A lightweight, hydrophobic, frost-resistant fly ash-based precast component, its preparation method, and its applications.

Abstract

This invention belongs to the technical field of precast concrete components, specifically relating to a lightweight, hydrophobic, frost-resistant fly ash-based precast component, its preparation method, and its applications. The precast component comprises a filling core layer, a matrix layer enclosing the filling core layer, a hydrophobic surface layer enclosing the matrix layer, and pre-sealed pre-drilled holes; the pre-drilled holes penetrate one side of the matrix layer and the hydrophobic surface layer; the hydrophobic surface layer is made of stearic acid-modified bentonite, cement, mineral powder, and water, with a water-cement ratio of 0.1~0.3; the matrix layer is made of cement, fly ash, silica fume, stone chips, water-reducing agent, and water, with a water-cement ratio of 0.1~0.3; the filling core layer is composed of one or more of fly ash, red mud, and sawdust. The flexural and compressive strengths of this precast component are comparable to those of cement precast components of the same specifications, but its density is significantly reduced, its water absorption is low, and its frost resistance and salt-freezing resistance are greatly improved, achieving efficient utilization of solid waste.

Description

Technical Field

[0001] This invention belongs to the field of precast concrete technology, specifically relating to a lightweight, hydrophobic, frost-resistant fly ash-based precast component, its preparation method, and its applications. Background Technology

[0002] Traditional precast concrete components generally suffer from two major drawbacks: high self-weight (density ≥2400 kg / m³) and low solid waste disposal capacity. On the one hand, high density increases transportation and installation energy consumption by more than 30%, significantly increasing project costs. On the other hand, my country generates a huge amount of industrial solid waste such as fly ash and red mud every year, but the amount of solid waste in existing components is generally very low. Large-scale stockpiling not only occupies land but also causes heavy metal leaching pollution. Conventional single-material structures cannot overcome performance bottlenecks: when the fly ash content is too high, the compressive strength drops sharply due to insufficient active components and increased porosity, failing to meet the high strength requirement of more than 50 MPa, which seriously restricts the process of solid waste resource utilization.

[0003] Furthermore, the water absorption rate of concrete components is generally higher than 5%. Under freeze-thaw cycles, moisture easily penetrates and causes internal crystallization pressure. After 300 freeze-thaw cycles, the mass loss rate can reach 3% to 5%, far exceeding the national standard limit (≤1.5%). Traditional technical approaches attempt to achieve lightweighting by adding lightweight aggregates, but the weakening of the aggregate-paste interface leads to a reduction in strength (by 35% to 50%). According to some existing studies (CN108892451A, CN112723844A), adding porous ceramics, high-strength lightweight fibers, and other materials has achieved a reduction in density without compromising material performance. However, this has resulted in a significant increase in production costs, creating a technical dilemma of "lightweight inevitably means lower strength" and "higher costs". The deep-seated technical obstacles manifest in two aspects: at the material level, the strong hydrophilicity (contact angle < 90°) of mineral admixtures such as bentonite contradicts the waterproofing requirements, while conventional hydrophobic modification easily disrupts the cement hydration process; at the structural level, solid waste-filled core materials are prone to component cracking due to their poor volume stability (drying shrinkage rate > 0.08%). Although existing research attempts to improve performance through fiber reinforcement or chemical foaming, it is difficult to achieve a synergistic development of lightweight, high strength, and hydrophobicity. Summary of the Invention

[0004] To address the above problems, the purpose of this invention is to provide a lightweight, hydrophobic fly ash-based precast component, its preparation method, and its applications. The technical solution of this invention includes:

[0005] A lightweight, hydrophobic, frost-resistant fly ash-based precast component comprises a filling core layer, a matrix layer enclosing the filling core layer, a hydrophobic surface layer enclosing the matrix layer, and pre-sealed holes; the pre-sealed holes penetrate one side of the matrix layer and the hydrophobic surface layer; the hydrophobic surface layer is made of water and stearic acid-modified bentonite, cement, and mineral powder in a mass ratio of (1~3):(16~20):(4~6) as raw materials for the hydrophobic surface layer slurry, wherein the mass ratio of bentonite to stearic acid in the stearic acid-modified bentonite is 100:(1~3); the water-cement ratio of the hydrophobic surface layer slurry is 0.1~0.3; the matrix layer is made of water and stearic acid in a mass ratio of (45~60):( The matrix layer mixture is made of cement, fly ash, silica fume, stone chips and water-reducing agent of 50~70):(3~8):(25~40):(0.2~0.4) as raw materials, and the water-cement ratio of the matrix layer mixture is 0.1~0.3; the filling core layer is mainly composed of one or more of fly ash, red mud and sawdust.

[0006] The infill core layer is used to contain solid waste materials, improving the recycling rate of solid waste materials and reducing the density of precast components, thereby increasing the lightweight nature of precast components. The matrix layer and hydrophobic surface layer ensure the moisture resistance, frost resistance, and hardness of the precast components, and reduce the impact on the cement hydration reaction of concrete materials. The term "mainly composed of one or more materials" means that when the precast components are prepared using molds, some residual mold components may inevitably exist, such as polycaprolactone materials with phase change characteristics.

[0007] Preferably, the prefabricated component is either a cubic prefabricated component or a cylindrical prefabricated component.

[0008] Preferably, the filling core layer accounts for 5% to 12% of the volume of the prefabricated component.

[0009] Preferably, the thickness ratio of the substrate layer to the hydrophobic surface layer is 4:(1~3).

[0010] Preferably, the water-reducing agent is a polycarboxylate water-reducing agent.

[0011] Preferably, the fluidity of the matrix layer mixture is ≥180mm.

[0012] Preferably, the cement is PI cement of grade 52.5; the mineral powder is S95 grade mineral powder.

[0013] Preferably, the reserved holes are sealed and filled with quick-drying cement.

[0014] The preparation method of any of the aforementioned lightweight hydrophobic and frost-resistant fly ash-based precast components includes the following steps:

[0015] Preparation of stearic acid modified bentonite: Bentonite and stearic acid were mixed and reacted at 75℃~90℃ for 1h~3h, and then ball-milled until the average particle size was ≤10μm to obtain stearic acid modified bentonite.

[0016] Preparation of hydrophobic surface layer slurry: Cement, mineral powder, stearic acid modified bentonite and water are mixed to prepare a fabric premix slurry. The fabric premix slurry is added to a colloid mill for shearing treatment to prepare a fabric premix. The fabric premix is ​​then subjected to pressure filtration using a pressure filter device to separate excess free water and prepare a hydrophobic surface layer slurry.

[0017] Preparation of matrix layer mixture: Cement, fly ash, stone chips, silica fume, water-reducing agent and water are mixed to prepare the matrix layer mixture;

[0018] Preparation of the core filling material: Take the raw materials required for the core filling and prepare the core filling material.

[0019] Furthermore, the preparation method further includes the following steps:

[0020] Precast component preparation:

[0021] (1) Construct the mold and pour the concrete in the following order: top surface of the component, top surface of the substrate layer, inserted hollow paraffin wax, and substrate layer in the remaining space. According to the structure of the precast component, first pour the hydrophobic surface layer slurry except for the top hydrophobic surface layer, and squeeze the hydrophobic surface layer slurry into the mold to form a hydrophobic surface layer frame;

[0022] (2) Pour the bottom matrix layer mixture, then put in the polycaprolactone block that matches the size of the filling core layer, and place the hole mold that matches the reserved hole on the top of the polycaprolactone block to complete the pouring of the matrix layer mixture. Use a standard vibration table to vibrate and form the matrix layer with a vibration frequency of 40Hz to 60Hz and a vibration forming time of 15s to 30s to make the matrix layer dense. Pour the hydrophobic surface layer slurry used for the top hydrophobic surface layer and squeeze the top hydrophobic surface layer slurry to make the top hydrophobic surface layer dense.

[0023] After steam curing for 6-12 hours under heating and relative humidity ≥95%, turn the mold over, remove the perforated mold, pour out the molten polycaprolactone, and then fill the core layer material through the reserved holes to seal and fill the reserved holes. Then, cure for 20-40 days.

[0024] Preferably, the steam curing temperature is 50℃~70℃; the conventional curing conditions are 20℃~23℃ and relative humidity ≥90%.

[0025] The present invention further provides the use of any of the aforementioned lightweight hydrophobic and frost-resistant fly ash-based precast components as curb stones.

[0026] Beneficial effects

[0027] (1) Firstly, this invention provides a three-layer sandwich-type lightweight hydrophobic and frost-resistant fly ash-based precast component, and overcomes the problem that the existing technology lacks the molds required for this type of precast component, making the preparation method difficult to implement. In traditional concrete precast component molds (such as metal molds or plastic molds with four or five sides), a core mold made of polycaprolactone is introduced. Since the optimal steam curing temperature of the designed precast component is exactly the same as the temperature at which polycaprolactone melts into a liquid state, it is convenient to reserve the internal cavity for filling the core layer. Moreover, the polycaprolactone core mold can be reused through phase change and can withstand the pressure required by the preparation method of this invention, which greatly simplifies the preparation of precast components and improves the reusability of materials.

[0028] (2) Secondly, the sandwich precast component of the present invention overcomes the shortcomings of existing simple mixed precast components (e.g., mixing solid waste with the base material), which can significantly improve the utilization rate of solid waste and thus reduce construction costs. At the same time, it realizes the lightweighting of materials and improves the convenience of replacing building materials. It avoids the natural technical contradiction that simple mixed precast components cannot add a large amount of solid waste material, otherwise it will affect the strength and performance of the precast components (solid waste often has poor water absorption and requires the addition of a large amount of cement to achieve solidification and fixation, but it still significantly affects the strength of the precast components). It also overcomes the problems of flat-layer stacked precast components, which, although solid waste material can be used in a certain layer to improve lightweighting, have weak interlayer bonding strength, leading to easy delamination and cracking and damage to overall strength. For example, the upper layer is cement concrete and the lower layer is a base layer containing solid waste or foam. Thus, it provides conditions for the application of precast components based on solid waste materials in the field of high-strength precast components.

[0029] (3) The sandwich precast component of the present invention, through screening, investigation and improvement of the surface layer, improves the hydrophobicity of the surface layer, and the surface layer material preparation process is simple and the material utilization effect is high, thereby improving the hydrophobicity and frost resistance of the precast component while maintaining the strength of the precast component. It overcomes the shortcomings of traditional concrete materials that are difficult to achieve a good balance between hydrophobicity, frost resistance and material strength. The resulting component is hydrophobic and frost-resistant, which helps to improve the service life of the precast component, reduce the frequency of material replacement, and further reduce construction and maintenance costs.

[0030] This prefabricated component combines lightweight, high solid waste utilization, hydrophobicity, frost resistance, and high strength, making it suitable for applications such as curb stones that require high acidity, alkalinity, frost resistance, and strength. Attached Figure Description

[0031] Figure 1 This is a three-dimensional structural diagram of a prefabricated component according to the present invention;

[0032] Figure 2 This is a schematic cross-sectional view of a prefabricated component according to the present invention;

[0033] Figure 3 This is a longitudinal sectional view of a prefabricated component according to the present invention;

[0034] Figure 4 This is a physical image of the prefabricated component from Example 1. Detailed Implementation

[0035] The technical solution and effects of the present invention will be demonstrated and explained below with reference to specific embodiments and accompanying drawings. In the following embodiments, directional terms such as "top layer" and "bottom layer" are based on the mold placement characteristics and do not represent the actual installation characteristics of the prefabricated components in actual use. (Appendix) Figure 1-3 In this process, the vertical positions of each layer and the positional relationship of the reserved holes are based on the mold placement characteristics during preparation, and do not represent the actual installation characteristics of the prefabricated components in actual use.

[0036] It should be understood that the following embodiments are merely preferred examples for illustrative purposes and are not intended to limit the scope of the invention. Therefore, it should be understood that other equivalent or improved methods can be obtained without departing from the spirit and scope of the invention. Modifications made by those skilled in the art without departing from the essence and concept of the invention fall within the protection scope of the invention. Unless otherwise specified, the materials and instruments used in the following embodiments are commercially available products, and raw materials with the same name are all selected from materials obtained using the same specifications and methods. The steam curing conditions and conventional curing conditions for the precast components in the embodiments and comparative examples 1-3 are the same.

[0037] A schematic diagram of the structure of the lightweight hydrophobic fly ash-based prefabricated component of the present invention is shown below. Figure 1 As shown, the schematic diagrams of the cross-section and longitudinal section are respectively as follows: Figure 2 , 3 As shown, the main body of this prefabricated component consists of three parts: a central infill core layer, a matrix layer surrounding the infill core layer, and a hydrophobic surface layer surrounding the matrix layer. In the case of a cubic prefabricated component, pre-drilled holes are located on one side of the cube, penetrating the matrix layer and the hydrophobic surface layer on that side.

[0038] To ensure comparability of the prefabricated components in the embodiments and comparative examples, the prefabricated components in the following embodiments and comparative examples were all prepared using the same mold. The main body of the mold uses a metal plate as an outer shaping enclosure, and a solid polycaprolactone block (melted into a liquid state at 60°C~70°C) is the mixture that fills the cavity of the core layer and supports the matrix layer from the inside. The mold with reserved holes uses a solid plastic cylinder with a diameter of 50mm (i.e., a hole mold, which can also be a cubic column). The dimensions of the prefabricated components are uniformly 750mm×200mm×270mm (length*width*height), of which the cavity of the core layer (solid polycaprolactone block) has a size of 600mm×50mm×120mm (length*width*height), the thickness of the matrix layer (the thickness between one side of the core layer and the corresponding side of the hydrophobic surface layer) is 60mm; the thickness of the hydrophobic surface layer (the thickness between one side of the matrix layer and the corresponding side of the outer surface of the prefabricated component) is 15mm. That is, the volume of the filling core layer accounts for approximately 8.9% of the total volume of the precast component (600mm×50mm×120mm) / (750mm×200mm×270mm)×100%=8.9%. The sandwich precast component is prepared in the order of outer layer to inner layer, then top hydrophobic surface layer, and finally the filling core layer material is poured in and sealed. This ensures the pouring operation of the filling core layer material and also ensures that the hydrophobic surface layer and matrix layer can be vibrated or compacted before the filling core layer material is poured in without affecting the stability of the internal reserved cavity (the cavity corresponding to the filling core layer).

[0039] Example 1: A lightweight hydrophobic fly ash-based precast component

[0040] The raw materials used for each layer of the lightweight, hydrophobic fly ash-based precast component in this embodiment are as follows:

[0041] The hydrophobic surface layer is made of water and raw materials in the following mass ratio: stearic acid modified bentonite: cement: mineral powder = 1:16:4; the matrix layer is made of water and raw materials in the following mass ratio: cement: fly ash: silica fume: stone chips: water-reducing agent = 55:70:8:40:0.4. The filling core layer is made of fly ash and red mud mixed in a 1:1 mass ratio.

[0042] The preparation method of stearic acid modified bentonite is as follows: bentonite and stearic acid are mixed at a mass ratio of 100:3, reacted at 80℃ for 2 hours, and then ball-milled to an average particle size of 4μm. The modified bentonite has a hydrophobic angle of 160°. The cement used is PI cement of grade 52.5; the mineral powder is S95 grade mineral powder; the fly ash is raw ash from a power plant; the stone chips are 0~5mm continuously graded limestone stone chips; the water-reducing agent is a polycarboxylate high-performance water-reducing agent (purchased from Jiangsu Subote New Materials Co., Ltd., with a solid content of 40% and a water reduction rate of 30%); and the red mud is Bayer process red mud.

[0043] (1) Preparation of hydrophobic surface layer slurry: The raw materials are mixed to prepare a fabric premix slurry. The fabric premix slurry is then added to a colloid mill for shearing treatment to prepare a fabric premix. The premix is ​​then subjected to pressure filtration using a filter press to separate excess free water, thus preparing a hydrophobic surface layer slurry with a water-cement ratio of 0.20. The pressure range of the pressure filtration treatment is 10KN to 15KN (15KN in this embodiment, with a filter press area of ​​0.04m²). 2 That is, the pressure range is 250 to 375 kPa.

[0044] (2) Preparation of matrix layer mixture: Mix the raw materials to prepare a matrix layer mixture with a water-cement ratio of 0.20 and a flowability of not less than 180 mm (200 mm in this example).

[0045] (3) Preparation of filling core material: fly ash and red mud are mixed in a 1:1 ratio.

[0046] (4) Preparation of prefabricated components:

[0047] 1) Construct a mold without a top cover. First, pour the hydrophobic surface layer slurry (excluding the top hydrophobic surface layer). Apply pressure of 30KN–40KN (35KN in this embodiment) to compress the hydrophobic surface layer slurry within the mold to form a hydrophobic surface layer framework. The effective compression areas of each surface are 0.0408, 0.1224, and 0.1728 m², respectively. 2 Therefore, the pressure range is 173 kPa to 981 kPa.

[0048] 2) After pouring the bottom matrix layer mixture, place a solid polycaprolactone block that matches the size of the filling core layer. Place a hole mold that matches the reserved holes on top of the solid polycaprolactone block to complete the pouring of the other sides of the matrix layer mixture. Use a standard vibrating table for vibration molding at a vibration frequency of 50Hz and a vibration molding time of 20s to make the matrix layer dense. Pour the hydrophobic surface layer slurry used for the top hydrophobic surface layer. Extrude the top hydrophobic surface layer slurry (35KN) to make the top hydrophobic surface layer dense.

[0049] 3) After steam curing at 65±5℃ and relative humidity ≥95% for 8 hours (using 95% relative humidity as an example in this embodiment), turn the mold over, remove the perforated mold, pour out the molten polycaprolactone, and fill the core layer material through the reserved holes. Seal the reserved holes with quick-drying cement and then cure them for 28 days at 20℃~23℃ and relative humidity ≥90% (using 90% relative humidity as an example in this embodiment).

[0050] Example 2: A lightweight hydrophobic fly ash-based precast component

[0051] The difference between the lightweight hydrophobic fly ash-based precast component in this embodiment and that in Embodiment 1 is: the material ratio is different, the water-cement ratio of the hydrophobic surface slurry and the matrix layer mixture is different, the preparation method of the modified bentonite is different, and the fluidity is different. Other parameters and preparation methods are the same as in Embodiment 1.

[0052] The hydrophobic surface layer is made of water and raw materials in the following mass ratio: stearic acid modified bentonite: cement: mineral powder = 3:20:6; the matrix layer is made of water and raw materials in the following mass ratio: cement: fly ash: silica fume: stone chips: water-reducing agent = 45:50:6:35:0.3. The filling core layer is made of fly ash and red mud mixed in a 1:1 ratio.

[0053] The preparation process of stearic acid modified bentonite is as follows: bentonite and stearic acid are mixed at a ratio of 100:1, reacted at 80℃ for 2 hours, and then ball-milled to an average particle size of 8μm. The modified bentonite has a hydrophobic angle of 130°.

[0054] The water-cement ratio of the hydrophobic surface layer slurry is 0.15. The water-cement ratio of the matrix layer mixture is 0.30, and the fluidity is 260 mm.

[0055] Preparation of filling core material: fly ash and red mud are mixed in a 1:1 ratio.

[0056] Example 3: Performance evaluation of different prefabricated components

[0057] The performance of the prefabricated components of Examples 1 and 2, as well as the exploratory prefabricated components (comparative examples) used in the study, was investigated. Information on the prefabricated components of the different comparative examples is as follows:

[0058] Precast components of Comparative Example 1: The only difference from Example 1 is that bentonite and stearic acid are mixed at a ratio of 100:0.1, otherwise the same as in Example 1;

[0059] The precast components of Comparative Example 2 differ from those of Example 1 only in that the bentonite was not modified (stearic acid modified bentonite was replaced with an equal amount of bentonite), otherwise they were the same as those of Example 1.

[0060] The precast component of Comparative Example 3 differs from that of Example 1 only in that the hydrophobic layer is made of PI cement with a strength grade of 52.5 for the hydrophobic surface layer of the component; otherwise, it is the same as that of Example 1.

[0061] The precast components of Comparative Example 4 differ from those of Example 1 only in that the bentonite and stearic acid are physically mixed without heat treatment;

[0062] The precast component of Comparative Example 5 differs from that of Example 1 only in that stearic acid is replaced with an equal amount of dispersible latex powder, hydroxypropyl methylcellulose and polyacrylamide hydrophobic mixture in a mass ratio of 8:11:1, and the bentonite and hydrophobic mixture are not subjected to heat treatment.

[0063] The precast component of Comparative Example 6 differs from that of Example 1 only in that the stearic acid modified bentonite is replaced with an equal amount of lauric acid pretreated zeolite (preparation method: add 25 times the weight of lauric acid to anhydrous ethanol, stir and dissolve at room temperature, then add 10 times the weight of lauric acid to 400 mesh zeolite powder, stir at 40°C and 800 rpm for 2 hours, let stand overnight, filter and wash the solid with anhydrous ethanol, and then vacuum dry at 50°C for 16 hours).

[0064] Precast components of Comparative Example 7: conventional cement-based precast components (made entirely of cement and without delamination).

[0065] Referring to relevant industry standards and methods of the People's Republic of China, the cement-based precast components of the embodiments and comparative examples were tested for flexural strength (test method according to Appendix B of JC / T-899-2016), compressive strength (test method according to Appendix C of JC / T-899-2016, the specimen size is 70mm×70mm×70mm cube, i.e., 15mm hydrophobic surface layer + 55mm matrix layer; the sampling locations are the same for all embodiments and comparative examples), correction factor 0.88), water absorption (test method according to Appendix D of JC / T-899-2016, the specimen size is 70mm×70mm×70mm cube, the location is the same as the compressive strength specimen, the hydrophobic surface layer is the test surface; the sampling locations are the same for all embodiments and comparative examples), and frost resistance (test method according to GB / T). 50082-2019, the specimen size is 70mm×70mm×70mm cube, the location is the same as the compressive strength specimen, the hydrophobic surface is the test surface; the sampling locations of each embodiment and comparative example are the same), salt freeze resistance (test method according to Appendix E of JC / T-899-2016), density (volume method, ρ=m / V) test, the results are shown in Table 1.

[0066] Table 1 Performance of precast components

[0067]

[0068] Density measurements showed that the precast components of Examples 1, 2, and Comparative Examples 1-6 had relatively low densities, while the precast component of Comparative Example 7 had a much higher density than the other precast components. This is because the precast components of Examples 1, 2, and Comparative Examples 1-6 all adopted the same sandwich structure as the present invention, which facilitates the addition of more lightweight solid waste materials, improves the utilization rate of solid waste, and achieves lightweighting.

[0069] The test results show that the water absorption rate of the precast components in Examples 1 and 2 is much lower than that of the precast components in the comparative examples, and their frost resistance and salt-frost resistance are far superior to those of the precast components in the comparative examples, and are lower than the standard requirements in the specifications. Although the cement precast component in Comparative Example 7 has higher strength, its water absorption rate, frost resistance, and salt-frost resistance are all poor, and its density is too high (far higher than that of Examples 1 and 2). The flexural strength and compressive strength of the precast components in Examples 1 and 2 are higher than those of the precast components in Comparative Examples 1-6, and are higher than or basically equivalent to those of the cement precast component in Comparative Example 7.

[0070] Analysis of the test results from the comparative examples of different hydrophobic surface layers revealed that changes in the amount of stearic acid and bentonite (Comparative Example 1), whether the bentonite was modified (Comparative Example 2), and whether the mixture of bentonite and stearic acid was heated (Comparative Example 3) all led to a significant reduction in the performance of the precast components. This is presumably related to the reduced hydrophobicity caused by changes in the material ratio or the difficulty in effectively mixing the materials due to modification. Furthermore, the introduction of other hydrophobic agents (such as those in Comparative Example 5 or Comparative Example 6) also resulted in a significant reduction in the performance of the precast components due to the effects of material mixing and cement hydration.

[0071] The above results demonstrate that the precast components of this invention possess excellent physical and mechanical properties, comparable to those of ordinary cement-based precast components, and exhibit significantly reduced water absorption and mass loss due to dry-wet freeze-thaw cycles. Using the precast components disclosed in this invention in engineering construction not only reduces the demand for raw materials such as cement but also consumes a large amount of solid waste materials. Furthermore, its density is significantly lower than that of cement concrete, facilitating the installation and replacement of precast components, delaying freeze-thaw damage and other defects caused by water absorption in components such as curbs, thereby extending the service life of the components and reducing construction costs. This invention is applicable to prefabricated buildings, municipal road engineering, and solid waste resource utilization, and is particularly suitable for use in humid and low-temperature environments in building or municipal engineering projects.

[0072] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. 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. These modifications or substitutions (e.g., changing the filling core layer from a whole to a division into multiple dispersed small filling core layer units; modifying or substituting the shape, size, and side of the reserved holes; modifying or substituting the thickness of the matrix layer and the hydrophobic surface layer; or modifying or substituting the filling material of the filling core layer) do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions claimed by the present invention.

Claims

1. A process for the preparation of lightweight, hydrophobic, frost resistant fly ash based precast elements, characterized in that, Includes the following steps: The precast component consists of a core layer, a matrix layer enclosing the core layer, a hydrophobic surface layer enclosing the matrix layer, and pre-sealed holes; the pre-sealed holes penetrate one side of the matrix layer and the hydrophobic surface layer; the hydrophobic surface layer is made of water and stearic acid-modified bentonite, cement, and mineral powder in a mass ratio of (1~3):(16~20):(4~6) as raw materials for the hydrophobic surface layer slurry, wherein the mass ratio of bentonite to stearic acid in the stearic acid-modified bentonite is 100:(1~3); the water-cement ratio of the hydrophobic surface layer slurry is 0.1~0.3; the matrix layer is made of water and stearic acid in a mass ratio of (45~60):( The matrix layer mixture is made of cement, fly ash, silica fume, stone chips and water-reducing agent in the proportions of 50~70):(3~8):(25~40):(0.2~0.4), and the water-cement ratio of the matrix layer mixture is 0.1~0.3; the filling core layer is mainly composed of one or more of fly ash, red mud and sawdust. Preparation of stearic acid modified bentonite: Bentonite and stearic acid were mixed and reacted at 75℃~90℃ for 1h~3h, and then ball-milled until the average particle size was ≤10μm to obtain stearic acid modified bentonite. Preparation of hydrophobic surface layer slurry: Cement, mineral powder, stearic acid modified bentonite and water are mixed to prepare a fabric premix slurry. The fabric premix slurry is added to a colloid mill for shearing treatment to prepare a fabric premix. The fabric premix is ​​then subjected to pressure filtration using a pressure filter device to separate excess free water and prepare a hydrophobic surface layer slurry. Preparation of matrix layer mixture: Cement, fly ash, stone chips, silica fume, water-reducing agent and water are mixed to prepare the matrix layer mixture; Preparation of the core filling material: The raw materials required for the core filling are mixed and prepared to form the core filling material; Precast component preparation: Construct a mold, and according to the structure of the prefabricated component, first pour the hydrophobic surface layer slurry except for the top hydrophobic surface layer, and squeeze the hydrophobic surface layer slurry into the mold to form a hydrophobic surface layer frame; After pouring the bottom matrix layer mixture, place a polycaprolactone block that matches the size of the filling core layer. Place a hole mold that matches the reserved holes on top of the polycaprolactone block to complete the pouring of the matrix layer mixture. Use a standard vibrating table to vibrate and form the matrix layer to make it dense. Pour the hydrophobic surface layer slurry used for the top hydrophobic surface layer and squeeze the top hydrophobic surface layer slurry to make the top hydrophobic surface layer dense. After steam curing for 6-12 hours under heating and relative humidity ≥95%, the mold is turned over, the perforated mold is removed, the molten polycaprolactone is poured out, and then the core material is poured in through the reserved holes to seal and fill the reserved holes. Conventional curing is carried out for 20-40 days.

2. The method for preparing a lightweight, hydrophobic, frost-resistant fly ash-based precast component according to claim 1, characterized in that, The filling core layer accounts for 5% to 12% of the volume of the precast component.

3. The method for preparing a lightweight, hydrophobic, frost-resistant fly ash-based precast component according to claim 1, characterized in that, The thickness ratio of the substrate layer to the hydrophobic surface layer is 4:(1~3).

4. The method for preparing a lightweight, hydrophobic, frost-resistant fly ash-based precast component according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate water-reducing agent.

5. The method for preparing a lightweight, hydrophobic, frost-resistant fly ash-based precast component according to claim 1, characterized in that, The fluidity of the matrix layer mixture is ≥180mm.

6. The method for preparing a lightweight, hydrophobic, frost-resistant fly ash-based precast component according to claim 1, characterized in that, The cement is grade 52.5 PI cement; the mineral powder is grade S95 mineral powder; the reserved holes are sealed and filled with quick-drying cement.

7. The method for preparing a lightweight, hydrophobic, frost-resistant fly ash-based precast component according to claim 1, characterized in that, The steam curing temperature is 50℃~70℃; the conventional curing conditions are 20℃~23℃ and relative humidity ≥90%.

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