Method for preparing high-water-absorption set cement from rice hull ash

Abstract

The invention relates to a method for preparing high-water-absorption set cement from rice hull ash, and belongs to the field of resource utilization of building materials and solid waste materials. Comprising the following steps: S1, preparing materials: cement, rice hull ash, fly ash and water; s2, dry material premixing; s3, adding water and carrying out wet mixing; s4, performing injection molding and vibrating on the test piece for molding; and S5, performing water curing and standard curing on the test piece. According to the preparation method, the porous structure and the volcanic ash effect of the rice hull ash are utilized, the rice hull ash is adopted to replace a traditional mineral admixture, the material cost is reduced, and the utilization rate of agricultural waste is increased; the micro-filling effect of the fly ash is combined, so that the pore structure and the mechanical property of the set cement are optimized. By controlling the material proportion and the water-binder ratio (0.4-0.55) after mixing, the water absorption rate is greater than or equal to 25%, the 28-day compressive strength is maintained to be greater than or equal to 11 MPa, the bottleneck of low-efficiency utilization of the rice hull ash is broken through, and a green building material preparation material with high water absorption, stable mechanical property and environmental friendliness is formed.

Description

Technical Field

[0001] The present invention belongs to the field of building materials and resource utilization of solid waste materials, and relates to a preparation method of highly water-absorbent cement stone from rice husk ash. Background Art

[0002] The performance of water-absorbent cement stone is closely related to its pore structure. Research shows that there is a significant correlation between porosity and compressive strength, and the square of the correlation coefficient reaches 0.96, providing a theoretical basis for the design of permeable concrete. Nuclear magnetic resonance technology analysis reveals that the water-cement ratio, temperature, and fluid characteristics directly affect capillary water absorption, among which the initial moisture content plays a decisive role in the water distribution. Experiments show that the capillary water absorption process presents typical "fast-slow" two-stage characteristics. In the initial linear stage, the water absorption accounts for more than 60%, and it tends to be flat in the later stage. Mineral admixtures (such as fly ash and silica fume) can reduce the capillary water absorption height by 15%-30% by refining pores (the proportion of pores <100nm increases by 20%) and blocking connected pore channels. Optimization of the cementitious material ratio can directionally construct a multi-level pore structure, but the coordinated regulation of high water absorption (>20%) and mechanical properties is still a technical difficulty, and long-term water absorption-drying cycles easily lead to an increase in porosity and strength attenuation.

[0003] As a by-product of rice processing, rice husk ash has attracted much attention in the field of green building materials in recent years due to its rich amorphous silica (content up to 85-95%). Current research mainly focuses on the replacement of concrete admixtures. After rice husk ash is calcined at 600-800°C under controlled temperature, the active silica can undergo a pozzolanic reaction with the hydration products of cement, increasing the 28-day compressive strength of concrete by 20-35% and reducing carbon dioxide emissions by more than 40%. Some engineering practices show that concrete incorporated with 15%-20% rice husk ash has been successfully applied to road bases and low-rise buildings. In addition, rice husk ash also shows potential in the preparation of lightweight aggregates, thermal insulation mortars, and geopolymers, and its porous structure can improve the thermal insulation performance of building materials.

[0004] In the prior art, rice husk ash is mainly used as a concrete admixture to improve mechanical properties. After calcination activation, it replaces 10-30% of cement, and its pozzolanic effect can enhance the compactness of hydration products. In the field of highly water-absorbent cement stone, existing solutions mostly use fly ash or silica fume as mineral admixtures to optimize the pore structure and reduce the capillary water absorption height through the nano-particle filling effect. In addition, there are also some disclosed methods for preparing permeable concrete with porous ceramsite as aggregate, using the pores of the aggregate to store water to improve the water absorption performance. However, the above technologies still have the following defects: (1) Traditional mineral admixtures (such as fly ash) have high costs and rely on the supply of industrial by-products, resulting in limited resource utilization; (2) Existing highly water-absorbent cement stones are difficult to balance high water absorption (>25%) and mechanical strength (28-day compressive strength ≥ 11 MPa); (3) Although the aggregate modification scheme can store water, it significantly increases the material density and preparation cost. However, the current research on using rice husk ash to replace part of the cement to prepare highly water-absorbent cement stone is in a blank state.

[0005] In the prior art, the preparation of highly water-absorbent cement stone mostly relies on high-cost materials (such as superabsorbent polymer SAP) or complex process conditions, making it difficult to popularize in practical applications. At the same time, it is difficult to balance the water absorption performance and mechanical performance of traditional cement stone, restricting its application in non-load-bearing structures (such as roof gardens, ecological slopes). Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a preparation method of highly water-absorbent cement stone made from rice husk ash. Through the porous structure and pozzolanic effect of rice husk ash, combined with the micro-filling effect of fly ash, the pore structure and mechanical properties of the cement stone are optimized.

[0007] To achieve the above purpose, the present invention provides the following technical solutions:

[0008] A preparation method of highly water-absorbent cement stone made from rice husk ash, comprising the following steps:

[0009] S1, Prepare materials: cement, rice husk ash, fly ash, water; wherein the rice husk ash is pre-calcined at 600 °C and then ground to a surface area ≥ 400 m 2 / kg; the proportion of cement is 20%-40%, the proportion of rice husk ash is 20%-70%, and the proportion of fly ash is 20%-40%;

[0010] S2, Premix dry materials: Put the materials in S1 into a mixer and dry mix at a low speed (30 ± 2 r / min) for 3 minutes until the materials are evenly dispersed;

[0011] S3, Adding water for wet mixing: Add mixing water in two times. First, add 70% of the total water volume. After stirring for 1 minute, add the remaining 30% of the water volume. Then switch to medium speed (60±5 r / min) and continue stirring for 5 minutes until the slurry is uniform and free of lumps, with a water-binder ratio of 0.4 - 0.55;

[0012] S4, Specimen molding: Inject the slurry into the mold in two layers, vibrate each layer separately, then scrape the surface flat and leave it standing for 24 hours before demolding;

[0013] S5, Specimen curing: First, carry out water curing, and then carry out standard curing; Water curing means soaking the specimen in water at 20°C for 3 days; Standard curing means placing the specimen in a curing chamber at a temperature of (20±2)°C and a relative humidity of ≥95%, and curing it to the age of 7d, 14d, 28d or 90d.

[0014] Optionally, the material ratio is: 20% cement, 40% rice husk ash, 40% fly ash, with a water-binder ratio of 0.5, and standard curing for 28d.

[0015] Optionally, the material ratio is: 20% cement, 70% rice husk ash, 10% fly ash, with a water-binder ratio of 0.55, and standard curing for 28d.

[0016] Optionally, the cement is ordinary Portland cement with a strength grade of 42.5 MPa.

[0017] Optionally, the fly ash used is Class II fly ash.

[0018] Optionally, the mixing water is municipal tap water, and the water temperature is controlled at (20±2)°C.

[0019] Optionally, in S4, each layer is vibrated for 15 seconds, with a frequency of 50 Hz and an amplitude of 0.5 mm.

[0020] Optionally, the mold in S4 is a 40 mm×40 mm×160 mm triple steel mold.

[0021] Optionally, the mixer used is an HJW-60 type forced mixer.

[0022] Optionally, the materials in S1 also include polypropylene fibers to make up for the strength loss.

[0023] The beneficial effects of the present invention are as follows:

[0024] Aiming at the problems existing in the existing high water-absorbing cement stone materials, such as the difficulty in synergistically improving the water absorption rate and mechanical properties, the high cost of traditional mineral admixtures and the low resource utilization rate, the present invention provides a high water-absorbing cement stone prepared from rice husk ash and its preparation method. Using rice husk ash (RHA) and fly ash (FA) as the core materials, and utilizing the highly active amorphous silica and porous characteristics in the rice husk ash, through the optimized proportion of cementitious materials and a specific calcination process, a low-cost and high-performance high water-absorbing cement stone is developed, optimizing the multi-level pore structure inside the cement stone, breaking through the limitation of the single function of rice husk ash in cement-based materials, and developing the synergistic action mechanism of its porous characteristics and active components; by replacing traditional mineral admixtures with rice husk ash, the material cost is reduced and the utilization rate of agricultural waste is improved; while achieving a water absorption rate of ≥25%, maintaining a compressive strength of ≥11 MPa at 28 days. Breaking through the bottleneck of the inefficient utilization of rice husk ash in cement-based materials, a green building material preparation technology with both high water absorption characteristics, stable mechanical properties and environmental friendliness characteristics is formed.

[0025] In the present invention, the rice husk ash is calcined at a high temperature of 600 °C, so that the specific surface area of the rice husk ash is ≥400 m 2 / kg, optimizing the porous structure of the rice husk ash, significantly increasing the porosity, and forming a through-water absorption channel; the pozzolanic effect of the rice husk ash - the reactive silica reacts with calcium hydroxide to form C-S-H gel, enhancing the matrix density and partially compensating for the strength loss.

[0026] Fly ash is used to fill the pores of the rice husk ash, utilizing the micro-filling effect of fly ash, optimizing the structure of the interfacial transition zone (ITZ), and improving the mechanical properties; the spherical particles of fly ash improve the fluidity of the slurry and reduce the water-binder ratio requirement.

[0027] When the water-binder ratio is 0.5 - 0.55, the water absorption rate and strength reach the best balance; a high water-binder ratio (0.55) is beneficial to the formation of a through-pore network. In the present invention, the water absorption rate is improved by precisely controlling the water-binder ratio, and the strength loss can be compensated by adding polypropylene fibers.

[0028] The present invention also optimizes the curing regime. Water curing for 3 days can quickly activate the porous structure of the rice husk ash, improving the initial water absorption rate, while standard curing ensures the long-term strength development and avoids the performance deterioration caused by pore closure.

[0029] Other advantages, objectives and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the following specification. Description of the Drawings

[0030] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail and preferably below in conjunction with the accompanying drawings, wherein:

[0031] Figure 1 It is a flowchart of the steps of the preparation method of the present invention. Specific embodiments

[0032] The following uses specific specific examples to illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0033] Among them, the drawings are only for illustrative purposes, showing only schematic diagrams, not physical diagrams, and cannot be understood as a limitation to the present invention; in order to better illustrate the embodiments of the present invention, some components in the drawings will be omitted, enlarged or reduced, which does not represent the size of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0034] In the drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only for illustrative purposes and cannot be understood as a limitation to the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0035] Please refer to Figure 1 , which is a preparation method of highly water-absorbent cement stone from rice husk ash, and includes the following steps:

[0036] S1. Prepare materials: cement, rice husk ash, Class II fly ash, water; among them, the rice husk ash is pre-calcined at 600 °C and then ground to a surface area ≥ 400 m 2 / kg; the proportion of cement is 20%-40%, the proportion of rice husk ash is 20%-70%, and the proportion of fly ash is 20%-40%; the cement used is ordinary Portland cement with a strength grade of 42.5 MPa;

[0037] S2, Premixing of dry materials: Put the materials in S1 into a HJW-60 type forced mixer and dry mix at a low speed (30±2 r / min) for 3 minutes until the materials are evenly dispersed;

[0038] S3, Wet mixing with water: Add mixing water in two times. First, add 70% of the total water volume. After stirring for 1 minute, add the remaining 30% of the water volume, and then switch to medium speed (60±5 r / min) and continue to stir for 5 minutes until the slurry is evenly distributed without lumps, and the water-binder ratio is 0.4 - 0.55; The mixing water uses municipal tap water, and the water temperature is controlled at (20±2)°C.

[0039] S4, Specimen forming: Pour the slurry into a triple steel mold of 40mm×40mm×160mm in two layers, vibrate each layer separately, vibrate for 15 seconds for each layer, the frequency is 50Hz, the amplitude is 0.5mm, then scrape the surface flat and leave it to stand for 24 hours before demolding;

[0040] S5, Specimen curing: First carry out water curing, and then carry out standard curing; Water curing is to soak the specimen in water at 20°C for 3 days; Standard curing is to place the specimen in a curing room with a temperature of (20±2)°C and a relative humidity of ≥95%, and cure until the age of 7d, 14d, 28d or 90d.

[0041] Example 1

[0042] This example is the first group of test comparison groups (such as the YA-21 group in Tables 5-3 and 5-4), and the material ratio is: 20% cement, 40% rice husk ash, 40% fly ash, the water-binder ratio is 0.5, and it is cured under standard conditions for 28d.

[0043] The comprehensive performance of this test comparison group is the best. After the specimen is prepared by the preparation method of the present invention and then cured under standard conditions for 28d, the measured water absorption rate is 11.95%, and the compressive strength is 17.27MPa, taking into account both water absorption and bearing capacity.

[0044] Example 2

[0045] This example is the second group of test comparison groups (such as the YC-12 group in Tables 5-3 and 5-4), and the material ratio is: 20% cement, 70% rice husk ash, 10% fly ash, the water-binder ratio is 0.55, and it is cured under standard conditions for 28d.

[0046] This test comparison group meets the high water absorption requirement. After the specimen is prepared by the preparation method of the present invention and then cured under standard conditions for 28d, the measured water absorption rate is 22.46%, and the compressive strength is 11.75MPa; After being cured under standard conditions for 28d, the measured water absorption rate is 27.31%, which is suitable for greening projects or humidity regulating materials, and fibers (such as polypropylene fibers) can be added to the material to make up for the strength loss.

[0047] Table 5-1 Cement paste mix ratio

[0048] Number Cement Rice husk ash Fly ash Water Water-binder ratio 0 300g(100％) 120g 0.4 A-1 60g(20％) 120g(40％) 120g(40％) 120g 0.4 A-2 60g(20％) 120g(40％) 120g(40％) 150g 0.5 A-3 60g(20％) 120g(40％) 120g(40％) 165g 0.55 B-1 60g(20％) 180g(60％) 60g(20％) 150g 0.5 C-1 60g(20％) 210g(70％) 30g(10％) 150g 0.55

[0049] Table 5-2 Experimental Results of Cement Stones with Different Proportions

[0050]

[0051] Table 5-3 Mix Proportions of Cement Stones with Optimized Proportions

[0052] Number Cement Rice husk ash Fly ash Water Water-binder ratio 01 300g(100％) —— —— 150g 0.5 02 300g(100％) —— —— 165g 0.55 YA-21 60g(20％) 120g(40％) 120g(40％) 150g 0.5 YA-22 60g(20％) 120g(40％) 120g(40％) 165g 0.55 YB-11 60g(20％) 180g(60％) 60g(20％) 150g 0.5 YB-12 60g(20％) 180g(60％) 60g(20％) 165g 0.55 YC-11 60g(20％) 210g(70％) 30g(10％) 150g 0.5 YC-12 60g(20％) 210g(70％) 30g(10％) 165g 0.55

[0053] Table 5-4 Test Results of Specimens of Cement Stones with Optimized Proportions Cured in Water for 3d at Different Ages

[0054]

[0055] From the experimental data of the above-mentioned experimental comparison groups, it can be seen that:

[0056] (1) The ultrasonic velocity of the YC-12 group at 28d is 2.581 km / s, and the water absorption rate is 23.81%. Based on the correlation between ultrasonic velocity and pore structure - the decrease in ultrasonic velocity directly reflects the increase in the porosity of the material, verifying the correlation between high porosity and low strength.

[0057] (2) The water absorption rate of the YB-12 group at 90d is 22.91%, indicating that the water absorption rate still continues to increase after the water curing stops, reflecting that the cement stones prepared by this method have long-term performance.

[0058] The preparation method of the present invention realizes the coordinated optimization of high water absorption rate and mechanical properties. Through the calcination activation (600 - 800 °C) of rice husk ash and the multi-level pore structure design, the water absorption rate of the cement stone of the present invention is greater than 25% (the water absorption rate of the YC-11 group at 90 days reaches 30.26%, Table 5-4), and at the same time, the compressive strength at 28 days ≥ 11 MPa (the compressive strength of Specimen C-1 is 11.75 MPa, Table 5-2), breaking through the technical bottleneck that it is difficult to balance the water absorption rate and strength in traditional materials. This innovation enables the material to still have sufficient mechanical strength while maintaining a high water absorption performance, and is applicable to a variety of engineering scenarios.

[0059] The efficient resource utilization of rice husk ash is also realized, and the problem of low-efficiency utilization of rice husk ash is solved. In the prior art, rice husk ash is mainly used for mechanical strengthening, and the potential of its porous characteristics and active components cannot be fully exerted. In the present invention, by exploring the porous characteristics and active components of rice husk ash, 30% of the traditional admixtures (such as fly ash) are replaced with rice husk ash, significantly reducing the material cost. The amorphous silica (with a content of 85%-95%) in rice husk ash has a significant pozzolanic effect, which can enhance the interfacial bonding force and inhibit the long-term pore deterioration, thereby improving the long-term stability of the material. The coordinated improvement of the triple functions of water absorption, mechanical properties, and durability is realized, significantly improving the utilization efficiency of rice husk ash. As an agricultural waste replacing industrial by-products, the efficient utilization of rice husk ash not only reduces the treatment pressure on industrial solid waste but also reduces the raw material cost. In addition, the preparation process does not require additional equipment investment and can be realized by using conventional calcination and stirring technologies, further reducing the production cost.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the present technical solution, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A preparation method of high water-absorbing cement stone made from rice husk ash, characterized in that: It includes the following steps: S1, Prepare materials: cement, rice husk ash, fly ash, water; Among them, the rice husk ash is pre-calcined at 600 °C and then ground to a surface area of ≥ 400 m 2 / kg; the proportion of cement is 20%-40%, the proportion of rice husk ash is 20%-70%, and the proportion of fly ash is 20%-40%; S2, Premix dry materials: Put the materials in S1 into a mixer and dry mix at a low speed (30±2 r / min) for 3 minutes until the materials are evenly dispersed; S3, Wet mix with water: Add mixing water in two times. First, add 70% of the total water volume, stir for 1 minute, then add the remaining 30% of the water volume, and then switch to medium speed (60±5 r / min) and continue to stir for 5 minutes until the slurry is evenly distributed without lumps, and the water-cement ratio is 0.4 - 0.55; S4, Molding of specimens: Pour the slurry into the mold in two layers, vibrate each layer separately, then scrape the surface flat and let it stand for 24 hours to demold; S5, Curing of specimens: First, carry out water curing, and then carry out standard curing; Water curing is to soak the specimens in water at 20°C for 3 days; Standard curing is to place the specimens in a curing room at a temperature of (20±2)°C and a relative humidity of ≥95%, and cure until the age of 7d, 14d, 28d or 90d.

2. The preparation method of the highly water-absorbent cement stone made from rice husk ash according to claim 1, characterized in that: The material ratio is: 20% cement, 40% rice husk ash, 40% fly ash, the water-cement ratio is 0.5, and the standard curing is 28d.

3. The preparation method of the highly water-absorbent cement stone made from rice husk ash according to claim 1, characterized in that: The material ratio is: 20% cement, 70% rice husk ash, 10% fly ash, the water-cement ratio is 0.55, and the standard curing is 28d.

4. The preparation method of the highly water-absorbent cement stone made from rice husk ash according to claim 1, characterized in that: The cement is ordinary Portland cement with a strength grade of 42.5 MPa.

5. The preparation method of the highly water-absorbent cement stone made from rice husk ash according to claim 1, characterized in that: The fly ash used is Class II fly ash.

6. The preparation method of the highly water-absorbent cement stone made from rice husk ash according to claim 1, characterized in that: The mixing water uses municipal tap water, and the water temperature is controlled at (20±2)°C.

7. The preparation method of the highly water-absorbent cement stone made from rice husk ash according to claim 1, characterized in that: In S4, each layer is vibrated for 15 seconds, the frequency is 50 Hz, and the amplitude is 0.5 mm.

8. The preparation method of highly water-absorbent cement stone made from rice husk ash according to claim 1, characterized in that: The mold in S4 is a 40mm×40mm×160mm triple steel mold.

9. The preparation method of the highly water-absorbent cement stone made from rice husk ash according to claim 1, characterized in that: The mixer uses an HJW-60 type forced mixer.

10. The preparation method of the highly water-absorbent cement stone made from rice husk ash according to claim 1, characterized in that: The materials in S1 also include polypropylene fibers to make up for the strength loss.

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