A kind of high performance concrete with flexural and crack resistance and preparation method thereof

Abstract

The invention discloses a flexural and crack-resistant high-performance concrete and a preparation method thereof. The preparation method comprises the following steps: adding coarse aggregate, cement and modified fly ash into a mixer and stirring evenly; adding water and a water reducer and stirring evenly; then adding fine aggregate, silica fume and mineral powder and mixing evenly to obtain a concrete slurry; and finally filling a mold, vibrating, shaping and steam curing the concrete to obtain the flexural and crack-resistant high-performance concrete. The invention utilizes the modified fly ash, mineral powder and silica fume 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 the concrete with excellent flexural and crack-resistant properties.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete, and in particular to a high-performance concrete that is resistant to bending and cracking 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 main solid waste emitted by coal-fired power plants. Its output is gradually increasing. It is cheap and is an active powder material. At present, the task of resource utilization of solid waste is arduous.

[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 high-performance concrete that is resistant to flexure and cracking and a preparation method thereof. Modified fly ash, mineral powder, and silica fume 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 high-performance concrete with flexural and crack resistance is prepared from the following components, calculated by weight: 500-600 parts of cement, 600-720 parts of coarse aggregate, 300-450 parts of fine aggregate, 120-180 parts of modified fly ash, 80-100 parts of silica fume, 60-100 parts of mineral powder, 8-12 parts of water reducer and 300-500 parts of water.

[0010] Preferably, the preparation method of the modified fly ash comprises the following steps:

[0011] (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;

[0012] (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;

[0013] (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.

[0014] 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.

[0015] Preferably, in step (1), the fly ash density is 2.40-2.58 g / cm 3 The fineness is 45μm square hole sieve residue is 12.0~25.0%, the ignition loss is 0.40~0.60%, the water requirement is 80~100%, and the total content of silicon dioxide, aluminum oxide and iron oxide is 70~80%.

[0016] 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.

[0017] Preferably, in step (2), the mass ratio of hydroxylated fly ash, dimethyl sulfoxide, and allyl succinic anhydride is 10:50-80:0.5-3.

[0018] Preferably, in step (2), the stirring reaction condition is 40-60° C. for 3-6 hours.

[0019] 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%.

[0020] 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.

[0021] The present invention also claims protection for a preparation method of the flexural and crack-resistant high-performance concrete, which comprises the following steps: adding coarse aggregate, cement, and modified fly ash into a mixer and stirring evenly; adding water and a water reducer and stirring evenly; then adding fine aggregate, silica fume, and mineral powder and mixing evenly to obtain a concrete slurry; and finally molding, vibrating, shaping, and steam curing to obtain the flexural and crack-resistant high-performance concrete.

[0022] Preferably, the cement is P·O42.5R grade ordinary Portland cement.

[0023] Preferably, the coarse aggregate is a continuously graded crushed stone with a particle size of 5 to 20 mm and an apparent density of 2650 to 2700 kg / m 3 , bulk density is 1700~1750kg / m 3 The mud content is 0.3-0.5%, and the needle-like particle content is 6-8%.

[0024] Preferably, the fine aggregate is machine-made sand, the fineness modulus of the machine-made sand is 2.3-3.1, and the apparent density is 2400-2600 kg / m 3 , bulk density is 1400~1500kg / m 3The mud content is 0.3~0.6%, and the mass percentage of chloride ions is 0.00016~0.00019%.

[0025] Preferably, the mineral powder is S95 grade mineral powder, and the specific surface area of ​​the mineral powder is 400-450m 2 / kg, the activity index after 28 days was 95%, and the mobility ratio was 99%.

[0026] Preferably, the mass percentage of silicon dioxide in the silica ash is not less than 93%, the pozzolanic activity index is greater than 90%, the average particle size is 0.1 to 0.15 μm, and the specific surface area is greater than 15 m 2 / g.

[0027] Preferably, the water reducer is a polycarboxylic acid-based high-performance water reducer with a solid content of 20% and a water reduction rate of more than 25%.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1) The present invention provides a high-performance concrete with flexural and crack resistance. Coarse aggregate and fine aggregate serve as the basic overlapping skeleton of concrete. Continuously graded crushed stone and machine-made sand are filled in the skeleton to further enhance the strength of the overlapping skeleton. Cement, silica powder and mineral 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. Mineral admixtures such as fly ash, mineral powder and silica 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, 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 the microcracks of the concrete, and enhance the flexural and crack resistance of the concrete.

[0030] 2) 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, thereby increasing its porosity. Then, allyl succinic anhydride is used to react with the hydroxyl groups on the surface of the hydroxylated fly ash to produce a ring-opening reaction, thereby introducing 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. DETAILED DESCRIPTION

[0031] 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.

[0032] Unless otherwise specified, the chemical reagents and materials in the present invention are purchased from commercial sources or synthesized from commercially purchased raw materials.

[0033] A method for preparing high-performance concrete with flexural and crack resistance, comprising 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, stirring and 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) Add 600-720 parts of coarse aggregate, 500-600 parts of cement, and 120-180 parts of modified fly ash into a mixer and mix them evenly; add 300-500 parts of water and 8-12 parts of water reducer and mix them evenly; then add 300-450 parts of fine aggregate, 80-100 parts of silica fume, and 60-100 parts of mineral powder and mix them evenly to obtain a concrete slurry; finally, fill the mold, vibrate, shape, and steam-cured the mixture to obtain the flexural and crack-resistant high-performance concrete.

[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 with flexural and crack resistance, comprising 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 a 30 wt% NaOH solution and stirred at 100 rpm 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 stirred 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 45 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) 660 g of coarse aggregate, 550 g of cement, and 180 g of modified fly ash were added to a mixer and stirred evenly. 400 g of water and 10 g of a water reducer were added and stirred evenly. 360 g of fine aggregate, 90 g of silica fume, and 80 g of mineral powder were added and mixed evenly to obtain a concrete slurry. Finally, the mixture was molded, vibrated, formed, and steam-cured to obtain the flexural and crack-resistant high-performance concrete.

[0045] Example 2

[0046] A method for preparing high-performance concrete with flexural and crack resistance, comprising 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 2 g of allyl succinic anhydride was added. The mixture was stirred at 50° C. for 4.5 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 the reaction was kept at this temperature for 4.5 h. The product was cooled, filtered, washed, and dried to obtain modified fly ash;

[0050] (4) 660 g of coarse aggregate, 550 g of cement, and 150 g of modified fly ash were added to a mixer and stirred evenly. 400 g of water and 10 g of a water reducer were added and stirred evenly. 360 g of fine aggregate, 90 g of silica fume, and 80 g of mineral powder were added and mixed evenly to obtain a concrete slurry. Finally, the concrete slurry was molded, vibrated, formed, and steam-cured to obtain the flexural and crack-resistant high-performance concrete.

[0051] Example 3

[0052] A method for preparing high-performance concrete with flexural and crack resistance, comprising 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 stirred at 40 °C for 3 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 30 wt% fly ash suspension, and then 1.5 g of methyl allyl alcohol polyoxyethylene ether was added, stirred and mixed, and 0.01 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) 660 g of coarse aggregate, 550 g of cement, and 120 g of modified fly ash were added to a mixer and stirred evenly. 400 g of water and 10 g of a water reducer were added and stirred evenly. 360 g of fine aggregate, 90 g of silica fume, and 80 g of mineral powder were added and mixed evenly to obtain a concrete slurry. Finally, the concrete slurry was molded, vibrated, formed, and steam-cured to obtain the flexural and crack-resistant high-performance concrete.

[0057] Comparative Example 1

[0058] A method for preparing high-performance concrete with flexural and crack resistance, comprising 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 a 30 wt% NaOH solution and stirred at 100 rpm 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 stirred at 60 °C for 3 h. The product was centrifuged, washed, and dried to obtain carboxylated fly ash.

[0061] (3) 660 g of coarse aggregate, 550 g of cement, and 180 g of carboxylated fly ash were added to a mixer and stirred evenly. 400 g of water and 10 g of a water reducer were added and stirred evenly. 360 g of fine aggregate, 90 g of silica fume, and 80 g of mineral powder were added and mixed evenly to obtain a concrete slurry. Finally, the concrete slurry was molded, vibrated, formed, and steam-cured to obtain the flexural and crack-resistant high-performance concrete.

[0062] Comparative Example 2

[0063] A method for preparing high-performance concrete with flexural and crack resistance, comprising 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 a 30 wt% NaOH solution and stirred at 100 rpm for 30 min. The product was centrifuged, washed, and dried to obtain hydroxylated fly ash;

[0065] (2) 660 g of coarse aggregate, 550 g of cement, and 180 g of hydroxylated fly ash were added to a mixer and stirred evenly. 400 g of water and 10 g of a water reducer were added and stirred evenly. 360 g of fine aggregate, 90 g of silica fume, and 80 g of mineral powder were added and mixed evenly to obtain a concrete slurry. Finally, the concrete slurry was molded, vibrated, formed, and steam-cured to obtain the flexural and crack-resistant high-performance concrete.

[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) 267 262 263 254 250 28d compressive strength (MPa) 75.2 74.5 74.1 63.4 58.7 28d flexural strength (MPa) 8.1 7.9 7.8 6.2 5.7 Crack resistance Uncracked Uncracked Uncracked Cracking Cracking <![CDATA[Shrinkage rate (10×10 -6 m / m)]]> 23 24 26 39 42

[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 high performance concrete with flexural and crack resistance, characterized in that: The invention is made of the following components in parts by weight: 500-600 parts of cement, 600-720 parts of coarse aggregate, 300-450 parts of fine aggregate, 120-180 parts of modified fly ash, 80-100 parts of silica fume, 60-100 parts of mineral powder, 8-12 parts of water reducer and 300-500 parts of water; The preparation method of the modified fly ash comprises the following steps: (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; (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; (3) adding the carboxylated fly ash to 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 mass ratio of hydroxylated fly ash, dimethyl sulfoxide, and allyl succinic anhydride is 10: (50-80): (0.5-3); In step (2), the stirring reaction condition is 40-60° C. for 3-6 hours; 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; In step (3), the temperature-raising reaction condition is to raise the temperature to 60-70° C. and keep the temperature for reaction for 3-6 hours.

2. The flexural and crack-resistant high-performance concrete according to claim 1, characterized in that: 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.

3. The flexural and crack resistant high performance concrete according to claim 1, characterized in that: In step (1), the fly ash density is 2.40-2.58 g / cm 3 The fineness is 45μm square hole sieve residue is 12.0~25.0%, the ignition loss is 0.40~0.60%, the water requirement is 80~100%, and the total content of silicon dioxide, aluminum oxide and iron oxide is 70~80%.

4. The flexural and crack resistant high performance concrete 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.

5. The flexural and crack resistant high performance concrete according to claim 1, characterized in that: In step (3), the solid content of the fly ash suspension is 30 to 45 wt%.

6. A method for preparing the flexural and crack resistant high performance concrete according to any one of claims 1 to 5, characterized in that: The steps are as follows: adding coarse aggregate, cement, and modified fly ash into a mixer and stirring evenly, adding water and a water reducer and stirring evenly, then adding fine aggregate, silica fume, and mineral powder and mixing evenly to obtain concrete slurry, and finally filling a mold, vibrating, shaping, and steam curing to obtain the flexural and crack-resistant high-performance concrete.