Ultra-high performance concrete based on high-valued utilization of ground graphite tailings and preparation method of ultra-high performance concrete

Abstract

The invention discloses ultra-high performance concrete based on high-value utilization of levigated graphite tailings and a preparation method of the ultra-high performance concrete, belongs to the field of ultra-high performance concrete, and particularly relates to the ultra-high performance concrete based on high-value utilization of the levigated graphite tailings and the preparation method of the ultra-high performance concrete. The invention aims to solve the problems of high demand and high dependence of ultra-high performance concrete on quartz powder and reduction of environmental problems caused by preparation of the quartz powder. The material is prepared from the following components in parts by mass: 869 to 960 parts of river sand, 30 to 122 parts of quartz powder, 30 to 122 parts of ground graphite tailings, 714 to 790 parts of cement, 116 to 128 parts of microbeads, 136 to 150 parts of silica fume, 30 to 32 parts of water reducing agent, 2 parts of defoaming agent and 171 to 189 parts of water. The ground graphite tailings are adopted to replace quartz powder, the graphite tailings are ground to obtain the ground graphite tailings similar to the quartz powder in grain composition, and the ground graphite tailings serving as a filling material in the ultra-high-performance concrete have more economic feasibility.

Description

Technical Field

[0001] The invention belongs to the field of ultra-high performance concrete, and specifically relates to ultra-high performance concrete based on high-value utilization of ground graphite tailings and a preparation method thereof. Background Art

[0002] Ultra-high performance concrete (UHPC), as a new type of cement-based composite material, stands out in the field of modern construction for its high strength, high toughness and excellent durability. Compared with ordinary concrete, the excellent performance of UHPC stems from its extremely dense microstructure, the formation of which is based on the particle packing theory. Through precise mathematical models, this theory optimizes the particle size distribution of particles at each level, greatly improving the packing density of the matrix, thereby creating a high-density internal structure and significantly enhancing the strength and durability of the material. With these characteristics, UHPC has been widely used in structures such as bridges, offshore platforms, and super high-rise buildings that have extremely high requirements for bearing capacity and durability.

[0003] Among the various materials that improve the performance of UHPC, quartz powder plays an important role due to its ultrafine particle size and good chemical stability. However, quartz powder faces many challenges in the production and use process, which seriously limits its sustainable application in large-scale projects. From a technical perspective, the preparation process of quartz powder used for filling in ultra-high performance concrete is complicated, covering multiple links such as 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 workers. At the same time, if the industrial wastewater discharged during the production process is not effectively treated, it is very likely to pollute the surrounding water resources and damage the ecological environment. What is more serious is that the International Agency for Research on Cancer (IARC) has clearly listed long-term occupational exposure to inhalable quartz powder as a Class I carcinogen, which further highlights the health risks of quartz powder during production and construction.

[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 ultrafine quartz powder is obviously limited in terms of region. Moreover, its refined processing consumes a lot of energy and is costly. These factors together lead to high prices for quartz powder, making it difficult to meet the growing demand for UHPC in large-scale infrastructure projects, hindering the large-scale application and promotion of UHPC. Summary of the invention

[0005] The present invention aims to solve the high demand and high dependence of ultra-high performance concrete on quartz powder, reduce the environmental problems caused by the preparation of quartz powder, and further provide an ultra-high performance concrete based on the high-value utilization of ground graphite tailings and a preparation method thereof.

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

[0007] Preferably, the concrete consists of 915 parts of river sand, 91 parts of quartz powder, 30 parts of ground graphite tailings, 752 parts of cement, 122 parts of microspheres, 142 parts of silica fume, 30 parts of water reducer, 2 parts of defoamer and 180 parts of water in parts by mass.

[0008] Preferably, the concrete consists of 915 parts of river sand, 61 parts of quartz powder, 61 parts of ground graphite tailings, 752 parts of cement, 122 parts of microspheres, 142 parts of silica fume, 30 parts of water reducer, 2 parts of defoamer and 180 parts of water in parts by mass.

[0009] Preferably, the ground graphite tailings are obtained by grinding the graphite tailings using a YXQM-1L high-throughput planetary ball mill at a ball mill 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 , apparent density is 2902kg / m 3 , moisture content is 0.411%, and mud content is 2.5%.

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

[0011] Preferably, the gradation of the ground graphite tailings is: 257μm sieve pass rate is 100%, 125μm sieve pass rate is 78%, 88μm sieve pass rate is 63%, 61μm sieve pass rate is 51%, 43μm sieve pass rate is 41%, 30μm sieve pass rate is 34%, 21μm sieve pass rate is 27%, 14μm sieve pass rate is 21%, 6μm sieve pass rate is 9%; the gradation of the quartz powder is: 257μm sieve pass rate is 100%, 125μm sieve pass rate is 94%, 88μm sieve pass rate is 78%, 61μm sieve pass rate is 53%, 43μm sieve pass rate is 28%, 30μm sieve pass rate is 10%, 21μm sieve pass rate is 3%, 14μm sieve pass rate is 0.6%, 6μm sieve pass rate is 0%.

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

[0013] Preferably, the cement is P.II52.5 ordinary Portland cement, with a 28d compressive strength of 55.62MPa, a 28d flexural strength of 7.1MPa, and a density of 3111kg / m 3 The properties of the silica fume are: water requirement ratio is 122%, loss on ignition ratio is 1.52%, and apparent density is 2236kg / m 3 , the specific surface area is 11078m 2 / kg, 28d activity index is 144%; the micro-beads have the following properties: water requirement ratio is 83%, ignition loss ratio is 0.3%, apparent density is 2539kg / m 3 , with a specific surface area of ​​2208m 2 / kg, and the activity index at 28 days was 101%.

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

[0015] Preferably, the water reducer is a polycarboxylic acid high-efficiency water reducer, which is a transparent colloidal liquid with a water reduction rate of 30% and a solid content of 25%, and is a light yellow powder; the defoamer is a white powder with a pH value of 7.0 and a defoaming performance of 1.9011 g / mL.

[0016] The above-mentioned method for preparing ultra-high performance concrete based on high-value utilization of ground graphite tailings is specifically carried out according to the following steps:

[0017] 1. Weigh 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 reducer, 2 parts of defoamer and 171-189 parts of water as raw materials by mass;

[0018] 2. Add cement, silica fume, microbeads and graphite tailings into the mixer to obtain aggregates, and pre-mix the aggregates for 120 seconds at a rotation speed of 60 r / min to make the aggregates dry-mixed evenly;

[0019] 3. Mix the water reducer, defoamer and water to obtain an admixture mixture, divide the admixture mixture into two parts according to the mass ratio of 80% and 20%, add 80% of the admixture mixture into the mixer, stir for 180 seconds at a speed of 60 r / min, stop stirring, add 20% of the admixture mixture into the mixer, stir for 300 seconds at a speed of 60 r / min, turn off the mixer, discharge the materials, prepare test pieces, and perform curing to obtain ultra-high performance concrete based on high-value utilization of ground graphite tailings.

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

[0021] Beneficial effects of the present invention:

[0022] The present invention replaces quartz powder in ultra-high performance concrete with ground graphite tailings, which helps to promote the application of ultra-high performance concrete and alleviate the dependence of ultra-high performance concrete on quartz powder to a large extent, while solving the ecological problems caused by the large accumulation of graphite tailings, and at the same time reducing the cost of UHPC. It is reasonable to appropriately replace part of the quartz powder with graphite tailings, which can form advanced "green" UHPC and is beneficial to the sustainable development of the construction industry.

[0023] The present invention adopts ground graphite tailings instead of quartz powder to prepare green ultra-high performance concrete, which breaks through the traditional thinking in raw material ratio. While solving the dependence of ultra-high performance concrete on quartz powder, it achieves a win-win situation of environmental and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The scanning electron microscope comparison diagram of the ground graphite tailings and quartz powder described in the embodiment; wherein a represents the ground graphite tailings and b represents the quartz powder;

[0025] Figure 2 Schematic diagram of the effect of different amounts of ground graphite tailings on the wet bulk density of quartz powder UHPC;

[0026] Figure 3 The bar graph of the slump and expansion of quartz powder UHPC with different amounts of ground graphite tailings;

[0027] Figure 4 Effect of different grinding graphite tailings content on T of quartz powder UHPC 500 Line chart;

[0028] Figure 5 It is the comparison curve of pore quantity distribution of ground graphite tailings and quartz powder UHPC;

[0029] Figure 6 It is a comparison chart of the pore proportion of different pore sizes of ground graphite tailings and quartz powder UHPC;

[0030] Figure 7 This is the effect of different ground graphite tailings dosage on the autogenous shrinkage of quartz powder UHPC;

[0031] Figure 8 This is a comparison chart of the compressive strength of quartz powder UHPC with different amounts of ground graphite tailings added;

[0032] Fig. 9 This is a comparison chart of the flexural strength of quartz powder UHPC with different amounts of ground graphite tailings added;

[0033] Fig.10 This is a comparison chart of the electrical flux of quartz powder UHPC with different amounts of ground graphite tailings added;

[0034] Fig.11 This is the effect of the amount of ground graphite tailings on the ecological-economic performance of quartz powder UHPC;

[0035] Fig.12 XRD patterns of quartz powder UHPC with different amounts of ground graphite tailings added. DETAILED DESCRIPTION

[0036] Specific implementation method 1: In this implementation method, the concrete 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 microspheres, 136-150 parts of silica fume, 30-32 parts of water reducer, 2 parts of defoamer and 171-189 parts of water by mass.

[0037] Specific embodiment 2: This embodiment is different from the specific embodiment 1 in that 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 microspheres, 142 parts of silica fume, 30 parts of water reducer, 2 parts of defoamer and 180 parts of water by mass. The rest is the same as the specific embodiment 1.

[0038] Specific embodiment 3: This embodiment is different from the specific embodiment 1 in that 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 microspheres, 142 parts of silica fume, 30 parts of water reducer, 2 parts of defoamer and 180 parts of water by mass. The rest is the same as the specific embodiment 1.

[0039] In this embodiment, when the ground graphite tailings replace the quartz powder at a ratio of 25% to 50%, its particles can be well filled in the gaps between the cement paste and other aggregates. On the one hand, an appropriate amount of ground graphite tailings particles can participate in the particle stacking system, match with river sand, cement and other particles, optimize the overall stacking structure, reduce the presence of large pores, make the internal structure of the concrete more compact, and thus improve the compressive strength. On the other hand, too much ground graphite tailings may cause mutual interference between particles, affect the orderliness of the stacking, increase the porosity, and reduce the strength; while the replacement rate is too low, it cannot give full play to its optimization effect on the stacking structure. The replacement rate of 25% to 50% can reasonably control the porosity and ensure the strength performance while improving the density. 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 interface structure. Products such as CSH gel generated by cement hydration can wrap the ground graphite tailings particles to form a tight bond. This good interfacial bonding helps to effectively transfer stress between different phases, reduce stress concentration, and thus improve unit compressive strength and unit cement contribution strength. If the replacement rate is too high, the structure of the interface transition zone will become complicated due to excessive ground graphite tailing particles, and the bonding quality will decrease, which is not conducive to strength development.

[0040] Ground graphite tailings are mainly composed of high content of SiO2 and trace metal oxides, which have certain inertness, but also have weak volcanic ash activity. At a substitution rate of 25% to 50%, its inert components can act as a stable skeleton structure like quartz powder, provide physical support, and ensure the basic strength of concrete. At the same time, its weak volcanic ash active components can react with Ca(OH)2 in cement hydration products in the late stage of cement hydration to produce more CSH gel and other products, further enhancing the structural strength of concrete. This synergistic effect of activity and inertness can be better exerted within the substitution rate range. If the substitution rate exceeds this range, this balance will be broken. For example, when the substitution rate is too high, the active components will over-react or under-react, affecting the overall strength development. Trace metal oxides and other components in ground graphite tailings may have a certain effect on the hydration reaction of cement. At a suitable substitution rate (25% to 50%), these components can play a role similar to admixtures in the cement hydration process, regulating the rate and progress of the hydration reaction. Some metal ions may promote the early hydration of cement minerals and accelerate the development of strength, or stabilize the structure of hydration products in the later stage to improve durability. However, when the substitution rate is too high or too low, this regulatory effect on the hydration reaction may be unbalanced, which is not conducive to the optimization of properties such as strength.

[0041] The replacement rate of 25% to 50% of ground graphite tailings can make its particle gradation well compatible with river sand, cement particles, etc. After grinding, the particle size of ground graphite tailings can reach a level similar to that of quartz powder. Within this replacement rate range, particles of different particle sizes can fill and match each other to form a continuous gradation system. This continuous gradation is conducive to improving the workability of concrete mixtures, enabling concrete to be better compacted and formed during the pouring process, reducing defects, and thus improving strength. If the replacement rate is not appropriate, it will lead to unreasonable particle gradation, excessive coarse particles or excessive fine particles, affecting the workability and strength development of concrete. Within this replacement rate range, the number of ground graphite tailings particles is moderate, and cement slurry can better wrap these particles and other aggregates. An appropriate amount of ground graphite tailings can increase the specific surface area of ​​the system without excessively consuming cement slurry, ensuring that the slurry fully wraps and lubricates the aggregates. In this way, when subjected to force, the aggregates can effectively transfer stress through the slurry, improving the unit compressive strength and unit cement contribution strength. If the replacement rate is too high, the specific surface area of ​​the particles will increase, resulting in a relatively insufficient cement paste, affecting the encapsulation and strength; if the replacement rate is too low, its optimization effect on the encapsulation of the paste cannot be fully utilized.

[0042] Specific embodiment 4: This embodiment is different from the specific embodiment 1 in that the ground graphite tailings are obtained by grinding the graphite tailings using a YXQM-1L high-throughput planetary ball mill at a ball mill speed of 600r / min and a ball-to-material ratio of 1:1, and the grinding time is 15min; the bulk density of the graphite tailings is 1328kg / m 3 , apparent density is 2902kg / m 3 , water content is 0.411%, mud content is 2.5%. Others are the same as the first embodiment.

[0043] This embodiment grinds the graphite tailings to obtain ground graphite tailings with a particle size distribution similar to that of quartz powder. The present invention utilizes the waste of 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] This embodiment uses ground graphite tailings to replace quartz powder, which not only reduces the environmental problems generated in the preparation of quartz powder, but also effectively treats a large amount of solid waste generated in the process of graphite mining and beneficiation. Ground graphite tailings, as waste, are widely available and low-cost. Using ground graphite tailings as a filling material in ultra-high performance concrete greatly reduces production costs, making ultra-high performance concrete more economically feasible in large-scale applications.

[0045] Specific embodiment 5: This embodiment is different from the specific embodiment 1 in that the particle size of the river sand is 0.1-1 mm, and the particle size of the quartz powder is 0.1-0.25 mm. The rest is the same as the specific embodiment 1.

[0046] Specific embodiment 6: This embodiment is different from specific embodiments 4 and 5 in that the gradation of the ground graphite tailings is: 257μm sieve hole pass rate is 100%, 125μm sieve hole pass rate is 78%, 88μm sieve hole pass rate is 63%, 61μm sieve hole pass rate is 51%, 43μm sieve hole pass rate is 41%, 30μm sieve hole pass rate is 34%, 21μm sieve hole pass rate is 27%, 14μm sieve hole pass rate is 21%, 6μm sieve pass rate is 9%; the gradation of the quartz powder is: 257μm sieve pass rate is 100%, 125μm sieve pass rate is 94%, 88μm sieve pass rate is 78%, 61μm sieve pass rate is 53%, 43μm sieve pass rate is 28%, 30μm sieve pass rate is 10%, 21μm sieve pass rate is 3%, 14μm sieve pass rate is 0.6%, 6μm sieve pass rate is 0%. Others are the same as the fourth and fifth embodiments.

[0047] Specific embodiment 7: This embodiment differs from the specific embodiment 1 in that the specific surface area of ​​the quartz powder is 0.354m 2 / g, pore volume is 0.001cm 3 / g, an average pore size of 146.3nm; the specific surface area of ​​the ground graphite tailings is 6.325m 2 / g, pore volume is 0.01cm 3 / g, an average pore diameter of 110.2nm, and a volcanic ash activity of 60.72%. Other aspects are the same as those of the first embodiment.

[0048] Specific embodiment eight: This embodiment differs from the specific embodiment one in that the cement is P.Ⅱ52.5 ordinary Portland cement, with a 28d compressive strength of 55.62MPa, a 28d flexural strength of 7.1MPa, and a density of 3111kg / m 3 The properties of the silica fume are: water requirement ratio is 122%, loss on ignition ratio is 1.52%, and apparent density is 2236kg / m 3 , the specific surface area is 11078m 2 / kg, 28d activity index is 144%; the micro-beads have the following properties: water requirement ratio is 83%, ignition loss ratio is 0.3%, apparent density is 2539kg / m 3 , with a specific surface area of ​​2208m 2 / kg, and the activity index at 28 days was 101%. Other aspects are the same as those in the first embodiment.

[0049] Specific embodiment 9: This embodiment is different from specific embodiment 1 in that: the water reducing agent is a polycarboxylic acid high-efficiency water reducing agent, the water reducing rate is measured to be 30%, the solid content is 25%, and it is a light yellow powder; the defoaming agent is a white powder. Others are the same as specific embodiment 1.

[0050] Specific embodiment 10: In this embodiment, a method for preparing ultra-high performance concrete based on high-value utilization of ground graphite tailings is specifically carried out according to the following steps:

[0051] 1. Weigh 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 reducer, 2 parts of defoamer and 171-189 parts of water as raw materials by mass;

[0052] 2. Add cement, silica fume, microbeads and graphite tailings into the mixer to obtain aggregates, and pre-mix the aggregates for 120 seconds at a rotation speed of 60 r / min to make the aggregates dry-mixed evenly;

[0053] 3. Mix the water reducer, defoamer and water to obtain an admixture mixture, divide the admixture mixture into two parts according to the mass ratio of 80% and 20%, add 80% of the admixture mixture into the mixer, stir for 180 seconds at a speed of 60 r / min, stop stirring, add 20% of the admixture mixture into the mixer, stir for 300 seconds at a speed of 60 r / min, turn off the mixer, discharge the materials, prepare test pieces, and perform curing to obtain ultra-high performance concrete based on high-value utilization of ground graphite tailings.

[0054] The effect of the present invention is verified by the following experiments:

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

[0056] The cement is P.Ⅱ52.5 ordinary Portland cement, with a 28d compressive strength of 55.62MPa, a 28d flexural strength of 7.1MPa, and a density of 3111kg / m 3 The graphite tailings used are produced in Jixi City, Heilongjiang Province, with a bulk density of 1328kg / m 3 , the apparent density is 2902kg / m 3, the moisture content is 0.411%, and the mud content is 2.5%. The YXQM-1L high-throughput planetary ball mill is used to grind the graphite tailings raw materials to obtain ground graphite tailings with a particle size close to that of quartz powder. The particle size of the river sand used is 0.1-1mm, and the particle size range of the quartz powder is 0.1-0.25mm. The experimental water used is tap water at room temperature. The water reducer used is a polycarboxylic acid high-efficiency water reducer with a transparent colloidal liquid. The water reduction rate is measured to be 30%, the solid content is 25%, and it is a light yellow powder. The defoaming agent is a white powder, the pH value is measured to be 7.0, and the defoaming performance is measured to be 1.9011g / mL. The water requirement ratio of the silica ash experimental supplies used is 122%, the ignition loss ratio is 1.52%, and the apparent density is 2236kg / m 3 , the specific surface area is 11078m 2 / kg, and the activity index at 28 days was 144%.

[0057] Using fine fly ash microbeads experimental supplies, the water requirement ratio is 83%, the ignition loss ratio is 0.3%, and the apparent density is 2539kg / m 3 , with a specific surface area of ​​2539m 2 / kg, and the activity index at 28 days was 101%. A YXQM-1L high-throughput planetary ball mill was used, with a rotation speed of 600r / min. A GMP50 vertical axis planetary mixer was used, with a rotation speed of 60r / min. The chemical compositions of the above materials are shown in Table 1.

[0058] Table 1 Chemical composition of materials used in this test (%)

[0059]

[0060] Experimental methods:

[0061] 1. Wet bulk density: This example uses the "wet bulk density test method" proposed by Wong and Kwan in 2008 to evaluate the wet bulk density of quartz powder UHPC with different amounts of ground graphite tailings. The freshly mixed UHPC slurry was poured into three 250mL containers, which were then placed on a vibration table and vibrated thoroughly to remove excess slurry until the whole was dense, and then weighed. The wet bulk density was calculated according to the following formula, and the result was the average value 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, M represents the mass of the mixture in the container, and ρw represents the density of water, μ w It represents the volume ratio of mixing water to solid in wet state in the mixture proportion, ρ α , β , γ Respectively represent the apparent density of a solid component in the mixture, V α 、V β 、V γ Respectively represent the volume of a solid component in the mixture, μ α , μ β , μ γ Respectively represent the volume ratio of a solid component in the mixture to the solid component, V w Mixing water in the mixture proportion, V α / β / γ..... Indicates V α 、V β 、V γ One of them, μ α / β / γ..... It indicates the volume ratio of a certain solid component to the total solid in a mixture.

[0065] 2. Working performance: The slump, expansion and expansion time of fresh UHPC are tested in accordance with the "Standard for Test Methods for Performance of Ordinary Concrete Mixtures GB / T50080-2016".

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

[0067] 4. Chloride ion penetration performance: The chloride ion penetration resistance of fresh UHPC was tested in accordance with the "Standard for Test Methods for Long-term Performance and Durability of Ordinary Concrete GB / T50082-2009".

[0068] 5. The present invention systematically analyzes the impact of different ground graphite tailings replacement rates (0%, 25%, 50%, 75% and 100%) on the environmental sustainability and cost-effectiveness of quartz powder-based UHPC through a comprehensive evaluation of three environmental indicators and two economic indicators. The environmental indicators include: (1) carbon emission index per unit compressive strength (CCI), which is used to measure the carbon dioxide emissions generated per unit compressive strength; (2) carbon emission index per unit flexural strength (CFI), which reflects the carbon dioxide emissions corresponding to each unit flexural strength; (3) cement strength contribution index (CEI), which is used to evaluate the compressive strength contribution of each unit of cement in UHPC. The calculation of the above three indicators is based on formulas (2) to (4). The economic evaluation includes: (1) cost index (NCI), which is used to measure the overall cost of the material; (2) cost index per unit compressive strength (C P), which is used to characterize the technical and material cost input required to obtain unit compressive strength. The above indicators are obtained through the following formula:

[0069]

[0070]

[0071] where f c Indicates the compressive strength at 28 days of curing age, f f represents the compressive strength at 28 days of curing age, C represents the manufacturing cost of UHPC, and C ref represents the manufacturing cost of the benchmark UHPC mix, i.e., the manufacturing cost of FGGT0, M i Represents the quantity of each component in UHPC, P i Indicates the unit price of each component in UHPC;

[0072] 6. The present invention uses TD-3500 X-ray to analyze quartz powder UHPC with different grinding graphite tailings dosage. At the end of the 28d compression test of the specimen, a small part of the broken pieces is taken, and the pieces are immersed in 95% anhydrous ethanol for 24 hours to stop the hydration reaction inside. Then the treated pieces are taken out and placed in an oven at an ambient temperature of 60°C for 48 hours. After the treatment, X-ray analysis is performed, and the scanning range is set at 10-80° and the scanning speed is 3° / min.

[0073] The present invention adopts the Andreasen-Anderson (MAA) model, a widely used UHPC (ultra-high performance concrete) mix optimization method, to optimize the proportion of UHPC solid particles prepared in this experiment. The solid particle materials used in this experiment include river sand, quartz powder, ground graphite tailings, cement, silica fume and ultrafine 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 stacking at this time has reached the most compact state. In order to clarify the degree of fit between the curves, the present invention adopts residual analysis and least squares method R 2 The specific formula for evaluation is as follows:

[0074]

[0075]

[0076] Where P(D) is the content (%) of particles at a certain particle size (D), D is the particle size, and Dmin is the minimum particle size in the particle system, D max is the maximum particle size in the particle system, q is the distribution modulus, which is taken as 0.23 in this experiment, RRS is the square of the residual used to quantify the square of the deviation between the true value and the estimated value, P mix

[0077] is the mixing curve function formed by mixing all solid materials, P tar The theoretical tightest curve calculated by the MAA model, D i i+1 is the particle size distribution range, R 2 is the degree of fit between the reaction mixing curve and the target interval of the MAA model, is the average particle size in the mixing curve.

[0078] The following methods were used to prepare five groups of concrete, namely, Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4, and the specific mix ratios are shown in Table 2:

[0079] Cement, silica fume, microbeads and graphite tailings are added into a mixer to obtain aggregates, and the aggregates are pre-mixed for 120 seconds at a rotation speed of 60 r / min to make the aggregates dry-mixed evenly; a water reducer, a defoamer and water are mixed to obtain an admixture mixture, and the admixture mixture is divided into two parts according to a mass ratio of 80% and 20%, 80% of the admixture mixture is added into the mixer, stirred for 180 seconds at a rotation speed of 60 r / min, the stirring is stopped, and 20% of the admixture mixture is added into the mixer, stirred for 300 seconds at a rotation speed of 60 r / min, and the mixer is turned off, the materials are discharged, test pieces are prepared, and the concrete is cured to obtain ultra-high performance concrete based on high-value utilization of ground graphite tailings.

[0080] Table 2 UHPC mix ratio (parts)

[0081]

[0082] (Note: Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 represent quartz powder replacement rates of 0%, 25%, 50%, 75%, and 100%, respectively)

[0083] Experimental results and analysis:

[0084] Material morphology: Scanning electron microscopy (SEM) was used to test the microscopic morphology of the two materials. The results are as follows: Figure 1As shown in the image, it can be clearly seen that there are significant differences in the particle shapes of ground graphite tailings and quartz powder. Among them, the particles of ground graphite tailings show a more rounded shape, while the particle shape of quartz powder shows obvious angularity and irregularity. In addition, it can be found that there are different degrees of aggregation between the particles of ground graphite tailings, which is mainly caused by the agglomeration of more ultrafine particles in ground graphite. In addition, the particle composition of ground graphite tailings shows a large difference in particle size. It can be clearly observed that there is an irregular distribution between large particles and ultrafine particles, while the particle distribution of quartz powder is relatively uniform.

[0085] Wet bulk density: Figure 2 The specific effects of different amounts of ground graphite tailings on the wet bulk density of quartz powder UHPC are shown. The values ​​of Example-Comparative Example 4 are 0.837, 0.823, 0.812, 0.792, and 0.782, respectively. Compared with the embodiment, the wet bulk density 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 develops in a linear monotonically decreasing trend with the increase of ground graphite tailings. The larger the value of the wet bulk density, the higher the slurry density of UHPC. The wet density is guaranteed to the greatest extent at a dosage of 25-50% of ground graphite tailings, and the effect on the slurry density of UHPC is relatively small.

[0086] The working performance of quartz powder UHPC with different amounts of ground graphite tailings is shown in the figure. Figure 3 It can be seen that the expansion degrees of Example 1-Comparative Example 4 are 748, 755, 765, 782, and 778 mm, respectively. Compared with the example, the expansion degrees of Comparative Examples 1 to 4 increased by 0.93%, 2.27%, 4.54%, and 4.01%, respectively. With the increase of the amount of ground graphite tailings, the expansion degree of quartz powder UHPC shows a trend of first rising and then falling, and the expansion degree of Comparative Example 3 is the maximum value of the whole group.

[0087] Extension time T 500 To a certain extent, it can reflect the consistency and filling rate of the concrete mixture slurry. The expansion time T of the embodiment without adding ground graphite tailings 500 The results of Comparative Examples 1 to 4 show different decreases compared with the embodiment, which are 5.8%, 7.14%, 6.90% and 3.57% respectively. Figure 4 It can be seen that after 25% of the ground graphite tailings were added, the T500 of UHPC decreased significantly, and as the addition continued to increase, T 500It can be seen that when the dosage is between 25% and 75%, the expansion time decreases significantly, indicating that the filling rate of the concrete mixture is enhanced at this dosage.

[0088] Industrial CT: As shown in Table 3. It can be found from the table that the porosities of Example 1 to Comparative Example 4 are 1.963, 1.999, 3.330, 3.668 and 3.844% respectively, and the porosity of UHPC increases as the amount of ground graphite tailings increases. Among them, the addition of ground graphite tailings in Comparative Example 1 has no obvious effect on the porosity of UHPC, and its pore number and total pore area are reduced compared with the embodiment.

[0089] from Figure 5 It can be found from the pore number distribution curve shown that the pore number distribution of UHPC with different amounts of ground graphite tailings is similar, mainly concentrated in the range of 0.0001 to 0.01 mm. 3 About 0.001mm 3 The pore volume is a cut-off point. <0.001mm 3 When the pore volume exceeds 0.001 mm, the number of pores increases with the increase of pore volume and the amount of ground graphite tailings. 3 After that, the number of pores shows an overall downward trend as the pore volume increases. Figure 6 It can be found that in the low pore volume range (0.0001~0.001mm 3 ), the pore volume ratios of Comparative Examples 1 to 4 are all higher than those of the embodiment. 3 After that, the pore proportion of the embodiment reached 19.22%, which is the maximum value of the whole group. With the addition of graphite tailings, the pore proportion decreased. After 50% addition, the pore proportion tended to be stable and distributed between 7.59% and 9.66%. Based on the above pore distribution, it can be seen that the addition of 25% ground graphite tailings reduces the pore number of UHPC, the pore volume tends to be smaller, and the number of larger pores is reduced.

[0090] Table 3 Pore structure

[0091]

[0092] Autogenous shrinkage: Figure 7 As shown in the figure, the shrinkage of quartz powder UHPC with different amounts of ground graphite tailings increases with time. The growth rate of shrinkage is faster within 0 to 10 hours, and the growth rate of shrinkage tends to be slow after more than 10 hours, and reaches the maximum value at 72 hours. Figure 7It can be found that the self-shrinkage rates of the quartz powder UHPC specimens of Example 1 to Comparative Example 4 with different replacement rates of ground graphite tailings at 72h are 914με, 748με, 513με, 435με, and 294με, respectively. At the same time, the shrinkage degree of the quartz powder UHPC gradually decreases with the increase of the amount of ground graphite tailings. The self-shrinkage of Comparative Example 4 is the smallest value of the whole group, and its maximum self-shrinkage is reduced by 620με compared with the embodiment (without the addition of ground graphite tailings). The addition of ground graphite tailings can effectively reduce the self-shrinkage of UHPC and reduce the risk of cracking of UHPC.

[0093] Mechanical properties: Figure 8 As shown in Figure 2, the compressive strength of quartz powder UHPC with different amounts of ground graphite tailings increases with the increase of age. The overall growth rate of its compressive strength is fastest in the first 3 days, accounting for 50% of the 28d strength.

[0094] More than 3 days. After more than 3 days, the growth rate of compressive strength is relatively uniform in each age period. The 28d compressive strength of quartz powder UHPC shows a trend of first increasing and then decreasing with the increase of the amount of ground graphite tailings added. Specifically, the substitution rate increases when it is 0-25%, and decreases monotonically when it is 25-100%. As can be seen from the figure, the 28d compressive strength of Example 1-Comparative Example 4 is 126.79, 130.66, 127.65, 124.61, and 119.74MPa, respectively. When the amount of ground graphite tailings added in Comparative Example 1 is 25%, the quartz powder UHPC reaches its maximum value. Compared with the embodiment, the 28d compressive strength of Comparative Example 1 increased by 3.05%.

[0096] like Fig. 9 As shown, the flexural strength of quartz powder UHPC increases with the increase of age, and its 28d flexural strength shows a trend of first increasing and then decreasing with the increase of the amount of ground graphite tailings. The 28d flexural strengths of Example 1 to Comparative Example 4 are 21.34, 22.67, 22.51, 21.4, and 20.82 MPa, respectively. Compared with the example, the changes of Comparative Examples 1 to 4 are 6.23%, 5.48%, 0.28%, and -2.44%, and their change rules are similar to the changes of 28d compressive strength. It can be seen that the addition of 25% of ground graphite tailings has a positive effect on the compressive strength and flexural strength, and improves the mechanical properties of UHPC.

[0097] Chloride ion permeability: Effect of different amounts of ground graphite tailings on the electrical flux of quartz powder UHPC Fig.10As shown. The average values ​​of the electric flux of Example 1 to Comparative Example 4 are 46C, 46.1C, 46.8C, 48.4C, and 59.8C, respectively. Compared with the example, the electric flux of Comparative Examples 1 to 4 increased by 0.21%, 1.73%, 5.21%, and 30%, respectively. With the increase of the amount of ground graphite tailings, the electric flux of quartz powder UHPC shows a monotonically increasing trend. When the replacement rate of ground graphite tailings is 25-50%, the overall change in the electric flux of quartz powder UHPC is small. The larger pores in the quartz powder UHPC matrix will be filled with fine ground graphite tailings particles, and the reduction of larger pores will help to reduce the penetration path of chloride ions in the quartz powder UHPC matrix to a certain extent. When the amount of ground graphite tailings continues to increase to 75%, the growth rate of the electric flux begins to increase rapidly, and the electric flux of quartz powder UHPC reaches its maximum value at 100% dosage.

[0098] Ecological and economic analysis: Fig.11 The radar chart in the figure clearly shows the ecological and economic indicators of using different proportions of ground graphite tailings to replace quartz powder to prepare UHPC. It can be clearly seen from the figure that compared with the example, CCI shows a downward trend in the low substitution rate (25% to 50%) range, but it rises sharply in the high substitution rate (75% to 100%) range.

[0099] The changing trends of CFI and CCI are similar. They decrease significantly at low substitution rates (25% to 50%). As the substitution rate increases, their carbon emissions first gradually approach those of the embodiment and then show a gradual upward trend.

[0100] The replacement of 25-50% of ground graphite tailings powder has a significant effect on reducing the carbon emissions per unit compressive strength and unit flexural strength, and performs well in carbon emission control; in terms of economy, NCI steadily decreases from 1 in the baseline group embodiment to 0.855 in comparative example four. This trend strongly proves that increasing the proportion of graphite tailings powder can effectively reduce material costs.

[0101] Cp gradually decreases from 39.84 in Example 1 to 36.07 in Comparative Example 4, showing a relatively stable downward trend, which further indicates that the use of ground graphite tailings instead of quartz powder can effectively reduce the cost required for unit compressive strength.

[0102] XRD: The XRD diffraction peak patterns of quartz powder UHPC with different amounts of ground graphite tailings are as follows Fig.12As shown. Analysis of the spectrum shows that in the test piece embodiment to comparative example four, the main phases all contain calcium sulfonate, SiO2, Ca(OH)2, C3S and C2S. Among them, calcium sulfonate and Ca(OH)2 are cement hydration products, SiO2 mainly comes from raw materials, and C3S and C2S are cement clinkers that have not yet been hydrated in the UHPC matrix. With the increase of the replacement rate of ground graphite tailings, the intensity of the SiO2 diffraction peak near 26.9° shows a trend of gradual decrease, and when the ground graphite tailings replace the quartz powder by more than 50%, the intensity of the diffraction peak is significantly weakened. Moreover, it can be found from the spectrum that after the addition of ground graphite tailings, the intensity of the Ca(OH)2 diffraction peak of UHPC near 34.6° decreases. This is because although the main component of quartz powder is SiO2, its activity is low under normal temperature conditions and it is not easy to react directly with Ca(OH)2 in the hydrate. The activity index of graphite tailings after 15 minutes of ball milling and particle refinement reached 60.72% at 28 days, exceeding that of quartz powder. This indicates that after the ground graphite tailings replaced quartz powder and were added to UHPC, a certain volcanic ash effect may have been produced, which in turn consumed Ca(OH)2 and ultimately led to a decrease in the diffraction peak intensity of Ca(OH)2.

[0103] Comprehensive analysis: The wet bulk density of quartz powder UHPC shows a linear monotonically decreasing trend with the increase of ground graphite tailings. The addition of 25% to 50% ground graphite tailings can ensure the wet bulk density to the greatest extent and has a small impact on the density of UHPC. 500 To a certain extent, it can reflect the consistency and filling rate of the concrete mixture slurry. Comparative Examples 1 to 4 all have different degrees of decline compared with the embodiment. Among them, the ground graphite tailings are added with 25% to 50%, and the T of UHPC 500There is a significant decline, indicating that the filling rate of the concrete mixture is enhanced at this dosage. Compared with the electric flux of comparative examples 1 to 4, the electric flux of the embodiment shows a monotonically increasing trend. The electric flux of UHPC increases with the increase of the dosage of ground graphite tailings. The dosage of 25% to 50% of ground graphite tailings has little effect on the porosity of ultra-high performance concrete. The overall change of the electric flux of quartz powder UHPC is small. The larger pores in the quartz powder UHPC matrix will be filled with fine ground graphite tailings particles. The reduction of larger pores will help to reduce the penetration path of chloride ions in the quartz powder UHPC matrix to a certain extent, ensuring the strength of UHPC. The addition of 25% ground graphite tailings can not only improve the 28d compressive and flexural strength of quartz powder UHPC, making quartz powder UHPC have better mechanical properties, but also effectively reduce its production cost and carbon emissions. Compared with the embodiment, the unit cement contribution strength is higher at a low substitution rate (25% to 50%), but the strength contribution rate continues to decrease at a high substitution rate (75% to 100%). This fully demonstrates that the substitution rates of Comparative Examples 1 and 2 can not only effectively reduce cement consumption, but also maintain a relatively considerable strength contribution. Within the substitution rate range of 75% to 100%, although the material cost and unit compressive strength cost of quartz powder UHPC are significantly reduced, it is also accompanied by a substantial increase in unit strength carbon emissions and a continuous decline in the cement strength contribution index, which has a serious negative impact on ecological performance. Based on the above analysis, the replacement rate of 25% to 50% of ground graphite tailings shows an excellent performance balance in all aspects, and can be considered to be the best balance between strength, ecological performance and economic cost.

Claims

1. An ultra-high performance concrete based on high-value utilization of ground graphite tailings, characterized in that The concrete consists 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 microspheres, 136-150 parts of silica fume, 30-32 parts of water reducer, 2 parts of defoamer and 171-189 parts of water by mass.

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

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

4. The ultra-high performance concrete based on high-value utilization of ground graphite tailings according to claim 1 is characterized in that The ground graphite tailings are obtained by grinding the graphite tailings using a YXQM-1L high-throughput planetary ball mill at a ball mill speed of 600 r / min and a ball-to-material ratio of 1:

1. The grinding time is 15 min. The bulk density of the graphite tailings is 1328 kg / m 3 , apparent density is 2902kg / m 3 , moisture content is 0.411%, and mud content is 2.5%.

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

6. The ultra-high performance concrete based on high-value utilization of ground graphite tailings according to claims 4 and 5 is characterized in that The gradation of the ground graphite tailings is as follows: the passing rate of 257 μm sieve is 100%, the passing rate of 125 μm sieve is 78%, the passing rate of 88 μm sieve is 63%, the passing rate of 61 μm sieve is 51%, the passing rate of 43 μm sieve is 41%, the passing rate of 30 μm sieve is 34%, the passing rate of 21 μm sieve is 27%, the passing rate of 14 μm sieve is 21%, and the passing rate of 6 μm sieve is 9%; the gradation of the quartz powder is as follows: the passing rate of 257 μm sieve is 100%, the passing rate of 125 μm sieve is 94%, the passing rate of 88 μm sieve is 78%, the passing rate of 61 μm sieve is 53%, the passing rate of 43 μm sieve is 28%, the passing rate of 30 μm sieve is 10%, the passing rate of 21 μm sieve is 3%, the passing rate of 14 μm sieve is 0.6%, and the passing rate of 6 μm sieve is 0%.

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

8. The ultra-high performance concrete based on 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 28d compressive strength of 55.62MPa, a 28d flexural strength of 7.1MPa, and a density of 3111kg / m 3 The properties of the silica fume are: water requirement ratio is 122%, loss on ignition ratio is 1.52%, and apparent density is 2236kg / m 3 , the specific surface area is 11078m 2 / kg, 28d activity index is 144%; the micro-beads have the following properties: water requirement ratio is 83%, ignition loss ratio is 0.3%, apparent density is 2539kg / m 3 , with a specific surface area of ​​2208m 2 / kg, and the activity index at 28 days was 101%.

9. The ultra-high performance concrete based on high-value utilization of ground graphite tailings according to claim 1, characterized in that The water reducing agent is a polycarboxylic acid high-efficiency water reducing agent, the water reducing rate is measured to be 30%, the solid content is 25%, and it is a light yellow powder; the defoaming agent is a white powder.

10. A method for preparing ultra-high performance concrete based on high-value utilization of ground graphite tailings as claimed in claim 1, characterized in that The preparation method of ultra-high performance concrete based on high-value utilization of ground graphite tailings is specifically carried out in the following steps:

1. Weigh 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 reducer, 2 parts of defoamer and 171-189 parts of water as raw materials by mass; 2. Add cement, silica fume, microbeads and graphite tailings into the mixer to obtain aggregates, and pre-mix the aggregates for 120 seconds at a rotation speed of 60 r / min to make the aggregates dry-mixed evenly; 3. Mix the water reducer, defoamer and water to obtain an admixture mixture, divide the admixture mixture into two parts according to the mass ratio of 80% and 20%, add 80% of the admixture mixture into the mixer, stir for 180 seconds at a speed of 60 r / min, stop stirring, add 20% of the admixture mixture into the mixer, stir for 300 seconds at a speed of 60 r / min, turn off the mixer, discharge the materials, prepare test pieces, and perform curing to obtain ultra-high performance concrete based on high-value utilization of ground graphite tailings.

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