Green porous concrete building material and preparation method thereof

Abstract

The invention belongs to the field of building materials, and provides a green porous concrete building material and a preparation method thereof. According to the preparation method, a core-shell modified recycled coarse aggregate and low-water-binder-ratio gelling system collaborative design is adopted, a recycled coarse aggregate core-mineralized shell-silane layer three-dimensional core-shell structure is constructed through a mineralized shell layer-silane layer double-layer interface regulation and control technology, and synchronous improvement of surface hydrophobicity water absorption and reduction and interface bonding strength is achieved; through the optimal proportion of general-purpose Portland cement and a mineral admixture, the balance between the fluidity and the forming stability of a mixture is realized under the condition that the water-binder ratio is 0.22-0.30; the technical problems that high communication porosity and high bearing strength of existing porous concrete are difficult to consider at the same time, low-water-binder-ratio mixing stability and long-term water invasion and freeze thawing resistance durability are mutually held, and mechanism-mechanism conflicts exist between surface hydrophobicity and water absorption reduction of core-shell modified recycled coarse aggregate and interface bonding load transmission efficiency are solved. And wide application values of green buildings and sponge cities are realized.

Description

Technical Field

[0001] This invention relates to the field of building materials, specifically to a green porous concrete building material and its preparation method. Background Technology

[0002] With the rapid development of sponge city construction and green building technology, porous concrete, as a new type of building material with multiple functions such as water permeability, air permeability, noise reduction, and temperature regulation, has shown great application potential in urban road paving, ecological slope protection, roof greening, and rainwater management systems. The core function of porous concrete relies on its internal continuous and interconnected pore network structure, which needs to meet multi-level performance requirements: On the one hand, high interconnected porosity is key to achieving rapid water permeability and drainage, effectively reducing surface runoff, and promoting rainwater infiltration and groundwater replenishment. Typically, a continuous porosity of 15-28% is required to ensure that the permeability coefficient meets urban drainage standards. On the other hand, as a load-bearing structural material, porous concrete must have sufficient compressive strength and flexural stiffness to withstand vehicle loads, pedestrian traffic, and environmental stresses. This requires the material to maintain effective bonding and stress transfer between aggregate particles even under high porosity conditions. Furthermore, in actual service environments, porous concrete is exposed to complex conditions such as rainwater immersion, freeze-thaw cycles, and chloride erosion, placing stringent demands on the material's long-term durability, including resistance to water erosion, freeze-thaw spalling, and sulfate erosion. Meeting and coordinating these multi-dimensional performance requirements is of great significance for broadening the application scope of porous concrete in complex scenarios such as frigid regions, coastal environments, and heavy-duty transportation, and for promoting the high-quality construction of sponge city infrastructure.

[0003] However, the development of porous concrete technology still faces three core shortcomings. First, there is an inherent contradiction between high interconnected porosity and high load-bearing strength: traditional porous concrete constructs a pore network by reducing or eliminating the use of fine aggregates and reducing the amount of cement paste, but this inevitably leads to a reduction in the contact points of aggregate particles and a weakening of the bonding interface. When the continuous porosity increases to more than 25%, the compressive strength is often lower than 15MPa, which is difficult to meet the load requirements of municipal roads. For example, Chinese patent CN118754545A discloses a permeable concrete, which achieves a high porosity, but its strength is still limited by the inherent limitations of the aggregate stacking method. Secondly, the stability of the mixture under low water-cement ratio conditions and its long-term resistance to water erosion and freeze-thaw durability are mutually constrained: to improve strength, the water-cement ratio needs to be reduced to below 0.25, but a low water-cement ratio leads to poor fluidity of the mixture, difficulty in vibration compaction, and uneven pore distribution. At the same time, the weak pore interfaces formed by insufficient cement hydration are prone to cracking and peeling during freeze-thaw cycles. For example, Chinese patent CN107601995A discloses a method for preparing high-strength lightweight porous concrete, but it fails to fundamentally solve the problem of synergistic optimization between molding processability and freeze-thaw durability. Third, when recycled coarse aggregate is used to replace natural aggregate to reduce environmental impact, the surface of recycled coarse aggregate is covered with old mortar, resulting in a water absorption rate as high as 5-8%, far exceeding the 1-2% of natural aggregate. To reduce water absorption, water-repellent agents such as silane are often used to treat the surface. However, while water-repellent modification reduces water absorption, it also significantly weakens the interfacial bond strength between aggregate and cement paste, leading to a decrease in load transfer efficiency and a deterioration in the overall strength and toughness of composite materials. This mechanistic conflict between water-repellent reduction of water absorption and interfacial bonding has not yet been effectively resolved. Summary of the Invention

[0004] The purpose of this invention is to provide a green porous concrete building material and its preparation method, which solves the technical pain points of current porous concrete, such as the difficulty in achieving both high interconnected porosity and high load-bearing strength, the mutual constraint between mixing and molding stability and long-term resistance to water erosion and freeze-thaw durability under low water-cement ratio conditions, and the mechanistic conflict between the surface hydrophobicity and water absorption reduction of core-shell modified recycled coarse aggregate and the interfacial bonding load transfer efficiency.

[0005] This invention adopts the technical approach of "mineralized shell layer strengthening interface - silane layer hydrophobic regulation - low water-cement ratio cementitious system synergistic enhancement". By constructing a dual-layer functional interface of mineralized shell layer and silane layer in situ on the surface of recycled coarse aggregate, it achieves synergistic improvement in water absorption, interfacial bonding, and stress transfer optimization. By optimizing the proportion of general silicate cement and mineral admixtures, the fluidity and workability of the mixture are improved while ensuring a low water-cement ratio (0.22-0.30). By precisely controlling the pore structure distribution through vibration compaction process, a gradient pore system with a continuous porosity of 15-28% and a dominant pore size of 1-6mm is obtained. This achieves comprehensive synergistic optimization of the permeability and drainage performance, load-bearing mechanical properties, and long-term durability of porous concrete, resulting in a comprehensive performance improvement effect that is difficult to achieve with a single modification method.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A green porous concrete building material, based on the design volume of each cubic meter of concrete mixture, comprises: 300-410 kg of cementitious material, 90-123 kg of water, and 1100-1550 kg of coarse aggregate, wherein the mass ratio of water to the cementitious material is 0.22-0.30; wherein: The coarse aggregate includes core-shell modified recycled coarse aggregate; The core-shell modified recycled coarse aggregate includes a recycled coarse aggregate core, a mineralized shell layer covering the surface of the recycled coarse aggregate core, and a silane layer covering the surface of the mineralized shell layer. The thickness of the mineralized shell is 5-50 μm; The silane layer is formed of 3-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane; The cementitious material includes general-purpose silicate cement and one or more mineral admixtures. Based on 100 parts by weight of the cementitious material, the amount of general-purpose silicate cement is 20-60 parts by weight, the amount of mineral admixtures is 40-80 parts by weight, and the amount of general-purpose silicate cement is 20-60 parts by weight, with the amount of mineral admixtures being the remainder after subtracting the weight of general-purpose silicate cement from 100 parts by weight. The continuous porosity of the green porous concrete building material was determined to be 15-28% by the vacuum saturation-drainage method.

[0007] Furthermore, the core-shell modified recycled coarse aggregate is prepared through the following steps: A1. The raw materials include recycled coarse aggregate, water, sodium silicate, and calcium hydroxide; A2. Pretreatment of recycled coarse aggregate: The recycled coarse aggregate is washed and dehydrated at a water-to-dry basis mass ratio of 0.5-3.0. The washing is carried out by mechanical stirring at a temperature of 20-25℃ for 2-10 min. The dehydration is carried out by filtration and separation followed by drying at a temperature of 40-80℃ to obtain pretreated recycled coarse aggregate with a moisture content of 1.0-6.0 wt%. A3. Preparation of mineralization precursor solution: Based on the total mass of the mineralization precursor solution, prepare an aqueous solution or suspension with a sodium silicate mass fraction of 5.0-20.0 wt% and a calcium hydroxide mass fraction of 0.5-5.0 wt%, with the remainder being water, so that the pH value of the mineralization precursor solution is 11.0-13.0. A4. Vacuum impregnation: The pretreated recycled coarse aggregate is completely immersed in the mineralization precursor solution, wherein the liquid-solid mass ratio of the pretreated recycled coarse aggregate to the mineralization precursor solution is 1.5-5.0. The solution is maintained at an absolute pressure of 0.005-0.020 MPa for 5-20 min, and then restored to normal pressure and impregnated at a temperature of 20-60℃ for 10-60 min to obtain the mineralization precursor impregnated aggregate.

[0008] Furthermore, the mineralized precursor impregnated aggregate forms a mineralized shell through the following carbonization steps: B1. The carbonization medium is carbon dioxide; B2) Carbonation curing: Place the mineralized precursor impregnated aggregate in an atmosphere with a carbon dioxide volume fraction of 5-30 vol%, and replace it with a mixture of carbon dioxide and air 2-5 times under normal pressure to achieve a carbon dioxide volume fraction of 5-30 vol%, and maintain it at a temperature of 20-60℃ for 2-24 hours. B3) Endpoint criterion: Based on the mass of the dried pretreated recycled coarse aggregate, when the mass gain rate of the mineralized precursor impregnated aggregate reaches 0.5-5.0 wt%, carbonization curing is stopped to obtain a core-shell aggregate precursor with a mineralized shell.

[0009] Furthermore, the core-shell aggregate precursor with a mineralized shell forms a silane layer through the following silane treatment steps: C1. The raw materials include ethanol, acetic acid, water, and 3-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane; C2. Preparation of silane hydrolysate: Based on the total mass of the silane hydrolysate, prepare an ethanol-water mixed solvent with an ethanol volume fraction of 60-95 vol%, add acetic acid to adjust the pH of the silane hydrolysate to 3.5-5.5, then add the silane to adjust the silane mass fraction to 0.2-2.0 wt%, and hydrolyze at 200-800 rpm for 10-30 min at a temperature of 20-40℃. C3. Silane treatment: The core-shell aggregate precursor with mineralized shell is immersed in silane hydrolysate and stirred for 5-30 min, then filtered and dried to obtain core-shell modified recycled coarse aggregate.

[0010] Furthermore, the drying process involves drying at a temperature of 40-80℃ for 2-6 hours, while meeting the following quality control conditions: The dried moisture content of the core-shell modified recycled coarse aggregate is 0-1.0 wt%; where a dried moisture content of 0% indicates a test result of 0 or below the detection limit. The thickness of the mineralized crust is 5-50 μm; The water absorption rate of the core-shell modified recycled coarse aggregate is 1.0-6.0 wt%; the particle size of the core of the recycled coarse aggregate is 5-20 mm.

[0011] Furthermore, the mineral admixture is selected from one or more of granulated blast furnace slag powder, fly ash, limestone powder and metakaolin; the dominant pore size of the green porous concrete building material is 1-6 mm; and it also includes 0-120 kg of fine aggregate per cubic meter of concrete mixture.

[0012] As a concept of this invention, a core-shell modified recycled coarse aggregate is designed using a mineralized shell-silane layer dual-layer interface control technology. This is primarily used to enhance the interfacial bonding performance of porous concrete, reduce aggregate water absorption, and improve overall load-bearing mechanical properties and long-term durability. The loose and porous old mortar layer adhering to the surface of the recycled coarse aggregate results in high water absorption and weak interfacial bonding. This invention utilizes a vacuum impregnation process to deeply penetrate the sodium silicate-calcium hydroxide mineralization precursor solution into the pore network of the old mortar. Subsequently, carbonization curing in a carbon dioxide atmosphere induces the in-situ precipitation of calcium silicate hydrates and calcium carbonate mineralization products within the pores, forming a dense mineralized shell layer with a thickness of 5-50 μm. This mineralized shell layer, on the one hand, fills and seals the pores of the old mortar, reducing water absorption channels; on the other hand, it enhances the structural strength of the matrix through chemical bonding between the mineralization products and the old mortar matrix. Simultaneously, the calcium silicate components rich in the mineralized shell layer exhibit good chemical compatibility and interfacial reactivity with freshly mixed cement paste. A silane layer is further grafted onto the surface of the mineralized shell. After hydrolysis, the alkoxy groups (-OC2H5 or -OCH3) in 3-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane molecules undergo a condensation reaction with the hydroxyl groups (-OH) on the surface of the mineralized shell to form covalent bonds Si-O-Si, anchoring the organosilane molecules to the surface of the mineralized shell. The amino (-NH2) or epoxy groups at the other end of the silane molecules can chemically interact with calcium hydroxide, ettringite, etc. in cement hydration products to form a transition interface layer. This maintains hydrophobicity while establishing strong interfacial bonding between aggregate and paste, achieving synergistic optimization of "hydrophobicity and reduced water absorption" and "enhanced interfacial bonding", breaking through the bond weakening dilemma caused by traditional single hydrophobic modification.

[0013] This invention also discloses a method for preparing a green porous concrete building material, characterized by comprising the following steps: S1. Provide core-shell modified recycled coarse aggregate; S2. Dry mixing: Mix the cementitious material with the core-shell modified recycled coarse aggregate for 30-180 seconds; S3. Mixing: Add water and mix for 60-240 seconds to make the water-cement mass ratio 0.22-0.30, thus obtaining the concrete mixture; S4. Molding: The concrete mixture is laid or molded and vibrated to compact it. The vibration frequency is 30-60 Hz and the compaction pressure is 0.1-1.0 MPa. S5. Curing: Curing the molded body at a temperature of 10-80℃ for 12-168 hours.

[0014] Furthermore, the provision of core-shell modified recycled coarse aggregate includes mineralization treatment of the recycled coarse aggregate. The mineralization treatment uses a mineralization precursor solution, in which the mass fraction of sodium silicate is 5.0-20.0 wt% and the mass fraction of calcium hydroxide is 0.5-5.0 wt%. The mineralization treatment includes vacuum impregnation, in which the absolute pressure of vacuum impregnation is 0.005-0.020 MPa and the holding time is 5-20 min.

[0015] Furthermore, the provision of core-shell modified recycled coarse aggregate includes carbonization treatment and silane treatment, wherein the carbonization treatment is carried out in an atmosphere with a carbon dioxide volume fraction of 5-30 vol%, the carbonization temperature is 20-60℃, and the carbonization time is 2-24 h; the silane treatment uses a silane hydrolysate, which is prepared by ethanol, acetic acid, water, and 3-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane, wherein the volume fraction of ethanol is 60-95 vol%, the mass fraction of silane is 0.2-2.0 wt%, and the pH value of the silane hydrolysate is 3.5-5.5.

[0016] Furthermore, based on the designed volume of each cubic meter of concrete mixture, the amount of water used is 90-123 kg; the compaction duration is 5-60 s; and the continuous porosity of the resulting green porous concrete building material is 15-28%.

[0017] Furthermore, the continuous porosity is the percentage of the volume of connected pores to the total volume of the sample.

[0018] Furthermore, the dominant pore size is obtained by image analysis of the concrete sample cross-section, which is the pore size corresponding to the highest frequency in the pore size distribution; the sample is cut to obtain the cross-section and the floating dust is removed, and at least 5 non-overlapping fields of view are randomly selected on each sample to take cross-sectional images with a scale bar, the images are binarized and segmented, and the pore size distribution is statistically analyzed.

[0019] Furthermore, the moisture content of the core-shell modified recycled coarse aggregate after drying is determined by the following method: the sample is dried at a temperature of 105℃, then cooled to room temperature in a desiccator and weighed; the drying-cooling-weighing process is repeated until the mass change between two consecutive weighings does not exceed 0.1%, which is recorded as constant weight; the moisture content after drying is expressed as the percentage of the mass difference before and after drying to the mass after drying.

[0020] Furthermore, the water absorption rate of the core-shell modified recycled coarse aggregate is determined by the following method: the sample is soaked in water at a temperature of 20-25℃ for 24 h, then taken out and placed on a sieve to drain for 60 s. Then, the sample surface is gently touched with dry absorbent paper until no continuous wet marks appear on the absorbent paper, which is recorded as the surface dry state; the water absorption rate is the percentage of the difference between the sample mass and the dry mass in this state to the dry mass.

[0021] Furthermore, the thickness of the mineralized shell was determined by observing the aggregate cross-section using a scanning electron microscope. At least five different locations were measured for each sample, and the average value was taken.

[0022] Furthermore, the sodium silicate is water glass with a modulus of 2.0-3.5.

[0023] Furthermore, in the pretreatment of the recycled coarse aggregate, the washing method is mechanical stirring and washing for 2-10 minutes at a temperature of 20-25℃; the dewatering method is drying after filtration and separation at a temperature of 40-80℃.

[0024] Furthermore, the water-to-solid mass ratio is based on the dry basis mass of the recycled coarse aggregate as the solid basis.

[0025] Furthermore, the carbonization curing is carried out in a carbonization chamber, where a mixture of carbon dioxide and air is used to replace the carbon dioxide 2-5 times under normal pressure, so that the volume fraction of carbon dioxide in the chamber reaches 5-30 vol.

[0026] Furthermore, the mineralization products of the mineralized shell contain at least one of calcium carbonate or calcium silicate hydrate.

[0027] Furthermore, the dry mixing and blending are carried out in a forced mixer.

[0028] Furthermore, the curing method is either standard curing or steam curing. The conditions for standard curing are a temperature of 20±2℃ and a relative humidity of ≥95%; the conditions for steam curing are a temperature of 60-80℃, a relative humidity of ≥95%, and a constant temperature time of 4-8 hours.

[0029] Furthermore, the core-shell modified recycled coarse aggregate accounts for 45-100 wt% of the total coarse aggregate.

[0030] Furthermore, the mineral admixture is a composite admixture of granulated blast furnace slag powder and fly ash, wherein the mass ratio of granulated blast furnace slag powder to fly ash is 1:0.5-2.

[0031] Furthermore, the moisture content and water absorption rate are both calculated on a dry basis.

[0032] As another aspect of this invention, it employs a synergistic optimization design of a low water-cement ratio cementitious system and a vibration compaction molding process. This design primarily aims to enhance the mixing and molding stability of porous concrete, improve its load-bearing strength, and enhance its long-term freeze-thaw resistance. Traditional porous concrete requires a lower water-cement ratio to increase strength, but a low water-cement ratio leads to poor flowability, uneven aggregate coating, and difficulties in vibration molding. This invention addresses this by compounding general-purpose silicate cement with mineral admixtures (granulated blast furnace slag powder, fly ash, etc.) at 20-60 parts and 40-80 parts respectively. The spherical particle morphology and micro-aggregate filling effect of the mineral admixtures improve the slurry flowability and workability, allowing the mixture to maintain good coating and formability even at a low water-cement ratio of 0.22-0.30. Simultaneously, the pozzolanic activity of the mineral admixtures consumes calcium hydroxide during the later hydration process to generate CSH gel, refining the pore structure and optimizing the interfacial transition zone, thereby improving the slurry density and impermeability. Vibration compaction, through the synergistic effect of a vibration frequency of 30-60 Hz and a compaction pressure of 0.1-1.0 MPa, promotes the full filling of aggregate particle contact points by the slurry in the mixture, eliminates encapsulated air bubbles, and optimizes the uniformity of pore distribution, forming a gradient pore network with a continuous porosity of 15-28% and a dominant pore size of 1-6 mm. This ensures both water permeability and drainage, and enhances load-bearing strength by increasing the density of effective bonding points between aggregate particles. The flexible control of curing temperature (10-60℃) and curing time (12-168 h) allows for the selection of standard curing or steam curing according to project requirements. Steam curing accelerates early cement hydration and shortens the demolding cycle, while standard curing ensures long-term strength development and durability, thereby achieving comprehensive synergistic optimization of mixing stability, molding processability, mechanical properties, and durability.

[0033] The synergistic effect of the mineralized shell and silane layer in the core-shell modified recycled coarse aggregate system of this invention is manifested as a multi-level effect of "structural enhancement - interface regulation - performance synergy". The mineralized shell focuses on filling and sealing the pores of old mortar, improving the strength of the aggregate matrix, and establishing a chemically compatible interface. Through vacuum impregnation-carbonation mineralization process, calcium carbonate and calcium silicate hydrates are generated in situ in the pores on the surface of the recycled coarse aggregate, significantly reducing the water absorption rate of the aggregate to 1.0-6.0 wt% and providing good chemical bonding sites with cement paste. The silane layer focuses on surface hydrophobic modification, establishing an organic-inorganic transition interface, and improving the interfacial bonding strength. One end of the silane molecule is covalently bonded to the mineralized shell, and the other end chemically interacts with the cement hydration products to form a gradient transition interface layer. The synergistic mechanism between the two lies in the following: the mineralized shell first reduces water absorption channels by filling pores, providing a high-strength substrate and a chemically active interface, thus providing a stable carrier for the anchoring of the silane layer and enhancing the bonding force between silane molecules and aggregates; the silane layer forms a hydrophobic protective film on the surface of the mineralized shell, further blocking water penetration while establishing a strong interfacial bond with the cement paste through amino or epoxy groups, solving the problem of interfacial weakening caused by single hydrophobic modification. This dual-layer synergistic structure enables core-shell modified recycled coarse aggregate to simultaneously possess comprehensive properties such as low water absorption (60-80% lower than unmodified), high interfacial bond strength (40-60% higher than single silane modification), and excellent stress transfer efficiency, laying the material foundation for porous concrete to achieve high strength and high durability under high porosity conditions.

[0034] Beneficial technical effects 1. Overcoming the contradiction between high porosity and high load-bearing strength: Through the dual-layer interface control technology of mineralized shell layer and silane layer of core-shell modified recycled coarse aggregate, while maintaining high permeability with a continuous porosity of 15-28%, the bonding strength and stress transfer efficiency of aggregate-slurry interface are significantly improved. The mineralized shell layer fills the pores of old mortar to provide a high-strength substrate, and the silane layer establishes an organic-inorganic transition interface to enhance bonding. This increases the compressive strength of porous concrete by 30-50% compared to traditional solutions, achieving synergistic optimization of permeability and drainage function and load-bearing mechanical properties. This broadens the application range of porous concrete in scenarios with high load requirements such as municipal roads and square paving.

[0035] 2. Overcoming the constraints of low water-cement ratio mixing stability and freeze-thaw durability: By optimizing the mix ratio of general-purpose silicate cement to mineral admixtures (20-60 parts to 40-80 parts), the spherical particles of the mineral admixtures improve the fluidity and workability of the slurry, ensuring that the mixture maintains good encapsulation and formability even at a low water-cement ratio of 0.22-0.30. The synergistic effect of the vibration compaction process (30-60 Hz frequency and 0.1-1.0 MPa pressure) promotes the slurry to fully fill the aggregate contact points, eliminate air bubbles, and optimize pore distribution. The active volcanic ash of the mineral admixture consumes calcium hydroxide to generate CSH gel, refining the pore structure. This comprehensively improves molding stability, density of the interface transition zone, and impermeability, increasing the number of freeze-thaw cycles of porous concrete by 40-60% compared to traditional methods, meeting the long-term service requirements in extremely cold regions.

[0036] 3. Overcoming the conflict between hydrophobicity and reduced water absorption and interfacial bonding: Traditional single-silane hydrophobic modification reduces water absorption but significantly weakens interfacial bonding. This invention adopts a two-layer structure design with a mineralized shell followed by a silane layer. The mineralized shell provides a chemically compatible interface and silane anchoring sites, while the amino or epoxy groups in the silane layer chemically interact with cement hydration products to establish strong interfacial bonding. This achieves simultaneous optimization of a 60-80% reduction in water absorption (compared to unmodified recycled coarse aggregate) and a 40-60% increase in interfacial bonding strength (compared to single-silane modification). The load transfer efficiency is significantly enhanced, providing a technical path for the large-scale application of recycled aggregates in high-performance porous concrete.

[0037] 4. Achieving the dual goals of green environmental protection and performance improvement: Recycled coarse aggregates made from construction waste concrete are used to replace natural aggregates, reducing the consumption of natural resources and the landfilling of construction waste. At the same time, granulated blast furnace slag powder and fly ash from industrial waste are used as mineral admixtures to partially replace cement, reducing carbon emissions and improving the overall performance of concrete. The core-shell modification process uses ambient or medium-low temperature (20-60℃) carbonization and silane treatment, which has low energy consumption, simple process, and is easy to implement industrially. It is in line with the concept of green building and circular economy development and has good economic and environmental benefits.

[0038] 5. Constructing a gradient pore network to optimize multifunctional performance: By precisely controlling the pore structure distribution through vibration compaction process parameters, a gradient pore system with a dominant pore size of 1-6 mm is obtained. Larger pore sizes (4-6 mm) provide rapid water permeability channels to meet the needs of rainstorm drainage, medium pore sizes (2-4 mm) balance water permeability and strength, and smaller pore sizes (1-2 mm) enhance capillary action to promote water evaporation and temperature regulation. The continuous porosity of 15-28% can be flexibly adjusted according to the application scenario, enabling porous concrete to simultaneously possess multifunctional characteristics such as water permeability and drainage, noise reduction and sound absorption, temperature and humidity regulation, and eco-friendliness, meeting the diverse needs of sponge city infrastructure. Attached Figure Description

[0039] Figure 1 X-ray diffraction analysis diagrams of core-shell modified recycled coarse aggregate in Example 1, ordinary recycled coarse aggregate in Comparative Example 3, and recycled coarse aggregate with only mineralized layer and no silane layer in Comparative Example 4.

[0040] Figure 2 The image shows the high-resolution Si 2p X-ray photoelectron spectroscopy (XPS) spectra of the core-shell modified recycled coarse aggregate of Example 1 and the recycled coarse aggregate of Comparative Example 4 with only a mineralized layer and no silane layer.

[0041] Figure 3 The X-ray photoelectron spectroscopy (N 1s) high-resolution analysis images are of the core-shell modified recycled coarse aggregate of Example 1 and the recycled coarse aggregate of Comparative Example 4 with only a mineralized layer and no silane layer.

[0042] Figure 4 The graphs show the pore size distribution of Example 1, Comparative Example 5 (water-binder ratio 0.35), and Comparative Example 6 (water-binder ratio 0.20).

[0043] Figure 5 The cumulative pore size distribution curves are for Example 1, Comparative Example 5 with a water-to-binder ratio of 0.35, and Comparative Example 6 with a water-to-binder ratio of 0.20.

[0044] Figure 6 The graph shows the frequency distribution of micropore throats using mercury intrusion porosimetry for Example 1, Comparative Example 5 (water-to-binder ratio 0.35), and Comparative Example 6 (water-to-binder ratio 0.20).

[0045] Figure 7 The cumulative pore volume curves of mercury intrusion porosimetry for Example 1, Comparative Example 5 with a water-to-binder ratio of 0.35 and Comparative Example 6 with a water-to-binder ratio of 0.20 are shown.

[0046] Figure 8 The image shows the scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) curves of the Ca / Si molar ratio along the interface line for the core-shell modified recycled coarse aggregate of Example 1 and the ordinary recycled coarse aggregate of Comparative Example 3.

[0047] Figure 9 The image shows a scanning electron microscope (SEM) image of the overall cross-sectional morphology of the core-shell modified recycled coarse aggregate in Example 1.

[0048] Figure 10 This is a scanning electron microscope image of the mineralized shell thickness measurement in Example 1.

[0049] Figure 11 This is a scanning electron microscope image of the microstructure of the mineralized products within the shell of Example 1. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0051] Example 1 A green porous concrete building material, based on the design volume of each cubic meter of concrete mixture, comprises: 350 kg of cementitious material, 105 kg of water, 1325 kg of coarse aggregate, and 50 kg of fine aggregate, with the mass ratio of water to cementitious material in this embodiment being 0.30. The coarse aggregate in this embodiment is core-shell modified recycled coarse aggregate; this core-shell modified recycled coarse aggregate includes a recycled coarse aggregate core, a mineralized shell layer covering the surface of the recycled coarse aggregate core, and a silane layer covering the surface of the mineralized shell layer; the thickness of the mineralized shell layer in this embodiment is 27.5 mm. μm; The silane layer in this embodiment is formed of 3-aminopropyltriethoxysilane; The cementitious material in this embodiment includes general-purpose silicate cement and mineral admixtures. Based on 100 parts by weight of the cementitious material in this embodiment, the amount of general-purpose silicate cement is 40 parts by weight, the amount of mineral admixtures is 60 parts by weight, and the sum of the weight parts of general-purpose silicate cement and mineral admixtures in this embodiment is 100 parts by weight; The mineral admixture in this embodiment is a composite admixture of granulated blast furnace slag powder and fly ash, wherein the mass ratio of 30 parts by weight of granulated blast furnace slag powder to 30 parts by weight of fly ash is 1:1; The continuous porosity of the green porous concrete building material in this embodiment, measured by the vacuum saturation-drainage method, is 21.5%, and the dominant pore diameter is 3.5 mm.

[0052] The core-shell modified recycled coarse aggregate of this embodiment is prepared through the following steps: Raw materials include recycled coarse aggregate, water, sodium silicate, and calcium hydroxide; in the pretreatment stage of the recycled coarse aggregate, the recycled coarse aggregate is washed at a water-to-solid mass ratio of 1.5 by mechanical stirring for 6 minutes at a temperature of 20-25℃, followed by filtration and drying at 60℃ to obtain pretreated recycled coarse aggregate with a water content of 3.5 wt%. In this embodiment, the water-to-solid mass ratio is based on the dry weight of the recycled coarse aggregate; in the mineralization precursor solution preparation stage, a solution is prepared with a sodium silicate mass fraction of 12.5 wt% and a calcium hydroxide mass fraction of 2.75 wt%, based on the total mass of the mineralization precursor solution. A wt% aqueous solution or suspension is used to make the pH of the mineralization precursor solution 12.0. In this embodiment, the sodium silicate is water glass with a modulus of 2.8. In the vacuum impregnation stage, the pretreated recycled coarse aggregate is completely immersed in the mineralization precursor solution, wherein the liquid-solid mass ratio of the pretreated recycled coarse aggregate to the mineralization precursor solution is 3.0. The solution is kept under an absolute pressure of 0.012 MPa for 12 min, and then restored to normal pressure and impregnated at a temperature of 40°C for 35 min to obtain the mineralization precursor impregnated aggregate.

[0053] In this embodiment, the mineralized precursor impregnated aggregate forms a mineralized shell through the following carbonization steps: the carbonization medium is carbon dioxide; during the carbonization curing stage, the mineralized precursor impregnated aggregate is placed in an atmosphere with a carbon dioxide volume fraction of 17 vol%, and the carbonization curing is carried out in a carbonization chamber. Under normal pressure, the carbon dioxide and air mixture is replaced three times to achieve a carbon dioxide volume fraction of 17 vol%, and the chamber is maintained at a temperature of 40°C for 13 hours; in the endpoint determination stage, the weight gain of the mineralized precursor impregnated aggregate is calculated based on the mass of the dried pretreated recycled coarse aggregate. When the weight gain rate of the mineralized precursor impregnated aggregate reaches 2.75 wt%, the carbonization curing is stopped, and a core-shell aggregate precursor with a mineralized shell is obtained. The mineralization products of the mineralized shell in this embodiment include calcium carbonate and calcium silicate hydrate.

[0054] In this embodiment, the core-shell aggregate precursor with a mineralized shell forms a silane layer through the following silane treatment steps: the raw materials include ethanol, acetic acid, water, and 3-aminopropyltriethoxysilane; in the silane hydrolysis solution preparation stage, based on the total mass of the silane hydrolysis solution, an ethanol-water mixed solvent with a volume fraction of 77.5 vol% is prepared, acetic acid is added to make the pH value of the silane hydrolysis solution of this embodiment 4.5, and then the silane of this embodiment is added to make the mass fraction of the silane of this embodiment 1.1 wt%, and the mixture is stirred and hydrolyzed at 500 rpm for 20 min at a temperature of 30°C; in the silane treatment stage, the core-shell aggregate precursor with a mineralized shell is immersed in the silane hydrolysis solution and stirred for 17 min, then filtered and dried, and dried at a temperature of 60°C for 4 h to obtain core-shell modified recycled coarse aggregate.

[0055] The core-shell modified recycled coarse aggregate of this embodiment meets the following quality control conditions: the moisture content of the core-shell modified recycled coarse aggregate after drying is 0.5 wt%. The moisture content after drying in this embodiment is determined by the following method: the sample is dried at a temperature of 105℃, then cooled to room temperature in a desiccator and weighed. The drying-cooling-weighing process is repeated until the mass change between two consecutive weighings does not exceed 0.1%, which is recorded as constant weight. The moisture content after drying in this embodiment is expressed as the percentage of the mass difference before and after drying to the mass after drying. The thickness of the mineralized shell layer is 27.5 μm. The thickness of the mineralized shell layer in this embodiment is determined by observing the cross-section of the aggregate using a scanning electron microscope. Five different locations are measured for each sample, and the average value is taken. The water absorption rate of the core-shell modified recycled coarse aggregate is 3.5 wt%. The water absorption rate in this embodiment is determined by the following method: the sample is soaked in water at a temperature of 20-25℃ for 24 h, then removed and placed on a sieve to drain for 60 h. s, then gently touch the sample surface with dry absorbent paper until no continuous wet marks appear on the absorbent paper, which is recorded as the surface dry state. The water absorption rate is the percentage of the difference between the sample mass and the dry mass in this state to the dry mass. The particle size of the recycled coarse aggregate core in this embodiment is 12.5 mm. The mass ratio of the core-shell modified recycled coarse aggregate in the coarse aggregate in this embodiment is 72.5 wt%. The moisture content and water absorption rate in this embodiment are both on a dry basis.

[0056] The preparation method of the green porous concrete building material in this embodiment includes the following steps: providing core-shell modified recycled coarse aggregate. In this embodiment, providing core-shell modified recycled coarse aggregate includes mineralization treatment of the recycled coarse aggregate. The mineralization treatment in this embodiment uses a mineralization precursor solution. The mass fraction of sodium silicate in the mineralization precursor solution is 12.5 wt%, and the mass fraction of calcium hydroxide is 2.75 wt%. The mineralization treatment in this embodiment includes vacuum impregnation. The absolute pressure of vacuum impregnation in this embodiment is 0.012 MPa, and the holding time is 12 min. Providing core-shell modified recycled coarse aggregate in this embodiment includes carbonization treatment and silane treatment. In this embodiment, the carbonization treatment is carried out in an atmosphere with a carbon dioxide volume fraction of 17 vol%, the carbonization temperature is 40℃, and the carbonization time is 13 h. In this embodiment, the silane treatment uses a silane hydrolysis solution. The silane hydrolysis solution in this embodiment is prepared from ethanol, acetic acid, water, and 3-aminopropyltriethoxysilane, wherein the volume fraction of ethanol is 77.5 vol%, and the mass fraction of silane in this embodiment is 1.1 wt%. The pH value of the silane hydrolysate in this embodiment is 4.5 (wt%). In the dry mixing stage, the cementitious material and the core-shell modified recycled coarse aggregate are mixed in a forced mixer for 105 s. In the mixing stage, water is added and mixed in a forced mixer for 150 s to make the water-cement mass ratio 0.30, thus obtaining a concrete mixture. The amount of water used in this embodiment is 105 kg per cubic meter of concrete mixture, based on the design volume. In the molding stage, the concrete mixture of this embodiment is laid or molded and vibrated and compacted. The vibration frequency is 45 Hz, the compaction pressure is 0.55 MPa, and the compaction duration in this embodiment is 32 s. In the curing stage, the molded body is subjected to standard curing at a curing temperature of 20℃, a relative humidity of ≥95%, and a curing time of 90 h. The continuous porosity of the green porous concrete building material obtained in this embodiment is 21.5%, and the continuous porosity in this embodiment is the percentage of the volume of connected pores to the total volume of the sample. The dominant pore diameter in this embodiment is 3.5 mm, which is the pore diameter with the highest frequency in the pore diameter distribution, obtained by image analysis of the concrete sample cross-section. The sample is cut to obtain the cross-section and the floating dust is removed. Five non-overlapping fields of view are randomly selected on each sample to take cross-sectional images with scale bars. The images are binarized and segmented, and the pore diameter distribution is statistically analyzed.

[0057] Features of Example 1: This example adopts a medium-ratio scheme. The amount of cementitious material is 350 kg, which is at a reasonable middle level. The water-cement ratio of 0.30 ensures the balance between the fluidity and strength of the slurry. The general silicate cement and mineral admixture are mixed in a ratio of 40:60 to achieve coordination between cementitious performance and economy. The equal proportion of granulated blast furnace slag powder and fly ash in the mineral admixture provides good workability. The core-shell modified recycled coarse aggregate accounts for 72.5% of the coarse aggregate, which reflects a high utilization rate of recycled materials. The synergistic effect of the mineralized shell layer thickness of 27.5 μm and the silane layer effectively improves the interfacial performance of the recycled aggregate. The continuous porosity of 21.5% and the dominant pore size of 3.5 mm form a moderate pore structure, which is suitable for medium-load scenarios requiring permeability, such as urban roads, parking lots, and squares. It can also be applied to environmentally friendly municipal engineering projects such as garden landscape paving and pedestrian walkways. This scheme has high process stability, controllable cost, and balanced performance, and is particularly suitable as a standardized production formula for permeable concrete.

[0058] Example 2 A green porous concrete building material, based on the design volume of each cubic meter of concrete mixture, comprises: 390 kg of cementitious material, 95 kg of water, 1200 kg of coarse aggregate, and 90 kg of fine aggregate. The mass ratio of water to cementitious material in this embodiment is 0.244. The coarse aggregate in this embodiment is core-shell modified recycled coarse aggregate; the core-shell modified recycled coarse aggregate in this embodiment includes a recycled coarse aggregate core, a mineralized shell layer covering the surface of the recycled coarse aggregate core, and a silane layer covering the surface of the mineralized shell layer; the thickness of the mineralized shell layer in this embodiment is 38 mm. μm; The silane layer in this embodiment is formed by γ-glycidyl etheroxypropyltrimethoxysilane; The cementitious material in this embodiment includes general-purpose silicate cement and mineral admixtures. Based on 100 parts by weight of the cementitious material in this embodiment, the amount of general-purpose silicate cement is 52 parts by weight, the amount of mineral admixtures is 48 parts by weight, and the sum of the weight parts of general-purpose silicate cement and mineral admixtures in this embodiment is 100 parts by weight; The mineral admixture in this embodiment is a composite admixture of granulated blast furnace slag powder and fly ash, wherein the mass ratio of 32 parts by weight of granulated blast furnace slag powder to 16 parts by weight of fly ash is 2:1; The continuous porosity of the green porous concrete building material in this embodiment, measured by the vacuum saturation-drainage method, is 17.5%, and the dominant pore diameter is 2.0 mm.

[0059] The core-shell modified recycled coarse aggregate of this embodiment is prepared through the following steps: Raw materials include recycled coarse aggregate, water, sodium silicate, and calcium hydroxide; in the pretreatment stage of the recycled coarse aggregate, the recycled coarse aggregate is washed at a water-to-solid mass ratio of 1.0 by mechanical stirring for 4 minutes at a temperature of 20-25℃, followed by filtration and drying at a temperature of 70℃ to obtain pretreated recycled coarse aggregate with a water content of 2.0 wt%. In this embodiment, the water-to-solid mass ratio is based on the dry weight of the recycled coarse aggregate; in the mineralization precursor solution preparation stage, a solution is prepared with a sodium silicate mass fraction of 16.0 wt% and a calcium hydroxide mass fraction of 3.5 wt%, based on the total mass of the mineralization precursor solution. A wt% aqueous solution or suspension is used to make the pH value of the mineralization precursor solution 12.5. In this embodiment, the sodium silicate is water glass with a modulus of 2.5. In the vacuum impregnation stage, the pretreated recycled coarse aggregate is completely immersed in the mineralization precursor solution, wherein the liquid-solid mass ratio of the pretreated recycled coarse aggregate to the mineralization precursor solution is 2.5. The solution is kept under an absolute pressure of 0.008 MPa for 15 min, and then restored to normal pressure and impregnated at a temperature of 50°C for 45 min to obtain the mineralization precursor impregnated aggregate.

[0060] In this embodiment, the mineralized precursor impregnated aggregate forms a mineralized shell through the following carbonization steps: the carbonization medium is carbon dioxide; during the carbonization curing stage, the mineralized precursor impregnated aggregate is placed in an atmosphere with a carbon dioxide volume fraction of 22 vol%, and the carbonization curing is carried out in a carbonization chamber. Under normal pressure, the carbon dioxide and air mixture is replaced four times to achieve a carbon dioxide volume fraction of 22 vol%, and the chamber is maintained at a temperature of 50°C for 18 hours; in the endpoint determination stage, the weight gain of the pretreated recycled coarse aggregate after drying is used as a benchmark. When the weight gain of the mineralized precursor impregnated aggregate reaches 3.8 wt%, the carbonization curing is stopped, and a core-shell aggregate precursor with a mineralized shell is obtained. The mineralization products of the mineralized shell in this embodiment include calcium carbonate and calcium silicate hydrate.

[0061] In this embodiment, the core-shell aggregate precursor with a mineralized shell forms a silane layer through the following silane treatment steps: the raw materials include ethanol, acetic acid, water, and γ-glycidoxypropyltrimethoxysilane; in the silane hydrolysis solution preparation stage, based on the total mass of the silane hydrolysis solution, an ethanol-water mixed solvent with a volume fraction of 85 vol% is prepared, acetic acid is added to make the pH value of the silane hydrolysis solution of this embodiment 4.0, and then the silane of this embodiment is added to make the mass fraction of the silane of this embodiment 1.5 wt%, and the mixture is stirred and hydrolyzed at 650 rpm for 25 min at a temperature of 25°C; in the silane treatment stage, the core-shell aggregate precursor with a mineralized shell is immersed in the silane hydrolysis solution and stirred for 22 min, then filtered and dried, and dried at a temperature of 70°C for 5 h to obtain core-shell modified recycled coarse aggregate.

[0062] The core-shell modified recycled coarse aggregate of this embodiment meets the following quality control conditions: the moisture content of the core-shell modified recycled coarse aggregate after drying is 0.3 wt%. The moisture content after drying in this embodiment is determined by the following method: the sample is dried at a temperature of 105℃, then cooled to room temperature in a desiccator and weighed. The drying-cooling-weighing process is repeated until the mass change between two consecutive weighings does not exceed 0.1%, which is recorded as constant weight. The moisture content after drying in this embodiment is expressed as the percentage of the mass difference before and after drying to the mass after drying. The thickness of the mineralized shell layer is 38 μm. The thickness of the mineralized shell layer in this embodiment is determined by observing the aggregate cross-section using a scanning electron microscope. Five different locations are measured for each sample, and the average value is taken. The water absorption rate of the core-shell modified recycled coarse aggregate is 2.2 wt%. The water absorption rate in this embodiment is determined by the following method: the sample is soaked in water at a temperature of 20-25℃ for 24 h, then removed and placed on a sieve to drain for 60 h. s, then gently touch the sample surface with dry absorbent paper until no continuous wet marks appear on the absorbent paper, which is recorded as the surface dry state. The water absorption rate is the percentage of the difference between the sample mass and the dry mass in this state to the dry mass. The particle size of the recycled coarse aggregate core in this embodiment is 10 mm. The mass ratio of the core-shell modified recycled coarse aggregate in the coarse aggregate in this embodiment is 88 wt%. The moisture content and water absorption rate in this embodiment are both on a dry basis.

[0063] The preparation method of the green porous concrete building material in this embodiment includes the following steps: providing core-shell modified recycled coarse aggregate. In this embodiment, providing core-shell modified recycled coarse aggregate includes mineralization treatment of the recycled coarse aggregate. The mineralization treatment in this embodiment uses a mineralization precursor solution. The mineralization precursor solution in this embodiment contains 16.0 wt% sodium silicate and 3.5 wt% calcium hydroxide. The mineralization treatment in this embodiment includes vacuum impregnation. The absolute pressure of vacuum impregnation in this embodiment is 0.008 MPa, and the holding time is 15 min. Providing core-shell modified recycled coarse aggregate in this embodiment includes carbonization treatment and silane treatment. In this embodiment, the carbonization treatment is carried out in an atmosphere with a carbon dioxide volume fraction of 22 vol%, a carbonization temperature of 50℃, and a carbonization time of 18 h. In this embodiment, the silane treatment uses a silane hydrolysis solution. The silane hydrolysis solution in this embodiment is prepared from ethanol, acetic acid, water, and γ-glycidyl etheroxypropyltrimethoxysilane, wherein the volume fraction of ethanol is 85 vol%, and the mass fraction of silane in this embodiment is 1.5%. The pH value of the silane hydrolysate in this embodiment is 4.0 (wt%). In the dry mixing stage, the cementitious material and the core-shell modified recycled coarse aggregate are mixed in a forced mixer for 140 s. In the mixing stage, water is added and mixed in a forced mixer for 190 s to make the water-cement mass ratio 0.244, thus obtaining a concrete mixture. The amount of water used in this embodiment is 95 kg per cubic meter of concrete mixture, based on the design volume. In the molding stage, the concrete mixture of this embodiment is laid or molded and vibrated and compacted. The vibration frequency is 52 Hz, the compaction pressure is 0.75 MPa, and the compaction duration in this embodiment is 45 s. In the curing stage, the molded body is subjected to standard curing at a curing temperature of 20℃, a relative humidity of ≥95%, and a curing time of 140 h. The continuous porosity of the green porous concrete building material obtained in this embodiment is 17.5%, and the continuous porosity in this embodiment is the percentage of the volume of connected pores to the total volume of the sample. The dominant pore diameter in this embodiment is 2.0 mm, which is the pore diameter with the highest frequency in the pore diameter distribution, obtained by image analysis of the concrete sample cross-section. The sample is cut to obtain the cross-section and the floating dust is removed. Five non-overlapping fields of view are randomly selected on each sample to take cross-sectional images with scale bars. The images are binarized and segmented, and the pore diameter distribution is statistically analyzed.

[0064] Features of Example 2: This example employs a high-strength, low-porosity mix design. The cementitious material dosage of 390 kg is sufficient, and the low water-cement ratio of 0.244 ensures good slurry density and strength development. The high proportion of general-purpose silicate cement (52%) provides good early strength and later-stage stability. The granulated blast furnace slag powder and fly ash in a 2:1 ratio among the mineral admixtures enhance the slurry's compactness and durability. The core-shell modified recycled coarse aggregate accounts for 88% of the coarse aggregate, achieving a high proportion of recycled materials. The relatively thick mineralized shell layer (38 μm) and the silane layer formed by γ-glycidoxypropyltrimethoxysilane significantly improve the interfacial bonding between the recycled aggregate and the slurry. The weight gain of 3.8% and water absorption of 2.2% reflect the significant modification effect of the recycled aggregate. The continuous porosity is 17.5%, and the dominant pore size is 2.0 mm. mm forms a relatively dense porous structure, suitable for permeable pavements requiring high load-bearing capacity, such as light vehicle roads, industrial plant floors, and airport runway auxiliary areas. It can also be applied to bridge deck waterproofing layers, underground garage ramps, and other applications requiring high strength and durability. This solution achieves high mechanical properties while ensuring permeability, making it particularly suitable for load-bearing permeable concrete structures.

[0065] Example 3 A green porous concrete building material, based on the design volume of each cubic meter of concrete mixture, comprises: 310 kg of cementitious material, 93 kg of water, 1480 kg of coarse aggregate, and 15 kg of fine aggregate, with the mass ratio of water to cementitious material in this embodiment being 0.30. The coarse aggregate in this embodiment is core-shell modified recycled coarse aggregate; this core-shell modified recycled coarse aggregate includes a recycled coarse aggregate core, a mineralized shell layer covering the surface of the recycled coarse aggregate core, and a silane layer covering the surface of the mineralized shell layer; the thickness of the mineralized shell layer in this embodiment is 15 mm. μm; the silane layer in this embodiment is formed of 3-aminopropyltriethoxysilane; the cementitious material in this embodiment includes general-purpose silicate cement and mineral admixtures, and based on 100 parts by weight of the cementitious material in this embodiment, the amount of general-purpose silicate cement in this embodiment is 25 parts by weight, the amount of mineral admixtures in this embodiment is 75 parts by weight, and the sum of the weight parts of general-purpose silicate cement and mineral admixtures in this embodiment is 100 parts by weight; the mineral admixture in this embodiment is a composite admixture of granulated blast furnace slag powder and fly ash, wherein the mass ratio of 25 parts by weight of granulated blast furnace slag powder to 50 parts by weight of fly ash is 1:2; the continuous porosity of the green porous concrete building material in this embodiment is 25.5% as determined by the vacuum saturation-drainage method, and the dominant pore diameter is 5.0 mm.

[0066] The core-shell modified recycled coarse aggregate of this embodiment is prepared through the following steps: Raw materials include recycled coarse aggregate, water, sodium silicate, and calcium hydroxide; in the pretreatment stage of the recycled coarse aggregate, the recycled coarse aggregate is washed at a water-to-solid mass ratio of 2.3 by mechanical stirring for 8 minutes at a temperature of 20-25℃, followed by filtration and drying at a temperature of 50℃ to obtain pretreated recycled coarse aggregate with a water content of 5.0 wt%. In this embodiment, the water-to-solid mass ratio is based on the dry weight of the recycled coarse aggregate; in the mineralization precursor solution preparation stage, a solution is prepared with a sodium silicate mass fraction of 8.0 wt% and a calcium hydroxide mass fraction of 1.5 wt%, based on the total mass of the mineralization precursor solution. A wt% aqueous solution or suspension was used to make the pH of the mineralization precursor solution 11.5. In this embodiment, the sodium silicate was water glass with a modulus of 3.0. In the vacuum impregnation stage, the pretreated recycled coarse aggregate was completely immersed in the mineralization precursor solution, wherein the liquid-solid mass ratio of the pretreated recycled coarse aggregate to the mineralization precursor solution was 4.0. The solution was kept under an absolute pressure of 0.016 MPa for 8 min, and then restored to normal pressure and impregnated at a temperature of 30°C for 20 min to obtain the mineralization precursor impregnated aggregate.

[0067] In this embodiment, the mineralized precursor impregnated aggregate forms a mineralized shell through the following carbonization steps: the carbonization medium is carbon dioxide; during the carbonization curing stage, the mineralized precursor impregnated aggregate is placed in an atmosphere with a carbon dioxide volume fraction of 10 vol%, and the carbonization curing is carried out in a carbonization chamber. Under normal pressure, the carbon dioxide and air mixture is used to replace the carbon dioxide in the chamber twice to achieve a carbon dioxide volume fraction of 10 vol%, and the chamber is maintained at a temperature of 30°C for 8 hours; in the endpoint determination stage, the weight gain of the pretreated recycled coarse aggregate after drying is used as a benchmark. When the weight gain of the mineralized precursor impregnated aggregate reaches 1.5 wt%, the carbonization curing is stopped, and a core-shell aggregate precursor with a mineralized shell is obtained. The mineralization products of the mineralized shell in this embodiment include calcium carbonate and calcium silicate hydrate.

[0068] In this embodiment, the core-shell aggregate precursor with a mineralized shell forms a silane layer through the following silane treatment steps: the raw materials include ethanol, acetic acid, water, and 3-aminopropyltriethoxysilane; in the silane hydrolysis solution preparation stage, based on the total mass of the silane hydrolysis solution, an ethanol-water mixed solvent with a volume fraction of 68 vol% is prepared, acetic acid is added to make the pH value of the silane hydrolysis solution of this embodiment 5.0, and then the silane of this embodiment is added to make the mass fraction of the silane of this embodiment 0.6 wt%, and the mixture is stirred and hydrolyzed at 350 rpm for 15 min at a temperature of 35°C; in the silane treatment stage, the core-shell aggregate precursor with a mineralized shell is immersed in the silane hydrolysis solution and stirred for 10 min, then filtered and dried, and dried at a temperature of 50°C for 3 h to obtain core-shell modified recycled coarse aggregate.

[0069] The core-shell modified recycled coarse aggregate of this embodiment meets the following quality control conditions: the moisture content of the core-shell modified recycled coarse aggregate after drying is 0.8 wt%. The moisture content after drying in this embodiment is determined by the following method: the sample is dried at a temperature of 105℃, then cooled to room temperature in a desiccator and weighed. The drying-cooling-weighing process is repeated until the mass change between two consecutive weighings does not exceed 0.1%, which is recorded as constant weight. The moisture content after drying in this embodiment is expressed as the percentage of the mass difference before and after drying to the mass after drying. The thickness of the mineralized shell layer is 15 μm. The thickness of the mineralized shell layer in this embodiment is determined by observing the cross-section of the aggregate using a scanning electron microscope. Five different locations are measured for each sample, and the average value is taken. The water absorption rate of the core-shell modified recycled coarse aggregate is 5.0 wt%. The water absorption rate in this embodiment is determined by the following method: the sample is soaked in water at a temperature of 20-25℃ for 24 h, then removed and placed on a sieve to drain for 60 h. s, then gently touch the sample surface with dry absorbent paper until no continuous wet marks appear on the absorbent paper, which is recorded as the surface dry state. The water absorption rate is the percentage of the difference between the sample mass and the dry mass in this state to the dry mass. The particle size of the recycled coarse aggregate core in this embodiment is 15 mm. The mass ratio of the core-shell modified recycled coarse aggregate in the coarse aggregate in this embodiment is 60 wt%. The moisture content and water absorption rate in this embodiment are both on a dry basis.

[0070] The preparation method of the green porous concrete building material in this embodiment includes the following steps: providing core-shell modified recycled coarse aggregate. In this embodiment, providing core-shell modified recycled coarse aggregate includes mineralization treatment of the recycled coarse aggregate. The mineralization treatment in this embodiment uses a mineralization precursor solution. The mineralization precursor solution in this embodiment contains 8.0 wt% sodium silicate and 1.5 wt% calcium hydroxide. The mineralization treatment in this embodiment includes vacuum impregnation. The absolute pressure of vacuum impregnation in this embodiment is 0.016 MPa, and the holding time is 8 min. Providing core-shell modified recycled coarse aggregate in this embodiment includes carbonization treatment and silane treatment. In this embodiment, the carbonization treatment is carried out in an atmosphere with a carbon dioxide volume fraction of 10 vol%, a carbonization temperature of 30℃, and a carbonization time of 8 h. In this embodiment, the silane treatment uses a silane hydrolysis solution. The silane hydrolysis solution in this embodiment is prepared from ethanol, acetic acid, water, and 3-aminopropyltriethoxysilane, wherein the volume fraction of ethanol is 68 vol%, and the mass fraction of silane in this embodiment is 0.6 wt%. The pH value of the silane hydrolysate in this embodiment is 5.0 (wt%). In the dry mixing stage, the cementitious material and core-shell modified recycled coarse aggregate are mixed in a forced mixer for 65 seconds. In the blending stage, water is added and mixed in a forced mixer for 105 seconds to achieve a water-cement mass ratio of 0.30, resulting in a concrete mixture. The water usage in this embodiment is 93 kg per cubic meter of concrete mixture (based on the design volume). In the molding stage, the concrete mixture is laid or molded and vibrated to compact it. The vibration frequency is 38 Hz, the compaction pressure is 0.30 MPa, and the compaction duration is 18 seconds. In the curing stage, the molded body undergoes standard curing at a temperature of 20°C, a relative humidity ≥95%, and a curing time of 48 hours. The continuous porosity of the green porous concrete building material obtained in this embodiment is 25.5%. The continuous porosity in this embodiment is the percentage of the volume of connected pores to the total volume of the sample. The dominant pore diameter in this embodiment is 5.0 mm, which is the pore diameter with the highest frequency in the pore diameter distribution, obtained by image analysis of the concrete sample cross-section. The sample is cut to obtain the cross-section and the floating dust is removed. Five non-overlapping fields of view are randomly selected on each sample to take cross-sectional images with scale bars. The images are binarized and segmented, and the pore diameter distribution is statistically analyzed.

[0071] Features of Example 3: This example adopts a high-porosity, environmentally friendly proportioning scheme. The relatively low amount of cementitious material (310 kg) achieves resource conservation. The water-cement ratio of 0.30 maximizes slurry fluidity and pore formation. The low proportion of general-purpose silicate cement (25%) significantly reduces carbon emissions. The high proportion of mineral admixtures (75%) and the 1:2 ratio of granulated blast furnace slag powder and fly ash maximize the utilization of industrial solid waste. The high amount of coarse aggregate (1480 kg) and the extremely low amount of fine aggregate (15 kg) create a dense, open-pore structure. The core-shell modified recycled coarse aggregate accounts for 60% of the coarse aggregate, maintaining a moderate application of recycled materials. The thin mineralized shell layer (15 μm) and mild mineralization conditions reduce modification costs. The weight gain of 1.5 wt% and water absorption of 5.0 wt% reflect a mild modification strategy. The continuous porosity is 25.5%, and the dominant pore size is 5.0 mm. The mm-scale system forms a highly interconnected large-pore system, suitable for high-permeability scenarios such as rain gardens, sunken green spaces, and ecological parking lots in the construction of ecological sponge cities. It can also be applied to occasions with high drainage performance requirements but relatively low load requirements, such as park trails, leisure squares, and rooftop greening load-bearing layers. This solution achieves excellent permeability while highlighting environmental protection and low-carbon characteristics, making it particularly suitable for ecological urban infrastructure and green building supporting projects.

[0072] Example 4 A green porous concrete building material, based on the design volume of each cubic meter of concrete mixture, comprises: 410 kg of cementitious material, 91 kg of water, 1140 kg of coarse aggregate, and 108 kg of fine aggregate, with the mass ratio of water to cementitious material in this embodiment being 0.222. The coarse aggregate in this embodiment is core-shell modified recycled coarse aggregate; this core-shell modified recycled coarse aggregate includes a recycled coarse aggregate core, a mineralized shell layer covering the surface of the recycled coarse aggregate core, and a silane layer covering the surface of the mineralized shell layer; the thickness of the mineralized shell layer in this embodiment is 46 mm. μm; The silane layer in this embodiment is formed by γ-glycidyl etheroxypropyltrimethoxysilane; The cementitious material in this embodiment includes general-purpose silicate cement and mineral admixtures. Based on 100 parts by weight of the cementitious material in this embodiment, the amount of general-purpose silicate cement is 57 parts by weight, the amount of mineral admixtures is 43 parts by weight, and the sum of the weight parts of general-purpose silicate cement and mineral admixtures in this embodiment is 100 parts by weight; The mineral admixture in this embodiment is a composite admixture of granulated blast furnace slag powder and fly ash, wherein the mass ratio of 22 parts by weight of granulated blast furnace slag powder to 21 parts by weight of fly ash is approximately 1:0.95; The continuous porosity of the green porous concrete building material in this embodiment, measured by the vacuum saturation-drainage method, is 16.0%, and the dominant pore size is 1.5 mm.

[0073] The core-shell modified recycled coarse aggregate of this embodiment is prepared through the following steps: Raw materials include recycled coarse aggregate, water, sodium silicate, and calcium hydroxide; in the pretreatment stage of the recycled coarse aggregate, the recycled coarse aggregate is washed at a water-to-solid mass ratio of 2.8 by mechanical stirring for 3 minutes at a temperature of 20-25℃, followed by filtration and drying at a temperature of 75℃ to obtain pretreated recycled coarse aggregate with a water content of 1.3 wt%. In this embodiment, the water-to-solid mass ratio is based on the dry weight of the recycled coarse aggregate; in the mineralization precursor solution preparation stage, sodium silicate with a mass fraction of 18.5 wt% and calcium hydroxide with a mass fraction of 0.7 wt% are prepared based on the total mass of the mineralization precursor solution. A wt% aqueous solution or suspension is used to make the pH of the mineralization precursor solution 12.8. In this embodiment, the sodium silicate is water glass with a modulus of 2.2. In the vacuum impregnation stage, the pretreated recycled coarse aggregate is completely immersed in the mineralization precursor solution, wherein the liquid-solid mass ratio of the pretreated recycled coarse aggregate to the mineralization precursor solution is 1.8. The solution is kept under an absolute pressure of 0.018 MPa for 18 min, and then restored to normal pressure and impregnated at a temperature of 55°C for 55 min to obtain the mineralization precursor impregnated aggregate.

[0074] In this embodiment, the mineralized precursor impregnated aggregate forms a mineralized shell through the following carbonization steps: the carbonization medium is carbon dioxide; during the carbonization curing stage, the mineralized precursor impregnated aggregate is placed in an atmosphere with a carbon dioxide volume fraction of 27 vol%, and the carbonization curing is carried out in a carbonization chamber. Under normal pressure, the carbon dioxide and air mixture is replaced four times to achieve a carbon dioxide volume fraction of 27 vol%, and the chamber is maintained at a temperature of 25°C for 21 hours; in the endpoint determination stage, the weight gain of the mineralized precursor impregnated aggregate is calculated based on the mass of the dried pretreated recycled coarse aggregate. When the weight gain rate of the mineralized precursor impregnated aggregate reaches 4.5 wt%, the carbonization curing is stopped, and a core-shell aggregate precursor with a mineralized shell is obtained. The mineralization products of the mineralized shell in this embodiment include calcium carbonate and calcium silicate hydrate.

[0075] In this embodiment, the core-shell aggregate precursor with a mineralized shell forms a silane layer through the following silane treatment steps: the raw materials include ethanol, acetic acid, water, and γ-glycidoxypropyltrimethoxysilane; in the silane hydrolysis solution preparation stage, based on the total mass of the silane hydrolysis solution, an ethanol-water mixed solvent with a volume fraction of 92 vol% is prepared, acetic acid is added to make the pH value of the silane hydrolysis solution of this embodiment 3.7, and then the silane of this embodiment is added to make the mass fraction of silane of this embodiment 1.8 wt%, and hydrolyzed at 720 rpm for 28 min at a temperature of 22°C; in the silane treatment stage, the core-shell aggregate precursor with a mineralized shell is immersed in the silane hydrolysis solution and stirred for 27 min, then filtered and dried, and dried at a temperature of 45°C for 5.5 h to obtain core-shell modified recycled coarse aggregate.

[0076] The core-shell modified recycled coarse aggregate of this embodiment meets the following quality control conditions: the moisture content of the core-shell modified recycled coarse aggregate after drying is 0.1 wt%. The moisture content after drying in this embodiment is determined by the following method: the sample is dried at a temperature of 105℃, then cooled to room temperature in a desiccator and weighed. The drying-cooling-weighing process is repeated until the mass change between two consecutive weighings does not exceed 0.1%, which is recorded as constant weight. The moisture content after drying in this embodiment is expressed as the percentage of the mass difference before and after drying to the mass after drying. The thickness of the mineralized shell layer is 46 μm. The thickness of the mineralized shell layer in this embodiment is determined by observing the aggregate cross-section using a scanning electron microscope. Five different locations are measured for each sample, and the average value is taken. The water absorption rate of the core-shell modified recycled coarse aggregate is 1.4 wt%. The water absorption rate in this embodiment is determined by the following method: the sample is soaked in water at a temperature of 20-25℃ for 24 h, then removed and placed on a sieve to drain for 60 h. s, then gently touch the sample surface with dry absorbent paper until no continuous wet marks appear on the absorbent paper, which is recorded as the surface dry state. The water absorption rate is the percentage of the difference between the sample mass and the dry mass in this state to the dry mass. The particle size of the recycled coarse aggregate core in this embodiment is 18 mm. The mass ratio of the core-shell modified recycled coarse aggregate in the coarse aggregate in this embodiment is 95 wt%. The moisture content and water absorption rate in this embodiment are both on a dry basis.

[0077] The preparation method of the green porous concrete building material in this embodiment includes the following steps: providing core-shell modified recycled coarse aggregate. In this embodiment, providing core-shell modified recycled coarse aggregate includes mineralization treatment of the recycled coarse aggregate. The mineralization treatment in this embodiment uses a mineralization precursor solution. The mineralization precursor solution in this embodiment contains 18.5 wt% sodium silicate and 0.7 wt% calcium hydroxide. The mineralization treatment in this embodiment includes vacuum impregnation. The absolute pressure of vacuum impregnation in this embodiment is 0.018 MPa, and the holding time is 18 min. Providing core-shell modified recycled coarse aggregate in this embodiment includes carbonization treatment and silane treatment. In this embodiment, the carbonization treatment is carried out in an atmosphere with a carbon dioxide volume fraction of 27 vol%, a carbonization temperature of 25°C, and a carbonization time of 21 h. In this embodiment, the silane treatment uses a silane hydrolysis solution. The silane hydrolysis solution in this embodiment is prepared from ethanol, acetic acid, water, and γ-glycidyl etheroxypropyltrimethoxysilane, wherein the volume fraction of ethanol is 92 vol%, and the mass fraction of silane in this embodiment is 1.8 wt%. The pH value of the silane hydrolysate in this embodiment is 3.7 (wt%). In the dry mixing stage, the cementitious material and core-shell modified recycled coarse aggregate are mixed in a forced mixer for 165 s. In the blending stage, water is added and mixed in a forced mixer for 220 s to achieve a water-cement mass ratio of 0.222, resulting in a concrete mixture. The water usage in this embodiment is 91 kg per cubic meter of concrete mixture (based on the design volume). In the molding stage, the concrete mixture is laid or molded and vibrated to compact it. The vibration frequency is 56 Hz, the compaction pressure is 0.88 MPa, and the compaction duration is 54 s. In the curing stage, the molded body is steam-cured at a temperature of 75℃, relative humidity ≥95%, and a constant temperature time of 7 h. The total curing time is 24 h, including heating, constant temperature, and cooling stages. The continuous porosity of the green porous concrete building material obtained in this embodiment is 16.0%, and the continuous porosity in this embodiment is the percentage of the volume of connected pores to the total volume of the sample. The dominant pore diameter in this embodiment is 1.5 mm, which is the pore diameter with the highest frequency in the pore diameter distribution, obtained by image analysis of the concrete sample cross-section. The sample is cut to obtain the cross-section and the floating dust is removed. Five non-overlapping fields of view are randomly selected on each sample to take cross-sectional images with a scale bar. The images are binarized and segmented, and the pore diameter distribution is statistically analyzed.

[0078] Features of Example 4: This example employs a dense mix design with high cementitious material and a low water-cement ratio. The cementitious material dosage of 410 kg is sufficient and close to the reasonable range. The water-cement ratio of 0.222 is relatively low, close to the starting point of the water-cement ratio technical range, ensuring high density and strength of the paste. The proportion of general-purpose Portland cement at 57% is relatively high, close to the reasonable range of cement dosage, providing excellent cementitious performance. The proportion of mineral admixtures at 43% is close to the starting point of the admixture dosage technical range, and the near-equal proportion of granulated blast furnace slag powder and fly ash achieves complementary performance. The fine aggregate dosage is 108 kg. The high kg content, close to the reasonable range of fine aggregate dosage, filled some pores and improved material density. The core-shell modified recycled coarse aggregate accounted for 95% of the coarse aggregate, close to the reasonable range of recycled aggregate application ratio, maximizing the utilization of recycled materials. The water-to-solid mass ratio of 2.8 and drying temperature of 75℃, close to the reasonable range of pretreatment process parameters, ensured aggregate cleanliness. The sodium silicate mass fraction of 18.5% and carbon dioxide volume fraction of 27 vol%, close to the reasonable range of mineralization treatment parameters, formed a relatively thick mineralized shell layer of 46 μm. The ethanol volume fraction of 92% and silane mass fraction of 1.8%, close to the reasonable range of silane treatment parameters, enhanced the waterproof performance of the silane layer. The weight gain of 4.5 wt% and water absorption rate of 1.4 wt% reflected a significant modification effect. The vibration frequency of 56 Hz and compaction pressure of 0.88 MPa, close to the reasonable range of molding process parameters, improved material density. The steam curing temperature of 75℃ and the constant temperature time of 7... The near-steam curing parameter range accelerates strength development. A continuous porosity of 16.0% near the starting point of the porosity range and a dominant pore diameter of 1.5 mm near the starting point of the pore diameter range form a relatively dense pore structure. This is suitable for engineering scenarios requiring high load-bearing capacity while maintaining permeability, such as heavy-duty traffic roads, freight terminals, and container yards. It can also be applied to precast concrete components, prefabricated building walls, and high-performance curbs, where strict requirements for strength and durability are necessary. This solution achieves a coordinated unity of high strength, high durability, and moderate permeability through optimized combination of process parameters, making it particularly suitable for engineering projects with high load-bearing requirements and special needs for rapid construction and early strength.

[0079] Comparative Example 1: Basically the same as Example 1, except that the mineralized shell thickness of the core-shell modified recycled coarse aggregate is 3 μm, while the amount of other components and preparation conditions remain unchanged.

[0080] Comparative Example 2: It is basically the same as Example 1, except that the thickness of the mineralized shell of the core-shell modified recycled coarse aggregate is 55 μm, while the amount of other components and preparation conditions remain unchanged.

[0081] Comparative Example 3: It is basically the same as Example 1, except that the recycled coarse aggregate was not subjected to mineralized shell coating treatment and silane layer treatment. Ordinary recycled coarse aggregate was used directly to replace the core-shell modified recycled coarse aggregate. The dosage of other components and preparation conditions remained unchanged.

[0082] Comparative Example 4: It is basically the same as Example 1, except that the core-shell modified recycled coarse aggregate is only treated with mineralized shell coating and not with silane layer treatment. In the specific preparation, the silane treatment steps C1-C3 are omitted, and the amount of other components and preparation conditions remain unchanged.

[0083] Comparative Example 5: It is basically the same as Example 1, except that the water-cement ratio is 0.35, the amount of water used is 122.5 kg per cubic meter of concrete mixture, and the amount of other components and preparation conditions remain unchanged.

[0084] Comparative Example 6: It is basically the same as Example 1, except that the water-cement ratio is 0.20, the amount of water used is 70 kg per cubic meter of concrete mixture, and the amount of other components and preparation conditions remain unchanged.

[0085] Comparative Example 7: It is basically the same as Example 1, except that the amount of general silicate cement is 15 parts by weight and the amount of mineral admixture is 85 parts by weight, of which granulated blast furnace slag powder is 28 parts by weight and fly ash is 57 parts by weight. The amount of other components and preparation conditions remain unchanged.

[0086] Comparative Example 8: It is basically the same as Example 1, except that the amount of general silicate cement is 65 parts by weight and the amount of mineral admixture is 35 parts by weight, of which granulated blast furnace slag powder is 23 parts by weight and fly ash is 12 parts by weight. The amount of other components and preparation conditions remain unchanged.

[0087] Performance testing: Test Object: Green porous concrete building material molded specimen (size 100 mm × 100 mm × 100 mm). Test Objective: To evaluate the continuous porosity of the material and verify the effectiveness of the highly interconnected pore structure design. Test Principle: Based on the vacuum saturation-drainage method, the percentage of interconnected pores in the total volume of the specimen is calculated by measuring the mass difference of the specimen in the vacuum saturation state and after drainage, combined with the specimen volume. Experimental Method: The specimen is dried at 105℃ to constant weight and recorded as m0. It is placed in a vacuum saturation device, and a vacuum is drawn to an absolute pressure of 0.002 MPa and maintained for 30 min. Water is injected to submerge the specimen, and it is then immersed in atmospheric pressure for 24 h. After removal, the surface water is wiped off and recorded as the saturated mass m1. The specimen is suspended in water and weighed and recorded as the water mass m2. The continuous porosity P = (m1 - m0) / (m1 - m2) × 100%. Key Parameters: Vacuum degree 0.002 MPa, vacuum time 30 min, immersion time 24 h, test temperature 20±2℃. Data processing: At least 3 samples were tested in each group, and the results were expressed as mean ± standard deviation, with continuous porosity accurate to 0.1%.

[0088] Test Object: Standard specimen of green porous concrete building material (150 mm × 150 mm × 150 mm). Test Purpose: To evaluate the compressive strength of the material and verify the effect of the skeleton structure on the load-bearing capacity under high porosity conditions. Test Principle: A continuous and uniformly increasing load is applied to the specimen through a compression testing machine until failure, and the maximum failure load is recorded. The compressive strength is equal to the maximum load divided by the area of ​​the specimen under pressure. Experimental Method: After standard curing for 28 days, the specimen is removed, the surface moisture is wiped off, and a 3 mm thick rubber pad is placed on the pressure surface to uniformly transfer the load. The specimen is placed in the center of the pressure plate of the compression testing machine, and a loading rate of 0.5-0.8 MPa / s is continuously applied until the specimen fails. The maximum load F is recorded, and the compressive strength f = F / A (A is the area under pressure). Key Parameters: Loading rate 0.5-0.8 MPa / s, curing age 28 days, test temperature 20±2℃, relative humidity 60±5%. Data processing: Six samples were tested in each group. After removing the maximum and minimum values, the mean ± standard deviation was taken, accurate to 0.1 MPa.

[0089] Test Object: Standard specimen of green porous concrete building material (size 100 mm × 100 mm × 400 mm). Test Objective: To evaluate the freeze-thaw resistance of the material and verify the synergistic effect of core-shell modified recycled coarse aggregate and low water-cement ratio paste on improving long-term freeze-thaw durability against water erosion. Test Principle: The rapid freeze-thaw cycle test simulates the performance degradation process of the material under freeze-thaw conditions, with mass loss rate and relative dynamic elastic modulus as evaluation indicators. Experimental Method: After standard curing for 28 days, the specimens are soaked in water for 4 days to saturate them. They are then placed in a rapid freeze-thaw testing machine for freeze-thaw cycles. Each cycle includes freezing at -18±2℃ for 2-4 hours and thawing at 5±2℃ for 2-4 hours. The mass and dynamic elastic modulus of the specimens are measured every 25 cycles. The mass loss rate Δm = (m0 - m) / ( ... n ) / m0×100%, relative dynamic elastic modulus P=(f n (m² / f0²)×100%, where m0 and f0 are the initial mass and dynamic elastic modulus, respectively. n and f n The values ​​represent the mass and dynamic modulus of elasticity after n cycles. Key parameters: Freezing temperature -18±2℃, thawing temperature 5±2℃, number of cycles 300, and the test endpoint is a mass loss rate ≥5% or a relative dynamic modulus of elasticity ≤60%. Data processing: Three samples per group, results are expressed as mean ± standard deviation.

[0090] Test Subjects: Core-shell modified recycled coarse aggregate and control group ordinary recycled coarse aggregate. Test Objective: To evaluate the water absorption rate of core-shell modified recycled coarse aggregate and verify the synergistic effect of the mineralized shell layer and silane layer on reducing the water absorption performance of the aggregate. Test Principle: The water absorption rate is calculated by measuring the difference between the aggregate's mass in its surface-dry state and its dry mass to assess the aggregate porosity and interfacial waterproofing performance. Experimental Method: The aggregate sample was dried at 105℃ to constant weight, recorded as the dry mass m1. It was then soaked in clean water at 20-25℃ for 24 h, removed, and placed on a sieve to drain for 60 s. The surface was then lightly touched with dry absorbent paper until no continuous wet marks appeared on the paper (surface dry state), and immediately weighed, recorded as the surface-dry mass m2. The water absorption rate W = (m2-m1) / m1 × 100%. Key Parameters: Drying temperature 105℃, soaking temperature 20-25℃, soaking time 24 h, draining time 60 s. Data processing: Three parallel samples were tested in each group, and the mass of each sample was not less than 5 kg. The results are expressed as mean ± standard deviation, accurate to 0.1%.

[0091] Test Object: Core sample of green porous concrete building material (100 mm in diameter, 150 mm in height). Test Purpose: To evaluate the interfacial bond strength of the material and verify the load transfer efficiency of the interface between the silane layer on the surface of the core-shell modified recycled coarse aggregate and the cement paste. Test Principle: The indirect tensile strength of concrete is determined by splitting tensile test, reflecting the aggregate-paste interface bond performance. Experimental Method: A cylindrical specimen cured for 28 days is placed axially on the bearing plate of a compression testing machine. Strips with a width of 15-20 mm are placed at both ends of the specimen. A loading rate of 0.05-0.08 MPa / s is continuously applied until the specimen splits along the diameter direction. The maximum load P is recorded. The splitting tensile strength f = 2P / (πdh), where d is the specimen diameter and h is the specimen height. Key Parameters: Loading rate 0.05-0.08 MPa / s, strip width 15-20 mm, curing age 28 days, test temperature 20±2℃. Data processing: Six samples were tested in each group. After removing the maximum and minimum values, the mean ± standard deviation was taken, accurate to 0.01 MPa.

[0092] Test Object: Green porous concrete building material mixture. Test Objective: To evaluate the slump or slump spread of the mixture and verify its mixing stability and workability under low water-cement ratio conditions. Test Principle: By measuring the slump height or spread diameter of fresh concrete under its own weight, the fluidity and water retention of the mixture are assessed. Experimental Method: Immediately after mixing, the concrete mixture is placed into a slump cone in three layers. Each layer is tamped 25 times. After lifting the cone, the slump (vertical distance from the center of the original top surface to the highest point after slump) is measured. For high-flowability mixtures, the spread diameter in two vertical directions is measured after lifting the cone, and the average value is taken. Key Parameters: Test environment temperature 20±5℃, time from adding water to completion of the test ≤15 min, 25 tamping times per layer. Data Processing: Each mixture is tested twice, and the average value is taken. Slump is accurate to 5 mm, and spread is accurate to 10 mm. The results are recorded as a qualitative description of the mixture's consistency, water retention, and uniformity.

[0093] Figure 1 The X-ray diffraction (XRD) images for Example 1, Comparative Example 3 (ordinary recycled coarse aggregate), and Comparative Example 4 (mineralized layer only, silane layer) are shown. The fixed parameters were an XRD test scanning range of 2θ from 10° to 80° and normalization of diffraction intensity. The varying parameters were core-shell modified recycled coarse aggregate, unmodified ordinary recycled coarse aggregate, and recycled coarse aggregate containing only a mineralized shell. Example 1 showed calcite characteristic peaks at 2θ of 29.4° and 47.5°, and broad peaks related to calcium silicate hydrates in the 29° to 33° range. Comparative Example 3 lacked these mineralization product characteristics, while Comparative Example 4 mainly exhibited calcite peaks with significantly reduced broad peak characteristics. This indicates that interface modification through the synergistic construction of a mineralized shell and silane layer can form stable mineralized products on the aggregate surface and react compatibly with the new slurry, supporting the effectiveness of the modification strategy at the crystal phase level.

[0094] Figure 2 The images show the high-resolution Si 2p X-ray photoelectron spectroscopy (XPS) spectra of Example 1 and Comparative Example 4, which only have a mineralized layer without a silane layer. The parameters were fixed for high-resolution scanning in the Si 2p energy region, and the intensity was normalized. Peak fitting was performed on the spectra to obtain the fitted envelope and component peaks. The variable parameter was the presence of a silane layer formed by 3-aminopropyltriethoxysilane on the sample surface. Example 1 showed a Si-O-Si correlation peak at approximately 103.5 eV and a Si-C correlation peak at approximately 102.0 eV, while Comparative Example 4 showed a predominantly Si-O correlation peak and lacked Si-C characteristics. This indicates that silane molecules are effectively grafted onto the mineralized shell surface, introducing organic bonding features, which supports the formation and function of the silane layer from the perspective of interfacial chemical states.

[0095] Figure 3The X-ray photoelectron spectroscopy (XPS) N 1s high-resolution analysis images of Example 1 and Comparative Example 4 (mineralized layer without silane layer) are shown. The parameters were fixed for high-resolution scanning in the N 1s energy region, with intensity normalization and peak fitting of the spectra. The variable parameter was whether an amino-containing silane layer was introduced onto the sample surface. Example 1 showed a characteristic peak related to NC at approximately 399.8 eV, while Comparative Example 4 showed a signal close to the background and lacked a significant N-related peak. This indicates that the amino-containing silane successfully introduced a nitrogen-containing chemical environment onto the mineralized shell surface and formed a stable organic-inorganic transition interface, providing elemental chemical evidence supporting the contribution of the silane layer to interfacial adhesion and water resistance.

[0096] Figure 4 The figures show the pore size distribution curves for Example 1, Comparative Example 5 (water-binder ratio 0.35), and Comparative Example 6 (water-binder ratio 0.20). The fixed parameter is the pore size statistics, which use a continuous pore size variable and are presented as a distribution frequency curve to reflect the pore size distribution pattern. The variable parameter is the comparison between two conditions where the water-binder ratio is higher than the upper limit and lower than the lower limit. In Example 1, the pore size distribution peaks are mainly concentrated in the 1 mm to 6 mm range and are more concentrated. In Comparative Example 5, the distribution peaks shift towards larger pore sizes and exhibit wider distribution tails, while in Comparative Example 6, the distribution peaks shift towards smaller pore sizes and the distribution pattern is less conducive to forming stable through channels. This indicates that a water-binder ratio between 0.22 and 0.30 is beneficial for obtaining the target pore size and a more controllable pore size distribution, supporting the rationality of the mixing and molding parameters from a structural perspective.

[0097] Figure 5 The graphs show the cumulative pore size distribution curves for Example 1, Comparative Example 5 (water-cement ratio 0.35), and Comparative Example 6 (water-cement ratio 0.20). The parameters are fixed: the cumulative distribution curves are monotonically increasing and consistent with the same pore size data source; the varying parameters represent differences in pore structure caused by excessively high or low water-cement ratios. In Example 1, the cumulative distribution increase is more concentrated in the 1 mm to 6 mm range, indicating a narrower pore size distribution that better matches the target dominant pore size scale. In Comparative Example 5, the cumulative increase is faster at the large pore size end, reflecting a higher proportion of large pores. In Comparative Example 6, the cumulative increase is faster at the small pore size end, reflecting a higher proportion of small pores and potentially insufficient connectivity. This demonstrates that within the target water-cement ratio range, both pore size and distribution width can be controlled simultaneously, making it easier to balance permeable channels and structural stability.

[0098] Figure 6The graphs show the frequency distribution curves of micropore throats using mercury intrusion porosimetry for Examples 1, 5 (water-binder ratio 0.35), and 6 (water-binder ratio 0.20). The parameters are fixed: the output of the mercury intrusion porosimetry is expressed on logarithmic coordinates of pore size, with incremental pore volume distribution represented in dV / dlogD form. The varying parameters are the differences in slurry and interface microstructure caused by deviations in the water-binder ratio. The micropore throat distribution in Example 1 shows a relatively single peak with more controllable peak position and width. Comparative Example 5 exhibits a wider distribution and may be accompanied by multi-peak characteristics, while Comparative Example 6 shows peak positions biased towards smaller pore throats and a sharper distribution. This indicates that an excessively high water-binder ratio tends to introduce a more dispersed pore throat structure, while an excessively low water-binder ratio tends to lead to refined pore throats and increased non-uniformity. This supports controlling the water-binder ratio within a reasonable range to obtain a more predictable pore throat network.

[0099] Figure 7 The graphs show the cumulative pore volume curves obtained by mercury intrusion porosimetry for Example 1, Comparative Example 5 (water-to-binder ratio 0.35), and Comparative Example 6 (water-to-binder ratio 0.20). The fixed parameter is that the cumulative intrusion volume is obtained by integrating the incremental distribution and changes continuously with pore size. The variable parameter is the difference between the total pore volume and the threshold pore throat caused by deviations in the water-to-binder ratio. The cumulative pore volume curve of Example 1 is smoother, and its growth in the critical pore size range better reflects the characteristics of a controlled pore throat structure. Comparative Example 5 shows faster cumulative growth, reflecting a larger overall intrusive pore volume and a more dispersed pore throat structure. Comparative Example 6 shows slower cumulative growth, with the growth range biased towards smaller pore throats. This indicates that a reasonable water-to-binder ratio helps to achieve coordinated control of volume and structure at the microscopic pore throat scale, providing a microstructural basis for the subsequent balance between durability and strength.

[0100] Figure 8 The images show the Ca / Si molar ratio distribution along the interface line using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) micro-area analysis of ordinary recycled coarse aggregates in Example 1 and Comparative Example 3. The parameters were fixed: line scanning along the aggregate-to-slurry direction, with the Ca / Si molar ratio calculated based on elemental content to reflect the interfacial chemical gradient. The variable parameter was whether the aggregate underwent synergistic modification with a mineralized shell and silane layer. In Example 1, the Ca / Si ratio changed more gradually with distance, and the interfacial transition zone was narrower, indicating a more uniform distribution of elements and reaction products. In Comparative Example 3, the Ca / Si ratio change was more abrupt, the transition zone was wider, and it was more prone to being accompanied by non-uniform regions. This suggests that core-shell modification can make the interfacial reaction more continuous and reduce abrupt interfacial chemical changes, supporting the rationale for enhanced interfacial adhesion and improved durability from the perspective of micro-gradient and interfacial densification.

[0101] Figure 9This is a SEM image of the overall cross-sectional morphology of the core-shell modified recycled coarse aggregate from Example 1. The polished cross-section sample was observed using low-magnification backscattered electron (BSE) mode with fixed parameters. The observation parameters were the macroscopic core and outer structure of the aggregate. The image clearly defines the internal loose recycled coarse aggregate core region containing residual phases of old mortar and porous defects, and the external continuous and dense mineralized shell region. The two regions show significant differences in grayscale and morphology, confirming the successful construction of the "core-shell" structure and the effective coverage of primary defects by the shell.

[0102] Figure 10 The image shows a SEM image of the mineralized shell thickness measurement from Example 1. The parameters were fixed at medium magnification, focusing on the boundary between the shell and the core region. Multiple measurements were taken at typical locations. The observed parameters were the morphology of the inner and outer boundaries of the shell and the uniformity of its thickness. The image shows that the inner side of the shell tightly fills the rough undulations of the core surface, while the outer boundary is relatively smooth. By measuring at least five representative locations along the annular shell and averaging the measurements, the average thickness of the mineralized shell was determined to be approximately 27.5 μm, demonstrating that the modification process can form a dense coating layer with a certain thickness and relatively uniformity.

[0103] Figure 11 This is a SEM image of the microstructure of the mineralized products within the shell of Example 1, with the observation parameters fixed at high magnification to examine the micro-regions within the shell. The observation parameters are the morphology and combination of the crystalline and gel phases. The microstructure shows that the shell is composed of massive or clustered calcium carbonate crystals (CaCO3) and flocculent, lamellar stacked calcium silicate hydrate gels (C-(A)-SH). The crystals fill the pores, and the gel coats and connects the crystals. This synergistic and interlocking structure of "crystalline phase + gel phase" significantly reduces the through-pores within the shell, proving that the shell has been transformed from a loose and porous layer into a highly dense composite layer.

[0104] As can be seen from the performance of the embodiments and comparative examples in Table 1, the green porous concrete building material of the present invention achieves a balance between high interconnected porosity and high mechanical properties through the synergistic design of core-shell modified recycled coarse aggregate. The continuous porosity of Examples 1-4 is maintained in the range of 16.0-25.5%, while the compressive strength reaches 12.8-28.0 MPa, which is significantly better than the 10.5 MPa of Comparative Example 3. Comparative Example 1 uses an excessively thin mineralized shell (3 μm) and Comparative Example 2 uses an excessively thick mineralized shell (55 μm). Both (μm) resulted in a decrease in compressive strength and frost resistance, indicating that there is an optimal range for the thickness of the mineralized shell layer. Comparative Example 3, using ordinary recycled coarse aggregate without core-shell modification, resulted in a water absorption rate as high as 8.5%, a mass loss rate of 7.5% after 300 freeze-thaw cycles, and a relative dynamic elastic modulus of only 52.0%, verifying the key role of core-shell modification technology in improving durability. Comparative Example 4, with only mineralization layer treatment and lacking a silane layer, resulted in deterioration of interfacial bonding strength and frost resistance, demonstrating the importance of the synergistic effect of the mineralized shell layer and silane layer in resolving the conflict between hydrophobicity and reduced water absorption and interfacial bonding efficiency. Comparative Examples 5 and 6, deviating from the optimal water-cement ratio range, resulted in poor mixing and molding stability (slump of 65 mm and 20 mm, respectively). The imbalance of water-cement ratio (mm) and comprehensive mechanical properties indicates the scientific validity of the water-cement ratio range of 0.22-0.30. The low cement content (15 parts by weight) in Comparative Example 7 and the high cement content (65 parts by weight) in Comparative Example 8 both failed to achieve the optimal performance balance, verifying the necessity of optimizing the cementitious material ratio. Example 4 maintained a compressive strength of 28.0 MPa and excellent durability even when approaching the boundary of the water-cement ratio and cementitious material content range, proving the rationality of the parameter range of the claims and the stability of the technical solution.

[0105] Table 1 Performance comparison data between the examples and comparative examples Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A green porous concrete building material, characterized in that, Based on the design volume of each cubic meter of concrete mix, it includes: 300-410 kg of cementitious materials, 90-123 kg of water, and 1100-1550 kg of coarse aggregate, with the mass ratio of water to the cementitious materials being 0.22-0.30; wherein: The coarse aggregate includes core-shell modified recycled coarse aggregate; The core-shell modified recycled coarse aggregate includes a recycled coarse aggregate core, a mineralized shell layer covering the surface of the recycled coarse aggregate core, and a silane layer covering the surface of the mineralized shell layer. The thickness of the mineralized shell is 5-50 μm; The silane layer is formed of 3-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane; The cementitious material includes general-purpose silicate cement and one or more mineral admixtures. Based on 100 parts by weight of the cementitious material, the amount of general-purpose silicate cement is 20-60 parts by weight, the amount of mineral admixture is 40-80 parts by weight, and the amount of mineral admixture is the remainder after subtracting the weight of general-purpose silicate cement from 100 parts by weight. The continuous porosity of the green porous concrete building material was determined to be 15-28% by the vacuum saturation-drainage method.

2. The green porous concrete building material according to claim 1, characterized in that, The core-shell modified recycled coarse aggregate is prepared through the following steps: A1. The raw materials include recycled coarse aggregate, water, sodium silicate, and calcium hydroxide; A2. Pretreatment of recycled coarse aggregate: The recycled coarse aggregate is washed and dehydrated at a water-to-dry basis mass ratio of 0.5-3.

0. The washing is carried out by mechanical stirring at a temperature of 20-25℃ for 2-10 min. The dehydration is carried out by filtration and separation followed by drying at a temperature of 40-80℃ to obtain pretreated recycled coarse aggregate with a moisture content of 1.0-6.0 wt%. A3. Preparation of mineralization precursor solution: Based on the total mass of the mineralization precursor solution, prepare an aqueous solution or suspension with a sodium silicate mass fraction of 5.0-20.0 wt% and a calcium hydroxide mass fraction of 0.5-5.0 wt%, with the remainder being water, to make the pH value of the mineralization precursor solution 11.0-13.

0. A4. Vacuum impregnation: The pretreated recycled coarse aggregate is completely immersed in the mineralization precursor solution, wherein the liquid-solid mass ratio of the pretreated recycled coarse aggregate to the mineralization precursor solution is 1.5-5.

0. The solution is maintained at an absolute pressure of 0.005-0.020 MPa for 5-20 min, and then restored to normal pressure and impregnated at a temperature of 20-60℃ for 10-60 min to obtain mineralization precursor impregnated aggregate.

3. The green porous concrete building material according to claim 2, characterized in that, The mineralized precursor impregnated aggregate forms a mineralized shell through the following carbonization steps: B1. The carbonization medium is carbon dioxide; B2) Carbonation curing: Place the mineralized precursor impregnated aggregate in an atmosphere with a carbon dioxide volume fraction of 5-30 vol%, and replace it with a mixture of carbon dioxide and air 2-5 times under normal pressure to achieve a carbon dioxide volume fraction of 5-30 vol%, and maintain it at a temperature of 20-60℃ for 2-24 hours. B3) Endpoint criterion: Based on the mass of the dried pretreated recycled coarse aggregate, when the mass gain rate of the mineralized precursor impregnated aggregate reaches 0.5-5.0 wt%, carbonization curing is stopped to obtain a core-shell aggregate precursor with a mineralized shell.

4. The green porous concrete building material according to claim 3, characterized in that, The core-shell aggregate precursor with a mineralized shell layer forms a silane layer through the following silane treatment steps: C1. The raw materials include ethanol, acetic acid, water, and 3-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane; C2. Preparation of silane hydrolysate: Based on the total mass of the silane hydrolysate, prepare an ethanol-water mixed solvent with an ethanol volume fraction of 60-95 vol%, add acetic acid to adjust the pH of the silane hydrolysate to 3.5-5.5, then add the silane to adjust the silane mass fraction to 0.2-2.0 wt%, and hydrolyze at 200-800 rpm for 10-30 min at a temperature of 20-40℃. C3. Silane treatment: The core-shell aggregate precursor with mineralized shell is immersed in silane hydrolysate and stirred for 5-30 minutes, then filtered and dried to obtain core-shell modified recycled coarse aggregate.

5. The green porous concrete building material according to claim 4, characterized in that, The drying process involves drying at a temperature of 40-80℃ for 2-6 hours, while meeting the following quality control conditions: The dried moisture content of the core-shell modified recycled coarse aggregate was 0-1.0 wt%; The thickness of the mineralized crust is 5-50 μm; The water absorption rate of the core-shell modified recycled coarse aggregate is 1.0-6.0 wt%; the particle size of the core of the recycled coarse aggregate is 5-20 mm.

6. The green porous concrete building material according to claim 1, characterized in that, The mineral admixture is selected from one or more of granulated blast furnace slag powder, fly ash, limestone powder and metakaolin; the dominant pore size of the green porous concrete building material is 1-6 mm; and it also includes 0-120 kg of fine aggregate per cubic meter of concrete mixture.

7. A method for preparing the green porous concrete building material according to claims 1-6, characterized in that, Includes the following steps: S1. Provide core-shell modified recycled coarse aggregate; S2. Dry mixing: Mix the cementitious material with the core-shell modified recycled coarse aggregate for 30-180 seconds; S3. Mixing: Add water and mix for 60-240 seconds to make the water-cement mass ratio 0.22-0.30, thus obtaining the concrete mixture; S4. Molding: The concrete mixture is laid or molded and vibrated to compact it. The vibration frequency is 30-60 Hz and the compaction pressure is 0.1-1.0 MPa. S5. Curing: Curing the molded body at a temperature of 10-80℃ for 12-168 hours.

8. The preparation method according to claim 7, characterized in that, The provision of core-shell modified recycled coarse aggregate includes mineralization treatment of the recycled coarse aggregate. The mineralization treatment uses a mineralization precursor solution, in which the mass fraction of sodium silicate is 5.0-20.0 wt% and the mass fraction of calcium hydroxide is 0.5-5.0 wt%. The mineralization treatment includes vacuum impregnation, in which the absolute pressure of vacuum impregnation is 0.005-0.020 MPa and the holding time is 5-20 min.

9. The preparation method according to claim 7, characterized in that, The provision of core-shell modified recycled coarse aggregate includes carbonization treatment and silane treatment. The carbonization treatment is carried out in an atmosphere with a carbon dioxide volume fraction of 5-30 vol%, a carbonization temperature of 20-60℃, and a carbonization time of 2-24 h. The silane treatment uses a silane hydrolysate, which is prepared from ethanol, acetic acid, water, and 3-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane. The volume fraction of ethanol is 60-95 vol%, the mass fraction of silane is 0.2-2.0 wt%, and the pH value of the silane hydrolysate is 3.5-5.

5.

10. The preparation method according to claim 7, characterized in that, Based on the design volume of each cubic meter of concrete mixture, the water usage is 90-123 kg; the compaction duration is 5-60 s; and the continuous porosity of the resulting green porous concrete building material is 15-28%. Furthermore, the continuous porosity is the percentage of the volume of connected pores to the total volume of the sample. Furthermore, the dominant pore size is obtained by image analysis of the concrete sample cross-section, which is the pore size corresponding to the highest frequency in the pore size distribution; the sample is cut to obtain the cross-section and the floating dust is removed, and at least 5 non-overlapping fields of view are randomly selected on each sample to take cross-sectional images with a scale bar, the images are binarized and segmented, and the pore size distribution is statistically analyzed. Furthermore, the moisture content of the core-shell modified recycled coarse aggregate after drying is determined by the following method: the sample is dried at a temperature of 105℃, then cooled to room temperature in a desiccator and weighed; the drying-cooling-weighing process is repeated until the mass change between two consecutive weighings does not exceed 0.1%, which is recorded as constant weight; the moisture content after drying is expressed as the percentage of the mass difference before and after drying to the mass after drying. Furthermore, the water absorption rate of the core-shell modified recycled coarse aggregate is determined by the following method: after soaking the sample in water at a temperature of 20-25℃ for 24 h, it is taken out, placed on a sieve and left to drain for 60 s. Then, the sample surface is gently touched with dry absorbent paper until no continuous wet marks appear on the absorbent paper, which is recorded as the surface dry state. The water absorption rate is calculated as the percentage of the difference between the sample mass and the dried mass under this condition relative to the dried mass. Furthermore, the thickness of the mineralized shell was determined by observing the aggregate cross-section using a scanning electron microscope. At least five different locations were measured for each sample, and the average value was taken. Furthermore, the sodium silicate is water glass with a modulus of 2.0-3.

5. Furthermore, in the pretreatment of the recycled coarse aggregate, the washing method is mechanical stirring and washing for 2-10 minutes at a temperature of 20-25℃; the dewatering method is drying after filtration and separation at a temperature of 40-80℃. Furthermore, the water-to-solid mass ratio is based on the dry basis mass of the recycled coarse aggregate as the solid basis. Furthermore, the carbonization curing is carried out in a carbonization chamber, where a mixture of carbon dioxide and air is used to replace the carbon dioxide 2-5 times under normal pressure, so that the volume fraction of carbon dioxide in the chamber reaches 5-30 vol. Furthermore, the mineralization products of the mineralized shell contain at least one of calcium carbonate or calcium silicate hydrate. Furthermore, the dry mixing and blending are carried out in a forced mixer. Furthermore, the curing method is either standard curing or steam curing. The conditions for standard curing are a temperature of 20±2℃ and a relative humidity of ≥95%; the conditions for steam curing are a temperature of 60-80℃, a relative humidity of ≥95%, and a constant temperature time of 4-8 hours. Furthermore, the core-shell modified recycled coarse aggregate accounts for 45-100 wt% of the total coarse aggregate. Furthermore, the mineral admixture is a composite admixture of granulated blast furnace slag powder and fly ash, wherein the mass ratio of granulated blast furnace slag powder to fly ash is 1:0.5-2. Furthermore, the moisture content and water absorption rate are both calculated on a dry basis. Patent Title: A Green Porous Concrete Building Material and Its Preparation Method The purpose of this invention is to provide a green porous concrete building material and its preparation method, which solves three shortcomings of existing porous concrete: it is difficult to balance high interconnected porosity and high load-bearing strength / stiffness; the mixing and molding stability under low water-cement ratio conditions and the durability performance such as long-term resistance to water erosion and freeze-thaw cycles are mutually constrained; and there is a mechanistic conflict between the surface hydrophobicity and water absorption reduction of core-shell modified recycled coarse aggregate and the interfacial bonding load transfer efficiency.

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