Fly ash cementing material, concrete and preparation method thereof

Abstract

The invention relates to the technical field of building materials, and particularly discloses a fly ash cementing material, concrete and a preparation method thereof. The fly ash cementing material is prepared from fly ash, mineral powder, steel slag, a low-temperature curing agent, a thixotropic agent and a micromolecular retarder, wherein the thixotropic agent comprises an organic fiber material. Through component optimization and compounding design of the system, the cementing material system which is simple in component, rapid in low-temperature curing, high in strength, low in shrinkage rate, excellent in elastic modulus and excellent in low-temperature resistance is successfully prepared. Particularly, in the scheme of the invention, through special compounding of the organic fiber material and the micromolecular retarder, the curing process of the fly ash cementing material under a low-temperature condition is remarkably accelerated, and the comprehensive performance of the cementing material is also improved; the problems that an existing 3D printing material is low in low-temperature curing rate, low in strength and high in shrinkage rate are solved.

Description

Technical Field

[0001] The present application relates to the technical field of building materials, and in particular to a fly ash cementitious material and concrete and a preparation method thereof. Background Art

[0002] In the research scope of 3D printing building materials, traditional ordinary Portland cement, as the mainstream building material for a long time, has exposed many performance shortcomings in low temperature environments, such as slow strength development, low hydration reaction rate at low temperatures, etc., which cannot provide sufficient support for building structures in time; and the fluidity of cement paste is poor, which is difficult to be smoothly extruded in the 3D printing nozzle, seriously affecting the continuity and accuracy of the printing process; excessive shrinkage can easily lead to cracks in printed components, reducing the integrity and durability of the structure. These problems have greatly restricted the smooth advancement of 3D printing technology in the field of construction.

[0003] In order to match the existing 3D printing technology, researchers have made improvements based on traditional ordinary silicate cement in order to prepare building materials suitable for 3D printing technology. However, from the comprehensive consideration of practical application effects and material properties, such improved materials still expose many significant defects. Taking patent CN111847917A as an example, this technology improves the shrinkage characteristics of ordinary cement and reduces the firing temperature to a certain extent. However, it does not effectively improve the fluidity and cohesiveness of cement, making it difficult for the material to achieve tight bonding and precise molding between layers during 3D printing. The process adopted by patent CN112125618A uses highly corrosive hydrofluoric acid, which not only has extremely high requirements for production equipment and serious safety hazards, but also is extremely difficult to control in large-scale industrial production and is not feasible for practical application. Patent CN114956772A successfully changes the thixotropy and strength of cementitious materials by adding specific additives, which has certain advantages under normal temperature. However, in a low temperature environment, its curing performance is seriously insufficient, and it cannot be effectively cured within the specified time, resulting in low printing efficiency.

[0004] However, with the rapid development of 3D printing construction technology, more stringent and comprehensive performance requirements have been put forward for suitable building materials, such as: the material must have the characteristics of low-temperature rapid solidification, excellent early and late strength, excellent freeze-thaw resistance, suitable elastic modulus, etc. Therefore, the development of a building material that can take into account rapid solidification characteristics and excellent mechanical properties in a low-temperature environment and can be used in 3D printing efficiently and with high quality has become an important issue that needs to be overcome in this field. Summary of the invention

[0005] In view of this, the purpose of this application is to provide a fly ash cementitious material and concrete and a preparation method thereof, so as to solve the problems of low low-temperature curing rate, low strength and high shrinkage rate of existing 3D printing materials.

[0006] To achieve the above technical objectives, the present application provides a fly ash cementitious material, which comprises the following components in parts by mass:

[0007] 100 parts of fly ash;

[0008] 10 - 20 parts of slag powder;

[0009] 5 - 10 parts of steel slag;

[0010] 11 - 21 parts of low - temperature curing agent;

[0011] 0.05 - 5.3 parts of thixotropic agent, and the thixotropic agent includes organic fiber materials;

[0012] 0 - 1 part of small - molecule retarder;

[0013] Further, for the components in powder form, the specific surface area of the components is greater than or equal to 550 g / m 2 .

[0014] Further, the low - temperature curing agent includes an activator and an alcohol amine coagulant promoter, and the mass ratio of the activator to the alcohol amine coagulant promoter is (11 - 20):(0 - 1).

[0015] Further, the thixotropic agent further includes inorganic nanoparticles.

[0016] Further, the alcohol amine coagulant promoter includes at least one of triethanolamine, triisopropanolamine, diethanol isopropanolamine, ethanol diisopropanolamine, and methyldiethanolamine; the activator includes at least one of low - basicity activators, sulfate activators, aluminate activators, and organic activators; the inorganic nanoparticles include at least one of nano - silica, nano - calcium carbonate, and nano - titanium dioxide; the organic fiber materials include at least one of cellulose ether, methyl cellulose ether, ethyl cellulose ether, polyacrylonitrile fiber, and polyvinyl alcohol fiber; the small - molecule retarder includes at least one of gluconate, citric acid, boric acid, and tartaric acid.

[0017] Further, the thixotropic agent includes nano - silica and cellulose ether, and the mass ratio of nano - silica to cellulose ether is (0 - 5):(0.01 - 0.3).

[0018] The present application provides a concrete, which comprises the following components in parts by mass:

[0019] 800 parts of the fly ash cementitious material according to any one of claims 1 - 5;

[0020] 1200 parts of aggregate, and the particle size of the aggregate is less than or equal to 10 mm;

[0021] 260 parts of water;

[0022] 2 parts of fiber material;

[0023] 8 parts of polycarboxylate water reducer.

[0024] Furthermore, the mass ratio of fly ash cementitious material to water is (0.34 - 0.4):1.

[0025] Furthermore, the fiber material is selected from one of steel fiber and polypropylene fiber.

[0026] This application provides a method for preparing concrete, including the following steps:

[0027] Step S1, prefabricate solid components and liquid components:

[0028] Prepare solid components: Mix fly ash cementitious material, aggregate, and fiber material evenly for standby;

[0029] Prepare liquid components: Mix polycarboxylate water reducer and water evenly for standby;

[0030] Step S2, mix the solid components and the liquid components evenly to obtain concrete.

[0031] In summary, this study proposes a fly ash cementitious material, concrete, and their preparation and transportation methods suitable for 3D printing in low-temperature environments. The fly ash cementitious material is composed of fly ash, mineral powder, steel slag, low-temperature curing agent, thixotropic agent, and small molecule retarder, where the thixotropic agent contains organic fiber material. Through systematic component optimization and compound design, this application successfully prepares a cementitious material system with streamlined components, rapid low-temperature curing, high strength, low shrinkage rate, excellent elastic modulus, and outstanding low-temperature resistance. In the solution of this application, through the special compounding of organic fiber material and small molecule retarder, the curing process of fly ash cementitious material under low-temperature conditions is significantly accelerated, and the comprehensive performance of the cementitious material is improved.

[0032] Compared with the prior art, this application achieves double breakthroughs in material components and performance regulation. On the one hand, by simplifying the raw material composition, the production cost is reduced and the material preparation efficiency is improved; on the other hand, it is revealed that organic fiber material and small molecule retarder can improve the retardation efficiency through antagonistic action in the fly ash cementitious material system, providing a theoretical basis and technical support for the research and development of 3D printing building materials in low-temperature environments. Specific Embodiments

[0033] The technical solutions of the embodiments of this application will be described clearly and completely below. Obviously, the described embodiments are some, but not all, of the embodiments of this application. Based on the embodiments in this application specification, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope claimed by this application.

[0034] Among them, there are no special restrictions on the sources of all raw materials of the present invention, and they can be purchased on the market or prepared by conventional methods well-known to those skilled in the art.

[0035] The embodiment of the present application provides a fly ash cementitious material, which includes the following components in parts by mass:

[0036] 100 parts of fly ash;

[0037] 10 - 20 parts of mineral powder;

[0038] 5 - 10 parts of steel slag;

[0039] 11 - 21 parts of low-temperature curing agent;

[0040] 0.05 - 5.3 parts of thixotropic agent, and the thixotropic agent includes organic fiber materials;

[0041] 0 - 1 part of small molecule retarder.

[0042] It should be noted that after the physical or chemical activation treatment of the mineral powder and steel slag, the depolymerization of their vitreous structure exposes a large number of active sites, providing significant pozzolanic reactivity for the cementitious material system. During the hydration process, the two not only undergo a secondary hydration reaction with alkaline substances such as calcium hydroxide in the system to generate hydration products such as C-S-H gel, effectively improving the curing strength of the cementitious material; at the same time, as a calcium source, it provides the necessary calcium ions for the formation of ettringite (AFt). The ettringite generates a moderate expansion stress during the crystal growth process, endowing the cementitious material with a micro-expansion characteristic, thereby compensating for the volume shrinkage caused by factors such as water evaporation and hydration shrinkage in the later stage of curing of the 3D printing structure, and effectively avoiding the risk of shrinkage cracking.

[0043] As the core coagulation-promoting component of the system, the low-temperature curing agent significantly reduces the activation energy of the hydration reaction through the synergistic effect of a low-alkali activator and an alcohol amine-based coagulation promoter, accelerating the hydration process of the cementitious material in a low-temperature environment and realizing the rapid curing of the material; at the same time, the present application also finds that the introduction of the "alcohol amine-based coagulation promoter" can significantly reduce the shrinkage of the cementitious material in this solution.

[0044] The thixotropic agent endows the cementitious material with thixotropic properties of shear thinning and static thickening by changing its rheological properties. During the 3D printing process, the fluidity of the material is enhanced when it is subjected to extrusion shear, ensuring smooth extrusion and forming; when the printing is paused or a layer of stacking is completed, the material quickly resumes its consistency, effectively improving the interlayer bonding strength and ensuring the interlayer continuity and overall stability of the printed structure.

[0045] Small molecule retarders inhibit the rapid progress in the initial stage of the hydration reaction and extend the open time of the gelling material by mechanisms such as adsorbing on the surface of cement particles to form a protective film and complexing metal ions in the system, providing an ample operation time window for 3D printing construction.

[0046] In this embodiment, the antagonistic effect between the organic fiber material thixotropic agent and the small molecule retarder significantly shortens the curing time of the fly ash gelling material and improves the comprehensive performance of the gelling material.

[0047] In some embodiments, for the component in powder form, the specific surface area of the component is greater than or equal to 550 g / m 2 。

[0048] In some embodiments, the low-temperature curing agent includes an activator and an alkanolamine accelerating agent; the mass ratio of the activator to the alkanolamine accelerating agent is (11-20):(0-1).

[0049] In some specific embodiments, the activator is a low-alkali activator; the alkanolamine accelerating agent is triethanolamine.

[0050] It should be noted that the low-alkali composite activator used in this embodiment is compounded by sodium carbonate and water glass with a modulus of 1.2-1.8, and the mass ratio of water glass is 60%-80%. This low-alkali activator effectively controls the pH value of the fly ash gelling material below 12.5, significantly reducing the corrosion of the 3D printing equipment and tools in industrial applications by the alkaline environment, laying a foundation for its large-scale engineering promotion. As a typical representative of alkanolamine accelerating agents, triethanolamine plays multiple mechanism roles in the low-temperature gelling material system. In addition to accelerating the low-temperature curing process and increasing the early and late strength, it can also effectively relieve the internal shrinkage stress of the gel, further reducing the shrinkage rate of the gelling system and enhancing the volume stability of the material.

[0051] In some embodiments, the thixotropic agent further includes inorganic nanoparticles.

[0052] In some embodiments, the alkanolamine accelerating agent includes at least one of triethanolamine, triisopropanolamine, diethanol isopropanolamine, ethanol diisopropanolamine, and methyldiethanolamine; the activator includes at least one of a low-alkali activator, a sulfate activator, an aluminate activator, and an organic activator; the inorganic nanoparticles include at least one of nano-silica, nano-calcium carbonate, and nano-titanium dioxide; the organic fiber material includes at least one of cellulose ether, methyl cellulose ether, ethyl cellulose ether, polyacrylonitrile fiber, and polyvinyl alcohol fiber; the small molecule retarder includes at least one of gluconate, citric acid, boric acid, and tartaric acid. In some specific embodiments, the gluconate is sodium gluconate.

[0053] Preferably, the thixotropic agent includes nano-silica and cellulose ether, and the mass ratio of nano-silica to cellulose ether is (0-5):(0.01-0.3).

[0054] It should be noted that, due to its high specific surface area and surface activity, nano-silica forms a physical overlapping network structure in the gelling system. Under the action of shear force, this network structure is reversibly damaged, reducing the viscosity of the material and endowing it with good extrusion fluidity; when the shear force is removed, the van der Waals force and hydrogen bond interaction between nano-particles prompt the rapid restoration of the network structure, achieving the thickening effect of the material, thereby endowing the gelling material with excellent thixotropic properties. At the same time, nano-silica participates in the hydration reaction, reacts with the aluminous components in the system as a silicon source, effectively adjusts the silica-alumina ratio of the gelling material, and promotes the formation and structure optimization of hydration products such as C-S-H gel. Cellulose ether plays a role through the water solubility and steric hindrance effect of its molecular chain. The polymer network formed by it in the aqueous solution is intertwined with the physical network constructed by nano-silica, further enhancing the thixotropic effect.

[0055] The embodiment of the present application provides a kind of concrete, which comprises the following components in parts by mass:

[0056] 800 parts of fly ash gelling material according to any one of claims 1-5;

[0057] 1200 parts of aggregate, and the particle size of the aggregate is less than or equal to 10 mm;

[0058] 260 parts of water;

[0059] 2 parts of fiber material;

[0060] 8 parts of polycarboxylate water reducer.

[0061] Preferably, the particle size of the aggregate is less than or equal to 5 mm. It should be noted that the aggregate has a continuous particle size and a shape close to spherical, which is helpful for the fluidity of the concrete and reduces the risk of blockage.

[0062] In some embodiments, the mass ratio of fly ash gelling material to water is (0.34-0.4):1.

[0063] In some embodiments, the fiber material is selected from one of steel fiber and polypropylene fiber.

[0064] The embodiment of the present application provides a preparation method of a kind of concrete, which comprises the following steps:

[0065] Step S1, prefabricate the solid components and liquid components:

[0066] Prepare the solid components: Mix the fly ash gelling material, aggregate and fiber material evenly and set aside;

[0067] Preparing the liquid component: Mix the polycarboxylate water reducer and water evenly for standby;

[0068] Step S2: Mix the solid component and the liquid component evenly to obtain concrete.

[0069] The applicant further provides the following specific reference examples to describe the present invention. It should be noted that these examples are only descriptive and do not limit the present invention in any way.

[0070] Examples 1 to 14

[0071] This example provides a fly ash cementitious material, and its component ratio is shown in Table 1.

[0072] Comparative Example 1

[0073] This comparative example provides an ordinary 42.5 Portland cement purchased from the market.

[0074] Prepare the fly ash cementitious material and cement provided in the above examples and comparative examples into concrete according to the following formula: 800 parts of fly ash cementitious material; 1200 parts of aggregate, and the particle size of the aggregate is less than or equal to 10 mm; 260 parts of water; 2 parts of fiber material; 8 parts of polycarboxylate water reducer. And conduct effect performance tests on the concrete. The test standards refer to GB / T 50081-2019 and GB / T 50082-2019, and the test results are shown in Table 1.

[0075] Table 1. Comprehensive performance test data table of fly ash cementitious material and cement

[0076]

[0077] According to the analysis of the data in Table 1,

[0078] (1) Influence of different component contents and component changes on the performance of fly ash cementitious material

[0079] From the data comparison of Examples 1 to 3, Examples 4 to 5, Examples 6 to 8, and Examples 9 to 10, it can be seen that synchronously adjusting the component contents in the following combinations, such as "slag powder and steel slag", "low-alkali activator, nano-silica and triethanolamine", "cellulose ether and nano-silica", "cellulose ether and gluconate", can significantly improve the comprehensive performance of fly ash cementitious material. From the data comparison between Example 10 and Examples 11 to 14, it can be seen that Examples 11 to 14 do not add nano-silica, nano-silica, gluconate, and triethanolamine respectively, and the comprehensive performance of the prepared fly ash cementitious material is significantly reduced. This shows that the above components play an important role in improving the comprehensive performance of fly ash cementitious material.

[0080] (2) Influence of the combination of "cellulose ether and gluconate" on the properties of fly ash cementitious materials

[0081] From the data analysis of Examples 9 - 10, it can be seen that simultaneously increasing the dosage gradients of cellulose ether and gluconate can significantly optimize the multi - dimensional performance indicators of fly ash cementitious materials. Specifically, the initial setting time is regularly shortened, the compressive / flexural strength is significantly increased, the drying shrinkage rate is reduced, and the interlayer bonding strength and elastic modulus show significant increases. Among them, the formulation of Example 10 exhibits the optimal initial setting time characteristics in the whole system.

[0082] It is worth noting that in the traditional understanding in the field of cement - based materials, cellulose ether (as a polymer water - retaining agent / thixotropic agent) and gluconate (a small - molecule retarder of hydroxycarboxylic acid type) have both been proven to delay cement hydration and prolong the retardation process through different mechanisms. However, in the fly ash cementitious material system of this study, the synergistic effect between the two shows a significant antagonistic effect - when they are compounded in the specific ratio of Example 10, the initial setting time is shortened by 13 minutes compared with Example 13 with only cellulose ether added, and key performance indicators such as strength and shrinkage rate are optimized simultaneously. By comparing the formulation differences between Example 10 and Example 13 (gluconate is not introduced in Example 13), a counter - intuitive performance can be observed: the initial setting time of Example 13 without the retardation component is significantly longer than that of Example 10 with both retardation components added. This phenomenon reveals a possible special mechanism in this compound system: the chelation of gluconate may change the adsorption configuration of cellulose ether on the surface of fly ash - cement particles, weakening the steric hindrance effect of the polymer chain segments on the early hydration products; at the same time, the compounding of the two may synergistically regulate the hydration kinetics of the aluminate phase, accelerating the early formation of the ettringite crystallization network.

[0083] In summary, the formulation of Example 10 breaks through the retardation effect limitation of single components through the specific ratio synergy of cellulose ether and gluconate, achieving a double gain in setting time control and mechanical property optimization. This phenomenon implies that there may be complex colloid - chemical interactions between polymer organic polymers and small - molecule retarders in the fly ash - based cementitious material system, and its mechanism is worthy of in - depth study through molecular dynamics simulation and hydration heat analysis.

[0084] The above are the preferred embodiments of this application and are not used to limit the present invention. Although this application has been described in detail with reference to the examples, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing examples, or perform equivalent replacements for some of the technical features. However, any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of this application shall be included within the protection scope of this application.

Claims

1. A fly ash cementitious material, characterized in that, Comprising the following components in parts by mass: 100 parts of fly ash; 10 - 20 parts of ground granulated blast - furnace slag; 5 - 10 parts of steel slag; 11 - 21 parts of low - temperature curing agent; 0.05 - 5.3 parts of thixotropic agent, and the thixotropic agent comprises organic fiber materials; 0 - 1 part of small - molecule retarder.

2. The fly ash cementitious material according to claim 1, characterized in that, The component in powder form, and the specific surface area of the component is greater than or equal to 550 g / m 2 .

3. The fly ash cementitious material according to claim 1, characterized in that: The low - temperature curing agent comprises an activator, an alcohol - amine accelerator, and the mass ratio of the activator to the alcohol - amine accelerator is (11 - 20):(0 - 1).

4. The fly ash cementitious material according to claim 1, wherein The thixotropic agent further comprises inorganic nanoparticles.

5. The fly ash cementitious material according to any one of claims 1 - 4, characterized in that: The alcohol - amine accelerator comprises at least one of triethanolamine, triisopropanolamine, diethanol isopropanolamine, ethanol diisopropanolamine, and methyldiethanolamine; The activator comprises at least one of low - basicity activators, sulfate activators, aluminate activators, and organic activators; The inorganic nanoparticles comprise at least one of nano - silica, nano - calcium carbonate, and nano - titanium dioxide; The organic fiber materials comprise at least one of cellulose ether, methyl cellulose ether, ethyl cellulose ether, polyacrylonitrile fiber, and polyvinyl alcohol fiber; The small - molecule retarder comprises at least one of gluconate, citric acid, boric acid, and tartaric acid.

6. The fly ash cementitious material according to claim 5, characterized in that The thixotropic agent comprises nano - silica and cellulose ether, and the mass ratio of nano - silica to cellulose ether is (0 - 5):(0.01 - 0.3).

7. A kind of concrete, characterized in that, Comprising the following components in parts by mass: 800 parts of the fly ash cementitious material according to any one of claims 1 - 6; 1200 parts of aggregate, and the particle size of the aggregate is less than or equal to 10 mm; 260 parts of water; 2 parts of fiber material; 8 parts of polycarboxylate superplasticizer.

8. The concrete according to claim 7, wherein, The mass ratio of the fly ash cementitious material to water is (0.34 - 0.4):

1.

9. The concrete according to claim 7, wherein The fiber material is selected from steel fiber and polypropylene fiber.

10. A method for preparing concrete containing the fly ash cementitious material according to any one of claims 1 to 6 or the concrete according to any one of claims 7 to 9, characterized in that, Comprising the following steps: Step S1, prefabricating solid components and liquid components: Preparing solid components: Mixing fly ash cementitious material, aggregate, and fiber material evenly for standby; Preparing liquid components: Mixing polycarboxylate superplasticizer and water evenly for standby; Step S2, mixing the solid components and the liquid components evenly to obtain concrete.

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