A full solid waste-based core-shell type carbonized artificial aggregate and a preparation method thereof

Abstract

A core-shell type carbonized artificial aggregate based entirely on solid waste and its preparation method are disclosed, relating to the field of artificial aggregate technology. The water-cement ratio is 0.15–0.25, comprising, by mass percentage: 10%–30% red mud, 10%–30% steel slag, 35%–50% granulated blast furnace slag, 5%–15% fly ash, 3%–7% alkali activator, and 0.5%–1% water-reducing agent. During the preparation process, a mixture of alkali activator and water-reducing agent is sprayed during granulation. The core is obtained by granulation of a mixture of red mud, steel slag, fly ash, and 37%–60% granulated blast furnace slag. The outer shell is obtained by further granulation of the remaining granulated blast furnace slag on top of the core. Under the condition of meeting national standards, this method helps reduce the excessive use of natural aggregates and the environmental problems caused by the accumulation of industrial solid waste. The preparation method uses a cold bonding method, which is simple and has low energy consumption.

Description

Technical Field

[0001] This invention relates to the field of artificial aggregate technology, specifically to a core-shell type carbonized artificial aggregate based on all solid waste and its preparation method. Background Technology

[0002] In recent years, the development of infrastructure construction worldwide has led to the rapid consumption of building resources, especially key materials such as sand and gravel. Furthermore, the emission of bulk solid waste has significantly exacerbated global warming and had an adverse impact on the environment.

[0003] The preparation technologies for artificial aggregates mainly include high-temperature sintering and cold bonding technologies. High-temperature sintering technology involves huge energy consumption and carbon dioxide emissions, and it is also prone to causing the volatilization of pollutants such as heavy metals in industrial waste, resulting in secondary pollution problems. Therefore, this technology is not suitable for the resource utilization of fly ash from waste incineration. On the other hand, cold bonding technology is based on different cementing systems and uses the hydration reaction or geopolymerization reaction of cementing materials to achieve aggregate hardening. It also achieves the fixation of endogenous pollutants in raw materials through various physicochemical mechanisms such as physical encapsulation, chemical adsorption, and covalent bonding of reaction products. It has the advantages of low energy consumption and high environmental benefits.

[0004] Chinese invention patent application CN202110353517.9 discloses a non-sintering lightweight aggregate, its preparation method, and lightweight concrete. It involves preparing an epoxy resin using epoxy resin, epoxy diluent, epoxy defoamer, and reinforcing powder; adding an epoxy curing agent to the epoxy resin to prepare an epoxy preparative liquid; placing expanded polystyrene in the epoxy preparative liquid to prepare pre-lightweight aggregate; tumbling the pre-lightweight aggregate in construction waste powder to prepare pre-non-sintering lightweight aggregate; and then curing at room temperature to obtain the non-sintering lightweight aggregate. This patent's non-sintering lightweight aggregate can be used to prepare lightweight concrete, offering the advantage of reduced energy consumption. However, its structure consists solely of lightweight aggregate, lacking the structural strength enhancement provided by an outer shell. Chinese invention patent application CN202011103873.7 discloses an artificial steel... Steel slag aggregate and its preparation method, which promotes the precipitation of free calcium oxide in low-activity mineral phases through admixtures, fully utilizes the absorption of CO2 by steel slag, solves the stability problem of steel slag, and improves the workability of steel slag aggregate. However, the use of cement in cementitious materials brings higher raw material costs and indirect carbon emissions. Chinese invention patent application No. CN202011103706.2 discloses a green and energy-saving artificial lightweight aggregate and its preparation method, which is low in cost and can fix CO2. However, the cementitious material used is a steel slag monopolymer cementitious material, and the activity of steel slag needs to be fully activated. The synchronous carbonization equipment used needs to be specially customized, which poses certain difficulties for large-scale industrial use. In addition, the CO2 used is enriched high-concentration CO2, and the enrichment process is accompanied by increased operating and construction costs.

[0005] In summary, given the waste of natural aggregates and the adverse environmental impact of solid waste emissions, there is an urgent need to provide a safe and environmentally friendly artificial aggregate, which is of great significance for the resource utilization of industrial waste and environmental protection. Summary of the Invention

[0006] To address the shortcomings of the prior art, this invention provides a core-shell type carbonized artificial aggregate based on solid waste and its preparation method. Under the condition of meeting national standards, it helps to reduce the environmental problems caused by the overuse of natural aggregates and the accumulation of industrial solid waste. It is prepared by a cold bonding method, which is simple and has low production energy consumption.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A core-shell type carbonized artificial aggregate based on solid waste, wherein the water-cement ratio of the artificial aggregate is 0.15-0.25, and the aggregate comprises the following components by mass percentage: 10%-30% red mud, 10%-30% steel slag, 35%-50% granulated blast furnace slag, 5%-15% fly ash, 3%-7% alkali activator, and 0.5%-1% water-reducing agent. During the preparation process, a mixture of alkali activator and water-reducing agent is sprayed during granulation. The mixture of red mud, steel slag, fly ash, and 37%-60% granulated blast furnace slag is granulated to obtain a core with a diameter of 4.75-8 mm. The remaining granulated blast furnace slag is then granulated on the basis of the core to obtain a shell with a thickness of 1-3 mm.

[0009] Furthermore, the red mud has a SiO2 content of 43.02%–45%, an Al2O3 content of 14.5%–15.7%, and an average particle size of 20–44 μm.

[0010] Furthermore, the steel slag has a SiO2 content of 48%–52%, a CaO content of 20%–23%, and an average particle size of 20–44 μm.

[0011] Furthermore, the strength ratio of the granulated blast furnace slag at 28 days is not less than 95%.

[0012] Furthermore, the fly ash is Class F, Grade I low-calcium fly ash, wherein the mass content of free CaO is <1%.

[0013] Furthermore, the alkaline activator is composed of a water glass solution and sodium hydroxide particles, wherein the water glass solution has a water content of 52.77% and the sodium hydroxide particles have a purity of greater than 90%.

[0014] Furthermore, the water-reducing agent is a polycarboxylate-based water-reducing agent with a solid content ≥40% and a water reduction rate ≥40%.

[0015] A method for preparing a core-shell type carbonized artificial aggregate based entirely on solid waste includes the following steps:

[0016] S1, Mixture Preparation

[0017] Sodium hydroxide particles are added to the water glass solution to adjust the modulus of the water glass solution to 1. Then, the corresponding amount of water is added and the solution is allowed to stand for 24 hours. After cooling to room temperature, an alkali activator is obtained. Then, a water-reducing agent is added to the alkali activator and stirred to form a mixture for later use.

[0018] S2, Aggregate Granulation

[0019] All red mud, steel slag, fly ash, and 37%–60% granulated blast furnace slag are mixed in a mixer for 5–10 minutes to obtain a mixture. The disc granulator is set with a disc inclination angle of 45°–50° and a disc rotation speed of 35–55 rpm. 5%–10% of the mixture is added to the disc granulator while continuously spraying the mixture to form initial spheres. Then, the remaining mixture is continuously added to the disc granulator while continuously spraying the mixture for granulation. The granulation time is 15–20 minutes. After standing for 24 hours, the core is obtained. Then, the core is sprayed with the mixture until the surface is moist. The remaining granulated blast furnace slag is added to the disc granulator while continuously spraying the mixture for granulation. The granulation time is 8–10 minutes, so that the granulated blast furnace slag forms an outer shell on the surface of the core. Finally, the core is carbonized and cured for 1 day, and then steam-cured at 60°C–85°C for 2 days to obtain a core-shell type carbonized artificial aggregate based on solid waste.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. This invention uses red mud, steel slag, fly ash, and granulated blast furnace slag as the core and granulated blast furnace slag as the outer shell, and uses a cold bonding method to prepare core-shell type artificial aggregates. This helps to consume large amounts of industrial solid waste, reduce the environmental problems caused by the large accumulation of red mud and steel slag, and the artificial aggregates after curing can meet the requirements of GB / T17431.1–2010 in terms of density and compressive strength, effectively alleviating the demand for natural aggregates and reducing the overuse of natural aggregates.

[0022] 2. Compared with the traditional sintering process for preparing artificial aggregates, the core-shell type artificial aggregates prepared by this invention are not only simple to produce, but also do not require high-temperature calcination throughout the process, resulting in low energy consumption and suitability for large-scale production.

[0023] 3. The core of the artificial aggregate of the present invention is prepared by using red mud and steel slag, which are industrial solid wastes. The core is combined with fly ash and granulated blast furnace slag, which have high alkali activation activity to provide strength. The outer shell of the artificial aggregate is made of granulated blast furnace slag alone, which reduces the precipitation rate of heavy metal ions in red mud and steel slag. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the preparation method of the artificial aggregate of the present invention;

[0025] Figure 2 These are trend graphs of the test results for each embodiment. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0027] A core-shell type carbonized artificial aggregate based entirely on solid waste, with a water-cement ratio of 0.15–0.25, comprises the following components by mass percentage: red mud (RM) 10%–30%, steel slag (SS) 10%–30%, granulated blast furnace slag (GGBS) 35%–50%, fly ash (FA) 5%–15%, alkali activator 3%–7%, and water-reducing agent 0.5%–1%. Wherein:

[0028] The red mud has a SiO2 content of 43.02%–45%, an Al2O3 content of 14.5%–15.7%, and an average particle size of 20–44 μm.

[0029] The steel slag has a SiO2 content of 48%–52%, a CaO content of 20%–23%, and an average particle size of 20–44 μm.

[0030] The strength ratio of the granulated blast furnace slag at 28 days is not less than 95%.

[0031] The fly ash is Class F, Grade I low-calcium fly ash, in which the mass content of free CaO is <1%.

[0032] The alkali activator is a compound of water glass solution and sodium hydroxide particles. The water glass solution has a water content of 52.77%, and the sodium hydroxide particles have a purity of more than 90%. The prepared alkali activator needs to stand for 24 hours before it can be used.

[0033] The water-reducing agent is a polycarboxylate-based water-reducing agent with a solid content ≥40% and a water reduction rate ≥40%.

[0034] During the preparation process, a mixture of alkali activator and water-reducing agent is sprayed during granulation. A core is obtained by granulation of a mixture of red mud, steel slag, fly ash and 37% to 60% granulated blast furnace slag. The core diameter is 4.75 to 8 mm. The remaining granulated blast furnace slag is then used to granulate the core to obtain an outer shell with a thickness of 1 to 3 mm.

[0035] A method for preparing a core-shell type carbonized artificial aggregate based entirely on solid waste, the process of which combines Figure 1 As shown, it includes the following steps:

[0036] S1, Mixture Preparation

[0037] Sodium hydroxide particles are added to the water glass solution to adjust the modulus of the water glass solution to 1. Then, the corresponding amount of water is added and the solution is allowed to stand for 24 hours. After cooling to room temperature, an alkali activator is obtained. Then, a water-reducing agent is added to the alkali activator and stirred to form a mixture for later use.

[0038] S2, Aggregate Granulation

[0039] All red mud, steel slag, fly ash, and 37%–60% granulated blast furnace slag are mixed in a mixer for 5–10 minutes to obtain a mixture. The disc granulator is set with a disc inclination angle of 45°–50° and a disc rotation speed of 35–55 rpm. 5%–10% of the mixture is added to the disc granulator while continuously spraying the mixture to form initial spheres. Then, the remaining mixture is continuously added to the disc granulator while continuously spraying the mixture for granulation. The granulation time is 15–20 minutes. After standing for 24 hours, the core is obtained. Then, the core is sprayed with the mixture until the surface is moist. The remaining granulated blast furnace slag is added to the disc granulator while continuously spraying the mixture for granulation. The granulation time is 8–10 minutes, so that the granulated blast furnace slag forms an outer shell on the surface of the core. Finally, the core is carbonized and cured for 1 day, and then steam-cured at 60°C–85°C for 2 days to obtain a core-shell type carbonized artificial aggregate based on solid waste. Carbonization serves to enhance the absorption and storage capacity of CO2 in artificial aggregates by forming a three-dimensional network structure after the raw materials are activated by alkali.

[0040] The following five examples demonstrate the superior properties of the artificial aggregate prepared by this invention:

[0041] Example 1

[0042] The water-cement ratio by weight is 0.2, and the following percentages by mass are: red mud 23%, steel slag 20%, granulated blast furnace slag 47% (core 25%, outer shell 22%), Class I low-calcium fly ash 10%, alkali activator 6%, and polycarboxylate superplasticizer 0.75%.

[0043] Example 2

[0044] The water-cement ratio by weight is 0.2, and the following percentages by mass are: 20% red mud, 20% steel slag, 50% granulated blast furnace slag (30% core, 20% outer shell), 10% Class I low-calcium fly ash (F), 5% alkali activator, and 0.75% polycarboxylate superplasticizer.

[0045] Example 3

[0046] The water-cement ratio by weight is 0.15, and the following percentages by mass are: 25% red mud, 10% steel slag, 50% granulated blast furnace slag (28% core, 22% shell), 15% Class I low-calcium fly ash, 7% alkali activator, and 1% polycarboxylate superplasticizer.

[0047] Example 4

[0048] The water-cement ratio by weight is 0.25, and the following percentages by mass are: red mud 30%, steel slag 30%, granulated blast furnace slag 35% (core 13%, outer shell 22%), Class I low-calcium fly ash 5%, alkali activator 3%, and polycarboxylate superplasticizer 0.5%.

[0049] Example 5

[0050] The water-cement ratio is 0.2 by weight, and the following percentages are by mass: red mud 10%, steel slag 25%, granulated blast furnace slag 50% (core 30%, shell 20%), Class I low-calcium fly ash 15%, alkali activator 7%, and polycarboxylate superplasticizer 0.5%.

[0051] The raw materials from the above five embodiments were used to prepare core-shell carbonized artificial aggregates based on solid waste according to the method of the present invention. The compressive strength and 1-hour water absorption rate were tested, and the apparent density and bulk density were obtained. The compressive strength and water absorption rate tests were conducted according to the requirements of GB / T17431.2–2010, and the calculation formulas are as follows:

[0052]

[0053] In the formula, f a The values ​​represent the cylinder compressive strength, p1 represents the pressure (N) when the stamping die presses in 20mm, p2 represents the mass (N) of the stamping die, and F represents the area of ​​the stamping die (F = 10000mm²). 2 ).

[0054]

[0055] In the formula, ω a The values ​​represent the water absorption rate (%), m0 represents the mass of the dried artificial aggregate (g), and m1 represents the mass of the artificial aggregate in the surface-dried saturated state (g).

[0056] The final experimental data for each embodiment are shown in Table 1:

[0057] Table 1 Experimental data for each embodiment

[0058]

[0059] To clearly demonstrate the trends in strength and strain of the all-solid-waste-based core-shell carbonized artificial aggregates prepared in each embodiment, a trend graph of the experimental results was plotted, combined with... Figure 2 As shown.

[0060] In summary, the innovation of this invention compared to traditional aggregates lies in:

[0061] (1) Material system innovation: Breaking through the traditional single-component solid waste utilization model, the aggregate core is formed by the composite system of red mud-steel slag-fly ash-granulated blast furnace slag, which forms a gradient activation structure with the outer shell of granulated blast furnace slag, and a functional design of solid waste of "calcium source supply-silicon-aluminum activation" is established.

[0062] (2) Structural design innovation: The core-shell heterostructure is constructed using a cold bonding process. The high calcium content of the core steel slag promotes the CO2 mineralization reaction. At the same time, the volcanic ash effect generated by the microcrystalline phase of the granulated blast furnace slag in the shell forms a dense cementing layer, achieving the synergistic effect of physical coating and chemical activation.

[0063] (3) Performance optimization mechanism: By adjusting the ratio of core and shell components and particle size distribution, an interpenetrating network structure of ettringite and CSH gel is induced at the heterogeneous interface, which effectively improves the compressive strength of aggregate and reduces water absorption.

[0064] The all-solid-waste-based core-shell carbonized artificial aggregate of the present invention not only meets the technical indicators of high-strength lightweight aggregate in GB / T17431.1-2010, shortening the curing cycle by 82%-93% compared with the conventional 28-day curing cycle, but also provides a new interface engineering path for low-carbon preparation of building aggregates while realizing the comprehensive utilization of industrial solid waste. Compared with the traditional sintering process, the preparation method has the advantages of convenient operation, simple process, and energy saving.

[0065] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0066] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A core-shell type carbonized artificial aggregate based entirely on solid waste, characterized in that: The artificial aggregate has a water-cement ratio of 0.15 to 0.25 and comprises the following components by mass percentage: 10% to 30% red mud, 10% to 30% steel slag, 35% to 50% granulated blast furnace slag, 5% to 15% fly ash, 3% to 7% alkali activator, and 0.5% to 1% water-reducing agent, wherein the sum of the amounts of red mud, steel slag, granulated blast furnace slag, and fly ash is 100%. The alkali activator is a compound of water glass solution and sodium hydroxide particles, wherein the water glass solution has a water content of 52.77% and the sodium hydroxide particles have a purity greater than 90%; the water-reducing agent is a polycarboxylate-based water-reducing agent with a solid content ≥40% and a water reduction rate ≥40%. During the preparation process, a mixture is sprayed during granulation. A mixture of red mud, steel slag, fly ash, and 37% to 60% granulated blast furnace slag is granulated to obtain a core with a diameter of 4.75 to 8 mm. The remaining granulated blast furnace slag is then used to granulate the core for 8 to 10 minutes to obtain a shell with a thickness of 1 to 3 mm. Finally, the mixture is first carbonized and cured for 1 day and then steam-cured at 60℃ to 85℃ for 2 days to obtain a core-shell type carbonized artificial aggregate based on solid waste. The mixture is prepared as follows: sodium hydroxide particles are added to a water glass solution to adjust the modulus of the water glass solution to 1, then the corresponding amount of water is added and the mixture is allowed to stand for 24 hours. After cooling to room temperature, an alkali activator is obtained. Then, a water-reducing agent is added to the alkali activator and stirred to form a mixture for later use.

2. The all-solid-waste-based core-shell carbonized artificial aggregate according to claim 1, characterized in that: The red mud has a SiO2 content of 43.02%~45%, an Al2O3 content of 14.5%~15.7%, and an average particle size of 20~44μm.

3. The all-solid-waste-based core-shell carbonized artificial aggregate according to claim 1, characterized in that: The steel slag has a SiO2 content of 48%~52%, a CaO content of 20%~23%, and an average particle size of 20~44μm.

4. The all-solid-waste-based core-shell carbonized artificial aggregate according to claim 1, characterized in that: The strength ratio of the granulated blast furnace slag at 28 days is not less than 95%.

5. The all-solid-waste-based core-shell carbonized artificial aggregate according to claim 1, characterized in that: The fly ash is Class F, Grade I low-calcium fly ash, in which the mass content of free CaO is <1%.

6. A method for preparing a core-shell type carbonized artificial aggregate based entirely on solid waste, characterized in that: The artificial aggregate according to any one of claims 1-5 is prepared by the following steps: S1, Mixture Preparation Sodium hydroxide particles are added to the water glass solution to adjust the modulus of the water glass solution to 1. Then, the corresponding amount of water is added and the solution is allowed to stand for 24 hours. After cooling to room temperature, an alkali activator is obtained. Then, a water-reducing agent is added to the alkali activator and stirred to form a mixture for later use. S2, Aggregate Granulation All red mud, steel slag, fly ash, and 37%–60% granulated blast furnace slag are mixed in a mixer for 5–10 minutes to obtain a mixture. The disc granulator is set with a disc inclination angle of 45°–50° and a disc rotation speed of 35–55 rpm. 5%–10% of the mixture is added to the disc granulator while continuously spraying the mixture to form initial spheres. The remaining mixture is then continuously added to the disc granulator while continuously spraying the mixture for granulation. The granulation time is 15–20 minutes. After standing for 24 hours, the core is obtained. The core is then sprayed with the mixture until the surface is moist. The remaining granulated blast furnace slag is then added to the disc granulator while continuously spraying the mixture for granulation. The granulation time is 8–10 minutes, allowing the granulated blast furnace slag to form an outer shell covering the core surface. Finally, the core is carbonized for 1 day and then steam-cured at 60°C–85°C for 2 days to obtain a core-shell type carbonized artificial aggregate based on solid waste.

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