An ultra-high performance concrete based on high-value utilization of fine graphite tailings and a preparation method thereof

Abstract

The application relates to an ultra-high performance concrete based on high-value utilization of finely ground graphite tailings and a preparation method thereof, and belongs to the field of ultra-high performance concrete, in particular to an ultra-high performance concrete based on high-value utilization of finely ground graphite tailings and a preparation method thereof. The application aims to solve the high demand and high dependence of the ultra-high performance concrete on quartz powder and reduce the environmental problems caused by the preparation of the quartz powder. The material is composed of 869-960 parts of river sand, 30-122 parts of quartz powder, 30-122 parts of finely ground graphite tailings, 714-790 parts of cement, 116-128 parts of microbeads, 136-150 parts of silica fume, 30-32 parts of water reducing agent, 2 parts of defoaming agent and 171-189 parts of water according to mass fraction. The finely ground graphite tailings are used to replace the quartz powder, the graphite tailings are ground to obtain the finely ground graphite tailings with similar particle size distribution to the quartz powder, and the finely ground graphite tailings are more economically feasible as the filling material in the ultra-high performance concrete.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of ultra-high performance concrete, and particularly relates to an ultra-high performance concrete based on high-value utilization of finely ground graphite tailings and a preparation method thereof. BACKGROUND

[0002] As a new type of cement-based composite material, ultra-high performance concrete (UHPC) stands out in the modern construction field with its high strength, high toughness and excellent durability. Compared with ordinary concrete, the outstanding performance of UHPC is due to its extremely dense microstructure, which is based on the particle packing theory. Through precise mathematical modeling, this theory optimizes the particle size distribution at all levels, greatly improving the packing density of the matrix, thus creating a high-density internal structure that significantly enhances the strength and durability of the material. With these characteristics, UHPC has been widely used in structures with extremely high requirements for bearing capacity and durability, such as bridges, offshore platforms and super high-rise buildings.

[0003] Among the various materials that enhance the performance of UHPC, quartz powder plays an important role due to its ultra-fine particle size and good chemical stability. However, quartz powder faces many challenges in production and use, which severely limits its sustainable application in large-scale engineering. From a technical perspective, the preparation process of quartz powder used for filling in ultra-high performance concrete is complex, involving blasting, drilling, crushing and screening. These mechanical processing processes not only produce a large amount of harmful dust, causing serious pollution to the construction environment, but also pose a direct threat to the health of construction personnel. At the same time, industrial wastewater discharged during production, if not effectively treated, is likely to pollute the surrounding water resources and damage the ecological environment. More seriously, the International Agency for Research on Cancer (IARC) has clearly classified long-term occupational exposure to respirable quartz powder as a class 1 carcinogen, further highlighting the health risks of quartz powder in production and construction processes.

[0004] From an economic and resource perspective, quartz powder also has problems. Quartz powder resources are unevenly distributed, and the market supply of high-quality ultra-fine quartz powder is obviously limited in terms of region. Moreover, its fine processing requires a large amount of energy and is costly. These factors together result in high prices for quartz powder, making it difficult to meet the growing demand for UHPC in large infrastructure projects and hindering the large-scale application and promotion of UHPC. SUMMARY

[0005] The present application addresses the high demand and high dependence of ultra-high performance concrete on quartz powder, reduces the environmental problems caused by the preparation of quartz powder, and further provides an ultra-high performance concrete based on high-value utilization of finely ground graphite tailings and a preparation method thereof.

[0006] An ultra-high performance concrete based on high-value utilization of ground graphite tailings is composed of 869-960 parts of river sand, 30-122 parts of quartz powder, 30-122 parts of ground graphite tailings, 714-790 parts of cement, 116-128 parts of microbeads, 136-150 parts of silica fume, 30-32 parts of water reducing agent, 2 parts of defoaming agent and 171-189 parts of water by mass fraction.

[0007] Preferably, the concrete is composed of 915 parts of river sand, 91 parts of quartz powder, 30 parts of ground graphite tailings, 752 parts of cement, 122 parts of microbeads, 142 parts of silica fume, 30 parts of water reducing agent, 2 parts of defoaming agent and 180 parts of water by mass fraction.

[0008] Preferably, the concrete is composed of 915 parts of river sand, 61 parts of quartz powder, 61 parts of ground graphite tailings, 752 parts of cement, 122 parts of microbeads, 142 parts of silica fume, 30 parts of water reducing agent, 2 parts of defoaming agent and 180 parts of water by mass fraction.

[0009] Preferably, the ground graphite tailings are obtained by grinding the graphite tailings using a YXQM-1L high-throughput planetary ball mill under the conditions of a ball mill rotation speed of 600 r / min and a ball-to-material ratio of 1:1, and the grinding time is 15 min; the graphite tailings have a bulk density of 1328 kg / m 3 , an apparent density of 2902 kg / m 3 , a moisture content of 0.411%, and a silt content of 2.5%.

[0010] Preferably, the river sand has a particle size of 0.1-1 mm, and the quartz powder has a particle size of 0.1-0.25 mm.

[0011] Preferably, the ground graphite tailings have a grading of 100% passing through a 257 μm sieve, 78% passing through a 125 μm sieve, 63% passing through an 88 μm sieve, 51% passing through a 61 μm sieve, 41% passing through a 43 μm sieve, 34% passing through a 30 μm sieve, 27% passing through a 21 μm sieve, 21% passing through a 14 μm sieve, and 9% passing through a 6 μm sieve; and the quartz powder has a grading of 100% passing through a 257 μm sieve, 94% passing through a 125 μm sieve, 78% passing through an 88 μm sieve, 53% passing through a 61 μm sieve, 28% passing through a 43 μm sieve, 10% passing through a 30 μm sieve, 3% passing through a 21 μm sieve, 0.6% passing through a 14 μm sieve, and 0% passing through a 6 μm sieve.

[0012] Preferably, the quartz powder has a specific surface area of 0.354 m 2 / g, and a pore volume of 0.001 cm 3 / g, the average pore size is 146.3 nm; the specific surface area of the ground graphite tailings is 6.325 m 2 / g, the pore volume is 0.01 cm 3 / g, the average pore size is 110.2 nm, and the pozzolanic activity is 60.72%.

[0013] Preferably, the cement is P. II 52.5 ordinary portland cement, the 28d compressive strength is 55.62 MPa, the 28d flexural strength is 7.1 MPa, and the density is 3111 kg / m 3 ; the properties of the silica fume are: water demand ratio is 122%, loss on ignition ratio is 1.52%, apparent density is 2236 kg / m 3 , specific surface area is 11078 m 2 / kg, and 28d activity index is 144%; the properties of the microsphere are: water demand ratio is 83%, loss on ignition ratio is 0.3%, apparent density is 2539 kg / m 3 , specific surface area is 2208 m 2 / kg, and 28d activity index is 101%.

[0014] Preferably, the mixing water is ordinary tap water.

[0015] Preferably, the water reducing agent is a polycarboxylic acid superplasticizer, a transparent gelatinous liquid, the actual measured water-reducing rate is 30%, the solid content is 25%, and the color is light yellow powder; the defoaming agent is a white powder, the pH value is measured to be 7.0, and the actual measured defoaming performance is 1.9011 g / mL.

[0016] The preparation method of the above-mentioned one kind of super high performance concrete based on high value utilization of ground graphite tailings is specifically performed according to the following steps:

[0017] I. The raw materials are 869-960 parts of river sand, 30-122 parts of quartz powder, 30-122 parts of ground graphite tailings, 714-790 parts of cement, 116-128 parts of microspheres, 136-150 parts of silica fume, 30-32 parts of water reducing agent, 2 parts of defoaming agent, and 171-189 parts of water according to the mass fraction.

[0018] II. The cement, silica fume, microspheres, and graphite tailings are added to the mixer to obtain the aggregate, and the aggregate is pre-mixed for 120 s under the condition that the rotation speed is 60 r / min, so that the aggregate is uniformly dry-mixed;

[0019] 3. The water-reducing agent, defoamer and water are mixed to obtain an admixture mixture. The admixture mixture is divided into two parts by mass ratio of 80% and 20%. The 80% part of the admixture mixture is added to the mixer and stirred for 180s at a speed of 60r / min. Then the stirring is stopped. The 20% part of the admixture mixture is added to the mixer and stirred for 300s at a speed of 60r / min. The mixer is then turned off, the material is discharged, test specimens are prepared and cured to obtain ultra-high performance concrete based on the high-value utilization of finely ground graphite tailings.

[0020] Preferably, the mixer is a GMP50 vertical shaft planetary mixer.

[0021] The beneficial effects of this invention are:

[0022] This invention replaces quartz powder in ultra-high performance concrete (UHPC) with finely ground graphite tailings, which helps promote the application of UHPC and greatly alleviates its dependence on quartz powder. It also solves the ecological problems caused by the large accumulation of graphite tailings and reduces the cost of UHPC. Appropriately replacing part of the quartz powder with graphite tailings is reasonable and can form advanced "green" UHPC, which is conducive to the sustainable development of the construction industry.

[0023] This invention uses finely ground graphite tailings to replace quartz powder in the preparation of green ultra-high performance concrete. It breaks through the traditional thinking in terms of raw material ratio, and achieves a win-win situation of environmental and economic benefits while solving the dependence of ultra-high performance concrete on quartz powder. Attached Figure Description

[0024] Figure 1 These are scanning electron microscope (SEM) comparison images of the ground graphite tailings and quartz powder described in the embodiments; where a represents the ground graphite tailings and b represents the quartz powder.

[0025] Figure 2 A schematic diagram showing the effect of different amounts of finely ground graphite tailings on the wet bulk density of quartz powder UHPC.

[0026] Figure 3 Bar chart showing the effect of different amounts of finely ground graphite tailings on the slump and spread of quartz powder UHPC.

[0027] Figure 4 The effect of different amounts of finely ground graphite tailings on the T of quartz powder UHPC 500 Line chart;

[0028] Figure 5 Comparison curves of pore number distribution of quartz powder UHPC based on finely ground graphite tailings;

[0029] Figure 6 A comparison of the porosity of different pore sizes in UHPC quartz powder from finely ground graphite tailings.

[0030] Figure 7 The influence diagram of different fine ground graphite tailings content on the autogenous shrinkage of quartz powder UHPC;

[0031] Figure 8 The compressive strength comparison diagram of quartz powder UHPC with different fine ground graphite tailings content;

[0032] Figure 9 The flexural strength comparison diagram of quartz powder UHPC with different fine ground graphite tailings content;

[0033] Figure 10 The electric flux comparison diagram of quartz powder UHPC with different fine ground graphite tailings content;

[0034] Figure 11 The eco-economic performance influence diagram of fine ground graphite tailings content on quartz powder UHPC;

[0035] Figure 12 The XRD spectrum of quartz powder UHPC with different fine ground graphite tailings content. DETAILED DESCRIPTION

[0036] Specific implementation one: the concrete of the embodiment is composed of 869-960 parts of river sand, 30-122 parts of quartz powder, 30-122 parts of fine ground graphite tailings, 714-790 parts of cement, 116-128 parts of microbeads, 136-150 parts of silica fume, 30-32 parts of water reducing agent, 2 parts of defoaming agent, and 171-189 parts of water.

[0037] Specific implementation two: the concrete of the embodiment is composed of 915 parts of river sand, 91 parts of quartz powder, 30 parts of fine ground graphite tailings, 752 parts of cement, 122 parts of microbeads, 142 parts of silica fume, 30 parts of water reducing agent, 2 parts of defoaming agent, and 180 parts of water. The other parts are the same as those of specific implementation one.

[0038] Specific implementation three: the concrete of the embodiment is composed of 915 parts of river sand, 61 parts of quartz powder, 61 parts of fine ground graphite tailings, 752 parts of cement, 122 parts of microbeads, 142 parts of silica fume, 30 parts of water reducing agent, 2 parts of defoaming agent, and 180 parts of water. The other parts are the same as those of specific implementation one.

[0039] When the ground graphite tailings replace the quartz powder at a ratio of 25% to 50%, the particles can better fill the voids between the cement paste and other aggregates. On the one hand, an appropriate amount of ground graphite tailings particles can participate in the particle packing system, intercalate with river sand, cement and other particles, optimize the overall packing structure, reduce the existence of large pores, make the internal structure of concrete more dense, and thus improve the compressive strength. On the other hand, too much ground graphite tailings may cause mutual interference between particles, affect the order of packing, increase the porosity, and reduce the strength; and too low a replacement rate cannot fully play its role in optimizing the packing structure. A replacement rate of 25% to 50% can improve the density while reasonably controlling the porosity and ensuring the strength performance. Within this replacement rate range, the surface of the ground graphite tailings particles can be well bonded with the cement hydration products to form a relatively stable interfacial structure. The C-S-H gel and other products generated by cement hydration can encapsulate the ground graphite tailings particles to form a tight bond. This good interfacial bonding helps to effectively transfer stress between different phases, reduces stress concentration, and thus improves the unit compressive strength and the unit cement contribution strength. If the replacement rate is too high, the excessive ground graphite tailings particles will cause the structure of the interfacial transition zone to become complex and the bonding quality to decrease, which is not conducive to strength development.

[0040] The ground graphite tailings are mainly composed of a high content of SiO2 and a small amount of metal oxides, which have a certain inertness but also have weak pozzolanic activity. At a replacement rate of 25% to 50%, the inert components can act as a stable skeletal structure like quartz powder, providing physical support and ensuring the basic strength of concrete. At the same time, the weak pozzolanic active components can undergo a secondary hydration reaction with Ca(OH)2 in the cement hydration products in the later stage of cement hydration, generating more C-S-H gel and other products to further enhance the structural strength of concrete. This synergistic effect of activity and inertia can be well played within this replacement rate range, and if the replacement rate exceeds this range, the overall strength development will be affected, for example, when the replacement rate is too high, the active components may react excessively or insufficiently. The trace amounts of metal oxides and other components in the ground graphite tailings may have some impact on the cement hydration reaction. At a suitable replacement rate (25% to 50%), these components can act like an external additive during the cement hydration process, adjusting the rate and progress of the hydration reaction. Certain metal ions may promote the early hydration of cement minerals, accelerate strength development, or stabilize the structure of hydration products in the later stage to improve durability. When the replacement rate is too high or too low, the regulation of the hydration reaction may be out of balance, which is not conducive to the optimization of strength and other properties.

[0041] 25%~50% of the fine ground graphite tailings replacement rate can make its particle size distribution and river sand, cement particles form a good adaptation. After grinding, the particle size of the fine ground graphite tailings can reach the similar level of quartz powder, and in this replacement rate range, particles of different sizes can fill and match each other to form a continuous grading system. This continuous grading is conducive to improving the workability of concrete mixture, allowing the concrete to be better compacted during pouring, reducing defects, and thus improving strength. If the replacement rate is not appropriate, it will lead to unreasonable particle size distribution, resulting in too many coarse or fine particles, affecting the workability and strength development of concrete. Within this replacement rate range, the number of fine ground graphite tailings particles is moderate, and the cement paste can better wrap these particles and other aggregates. The right amount of fine ground graphite tailings can increase the specific surface area of the system, but it will not excessively consume the cement paste, ensuring that the paste fully wraps and lubricates the aggregate. In this way, when stressed, the aggregate can effectively transfer stress through the paste, improving unit compressive strength and unit cement contribution strength. If the replacement rate is too high, it will increase the specific surface area of the particles, leading to a relative lack of cement paste, affecting the wrapping and strength; if the replacement rate is too low, it cannot fully utilize the optimization effect of the paste wrapping.

[0042] Specific embodiment four: different from the specific embodiment one is that: the fine ground graphite tailings is obtained by grinding the graphite tailings using a YXQM-1L type high-throughput planetary ball mill under the conditions of a ball mill rotation speed of 600 r / min and a ball-to-material ratio of 1:1, and the grinding time is 15 min; the graphite tailings has a bulk density of 1328 kg / m 3 , an apparent density of 2902 kg / m 3 , a moisture content of 0.411%, and a clay content of 2.5%. The others are the same as in the specific embodiment one.

[0043] The specific embodiment obtains fine ground graphite tailings with a particle size distribution similar to that of quartz powder by grinding the graphite tailings. The present application uses the waste graphite tailings to achieve the same particle size distribution effect, solving the problem of high demand and high dependence on quartz powder in ultra-high performance concrete.

[0044] The specific embodiment uses fine ground graphite tailings to replace quartz powder, not only reducing the environmental problems caused by the preparation process of quartz powder, but also effectively treating a large amount of solid waste generated during graphite mining and beneficiation. As a waste product, fine ground graphite tailings is widely available and inexpensive. Using fine ground graphite tailings as a filler material in ultra-high performance concrete can significantly reduce production costs, making ultra-high performance concrete more economically feasible for large-scale applications.

[0045] Embodiment five: different from embodiment one, the particle size of the river sand is 0.1-1mm, and the particle size of the quartz powder is 0.1-0.25mm. The other parts are the same as embodiment one.

[0046] Embodiment six: different from embodiments four and five, the grading of the fine ground graphite tailings is: 100% of the 257μm sieve passes, 78% of the 125μm sieve passes, 63% of the 88μm sieve passes, 51% of the 61μm sieve passes, 41% of the 43μm sieve passes, 34% of the 30μm sieve passes, 27% of the 21μm sieve passes, 21% of the 14μm sieve passes, and 9% of the 6μm sieve passes; the grading of the quartz powder is: 100% of the 257μm sieve passes, 94% of the 125μm sieve passes, 78% of the 88μm sieve passes, 53% of the 61μm sieve passes, 28% of the 43μm sieve passes, 10% of the 30μm sieve passes, 3% of the 21μm sieve passes, 0.6% of the 14μm sieve passes, and 0% of the 6μm sieve passes. The other parts are the same as embodiments four and five.

[0047] Embodiment seven: different from embodiment one, the specific surface area of the quartz powder is 0.354m 2 / g, the pore volume is 0.001cm 3 / g, and the average pore size is 146.3nm; the specific surface area of the fine ground graphite tailings is 6.325m 2 / g, the pore volume is 0.01cm 3 / g, the average pore size is 110.2nm, and the pozzolanic activity is 60.72%. The other parts are the same as embodiment one.

[0048] Embodiment eight: different from embodiment one, the cement is P.Ⅱ52.5 ordinary portland cement, the 28d compressive strength is 55.62MPa, the 28d flexural strength is 7.1MPa, and the density is 3111kg / m 3 ; the properties of the silica fume are: water demand ratio is 122%, loss on ignition ratio is 1.52%, apparent density is 2236kg / m 3 , specific surface area is 11078m 2 / kg, and 28d activity index is 144%; the properties of the microbead are: water demand ratio is 83%, loss on ignition ratio is 0.3%, apparent density is 2539kg / m 3 , specific surface area is 2208m 2 / kg, and 28d activity index is 101%. The other parts are the same as embodiment one.

[0049] Specific embodiment nine: the difference between this embodiment and specific embodiment one is that the water reducing agent is a polycarboxylic acid superplasticizer, the water reducing rate is actually measured as 30%, the solid content is 25%, and the water reducing agent is a light yellow powder; the defoaming agent is a white powder. The others are the same as specific embodiment one.

[0050] Specific embodiment ten: a preparation method of the super high performance concrete based on high value utilization of the ground graphite tailings is specifically performed according to the following steps:

[0051] I. 869-960 parts of river sand, 30-122 parts of quartz powder, 30-122 parts of ground graphite tailings, 714-790 parts of cement, 116-128 parts of microbeads, 136-150 parts of silica fume, 30-32 parts of water reducing agent, 2 parts of defoaming agent and 171-189 parts of water are taken as raw materials according to mass fraction;

[0052] II. The cement, silica fume, microbeads and graphite tailings are added into a mixer to obtain aggregate, and the aggregate is pre-mixed for 120 s under the condition that the rotation speed is 60 r / min, so that the aggregate is uniformly dry-mixed;

[0053] III. The water reducing agent, the defoaming agent and the water are mixed to obtain an admixture, the admixture is divided into two parts according to the mass ratio of 80%, 20%, 80% of the admixture is added into the mixer and stirred for 180 s under the condition that the rotation speed is 60 r / min, the mixer is stopped, and then 20% of the admixture is added into the mixer and stirred for 300 s under the condition that the rotation speed is 60 r / min, then the mixer is turned off, the material is discharged, the test piece is prepared, and the maintenance is performed, so that the super high performance concrete based on high value utilization of the ground graphite tailings is obtained.

[0054] The effect of the present application is verified by the following test:

[0055] The specific raw materials and specifications used in the examples and comparative examples are as follows:

[0056] The cement is P. II 52.5 ordinary portland cement, the 28d compressive strength is 55.62 MPa, the 28d flexural strength is 7.1 MPa, and the density is 3111 kg / m 3 . The graphite tailings raw material is produced in Jixi City, Heilongjiang Province, the bulk density is 1328 kg / m 3 , and the apparent density is 2902 kg / m 3, the water content is 0.411%, and the silt content is 2.5%. A YXQM-1L high-throughput planetary ball mill is used to grind the graphite tailings raw material to obtain finely ground graphite tailings with a particle size distribution close to that of the quartz powder. The particle size of the river sand used is 0.1-1mm, and the particle size of the quartz powder is 0.1-0.25mm. The experimental water used is tap water at room temperature. The water reducing agent used is a transparent gel-like liquid polycarboxylic acid superplasticizer, with a measured water reducing rate of 30%, a solid content of 25%, a light yellow powder, a defoaming agent which is a white powder, a pH value of 7.0, and a measured defoaming performance of 1.9011g / mL. The water demand ratio of the silica fume experimental product is 122%, the loss on ignition ratio is 1.52%, the apparent density is 2236kg / m 3 , the specific surface area is 11078m 2 / kg, and the 28d activity index is 144%.

[0057] The water demand ratio of the fine fly ash microbead experimental product is 83%, the loss on ignition ratio is 0.3%, the apparent density is 2539kg / m 3 , the specific surface area is 2539m 2 / kg, and the 28d activity index is 101%. A YXQM-1L high-throughput planetary ball mill is used, with a rotation speed of 600r / min. A GMP50 vertical shaft planetary mixer is used, with a rotation speed of 60r / min. The chemical composition of the materials used is shown in Table 1.

[0058] Table 1 Chemical composition of the materials used in the experiment (%)

[0059]

[0060] Experimental method:

[0061] 1. Wet bulk density: In this embodiment, the "wet bulk density test method" proposed by Wong and Kwan in 2008 is used to evaluate the wet bulk density of quartz powder UHPC with different amounts of finely ground graphite tailings. The freshly mixed UHPC slurry is poured into three 250mL containers, then placed on a vibration table and vibrated thoroughly to remove excess slurry until the whole is compacted and weighed, and the wet bulk density is calculated according to the following formula, with the result being the average of the three containers.

[0062]

[0063]

[0064] where φ represents the wet bulk density of the mixture, V s represents the volume of the solid in a wet state, V represents the volume of the mixture in the container, and M represents the mass of the mixture in the container.w denotes the density of water, μ w denotes the volume ratio of mixing water to solids in wet state in mixture proportion, ρ α , ρ β , ρ γ denotes the apparent density of a certain solid component in mixture, V α , V β , V γ denotes the volume of a certain solid component in mixture, μ α , μ β , μ γ denotes the volume ratio of a certain solid component to the total solid in mixture, V w mixing water in mixture proportion, V α / β / γ..... denotes V α , V β , V γ one of, μ α / β / γ..... denotes the volume ratio of a certain solid component to the total solid in mixture.

[0065] 2. Workability: The slump, spread and time of spread of fresh UHPC were tested according to the Standard Test Methods for Properties of Fresh Ordinary Concrete GB / T 50080-2016.

[0066] 3. Mechanical properties: The compressive and flexural strength of fresh UHPC were tested according to BS-EN-196-1.

[0067] 4. Chloride ion permeability: The resistance to chloride ion penetration of fresh UHPC was tested according to the Standard Test Methods for Long-term Properties and Durability of Ordinary Concrete GB / T 50082-2009.

[0068] 5. The present application comprehensively evaluates the influence of different replacement rates of finely ground graphite tailings (0%, 25%, 50%, 75%, and 100%) on the environmental sustainability and cost-effectiveness of quartz powder-based UHPC through three environmental indicators and two economic indicators. The environmental indicators include: (1) Carbon emission per unit compressive strength indicator (CCI), which measures the amount of carbon dioxide emissions per unit of compressive strength; (2) Carbon emission per unit flexural strength indicator (CFI), which reflects the amount of carbon dioxide emissions corresponding to each unit of flexural strength; (3) Cement strength contribution per unit indicator (CEI), which evaluates the contribution of each unit of cement to the compressive strength of UHPC. The calculation of the above three indicators is based on formulas (2)-(4). The economic evaluation includes: (1) Cost indicator (NCI), which measures the total cost of materials; (2) Cost per unit compressive strength indicator (C P), for characterizing the technical and material cost inputs required to obtain a unit of compressive strength. The above index is obtained by the following formula:

[0069]

[0070]

[0071] wherein f c represents the compressive strength at the curing age of 28d, f f represents the compressive strength at the curing age of 28d, C represents the manufacturing cost of UHPC, C ref represents the manufacturing cost of the reference UHPC mix proportion, i.e., the manufacturing cost of FGGT0, M i represents the quantity of each component in UHPC, P i represents the unit price of each component in UHPC;

[0072] 6. The present application uses a TD-3500 type X-ray to analyze the quartz powder UHPC under different dosages of finely ground graphite tailings. At the end of the 28d compressive test of the test piece, a small part of the broken pieces is taken, and the broken pieces are soaked in 95% anhydrous ethanol for 24h to stop the internal hydration reaction, and then the treated broken pieces are taken out and placed in an oven at an ambient temperature of 60℃ for drying for 48 hours. After the treatment is completed, X-ray analysis is performed, and the scanning range is specified at 10-80°, and the scanning speed is 3° / min.

[0073] The present application uses the currently widely used UHPC (ultra-high performance concrete) mix proportion optimization method Andreasen-Anderson (MAA) model to optimize the proportion of UHPC solid particles prepared in this test. The solid particle materials used in this test include river sand, quartz powder, finely ground graphite tailings, cement, silica fume and superfine fly ash microbeads. By mixing these solid particles in the optimal proportion, a solid particle mixing curve can be formed. When the curve is closest to the ideal curve predicted by the Andreasen-Anderson model (MAA model), it means that the particle packing has reached the most compact state. In order to clarify the degree of coincidence between the curves, the present application uses residual analysis and least squares method R 2 to evaluate, and the specific formula is as follows:

[0074]

[0075]

[0076] wherein P(D) is the content of particles at a certain particle size (D) (%), D is the particle size, Dmin D is the minimum particle size in the particle system max D is the maximum particle size in the particle system, q is the distribution modulus, 0.23 in this test, RRS is the residual square sum for quantifying the square sum of the deviation between the true value and the estimated value, P mix

[0077] is the mixed curve function formed by mixing all solid materials, P tar D is the theoretical closest curve calculated by the MAA model i i+1 R is the particle size distribution interval 2 is the fitting degree for the reaction mixed curve and the target interval of the MAA model is the average value of the particle size in the mixed curve.

[0078] The following method was used to prepare the five groups of concrete of the example, comparative example 1, comparative example 2, comparative example 3, comparative example 4, and comparative example 5, and the specific mixing ratio is shown in Table 2:

[0079] The cement, silica fume, microbeads, and graphite tailings were added to the mixer to obtain aggregates, and the aggregates were pre-mixed at a speed of 60 r / min for 120 s to uniformly dry-mix the aggregates; the water reducing agent, defoaming agent, and water were mixed to obtain an admixture, and the admixture was divided into two parts with a mass ratio of 80% and 20%; 80% of the admixture was added to the mixer and stirred at a speed of 60 r / min for 180 s, the stirring was stopped, and then 20% of the admixture was added to the mixer and stirred at a speed of 60 r / min for 300 s, after which the mixer was turned off, the material was discharged, the test piece was prepared, and the curing was performed, to obtain the ultra-high performance concrete based on the high-value utilization of the ground graphite tailings.

[0080] Table 2 Mixing ratio of UHPC (parts)

[0081]

[0082] (Note: the example, comparative example 1, comparative example 2, comparative example 3, and comparative example 4 represent the replacement rate of quartz powder of 0%, 25%, 50%, 75%, and 100%, respectively)

[0083] Experimental results and analysis:

[0084] Material appearance: scanning electron microscopy (SEM) was used to test the microstructure of the two materials, and the results are shown in Figure 1As clearly shown in the images, there is a significant difference in particle shape between finely ground graphite tailings and quartz powder. Finely ground graphite tailings particles exhibit a more rounded shape, while quartz powder particles show obvious angularity and irregularity. Furthermore, varying degrees of aggregation can be observed among the particles in the finely ground graphite tailings, primarily due to the agglomeration of numerous ultrafine particles within the graphite. Moreover, the particle composition of the finely ground graphite tailings shows a large variation in particle size, with a clearly observable irregular distribution between large and ultrafine particles, while the particle distribution of quartz powder is relatively uniform.

[0085] wet bulk density: Figure 2 The effects of different amounts of finely ground graphite tailings on the wet bulk density of quartz powder UHPC were demonstrated. The values ​​for Example 1 – Comparative Example 4 were 0.837, 0.823, 0.812, 0.792, and 0.782, respectively. Compared to the Example 1, the wet bulk densities of Comparative Examples 1 to 4 decreased by 1.67%, 2.98%, 5.37%, and 6.57%, respectively. The wet bulk density of quartz powder UHPC showed a linear and monotonically decreasing trend with increasing amounts of finely ground graphite tailings. A higher wet bulk density indicates higher slurry density of UHPC. A finely ground graphite tailings content of 25–50% maximized the wet density while having a relatively small impact on the slurry density of UHPC.

[0086] The working properties of UHPC for quartz powder with different amounts of ground graphite tailings sand are shown in the figure. Figure 3 As can be seen from the data, the expansion of Examples 1-4 was 748, 755, 765, 782, and 778 mm, respectively. Compared with Examples 1, Comparative Examples 1-4 increased their expansion by 0.93%, 2.27%, 4.54%, and 4.01%, respectively. With the increase of the amount of finely ground graphite tailings, the expansion of quartz powder UHPC showed a trend of first increasing and then decreasing, with Comparative Example 3 having the highest expansion of the entire group.

[0087] Extended time T 500 To some extent, it can reflect the consistency and filling rate of the concrete mixture slurry. The extended time T in the example without the addition of finely ground graphite tailings... 500 The time was 8.40 seconds, the maximum value for the entire group. Comparative Examples 1 through 4 all showed varying degrees of decrease compared to the previous example, at 5.8%, 7.14%, 6.90%, and 3.57%, respectively. From... Figure 4 It can be seen that after adding 25% of finely ground graphite tailings, the T500 of UHPC showed a relatively significant decrease, and with the continued increase in the amount added, T... 500The growth rate of the expansion time tends to be flat. It can be seen that when the mixing amount is 25% to 75%, the expansion time decreases more obviously, indicating that the filling rate of the concrete mixture is enhanced at this mixing amount.

[0088] Industrial CT: As shown in Table 3, the porosities of Examples ~ Comparative Examples four are 1.963, 1.999, 3.330, 3.668 and 3.844%, respectively, and the porosity of the UHPC as a whole increases with the increase of the mixing amount of the ground graphite tailings. Among them, the incorporation of the ground graphite tailings in Comparative Example One does not have a significant effect on the porosity of the UHPC, and the number of pores and the total pore area are both reduced compared with the examples.

[0089] From Figure 5 the pore number distribution curve shown in the figure, it can be found that the pore number distribution of the UHPC with different mixing amounts of ground graphite tailings is similar, mainly concentrated in 0.0001 ~ 0.01mm 3 around. The pore volume of 0.001mm 3 is a dividing point. When <0.001mm 3 , the number of pores increases with the increase of the pore volume and the mixing amount of the ground graphite tailings. When the pore volume is more than 0.001mm 3 , the number of pores as a whole shows a downward trend with the increase of the pore volume. From Figure 6 it can be found that in the low pore volume range (0.0001 ~ 0.001mm 3 ), the proportion of the number of pores of Comparative Examples One ~ Four is higher than that of the examples. When the pore volume is >0.01mm 3 , the proportion of the number of pores of the examples reaches 19.22%, which is the maximum value in the whole group, and the proportion of the number of pores decreases with the incorporation of the graphite tailings, and the proportion of the number of pores tends to be stable after 50% mixing amount, and is distributed between 7.59% ~ 9.66%. According to the above pore distribution, the incorporation of 25% ground graphite tailings reduces the number of pores of the UHPC, the pore volume tends to be smaller, and the number of large pores is reduced.

[0090] Table 3 Pore structure

[0091]

[0092] Autogenous shrinkage: As shown in Figure 7 , the autogenous shrinkage of the quartz powder UHPC with different mixing amounts of ground graphite tailings increases with the extension of time, and the growth rate of the autogenous shrinkage is faster within 0 ~ 10h, and the growth rate of the autogenous shrinkage tends to be flat after more than 10h, and reaches the maximum value at 72h. Figure 7It can be found that the autogenous shrinkage of quartz powder UHPC specimens of examples ~ comparative examples four at 72h is 914με, 748με, 513με, 435με, 294με, respectively. At the same time, the shrinkage of quartz powder UHPC gradually decreases with the increase of the content of ground graphite tailings. The autogenous shrinkage of comparative example four is the smallest in the group, and compared with the example (without adding ground graphite tailings), the maximum reduction of autogenous shrinkage is 620με. The incorporation of ground graphite tailings can effectively reduce the autogenous shrinkage of UHPC and reduce the risk of cracking of UHPC.

[0093] Mechanical properties: as shown in Figure 8 , the compressive strength of quartz powder UHPC with different contents of ground graphite tailings increases with the increase of age, and the overall growth rate of compressive strength is the fastest in the first 3d, accounting for 50% of the 28d strength

[0094] above. And after 3d, the growth rate of compressive strength increases uniformly in each age. The 28d compressive strength of quartz powder UHPC increases first and then decreases with the increase of the content of ground graphite tailings, which is manifested as an increase when the replacement rate is 0-25%, and a monotonic decrease when the replacement rate is 25-100%. As can be seen from the figure, the 28d compressive strength of examples ~ comparative examples four is 126.79, 130.66, 127.65, 124.61, 119.74MPa, respectively. The quartz powder UHPC reaches the maximum value when the content of ground graphite tailings is 25% in comparative example one. Compared with the example, the 28d compressive strength of comparative example one increases by 3.05%.

[0095] As shown in Figure 9 , the flexural strength of quartz powder UHPC increases with the increase of age, and the 28d flexural strength increases first and then decreases with the increase of the content of ground graphite tailings. The 28d flexural strength of examples ~ comparative examples four is 21.34, 22.67, 22.51, 21.4, 20.82MPa, respectively, and the change of comparative examples one ~ four is 6.23%, 5.48%, 0.28%, -2.44% compared with the example. The change rule is similar to the change of 28d compressive strength, and it can be seen that the incorporation of 25% ground graphite tailings has a positive effect on compressive strength and flexural strength, and improves the mechanical properties of UHPC.

[0096] Chloride ion permeability: the effect of different contents of ground graphite tailings on the electric flux of quartz powder UHPC is shown in Figure 10The average of the electric flux of Example 4 to Comparative Example 4 is 46C, 46.1C, 46.8C, 48.4C, 59.8C respectively. Compared with Example, the electric flux of Comparative Example 1 to Comparative Example 4 is increased by 0.21%, 1.73%, 5.21%, 30% respectively. The electric flux of quartz powder UHPC shows a monotonic increasing trend with the increase of the content of ground graphite tailings. When the replacement rate of ground graphite tailings is 25% to 50%, the electric flux of quartz powder UHPC changes little. The larger pores in the quartz powder UHPC matrix are filled with fine ground graphite tailings particles, and the reduction of larger pores helps to reduce the penetration path of chloride ions in the quartz powder UHPC matrix to some extent. When the content of ground graphite tailings continues to increase to 75%, the growth rate of electric flux begins to increase rapidly, and the electric flux of quartz powder UHPC reaches the maximum value at 100% content.

[0097] Ecological and economic analysis: Figure 11 The radar chart in Table 6 clearly shows the ecological and economic index conditions of UHPC prepared by replacing quartz powder with different proportions of ground graphite tailings. As can be seen from the chart, compared with Example, CCI shows a downward trend in the low replacement rate (25% to 50%) interval, but it rises sharply in the high replacement rate (75% to 100%) interval.

[0098] CFI and CCI show similar trends. At low replacement rates (25% to 50%), they decrease significantly, and as the replacement rate increases, their carbon emissions gradually approach Example, and then show a gradual upward trend.

[0099] The replacement of 25% to 50% of ground graphite tailings powder has a significant effect on reducing the carbon emissions of unit compressive strength and unit flexural strength, and performs well in carbon emission control. In terms of economy, NCI steadily decreases from the baseline group Example 1 to Comparative Example 4 0.855. This trend strongly proves that increasing the proportion of graphite tailings powder can effectively reduce material costs.

[0100] Cp gradually decreases from Example 39.84 to Comparative Example 4 36.07, showing a relatively stable downward trend, which further indicates that replacing quartz powder with ground graphite tailings can effectively reduce the cost of unit compressive strength.

[0101] XRD: The XRD diffraction peak spectrum of quartz powder UHPC with different contents of ground graphite tailings is as shown in Figure 6. Figure 12The analysis of the XRD patterns shows that the main phases of the test pieces of Examples 1 to 4 and Comparative Examples 1 to 4 all contain ettringite, SiO2, Ca(OH)2, C3S and C2S. Among them, ettringite and Ca(OH)2 are cement hydration products, SiO2 mainly comes from raw materials, and C3S and C2S are cement clinker in the UHPC matrix which has not been hydrated. With the increase of the replacement rate of the ground graphite tailings, the intensity of the SiO2 diffraction peak near 26.9° shows a gradually decreasing trend, and when the ground graphite tailings replace quartz powder by more than 50%, the diffraction peak intensity is significantly weakened. Moreover, it can also be found from the XRD patterns that after the incorporation of the ground graphite tailings, the intensity of the Ca(OH)2 diffraction peak near 34.6° of the UHPC decreases. This is because although the main component of quartz powder is SiO2, it has low activity at room temperature and is not easy to react with Ca(OH)2 in the hydrate. The ground graphite tailings which are ground for 15 minutes by the ball mill and have been refined in particles have an activity index of 60.72% at 28d, which is higher than that of the quartz powder. This shows that after the ground graphite tailings replace the quartz powder and are incorporated into the UHPC, a certain amount of pozzolanic effect may be produced, thereby consuming Ca(OH)2, and finally leading to the decrease of the intensity of the Ca(OH)2 diffraction peak.

[0102] Comprehensive analysis: The wet bulk density of the quartz powder UHPC shows a linear and monotonous decreasing trend with the increase of the ground graphite tailings. The incorporation of 25% to 50% of the ground graphite tailings can maximize the guarantee of the wet bulk density and has a smaller impact on the compactness of the UHPC. The expansion time T 500 To a certain extent, it can reflect the consistency and filling rate of the concrete slurry. Compared with Comparative Examples 1 to 4, the T 500The obvious decrease indicates that the filling rate of the concrete mixture is enhanced at this content. The trend of the electric flux of the examples is monotonically increasing compared with the comparative examples 1-4. The electric flux of the UHPC increases with the increase of the content of the ground graphite tailings. The content of 25%-50% of the ground graphite tailings has little effect on the porosity of the ultra-high performance concrete. The overall change range of the electric flux of the quartz powder UHPC is small. The larger pores in the quartz powder UHPC matrix are filled with fine ground graphite tailings particles. The reduction of the larger pores helps to reduce the penetration path of chloride ions in the quartz powder UHPC matrix to a certain extent, thereby ensuring the strength of the UHPC. The incorporation of 25% ground graphite tailings can not only improve the 28d compressive and flexural strength of the quartz powder UHPC, but also effectively reduce the production cost and carbon emissions of the quartz powder UHPC. Compared with the examples, the unit cement contribution strength is higher at a low replacement rate (25%-50%), but the strength contribution rate continues to decrease at a high replacement rate (75%-100%). This fully shows that the replacement rate of the comparative examples 1 and 2 can effectively reduce the cement consumption and maintain a relatively considerable strength contribution. Within the range of 75%-100% replacement rate, although the material cost and unit compressive strength cost of the quartz powder UHPC are significantly reduced, the unit strength carbon emission is also significantly increased and the cement strength contribution index continues to decline, thereby seriously affecting the ecological performance. In summary, the replacement rate of 25%-50% of the ground graphite tailings exhibits excellent performance balance in all aspects and can be considered as the best balance point between strength, ecological performance and economic cost.

Claims

1. A high-performance concrete based on the high-value utilization of ground graphite tailings, characterized in that... The concrete is composed of 869–960 parts river sand, 30–122 parts quartz powder, 30–122 parts finely ground graphite tailings, 714–790 parts cement, 116–128 parts microspheres, 136–150 parts silica fume, 30–32 parts water-reducing agent, 2 parts defoamer, and 171–189 parts water by weight. The finely ground graphite tailings were obtained by grinding the graphite tailings using a YXQM-1L high-throughput planetary ball mill at a mill speed of 600 r / min and a ball-to-material ratio of 1:1 for 15 min; the bulk density of the graphite tailings was 1328 kg / m³. 3 The apparent density is 2902 kg / m³. 3 The moisture content is 0.411%, and the mud content is 2.5%. The gradation of the finely ground graphite tailings is as follows: 100% pass rate through a 257μm sieve, 78% pass rate through a 125μm sieve, 63% pass rate through an 88μm sieve, 51% pass rate through a 61μm sieve, 41% pass rate through a 43μm sieve, 34% pass rate through a 30μm sieve, 27% pass rate through a 21μm sieve, 21% pass rate through a 14μm sieve, and 9% pass rate through a 6μm sieve. The gradation of the quartz powder is as follows: 100% pass rate through a 257μm sieve, 94% pass rate through a 125μm sieve, 78% pass rate through an 88μm sieve, 53% pass rate through a 61μm sieve, 28% pass rate through a 43μm sieve, 10% pass rate through a 30μm sieve, 3% pass rate through a 21μm sieve, 0.6% pass rate through a 14μm sieve, and 0% pass rate through a 6μm sieve. The preparation method of ultra-high performance concrete based on the high-value utilization of ground graphite tailings is carried out according to the following steps: I. Weigh out 869–960 parts by weight of river sand, 30–122 parts by weight of quartz powder, 30–122 parts by weight of finely ground graphite tailings, 714–790 parts by weight of cement, 116–128 parts by weight of microspheres, 136–150 parts by weight of silica fume, 30–32 parts by weight of water-reducing agent, 2 parts by weight of defoamer and 171–189 parts by weight of water as raw materials; 2. Add cement, silica fume, microspheres and graphite tailings to the mixer to obtain aggregate. Pre-mix the aggregate for 120 seconds at a speed of 60 r / min to make the aggregate dry and uniform.

3. The water-reducing agent, defoamer and water are mixed to obtain an admixture mixture. The admixture mixture is divided into two parts by mass ratio of 80% and 20%. The 80% part of the admixture mixture is added to the mixer and stirred for 180s at a speed of 60r / min. Then the stirring is stopped. The 20% part of the admixture mixture is added to the mixer and stirred for 300s at a speed of 60r / min. The mixer is then turned off, the material is discharged, test specimens are prepared and cured to obtain ultra-high performance concrete based on the high-value utilization of finely ground graphite tailings.

2. The ultra-high performance concrete based on the high-value utilization of ground graphite tailings according to claim 1, characterized in that... The concrete is composed of 915 parts river sand, 91 parts quartz powder, 30 parts finely ground graphite tailings, 752 parts cement, 122 parts microspheres, 142 parts silica fume, 30 parts water-reducing agent, 2 parts defoamer and 180 parts water by weight.

3. The ultra-high performance concrete based on the high-value utilization of ground graphite tailings according to claim 1, characterized in that... The concrete is composed of 915 parts river sand, 61 parts quartz powder, 61 parts finely ground graphite tailings, 752 parts cement, 122 parts microspheres, 142 parts silica fume, 30 parts water-reducing agent, 2 parts defoamer and 180 parts water by weight.

4. The ultra-high performance concrete based on the high-value utilization of ground graphite tailings according to claim 1, characterized in that... The river sand has a particle size of 0.1–1 mm, and the quartz powder has a particle size of 0.1–0.25 mm.

5. The ultra-high performance concrete based on the high-value utilization of ground graphite tailings according to claim 1, characterized in that... The specific surface area of ​​the quartz powder is 0.354 m². 2 / g, pore volume 0.001cm³ 3 / g, with an average pore size of 146.3nm; the specific surface area of ​​the ground graphite tailings is 6.325m². 2 / g, pore volume 0.01cm³ 3 / g, average pore size of 110.2nm, and pozzolanic activity of 60.72%.

6. The ultra-high performance concrete based on the high-value utilization of ground graphite tailings according to claim 1, characterized in that... The cement is P.Ⅱ52.5 ordinary Portland cement, with a 28-day compressive strength of 55.62 MPa, a 28-day flexural strength of 7.1 MPa, and a density of 3111 kg / m³. 3 The silica fume has the following properties: water requirement ratio of 122%, loss on ignition ratio of 1.52%, and apparent density of 2236 kg / m³. 3 The specific surface area is 11078 m². 2 / kg, with an activity index of 144% after 28 days; the properties of the microspheres are as follows: water requirement ratio 83%, loss on ignition ratio 0.3%, and apparent density 2539 kg / m³. 3 Specific surface area is 2208 m² 2 / kg, with an activity index of 101% after 28 days.

7. The ultra-high performance concrete based on the high-value utilization of ground graphite tailings according to claim 1, characterized in that... The water-reducing agent is a polycarboxylate high-efficiency water-reducing agent with a measured water reduction rate of 30% and a solid content of 25%, and is a light yellow powder; the defoamer is a white powder.

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