Water-retaining aggregate with core-shell structure as well as preparation method and application of water-retaining aggregate

Abstract

The invention discloses water-retaining aggregate with a core-shell structure as well as a preparation method and application of the water-retaining aggregate, and relates to the technical field of building materials. The preparation method of the water-retaining aggregate with the core-shell structure comprises the following steps: adding a polyacrylamide flocculant aqueous solution into sand washing mud, stirring to obtain flocculated mud, and dehydrating; granulating and forming the dehydrated material; spraying cement paste on the surface of the granulation product; and performing standard curing or steam curing on the slurry-coated particles to obtain the water-retaining aggregate. The invention discloses the core-shell structured water-retaining aggregate prepared by the method and application of the core-shell structured water-retaining aggregate in preparation of vegetation concrete. According to the invention, a core-shell structure is constructed through a synergistic hydration reaction between a surface cement coating and water in washed sand mud, so that the strength and water retention capacity of the aggregate are synchronously enhanced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building materials, and in particular to a water-retaining aggregate with a core-shell structure, a preparation method therefor, and an application thereof. BACKGROUND

[0002] With the continuous advancement of ecological restoration and sponge city construction, as a new type of material that can balance structural performance and ecological function, vegetation concrete is increasingly widely used in slope treatment, roof greening, and water and soil conservation engineering. The basic principle is to use the porous concrete framework to form a space for plant root growth and to realize rainwater infiltration and storage through internal pores. However, the existing vegetation concrete still faces significant technical defects in actual promotion: the water-retaining performance of traditional aggregates (such as gravel and sand) is poor, and it is difficult to ensure continuous water supply during drought or rainfall intervals, which directly affects the stability of vegetation survival rate and ecological restoration effect; on the other hand, although the water-holding capacity can be improved by adding a high-molecular water-retaining agent (such as sodium polyacrylate), such materials easily block the pores of the concrete, resulting in a loss of strength, and there are long-term degradation difficulties and environmental pollution risks.

[0003] In view of the above problems, some improvement schemes have been proposed in the prior art. For example, patent CN104150799A proposes a slow-release fertilizer type lightweight aggregate, which uses polystyrene particles and sulphoaluminate cement as main raw materials, although it has improved strength and slow-release performance, but it is not economical and environmentally friendly: the cost of polystyrene particles is high, which is not conducive to large-scale promotion, and the degradation period in the natural environment is extremely long, which can easily cause white pollution. Another patent

[0004] CN109095800A uses construction waste to prepare ecological aggregate by surface coating modification, but its structure is dense and the water absorption rate is low, which cannot meet the functional requirements of vegetation concrete for water conservation.

[0005] At the same time, washing sand mud, as a large amount of waste material generated during the washing process of sand and gravel aggregate, is mainly disposed by stacking and landfilling in the traditional way, which not only occupies land but also has environmental risks such as heavy metal ion leaching. According to statistics, the annual washing sand mud discharge in China exceeds 10 million tons, and the comprehensive utilization rate is less than 30%, so the resource utilization of washing sand mud has become an urgent need for the green development of the sand and gravel industry. In recent years, patents such as CN119330640A, CN119330667A, and CN120117817A have proposed technical paths for converting washing sand mud into building materials through dehydration, modification, and solidification processes, providing a feasible direction for promoting the efficient use of washing sand mud, indicating that such solid waste has significant resource development potential.

[0006] In the aspects of improving the pore structure and water retention capacity of the vegetation concrete, the existing researches mostly use natural porous minerals such as ceramsite and vermiculite as aggregates. Although these materials have certain water storage capacity, they still have application bottlenecks such as slow water absorption rate and short water retention time. Some researches also attempt to enhance the water retention performance by coating a water-retaining coating on the surface or adding inorganic water-retaining agents (such as diatomite), but the coating is easy to fall off, and the water absorption expansion of the inorganic material may also cause the internal structure of the concrete to crack.

[0007] Therefore, it is urgent to develop a vegetation concrete material with good water retention performance, high strength, environmental friendliness and economic feasibility, especially to break through the functional limitations of the existing aggregate, realize the high-value utilization of bulk solid waste (such as washed sand mud), and solve the coordination problem between water retention and strength, so as to promote the large-scale and sustainable application of vegetation concrete in ecological engineering. SUMMARY

[0008] One of the purposes of the present application is to provide a high-performance water-retaining aggregate using washed sand mud as the main raw material. The aggregate has high strength and high water retention characteristics, can effectively realize the high-value resource utilization of bulk solid waste, and cooperatively solve the balance problem between water retention and mechanical strength.

[0009] The second purpose of the present application is to provide a preparation method of the above-mentioned water-retaining aggregate.

[0010] The third purpose of the present application is to provide the application of the water-retaining aggregate.

[0011] To achieve the above-mentioned purposes, the technical solutions adopted by the present application are as follows:

[0012] The first aspect of the present application discloses a preparation method of a water-retaining aggregate with core-shell structure, comprising the following steps:

[0013] S1. Raw material pretreatment: adding a polyacrylamide flocculant aqueous solution into the washed sand mud slurry, stirring to obtain a flocculated mud slurry, and dewatering;

[0014] S2. Granulation molding: granulating and molding the dewatered material;

[0015] S3. Surface slurry coating: spraying cement slurry on the surface of the granulation product;

[0016] S4. Curing: curing the slurry-coated particles using standard curing or steam curing to obtain the water-retaining aggregate.

[0017] In some embodiments of the present application, in step S1, the concentration of the polyacrylamide flocculant aqueous solution is 0.07-0.3wt%, preferably 0.15wt%;

[0018] The mass of the polyacrylamide flocculant is 0.5-3% of the dry weight of the washed sand mud slurry;

[0019] Preferably, the flocculation slurry is dewatered to a water content of 25-40%.

[0020] In some embodiments of the present application, in step S1, sodium-based bentonite is added to the water-washed sand slurry, stirred uniformly, and then a polyacrylamide flocculant aqueous solution is added, stirred, to obtain a flocculation slurry, which is dewatered.

[0021] Preferably, the mass of sodium-based bentonite is 3-5% of the dry weight of the water-washed sand slurry.

[0022] In some embodiments of the present application, in step S2, the dewatered material is granulated into a shape by roller compaction granulation or disc granulation.

[0023] Preferably, the wet granules obtained by roller compaction granulation have a particle size of 5-20mm.

[0024] Preferably, the wet granules obtained by disc granulation have a particle size of 10-25mm.

[0025] Preferably, the wet granules are coated with slurry after standing for 12-48h.

[0026] In some embodiments of the present application, in step S3, the water-cement ratio of the cement slurry is 0.30-0.40, preferably 0.35.

[0027] Preferably, the dry weight of the cement slurry is 8-15% of the dry weight of the water-washed sand slurry.

[0028] In some embodiments of the present application, the cement slurry comprises cement and silica fume in an amount of 0-20% of the mass of the cement.

[0029] Preferably, the cement is selected from at least one of P.O425 Portland cement and sulphoaluminate cement.

[0030] In some embodiments of the present application, in step S4, the standard curing step comprises: placing the coated granules in an environment with a temperature of 20-30℃ and a relative humidity of ≥90% for 72h, to allow the cement shell to hydrate and form a porous structure.

[0031] The steam curing step comprises: placing the coated granules in a steam curing chamber at a curing temperature of 40-70℃ for 4-16h.

[0032] The second aspect of the present application discloses a core-shell structure water-retaining aggregate prepared by the method described above.

[0033] In some embodiments of the present application, the water-retaining aggregate has a water retention rate of >30% and a cylinder compressive strength of ≥5MPa.

[0034] In some embodiments of the present application, the water-washed sand and mud particles as the inner core of the water-retaining aggregate have a moisture content of 18-35% and a particle size of 5-20mm; the cement-based hydration product layer wrapping the inner core has a thickness of 0.5-2mm.

[0035] The third aspect of the present application discloses the use of the above-mentioned water-retaining aggregate in the preparation of vegetation concrete.

[0036] Compared with the prior art, the present application has the following beneficial effects:

[0037] The present application builds a "core-shell structure" through the synergistic hydration reaction between the surface cement coating and the internal moisture of the water-washed sand and mud, thereby simultaneously enhancing the strength and water-retaining performance of the aggregate. In terms of resource utilization, the water-retaining aggregate of the present application can efficiently absorb water-washed sand and mud solid waste, with a dry base content of 0.9-1.1 tons per ton of aggregate. In terms of preparation process, the sintering-free process used in the present application can reduce energy consumption by more than 80% compared with the traditional ceramsite preparation method, achieving significant energy-saving effect. In terms of material performance, the water-retaining aggregate of the present application has excellent comprehensive characteristics: water retention rate of 30%-45%, cylinder compression strength of 5-8MPa; at the same time, the dense structure formed on the surface effectively controls the water absorption rate to be below 10%.

[0038] The synergistic optimization of the performance of the water-retaining aggregate of the present application, i.e. the good combination of high water-retaining property and relatively high structural strength, makes it particularly suitable for applications such as roof greening substrate layer and ecological slope protection engineering, which require the combination of both. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 is a flowchart of the preparation method of the water-retaining aggregate of the present application; Figure 1 Figure 2 is a schematic diagram of the core-shell structure of the water-retaining aggregate of the present application.

[0040] Figure 3 is a schematic diagram of the core-shell structure of the water-retaining aggregate of the present application. Figure 2 DETAILED DESCRIPTION

[0041] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme of the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0042] A preparation method of a water-retaining aggregate with a core-shell structure, comprising the following steps:

[0043] S1. Raw material pretreatment: add a polyacrylamide flocculant aqueous solution with a concentration of 0.07-0.3wt% to the sand and mud slurry, stir to obtain flocculated mud slurry, and dewater to a moisture content of 25-40%;

[0044] ​The concentration of the polyacrylamide flocculant aqueous solution is preferably 0.15 wt%; the mass of the polyacrylamide flocculant is 0.5-3% of the dry weight of the washed sand and mud slurry.

[0045] S2. Granulation molding: the dewatered material is granulated and molded by roller compaction or disc granulation; wherein the wet granules obtained by roller compaction have a particle size of 5-20 mm; the wet granules obtained by disc granulation have a particle size of 10-25 mm; the wet granules are allowed to stand for 12-48 h before being coated with a slurry.

[0046] S3. Surface coating with a slurry: the granulation product is sprayed with a cement slurry;

[0047] The water-cement ratio of the cement slurry is 0.30-0.40, preferably 0.35; the dry weight of the cement slurry accounts for 8-15% of the dry weight of the washed sand and mud; the cement slurry comprises cement and 0-20% of silica fume by mass of the cement; preferably, the cement is selected from at least one of P.O425 Portland cement and sulphoaluminate cement.

[0048] S4. Curing: the coated granules are cured by standard curing or steam curing to obtain the water-retaining aggregate; wherein the standard curing step comprises: placing the coated granules in an environment with a temperature of 20-30℃ and a relative humidity of ≥90% for curing for 72 h, so that the cement shell is hydrated to form a porous structure;

[0049] The steam curing step comprises: placing the coated granules into a steam curing chamber, curing at a temperature of 40-70℃ for 4-16 h.

[0050] In some preferred embodiments of the present application, in step S1, sodium-based bentonite is added to the washed sand and mud slurry, stirred uniformly, and then polyacrylamide flocculant aqueous solution is added and stirred to obtain a flocculated slurry, which is dewatered; preferably, the mass of the sodium-based bentonite is 3-5% of the dry weight of the washed sand and mud slurry.

[0051] In some embodiments of the present application, in step S4, the standard curing step comprises: placing the coated granules in an environment with a temperature of 20-30℃ and a relative humidity of ≥90% for curing for 72 h, so that the cement shell is hydrated to form a porous structure;

[0052] The steam curing step comprises: placing the coated granules into a steam curing chamber, curing at a temperature of 40-70℃ for 4-16 h.

[0053] The second aspect of the present application discloses a water-retaining aggregate with a core-shell structure, which is obtained by the above method.

[0054] In some embodiments of the present application, the water-retaining rate of the water-retaining aggregate is >30%, and the cylinder compressive strength is ≥5 MPa.

[0055] In some embodiments of the present application, the water-washed sand mud particles as the inner core in the water-retaining aggregate have a water content of 18-35% and a particle size of 5-20 mm; the cement-based hydration product layer wrapping the inner core has a thickness of 0.5-2 mm.

[0056] The third aspect of the present application discloses the application of the water-retaining aggregate in preparing the vegetation concrete.

[0057] The sand mud slurry in the embodiments of the present application is from the water-washed sand mud of a sandstone factory.

[0058] The cement in the embodiments of the present application is from Jiahua Special Cement Co., Ltd.

[0059] Example 1

[0060] The present embodiment discloses a preparation method of the water-retaining aggregate with a core-shell structure of the present application, and specifically as follows:

[0061] S1. Raw material pretreatment: a polyacrylamide flocculant (PAM) aqueous solution with a concentration of 0.15wt% is prepared, and the total mass of PAM in the aqueous solution is 1.5% of the dry weight of the sand mud slurry. Under the condition of continuous stirring in the slurry collection pool, the entire solution is added in three equal amounts, with an interval of 3 minutes each time, and the total reaction time is 15 minutes. Then, the slurry is dewatered by a belt filter, and the final water content is controlled to be 28%±1%.

[0062] S2. Granulation forming: the dewatered slurry is poured into a roller granulator, the roller gap is adjusted to 8 mm, and the rotating speed is 40 r / min, so as to form Φ12 mm wet particles, which are left to stand for 24 h.

[0063] S3. Surface coating: a P.O42.5 cement slurry with a water-cement ratio of 0.35 is prepared; the wet particles left to stand for 24 h in step S2 are sent into a rotary drum granulator, the rotating speed of the granulator is adjusted to 15 r / min, and the cement slurry is sprayed in two stages, with a spraying amount of 70% in the first stage and 30% in the second stage, and the total spraying time is 8-10 min, so as to ensure uniform adhesion of the cement slurry. The dry weight of the cement slurry accounts for 12% of the dry weight of the water-washed sand mud.

[0064] S4. Curing: the coated particles are cured in a standard curing environment of 25℃ and RH≥90% for 72 h, so as to obtain the water-retaining aggregate with a core-shell structure.

[0065] Example 2

[0066] The present embodiment discloses a preparation method of the water-retaining aggregate with a core-shell structure of the present application, and specifically as follows:

[0067] S1. Raw material pretreatment: prepare a polyacrylamide flocculant (PAM) aqueous solution with a concentration of 0.3wt%, and the total mass of PAM in the aqueous solution is 0.5% of the dry weight of the sand washing mud slurry. Under the condition of continuous stirring in the mud collection tank, 5% of sodium-based bentonite of the dry weight of the sand washing mud slurry is added, and stirring is performed for 35 min to ensure uniform stirring; then the entire PAM aqueous solution is added in three equal portions, with an interval of 3 min between each addition, and the total reaction time is 15 min, after which the mud is dewatered by a belt filter, and the final water content is controlled to be 25%±1%.

[0068] S2. Granulation molding: pour the dewatered mud into a roller compaction granulator, adjust the compaction gap to 8 mm, and the rotating speed to 40 r / min, to form Φ12 mm wet granules, and then stand for 24 h;

[0069] S3. Surface coating: prepare a P.O 42.5 cement-silica fume slurry with a water-cement ratio of 0.35; wherein the mass of silica fume is 20% of the mass of P.O 42.5 cement. The wet granules standing for 24 h in step S2 are sent to a rotary drum granulator, the rotating speed of the granulator is adjusted to 15 r / min, and the cement slurry is sprayed in two stages, with a spraying amount of 70% in the first stage and 30% in the second stage, and the total spraying time is 8-10 min to ensure uniform adhesion of the cement slurry. The dry weight of the cement-silica fume slurry accounts for 15% of the dry weight of the sand washing mud.

[0070] S4. Curing: the coated granules are cured in a standard curing environment of 25℃ and RH≥90% for 72 h, to obtain the core-shell structure water-retaining aggregate.

[0071] Example 3

[0072] The present embodiment discloses a preparation method of the core-shell structure water-retaining aggregate of the present application, which is specifically as follows:

[0073] S1. Raw material pretreatment: prepare a polyacrylamide flocculant (PAM) aqueous solution with a concentration of 0.7wt%, and the total mass of PAM in the aqueous solution is 3% of the dry weight of the sand washing mud slurry. Under the condition of continuous stirring in the mud collection tank, 5% of sodium-based bentonite of the dry weight of the sand washing mud slurry is added, and stirring is performed for 35 min to ensure uniform stirring; then the entire PAM aqueous solution is added in three equal portions, with an interval of 3 min between each addition, and the total reaction time is 15 min, after which the mud is dewatered by a belt filter, and the final water content is controlled to be 28%±1%.

[0074] S2. Granulation molding: pour the dewatered mud into a roller compaction granulator, adjust the compaction gap to 8 mm, and the rotating speed to 40 r / min, to form Φ12 mm wet granules, and then stand for 24 h;

[0075] S3. Surface coating: P.O 42.5 cement-silica fume paste with water-cement ratio of 0.35 is prepared; the mass of silica fume is 20% of the mass of P.O 42.5 cement. The wet particles of step S2 which are placed for 24h are sent to the rotary drum granulator, the rotation speed of the granulator is adjusted to 15r / min, the cement paste is sprayed in two stages, the first stage spraying amount is 70%, the second stage spraying amount is 30%, the total spraying time is 8-10min, and the cement paste is uniformly attached. The dry weight of the cement-silica fume paste accounts for 8% of the dry weight of the washed sand and mud.

[0076] S4. Curing: the coated particles are placed in a steam curing box, and the curing system is set as follows: heating for 2h, from room temperature to 45℃; constant temperature of 45℃ for 8h, relative humidity ≥98%; cooling for 4h, to room temperature, to obtain the water-retaining aggregate with core-shell structure.

[0077] Example 4

[0078] The embodiment discloses a preparation method of the water-retaining aggregate with core-shell structure of the application, and specifically as follows:

[0079] S1. Raw material pretreatment: a polyacrylamide flocculant (PAM) aqueous solution with a concentration of 0.20wt% is prepared, and the total mass of PAM in the aqueous solution is 1.5% of the dry weight of the washed sand and mud slurry. Under the condition of continuous stirring in the slurry collection tank, 5% of sodium-based bentonite of the dry weight of the washed sand and mud slurry is added, and stirring is performed for 35min to ensure uniform stirring; then the whole PAM aqueous solution is added in three equal amounts with an interval of 3min, and the total reaction time is 15min, and then the slurry is dewatered by a belt filter, and the final water content is controlled to be 35%±1%.

[0080] S2. Granulation and molding: the dewatered slurry is poured into a roller granulator, the roller gap is adjusted to 8mm, and the rotation speed is adjusted to 40r / min, so that the wet particles with a diameter of Φ12mm are formed, and the wet particles are placed for 36h.

[0081] S3. Surface coating: P.O 42.5 cement-silica fume paste with water-cement ratio of 0.35 is prepared; the mass of silica fume is 20% of the mass of P.O 42.5 cement. The wet particles of step S2 which are placed for 24h are sent to the rotary drum granulator, the rotation speed of the granulator is adjusted to 15r / min, the cement paste is sprayed in two stages, the first stage spraying amount is 70%, the second stage spraying amount is 30%, the total spraying time is 8-10min, and the cement paste is uniformly attached. The dry weight of the cement-silica fume paste accounts for 8% of the dry weight of the washed sand and mud.

[0082] S4. Curing: the coated particles are placed in a steam curing box, and the curing system is set as follows: heating for 2h, from room temperature to 45℃; constant temperature of 45℃ for 8h, relative humidity ≥98%; cooling for 4h, to room temperature, to obtain the water-retaining aggregate with core-shell structure.

[0083] Example 5

[0084] This embodiment discloses a method for preparing the core-shell structured water-retaining aggregate of the present invention, as detailed below:

[0085] S1. Raw material pretreatment: Prepare a 0.15wt% polyacrylamide flocculant (PAM) aqueous solution, with the total mass of PAM in the aqueous solution being 1.5% of the dry weight of the washed sand and mud slurry. Under continuous stirring in the slurry collection tank, add 5% sodium bentonite based on the dry weight of the washed sand and mud slurry, and stir for 35 minutes to ensure uniform mixing; then add the entire PAM aqueous solution in three equal portions, with an interval of 3 minutes between each addition, for a total reaction time of 15 minutes. The slurry is then dewatered through a belt filter press, and the final moisture content is controlled at 40% ± 1%.

[0086] S2. Granulation and Forming: The dewatered slurry is fed into a disc granulator, with the disc tilt angle set to 45° and the rotation speed at 50 rpm. Approximately 10% of the dewatered slurry is initially used as crystal nuclei, and water is continuously sprayed during rotation to form initial small spheres. Subsequently, the remaining dewatered slurry is continuously and evenly added to the disc, allowing the spheres to gradually encapsulate the material and grow larger as they roll, ultimately forming uniformly sized wet granules (Φ15mm in diameter).

[0087] S3. Surface Coating: Prepare a sulfoaluminate cement-fiber silicate slurry with a water-cement ratio of 0.35; wherein the silicate mass is 20% of the sulfoaluminate cement mass. Feed the wet granules from step S2, which have been left to stand for 48 hours, into a rotary granulator. Adjust the granulator speed to 15 r / min and spray the cement slurry in two stages: 70% in the first stage and 30% in the second stage, with a total spraying time of 8-10 minutes, ensuring uniform adhesion of the cement slurry. The dry weight of the sulfoaluminate cement-fiber silicate slurry accounts for 12% of the dry weight of the washed sand and mud.

[0088] S4. Curing and solidification: The coated particles are placed in a steam curing chamber and the curing regime is set as follows: heating up for 2 hours, from room temperature to 45°C; maintaining a constant temperature of 45°C for 8 hours with a relative humidity of ≥98%; cooling down for 4 hours to room temperature, thus obtaining a core-shell structured water-retaining aggregate.

[0089] Test case

[0090] The water-retaining aggregates obtained in Examples 1-5 were tested for compressive strength, water absorption, and water retention. The compressive strength and water absorption tests were conducted according to the requirements of GB / T17431.2-2010. The formula for calculating the compressive strength is as follows:

[0091]

[0092] In the formula for calculating cylinder compressive strength:

[0093] f a —Cylinder compressive strength of coarse aggregate, MPa;

[0094] p1 — Pressure value when the indentation depth is 20mm, in N;

[0095] p2 — Mass of the stamping die, N;

[0096] F – bearing area, i.e., the area of ​​the stamping die F = 10000 mm² 2 .

[0097] The formula for calculating the 24-hour water absorption rate of aggregates is as follows:

[0098]

[0099] In the formula for calculating the 24-hour water absorption rate of aggregates:

[0100] w a — Aggregate water absorption rate (24h), %;

[0101] m0 — Mass of aggregate after soaking in water for 24 hours, in grams;

[0102] m1 — Mass of dried aggregate, in grams.

[0103] The formula for calculating water retention rate is as follows:

[0104]

[0105] In the formula for calculating water retention rate:

[0106] w b —Aggregate water retention rate after 72 hours, %;

[0107] m1—mass of dried aggregate, in grams;

[0108] m2 — the mass of aggregate when it absorbs water to saturation, in grams;

[0109] m3 — the mass (in grams) of water-saturated aggregate placed in a natural environment for 72 hours.

[0110] The test results for each embodiment are shown in Table 1:

[0111] Table 1 Experimental data for each embodiment

[0112] Examples Cylinder pressure strength Water retention Water absorption Example 1 6.2 MPa 38.7％ 8.2％ Example 2 7.1 MPa 31.3％ 6.5％ Example 3 8.7 MPa 32.8％ 6.3％ Example 4 9.2 MPa 30.2％ 5.8％ Example 5 6.5 MPa 37.5％ 8.0％

[0113] As can be seen from the test results in Table 1, the water-retaining aggregate of the present invention not only has good compressive strength but also high water retention rate, achieving a synergistic breakthrough in both water retention rate and compressive strength.

[0114] In summary, compared with traditional aggregates, this invention achieves systematic innovation in four aspects: raw materials, process, structure, and application.

[0115] In terms of raw materials, this invention uses washed sand and mud (waste from sand and gravel processing) as the main raw material, replacing natural sand and gravel or polystyrene particles in traditional aggregates. This not only significantly reduces raw material costs by more than 40%, but also realizes the resource utilization of solid waste. For every ton of aggregate produced, 0.9-1.1 tons of sand and mud can be consumed, reducing the pressure on environmental landfills.

[0116] In terms of technology, this invention breaks through the constraint that traditional ceramsite must be sintered, and adopts the "roller pressing / disc granulation + rotary drum coating" process to form non-firing ceramsite, which shortens the production process, reduces production costs, and reduces production energy consumption and carbon emissions.

[0117] In terms of structure, this invention creatively constructs a dual-reinforcement system of "core-shell structure": the core forms a porous water-retaining matrix, and the cement-based hydration product layer of the outer shell forms a dense protective layer through synergistic hydration reaction, so that the aggregate of this invention has both high water retention and high compressive strength, solving the problem that it is difficult to achieve both in traditional materials.

[0118] In terms of applications, this invention breaks through the traditional contradiction between "strength and water retention" in aggregates, and is innovatively applicable to rooftop greening, ecological slope protection, and vegetation restoration in arid regions.

[0119] This invention constructs a new paradigm for green building materials technology through triple innovation of "waste conversion, process innovation, and structural optimization," providing core solutions for the resource utilization of solid waste and the development of ecological building materials.

[0120] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a core-shell structured water-retaining aggregate, characterized in that, Includes the following steps: S1. Raw material pretreatment: Add polyacrylamide flocculant aqueous solution to the washed sand mud slurry, stir, and obtain flocculent mud slurry, then dehydrate; S2. Granulation and molding: Granulating dehydrated materials into pellets; S3. Surface coating: Cement slurry is sprayed onto the surface of the granulated product; S4. Curing and solidification: The slurry-coated particles are cured using standard curing or steam curing to obtain the water-retaining aggregate.

2. The method for preparing a core-shell structured water-retaining aggregate according to claim 1, characterized in that, In step S1, the concentration of the polyacrylamide flocculant aqueous solution is 0.07-0.3 wt%, preferably 0.15 wt%. The mass of polyacrylamide flocculant is 0.5% to 3% of the dry weight of the washed sand and mud slurry; Preferably, the flocculated slurry is dewatered to a moisture content of 25-40%.

3. The method for preparing a core-shell structured water-retaining aggregate according to claim 1, characterized in that, In step S1, sodium bentonite is added to the washed sand slurry and stirred evenly. Then, an aqueous solution of polyacrylamide flocculant is added and stirred to obtain flocculated slurry, which is then dehydrated. Preferably, the mass of sodium-based bentonite is 3-5% of the dry weight of the washed sand slurry.

4. A method for preparing a core-shell structured water-retaining aggregate according to any one of claims 1-3, characterized in that, In step S2, the dehydrated material is granulated by roller pressing or disc granulation. Preferably, the wet granules obtained by roller pressing have a particle size of 5-20 mm; Preferably, the wet particles obtained by disc granulation have a particle size of 10-25 mm; Preferably, the wet granules are left to stand for 12 to 48 hours before being coated with slurry.

5. A method for preparing a core-shell structured water-retaining aggregate according to any one of claims 1-3, characterized in that, In step S3, the water-cement ratio of the cement slurry is 0.30 to 0.40, preferably 0.35; Preferably, the dry weight of the cement slurry accounts for 8-15% of the dry weight of the washed sand and mud.

6. A method for preparing a core-shell structured water-retaining aggregate according to any one of claims 1-3, characterized in that, The cement slurry includes cement and 0-20% silica fume by weight of the cement. Preferably, the cement is selected from at least one of P.O425 silicate cement and sulfoaluminate cement.

7. The method for preparing a core-shell structured water-retaining aggregate according to claim 1, characterized in that, In step S4, the standard curing steps include: placing the mortar-coated particles in an environment with a temperature of 20-30℃ and a relative humidity of ≥90% for 72 hours to allow the cement shell to hydrate and form a porous structure; The steam curing step includes: sending the coated particles into a steam curing chamber, curing at a temperature of 40-70℃ for 4-16 hours.

8. A core-shell structured water-retaining aggregate, characterized in that, It is prepared by the method described in any one of claims 1-7.

9. The water-retaining aggregate according to claim 8, characterized in that, Water retention rate > 30%, cylinder compressive strength ≥ 5 MPa; Preferably, the water-retaining aggregate contains washed sand and mud particles with a moisture content of 18-35% and a particle size of 5-20 mm as the core; the cement-based hydration product layer surrounding the core has a thickness of 0.5-2 mm.

10. The application of the water-retaining aggregate according to claim 8 or 9, characterized in that, Application in the preparation of vegetation concrete.

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