Low-carbon red-mud-based alkali-activated foam concrete and preparation method thereof

Abstract

The invention discloses low-carbon red-mud-based alkali-activated foam concrete and a preparation method thereof, and belongs to the field of low-carbon foam concrete. Specifically, the mix proportion and the preparation method of the low-carbon red-mud-based alkali-activated foam concrete are as follows: P.O42.5 ordinary Portland cement provided by building materials in Qingdao Weidong macro, the I-grade fly ash is S95-grade granulated blast-furnace slag produced by Henan Province Platinon Casting Material Co., Ltd., and Jinshu New Material Co., Ltd., the I-grade fly ash is S95-grade granulated blast-furnace slag produced by Henan Province Platinon Casting Material Co., Ltd. The Bayer process red mud powder is produced by Hebei Province Shihozhuangfei Mine Product Co., Ltd. The exciting agent is selected from an industrial liquid sodium silicate solution produced by Henan Jinmoistening New Material Co., Ltd. And solid sodium hydroxide particles with AR analytical purity of 96%; the admixture is selected from a TR-26C type polycarboxylate superplasticizer produced by Henan Fuhua Information Science and Technology Co., Ltd. And the foaming agent is a TR-E type animal protein foaming agent produced by Henan Zhuichun Information Science and Technology Co., Ltd. Compared with existing foam concrete, the low-carbon alkali-activated foam concrete provided by the invention uses a large amount of industrial solid waste, reduces the use cost, reduces the use amount of cement under the condition of ensuring the compressive strength, and is simple and convenient to operate, reasonable in process, low-carbon, environment-friendly, rapid in cement setting and hardening, and suitable for large-scale use.

Description

Technical Field

[0001] This invention belongs to the field of low-carbon renewable foamed concrete, specifically, it relates to a low-carbon red mud-based alkali-activated foamed concrete and its preparation method. Background Technology

[0002] Foamed concrete is a type of concrete composed of cementitious materials and foam, rich in internal voids. It boasts advantages such as lightweight, good fluidity, and high construction efficiency. The dry density of foamed concrete ranges from 300-1600 kg / m³, equivalent to 1 / 12 to 1 / 2 that of ordinary concrete. Due to its engineering advantages, foamed concrete is widely used in building construction and special projects. Traditional foamed concrete uses cement as its cementitious material. However, cement raw materials are non-renewable, and the preparation process requires high-temperature calcination, resulting in high energy consumption and heavy pollution. Therefore, there is an urgent need for a new material to reduce the dependence of foamed concrete on traditional cement. Alkali-activated cementitious materials are hydraulic cementitious materials formed from raw materials such as slag, fly ash, and kaolinite under the action of alkaline activators (such as water glass). They feature low energy consumption and low emissions, and their performance is comparable to silicate cement. Alkali-activated cementitious materials, formed by activating industrial solid wastes such as slag and fly ash, and natural silica-alumina raw materials such as kaolin with alkaline activators (such as water glass), have become a key path for civil engineering to support the construction of an environmentally friendly society and a core measure for the industry's green transformation due to their low-carbon characteristics (carbon emissions are only 10%-20% of traditional cement) and solid waste disposal capacity (0.8-1.2 tons of solid waste can be consumed per ton of product). Compared with ordinary concrete cementitious materials, alkali-activated cementitious materials have advantages such as early strength, high strength, high temperature resistance, freeze resistance, acid corrosion resistance, and impermeability. In terms of raw materials, ordinary concrete mainly uses silicate cement clinker, which is made by calcining limestone, clay, etc., consuming natural resources and having high energy consumption, while alkali-activated concrete uses industrial waste (such as slag, fly ash, nickel slag) or natural silica-alumina materials (such as metakaolin), without the need for calcination. In terms of reaction products, the main product of ordinary concrete is hydrated calcium silicate gel, commonly known as CSH, with calcium hydroxide crystals as a secondary product. In contrast, alkali-activated concrete produces hydration products including hydrated calcium silicate, hydrated calcium aluminate, hydrated sodium aluminosilicate (NASH), and hydrated calcium aluminosilicate (CASH) gels. Because the reaction process involves dissolving the raw materials and then repolymerizing and reorganizing them, the resulting gels are denser. Red mud is a polluting waste residue discharged after extracting alumina from bauxite. Due to its high Fe2O3 content, it appears red and is commonly called red mud. Currently, red mud is mainly disposed of through stockpiling, which not only occupies a large amount of land but also pollutes the air, soil, and groundwater. Red mud is characterized by its alkalinity, high silica content, high sulfur content, high calcium content, and radioactivity. It contains a large amount of harmful substances, such as heavy metals and fluorides, which, if left untreated, will cause secondary pollution to the environment. Against this backdrop, how to effectively utilize red mud has become one of the most important issues that urgently needs to be addressed. Currently, the utilization rate of red mud remains low, and achieving its high-value utilization remains a long and arduous task. The silica and aluminum oxides in red mud exist as quartz, sodalite, and nepheline, and possess potential cementing activity. Furthermore, the SiO2, Na2O, Al2O3, and CaO it contains are also key components required for alkali-activated cementitious materials.

[0003] Chinese patents CN119930221A, CN119874295A, CN120081641A, and CN120040129A all disclose different methods for preparing foamed concrete. The methods for preparing the foaming agent in all cases involve animal protein or plant protein foaming agents, and different mixing ratios are used to achieve different mechanical and performance properties in the foamed concrete. Most foamed concrete uses cement as the cementitious material. Although cement hydration products have high binding properties, cement production has high carbon emissions. There is still a significant gap in the market for low-carbon, environmentally friendly, lightweight, and early-strength foamed concrete. Summary of the Invention

[0004] To address the current gap in the field of low-carbon foamed concrete, this invention provides a low-carbon alkali-activated foamed concrete and its preparation method. Specifically, P·O 42.5 ordinary Portland cement, Grade I fly ash, S95 grade granulated blast furnace slag, and Bayer process red mud powder are selected as cementitious materials; industrial sodium silicate solution with a modulus of 2.23 and AR analytical grade sodium hydroxide solid particles are selected as alkali activators; TR-E type animal protein foaming agent is used to prepare the foaming liquid at a ratio of 1:30. TR-26C type polycarboxylate superplasticizer and nano-modifier are added as admixtures to obtain lightweight, early-strength, low-carbon, and environmentally friendly alkali-activated foamed concrete, achieving the goal of environmental friendliness.

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

[0006] The preparation scheme for the alkali activator is as follows:

[0007] S1. Take 500 parts of industrial sodium silicate solution, add 500 parts of water and stir evenly, then add 84.5 parts of solid sodium hydroxide granules and stir evenly. Let stand for 24 hours to obtain the product.

[0008] Preferably, the solid sodium hydroxide particles are of analytical grade, 96%;

[0009] Preferably, the industrial sodium silicate solution has a modulus of 2.23 and a Baume degree of 50.5;

[0010] Preferably, municipal tap water is used for the solution;

[0011] Preferably, the solution temperature is 20°C after standing for 24 hours.

[0012] The preparation scheme for the cementitious material is as follows:

[0013] S2. Add 2160 parts of P·O42.5 ordinary Portland cement, 1037 parts of Grade I fly ash, 4147 parts of S95 grade granulated blast furnace slag, and 3460 parts of Bayer process red mud powder in batches. Use a concrete mixer to mix at high speed until the cementitious materials are evenly mixed.

[0014] Preferably, the concrete mixer is a single-shaft horizontal concrete mixer, model HJW-60;

[0015] Preferably, the mixer rotates at 60 revolutions per minute.

[0016] The concrete preparation method is as follows:

[0017] S3. Prepare the foaming liquid at a ratio of 1:30 and foam it using a foam concrete foaming machine. Add all the prepared activator solution to the well-mixed cementitious material and stir thoroughly. After stirring evenly, add 4300 parts of foam to the mixture and continue stirring until uniform.

[0018] Preferably, the activator should be poured in quickly and all at once.

[0019] Preferably, the foaming machine for foamed concrete is the BL-8 model.

[0020] Preferably, the mixer rotates at 60 revolutions per minute.

[0021] Preferably, the stirring time after adding the foam should not exceed 120 seconds.

[0022] After thorough mixing, the low-carbon alkali-activated foamed concrete is ready.

[0023] Compared with existing foamed concrete, the low-carbon alkali-activated foamed concrete of the present invention has the following beneficial effects:

[0024] Alkali activators are simple to prepare, easy to operate, inexpensive, require a short preparation time, and have minimal environmental and human health hazards.

[0025] The alkali activator is liquid and does not require the addition of other hazardous solvents. Furthermore, the entire preparation process involves physical changes and produces no toxic or harmful byproducts.

[0026] Alkali activators have fewer operating steps and a more optimized process, making them suitable for large-scale industrial production.

[0027] Cementitious materials are mostly solid wastes, which can be effectively utilized to reduce cement usage. They achieve low-carbon and environmentally friendly effects while making use of waste. They can be widely used in major infrastructure construction such as road and bridge construction, filling projects, pothole backfilling, building blocks, and wall filling.

[0028] The foamed concrete developed its early strength quickly, reaching more than 80% of its 28-day strength in 7 days.

[0029] The resulting foamed concrete has a uniform distribution of micropores, without any foam floating or concrete bleeding. The pores are also uniformly distributed and relatively concentrated in size, ranging from 100 to 250 μm, which is superior to ordinary foamed concrete.

[0030] The resulting foamed concrete has a dry density of 1200 kg / m³, which is much lower than that of ordinary concrete. Attached Figure Description

[0031] Figure 1 The 7-day, 14-day, and 28-day compressive strengths of specimens with different cementitious material mix ratios;

[0032] Figure 2 The initial and final setting times of test blocks with different cementitious material mix ratios. Detailed Implementation

[0033] The main raw materials and instruments required for this invention are as follows:

[0034] Raw materials for the alkali activator: industrial liquid sodium silicate solution with a modulus of 2.23, a Baumé degree of 50.5, a solution density of 1.53 g / cm3, and solid sodium hydroxide granules with an AR analytical purity of 96%. The water used for the solution is municipal water from Qingdao.

[0035] Cementing materials raw materials: P·O42.5 ordinary Portland cement from Weidong Hongyuan Building Materials Co., Ltd. in Qingdao, Shandong Province; Class I fly ash from Borun Casting Materials Co., Ltd. in Henan Province; S95 grade granulated blast furnace slag from Jinhong New Materials Co., Ltd. in Lingshou County; Bayer process red mud powder from Lianhang Mineral Products Co., Ltd. in Shijiazhuang, Hebei Province; and municipal water from Qingdao City for mixing.

[0036] Foaming agent raw materials: TR-E type animal protein foaming agent from Henan Tongrun Information Technology Co., Ltd.; the water used for the solution is municipal water from Qingdao.

[0037] Raw materials for admixtures: TR-26C type polycarboxylate superplasticizer and nano-modifier from Henan Tongrun Information Technology Co., Ltd.

[0038] Instruments: Single-shaft horizontal rail forced concrete mixer, model HJW-60, universal testing machine, foam quality tester, foamed concrete foaming machine, standard concrete test mold, and concrete curing box.

[0039] The preparation method of low-carbon alkali-activated foamed concrete includes the preparation of alkali activator, the mixing of cementitious materials, and the production of foamed concrete:

[0040] S1. Take 500 parts of industrial sodium silicate solution, add 500 parts of water and stir evenly, then add 84.5 parts of solid sodium hydroxide granules and stir evenly. Let stand for 24 hours to obtain the product.

[0041] S2. Add 2160 parts of P·O42.5 ordinary Portland cement, 1037 parts of Grade I fly ash, 4147 parts of S95 grade granulated blast furnace slag, and 3460 parts of Bayer process red mud powder in batches. Use a concrete mixer to mix at high speed until the cementitious materials are evenly mixed.

[0042] S3. Prepare the foaming liquid at a ratio of 1:30 and foam it using a foam concrete foaming machine. Add all the prepared activator solution to the well-mixed cementitious material and stir thoroughly. After stirring evenly, add 4300 parts of foam to the mixture and continue stirring until uniform.

[0043] The specific implementation method is as follows:

[0044] Example 1

[0045] A low-carbon alkali-activated foamed concrete comprises: an alkali activator, a foaming agent, cementitious materials, and admixtures. The alkali activator includes industrial sodium silicate solution and sodium hydroxide solid particles; the foaming agent includes TR-E type animal protein foaming agent; the cementitious materials include P·O 42.5 ordinary Portland cement, Grade I fly ash, S95 grade granulated blast furnace slag, and Bayer process red mud powder; the admixtures include TR-26C type polycarboxylate superplasticizer and nano-modifiers. The test water was municipal water from Qingdao City.

[0046] The Bayer process red mud powder accounts for 40% of the total mass of the cementitious materials, P·O 42.5 ordinary Portland cement accounts for 10%, Grade I fly ash accounts for 25%, and S95 grade granulated blast furnace slag accounts for 25%. The activator is prepared according to the aforementioned method, and the foaming agent is prepared as a foaming liquid at a dilution ratio of 1:30. Based on the total mass of the cementitious materials, the addition amount of TR-26C type polycarboxylate superplasticizer and nano-modifier is 1%.

[0047] Example 2

[0048] A low-carbon alkali-activated foamed concrete comprises: an alkali activator, a foaming agent, cementitious materials, and admixtures. The alkali activator includes industrial sodium silicate solution and sodium hydroxide solid particles; the foaming agent includes TR-E type animal protein foaming agent; the cementitious materials include P·O 42.5 ordinary Portland cement, Grade I fly ash, S95 grade granulated blast furnace slag, and Bayer process red mud powder; the admixtures include TR-26C type polycarboxylate superplasticizer and nano-modifiers. The test water was municipal water from Qingdao City.

[0049] The Bayer process red mud powder accounts for 40% of the total mass of the cementitious materials, P·O 42.5 ordinary Portland cement accounts for 10%, Grade I fly ash accounts for 16.7%, and S95 grade granulated blast furnace slag accounts for 33.3%. The activator is prepared according to the aforementioned method, and the foaming agent is prepared as a foaming liquid at a dilution ratio of 1:30. Based on the total mass of the cementitious materials, the addition amount of TR-26C type polycarboxylate superplasticizer and nano-modifier is 1%.

[0050] Example 3

[0051] A low-carbon alkali-activated foamed concrete comprises: an alkali activator, a foaming agent, cementitious materials, and admixtures. The alkali activator includes industrial sodium silicate solution and sodium hydroxide solid particles; the foaming agent includes TR-E type animal protein foaming agent; the cementitious materials include P·O 42.5 ordinary Portland cement, Grade I fly ash, S95 grade granulated blast furnace slag, and Bayer process red mud powder; the admixtures include TR-26C type polycarboxylate superplasticizer and nano-modifiers. The test water was municipal water from Qingdao City.

[0052] The Bayer process red mud powder accounts for 40% of the total mass of the cementitious materials, P·O 42.5 ordinary Portland cement accounts for 10%, Grade I fly ash accounts for 12.5%, and S95 grade granulated blast furnace slag accounts for 37.5%. The activator is prepared according to the aforementioned method, and the foaming agent is prepared as a foaming liquid at a dilution ratio of 1:30. Based on the total mass of the cementitious materials, the addition amount of TR-26C type polycarboxylate superplasticizer and nano-modifier is 1%.

[0053] Example 4

[0054] A low-carbon alkali-activated foamed concrete comprises: an alkali activator, a foaming agent, cementitious materials, and admixtures. The alkali activator includes industrial sodium silicate solution and sodium hydroxide solid particles; the foaming agent includes TR-E type animal protein foaming agent; the cementitious materials include P·O 42.5 ordinary Portland cement, Grade I fly ash, S95 grade granulated blast furnace slag, and Bayer process red mud powder; the admixtures include TR-26C type polycarboxylate superplasticizer and nano-modifiers. The test water was municipal water from Qingdao City.

[0055] The Bayer process red mud powder accounts for 40% of the total mass of the cementitious materials, P·O 42.5 ordinary Portland cement accounts for 10%, Grade I fly ash accounts for 10%, and S95 grade granulated blast furnace slag accounts for 40%. The activator is prepared according to the aforementioned method, and the foaming agent is prepared as a foaming liquid at a dilution ratio of 1:30. Based on the total mass of the cementitious materials, the addition amount of TR-26C type polycarboxylate superplasticizer and nano-modifier is 1%.

[0056] The experimental results are shown in Table 1. Figure 1 .

[0057] Table 1. Compressive strength of specimens with different cementitious material mix proportions at 7d, 14d, and 28d.

[0058]

[0059] In Examples 1, 2, 3, and 4, the foaming agent was diluted 30 times. All three examples achieved a 7-day compressive strength greater than 80% of the 28-day compressive strength. Early strength development was rapid in each group, while mid-to-late-stage strength development slowed down. Increasing the slag content significantly improved the concrete strength.

[0060] Setting time is an important indicator used in actual concrete engineering. If the initial setting is too early, it will lead to insufficient construction operation time; if the final setting is too late, it will affect the progress of formwork removal and subsequent procedures.

[0061] The results of the setting time are shown in Table 2. Figure 2 .

[0062] Table 2 Initial and final setting times of specimens with different cementitious material mix proportions

[0063] Group Initial setting time / min Final setting time / min Example 1 28 74 Example 2 25 65 Example 3 27 58 Example 4 24 40

[0064] According to the results, the alkali-activated reaction process is faster than that of ordinary Portland cement, and the initial and final setting times of each mix proportion of cementitious materials are significantly shortened compared to cement cementitious materials (initial setting time 70 min, final setting time 240 min).

[0065] The initial setting time and final setting time were the shortest in Example 4. The main reason for this is that the slag content in Example 4 was 40%, and slag has higher alkali activation activity than fly ash, which makes the polymerization reaction more rapid and complete. The cementitious products bond together to form a skeleton, which ultimately results in a shorter setting time.

Claims

1. A low-carbon alkali-activated foamed concrete, characterized in that, The formula components are as follows: Foaming agent 1: TR-E type animal protein foaming agent, diluted at a ratio of 1:30; Cementitious material 1: Ordinary Portland cement, with a mass fraction of 10%; Cementitious material 2: fly ash, with a mass fraction of 10%; Cementitious material 3: Granulated blast furnace slag, with a mass fraction of 40%; Cementitious material 4: Red mud powder, mass fraction 40%; Activator 1: Industrial liquid sodium silicate solution, modulus 2.23; Activator 2: Solid sodium hydroxide granules, AR analytical grade 96%; Admixture 1: TR-26C type polycarboxylate superplasticizer, with a mass fraction of 1% of the cementitious material; Additive 2; Nano-modifier, with a mass fraction of 1% of the cementitious material; Tap water was used for mixing, and its mass fraction was 45% of the cementitious material.

2. The low-carbon red mud-based alkali-activated foamed concrete according to claim 1, characterized in that, Ordinary Portland cement P·O42.5 ordinary Portland cement was selected; Grade I fly ash was selected; S95 grade granulated blast furnace slag produced by Lingshou County Jinhong New Materials Co., Ltd. was selected; Bayer process red mud powder was selected; the industrial liquid sodium silicate solution had a modulus of 2.23, a Baume degree of 50.5, and a water glass density of 1.53 g / cm³. 3 .

3. The method for preparing low-carbon red mud-based alkali-activated foamed concrete according to claim 1, comprising the preparation of the alkali activator, the mixing of the cementitious materials, and the production of the foamed concrete: S1. Take 500 parts of industrial sodium silicate solution, add 500 parts of water and stir evenly, then add 84.5 parts of solid sodium hydroxide granules and stir evenly. Let stand for 24 hours to obtain the product. Preferably, the solid sodium hydroxide particles are of analytical grade, 96%; Preferably, the industrial sodium silicate solution has a modulus of 2.23 and a Baume degree of 50.5; Preferably, municipal tap water is used for the solution; Preferably, the solution temperature is 20°C after standing for 24 hours. S2. Add 2160 parts of P·O42.5 ordinary Portland cement, 1037 parts of Grade I fly ash, 4147 parts of S95 grade granulated blast furnace slag, and 3460 parts of Bayer process red mud powder in batches. Use a concrete mixer to mix at high speed until the cementitious materials are evenly mixed. Preferably, the concrete mixer is a single-shaft horizontal concrete mixer, model HJW-60; Preferably, the mixer rotates at 60 revolutions per minute. S3. Prepare the foaming liquid at a ratio of 1:30 and foam it using a foam concrete foaming machine. Add all the prepared activator solution to the well-mixed cementitious material and stir thoroughly. After stirring evenly, add 4300 parts of foam to the mixture and continue stirring until uniform. Preferably, the activator should be poured in quickly and all at once. Preferably, the foaming machine for foamed concrete is the BL-8 model. Preferably, the mixer rotates at 60 revolutions per minute. Preferably, the stirring time after adding the foam should not exceed 120 seconds. After thorough mixing, the low-carbon alkali-activated foamed concrete is ready.

4. A low-carbon red mud-based alkali-activated foamed concrete, wherein the foamed concrete is prepared according to claim 3, characterized in that, The dry density of the foamed concrete prepared at a dilution ratio of 30 times is 1200 kg / cm³. 3 The compressive strength is greater than 10 MPa, and the 7-day compressive strength is more than 80% of the 28-day compressive strength.

5. The low-carbon red mud-based alkali-activated foamed concrete according to claim 4, characterized in that, The pore size of the foamed concrete prepared at a dilution ratio of 30 times is 100-250μm.

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