A large amount of superfine fly ash light-weight concrete and its preparation method

Abstract

The present application relates to the technical field of concrete, and particularly relates to a large-mixing-amount superfine fly ash light concrete and a preparation method thereof, which comprises, by weight parts, cement in an amount of 28-50 parts, silica fume in an amount of 10-18 parts, fly ash in an amount of 40-60 parts, water in an amount of 26-28 parts, ceramsite in an amount of 12-18 parts, machine-made sand in an amount of 12-14 parts, water reducing agent in an amount of 0.75-1 part, polypropylene fiber in an amount of 0.15-0.2 part, and defoaming agent in an amount of 0.1 part. The present application realizes large-mixing-amount superfine fly ash (cementitious material ratio is more than 50%) and low bulk density (1835-1863 kg / cm3) by optimizing the cementitious system and adding polypropylene fiber, effectively solves the light aggregate floating problem, and endows the concrete with better compressive strength.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, specifically to a lightweight concrete with a high dosage of ultrafine fly ash and its preparation method. Background Technology

[0002] Inner Mongolia, as an important energy and raw material base in my country, has formed an industrial system centered on coal and electricity. Long-term industrial production has generated a large amount of industrial solid waste, among which fly ash is a major solid byproduct of coal-fired power plants. Collected by dust removal devices, it is characterized by large output and high concentration, leading to significant long-term storage pressure. Statistics show that my country's annual fly ash production exceeds 600 million tons, with Inner Mongolia accounting for a high proportion and having a concentrated distribution, making the demand for solid waste resource utilization particularly urgent. Large-scale open-air storage of fly ash not only occupies valuable land resources but also easily causes a series of environmental problems such as dust dispersion and groundwater pollution, becoming one of the key factors restricting the region's green development. Utilizing fly ash in the concrete industry is an effective way to dispose of this type of solid waste. Ultrafine fly ash, due to its advantages such as finer particle size and increased activity, makes large-scale admixture utilization possible.

[0003] Transportation infrastructure and municipal engineering construction, due to their large scale and concentrated material consumption, are important scenarios for the disposal of bulk industrial solid waste such as fly ash. Adding fly ash to concrete can partially replace cement, reducing resource and energy consumption and carbon dioxide emissions, thus achieving low-carbon engineering construction. However, limited by the activity level and particle characteristics of conventional fly ash, the replacement rate of conventional fly ash in existing ordinary fly ash concrete is usually no more than 30%–40%. High admixture levels can easily lead to insufficient early strength and poor mixture stability, limiting its large-scale, high-value utilization. Meanwhile, with the development of lightweight building structures and prefabricated building technologies, the demand for lightweight concrete in roadbed filling, bridge weight reduction, and other fields is increasing. Existing lightweight concrete mostly uses ordinary cement as the main cementing material, resulting in high cement consumption and high self-weight. Furthermore, the introduction of lightweight aggregates can easily lead to defects such as insufficient paste encapsulation, aggregate floating, and uncontrolled pore structure, making it difficult to simultaneously achieve low density and mechanical properties. If ultrafine fly ash can be applied in large quantities to lightweight concrete, it can simultaneously address three major needs: solid waste disposal, low-carbon emission reduction, and performance optimization of lightweight concrete. However, current technologies have not yet achieved this goal.

[0004] Current research has attempted to use fly ash in lightweight concrete to reduce cement usage, but most studies focus on conventional fly ash. Limited by its reactivity and particle-filling capacity, increasing the admixture dosage easily leads to defects such as decreased early strength and insufficient structural density in concrete, making large-scale application difficult. Furthermore, even with small amounts of ultrafine fly ash, there are problems such as poor system compatibility and the introduction of excessive air bubbles under the action of admixtures, resulting in increased air content and exacerbated strength fluctuations. Existing technologies lack systematic control methods for lightweight concrete systems with large admixture dosages of ultrafine fly ash. Therefore, this invention proposes a lightweight concrete with a large admixture dosage of ultrafine fly ash and its preparation method. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the purpose of this invention is to provide a lightweight concrete with a large amount of ultrafine fly ash and its preparation method, so as to solve the problems mentioned in the background art.

[0006] The present invention solves the technical problem by adopting the following technical solution: This invention provides a lightweight concrete with high-volume ultrafine fly ash and its preparation method, comprising the following raw materials in parts by weight: The cement content is 28-50 parts by weight, the silica fume content is 10-18 parts by weight, the fly ash content is 40-60 parts by weight, the water content is 26-28 parts by weight, the ceramsite content is 12-18 parts by weight, the manufactured sand content is 12-14 parts by weight, the water-reducing agent content is 0.75-1 parts by weight, the polypropylene fiber content is 0.15-0.2 parts by weight, and the defoamer content is 0.1 parts by weight; wherein, the ultrafine fly ash accounts for 40%-60% of the total mass of the cementitious material.

[0007] Preferably, the fly ash is ultrafine fly ash with a water requirement ratio of 95%-97%, a loss on ignition of 1.5%-2%, a fineness of 45 μm, a residue of 1.5%-3% on a square-hole sieve, and a strength activity index of 85%-90%.

[0008] Preferably, the cement is P·O 52.5 silicate cement; the specific surface area of ​​silica fume is ≥19000 m². 2 / kg, of which SiO2 content ≥90%.

[0009] Preferably, the water-reducing agent is a polycarboxylate superplasticizer; the main component of the defoamer is modified organosilicon; and the water is ordinary domestic water.

[0010] Preferably, the polypropylene fiber has a length of 12 mm, a diameter of 27 μm, and a tensile strength of 625 MPa.

[0011] Preferably, the bulk density of shale ceramsite is 1000 kg / m³. 3 ~1400kg / m 3It consists of particles ranging from 5 to 10 mm in size, with an irregular polyhedral shape, a compressive strength greater than 3 MPa, a 24-hour water absorption rate of 9%, and a packing porosity greater than 26%. The particle size of the manufactured sand is ≤4.75 mm.

[0012] This invention provides a method for preparing lightweight concrete with a large amount of ultrafine fly ash, comprising the following steps: Step (1) Pre-wet the shale ceramsite to obtain pre-wetted shale ceramsite; Step (2) The cement, fly ash and silica fume are added to a forced mixer and dry-mixed inside to obtain mixture A. Step (3) Mix water with water-reducing agent and defoamer and stir evenly. Add the mixture to mixture A and continue stirring until a uniform viscous slurry is formed, thus obtaining mixture B. Step (4) Add manufactured sand and pre-wetted shale ceramsite to mixture B, and stir so that the shale ceramsite can be coated by mortar; finally, add polypropylene fiber to the mixing equipment and stir thoroughly to obtain mixture C; Step (5) Apply release agent evenly to the inner surface of the plastic mold, then pour mixture C evenly into the mold, let it stand, demold, and place it in a standard curing room for curing. Once curing is complete, the high-volume ultrafine fly ash lightweight concrete as described in claims 1-6 can be obtained.

[0013] Preferably, the stirring rate in step (2) is 60-65 r / min and the stirring time is 1-2 min; the stirring rate in step (3) is 60-65 r / min and the stirring time is 2-3 min; and the stirring rate in step (4) is 120-150 r / min and the stirring time is 4-5 min.

[0014] Preferably, the static curing time in step (5) is 24-36 hours; the curing conditions of the standard curing room are: temperature controlled at 20±2℃, humidity greater than or equal to 95%.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention urgently needs to optimize the cementitious system through synergistic optimization, using ultrafine fly ash as the core and synergistically optimizing the cementitious system with highly active mineral admixtures. While ensuring the workability and mechanical properties of lightweight concrete, it achieves the large-scale application of ultrafine fly ash, unifying lightweight, low-carbon, and high-performance properties, providing a new path for the large-scale, high-value utilization of fly ash as a bulk solid waste. High-value utilization and low-carbon emission reduction: Through the synergistic effect of ultrafine fly ash and silica fume, the fly ash content can be increased to 40%–60%, significantly reducing cement usage and effectively reducing carbon emissions. Excellent product performance: The combination of a multi-component cementitious system and reasonable aggregate gradation ensures that lightweight concrete still has good mechanical properties under low density conditions; at the same time, the introduction of defoamers effectively reduces the air content of the high-volume fly ash system, improving material density and strength stability. Advantages of the preparation process: The preparation process is simple, raw materials are widely available, no special equipment investment is required, and a room-temperature curing process is used, resulting in low energy consumption; suitable for large-scale engineering application. Attached Figure Description

[0016] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to specific examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0018] This embodiment of a lightweight concrete with high admixture of ultrafine fly ash includes the following raw materials in parts by weight: The cement content is 28-50 parts by weight, the silica fume content is 10-18 parts by weight, the fly ash content is 40-60 parts by weight, the water content is 26-28 parts by weight, the ceramsite content is 12-18 parts by weight, the manufactured sand content is 12-14 parts by weight, the water-reducing agent content is 0.75-1 parts by weight, the polypropylene fiber content is 0.15-0.2 parts by weight, and the defoamer content is 0.1 parts by weight; wherein, the ultrafine fly ash accounts for 40%-60% of the total mass of the cementitious material.

[0019] The fly ash in this embodiment is ultrafine fly ash with a water requirement ratio of 95%-97%, a loss on ignition of 1.5%-2%, a fineness of 45μm, a square hole sieve residue of 1.5%-3%, and a strength activity index of 85%-90%.

[0020] The cement used in this embodiment is P·O 52.5 silicate cement; the specific surface area of ​​silica fume is ≥19000 m². 2 / kg, of which SiO2 content ≥90%.

[0021] In this embodiment, the water-reducing agent is a polycarboxylate high-efficiency water-reducing agent; the main component of the defoamer is modified organosilicon; and the water is ordinary domestic water.

[0022] The polypropylene fiber in this embodiment is 12 mm in length, 27 μm in diameter, and has a tensile strength of 625 MPa.

[0023] The bulk density of the shale ceramsite in this embodiment is 1000 kg / m³. 3 ~1400kg / m 3 It consists of particles ranging from 5 to 10 mm in size, with an irregular polyhedral shape, a compressive strength greater than 3 MPa, a 24-hour water absorption rate of 9%, and a packing porosity greater than 26%. The particle size of the manufactured sand is ≤4.75 mm.

[0024] The method for preparing lightweight concrete with high admixture of ultrafine fly ash in this embodiment includes the following steps: Step (1) Pre-wet the shale ceramsite to obtain pre-wetted shale ceramsite; Step (2) The cement, fly ash and silica fume are added to a mixer and dry-mixed to obtain mixture A. Step (3) Mix water with water-reducing agent and defoamer and stir evenly. Add the mixture to mixture A and continue stirring until a uniform viscous slurry is formed, thus obtaining mixture B. Step (4) Add manufactured sand and pre-wetted shale ceramsite to mixture B, and stir so that the shale ceramsite can be coated by mortar; finally, add polypropylene fiber to the mixing equipment and stir thoroughly to obtain mixture C; Step (5) Apply release agent evenly to the inner surface of the plastic mold, then pour mixture C evenly into the mold, let it stand, demold, and place it in a standard curing room for curing. Once curing is complete, the high-volume ultrafine fly ash lightweight concrete as described in claims 1-6 can be obtained.

[0025] In this embodiment, the stirring rate in step (2) is 60-65 r / min and the stirring time is 1-2 min; the stirring rate in step (3) is 60-65 r / min and the stirring time is 2-3 min; and the stirring rate in step (4) is 120-150 r / min and the stirring time is 4-5 min.

[0026] In step (5) of this embodiment, the static curing time is 24-36 hours; the curing conditions of the standard curing room are: temperature controlled at 20±2℃, humidity greater than or equal to 95%.

[0027] Example 1 This embodiment of lightweight concrete with high-volume ultrafine fly ash comprises the following components by weight: 50 parts cement, 10 parts silica fume, 40 parts fly ash, 26 parts water, 12 parts ceramsite, 14 parts manufactured sand, 1 part water-reducing agent, 0.15 parts polypropylene fiber, and 0.1 parts defoamer; wherein, the fly ash content accounts for 40%-60% of the total mass of the cementitious materials. The fly ash is ultrafine fly ash, with a water requirement ratio of 95%-97%, a loss on ignition of 1.5%-2%, a fineness of 45μm, a square-hole sieve residue of 1.5%-3%, and a strength activity index of 85%-90%. The cement type is P·O 52.5 silicate cement; the specific surface area of ​​the silica fume is ≥19000m². 2 / kg, with SiO2 content ≥90%. The water-reducing agent is a polycarboxylate high-efficiency water-reducing agent; the defoamer's main component is modified organosilicon; the water is ordinary domestic water. The polypropylene fiber is 12mm in length, 27μm in diameter, and has a tensile strength of 625MPa. The shale ceramsite bulk density is 1000kg / m³. 3 ~1400kg / m 3 It consists of particles ranging from 5 to 10 mm in size, with an irregular polyhedral shape, a compressive strength greater than 3 MPa, a 24-hour water absorption rate of 9%, and a packing porosity greater than 26%. The particle size of the manufactured sand is ≤4.75 mm.

[0028] The method for preparing lightweight concrete with high-volume ultrafine fly ash in this embodiment includes the following steps: Step (1) Pre-wet 12 portions of shale ceramsite to obtain pre-wetted shale ceramsite; Step (2) Add 50 parts cement, 40 parts fly ash and 10 parts silica fume into the mixer in sequence and dry mix at a mixing speed of 62.5 r / min for 1-2 minutes to obtain mixture A; Step (3) Mix 26 parts water with 1 part water-reducing agent and 0.1 parts defoamer and stir evenly. Add the mixture to mixture A and continue stirring at a stirring rate of 62.5 r / min for 2-3 minutes until a uniform viscous slurry is formed, thus obtaining mixture B. Step (4) Add 14 parts of manufactured sand and pre-wetted shale ceramsite to mixture B, and stir so that the shale ceramsite can be coated with mortar; finally, add polypropylene fiber to the mixing equipment and stir at a stirring rate of 130 r / min for 4-5 min. Mixture C can then be obtained; Step (5) Apply release agent evenly to the inner surface of the plastic mold, then pour mixture C evenly into the mold, let it stand, 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 greater than or equal to 95%.

[0029] To conduct basic performance tests on the high-volume ultrafine fly ash lightweight concrete prepared in this example, the casting mold used in this example was a 100 mm × 100 mm × 100 mm plastic mold. The density and compressive strength of the specimens were tested in accordance with the "GB / T 50081-2019 Standard for Test Methods of Physical and Mechanical Properties of Concrete", and the performance indicators were measured at 7 days and 28 days of curing age, respectively.

[0030] Example 2 The lightweight concrete with high-volume ultrafine fly ash in this embodiment is composed of the following components in parts by weight: 38 parts cement, 12 parts silica fume, 50 parts fly ash, 27 parts water, 14 parts ceramsite, 14 parts manufactured sand, 1 part water-reducing agent, 0.18 parts polypropylene fiber, and 0.1 parts defoamer.

[0031] The preparation method of lightweight concrete with high dosage of ultrafine fly ash in this embodiment is the same as that in Example 1.

[0032] The mold dimensions and density tests for the lightweight concrete with high-volume ultrafine fly ash in this embodiment, as well as the compressive strength test methods, are the same as in Embodiment 1.

[0033] Example 3 The lightweight concrete with high admixture of ultrafine fly ash in this embodiment is composed of the following components in parts by weight: 28 parts cement, 18 parts silica fume, 60 parts fly ash, 28 parts water, 18 parts ceramsite, 12 parts manufactured sand, 1 part water-reducing agent, 0.2 parts polypropylene fiber, and 0.1 parts defoamer.

[0034] The preparation method of lightweight concrete with high dosage of ultrafine fly ash in this embodiment is the same as that in Example 1.

[0035] The mold dimensions and density tests for the lightweight concrete with high-volume ultrafine fly ash in this embodiment, as well as the compressive strength test methods, are the same as in Embodiment 1.

[0036] Comparative Example 1 This comparative concrete is composed of the following components in parts by weight: 38 parts cement, 12 parts silica fume, 50 parts fly ash, 27 parts water, 14 parts crushed stone, 14 parts manufactured sand, and 1 part water-reducing agent.

[0037] The concrete preparation method for this comparative example is the same as that in Example 1.

[0038] The dimensions of the concrete molds used in this comparative example, the density test, and the compressive strength test methods are the same as those in Example 1.

[0039] The compressive strength of the lightweight concrete with high admixture of ultrafine fly ash in Examples 1 to 3 is shown in Table 1.

[0040] Table 1 Compressive strength of lightweight concrete with high admixture of ultrafine fly ash The bulk density test results of the high-volume ultrafine fly ash lightweight concrete of Examples 1 to 3 are shown in Table 2.

[0041] Table 2. Bulk density data of lightweight concrete with high admixture of ultrafine fly ash Therefore, analysis of the performance data from the embodiments and comparative examples shows that, under the condition that the ultrafine fly ash content is as high as 40%–60% of the total cementitious material, the present invention successfully prepared lightweight high-strength concrete with a bulk density of 1835–1863 kg / m³, a 7-day compressive strength of 42.6–46.7 MPa, and a 28-day compressive strength of 44–50.7 MPa, achieving a synergistic improvement in lightweight and high mechanical properties. Compared with the traditional concrete in the comparative example, which uses ordinary aggregate and has a bulk density as high as 2483 kg / m³, the present invention significantly reduces the material's self-weight while still maintaining good compressive bearing capacity.

[0042] This performance improvement is attributed to the synergistic effect of the cement-silica fume-ultrafine fly ash composite cementitious system and polypropylene fiber stabilization technology. This system fully leverages the micro-aggregate filling effect of ultrafine fly ash and the activation effect of silica fume, while the physical constraint of the fiber network effectively suppresses lightweight aggregate floating and slurry segregation. Simultaneously, by optimizing the mix proportions and mixing process, the rheological properties, encapsulation properties, and uniformity of the slurry are controlled, resulting in a denser internal structure and a stronger interfacial transition zone in the concrete. This allows for the achievement of lightweight and high-strength structures even with low cement content and high solid waste content.

[0043] In summary, this invention not only achieves the large-scale resource utilization of fly ash (with solid waste accounting for over 50% of cementitious materials), significantly reducing cement usage and carbon emissions, but also endows concrete with excellent workability and stability through systematic optimization of materials and processes. This technology boasts multiple advantages, including lightweight, high strength, good workability, and low cost, making it suitable for non-load-bearing and secondary load-bearing structures in buildings, lightweight backfill in municipal engineering, and prefabricated components, demonstrating significant environmental, economic, and engineering promotion value.

[0044] 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 specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0045] 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 lightweight concrete with a high dosage of ultrafine fly ash, characterized in that, Raw materials, by weight, include: The cement content is 28-50 parts by weight, the silica fume content is 10-18 parts by weight, the ultrafine fly ash content is 40-60 parts by weight, the water content is 26-28 parts by weight, the ceramsite content is 12-18 parts by weight, the manufactured sand content is 12-14 parts by weight, the water-reducing agent content is 0.75-1 parts by weight, the polypropylene fiber content is 0.15-0.2 parts by weight, and the defoamer content is 0.1 parts by weight; wherein, the ultrafine fly ash content accounts for 40%-60% of the total mass of the cementitious material.

2. The lightweight concrete with high admixture of ultrafine fly ash according to claim 1, characterized in that, The fly ash is ultrafine fly ash with a water requirement of 95%-97% and a loss on ignition of 1.5%-2%; the fineness is 45 μm, the residue on a square-hole sieve is 1.5%-3%, and the strength activity index is 85%-90%.

3. The lightweight concrete with high admixture of ultrafine fly ash according to claim 1, characterized in that, The cement is P·O 52.5 silicate cement; the specific surface area of ​​silica fume is ≥19000 m². 2 / kg, of which SiO2 content ≥90%.

4. The lightweight concrete with high admixture of ultrafine fly ash according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate high-efficiency water-reducing agent; the defoamer's main component is modified organosilicon; and the water is ordinary domestic water.

5. The lightweight concrete with high admixture of ultrafine fly ash according to claim 1, characterized in that, The polypropylene fiber has a length of 12 mm, a diameter of 27 μm, and a tensile strength of 625 MPa.

6. The lightweight concrete with high admixture of ultrafine fly ash according to claim 1, characterized in that, The bulk density of the shale ceramsite is 1000 kg / m³. 3 ~1400kg / m 3 It consists of particles ranging from 5 to 10 mm in size, with an irregular polyhedral shape, a compressive strength greater than 3 MPa, a 24-hour water absorption rate of 9%, and a packing porosity greater than 26%. The particle size of the manufactured sand is ≤4.75 mm.

7. The method for preparing lightweight concrete with high admixture of ultrafine fly ash as described in any one of claims 1-6, characterized in that, Includes the following steps: Step (1) Pre-wet the shale ceramsite to obtain pre-wetted shale ceramsite; Step (2) The cement, fly ash and silica fume are added to a mixer and dry-mixed to obtain mixture A. Step (3) Mix water with water-reducing agent and defoamer and stir evenly. Add the mixture to mixture A and continue stirring until a uniform viscous slurry is formed to obtain mixture B. Step (4) Add manufactured sand and pre-wetted shale ceramsite to mixture B, and stir so that the shale ceramsite can be coated by mortar; finally, add polypropylene fiber to the mixing equipment and stir thoroughly to obtain mixture C; Step (5) Apply release agent evenly to the inner surface of the plastic mold, then pour mixture C evenly into the mold, let it stand, demold, and place it in a standard curing room for curing. Once curing is complete, the high-volume ultrafine fly ash lightweight concrete as described in claims 1-6 can be obtained.

8. The method for preparing lightweight concrete with high admixture of ultrafine fly ash according to claim 7, characterized in that, The stirring rate in step (2) is 60-65 r / min and the stirring time is 1-2 min; the stirring rate in step (3) is 60-65 r / min and the stirring time is 2-3 min; the stirring rate in step (4) is 120-150 r / min and the stirring time is 4-5 min.

9. The method for preparing lightweight concrete with high admixture of ultrafine fly ash according to claim 7, characterized in that, In step (5), the static curing time is 24-36 hours; the curing conditions in the standard curing room are: temperature controlled at 20±2℃, humidity greater than or equal to 95%.

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