Sintering-free artificial aggregate ultra-high performance concrete doped with iron tailings and preparation method of sintering-free artificial aggregate ultra-high performance concrete

Abstract

The invention provides iron tailing-doped sintering-free artificial aggregate ultra-high performance concrete and a preparation method thereof. The concrete is prepared from the following components: cement, silica fume, quartz sand, iron tailing sintering-free artificial aggregate, steel fibers, nano silicon dioxide, polyacrylamide, a silane coupling agent, an air entraining agent, a retarder, a water reducing agent and water. Wherein the mass ratio of the quartz sand to the iron tailing sintering-free artificial aggregate is (10-15): 1, the iron tailing sintering-free artificial aggregate further needs to be treated by a composite exciting agent and carbonized, and the composite exciting agent comprises water glass, NaOH, a sulfate exciting agent and triethanolamine. According to the concrete, the iron tailing sintering-free artificial aggregate is used for replacing part of natural aggregate, so that the problems of iron tailing stockpiling and environmental pollution are effectively solved, the resource utilization of industrial solid wastes is realized, the exploitation of natural gravel resources is reduced, the damage to the ecological environment is reduced, and the cost is reduced. And the method has remarkable environmental protection benefits and social benefits.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete production, and in particular relates to an ultra-high performance concrete containing iron tailings-added sinter-free artificial aggregate and a preparation method thereof. Background Art

[0002] Iron tailings are industrial waste products discharged after raw ore is crushed, ground, and magnetically separated to extract iron concentrate. With rapid economic development, demand for steel products is growing, and the resulting iron tailings generated during the beneficiation process is increasing. Large amounts of fine iron tailings mud accumulate in tailings dams, which not only consume significant land resources but also carry heavy metals that flow into the ground with rainwater, causing heavy metal contamination of soil and groundwater. Furthermore, the potential for tailings dam failures poses a significant threat to life and property. Therefore, research on the resource utilization of iron tailings is currently receiving widespread attention.

[0003] Studies have shown that some properties of iron tailings sludge are similar to those of building materials. Currently, iron tailings are mainly used to prepare building blocks, bricks, ceramics and microcrystalline glass, but their absorption capacity is small and insufficient to absorb the large amount of stockpiled iron tailings sludge. It has little effect on solving the environmental and social problems caused by the storage of iron tailings sludge. Summary of the Invention

[0004] In view of this, the present invention aims to propose an ultra-high performance concrete added with iron tailings unsintered artificial aggregate and a preparation method thereof, and uses the iron tailings unsintered artificial aggregate to replace part of the natural aggregate, which not only effectively solves the storage and environmental pollution problems of iron tailings and realizes the resource utilization of industrial solid waste, but also reduces the exploitation of natural sand and gravel resources and reduces the damage to the ecological environment, with significant environmental and social benefits.

[0005] To achieve the above object, the technical solution of the present invention is achieved as follows: Disclosed is an ultra-high performance concrete added with sinter-free artificial aggregate from iron tailings. The concrete comprises the following components, by weight: 600-700 parts of cement, 150-200 parts of silica fume, 1000-1200 parts of quartz sand, 50-150 parts of sinter-free artificial aggregate from iron tailings, 100-200 parts of steel fiber, 3-9 parts of nano-silicon dioxide, 0.6-1.8 parts of polyacrylamide, 1-3 parts of a silane coupling agent, 0.06-0.3 parts of an air entraining agent, 0.6-1.8 parts of a retarder, 10-40 parts of a water reducer, and 160-220 parts of water. The mass ratio of quartz sand to sinter-free artificial aggregate from iron tailings is (10-15):1. The sinter-free artificial aggregate from iron tailings is further treated with a composite activator and carbonized. The composite activator comprises water glass, NaOH, a sulfate activator, and triethanolamine.

[0006] Cement, silica fume, and nano-silica are the cementitious materials, while quartz sand and iron ore tailings unsintered artificial aggregate are the aggregates. The cement serves as the matrix, while the silica fume fills the gaps between cement particles. The nano-silica fills the micropores between the silica fume and cement, increasing the density of the cementitious system.

[0007] Quartz sand provides a high-strength skeleton, and the iron tailings aggregate, after treatment, has both inert filling and active participation - the CaCO3 layer on its surface reacts with the cement paste to generate CSH, achieving chemical bonding at the "aggregate-cementitious" interface and avoiding the "weak interface" problem of traditional aggregates.

[0008] Furthermore, the iron tailings-free sintered artificial aggregate is prepared from the following raw materials in percentage by weight: 50%-80% iron tailings powder, 5%-25% activator, 1%-15% inert filler, and 5%-30% auxiliary binder. The auxiliary binders include cement, fly ash, mineral powder, and silica fume, and the activators include calcium hydroxide and water glass. The iron tailings-free sintered artificial aggregate utilizes the iron tailings-based artificial high-strength fine aggregate proposed in patent application number CN202311054552.6.

[0009] Furthermore, the cement is Portland cement, and the strength grade of the cement is 42.5 or 52.5; the Portland cement should comply with the requirements of the national standard GB 175-2007 to ensure its quality stability and compatibility with the concrete system of the present invention; The strength grade of silica fume is 95 or 92, and the particle size distribution range of silica fume is 0.1-1.0μm, of which particles with a size less than 0.5μm account for no less than 80%. This allows for more precise control of the microstructure of silica fume, thereby better exerting its pozzolanic effect in concrete. The particle size distribution range of nano-silica should be 10-100nm to better play its filling and reinforcing role in concrete, and the specific surface area should be greater than 100m 2 / g to improve its dispersibility and activity in concrete, and the purity should be no less than 99% to ensure its quality stability and effect in concrete.

[0010] Furthermore, the particle size of the quartz sand is in the range of 0.315-2.50 mm, and the shape of the quartz sand is well-shaped spherical or nearly spherical particles to reduce friction resistance between particles and improve the fluidity of the concrete. The mud content in the quartz sand does not exceed 0.5%, and the mica content does not exceed 0.3% to ensure the workability and durability of the concrete. The iron tailings sinter-free artificial aggregate is spherical particles with a particle size range of 1.25-2.50mm. The chemical composition of the iron tailings sinter-free artificial aggregate contains SiO2 content of not less than 40%, Al2O3 content of not less than 10%, and Fe2O3 content of not more than 15%, to ensure its good chemical stability and compatibility with the cement matrix. Before use, the iron tailings sinter-free artificial aggregate is cleaned with anionic surfactant to remove surface dust and impurities to improve its bonding strength with the cement matrix.

[0011] The artificial aggregate can play an internal curing role due to its porous structure. Its uniform spherical shape can optimize the rheological properties of the mixture and improve the uniformity and orientation of the fiber distribution in the matrix.

[0012] Furthermore, the specific processing method of iron tailings sinter-free artificial aggregate is as follows: S1. Composite activator treatment Spray the iron tailings sinter-free artificial aggregate with a composite activator solution containing water glass, NaOH, sulfate activator and triethanolamine for 3-4 hours at a temperature of 20-40°C; the water glass content is 5-8wt%, the NaOH content is 2-4wt%, the sulfate activator content is 1-2wt%, and the triethanolamine content is 1-2wt%. S2. Carbonization treatment The iron tailings sinter-free artificial aggregate treated with the composite activator is placed in a CO2 environment at a temperature of 50-60°C, a humidity of 80-95%, and a pressure of 2-4MPa for carbonization for 4-8 hours.

[0013] In the composite activator treatment, water glass and NaOH form a high alkaline environment, which directionally destroys the Si-O bond of the aluminosilicate glass in the iron tailings, thereby increasing the amount of active SiO2 dissolved; the sulfate activator introduces SO4 2- , and Ca 2+ The reaction generates ettringite, which fills the pores on the aggregate surface; triethanolamine accelerates cement hydration through complexation, and the three work together to increase the active sites on the aggregate surface, providing sufficient Ca for the subsequent carbonization reaction. 2+ source.

[0014] Carbonization treatment "densification finishing": CO2 quickly penetrates into the aggregate, and reacts with Ca(OH)2 generated after excitation and Ca in CSH. 2+ The reaction generates CaCO3 crystals, forming a triple filling structure of "ettringite-CSH-calcium carbonate". This process reduces the porosity of the aggregate, increases the surface hardness, and improves the interfacial bonding strength with the cement paste.

[0015] Furthermore, the steel fiber is a stainless steel fiber or a high-strength carbon steel fiber with good corrosion resistance, a length of 10-30 mm, a diameter of 0.2-0.5 mm, and a tensile strength of not less than 600 MPa to enhance the crack resistance and toughness of the concrete. The surface of the steel fiber can also be copper-plated or epoxy-coated to prevent rust during the concrete mixing process, which may affect the performance of the concrete.

[0016] Furthermore, the molecular weight of polyacrylamide is 10 million to 20 million to ensure that it has good thickening and dispersing properties and improves the fluidity and workability of concrete, and the ionicity is 10% to 30% to adjust its adsorption and dispersion effects in concrete.

[0017] Furthermore, the silane coupling agent is one or more of KH550, KH560, and KH570; the specific type should be selected according to the performance requirements of the concrete and the properties of the raw materials, the purity should be no less than 98% to ensure its quality stability and effect in the concrete, and the active group content should be no less than 10% to improve its chemical bonding ability with quartz sand, iron tailings unsintered artificial aggregate and cement matrix, thereby enhancing the interface strength of the concrete; The air-entraining agent should be one or more of rosin thermopolymer air-entraining agent, alkylbenzene sulfonate air-entraining agent or synthetic air-entraining agent. The foaming capacity should be no less than 50% (volume increase rate). The introduced bubbles should have good stability in the concrete, and the bubble half-life should be no less than 60 minutes. The air-entraining agent should have good compatibility with other components such as cement, silica fume, nano-silica, and should not produce chemical reactions or negative effects. The retarder is one or more of a sugar retarder (such as sucrose, sodium gluconate), a lignin sulfonate retarder, or a polycarboxylate retarder. The retarder should be able to extend the initial setting time of concrete to no less than 4 hours and the final setting time to no less than 6 hours. The retarder should have a certain water-reducing function, with a water-reducing rate of no less than 10%. The retarder should have good compatibility with other components such as cement, silica fume, nano-silica, and should not produce chemical reactions or negative effects. The water reducer is a polycarboxylic acid-based high-efficiency water reducer, which is a light yellow viscous liquid with a water reduction rate of 35% and a solid content of 40%.

[0018] The present invention also provides a method for preparing the ultra-high performance concrete containing the iron tailings-added sinter-free artificial aggregate as described above, the method comprising the following steps: 1. First, the iron tailings sinter-free artificial aggregate is treated with a composite activator and carbonized; 2. Pour quartz sand, iron tailings sinter-free artificial aggregate, cement, silica fume, nano-silica, polyacrylamide and silane coupling agent into a concrete mixer and stir; 3. Pre-mix the air entraining agent, retarder and water reducer with water, then pour them into the concrete mixer and mix evenly; 4. Slowly pour the steel fiber into the concrete mixer at a speed of 0.5-1.0 kg / min. Keep the mixer stirring at a low speed of 20-30 r / min during the addition process to prevent the steel fiber from agglomerating and ensure that it is evenly distributed in the concrete mixture. After all the steel fiber is poured in, stir for another 2-5 minutes to ensure that the steel fiber is evenly distributed in the mixture. 5. Put the evenly mixed concrete into the test mold, vibrate the mold on a vibration table, and cure the test piece.

[0019] Furthermore, in step 2, the stirring speed is 30-50 r / min, the stirring time is 4-10 min, and the temperature during the stirring process is 10-30°C to prevent the performance of the concrete from being affected by excessively high or low temperature; in step 3, the stirring speed is 40-60 r / min, and the stirring time is 3-8 min.

[0020] Furthermore, in step three, the premixing time is not less than 2 minutes, and a high-speed stirrer is used for sufficient stirring to ensure that the water reducer is evenly dispersed in the water, thereby improving the dispersion effect of the water reducer and the working performance of the concrete.

[0021] Furthermore, in step 5, the vibration molding time is 10-30 seconds, the vibration frequency is 30-50 Hz, and the amplitude is 0.5-1.0 mm to ensure the density and molding quality of the concrete specimen; the test mold should be a standard size concrete test mold, and a thin layer of release agent should be applied to the inner wall of the test mold to facilitate demolding of the specimen and ensure the appearance quality of the specimen; The curing method is steam curing and / or standard curing; The iron tailings sinter-free artificial aggregate treated in step 1 is surface cleaned using an anionic surfactant.

[0022] Furthermore, during steam curing, the specimens were placed under constant temperature and humidity conditions for 24 hours before being demolded and immediately placed in a curing box. They were cured at 45°C for 2 hours, then raised to 60°C for 2 hours, and finally raised to 75°C for 68 hours. During the steam curing process, the humidity in the curing box should be maintained at 90%-95% to prevent shrinkage cracks on the concrete surface. Standard curing could then be carried out.

[0023] Furthermore, during standard curing, the curing temperature is 20±1℃ and the humidity RH≥95%. During the standard curing process, the surface of the specimen in the curing room should be sprayed with moisturizing spray regularly to ensure that the surface of the specimen is always kept moist.

[0024] Compared with the prior art, the ultra-high performance concrete with iron tailings added and sinter-free artificial aggregate of the present invention has the following advantages: (1) The ultra-high performance concrete with iron tailings unsintered artificial aggregate of the present invention replaces part of the quartz sand with iron tailings unsintered artificial aggregate. The iron tailings unsintered artificial aggregate can play a good internal curing role in concrete. At the same time, the strengthening effect on the matrix-aggregate interface transition zone and the volcanic ash activity of the artificial aggregate itself will compact the microstructure of the ultra-high performance concrete, thereby improving the mechanical properties and durability of the concrete. At the same time, the spherical particle shape of the artificial aggregate will also optimize the rheological properties of the concrete mixture, such as yield stress and plastic viscosity, thereby improving the uniformity and orientation of the fiber distribution in the concrete, and thus improving the crack resistance of the concrete. Replacing part of the quartz sand with iron tailings unsintered artificial aggregate reduces the consumption of quartz sand and the production cost of ultra-high performance concrete, making the prepared ultra-high performance concrete more economical.

[0025] (2) The present invention utilizes iron tailings unsintered artificial aggregate to replace quartz sand in the preparation of ultra-high performance concrete. On the one hand, this reduces the preparation cost of ultra-high performance concrete, reduces the amount of quartz sand used, and thus reduces mining, thus protecting natural resources. On the other hand, the iron tailings unsintered artificial aggregate is made from iron tailings fine mud. There is no sintering process in the preparation of artificial aggregate, which saves a lot of energy consumption while absorbing a large amount of iron tailings fine mud. This solves the threats to the natural environment caused by the storage of iron tailings mud, such as dam collapse, occupation of land resources, and pollution of soil and groundwater. Compared with other treatment methods, the use of iron tailings fine mud in the preparation of iron tailings unsintered artificial aggregate in ultra-high performance concrete is safer and more reliable, has a huge absorption capacity, and can give full play to the material advantages of artificial aggregate itself. The process adopted by the present invention is simple, highly operable, and has a wide range of applications.

[0026] (3) The ultra-high performance concrete prepared by the present invention using the iron tailings unsintered artificial aggregate instead of quartz sand has good mechanical properties. The prepared concrete specimens have a 3-day compressive strength of >60MPa, a 7-day compressive strength of >80MPa, and a 28-day compressive strength of >130MPa. The microscopic test results show that the microstructure of the concrete matrix added with the iron tailings artificial aggregate is denser, the pore structure is finer, and the interface transition zone is denser. The prepared ultra-high performance concrete has excellent performance and is green and environmentally friendly, with both environmental and economic advantages, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings: Figure 1Comparison of relative humidity of concrete prepared in Examples 1-2 of the present invention and the comparative example; Figure 2 The microscopic morphology of the concrete specimen prepared in Example 1; Figure 3 The microscopic morphology of the concrete specimen prepared in Example 2; Figure 4 This is the microscopic morphology of the concrete specimen prepared in Comparative Example 1. DETAILED DESCRIPTION

[0028] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] Example 1 An ultra-high performance concrete with iron tailings-added sinter-free artificial aggregate comprises the following components: gel material: 600 parts of ordinary Portland cement, 160 parts of silica fume and 4 parts of nano-silicon dioxide; Aggregate: 1000 parts quartz sand, 75 parts iron ore tailings unsintered artificial aggregate; Steel fiber: 100 parts; Polyacrylamide: 0.9 parts; Silane coupling agent: 1 part; Air entraining agent: 0.1 part; Retarder: 0.6 parts; Water reducer: 15 parts, polycarboxylic acid-based high-efficiency water reducer; Water: 170 parts.

[0031] Among them, the strength grade of ordinary Portland cement is PO 42.5, the strength grade of silica fume is 95, the particle size distribution range of silica fume is 0.1-1.0μm, of which the particle size less than 0.5μm accounts for no less than 80%; the particle size distribution range of nano-silicon dioxide should be 20-30nm, and the specific surface area should be greater than 100m 2 / g, purity not less than 99%.

[0032] The particle size of quartz sand ranges from 1.25 to 2.50 mm. The shape of quartz sand is well-shaped spherical or nearly spherical particles. The mud content in quartz sand does not exceed 0.5%, and the mica content does not exceed 0.3%. The iron tailings-free sintered artificial aggregate uses the iron tailings-based artificial high-strength fine aggregate proposed in application number CN202311054552.6. It is prepared from the following raw materials by weight: 50%-80% iron tailings powder, 5%-25% activator, 1%-15% inert filler, and 5%-30% auxiliary binder. The auxiliary binder is composed of cement, fly ash, mineral powder, and silica fume, and the activator is composed of calcium hydroxide and water glass.

[0033] The iron tailings sinter-free artificial aggregate is spherical particles with a particle size range of 1.25-2.50mm. The chemical composition of the iron tailings sinter-free artificial aggregate contains SiO2 content of not less than 40%, Al2O3 content of not less than 10%, and Fe2O3 content of not more than 15%. Before use, the iron tailings sinter-free artificial aggregate is cleaned with an anionic surfactant sodium dodecylbenzene sulfonate (0.8% concentration) to remove floating dust and impurities on the surface.

[0034] The steel fiber is a stainless steel fiber with a length of 10 mm, a diameter of 0.2 mm, and a tensile strength of not less than 600 MPa.

[0035] The molecular weight of polyacrylamide is 12 million and the ionicity is 15%.

[0036] The silane coupling agent is KH550, the air entraining agent is a rosin thermal polymer air entraining agent, and the retarder is a sugar retarder sodium gluconate.

[0037] The preparation method of the above-mentioned ultra-high performance concrete with iron tailings-added sinter-free artificial aggregate is as follows: (1) Pretreatment of iron tailings-free artificial aggregate (1-1) Composite activator treatment A composite activator solution containing 5wt% water glass, 2wt% NaOH, 1wt% sulfate activator Na2SO4 and 1wt% triethanolamine was sprayed on the iron tailings sinter-free artificial aggregate for 3 hours at a temperature of 25°C. (1-2) Carbonization treatment The iron tailings sinter-free artificial aggregate treated with the composite activator was placed in a CO2 environment at a temperature of 50°C, a humidity of 80%, and a pressure of 2 MPa for 4.5 hours of carbonization. (1-3) Surface treatment Use anionic surfactant sodium dodecylbenzene sulfonate (0.8% concentration) to clean the surface and remove dust and impurities; (2) First, pour quartz sand, iron tailings unsintered artificial aggregate, ordinary Portland cement, silica fume, nano-silica, polyacrylamide, and silane coupling agent into a concrete mixer at the same time, and stir at 30 r / min for 4 minutes. The temperature during the stirring process is 25°C; (3) Premix water, polycarboxylic acid-based high-efficiency water reducer, air entraining agent, and retarder for 2 minutes, then pour into a concrete mixer and stir at 60 r / min for 8 minutes; (4) Slowly pour the steel fiber into the concrete mixer. The addition speed of the steel fiber is controlled at 0.5 kg / min. During the addition process, the mixer is kept stirring at a low speed of 20 r / min to prevent the steel fiber from agglomerating and ensure that it is evenly distributed in the concrete mixture. After all the steel fibers are poured in, stir for another 2 minutes to ensure that the steel fibers are evenly distributed in the mixture. (5) The concrete mixture is placed in a test mold, and the test mold is vibrated on a vibration table; the vibration molding time is 20 seconds, the vibration frequency is 35 Hz, and the amplitude is 0.5 mm; (6) The specimens were cured using standard curing. The specimens were placed under constant temperature and humidity for 24 hours before demolding. Standard curing was then performed until the specimens reached the respective age stages. The curing temperature was 20±1°C and the humidity was ≥95%.

[0038] The prepared ultra-high performance concrete has a dense structure, a slump of 240 mm, a slump spread of 540 mm, a 3-day compressive strength of 67 MPa, a 7-day compressive strength of 85 MPa, a 28-day compressive strength of 136 MPa, a 28-day flexural strength of 21 MPa, a 28-day tensile strength of 6.5 MPa, a 28-day elastic modulus of 44 MPa, and a chloride ion diffusion coefficient of 0.12×10 -12 m 2 / s, drying shrinkage is 210×10 -6 The performance, mechanical properties and durability of the mixture all meet the relevant requirements of national standards and industry standards.

[0039] Example 2 An ultra-high performance concrete with iron tailings-added sinter-free artificial aggregate comprises the following components: gel material: 700 parts of ordinary Portland cement, 200 parts of silica fume and 7 parts of nano-silicon dioxide; Aggregate: 1200 parts of quartz sand, 120 parts of iron ore tailings unsintered artificial aggregate; Steel fiber: 180 parts; Polyacrylamide: 1.5 parts; Silane coupling agent: 3 parts; Air entraining agent: 0.25 parts; Retarder: 1.7 parts; Water reducing agent: 30 parts, polycarboxylic acid-based high-efficiency water reducing agent; Water: 210 parts.

[0040] Among them, the strength grade of ordinary Portland cement is PO 42.5, the strength grade of silica fume is 95, the particle size distribution range of silica fume is 0.1-1.0μm, of which the particle size less than 0.5μm accounts for no less than 80%; the particle size distribution range of nano-silicon dioxide should be 30-40nm, and the specific surface area should be greater than 100m 2 / g, purity not less than 99%.

[0041] The particle size of quartz sand ranges from 1.25 to 2.50 mm. The shape of quartz sand is well-shaped spherical or nearly spherical particles. The mud content in quartz sand does not exceed 0.5%, and the mica content does not exceed 0.3%. The iron tailings-free sintered artificial aggregate uses the iron tailings-based artificial high-strength fine aggregate proposed in application number CN202311054552.6. The iron tailings-free sintered artificial aggregate is spherical with a particle size range of 1.25-2.50 mm. Its chemical composition contains no less than 40% SiO2, no less than 10% Al2O3, and no more than 15% Fe2O3. Before use, the surface of the iron tailings-free sintered artificial aggregate is cleaned with the anionic surfactant sodium dodecylbenzenesulfonate (0.8% concentration) to remove surface dust and impurities.

[0042] The steel fiber is a carbon steel fiber with a length of 15 mm, a diameter of 0.3 mm, and a tensile strength of not less than 600 MPa.

[0043] The molecular weight of polyacrylamide is 15 million and the ionicity is 20%.

[0044] The silane coupling agent is KH560, the air entraining agent is an alkylbenzene sulfonate air entraining agent, and the retarder is a lignin sulfonate retarder.

[0045] The preparation method of the above-mentioned ultra-high performance concrete with iron tailings-added sinter-free artificial aggregate is as follows: (1) Pretreatment of iron tailings-free artificial aggregate (1-1) Composite activator treatment A composite activator solution containing 8wt% water glass, 4wt% NaOH, 2wt% sulfate activator Na2SO4 and 1.5wt% triethanolamine was sprayed on the iron tailings sinter-free artificial aggregate for 4 hours at a temperature of 38°C. (1-2) Carbonization treatment The iron tailings sinter-free artificial aggregate treated with the composite activator was placed in a CO2 environment at a temperature of 60°C, a humidity of 92%, and a pressure of 4 MPa for 7 hours of carbonization. (1-3) Surface treatment Use anionic surfactant sodium dodecylbenzene sulfonate (0.8% concentration) to clean the surface and remove dust and impurities; (2) First, pour quartz sand, iron tailings unsintered artificial aggregate, ordinary Portland cement, silica fume, nano-silica, polyacrylamide, and silane coupling agent into a concrete mixer at the same time, and stir at 30 r / min for 4 minutes. The temperature during the stirring process is 25°C; (3) Premix water, polycarboxylic acid-based high-efficiency water reducer, air entraining agent, and retarder for 2 minutes, then pour into a concrete mixer and stir at 60 r / min for 8 minutes; (4) Slowly pour the steel fiber into the concrete mixer. The addition speed of the steel fiber is controlled at 0.9 kg / min. During the addition process, the mixer is kept stirring at a low speed of 30 r / min to prevent the steel fiber from agglomerating and ensure that it is evenly distributed in the concrete mixture. After all the steel fibers are poured in, stir for another 2 minutes to ensure that the steel fibers are evenly distributed in the mixture. (5) The concrete mixture is placed in a test mold, and the test mold is vibrated on a vibration table; the vibration molding time is 20 seconds, the vibration frequency is 40 Hz, and the amplitude is 1.0 mm; (6) The curing method of the specimen is to first perform steam curing: the specimen is placed under constant temperature and humidity conditions for 24 hours, then demolded and immediately placed in a curing box. It is cured at 45°C for 2 hours, then raised to 60°C for 2 hours, and finally raised to 75°C for 68 hours. During the steam curing process, the humidity in the curing box should be maintained at 90-95% to prevent shrinkage cracks on the concrete surface. Standard curing can then be carried out.

[0046] During standard curing, the curing temperature is 20±1℃ and the humidity RH≥95%. During the standard curing process, the surface of the specimens in the curing room should be sprayed with moisturizing spray regularly to ensure that the surface of the specimens remains moist at all times.

[0047] The prepared ultra-high performance concrete has a dense structure, a slump of 250 mm, a slump spread of 550 mm, a 3-day compressive strength of 64 MPa, a 7-day compressive strength of 81 MPa, a 28-day compressive strength of 134 MPa, a 28-day flexural strength of 23 MPa, a 28-day tensile strength of 6.1 MPa, a 28-day elastic modulus of 41 MPa, and a chloride ion diffusion coefficient of 0.13×10 -12 m 2 / s, drying shrinkage is 220×10 -6 The performance, mechanical properties and durability of the mixture all meet the relevant requirements of national standards and industry standards.

[0048] Comparative Example 1: Sintering-free artificial aggregate without adding iron tailings An ultra-high performance concrete with iron tailings-added sinter-free artificial aggregate comprises the following components: gel material: 600 parts of ordinary Portland cement, 160 parts of silica fume and 4 parts of nano-silicon dioxide; Aggregate: 1075 parts of quartz sand; Steel fiber: 100 parts; Polyacrylamide: 0.9 parts; Silane coupling agent: 1 part; Air entraining agent: 0.1 part; Retarder: 0.6 parts; Water reducer: 15 parts, polycarboxylic acid-based high-efficiency water reducer; Water: 170 parts.

[0049] The preparation is the same as Example 1.

[0050] The relative humidity change curves inside the ultra-high performance concrete specimens of Examples 1-2 and Comparative Example 1 are as follows: Figure 1 It can be seen that the addition of iron tailings unsintered artificial aggregate can effectively delay the decrease of relative humidity inside the concrete matrix and play a good role in internal curing.

[0051] The microscopic morphology of the concrete specimens of Example 1, Example 2 and Comparative Example 1 is as follows: Figure 2-4 As shown in the figure, the addition of iron tailings unsintered artificial aggregate does not affect the density of the concrete matrix, and the microstructure of the concrete matrix added with iron tailings artificial aggregate is denser, the pore structure is finer, and the interface transition zone is denser.

[0052] Comparative Example 2 The difference from the above-mentioned Example 1 is that the amount of the iron tailings sinter-free artificial aggregate is different, that is, 50 parts, and the mass ratio of quartz sand to the iron tailings sinter-free artificial aggregate is 20:1. Others are the same as in Example 1.

[0053] Comparative Example 3 The difference from the above-mentioned Example 1 is that the amount of the iron tailings sinter-free artificial aggregate is different, that is, 150 parts, and the mass ratio of quartz sand to the iron tailings sinter-free artificial aggregate is 6.7:1. Others are the same as in Example 1.

[0054] Comparative Example 4 The difference from the above-mentioned Example 1 is that the amount of the iron tailings sinter-free artificial aggregate is different, that is, 300 parts, and the rest is the same as Example 1.

[0055] Comparative Example 5 The difference from the above-mentioned Example 1 is that the iron tailings sinter-free artificial aggregate is not subjected to any pretreatment (ie, no composite activator treatment and carbonization treatment are performed), and the rest is the same as Example 1.

[0056] Comparative Example 6 The difference from the above-mentioned embodiment 1 is that the carbonization treatment is removed from the pretreatment of the sintering-free artificial aggregate of iron tailings, and the rest is the same as that of embodiment 1.

[0057] Comparative Example 7 The difference from the above-mentioned Example 1 is that the composite activator treatment is removed from the pretreatment of the sintering-free artificial aggregate of iron tailings, and the rest is the same as Example 1.

[0058] Comparative Example 8 The difference from the above-mentioned embodiment 1 is that the pretreatment steps of the iron tailings sinter-free artificial aggregate are different, namely, carbonization treatment is performed first, and then composite activator treatment is performed. The rest is the same as in embodiment 1.

[0059] Table 1 Performance comparison of various examples and comparative examples

[0060] By comparing Example 1 with Comparative Example 1, it can be seen that the addition of an appropriate amount of iron tailings-free sintered artificial aggregate can improve the mechanical properties and durability of ultra-high performance concrete, because the iron tailings-free sintered artificial aggregate can play an internal curing role in concrete. During the curing process of the concrete specimens, the water release effect of the iron tailings-free sintered artificial aggregate can cause the concrete matrix to undergo secondary hydration, thereby compacting the concrete matrix and making the concrete matrix denser, thereby improving the mechanical properties and durability of the concrete.

[0061] By comparing Example 1 with Comparative Examples 2-4, it can be seen that only by adding an appropriate amount of iron tailings-free sintered artificial aggregate can concrete with better performance be obtained, and adding excessive or insufficient iron tailings-free sintered artificial aggregate will reduce the mechanical properties and durability of ultra-high performance concrete; because the cylinder compressive strength of iron tailings-free sintered artificial aggregate is lower than the cylinder compressive strength of quartz sand, when excessive iron tailings-free sintered artificial aggregate is added, the side effect caused by the low strength of the artificial aggregate will be greater than the positive effect of the self-curing of the artificial aggregate, so the mechanical properties of the ultra-high performance concrete will be reduced, because the artificial aggregate has a porous structure, so excessive addition will reduce the overall density of the concrete, so excessive addition of artificial aggregate will reduce the durability of the concrete.

[0062] By comparing Example 1 with Comparative Examples 5-8, it can be seen that pretreatment can improve the performance of iron tailings artificial aggregate, thereby improving the mechanical properties and durability of the prepared ultra-high performance concrete. The lack of either the composite activator treatment or the carbonization treatment, or the lack of both treatments, will affect the performance of the concrete to varying degrees. This is because after the artificial aggregate is pretreated, the surface activity of the aggregate will be improved, the interfacial bonding strength with the cement paste will be enhanced, the porosity in the interface transition zone will be reduced, and the interface density and impermeability will be improved.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An ultra-high performance concrete containing iron tailings-free sintered artificial aggregate, characterized by: The concrete comprises the following components by weight: 600-700 parts of cement, 150-200 parts of silica fume, 1000-1200 parts of quartz sand, 50-150 parts of iron tailings unsintered artificial aggregate, 100-200 parts of steel fiber, 3-9 parts of nano-silicon dioxide, 0.6-1.8 parts of polyacrylamide, 1-3 parts of silane coupling agent, 0.06-0.3 parts of air entraining agent, 0.6-1.8 parts of retarder, 10-40 parts of water reducer, and 160-220 parts of water. The mass ratio of quartz sand to the iron tailings unsintered artificial aggregate is (10-15):1, and the iron tailings unsintered artificial aggregate is further treated with a composite activator and carbonized, and the composite activator comprises water glass, NaOH, a sulfate activator, and triethanolamine.

2. The ultra-high performance concrete containing iron tailings and sinter-free artificial aggregate according to claim 1, characterized in that: The iron tailings sinter-free artificial aggregate is prepared from raw materials including the following weight percentages: 50%-80% iron tailings powder, 5%-25% activator, 1%-15% inert filler, and 5%-30% auxiliary binder; wherein the auxiliary binder is cement, fly ash, mineral powder and silica fume, and the activator is calcium hydroxide and water glass.

3. The ultra-high performance concrete containing iron tailings and sinter-free artificial aggregate according to claim 1, characterized in that: The cement is silicate cement, and the strength grade of the cement is 42.5 or 52.5; The strength grade of silica fume is 95 or 92, and the particle size distribution range of silica fume is 0.1-1.0μm, of which particles with a size less than 0.5μm account for no less than 80%; The particle size distribution range of nano-silicon dioxide should be 10-100nm, and the specific surface area should be greater than 100m 2 / g, purity not less than 99%.

4. The ultra-high performance concrete containing sinter-free artificial aggregates added with iron tailings according to claim 1, characterized in that: The particle size of quartz sand ranges from 0.315 to 2.50 mm. The shape of quartz sand is well-shaped spherical or nearly spherical particles. The mud content in quartz sand does not exceed 0.5%, and the mica content does not exceed 0.3%. The iron tailings sinter-free artificial aggregate is spherical particles with a particle size range of 1.25-2.50mm. The chemical composition of the iron tailings sinter-free artificial aggregate contains SiO2 content of not less than 40%, Al2O3 content of not less than 10%, and Fe2O3 content of not more than 15%. Before use, the iron tailings sinter-free artificial aggregate is cleaned with anionic surfactant to remove floating dust and impurities on the surface.

5. The ultra-high performance concrete containing sinter-free artificial aggregates added with iron tailings according to claim 1, characterized in that: The specific treatment method of iron tailings sinter-free artificial aggregate is: S1. Composite activator treatment Spray the iron tailings sinter-free artificial aggregate with a composite activator solution containing water glass, NaOH, sulfate activator and triethanolamine for 3-4 hours at a temperature of 20-40°C; the water glass content is 5-8wt%, the NaOH content is 2-4wt%, the sulfate activator content is 1-2wt%, and the triethanolamine content is 1-2wt%. S2. Carbonization treatment The iron tailings sinter-free artificial aggregate treated with the composite activator is placed in a CO2 environment at a temperature of 50-60°C, a humidity of 80-95%, and a pressure of 2-4MPa for carbonization for 4-8 hours.

6. The ultra-high performance concrete containing iron tailings and sinter-free artificial aggregate according to claim 1, characterized in that: The steel fiber is stainless steel fiber or carbon steel fiber, with a length of 10-30 mm, a diameter of 0.2-0.5 mm, and a tensile strength of not less than 600 MPa.

7. The ultra-high performance concrete containing sinter-free artificial aggregates added with iron tailings according to claim 1, characterized in that: The molecular weight of polyacrylamide is 10 million to 20 million, and the ionicity is 10% to 30%; The silane coupling agent is one or more of KH550, KH560, and KH570; The air-entraining agent is one or more of rosin thermal polymer air-entraining agent, alkylbenzene sulfonate air-entraining agent or synthetic air-entraining agent; the foaming capacity of the air-entraining agent should be not less than 50%, and the bubble half-life should be not less than 60 minutes; The retarder is one or more of a sugar retarder, a lignin sulfonate retarder or a polycarboxylate retarder; The water reducer is a polycarboxylic acid-based high-efficiency water reducer, which is a light yellow viscous liquid with a water reduction rate of 35% and a solid content of 40%.

8. A method for preparing ultra-high performance concrete containing sinter-free artificial aggregates added with iron tailings according to any one of claims 1 to 7, characterized in that: The method comprises the following steps:

1. First, the iron tailings sinter-free artificial aggregate is treated with a composite activator and carbonized; 2. Pour quartz sand, iron tailings sinter-free artificial aggregate, cement, silica fume, nano-silica, polyacrylamide and silane coupling agent into a concrete mixer and stir; 3. Pre-mix the air entraining agent, retarder and water reducer with water, then pour them into the concrete mixer and mix evenly; 4. Slowly pour the steel fiber into the concrete mixer. The adding speed of steel fiber should be controlled at 0.5-1.0kg / min. During the adding process, keep the mixer stirring at a low speed of 20-30r / min. Stir for 2-5 minutes after all the steel fiber is poured in.

5. Put the evenly mixed concrete into the test mold, vibrate the mold on a vibration table, and cure the test piece.

9. The method for preparing ultra-high performance concrete containing sinter-free artificial aggregates added with iron tailings according to claim 8, characterized in that: In step 2, the stirring speed is 30-50 r / min, the stirring time is 4-10 min, and the temperature during the stirring process is 10-30° C.; in step 3, the stirring speed is 40-60 r / min, and the stirring time is 3-8 min.

10. The method for preparing ultra-high performance concrete containing sinter-free artificial aggregates added with iron tailings according to claim 8, characterized in that: In step 5, the vibration molding time is 10-30s, the vibration frequency is 30-50Hz, and the amplitude is 0.5-1.0mm; The curing method is steam curing and / or standard curing; The iron tailings sinter-free artificial aggregate treated in step 1 is surface cleaned using an anionic surfactant.

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