dried, and then added to 30-50 mL of a 15-30 wt% NaOH solution, stirred at 50-100 r / min for 30-90 min, and the product was centrifuged, washed, and dried to obtain hydroxylated fly ash;

[0035] (2) Dispersing 10 g of hydroxylated fly ash into 50-80 g of dimethyl sulfoxide, then adding 0.5-3 g of allyl succinic anhydride, reacting at 40-60° C. for 3-6 h, centrifuging, washing, and drying the product to obtain carboxylated fly ash;

[0036] (3) adding 10 g of carboxylated fly ash to deionized water to prepare a 30-45 wt% fly ash suspension, then adding 1.5-2.3 g of methyl allyl alcohol polyoxyethylene ether, stirring and mixing, adding dropwise 0.005-0.03 g of ammonium persulfate, heating to 60-70° C. and keeping the temperature for reaction for 3-6 hours, cooling, filtering, washing, and drying the product to obtain modified fly ash;

[0037] (4) 40-100 g of slag powder is soaked in water until saturated with water to obtain pre-wetted slag powder, which is then mixed evenly with 200-350 g of cement and 60-120 g of modified fly ash. Subsequently, 6-10 g of water reducer, 150-300 g of water, 600-720 g of coarse aggregate, and 400-500 g of fine aggregate are added and mixed evenly. The obtained mixture is molded, vibrated, and formed. After film curing, the mold is removed and steam cured to a specified age to obtain the high-performance concrete containing modified fly ash.

[0038] The present invention will be further described below with reference to specific examples.

[0039] Example 1

[0040] A method for preparing high-performance concrete containing modified fly ash comprises the following steps:

[0041] (1) 10 g of fly ash was added to 150 mL of anhydrous ethanol, ultrasonically treated for 30 min, centrifuged, washed, and dried, and then added to 50 mL of 20 wt% NaOH solution and stirred at 100 r / min for 30 min. The product was centrifuged, washed, and dried to obtain hydroxylated fly ash;

[0042] (2) 10 g of hydroxylated fly ash was dispersed in 80 g of dimethyl sulfoxide, and then 3 g of allyl succinic anhydride was added. The mixture was reacted at 60 °C for 3 h. The product was centrifuged, washed, and dried to obtain carboxylated fly ash.

[0043] (3) 10 g of carboxylated fly ash was added to deionized water to prepare a 40 wt% fly ash suspension, and then 2.3 g of methyl allyl alcohol polyoxyethylene ether was added, stirred and mixed, and 0.03 g of ammonium persulfate was added dropwise. The temperature was raised to 70° C. and the reaction was kept at this temperature for 3 h. The product was cooled, filtered, washed, and dried to obtain modified fly ash;

[0044] (4) 70 g of slag powder was soaked in water until saturated to obtain pre-wetted slag powder, which was then mixed evenly with 275 g of cement and 120 g of modified fly ash. Subsequently, 8 g of water reducer, 230 g of water, 660 g of coarse aggregate, and 450 g of fine aggregate were added and mixed evenly. The obtained mixture was molded, vibrated, and formed. After film curing, the mold was removed and steam cured to a specified age to obtain the high-performance concrete containing modified fly ash.

[0045] Example 2

[0046] A method for preparing high-performance concrete containing modified fly ash comprises the following steps:

[0047] (1) 10 g of fly ash was added to 120 mL of anhydrous ethanol, ultrasonically treated for 20 min, centrifuged, washed, and dried, and then added to 40 mL of 20 wt% NaOH solution, stirred at 80 rpm for 60 min, and the product was centrifuged, washed, and dried to obtain hydroxylated fly ash;

[0048] (2) 10 g of hydroxylated fly ash was dispersed in 65 g of dimethyl sulfoxide, and then 1.7 g of allyl succinic anhydride was added. The mixture was reacted at 50 °C for 5 h. The product was centrifuged, washed, and dried to obtain carboxylated fly ash.

[0049] (3) 10 g of carboxylated fly ash was added to deionized water to prepare a 40 wt% fly ash suspension, and then 1.9 g of methyl allyl alcohol polyoxyethylene ether was added, stirred and mixed, and 0.02 g of ammonium persulfate was added dropwise. The temperature was raised to 65° C. and kept in the reaction for 5 h. The product was cooled, filtered, washed, and dried to obtain modified fly ash;

[0050] (4) 70 g of slag powder was soaked in water until saturated to obtain pre-wetted slag powder, which was then mixed evenly with 275 g of cement and 90 g of modified fly ash. Subsequently, 8 g of water reducer, 230 g of water, 660 g of coarse aggregate, and 450 g of fine aggregate were added and mixed evenly. The obtained mixture was molded, vibrated, and formed. After film curing, the mold was removed and steam cured to a specified age to obtain the high-performance concrete containing modified fly ash.

[0051] Example 3

[0052] A method for preparing high-performance concrete containing modified fly ash comprises the following steps:

[0053] (1) 10 g of fly ash was added to 100 mL of anhydrous ethanol, ultrasonically treated for 10 min, centrifuged, washed, and dried, and then added to 30 mL of 20 wt% NaOH solution, stirred at 50 rpm for 90 min, and the product was centrifuged, washed, and dried to obtain hydroxylated fly ash;

[0054] (2) 10 g of hydroxylated fly ash was dispersed in 50 g of dimethyl sulfoxide, and then 0.5 g of allyl succinic anhydride was added. The mixture was reacted at 40 °C for 6 h. The product was centrifuged, washed, and dried to obtain carboxylated fly ash.

[0055] (3) 10 g of carboxylated fly ash was added to deionized water to prepare a 40 wt% fly ash suspension, and then 1.5 g of methyl allyl alcohol polyoxyethylene ether was added, stirred and mixed, and 0.005 g of ammonium persulfate was added dropwise. The temperature was raised to 60° C. and kept for 6 h. The product was cooled, filtered, washed, and dried to obtain modified fly ash;

[0056] (4) 70 g of slag powder was soaked in water until saturated to obtain pre-wetted slag powder, which was then mixed evenly with 275 g of cement and 60 g of modified fly ash. Subsequently, 8 g of water reducer, 230 g of water, 660 g of coarse aggregate, and 450 g of fine aggregate were added and mixed evenly. The obtained mixture was molded, vibrated, and formed. After film curing, the mold was removed and steam cured to a specified age to obtain the high-performance concrete containing modified fly ash.

[0057] Comparative Example 1

[0058] A method for preparing high-performance concrete containing modified fly ash comprises the following steps:

[0059] (1) 10 g of fly ash was added to 150 mL of anhydrous ethanol, ultrasonically treated for 30 min, centrifuged, washed, and dried, and then added to 50 mL of 20 wt% NaOH solution and stirred at 100 r / min for 30 min. The product was centrifuged, washed, and dried to obtain hydroxylated fly ash;

[0060] (2) 10 g of hydroxylated fly ash was dispersed in 80 g of dimethyl sulfoxide, and then 3 g of allyl succinic anhydride was added. The mixture was reacted at 60 °C for 3 h. The product was centrifuged, washed, and dried to obtain carboxylated fly ash.

[0061] (3) 70 g of slag powder was soaked in water until saturated to obtain pre-wetted slag powder, which was then mixed evenly with 275 g of cement and 120 g of carboxylated fly ash. Subsequently, 8 g of water reducer, 230 g of water, 660 g of coarse aggregate, and 450 g of fine aggregate were added and mixed evenly. The obtained mixture was molded, vibrated, and formed. After film curing, the mold was removed and steam cured to a specified age to obtain the high-performance concrete containing modified fly ash.

[0062] Comparative Example 2

[0063] A method for preparing high-performance concrete containing modified fly ash comprises the following steps:

[0064] (1) 10 g of fly ash was added to 150 mL of anhydrous ethanol, ultrasonically treated for 30 min, centrifuged, washed, and dried, and then added to 50 mL of 20 wt% NaOH solution and stirred at 100 r / min for 30 min. The product was centrifuged, washed, and dried to obtain hydroxylated fly ash;

[0065] (2) 70 g of slag powder was soaked in water until saturated with water to obtain pre-wetted slag powder, which was then mixed evenly with 275 g of cement and 120 g of hydroxylated fly ash. Subsequently, 8 g of water reducer, 230 g of water, 660 g of coarse aggregate, and 450 g of fine aggregate were added and mixed evenly. The obtained mixture was molded, vibrated, and formed. After film curing, the mold was removed and steam cured to a specified age to obtain the high-performance concrete containing modified fly ash.

[0066] For the concrete raw materials prepared in Examples 1 to 3 and Comparative Examples 1 to 2, the slump of the concrete raw materials was tested with reference to GB / T50080-2016 "Standard for Test Methods for Performance of Ordinary Concrete Mixtures", and with reference to BYSMC-ES-04-2007 "EC Anti-cracking Mortar", the concrete raw materials were smeared on a 160 mm × 120 × 5 mm cement fiber board with a smear thickness of 10 mm, and placed in an oven heated to 70 ° C with hot air circulation for 4 h to observe the cracking; 10 100 mm × 100 mm × 100 mm test blocks were prepared from the concrete raw materials, and the compressive strength and flexural strength of the test blocks were tested with reference to GB / T50081-2019 "Standard for Test Methods for Physical and Mechanical Properties of Concrete". The self-shrinkage rate of the concrete after casting (20 ± 2 ° C) was tested using a CABR-NES non-contact shrinkage deformation instrument. The specific data are shown in Table 1.

[0067] Table 1 Concrete performance test results

[0068] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Slump out of machine (mm) 262 258 256 248 245 28d compressive strength (MPa) 66.9 66.1 65.7 58.4 52.3 28d flexural strength (MPa) 7.8 7.6 7.5 5.9 5.5 Crack resistance Uncracked Uncracked Uncracked Cracking Cracking <![CDATA[Shrinkage rate (10×10 -6 m / m)]]> 25 27 28 41 46

[0069] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing modified fly ash, characterized in that: The steps include: (1) Fly ash is added to anhydrous ethanol, ultrasonically treated, centrifuged, washed, and dried, and then added to a NaOH solution. After stirring evenly, the product is centrifuged, washed, and dried to obtain hydroxylated fly ash; (2) dispersing the hydroxylated fly ash in dimethyl sulfoxide, then adding allyl succinic anhydride, stirring the mixture for reaction, centrifuging, washing, and drying the product to obtain carboxylated fly ash; (3) adding the carboxylated fly ash into deionized water to prepare a fly ash suspension, then adding methyl allyl alcohol polyoxyethylene ether, stirring and mixing, adding ammonium persulfate dropwise, heating to react, cooling, filtering, washing, and drying the product to obtain modified fly ash; In step (2), the stirring reaction condition is 40-60°C for 3-6 hours; In step (2), the mass ratio of hydroxylated fly ash, dimethyl sulfoxide, and allyl succinic anhydride is 10:50-80:0.5-3; In step (3), the usage ratio of carboxylated fly ash, methyl allyl alcohol polyoxyethylene ether, and ammonium persulfate is 10 g: 1.5-2.3 g: 0.005-0.03 g; and the solid content of the fly ash suspension is 30-45 wt%.

2. The preparation method according to claim 1, characterized in that In step (1), the ultrasonic treatment time is 10-30 min, the concentration of the NaOH solution is 15-30 wt%, and the stirring condition is 50-100 r / min for 30-90 min.

3. The preparation method according to claim 1, characterized in that In step (1), the usage ratio of fly ash and anhydrous ethanol is 10 g: 100-150 mL; the usage ratio of fly ash and NaOH solution is 10 g: 30-50 mL.

4. The preparation method according to claim 1, characterized in that In step (3), the temperature-raising reaction condition is to raise the temperature to 60-70° C. and keep the temperature for 3-6 hours.

5. A modified fly ash prepared by the preparation method according to any one of claims 1 to 4.

6. A high performance concrete containing the modified fly ash according to claim 5, characterized in that: The concrete is made of the following components in parts by weight: 200-350 parts of cement, 600-720 parts of coarse aggregate, 400-500 parts of fine aggregate, 60-120 parts of modified fly ash, 40-100 parts of slag powder, 6-10 parts of water reducer, and 150-300 parts of water.

7. A method for preparing high performance concrete according to claim 6, characterized in that: The method comprises the following steps: soaking slag powder in water until saturated with water to obtain pre-wetted slag powder, uniformly mixing the pre-wetted slag powder with cement and modified fly ash, subsequently adding a water reducer, water, coarse aggregate and fine aggregate, and uniformly mixing the pre-wetted slag powder; molding, vibrating and shaping the obtained mixture; removing the mold after film curing; and steam curing to a specified age to obtain high-performance concrete containing modified fly ash.