Ultra-high performance concrete containing fine graphite tailings aggregate and preparation method thereof

Abstract

The present invention provides a ultra-high performance concrete containing fine aggregate of graphite tailings and a preparation method thereof, relating to the technical field of concrete. The concrete comprises the following components in parts by weight: 7.8 to 9.3 parts of water, a cementitious material, fine aggregate, 1.5 parts of a water reducing agent, and 4.2 parts of steel fiber; the cementitious material comprises 34 parts of cement, 9.7 parts of silica fume, and 4.9 parts of fly ash; the fine aggregate comprises graphite tailings and river sand; the graphite tailings comprise 2.2 to 8.8 parts of medium-sized graphite tailings and 1.5 to 6.2 parts of fine-sized graphite tailings; the river sand comprises 14.2 to 21.3 parts of coarse-sized river sand, 6.1 to 9.1 parts of medium-sized river sand, and 2.2 to 3.3 parts of fine-sized river sand. The present invention uses graphite tailings as raw materials, optimizes the replacement of river sand according to its mineral composition and morphological characteristics, optimizes the internal microstructure of the material, improves the mechanical strength and performance of the material, and solves the problems of graphite tailings accumulation and pollution, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete, and particularly relates to a ultra-high performance concrete containing graphite tailings fine aggregate and a preparation method thereof. Background Art

[0002] With the rapid development of infrastructure construction and more complex engineering requirements, ultra-high performance concrete has become the target of engineering construction. During the period when the demand for cement has been increasing year by year, the production carbon emissions in recent years have reached as much as 1.189 - 1.379 billion tons. Therefore, the construction industry urgently needs to open up a green and sustainable development track. The ultra-high performance concrete has high mechanical properties, and can meet higher engineering requirements with a smaller volume. The higher density can bring better durability and extend the service life of buildings. Under such a background, since the ultra-high performance concrete is composed of a variety of cementitious materials and is prepared by removing coarse aggregate to increase density and uniformity. Therefore, its development and popularization are restricted in terms of material complexity and preparation cost.

[0003] Currently, in the face of such problems, many technologies choose river sand to completely replace the original quartz sand, which has made certain optimizations in terms of aggregate cost, and the strength change of the prepared components can be almost ignored. However, in the context of development, the demand for river sand also shows an upward trend. As a non-renewable resource, the application of river sand in the material optimization of ultra-high performance concrete is not a long-term solution. On the other hand, many technologies apply, for example, nano materials, various admixtures, composite fibers, etc. to ultra-high performance concrete in order to pursue further optimization of performance. Although the performance parameters have been improved to a certain extent, the controllability of the materials is further complicated, which delays the practical engineering application of ultra-high performance concrete.

[0004] At the same time, graphite tailings are a large amount of industrial slag generated during the mining process of graphite ore. The traditional way of dealing with the production emissions of graphite tailings by enclosing and piling up not only occupies a large amount of land resources, has an adverse impact on the surrounding environment, but also needs to be solved urgently. And currently, existing technologies apply graphite tailings to the preparation system of traditional cement-based materials, using graphite tailings as fine aggregate to replace river sand or machine-made sand, etc., but the replacement ratio is basically between 10% and 20%, and there is no high capacity for consumption. And some technologies apply graphite tailings to the traditional cement-based material system after high-temperature activation, but it is not a good optimization method for the life cycle cost. At present, the technology of using graphite tailings to prepare cement-based ultra-high performance concrete has just started, and there are still gaps in aspects such as the composition and optimization control of the material system and the functional properties of graphite tailings concrete. Summary of the Invention

[0005] The present invention provides a ultra-high performance concrete containing graphite tailings fine aggregate and a preparation method thereof, aiming to solve the above problems existing in the background technology.

[0006] To achieve the above object, an embodiment of the present invention provides a ultra-high performance concrete containing graphite tailings fine aggregate and a preparation method thereof. The present invention uses graphite tailings as raw materials, and in view of its mineral composition and morphological characteristics, etc., makes it replace river sand as the aggregate for preparing ultra-high performance concrete containing graphite tailings fine aggregate, so as to improve the mechanical strength and workability of ultra-high performance concrete with river sand as the aggregate, optimize its internal microstructure, and establish the connection between the microstructure and macroscopic mechanics of graphite tailings cement-based ultra-high performance concrete, providing a theoretical basis for the practical engineering application of graphite tailings and corresponding technical support for the mineral industry to solve problems such as the accumulation and pollution of graphite tailings.

[0007] An object of an embodiment of the present invention is to provide a ultra-high performance concrete containing graphite tailings fine aggregate, which includes the following components by weight: 7.8 - 9.3 parts of water, a cementitious material, fine aggregate, 1.5 parts of a water reducer, and 4.2 parts of steel fiber;

[0008] Among them, the cementitious material includes 34 parts of cement, 9.7 parts of silica fume, and 4.9 parts of fly ash;

[0009] The fine aggregate includes graphite tailings and river sand;

[0010] The graphite tailings include 2.2 - 8.8 parts of medium-sized graphite tailings and 1.5 - 6.2 parts of fine-sized graphite tailings; the river sand includes 14.2 - 21.3 parts of coarse-sized river sand, 6.1 - 9.1 parts of medium-sized river sand, and 2.2 - 3.3 parts of fine-sized river sand.

[0011] According to one aspect of the embodiment of the present invention, the weight ratio of the water to the cementitious material is 0.16 - 0.19:1.

[0012] According to one aspect of the embodiment of the present invention, the weight ratio of the water to the cementitious material is 0.17:1.

[0013] According to one aspect of the embodiment of the present invention, the cement is 42.5-grade ordinary Portland cement.

[0014] According to one aspect of the embodiment of the present invention, the silica fume is microsilica powder, and the specific surface area is 19.1m 2 / g.

[0015] According to one aspect of the embodiment of the present invention, the fly ash is grade 1 and 3000 mesh.

[0016] According to one aspect of the embodiments of the present invention, the screening and classification criteria for river sand and graphite tailings are as follows: 1.25 - 0.63 mm is the coarse particle size, 0.63 - 0.315 mm is the medium particle size, and 0.315 - 0.16 mm is the fine particle size.

[0017] According to one aspect of the embodiments of the present invention, the water reducing agent is a high - efficiency polycarboxylate water reducing agent, and the water reducing efficiency is ≥30%.

[0018] According to one aspect of the embodiments of the present invention, the steel fiber is a copper - plated steel fiber, the aspect ratio is 66.67, and the tensile strength is 2500 - 3000 MPa.

[0019] Based on the general concept of an invention, the embodiments of the present invention provide a preparation method of the above - mentioned ultra - high performance concrete containing graphite tailings fine aggregate, including the following steps:

[0020] S1: Screen and classify river sand and graphite tailings according to different particle sizes to obtain medium - particle - size graphite tailings, fine - particle - size graphite tailings, coarse - particle - size river sand, medium - particle - size river sand, and fine - particle - size river sand;

[0021] S2: Weigh the obtained medium - particle - size graphite tailings, fine - particle - size graphite tailings, coarse - particle - size river sand, medium - particle - size river sand, and fine - particle - size river sand by weight, and stir at 62 r / min for 4 min to obtain fine aggregate;

[0022] S3: Weigh cement, silica fume, and fly ash by weight and pour them into a concrete mixer in sequence, automatically stir for 1 min, then add water and a water reducing agent and stir for 1 - 2 min to obtain a composite slurry;

[0023] S4: Add steel fiber and fine aggregate to the composite slurry and stir for 2 - 3 min to obtain ultra - high performance concrete containing graphite tailings fine aggregate.

[0024] The above - mentioned solution of the present invention has the following beneficial effects:

[0025] (1) By regulating the particle size and proportion of graphite tailings, this application not only improves the performance of concrete, but also enhances the consumption capacity of graphite tailings, and fully demonstrates the advantages of different particle size proportions of graphite tailings, meeting the requirements of engineering - required regulation.

[0026] (2) The present invention uses fine - particle - size graphite tailings with pozzolanic effect, which can promote the secondary hydration reaction of the matrix, increase the gel phase content, and the morphology of graphite tailings enables it to better fill the pores of concrete, optimizing the pore structure and improving the mechanical properties of concrete. Brief Description of the Drawings

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0028] Figure 1 It is a graph showing the change of the fluidity of ultra-high performance concrete containing graphite tailings fine aggregate with different particle size ratios of graphite tailings in an embodiment of the present invention;

[0029] Figure 2 It is a graph showing the change of the shrinkage change amount of ultra-high performance concrete containing graphite tailings fine aggregate with different particle size ratios of graphite tailings in an embodiment of the present invention;

[0030] Figure 3 It is a graph showing the change of the flexural strength of ultra-high performance concrete containing graphite tailings fine aggregate with different particle size ratios of graphite tailings in an embodiment of the present invention;

[0031] Figure 4 It is a graph showing the change of the compressive strength of ultra-high performance concrete containing graphite tailings fine aggregate with different particle size ratios of graphite tailings in an embodiment of the present invention.

[0032] Figure 5 It is a graph showing the change of the resistivity of ultra-high performance concrete containing graphite tailings fine aggregate with different particle size ratios of graphite tailings in an embodiment of the present invention. Detailed implementation manners

[0033] To make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the drawings and specific embodiments.

[0034] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0035] Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the present invention can be obtained through the market or can be prepared by existing methods.

[0036] Aiming at the problems that the proportion of existing graphite tailings as fine aggregate replacing river sand or manufactured sand is relatively low, at 10% - 20%, and the performance of concrete prepared by replacing river sand or manufactured sand with existing graphite tailings is insufficient, such as limitations in plasticity, flexural strength, toughness, stability, etc.

[0037] An object of an embodiment of the present invention is to provide a ultra-high performance concrete containing fine aggregate of graphite tailings, which comprises the following components by weight: 7.8 to 9.3 parts of water, a cementitious material, fine aggregate, 1.5 parts of a water reducing agent, and 4.2 parts of steel fiber;

[0038] Among them, the cementitious material comprises 34 parts of cement, 9.7 parts of silica fume, and 4.9 parts of fly ash;

[0039] The fine aggregate comprises graphite tailings and river sand;

[0040] The graphite tailings comprise 2.2 to 8.8 parts of medium-sized graphite tailings and 1.5 to 6.2 parts of fine-sized graphite tailings; the river sand comprises 14.2 to 21.3 parts of coarse-sized river sand, 6.1 to 9.1 parts of medium-sized river sand, and 2.2 to 3.3 parts of fine-sized river sand.

[0041] According to one aspect of an embodiment of the present invention, the weight ratio of the water to the cementitious material is 0.16 to 0.19:1.

[0042] According to one aspect of an embodiment of the present invention, the weight ratio of the water to the cementitious material is 0.17:1.

[0043] According to one aspect of an embodiment of the present invention, the cement is ordinary Portland cement of grade 42.5.

[0044] According to one aspect of an embodiment of the present invention, the silica fume is microsilica, and the specific surface area is 19.1m 2 / g.

[0045] According to one aspect of an embodiment of the present invention, the fly ash is grade 1 and 3000 mesh.

[0046] According to one aspect of an embodiment of the present invention, the screening and classification criteria for the river sand and graphite tailings are: 1.25 to 0.63mm is coarse-sized, 0.63 to 0.315mm is medium-sized, and 0.315 to 0.16mm is fine-sized.

[0047] According to one aspect of an embodiment of the present invention, the water reducing agent is a high-efficiency polycarboxylate water reducing agent, and the water reducing efficiency is ≥30%.

[0048] According to one aspect of an embodiment of the present invention, the steel fiber is copper-plated steel fiber, the aspect ratio is 66.67, and the tensile strength is 2500 to 3000MPa.

[0049] Based on the general concept of an invention, an embodiment of the present invention provides a preparation method of the above ultra-high performance concrete containing fine aggregate of graphite tailings, which comprises the following steps:

[0050] S1: Screen and classify river sand and graphite tailings according to different particle sizes to obtain medium-sized graphite tailings, fine-sized graphite tailings, coarse-sized river sand, medium-sized river sand, and fine-sized river sand;

[0051] S2: Weigh the medium-sized graphite tailings, fine-sized graphite tailings, coarse-sized river sand, medium-sized river sand, and fine-sized river sand obtained by screening according to parts by weight, stir at 62 r / min for 4 min to obtain fine aggregate;

[0052] S3: Weigh cement, silica fume, and fly ash according to parts by weight and pour them into a concrete mixer in sequence, automatically stir for 1 min, then add water and water reducer and stir for 1 - 2 min to obtain a composite slurry;

[0053] S4: Add steel fibers and fine aggregate to the composite slurry and stir for 2 - 3 min to obtain ultra-high performance concrete containing graphite tailings fine aggregate.

[0054] The forming and curing method of the above ultra-high performance concrete containing graphite tailings fine aggregate includes the following steps:

[0055] Put the stirred and formed concrete into a mold. After filling, fix the mold on a vibrating table and vibrate it for 1 minute. After vibration, use a trowel to slowly move from one end of the mold to the other end at 45°, scrape off the excess material and smooth the surface of the specimen. After mold filling, wrap it with plastic wrap and put it into a standard constant temperature and humidity curing room at a temperature of 20°C ± 2°C and a relative humidity of more than 95%. Demold after 24 hours. After demolding, put the specimen into the standard constant temperature and humidity curing room for curing until 28 days, then it is ready.

[0056] The following will be described in detail through specific examples. The following examples use graphite tailings as raw materials, with a fineness modulus of 0.8; the apparent density is 2860 kg / m 3 ; the bulk density is 1550 kg / m 3 . And the chemical composition of the graphite tailings is shown in Table 1 below.

[0057] Table 1 Chemical composition of graphite tailings

[0058]

[0059] Example 1

[0060] An ultra-high performance concrete containing graphite tailings fine aggregate, including the following components by weight: 7.8 parts of water, 34 parts of ordinary Portland cement of grade 42.5, 21.3 parts of coarse-sized river sand, 9.1 parts of medium-sized river sand, 3.3 parts of fine-sized river sand, 9.7 parts of silica fume, 4.9 parts of fly ash, 1.5 parts of water reducer, 2.2 parts of medium-sized graphite tailings, 1.5 parts of fine-sized graphite tailings, and 4.2 parts of steel fibers.

[0061] The preparation process of the ultra-high performance concrete containing graphite tailings fine aggregate includes the following steps:

[0062] Step 1. Screening of river sand and graphite tailings: Screen the river sand and graphite tailings so that the particles with a size of 1.25 - 0.63 mm are coarse aggregates, those with a size of 0.63 - 0.315 mm are medium aggregates, and those with a size of 0.315 - 0.16 mm are fine aggregates.

[0063] Step 2. Mixing of graphite tailings and river sand fine aggregate: Mix 2.2 parts of medium-sized graphite tailings, 1.5 parts of fine-sized graphite tailings, 21.3 parts of coarse-sized river sand, 9.1 parts of medium-sized river sand, and 3.3 parts of fine-sized river sand in an automatic mixing blender for 4 minutes at a rotation speed of 62 revolutions per minute to obtain a fine aggregate mixture.

[0064] Step 3. Pour 34 parts of 42.5-grade ordinary Portland cement, 9.7 parts of silica fume, and 4.9 parts of fly ash into a concrete mixer in sequence. After automatic stirring for 1 minute, add 8.8 parts of water and 1.5 parts of water reducer and stir for 1 - 2 minutes. After obtaining the composite paste, add 4.2 parts of steel fiber and the pre-mixed aggregate mixture of graphite tailings and river sand, and continue to stir for 2 - 3 minutes and then stop. After the stirring is completed, directly shovel the stirred and formed concrete into the mold. After filling, fix the mold on a vibrating table and vibrate it for about 1 minute. After the vibration is completed, use a spatula to slowly move from one end of the mold to the other end at a 45° angle, scrape off the excess material and level the surface of the specimen. After the mold filling work is completed, wrap it with plastic wrap and place it in a standard constant temperature and humidity curing room at a temperature of 20°C ± 2°C and a relative humidity of over 95%. Demold after 24 hours. After demolding, place the specimen in the standard constant temperature and humidity curing room for curing until the 28-day standard age.

[0065] Comparative Example 1

[0066] The difference is that the medium-sized particle size in the graphite tailings is 1.5 parts, the fine particle size is 2.2 parts, the coarse particle size in the river sand is 16.6 parts, the medium particle size is 9.8 parts, the fine particle size is 2.6 parts, the silica fume is 4.9 parts, and the fly ash is 9.7 parts. Other raw materials and composition ratios are the same as those in Example 1, and the preparation steps and parameters are also the same as those in Example 1. The flexural and compressive strength properties of the prepared material are 24.36 MPa and 135.97 MPa respectively. Compared with Example 1, its flexural strength is increased by 0.04%, and its compressive strength is decreased by 0.19%.

[0067] Example 2

[0068] A ultra-high performance concrete containing fine aggregate of graphite tailings, comprising the following components in parts by weight: 7.8 parts of water, 34 parts of 42.5-grade ordinary Portland cement, 18.9 parts of coarse river sand, 8.1 parts of medium-sized river sand, 3.0 parts of fine river sand, 9.7 parts of silica fume, 4.9 parts of fly ash, 1.5 parts of water reducer, 4.4 parts of medium-sized graphite tailings, 3.1 parts of fine-sized graphite tailings, and 4.2 parts of steel fiber.

[0069] The preparation process of the above ultra-high performance concrete containing fine aggregate of graphite tailings includes the following steps:

[0070] Step 1, screening of river sand and graphite tailings: Screen the river sand and graphite tailings so that those with a particle size of 1.25 - 0.63 mm are coarse aggregates, those with a particle size of 0.63 - 0.315 mm are medium aggregates, and those with a particle size of 0.315 - 0.16 mm are fine aggregates.

[0071] Step 2, mixing of graphite tailings and fine aggregate of river sand: Mix 4.4 parts of medium-sized graphite tailings, 3.1 parts of fine-sized graphite tailings, 18.9 parts of coarse river sand, 8.1 parts of medium-sized river sand, and 3.0 parts of fine river sand in an automatic mixing blender for 4 minutes at a rotation speed of 62 revolutions per minute to obtain a fine aggregate mixture.

[0072] Step 3, pour 34 parts of 4.25-grade ordinary Portland cement, 9.7 parts of silica fume, and 4.9 parts of fly ash into a concrete mixer in sequence. After automatic stirring for 1 minute, add 8.8 parts of water and 1.5 parts of water reducer and stir for 1 - 2 minutes. After obtaining a composite slurry, add 4.2 parts of steel fiber and the pre-mixed aggregate mixture of graphite tailings and river sand, and continue stirring for 2 - 3 minutes before stopping. After the stirring is completed, directly shovel the stirred and formed concrete into a mold. After filling, fix the mold on a vibrating table and vibrate for about 1 minute. After the vibration is completed, use a spatula to slowly move from one end of the mold to the other end at an angle of 45°, scrape off the excess material and level the surface of the specimen. After the mold filling work is completed, wrap it with plastic wrap and place it in a standard constant temperature and humidity curing room at a temperature of 20°C ± 2°C and a relative humidity of over 95%. Demold after 24 hours. After demolding, place the specimen in a standard constant temperature and humidity curing room for curing until the 28-day standard age.

[0073] Comparative Example 2

[0074] The difference lies in that the medium particle size in the graphite tailings is 3.1 parts, the fine particle size is 4.4 parts, the coarse particle size in the river sand is 18.9 parts, the medium particle size is 9.4 parts, the fine particle size is 1.7 parts, the silica fume is 4.9 parts, the fly ash is 9.7 parts, and the other raw materials and composition ratios are the same as those in Example 2. The preparation steps and parameters are also the same as those in Example 2. The flexural and compressive strength properties of the prepared material are 24.62 MPa and 136.74 MPa respectively. Compared with Example 2, its flexural strength is reduced by 0.08% and its compressive strength is reduced by 0.39%.

[0075] Example 3

[0076] A ultra-high performance concrete containing fine aggregate of graphite tailings, comprising the following components in parts by weight: 7.8 parts of water, 34 parts of 42.5-grade ordinary Portland cement, 16.6 parts of coarse particle size river sand, 7.1 parts of medium particle size river sand, 2.6 parts of fine particle size river sand, 9.7 parts of silica fume, 4.9 parts of fly ash, 1.5 parts of water reducing agent, 6.6 parts of medium particle size graphite tailings, 4.6 parts of fine particle size graphite tailings, and 4.2 parts of steel fiber.

[0077] The preparation process of the above ultra-high performance concrete containing fine aggregate of graphite tailings includes the following steps:

[0078] Step 1, screening of river sand and graphite tailings: Screen the river sand and graphite tailings so that the particle size of 1.25 - 0.63 mm is coarse aggregate, 0.63 - 0.315 mm is medium aggregate, and 0.315 - 0.16 mm is fine aggregate.

[0079] Step 2, mixing of graphite tailings and fine aggregate of river sand: Mix 6.6 parts of medium particle size graphite tailings, 4.6 parts of fine particle size graphite tailings, 16.6 parts of coarse particle size river sand, 7.1 parts of medium particle size river sand, and 2.6 parts of fine particle size river sand in an automatic mixing blender for 4 minutes at a rotation speed of 62 revolutions per minute to obtain a fine aggregate mixture.

[0080] Step 3: Pour 34 parts of 42.5-grade ordinary Portland cement, 9.7 parts of silica fume, and 4.9 parts of fly ash into a concrete mixer in sequence. After automatic stirring for 1 minute, add 8.8 parts of water and 1.5 parts of water reducer and stir for 1 - 2 minutes. After obtaining the composite paste, add 4.2 parts of steel fibers and the pre-mixed aggregate mixture of graphite tailings and river sand, and continue to stir for 2 - 3 minutes and then stop. After the stirring is completed, directly use a shovel to load the stirred and formed concrete into the mold. After filling, fix the mold on the vibrating table and vibrate it for about 1 minute. After the vibration is completed, use a spatula to slowly move from one end of the mold to the other end at a 45° angle, scrape off the excess material and level the surface of the specimen. After the mold filling work is completed, wrap it with plastic wrap and place it in a standard constant temperature and humidity curing room at a temperature of 20°C ± 2°C and a relative humidity of over 95%. Demold after 24 hours. After demolding, place the specimen in the standard constant temperature and humidity curing room for curing until the standard age of 28 days.

[0081] Comparative Example 3

[0082] The difference is that the medium particle size in the graphite tailings is 4.6 parts, the fine particle size is 6.6 parts, the coarse particle size in the river sand is 16.6 parts, the medium particle size is 9.1 parts, the fine particle size is 0.6 parts, the silica fume is 4.9 parts, the fly ash is 9.7 parts, and the other raw materials and composition ratios are the same as in Example 3, and the preparation steps and parameters are also the same as in Example 3. The flexural and compressive strength properties of the prepared material are 24.8 MPa and 138.11 MPa respectively. Compared with Example 3, its flexural strength has increased by 0.04% and its compressive strength has decreased by 0.28%.

[0083] Example 4

[0084] A ultra-high performance concrete containing fine aggregate of graphite tailings, comprising the following components in parts by weight: 7.8 parts of water, 34 parts of 42.5-grade ordinary Portland cement, 14.2 parts of coarse particle size river sand, 6.1 parts of medium particle size river sand, 2.2 parts of fine particle size river sand, 9.7 parts of silica fume, 4.9 parts of fly ash, 1.5 parts of water reducer, 8.8 parts of medium particle size graphite tailings, 6.2 parts of fine particle size graphite tailings, and 4.2 parts of steel fibers.

[0085] The preparation process of the above ultra-high performance concrete containing fine aggregate of graphite tailings includes the following steps:

[0086] Step 1: Screening of river sand and graphite tailings: Screen the river sand and graphite tailings into coarse aggregate with a size of 1.25 - 0.63 mm, medium aggregate with a size of 0.63 - 0.315 mm, and fine aggregate with a size of 0.315 - 0.16 mm.

[0087] Step 2. Mixing of graphite tailings and river sand fine aggregate: Mix 8.8 parts of medium-sized graphite tailings, 6.2 parts of fine-sized graphite tailings, 14.2 parts of coarse-sized river sand, 6.1 parts of medium-sized river sand, and 2.2 parts of fine-sized river sand in an automatic mixing blender for 4 minutes at a rotation speed of 62 revolutions per minute to obtain a fine aggregate mixture.

[0088] Step 3. Pour 34 parts of 42.5-grade ordinary Portland cement, 9.7 parts of silica fume, and 4.9 parts of fly ash into a concrete mixer in sequence. After automatic mixing for 1 minute, add 8.8 parts of water and 1.5 parts of water reducer and mix for 1 - 2 minutes. After obtaining the composite paste, add 4.2 parts of steel fiber and the pre-mixed aggregate mixture of graphite tailings and river sand, and continue to mix for 2 - 3 minutes before stopping. After the mixing is completed, directly shovel the mixed concrete into the mold. After filling, fix the mold on a vibrating table and vibrate for about 1 minute. After the vibration is completed, use a spatula to slowly move from one end of the mold to the other end at a 45° angle, scrape off the excess material, and smooth the surface of the specimen. After the mold filling work is completed, wrap it with plastic wrap and place it in a standard constant temperature and humidity curing room at a temperature of 20°C ± 2°C and a relative humidity of over 95%. Demold after 24 hours. After demolding, place the specimen in the standard constant temperature and humidity curing room for curing until the 28-day standard age.

[0089] Comparative Example 4

[0090] The difference is that the medium-sized particle size in the graphite tailings is 6.2 parts, the fine particle size is 8.1 parts, the coarse particle size in the river sand is 16.6 parts, the medium particle size is 8.7 parts, the fine particle size is 0.3 parts, the silica fume is 4.9 parts, and the fly ash is 9.7 parts. The other raw materials and composition ratios are the same as in Example 4, and the preparation steps and parameters are also the same as in Example 4. The flexural and compressive strength properties of the prepared material are 24.9 MPa and 135.82 MPa respectively. Compared with Example 4, its flexural strength is reduced by 0.72%, and its compressive strength is increased by 0.31%.

[0091] No substitution group

[0092] A super high-performance concrete, comprising the following components in parts by weight: 7.8 parts of water, 34 parts of 42.5-grade ordinary Portland cement, 21.3 parts of coarse-sized river sand, 11.3 parts of medium-sized river sand, 4.8 parts of fine-sized river sand, 9.7 parts of silica fume, 4.9 parts of fly ash, 1.5 parts of water reducer, and 4.2 parts of steel fiber.

[0093] The preparation process of the above super high-performance concrete includes the following steps:

[0094] Step 1. Screening of river sand: Screen the river sand so that 1.25 - 0.63 mm is the coarse aggregate, 0.63 - 0.315 mm is the medium aggregate, and 0.315 - 0.16 mm is the fine aggregate.

[0095] Step 2: Pour 34 parts of 42.5-grade ordinary Portland cement, 9.7 parts of silica fume, and 4.9 parts of fly ash into a concrete mixer in sequence. After automatically mixing for 1 minute, add 7.8 parts of water and 1.5 parts of water reducer and mix for 1 - 2 minutes. After obtaining the composite slurry, add 4.2 parts of steel fibers and river sand aggregate, and continue to mix for 2 - 3 minutes before stopping. After the mixing is completed, directly shovel the mixed and formed concrete into the mold. After filling, fix the mold on the vibrating table and vibrate it for about 1 minute. After the vibration is completed, use a spatula to slowly move from one end of the mold to the other end at a 45° angle, scrape off the excess material, and level the surface of the specimen. After the mold filling work is completed, wrap it with plastic wrap and place it in a standard constant temperature and humidity curing room at a temperature of 20°C ± 2°C and a relative humidity of over 95%. Demold after 24 hours. After demolding, place the specimen in the standard constant temperature and humidity curing room for curing until the 28-day standard age.

[0096] The pore test results of the ultra-high performance concrete containing graphite tailings fine aggregate in the above Examples 1 to 4 and the non-replacement group are shown in Table 2 below.

[0097] Table 2 Pore structure of ultra-high performance concrete containing graphite tailings fine aggregate

[0098]

[0099] As can be seen from Table 2, with the increase in the fraction of graphite tailings in the concrete, both the total porosity and the particle size distribution have changed significantly. The total porosity shows a trend of first decreasing and then increasing. Among them, the pores in Example 3 are mainly concentrated below 20 nm, the pores larger than 1000 nm are significantly reduced, and most of the pores are mainly harmless pores (accounting for 33.7%). The optimized particle size and proportion of graphite tailings improve the pore size distribution of the concrete, reduce the number of large-pore-size pores, and make the pore size tend to be smaller, especially harmless pores. Due to the optimization of the pore structure of the concrete, the matrix inside is more dense, which is directly reflected in the improvement of the macroscopic properties. When the fraction of medium-fine particle size graphite tailings is 6.6 / 4.6, the total porosity of the concrete reaches the optimum, the pore distribution is relatively uniform, and it is mainly composed of harmless pores. Moreover, the compressive strength of the concrete reaches the optimum.

[0100] It can be seen from Figure 1 that the fluidity of the concrete of the present invention shows a trend of first decreasing and then increasing with the increase in the fraction of medium-fine particle size graphite tailings. Among them, the fluidity of 6.6 / 4.6 in Example 3 decreased by 5.8% compared with the blank control group. Therefore, the fluidity can be adjusted according to the construction conditions. It can be seen from Figure 2 that the application of the proportion of graphite tailings with different particle sizes provides a certain stability to the concrete. It can be seen from Figure 3It can be seen that the flexural strength of the concrete of the present invention increases with the increase in the proportion of medium-fine particle size graphite tailings. When the proportion of graphite tailings reaches 8.8 / 6.2, the maximum flexural strength of the concrete is 25.08 MPa. From Figure 4 It can be seen that the compressive strength of the concrete of the present invention first increases and then decreases with the increase in the proportion of medium-fine particle size graphite tailings. When the proportion of graphite tailings reaches 6.6 / 4.6, the concrete reaches the maximum compressive strength of 138.5 MPa. From Figure 5 It can be seen that the change in the resistivity of the concrete of the present invention also first increases and then decreases with the increase in the proportion of graphite tailings. When the proportion of graphite tailings reaches 6.6 / 4.6, the concrete reaches the maximum resistivity of 1166 kΩ.cm.

[0101] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An ultra-high performance concrete containing graphite tailings fine aggregate, characterized in that: The components include the following in parts by weight: 7.8 parts of water, cementitious material, fine aggregate, 1.5 parts of water reducing agent and 4.2 parts of steel fiber; Among them, the cementitious materials include 34 parts of cement, 9.7 parts of silica fume and 4.9 parts of fly ash; Fine aggregates include graphite tailings and river sand; The graphite tailings include 6.6 parts of medium-sized graphite tailings and 4.6 parts of fine-sized graphite tailings; the river sand includes 16.6 parts of coarse-sized river sand, 7.1 parts of medium-sized river sand and 2.6 parts of fine-sized river sand; the screening and classification standards of the river sand and graphite tailings are: 1.25-0.63 mm for coarse-sized particles, 0.63-0.315 mm for medium-sized particles, and 0.315-0.16 mm for fine-sized particles; The method for preparing the ultra-high performance concrete comprises the following steps: S1: screening and classifying river sand and graphite tailings according to different particle sizes to obtain medium-sized graphite tailings, fine-sized graphite tailings, coarse-sized river sand, medium-sized river sand, and fine-sized river sand; S2: Weigh the medium-sized graphite tailings, fine-sized graphite tailings, coarse-sized river sand, medium-sized river sand and fine-sized river sand obtained by screening according to weight, and stir at 62 r / min for 4 min to obtain fine aggregate; S3: Weigh cement, silica fume and fly ash in parts by weight and pour them into a concrete mixer in order, stir them automatically for 1 minute, then add water and water reducing agent and stir for 1 to 2 minutes to obtain a composite slurry; S4: adding steel fiber and fine aggregate into the composite slurry and stirring for 2 to 3 minutes to obtain ultra-high performance concrete containing graphite tailings fine aggregate.

2. The ultra-high performance concrete containing graphite tailings fine aggregate according to claim 1, characterized in that: The weight ratio of water to gelling material is 0.16-0.19:

1.

3. The ultra-high performance concrete containing graphite tailings fine aggregate according to claim 1, characterized in that: The weight ratio of water to gelling material is 0.17:

1.

4. The ultra-high performance concrete containing graphite tailings fine aggregate according to claim 1, characterized in that: The cement is 42.5 grade ordinary Portland cement.

5. The ultra-high performance concrete containing graphite tailings fine aggregate according to claim 1, characterized in that: The silica fume is microsilica powder with a specific surface area of ​​19.1 m 2 / g.

6. The ultra-high performance concrete containing graphite tailings fine aggregate according to claim 1, characterized in that: The fly ash is first-grade 3000 mesh.

7. The ultra-high performance concrete containing graphite tailings fine aggregate according to claim 1, characterized in that: The water reducing agent is a high-efficiency polycarboxylic acid water reducing agent, and the water reducing efficiency is ≥30%.

8. The ultra-high performance concrete containing graphite tailings fine aggregate according to claim 1, characterized in that: The steel fiber is a copper-plated steel fiber with an aspect ratio of 66.67 and a tensile strength of 2500-3000 MPa.

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