Non-sintered ceramsite and its preparation method and application

Abstract

This invention relates to a non-sintered ceramsite, its preparation method, and its application, belonging to the field of building materials technology. The preparation method includes: drying straw ash and blast furnace slag separately, mixing them in a ratio of (60~80):(20~40) to obtain a cementitious material, adding an alkali activator to the cementitious material and stirring to obtain a wet material, granulating the wet material, and curing it at 100~120℃ for 24~36 hours to obtain non-sintered ceramsite; the alkali activator is a compound system of water glass and sodium hydroxide, the sodium silicate modulus is 0.8~1.2, and the alkali equivalent is 5~15% of the mass of the cementitious material. It was found that the compressive strength exhibits a non-monotonic change characteristic of "first increasing and then decreasing" with increasing temperature, correcting the conventional misconception that "the higher the temperature, the better the performance." The obtained ceramsite can meet the application requirements of special environments such as cold-region engineering, fire protection engineering, and chemical corrosion prevention.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a non-sintered ceramsite, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Non-sintered ceramsite, also known as unfired ceramsite, is typically made from industrial solid waste and does not require high-temperature sintering, making it a green building material. Because its bulk density is usually lower than that of ordinary crushed stone, it is often used to prepare lightweight concrete. Due to its porous structure, it can also improve the thermal insulation performance of buildings.

[0004] Non-fired ceramsite is typically prepared using natural curing or steam curing methods. It is generally believed that higher temperatures or longer reaction times result in more complete reactions and stronger mechanical properties. However, current research usually focuses on performance verification at a single temperature point and lacks optimization for the specific service requirements of cold-region engineering, chemical corrosion protection, and fire protection engineering. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a non-sintered ceramsite, its preparation method, and its application. The invention focuses on the dual gradient effect of curing temperature and time in a straw ash-blast furnace slag dual solid waste system, and optimizes the curing process accordingly. The resulting non-sintered ceramsite exhibits material properties with further enhanced compressive strength under freeze-thaw cycles and high-temperature treatment.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: Firstly, a method for preparing non-sintered ceramsite includes the following steps: Straw ash and blast furnace slag are dried separately and then mixed in a ratio of (60~80):(20~40) to obtain a cementitious material. An alkali activator is added to the cementitious material and stirred to obtain a wet material. The wet material is granulated and cured at 100~120℃ for 24~36 hours to obtain non-sintered ceramsite. The alkali activator is a compound system of water glass and sodium hydroxide, the sodium silicate modulus is 0.8~1.2, and the alkali equivalent is 5~15% of the mass of the cementitious material.

[0007] Secondly, the non-sintered ceramsite prepared by the above-mentioned method is used to obtain non-sintered ceramsite.

[0008] Thirdly, the above-mentioned non-sintered ceramsite is used in building materials for cold-region engineering, fire protection engineering, or chemical corrosion protection.

[0009] Fourthly, a building material comprising the aforementioned non-sintered ceramsite.

[0010] The beneficial effects of this invention are as follows: This invention breaks through the limitations of existing drying and curing research, which focuses on verification at a single temperature point. It systematically studies straw ash-blast furnace slag-based non-sintered ceramsite at four temperature points (80℃, 100℃, 120℃, and 140℃) and three time points (12h, 24h, and 36h), establishing a "temperature-time dual-gradient" drying and curing research system. The influence of curing temperature and time on the bulk density, 1-hour water absorption rate, and compressive strength of the ceramsite is clarified. In particular, it discovers that the compressive strength exhibits a non-monotonic change characteristic of "first increasing and then decreasing" with increasing temperature, correcting the conventional misconception that "higher temperature equals better performance."

[0011] The non-sintered ceramsite obtained by the present invention under the selected process parameters shows that its performance is further improved after freeze-thaw cycles or high-temperature treatment. It has a low compressive loss rate under harsh acid and alkali conditions, which can meet the application requirements of special environments such as cold region engineering, fire protection engineering, and chemical corrosion protection. Attached Figure Description

[0012] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0013] Figure 1 This is an image of the ceramsite prepared by curing at 100℃ for 24 hours in Example 1.

[0014] Figure 2 This is a microstructure diagram of the ceramsite prepared by curing at 100℃ for 24 hours in Example 1.

[0015] Figure 3 The image shows the XRD pattern of the ceramsite prepared by curing at 100℃ for 24 hours in Example 1. Detailed Implementation

[0016] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0017] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0018] The key to the mechanical strength formation of non-sintered ceramsite lies in alkali activation technology. This refers to the depolymerization-polymerization reaction of aluminosilicate raw materials under the action of an alkaline activator, generating hydrated calcium aluminosilicate gel (e.g., C-(A)-SH) or geopolymer networks with gelling properties. Compared with traditional cement materials, alkali-activated materials have advantages such as high early strength, good durability, and low carbon emissions. In the preparation process of non-sintered ceramsite, the curing method is a key factor determining product performance. Currently, commonly used curing methods mainly include natural curing and steam curing. Steam curing can significantly shorten the curing cycle and stabilize product quality, making it the mainstream process for non-sintered ceramsite production. However, it requires specialized equipment such as boilers and steam pipelines, resulting in high investment costs, high energy consumption, and difficulty in humidity control, which limits its widespread application. Natural curing is simple and energy-efficient, but it suffers from long curing cycles (usually requiring 28 days or more) and slow early strength development.

[0019] To address the issue of long natural curing cycles, some researchers have attempted to use drying oven curing as an alternative to natural or steam curing. Practice has shown that drying curing offers advantages such as simple equipment, low energy consumption, and precise temperature control. However, existing research on drying curing largely focuses on performance verification at a single temperature point, lacking systematic comparative studies of different temperatures. This single-point verification method cannot reveal the influence of curing temperature on material properties, let alone determine the optimal curing temperature. Current research primarily focuses on the impact of drying curing on mechanical properties (such as compressive strength), with insufficient systematic evaluation of durability properties such as freeze-thaw cycles, acid and alkali corrosion resistance, and fire resistance. This limits the application prospects of products in specialized fields such as cold-region engineering, chemical corrosion protection, and fire protection engineering. In addition, most studies on drying and curing focus on single solid waste systems such as fly ash, and do not involve the study of the behavior of the straw ash-blast furnace slag dual solid waste system under drying and curing conditions. It is difficult to know the synergistic effect of the high K2O (7.62%) and Fe2O3 (7.50%) content in straw ash and CaO (33.77%) in blast furnace slag on the products of alkali-activated reaction.

[0020] Conventional understanding often holds that "the higher the temperature, the more complete the reaction," but whether this inference applies to the straw ash-blast furnace slag system, and within what temperature range, remains inconclusive. Furthermore, the influence of the coupling effect of curing time and curing temperature on the microstructure and macroscopic properties of the material is also lacking systematic research.

[0021] One or more embodiments of the present invention provide a method for preparing non-sintered ceramsite, comprising the steps of: Straw ash and blast furnace slag are dried separately and then mixed in a ratio of (65~75):(25~35) to obtain a cementitious material. An alkali activator is added to the cementitious material and stirred to obtain a wet material. The wet material is granulated and cured at 100~120℃ for 24~36 hours to obtain non-sintered ceramsite. The alkali activator is a compound system of water glass and sodium hydroxide, the sodium silicate modulus is 0.8~1.2, and the alkali equivalent is 5~15% of the mass of the cementitious material.

[0022] Straw ash is a solid waste produced by burning crop straw in biomass power plants; blast furnace slag is an industrial byproduct generated during blast furnace ironmaking. In these processes, a composite gel system is formed between straw ash and blast furnace slag under alkali activation. The synergistic effect of the high K₂O (7.62%) and Fe₂O₃ (7.50%) in straw ash and the CaO (33.77%) in blast furnace slag results in the simultaneous generation of sufficient hydrated calcium aluminosilicate gel (e.g., C-(A)-SH) and hydrated potassium aluminosilicate gel (KASH) within the system, forming an interpenetrating network structure. The C-(A)-SH gel is the main contributor to the system's compressive strength, forming a dense strength skeleton by filling interparticle gaps and bonding unreacted raw material particles. The KASH gel primarily imparts excellent durability to the system; the K₂O released from the straw ash... + It participates in the construction of a three-dimensional aluminosilicate network, fills the micropores in the C-(A)-SH network, and enhances the thermal stability and impermeability of the gel system. Furthermore, the high Fe2O3 content in straw ash dissolves Fe in an alkaline-activated environment. 3+ It can partially replace Al 3+ The Fe-O-Si bonds are formed within the aluminosilicate gel network, further enhancing the chemical and high-temperature stability of the gel skeleton. Simultaneously, the ferrite polymer fills the micropores, further improving the density and refractory properties of the unsintered ceramsite. Through dual-gradient comparative experiments, this invention determined approximately 100℃ and 24h as the optimal curing process parameters. Under these conditions, the compressive strength of the ceramsite reached 13.01 MPa, significantly higher than the expected level under conventional dry curing.

[0023] Optionally, the drying method of the straw ash includes drying at 100~110℃ for 24~36h; the purpose is to remove free moisture from the straw ash, prevent it from agglomerating and clumping due to moisture absorption during the mixing process, and at the same time avoid the dilution of the alkali equivalent concentration in the alkali activation reaction by excess moisture, so as to ensure the stable performance of the activator activity.

[0024] Optionally, the drying method for the blast furnace slag includes drying at 100~110℃ for 24~36h; the purpose is to remove free moisture from the blast furnace slag, reduce its surface adsorption energy, promote uniform mixing with the alkali activator, and prevent moisture fluctuations from interfering with the alkali activation reaction system, thereby ensuring the stability of the non-sintered ceramsite raw material pellet forming.

[0025] Optionally, the mass ratio of straw ash to blast furnace slag is 70:30, in which case the Ca provided by the blast furnace slag... 2+ Si, Al, and K released from straw ash + To achieve the appropriate ratio, specifically: Ca 2+ With K + The molar ratio of Ca²⁺ to Al is (2.0~2.5):1, preferably 2.2:1, and the molar ratio of Si to Al is (1.5~2.0):1, preferably 1.9:1. The synergistic effect of this ratio is as follows: + It preferentially promotes the rapid formation of C-(A)-SH gel, forming an early strength framework; K + The three-dimensional aluminosilicate network involved in constructing the KASH gel fills the micropores in the C-(A)-SH network and enhances the thermal and chemical stability of the gel system. The two gels interpenetrate spatially and grow synergistically over time to form an interpenetrating network structure, enabling the non-sintered ceramsite to possess high early strength, excellent later durability, and high-temperature stability.

[0026] Optionally, the alkali activator comprises water glass and sodium hydroxide in a predetermined ratio, with sodium silicate having a modulus of 0.9 to 1.1. The amount of alkali activator added is based on alkali equivalent, i.e., the mass of Na₂O accounts for 10% of the total mass of the cementitious material. A suitable alkali equivalent can provide sufficient OH⁻ for the reaction. - Concentration promotes the depolymerization and dissolution of aluminosilicate glass in straw ash and blast furnace slag, accelerating the formation of C-(A)-SH and KASH gels. The sodium silicate modulus refers to the molar ratio of SiO2 to Na2O in water glass, which determines the degree of silicate polymerization and buffering capacity of the alkali-activated system, directly affecting the type, structure, and properties of the reaction products. When the modulus is too low, the Na2O content in the system is relatively high, resulting in excessive alkalinity, leading to a too-fast gel reaction, premature precipitation of products forming structural defects, and excessive Na2O. +Reducing the chemical stability of the gel increases the risk of alkali blooming. When the modulus is too high, the SiO2 content in the system is relatively high, the solution viscosity increases, which is not conducive to ion migration and diffusion, and the reaction rate decreases. At the same time, the excessive degree of silicate polymerization leads to excessive cross-linking of the gel network and the generation of internal stress, which increases the brittleness of the material and reduces its crack resistance.

[0027] Optionally, the straw ash and blast furnace slag are dried and then passed through a 100-mesh sieve, with a sieve passing rate ≥95%. The set particle size of the raw materials can achieve the required gelling activity and maintain the set porosity, giving full play to their lightweight advantages. When the particle size of the raw materials is too large, the specific surface area of ​​the particles is small, resulting in insufficient contact area with the alkali activator, reduced reactivity, and incomplete depolymerization and polymerization reactions. At the same time, large particles are difficult to disperse uniformly during granulation, easily forming local defects and affecting the consistency of the performance of non-sintered ceramsite. Particles with too small a particle size will overfill the pores, increasing the bulk density of the non-sintered ceramsite. Although this may improve the compressive strength, it will weaken its lightweight characteristics.

[0028] Optionally, the granulation method includes: controlling the tilt angle of the granulation disc to 45~55°, the rotation speed to 20~30 r / min, and the granulation time to 10~15 min, to obtain ceramsite raw material balls with a particle size of 8~10 mm.

[0029] Optionally, curing can be carried out in an atmospheric pressure drying chamber; no steam boiler or supporting piping facilities are required, the equipment investment cost is low, the energy consumption is low, the operation is simple, the curing cycle is short (24 hours), and it is not limited by climate conditions.

[0030] Optionally, the wet material was granulated and then cured at 100℃ for 24 hours. Through the "temperature-time dual gradient", it was found that the compressive strength showed a non-monotonic change characteristic of "first rising and then falling" with the increase of temperature, reaching a peak at 100℃. This provided a scientific basis for determining suitable curing process parameters and also corrected the conventional cognitive bias that "the higher the temperature, the more complete the reaction".

[0031] One or more embodiments of the present invention provide non-sintered ceramsite prepared by the above-described method for preparing non-sintered ceramsite.

[0032] The bulk density of the ceramsite was tested to be 760-790 kg / m³. 3 The water absorption rate is approximately 8.5% in 1 hour, and the compressive strength is ≥12.5 MPa. After 30 freeze-thaw cycles, the compressive strength increases by ≥20% compared to before the cycles. After soaking in an acidic solution with pH=1 for 30 days, the compressive strength loss rate is ≤40%. After soaking in an alkaline solution with pH=13 for 30 days, the compressive strength loss rate is ≤40%. After being treated at 700℃ for 1 hour, the compressive strength increases by ≥60% compared to before the treatment without cracking.

[0033] Optionally, the particle size of non-sintered ceramsite is 8~10mm, which is determined by the granulation size, and it is suitable for use as a lightweight aggregate added to building materials such as concrete.

[0034] One or more embodiments of the present invention provide the application of the above-mentioned non-sintered ceramsite in building materials for cold-region engineering, building materials for fire protection engineering, or building materials for chemical corrosion protection.

[0035] During freeze-thaw cycles, the various gels present in the system exhibit various effects. Moisture promotes the continued hydration of unreacted aluminosilicate components, generating more gels. Simultaneously, repeated freeze-thaw stress induces gel structural rearrangement and densification. In high-temperature environments, Fe... 3+ It participates in the formation of ferrite polymer network, further enhancing the high-temperature stability of the gel structure; in strong acid and alkali environments, the three-dimensional network structure of KASH gel endows the material with excellent chemical stability.

[0036] One or more embodiments of the present invention provide a building material comprising the above-described non-sintered ceramsite.

[0037] The present invention will be further described below with reference to specific embodiments.

[0038] Example 1 A non-sintered ceramsite, the raw materials for which are prepared include straw ash, blast furnace slag and alkali activator.

[0039] The straw ash was taken from a biomass power plant, and its chemical composition by mass ratio, as determined by XRF analysis, was as follows: SiO2 48.00%, Al2O3 20.35%, CaO 5.60%, K2O 7.62%, Fe2O3 7.50%, MgO 2.01%, Na2O 1.46%.

[0040] The blast furnace slag was taken from a steel plant, and its chemical composition by mass ratio, as determined by XRF analysis, was as follows: SiO2 33.01%, Al2O3 17.47%, CaO 33.77%, K2O 0.37%, Fe2O3 0.41%, MgO 11.02%, Na2O 0.45%.

[0041] The alkali activator is a compound system of water glass (sodium silicate solution) and sodium hydroxide, with the modulus adjusted to 1.0, and the alkali equivalent is calculated as 10% of the total mass of the cementitious material.

[0042] Preparation methods include: S1, Raw material pretreatment: The straw ash and blast furnace slag are dried in a drying oven at 105℃ for 24 hours, then crushed and passed through a 100-mesh sieve. The fineness of the raw materials is controlled so that the sieve passing rate is ≥95%, and then set aside.

[0043] S2, Preparation of alkali activator solution: Water glass (sodium silicate solution) and sodium hydroxide are mixed in proportion, water is added, and the mixture is stirred evenly to prepare an alkali activator solution; the sodium silicate modulus of the alkali activator is 1.0, and the alkali equivalent is 10% of the total mass of the cementitious material.

[0044] S3, Raw material mixing: Take 420g of straw ash and 180g of blast furnace slag after pretreatment in step S1 (the mass ratio of straw ash to blast furnace slag is 70:30), add them to a mixer and dry mix them evenly; then add the alkali activator solution prepared in step S2, and continue to stir for 3~5 minutes to obtain a uniformly mixed wet material.

[0045] S4, Granulation and molding: The wet material obtained in step S3 is placed in a disc granulator for granulation and molding. The disc inclination angle is controlled at 50°, the rotation speed is 25r / min, and the granulation time is 13±2min to obtain ceramsite raw material balls with a particle size of 9±1mm.

[0046] S5, Gradient Drying and Curing: The ceramsite raw pellets obtained in step S4 were placed in an atmospheric pressure drying oven and cured in parallel at four temperature points: 80℃, 100℃, 120℃, and 140℃. The curing times at each temperature point were 12h, 24h, and 36h, respectively. Ceramsite samples under different temperature-time combinations were obtained, with a particle size of 9±1mm and an appearance as shown. Figure 1 As shown.

[0047] The performance of the expanded clay samples that reached the curing time was tested, including bulk density, 1-hour water absorption rate and compressive strength, according to GB / T 17431.2-2010. The results are shown in Table 1.

[0048] Table 1 Physical properties of expanded clay aggregate under different curing conditions

[0049] It can be seen that curing temperature and time have a significant impact on the performance of ceramsite. With increasing curing temperature, the compressive strength of ceramsite shows a trend of first increasing and then decreasing. In the range of 80℃ to 100℃, the compressive strength increases with increasing temperature; it reaches its peak at 100℃, with compressive strengths of 13.01 MPa and 13.25 MPa at 24h and 36h, respectively. When the temperature continues to rise to 120℃ and 140℃, the compressive strength decreases significantly. This non-monotonic change characteristic of "first increasing and then decreasing" indicates that higher temperatures do not necessarily lead to a more complete reaction, but rather there exists an optimal curing temperature range. Furthermore, with prolonged curing time, the compressive strength of ceramsite shows a continuous increasing trend under all temperature conditions. The increase in compressive strength is more significant in the range of 12h to 24h; in the range of 24h to 36h, the increase in compressive strength decreases, indicating that the reaction gradually becomes complete after 24h. The variation patterns of bulk density and 1-hour water absorption rate with curing conditions are relatively complex. However, overall, under the condition of curing at 100℃ for 24 hours, the ceramsite exhibits superior comprehensive performance, with a bulk density of 760.5 kg / m³. 3 The water absorption rate is 8.60% in 1 hour, and the compressive strength reaches 13.01 MPa.

[0050] Observe the microstructure of ceramsite cured at 100℃ for 24 hours, such as... Figure 2 As shown, a dense microstructure is formed inside the ceramsite, with a large number of flocculent and network gels evenly distributed on the particle surface and in the interparticle spaces. Unreacted raw material particles are tightly wrapped by a thick gel layer, and the interfacial transition zones between particles are almost completely eliminated, exhibiting a typical "sea-island" structural characteristic. This highly cemented interpenetrating network structure effectively fills the original packing pores, enabling the material to achieve high compressive strength and low water absorption, while providing a structural basis for excellent durability.

[0051] Example 2 Further tests were conducted on the best-performing ceramsite sample in Example 1, namely the ceramsite sample cured at 100℃ for 24 hours, including: freeze-thaw cycle, acid resistance, alkali resistance and fire resistance. The test results are shown in Table 2.

[0052] The freeze-thaw cycle test method includes: referring to the principle of slow freezing in GB / T 50082-2009, and combining the characteristics of ceramsite materials, the ceramsite is frozen at -18℃ for 12 hours and thawed at room temperature for 12 hours for 30 cycles, and the compressive strength before and after the cycle is tested.

[0053] The acid resistance and alkali resistance test methods are as follows: the ceramsite is soaked in hydrochloric acid solution with pH=1 and sodium hydroxide solution with pH=13 for 30 days respectively, and the compressive strength before and after soaking is tested.

[0054] The fire resistance test method includes: placing the ceramsite in a muffle furnace and treating it at 700℃ for 1 hour, observing the appearance changes and testing the compressive strength before and after treatment.

[0055] Table 2. Durability test results of expanded clay aggregate.

[0056] It can be seen that the ceramsite prepared by this invention exhibits excellent durability, especially with a significant increase in compressive strength after freeze-thaw cycles and high-temperature treatment. After 30 freeze-dry cycles, the compressive strength increased by 22.5% compared to before the cycles, indicating that it not only did not deteriorate under repeated freeze-thaw cycles but also achieved an increase in compressive strength. After being treated at 700℃ for 1 hour, the compressive strength increased by 61.3% compared to before the treatment, and the sample showed no cracking. In extremely harsh acid and alkaline environments, the ceramsite exhibits good corrosion resistance: after soaking in hydrochloric acid solution at pH=1 for 30 days, the compressive strength loss rate was 35.5%; after soaking in sodium hydroxide solution at pH=13 for 30 days, the compressive strength loss rate was 38.2%. The above properties indicate that the ceramsite can meet the application requirements of special environments such as cold-region engineering, fire protection engineering, and chemical corrosion protection.

[0057] Example 3 A non-sintered ceramsite, the raw materials for which are prepared include straw ash, blast furnace slag and alkali activator.

[0058] The ratio of straw ash to blast furnace slag was one of 60:40 and 80:20, that is, the relative proportion of raw materials was adjusted compared with Example 1, and the raw material requirements were the same as in Example 1. The preparation method was the same as in Example 1, and the curing method of 100℃ for 24h was used to test its bulk density, 1h water absorption rate and compressive strength. The results are shown in Table 3.

[0059] Table 3. Performance of ceramsite with different raw material ratios (100℃, 24h)

[0060] It can be seen that the ratio of straw ash to blast furnace slag has a significant impact on the performance of ceramsite. When the straw ash ratio is 70%, the overall performance of the ceramsite is better; when the straw ash ratio is 60%, the bulk density increases to 795.8 kg / m³. 3 The compressive strength decreased to 10.00 MPa; when the straw ash content was 80%, the bulk density decreased to 740.7 kg / m³. 3 However, the water absorption rate increased to 8.82%, and the compressive strength decreased to 10.43 MPa.

[0061] The XRD pattern of ceramsite with a straw ash to blast furnace slag mass ratio of 70:30 and at 100℃ for 24 hours was analyzed, as shown below. Figure 3As shown in the figure, the phase composition of the expanded clay aggregate mainly consists of quartz, calcite, and calcium sulfate hydrate. Quartz primarily originates from unreacted straw ash, while calcite is the CaO component in the system. 2+ The calcium sulfate hydrate, a product of the carbonization reaction with CO2 in the air, originates from the mineralization reaction of sulfur components in straw ash or blast furnace slag. No obvious amorphous diffuse peaks were observed in the spectra. This is because the high content and strong diffraction signals of crystalline phases such as quartz and calcite mask the diffuse background of the amorphous gel phase; the non-amorphous gel is not absent. Combining the mechanical property test results and SEM microscopic morphology observations, it can be inferred that a considerable amount of amorphous C-(A)-SH and KASH gels were generated in the system, which, together with the crystalline particles, constitute the source of the compressive strength of the ceramsite.

[0062] Chemical composition analysis of straw ash (K2O content 7.62%, Fe2O3 content 7.50%) shows that the high potassium and iron content in straw ash has a synergistic effect in the alkali-activated reaction. When the straw ash content is 70%, the Ca provided by the blast furnace slag... 2+ Si, Al, and K released from straw ash + To achieve the appropriate ratio, specifically: Ca 2+ With K + The molar ratio of C-(A)-SH gel (providing a strength framework) and KASH gel (filling pores and enhancing durability) is 2.2:1, and the molar ratio of Si to Al is 1.9:1. Sufficient amounts of C-(A)-SH gel (providing a strong framework) and KASH gel (filling pores and enhancing durability) are simultaneously generated in the system. These two gels form an interpenetrating network structure, giving the ceramsite superior mechanical and durability properties. When the straw ash content is too high, Ca... 2+ Relative deficiency leads to reduced C-(A)-SH gel formation and increased unreacted straw ash particles, resulting in increased water absorption and decreased compressive strength; when the straw ash content is too low, K... + The synergistic effect of K₂O in straw ash and CaO in blast furnace slag was not fully realized, resulting in insufficient KASH gel formation, reduced gel structure order, and suboptimal compressive strength. Appropriate straw ash content helps to fully utilize the synergistic effect of K₂O in straw ash and CaO in blast furnace slag, while the higher Fe₂O₃ content in straw ash dissolves Fe₂O₃ in an alkaline-activated environment. 3+ It can partially replace Al 3+ Integrating into the aluminosilicate gel network further enhances the chemical and high-temperature stability of the gel skeleton, forming a dense composite gel structure. Both excessively high and excessively low doping levels are detrimental to performance optimization.

[0063] In summary, this invention reveals that curing temperature and time significantly affect the performance of ceramsite. Furthermore, as temperature increases, the compressive strength exhibits a non-monotonic change characteristic, first increasing and then decreasing, reaching a peak at 100℃. With prolonged curing time, the compressive strength continues to increase and tends to stabilize after 24 hours. Overall, ceramsite exhibits superior comprehensive performance under the condition of curing at 100℃ for 24 hours.

[0064] The ceramsite obtained under curing conditions of 100℃ for 24 hours exhibits excellent durability. After 30 freeze-thaw cycles, the compressive strength increased by 22.5%. After soaking in hydrochloric acid solution (pH=1) and sodium hydroxide solution (pH=13) for 30 days, the compressive strength loss rates were 35.5% and 38.2%, respectively. After treatment at 700℃ for 1 hour, the compressive strength increased by 61.3% without cracking. It can meet the application requirements of special environments such as cold-region engineering, fire protection engineering, and chemical corrosion protection.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing non-sintered ceramsite, characterized in that, Including the following steps: Straw ash and blast furnace slag are dried separately and then mixed in a ratio of (60~80):(20~40) to obtain a cementitious material. An alkali activator is added to the cementitious material and stirred to obtain a wet material. The wet material is granulated and cured at 100~120℃ for 24~36 hours to obtain non-sintered ceramsite. The alkali activator is a compound system of water glass and sodium hydroxide, the sodium silicate modulus is 0.8~1.2, and the alkali equivalent is 5~15% of the mass of the cementitious material.

2. The method for preparing non-sintered ceramsite as described in claim 1, characterized in that, The drying method for the straw ash includes drying at 100~110℃ for 24~36 hours; the drying method for the blast furnace slag includes drying at 100~110℃ for 24~36 hours.

3. The method for preparing non-sintered ceramsite as described in claim 1, characterized in that, The sodium silicate modulus of the alkali activator is 0.9~1.1, and the amount of alkali activator added accounts for 10% of the total mass of the cementitious material in terms of alkali equivalent.

4. The method for preparing non-sintered ceramsite as described in claim 1, characterized in that, The mass ratio of straw ash to blast furnace slag is 70:

30.

5. The method for preparing non-sintered ceramsite as described in claim 1, characterized in that, The straw ash and blast furnace slag are dried and then passed through a 100-mesh sieve, with a sieve passing rate of ≥95%.

6. The method for preparing non-sintered ceramsite as described in claim 1, characterized in that, Curing is carried out in an atmospheric pressure drying oven.

7. The method for preparing non-sintered ceramsite as described in claim 6, characterized in that, After granulation, the wet material is cured at 100℃ for 24 hours.

8. Non-sintered ceramsite prepared by a method for preparing non-sintered ceramsite as described in any one of claims 1-7.

9. The application of the non-sintered ceramsite as described in claim 8 in building materials for cold-region engineering, fire protection engineering, or chemical corrosion protection.

10. A building material, characterized in that, Includes the non-sintered ceramsite as described in claim 8.

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