Red mud-based multi-element solid waste cementing material as well as preparation method and application thereof

Abstract

The invention discloses a red-mud-based multi-element solid waste cementing material as well as a preparation method and application thereof, and belongs to the technical field of building materials. The red-mud-based multi-element solid waste cementing material comprises the following components in parts by mass: 30-40 parts of red mud, 5-15 parts of fly ash, 10-20 parts of superfine slag powder, 30 parts of Portland cement, 4 parts of dihydrate gypsum and 2-25 parts of an alkali activator, alkaline components of the red mud are utilized to excite potential activity of the superfine slag powder and the fly ash, the additional alkaline activator excites potential activity in the red mud, and meanwhile, several industrial solid wastes and the Portland cement generate gel substances such as hydrated aluminosilicate under the synergistic effect, so that the mechanical property of the cement is improved; the building material meeting the strength requirement is provided while a large amount of red mud is consumed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of building materials, and particularly relates to a red mud-based multi-element solid waste cementing material and a preparation method and application thereof. BACKGROUND

[0002] Red mud is an insoluble solid waste discharged in the industrial production of alumina. In recent years, with the increase of the annual output of alumina, the amount of red mud generated is also very large. The red mud is highly alkaline and has low activity. The accumulation of a large amount of red mud not only occupies a large amount of land, but also causes a series of environmental problems such as soil and water pollution due to the direct use of metal ions contained in the red mud for damming without treatment. How to stimulate the activity of the red mud and reduce its high alkalinity is the key to the utilization of the red mud. The existing technology has low utilization rate of the red mud and has many problems in utilization. Due to the nature of the red mud and its discharge mode, the difficulty of recycling the red mud is increased. Therefore, it is necessary to actively develop and utilize the red mud, and comprehensively utilize the red mud to avoid pollution caused by the utilization of the red mud. The chemical composition of the red mud mainly includes SiO2, CaO, Al2O3, Na2O and Fe2O3. The SiO2 and Al2O3 have certain activity, and the activity thereof can be enhanced through corresponding treatment, so that the red mud has certain hydration gelation capacity. SUMMARY

[0003] In view of the above existing technology, the application provides a red mud-based multi-element solid waste cementing material, a preparation method and application thereof, and solves the problem of low utilization rate of the red mud in the prior art.

[0004] In order to achieve the above purpose, the technical scheme adopted by the application is as follows: a red mud-based multi-element solid waste cementing material is provided, which comprises the following components in mass fraction: 30-40 parts of red mud, 5-15 parts of fly ash, 10-20 parts of slag powder, 30 parts of Portland cement, 4 parts of dihydrate gypsum and 2-25 parts of alkaline activator.

[0005] The red mud-based multi-element solid waste cementing material provided by the application consumes a large amount of red mud, solves the problem of low utilization rate of the red mud, and contains an alkaline activator in the raw material components of the red mud-based multi-element solid waste cementing material. The activity of the red mud is stimulated, gel material is generated, the mechanical properties are improved, the 7d compressive strength of the red mud-based cementing material can reach 20.6 MPa, the 28d compressive strength can reach 25.3 MPa, a high-strength building material is provided while a large amount of red mud is consumed.

[0006] On the basis of the above technical scheme, the application can also be improved as follows.

[0007] Further, the alkaline activator is water glass.

[0008] Further, the modulus of water glass is 1.7-3.4.

[0009] Further, further, the components include the following mass fractions: 40 parts of red mud, 10 parts of fly ash, 20 parts of slag powder, 30 parts of Portland cement, 4 parts of dihydrate gypsum and 4 parts of water glass.

[0010] The beneficial effect of the further technical solution is that the preferred ratio of the red mud-based multi-solid waste cementitious material can consume a large amount of red mud, improve the mechanical properties, and the strong alkaline water glass provides an alkaline environment to promote the dissolution of aluminum silicate minerals in the red mud to generate C-S-H gel, and the reaction is fast, and the early strength is obviously improved.

[0011] Further, the alkaline activator is limestone powder.

[0012] Further, the components include the following mass fractions: 40 parts of red mud, 10 parts of fly ash, 20 parts of slag powder, 30 parts of Portland cement, 4 parts of dihydrate gypsum and 10 parts of limestone powder.

[0013] The beneficial effect of the further technical solution is that the preferred ratio of the red mud-based multi-solid waste cementitious material can consume a large amount of red mud, improve the mechanical properties, and the weak alkaline limestone powder mainly provides Ca 2+ indirectly activates the red mud, the reaction is slow, and Ca 2+ reacts with active silicon and aluminum in the red mud to generate C-S-H gel and C-A-H gel, thereby improving the strength of the red mud-based cementitious material.

[0014] The application further provides a preparation method of the red mud-based multi-solid waste cementitious material, which includes the following steps: S1: grinding the red mud into powder, drying, and then filtering the red mud powder through a 0.075mm sieve; S2: weighing the raw materials according to the mass fraction, and then mixing and stirring for 3-5min until uniform, to obtain the red mud-based cementitious material.

[0015] The application has the beneficial effect that the preparation method provided by the application has simple steps, is easy to operate, is suitable for large-scale industrial scenes, and has excellent industrial application prospects.

[0016] The application further provides an application of the red mud-based multi-solid waste cementitious material in preparing building materials.

[0017] The application has the advantages that the red mud-based cementing material provided by the application achieves excellent effects in the preparation of baking-free bricks and concrete, the baking-free bricks can reach the relevant standards through mechanical property detection, the quality ratio of the red mud concrete is determined as water: cementing material: fine aggregate: coarse aggregate = 0.47: 1: 1.87: 2.79, the water reducing agent content is 0.6% of the cementing material, and the concrete performance can reach the relevant standards through mechanical property tests, wear resistance tests, frost resistance tests, anti-melting snow agent erosion tests and the like. BRIEF DESCRIPTION OF DRAWINGS

[0018] Fig. 1 The XRD graph of the red mud-based multi-solid waste cementing material baking-free brick of the base group; Fig. 2 The XRD graph of the red mud-based multi-solid waste cementing material baking-free brick of the water glass group 1; Fig. 3 The XRD graph of the red mud-based multi-solid waste cementing material baking-free brick of the limestone powder group; Fig. 4 The SEM graph of the red mud-based multi-solid waste cementing material baking-free brick of the base group; Fig. 5 The SEM graph of the red mud-based multi-solid waste cementing material baking-free brick of the water glass group 1; Fig. 6 The SEM graph of the red mud-based multi-solid waste cementing material baking-free brick of the limestone powder group. DETAILED DESCRIPTION

[0019] The specific embodiments of the application will be described in detail below with reference to the examples.

[0020] Example 1 A red mud-based multi-solid waste cementing material, comprising the following components in mass fraction: 40 parts of red mud, 10 parts of fly ash, 20 parts of slag powder, 30 parts of Portland cement, 4 parts of dihydrate gypsum and 4 parts of water glass with a modulus of 1.78.

[0021] The red mud-based multi-solid waste cementing material of the example is prepared through the following steps: S1: ball milling the red mud into powder, drying, and then filtering the red mud powder through a 0.075 mm sieve; S2: weighing the raw materials according to the mass fraction, and then mixing and stirring for 4 min until uniform, to obtain the red mud-based multi-solid waste cementing material.

[0022] Example 2 The preparation steps are the same as those of Example 1, except that water glass with a modulus of 2.23 is used.

[0023] Example 3 The same as the preparation steps of Example 1, except that a water glass with a modulus of 2.68 is used.

[0024] Example 4 The same as the preparation steps of Example 1, except that a water glass with a modulus of 3.32 is used.

[0025] Example 5 A red mud-based multi-solid waste cementing material, comprising the following components in mass fraction: red mud 30 parts, fly ash 15 parts, slag powder 10 parts, Portland cement 30 parts, dihydrate gypsum 4 parts, and water glass with a modulus of 1.78 2 parts.

[0026] The red mud-based multi-solid waste cementing material of the present embodiment is prepared by the following steps: S1: Ball milling the red mud into powder, drying, and then filtering with a 0.075 mm sieve to obtain red mud powder; S2: Measuring the raw materials by mass fraction, then mixing and stirring for 3 min until uniform, to obtain the red mud-based multi-solid waste cementing material.

[0027] Example 6 The same as the preparation steps of Example 5, except that a water glass with a modulus of 2.23 is used.

[0028] Example 7 The same as the preparation steps of Example 5, except that a water glass with a modulus of 2.68 is used.

[0029] Example 8 The same as the preparation steps of Example 5, except that a water glass with a modulus of 3.32 is used.

[0030] Example 9 A red mud-based multi-solid waste cementing material, comprising the following components in mass fraction: red mud 40 parts, fly ash 5 parts, slag powder 10 parts, Portland cement 30 parts, dihydrate gypsum 4 parts, and water glass with a modulus of 1.78 3 parts.

[0031] The red mud-based multi-solid waste cementing material of the present embodiment is prepared by the following steps: S1: Ball milling the red mud into powder, drying, and then filtering with a 0.075 mm sieve to obtain red mud powder; S2: Measuring the raw materials by mass fraction, then mixing and stirring for 5 min until uniform, to obtain the red mud-based multi-solid waste cementing material.

[0032] Example 10 The same as the preparation steps of Example 9, except that a water glass with a modulus of 2.23 is used.

[0033] Example 11 The same as the preparation steps of Example 9, except that a water glass with a modulus of 2.68 is used.

[0034] Example 12 The same as the preparation steps of Example 9, except that a water glass with a modulus of 3.32 is used.

[0035] Example 13 A red mud-based multi-solid waste cementing material, comprising the following components in mass fraction: red mud 40 parts, fly ash 10 parts, slag powder 20 parts, Portland cement 30 parts, dihydrate gypsum 4 parts, and water glass with a modulus of 1.78 5 parts.

[0036] The red mud-based multi-solid waste cementing material of the present example is prepared by the following steps: S1: Ball milling the red mud into powder, drying, and then filtering with a 0.075 mm sieve to obtain red mud powder; S2: Measuring the raw materials by mass fraction, then mixing and stirring for 4 min until uniform, to obtain the red mud-based multi-solid waste cementing material.

[0037] Example 14 The same as the preparation steps of Example 13, except that a water glass with a modulus of 2.23 is used.

[0038] Example 15 The same as the preparation steps of Example 13, except that a water glass with a modulus of 2.68 is used.

[0039] Example 16 The same as the preparation steps of Example 13, except that a water glass with a modulus of 3.32 is used.

[0040] Example 17 A red mud-based multi-solid waste cementing material, comprising the following components in mass fraction: red mud 40 parts, fly ash 10 parts, slag powder 20 parts, Portland cement 30 parts, dihydrate gypsum 4 parts, and limestone powder 10 parts.

[0041] The red mud-based multi-solid waste cementing material of the present example is prepared by the following steps: S1: Ball milling the red mud into powder, drying, and then filtering with a 0.075 mm sieve to obtain red mud powder; S2: Measuring the raw materials by mass fraction, then mixing and stirring for 4 min until uniform, to obtain the red mud-based multi-solid waste cementing material.

[0042] Example 18 The same as the preparation steps of Example 17, except that the limestone powder is 5 parts.

[0043] Example 19 The same as the preparation steps of Example 17, except that the limestone powder is 15 parts.

[0044] Example 20 The same as the preparation steps of Example 17, except that the limestone powder is 20 parts.

[0045] Example 21 The same as the preparation steps of Example 17, except that the limestone powder is 25 parts.

[0046] Comparative Example 1 A red mud-based multi-solid waste cementing material, comprising the following components in mass fractions: red mud 40 parts, fly ash 10 parts, slag powder 20 parts, Portland cement 30 parts, and dihydrate gypsum 4 parts.

[0047] The red mud-based multi-solid waste cementing material of the present comparative example is prepared by the following steps: S1: Ball milling the red mud into powder, drying, and then filtering with a 0.075 mm sieve to obtain red mud powder; S2: Measuring the raw materials by mass fraction, and then mixing and stirring for 4 min to obtain the red mud-based multi-solid waste cementing material.

[0048] Comparative Example 2 The same as the preparation steps of Comparative Example 1, except that the mass fractions of the raw material components are: red mud 30 parts, fly ash 5 parts, slag powder 10 parts, Portland cement 30 parts, and dihydrate gypsum 4 parts.

[0049] Comparative Example 3 The same as the preparation steps of Comparative Example 1, except that the mass fractions of the raw material components are: red mud 30 parts, fly ash 10 parts, slag powder 15 parts, Portland cement 30 parts, and dihydrate gypsum 4 parts.

[0050] Comparative Example 4 The same as the preparation steps of Comparative Example 1, except that the mass fractions of the raw material components are: red mud 30 parts, 15 parts, slag powder 20 parts, Portland cement 30 parts, and dihydrate gypsum 4 parts.

[0051] Comparative Example 5 The same as the preparation steps of Comparative Example 1, except that the mass fractions of the raw material components are: red mud 40 parts, fly ash 5 parts, slag powder 15 parts, Portland cement 30 parts, and dihydrate gypsum 4 parts.

[0052] Comparative Example 6 The same as the preparation steps of Comparative Example 1, except that the mass fractions of the raw material components are: red mud 40 parts, fly ash 15 parts, slag powder 10 parts, Portland cement 30 parts, and dihydrate gypsum 4 parts.

[0053] Comparative Example 7 The preparation steps are the same as those of Comparative Example 1, except that the mass fractions of the raw material components are as follows: red mud 50 parts, fly ash 5 parts, slag powder 20 parts, Portland cement 30 parts, and dihydrate gypsum 4 parts.

[0054] Comparative Example 8 The preparation steps are the same as those of Comparative Example 1, except that the mass fractions of the raw material components are as follows: red mud 50 parts, fly ash 10 parts, slag powder 10 parts, Portland cement 30 parts, and dihydrate gypsum 4 parts.

[0055] Comparative Example 9 The preparation steps are the same as those of Comparative Example 1, except that the mass fractions of the raw material components are as follows: red mud 50 parts, fly ash 15 parts, slag powder 10 parts, Portland cement 30 parts, and dihydrate gypsum 4 parts.

[0056] Experimental Example 1 Strength test: The red mud-based multi-solid waste cementitious materials prepared in Examples 1-21 and Comparative Examples 1-9 were respectively poured into a mixing pot, then water (water-cement ratio 0.53) was added and stirred for 30 s, and then standard sand was added and stirred for 90 s. Finally, the stirred slurry was poured into a test mold, and after the slurry was solidified, it was cured at room temperature for 24 h, and then cured in water for 7 d and 28 d. The compressive strengths were tested, and the results are shown in Table 1.

[0057] Table 1: Compressive strength test results

[0058] From the experimental results, the 7d and 28d compressive strengths of Comparative Examples 2-4 are relatively large, but the red mud content is 30 parts, while the red mud content of Comparative Example 1 is 40 parts, and the 7d and 28d compressive strengths are close to those of Comparative Examples 2-4. The red mud content of 40 parts can consume as much red mud as possible and provide higher compressive strength, so the red mud mass fraction in Examples 1-21 of the present application is 40 parts.

[0059] Examples 1-16 selected 1.78, 2.23, 2.68, 3.32 four different modulus of water glass, the content is 2, 3, 4, 5 parts, in the same modulus, 7d and 28d compressive strength with the increase of water glass content, showing first increase and then decrease trend. This is because, with the incorporation of water glass, Na + and SiO3 2-The increase of modulus promotes more active components of red mud to dissolve, generates more gelatinous substances, and thus improves the strength. With the same dosage, the change of the compressive strength of red mud does not show a clear regularity with the increase of the modulus of water glass. When the dosage of water glass is 2 parts, the 28d compressive strength of the red mud-based cementitious material decreases from the modulus of 1.78 to 2.69, and then increases at the modulus of 3.32, while the 7d compressive strength is always decreasing; when the dosage of water glass is 3 parts, the 7d and 28d compressive strengths of the red mud-based cementitious material are always decreasing; when the dosage of water glass is 4 parts, the 7d compressive strength of the red mud-based cementitious material increases at the modulus of 2.23 and then decreases, while the 28d compressive strength decreases at the modulus of 2.23 and then increases at the modulus of 2.68, and decreases to the lowest at the modulus of 3.32; when the dosage of water glass is 5 parts, the change trend of the 7d compressive strength of the red mud-based cementitious material is the same as that of the 28d compressive strength. This is because the modulus is the molar ratio of SiO2 and Na2O in water glass. When the dosage is the same, the water glass with low modulus means high content of Na2O, which quickly dissolves the silicon-aluminum phase in red mud, and SiO3 2- easily combines with dissolved Al 3+ to form a dense gel structure. When the modulus is too high, the content of Na2O is low, the dissolution of active components in red mud is limited, and the reaction is incomplete, at this time SiO3 2- exists in a long-chain or network structure, and it is difficult to effectively participate in the reaction, so the strength of red mud decreases. In the process of increasing the modulus, the imbalance of the content of Na + and SiO3 2- in the solution may occur at this time, and the strength of the red mud-based cementitious material is relatively low, so when the dosage is the same, the strength of the red mud-based cementitious material does not show a regular change trend with the change of the modulus of water glass.

[0060] Examples 17-21 are red mud-based multi-solid waste cementitious materials with limestone powder. The particles in limestone powder are small, which can fill the cracks between red mud particles, improve the particle size distribution of the slurry, optimize the microstructure, reduce the porosity, and improve the density. The calcium carbonate (CaCO3) in limestone powder can react with aluminate minerals in red mud, which can accelerate the early hydration of red mud and promote the formation of C-S-H gel, and improve the early strength, but limestone powder itself does not have cementitious property, and excessive addition of limestone powder will produce accumulation, which not only increases the porosity, but also reduces the bonding force between the slurry, so the dosage of 10 parts (Example 17) has the best 7d and 28d compressive strength.

[0061] Experimental Example 2 Actual application 1: prepare the unfired brick with the mass ratio of cementitious material and sand being 1:3, the preparation process is as follows: after weighing the various raw material components of the cementitious material, pour them into the mixer for dry mixing for 3-5 minutes until uniform, add water and stir, then add sand and continue stirring, uniformly load the mixed cement and sand into the test mold for pressing and forming, after demolding, the test piece is cured; the experiment is divided into a basic group (water-cement ratio 0.53), a water glass group 1 (water-cement ratio 0.53), a water glass group 2 (water-cement ratio 0.53) and a limestone powder group (water-cement ratio 0.55), the cementitious material in the basic group includes the following components in mass fraction: 40 parts of red mud, 10 parts of fly ash, 20 parts of slag powder, 30 parts of Portland cement and 4 parts of dihydrate gypsum; the cementitious material in the water glass group 1 includes the following components in mass fraction: 40 parts of red mud, 10 parts of fly ash, 20 parts of slag powder, 30 parts of Portland cement, 4 parts of dihydrate gypsum and 3 parts of water glass with modulus 1.78; the cementitious material in the water glass group 2 includes the following components in mass fraction: 40 parts of red mud, 10 parts of fly ash, 20 parts of slag powder, 30 parts of Portland cement, 4 parts of dihydrate gypsum and 4 parts of water glass with modulus 2.68; the cementitious material in the limestone powder group includes the following components in mass fraction: 40 parts of red mud, 10 parts of fly ash, 20 parts of slag powder, 30 parts of Portland cement, 4 parts of dihydrate gypsum and 10 parts of limestone powder; in the experiment, the forming pressure of 15, 20 and 25 MPa is used respectively to press the unfired brick during pressing and forming, and the experimental results are shown in Table 2.

[0062] Table 2 Performance test results of unfired brick

[0063] From the experimental results, the pressure forming can make the raw material particles closely arranged, increase the density of the brick embryo, increase the contact area between the particles of each raw material, accelerate the hydration reaction and pozzolanic reaction, and form a dense gel network. The strength of the unfired brick has a certain relationship with the pressure, the higher the pressure, the strength of the unfired brick increases slightly, but the increment is not obvious, and if the forming pressure is too large, the concrete will be in a state of high extrusion during the forming process, and the internal structure of the unfired brick after drying and forming will be damaged, which cannot meet the strength requirement. If considering the actual energy consumption, the strength requirement of the unfired brick can be met and the energy consumption can be saved when the forming pressure is 15 MPa. Compared with the mechanical properties of the unfired brick, the average compressive strength of the test piece of the basic group is 20.3 MPa, the average compressive strength of the water glass group is 25.1 MPa and 24.9 MPa, which is increased by 23.6%-26.1% compared with the basic group, and the average compressive strength of the limestone powder group is 25.6 MPa, which is increased by 26.1% compared with the basic group. In terms of bending performance, the basic group is 4.9 MPa, the water glass group is 7.2 MPa and 7.4 MPa, and the limestone powder group is 6.9 MPa, which is increased by 46.9%-51.0% and 40.8% respectively, showing a similar strengthening trend.

[0064] The unfired bricks of the base group, the water glass group 1 and the limestone powder group were physically broken into small pieces, about 2 g of the middle part of the bricks was ground into powder, and the phase thereof was analyzed by using an X-ray diffractometer, and the results are shown in Figs. 1-3 The phase of the unfired bricks of the base group is mainly calcium-based silicate minerals, free SiO2 and CaO, the silicate cement dominates the hydration reaction, and the dicalcium silicate and tricalcium silicate generate calcium silicate gel (C-S-H) to provide the early strength of the unfired red mud bricks, the hydration of free CaO in the red mud increases the pH value of the system, accelerates the dissolution of the slag powder and fly ash, and promotes the progress of the pozzolanic reaction; the detected phases in the XRD pattern of the unfired bricks of the water glass group are Na2Si3O7, CaSiO3, Al6Si2O 13 , NaAlSiO4. After the incorporation of the water glass, OH - and SiO3 2- are generated by the hydrolysis of the water glass, which increases the pH value of the system. OH - provides an alkaline environment, and the CaO and SiO2 in the red mud dissolve in the strong alkaline environment to release Ca 2+ , SiO3 2- and AlO 2- ions. Ca 2+ forms crystalline wollastonite (CaSiO3) with SiO3 2- to enhance the early strength of the material. SiO3 2- in the water glass polymerizes under alkaline conditions to form a complex silicate network to stabilize Na + in the system. Al2O3 in the red mud partially reacts with SiO2 under alkaline conditions to form an aluminosilicate transition phase to provide conditions for the subsequent generation of aluminosilicate gel, and then Na + is embedded in the aluminosilicate network to reduce the content of free Na + ; the XRD pattern of the unfired bricks of the limestone powder group detects the phases of CaSiO3 and Al2O3, wherein Al2O3 is part of the residual Al2O3 in the fly ash and slag powder, CaCO3 partially dissolves under alkaline conditions to release Ca 2+ and CO3 2- , increasing the concentration of calcium ions in the solution, and the limestone powder provides a large amount of Ca 2+ to form CaSiO3 with SiO3 2- in the red mud to enhance the early strength of the material, accelerate the depolymerization and reorganization of aluminosilicates, generate hydrated calcium silicate (C-S-H), fill voids, and form a continuous cementitious network.

[0065] The unfired bricks of the base group, the water glass group 1 and the limestone powder group were physically broken into small pieces, and small pieces with a length, width and thickness of no more than 1 cm in the middle part of the bricks were selected as samples for analysis by using a scanning electron microscope, and the results are shown inFigs. 4-6 As shown, Fig. 4 The red mud particles in the red mud unfired brick without activator are aggregated, and the structure is loose. There are many pores on the surface of the particles under high magnification, and the pores are unevenly distributed. Under the synergistic effect of fly ash and slag powder, the hydration reaction and pozzolanic reaction of red mud and Portland cement occur, and the C-S-H gel does not form a continuous network. The surface is also attached to the unreacted red mud minerals, and the strength of the specimen is low. After the addition of water glass, the strong alkalinity (Na + ) and silicate (SiO3 2- ) of water glass promote the formation of gel, form a dense gel structure, and greatly improve the early strength, such as Fig. 5 As shown in the left side, the gel matrix presents a honeycomb-like porous structure, which is the typical morphology of N-A-S-H gel, Fig. 5 The right side high magnification figure shows that the particles are wrapped by gel, and the boundary is blurred, indicating that the active ingredients (Al / Si phase) are fully dissolved and participate in the reaction. The gap between the particles is completely filled with a dense gel network, and a large number of continuously distributed C-S-H gel coexists with N-A-S-H, forming a composite network; after the addition of limestone powder, CaCO3 is partially dissolved under alkaline conditions, releasing Ca 2+ and CO3 2- , increasing the concentration of calcium ions in the solution, providing raw materials for the formation of the gel phase. Ca 2+ reacts with AlO 2- , SiO3 2- in red mud to accelerate the depolymerization and recombination of aluminosilicates, generate C-S-H gel and C-A-S-H gel, fill the voids, and form a continuous gel network. CO3 2- reacts with calcium aluminate in red mud to generate calcium aluminum carbonate with a plate-like structure, as shown in Fig. 6 CO3 2- may compete with SO4 2- in dihydrate gypsum for reaction with aluminate, inhibiting the risk of excessive ettringite (AFt) expansion and enhancing the strength of the unfired brick. Calcium aluminum carbonate can solidify the free Na + in red mud, reduce the leaching of alkali, and avoid the strength degradation caused by alkaline erosion. The physical filling of limestone powder mainly fills micron-sized pores, but part of the large pores is not completely blocked. There are fewer honeycomb-like structures in the hydration products, and it is speculated that the honeycomb-like structure may be filled with calcium carbonate in the system. Compared with the unfired brick with water glass, there are more white flocculent substances in the limestone powder, and it can be seen that the white flocculent substances are indeed carbonate crystals.

[0066] Experimental Example 3 Actual application 2: prepare red mud concrete by mixing water, red mud-based multi-component solid waste cementitious material, fine aggregate and coarse aggregate in a mass ratio of 0.45:1:1.87:2.79, and then adding polycarboxylate high-performance water reducing agent, wherein the coarse aggregate is a mixture of 30% 16-31.5 mm particle size gravel, 50% 10-20 mm particle size gravel and 20% 5-10 mm particle size gravel, the fine aggregate is quartz sand with a modulus of 2.73, and the polycarboxylate high-performance water reducing agent is added in an amount of 0.6% of the red mud-based cementitious material; the experiment is divided into a basic group (water-cement ratio 0.47), a water glass group 1 (water-cement ratio 0.47), a water glass group 2 (water-cement ratio 0.47) and a limestone powder group (water-cement ratio 0.47); the cementitious material in the basic group includes the following components in mass fraction: red mud 40 parts, fly ash 10 parts, slag powder 20 parts, Portland cement 30 parts and gypsum 4 parts; the cementitious material in the water glass group 1 includes the following components in mass fraction: red mud 40 parts, fly ash 10 parts, slag powder 20 parts, Portland cement 30 parts, gypsum 4 parts and water glass with a modulus of 1.78 3 parts; the cementitious material in the water glass group 2 includes the following components in mass fraction: red mud 40 parts, fly ash 10 parts, slag powder 20 parts, Portland cement 30 parts, gypsum 4 parts and water glass with a modulus of 2.68 4 parts; the cementitious material in the limestone powder group includes the following components in mass fraction: red mud 40 parts, fly ash 10 parts, slag powder 20 parts, Portland cement 30 parts, gypsum 4 parts and limestone powder 10 parts; for each compressive strength test group, 3 red mud concrete test pieces each with a size of 100 mm x 100 mm x 100 mm are prepared, and the compressive strength test is performed after 7 days and 28 days of curing, respectively; for each flexural strength test group, 3 red mud concrete test pieces each with a size of 400 mm x 100 mm x 100 mm are prepared, and the flexural strength test is performed after 7 days and 28 days of curing, respectively; and the results are shown in Table 3.

[0067] Table 3 Compressive strength test results of red mud concrete

[0068] The Concrete Curbstone (JC / T 899-2016) requires that the average compressive strength of the concrete curbstone is 30 MPa, and the minimum value of a single piece is 24 MPa. Analyzing the data in the table, the 7-day and 28-day compressive strengths of the basic group are 19.6 MPa and 23.5 MPa, respectively, the 7-day and 28-day compressive strengths of the water glass group are 26.3 MPa and 31.5 MPa, 26.8 MPa and 31.8 MPa, respectively, and the 7-day and 28-day compressive strengths of the limestone powder group are 25.2 MPa and 32.7 MPa, respectively. The compressive strength of the basic group does not meet the specification requirements, and after the addition of water glass and limestone powder, the alkali activation enhances the activity of red mud, produces more gel materials, and the 7-day and 28-day compressive strengths of the concrete are significantly improved.

[0069] The specimens in the base group fractured after 24 hours of curing, indicating poor flexural strength. However, the addition of an alkali activator gave the red mud concrete some flexural strength. Limestone powder can activate the red mud and generate more gel material, but the granular limestone powder reduces the adhesion between the gel material and the aggregate, thus having a limited effect on improving the flexural strength of the red mud concrete. Its 28-day strength was 3.8 MPa, slightly lower than that of the water glass group. The mixing effect of water glass and red mud was better than that of limestone powder, with 28-day flexural strengths of 4.7 MPa and 4.4 MPa respectively. The specification requires an average flexural strength of 3.5 MPa, and both groups meet the specification requirements.

[0070] The water absorption of the red mud concrete specimens was tested. The 100mm×100mm×100mm specimens were placed in an oven and dried at 105℃. They were weighed every 4 hours until a constant weight m1 was reached. Then they were taken out and immersed in water for 24 hours. After being wiped dry, the mass m2 was measured. The results are shown in Table 4.

[0071] Table 4 Water absorption rate of red mud concrete

[0072] According to the specifications, the water absorption rate of red mud concrete should not exceed 6.0%. The average water absorption rate of the red mud concrete in the foundation group was 3.36%, while the average water absorption rate of the water glass group decreased to 2.18% and 2.61%, and the average water absorption rate of the limestone powder group was 2.89%. All groups were significantly lower than the specified values. This indicates that both water glass and limestone powder can effectively improve the pore structure of red mud concrete. The SiO3 produced by the dissociation of water glass in an alkaline environment... 2- With Ca in red mud 2+ The reaction produces calcium silicate gel (CSH) to fill the pores, and water glass forms a dense sodium silicate protective layer on the concrete surface, reducing the water absorption rate of red mud. The dissolution of limestone powder provides Ca. 2+ It reacts with SiO2 in red mud to form calcium silicate gel (CSH) to fill the pores. Limestone powder particles can also fill the pores, but they lack active silica-alumina components and have low chemical reactivity, so they cannot produce enough calcium silicate gel to fill the pores. Therefore, the water absorption rate is slightly higher than that of the water glass group.

[0073] The abrasion resistance of the red mud concrete specimens was tested. The 100 mm x 100 mm x 100 mm specimens were maintained for 28 days, then naturally air-dried for 12 hours, and then dried in an oven at 60°C for 12 hours until constant weight. The floating dust on the surface of the specimen was brushed off, the specimen was placed on the horizontal turntable of the abrasion tester and clamped with a clamp, then abraded for 30 turns under a load of 200N, the dust on the surface of the specimen was brushed off and weighed, and the initial mass m1 of the specimen was recorded. Then the specimen was abraded for 60 turns under a load of 200N, the dust on the surface of the specimen was brushed off and the remaining mass m2 of the specimen was weighed, and the abrasion amount was calculated according to the formula: ; wherein G c is the abrasion amount per unit area (kg / m 2 ), m1 is the initial mass, m2 is the remaining mass, and A is the abrasion area (m 2 ); The arithmetic mean of the abrasion amount of the specimen was calculated, and the results are shown in Table 5.

[0074] Table 5. Abrasion resistance test results of red mud concrete

[0075] The abrasion amount per unit area of the red mud concrete of the base group was 2.925 kg / m 2 , the abrasion amount per unit area of the water glass group was 1.573 kg / m 2 and 1.549 kg / m 2 , and the abrasion amount per unit area of the limestone powder group was 1.851 kg / m 2 . The abrasion amount of the red mud concrete of the water glass group was lower, indicating that the adhesion inside the specimen was good. As a strong alkaline activator, water glass can activate the active silica-aluminum components in red mud, promote the formation of more hydrated calcium silicate gel and aluminosilicate network, improve the compactness of the cementitious system inside the specimen, improve the adhesion strength of the interfacial transition zone between the aggregate and the paste, and there is also a dense silicate gel film on the surface, reducing the peeling during abrasion and enhancing the abrasion resistance. The interfacial transition zone between limestone powder and red mud is weak, and the surface layer is easy to peel off under external load, so the abrasion amount per unit area of the concrete specimen of the limestone powder group is relatively high compared to the water glass group.

[0076] The frost resistance of the red mud concrete test piece was tested, and the test piece was placed in water at 18-22°C for 4d, and then taken out and dried before being subjected to freeze-thaw cycle test. The freeze-thaw temperature was -18-20°C, and the slow freezing method was used. The freezing time was set to 4h, and the thawing time was set to 2h. The freeze-thaw cycle was performed for 50 times, and the appearance of the test piece was checked every 25 times. The results are shown in Table 6.

[0077] Table 6 Frost resistance test results of red mud concrete

[0078] The specification requires that the mass loss rate of red mud concrete after 50 freeze-thaw experiments be not more than 3%. The average mass loss rate of the red mud concrete test piece of the base group was 3.25%, which exceeded the specification limit. The average mass loss rate of the water glass group was 1.35% and 1.38%, which was reduced by 58% compared with the base group. The average mass loss rate of the limestone powder group was 2.02%, which was reduced by 38% compared with the base group. The water glass group and the limestone powder group both met the specification requirements.

[0079] The red mud concrete test piece was subjected to anti-melting agent erosion test according to the “Standard for Testing Methods for Long-term Performance and Durability of Ordinary Concrete”. The test piece of 100mmx100mmx100mm was cured for 28d, then the surface was cleaned and placed in an oven at 80°C for 2d. The test piece was taken out, naturally cooled to room temperature and kept dry. The test piece was placed in a test piece box, with a 20mm gap between adjacent test pieces. Then the melting agent (sodium chloride) was fully dissolved and poured into the test piece box, with the liquid level being 20mm higher than the test piece. After soaking for 8h, the test piece was taken out and air dried, and then placed in an oven at 20°C for 6h, which was one freeze-thaw cycle. Then the test piece was placed in the solution again for the next freeze-thaw cycle. The corrosion resistance coefficient of compressive strength was calculated according to the formula: ; In the formula, K f is the corrosion resistance coefficient of compressive strength, f cn is the measured value of compressive strength after N freeze-thaw cycles; f c0 is the initial compressive strength of the test piece. The results are shown in Table 7.

[0080] Table 7 Freeze-thaw cycle results of red mud concrete

[0081] The average compressive strength corrosion resistance coefficient of the base group of red mud concrete after 15 freeze-thaw cycles is 95.13%, the average compressive strength corrosion resistance coefficient after 30 freeze-thaw cycles is 86.92%, the average corrosion resistance coefficient of the water glass group of red mud concrete after 15 freeze-thaw cycles is 96.61% and 97.16%, the average corrosion resistance coefficient after 30 freeze-thaw cycles is 94.81% and 94.03%, the corrosion resistance coefficient of the limestone powder group of red mud concrete after 15 freeze-thaw cycles is 97.55%, and the corrosion resistance coefficient after 30 freeze-thaw cycles is 96.95%. According to the specification requirements, the corrosion resistance coefficient of the concrete curb test piece after 30 freeze-thaw cycles is not less than 75%, which meets the strength grade KS30.

[0082] Although the specific embodiments of the present application are described in detail with reference to the embodiments, it should not be understood as limiting the scope of protection of the patent. Various modifications and variations that can be made by those skilled in the art within the scope described in the claims are still within the scope of protection of the patent.

Claims

1. A red mud-based multi-component solid waste cementitious material, characterized in that, The components include the following parts by weight: 30-40 parts red mud, 5-15 parts fly ash, 10-20 parts slag powder, 30 parts silicate cement, 4 parts dihydrate gypsum, and 2-25 parts alkaline activator.

2. The red mud-based multi-component solid waste cementitious material according to claim 1, characterized in that: The alkaline activator is water glass.

3. The red mud-based multi-element solid waste cementitious material according to claim 2, characterized in that: The modulus of the water glass is 1.7 to 3.

4.

4. The red mud-based multi-component solid waste cementitious material according to claim 3, characterized in that, The components include the following parts by weight: 40 parts red mud, 10 parts fly ash, 20 parts slag powder, 30 parts silicate cement, 4 parts dihydrate gypsum, and 4 parts water glass.

5. The red mud-based multi-element solid waste cementitious material according to claim 1, characterized in that: The alkaline activator is limestone powder.

6. The red mud-based multi-component solid waste cementitious material according to claim 5, characterized in that, The components include the following parts by weight: 40 parts red mud, 10 parts fly ash, 20 parts slag powder, 30 parts silicate cement, 4 parts dihydrate gypsum, and 10 parts limestone powder.

7. The method for preparing the red mud-based multi-component solid waste cementitious material according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1: Grind the red mud into powder, dry it, and then filter it through a 0.075mm sieve to obtain red mud powder; S2: Weigh the raw materials according to the mass fraction, then mix and stir for 3-5 minutes until uniform to obtain red mud-based cementitious material.

8. The application of the red mud-based multi-component solid waste cementitious material according to any one of claims 1 to 6 in the preparation of building materials.

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