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

Abstract

The invention provides ultra-high performance concrete containing graphite tailing fine aggregate and a preparation method of the ultra-high performance concrete, and relates to the technical field of concrete. The concrete comprises the following components in parts by weight: 7.8-9.3 parts of water, a cementing material, fine aggregate, 1.5 parts of a water reducing agent and 4.2 parts of steel fibers, the cementing 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 2.2-8.8 parts of medium-particle-size graphite tailings and 1.5-6.2 parts of fine-particle-size graphite tailings; the river sand comprises 14.2 to 21.3 parts of large-particle-size river sand, 6.1 to 9.1 parts of medium-particle-size river sand and 2.2 to 3.3 parts of fine-particle-size river sand. The graphite tailings are used as raw materials, river sand is optimized and replaced according to mineral composition and morphological characteristics of the graphite tailings, the internal microstructure of the material is optimized, the mechanical strength and performance of the material are improved, and the problems of accumulation, pollution and the like of the graphite tailings are solved.

Description

Technical Field

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

[0002] With the rapid development of infrastructure and more complex engineering needs, ultra-high performance concrete has become the target of choice for engineering construction. In the period when the demand for cement has increased year by year, the carbon emissions from production in recent years have reached 1.189 billion to 1.379 billion tons. Therefore, the construction industry urgently needs to open up a green and sustainable development track. The high-strength mechanical properties of ultra-high performance concrete can meet higher engineering requirements with a small volume. Higher density can bring better durability and extend the service life of the building. In this context, ultra-high performance concrete itself is composed of a mixture of various cementitious materials, and is prepared by removing coarse aggregates to increase density and uniformity. Therefore, its own development and promotion are limited in terms of material complexity and preparation cost.

[0003] At present, facing this kind of problem, many technologies use river sand to completely replace the original quartz sand, making certain optimizations in aggregate costs, and the strength changes of the prepared components are almost negligible. However, under the background of development, the demand for river sand is also on the rise. As a non-renewable resource, river sand is not a long-term solution for the optimization of materials used in ultra-high performance concrete. On the other hand, in pursuit of further optimization of performance, many technologies apply nanomaterials, various admixtures, composite fibers, etc. to ultra-high performance concrete. Although the performance parameters have been improved to a certain extent, the controllability of the material has been further complicated, which has slowed down the practical engineering application of ultra-high performance concrete.

[0004] At the same time, graphite tailings are a large amount of industrial slag produced during the mining process of graphite mines. The traditional way of dealing with graphite tailings discharged from production is to enclose land and pile them up, which not only occupies a large amount of land resources, but also has an adverse impact on the surrounding environment and needs to be solved urgently. At present, there are technologies that apply graphite tailings to the preparation system of traditional cement-based materials, and use graphite tailings as fine aggregate to replace river sand or machine-made sand, but the replacement ratio is basically between 10% and 20%, and there is no high absorption capacity. In addition, some technologies activate graphite tailings at high temperatures and then apply them to traditional cement-based material systems, but this is not a good optimization method for life cycle costs. At present, the technology of preparing cement-based ultra-high performance concrete using graphite tailings has just started, and there are still gaps in the composition and optimization of the material system and the functional performance of graphite tailings concrete. Summary of the invention

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

[0006] In order to achieve the above-mentioned purpose, an embodiment of the present invention provides an ultra-high performance concrete containing graphite tailings fine aggregate and a preparation method thereof. The present invention uses graphite tailings as raw material, and according to its mineral composition and morphological characteristics, 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 working performance of ultra-high performance concrete with river sand as aggregate, optimize its internal microstructure, and establish the connection between the microstructure and macroscopic mechanics of graphite tailings cement-based ultra-high performance concrete, so as to provide a theoretical basis for the actual engineering application of graphite tailings, and provide corresponding technical support for the mineral industry to solve the problems of graphite tailings accumulation and pollution.

[0007] An object of an embodiment of the present invention is to provide an ultra-high performance concrete containing graphite tailings fine aggregate, 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;

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

[0009] Fine aggregates include graphite tailings and river sand;

[0010] The graphite tailings include 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 includes 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.

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

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

[0013] According to one aspect of the embodiments 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 with a specific surface area of ​​19.1 m 2 / g.

[0015] According to one aspect of the embodiments of the present invention, the fly ash is of first-grade 3000 mesh.

[0016] According to one aspect of the embodiments of the present invention, the screening and classification standards for river sand and graphite tailings are: 1.25-0.63 mm for coarse particle size, 0.63-0.315 mm for medium particle size, and 0.315-0.16 mm for 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 with an aspect ratio of 66.67 and a tensile strength of 2500 to 3000 MPa.

[0019] Based on a general concept of the invention, an embodiment of the present invention provides a method for preparing the above-mentioned ultra-high performance concrete containing graphite tailings fine aggregate, comprising the following steps:

[0020] 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;

[0021] 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;

[0022] 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;

[0023] 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.

[0024] The above scheme of the present invention has the following beneficial effects:

[0025] (1) This application not only improves the performance of concrete, but also improves the graphite tailings disposal capacity by regulating the particle size and proportion of graphite tailings. It also fully demonstrates the advantages of different graphite tailings particle size proportions and meets the requirements of engineering demand regulation.

[0026] (2) The present invention uses fine-grained graphite tailings with a volcanic ash effect to promote secondary hydration reaction of the matrix and increase the gel phase content. The morphology of the graphite tailings enables it to better fill the pores of concrete, optimize the pore structure, and improve the mechanical properties of concrete. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 This is a graph showing the change in fluidity of ultra-high performance concrete containing graphite tailings fine aggregate according to an embodiment of the present invention as a function of the proportion of different graphite tailings particle sizes;

[0029] Figure 2 This is a graph showing the change in shrinkage of ultra-high performance concrete containing graphite tailings fine aggregate according to an embodiment of the present invention as a function of the proportion of different graphite tailings particle sizes;

[0030] Figure 3 This is a graph showing the change in flexural strength of ultra-high performance concrete containing graphite tailings fine aggregate according to an embodiment of the present invention as a function of the proportion of different graphite tailings particle sizes;

[0031] Figure 4 This is a graph showing the compressive strength of ultra-high performance concrete containing graphite tailings fine aggregate according to an embodiment of the present invention as a function of the proportion of different graphite tailings particle sizes.

[0032] Figure 5 This is a graph showing the change in resistivity of ultra-high performance concrete containing graphite tailings fine aggregate according to an embodiment of the present invention as a function of the proportion of different graphite tailings particle sizes. DETAILED DESCRIPTION

[0033] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0034] Unless otherwise defined, all professional terms used below have the same meanings as those generally 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 scope of protection of the present invention.

[0035] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0036] The proportion of existing graphite tailings as fine aggregate replacing river sand or machine-made sand is low at 10% to 20%, and the concrete prepared by existing graphite tailings replacing river sand or machine-made sand has insufficient performance, such as limited plasticity, flexural strength, toughness and stability.

[0037] An object of an embodiment of the present invention is to provide an ultra-high performance concrete containing graphite tailings fine aggregate, 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 materials include 34 parts of cement, 9.7 parts of silica fume and 4.9 parts of fly ash;

[0039] Fine aggregates include graphite tailings and river sand;

[0040] The graphite tailings include 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 includes 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 the embodiments of the present invention, the weight ratio of water to gelling material is 0.16-0.19:1.

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

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

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

[0045] According to one aspect of the embodiments of the present invention, the fly ash is of first-grade 3000 mesh.

[0046] According to one aspect of the embodiments of the present invention, the screening and classification standards for river sand and graphite tailings are: 1.25-0.63 mm for coarse particle size, 0.63-0.315 mm for medium particle size, and 0.315-0.16 mm for fine particle size.

[0047] 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%.

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

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

[0050] 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;

[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 weight, and stir at 62 r / min for 4 min to obtain fine aggregate;

[0052] 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;

[0053] 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.

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

[0055] Put the mixed concrete into the mold, and fix the mold on the vibration table to vibrate for 1 minute after filling. After the vibration is completed, use a spatula to slowly move from one end of the mold to the other end at 45 degrees, scrape off the excess material and smooth the surface of the specimen. After the mold is completed, wrap it with plastic wrap and put it in a standard constant temperature and humidity curing room with a temperature of 20℃±2℃ and a relative humidity of more than 95%. Remove the mold after 24 hours. After demolding, place the specimen in a standard constant temperature and humidity curing room for curing for up to 28 days.

[0056] The following is a detailed description of the embodiment. The following embodiment uses graphite tailings as raw materials, with a fineness modulus of 0.8 and an apparent density of 2860 kg / m 3 ; Bulk density is 1550kg / m 3 The chemical composition of 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 comprises 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-grained river sand, 9.1 parts of medium-grained river sand, 3.3 parts of fine-grained river sand, 9.7 parts of silica fume, 4.9 parts of fly ash, 1.5 parts of water reducing agent, 2.2 parts of medium-grained graphite tailings, 1.5 parts of fine-grained graphite tailings, and 4.2 parts of steel fiber.

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

[0062] Step 1, screening of river sand and graphite tailings: The river sand and graphite tailings are screened into 1.25-0.63 mm as coarse aggregate, 0.63-0.315 mm as medium aggregate, and 0.315-0.16 mm as fine aggregate.

[0063] Step 2, mixing graphite tailings with river sand fine aggregate: 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 were stirred in an automatic mixer for 4 minutes at a speed of 62 rpm 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 the concrete mixer in order, stir automatically for 1 minute, then add 8.8 parts of water and 1.5 parts of water reducer and stir for 1 to 2 minutes. After obtaining the composite slurry, add 4.2 parts of steel fiber and a pre-mixed aggregate mixture of graphite tailings and river sand, and continue stirring for 2 to 3 minutes before stopping. After the mixing is completed, use a shovel to directly load the stirred concrete into the mold. After filling, fix the mold on the vibration table and vibrate it for about 1 minute. After the vibration is completed, use a shovel 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 is completed, wrap it with plastic wrap and put it in a standard constant temperature and humidity curing room with a temperature of 20℃±2℃ and a relative humidity of more than 95%, and demold it after 24 hours. After demolding, put the specimen in a standard constant temperature and humidity curing room and cure it to a standard age of 28 days.

[0065] Comparative Example 1

[0066] The difference is that the medium 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, the fly ash is 9.7 parts, and the other raw materials and composition ratios are the same as in Example 1, and the preparation steps and parameters are also the same as in Example 1. The flexural and compressive strength properties of the prepared materials are 24.36MPa and 135.97MPa, respectively. Compared with Example 1, the flexural strength is increased by 0.04% and the compressive strength is reduced by 0.19%.

[0067] Example 2

[0068] An ultra-high performance concrete containing graphite tailings fine aggregate comprises 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-grained river sand, 8.1 parts of medium-grained river sand, 3.0 parts of fine-grained river sand, 9.7 parts of silica fume, 4.9 parts of fly ash, 1.5 parts of water reducing agent, 4.4 parts of medium-grained graphite tailings, 3.1 parts of fine-grained graphite tailings, and 4.2 parts of steel fiber.

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

[0070] Step 1, screening of river sand and graphite tailings: The river sand and graphite tailings are screened into 1.25-0.63 mm as coarse aggregate, 0.63-0.315 mm as medium aggregate, and 0.315-0.16 mm as fine aggregate.

[0071] Step 2, mixing graphite tailings and river sand fine aggregate: Mixing graphite tailings and river sand fine aggregate: 4.4 parts of medium-sized graphite tailings, 3.1 parts of fine-sized graphite tailings, 18.9 parts of coarse-sized river sand, 8.1 parts of medium-sized river sand, and 3.0 parts of fine-sized river sand are stirred in an automatic mixer for 4 minutes at a speed of 62 rpm to obtain a fine aggregate mixture.

[0072] 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 the concrete mixer in order, stir automatically for 1 minute, then add 8.8 parts of water and 1.5 parts of water reducer and stir for 1 to 2 minutes. After obtaining the composite slurry, add 4.2 parts of steel fiber and a pre-mixed aggregate mixture of graphite tailings and river sand, and continue stirring for 2 to 3 minutes before stopping. After the mixing is completed, use a shovel to directly load the stirred concrete into the mold. After filling, fix the mold on the vibration table and vibrate it for about 1 minute. After the vibration is completed, use a shovel 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 is completed, wrap it with plastic wrap and put it in a standard constant temperature and humidity curing room with a temperature of 20℃±2℃ and a relative humidity of more than 95%, and demold it after 24 hours. After demolding, put the specimen in a standard constant temperature and humidity curing room and cure it to a standard age of 28 days.

[0073] Comparative Example 2

[0074] The difference is 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 in Example 2, and the preparation steps and parameters are also the same as in Example 2. The flexural and compressive strength properties of the prepared materials are 24.62MPa and 136.74MPa, respectively. Compared with Example 2, the flexural strength is reduced by 0.08%, and the compressive strength is reduced by 0.39%.

[0075] Example 3

[0076] An ultra-high performance concrete containing graphite tailings fine aggregate comprises 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-grained river sand, 7.1 parts of medium-grained river sand, 2.6 parts of fine-grained 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-grained graphite tailings, 4.6 parts of fine-grained graphite tailings, and 4.2 parts of steel fiber.

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

[0078] Step 1, screening of river sand and graphite tailings: The river sand and graphite tailings are screened into 1.25-0.63 mm as coarse aggregate, 0.63-0.315 mm as medium aggregate, and 0.315-0.16 mm as fine aggregate.

[0079] Step 2, mixing graphite tailings with river sand fine aggregate: Mixing graphite tailings with river sand fine aggregate: 6.6 parts of medium-sized graphite tailings, 4.6 parts of fine-sized graphite tailings, 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 are stirred in an automatic mixer for 4 minutes at a speed of 62 rpm 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 the concrete mixer in order, stir automatically for 1 minute, then add 8.8 parts of water and 1.5 parts of water reducer and stir for 1 to 2 minutes. After obtaining the composite slurry, add 4.2 parts of steel fiber and a pre-mixed aggregate mixture of graphite tailings and river sand, and continue stirring for 2 to 3 minutes before stopping. After the mixing is completed, use a shovel to directly load the stirred concrete into the mold. After filling, fix the mold on the vibration table and vibrate it for about 1 minute. After the vibration is completed, use a shovel 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 is completed, wrap it with plastic wrap and put it in a standard constant temperature and humidity curing room with a temperature of 20℃±2℃ and a relative humidity of more than 95%, and demold it after 24 hours. After demolding, put the specimen in a standard constant temperature and humidity curing room and cure it to a 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 materials are 24.8MPa and 138.11MPa, respectively. Compared with Example 3, the flexural strength is increased by 0.04% and the compressive strength is reduced by 0.28%.

[0083] Example 4

[0084] An ultra-high performance concrete containing graphite tailings fine aggregate comprises 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-grained river sand, 6.1 parts of medium-grained river sand, 2.2 parts of fine-grained river sand, 9.7 parts of silica fume, 4.9 parts of fly ash, 1.5 parts of water reducing agent, 8.8 parts of medium-grained graphite tailings, 6.2 parts of fine-grained graphite tailings, and 4.2 parts of steel fiber.

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

[0086] Step 1, screening of river sand and graphite tailings: The river sand and graphite tailings are screened into 1.25-0.63 mm as coarse aggregate, 0.63-0.315 mm as medium aggregate, and 0.315-0.16 mm as fine aggregate.

[0087] Step 2, mixing graphite tailings with river sand fine aggregate: Mixing graphite tailings with river sand fine aggregate: 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 are stirred in an automatic mixer for 4 minutes at a speed of 62 rpm 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 the concrete mixer in order, stir automatically for 1 minute, then add 8.8 parts of water and 1.5 parts of water reducer and stir for 1 to 2 minutes. After obtaining the composite slurry, add 4.2 parts of steel fiber and a pre-mixed aggregate mixture of graphite tailings and river sand, and continue stirring for 2 to 3 minutes before stopping. After the mixing is completed, use a shovel to directly load the stirred concrete into the mold. After filling, fix the mold on the vibration table and vibrate it for about 1 minute. After the vibration is completed, use a shovel 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 is completed, wrap it with plastic wrap and put it in a standard constant temperature and humidity curing room with a temperature of 20℃±2℃ and a relative humidity of more than 95%, and demold it after 24 hours. After demolding, put the specimen in a standard constant temperature and humidity curing room and cure it to a standard age of 28 days.

[0089] Comparative Example 4

[0090] The difference is that the medium 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, the fly ash is 9.7 parts, and 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 materials are 24.9 MPa and 135.82 MPa, respectively. Compared with Example 4, the flexural strength is reduced by 0.72% and the compressive strength is increased by 0.31%.

[0091] No replacement group

[0092] An ultra-high performance concrete comprises 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-grained river sand, 11.3 parts of medium-grained river sand, 4.8 parts of fine-grained river sand, 9.7 parts of silica fume, 4.9 parts of fly ash, 1.5 parts of a water reducing agent, and 4.2 parts of steel fiber.

[0093] The preparation process of the ultra-high performance concrete comprises the following steps:

[0094] Step 1: Screening of river sand: Screen the river sand into 1.25-0.63 mm as coarse aggregate, 0.63-0.315 mm as medium aggregate, and 0.315-0.16 mm as 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 the concrete mixer in order, stir automatically for 1 minute, then add 7.8 parts of water and 1.5 parts of water reducer and stir for 1 to 2 minutes. After obtaining the composite slurry, add 4.2 parts of steel fiber and river sand aggregate, and continue stirring for 2 to 3 minutes before stopping. After the mixing is completed, use a shovel to directly load the stirred concrete into the mold. After filling, fix the mold on the vibration table and vibrate it for about 1 minute. After the vibration is completed, use a shovel 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 work is completed, wrap it with plastic wrap and put it in a standard constant temperature and humidity curing room with a temperature of 20℃±2℃ and a relative humidity of more than 95%, and demold it after 24 hours. After demolding, put the specimen in a standard constant temperature and humidity curing room and cure it to a standard age of 28 days.

[0096] The porosity test results of the ultra-high performance concrete containing graphite tailings fine aggregate of 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 of the proportion of graphite tailings in concrete, the total porosity and particle size distribution have undergone significant changes, and the total porosity shows a trend of first decreasing and then increasing. Among them, the pores of Example 3 are mainly concentrated below 20nm, the pores greater than 1000nm are significantly reduced, and most of the pores are mainly harmless pores (accounting for 33.7%). The graphite tailings after optimizing the particle size and proportion improves the pore size distribution of concrete, reduces the number of large-diameter pores, and makes the pore size tend to be smaller, especially harmless pores. Because the pore structure of concrete is optimized, the inside of the matrix is ​​more dense, which is directly reflected in the improvement of macroscopic performance. When the proportion of fine-grained graphite tailings is 6.6 / 4.6, the total porosity of concrete reaches the best, the pore distribution is relatively uniform, and it is mainly harmless pores. And the compressive strength of concrete reaches the best.

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

[0101] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An ultra-high performance concrete containing graphite tailings fine aggregate, It is characterized in that The components include the following in parts by weight: 7.8 to 9.3 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 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 includes 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.

2. The ultra-high performance concrete containing graphite tailings fine aggregate according to claim 1, It is 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, It is 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, It is 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, It is 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, It is 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, It is characterized in that The screening and classification standards for river sand and graphite tailings are: 1.25-0.63 mm for coarse particle size, 0.63-0.315 mm for medium particle size, and 0.315-0.16 mm for fine particle size.

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

9. The ultra-high performance concrete containing graphite tailings fine aggregate according to claim 1, It is 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.

10. A method for preparing ultra-high performance concrete containing graphite tailings fine aggregate according to any one of claims 1 to 9, It is characterized in that The steps include: 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.

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