Red mud-based super-high-strength geopolymer concrete and preparation process thereof

Abstract

The application provides a red mud-based super-high-strength geopolymer concrete and a preparation method thereof, and belongs to the field of civil engineering materials. The concrete uses granulated blast furnace slag, fly ash, silica fume and red mud as a composite cementitious material, uses a sodium silicate solution as an alkali activator, and is reinforced by mixing in steel fibers. By optimizing the ratio of silica fume to red mud, the alkali content and the heat curing process, the problems of insufficient formation of geopolymer gel network and limited strength development caused by the separate or excessive use of red mud are solved. The concrete prepared by the application has a 28-day compressive strength of up to 147 MPa and a flexural strength of up to 14 MPa without the need for high-efficiency water reducing agents, realizes the resource utilization of red mud in a large amount and with high added value, and has the characteristics of high strength and environmental protection.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a geopolymer concrete prepared using red mud, an industrial solid waste, and particularly to a red mud-based polymer concrete with ultra-high strength and its preparation method. Background Technology

[0002] Geopolymers are inorganic polymer materials formed by activating siliceous alumina raw materials with alkali activators. They possess advantages such as high early strength, high temperature resistance, and corrosion resistance, and are considered a potential green alternative to ordinary silicate cement. Red mud is a highly alkaline solid waste discharged from the alumina industry, and its large-scale accumulation poses a serious threat to the environment. Applying red mud to geopolymer concrete can realize the resource utilization of solid waste, resulting in significant environmental and economic benefits.

[0003] However, when used alone, red mud exhibits low activity, high water demand, and significant shrinkage, resulting in slow strength development and poor durability in the prepared geopolymer concrete. Existing technologies often employ mechanical activation, chemical activation, or compounding with other admixtures to improve its performance; however, the composition is generally not optimized. Especially when compounded with highly active silica fume, the ratio of the two is often determined empirically, and no technology has been developed to deeply explore their interaction relationship and synergistic effect range. Therefore, existing technologies struggle to simultaneously achieve both high strength and high workability in these materials. Summary of the Invention

[0004] The present invention aims to solve the shortcomings of the existing technology in the control of the ratio of silica fume to red mud and the problem of synergy with other processes, as well as to avoid the technical problems of dependence on high-efficiency water-reducing agents and high alkali content in the preparation of ultra-high strength polymer concrete in the existing technology.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A red mud-based ultra-high strength geopolymer concrete comprises the following raw materials, in the following proportions by weight:

[0007] Granulated blast furnace slag 60-70 parts, fly ash 8-12 parts, silica fume 0-20 parts, red mud 5-25 parts, alkali activator 18-23 parts, fine aggregate 60-70 parts, water 25-35 parts;

[0008] The preparation process of the red mud-based ultra-high strength geopolymer concrete adopts heat curing, and the heat curing conditions are: curing at 75-85℃ for 45-50 hours.

[0009] Preferably, it also includes metal fibers, wherein the metal fibers are added at a volume ratio of 1%-3% of the total volume.

[0010] Preferably, the weight ratio of silica fume to red mud is in the range of 2:3 to 3:2.

[0011] Preferably, in each weight proportion, there are 10-15 parts of silica fume and 10-15 parts of red mud.

[0012] Preferably, the weight ratio of each component is as follows: 62-68 parts granulated blast furnace slag, 8-12 parts fly ash, 0-20 parts silica fume, 5-25 parts red mud, 18-23 parts alkali activator, 60-65 parts fine aggregate, and 28-32 parts water; the volume content of metal fiber is 1%-3%; and the weight ratio of silica fume to red mud is 2:3 to 3:2.

[0013] Preferably, the weight ratio of the alkali activator in each component is 18 parts.

[0014] Preferably, the fine aggregate is a well-graded fine aggregate; the well-graded fine aggregate is quartz sand, and contains 12-18 parts of 26-40 mesh fine sand, 12-18 parts of 40-70 mesh fine sand, 8-12 parts of 70-110 mesh fine sand, 8-12 parts of 110-160 mesh fine sand, and 8-12 parts of 160-200 mesh fine sand; the maximum particle size of the quartz sand does not exceed 710 μm, and it is in a saturated surface-dry state.

[0015] Preferably, the metal fiber is a steel fiber with a diameter of 0.1-0.3 mm and a length of 10-15 mm.

[0016] This invention also provides a method for making red mud-based ultra-high strength geopolymer concrete, comprising the following steps:

[0017] S1. Dry mix the slag, fly ash, silica fume, and red mud evenly;

[0018] S2. Add saturated, surface-dry fine aggregate and continue dry mixing;

[0019] S3. Add the pre-prepared alkali activator and the remaining mixing water, and stir to form a uniform slurry;

[0020] S4. Add the metal fibers and continue stirring until the metal fibers are evenly dispersed;

[0021] S5. Pour the mixture into a mold, let it stand to cure, and then demold it.

[0022] S6. After demolding, the specimens are subjected to heat curing, followed by standard curing.

[0023] Preferably, the heat curing conditions in step S6 are: curing at 75-85℃ for 45-50 hours; in step S6, the compressive strength after 28 days of curing is not less than 120MPa, preferably not less than 140MPa.

[0024] This invention also provides the application of the above-mentioned red mud-based ultra-high strength geopolymer concrete in the construction field.

[0025] This invention achieves efficient utilization of red mud and yields high-performance concrete by synergistically optimizing the cementitious material system, particularly the ratio of silica fume to red mud, the dosage of alkali activator, and the curing regime. The concrete exhibits an optimal compressive strength exceeding 140 MPa at 28 days, an optimal flexural strength exceeding 14 MPa at 28 days, and a spread exceeding 200 mm. This invention discovers an optimal range (2:3 to 3:2) for the ratio of silica fume to red mud. Within this range, combined with a specific alkali dosage (8%-10%, preferably 8%) and a heat curing process, a dense NASH gel structure can be formed, thereby achieving the aforementioned superior mechanical properties. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating the preparation process of the red mud-based ultra-high strength geopolymer concrete of this invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to specific embodiments.

[0029] This invention provides a red mud-based ultra-high strength geopolymer concrete, comprising the following raw materials, in the following proportions by weight:

[0030] The mixture consists of 60-70 parts granulated blast furnace slag, 8-12 parts fly ash, 0-20 parts silica fume, 5-25 parts red mud, 18-23 parts alkali activator, 60-70 parts well-graded fine aggregate, and 25-35 parts water; it also includes steel fiber, with a steel fiber volume content of 1%-3%.

[0031] Preferably, the weight ratio is: 60-70 parts granulated blast furnace slag, 8-12 parts fly ash, 0-20 parts silica fume, 5-25 parts red mud, 18-23 parts alkali activator, 60-70 parts well-graded fine aggregate, and 25-35 parts water; wherein, it also includes steel fiber, with a steel fiber volume content of 1%-3%; the weight ratio of silica fume and red mud is in the range of 2:3 to 3:2.

[0032] Preferably, the weight ratio is: 60-70 parts granulated blast furnace slag, 8-12 parts fly ash, 10-15 parts silica fume, 10-15 parts red mud, 18-23 parts alkali activator, 60-70 parts well-graded fine aggregate, and 25-35 parts water; wherein, it also includes steel fiber, and the volume content of steel fiber is 1%-3%.

[0033] Preferably, the weight ratio is: 62-68 parts granulated blast furnace slag, 8-12 parts fly ash, 0-20 parts silica fume, 5-25 parts red mud, 18-23 parts alkali activator, 60-65 parts well-graded fine aggregate, and 28-32 parts water. The volumetric content of steel fiber is 1%-3%; the weight ratio of silica fume to red mud ranges from 2:3 to 3:2.

[0034] More preferably, the weight ratio is: 65 parts blast furnace slag, 10 parts fly ash, 10-15 parts silica fume, 10-15 parts red mud, 60-65 parts well-graded fine aggregate, 18 parts alkali activator, and 30 parts water; the volume content of steel fiber is 1%-3%.

[0035] Blast furnace slag, as a major cementitious component, has a core advantage in its extremely high potential hydraulic activity. Under alkaline activation conditions, slag can rapidly dissociate and provide abundant sources of calcium, silicon, and aluminum, participating in the formation of high-strength, dense geopolymer gels (such as C-(A)-SH gel), which is the fundamental basis for concrete to obtain high early and late strength.

[0036] The introduction of fly ash (usually low-calcium grade F) mainly leverages its morphological effect, micro-aggregate effect, and long-term pozzolanic effect. Its smooth, spherical particles improve the workability of the mixture and reduce water consumption; its continued reaction in an alkaline environment helps refine the pore structure, enhances the long-term strength development and durability of concrete, and strengthens early-stage strength.

[0037] The core advantage of silica fume lies in its extremely strong physical filling effect and pozzolanic activity. Its ultrafine particles can effectively fill the nanoscale pores between slag, fly ash, and red mud particles, significantly reducing the porosity of the matrix and optimizing the pore structure. Simultaneously, its highly active amorphous... It can rapidly participate in the reaction, significantly enhancing the strength of the interfacial transition zone between the paste and aggregate, making it a key material for overcoming strength bottlenecks. It exhibits good adaptability to cement and mineral admixtures, allowing concrete to maintain good fluidity even at low water-cement ratios.

[0038] The primary advantage of using red mud, a major industrial solid waste, in this system lies in its environmental protection and resource utilization benefits. Its alkaline components (such as...) The presence of a partial active silica-alumina phase can provide an initial alkaline environment and supplementary reactants in the system, assisting the alkaline activation process and achieving the effect of "treating waste with waste and synergistic activation".

[0039] An aggregate system composed of graded fine sand is employed. By carefully selecting and blending fine sand within a specific particle size range (16 parts 26-40 mesh, 16 parts 40-70 mesh, 10.6 parts 70-110 mesh, 10.6 parts 110-160 mesh, and 10.6 parts 160-200 mesh), this system achieves excellent bulk density between fine aggregate particles and cementitious materials. The core of this design lies in replacing the traditional coarse and fine aggregate combination with a graded, fine particle group, thereby significantly reducing the amount of cementitious paste required to fill pores. This not only ensures the high fluidity and final strength of the concrete but also significantly improves its shrinkage resistance and long-term volume stability.

[0040] Sodium silicate solution is a highly efficient activator in this system. Its advantage lies in providing a stable and potent alkaline environment. ) and soluble silicate ( It rapidly disrupts the glassy structure of powder raw materials, accelerates the depolymerization and repolymerization of aluminosilicates, and directionally guides the formation of geopolymers with a three-dimensional network structure, which is the chemical driving force for the efficient reaction.

[0041] Strictly controlling the low water-cement ratio is one of the advantages of this invention. The limited moisture content aims to meet the basic requirements of the alkali-activated reaction and ensure the necessary workability. Its advantage lies in greatly reducing the capillary pores and voids left by the evaporation of excess moisture, thereby directly creating a microstructure with extremely high density. This is the key physical guarantee for achieving high strength in concrete.

[0042] The core advantage of incorporating steel fibers lies in achieving a performance transformation from brittle to tough. Steel fibers can effectively bridge microcracks generated in concrete under load, preventing their rapid propagation, thereby significantly improving the tensile strength, flexural toughness, impact resistance, and fracture energy of the composite material. This improves the brittle failure mode often found in high-strength concrete and enhances its safety and reliability.

[0043] In the following examples and comparative examples, the granulated blast furnace slag was composed of the following components by mass percentage: CaO 46.5%, SiO2 36.18%, Al2O3 15.1%, Fe2O3 1.35%, Na2O 0.91%, MgO 2.7%, K2O 0.04%, with the balance being unavoidable impurities. The apparent density of the granulated blast furnace slag was 2.84 g / cm³. 3 Specific surface area is 472 m² 2 / kg, with a loss on ignition of 0.4%. The granulated blast furnace slag is sourced from Shifeng Mining Processing Plant in China.

[0044] In the following examples and comparative examples, the fly ash consisted of the following components by mass percentage: CaO 5.1%, SiO2 48%, Al2O3 37%, Fe2O3 2.2%, Na2O 2.14%, MgO 1.6%, SO3 1.43%, with the balance being unavoidable impurities. The apparent density of the fly ash was 2.10 g / cm³. 3 Specific surface area is 340 m² 2 / kg, with a loss on ignition of 2.53%. The fly ash is sourced from China Jinfeng Water Purification Materials Co., Ltd.

[0045] In the following examples and comparative examples, the silica fume consisted of the following components by mass percentage: 98.1% SiO2, 0.01% Al2O3, with the balance being unavoidable impurities. The silica fume had a specific surface area of ​​21 m². 2 / kg, with a loss on ignition of 1.48%. The silica ash was sourced from Henan Borun Foundry Materials Co., Ltd., China.

[0046] In the following examples and comparative examples, the red mud was composed of the following components by mass percentage: CaO 0.867%, SiO2 14.6%, Al2O3 22.6%, Fe2O3 44.7%, Na2O 10.1%, MgO 0.13%, K2O 0.182%, SO3 0.688%, with the balance being unavoidable impurities. The red mud had a specific surface area of ​​1262 m². 2 / kg, the red mud is sourced from Malvern Instruments Co., Ltd. in China.

[0047] In the following examples and comparative examples, the quartz sand is sourced from Henan, China. To alleviate the problem of weak internal bonding, the coarse aggregate is removed from the mix proportion in the red mud-based ultra-high strength geopolymer concrete. The quartz sand is divided into five particle sizes: 16 parts of 26-40 mesh fine sand, 16 parts of 40-70 mesh fine sand, 10.6 parts of 70-110 mesh fine sand, 10.6 parts of 110-160 mesh fine sand, and 10.6 parts of 160-200 mesh fine sand.

[0048] The quartz sand is in a saturated, surface-dry state, and the determination steps are as follows:

[0049] First, soak the raw sand in water for about 24 hours to ensure it is fully saturated. After soaking, remove the sand from the water and spread it on a dry table to air dry naturally. Once the sand has reached a suitable dry state or the surface moisture has begun to dissipate, start the measurement process.

[0050] Next, fill the conical mold with sand, initially filling it slightly above the edge of the mold. Then, use a tamper to lightly press down about 25 times from a height of 5 mm. After removing the mold, use your fingers to give the sand layer a final light compaction.

[0051] Finally, it was confirmed that about half of the sand particles collapsed when the mold was removed, indicating that the sand body had reached a saturated, surface-dry state.

[0052] In the following embodiments, the fiber is copper-plated steel fiber with a diameter of 0.2 mm, a length of 13 mm, and a density of 7800 kg / m³. 3 The tensile strength is 2850 MPa, and the steel fiber is sourced from Liaocheng Hongshengyuan Metal Products Co., Ltd.

[0053] In the following comparative examples, the fiber is polyvinyl alcohol fiber with a diameter of 0.04 mm, a length of 13 mm, and a density of 1300 kg / m³. 3 The tensile strength is 1650 MPa, and the polyvinyl alcohol fiber is sourced from Shandong Jinhongyao Engineering Materials Co., Ltd.

[0054] In the following examples and comparative examples, the activator is a sodium silicate solution (water glass). The optimal dosage of the sodium silicate activator is 8% of the total mass of the material, and the modulus of the sodium silicate solution ranges from 1 to 1.5, exhibiting high strength regardless of curing conditions and binder type.

[0055] Preferably, the optimal dosage of sodium silicate activator is 8% of the total mass of the material, wherein the composition of the activator by weight percentage is: Na2O 19.04%, SiO2 23.79%, H2O 57.17%.

[0056] This invention also provides a method for preparing red mud-based ultra-high strength geopolymer concrete, which includes the following steps:

[0057] S1. Dry mix the slag, fly ash, silica fume, and red mud evenly for 2 minutes;

[0058] S2. Add well-graded fine aggregate in a saturated, surface-dry state, and continue dry mixing for 1 minute to ensure that the powder evenly coats the aggregate.

[0059] S3. Preparation of alkaline activation solution: When preparing the activator solution, first boil the tap water to remove carbon dioxide. Use an electronic balance with an accuracy of 0.01 g to weigh a certain amount of sodium silicate and silica particles and dissolve them in a certain amount of tap water. Then let it stand at room temperature for 24 h to ensure that the silica particles are completely dissolved in the alkaline solution. After stirring evenly, cool it to room temperature for later use.

[0060] S4. Add the pre-prepared sodium silicate alkali activator and the remaining mixing water. The remaining mixing water is the total water volume minus the saturated surface dry water absorption rate of the aggregate and the water in the alkali activator. Stir for 4 minutes to form a uniform slurry.

[0061] S5. Add the fiber and continue stirring for 2-3 minutes until the fiber is evenly dispersed and there are no clumps.

[0062] S6. Casting the mixture into shape: Pour the mixture into a mold coated with a release agent, place it on a vibrating table to compact it and remove air bubbles, cover the surface with a plastic film to prevent moisture evaporation, and demold after standing and curing at room temperature for 24 hours.

[0063] S7. Post-molding heat curing: After the mixture is poured into molds and allowed to stand for 24 hours for curing, it is demolded. The demolded specimens are then subjected to heat curing, followed by standard curing for 28 days. The heat curing conditions are: curing at 75-85℃ for 45-50 hours. This heat treatment process can significantly accelerate the polymerization reaction process and improve early and late strength. Preferably, the curing conditions are curing at 80℃ for 48 hours. Afterwards, it is transferred to a standard curing room (temperature 20±2℃, humidity ≥95%) for curing for 28 days.

[0064] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0065] Example 1

[0066] Prepare the ingredients according to the following recipe:

[0067] The ingredients are: 65 parts blast furnace slag, 10 parts fly ash, 10 parts silica fume, 15 parts red mud, 64 parts well-graded fine aggregate, 18 parts sodium silicate solution, and 30 parts water; the steel fiber content is 2% by volume.

[0068] The concrete for this embodiment is prepared according to the following steps:

[0069] Slag, fly ash, silica fume, and red mud are put into a mixer for dry mixing; well-graded fine aggregate in a saturated surface-dry state is added, and mixing continues. Then, pre-prepared sodium silicate alkali activator and the remaining mixing water are added and stirred to form a uniform slurry. Steel fibers are then added and stirred until the fibers are evenly dispersed. The mixture is then stirred until it can be molded, thus obtaining the concrete.

[0070] The prepared concrete was poured into the mold and vibrated for 30 seconds. After curing at room temperature for 24 hours, the specimens were demolded. The demolded specimens were then subjected to heat curing at 80°C for 48 hours, and then transferred to a standard curing room (temperature 20±2°C, humidity ≥95%) for curing for 28 days.

[0071] Example 2

[0072] Prepare the ingredients according to the following recipe:

[0073] The ingredients are: 65 parts blast furnace slag, 10 parts fly ash, 15 parts silica fume, 10 parts red mud, 64 parts well-graded fine aggregate, 18 parts sodium silicate solution, and 30 parts water; the steel fiber content is 2% by volume.

[0074] The concrete for this embodiment is prepared according to the following steps:

[0075] Slag, fly ash, silica fume, and red mud are put into a mixer for dry mixing; well-graded fine aggregate in a saturated surface-dry state is added, and mixing continues. Then, pre-prepared sodium silicate alkali activator and the remaining mixing water are added and stirred to form a uniform slurry. Steel fibers are then added and stirred until the fibers are evenly dispersed. The mixture is then stirred until it can be molded, thus obtaining the concrete.

[0076] The prepared concrete was poured into the mold and vibrated for 30 seconds. After curing at room temperature for 24 hours, the specimens were demolded. The demolded specimens were then subjected to heat curing at 80°C for 48 hours, and then transferred to a standard curing room (temperature 20±2°C, humidity ≥95%) for curing for 28 days.

[0077] Comparative Example 1

[0078] The difference from Examples 1-2 is that the amount of silica fume is 20 parts and the amount of red mud is 5 parts, in order to explore the optimal dosage range of red mud and silica fume. The other raw material dosages and preparation methods are the same as those in Examples 1-2.

[0079] Comparative Example 2

[0080] The difference from Examples 1-2 is that the amount of silica fume is 5 parts and the amount of red mud is 20 parts, to explore the optimal dosage range of red mud and silica fume. The other raw material dosages and preparation methods are the same as those in Examples 1-2.

[0081] Comparative Example 3

[0082] The difference from Examples 1-2 is that the silica fume content is 0 parts and the red mud content is 25 parts, to explore the optimal content range of red mud and silica fume. The other raw material amounts and preparation methods are the same as those in Examples 1-2.

[0083] Comparative Example 4

[0084] The difference from Example 1 is that the dosage of the alkali activator is increased to 10%, wherein the alkali activator is Na2SiO3, and the dosage is the weight ratio of the cementitious material. The remaining raw material dosages and preparation methods are the same as in Example 1.

[0085] Comparative Example 5

[0086] The difference from Example 2 is that the dosage of the alkali activator is increased to 10%, wherein the alkali activator is Na2SiO3, and the dosage is the weight ratio of the cementitious material. The remaining raw material dosages and preparation methods are the same as in Example 1.

[0087] Comparative Example 6

[0088] The difference from Example 1 is that no fibers are added, while the remaining raw material amounts and preparation methods are the same as in Example 1.

[0089] Comparative Example 7

[0090] The difference from Example 1 is that no heat curing was performed. The prepared concrete was poured into the mold and vibrated for 30 seconds. After curing at room temperature for 24 hours, it was demolded. The demolded specimens were then transferred to a standard curing room (temperature 20±2°C, humidity ≥95%) for curing for 28 days. The remaining raw material quantities and preparation methods were the same as in Example 1.

[0091] Comparative Example 8

[0092] The difference from Example 1 is that heat curing is not performed; the curing conditions are the same as in Comparative Example 1. Steel fibers are not added; instead, 2% polyvinyl alcohol fibers by volume are added. The remaining raw material amounts and preparation methods are the same as in Example 1. The only difference from Comparative Example 7 is the type of fiber.

[0093] Comparative Example 9

[0094] The difference from Example 1 is that heat curing was not performed, the dosage of alkali activator was increased to 10%, the prepared concrete was poured into the mold and vibrated for 30 seconds, and then allowed to cure at room temperature for 24 hours before demolding. The demolded specimens were transferred to a standard curing room (temperature 20±2°C, humidity ≥95%) for curing for 28 days. The remaining raw material dosages and preparation methods were the same as in Example 1.

[0095] Experimental Example

[0096] The cured concrete obtained in Examples 1-2 and Comparative Examples 1-9 was tested for its 28-day flexural strength, compressive strength, and fresh concrete flowability. The testing methods are as follows:

[0097] (1) Flexural strength at 28 days

[0098] Test method: Specimen size is The cross-sectional area of ​​the test specimen is The specimen is placed sideways on the support cylinder of the flexural testing machine, with its major axis perpendicular to the support cylinder. A load is applied uniformly and vertically to the opposite sides of the prism at a rate of 50 N / s ± 10 N / s through a loading cylinder until it breaks. The two halves of the prism are kept moist until the compressive strength test. To reduce experimental error, the test result is the average of the flexural strength of three specimens. If any of the three strength values ​​exceeds ±10% of the average, it should be discarded, and the average value should be taken as the flexural strength test result. If two of the three strength values ​​exceed ±10% of the average, the remaining one is used as the flexural strength result.

[0099] Testing standards and basis: According to the "Test Method for Strength of Cement Mortar (ISO)" (GB / T 17671-2021), this standard covers the test method for the flexural strength of alkali-activated geopolymer concrete and can be used to test the flexural strength of geopolymer concrete.

[0100] (2) 28-day compressive strength

[0101] Test method: After the flexural strength test is completed, two halves of the specimen are removed for compressive strength testing. The compressive strength test is conducted using a compression testing machine on the side of the half-prism ( The test should be conducted on a press plate. The difference between the center of the truncated prism and the center of the press plate should be within ±0.5mm, and the portion of the prism protruding from the press plate should be approximately 10mm. The load should be applied uniformly at a rate of 2400N / s ± 200N / s throughout the loading process until failure. To reduce experimental error, the average compressive strength of six specimens should be used as the test result. The average of the six compressive strength measurements obtained from a set of three prisms should be taken as the test result. If any of the six measurements exceeds ±10% of the average, that result should be discarded, and the average of the remaining five should be used as the result. If any of the five measurements also exceeds ±10% of their average, the result set should be invalid. If two or more of the six measurements simultaneously exceed ±10% of the average, the result set should be invalid.

[0102] Testing standards and basis: According to the "Test Method for Strength of Cement Mortar (ISO)" (GB / T 17671-2021), this standard covers the test method for the compressive strength of alkali-activated geopolymer concrete and can be used to test the compressive strength of geopolymer concrete.

[0103] (3) Spread of freshly mixed concrete

[0104] Test Method: The slump spread test method was used. Fresh concrete was poured in two layers into a miniature truncated cone mold. The mold had an inner diameter of 65 mm at the top, 75 mm at the bottom, and a height of 40 mm. During this process, each layer of mixture was tamped 10 times with a tamping rod to ensure compaction. Immediately after pouring, the cone mold was removed, allowing the mixture to spread out on a table within 1 minute. The diameters of the spread mixture in two vertical directions were then measured, and the average value was taken as the slump spread index of the fresh concrete.

[0105] Testing standards and basis: According to the "Standard for Test Methods of Performance of Ordinary Concrete Mixtures" (GB / T 50080-2016), this standard covers the test method for the spread of alkali-activated geopolymer concrete and can be used to test the spread of geopolymer concrete.

[0106] The components of each type of concrete are shown in Table 1.

[0107] Table 1. Components of various concrete types

[0108]

[0109] The comparative contents of the examples in Table 1 are underlined, and the mass percentages are marked in italics (mass percentages refer to the proportion of a certain item other than fiber in the total mass of the system). Among them, the amount of alkali activator was increased in examples 4, 5, and 9, which resulted in changes in the total mass.

[0110] The test results for each type of concrete are shown in Table 2.

[0111] Table 2 Test results for various types of concrete

[0112]

[0113] Table 2 shows that Example 1 of the present invention exhibits the best overall performance, with a 28-day compressive strength of 147.8 MPa and a flexural strength of 14.9 MPa, while maintaining good workability (spread 203 mm). Example 2 shows the second best overall performance, with a 28-day compressive strength of 135.6 MPa and a flexural strength of 13.1 MPa, while maintaining good workability (spread 214 mm). This confirms that the technical solution of synergistically using a silica fume to red mud ratio of 2:3-3:2 (preferably 2:3), 8% alkali content, 2% volumetric steel fiber, and 80℃ heat curing in the red mud-based ultra-high strength geopolymer concrete system fully utilizes the active components in red mud and the micro-filling effect of silica fume, which helps to form a denser geopolymer gel structure within the system, achieving a perfect combination of large-scale utilization of solid waste and high material performance.

[0114] Compared to Example 1, Comparative Example 1 (increasing silica fume content to 10% and decreasing red mud content to 2%) showed a decrease in compressive strength of approximately 12.11% and a decrease in flexural strength of approximately 21.5% after 28 days, while the spread increased slightly. This indicates that, under the condition of keeping other factors constant, adjusting the ratio of silica fume to red mud to 4:1 leads to a decrease in system strength. The imbalance in the ratio of silica fume to red mud, with an excessively high silica fume ratio that, while beneficial for fluidity, significantly deteriorates the mechanical properties of the material, demonstrates that the ratio of the two has a crucial impact on the formation of hydration products and the stability of the microstructure of the system.

[0115] Comparative Example 2 (with silica fume content reduced to 2% and red mud content increased to 10%) showed a decrease in compressive strength of approximately 13.37% and flexural strength of approximately 28.86% after 28 days, compared to Example 1, and a reduction in elongation to 185 mm. Adjusting the silica fume to red mud ratio to 1:4 resulted in a significant decrease in strength and a deterioration in workability. This indicates that when the proportion of red mud is too high and the proportion of silica fume is too low, the activity in the system... Insufficient supply and weakened micro-aggregate filling effect lead to inadequate development of the geopolymer gel structure, resulting in a simultaneous decline in mechanical properties and workability. This result indirectly illustrates that rationally controlling the red mud content and ensuring sufficient silica fume content are crucial for maintaining the system's reactivity and microstructure density.

[0116] Compared to Example 1, Comparative Example 3 (0% silica fume and 12% red mud) showed a decrease in compressive strength of approximately 22.54% and flexural strength of approximately 32.89% after 28 days, with the elongation decreasing to 177 mm. This indicates that in the absence of silica fume, red mud alone, as a silica-alumina source, struggles to form a dense geopolymer network, significantly limiting the system's reactivity and cementing capacity, leading to further deterioration in strength and flow properties. The results of Comparative Example 3 further confirm that silica fume is indispensable in this system, and that it must be maintained in an appropriate ratio with red mud (such as 2:3 or 3:2 in the examples) to achieve synergistic performance optimization.

[0117] Compared to Example 1, Comparative Example 4 (with increased alkali content to 10%) showed a decrease in compressive strength of approximately 22.12% and a decrease in flexural strength of approximately 9.4% after 28 days, while the spread was slightly improved. This indicates that even with a suitable ratio of silica fume to red mud, simply increasing the alkali content can still disrupt the chemical balance and microstructure formation of the system, leading to a decrease in final strength. Therefore, Example 1 combined optimized silica fume to red mud ratio (maintaining the synergy between active components and microfilling effects) with a moderate alkali content (8%) to jointly ensure reaction stability and structural density.

[0118] Compared to Example 2, Comparative Example 5 (with an increased alkali content of 10%) showed a decrease in compressive strength of approximately 17.26% and a decrease in flexural strength of approximately 7.6% after 28 days. Excessive alkali content leads to a decrease in strength. These results indicate that optimizing the alkali content based on a suitable silica fume to red mud ratio can fully realize the system's reaction potential, avoid structural loosening and performance loss caused by excessive alkali, and improve product strength.

[0119] Compared to Example 1, Comparative Example 6 (without fiber) showed a decrease of approximately 26.82% in compressive strength and approximately 63.76% in flexural strength after 28 days, indicating that fibers play a crucial and indispensable role in improving the flexural strength and overall toughness of the material.

[0120] Compared to Example 1, Comparative Example 7 (cured at room temperature) showed a decrease of approximately 7.31% in compressive strength and approximately 14.09% in flexural strength after 28 days, indicating that curing temperature affects material properties and that hot curing is more effective in enhancing the strength of red mud polymer concrete.

[0121] Compared to Comparative Example 7, Comparative Example 8 (using polyvinyl alcohol fibers) showed a decrease of approximately 34.38% in compressive strength and 18.75% in flexural strength after 28 days, with a significant reduction in fiber spread to 105 mm. This indicates that under the same curing regime (normal temperature curing), the type of fiber has a crucial impact on the mechanical and workability of geopolymer concrete. Steel fibers, due to their higher elastic modulus and interfacial bonding performance, can more effectively transfer stress and inhibit crack propagation in this system, thereby significantly improving strength. Polyvinyl alcohol fibers, however, failed to exert a similar reinforcing effect and may have adversely affected flowability. This result further confirms the beneficial effects of selecting steel fibers as the reinforcing phase in this invention.

[0122] Compared to Example 1, Comparative Example 9 (cured at room temperature, with alkali content increased to 10%) showed a decrease in compressive strength of approximately 29.2% and a decrease in flexural strength of approximately 26.17% after 28 days. This further illustrates that simply increasing the alkali content cannot compensate for the insufficient strength development momentum caused by the change in curing regime. The combination of hot curing (80°C) and a moderate alkali content (8%) established in this invention, under the premise of coordinated silica fume and red mud ratios, jointly promotes the full reaction and early strength development of the geopolymer system, thereby achieving high mechanical properties while ensuring workability.

[0123] In summary, this invention, through the optimal combination of the ratio of silica fume to red mud (2:3-3:2, preferably 2:3), the amount of alkali added (8%-10%, preferably 8%), the amount of steel fiber (approximately 2% by volume), and the heat curing regime (approximately 80°C, 48h), has successfully prepared red mud-based polymer concrete with a 28-day compressive strength exceeding 140MPa, reaching a maximum of 147.8MPa, and also possessing good toughness and workability.

[0124] This invention not only provides a practical and feasible technical path for the large-scale, high-value-added resource utilization of industrial solid wastes such as red mud, fly ash, and blast furnace slag, but also achieves product performance at the advanced level of high-strength concrete, with significant environmental benefits and application prospects.

[0125] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A red mud-based ultra-high strength geopolymer concrete, characterized in that, The following raw materials are included, in parts by weight, in the following proportions: Granulated blast furnace slag 60-70 parts, fly ash 8-12 parts, silica fume 0-20 parts, red mud 5-25 parts, alkali activator 18-23 parts, fine aggregate 60-70 parts, water 25-35 parts; The weight ratio of silica fume to red mud incorporated ranges from 2:3 to 3:2; The fine aggregate is well-graded fine aggregate; the well-graded fine aggregate is quartz sand, and contains 12-18 parts of 26-40 mesh fine sand, 12-18 parts of 40-70 mesh fine sand, 8-12 parts of 70-110 mesh fine sand, 8-12 parts of 110-160 mesh fine sand, and 8-12 parts of 160-200 mesh fine sand; the maximum particle size of the quartz sand does not exceed 710 μm, and it is in a saturated surface-dry state; The raw materials also include metal fibers, which are added at a volume ratio of 1%-3% of the total volume. The preparation process of the red mud-based ultra-high strength geopolymer concrete adopts heat curing, and the heat curing conditions are: curing at 75-85℃ for 45-50 hours.

2. The red mud-based ultra-high strength geopolymer concrete according to claim 1, characterized in that, In the proportions of each weight, there are 10-15 parts silica fume and 10-15 parts red mud.

3. The red mud-based ultra-high strength geopolymer concrete according to claim 1, characterized in that, The weight ratio of each component is as follows: 62-68 parts granulated blast furnace slag, 8-12 parts fly ash, 0-20 parts silica fume, 5-25 parts red mud, 18-23 parts alkali activator, 60-65 parts fine aggregate, and 28-32 parts water.

4. The red mud-based ultra-high strength geopolymer concrete according to claim 3, characterized in that, Of the components, the alkali activator is 18 parts by weight.

5. The red mud-based ultra-high strength geopolymer concrete according to claim 1, characterized in that, The metal fibers are steel fibers with a diameter of 0.1-0.3 mm and a length of 10-15 mm.

6. A method for preparing red mud-based ultra-high strength geopolymer concrete according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Dry mix the slag, fly ash, silica fume, and red mud evenly; S2. Add saturated, surface-dry fine aggregate and continue dry mixing; S3. Add the pre-prepared alkali activator and the remaining mixing water, and stir to form a uniform slurry; S4. Add the metal fibers and continue stirring until the metal fibers are evenly dispersed; S5. Pour the mixture into a mold, let it stand to cure, and then demold it. S6. After demolding, the specimens are subjected to heat curing, followed by standard curing.

7. The method according to claim 6, characterized in that, The conditions for heat curing in step S6 are: curing at 75-85℃ for 45-50 hours; and the compressive strength after curing for 28 days in step S6 shall not be less than 120MPa.

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