Fly ash-desulfurized gypsum ultra-lightweight foam concrete and preparation method thereof

Abstract

The application is suitable for the technical field of building materials and solid waste resource utilization, and provides fly ash-desulfurization gypsum ultra-light foam concrete and a preparation method thereof.The ultra-light foam concrete comprises the following raw materials by weight: 600-800 parts of fly ash, 350-500 parts of desulfurization gypsum, 300-450 parts of cement, 400-630 parts of water, 2-5 parts of foam stabilizer, 3-6 parts of water reducing agent, 40-60 parts of hydrogen peroxide, and 0.5-1 part of manganese dioxide; wherein, the sum of the mass of the fly ash and the desulfurization gypsum accounts for 65%-75% of the total mass of the cementitious material, and the cementitious material is composed of the fly ash, the desulfurization gypsum and the sulphoaluminate cement; the application guarantees the ultra-light property and early strength of the material, has low manufacturing cost, simple process, provides technical support for high-value utilization of industrial solid waste, and is suitable for the field of building thermal insulation and non-load bearing structure.

Description

Technical Field

[0001] This invention relates to the field of building materials and solid waste resource utilization technology, specifically a fly ash-desulfurized gypsum ultralightweight foamed concrete and its preparation method. Background Technology

[0002] Fly ash and desulfurization gypsum are two typical bulk solid wastes generated during the operation of coal-fired power plants. Fly ash mainly originates from the fine ash in the high-temperature flue gas after coal combustion, collected and settled by electrostatic precipitators. Desulfurization gypsum, on the other hand, is generated during the flue gas desulfurization process of coal-fired units and is a major byproduct of the limestone-gypsum wet desulfurization process. The large-scale storage of solid waste not only occupies land resources but also poses environmental risks such as dust pollution and groundwater contamination. Against this backdrop, promoting the synergistic utilization of bulk solid wastes such as fly ash and desulfurization gypsum in the construction and operation of transportation infrastructure can not only reduce the consumption of natural sand and gravel resources but also effectively dispose of industrial solid waste, reduce environmental burden, and save on engineering construction and solid waste disposal costs. This is of great significance for improving the comprehensive utilization of resources and promoting the green and low-carbon transformation of transportation infrastructure.

[0003] Foamed concrete, as a building material with excellent properties such as lightweight, thermal insulation, sound insulation, and non-combustibility, provides an important pathway for the resource utilization of solid waste. However, traditional foamed concrete mainly uses ordinary Portland cement as a cementing material, which has problems such as high carbon emissions and high costs. Existing fly ash-desulfurized gypsum-based foamed concrete technology still has significant shortcomings: First, the amount of solid waste added is limited, generally not exceeding 50% of the total cementing material, failing to fully realize the potential for absorbing large quantities of solid waste; second, fly ash and desulfurized gypsum have low activity, and large-scale use often leads to slow early strength development of the material, failing to meet construction schedule requirements; third, poor foam stability is a key factor restricting product performance, easily resulting in defects such as formwork collapse and interconnected holes, affecting the physical and mechanical properties of the product.

[0004] Chinese patent CN105859233B discloses a method for preparing unrefined desulfurized gypsum foamed concrete. This patent uses a compound of desulfurized gypsum, slag, and cement, and utilizes an H2O2–MnO2 chemical foaming system to prepare the foamed concrete. While this method improves the utilization of desulfurized gypsum, the cement content in its cementitious system remains high, the amount of solid waste added is limited, and the dry density of the finished product is generally higher than 600 kg / m³. 3 However, achieving the goal of "ultra-lightweight" is difficult. Chinese patent CN102584317A discloses a method for preparing foamed concrete through physical self-foaming, which introduces air into the slurry to form bubbles through mechanical stirring. This process has simple equipment, but the cell structure is large and unstable, and the bubbles are prone to merging and breaking, resulting in insufficient strength of the product and making it difficult to meet the engineering requirements of both lightweight and mechanical properties.

[0005] Therefore, in view of the above situation, there is an urgent need to provide a fly ash-desulfurized gypsum ultralightweight foamed concrete and its preparation method to overcome the shortcomings in current practical applications. Summary of the Invention

[0006] The purpose of this invention is to provide a fly ash-desulfurized gypsum ultralightweight foamed concrete and its preparation method, effectively solving the problems in the background art.

[0007] This invention is achieved by providing a fly ash-desulfurized gypsum ultralightweight foamed concrete, comprising the following raw materials in parts by weight:

[0008] The composition includes 600-800 parts fly ash, 350-500 parts desulfurized gypsum, 300-450 parts cement, 400-630 parts water, 2-5 parts foam stabilizer, 3-6 parts water-reducing agent, 40-60 parts hydrogen peroxide, and 0.5-1 parts manganese dioxide. The sum of the mass of the fly ash and desulfurized gypsum accounts for 65%-75% of the total mass of the cementitious material, which is composed of fly ash, desulfurized gypsum, and sulfoaluminate cement.

[0009] As a further aspect of the present invention: the fly ash is secondary fly ash, with a water requirement ratio of 95%-97%, a loss on ignition of 1.5%-2%, a fineness of 14%-16% residue on a 45μm square hole sieve, and a strength activity index of 75%-80%.

[0010] As a further aspect of the present invention: the cement is grade 52.5 sulfoaluminate cement.

[0011] As a further aspect of the present invention: the water-reducing agent is a polycarboxylate high-efficiency water-reducing agent.

[0012] As a further aspect of the present invention: the foam stabilizer is calcium stearate, which passes through a 200-mesh sieve.

[0013] As a further aspect of the present invention: the hydrogen peroxide is industrial-grade hydrogen peroxide with a mass concentration of 30%.

[0014] As a further aspect of the present invention: the manganese dioxide used as a foaming catalyst has a purity of not less than 90% and passes through a 325-mesh sieve.

[0015] The present invention also provides a method for preparing the fly ash-desulfurized gypsum ultralightweight foamed concrete as described above, the method comprising the following steps:

[0016] Step (1): Put fly ash, desulfurized gypsum and cement into a mixer in sequence and mix until uniform to obtain mixed dry material A;

[0017] Step (2): Add water, water-reducing agent and foam stabilizer, and stir until a uniform viscous slurry is formed to obtain mixture B;

[0018] Step (3): Add manganese dioxide, stir, and then slowly add hydrogen peroxide. Continue stirring until the slurry is fully foamed to obtain foam slurry C.

[0019] Step (4): Apply release agent evenly to the inner surface of the steel mold, then pour foam slurry C evenly into the steel mold, let it stand, demold, and place it in a standard curing room for curing. After curing, ultra-lightweight foamed concrete can be obtained.

[0020] As a further aspect of the present invention: in step (1), the stirring rate is 60-65 r / min and the stirring time is 2-3 min;

[0021] In step (2), the stirring rate is 120-150 r / min and the stirring time is 4-5 min;

[0022] In step (3), the stirring rate after adding hydrogen peroxide is 60-65 r / min, and the stirring time is 1-2 min.

[0023] As a further aspect of the present invention: in step (4), the static curing time is 24-36 hours;

[0024] The curing conditions in the standard curing room are: temperature controlled at 20±2℃, humidity ≥95%.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] This invention enables the high-value utilization of solid waste, specifically: the total proportion of fly ash and desulfurized gypsum in cementitious materials exceeds 70%, which is much higher than the existing technology (generally less than 50%), thus significantly improving the resource utilization rate of industrial solid waste.

[0027] The product boasts excellent performance, specifically a dry density of 400-500 kg / m³. 3 It has ultra-lightweight properties and a 28-day compressive strength ≥1.0MPa, meeting the requirements for early construction. At the same time, it forms a uniform and fine cell structure with high closed-cell rate through calcium stearate foam stabilizer.

[0028] The low-carbon and low-cost preparation process is as follows: the main raw material is industrial solid waste, which reduces the cost by more than 30% compared with traditional foamed concrete. The process is simple, requires no special equipment, and adopts a normal temperature curing process, resulting in low energy consumption. Attached Figure Description

[0029] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0030] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0031] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] This invention relates to an ultra-lightweight foamed concrete prepared by a chemical foaming process using a fly ash-desulfurized gypsum-sulfoaluminate cement composite cementitious system.

[0033] The present invention will be further explained below with reference to specific embodiments.

[0034] This invention provides a fly ash-desulfurized gypsum ultralightweight foamed concrete, comprising the following raw materials in parts by weight:

[0035] The composition includes 600-800 parts fly ash, 350-500 parts desulfurized gypsum, 300-450 parts cement, 400-630 parts water, 2-5 parts foam stabilizer, 3-6 parts water-reducing agent, 40-60 parts hydrogen peroxide, and 0.5-1 parts manganese dioxide. The sum of the mass of the fly ash and desulfurized gypsum accounts for 65%-75% of the total mass of the cementitious material, which is composed of fly ash, desulfurized gypsum, and sulfoaluminate cement.

[0036] In this embodiment, the fly ash is secondary fly ash; the water requirement ratio is 95%-97%, the loss on ignition is 1.5%-2%; the fineness is 14%-16% residue on a 45μm square hole sieve, and the strength activity index is 75%-80%.

[0037] In this embodiment, the cement type is PO52.5 sulfoaluminate cement; the water-reducing agent is polycarboxylate high-efficiency water-reducing agent; and the water is ordinary domestic water.

[0038] In this embodiment, the foam stabilizer is calcium stearate, which is an industrial grade 1 product and its fineness passes through a 200-mesh sieve.

[0039] In this embodiment, the hydrogen peroxide is industrial-grade hydrogen peroxide with a mass concentration of 30%.

[0040] In this embodiment, manganese dioxide is used as a foaming catalyst with a purity of not less than 90% and a fineness that passes through a 325-mesh sieve.

[0041] Please see Figure 1 A method for preparing fly ash-desulfurized gypsum ultralightweight foamed concrete as described above, the method comprising the following steps:

[0042] Step (1) Put fly ash, desulfurized gypsum and cement into a mixer in sequence and mix until uniform to obtain mixed dry material A;

[0043] Step (2) Add water, water-reducing agent and foam stabilizer, and stir until a uniform viscous slurry is formed to obtain mixture B;

[0044] Step (3) Add manganese dioxide, stir briefly, then slowly add hydrogen peroxide and continue stirring until the slurry is fully foamed to obtain foam slurry C;

[0045] Step (4) Apply release agent evenly to the inner surface of the steel mold, then pour foam slurry C evenly into the steel mold, let it stand, demold, and place it in a standard curing room for curing. Once curing is complete, ultra-lightweight foamed concrete can be obtained.

[0046] In this embodiment, the stirring rate in step (1) is 60-65 r / min and the stirring time is 2-3 min; the stirring rate in step (2) is 120-150 r / min and the stirring time is 4-5 min; and the stirring rate after adding hydrogen peroxide in step (3) is 60-65 r / min and the stirring time is 2-3 min.

[0047] In this embodiment, the static curing time in step (4) is 24-36 hours; the curing conditions in the standard curing room are: temperature controlled at 20±2℃, humidity ≥95%.

[0048] Example 1: This example of fly ash-desulfurized gypsum ultra-lightweight foamed concrete consists of the following components by weight: 720 parts fly ash, 480 parts desulfurized gypsum, 400 parts cement, 500 parts mixing water, 3.2 parts foam stabilizer, 4.8 parts water-reducing agent, 48 parts hydrogen peroxide, and 0.8 parts manganese dioxide. The fly ash is grade II fly ash; the water requirement ratio is 95%-97%, and the loss on ignition is 1.5%-2%; the fineness is 14%-16% residue on a 45μm square-hole sieve, and the strength activity index is 75%-80%. The cement type is PO52.5 sulfoaluminate cement; the water-reducing agent is polycarboxylate high-efficiency water-reducing agent; the water is ordinary domestic water. The foam stabilizer is calcium stearate, an industrial grade I product, with a fineness passing through a 200-mesh sieve. The hydrogen peroxide is 30% industrial grade hydrogen peroxide. Manganese dioxide, used as a foaming catalyst, has a purity of no less than 90% and a fineness that passes through a 325-mesh sieve.

[0049] The method for preparing fly ash-desulfurized gypsum ultralightweight foamed concrete in this embodiment includes the following steps:

[0050] Step (1): Put 720 parts fly ash, 480 parts desulfurized gypsum and 400 parts cement into a mixer in sequence, and stir at a speed of 62.5 r / min for 2 minutes until uniform to obtain mixed dry material A.

[0051] Step (2): Add 500 parts water, 4.8 parts water-reducing agent and 3.2 parts foam stabilizer to the mixer and stir at a speed of 130 r / min for 4 min until a uniform viscous slurry is formed, thus obtaining mixture B.

[0052] Step (3): Add 0.8 parts of manganese dioxide, stir briefly, then slowly add 48 parts of hydrogen peroxide, and stir at a rate of 62.5 r / min for 2 minutes until the slurry is fully foamed to obtain foam slurry C.

[0053] Step (4): Apply release agent evenly to the inner surface of the steel mold, then pour foam slurry C evenly into the steel mold, let it stand for 24 hours; demold and place it in a standard curing room for curing. The curing conditions of the standard curing room are: temperature controlled at 20±2℃ and humidity ≥95%.

[0054] To conduct basic performance tests on the fly ash-desulfurized gypsum ultralightweight foamed concrete prepared in this example, a 100mm×100mm×100mm steel mold was used for casting. Steel molds are characterized by high rigidity, resistance to deformation, precise dimensions, and uniform thermal conductivity, effectively ensuring the dimensional stability of the specimens and avoiding damage to the foam structure during demolding. The dry density of the specimens was tested according to GB / T5486-2008 "Test Methods for Performance of Inorganic Rigid Thermal Insulation Products," and the compressive strength was tested according to GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete." Performance indicators were measured at 7 days and 28 days of curing.

[0055] Example 2: The fly ash-desulfurized gypsum ultra-lightweight foamed concrete of this example is composed of the following components in parts by weight: 720 parts fly ash, 480 parts desulfurized gypsum, 400 parts cement, 630 parts mixing water, 3.2 parts foam stabilizer, 4.8 parts water-reducing agent, 48 parts hydrogen peroxide, and 0.8 parts manganese dioxide.

[0056] The preparation method of fly ash-desulfurized gypsum ultralight foamed concrete in this embodiment is the same as that in Example 1.

[0057] The mold dimensions and dry density performance of the fly ash-desulfurized gypsum ultra-lightweight foamed concrete in this embodiment, as well as the compressive strength test method, are the same as in Embodiment 1.

[0058] Example 3: The fly ash-desulfurized gypsum ultra-lightweight foamed concrete of this example is composed of the following components in parts by weight: 720 parts fly ash, 480 parts desulfurized gypsum, 400 parts cement, 480 parts mixing water, 3.2 parts foam stabilizer, 4.8 parts water-reducing agent, 48 parts hydrogen peroxide, and 0.8 parts manganese dioxide.

[0059] The preparation method of fly ash-desulfurized gypsum ultralight foamed concrete in this embodiment is the same as that in Example 1.

[0060] The mold dimensions and dry density performance of the fly ash-desulfurized gypsum ultra-lightweight foamed concrete in this embodiment, as well as the compressive strength test method, are the same as in Embodiment 1.

[0061] Comparative Example 1: The fly ash-desulfurized gypsum ultralight foamed concrete of this embodiment is composed of the following components in parts by weight: 720 parts fly ash, 480 parts desulfurized gypsum, 600 parts cement, 500 parts mixing water, 3.2 parts foam stabilizer, 6 parts water-reducing agent, 48 parts hydrogen peroxide, and 0.8 parts manganese dioxide.

[0062] The preparation method of fly ash-desulfurized gypsum ultralight foamed concrete and the preparation method of additives in this embodiment are the same as those in Example 1;

[0063] The core variable in Comparative Example 1 is the amount of cement used (600 parts). The other raw material types, preparation processes, and curing conditions are the same as in the Example, and are used to compare the effect of cement usage on material properties.

[0064] The mold dimensions, compressive strength test, and frost resistance test methods for the fly ash-desulfurized gypsum ultralight foamed concrete in this embodiment are the same as those in Embodiment 1.

[0065] The compressive strength of the fly ash-desulfurized gypsum ultralight foamed concrete of Examples 1 to 3 and Comparative Example 1 is shown in Table 1.

[0066]

[0067] The dry density test results of fly ash-desulfurized gypsum ultralight foamed concrete in Examples 1 to 3 and Comparative Example 1 are shown in Table 2.

[0068]

[0069] Therefore, through analysis of the performance data of the embodiments and comparative examples, it can be seen that the present invention successfully prepared a product with a dry density of 400-500 kg / m³ under the condition that the total content of fly ash and desulfurized gypsum is as high as 75%. 3Ultra-lightweight foamed concrete with a 7-day compressive strength of 0.7–0.8 MPa and a 28-day compressive strength of 1.0–1.3 MPa achieves a good balance between lightweight and mechanical properties. This contrasts with the comparative example, which has a higher cement content and a dry density of 600 kg / m³. 3 Compared with the samples, the product prepared by the present invention maintains high structural strength and stability while significantly reducing material density and cement usage.

[0070] This performance improvement is attributed to the synergistic effect of the sulfoaluminate cement composite activation system and the H2O2–MnO2 chemical foaming system, which not only promotes the activation of fly ash and desulfurized gypsum but also achieves homogenization and stabilization of the cell structure. Simultaneously, by optimizing the water-to-material ratio and admixture proportions, the viscosity of the slurry and the foaming rate are effectively controlled, resulting in a finer pore distribution and a higher closed-cell rate, thus ensuring the product exhibits both low density and high strength.

[0071] In summary, this invention not only achieves efficient resource utilization of industrial solid wastes such as fly ash and desulfurization gypsum, increasing the solid waste content in the cementitious system to over 70%, but also significantly reduces energy consumption and production costs. Compared to traditional foamed concrete systems, it offers significant advantages in terms of lightweight, low carbon footprint, economy, and operability. This technical solution has outstanding practicality and promotional value, and can be widely applied in fields such as green building insulation, non-load-bearing structures, and prefabricated energy-saving building materials.

[0072] The dry densities of the examples are concentrated in the range of 430-500 kg / m³, all of which meet the "ultra-lightweight" (≤500 kg / m³) target. Among them, Example 3 has the lowest dry density (430 kg / m³) and the best lightweight effect.

[0073] The comparative example has a dry density of 600 kg / m³, which exceeds the ultralight range and is about 28%-39% higher than the average dry density of the example.

[0074] The example shows that by optimizing the amount of cement (400 parts), combined with the H2O2–MnO2 chemical foaming system and calcium stearate foam stabilizer, a uniform and fine closed-cell structure was formed; the comparative example shows that a high amount of cement (600 parts) leads to excessively high slurry viscosity, decreased foaming efficiency, reduced porosity, and naturally increased density.

[0075] 7-day compressive strength: 0.7-0.8 MPa in the example, 1.2 MPa in the comparative example, 50%-71% higher than the comparative example; 28-day compressive strength: 1.0-1.3 MPa in the example, 2.0 MPa in the comparative example, 54%-100% higher than the comparative example.

[0076] The logic behind the strength difference: Cement is the main source of early and later strength. In the comparative example, adding 200 more parts of cement (a 50% increase in proportion) results in a more complete hydration reaction in the cementitious system, leading to higher structural density and thus a significant increase in strength. However, the 28-day compressive strength of the example is ≥1.0 MPa, which already meets the strength requirements for building insulation and non-load-bearing structures, so there is no need to pursue excessively high strength.

[0077] Example: With a total content of 75% fly ash and desulfurized gypsum in cementitious materials, a balance of "ultra-lightweight + meeting strength requirements" is achieved, resulting in high solid waste utilization, low cost (low cement usage), and low carbon and environmental protection.

[0078] Comparative example: Although the strength is higher, the dry density exceeds the standard (not ultra-lightweight), the amount of cement used is large (cost is more than 30% higher), and the proportion of solid waste content is reduced (about 60%), which violates the core invention goal of "high-value utilization of solid waste + ultra-lightweight".

[0079] The high compressive strength and high dry density of the comparative ratio are the inevitable result of "sacrificing lightweight and high cement content". Its performance improvement comes at the cost of giving up "high solid waste content, low carbon and low cost", which does not conform to the original intention of the invention to improve "traditional foamed concrete with high cement content and low solid waste content".

[0080] The advantage of this embodiment is that it "maximizes the utilization and lightweighting of solid waste while meeting the performance requirements (strength ≥1.0MPa)," making it more practically valuable and worthy of promotion.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fly ash - desulfurization gypsum ultra-lightweight foamed concrete, having a dry density of 400-500 kg / m 3 characterized in that, It is composed of the following raw materials by weight parts: fly ash 600-800 parts, desulfurization gypsum 350-500 parts, sulphoaluminate cement 300-450 parts, water 400-630 parts, foam stabilizer 2-5 parts, water reducing agent 3-6 parts, hydrogen peroxide 40-60 parts, manganese dioxide 0.5-1 part; wherein the sum of the mass of the fly ash and the desulfurization gypsum accounts for 75% of the total mass of the cementitious material, and the cementitious material is composed of fly ash, desulfurization gypsum and sulphoaluminate cement; The fly ash is secondary fly ash, with a water requirement ratio of 95%-97%, a loss on ignition of 1.5%-2%, a fineness of 45 μm square hole sieve residue of 14%-16%, and a strength activity index of 75%-80%; The water reducing agent is a polycarboxylic acid high-efficiency water reducing agent; The foam stabilizer is calcium stearate and passes through a 200-mesh sieve; The manganese dioxide serves as a foaming catalyst, with a purity of not less than 90% and passing through a 325-mesh sieve.

2. The fly ash-desulfurized gypsum ultra-lightweight foamed concrete according to claim 1, characterized by, The cement type is 52.5 grade sulphoaluminate cement.

3. The fly ash-desulfurized gypsum ultra-lightweight foamed concrete according to claim 1, characterized by, The hydrogen peroxide is an industrial grade hydrogen peroxide with a mass concentration of 30%.

4. A method of preparing fly ash-desulfurized gypsum ultra-lightweight foamed concrete according to any one of claims 1 to 3, characterized in that, The method comprises the following steps: Step (1), placing the fly ash, desulfurization gypsum and sulphoaluminate cement into a mixer in sequence and stirring until uniform to obtain a mixed dry material A; Step (2), adding water, water reducing agent and foam stabilizer and stirring until a uniform viscous slurry is formed to obtain a mixed material B; Step (3), adding manganese dioxide, then slowly adding hydrogen peroxide after stirring, and continuously stirring until the slurry is fully foamed to obtain a foamed slurry C; Step (4), uniformly applying a release agent to the inner surface of a steel mold, then uniformly pouring the foamed slurry C into the steel mold, standing, demolding and placing in a standard curing chamber for curing, and the ultra-lightweight foamed concrete is obtained after the curing is completed.

5. The method for preparing fly ash-desulfurized gypsum ultralightweight foamed concrete according to claim 4, characterized in that, In step (1), the stirring rate is 60-65 r / min and the stirring time is 2-3 min; In step (2), the stirring rate is 120-150 r / min and the stirring time is 4-5 min; In step (3), the stirring rate after adding hydrogen peroxide is 60-65 r / min and the stirring time is 1-2 min.

6. The method for preparing fly ash-desulfurized gypsum ultralightweight foamed concrete according to claim 4, characterized in that, In step (4), the standing and curing time is 24-36 hours; The curing conditions of the standard curing chamber are that the temperature is controlled at 20±2℃ and the humidity is ≥95%.

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