A permeable concrete for efficient and sustainable sewage purification

Abstract

The present invention discloses a permeable concrete that can efficiently and sustainably purify runoff pollution and a preparation method thereof. The method comprises the following steps: first, using a saturated aqueous solution of calcium hydroxide as a solvent, ultrasonically dispersing water-soluble carbon nitride and hydroxylated boron nitride aerogel and stirring them magnetically to form a dispersion; then, immersing aggregate in the dispersion and drying the dispersion to obtain aggregate loaded with carbon nitride composite boron nitride aerogel; then, mixing a polycarboxylate water-reducing agent and a retarder dissolved in the dispersion with the aggregate loaded with carbon nitride composite boron nitride aerogel; and adding a cementitious material to mix the mixture; finally, spraying the dispersion again on the surface of the formed concrete, thereby combining the dispersion with the concrete through internal mixing and spraying; and obtaining the permeable concrete that can sustainably purify runoff pollution after carbonization curing. The permeable concrete obtained by the present invention has the effect of efficiently and sustainably purifying runoff pollution and has certain social benefits.

Description

Technical Field

[0001] The present invention belongs to the field of environmental materials, and in particular relates to a permeable concrete capable of efficiently and sustainably purifying runoff pollution and a preparation method thereof. Background Art

[0002] With the impact of global warming and the acceleration of urbanization, the area of ​​hard-paved roads and building density in cities are increasing, leading to an increase in surface rainwater runoff. The pollution caused by heavy metal ions, suspended solids, organic matter, and other pollutants in rainwater is becoming increasingly serious. In particular, heavy metal ions and organic pollutants in rainwater seep into the ground, posing a serious threat to the environment and residents' health. It is well known that rainwater can contaminate groundwater through the soil, and the odors and volatile organic compounds it emits can pollute the air, while also increasing the concentration of soil pollutants. Therefore, rainwater purification and self-cleaning are urgently needed. Combining green and sustainable photocatalytic environmental remediation technology with concrete pavement materials that come into direct contact with natural rainwater is the development of new concrete pavement materials with rainwater purification and self-cleaning capabilities. This is considered one of the most promising green methods for rapidly and maximally purifying rainwater.

[0003] Currently, research on photocatalytic concrete focuses on the preparation of photocatalytic concrete by internally incorporating photocatalytic materials. Patent CN 106478029A discloses a high-efficiency photocatalytic concrete material and its manufacturing method; Patent CN 108455908A discloses a photocatalytic self-cleaning cement material and its preparation method; Patent CN 108083720A discloses a nano-modified photocatalytic self-cleaning concrete and its preparation method; and Patent CN 110938297A discloses a method for preparing a polymer composite material containing boron nitride aerogel. However, since most of the photocatalytic material is located within the concrete, it is difficult to come into contact with photons and pollutants. Furthermore, the adsorption efficiency of pollutants is low, resulting in low photocatalytic material utilization, which in turn leads to relatively low efficiency of photocatalytic concrete.

[0004] Aerogel, a nanoporous material, has been widely studied for its applications in aerospace and defense, but few studies have examined its integration with concrete. Initial attempts have been made to combine aerogel with photocatalysis for pollution treatment, such as incorporating silica (SiO2) aerogel composites with fibers and TiO2 into a concrete matrix (CN 113636808A). However, little consideration has been given to the stability of the TiO2-aerogel bond and its photocatalytic efficiency.

[0005] Carbon nitride, an emerging non-metallic polymer photocatalyst with visible light response, high chemical stability, wide raw material availability, and low cost, has garnered significant attention in recent years in the field of photocatalytic environmental pollution control. Compared to TiO2, which only functions under violet light, carbon nitride functions under visible light. Boron nitride aerogel is also a visible light photocatalyst, suitable for use on rainy days and in environments with only visible light. It can also catalyze the degradation of wastewater containing soluble pollutants, offering broader application prospects. Summary of the Invention

[0006] The purpose of the present invention is to provide a permeable concrete that can efficiently and sustainably purify runoff pollution and a preparation method thereof. By simultaneously mixing photocatalytic materials and aerogel materials and spraying them on the surface for compaction, the concrete not only greatly improves the adsorption and retention of organic pollutants in runoff pollution, but also continuously degrades them while adsorbing them, reducing pollutant saturation, ensuring the long-term and stable photocatalytic purification effect of the concrete, and greatly improving the cost-effectiveness of the photocatalytic concrete.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A permeable concrete that can efficiently and sustainably purify runoff pollution, the preparation method of which comprises the following steps:

[0009] (1) dispersing water-soluble carbon nitride and hydroxylated boron nitride aerogel in an alkaline aqueous solution by ultrasonic and magnetic stirring to form a dispersion of carbon nitride composite boron nitride aerogel;

[0010] (2) fully soaking the aggregate in the dispersion of the carbon nitride composite boron nitride aerogel obtained in step (1), filtering the aggregate, and drying the aggregate to obtain the carbon nitride composite boron nitride aerogel-loaded aggregate;

[0011] (3) dissolving the polycarboxylic acid water reducer and the retarder boric acid in the dispersion of the carbon nitride composite boron nitride aerogel obtained in step (1), and then adding the loaded carbon nitride composite boron nitride aerogel and the gelling material obtained in step (2) and stirring and mixing;

[0012] (4) The mixture obtained in step (3) is loaded into a mold in layers, and is rammed 30 times in layers and then smoothed. After natural curing at room temperature for 1 to 8 hours, the dispersion of the carbon nitride composite boron nitride aerogel obtained in step (1) is sprayed on the surface of the obtained concrete, and then carbonized and cured for 7 days to obtain the permeable concrete that is efficient and sustainable in purifying runoff pollution.

[0013] Furthermore, the hydroxylated boron nitride aerogel in step (1) is prepared by adding boron nitride aerogel powder in an amount of 5-20 mg / ml to a sodium cholate aqueous solution with a mass concentration of 0.05%, ultrasonically dispersing for 0.1-0.5 hours, and then drying at a high temperature of 60-105° C. for 24-48 hours.

[0014] Furthermore, the contents of water-soluble carbon nitride and hydroxylated boron nitride aerogel in the dispersion obtained in step (1) are 1-10 g / L and 5-20 g / L, respectively; the Zeta potentials of water-soluble carbon nitride and hydroxylated boron nitride are 0-30 eV and -10-50 eV, respectively, and the particle sizes are 10-13 nm and 10-50 μm, respectively.

[0015] Furthermore, in step (1), the power of ultrasonic dispersion is 50-300 kHz, the time is 0.1-0.5 hours, and the speed of magnetic stirring is 300-800 rpm, and the time is 0.1-2 hours.

[0016] Furthermore, the alkaline aqueous solution in step (1) is specifically a saturated aqueous solution of calcium hydroxide.

[0017] Furthermore, the aggregate in step (2) is natural sand and gravel with a particle size of 5 to 15 mm.

[0018] Furthermore, the soaking time in step (2) is 8±2 hours, and the distance between the aggregate and the liquid surface during soaking is not less than 30 mm.

[0019] Furthermore, the drying temperature in step (2) is 60° C. and the drying time is 24 hours.

[0020] Furthermore, the type of cementitious material in step (3) includes any one of ordinary Portland cement, sulphoaluminate cement, and geopolymer cement.

[0021] Furthermore, in step (3), the stirring speed after adding the aggregate loaded with carbon nitride composite boron nitride aerogel is 45-100 rpm, and the stirring time is 30 seconds; the stirring speed after adding the gelling material is 60-200 rpm, and the stirring time is 120 seconds.

[0022] Furthermore, the content of the polycarboxylate water-reducing agent in the mixture obtained in step (3) is 0.1-1.0 wt%, the content of boric acid is 0.03-0.07 wt%, the content of the aggregate loaded with carbon nitride composite boron nitride aerogel is 65-67 wt%, and the content of the cementitious material is 20-25 wt%.

[0023] Furthermore, the thickness of each layer during the tamping in step (4) is 30 to 70 mm.

[0024] Furthermore, in step (4), the spraying amount of the dispersion of carbon nitride composite boron nitride aerogel is 0.1~1 L / m 2 .

[0025] Furthermore, the relative humidity of the carbonization curing in step (4) is 50-80%, and the carbon dioxide concentration is 10-80%.

[0026] The present invention utilizes the hydroxyl groups on the surface of the hydroxylated boron nitride aerogel to ensure that it can be better dispersed in water, overcoming the shortcoming that the boron nitride aerogel itself is prone to agglomeration. At the same time, the hydroxylated boron nitride aerogel can promote the effective transfer of photogenerated electrons in carbon nitride and inhibit their recombination with holes, thereby enhancing the photocatalytic purification effect of carbon nitride. Compared with the photocatalytic concrete prepared by the internal mixing method, the practice of simultaneously internally mixing the photocatalytic material and the aerogel material and spraying the surface for compaction not only greatly improves the adsorption and retention of organic pollutants in runoff pollution by concrete, but also can sustainably degrade while adsorbing, reducing pollutant saturation, and greatly improving the cost-effectiveness of photocatalytic concrete. The two substances complement each other, improving the effective transfer of photogenerated electrons, prompting them to participate more in the photocatalytic reaction, and greatly improving the photocatalytic efficiency.

[0027] The present invention has the following advantages:

[0028] (1) Compared with titanium dioxide, which can only function under ultraviolet light, carbon nitride has visible light response properties and can play a photocatalytic role in water purification and pollution removal in rainy environments.

[0029] (2) Compared with ordinary graphite-phase carbon nitride, negatively charged water-soluble carbon nitride can be loaded more stably and evenly on the positively charged boron nitride aerogel, and the boron nitride aerogel can serve as an acceptor for photogenerated holes in carbon nitride, thereby improving the separation efficiency of photogenerated electrons and holes in carbon nitride, and thus improving the sustainable photocatalytic performance of carbon nitride. At the same time, the hydroxylated boron nitride aerogel, with its ultra-high specific surface area, fully exposes the adsorption sites, reducing the resistance of pollutants entering the interior of the aerogel, and can maximize the loading of organic pollutants, thereby improving the catalytic performance.

[0030] (3) Compared with permeable concrete with only photocatalytic materials added, the boron nitride aerogel in the concrete of the present invention can efficiently intercept and adsorb pollutants, which helps carbon nitride to play a photocatalytic decontamination role, and will further improve the water purification efficiency of permeable concrete. At the same time, carbon nitride and hydroxylated boron nitride aerogel are loaded on the surface of permeable concrete and its internal pores by spraying and mixing. Boron nitride aerogel can play a role in efficiently intercepting and adsorbing pollutants, while carbon nitride can play a role in continuously purifying pollutants under light. The coupling of the two can achieve efficient and sustainable purification of runoff pollution.

[0031] (4) The present invention pre-loads carbon nitride composite boron nitride aerogel on the aggregate surface to utilize the nucleation effect of carbon nitride to promote cement hydration and generate more hydration products, while the boron nitride aerogel can play an internal curing role of "absorbing water and returning water". The two work together to improve the density of the interface transition zone and thus enhance the mechanical properties of permeable concrete.

[0032] (5) Carbonation curing can promote the conversion of calcium hydroxide in the dispersion into calcium carbonate. The calcium carbonate expands in volume and has a certain cohesiveness, which can promote the stable loading of carbon nitride composite boron nitride aerogel on permeable concrete. DETAILED DESCRIPTION

[0033] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0034] 2 g of boron nitride aerogel powder was added to 200 ml of a 0.05% sodium cholate aqueous solution, ultrasonically dispersed for 0.5 h, and then dried at 105 °C for 24 h to obtain hydroxylated boron nitride aerogel with a particle size of 30 μm and a Zeta potential of -30 eV.

[0035] The particle size of the water-soluble carbon nitride used was 10 nm and the zeta potential was 20 eV.

[0036] Example 1

[0037] The specific steps for preparing a permeable concrete that can efficiently and sustainably purify runoff pollution are as follows:

[0038] (1) 6 g of water-soluble carbon nitride and 9 g of hydroxylated boron nitride aerogel were mixed, dispersed under 70 kHz ultrasonication for 0.5 h, and then magnetically stirred at 500 rpm for 2 h to disperse the mixture in 600 ml of a saturated aqueous solution of calcium hydroxide to form a carbon nitride-boron nitride aerogel dispersion with a water-soluble carbon nitride and hydroxylated boron nitride aerogel content of 10 g / L and 15 g / L, respectively.

[0039] (2) 1350 g of natural sand and gravel aggregate was immersed in 375 g of the above-mentioned carbon nitride composite boron nitride aerogel dispersion (the liquid level was 1 cm higher than the aggregate) and kept for 8 hours, then filtered and dried at 60°C for 24 hours to obtain aggregate loaded with carbon nitride and boron nitride aerogel, i.e., photocatalytic aggregate;

[0040] (3) During the concrete mixing process, 2.8 g of polycarboxylic acid water reducer and 1.2 g of retarder boric acid were dissolved in 225 g of the carbon nitride composite hydroxylated boron nitride aerogel dispersion obtained in step (1), and then the aggregate loaded with carbon nitride composite hydroxylated boron nitride aerogel obtained in step (2) was added and stirred at a speed of 70 rpm for 30 seconds. Then, 450 g of PO 42.5 ordinary Portland cement was evenly added during the stirring process, and the stirring was continued at a speed of 150 rpm for 120 seconds;

[0041] (4) The fresh concrete was loaded into the mold layer by layer, and rammed 30 times before smoothing (the ramming layer thickness was 60 mm). After curing at room temperature for 1 hour, the concrete surface was heated at 0.5 L / m 2 The carbon nitride composite hydroxylated boron nitride aerogel dispersion obtained in step (1) is evenly sprayed, and then carbonized and cured for 7 days in an environment with a relative humidity of 80% and a carbon dioxide concentration of 80%, thereby obtaining a permeable concrete that can efficiently and sustainably purify sewage.

[0042] In this example, the particle size of the natural sand and gravel aggregate is 10 mm and the porosity is 5%.

[0043] In this example, the thickness of the dispersion sprayed on the concrete surface is 20 nm, and the specific surface area is 230 m 2 / g.

[0044] The photocatalytic water purification efficacy of the obtained permeable concrete for purifying runoff pollution was evaluated. Its photocatalytic efficiency in removing runoff pollutants in rainwater was 60%, and the efficiency was 55% after 30 cycle tests. After one year of outdoor natural weathering, the efficiency of photocatalytic removal of runoff pollutants in rainwater still remained at 50%. The mechanical properties of the permeable concrete were evaluated, and its 28-day compressive strength was 47 MPa and the permeability coefficient was 1.0 mm / s.

[0045] Example 2

[0046] The specific steps for preparing a permeable concrete that can efficiently and sustainably purify runoff pollution are as follows:

[0047] (1) 9 g of water-soluble carbon nitride and 12 g of hydroxylated boron nitride aerogel were mixed, dispersed under 50 kHz ultrasonication for 0.3 h, and then magnetically stirred at 500 rpm for 1.5 h to disperse the mixture in 600 ml of a saturated aqueous solution of calcium hydroxide to form a carbon nitride-boron nitride aerogel dispersion with a water-soluble carbon nitride and hydroxylated boron nitride aerogel content of 15 g / L and 20 g / L, respectively.

[0048] (2) 1350 g of natural sand and gravel aggregate was immersed in 375 g of the above-mentioned carbon nitride composite boron nitride aerogel dispersion (the liquid level was 1 cm higher than the aggregate) and kept for 8 hours, then filtered and dried at 60°C for 24 hours to obtain aggregate loaded with carbon nitride and boron nitride aerogel, i.e., photocatalytic aggregate;

[0049] (3) During the concrete mixing process, 2.8 g of polycarboxylic acid water reducer and 1.2 g of retarder boric acid were dissolved in 225 g of the carbon nitride composite hydroxylated boron nitride aerogel dispersion obtained in step (1), and then the aggregate loaded with carbon nitride composite hydroxylated boron nitride aerogel obtained in step (2) was added and stirred at a speed of 70 rpm for 30 seconds. Then, 450 g of PO 42.5 ordinary Portland cement was evenly added during the stirring process, and the stirring was continued at a speed of 150 rpm for 120 seconds;

[0050] (4) The fresh concrete was loaded into the mold layer by layer, and rammed 30 times before smoothing (the ramming layer thickness was 60 mm). After curing at room temperature for 1 hour, the concrete surface was heated at 1.0 L / m 2 The carbon nitride composite hydroxylated boron nitride aerogel dispersion obtained in step (1) is evenly sprayed, and then carbonized and cured for 7 days in an environment with a relative humidity of 70% and a carbon dioxide concentration of 70%, thereby obtaining a permeable concrete that can efficiently and sustainably purify sewage.

[0051] The particle size of the natural sand and gravel aggregate in this example is 3 mm and the porosity is 7%.

[0052] In this example, the thickness of the dispersion sprayed on the concrete surface is 30 nm, and the specific surface area is 200 m 2 / g.

[0053] The photocatalytic water purification efficacy of the obtained permeable concrete for purifying runoff pollution was evaluated. The efficiency of its photocatalytic removal of runoff pollutants in rainwater was 68%, and the efficiency was 60% after 30 cycle tests. After one year of outdoor natural weathering, the efficiency of photocatalytic removal of runoff pollutants in rainwater still remained at 55%. The mechanical properties of the permeable concrete were evaluated, and its 28d compressive strength was 45 MPa and the permeability coefficient was 1.5 mm / s.

[0054] Comparative Example 1

[0055] The specific steps for preparing a permeable concrete that can sustainably purify runoff pollution are as follows:

[0056] (1) 6 g of water-soluble carbon nitride and 9 g of boron nitride were mixed, ultrasonically dispersed at 70 kHz for 0.5 h, and then magnetically stirred at 500 rpm for 2 h. The mixture was dispersed in 600 ml of a saturated aqueous solution of calcium hydroxide to form carbon nitride dispersions with contents of 10 g / L and 15 g / L.

[0057] (2) 1350 g of natural sand and gravel aggregate was immersed in 375 g of the above-mentioned carbon nitride and boron nitride dispersion (the liquid level was 1 cm higher than the aggregate) and kept for 8 hours, then filtered and dried at 60°C for 24 hours to obtain carbon nitride-loaded aggregate, i.e., photocatalytic aggregate;

[0058] (3) During the concrete mixing process, 2.8 g of polycarboxylic acid water reducer and 1.2 g of boric acid retarder were dissolved in 225 g of the carbon nitride dispersion obtained in step (1), and then the aggregate loaded with carbon nitride composite boron nitride aerogel obtained in step (2) was added and stirred at a speed of 70 rpm for 30 seconds. Then, 450 g of PO 42.5 ordinary Portland cement was evenly added during the stirring process, and the stirring was continued at a speed of 150 rpm for 120 seconds;

[0059] (4) The fresh concrete was loaded into the mold layer by layer, and rammed 30 times before smoothing (the ramming layer thickness was 60 mm). After natural curing at room temperature for 1 hour, the concrete surface was heated at 0.5 L / m 2 The carbon nitride dispersion obtained in step (1) is evenly sprayed in an amount of 1000 nm, and then carbonized and cured for 7 days in an environment with a relative humidity of 80% and a carbon dioxide concentration of 80% to obtain a permeable concrete capable of purifying sewage.

[0060] In this example, the particle size of the natural sand and gravel aggregate is 10 mm and the porosity is 5%.

[0061] In this example, the thickness of the carbon nitride dispersion sprayed on the concrete surface is 20 nm, and the specific surface area is 230 m 2 / g.

[0062] The photocatalytic water purification efficacy of the permeable concrete obtained for purifying runoff pollution was evaluated. The photocatalytic removal efficiency of runoff pollutants in rainwater was 44%. After one year of outdoor natural weathering, the photocatalytic removal efficiency of runoff pollutants in rainwater was only 28%. The mechanical properties of the permeable concrete were evaluated. Its 28-day compressive strength was 42 MPa and the permeability coefficient was 12 mm / s.

[0063] Comparison of Example 1 with Comparative Example 1 shows that the permeable concrete prepared from a composite of water-soluble carbon nitride and hydroxylated boron nitride aerogel purifies rainwater runoff more efficiently than the permeable concrete prepared from a composite of carbon nitride and boron carbide, and this efficiency is even more pronounced after one year of outdoor natural weathering. This is primarily due to the highly efficient adsorption of the hydroxylated boron nitride aerogel. Its combination with carbon nitride not only improves the adhesion between the dispersion and the test piece, reducing the loss of photocatalyst due to wear, weathering, and rain, but also effectively intercepts and adsorbs organic pollutants, promoting the photocatalytic decontamination effect of the carbon nitride.

[0064] Comparative Example 2

[0065] The specific steps for preparing a permeable concrete capable of purifying runoff pollution in this example are as follows:

[0066] (1) 9 g of water-soluble carbon nitride and 12 g of hydroxylated boron nitride aerogel were mixed, dispersed under 50 kHz ultrasonication for 0.3 h, and then magnetically stirred at 500 rpm for 1.5 h to disperse the mixture in 600 ml of a saturated aqueous solution of calcium hydroxide to form a carbon nitride-boron nitride aerogel dispersion with a water-soluble carbon nitride and hydroxylated boron nitride aerogel content of 15 g / L and 20 g / L, respectively.

[0067] (2) During the concrete mixing process, 2.8 g of polycarboxylate water reducer and 1.2 g of boric acid retarder were dissolved in 225 g of the carbon nitride-boron nitride aerogel dispersion obtained in step (1), and 450 g of PO 42.5 ordinary Portland cement was evenly added during the stirring process, and the mixture was stirred at a speed of 150 rpm for 120 seconds;

[0068] (3) The fresh concrete was loaded into the mold layer by layer, and rammed 30 times before smoothing (the ramming layer thickness was 60 mm). After curing at room temperature for 1 hour, the concrete surface was heated at 1.0 L / m 2 The carbon nitride composite boron nitride aerogel dispersion obtained in step (1) is evenly sprayed, and then carbonized and cured for 7 days in an environment with a relative humidity of 70% and a carbon dioxide concentration of 70%, thereby obtaining a permeable concrete capable of purifying sewage.

[0069] In this example, the thickness of the dispersion sprayed on the concrete surface is 30 nm, and the specific surface area is 200 m 2 / g.

[0070] The photocatalytic water purification efficacy of the permeable concrete obtained for purifying runoff pollution was evaluated. The efficiency of photocatalytic removal of runoff pollutants in rainwater was 60%, 53% after 30 cycle tests, and 48% after one year of outdoor natural weathering. The mechanical properties of the permeable concrete were evaluated, and its 28-day compressive strength was 13 MPa and the permeability coefficient was 1.2 mm / s.

[0071] Comparing Example 2 with Comparative Example 2 shows that, compared to permeable concrete prepared with aggregate, the permeable concrete prepared without aggregate has a lower purification efficiency for runoff pollutants and a more pronounced impact on the mechanical properties of the permeable concrete specimens. This is primarily due to the pre-loading of carbon nitride-composite boron nitride aerogel on the aggregate surface. This utilizes the nucleation effect of carbon nitride to promote cement hydration and generate more hydration products, while the boron nitride aerogel exerts an internal curing effect by "absorbing and returning water." These two effects work together to improve the density of the interface transition zone, thereby enhancing the mechanical properties of the permeable concrete.

[0072] Comparative Example 3

[0073] The specific steps for preparing a permeable concrete capable of purifying runoff pollution in this example are as follows:

[0074] (1) 6 g of water-soluble carbon nitride and 9 g of hydroxylated boron nitride aerogel were mixed, dispersed under 70 kHz ultrasonication for 0.5 h, and then magnetically stirred at 500 rpm for 2 h to disperse the mixture in 600 ml of a saturated aqueous solution of calcium hydroxide to form a carbon nitride-boron nitride aerogel dispersion with a water-soluble carbon nitride and hydroxylated boron nitride aerogel content of 10 g / L and 15 g / L, respectively.

[0075] (2) 1350 g of natural sand and gravel aggregate was immersed in 375 g of the above-mentioned carbon nitride composite boron nitride aerogel dispersion (the liquid level was 1 cm higher than the aggregate) and kept for 8 hours, then filtered and dried at 60°C for 24 hours to obtain aggregate loaded with carbon nitride and boron nitride aerogel, i.e., photocatalytic aggregate;

[0076] (3) During the concrete mixing process, 2.8 g of polycarboxylic acid water reducer and 1.2 g of boric acid retarder were dissolved in 225 g of the carbon nitride composite boron nitride aerogel dispersion obtained in step (1), and then the aggregate loaded with carbon nitride composite boron nitride aerogel obtained in step (2) was added and stirred at a speed of 70 rpm for 30 seconds. Then, 450 g of PO 42.5 ordinary Portland cement was evenly added during the stirring process, and the stirring was continued at a speed of 150 rpm for 120 seconds.

[0077] (4) The fresh concrete was loaded into the mold layer by layer, and rammed 30 times before smoothing (the ramming layer thickness was 60 mm). After curing at room temperature for 1 hour, the concrete surface was heated at 0.5 L / m 2 The carbon nitride composite boron nitride aerogel dispersion obtained in step (1) is evenly sprayed, and then naturally cured for 7 days to obtain permeable concrete that can purify sewage.

[0078] In this example, the particle size of the natural sand and gravel aggregate is 10 mm and the porosity is 5%.

[0079] In this example, the thickness of the dispersion sprayed on the concrete surface is 20 nm, and the specific surface area is 230 m 2 / g.

[0080] The photocatalytic water purification efficacy of the permeable concrete obtained for purifying runoff pollution was evaluated. The efficiency of photocatalytic removal of runoff pollutants in rainwater was 64%, and the efficiency was 48% after 30 cycle tests. After one year of outdoor natural weathering, the efficiency of photocatalytic removal of runoff pollutants in rainwater was only 23%; the mechanical properties of the permeable concrete were evaluated, and its 28d compressive strength was 45 MPa and the permeability coefficient was 1.3 mm / s.

[0081] Comparing Example 2 with Comparative Example 3, the permeable concrete prepared with carbonization curing maintained a purification efficiency of approximately 60% after 30 cycles, while the naturally cured specimens experienced a nearly 20% drop in efficiency after 30 cycles. The drop in efficiency was even more pronounced after one year of natural weathering. This is primarily due to the fact that carbonization curing can convert calcium hydroxide in the carbon nitride-boron nitride aerogel dispersion into calcium carbonate. The calcium carbide expands in volume and exhibits a certain degree of cohesiveness, enhancing the stable loading of the carbon nitride-boron nitride aerogel on the permeable concrete and thereby improving the stability and durability of the permeable concrete.

[0082] The applicant declares that the present invention uses the above-described embodiments to illustrate the detailed compositions and methods of the present invention. However, the present invention is not limited to the above-described detailed compositions and methods, and does not necessarily rely on the above-described detailed compositions and methods for implementation. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the raw materials of the present invention, addition of auxiliary ingredients, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing permeable concrete that can efficiently and sustainably purify runoff pollution, characterized in that: The steps include: (1) dispersing water-soluble carbon nitride and hydroxylated boron nitride aerogel in an alkaline aqueous solution by ultrasonic and magnetic stirring to form a dispersion of carbon nitride composite boron nitride aerogel; (2) fully soaking the aggregate in the dispersion of the carbon nitride composite boron nitride aerogel obtained in step (1), filtering the aggregate, and drying the aggregate to obtain the carbon nitride composite boron nitride aerogel-loaded aggregate; (3) dissolving the polycarboxylic acid water reducer and the retarder boric acid in the carbon nitride composite boron nitride aerogel dispersion obtained in step (1), and then successively adding the aggregate loaded with the carbon nitride composite boron nitride aerogel obtained in step (2) and the cementitious material and stirring and mixing; (4) The mixture obtained in step (3) is loaded into a mold in layers, and is rammed 30 times in layers and then smoothed. After natural curing at room temperature for 1 to 8 hours, the dispersion of the carbon nitride composite boron nitride aerogel obtained in step (1) is sprayed on the surface of the obtained concrete, and then carbonized and cured for 7 days to obtain the permeable concrete that is efficient and sustainable in purifying runoff pollution; The hydroxylated boron nitride aerogel in step (1) is prepared by adding boron nitride aerogel powder in an amount of 5-20 mg / ml to a sodium cholate aqueous solution with a mass concentration of 0.05%, ultrasonically dispersing for 0.1-0.5 hours, and then drying at 60-105° C. for 24-48 hours; the alkaline aqueous solution is specifically a saturated aqueous solution of calcium hydroxide.

2. The preparation method according to claim 1, characterized in that The contents of water-soluble carbon nitride and hydroxylated boron nitride aerogel in the dispersion obtained in step (1) are 1-10 g / L and 5-20 g / L, respectively.

3. The preparation method according to claim 1, characterized in that In step (1), the power of ultrasonic dispersion is 50-300 kHz, the time is 0.1-0.5 hours, the speed of magnetic stirring is 300-800 rpm, and the time is 0.1-2 hours.

4. The preparation method according to claim 1, characterized in that The aggregate in step (2) is natural sand and gravel with a particle size of 5 to 15 mm.

5. The preparation method according to claim 1, characterized in that The soaking time in step (2) is 8±2 hours; the drying temperature is 60°C and the drying time is 24 hours.

6. The preparation method according to claim 1, characterized in that In step (3), the stirring speed after adding the aggregate loaded with carbon nitride composite boron nitride aerogel is 45-100 rpm, and the stirring time is 30 seconds; the stirring speed after adding the gelling material is 60-200 rpm, and the stirring time is 120 seconds.

7. The preparation method according to claim 1, characterized in that The mixture obtained in step (3) contains 0.1-1.0 wt% of polycarboxylic acid water-reducing agent, 0.03-0.07 wt% of boric acid, 65-67 wt% of aggregate loaded with carbon nitride composite boron nitride aerogel, and 20-25 wt% of cementitious material. The cementitious material includes any one of ordinary Portland cement, sulphoaluminate cement and geopolymer cement.

8. The preparation method according to claim 1, characterized in that The thickness of each layer during the tamping step (4) is 30-70 mm; the spraying amount of the dispersion of carbon nitride composite boron nitride aerogel is 0.1-1 L / m 2 The relative humidity of the carbonization curing is 50~80%, and the carbon dioxide concentration is 10~80%.

9. A permeable concrete prepared by the method according to any one of claims 1 to 8 for efficiently and sustainably purifying runoff pollution.