Nano material modified coal gangue coarse aggregate concrete and preparation method thereof

Abstract

The invention discloses nanometer material modified coal gangue coarse aggregate concrete and a preparation method thereof. The preparation method of the concrete comprises the following steps: (1) pretreating coal gangue; (2) preparing a nano SiO2 dispersion liquid; (3) carrying out modification treatment on the coal gangue coarse aggregate; and (4) preparing the modified coal gangue coarse aggregate concrete. According to the invention, the coal gangue is modified by using nano SiO2, so that the modified coal gangue aggregate and a cement matrix interface are bonded more tightly, the interface bonding force between the coal gangue aggregate and cement is enhanced, and the compressive strength of the obtained concrete is effectively improved; the method can effectively improve the utilization rate of the solid waste coal gangue, turns waste into wealth, not only can solve the environmental problem caused by coal gangue stockpiling, but also can relieve the pressure of shortage of natural gravel resources, can reduce the production cost of the concrete, and has remarkable social benefits and economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of building material resource utilization technology. Specifically, this invention relates to a nanomaterial-modified coal gangue coarse aggregate concrete and its preparation method. Background Technology

[0002] Coal gangue is a solid waste generated during coal mining and washing. With the rapid development of my country's industry, coal gangue production is increasing year by year, resulting in huge emissions. Long-term stockpiling not only occupies land resources but also causes environmental pollution. Utilizing coal gangue as concrete aggregate can not only solve the environmental problems caused by coal gangue stockpiling but also alleviate the pressure of natural crushed stone resource shortages, yielding significant social and economic benefits.

[0003] While the current application of coal gangue as aggregate in concrete has certain environmental benefits, its rough surface, high porosity, and high water absorption mean that direct use in concrete preparation results in low strength and poor durability. The mechanical properties of coal gangue aggregate concrete are far inferior to those of traditional aggregate concrete, especially in projects requiring high strength and durability, thus limiting its large-scale application. Currently, methods such as acid / alkali solution soaking, high-temperature calcination, and surface coating can be used to optimize coal gangue, but the improvement effects are unsatisfactory, and these methods also lead to complex processes and high costs.

[0004] In view of the above, this application is hereby submitted. Summary of the Invention

[0005] This invention proposes a nanomaterial-modified coal gangue coarse aggregate concrete and its preparation method. The aim is to improve the microstructure and enhance the bonding force between the coal gangue aggregate and cement by introducing nano-SiO2 materials to fill the pore structure inside the coal gangue and the interfacial transition zone between the coal gangue and cement. This method addresses the weaknesses in the mechanical properties and long-term use of coal gangue aggregate concrete by improving the density and strength of the coal gangue aggregate, providing a more efficient and environmentally friendly concrete material preparation technology.

[0006] One embodiment of the present invention provides a method for preparing nanomaterial-modified coal gangue coarse aggregate concrete, comprising the following steps:

[0007] (1) The coal gangue is crushed and screened to obtain coal gangue coarse aggregate; the coal gangue coarse aggregate is then ultrasonically cleaned and dried; then it is soaked in a mixed solution of silane coupling agent and ethanol, dried and solidified, washed until neutral, and dried to obtain pretreated coal gangue coarse aggregate.

[0008] (2) After mixing nano-SiO2 powder with water, a dispersant is added and the mixture is magnetically stirred to obtain a mixture; the mixture is ultrasonically pulverized to obtain a dispersion; the supernatant obtained after centrifugation of the dispersion is the nano-SiO2 dispersion.

[0009] (3) The pretreated coal gangue coarse aggregate is placed in a vacuum impregnation tank for vacuum treatment, and then the nano-SiO2 dispersion is injected, impregnated under pressure, and dried to obtain modified coal gangue coarse aggregate.

[0010] (4) Cement, fly ash, natural sand, water and water-reducing agent are mixed to form a uniform slurry. Then, the modified coal gangue coarse aggregate is added in small amounts and mixed at low speed. Then, a test mold is poured, vibrated and compacted, and covered with plastic wrap for static treatment. Finally, the concrete is demolded and cured to obtain the nanomaterial modified coal gangue coarse aggregate concrete.

[0011] This invention successfully prepared nanomaterial-modified coal gangue coarse aggregate concrete using coal gangue modification technology. This material system achieves efficient utilization of industrial solid waste through a solid waste resource recovery technology pathway. Employing a synergistic physical-chemical modification process, it significantly improves the interfacial bonding performance and volume stability of the coal gangue aggregate. The prepared novel coal gangue aggregate concrete meets strength requirements and slump requirements for pumping. Furthermore, replacing natural aggregates with modified coal gangue can reduce material costs by approximately 28%, effectively alleviating the pressure of natural crushed stone resource depletion and reducing carbon emissions from concrete preparation. This provides a new method for green concrete preparation technology and has significant demonstrative value for promoting the low-carbon transformation of the construction industry.

[0012] In some embodiments, when mixing cement, fly ash, natural sand, water, and water-reducing agent to form a uniform slurry in step (4), natural crushed stone may also be added.

[0013] In some embodiments, in step (4), the total amount of modified coal gangue coarse aggregate added accounts for 25% to 100% of the sum of the mass of the modified coal gangue coarse aggregate and the mass of the natural crushed stone.

[0014] In some embodiments, in step (1), the particle size of the coarse coal gangue aggregate is 5 to 20 mm;

[0015] And / or, the ultrasonic cleaning time is 15 to 20 minutes;

[0016] And / or, the drying temperature is 80-85°C.

[0017] In some embodiments, in step (1), the silane coupling agent includes at least one of silane coupling agent KH-550, silane coupling agent KH-560, and silane coupling agent KH-570;

[0018] And / or, the mass ratio of the silane coupling agent to the ethanol is (1-1.2):9;

[0019] And / or, the soaking time is 2 to 3 hours;

[0020] And / or, the drying and curing temperature is 100-110°C, and the time is 1-2 hours.

[0021] In some embodiments, in step (2), the particle size of the nano-SiO2 is 10-100 nm, and the amount of nano-SiO2 added is 1.2%-1.3% of the mass of the pretreated coal gangue coarse aggregate;

[0022] And / or, the mass ratio of the nano-SiO2 powder to the water is (1-1.5):100;

[0023] And / or, the dispersant is a polycarboxylate superplasticizer, and its addition amount is 0.1% to 0.2% of the mass of the nano-SiO2 powder;

[0024] And / or, the magnetic stirring time is 30 to 35 minutes.

[0025] In some embodiments, in step (2), the ultrasonic pulverization process is carried out in an ultrasonic cell pulverizer, and the working conditions of the ultrasonic pulverization process are: power of 300-310W, ultrasonic time of 30-35min, pulse mode of 2s working and 1s intermittent, and water temperature control ≤40℃.

[0026] And / or, the centrifugation speed is 3000-3100 r / min, and the centrifugation time is 10-15 min;

[0027] And / or, the D50 particle size of the nano-SiO2 dispersion is ≤50nm.

[0028] In some embodiments, in step (3), the vacuum degree of the vacuuming process is -0.08 to -0.1 MPa, and the holding time is 0.5 to 2 hours;

[0029] And / or, the pressure of the pressure impregnation is 0.5 to 2 MPa, and the impregnation time is 1 to 4 hours;

[0030] And / or, the drying temperature is 60-65°C, and the drying time is 22-24 hours.

[0031] In some embodiments, in step (4), the curing temperature is 20±2℃ and the humidity is ≥95%.

[0032] Another aspect of this invention provides a nanomaterial-modified coal gangue coarse aggregate concrete, which is prepared by the above-described preparation method.

[0033] The advantages and beneficial effects of the embodiments of the present invention are as follows:

[0034] (1) In this embodiment of the invention, nano-SiO2 is used to fill the pores of coal gangue, which can optimize its internal structure, thereby effectively reducing the porosity and water absorption rate of coal gangue and improving its density and strength.

[0035] (2) In this embodiment of the invention, by using nano-SiO2 to modify coal gangue, the modified coal gangue aggregate and cement matrix are more tightly bonded at the interface, which enhances the interfacial bonding force between the coal gangue aggregate and cement and effectively improves the compressive strength of concrete.

[0036] (3) The preparation method of the present invention not only realizes the efficient utilization of solid waste and makes a significant contribution to energy conservation and emission reduction; but also reduces the mining of natural aggregates, reduces the load on natural resources, and saves production costs by improving the utilization rate of coal gangue. This method provides a theoretical basis for the application of new green and low-carbon concrete.

[0037] (4) The preparation method of the present invention is simple to operate, has low equipment requirements, and is easy to promote and apply on a large scale in industrial applications. Attached Figure Description

[0038] Figure 1 The images show the internal microstructure of unmodified coal gangue aggregate concrete and nano-SiO2 modified coal gangue coarse aggregate concrete.

[0039] Figure 2 The images show the microstructure of unmodified coal gangue aggregate concrete and nano-SiO2 modified coal gangue coarse aggregate concrete in the transition zone between coal gangue aggregate and cement.

[0040] Figure 3 The values ​​represent the compressive strength of unmodified coal gangue aggregate concrete and nano-SiO2 modified coal gangue coarse aggregate concrete after 3 days of curing.

[0041] Figure 4 The values ​​represent the compressive strength of unmodified coal gangue aggregate concrete and nano-SiO2 modified coal gangue coarse aggregate concrete after 7 days of curing.

[0042] Figure 5 The values ​​represent the compressive strength of unmodified coal gangue aggregate concrete and nano-SiO2 modified coal gangue coarse aggregate concrete after 28 days of curing. Detailed Implementation

[0043] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0044] In this document, when values ​​are described as ranges, it should be understood that such disclosure includes disclosure of all possible subranges within that range, as well as the specific numerical values ​​falling within that range, regardless of whether the specific numerical value or specific subrange is explicitly specified.

[0045] In this article, the words “contain” and “include” and their various variations mean that other elements or wholes may be included but not specifically described.

[0046] In this article, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three kinds of relationships. For example, A and / or B can represent three cases: A exists alone, A and B exist simultaneously, and B exists alone.

[0047] One embodiment of the present invention provides a method for preparing nanomaterial-modified coal gangue coarse aggregate concrete, comprising the following steps:

[0048] (1) Coal gangue pretreatment: The coal gangue is crushed and screened to obtain coal gangue coarse aggregate; the coal gangue coarse aggregate is then ultrasonically cleaned and dried; then it is soaked in a mixed solution of silane coupling agent and ethanol, dried and solidified, washed until neutral, and dried to obtain pretreated coal gangue coarse aggregate.

[0049] (2) Preparation of nano-SiO2 dispersion: After mixing nano-SiO2 powder with water, a dispersant is added and the mixture is magnetically stirred to obtain a mixture; the mixture is ultrasonically pulverized to obtain a dispersion; the supernatant obtained after centrifugation of the dispersion is the nano-SiO2 dispersion.

[0050] (3) Nano-modification treatment of coal gangue coarse aggregate: The pretreated coal gangue coarse aggregate is placed in a vacuum impregnation tank for vacuum treatment, and then the nano-SiO2 dispersion is injected, impregnated under pressure, and dried to obtain modified coal gangue coarse aggregate.

[0051] (4) Preparation of modified coal gangue coarse aggregate concrete: Cement, fly ash, natural sand, water and water-reducing agent are mixed to form a uniform slurry. Then, the modified coal gangue coarse aggregate is added in small amounts and mixed at low speed. Then, a test mold is poured, vibrated and compacted, and covered with plastic wrap for static treatment. Finally, after demolding and curing, the nanomaterial modified coal gangue coarse aggregate concrete is obtained.

[0052] This invention utilizes nano-SiO2 to fill the pores of coal gangue and form a dense coating, which can improve the overall strength of coal gangue particles and reduce the probability of coal gangue aggregate self-destruction. Furthermore, nano-SiO2 can react with cement hydration product Ca(OH)2 to generate CSH gel, thereby reducing the thickness of the aggregate-cement interface transition zone (ITZ) and enhancing the interfacial bonding strength.

[0053] In addition, nano-SiO2 can improve the microstructure and workability of coal gangue coarse aggregate concrete: nano-SiO2 fills the micron-sized pores (0.1-10μm) inside the coal gangue and blocks the connecting channels, forming an "island-like" pore structure, reducing stress concentration; secondly, nano-SiO2 can also improve the workability of concrete, making the concrete more operable during construction.

[0054] In some embodiments, when mixing cement, fly ash, natural sand, water, and water-reducing agent to form a uniform slurry in step (4), natural crushed stone may also be added.

[0055] In some embodiments, in step (4), the total amount of modified coal gangue coarse aggregate added accounts for 25% to 100% of the sum of the mass of modified coal gangue coarse aggregate and the mass of natural crushed stone; that is, the replacement rate of modified coal gangue coarse aggregate is 25% to 100% (replacement rate of modified coal gangue coarse aggregate = mass of modified coal gangue coarse aggregate / (mass of modified coal gangue coarse aggregate + mass of natural crushed stone)).

[0056] In some embodiments, in step (1), the particle size of the coarse coal gangue aggregate is 5 to 20 mm;

[0057] And / or, the ultrasonic cleaning time is 15 to 20 minutes;

[0058] And / or, the drying temperature is 80-85°C.

[0059] In some embodiments, in step (1), the silane coupling agent includes at least one of silane coupling agent KH-550, silane coupling agent KH-560, and silane coupling agent KH-570;

[0060] And / or, the mass ratio of the silane coupling agent to the ethanol is (1-1.2):9;

[0061] And / or, the soaking time is 2 to 3 hours;

[0062] And / or, the drying and curing temperature is 100-110°C, and the time is 1-2 hours.

[0063] In some embodiments, in step (2), the particle size of the nano-SiO2 is 10-100 nm, and the amount of nano-SiO2 added is 1.2%-1.3% of the mass of the pretreated coal gangue coarse aggregate;

[0064] And / or, the mass ratio of the nano-SiO2 powder to the water is (1-1.5):100;

[0065] And / or, the dispersant is a polycarboxylate superplasticizer, and its addition amount is 0.1% to 0.2% of the mass of the nano-SiO2 powder;

[0066] And / or, the magnetic stirring time is 30 to 35 minutes.

[0067] In some embodiments, in step (2), the ultrasonic pulverization process is carried out in an ultrasonic cell pulverizer, and the working conditions of the ultrasonic pulverization process are: power of 300-310W, ultrasonic time of 30-35min, pulse mode of 2s working and 1s intermittent, and water temperature control ≤40℃.

[0068] And / or, the centrifugation speed is 3000-3100 r / min, and the centrifugation time is 10-15 min;

[0069] And / or, the D50 particle size of the nano-SiO2 dispersion is ≤50nm.

[0070] In some embodiments, in step (3), the vacuum degree of the vacuuming process is -0.08 to -0.1 MPa, and the holding time is 0.5 to 2 hours;

[0071] And / or, the pressure of the pressure impregnation is 0.5 to 2 MPa, and the impregnation time is 1 to 4 hours;

[0072] And / or, the drying temperature is 60-65°C, and the drying time is 22-24 hours.

[0073] In some embodiments, in step (4), the curing temperature is 20±2℃ and the humidity is ≥95%.

[0074] It should be noted that the type of water-reducing agent in step (4) is not particularly limited, and those skilled in the art can choose according to actual needs.

[0075] Another aspect of this invention provides a nanomaterial-modified coal gangue coarse aggregate concrete, which is prepared by the above-described preparation method.

[0076] The following are non-limiting embodiments and comparative examples of the present invention. It should be noted that the schemes in the comparative examples are not prior art, but are only set up for comparison with the schemes in the embodiments, and are not intended to limit the present invention. Unless otherwise stated, all raw materials used in the embodiments and comparative examples are conventional commercially available products, or can be prepared by known methods.

[0077] Example 1

[0078] This embodiment provides a method for preparing nanomaterial-modified coal gangue coarse aggregate concrete, including the following steps:

[0079] (1) Coal gangue pretreatment: Coal gangue is coarsely crushed by a crusher and then finely crushed by a vertical impact mill. It is then passed through a 4.75mm square hole sieve to remove needle-like and flaky particles, and coal gangue coarse aggregate with a particle size of 5mm to 20mm is screened out. The coal gangue coarse aggregate is then ultrasonically cleaned with deionized water for 15min to remove surface dust and dried at 80℃ to constant weight. Subsequently, the coal gangue coarse aggregate is soaked in a mixed solution of silane coupling agent KH560 and ethanol for 2h, dried and solidified at 110℃ for 1h, and then washed until neutral and dried to obtain pretreated coal gangue coarse aggregate.

[0080] (2) Preparation of nano-SiO2 dispersion: Nano-SiO2 powder and deionized water were mixed at a mass ratio of 3:100, and then polycarboxylate superplasticizer (0.2% of the mass of nano-SiO2 powder) was added. The mixture was magnetically stirred for 30 min to obtain a mixture. The mixture was placed in an ultrasonic cell disruptor, and the power was set to 300W, the ultrasonic time was 30 min (pulse mode: 2s working, 1s intermittent), and the water temperature was controlled to ≤40℃. The mixture was ultrasonically disrupted to obtain a dispersion. The dispersion was then centrifuged at 3000 r / min for 10 min. The supernatant was taken to remove undispersed large particle clusters to obtain nano-SiO2 dispersion. The particle size distribution of the dispersion was detected by a laser particle size analyzer to ensure that its D50 particle size was ≤50nm and that there was no secondary agglomeration.

[0081] (3) Nano-modification treatment of coal gangue coarse aggregate: The pretreated coal gangue coarse aggregate is placed in a vacuum impregnation tank, vacuumed to -0.08MPa and maintained for 30min; then nano-SiO2 dispersion is injected, pressurized to 0.5MPa and maintained for 2h, so that the dispersion can fully penetrate into the pores of the coal gangue coarse aggregate; then the coal gangue coarse aggregate is taken out, the surface liquid is drained, and dried at 60℃ for 24h to solidify the nano-SiO2 coating and obtain modified coal gangue coarse aggregate;

[0082] (4) Preparation of modified coal gangue coarse aggregate concrete: 304 kg / m³ of cement was used. 3 76 kg / m³ of fly ash 3855 kg / m³ of natural crushed stone 3 720kg / m³ of natural sand 3 175 kg / m³ of water 3 Polycarboxylate superplasticizer 0.76 kg / m 3 First, stir for 2 minutes to form a uniform slurry, then add the slurry in two batches, with a total volume of 285 kg / m³. 3 Modified coal gangue coarse aggregate was mixed at low speed for 3 minutes to avoid mechanical shearing that could cause the SiO2 nano-coating to peel off. The slurry was then poured into a mold (100mm*100mm*100mm cube) that had been pre-coated with a release agent to cast the test mold. After that, it was placed on a vibrating table to compact it. Then, it was covered with plastic wrap and left to stand to prevent moisture evaporation. After standing for 1 day, the mold was removed, and the test block was placed in a standard curing room (temperature 20±2°C, humidity ≥95%) for curing to obtain nano-SiO2 modified coal gangue coarse aggregate concrete.

[0083] Microstructure analysis was performed on the nanomaterial-modified coal gangue coarse aggregate concrete and the unmodified coal gangue aggregate concrete (as a control group) prepared in this embodiment. The specific analysis process was as follows: SEM was used to observe the microstructure of the unmodified coal gangue aggregate concrete and the nano-SiO2-modified coal gangue coarse aggregate concrete. For each sample, a cubic block with a side length of approximately 10 mm was taken from the center of the specimen. The samples were then subjected to vacuum degassing and gold plating in a vacuum coating machine for observation. The results are as follows: Figure 1 , Figure 2 As shown, where, Figure 1 The images show the internal microstructures of unmodified coal gangue aggregate concrete (a) and nano-SiO2 modified coal gangue coarse aggregate concrete (b). Figure 2 The images show the microstructure of unmodified coal gangue aggregate concrete and nano-SiO2 modified coal gangue coarse aggregate concrete in the transition zone between coal gangue aggregate and cement.

[0084] from Figure 1 As can be seen, the unmodified coal gangue aggregate concrete contains numerous cracks and pores, which is the main reason for its poor mechanical properties. However, modification with nano-SiO2 can effectively fill the interior of the coal gangue, thereby improving the overall density of the coal gangue aggregate and reducing its water absorption. Furthermore, it was found that the unmodified coal gangue aggregate concrete specimens have a relatively loose internal structure with multiple cracks. This is mainly due to the high water absorption of coal gangue, which reduces the cement hydration product CSH, decreasing density and strength.

[0085] And through Figure 1As can be seen, the internal structure of the nano-SiO2 modified coal gangue coarse aggregate concrete specimen is denser than that of the unmodified coal gangue concrete, and the number and size of cracks are reduced. This is mainly because nano-SiO2 can promote the secondary hydration of cement, consume Ca(OH)2 in the capillary pores of concrete, and produce more CSH gel, thereby effectively filling the cracks and pores of concrete, and enhancing both density and strength. This also shows that nano-SiO2 can reduce the water absorption of coal gangue, ensure more complete cement hydration, and at the same time make the interface between cement and coal gangue more tightly connected, ensuring the structural strength of concrete.

[0086] from Figure 2 As can be seen, the crack width at the interface between unmodified coal gangue aggregate and cement is relatively large, and the number of pores on the structural surface is relatively high. This directly affects the internal density of the concrete structure, which is the main reason for the poor mechanical properties of unmodified coal gangue concrete. However, after modification, the transition zone between the coal gangue aggregate and cement is filled more densely, resulting in a tighter bond between the aggregate and the cementitious material. At the same time, the number of pores in the structure is significantly reduced, indicating that modified coal gangue can effectively optimize the pore structure inside concrete, thereby further improving the mechanical properties of concrete.

[0087] The slump and 28-day compressive strength of the nanomaterial-modified coal gangue coarse aggregate concrete (with a modified coal gangue replacement rate of 25%) prepared in this embodiment and the concrete prepared using unmodified coal gangue aggregate with an unmodified coal gangue replacement rate of 25% (as a control group) were tested, and the results are shown in Table 1.

[0088] Table 1

[0089]

[0090] Note: CGC-25% represents concrete prepared with an unmodified coal gangue replacement rate of 25%; CGC-N-25% represents concrete prepared with a modified coal gangue replacement rate of 25%.

[0091] As shown in Table 1, when coal gangue replaced natural aggregate (i.e., crushed natural stone) at a replacement rate of 25% in concrete preparation, the slump of modified coal gangue concrete decreased by 16 mm compared to unmodified coal gangue concrete, indicating that modified coal gangue has a certain positive impact on the fluidity of concrete. Furthermore, the 3-day, 7-day, and 28-day compressive strengths of unmodified coal gangue coarse aggregate concrete were 25.9 MPa, 29.0 MPa, and 41.2 MPa, respectively; while the 3-day, 7-day, and 28-day compressive strengths of modified coal gangue coarse aggregate concrete were 27.2 MPa, 31.4 MPa, and 45.7 MPa, respectively, representing an increase in strength of approximately 10.9% compared to unmodified coal gangue concrete.

[0092] Example 2

[0093] This embodiment is basically the same as Embodiment 1, except that in step (4) of this embodiment, the total amount of modified coal gangue coarse aggregate added is 510 kg / m³. 3 The amount of natural crushed stone added is 510 kg / m³. 3 That is, the modified coal gangue replacement rate is 50%.

[0094] The slump and 28-day compressive strength of the nanomaterial-modified coal gangue coarse aggregate concrete (with a modified coal gangue replacement rate of 50%) prepared in this embodiment and the concrete prepared using unmodified coal gangue aggregate with an unmodified coal gangue replacement rate of 50% (as a control group) were tested, and the results are shown in Table 2.

[0095] Table 2

[0096]

[0097] Note: CGC-50% represents concrete prepared with a 50% replacement rate of unmodified coal gangue; CGC-N-50% represents concrete prepared with a 50% replacement rate of modified coal gangue.

[0098] As shown in Table 2, when coal gangue replaced natural aggregate in concrete preparation at a 50% replacement rate, the slump of modified coal gangue concrete decreased by 9 mm compared to unmodified coal gangue concrete. Furthermore, the 3-day, 7-day, and 28-day compressive strengths of unmodified coal gangue aggregate concrete were 25.1 MPa, 28.1 MPa, and 40.0 MPa, respectively; while the 3-day, 7-day, and 28-day compressive strengths of modified coal gangue aggregate concrete were 27.5 MPa, 30.2 MPa, and 44.3 MPa, respectively, representing an increase in strength of approximately 11.1% compared to unmodified coal gangue concrete.

[0099] Example 3

[0100] This embodiment is basically the same as embodiment 1, except that in step (4) of this embodiment, the amount of cement added is 380 kg / m³. 3 The total amount of modified coal gangue coarse aggregate added is 765 kg / m³. 3 The amount of natural crushed stone added is 254 kg / m³. 3 That is, the modified coal gangue replacement rate is 75%.

[0101] The slump and 28-day compressive strength of the nanomaterial-modified coal gangue coarse aggregate concrete (with a modified coal gangue replacement rate of 75%) prepared in this embodiment and the concrete prepared using unmodified coal gangue aggregate with an unmodified coal gangue replacement rate of 75% (as a control group) were tested, and the results are shown in Table 3.

[0102] Table 3

[0103]

[0104]

[0105] Note: CGC-75% represents concrete prepared with a 75% unmodified coal gangue replacement rate; CGC-N-75% represents concrete prepared with a 75% modified coal gangue replacement rate.

[0106] As shown in Table 3, when coal gangue replaced natural aggregate in concrete preparation at a 75% replacement rate, the slump of modified coal gangue concrete decreased by 10 mm compared to unmodified coal gangue concrete. The 3-day, 7-day, and 28-day compressive strengths of unmodified coal gangue aggregate concrete were 24.9 MPa, 26.1 MPa, and 33.4 MPa, respectively; while the 3-day, 7-day, and 28-day compressive strengths of modified coal gangue aggregate concrete were 26.9 MPa, 29.4 MPa, and 37.2 MPa, respectively, representing an increase of approximately 11.4% in strength compared to unmodified coal gangue concrete.

[0107] Example 4

[0108] This embodiment is basically the same as embodiment 3, except that in step (4) of this embodiment, the total amount of modified coal gangue coarse aggregate added is 1019 kg / m³. 3 The amount of natural crushed stone added is 0 kg / m³. 3 That is, the modified coal gangue replacement rate is 100%.

[0109] The slump and 28-day compressive strength of the nanomaterial-modified coal gangue coarse aggregate concrete (where the modified coal gangue replacement rate is 100%) prepared in this embodiment and the concrete prepared using unmodified coal gangue aggregate with an unmodified coal gangue replacement rate of 100% (as a control group) were tested, and the results are shown in Table 4.

[0110] Table 4

[0111]

[0112] Note: CGC-100% represents concrete prepared with 100% unmodified coal gangue replacement; CGC-N-100% represents concrete prepared with 100% modified coal gangue replacement.

[0113] As shown in Table 4, when coal gangue replaced natural aggregates at a 100% replacement rate in concrete preparation, the slump of modified coal gangue concrete decreased by 9 mm compared to unmodified coal gangue concrete. Furthermore, the 3-day, 7-day, and 28-day compressive strengths of unmodified coal gangue aggregate concrete were 23.7 MPa, 24.9 MPa, and 31.2 MPa, respectively; while the 3-day, 7-day, and 28-day compressive strengths of modified coal gangue aggregate concrete were 27.4 MPa, 30.2 MPa, and 35.6 MPa, respectively, representing an increase in strength of approximately 14.1% compared to unmodified coal gangue concrete.

[0114] Control group 1

[0115] This control group provides a method for preparing concrete using natural aggregates, including the following steps:

[0116] 304 kg / m³ of cement 3 76 kg / m³ of fly ash 3 1019 kg / m³ of natural crushed stone 3 720kg / m³ of natural sand 3 Water 171kg / m 3 With polycarboxylate superplasticizer 0.76kg / m 3 The mixture is stirred evenly to form a slurry. The slurry is then poured into a mold (100mm*100mm*100mm cube) that has been pre-coated with a release agent to form a test mold. The mold is then placed on a vibrating table to compact it. After that, it is covered with plastic wrap and left to stand to prevent moisture evaporation. After standing for 1 day, the mold is removed, and the test block is placed in a standard curing room (temperature 20±2°C, humidity ≥95%) for curing to obtain concrete.

[0117] The slump and compressive strength of the concrete obtained in this control group were tested, and the results are shown in Table 5.

[0118] Table 5

[0119]

[0120] Comparing Table 5 with Tables 1 and 2, it can be seen that, with comparable content of raw materials such as cement, the concrete prepared by using nano-SiO2 modified coal gangue coarse aggregate in this embodiment of the invention has a lower slump than the concrete prepared by the control group 1 using natural aggregate (natural crushed stone), and exhibits higher compressive strength after 28 days of curing. This further demonstrates the feasibility of using nano-SiO2 modified coal gangue coarse aggregate to replace natural aggregate in the preparation of high-performance concrete, thereby effectively alleviating the pressure of natural aggregate resource depletion and avoiding the potential environmental hazards caused by coal gangue waste, providing a new approach for the preparation of green concrete.

[0121] Macroscopic mechanical properties of the concrete prepared in the above embodiments and control groups were tested. Specifically, compressive strength tests were conducted on the specimens according to the relevant provisions of GB / T50081—2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". A TYA-2000 compression testing machine was used, with a loading rate of 0.5 MPa / s until the specimen failed. The recorded failure load was converted into the strength of a standard specimen, with a conversion factor of 0.95. The compressive strength values ​​of the coal gangue concrete at 3d, 7d, and 28d were finally measured. Figure 3-5 As shown.

[0122] from Figure 3-5 As can be seen, compared with the concrete prepared using unmodified coal gangue aggregate in the control groups, the concrete prepared using nano-SiO2 modified coal gangue in this embodiment of the invention showed varying degrees of improvement in compressive strength. The early strength improvement was relatively small, while the improvement in compressive strength was more significant after 28 days of curing, especially in coal gangue concrete with a high replacement rate. At a low replacement rate, it can meet the strength requirements of C40 concrete, while at a 100% replacement rate, it can meet the strength requirements of C30 concrete. The main reason for the improved compressive strength of nanomaterial-modified coal gangue coarse aggregate concrete is the increased strength of the modified coal gangue aggregate itself, thus preventing cracks from forming at the coal gangue aggregate first under pressure. Simultaneously, the nanomaterials improve the interface transition zone between the aggregate and cement, making the concrete more compact. The 28-day compressive strength of the modified concrete can be increased by 15%-25% (due to the enhanced synergistic bearing capacity of the aggregate and cement paste).

[0123] Compared with existing coal gangue modification technologies, the preparation method of nanomaterial-modified coal gangue coarse aggregate concrete of this invention improves both the strength of the coal gangue aggregate itself and the overall mechanical properties of the concrete. It optimizes both the pore structure of the material at the microscale and the macroscopic mechanical properties. At the same time, it can improve the utilization rate of solid waste coal gangue, reduce the waste of energy resources, turn waste into treasure, reduce the production cost of concrete, and enable coal gangue aggregate to be applied in practical engineering.

[0124] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0125] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing nanomaterial-modified coal gangue coarse aggregate concrete, characterized in that, Includes the following steps: (1) The coal gangue is crushed and screened to obtain coal gangue coarse aggregate; the coal gangue coarse aggregate is then ultrasonically cleaned and dried; then it is soaked in a mixed solution of silane coupling agent and ethanol, dried and solidified, washed until neutral, and dried to obtain pretreated coal gangue coarse aggregate. (2) After mixing nano-SiO2 powder with water, a dispersant is added and the mixture is magnetically stirred to obtain a mixture; the mixture is ultrasonically pulverized to obtain a dispersion; the supernatant obtained after centrifugation of the dispersion is the nano-SiO2 dispersion. (3) The pretreated coal gangue coarse aggregate is placed in a vacuum impregnation tank for vacuum treatment, and then the nano-SiO2 dispersion is injected, impregnated under pressure, and dried to obtain modified coal gangue coarse aggregate. (4) Cement, fly ash, natural sand, water and water-reducing agent are mixed to form a uniform slurry. Then, the modified coal gangue coarse aggregate is added in small amounts and mixed at low speed. Then, a test mold is poured, vibrated and compacted, and covered with plastic wrap for static treatment. Finally, the concrete is demolded and cured to obtain the nanomaterial modified coal gangue coarse aggregate concrete.

2. The method for preparing nanomaterial-modified coal gangue coarse aggregate concrete according to claim 1, characterized in that, In step (4), when cement, fly ash, natural sand, water and water-reducing agent are mixed to form a uniform slurry, natural crushed stone is also added.

3. The method for preparing nanomaterial-modified coal gangue coarse aggregate concrete according to claim 1 or 2, characterized in that, In step (4), the total amount of modified coal gangue coarse aggregate added accounts for 25% to 100% of the sum of the mass of the modified coal gangue coarse aggregate and the mass of the natural crushed stone.

4. The method for preparing nanomaterial-modified coal gangue coarse aggregate concrete according to claim 1, characterized in that, In step (1), the particle size of the coarse coal gangue aggregate is 5-20 mm. And / or, the ultrasonic cleaning time is 15 to 20 minutes; And / or, the drying temperature is 80-85°C.

5. The method for preparing nanomaterial-modified coal gangue coarse aggregate concrete according to claim 1, characterized in that, In step (1), the silane coupling agent includes at least one of silane coupling agent KH-550, silane coupling agent KH-560, and silane coupling agent KH-570. And / or, the mass ratio of the silane coupling agent to the ethanol is (1-1.2):9; And / or, the soaking time is 2 to 3 hours; And / or, the drying and curing temperature is 100-110°C, and the time is 1-2 hours.

6. The method for preparing nanomaterial-modified coal gangue coarse aggregate concrete according to claim 1, characterized in that, In step (2), the particle size of the nano-SiO2 is 10-100 nm, and the amount of nano-SiO2 added is 1.2%-1.3% of the mass of the pretreated coal gangue coarse aggregate. And / or, the mass ratio of the nano-SiO2 powder to the water is (1-1.5):100; And / or, the dispersant is a polycarboxylate superplasticizer, and its addition amount is 0.1% to 0.2% of the mass of the nano-SiO2 powder; And / or, the magnetic stirring time is 30 to 35 minutes.

7. The method for preparing nanomaterial-modified coal gangue coarse aggregate concrete according to claim 1, characterized in that, In step (2), the ultrasonic pulverization process is carried out in an ultrasonic cell pulverizer. The working conditions of the ultrasonic pulverization process are: power of 300-310W, ultrasonic time of 30-35min, pulse mode of 2s working and 1s intermittent, and water temperature control of ≤40℃. And / or, the centrifugation speed is 3000-3100 r / min, and the centrifugation time is 10-15 min; And / or, the D50 particle size of the nano-SiO2 dispersion is ≤50nm.

8. The method for preparing nanomaterial-modified coal gangue coarse aggregate concrete according to claim 1, characterized in that, In step (3), the vacuum degree of the vacuuming process is -0.08 to -0.1 MPa, and the holding time is 0.5 to 2 hours. And / or, the pressure of the pressure impregnation is 0.5 to 2 MPa, and the impregnation time is 1 to 4 hours; And / or, the drying temperature is 60-65°C, and the drying time is 22-24 hours.

9. The method for preparing nanomaterial-modified coal gangue coarse aggregate concrete according to claim 1, characterized in that, In step (4), the curing temperature is 20±2℃ and the humidity is ≥95%.

10. A nanomaterial-modified coal gangue coarse aggregate concrete, characterized in that, The nanomaterial-modified coal gangue coarse aggregate concrete is prepared by the preparation method according to any one of claims 1-9.

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