A microwave curing method for LC3 system

Abstract

The application is a microwave curing method for LC 3 system, comprising the following steps: mixing LC 3 slurry and sand evenly, and then loading into a mold to obtain LC 3 test block; placing the LC 3 test block into a microwave oven together with the mold for curing, and using a microwave temperature probe to measure and track the internal temperature in real time; stopping heating when the internal temperature of the LC 3 test block reaches 95-100 DEG C, and then gradually cooling for 25 min; after the cooling time, repeating the above process to heat and cool again; the heating and cooling cycle is 4-12 times, the microwave heating power is 200-600 W; and finally obtaining LC 3 test piece; and cooling the LC 3 test piece to room temperature, demolding after 6 h, and then placing into a standard curing room for curing. The method can not only effectively improve the early strength of LC 3 system, but also ensure the final quality of the material.

Description

Technical Field

[0001] This invention belongs to the field of cement-based material curing technology, and particularly relates to an LC 3 Microwave curing method for the system. Background Technology

[0002] To address the consumption of natural resources and carbon footprint of cement production, finding a new, low-carbon alternative to cementitious materials has become an urgent priority. Among these alternatives, the calcined clay-limestone-cement system (LC) is particularly relevant. 3 LC is a promising low-carbon cementitious material that improves its cementitious properties by adding large amounts of calcined clay and limestone. Compared to ordinary Portland cement, LC... 3 It can reduce carbon dioxide emissions by up to 40%, but currently LC 3 The main drawback is the slow early strength development. For ordinary cement-based materials, to promote early strength development and hydration, heating curing methods such as hot water curing, steam curing, dry heat curing, autoclaving, and their composite curing are commonly used. However, these curing methods all suffer from high energy consumption and low efficiency. Therefore, to address the bottlenecks of existing curing methods, a low-energy, high-efficiency curing method needs to be established to effectively improve LC (liquid crystal) strength. 3 Improving early strength is a pressing issue. Compared to traditional thermal curing methods, microwave curing is a volumetric thermal curing method that relies on absorbing microwave energy and converting it into heat. It features rapid heating, short processing time, and low energy consumption. Microwave curing of cement-based materials helps improve their early strength development, shortens the cement hydration induction period, and reduces the porosity of cement-based materials. Therefore, for LC... 3 The system establishes a temperature-controlled microwave curing regime and develops a method that can improve LC... 3 The maintenance methods that can enhance early strength while ensuring long-term performance are the focus of current research.

[0003] Current microwave curing methods are primarily designed for specific materials because different material systems exhibit varying dielectric properties. These properties further influence the temperature rise rate under microwave irradiation, resulting in different temperature increase rates during microwave heating. Excessively rapid temperature rise leads to uneven temperature distribution, negatively impacting the curing effect. Currently, LC... 3 Different chemical compositions and activities within the system affect the types and concentrations of ions in the pore solution, thus influencing its dielectric properties. Calcinated clay provides a large amount of CO3-AFm phases, such as monoaluminate (Mc) and hemialuminate (Hc), which promote LC. 3 The system undergoes a volcanic ash reaction to generate CASH. The calcined clay contains a relatively high amount of magnetic elements, which will inevitably play a role in microwave heat transfer, especially for LC systems with a clinker content of 50%.3 In pastes, the aluminum content in CASH increases with the increase of kaolinite content in calcined clay. Furthermore, water significantly affects the dielectric properties of the mixture, while LC… 3 The water content of C-(A)-SH varies with temperature (10℃, 20℃, 40℃, and 60℃), LC 3 The moisture content decreases with increasing temperature, which inevitably plays a role in microwave heat transfer. Therefore, LC 3 Compared to ordinary cement-based systems, this system exhibits superior dielectric properties, with a stronger dielectric response under microwave irradiation. However, existing microwave curing methods may cause LC... 3 An excessively rapid temperature rise in the system, even causing the internal curing temperature to exceed 100°C, can easily lead to LC (Liquid Crystallization) failure. 3 The system contains a large temperature gradient and an extremely non-uniform temperature field, leading to problems with the cured LC. 3 The early cracking and surface protrusion of the material lead to a decrease in material strength, which is detrimental to LC. 3 Microwave curing of the system. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the objective of this invention is to provide an LC 3 The microwave curing method of the system can effectively improve LC 3 The system's early strength also ensures the final quality of the material. To overcome conventional curing conditions, LC... 3 To overcome the limitations of early strength development in the system and the constraints of existing curing equipment, this method controls curing temperature and time by adjusting parameters such as microwave power, heating, and cooling time. This results in the preparation of LC molds with high early strength, rapid demolding, and a 28-day compressive strength approaching that under standard curing conditions. 3 Specimen.

[0005] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0006] A type of LC 3 A microwave curing method for the system, the curing method comprising the following:

[0007] (1) Mix cement, calcined clay, limestone, gypsum and sand evenly, and prepare LC with a water-cement ratio of 0.45. 3 slurry;

[0008] (2) Stir the LC 3 LC is obtained by uniformly mixing slurry and sand. 3 The mortar is then poured into a mold made of PEEK material to obtain LC. 3 Test block;

[0009] (3) Microwave heating process: LC 3 The test block, along with the mold, was placed in a microwave oven for curing. A microwave oven temperature probe was used to measure and track the internal temperature in real time. The microwave oven was then heated to LC temperature. 3 When the internal temperature of the test block reaches 95-100℃, heating is stopped, and then it is gradually cooled for 25 minutes. After the cooling time is reached, the microwave is turned on again to repeat the above process for the next heating and cooling cycle. The number of heating and cooling cycles is 4-12, and the microwave heating power is 200W-600W.

[0010] (4) Obtain LC after the final microwave heating is completed. 3 Specimen, LC 3 After the specimens cooled to room temperature and stood for 6 hours, they were demolded and then placed in a standard curing room for curing.

[0011] Further, the cement is PI 52.5 silicate cement with a particle size of 600-1200μm; the limestone is limestone powder with a particle size of 300-800μm, and the mass percentage of CaO in the limestone powder is >60%; the calcined clay has a particle size of 500-1500μm, and the mass percentage of SiO2 in the calcined clay is >50%, and the mass percentage of Al2O3 in the calcined clay is >40%; the gypsum is gypsum powder with a particle size of 300-600μm; and the sand is ISO standard cement sand with a particle size of 0.08-2.0mm.

[0012] Furthermore, the microwave heating power remains the same in each cycle, being 200W, 300W, 400W, 500W, or 600W, corresponding to internal heating rates of 0.115℃ / s, 0.17℃ / s, 0.24℃ / s, 0.455℃ / s, or 0.93℃ / s, respectively; when LC 3 When the internal temperature reaches 100℃, the heating time required by 200W microwave is 460s, 300W microwave is 310s, 400W microwave is 220s, 500W microwave is 120s, and 600W microwave is 60s.

[0013] Furthermore, the microwave heating power is 300W, and the number of cycles is 8; the standard curing room is used to maintain the product until the test age.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] The LC studied in this invention 3 Compared to ordinary cement-based materials, this system exhibits superior dielectric properties due to its chemical composition and activity affecting the types and concentrations of ions in the pore solution. Its dielectric response under microwave irradiation is more intense, thus influencing its internal temperature rise. (Regarding LC...) 3The system ensures LC during microwave heating. 3 The system temperature does not exceed 100℃. The final curing regime under microwave irradiation was determined to effectively prevent internal moisture evaporation, resulting in an intermittent microwave heating curing regime. The specific process is as follows: microwave to LC... 3 Heating is stopped when the internal temperature of the test block approaches 100°C. The test block is then cooled to room temperature before being heated again, with a cooling time of 25 minutes. This process is repeated until the final heating, after which the block is cooled to room temperature and demolded. Subsequent curing involves placing the block in a standard curing room to ensure adequate moisture. This curing method does not cause LC (Liquid Crystallization). 3 The rapid temperature rise of the system ensured that the internal curing temperature did not exceed 100℃. This effectively increased the curing temperature while preventing internal moisture evaporation, thereby promoting early hydration and significantly improving LC curing efficiency. 3 The material's early strength shortens the curing time.

[0016] In the curing method of this invention, a reasonable number of cycles and microwave frequency are set. If the number of cycles is less than 4, the specimen will not achieve the desired microwave curing effect. If the number of cycles exceeds 12, the specimen will experience excessive early hydration due to prolonged heating time, affecting the later hydration process and leading to insufficient compressive strength in the later stages. Different microwave powers are categorized as low power (<200W), medium power (200W-600W), and high power (>700W). At low power (<200W), due to the smaller output power, LC... 3 If the mortar heats up too slowly, the improvement in early compressive strength is not significant. At high power (>700W), short-duration pulsed microwave radiation is used to prevent excessive heating that could cause moisture evaporation and air expansion, thus avoiding mortar cracking. However, this results in insufficient microwave time, failing to achieve high early compressive strength. Therefore, the medium power setting in this invention achieves better curing results. While achieving the same effect as existing steam curing, it not only has the advantages of a shorter curing cycle but also lower energy consumption. Attached Figure Description

[0017] Figure 1 For the present invention LC 3 Flowchart of the system preparation process;

[0018] Figure 2 LC of Example 1 3 Physical images of the equipment and molds used for microwave curing of the system;

[0019] Figure 3 A comparison chart showing the compressive strength of different ages after different microwave cycles at a microwave heating power of 200W.

[0020] Figure 4 A comparison chart of compressive strength at different ages after different microwave cycles under a microwave heating power of 300W.

[0021] Figure 5 A comparison chart of compressive strength at different ages after different microwave cycles under a microwave heating power of 400W.

[0022] Figure 6 A comparison chart showing the compressive strength of different ages after different microwave cycles at a microwave heating power of 500W.

[0023] Figure 7 A comparison chart of compressive strength at different ages after different microwave cycles under a microwave heating power of 600W.

[0024] Figure 8 This is a comparison chart of compressive strength under different curing methods. Detailed Implementation

[0025] The present invention will be further explained below with reference to the embodiments and accompanying drawings, but this is not intended to limit the scope of protection of this application.

[0026] This invention when LC 3 When the internal temperature of the mortar reaches 100℃, the heating time required by a 200W microwave is 460s, 300W is 310s, 400W is 220s, 500W is 120s, and 600W is 60s. The internal heating rates under different heating powers are: 0.115℃ / s, 0.17℃ / s, 0.24℃ / s, 0.455℃ / s, and 0.93℃ / s for 200W, 300W, 400W, 500W, and 600W microwave powers, respectively; during microwave heating, LC... 3 The temperature never exceeds 100℃, and LC under different microwave powers 3 A heating period is defined as the time it takes for the internal temperature of the mortar to reach approximately 95℃-100℃, and a cycle is defined as the time it takes to cool to room temperature (25℃).

[0027] In this embodiment of the invention, the cement is PI 52.5 silicate cement from Shandong Kangjing New Material Technology Co., Ltd., with a particle size of 600-1200 μm. The limestone is limestone powder produced by Tianjin Yandongtian Mineral Products Co., Ltd., with a particle size of 300-800 μm, and the mass percentage of CaO in the limestone powder is >60%. The calcined clay is calcined clay from Shijiazhuang Jieling Mineral Products Trading Co., Ltd., with a particle size of 500-1500 μm, and the mass percentage of SiO2 in the calcined clay is >50%, and the mass percentage of Al2O3 in the calcined clay is >40%. The gypsum is gypsum powder produced by Sinopharm Chemical Reagent Co., Ltd., with a particle size of 300-600 μm.

[0028] LC 3The preparation process of the system is as follows: Figure 1 As shown: Various raw materials were prepared according to the following proportions by weight: 50 parts PI 52.5 grade silicate cement, 35 parts calcined clay, 15 parts limestone, 5 parts gypsum, 100 parts sand, and 45 parts water. To ensure thorough mixing of the matrix materials, a phased water addition method was used. The cement, calcined clay, limestone, and gypsum were slowly stirred in a mixing pot for 2 minutes; then, sand was added and slowly stirred for 2 minutes; 80% of the 45 parts water was added uniformly to the mixture within 10 seconds and quickly stirred for 2 minutes; finally, the remaining 20% ​​of the 45 parts water was added uniformly to the mixture within 10 seconds and quickly stirred for 2 minutes, yielding the desired LC. 3 Materials. The required LC 3 After the materials are well mixed, they are poured into a mold made of PEEK material, with dimensions of 40mm*40mm*40mm (length*width*thickness), and vibrated on a vibration table for 3-5 minutes until formed. After vibration forming, the prepared LC... 3 The specimens were cured to the required testing age, and their compressive strength was tested in accordance with JGJT70-2009 "Standard for Test Methods of Basic Performance of Building Mortar".

[0029] The microwave oven used in this experiment is the Qingdao Maikewei MKX-T8A industrial microwave oven.

[0030] Optionally, the aggregate is mixed with water in several batches and then poured into a mold to form an uncured LC. 3 The test block, along with the mold, was placed in a microwave curing reaction chamber at a microwave frequency of 2.45 GHz and a power range of 200 W. An intermittent microwave heating curing regime was established. Heating was stopped when the internal temperature of the test block approached 100°C. The test block was cooled to room temperature and then heated again, with each cooling time being 25 minutes. After the last heating, the test block was cooled to room temperature and then demolded. Subsequent curing was carried out in a standard curing room to ensure the curing moisture. The intermittent microwave heating curing regime was expressed as (MH 7.5 min + SS 25 min) * 3 + MH 7.5 min, which means: heating at 200 W microwave power for 7.5 minutes, resting for 25 minutes, repeating the heating cycle 3 times, and finally heating for 7.5 minutes.

[0031] The LC was cured using standard curing and steam curing at 80℃. 3 The samples underwent comparative curing. Standard curing required the use of newly prepared LC... 3The samples were sealed with plastic wrap and placed in a curing room at a temperature of 20±2℃ and a relative humidity of >95%. After 1 day, they were demolded and continued to be cured in a standard curing room until the specified age. Considering that the maximum microwave curing time is 6 hours at 200W power, for comparison, steam curing was performed at a constant temperature of 80℃ for 2 hours, with both steam heating and cooling times of 2 hours, before being placed in the standard curing room for further curing.

[0032] Examples 1-3: LC under 200W microwave power 3 The microwave curing method for the system, involving heating for 4 cycles, 8 cycles, and 12 cycles respectively, includes the following steps:

[0033] The obtained LC 3 After the test block has stood for 1 hour, the prepared LC... 3 The test block, along with the mold, was placed in a microwave oven at a frequency of 2.45 GHz for curing. Intermittent curing was performed at a power of 200 W. The specific procedure was as follows: heating at 200 W for 7.5 minutes until the internal temperature of the test block approached 100°C, then allowing it to stand for 25 minutes until the internal temperature cooled to room temperature (25°C) constituted one cycle. Four, eight, or twelve cycles were performed. A diagram of the microwave curing process is shown below. Figure 2 After microwave curing, allow the mold to stand for 6 hours before demolding, then transfer it to the curing room for curing until the appropriate test age. Figure 3 The figures show a comparison of compressive strength at different cycles for test ages of 8h, 1d, 3d, 7d, and 28d.

[0034] Examples 4-6: LC under 300W microwave power 3 The microwave curing method for the system, involving heating for 4 cycles, 8 cycles, and 12 cycles respectively, includes the following steps:

[0035] The obtained LC 3 After the test block has stood for 1 hour, the prepared LC... 3 The test block, along with the mold, was placed in a microwave oven at a frequency of 2.45 GHz for curing. Intermittent curing was performed at a power of 300 W. Specifically, the process involved heating at 300 W for 5 minutes until the internal temperature of the test block approached 100°C, then allowing it to stand for 25 minutes until the internal temperature cooled to room temperature (25°C), constituting one cycle. Four, eight, or twelve cycles were then performed. After microwave curing, the block was allowed to stand for 6 hours before demolding and then transferred to a curing chamber for further curing until the appropriate testing age was reached. Figure 4 The figures show a comparison of compressive strength at different cycles for test ages of 8h, 1d, 3d, 7d, and 28d.

[0036] Examples 7-9: LC at 400W microwave power 3The microwave curing method for the system, involving heating for 4 cycles, 8 cycles, and 12 cycles respectively, includes the following steps:

[0037] The obtained LC 3 After the test block has stood for 1 hour, the prepared LC... 3 The test block, along with the mold, was placed in a microwave oven at a frequency of 2.45 GHz for curing. Intermittent curing was performed at a power of 400 W. The specific procedure was as follows: heating at 400 W for 3 minutes until the internal temperature of the test block approached 100°C, then allowing it to stand for 25 minutes until the internal temperature cooled to room temperature (25°C) constituted one cycle. Four, eight, or twelve cycles were performed. After microwave curing, the block was allowed to stand for 6 hours before demolding and then transferred to a curing chamber for further curing until the appropriate testing age was reached. Figure 5 The figures show a comparison of compressive strength at different cycles for different test ages (from microwave curing to standard curing) of 8h, 1d, 3d, 7d, and 28d.

[0038] Examples 10-12: LC under 500W microwave power 3 The microwave curing method for the system, involving heating for 4 cycles, 8 cycles, and 12 cycles respectively, includes the following steps:

[0039] The obtained LC 3 After the test block has stood for 1 hour, the prepared LC... 3 The test block, along with the mold, was placed in a microwave oven at a frequency of 2.45 GHz for curing. Intermittent curing was performed at a power of 500 W. The specific procedure was as follows: heating at 500 W for 2 minutes until the internal temperature of the test block approached 100°C, then allowing it to stand for 25 minutes until the internal temperature cooled to room temperature (25°C) constituted one cycle. Four, eight, or twelve cycles were performed. After microwave curing, the block was allowed to stand for 6 hours before demolding and then transferred to a curing chamber for further curing until the appropriate testing age was reached. Figure 6 The figures show a comparison of compressive strength at different cycles for test ages of 8h, 1d, 3d, 7d, and 28d.

[0040] Examples 13-15: LC under 600W microwave power 3 The microwave curing method for the system, involving heating for 4 cycles, 8 cycles, and 12 cycles respectively, includes the following steps:

[0041] The obtained LC 3 After the test block has stood for 1 hour, the prepared LC... 3The test block, along with the mold, was placed in a microwave oven at a frequency of 2.45 GHz and cured intermittently at a power of 600 W. The specific procedure was as follows: heating at 600 W for 1 minute until the internal temperature of the test block reached 100°C, then allowing it to stand for 25 minutes until the internal temperature cooled to room temperature (25°C) constituted one cycle. Four, eight, or twelve cycles were performed. After microwave curing, the block was allowed to stand for 6 hours before demolding and then transferred to a curing chamber for further curing until the appropriate testing age was reached. Figure 7 The figures show a comparison of compressive strength under different cycles at curing ages of 8 hours, 1 day, 3 days, 7 days, and 28 days.

[0042] Comparative Examples 1-2: Microwave curing specimens cured by 8 cycles at 300W microwave power were compared with those cured by standard curing and steam curing at 80℃.

[0043] Standard maintenance: After the LC is formed 3 The test blocks, along with the molds, were placed in a standard curing room and cured under standard conditions (temperature 20±2℃, relative humidity >95%). After curing for 1 day, the blocks were immediately demolded and then placed at room temperature and sprayed with water for 3 days. The compressive strength at each test age was then measured in the standard curing room.

[0044] Steam curing at 80℃: The molded LC3 specimens, along with the mold, are placed in a steam curing chamber for heating, maintaining a constant temperature, and then cooling. After cooling to room temperature, the specimens are demolded and transferred to a curing room for curing at the appropriate age. The compressive strength at each test age is then measured. A 2-hour delay time is required before steam curing. Steam curing is performed at 80℃ for 2 hours, with both steam heating and cooling times being 2 hours each. The total steam curing time is 6 hours (excluding the delay time). After steam oxidation, the specimens are then placed in a standard curing room for curing at the test age.

[0045] As can be seen from Examples 1-3, at 200W, due to the relatively low output power, the LC... 3 The specimens heated too slowly, resulting in minimal improvement in early compressive strength. At high power (500W and 600W), to prevent excessive heating leading to moisture evaporation and air expansion, and to avoid mortar cracking, short-duration microwave radiation was used. However, this resulted in insufficient microwave time, failing to achieve high early compressive strength. Compared to LC cured with 400W microwave... 3 The compressive strength of the specimens increased by 1.2 MPa, 9.3 MPa, and 8.7 MPa after 4, 8, and 12 cycles of microwave heating at 300 W, respectively. Therefore, 300 W is the optimal microwave heating power. At 300 W microwave power, the 8-hour compressive strength after 8 cycles was 9.57 MPa higher than after 4 cycles, and the 28-day compressive strength after 8 cycles was 5.6 MPa higher than after 12 cycles.

[0046] Therefore, 8 cycles of 300W microwave power is the optimal microwave curing regime. This invention's microwave curing significantly improves early strength; the compressive strength after 8 hours of microwave curing is close to the strength after 3 days of standard curing. Comparing the three curing methods at 1d, 3d, 7d, and 28d curing ages, microwave curing showed the highest compressive strength. At 1d curing age, the LC of microwave curing was... 3 The compressive strength of the mortar was 1.78 times that of the standard curing mortar and 1.26 times that of the mortar cured at 80℃ steam curing mortar. The compressive strength at 28 days was close to that of the standard curing mortar and was 1.12 times that of the mortar cured at 80℃ steam curing mortar.

[0047] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. An LC 3 The microwave curing method of the system is characterized by, The maintenance method includes the following: (1) Mix cement, calcined clay, limestone and gypsum evenly, and prepare LC with a water-cement ratio of 0.

45. 3 slurry; (2) Stir the LC 3 LC is obtained by uniformly mixing slurry and sand. 3 The mortar is then poured into a mold to obtain LC. 3 Test block; (3) Microwave heating process: LC 3 The test block, along with the mold, was placed in a microwave oven for curing. A microwave oven temperature probe was used to measure and track the internal temperature in real time. The microwave oven was then heated to LC temperature. 3 When the internal temperature of the test block reaches 95-100℃, heating is stopped, and then it is gradually cooled for 25 minutes. After the cooling time is reached, the microwave is turned on again to repeat the above process for the next heating and cooling cycle. The number of heating and cooling cycles is 4-12, and the microwave heating power is 200 W-600 W. (4) Obtain LC after the final microwave heating is completed. 3 Specimen, LC 3 After the specimens cooled to room temperature and stood for 6 hours, they were demolded and then placed in a standard curing room for curing.

2. The maintenance method according to claim 1, characterized in that, The cement is PI 52.5 silicate cement with a particle size of 600-1200 μm; the limestone is limestone powder with a particle size of 300-800 μm, and the mass percentage of CaO in the limestone powder is > 60%; the calcined clay has a particle size of 500-1500 μm, and the mass percentage of SiO2 in the calcined clay is > 50%, and the mass percentage of Al2O3 in the calcined clay is > 40%; the gypsum is gypsum powder with a particle size of 300-600 μm; and the sand is ISO standard cement sand with a particle size of 0.08-2.0 mm.

3. The maintenance method according to claim 1, characterized in that, The microwave heating power is the same in each cycle, with power levels of 200W, 300W, 400W, 500W, or 600W. The corresponding internal temperature rise rates at these microwave heating powers are 0.115℃ / s, 0.17℃ / s, 0.24℃ / s, 0.455℃ / s, or 0.93℃ / s, respectively. When LC... 3 When the internal temperature reaches 100℃, the heating time required by 200 W microwave is 460 s, 300 W microwave is 310 s, 400 W microwave is 220 s, 500 W microwave is 120 s, and 600 W microwave is 60 s.

4. The maintenance method according to claim 1, characterized in that, The microwave heating power is 300W, and the number of cycles is 8; the product is cured in a standard curing room until the test age.

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