Joule heat curing multi-element solid waste geopolymer concrete and preparation method thereof

Abstract

This invention relates to Joule-cured multi-component solid waste polymer concrete and its preparation method. It utilizes Joule heat generated by electricity to cure the polymer, significantly improving curing efficiency and the mechanical properties of the polymer concrete. If the water-cement ratio in the concrete raw materials is not higher than 0.3, nano-carbon fibers need to be added to the raw materials; if the water-cement ratio is higher than 0.3, nano-carbon fibers are not initially added. Carbon fibers, or a mixture of carbon fibers and nano-carbon fibers, are uniformly dispersed in water before being added to a uniformly mixed precursor powder. Finally, steel fibers are added and mixed uniformly to form a slurry with a multi-level conductive network. The raw materials include: precursor powder, alkali activator, steel fibers, carbon fibers, and water. The steel fibers account for 0.5~2.5 vol% of the precursor powder, the carbon fibers for 0.4~1.0 vol%, the nano-carbon fibers for 0~0.10 vol%, and the water for 0.2~0.43 wt% of the precursor powder.

Description

Technical Field

[0001] This invention relates to the field of solid waste geopolymer preparation technology, specifically to a Joule-cured multi-component solid waste geopolymer concrete and its preparation method. Background Technology

[0002] Geopolymers are three-dimensional network alkali metal aluminosilicate materials formed by the reaction of aluminosilicate raw materials (usually industrial solid waste rich in active silicon and aluminum) with high-concentration alkali activators (usually sodium or potassium hydroxides, silicates, carbonates, etc.). Compared with ordinary silicate cement, geopolymers typically use industrial solid waste as raw material, which not only solves the problem of solid waste treatment but also avoids the greenhouse gas emissions generated by burning cement clinker, typically reducing greenhouse gas emissions by 45% to 80%. Appropriately increasing the curing temperature accelerates the polymerization process of geopolymers. Therefore, to ensure the mechanical properties of geopolymers, they are usually cured at high temperatures of 60℃ to 90℃, similar to the curing method of ultra-high performance concrete. Considering the limitations of traditional high-temperature curing methods, such as high carbon emissions and uneven heating, a new curing method needs to be found. Summary of the Invention

[0003] The purpose of this invention is to provide a Joule-cured multi-component solid waste polymer concrete and its preparation method, which utilizes Joule heat generated by electricity to cure the polymer, significantly improving curing efficiency and mechanical properties of the polymer concrete.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a Joule-cured multi-component solid waste polymer concrete, the raw materials of which include: precursor powder, alkali activator, steel fiber, carbon fiber, and water. If the water-cement ratio in the concrete raw materials is not higher than 0.3, then nano-carbon fiber needs to be added to the raw materials; if the water-cement ratio in the concrete raw materials is higher than 0.3, nano-carbon fiber is not added initially. Carbon fiber or carbon fiber and carbon nanofiber are evenly dispersed in water and then added to a uniformly mixed precursor powder. Finally, steel fibers are added and mixed evenly to form a slurry with a multi-level conductive network. After the slurry is molded, it undergoes Joule curing at 12.5V for 10 hours. The resistivity and temperature at the center of the specimen are measured to obtain resistivity and temperature curves. If the resistivity in the resistivity curve continues to increase without a stable phase, the conductive network has not been established. The conductive network can be corrected by increasing the type or amount of conductive medium. If the resistivity remains stable for a long time and 75% of the temperature data in the temperature curve fluctuates within ±20℃, the resistivity of the multi-stage conductive network is considered stable. When the resistivity of the multi-level conductive network is stable, the optimal Joule curing process corresponding to the formulation is determined: A suitable curing temperature range is preset. If the curing temperature falls within this range, then Joule heat curing at 12.5V for 10 hours is determined as the optimal Joule curing process. If the stable internal temperature in the temperature curve is significantly lower than the preset suitable curing temperature range, then the curing voltage is increased based on 12.5V for Joule curing. If the temperature drops rapidly in the later stages of the temperature curve, the abrupt curing time point is recorded. Then, the curing voltage is increased in stages at these abrupt curing time points for Joule curing, or the amount of conductive medium is increased to construct a denser conductive network. In this case, increasing the curing voltage for Joule curing is a simpler control method. Multi-component solid waste geopolymer concrete was prepared by formulating a multi-level conductive network with stable resistivity and then cured according to a determined Joule curing method.

[0005] If the point where the resistivity suddenly increases from a steady state in the resistivity curve occurs before 7 hours, it is recommended to increase the amount of conductive medium, without increasing the curing voltage, and adjust the formula. If it occurs after 7 hours, determine whether it is consistent with the curing time point of the temperature change curve. If it is consistent and occurs after the curing time point of the temperature change, increase the staged voltage or increase the amount of conductive medium.

[0006] Furthermore, in real-time resistivity detection, if the resistivity continues to increase, the voltage value is increased according to the rate of increase.

[0007] Furthermore, if the stable internal temperature in the temperature curve is significantly lower than the preset suitable curing temperature range, increase the curing voltage and observe whether the temperature can remain within the preset suitable curing temperature range for a long time. If it can, then use this voltage for curing. If it cannot be maintained, it is necessary to further improve the conductive network, increase the doping amount of conductive medium, and add conductive mediums of different sizes.

[0008] Furthermore, when modifying the conductive network by increasing the doping amount of the conductive medium, the doping amount should be adjusted slowly by 0.050-0.1 vol%.

[0009] Furthermore, the preset suitable curing temperature range is related to the calcium content in the geopolymer, and the resistivity of the multi-level conductive network is maintained at 4-8Ω under stable resistivity conditions. . Within the range of cm.

[0010] Secondly, this invention provides a method for preparing Joule-cured multi-component solid waste polymer concrete, the raw materials of which include: precursor powder, alkali activator, steel fiber, carbon fiber, and water, wherein the steel fiber accounts for 0.5~2.5 vol% of the precursor powder, the carbon fiber accounts for 0.4~1.0 vol% of the precursor powder, the nano-carbon fiber accounts for 0~0.10 vol% of the precursor powder, and the water accounts for 0.2~0.43 wt% of the precursor powder; The preparation method includes the following steps: (1) Carbon fiber pre-dispersion: Carbon fiber or carbon fiber and nano carbon fiber are placed in water and ultrasonically dispersed at a power of 250~400W for 10~20min. Then, 0.5-0.8 vol% of hydroxyethyl cellulose and 0.01~0.04 vol% of tributyl phosphate are added and stirred evenly. The amount of tributyl phosphate added is based on the volume of water. Then, ultrasonically dispersed at a power of 250~400W for 8-12min. Finally, let stand for 8-12min to obtain a slightly viscous and smooth mixture. (2) First, pour the precursor powder into the mixing pot and stir evenly; (3) Add the pre-dispersed fiber from step (1) to the material from step (2), stir for 40-50 seconds, then add the steel fiber and continue stirring for 40-50 seconds; (4) Quickly pour the mixture from step (3) into shape and vibrate it on a vibrating table for 1-2 minutes. Use constant voltage or stepped voltage to cure the specimen through Joule curing to the target curing time to complete the preparation of the geopolymer concrete. If only sodium silicate is used as the alkali activator, it is directly stirred and dispersed together with the precursor powder in step (2); if sodium hydroxide is also used as the alkali activator, a portion of water is taken out to dissolve all the alkali activator in advance, and then it is placed at room temperature before use.

[0011] Furthermore, the constant voltage is 10V-15V; the stepped voltage is selected during the curing process, with different curing voltages used in the early, middle and late stages of curing. In the early stage of curing, 15V is used for 0.5 hours to quickly reach the required temperature; in the middle stage of curing, 12.5V is used for 0.5-8 hours; and in the late stage of curing, the curing voltage is increased by 1V every hour for 8-10 hours.

[0012] Furthermore, the raw materials also include aggregates and retarders; the amount of carbon fiber, carbon nanofiber, and steel fiber added is based on the total volume of aggregates and precursor powders. After the precursor powders, retarders, and aggregates are mixed evenly, pre-dispersed carbon fiber and carbon nanofibers are added.

[0013] Thirdly, this invention also protects a Joule-cured multi-element solid waste geopolymer concrete, wherein steel fibers and carbon fibers are added to the geopolymer slurry, forming a point-to-line connection with the ions dissolved in the precursor powder contained in the matrix itself, especially the metal ions dissolved from steel slag, forming a multi-level conductive network that combines ionic conductivity and electronic conductivity; in addition, nano-carbon fibers are added to provide a "bridging" effect between carbon fibers and steel fibers, ensuring the density of the conductive network.

[0014] Compared with the prior art, the beneficial effects of the present invention are: (1) In this invention, carbon fiber and nano-carbon fiber are uniformly dispersed in the precursor powder, forming good contact with conductive media with different geometric properties such as steel fiber and steel slag, and constructing a multi-level interconnected conductive network. Through this conductive network, a synergistic effect is formed with the high alkali metal concentration ion conductivity in the geopolymer concrete pore solution, which significantly improves and ensures the conductivity of the geopolymer material throughout the Joule heat curing process, and improves the Joule heat curing efficiency. Under the same conditions, the strength of the specimen cured at 12.5V Joule for 10 hours and then cured at room temperature for 1 day is slightly higher than that of the specimen cured at 80℃ oven for 10 hours and then cured at room temperature for 1 day.

[0015] (2) The present invention utilizes stepped voltage (stepped voltage is the voltage that changes according to the resistivity change during the reaction process throughout the curing process, and each voltage is maintained for a certain time, like an upward or downward step, which is called stepped voltage) and pressurization time to effectively control the curing temperature of the geopolymer concrete, maintaining it between 60℃ and 100℃ (preferably 60-80℃), ensuring that the geopolymer accelerates the reaction under reasonable high temperature conditions and does not cause cracking or other problems caused by excessively high temperature.

[0016] (2) Geopolymer concrete is mostly made from industrial solid waste and has excellent conductivity due to its rich content of free alkali metal ions. This advantage not only achieves the resource reuse of industrial solid waste, but also effectively realizes the goal of energy conservation and carbon reduction, thus having both environmental benefits and ecological value.

[0017] (3) Nanofiber can effectively solve the problem of insufficient free ion concentration under extremely low water-cement ratio and after the specimen has hardened, ensuring the density of the conductive network and significantly improving the compressive strength of ultra-high performance geopolymer concrete.

[0018] (4) The construction of the multi-level conductive network in this invention significantly reduces the required curing voltage, effectively saving resources and reducing carbon emissions. If the resistivity of pure polymer concrete without multiple conductive media is high, from the formula... Where Q1 represents the Joule heat generated, U is the voltage, R is the specimen resistance, P is the electrical power, t is the curing time, ρ is the resistivity of the material, A is the cross-sectional area of ​​the specimen, and L is the length of the specimen. To achieve the same Joule heat, if the resistivity decreases, the voltage can be decreased accordingly.

[0019] This invention utilizes the abundant ions (including Na+) in the internal pore solution of geopolymers. + Ca 2+ OH - (etc.) Conductive materials are combined with conductive media of different geometric characteristics such as nanofibers, carbon fibers, steel fibers, and steel slag to form a highly efficient conductive network, ensuring that the specimen has a stable current and curing temperature and low resistivity throughout the curing process. At the same time, the curing voltage is adjusted, and under the given material conditions, an appropriate curing voltage and energizing time are selected to ensure stable and appropriate Joule heat, keeping the specimen at a suitable curing temperature, that is, maintaining a stable 60℃~100℃ for the first 8~10 hours after the fresh mixture has hardened. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the conductive network formed in the concrete slurry of the present invention.

[0021] Figure 2 The graph shows the trend of internal temperature of the specimens as a function of curing time in the examples and comparative examples.

[0022] Figure 3 The graph shows the trend of resistivity of the specimens as a function of curing time in the examples and comparative examples.

[0023] Figure 4 This is a particle size distribution diagram of the raw materials.

[0024] Figure 5 This is a SEM image of a portion of the raw material powder. 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] Joule curing is a volumetric heating method that directly applies electric current to concrete, generating uniform Joule heat within the concrete specimen to raise the temperature and accelerate the hydration of cementitious materials. This effectively improves energy conversion efficiency and reduces energy loss during the curing process. Furthermore, compared to ordinary Portland cement, geopolymers possess superior electrical conductivity due to their high concentration of free ions and the strong conductivity of sodium silicate solution. The required curing temperature can be flexibly provided to the geopolymer by controlling the Joule curing voltage, thus promoting the polymerization process of the specimen. Moreover, based on the conductivity mechanism of Joule-cured geopolymers, the curing voltage and curing time can be synergistically combined to effectively provide the desired curing effect while conserving resources. Geopolymer concrete primarily generates current through the abundant ionic conductivity of the alkaline solution in the fresh concrete mix. However, the concrete itself is a resistor. Curing is achieved by heating the concrete based on the Joule heating effect. As the concrete hardens, the amount of free water decreases, gradually weakening and eventually eliminating ionic conductivity, leading to an increase in resistivity. To maintain conductivity, an additional conductive medium is needed to continue generating current and utilizing the Joule heating effect for continued curing. This application incorporates a conductive medium into the formulation and uses ultrasound and a dispersant to pre-disperse the carbon fibers, ensuring uniform dispersion of the conductive medium within the system. This guarantees curing efficiency throughout the process and avoids the problem of decreased conductivity due to increased resistivity of the geopolymer during the later stages of Joule heat curing.

[0027] This invention utilizes high-content steel slag (rich in ferrite) as raw material, and combines the abundant ions (including Na+, Ca2+, OH-, etc.) in the porous solution within the geopolymer with conductive media of different geometric characteristics such as carbon nanofibers, carbon fibers, steel fibers, and steel slag to form a highly efficient, long-lasting, and stable multi-level conductive network (including point-like (conductive ions inside the geopolymer) and line-like (rod-like fiber overlaps), ions, and electrons). Furthermore, a graded and time-segmented voltage energizing regime is adopted for the multi-level conductive network. Through repeated experiments, the optimal regime was obtained, and the combination of materials and regime achieves the best curing effect.

[0028] This invention, by adding steel fibers and carbon fibers to geopolymer slurry, forms a multi-level conductive network (e.g., ionic and electronic conduction) with ions dissolved in the precursor powder contained in the matrix itself, especially metal ions dissolved from steel slag, creating point-to-line connections. Figure 1(As shown), to improve the Joule heat curing effect. In addition, due to the large diameter of carbon fibers and steel fibers, it is difficult to form a continuous and dense conductive network after hardening. In addition, if ultra-high performance geopolymer concrete is prepared, the physical and mechanical properties of ultra-high performance concrete require an extremely low water-cement ratio, generally between 0.2 and 0.3. If the water-cement ratio is increased, it will lead to a decrease in material strength and an increase in material porosity, which will affect the concentration of free ions. Therefore, carbon nanofibers can be appropriately added to provide a "bridging" effect and ensure the density of the conductive network.

[0029] This invention relates to a Joule-cured multi-component solid waste polymer concrete, the raw materials of which include: precursor powder, alkali activator, steel fiber, carbon fiber, and water. The steel fiber comprises 0.5-2.5 vol% of the precursor powder, the carbon fiber comprises 0.4-1.0 vol% of the precursor powder, the nano-carbon fiber comprises 0-0.10 vol% of the precursor powder, and the water comprises 0.2-0.43 wt% of the precursor powder. The preparation method of the Joule-cured multi-component solid waste polymer concrete includes the following steps: (1) Carbon fiber pre-dispersion: Carbon fiber or carbon fiber and nanofiber are placed in water and ultrasonically dispersed for 10-20 minutes with a power of 250-400W. Then, 0.5-0.8 vol% of hydroxyethyl cellulose and 0.01-0.04 vol% of tributyl phosphate (according to the volume of water added in this step) are added and stirred evenly. Then, ultrasonically dispersed for 8-12 minutes with a power of 250-400W. Finally, let stand for 8-12 minutes to obtain a slightly viscous and smooth mixture. (2) First, pour the precursor powder into the mixing pot and set the mixing pot (JJ-5 type) to low speed and mix evenly. (3) Add the pre-dispersed fiber from step (1) to the material from step (2), stir for 40-50 seconds, then add the steel fiber and continue stirring for 40-50 seconds; If only sodium silicate is used as the alkali activator, it is directly stirred and dispersed together with the precursor powder in step (2); if sodium hydroxide is also used as the alkali activator, a portion of water is taken out to dissolve all the alkali activator in advance, and then it is placed at room temperature before use.

[0030] (4) Quickly pour the mixture from step (3) into shape and vibrate it on a vibrating table for 1-2 minutes. Use a constant voltage (10V-15V) or stepped voltage (time and voltage synergistic effect) to cure the specimen through Joule curing to the target curing time (8-10h) to complete the preparation of geopolymer concrete.

[0031] In this invention, the dispersant hydroxyethyl cellulose is water-compatible and can fully disperse carbon fibers and carbon nanofibers. However, adding too much hydroxyethyl cellulose will result in a viscous consistency that is not conducive to dispersion. Tributyl phosphate is used as an antifoaming agent.

[0032] This invention allows for the selection of a more suitable curing method based on material properties. Stepped voltage refers to using different curing voltages in the early, middle, and late stages of curing, based on the changes in the specimen's resistance. For example, in the early stage, 0.5 hours (15V, to quickly reach the required temperature); in the middle stage, 0.5-8 hours (12.5V, to maintain the required temperature); and in the late stage, 8-10 hours (increasing the curing voltage by 1V every hour to address the increase in resistivity and maintain the required temperature), thus synergistically combining voltage and time. For water-cement ratios (the mass ratio of precursor powder + aggregate to water in geopolymers) not exceeding 0.3, both carbon fiber and carbon nanofibers should be added simultaneously; for water-cement ratios greater than 0.3, only carbon fiber should be added, with the addition or omission of carbon nanofibers optional depending on the situation.

[0033] Preferably, the resistivity of the formulation of the present invention is stably maintained at 4-6Ω. . Within a certain range (cm), the internal curing temperature remains stable at 75-95℃. Under these conditions, a good curing effect can be achieved, meeting higher strength requirements for the material, while also saving energy and achieving a balanced curing process. If the curing temperature is too high, carbon fiber charring may easily occur.

[0034] In this invention, the temperature at the center of the specimen is measured using a multi-channel thermometer, and it is observed whether 75% of the temperature data in the temperature curve fluctuates within the range of ±20℃. If so, it is considered stable.

[0035] In the following examples and comparative examples, the steel fibers had dimensions of 13 mm in length and 0.22 mm in diameter; the carbon fibers had dimensions of 12 mm in length and 5 μm in diameter; and the average size of the nanofibers was 10-50 nm. The steel slag powder (SS), granulated blast furnace slag (GBFS), and fly ash (FA) used were all from China Jintaicheng Technology Group Co., Ltd. The metal oxide content is shown in Table 1, and the particle size distribution is shown in [Table 1]. Figure 4 SEM images can be found Figure 5 Silica fume (SF) was purchased from Sanyuan Silicon Materials Co., Ltd. (Gansu, China). The alkali activator was anhydrous sodium silicate powder (Na2SiO3) with a modulus of 1.4 and a purity of 99%, produced by Shandong Yusuo Chemical Technology Co., Ltd. Sodium hydroxide had a purity of 99.7% and was produced by Yatai United Chemical Co., Ltd. (Jiangsu, China).

[0036] Table 1 Chemical composition and physical properties of raw materials Table 2.1 Chemical composition and physical properties of raw materials

[0037] Example 1 In this embodiment, the precursor powder (a mixture of fly ash, slag, and steel slag in a ratio of 3:5:2), steel fiber is 1.0 vol% of the precursor powder, carbon fiber is 0.5 vol% of the precursor powder, water is 0.38 wt% of the precursor powder, and alkali activator (sodium silicate) is 8 wt% of the precursor powder; in this embodiment, the water-ash ratio is higher than 0.3, and no nano-carbon fiber is added.

[0038] The preparation process is as follows: (1) First, the carbon fiber is pre-dispersed: the carbon fiber is put into all the water and ultrasonically dispersed for 15 minutes with a power of 250 W. Then, 0.7 wt% of hydroxyethyl cellulose and 0.03 vol% of tributyl ester are added and stirred evenly. Then, ultrasonically dispersed for 10 minutes with a power of 250 W. Finally, it is allowed to stand for 10 minutes to obtain a slightly sticky and smooth mixture. (2) First, the precursor powder and alkali activator are poured into the mixing pot and the mixing pot (JJ-5 type) is set to low speed for 2 minutes. (3) The pre-dispersed carbon fiber is added to the evenly stirred precursor powder and alkali activator. It is stirred at low speed for 45 seconds. Then, steel fiber is added and stirred at low speed for 45 seconds.

[0039] The mixture from step (3) is quickly poured into shape. After the mold is vibrated, it is poured into a prism of 40mm×40mm×160mm. It is placed in an insulated box and 40mm×50mm copper mesh is inserted along both ends of the long side. The upper end of the copper mesh is connected to an AC power supply and cured with a curing voltage of 12.5V for 10 hours.

[0040] The measured volume resistivity of the material remained at 5 Ω for the first 8 hours. The resistivity only increased to 24 Ω after about 10 hours of curing, and the temperature was around 1 cm. cm (see cm) Figure 3 This ensured the curing effect throughout the entire curing process. After 10 hours of Joule heat curing, the compressive strength of the geopolymer concrete reached over 45 MPa after 24 hours of room temperature curing, as shown in Table 1.

[0041] Example 2 In this embodiment, the precursor powder (fly ash: slag: steel slag = 3:5:2), steel fiber is 1.0 vol% of the precursor powder, carbon fiber is 0.5 vol% of the precursor powder, water is 0.38 wt% of the precursor powder, and alkali activator (sodium silicate) is 8 wt% of the precursor powder; the water-ash ratio is 0.38.

[0042] During preparation, (1) the carbon fibers were first pre-dispersed: the carbon fibers were placed in all water and ultrasonically dispersed for 15 min using a power of 250 W. Then, 0.7 wt% of hydroxyethyl cellulose and 0.03 vol% of tributyl ester were added and stirred evenly. Then, 250 W was used to disperse the carbon fibers. (1) Use W power to ultrasonically disperse for 10 minutes, and finally let stand for 10 minutes to obtain a slightly sticky and smooth mixture; (2) First, pour the precursor powder and alkali activator into the mixing pot and stir at low speed for 2 minutes; (3) Add the pre-dispersed carbon fiber to the evenly stirred precursor powder and alkali activator, stir at low speed for 45 seconds, then add steel fiber and continue to stir at low speed for 45 seconds; and all the stirring is at low speed. After the mold vibration is completed, it is cast into a prism of 40mm×40mm×160mm. Insert 40mm×50mm copper mesh along both ends of the long side. Connect the upper end of the copper mesh to the AC power supply for Joule curing. The specific Joule curing process is: first, quickly raise the voltage to 15V and maintain it for 0.5h (quickly reach the curing temperature), then quickly lower the voltage to 12.5V and maintain it for 8h, then quickly raise the voltage to 13.5V and maintain it for 9h, and finally raise the voltage to 14.5V and maintain it for 10h. The total curing time for Joules is 10 hours.

[0043] In the early stage of curing, the curing temperature of the specimens quickly reached 80℃ due to the increase in curing voltage. In the later stage of curing, although the resistivity of the specimens continued to rise, the curing temperature of the specimens was maintained above 80℃ due to the corresponding continuous increase in curing voltage, which ensured the curing effect throughout the entire curing process. After 10 hours of Joule heat curing, the geopolymer concrete was placed in an insulated box at room temperature for 24 hours after heating was stopped, and the compressive strength reached more than 55MPa.

[0044] Example 3 In this embodiment, the weight of the precursor powder plus aggregate is 1000g (of which fly ash accounts for 32.6 wt%, slag accounts for 13.1 wt%, steel slag accounts for 11.2 wt%, silica fume accounts for 9.8 wt%, and quartz sand accounts for 33.3 wt%), steel fiber accounts for 1.4 vol%, carbon fiber accounts for 0.5 vol%, nano-carbon fiber accounts for 0.10 vol%, water accounts for 0.28 wt%, sodium hydroxide accounts for 1.5 wt%, sodium silicate accounts for 6.7 wt%, and retarder (citric acid) accounts for 1.0 wt%. The water-cement ratio is low, so nano-carbon fiber needs to be introduced.

[0045] During preparation, in step (1), the alkali activator is dissolved in half of the water in advance and placed at room temperature; then the carbon fibers and nano-carbon fibers are pre-dispersed in the remaining half of the water, and the amount of hydroxyethyl cellulose added is reduced; in step (2), the precursor powder, retarder and aggregate are stirred at low speed for 2 minutes, then the pre-dissolved alkali activator and pre-dispersed fibers are added in sequence, stirred at low speed for 40 seconds, then stirred at high speed for 40 seconds, and finally the steel fibers are added and stirred at high speed for 30 seconds.

[0046] Cast into a prism of 40mm×40mm×160mm, insert 40mm×50mm copper mesh at both ends of the long side, connect the upper end of the copper mesh to an AC power source, first rapidly increase the voltage to 15V and maintain it for 0.5h, then rapidly decrease the voltage to 12.5V and maintain it for 8h, then rapidly increase the voltage to 13.5V and maintain it for 9h, and finally increase the voltage to 14.5V and maintain it for 10h.

[0047] The test results showed that the conductivity of the material was greatly improved, and the specimens were kept at a curing temperature of 60~90℃ for a longer period of time, which effectively ensured the Joule heat curing effect.

[0048] Comparative Example 1 In this comparative example, no carbon fiber was introduced. The precursor powder (a mixture of fly ash, slag, and steel slag in a ratio of 3:5:2), steel fiber, and water were all present in the precursor powder at 1.0 vol% and 0.38 wt% respectively. The alkali activator (sodium silicate) was also present in the precursor powder at 8 wt%.

[0049] Preparation: Mix the precursor powder, alkali activator and water together for 3 minutes; then add steel fiber directly and stir for 45 seconds. All stirring is done at low speed. After molding, cure with a Joule curing voltage of 15V for 8 hours.

[0050] The measured volume resistivity of the material continuously increased, and the curing temperature initially rose and then fell without a stable phase, indicating that the conductive network had not been established. After 8 hours of Joule heat curing, the compressive and flexural strengths of the geopolymer concrete, after 24 hours of room temperature curing, were only 31.56 MPa and 4.69 MPa, respectively, as shown in Table 1. The conductive network needs to be modified.

[0051] Comparative Example 2 In this comparative example, the precursor powder (a mixture of fly ash, slag, and steel slag in a ratio of 3:5:2), steel fiber accounted for 1.0 vol% of the precursor powder, carbon fiber accounted for 1.2 vol% of the precursor powder, water accounted for 0.38 wt% of the precursor powder, and alkali activator (sodium silicate) accounted for 8 wt% of the precursor powder. During preparation, (1) the carbon fiber is first pre-dispersed: the carbon fiber is placed in half water and ultrasonically dispersed for 15 min with a power of 250 W. Then, 0.7 wt% of hydroxyethyl cellulose and 0.03 vol% of tributyl ester are added and stirred evenly. Then, ultrasonically dispersed for 10 min with a power of 250 W. Finally, it is allowed to stand for 10 min to obtain a slightly viscous and smooth mixture. (2) the solution of the precursor powder, the remaining water and the alkali activator is first poured into a mixing pot and stirred at low speed for 2 min. (3) the pre-dispersed carbon fiber is added to the evenly stirred precursor powder and alkali activator and stirred at low speed for 45 s. Then, steel fiber is added and stirred at low speed for another 45 s. All stirring is done at low speed.

[0052] After the mold vibration is completed, it is cured with a curing voltage of 12.5V for 10 hours.

[0053] The measured volume resistivity of the material remained at 3 Ω for the first 6 hours. The curing temperature was around 120℃. Although a conductive network was built in the early stage of curing, the stability of this conductive network was poor due to the large amount of carbon fiber added. Moreover, the excessive curing temperature damaged the curing strength. As a result, the compressive strength of the geopolymer concrete was only 32.61MPa after 10 hours of Joule heat curing and 24 hours of room temperature curing, as shown in Table 1.

[0054] Comparative Example 3 In this embodiment, the water-cement ratio is low, the weight of the precursor powder plus aggregate is 1000g (of which, fly ash accounts for 32.6wt%, slag accounts for 13.1wt%, steel slag accounts for 11.2wt%, silica fume accounts for 9.8wt%, and quartz sand accounts for 33.3wt%), steel fiber accounts for 1.5 vol% of the precursor powder plus aggregate, carbon fiber accounts for 0.5 vol% of the precursor powder plus aggregate, water accounts for 0.3 wt% of the precursor powder plus aggregate, sodium hydroxide accounts for 1.5 wt% of the precursor powder plus aggregate, sodium silicate accounts for 6.7 wt% of the precursor powder plus aggregate, and retarder (citric acid) accounts for 1.0 wt% of the precursor powder plus aggregate; During preparation, in step (1), the alkali activator (sodium hydroxide and sodium silicate) is dissolved in half of the water in advance and placed at room temperature; then the carbon fibers are pre-dispersed in the remaining half of the water and the amount of hydroxyethyl cellulose added is reduced; in step (2), the precursor powder, retarder and aggregate are stirred at low speed for 2 minutes, then the pre-dissolved alkali activator and pre-dispersed fibers are added in sequence, stirred at low speed for 40 seconds, then stirred at high speed for 40 seconds, and finally the steel fibers are added and stirred at high speed for 30 seconds.

[0055] After molding, the specimens were cured at 12.5V for 10 hours. Poor conductivity was observed, especially a significant decrease in conductivity in the early stages. At lower cement-to-ash ratios, the ionic conductivity of the specimens decreased substantially, and the number of "points" in the point-to-line conductive network was insufficient. Nanofibers were added to supplement the network with smaller, denser "lines."

[0056] Table 2 presents the comparative data of the mechanical properties of the above comparative examples and embodiments.

[0057] Table 2 Mechanical strength of each comparative example and embodiment

[0058] Figure 2 and Figure 3 The changes in temperature and resistivity during the Joule curing process are presented in different comparative examples and implementation examples. Figure 3 In physics, resistivity can be categorized into two types: one where it increases linearly, in which case the temperature typically increases first and then decreases, without a plateau period; and another where the resistivity is initially relatively stable but then begins to rise, in which case the temperature curve generally presents a pattern of: heating phase - isothermal phase - cooling phase. (See [reference needed]). Figure 2 By properly controlling the conductive network, the Joule curing process can be regulated, and the resistivity can be kept at a relatively stable value throughout the curing process.

[0059] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A Joule-cured multi-component solid waste polymer concrete, the raw materials of which include: Precursor powder, alkali activator, steel fiber, carbon fiber and water, characterized in that, If the water-cement ratio in the concrete raw materials is not higher than 0.3, then nano-carbon fiber needs to be added to the raw materials; if the water-cement ratio in the concrete raw materials is higher than 0.3, nano-carbon fiber is not added initially. Carbon fiber or carbon fiber and carbon nanofiber are evenly dispersed in water and then added to a uniformly mixed precursor powder. Finally, steel fibers are added and mixed evenly to form a slurry with a multi-level conductive network. After the slurry is molded, it undergoes Joule curing at 12.5V for 10 hours. The resistivity and temperature at the center of the specimen are measured to obtain resistivity and temperature curves. If the resistivity in the resistivity curve continues to increase without a stable phase, the conductive network has not been established. The conductive network can be corrected by increasing the type or amount of conductive medium. If the resistivity remains stable for a long time and 75% of the temperature data in the temperature curve fluctuates within ±20℃, the resistivity of the multi-stage conductive network is considered stable. When the resistivity of the multi-level conductive network is stable, the optimal Joule curing process corresponding to the formulation is determined: a suitable curing temperature range is preset. If the curing temperature is within the preset suitable curing temperature range, then Joule heat curing at 12.5V for 10 hours is determined as the optimal Joule curing process; if the stable internal temperature in the temperature curve is significantly lower than the preset suitable curing temperature range, then the curing voltage is increased based on 12.5V for Joule curing; if the temperature drops rapidly in the later stage of the temperature curve, the abrupt curing time point is recorded, and then the curing voltage is increased in stages at the abrupt curing time point for Joule curing, or the doping of the conductive medium is increased to construct a denser conductive network; Multi-component solid waste geopolymer concrete was prepared by formulating a multi-level conductive network with stable resistivity and then cured according to a determined Joule curing method.

2. The concrete according to claim 1, characterized in that, If the point where the resistivity suddenly increases from a steady state in the resistivity curve occurs before 7 hours, it is recommended to increase the amount of conductive medium, without increasing the curing voltage, and adjust the formula. If it occurs after 7 hours, determine whether it is consistent with the curing time point of the temperature change curve. If it is consistent and occurs after the curing time point of the temperature change, increase the staged voltage or increase the amount of conductive medium.

3. The concrete according to claim 1, characterized in that, In real-time resistivity detection, if the resistivity continues to increase, the voltage value is increased according to the rate of increase.

4. The concrete according to claim 1, characterized in that, If the stable internal temperature in the temperature curve is significantly lower than the preset suitable curing temperature range, increase the curing voltage and observe whether the temperature can remain within the preset suitable curing temperature range for a long time. If it can, use this voltage for curing. If it cannot be maintained, it is necessary to further improve the conductive network, increase the doping amount of conductive medium, and add conductive mediums of different sizes.

5. The concrete according to claim 1, characterized in that, When increasing the doping amount of the conductive medium to modify the conductive network, the doping amount should be adjusted slowly by 0.050-0.1 vol%.

6. The concrete according to claim 1, characterized in that, The preset suitable curing temperature range depends on the calcium content in the geopolymer, and the resistivity of the multi-level conductive network is maintained at 4-8Ω under stable conditions. . Within the range of cm.

7. A method for preparing Joule-cured multi-component solid waste polymer concrete, characterized in that, Its raw materials include: precursor powder, alkali activator, steel fiber, carbon fiber, and water. The steel fiber accounts for 0.5~2.5 vol% of the precursor powder, the carbon fiber accounts for 0.4~1.0 vol% of the precursor powder, the nano-carbon fiber accounts for 0~0.10 vol% of the precursor powder, and the water accounts for 0.2~0.43 wt% of the precursor powder. The preparation method includes the following steps: (1) Carbon fiber pre-dispersion: Carbon fiber or carbon fiber and nano carbon fiber are placed in water and ultrasonically dispersed for 10-20 min with a power of 250-400W. Then, 0.5-0.8 vol% of hydroxyethyl cellulose and 0.01-0.04 vol% of tributyl phosphate are added and stirred evenly. The amount of tributyl phosphate added is based on the volume of water. Then, ultrasonically dispersed for 8-12 min with a power of 250-400W. Finally, let stand for 8-12 min to obtain a slightly viscous and smooth mixture. (2) First, pour the precursor powder into the mixing pot and stir evenly; (3) Add the pre-dispersed fiber from step (1) to the material from step (2), stir for 40-50 seconds, then add the steel fiber and continue stirring for 40-50 seconds; (4) Quickly pour the mixture from step (3) into shape and vibrate it on a vibrating table for 1-2 minutes. Use constant voltage or stepped voltage to cure the specimen through Joule curing to the target curing time to complete the preparation of the geopolymer concrete. If only sodium silicate is used as the alkali activator, it is directly stirred and dispersed together with the precursor powder in step (2); if sodium hydroxide is also used as the alkali activator, a portion of water is taken out to dissolve all the alkali activator in advance, and then it is placed at room temperature before use.

8. The preparation method according to claim 7, characterized in that, The constant voltage is 10V-15V; the stepped voltage During the curing process, different curing voltages are selected in the early, middle and late stages of curing. In the early stage of curing, 15V is used for 0.5 hours to quickly reach the required temperature. In the middle stage of curing, 12.5V is used for 0.5-8 hours. In the late stage of curing, the curing voltage is increased by 1V every hour for 8-10 hours.

9. The preparation method according to claim 7, characterized in that, The raw materials also include aggregates and retarder; the amount of carbon fiber, nano-carbon fiber and steel fiber added is based on the total volume of aggregates and precursor powders. After the precursor powders, retarder and aggregates are mixed evenly, pre-dispersed carbon fiber and nano-carbon fiber are added.

10. A Joule-cured multi-component solid waste polymer concrete, characterized in that, The concrete incorporates steel and carbon fibers into the geopolymer slurry, which form a point-to-line connection with the ions dissolved in the precursor powder contained in the matrix itself, especially the metal ions dissolved from steel slag, creating a multi-level conductive network that combines ionic and electronic conductivity. In addition, carbon nanofibers are added to provide a "bridging" effect between carbon fibers and steel fibers, ensuring the density of the conductive network.

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