An ultra-sulfate-activated low-carbon cementitious material based on alkali-containing solid waste as raw material and a preparation method thereof

Abstract

The application discloses a kind of based on containing alkali solid waste as raw material's super sulphate salt excitation low carbon cementing material and preparation method thereof, the cementing material includes the following raw material components by mass percentage: red mud precursor cementing material 30-50%, solid waste material 34-54%, alkali excitation agent 0.5-2%, sulphate salt excitation agent 10-20%.The application expands the application range of sulphate salt excitation low carbon cementing material system, can realize efficient utilization of red mud, makes red mud and other alkaline solid waste become its necessary component, can solve the problem of shortage of high-quality auxiliary cementing material and environmental problem caused by red mud stockpiling simultaneously;The hot activated red mud in the formula of the application not only provides high-activity aluminosilicate potential for the development of cementing material performance, but also provides suitable alkalinity to make up for the strength decline caused by the lack of alkali in the later stage of the system, promote the improvement of mechanical strength of cementing material, matrix densification.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of building materials, and particularly relates to a super-sulfate activated low-carbon cementitious material based on alkali-containing solid waste as raw material and a preparation method thereof. BACKGROUND

[0002] Red mud is a strong alkaline solid waste produced in the process of producing alumina by the Bayer method, and its discharge volume is huge, but its utilization rate is very low. The treatment method mainly by damming not only occupies a large amount of land resources, but also has major safety hazards such as alkali leaching of soil and pollution of underground water.

[0003] Aluminosilicate solid waste partially replacing cement clinker is a commonly used resource utilization method. For red mud, people often use the aluminum-silicon-rich components in red mud to prepare Portland cement clinker and sulfoaluminate cement clinker; and use the high-iron (about 40-60 wt.%) characteristics of red mud to prepare high-iron mineral phase raw materials or use it as a low-activity aluminosilicate solid waste activity activation component. Therefore, red mud has the potential to be used as an auxiliary cementitious material for cement.

[0004] Super-sulfate cement (SSC) is a kind of low-clinker cement which uses granulated blast furnace slag as the main raw material, gypsum as the sulfate activator, and clinker or lime as the alkali activator. The component ratio is usually 75%-85% of slag, 10%-20% of sulfate (such as dihydrate gypsum, anhydrite, phosphogypsum, etc.), and 1%-5% of alkali components (such as clinker, calcium hydroxide, lime, etc.). The energy consumption and CO2 emission of super-sulfate cement during preparation are extremely low, and it is a typical low-energy and low-carbon cement. However, high-quality mineral powder is widely used as an auxiliary cementitious material in the cement industry, leading to a shortage of supply. Therefore, activating the high-activity aluminum-silicon components in red mud and replacing a large amount of mineral powder in SSC to prepare red mud-super-sulfate cement (RM-SSC) can effectively solve the problem of shortage of high-quality mineral powder in the production process of SSC.

[0005] Using a thermal activation process can effectively activate the activity of the aluminum-silicon components in red mud. The optimal thermal activation temperature of red mud is 900°C, at which the most active aluminum is dissolved in red mud, and the highest activity (66.38%) is achieved. However, while meeting the high activity of red mud, the high-alkali characteristics of red mud (mainly Na2O, about 5-13 wt.%, and the alkali dissolved after cement hardening hinders the development of long-term strength of cement) will hinder the formation and growth of ettringite and C-S-H gel in the SSC hydration products and restrict the development of early and late strength. Therefore, reasonable regulation of the alkalinity of SSC is the key to the preparation of RM-SSC.

[0006] The alkali metal ions (Na + ) in red mud are solid-solved in calcium sulphoaluminate (C 5-x Na xS2$) crystal structure. In the process of calcining red mud, calcium carbonate (CaCO3, component ratio of 16.50-33.00wt.%) and gypsum (CaSO4·2H2O, component ratio of 7.15-14.30wt.%) are added to prepare a red mud precursor cementitious material containing 5-10wt.% of calcium sulpho-silicate (C5S2$), and the Na + Solid solution characteristics, regulating the alkalinity in the hydration process of red mud, can stabilize the early mechanical strength development of RM-SSC. In addition, C5S2$ is a mineral phase with certain late hydration potential in the presence of aluminum-containing liquid phase. The solid-solution Na + Slow and continuous dissolution in the late hydration process regulates the alkalinity in the late hydration of RM-SSC, continuously stimulates the hydrolysis of unreacted red mud and mineral powder, and provides the necessary environment for the development of late mechanical strength.

[0007] Chelating agents are a class of compounds that can form complexes with metal ions. The mechanism of action is that metal ions interact with ligands containing two or more coordination atoms to form complexes with ring structures, which are currently commonly used in agriculture, medicine, food and other fields. Current studies have shown that chelating agents are also suitable for use in the construction field to complex heavy metal ions in cement concrete. Disodium ethylenediaminetetraacetate is a typical sodium ion chelating agent that can be used to adsorb and complex sodium ions in the environment. Studies have shown that ethylenediamine compounds react with aldehydes, sulfonic acid groups and other functional groups to form intermediates with imine structures, which can be converted into ethylenediamine derivatives containing carbonyl groups through redox reactions, further improving the chelating ability of ethylenediamine and sodium ions. Therefore, the application of chelating agents in red mud-ultrasulphate cement is expected to reduce the influence of excessive alkali in red mud on the environment pH value and thus the early hydration rate of the cementitious material, and improve the early compressive strength.

[0008] Therefore, it is necessary to provide a reliable scheme for using red mud and aluminosilicate solid waste to prepare a cementitious material to realize resource utilization thereof. SUMMARY

[0009] The technical problem to be solved by the present application is to provide an ultra-sulphate activated low-carbon cementitious material based on alkali-containing solid waste as raw material and a preparation method thereof to solve the problems in the prior art. In view of the low activity and high alkalinity of red mud in the process of preparing cementitious materials by dealkalization of traditional high-alkali solid waste, the present application uses a thermal activation process to obtain a certain activity of red mud and to sinter calcium sulpho-silicate with alkali fixation characteristics in the process, so as to regulate the alkalinity in the hydration and hardening process of RM-SSC (red mud-ultrasulphate cement), design a new ultra-sulphate activated low-carbon cementitious material containing alkali solid waste and a preparation method thereof, and solve the problem of rational application of red mud resources, while reducing the over-reliance on high-quality mineral powder in the production process of ultra-sulphate cement.

[0010] To achieve the above object, the technical scheme adopted by the present application is: the present application provides a kind of super sulphate excited low carbon cementitious material based on alkali-containing solid waste as raw material, including the following raw material components by mass percentage: red mud precursor cementitious material 30-50%, solid waste material 34-54%, alkali activator 0.5-2%, sulphate activator 10-20%.

[0011] Preferably, the preparation method of the red mud precursor cementitious material is: mixing red mud, calcium carbonate and dihydrate gypsum, calcining at 950-1050 DEG C for 1-4h, cooling to obtain the red mud precursor cementitious material.

[0012] Preferably, the mass ratio of red mud: calcium carbonate: dihydrate gypsum is 6.9-13.9:2.3:1.

[0013] Preferably, the preparation method of the red mud precursor cementitious material is:

[0014] After drying red mud at 105 DEG C for 48h, using a ball mill to grind for 45min, passing through 80 mesh screen, then mixing uniformly with calcium carbonate and dihydrate gypsum, heating to 1000 DEG C at a heating rate of 5 DEG C / min, calcining for 2h, taking out and cooling in air to obtain the red mud precursor cementitious material;

[0015] Preferably, the mass ratio of red mud: calcium carbonate: dihydrate gypsum is 13.9:2.3:1.

[0016] Preferably, the solid waste material is blast furnace slag, the alkali activator is at least one of Portland cement, clinker and calcium hydroxide, and the sulphate activator is at least one of anhydrite, anhydrous gypsum, hemihydrate gypsum, dihydrate gypsum and phosphogypsum.

[0017] Preferably, the raw material components of the super sulphate excited low carbon cementitious material based on alkali-containing solid waste as raw material further include a composite additive with a mass ratio of 0.5-2%, and the composite additive is a mixture of concrete early strength agent, polycarboxylate superplasticizer and ion chelating agent.

[0018] Preferably, the mass ratio of concrete early strength agent: polycarboxylate superplasticizer: ion chelating agent is 4:1:2.

[0019] Preferably, the concrete early strength agent is triethanolamine, and the ion chelating agent is ethylenediamine ion chelating agent.

[0020] Preferably, the raw material components of the super sulphate excited low carbon cementitious material based on alkali-containing solid waste as raw material further include a composite additive with a mass ratio of 0.5-2%, and the composite additive is a mixture of polycarboxylate superplasticizer and modified ethylenediamine ion chelating agent, and the mass ratio of polycarboxylate superplasticizer: modified ethylenediamine ion chelating agent is 1:2.

[0021] The modified ethylenediamine ion chelator is prepared by the following method:

[0022] 100-400g ethylenediamine is added to a four-necked flask, 7.5-30g formaldehyde is added dropwise under continuous stirring at 0℃, triethanolamine is added dropwise at the same time to keep the pH of the reaction solution not less than 11, the dropwise adding time is 0.5-2h, then the reaction is carried out at 30-50℃ for 1.5-6h, and the modified ethylenediamine ion chelator is obtained.

[0023] Preferably, the modified ethylenediamine ion chelator is prepared by the following method:

[0024] 200g ethylenediamine is added to a four-necked flask, 15g formaldehyde is added dropwise under continuous stirring at 0℃, triethanolamine is added dropwise at the same time to keep the pH of the reaction solution as 11, the dropwise adding time is 1h, then the reaction is carried out at 40℃ for 3h, and the modified ethylenediamine ion chelator is obtained.

[0025] In the composite additive, the mass ratio of the polycarboxylic acid water reducing agent to the modified ethylenediamine ion chelator is 1:2.

[0026] Preferably, the super-sulphate-activated low-carbon cementitious material based on alkali-containing solid waste as raw material comprises the following raw material components in percentage by mass: 40% of red mud precursor cementitious material, 43% of solid waste material, 1% of alkali-activator, 15% of sulphate-activator, and 1% of composite additive.

[0027] In the second aspect of the present application, a preparation method of the super-sulphate-activated low-carbon cementitious material based on alkali-containing solid waste as raw material is provided, and the preparation method comprises the following steps:

[0028] 1) preparing red mud precursor cementitious material: mixing red mud, calcium carbonate and dihydrate gypsum, calcining at 950-1050℃ for 1-4h, and cooling to obtain the red mud precursor cementitious material;

[0029] 2) mixing the red mud precursor cementitious material with other raw material components for preparing the super-sulphate-activated low-carbon cementitious material to obtain the super-sulphate-activated low-carbon cementitious material based on alkali-containing solid waste as raw material.

[0030] The present application has the following beneficial effects:

[0031] The present application provides a super-sulphate-activated low-carbon cementitious material based on alkali-containing solid waste as raw material and a preparation method thereof, which expands the application range of the sulphate-activated low-carbon cementitious material system, makes red mud and other alkali solid waste become a necessary component, and can solve the problems of shortage of high-quality auxiliary cementitious material and environmental problems caused by red mud storage at the same time.

[0032] The heat-activated red mud (red mud precursor cementitious material) in the formula of the present application not only provides high-activity aluminum-silicon potential for the development of cementitious material performance, but also provides suitable alkalinity to make up for the strength reduction caused by the lack of alkali in the later stage of the system, and promote the improvement of the mechanical strength of the cementitious material and the densification of the matrix.

[0033] The high-iron and high-alkali characteristics of the red mud in the formula of the present application effectively reduce the sintering temperature of calcium sulphoaluminate by about 50-100 DEG C, improve the sinterability of calcium sulphoaluminate, reduce energy loss and carbon emissions in the calcination process; the calcium sulphoaluminate can regulate the concentration of alkali metal ions, and make up for the influence of the high alkalinity in the early stage and the lack of alkalinity in the later stage on the mechanical properties of the cementitious material.

[0034] The organic composite additive C containing the self-made modified ethylenediamine ion chelating agent in the formula of the present application has a significant effect on improving the compressive strength of the cementitious material, the modified ethylenediamine ion chelating agent can effectively chelate sodium ions in the early stage of hydration reaction, form a stable multi-chelating structure, and then reduce the alkalinity in the early hydration environment, which is beneficial to the hydrolysis reaction of the mineral powder and the red mud in the early stage, and promotes the development of the compressive strength.

[0035] The present application can realize the efficient utilization of red mud, provide theoretical support for the application of red mud and the development of sulphate-activated low-carbon cementitious material system; the present application can reduce carbon emissions in the production process of building materials; through solid waste resource utilization, environmental pollution is reduced and resources are saved, which promotes the development of green building and helps the environmental protection and sustainable transformation and upgrading of the building materials industry. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The compressive strength test results of the super-sulphate-activated low-carbon cementitious material of Comparative Example 1, Example Group 1-Example Group 3 are shown in the following table;

[0037] Figure 2 The compressive strength test results of the super-sulphate-activated low-carbon cementitious material of Example Group 2, Example Group 4 and Example Group 5 are shown in the following table;

[0038] Figure 3 The compressive strength test results of the super-sulphate-activated low-carbon cementitious material of Example Group 5 and Example Group 6 are compared. DETAILED DESCRIPTION

[0039] The present application will be further described in detail below with reference to the examples, so that those skilled in the art can implement the present application according to the description.

[0040] It should be understood that the terms such as "have", "contain" and "include" used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0041] The test methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples are commercially available unless otherwise specified. The specific conditions not specified in the following examples are carried out under conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer are conventional products that can be purchased on the market.

[0042] The present application provides a kind of based on containing alkali solid waste as raw material's ultra-sulfate excitation low carbon cementitious material, including the following raw material components by mass percentage: red mud precursor cementitious material 30-50%, solid waste material 34-54%, alkali excitation agent 0.5-2%, sulfate excitation agent 10-20%.

[0043] In a preferred embodiment, the preparation method of the red mud precursor cementitious material is: mixing red mud, calcium carbonate and dihydrate gypsum, calcining at 950-1050 DEG C for 1-4h, cooling to obtain the red mud precursor cementitious material. Among them, the mass ratio of red mud: calcium carbonate: dihydrate gypsum is 6.9-13.9:2.3:1.

[0044] After mixing red mud, calcium carbonate and dihydrate gypsum and high-temperature calcination, the activity of red mud can be excited. Generally, the red mud precursor cementitious material after firing contains 90-99% active red mud, 1-10% calcium sulphosilicate, and the main phases include hematite-Fe2O3, nepheline-KNa3[AlSiO4]4 and calcium sulphosilicate. The activation temperature of red mud is 950-1050 DEG C, and the calcined red mud at this temperature has the highest aluminum active mineral. Calcium sulphosilicate is affected by the iron phase in the red mud during the firing process in the calcium temperature range, and the firing temperature is reduced by 50-100 DEG C.

[0045] In a preferred embodiment, the solid waste material is blast furnace slag, wherein the content of active alumina and silicon oxide is not less than 35% and 15%, respectively.

[0046] In a preferred embodiment, the alkali excitation agent is at least one of commercially available Portland cement (such as P·II 42.5 Portland cement), clinker, calcium hydroxide, etc.

[0047] The sulfate excitation agent is a gypsum mineral, which can be selected from at least one of anhydrite, anhydrous gypsum, hemihydrate gypsum, dihydrate gypsum, phosphogypsum, etc., and the effective ingredient is ≥95%.

[0048] In a preferred embodiment, the raw material components of the ultra-sulfate excitation low carbon cementitious material based on containing alkali solid waste as raw material also include a composite additive with a mass ratio of 0.5-2%, and the composite additive is a mixture of concrete early strength agent, polycarboxylic acid water reducer and ion chelating agent.

[0049] The mass ratio of the concrete early strength agent, the polycarboxylate superplasticizer and the ion chelating agent is 4:1:2.

[0050] The concrete early strength agent is triethanolamine, and the ion chelating agent is ethylenediamine ion chelating agent.

[0051] In another preferred embodiment, the raw material component of the super-sulfate-activated low-carbon cementitious material based on the alkali-containing solid waste as the raw material further comprises 0.5-2% of a composite additive by mass, the composite additive is a mixture of polycarboxylate superplasticizer and modified ethylenediamine ion chelating agent, and the mass ratio of the polycarboxylate superplasticizer to the modified ethylenediamine ion chelating agent is 1:2.

[0052] The modified ethylenediamine ion chelating agent is prepared by the following method:

[0053] 100-400g of ethylenediamine is added to a four-necked flask, 7.5-30g of formaldehyde is added dropwise under continuous stirring at 0℃, triethanolamine is added dropwise at the same time to keep the pH of the reaction solution not less than 11, the dropwise adding time is 0.5-2h, and then the reaction is carried out at 30-50℃ for 1.5-6h to obtain the modified ethylenediamine ion chelating agent.

[0054] In a more preferred embodiment, the modified ethylenediamine ion chelating agent is prepared by the following method:

[0055] 200g of ethylenediamine is added to a four-necked flask, 15g of formaldehyde is added dropwise under continuous stirring at 0℃, triethanolamine is added dropwise at the same time to keep the pH of the reaction solution as 11, the dropwise adding time is 1h, and then the reaction is carried out at 40℃ for 3h to obtain the modified ethylenediamine ion chelating agent.

[0056] In the composite additive, the mass ratio of the polycarboxylate superplasticizer to the modified ethylenediamine ion chelating agent is 1:2.

[0057] In the preparation process of the modified ethylenediamine ion chelating agent, the triethanolamine added for pH control can also serve as the concrete early strength agent, so the composite additive does not need to add the concrete early strength agent at this time. In this embodiment, the triethanolamine can play the role of pH control in the preparation process of the modified ethylenediamine ion chelating agent, and can also serve as the active component of the composite additive as the concrete early strength agent in the subsequent process, which can save the production cost of the composite additive, and can make the triethanolamine and the ethylenediamine ion chelating agent have better uniformity, and be more conducive to their respective roles in the cementitious material.

[0058] The application further provides a preparation method of the super-sulfate-activated low-carbon cementitious material based on the alkali-containing solid waste as the raw material, which comprises the following steps:

[0059] 1) Preparing a red mud precursor gelling material: mixing red mud, calcium carbonate, and dihydrate gypsum, calcining at 950-1050° C. for 1-4 hours, and cooling to obtain a red mud precursor gelling material;

[0060] 2) The red mud precursor gelling material is uniformly mixed with other raw material components for preparing the supersulfate-activated low-carbon gelling material to obtain a supersulfate-activated low-carbon gelling material based on alkali-containing solid waste as a raw material.

[0061] The working principles of each part of the supersulfate-activated low-carbon cementitious material system of the present invention are as follows:

[0062] (1) Red mud thermal activation mechanism: Under high temperature, the common top connections of the stable silicon-oxygen tetrahedron and aluminum-oxygen octahedron structures in red mud are separated, and broken bonds and activation points exist. The inert phase decomposes to produce active silicon-aluminum substances, thus showing volcanic ash activity.

[0063] (2) Mechanism of action of calcium sulfosilicate: alkali metal ions (mainly Na + ) mainly replaces calcium ions (Ca 2+ ) is dissolved in calcium sulfosilicate (C5S2$) to alleviate the influence of the high alkalinity of red mud on the stability of early hydration products such as ettringite. At the same time, C5S2$ has a certain potential for late hydration reaction and can still slowly release Na after 28 days of hydration. + , regulate pH changes and continuously stimulate the hydration and decomposition of unreacted raw materials (mainly mineral powder) to promote later strength growth.

[0064] The hydration mechanism of sulfate-activated cementitious material system: The main hydration products are trisulfur-type hydrated calcium sulfoaluminate (ettringite) and hydrated calcium silicate gel. During the hydration process, sulfate and clinker are first dissolved in the system to form OH - ions, Ca 2+ ions, SO4 2- ions and a small amount of Al 3+ ions and Si 4+ At this time, a small amount of hydrated calcium silicate gel and hydrated calcium aluminate gel will be formed, and then the hydrated calcium aluminate gel will react with the SO4 in the system. 2- However, due to the limited amount of clinker, the Al in the system 3+ ions and Si 4+ As the reaction proceeds, the substances in the system continue to dissolve, causing the system alkalinity to reach a certain level. Under the action of OH- ions, the surface structure of the slag is destroyed, causing active SiO2 and active Al2O3 to precipitate, producing more Al 3+ ions and Si 4+ ions, thereby forming more hydrated calcium silicate gel and hydrated calcium aluminate gel, and then in SO4 2-Calcium aluminate is formed under the action of ions.

[0065] The hydrogen atom of the amino group in the ethylenediamine chelating agent forms a nitrogen-metal coordination bond with the metal ion, and the oxygen ion of the acetic acid group forms an oxygen-metal coordination bond with the metal ion, and finally a complex is formed; the triethanolamine is a surface active agent, which accelerates the hydration of C3A and the formation of calcium aluminate in the hydration process of cement, and promotes the development of early strength; the polycarboxylic acid water reducing agent is adsorbed on the surface of the cement particles to make the surface of the cement particles have a negative charge, thereby having an electrostatic repulsion effect, promoting the dispersion of the cement particles and releasing the wrapped water molecules.

[0066] The above is the general idea of the present application, and the following provides detailed examples and comparative examples based thereon to further illustrate the present application.

[0067] The main raw material sources are as follows:

[0068] Red mud from a certain aluminum company in Shandong, the content of alumina ≥20%, the content of silicon oxide ≥17%, the content of alkali ≥8%, and the content of calcium carbonate is analytical pure CaCO 3， Gypsum dihydrate is analytical pure CaSO4·2H2O, and the effective content is ≥99%;

[0069] Mineral powder from Jinan Luxin New Building Material Co., Ltd., the particle size is about 1-100 μm;

[0070] Triethanolamine is purchased from Shanghai Maikelin Biochemical Technology Co., Ltd.;

[0071] The ion chelating agent is ethylenediamine ion chelating agent, which is purchased from Jinan Delan Chemical Co., Ltd.;

[0072] The polycarboxylic acid water reducing agent is produced and manufactured by Jiangsu Subote Company.

[0073] The alkali activator is clinker, which is purchased from Shandong Shanshui Cement Group Co., Ltd.;

[0074] The sulfate activator is gypsum dihydrate.

[0075] I. First, three kinds of red mud precursor cementitious materials: RM0, RM1, RM2 are prepared

[0076] 1. Red mud precursor cementitious material RM0:

[0077] The as-received red mud is dried at 105℃ for 48h, and then ground by a ball mill for 45 minutes and passed through an 80 mesh screen. Subsequently, the red mud is calcined in a muffle furnace at 1000℃, with a heating rate of 5℃ / min, and after reaching the predetermined temperature, it is kept for 2h, and then taken out and rapidly cooled in air to room temperature to obtain RM0, which is stored in a sealed bag for use.

[0078] 2. Red mud precursor cementitious material RM1:

[0079] The raw red mud was dried at 105°C for 48h, then ground by a ball mill for 45min, and sieved through an 80-mesh screen. Then the raw red mud, calcium carbonate, and dihydrate gypsum were mixed uniformly according to the mass ratio of 13.9:2.3:1, and then calcined in a muffle furnace at 1000°C with a heating rate of 5°C / min, and then kept at the predetermined temperature for 2h. After that, RM1 was obtained by quenching in air to room temperature, and then stored in a sealed bag for later use.

[0080] 3. Red mud precursor cementitious material RM2:

[0081] The raw red mud was dried at 105°C for 48h, then ground by a ball mill for 45min, and sieved through an 80-mesh screen. Then the raw red mud, calcium carbonate, and dihydrate gypsum were mixed uniformly according to the mass ratio of 6.9:2.3:1, and then calcined in a muffle furnace at 1000°C with a heating rate of 5°C / min, and then kept at the predetermined temperature for 2h. After that, RM2 was obtained by quenching in air to room temperature, and then stored in a sealed bag for later use.

[0082] II. Preparation of two composite additives in advance

[0083] 1. Composite additive B

[0084] The concrete early strength agent (triethanolamine), polycarboxylate superplasticizer, and ion chelating agent (ethylenediamine ion chelating agent) were mixed uniformly according to the mass ratio of 4:1:2 of concrete early strength agent: polycarboxylate superplasticizer: ion chelating agent to obtain composite additive B.

[0085] 2. Composite additive C

[0086] (1) Preparation of modified ethylenediamine ion chelating agent:

[0087] 200g of ethylenediamine was added to a four-necked flask, and 15g of formaldehyde was added dropwise under continuous stirring at 0°C. During the process, triethanolamine was added dropwise to keep the pH of the reaction solution at 11. The dropwise addition time was 1h, and then the reaction was carried out at 40°C for 3h to obtain the modified ethylenediamine ion chelating agent.

[0088] (2) The polycarboxylate superplasticizer and the modified ethylenediamine ion chelating agent were mixed uniformly according to the mass ratio of 1:2 of polycarboxylate superplasticizer: modified ethylenediamine ion chelating agent to obtain composite additive C.

[0089] Example group 1

[0090] Example 1-1

[0091] RM0, mineral powder, dihydrate gypsum, clinker were dry mixed in a dry blender for 10 minutes with the following mass fractions: red mud precursor cementitious material 30%, mineral powder content 54%, dihydrate gypsum 15%, clinker 1% to obtain the cementitious material in Example 1-1, followed by preparation of mortar samples with water to cement (cement refers to the sum of RM0, mineral powder, dihydrate gypsum, clinker, the same below) mass ratio of 0.5.

[0092] Example 1-2

[0093] RM1, mineral powder, dihydrate gypsum, clinker were dry mixed in a dry blender for 10 minutes with the following mass fractions: red mud precursor cementitious material 30%, mineral powder content 54%, dihydrate gypsum 15%, clinker 1% to obtain the cementitious material in Example 1-2, followed by preparation of mortar samples with water to cement mass ratio of 0.5.

[0094] Example 1-3

[0095] RM2, mineral powder, dihydrate gypsum, clinker were dry mixed in a dry blender for 10 minutes with the following mass fractions: red mud precursor cementitious material 30%, mineral powder content 54%, dihydrate gypsum 15%, clinker 1% to obtain the cementitious material in Example 1-3, followed by preparation of mortar samples with water to cement mass ratio of 0.5.

[0096] Example Group 2

[0097] Example 2-1

[0098] RM0, mineral powder, dihydrate gypsum, clinker were dry mixed in a dry blender for 10 minutes with the following mass fractions: red mud precursor cementitious material 40%, mineral powder content 44%, dihydrate gypsum 15%, clinker 1% to obtain the cementitious material in Example 2-1, followed by preparation of mortar samples with water to cement mass ratio of 0.5.

[0099] Example 2-2

[0100] RM1, mineral powder, dihydrate gypsum, clinker were dry mixed in a dry blender for 10 minutes with the following mass fractions: red mud precursor cementitious material 40%, mineral powder content 44%, dihydrate gypsum 15%, clinker 1% to obtain the cementitious material in Example 2-2, followed by preparation of mortar samples with water to cement mass ratio of 0.5.

[0101] Example 2-3

[0102] RM2, mineral powder, dihydrate gypsum, clinker were dry mixed in a dry blender for 10 minutes with the following mass fractions: red mud precursor cementitious material 40%, mineral powder content 44%, dihydrate gypsum 15%, clinker 1% to obtain the cementitious material in Example 2-3, followed by preparation of mortar samples with water to cement mass ratio of 0.5.

[0103] Example Group 3

[0104] Example 3-1

[0105] RM0, mineral powder, dihydrate gypsum, clinker were dry mixed in a dry mixer for 10 minutes at the following mass fractions: red mud precursor cementitious material 50%, mineral powder content 34%, dihydrate gypsum 15%, clinker 1%, to obtain the cementitious material in Example 3-1, and then mortar samples were prepared at a water-cement ratio of 0.5.

[0106] Example 3-2

[0107] RM1, mineral powder, dihydrate gypsum, clinker were dry mixed in a dry mixer for 10 minutes at the following mass fractions: red mud precursor cementitious material 50%, mineral powder content 34%, dihydrate gypsum 15%, clinker 1%, to obtain the cementitious material in Example 3-2, and then mortar samples were prepared at a water-cement ratio of 0.5.

[0108] Example 3-3

[0109] RM2, mineral powder, dihydrate gypsum, clinker were dry mixed in a dry mixer for 10 minutes at the following mass fractions: red mud precursor cementitious material 50%, mineral powder content 34%, dihydrate gypsum 15%, clinker 1%, to obtain the cementitious material in Example 3-3, and then mortar samples were prepared at a water-cement ratio of 0.5.

[0110] Comparative Example 1

[0111] Mineral powder, dihydrate gypsum, clinker were dry mixed in a dry mixer for 10 minutes at the following mass fractions: mineral powder content 84%, dihydrate gypsum 15%, clinker 1%, to obtain a sulphate cement cementitious material, and then mortar samples were prepared at a water-cement ratio of 0.5.

[0112] The method for preparing the mortar samples is as follows:

[0113] The cementitious material and water were mixed and stirred at a slow stirring speed (62±5 r / min) for 120 s, then at a fast stirring speed (125±10 r / min) for 120 s after a 15 s pause; then the mixture was loaded into a 40 mm*40 mm*40 mm mold, compacted, and transferred to a curing chamber (203℃, RH 95%) for curing until 1 day demolding, and then continued to be cured in the curing chamber until 3 days and 28 days, after which the compressive strength of the sample was tested according to the “Cement mortar strength test method” (GB / T 17671-2021).

[0114] The mass proportions of the above Example Group 1-Example Group 3 and the compressive strength test results are shown in Table 1 and Figure 1

[0115] Table 1: Proportions of super-sulphate activated low-carbon cementitious materials of different types and dosages of red mud precursors and their compressive strengths​

[0116]

[0117]

[0118] According to the test results of Table 1 and Figure 1 , the compressive strength results of Example 3d, 28d are shown in Table 2. Figure 1 The compressive strength of the ultra-sulfated low-carbon cement without C5S2$ (i.e., the red mud precursor cementitious material compounded with calcium carbonate and dihydrate gypsum, namely RM1 and RM2) decreases with the increase of the red mud powder replacement rate when hydrated for 3d. This is because the red mud hydrolysis dissolves a large amount of alkali Na + ions, the alkalinity increases, hinders the formation of ettringite, and destroys the structural stability of ettringite, resulting in a decrease in early strength. The compressive strength of the ultra-sulfated low-carbon cement with C5S2$ increases with the increase of the C5S2$ content, because Na + is solid-solved in C5S2$, regulates the hydration alkalinity, and is conducive to the development of early strength. 2+

[0119] The change trend of the compressive strength of the ultra-sulfated low-carbon cement without C5S2$ is consistent with that at 3d when hydrated for 28d. However, the compressive strength of the ultra-sulfated low-carbon cement with C5S2$ increases significantly with the increase of the C5S2$ content, and when using RM1 red mud cementitious material, the 28d strength of each group of samples has exceeded or is close to the SSC strength, and when using RM2 cementitious material, the 28d strength of each group of samples is increased by 6.22%-14.51% compared with the SSC strength. This is because C5S2$ starts to slowly and continuously hydrolyze after hydration, sodium ions solid-solved in C5S2$ are gradually dissolved out, the environmental alkalinity is increased, which is conducive to making up for the problem of alkali deficiency of SSC in the later stage, further promoting the hydrolysis reaction of the mineral powder, and ensuring the development of the later strength. In addition, when using RM1 and RM2 red mud cementitious materials, the compressive strength of the red mud with 30% mineral powder replacement is basically the same as that of the red mud with 40% mineral powder replacement. Therefore, using RM1 cementitious material to replace 40% of the mineral powder to prepare red mud-ultra-sulfated cement can maximize the alleviation of the problems of red mud accumulation and shortage of mineral powder, and realize the resource utilization of solid waste.

[0120] Therefore, based on the addition amount of 40% of the red mud precursor cementitious material, the further optimization of the influence of the composite additive on the strength of the material is carried out.

[0121] Example group 4

[0122] In the proportions of Examples 2-1, 2-2, and 2-3, 1wt% of additive A (ethylenediamine ion chelating agent) is added, and the content of the mineral powder is correspondingly reduced to 43wt%; ​

[0123] The additive A was first added to the water used to prepare the mortar samples, stirred for 5 min to make it uniformly dispersed, and then mixed with the remaining raw materials together with the water to prepare the mortar samples, and the method was the same as that of Example 2 group, and the samples of Example 4-1, Example 4-2, and Example 4-3 were obtained in turn.

[0124] Example group 5

[0125] In the proportioning of Examples 2-1, 2-2, and 2-3, 1% of the self-made organic composite additive B was added, and the content of the mineral powder was correspondingly reduced to 43wt%;

[0126] The additive B was first added to the water used to prepare the mortar samples, stirred for 5 min to make it uniformly dispersed, and then mixed with the remaining raw materials together with the water to prepare the mortar samples, and the method was the same as that of Example 2 group, and the samples of Example 5-1, Example 5-2, and Example 5-3 were obtained in turn.

[0127] Example group 6

[0128] In the proportioning of Examples 2-1, 2-2, and 2-3, 1% of the self-made organic composite additive C was added, and the content of the mineral powder was correspondingly reduced to 43wt%;

[0129] The additive C was first added to the water used to prepare the mortar samples, stirred for 5 min to make it uniformly dispersed, and then mixed with the remaining raw materials together with the water to prepare the mortar samples, and the method was the same as that of Example 2 group, and the samples of Example 6-1, Example 6-2, and Example 6-3 were obtained in turn.

[0130] The proportioning summary and the compressive strength test results of the above Example groups 4-6 are shown in Table 2 and Figures 2-3

[0131] Table 2 Influence of different additives on the compressive strength of ultra-sulfate activated low-carbon cementitious materials

[0132]

[0133] According to the test results, the compressive strengths of 3d and 28d groups were compared Figure 2 ​), the compressive strength of Example 4-1 is only increased by 5% compared with that of Comparative Example 2-1, while the early strength of Example 5-1 is increased by up to 85% under the action of organic solvent B. After the RM1 and RM2 red mud cementitious materials are used to replace RM0, the early compressive strength is obviously increased, and the early strength of Example 5-2 and Example 5-3 exceeds that of Comparative Example 1, which shows that the organic composite additive B can effectively improve the 3d compressive strength of the red mud-ultrasulfated cementitious material, so that it reaches or exceeds the 3d compressive strength of the ultrasulfated cement. After 28d of hydration, the compressive strength of Example 4 is obviously improved compared with that of Comparative Example 1, and the compressive strength is increased by 4.3%, 2.52% and 4.11% respectively under the action of different red mud materials, while the compressive strength of Example 5 containing self-made organic solvent B is increased by 7.30%, 5.12% and 10.40% respectively, and at this time, the compressive strength of each group of samples reaches or exceeds the 28d compressive strength of the ultrasulfated cement.

[0134] The compressive strength test results of Example Group 5 and Example Group 6 are shown in Table 5 and Table 6 respectively. Figure 3

[0135] The improvement effect of the compressive strength by using the organic composite additive C containing the self-made modified ethylenediamine ion chelating agent is significantly higher than that of the organic composite additive B, which is due to the fact that the self-made modified ethylenediamine ion chelating agent can effectively chelate sodium ions in the early stage of hydration reaction to form a stable multi-chelating structure, thereby reducing the alkalinity in the early hydration environment, which is beneficial to the early hydrolysis reaction of the mineral powder and the red mud and promotes the development of the compressive strength.

[0136] In summary, the organic composite additive C added in the present application has a significant and stable effect of improving the early and late mechanical properties of the red mud-ultrasulfated cement (i.e. the above-mentioned ultrasulfated activated low-carbon cementitious material); and the present application can solve the problem of shortage of high-quality mineral powder in the preparation of ultrasulfated cement by activating the activity of the activated red mud cementitious material, so as to achieve the purpose of resource utilization of the red mud material.

[0137] Although the embodiments of the present application have been disclosed as above, they are not limited to the application listed in the specification and the embodiments, and can be fully applied to various fields suitable for the present application, and other modifications can be easily realized by those skilled in the art, and therefore the present application is not limited to specific details under the general concept defined by the claims and the equivalent scope.​

Claims

1. A super-sulfated activated low-carbon cementitious material based on alkali-containing solid waste as raw material, characterized in that, The raw material components include, by mass percentage, the following: red mud precursor cementitious material 30-50%, solid waste material 34-54%, alkali activator 0.5-2%, sulphate activator 10-20%; The raw material components of the super-sulphate activated low-carbon cementitious material further include a composite additive with a mass percentage of 0.5-2%, the composite additive being a mixture of polycarboxylate superplasticizer and modified ethylenediamine ion chelator, the mass ratio of polycarboxylate superplasticizer to modified ethylenediamine ion chelator being 1:2; The modified ethylenediamine ion chelator is prepared by the following method: 100-400g of ethylenediamine is added to a four-necked flask, 7.5-30g of formaldehyde is added dropwise under continuous stirring at 0℃, triethanolamine is added dropwise at the same time to keep the pH of the reaction solution not less than 11, the dropwise adding time is 0.5-2h, then the reaction is carried out at 30-50℃ for 1.5-6h to obtain the modified ethylenediamine ion chelator.

2. The ultra-sulfated activated low-carbon cementitious material based on alkali-containing solid waste as raw material according to claim 1, characterized in that, The preparation method of the red mud precursor cementitious material is as follows: red mud, calcium carbonate and dihydrate gypsum are mixed, calcined at 950-1050℃ for 1-4h, and then cooled to obtain the red mud precursor cementitious material.

3. The ultra-sulfated activated low-carbon cementitious material based on alkali-containing solid waste as raw material according to claim 2, characterized in that, The mass ratio of red mud:calcium carbonate: dihydrate gypsum is 6.9-13.9:2.3:

1. The preparation method of the red mud precursor cementitious material is as follows:

4. The ultra-sulfated salt-activated low-carbon cementitious material based on alkali-containing solid waste as raw material according to claim 3, characterized in that, After the red mud is dried at 105℃ for 48h, it is ground by a ball mill for 45min, then passed through an 80-mesh screen, and then mixed uniformly with calcium carbonate and dihydrate gypsum, heated to 1000℃ at a heating rate of 5℃ / min, calcined for 2h, and then cooled in air to obtain the red mud precursor cementitious material. The mass ratio of red mud:calcium carbonate: dihydrate gypsum is 13.9:2.3:

1. The solid waste material is blast furnace slag, the alkali activator is at least one of Portland cement, clinker and calcium hydroxide, and the sulphate activator is at least one of hard gypsum, anhydrous gypsum, hemihydrate gypsum, dihydrate gypsum and phosphogypsum.

5. The ultra-sulfated salt-activated low-carbon cementitious material based on alkali-containing solid waste as raw material according to claim 1, characterized in that, The raw material components further include a composite additive with a mass percentage of 0.5-2%, the composite additive being a mixture of concrete early strength agent, polycarboxylate superplasticizer and ion chelator; 6. The ultra-sulfated salt-activated low-carbon cementitious material based on alkali-containing solid waste as raw material according to claim 1, characterized in that, The mass ratio of concrete early strength agent:polycarboxylate superplasticizer:ion chelator is 4:1:2; The concrete early strength agent is triethanolamine, and the ion chelator is ethylenediamine ion chelator. The modified ethylenediamine ion chelator is prepared by the following method:

7. The ultra-sulfated salt activated low-carbon cementitious material based on alkali-containing solid waste as raw material according to claim 1, characterized in that, 200g of ethylenediamine is added to a four-necked flask, 15g of formaldehyde is added dropwise under continuous stirring at 0℃, triethanolamine is added dropwise at the same time to keep the pH of the reaction solution at 11, the dropwise adding time is 1h, then the reaction is carried out at 40℃ for 3h to obtain the modified ethylenediamine ion chelator. The mass ratio of polycarboxylate superplasticizer to modified ethylenediamine ion chelator in the composite additive is 1:

2. The raw material components include, by mass percentage, the following: red mud precursor cementitious material 40%, solid waste material 43%, alkali activator 1%, sulphate activator 15%, and composite additive 1%.

8. The hyper-sulphate-activated low-carbon cementitious material based on alkali-containing solid waste as raw material according to any one of claims 5-7, characterized in that, The method comprises the following steps:

9. A method for preparing an ultrahydrogensulfate-activated low-carbon cementitious material based on alkali-containing solid waste as a raw material according to any one of claims 1-8, characterized in that, The method comprises the following steps: 1) preparing a red mud precursor cementitious material: mixing red mud, calcium carbonate, dihydrate gypsum, calcining at 950-1050℃ for 1-4h, cooling to obtain a red mud precursor cementitious material; 2) mixing the red mud precursor cementitious material with other raw material components for preparing the super-sulfate activated low-carbon cementitious material, to obtain the super-sulfate activated low-carbon cementitious material based on the alkali-containing solid waste as raw material.

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