Fly ash and cement based non-fines ordinary medium-high strength concrete and preparation method thereof

Abstract

The application discloses fly ash and cement based aggregate-free high-strength concrete and a preparation method thereof, and belongs to the technical field of building materials. The concrete is made of the following raw materials in parts by mass: 50-70 parts of 42.5 grade and above Portland cement, 15-25 parts of fly ash, 15-25 parts of silica ash, 0.5-3.0 parts of high-performance composite foaming agent, and the total water-binder ratio is 0.25-0.40. The preparation method comprises the following steps: uniformly dry mixing the cementitious material and admixture, then adding water and stirring to form a slurry; uniformly mixing stable foam prepared by physically foaming the foaming agent into the slurry; and pouring and performing combined curing of standard curing and steam curing. The application controls the dry density of the concrete at 800-1600 kg / m3, and the 28-day compressive strength is stabilized at more than 10 MPa under the condition of no traditional sand aggregate, by optimizing the ratio of the ternary cementitious system of cement-fly ash-silica ash, using high-performance foam stabilizer and strictly controlling the low water-binder ratio, so that the problems of low strength and poor durability of the existing aggregate-free concrete are solved.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to an aggregate-free ordinary medium-high strength concrete based on fly ash and cement, and its preparation method. Background Technology

[0002] Traditional concrete requires the addition of large amounts of aggregates such as sand and stone, resulting in a significant environmental impact during production. Its high density also hinders lightweight structural design. Aggregate-free (also known as foamed) concrete, with its lightweight and insulating properties, is used in non-load-bearing infill applications. However, existing aggregate-free concrete typically suffers from the following drawbacks: 1) Low strength: Primarily using cement as the sole binder, or only adding fly ash, and employing ordinary animal or plant protein foaming agents, the high water-cement ratio leads to a loose structure after hardening, with compressive strength generally below 10 MPa, making it unsuitable for load-bearing structures; 2) Poor durability: The high water-cement ratio and unstable bubble structure easily cause cracking and water seepage in the hardened body, resulting in insufficient durability; 3) Limited functionality: The formulation focuses on insulation and filling, failing to meet the needs of engineering scenarios requiring higher strength. Some formulations excessively reduce the amount of binder in pursuit of even lower density, further exacerbating the strength and durability issues. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the technical defects of existing aggregate-free concrete, such as low compressive strength and insufficient durability due to the single cementitious material system, insufficient activity, poor foam stability and improper process control, and to provide a lightweight concrete with ordinary and medium-high strength that can be prepared without the use of traditional sand and gravel aggregates.

[0004] To achieve the above objectives, this application provides the following technical solution: a common medium-to-high strength concrete based on fly ash and cement without aggregates and its preparation method, wherein the raw materials include, by mass parts:

[0005] Portland cement (grade 42.5 and above): 50-70 parts.

[0006] Fly ash (Grade I or II): 15-25 parts,

[0007] Silica fume: 15-25 parts

[0008] High-performance composite foaming agent: 0.5-3.0 parts,

[0009] Water: The total water-cement ratio should be controlled between 0.25 and 0.40.

[0010] Preferably, the mass ratio of the silicate cement, fly ash, and silica fume is (6:2:2) to (7:1.5:1.5). Preferably, the fly ash is Class F, Grade I or Grade II. Preferably, the silica fume has an SiO2 content of not less than 90% and a specific surface area of ​​not less than 15,000 m² / kg.

[0011] Preferably, the high-performance composite foaming agent is a chemically synthesized or composite protein foaming agent with surfactant as the main component and compounded with foam stabilizer, thickener and other components, with a foaming ratio of not less than 20 times and a water bleeding rate of not more than 10% in 1 hour.

[0012] Preferably, the dry apparent density of the concrete is 800-1600 kg / m³, and the compressive strength after 28 days of standard curing is not less than 10 MPa, with a preferred compressive strength range of 15-35 MPa.

[0013] On the other hand, the present invention provides a method for preparing the above-mentioned aggregate-free ordinary medium- and high-strength concrete based on fly ash and cement, characterized by comprising the following steps:

[0014] S1. Metering and material preparation: Accurately weigh silicate cement, fly ash, silica fume, high-performance composite foaming agent and water according to the mixing ratio;

[0015] S2. Slurry preparation: Weigh the silicate cement, fly ash and silica fume into the mixer and premix the dry powder for 1-3 minutes to make it uniform; then add the total amount of water and mix thoroughly for 3-5 minutes to form a uniform slurry;

[0016] S3. Foam preparation and incorporation: Using a dedicated physical foaming equipment, the high-performance composite foaming agent is diluted with water in a certain proportion and foamed to prepare foam with stable density and uniform and fine bubbles; the prepared foam is slowly added to the slurry obtained in step S2 and stirred at low speed for 3-8 minutes until the foam and slurry are evenly mixed to obtain a uniformly flowing foamed concrete mixture.

[0017] S4. Pouring and Curing: Pour the mixture obtained in step S3 into the mold and gently vibrate or scrape it level; then cure: first, cure under standard conditions of 20±2℃ and relative humidity above 95% for 1-3 days, then transfer to a steam curing environment of 50-90℃ and relative humidity above 90% for 4-7 days; or, use standard curing for 28 days in total.

[0018] Preferably, in step S3, the amount of foam added is adjusted with the goal of controlling the wet density or hardened dry density of the final concrete mixture in order to obtain concrete of the target strength grade.

[0019] Preferably, the curing regimen is to first perform standard curing for 2-3 days, followed by steam curing at a temperature of 60-80℃ for 5-7 days to accelerate strength development.

[0020] In summary, the technical effects and advantages of this invention are as follows:

[0021] High strength: By adopting a ternary composite cementitious system of "cement-fly ash-silica fume", the proportion of active components has been optimized (mass ratio 6:2:2 to 7:1.5:1.5), and the low water-cement ratio (0.25-0.40) has been strictly controlled. Combined with a high-performance foam stabilizer, the density of the material and the strength of the interfacial transition zone have been significantly improved without traditional aggregates. This allows the 28-day compressive strength to stably reach more than 10MPa, and even reach ordinary to medium-high strength grades (15-35MPa), breaking through the bottleneck of low strength of traditional aggregate-free concrete.

[0022] Good durability: The low water-cement ratio reduces the internal free water content, and the ternary adhesive system (especially the filling of silica fume and the pozzolanic effect) improves the pore structure and matrix density. The stable foam structure reduces harmful interconnected pores, thereby effectively reducing the risk of shrinkage, cracking and seepage of concrete and improving long-term durability.

[0023] Expanding application scenarios: While maintaining its lightweight characteristics (dry density 800-1600 kg / m³), the concrete of this invention has achieved high mechanical properties, which expands its application beyond non-load-bearing thermal insulation filling fields to lightweight load-bearing walls, roof slope load-bearing layers, lightweight partition boards, composite wall panel surfaces and other engineering scenarios that require strength.

[0024] Environmental and economic benefits: It makes full use of industrial by-products such as fly ash and silica fume, reducing the amount of cement used; at the same time, it eliminates the need to mine and use natural sand and gravel aggregates, protecting the environment, reducing raw material transportation and pretreatment costs, simplifying the production process, and conforming to the development direction of green building materials.

[0025] Controllable process: The preparation process of "dry material premixing - slurry making - physical foaming and incorporation" and the curing system of "standard + steam" ensure the uniform distribution of foam and the full development of concrete strength. The production process is stable and controllable and easy to industrialize. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] In this document, the term "comprising" is intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0028] Example:

[0029] Example 1:

[0030] This embodiment provides an aggregate-free concrete with a dry density of approximately 1200 kg / m³ and a target strength of ≥20 MPa.

[0031] Accurately weigh the raw materials according to the following mass percentages: 60 parts of P·O 42.5 grade ordinary Portland cement, 20 parts of Class F II fly ash, 20 parts of silica fume with a specific surface area ≥20000 m² / kg, and 1.5 parts of composite protein-type high-performance foaming agent (foaming ratio 25 times, water bleeding rate 8% in 1 hour). The water content should be controlled so that the total water-cement ratio is 0.32.

[0032] The preparation process is as follows:

[0033] (1) Put the weighed cement, fly ash and silica fume into a forced mixer and dry mix for 2 minutes until they are evenly mixed.

[0034] (2) Add the calculated total amount of water to the dry mix and stir for 4 minutes to form a uniform and fluid cement paste.

[0035] (3) Using a physical foaming machine, the foaming agent is diluted with some water and then foamed to prepare a fine foam with stable density (about 50 kg / m³). The obtained foam is slowly added to the slurry in step (2), and the mixture is stirred at low speed for 5 minutes to make the foam and slurry fully and evenly mixed to obtain a fluid foamed concrete mixture.

[0036] (4) Pour the mixture into a 100mm×100mm×100mm mold, gently vibrate to remove large air bubbles and smooth the surface.

[0037] (5) The molded specimen was cured in a standard curing room at a temperature of 20±2℃ and a relative humidity of 95% or higher for 2 days. Then it was demolded and transferred to a steam curing chamber at a temperature of 75±5℃ and a relative humidity of 90% or higher for 6 days. After curing, the specimen was cooled to room temperature under laboratory conditions.

[0038] According to the test results, the dry apparent density of the concrete specimen prepared in this embodiment is 1180 kg / m³, and the compressive strength at 28 days (after steam curing, it is cured for another 28 days under standard conditions) is 26.5 MPa.

[0039] Example 2:

[0040] This embodiment provides a lightweight aggregate-free concrete with a lower dry density (approximately 900 kg / m³) and a strength meeting the requirement of ≥10 MPa.

[0041] Accurately weigh the raw materials according to the following mass percentages: 55 parts of P·O 42.5 grade ordinary Portland cement, 22.5 parts of F-class I fly ash, 22.5 parts of silica fume (mass ratio approximately 5.5:2.25:2.25), 2.2 parts of chemically synthesized high-performance foaming agent (foaming ratio 30 times, 1-hour water bleeding rate 5%), and control the total water-cement ratio to 0.28.

[0042] The preparation process is as follows:

[0043] (1) Same as step (1) in Example 1, dry mix cement, fly ash and silica fume evenly.

[0044] (2) Add the total amount of water and stir to form a slurry.

[0045] (3) Prepare a lower density foam (approximately 40 kg / m³) and incorporate it into the slurry, stirring at low speed for 6 minutes until homogeneous. The amount of foam incorporated in this step is greater than in Example 1 to obtain a lower finished product density.

[0046] (4) Perform the same pouring as in step (4) of Example 1.

[0047] (5) Adopt the full standard curing system: after 3 days of standard curing in the mold, demold and continue to cure in the standard curing room until 28 days old.

[0048] Tests showed that the dry apparent density of the concrete specimen prepared in this embodiment was 910 kg / m³, and the compressive strength after 28 days of standard curing was 14.8 MPa, which met the design requirements.

[0049] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A type of aggregate-free ordinary medium-to-high strength concrete based on fly ash and cement, and its preparation method, characterized in that: Including its raw materials by mass parts: Portland cement (grade 42.5 and above): 50-70 parts. Fly ash: 15-25 parts Silica fume: 15-25 parts High-performance composite foaming agent: 0.5-3.0 parts, Water: The total water-to-binder ratio should be controlled between 0.25 and 0.40; The dry apparent density of the concrete is 800-1600 kg / m³, and the 28-day compressive strength is not less than 10 MPa.

2. The aggregate-free high-strength concrete according to claim 1, characterized in that, The mass ratio of silicate cement, fly ash and silica fume is (6:2:2) to (7:1.5:1.5).

3. The aggregate-free high-strength concrete according to claim 1, characterized in that, The fly ash is Class I or Class II ash of type F; the silica fume has an SiO2 content of not less than 90% and a specific surface area of ​​not less than 15,000 m² / kg.

4. The aggregate-free high-strength concrete according to claim 1, characterized in that, The high-performance composite foaming agent is a chemically synthesized or composite protein foaming agent with a foaming ratio of not less than 20 times and a water bleeding rate of not more than 10% in 1 hour.

5. A method for preparing aggregate-free high-strength concrete according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Metering and material preparation: Accurately weigh silicate cement, fly ash, silica fume, high-performance composite foaming agent and water according to the mixing ratio; S2. Slurry preparation: Premix the weighed silicate cement, fly ash and silica fume dry powder for 1-3 minutes to make them evenly mixed; then add the total amount of water and stir thoroughly for 3-5 minutes to form a uniform slurry; S3. Foam preparation and incorporation: Dilute the high-performance composite foaming agent with water and foam it to prepare foam; add the prepared foam to the slurry obtained in step S2, stir at low speed for 3-8 minutes until it is evenly mixed to obtain foamed concrete mixture; S4. Pouring and curing: Pour the mixture obtained in step S3 into the mold and then cure it: First, cure it under standard conditions of 20±2℃ and relative humidity above 95% for 1-3 days, and then transfer it to a steam curing environment of 50-90℃ and relative humidity above 90% for 4-7 days; or, use standard curing for 28 days in total.

6. The preparation method according to claim 5, characterized in that, In step S2, both the premixing of the dry powder and the mixing after adding the total amount of water are carried out in a mixer.

7. The preparation method according to claim 5, characterized in that, In step S3, the foam is prepared using a physical foaming device.

8. The preparation method according to claim 5, characterized in that, In step S3, the amount of foam added is adjusted according to the dry apparent density of the target concrete.

9. The preparation method according to claim 5, characterized in that, In step S4, the temperature of the steam curing is 60-80℃.

10. The preparation method according to claim 5, characterized in that, The curing procedure described in step S4 is as follows: first, standard curing for 2-3 days, followed by steam curing at a temperature of 60-80℃ for 5-7 days.