Alkali-activated multi-source solid waste-based phase change heat storage aggregate and preparation thereof, and preparation method of phase change heat storage concrete

Abstract

The application discloses a kind of alkali-activated multi-source solid waste-based phase change heat storage aggregate and preparation, a kind of preparation method of phase change heat storage concrete, the heat storage aggregate includes heat storage core layer and wrapping layer from inside to outside in sequence;Heat storage core layer is composed of porous alkali-activated geopolymer matrix and phase change material loaded in the pore of the alkali-activated geopolymer matrix;The mass fraction of each raw material of heat storage core layer is as follows: blast furnace slag 70~80 parts, sludge ash 20~30 parts, bottom ash 5~15 parts, sodium silicate solution 25~35 parts, phase change material 18~30 parts, water 20~30 parts and polycarboxylic acid superplasticizer 0.5~1 part;The wrapping layer is dense alkali-activated geopolymer layer, and the wrapping layer wraps the heat storage core layer.The phase change heat storage aggregate has good mechanical properties and excellent heat storage capacity.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, specifically relating to an alkali-activated multi-source solid waste-based phase change thermal storage aggregate and its preparation, and a method for preparing phase change thermal storage concrete. Background Technology

[0002] With the global energy crisis and carbon emission problems becoming increasingly severe, the development and utilization of renewable energy has become an important direction for promoting sustainable development. Against this backdrop, how to improve energy efficiency and achieve efficient energy storage and release has become a key research topic. Phase change thermal energy storage technology has received widespread attention in recent years in engineering fields such as civil engineering, water conservancy, and transportation due to its excellent thermal management capabilities. In particular, combining phase change materials with cement-based materials can significantly improve the thermal energy storage and regulation performance of composite materials. However, direct contact between phase change materials and the cement matrix often interferes with the cement hydration process, leading to a significant decrease in the mechanical properties of the hardened thermal energy storage cement-based materials. Therefore, it is necessary to encapsulate phase change materials to enable them to be used as functional thermal energy storage aggregates in cement-based composite materials. Currently, commonly used encapsulation methods can be divided into two types: phase change microencapsulation and porous framework adsorption. Phase change microencapsulation involves encapsulating phase change materials within a micro-container to form a core-shell structure, where the phase change material acts as the thermal energy storage core, and the outer shell serves as a seal and prevents leakage. However, current mature phase change microcapsule synthesis technologies are typically complex and expensive, making them unsuitable for large-scale production. Furthermore, microcapsules exhibit poor dispersibility in cement matrices, easily agglomerating and negatively impacting the uniformity and stability of composite materials. In contrast, porous framework adsorption methods utilize the pore structure within porous media to encapsulate and load phase change materials through physical adsorption. This method boasts a simpler preparation process and lower production costs, making it suitable for large-scale production. However, commonly used porous framework materials often rely on natural porous aggregates or artificial aggregates (such as expanded vermiculite and expanded perlite) produced through high-temperature sintering. These porous support materials generally suffer from poor mechanical properties and high energy consumption during preparation. Moreover, natural aggregate resources are increasingly scarce, and their extraction can damage the ecological environment; while high-temperature sintering processes not only consume significant energy but also generate substantial carbon emissions. Therefore, there is an urgent need to develop a phase change energy storage aggregate with excellent mechanical strength, good shape retention, and low preparation cost.

[0003] Based on this, other inventions have also provided different technical paths to achieve this goal, but all of them have certain limitations. For example, although some technical solutions have improved the shaping ability of aggregates, they have failed to effectively solve the problem of insufficient mechanical strength of aggregates; while other solutions have reduced the preparation cost, they have performed poorly in terms of the loading capacity and thermal stability of phase change materials.

[0004] Patent application CN118993599B discloses a concrete aggregate, its preparation method, and its application. This aggregate uses inorganic hydrated salts as the phase change core, adsorbs and stabilizes the phase change material through a porous medium, and then sequentially encapsulates it through a hydrophobic layer, a polymer layer, and a hydrophilic layer to form composite phase change particles. These particles are then granulated with porous cementitious materials and finally encapsulated with a cementitious encapsulating material to form a monolithic aggregate. While this invention effectively solves the leakage problem, it still has certain limitations in terms of mechanical properties and heat storage capacity. Furthermore, the aggregate preparation process involves multiple steps, including vacuum impregnation, hydrophobic treatment, polymer encapsulation, and hydrophilic treatment, making the process relatively cumbersome and limiting its efficient application and large-scale promotion in practical engineering.

[0005] Patent application CN119750938A discloses a phase change aggregate and its preparation method. This aggregate uses construction waste as a base material and is prepared via a cold-bonding granulation method. This method aims to consume construction waste, reduce accumulation, and prevent leakage of the phase change material through microencapsulation technology. However, this invention also has significant drawbacks in terms of mechanical properties and heat storage capacity. The aggregate's 28-day compressive strength is only about 3 MPa, far below the strength level achievable by alkali-activated cementitious material systems. Furthermore, this technology still uses commercially available phase change paraffin microcapsules to enhance the thermal properties of the phase change aggregate, and the selected microcapsules have a low phase change enthalpy (only 15 J / g), limiting their heat storage capacity. Simultaneously, this aggregate faces the risk of phase change material migration and failure during long-term use, affecting its energy storage stability and durability.

[0006] Existing technologies for preparing phase change energy storage aggregates still suffer from varying degrees of shortcomings in terms of mechanical properties, thermal storage capacity, and complex production processes. Existing solutions often struggle to simultaneously achieve a high-strength framework structure, large-capacity stable encapsulation of the phase change material, and low-energy consumption and low-cost preparation requirements. Therefore, there is an urgent need to explore a novel phase change energy storage aggregate preparation technology that is simple to implement and possesses excellent mechanical and thermal storage properties. This technology can achieve efficient loading and reliable shaping of the phase change material while reducing energy consumption and environmental impact during production, thereby better promoting the large-scale application and sustainable development of phase change thermal storage materials in engineering fields. Summary of the Invention

[0007] This invention provides an alkali-activated multi-source solid waste-based phase change thermal storage aggregate, which has good mechanical properties and excellent thermal storage capacity.

[0008] This invention provides an alkali-activated multi-source solid waste-based phase change thermal storage aggregate, wherein the thermal storage aggregate comprises a thermal storage core layer and a wrapping layer from the inside out; The thermal storage core layer is composed of a porous alkali-activated geopolymer matrix and a phase change material loaded in the pores of the alkali-activated geopolymer matrix. The mass fractions of each raw material in the heat storage core layer are as follows: 70-80 parts blast furnace slag, 20-30 parts sludge ash, 5-15 parts bottom ash, 25-35 parts sodium silicate solution, 18-35 parts phase change material, 20-30 parts water and 0.5-1 parts polycarboxylate superplasticizer. The encapsulation layer is a dense alkali-activated geopolymer layer, which encapsulates the thermal storage core layer.

[0009] This invention incorporates sludge ash into a slag-based alkali-activated cementitious system. By synergistically regulating the autogenous shrinkage, drying shrinkage, and carbonation shrinkage behaviors, it effectively suppresses the phenomenon of reduced mechanical strength in aggregates during the later stages. Specifically, the porous mineral phases and inert or weakly reactive particles contained in the sludge ash form stable microstructure regulating units in the alkali-activated system. On the one hand, its porous structure can adsorb and slowly release free water and pore solution in the system, reducing the capillary negative pressure caused by gel formation during the alkali-activated reaction, thereby significantly reducing the autogenous shrinkage deformation of the aggregate and reducing early shrinkage stress concentration and the generation of microcracks. On the other hand, the sludge ash particles, as a low-reactivity and relatively stiff filling phase, can optimize the particle size distribution and skeleton structure of the cementitious system, reduce the drying shrinkage amplitude during water migration, and effectively suppress the weakening of the interface transition zone and the resulting crack propagation. Furthermore, the stable oxide components such as Ca, Al, and Fe abundant in sludge ash can participate in or regulate the alkali-activated reaction process of blast furnace slag, reduce the connectivity of the pore structure, and hinder carbon dioxide in the air from entering the pores and reacting with hydration products, thereby mitigating carbonization shrinkage deformation. Through the synergistic effect of the above multiple mechanisms, the cumulative degree of shrinkage damage within the system can be significantly reduced, maintaining the stability of the mid-to-late stage structure of alkali-activated cementitious aggregate in slag, thus effectively suppressing the reduction in mechanical strength.

[0010] The alkali-activated cementitious system constructed in this invention, with blast furnace slag, sludge ash, and bottom ash as its main components, not only effectively improves the comprehensive utilization level of solid waste but also provides a dense geopolymer skeleton for the aggregate. Through the highly alkaline environment formed by sodium silicate solution, the potential activity of blast furnace slag and sludge ash is fully activated, generating a dense aluminosilicate gel structure, thereby ensuring the excellent mechanical properties of the aggregate. Simultaneously, metallic aluminum and its active components in the bottom ash react under alkaline conditions and release gas, enriching the internal pore structure of the aggregate and increasing the loading space of the phase change material. In engineering applications, this thermal storage aggregate can be incorporated into cement-based systems as a functional aggregate, endowing the material with significant thermal energy storage and regulation capabilities without reducing structural strength, achieving a synergistic unity of energy saving, environmental protection, and performance improvement.

[0011] Preferably, the modulus of the sodium silicate solution is 1.5-2.5. By controlling the modulus of the sodium silicate solution and combining it with an appropriate amount of base ash, this invention achieves a pore size ratio of 100-100 nm in the phase change thermal storage aggregate provided by this invention of 48.4%-88.2%, resulting in a suitable ratio between the impregnation rate and leakage rate of the phase change material, and ensuring that an appropriate amount of phase change material adheres to the prepared thermal storage core layer. The leakage rate provided by this invention refers to the volume of phase change material leaking during the preparation process compared to the actual volume of impregnated phase change material, thus characterizing the amount of phase change material that can be loaded after preparation.

[0012] More preferably, the modulus of the sodium silicate solution is 1.8-1.9.

[0013] By further controlling the modulus, this invention enables the volume ratio of pores with a pore size of 100 nm to 1000 nm in the alkali-activated geopolymer matrix to be 77.9% to 88.2%, thereby achieving a high leakage rate and impregnation rate of the phase change material at this modulus.

[0014] Preferably, the mass fractions of the raw materials in the coating layer are: 6-7 parts blast furnace slag, 1.5-2 parts sodium silicate solution, and 1.5-2 parts water. This invention enables the formation of a dense alkali-activated geopolymer layer by controlling the components of the coating layer.

[0015] First, the formation of a continuous and dense coating layer on the outside of the porous aggregate skeleton can effectively seal the interconnected pores inside the porous aggregate, significantly reducing the risk of leakage of phase change materials in the molten state. This improves the structural stability of the thermal storage aggregate during repeated phase change processes and avoids the adverse effects of phase change material leakage on the performance of the cement matrix.

[0016] Secondly, the coating layer is composed of alkali-activated geopolymer, which has high density and excellent mechanical properties. It can effectively protect the internal porous skeleton and the impregnated phase change material, thereby enhancing the overall mechanical strength and wear resistance of the thermal storage aggregate, making it less prone to breakage or damage during subsequent mixing, molding and actual service.

[0017] In addition, the hydration products of the coating layer are mainly hydrated calcium aluminosilicate gel. This type of gel has good compatibility with the hydration products in cement-based materials, which helps to improve the interfacial bonding performance between alkali-activated multi-source solid waste-based phase change thermal storage aggregate and cement matrix, thereby alleviating to some extent the problem of mechanical property deterioration that may be caused by the incorporation of thermal storage aggregate into cement-based materials.

[0018] Meanwhile, the dense coating layer can also isolate moisture and external corrosive media to a certain extent, reduce the adverse effects of moisture, alkaline or other corrosive media on phase change materials, thereby significantly improving the durability and long-term service reliability of phase change thermal storage aggregates.

[0019] In summary, by coating the porous aggregate impregnated with phase change material with a layer of alkali-activated geopolymer slurry, it is possible not only to effectively inhibit the leakage of phase change material and improve the mechanical and durability properties of thermal storage aggregate, but also to balance its thermal regulation function and structural safety, thereby significantly improving the comprehensive application performance of phase change thermal storage aggregate.

[0020] Preferably, the phase change material is industrial paraffin.

[0021] Preferably, the compressive strength of the thermal storage aggregate is 10.8~13.2 MPa, and the latent heat of phase change is 20.2~31.2 J / g.

[0022] On the other hand, the present invention also provides a method for preparing the alkali-activated multi-source solid waste-based phase change thermal storage aggregate, comprising: (1) Dry, grind and sieve the blast furnace slag, sludge ash and bottom ash; (2) According to the proportion of each raw material in the heat storage core layer, the blast furnace slag, sludge ash and bottom ash after sieving in step (1) are mixed to obtain a dry mixture. The dry mixture, sodium silicate solution, water and polycarboxylate superplasticizer are stirred and mixed evenly to obtain a slurry. (3) After the slurry is injected into the mold, it is crushed, pre-cured and demolded, then mechanically crushed and graded to obtain coarse and fine aggregates. (4) Standard curing and vacuuming of the aggregates from step (3), then injecting molten phase change material until the aggregates are submerged, and restoring normal pressure; (5) Filter the aggregate obtained in step (4) to remove excess phase change material from the surface; (6) Immerse the aggregate obtained in step (5) into the coating slurry and cure at room temperature to obtain alkali-activated multi-source solid waste-based phase change thermal storage aggregate.

[0023] Preferably, the sieved blast furnace slag is added to sodium silicate solution and water according to the fraction of each raw material in the coating layer to obtain the coating layer slurry; The mass fractions of each raw material in the coating layer are: 6-7 parts blast furnace slag, 1.5-2 parts sodium silicate solution, and 1.5-2 parts water.

[0024] Preferably, in step (1), the core layer raw materials must all pass through a 0.15 mm sieve after grinding.

[0025] Preferably, in step (3), a natural stone crusher is used for crushing, and then the material is screened in sequence through a 20 mm aperture sieve, a 4-mesh standard sieve and an 8-mesh standard sieve to obtain fine aggregate with a particle size of 2.36~4.75 mm and coarse aggregate with a particle size of 4.75~20 mm.

[0026] On the other hand, the present invention provides a method for preparing phase change thermal storage concrete, comprising: S1. The raw materials are prepared according to the following mass proportions, including: 200-400 parts of ordinary Portland cement, 300-600 parts of sand, 500-1200 parts of crushed stone, 100-200 parts of alkali-activated multi-source solid waste-based phase change thermal storage aggregate according to any one of claims 1-9, 100-200 parts of water, and 0.5-1 parts of polycarboxylate superplasticizer; S2. The ordinary silicate cement, sand, crushed stone and alkali-activated multi-source solid waste-based phase change thermal storage aggregate are mixed to obtain dry material. Water and polycarboxylate superplasticizer are mixed evenly to obtain mixed solution. The mixed solution is added to the dry material and mechanically stirred to obtain a mixture. The mixture is poured into a mold, vibrated to compact it, covered with plastic film for natural curing, and then demolded. The demolded specimen is then subjected to standard curing to obtain phase change thermal storage concrete.

[0027] Preferably, the specimens are first naturally cured at 20℃ and relative humidity ≥90% for 24 hours before demolding. After demolding, the specimens are transferred to a standard curing room (temperature (20±2)℃, relative humidity ≥95%) and continuously cured for 28 days to obtain phase change thermal storage concrete products with heat storage capacity.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention controls the mass fraction of the bottom ash in the thermal storage core layer, effectively increasing the porosity of the aggregate matrix and significantly improving the loading capacity of the phase change material while maintaining suitable mechanical properties. This results in a phase change thermal storage aggregate with a high latent heat value and suitable compressive strength. If the bottom ash content is too low, the pore-forming ability is weak, the loading capacity of the phase change material is low, and the latent heat value is low. If the bottom ash content is too high, the excessive porosity weakens the density and mechanical strength of the matrix, leading to a significant decrease in mechanical properties.

[0029] This invention, by controlling the mass fraction of blast furnace slag and sludge ash in the thermal storage core layer, fully utilizes the irregular and porous characteristics of sludge ash particles. During the alkali-activated reaction, it effectively enriches the pore space inside the aggregate by changing the particle packing density and its own properties, thereby significantly increasing the loading capacity of the phase change material. Simultaneously, the active components abundant in the sludge ash participate in the alkali-activated reaction and regulate the spatial distribution of the geopolymer products, effectively suppressing the mechanical strength reduction caused by structural shrinkage in the mid-to-late stages of the thermal storage aggregate, achieving a synergistic improvement in high latent heat of thermal storage and high cylinder compressive strength. If the sludge ash content is too low, its ability to regulate the microstructure of the aggregate is insufficient, thus failing to effectively suppress the mechanical strength reduction and failing to provide a sufficient loading carrier, resulting in limited thermal storage performance. If the sludge ash content is too high, the excessive porosity will significantly weaken the structural compactness of the aggregate matrix, leading to a significant decrease in cylinder compressive strength. Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating the preparation process of the alkali-activated multi-source solid waste-based phase change thermal storage aggregate obtained in Example 1 of the present invention. Figure 2 The image shows the pore volume distribution of the aggregate prepared in Example 1. Figure 3 The following are DSC curves of the alkali-activated multi-source solid waste-based phase change thermal storage aggregates prepared in Examples 1, 3, and 5; Figure 4 The XRD diffraction patterns are of the alkali-activated multi-source solid waste-based aggregate prepared in Comparative Example 9 and the alkali-activated multi-source solid waste-based aggregate containing bottom ash prepared in Example 1. Figure 5 Infrared spectra of the alkali-activated multi-source solid waste-based aggregate prepared in Comparative Example 9 and the alkali-activated multi-source solid waste-based aggregate containing bottom ash prepared in Example 1. Figure 6 The TG and DTG curves are shown for the alkali-activated multi-source solid waste-based aggregate prepared in Comparative Example 9 and the alkali-activated multi-source solid waste-based aggregate containing bottom ash prepared in Example 1. Figure 6 (a) is the TG curve. Figure 6 (b) is a DTG curve.

[0031] Figure 7 This is a flowchart illustrating the preparation process of the phase change concrete obtained in Example 7. Figure 8 Infrared thermal imaging comparison of phase change concrete samples prepared in Example 7 and Comparative Example 10. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It should be noted that the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0033] This invention proposes a method for preparing alkali-activated multi-source solid waste-based phase change thermal energy storage aggregate. It primarily utilizes blast furnace slag and sludge ash as alkali-activated precursors, sodium silicate solution as an alkali activator, and bottom ash as a pore-forming agent. Through alkali activation, a high-strength aggregate matrix is ​​constructed, effectively suppressing the reduction of aggregate mechanical strength. Simultaneously, the aeration effect of the bottom ash generates a microporous structure within the aggregate, significantly improving its thermal energy storage performance. Furthermore, coating the prepared aggregate surface with solid waste slurry further enhances its compatibility with cement-based materials and endows the aggregate with excellent mechanical properties and thermal energy storage capacity.

[0034] This invention designs a series of embodiments and comparative examples. By reasonably adjusting the ratio of blast furnace slag and sludge ash, optimizing the ratio of bottom ash and the modulus of sodium silicate solution, an alkali-activated multi-source solid waste-based phase change thermal storage aggregate with excellent thermal storage performance and good mechanical properties was successfully prepared.

[0035] Example 1 The alkali-activated multi-source solid waste-based phase change thermal storage aggregate prepared in this embodiment is composed of the following raw materials in parts by weight: 86.5 parts blast furnace slag, 20 parts sludge ash, 5 parts bottom ash, 31.9 parts sodium silicate solution, 26.6 parts water, and 0.5 parts polycarboxylate superplasticizer. The core layer of the thermal storage consists of the following raw materials: 80 parts blast furnace slag, 20 parts sludge ash, 5 parts bottom ash, 30 parts sodium silicate solution, 25 parts water, and 0.5 parts polycarboxylate superplasticizer; the coating layer slurry consists of 10 parts, composed of the following raw materials: 6.5 parts blast furnace slag, 1.9 parts sodium silicate solution, and 1.6 parts water. The specific steps of its preparation method are as follows: Figure 1 As shown, it includes: Step 1: Dry, grind and sieve the blast furnace slag, sludge ash and bottom ash used to prepare the thermal storage core layer and the blast furnace slag used to prepare the coating layer to obtain raw materials with the required particle size.

[0036] Step 2: Place the heat storage core layer material processed in Step 1 into a mixer and mix thoroughly to obtain a dry mixture.

[0037] Step 3: Prepare the ingredients according to the mass percentage of each raw material, and add sodium silicate solution, water and polycarboxylate superplasticizer of specified modulus and concentration, and stir to mix evenly to obtain a viscous slurry.

[0038] Step 4: After injecting the slurry into a 50 mm × 50 mm × 50 mm cube mold, vibrate it, then cover it with a film and pre-cur it at room temperature for 24 hours before finally demolding.

[0039] Step 5: After mechanical crushing, the pre-cured specimens are graded and screened to obtain coarse and fine aggregates respectively.

[0040] Step 6: Cur the crushed aggregate for 28 days; then place the aggregate in a vacuum device and evacuate it to -0.08MPa and maintain it for 2 hours. Then inject molten industrial paraffin until the aggregate is submerged. Then restore normal pressure to allow the industrial paraffin to fully impregnate the pores of the aggregate.

[0041] Step 7: Filter the aggregate prepared in step 6 to remove excess industrial paraffin wax from the surface.

[0042] Step 8: Immerse the impregnated and filtered aggregate into the coating slurry to make the slurry adhere evenly to its surface, so as to obtain aggregate with the coating slurry evenly coated on its surface; place the coated aggregate at room temperature to cure, so as to obtain the alkali-activated multi-source solid waste-based phase change heat storage aggregate, and then standard cure the aggregate for 90 days.

[0043] In step 1, the core layer raw materials must all pass through a 0.15 mm sieve after grinding.

[0044] In step 3, the concentration of the sodium silicate solution used is 44%.

[0045] In step 5, a natural stone crusher is used for crushing, and then the material is sieved through a 20 mm aperture sieve, a 4-mesh standard sieve, and an 8-mesh standard sieve in sequence to obtain fine aggregate with a particle size of 2.36~4.75 mm and coarse aggregate with a particle size of 4.75~20 mm, respectively.

[0046] In step 6, the molten industrial paraffin is heated and melted in a water bath at 50~70℃.

[0047] In step 6, after the molten industrial paraffin is injected into the vacuum device, the vacuum state is maintained for 0.5 hours and the device is intermittently shaken to ensure that the pores inside the aggregate are fully filled and to avoid air residue affecting the load-bearing effect of the phase change material.

[0048] The aforementioned alkali-activated multi-source solid waste-based phase change thermal storage aggregate can be impregnated with 18.7 parts of industrial paraffin, thereby effectively improving the thermal storage capacity of the thermal storage aggregate.

[0049] To quantitatively evaluate the effect of the modulus of the alkali activator, under the premise of a fixed ratio of raw materials in the aggregate core layer, the modulus of the sodium silicate solution was set into 11 experimental groups with a gradient of 0.1 from 1.5 to 2.5. The pore size distribution of the aggregate in each group was determined by mercury porosimetry to obtain the average pore size and pore structure parameters. The amount of phase change material impregnated was accurately calculated by vacuum impregnating molten industrial paraffin (60℃) and weighing the mass change of the aggregate before and after impregnation. Then, the impregnated aggregate was placed in a constant temperature environment of 70℃ for 3 hours, and the phase change material leaking from the outside of the aggregate was wiped with filter paper. The mass of the aggregate was re-weighed, and the leakage rate was calculated. The calculation results are shown in Table 1.

[0050] Table 1. Impregnation rate and leakage rate of phase change materials based on different modulus ratios. Note: (1) Impregnation ratio: refers to the percentage of the actual volume of phase change material loaded in a unit mass of aggregate to the theoretical volume of pores that can be filled inside the aggregate. The calculation formula is: Impregnation ratio = (V actual / V theoretical ) × 100%. Where, V actual V is the ratio of the mass difference of the aggregate before and after impregnation to the density of the phase change material; theoretical (1) Aggregate pore volume measured by mercury intrusion porosimetry; (2) Leakage rate: defined as the percentage of phase change leakage volume to the total volume of phase change material under actual load. The calculation formula is: Leakage rate = (V leakage / V actual ) × 100%. Where, V leakage It is the ratio of aggregate quality difference to the density of phase change material. In one embodiment, the environmental conditions are heating at 70°C for 3 hours.

[0051] Figure 2The test data, pore volume distribution diagram, and Table 1 illustrate that: when the proportion of pores larger than 100 nm in the aggregate decreases, the impregnation rate of the phase change material decreases; when the proportion of pores larger than 1000 nm increases, the leakage rate of the phase change material increases. Therefore, it can be concluded that pores smaller than 100 nm are difficult to impregnate and also difficult to leak; while pores larger than 1000 nm are easy to impregnate and also easy to leak. This suggests that the impregnation rate of the aggregate is mainly determined by pores larger than 100 nm, while the leakage rate is affected by pores larger than 1000 nm. Considering both impregnation rate and leakage rate, the higher the proportion of pores with a diameter between 100 nm and 1000 nm, the higher the impregnation rate and the lower the leakage rate. Therefore, a pore size of 100 nm to 1000 nm can be considered the optimal pore size. When the modulus of the alkali activator solution is 1.8-1.9, the impregnation rate of the phase change material in the prepared phase change energy storage aggregate is significantly higher than that of aggregates with a modulus of 2.0-2.5, but lower than that of aggregates with a modulus of 1.5-1.7. This is because the proportion of pores larger than 100 nm in aggregates with a modulus of 1.8-1.9 is lower than that in aggregates with a modulus of 1.5-1.7, but significantly higher than that in aggregates with a modulus of 2.0-2.5. Furthermore, the aggregates prepared with a modulus of 1.8-1.9 exhibit the lowest leakage rate, strictly controlled below 30%. This is due to the effective limitation of the proportion of pores larger than 1000 nm in the aggregates to below 6.0%, far lower than the corresponding values ​​of other phase change energy storage aggregates. Therefore, based on experimental test results, this embodiment of the invention preferably uses a sodium silicate solution with a modulus of 1.8-1.9 as the alkali activator to ensure the synergistic optimization of high impregnation rate and low leakage rate of the phase change material in the aggregate.

[0052] Example 2 Compared to Example 1, this example differs in that the prepared alkali-activated multi-source solid waste-based phase change thermal storage aggregate is composed of the following raw materials in parts by weight: 76.5 parts blast furnace slag, 30 parts sludge ash, 5 parts bottom ash, 31.9 parts sodium silicate solution, 26.6 parts water, and 0.5 parts polycarboxylate superplasticizer. The thermal storage core layer is composed of the following raw materials: 70 parts blast furnace slag, 30 parts sludge ash, 5 parts bottom ash, 30 parts sodium silicate solution, 25 parts water, and 0.5 parts polycarboxylate superplasticizer; the coating layer slurry comprises 10 parts, with the following raw material composition: 6.5 parts blast furnace slag, 1.9 parts sodium silicate solution, and 1.6 parts water. The thermal storage core layer can support 22.8 parts industrial paraffin wax.

[0053] Comparative Example 1 Compared to Example 1, this comparative example differs in that the prepared alkali-activated multi-source solid waste-based phase change thermal storage aggregate is composed of the following raw materials in parts by weight: 106.5 parts blast furnace slag, 5 parts bottom ash, 31.9 parts sodium silicate solution, 26.6 parts water, and 0.5 parts polycarboxylate superplasticizer. The thermal storage core layer is composed of the following raw materials: 100 parts blast furnace slag, 5 parts bottom ash, 30 parts sodium silicate solution, 25 parts water, and 0.5 parts polycarboxylate superplasticizer; the coating layer slurry comprises 10 parts, with the following raw material composition: 6.5 parts blast furnace slag, 1.9 parts sodium silicate solution, and 1.6 parts water. The thermal storage core layer can support 12.1 parts industrial paraffin wax.

[0054] Comparative Example 2 Compared to Example 1, this comparative example differs in that the prepared alkali-activated multi-source solid waste-based phase change thermal storage aggregate is composed of the following raw materials in parts by weight: 96.5 parts blast furnace slag, 10 parts sludge ash, 5 parts bottom ash, 31.9 parts sodium silicate solution, 26.6 parts water, and 0.5 parts polycarboxylate superplasticizer. The thermal storage core layer is composed of the following raw materials: 90 parts blast furnace slag, 10 parts sludge ash, 5 parts bottom ash, 30 parts sodium silicate solution, 25 parts water, and 0.5 parts polycarboxylate superplasticizer; the coating layer slurry consists of 10 parts, composed of the following raw materials: 6.5 parts blast furnace slag, 1.9 parts sodium silicate solution, and 1.6 parts water. The thermal storage core layer can support 16.8 parts industrial paraffin wax.

[0055] Comparative Example 3 Compared to Example 1, this comparative example differs in that the prepared alkali-activated multi-source solid waste-based phase change thermal storage aggregate is composed of the following raw materials in parts by weight: 66.5 parts blast furnace slag, 40 parts sludge ash, 5 parts bottom ash, 31.9 parts sodium silicate solution, 26.6 parts water, and 0.5 parts polycarboxylate superplasticizer. The thermal storage core layer is composed of the following raw materials: 60 parts blast furnace slag, 40 parts sludge ash, 5 parts bottom ash, 30 parts sodium silicate solution, 25 parts water, and 0.5 parts polycarboxylate superplasticizer; the coating layer slurry comprises 10 parts, with the following raw material composition: 6.5 parts blast furnace slag, 1.9 parts sodium silicate solution, and 1.6 parts water. The thermal storage core layer can support 29.4 parts industrial paraffin wax.

[0056] Comparative Example 4 Compared to Example 1, this comparative example differs in that the prepared alkali-activated multi-source solid waste-based phase change thermal storage aggregate is composed of the following raw materials in parts by weight: 56.5 parts blast furnace slag, 50 parts sludge ash, 5 parts bottom ash, 31.9 parts sodium silicate solution, 26.6 parts water, and 0.5 parts polycarboxylate superplasticizer. The thermal storage core layer is composed of the following raw materials: 50 parts blast furnace slag, 50 parts sludge ash, 5 parts bottom ash, 30 parts sodium silicate solution, 25 parts water, and 0.5 parts polycarboxylate superplasticizer; the coating layer slurry comprises 10 parts, with the following raw material composition: 6.5 parts blast furnace slag, 1.9 parts sodium silicate solution, and 1.6 parts water. The thermal storage core layer can support 40.8 parts industrial paraffin wax.

[0057] The alkali-activated multi-source solid waste-based phase change thermal energy storage aggregates cured to 28 days and 90 days in the above examples and comparative examples were subjected to cylinder compressive strength and thermal energy storage capacity tests. The cylinder compressive strength test was conducted according to the standard test method for lightweight aggregates (GB / T 17431.2-2010). The thermal energy storage aggregates at different ages were dried, then stacked in a pressure cylinder until flush with the cylinder opening. Finally, the pressure cylinder containing the aggregates was placed on a press for loading and cylinder compressive strength testing. Simultaneously, the thermal energy storage capacity of the aggregates was determined using differential scanning calorimetry. The performance results of the aggregate products from Examples 1-2 and Comparative Examples 1-4 are shown in Table 2.

[0058] Table 2. Compressive strength and thermal properties of thermal storage aggregates with different sludge-ash ratios Analysis of the data in Table 1 shows that Comparative Example 1, without sludge ash, exhibited a high compressive strength (18.6 MPa) at 28 days, but its strength dropped significantly to 9.2 MPa at 90 days, showing a significant strength reduction phenomenon. Comparative Example 6, with 10 parts of sludge ash, alleviated the reduction, but its strength at 90 days was still below 10 MPa. When the sludge ash content was increased to 20 parts (Example 1) and 30 parts (Example 2), the compressive strength at 28 days and 90 days stabilized at 12.7 MPa / 13.2 MPa and 11.2 MPa / 12.4 MPa, respectively, without any reduction in mechanical strength. With the increase of sludge ash content, the strength at each age in Comparative Examples 7 and 8 dropped sharply to below 6.2 MPa. In terms of thermal properties, the latent heat value increased with the increase of sludge ash content, from 13.6 J / g in Comparative Example 1 to 24.1 J / g in Example 7, and even reached 39.5 J / g in Comparative Example 8.

[0059] Therefore, sludge ash plays a dual role in slag-based alkali-activated phase change thermal storage aggregates. On the one hand, the introduction of an appropriate amount of sludge ash can regulate the reaction composition and pore structure of the slag alkali-activated system, improving the structural stability of the system during long-term curing, thereby effectively mitigating or inhibiting the phenomenon of mechanical strength reduction. On the other hand, the incorporation of sludge ash makes the cement matrix structure relatively loose and porous, which is beneficial to improving the adsorption and loading capacity of the thermal storage core layer for phase change materials, thus significantly improving the latent heat value and thermal regulation performance of the thermal storage aggregate. However, when the sludge ash content exceeds a reasonable range, due to the relative insufficiency of its active components and the increase in the proportion of inert components, it easily weakens the continuity and compactness of the slag alkali-activated reaction, leading to a loose cementitious structure and increased porosity, which in turn causes a significant decrease in the mechanical properties of the thermal storage aggregate. Therefore, the sludge ash content needs to be controlled within a reasonable range to fully exert its role in improving thermal storage performance while ensuring mechanical properties.

[0060] Considering practical application environments, to ensure that the aggregate maintains high mechanical properties during production, transportation, and use, its compressive strength should not be less than 10 MPa. Simultaneously, to achieve effective heat storage and release, the latent heat value should be higher than 20 J / g to meet the heat storage requirements of most scenarios. Therefore, by balancing comprehensive mechanical properties and heat storage performance, when the amount of bottom ash is controlled between 5 and 15 parts, the aggregate not only possesses sufficient compressive strength but also a high latent heat value, exhibiting optimal comprehensive performance and suitable for large-scale application.

[0061] Therefore, the results show that when the sludge ash content is 20-30 parts, the prepared alkali-activated multi-source solid waste-based phase change thermal storage aggregate meets the optimal performance requirements.

[0062] To fully demonstrate the impact of the aeration and pore-forming mechanism of the bottom ash in the alkali-activated cementitious system on thermal storage aggregates, the following examples and comparative examples are provided.

[0063] Example 3 Unlike Example 1, the alkali-activated multi-source solid waste-based phase change thermal storage aggregate prepared in this example is composed of the following raw materials in parts by weight: 86.5 parts blast furnace slag, 20 parts sludge ash, 10 parts bottom ash, 31.9 parts sodium silicate solution, 26.6 parts water, and 0.5 parts polycarboxylate superplasticizer. The thermal storage core layer is composed of the following raw materials: 80 parts blast furnace slag, 20 parts sludge ash, 10 parts bottom ash, 30 parts sodium silicate solution, 25 parts water, and 0.5 parts polycarboxylate superplasticizer. The coating layer slurry consists of 10 parts, composed of the following raw materials: 6.5 parts blast furnace slag, 1.9 parts sodium silicate solution, and 1.6 parts water. The thermal storage core layer can support 23.2 parts industrial paraffin wax.

[0064] Example 4 Unlike Example 1, the alkali-activated multi-source solid waste-based phase change thermal storage aggregate prepared in this example is composed of the following raw materials in parts by weight: 76.5 parts blast furnace slag, 30 parts sludge ash, 10 parts bottom ash, 31.9 parts sodium silicate solution, 26.6 parts water, and 0.5 parts polycarboxylate superplasticizer. The thermal storage core layer is composed of the following raw materials: 70 parts blast furnace slag, 30 parts sludge ash, 10 parts bottom ash, 30 parts sodium silicate solution, 25 parts water, and 0.5 parts polycarboxylate superplasticizer. The coating layer slurry consists of 10 parts, composed of the following raw materials: 6.5 parts blast furnace slag, 1.9 parts sodium silicate solution, and 1.6 parts water. The thermal storage core layer can support 27.0 parts industrial paraffin wax.

[0065] Example 5 Unlike Example 1, the alkali-activated multi-source solid waste-based phase change thermal storage aggregate prepared in this example is composed of the following raw materials in parts by weight: 86.5 parts blast furnace slag, 20 parts sludge ash, 15 parts bottom ash, 31.9 parts sodium silicate solution, 26.6 parts water, and 0.5 parts polycarboxylate superplasticizer. The thermal storage core layer is composed of the following raw materials: 80 parts blast furnace slag, 20 parts sludge ash, 15 parts bottom ash, 30 parts sodium silicate solution, 25 parts water, and 0.5 parts polycarboxylate superplasticizer. The coating layer slurry consists of 10 parts, composed of the following raw materials: 6.5 parts blast furnace slag, 1.9 parts sodium silicate solution, and 1.6 parts water. The thermal storage core layer can support 27.9 parts industrial paraffin wax.

[0066] Example 6 Unlike Example 1, the alkali-activated multi-source solid waste-based phase change thermal storage aggregate prepared in this example is composed of the following raw materials in parts by weight: 76.5 parts blast furnace slag, 30 parts sludge ash, 15 parts bottom ash, 31.9 parts sodium silicate solution, 26.6 parts water, and 0.5 parts polycarboxylate superplasticizer. The thermal storage core layer is composed of the following raw materials: 70 parts blast furnace slag, 30 parts sludge ash, 15 parts bottom ash, 30 parts sodium silicate solution, 25 parts water, and 0.5 parts polycarboxylate superplasticizer. The coating layer slurry consists of 10 parts, composed of the following raw materials: 6.5 parts blast furnace slag, 1.9 parts sodium silicate solution, and 1.6 parts water. The thermal storage core layer can support 32.5 parts industrial paraffin wax.

[0067] Comparative Example 5 Unlike Example 1, the alkali-activated multi-source solid waste-based phase change thermal storage aggregate prepared in this comparative example is composed of the following raw materials in parts by weight: 86.5 parts blast furnace slag, 20 parts sludge ash, 3 parts bottom ash, 31.9 parts sodium silicate solution, 26.6 parts water, and 0.5 parts polycarboxylate superplasticizer. The thermal storage core layer is composed of the following raw materials: 80 parts blast furnace slag, 20 parts sludge ash, 3 parts bottom ash, 30 parts sodium silicate solution, 25 parts water, and 0.5 parts polycarboxylate superplasticizer. The coating layer slurry consists of 10 parts, composed of the following raw materials: 6.5 parts blast furnace slag, 1.9 parts sodium silicate solution, and 1.6 parts water. The thermal storage core layer can support 14.8 parts industrial paraffin wax.

[0068] Comparative Example 6 Unlike Example 1, the alkali-activated multi-source solid waste-based phase change thermal storage aggregate prepared in this comparative example is composed of the following raw materials in parts by weight: 76.5 parts blast furnace slag, 30 parts sludge ash, 3 parts bottom ash, 31.9 parts sodium silicate solution, 26.6 parts water, and 0.5 parts polycarboxylate superplasticizer. The thermal storage core layer is composed of the following raw materials: 70 parts blast furnace slag, 30 parts sludge ash, 15 parts bottom ash, 30 parts sodium silicate solution, 25 parts water, and 0.5 parts polycarboxylate superplasticizer. The coating layer slurry consists of 10 parts, composed of the following raw materials: 6.5 parts blast furnace slag, 1.9 parts sodium silicate solution, and 1.6 parts water. The thermal storage core layer can support 17.7 parts industrial paraffin wax.

[0069] Comparative Example 7 Unlike Example 1, the alkali-activated multi-source solid waste-based phase change thermal storage aggregate prepared in this comparative example is composed of the following raw materials in parts by weight: 86.5 parts blast furnace slag, 20 parts sludge ash, 20 parts bottom ash, 31.9 parts sodium silicate solution, 26.6 parts water, and 0.5 parts polycarboxylate superplasticizer. The thermal storage core layer is composed of the following raw materials: 80 parts blast furnace slag, 20 parts sludge ash, 20 parts bottom ash, 30 parts sodium silicate solution, 25 parts water, and 0.5 parts polycarboxylate superplasticizer. The coating layer slurry consists of 10 parts, composed of the following raw materials: 6.5 parts blast furnace slag, 1.9 parts sodium silicate solution, and 1.6 parts water. The thermal storage core layer can support 36.5 parts industrial paraffin wax.

[0070] Comparative Example 8 Unlike Example 1, the alkali-activated multi-source solid waste-based phase change thermal storage aggregate prepared in this comparative example is composed of the following raw materials in parts by weight: 76.5 parts blast furnace slag, 30 parts sludge ash, 20 parts bottom ash, 31.9 parts sodium silicate solution, 26.6 parts water, and 0.5 parts polycarboxylate superplasticizer. The thermal storage core layer is composed of the following raw materials: 70 parts blast furnace slag, 30 parts sludge ash, 15 parts bottom ash, 30 parts sodium silicate solution, 25 parts water, and 0.5 parts polycarboxylate superplasticizer; the coating layer slurry consists of 10 parts, composed of the following raw materials: 6.5 parts blast furnace slag, 1.9 parts sodium silicate solution, and 1.6 parts water. The thermal storage core layer can support 43.0 parts industrial paraffin wax.

[0071] The alkali-activated multi-source solid waste-based phase change thermal storage aggregate prepared by this invention has the advantages of excellent mechanical properties, good thermal storage capacity, and strong shaping ability. Therefore, the compressive strength and thermal storage capacity of the alkali-activated multi-source solid waste-based phase change thermal storage aggregate finished products cured to 28 days and 90 days in the above embodiments and comparative examples were tested. The performance results of the thermal storage aggregate are shown in Table 3.

[0072] Table 3. Compressive strength and thermal properties of thermal storage aggregates in the examples and comparative examples. Table 3 shows that the thermal storage aggregate prepared by this invention achieves a good balance between thermal storage capacity and mechanical strength. Experimental data indicate that the latent heat value of the aggregate exhibits a certain negative correlation with its cylinder compressive strength. This is mainly because the increased content of bottom ash and sludge ash increases the porosity inside the aggregate, thereby providing more loading space for the phase change material. Taking Examples 1, 3, and 5 as examples, when the amount of sludge ash is constant, as the amount of bottom ash increases from 5 parts to 15 parts, the loading capacity of the aggregate for industrial paraffin wax significantly increases, and the latent heat value increases from 20.2 J / g to 27.4 J / g (see Table 3). Figure 3Although the 90-day compressive strength decreased slightly from 13.2 MPa to 11.3 MPa, it still maintained high mechanical properties. In contrast, Comparative Examples 5 and 6, due to their lower bottom ash content (3 parts), although slightly higher in strength, had latent heat values ​​of only 16.5 J / g and 19.4 J / g, respectively, indicating insufficient heat storage capacity. Comparative Examples 7 and 8, while having higher latent heat values, saw their 90-day compressive strength decrease to 8.7 MPa and 6.6 MPa, respectively, resulting in significant mechanical property loss and making it difficult to meet engineering structural requirements. Furthermore, with increasing age, the compressive strength of the heat storage aggregates prepared in all examples and comparative examples increased to varying degrees, demonstrating that incorporating sludge ash into the slag-based alkali-activated cementitious system can indeed suppress the decline in mechanical strength. In summary, when the sludge ash content is within the preferred range of 20-30 parts and the bottom ash content is within the preferred range of 5-15 parts, the prepared alkali-activated multi-source solid waste-based phase change heat storage aggregate can achieve efficient synergy between mechanical properties and heat storage capacity. This proportioning range effectively balances the contradiction between the internal porosity of the aggregate and the strength of the cementitious matrix, ensuring that the thermal storage aggregate has a good latent heat of phase change value while possessing high compressive strength, thus meeting the application requirements of integrated structure and function.

[0073] By preparing alkali-activated multi-source solid waste-based aggregates, the influence of bottom ash on the formation and evolution of aggregate hydration products was analyzed from a microscopic level.

[0074] Comparative Example 9 The alkali-activated multi-source solid waste-based aggregate prepared in this comparative example consists of the following raw materials in parts by weight: 80 parts blast furnace slag, 20 parts sludge ash, 30 parts sodium silicate solution, 25 parts water, and 0.5 parts polycarboxylate superplasticizer. The aggregate prepared is intended to serve as a carrier for the core layer of impregnated phase change material thermal storage. The specific steps of its preparation are as follows: Step 1: Dry, grind and sieve the blast furnace slag and sludge bottom ash used to prepare the thermal storage core layer to obtain raw materials with the required particle size; Step 2: Place the processed material in a mixer and mix thoroughly to obtain a dry mixture; Step 3: Prepare the ingredients according to the mass percentage of each raw material, and add sodium silicate solution with a modulus of 1.8 and a concentration of 44.4%, water and polycarboxylate superplasticizer. Stir and mix evenly to obtain a viscous slurry. Step 4: After injecting the slurry into a 50 mm × 50 mm × 50 mm cubic mold, vibrate it, then cover it with a film and pre-cur it at room temperature for 24 hours before finally demolding. Step 5: After mechanical crushing, the pre-cured specimens are graded and sieved to obtain coarse and fine aggregates respectively; Step 6: Cur the crushed aggregate according to standard for 28 days to obtain alkali-activated multi-source solid waste-based aggregate.

[0075] The effects of bottom ash incorporation on the hydration products of alkali-activated multi-source solid waste-based aggregates were analyzed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TG-DTG). Based on XRD diffraction patterns... Figure 4 Analysis showed that the hydration products of the alkali-activated multi-source solid waste-based aggregate prepared in Comparative Example 9 without the addition of base ash were mainly calcium aluminosilicate gel hydrate. However, with the addition of base ash, no other characteristic peaks appeared in the alkali-activated multi-source solid waste-based aggregate prepared in Example 1 containing base ash, indicating that the introduction of base ash did not change the type of hydration products. FTIR spectroscopy analysis (…) Figure 5 This further demonstrates that the shape and intensity of the absorption peaks remained highly consistent before and after the addition of the base ash, proving that the base ash did not trigger any new chemical reactions or form a new phase. TG-DTG curve ( Figure 6 This provides further evidence from the perspective of thermal decomposition characteristics: the addition of the bottom ash does not affect the mass loss stage of the aggregate and the corresponding temperature range basically overlaps, and there is no significant difference in thermal decomposition behavior, which further confirms that the addition of the bottom ash has no substantial impact on the chemical composition and thermal stability of the hydration products.

[0076] To verify the applicability of the alkali-activated multi-source solid waste-based phase change thermal storage aggregate prepared in this invention in practical engineering, phase change thermal storage concrete was prepared using the alkali-activated multi-source solid waste-based phase change thermal storage aggregates prepared in Examples 1, 3, and 4, and the performance was compared. Referring to the concrete design mix proportion (mass ratio of cement:sand:crushed stone:water:polycarboxylate superplasticizer 400:600:1200:200:1), the solid waste-derived thermal storage aggregate replaced the sand, and after standard curing for 28 days, its compressive strength was measured.

[0077] Example 7 This embodiment provides a method for preparing phase change concrete, such as... Figure 7 The above includes: S1: Weigh the following raw materials according to the mass percentages: 400 parts of ordinary silicate cement, 500 parts of sand, 1200 parts of crushed stone, 100 parts of alkali-activated multi-source solid waste-based phase change thermal storage aggregate prepared in Example 1, 200 parts of water, and 1 part of polycarboxylate superplasticizer. S2: First, thoroughly mix water and polycarboxylate superplasticizer. Then, inject the solution into the uniformly mixed dry material and mechanically stir until the mixture reaches a homogeneous state, is free of lumps and particles, and has suitable workability. Subsequently, pour the mixture into a cubic mold with dimensions of 150 mm × 150 mm × 150 mm, place it on a vibrating table for vibration compaction, scrape off excess slurry from the surface, and cover with plastic film for curing. S3: First, the specimens are naturally cured at 20℃ and relative humidity ≥90% for 24 hours before demolding. After demolding, the specimens are transferred to a standard curing room (temperature (20±2)℃, relative humidity ≥95%) and continuously cured for 28 days to obtain phase change heat storage concrete with heat storage capacity.

[0078] Example 8 The difference from Example 7 is that the thermal storage aggregate was prepared in Example 3.

[0079] Example 9 The difference from Example 7 is that the thermal storage aggregate was prepared in Example 5.

[0080] Comparative Example 9 Phase change concrete disclosed in publication number CN110577386A.

[0081] Comparative Example 10 Unlike Example 7, the raw materials used in this comparative example include: 400 parts of ordinary silicate cement, 600 parts of sand, 1200 parts of crushed stone, 200 parts of water, and 1 part of polycarboxylate superplasticizer.

[0082] To evaluate the practical application effect of the alkali-activated multi-source solid waste-based phase change thermal storage aggregate prepared in this invention in concrete, mechanical properties of phase change thermal storage concrete specimens prepared in Examples 7-9 and Comparative Examples 9-10 were tested. All concrete specimens were molded according to standard methods and cured under standard curing conditions for 28 days. The compressive strength of the concrete was determined in accordance with the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T 50081-2019), as shown in Table 4.

[0083] Table 4. Concrete compressive strength of Examples 7-9 and Comparative Examples 9-10 The data show that the phase change thermal storage concrete incorporating alkali-activated multi-source solid waste-based phase change thermal storage aggregates prepared in different proportions according to this invention exhibits compressive strengths between 42.1 MPa and 45.2 MPa, demonstrating good overall mechanical properties. Notably, as the compressive strength of the incorporated phase change thermal storage aggregates decreases, the compressive strength of the concrete shows a slight decreasing trend, indicating that the mechanical properties of the thermal storage aggregates have a certain influence on the overall strength of the concrete. Furthermore, the strengths of the concrete are all higher than those of Comparative Examples 8 and 9, demonstrating that the phase change thermal storage concrete prepared according to this invention can meet practical engineering requirements while also providing thermal storage capacity.

[0084] Meanwhile, the heat storage capacity of phase change thermal storage concrete was observed using infrared thermal imaging analysis. The specific operating steps are as follows: The specimens of Example 7 and Comparative Example 10 were placed in a constant temperature chamber at 50°C for 2 hours to allow them to fully absorb heat energy and reach thermal equilibrium. Subsequently, the specimens were removed and placed in a room with a temperature of 15°C, and the cooling status of the specimens was recorded using an infrared thermal imager. The surface temperature changes of the specimens of Example 7 and Comparative Example 10 are shown in Table 5. Figure 8 Initially, the temperature distributions of both specimens were similar, but as time progressed, the temperature of specimen 10 decreased significantly faster, indicating rapid heat loss. Conversely, the color change of specimen 7 was slower, indicating a slower temperature decrease and less heat loss. This demonstrates that phase change thermal storage concrete, due to the internal phase change material, significantly delays heat release and possesses relatively good thermal storage capacity.

[0085] Table 5. Average surface temperature at different times for Examples 7 and Comparative Example 10 The present invention provides an alkali-activated multi-source solid waste-based phase change thermal storage aggregate, its preparation, and its application. By rationally utilizing industrial solid waste, it produces thermal storage aggregate with excellent thermal storage performance, achieving efficient resource recycling. Its core beneficial effects are reflected in the following aspects: 1. Except for the phase change material, all raw materials used in this invention are derived from industrial or municipal solid waste. Blast furnace slag and sludge ash serve as precursors for alkali-activated cementitious materials, while bottom ash acts as a pore-forming agent. Through a rational proportioning design, these three wastes with different properties are transformed into the basic framework of functional thermal storage aggregates. This solution not only provides an effective disposal method, reducing landfill pressure and potential environmental risks, but also achieves efficient and synergistic resource utilization of multiple solid wastes, resulting in significant environmental benefits.

[0086] 2. This invention introduces sludge ash into the slag alkali activation system, which effectively stabilizes the microstructure of the cementitious material through its unique physicochemical properties. This fundamentally suppresses the problem of mechanical strength reduction in alkali-activated materials, ensuring the long-term durability of the material while realizing the high-value utilization of solid waste, thus forming a high-performance, high-stability phase change thermal storage aggregate.

[0087] 3. This invention utilizes the active substances such as metallic aluminum (Al) and aluminum silicide contained in the base aggregate. During the reaction process, these substances undergo a redox reaction with the alkaline environment provided by sodium silicate, continuously releasing gases such as hydrogen, which serve as the source of pore formation. This pore-forming method originates from the internal reaction of the material system, eliminating the need for external pore-forming agents. This avoids problems such as uneven distribution and poor stability, ensuring that the final thermal storage aggregate forms a large number of uniformly distributed pores with a good pore structure.

[0088] 4. This invention uses sodium silicate solution as an alkaline activator, which can effectively activate the potential activity of blast furnace slag and sludge ash. Through the "dissolution-coagulation-condensation" reaction, an alkaline activated cementitious material with a three-dimensional network structure is formed, providing a strong skeleton and matrix strength for the aggregate; at the same time, it provides the necessary alkaline environment for the aeration and pore-forming process, promoting gas generation.

[0089] 5. This invention optimizes the design of aggregate porosity and pore size by adjusting the amount of base ash, thereby affecting the amount of gas generated. The pore structure directly affects the load-bearing capacity of industrial paraffin, resulting in aggregate products that maintain good mechanical strength while also possessing excellent thermophysical properties.

[0090] 6. This invention employs a process of crushing aggregates after one day of pre-curing, which fully utilizes the characteristic of low early-stage strength of the aggregates and significantly reduces energy consumption and equipment wear during the crushing process. This approach not only significantly reduces production costs and improves processing efficiency but also reduces carbon emissions, further enhancing its comprehensive advantages in energy conservation, emission reduction, and green manufacturing.

[0091] 7. The thermal storage aggregate prepared by this invention has a dense alkali-activated geopolymer coating layer that completely encapsulates the thermal storage core. The hydration products of the coating layer slurry are mainly hydrated aluminosilicate gel, which has good compatibility with cement-based materials. When applied to cement-based materials, it can effectively improve the overall stability of the composite material, while blocking the erosion of the phase change material by the external environment, enhancing durability, and ensuring the stability of its thermal storage performance during long-term service.

[0092] 8. The alkali-activated multi-source solid waste-based phase change thermal storage aggregate prepared by this invention can be applied to cement-based materials to prepare phase change thermal storage concrete, imparting thermal energy storage capacity to the material while ensuring that the mechanical properties of the concrete are not affected. This technology uses industrial solid waste as raw material, which not only improves thermal storage efficiency but also promotes resource recycling, achieving a dual optimization of environmental benefits and performance.

[0093] 9. This invention optimizes the pore size of the bottom ash aeration pore structure by preferably controlling the modulus of the alkali activator solution to 1.8~1.9, resulting in a pore size of 100 nm~1000 nm being the most optimal. This significantly improves the impregnation efficiency of the phase change material while ensuring excellent aggregate mechanical properties, and synergistically enhances the ability to prevent phase change material leakage.

[0094] Therefore, the alkali-activated multi-source solid waste-based phase change thermal energy storage aggregate developed in this invention exhibits excellent comprehensive performance in terms of both mechanical properties and thermal energy storage capacity. This aggregate uses various industrial solid wastes as raw materials, which not only realizes the high-value utilization of solid waste resources but also significantly reduces production costs, aligning with the concept of green and sustainable development and laying a solid foundation for its widespread application in practical engineering projects.

[0095] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the invention. The scope of the invention is defined by the appended claims and their equivalents.

Claims

1. An alkali-activated multi-source solid waste-based phase change thermal storage aggregate, characterized in that, The thermal storage aggregate comprises, from the inside out, a thermal storage core layer and a wrapping layer; The thermal storage core layer is composed of a porous alkali-activated geopolymer matrix and a phase change material loaded in the pores of the alkali-activated geopolymer matrix. The mass fractions of each raw material in the heat storage core layer are as follows: 70-80 parts blast furnace slag, 20-30 parts sludge ash, 5-15 parts bottom ash, 25-35 parts sodium silicate solution, 18-35 parts phase change material, 20-30 parts water and 0.5-1 parts polycarboxylate superplasticizer. The encapsulation layer is a dense alkali-activated geopolymer layer, which encapsulates the thermal storage core layer.

2. The alkali-activated multi-source solid waste-based phase change thermal storage aggregate according to claim 1, characterized in that, The modulus of the sodium silicate solution is 1.5-2.

5.

3. The alkali-activated multi-source solid waste-based phase change thermal storage aggregate according to claim 2, characterized in that, The modulus of the sodium silicate solution is 1.8-1.

9.

4. The alkali-activated multi-source solid waste-based phase change thermal storage aggregate according to claim 1 or 3, characterized in that, The alkali-activated geopolymer matrix has a pore size of 100 nm to 1000 nm, and the volume percentage of the pores is 77.9% to 88.2%.

5. The alkali-activated multi-source solid waste-based phase change thermal storage aggregate according to claim 1, characterized in that, The mass fractions of each raw material in the coating layer are: 6-7 parts blast furnace slag, 1.5-2 parts sodium silicate solution, and 1.5-2 parts water.

6. The alkali-activated multi-source solid waste-based phase change thermal storage aggregate according to claim 1, characterized in that, The phase change material is industrial paraffin.

7. The alkali-activated multi-source solid waste-based phase change thermal storage aggregate according to claim 1, characterized in that, The compressive strength of the thermal storage aggregate is 10.8~13.2 MPa, and the latent heat of phase change is 20.2~31.2 J / g.

8. A method for preparing alkali-activated multi-source solid waste-based phase change thermal storage aggregate according to any one of claims 1-7, characterized in that, include: (1) Dry, grind and sieve the blast furnace slag, sludge ash and bottom ash; (2) According to the proportion of each raw material in the heat storage core layer, the blast furnace slag, sludge ash and bottom ash after sieving in step (1) are mixed to obtain a dry mixture. The dry mixture, sodium silicate solution, water and polycarboxylate superplasticizer are stirred and mixed evenly to obtain a slurry. (3) After the slurry is injected into the mold, it is crushed, pre-cured and demolded, then mechanically crushed and graded to obtain coarse and fine aggregates. (4) Perform standard curing and vacuuming on the aggregate from step (3), then inject molten phase change material until the aggregate is submerged, and restore normal pressure; (5) Filter the aggregate obtained in step (4) to remove excess phase change material from the surface; (6) Immerse the aggregate obtained in step (5) into the coating slurry and cure at room temperature to obtain alkali-activated multi-source solid waste-based phase change thermal storage aggregate.

9. The method for preparing alkali-activated multi-source solid waste-based phase change thermal storage aggregate according to claim 8, characterized in that, According to the proportions of each raw material in the coating layer, the sieved blast furnace slag is added to sodium silicate solution and water to obtain the coating layer slurry; The mass fractions of each raw material in the coating layer are: 6-7 parts blast furnace slag, 1.5-2 parts sodium silicate solution, and 1.5-2 parts water.

10. A method for preparing phase change thermal storage concrete, characterized in that, include: S1. The raw materials are prepared according to the following mass proportions, including: 200-400 parts of ordinary Portland cement, 300-600 parts of sand, 500-1200 parts of crushed stone, 100-200 parts of alkali-activated multi-source solid waste-based phase change thermal storage aggregate according to any one of claims 1-9, 100-200 parts of water and 0.5-1 parts of polycarboxylate superplasticizer; S2. The ordinary silicate cement, sand, crushed stone and alkali-activated multi-source solid waste-based phase change thermal storage aggregate are mixed to obtain dry material. Water and polycarboxylate superplasticizer are mixed evenly to obtain mixed solution. The mixed solution is added to the dry material and mechanically stirred to obtain a mixture. The mixture is poured into a mold, vibrated to compact it, covered with plastic film for natural curing, and then demolded. The demolded specimen is then subjected to standard curing to obtain phase change thermal storage concrete.

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