A method for enhancing recycled coarse aggregate using biotechnology

Abstract

This invention provides a method for strengthening recycled coarse aggregate using biotechnology, belonging to the field of recycled aggregate concrete technology. The invention prepares recycled coarse aggregate with enhanced strength through steps such as crushing, baking and inactivating, soaking, inoculating with algae, cultivating, and curing waste concrete. The algae include one or more of the genera *Nostoc*, *Pseudoclado*, *Nostoc*, *Symplocos*, *Syngonium*, *Oscillatoria*, and *Ophioglossum*. This invention utilizes desert algae to strengthen the recycled coarse aggregate, reducing its water absorption, improving its compressive strength, increasing its density, and improving its compatibility with new mortar. This results in a denser interface between the recycled coarse aggregate and new mortar, significantly improving adhesion and thus further enhancing the strength of the recycled concrete. This broadens the application range of the recycled concrete, enabling the use of large quantities of waste construction concrete.

Description

Technical Field

[0001] This invention relates to the field of recycled aggregate concrete technology, and more specifically to a method for strengthening recycled coarse aggregate using biotechnology. Background Technology

[0002] Recycled aggregate concrete technology is one of the most common and direct ways to utilize construction waste. However, compared with natural aggregate concrete, recycled aggregate concrete has obvious performance deficiencies. The main reason is that the surface of recycled coarse aggregate is covered with old mortar, which has defects such as strong water absorption, high porosity, and low strength. During pouring, a complex microstructure and abnormally weak bonding performance of aggregate-mortar interface transition zone (ITZ) is formed between recycled coarse aggregate and new mortar, resulting in a reduction in the performance of recycled aggregate concrete.

[0003] The performance enhancement technology for recycled concrete mainly focuses on the modification of recycled aggregates, including physical and chemical methods. Physical strengthening involves using mechanical equipment to reprocess simply crushed recycled aggregates without altering their microstructure and phase properties. This removes cement mortar adhering to the surface and weakly connected particle edges, including mechanical grinding, heated grinding, and particle shaping. Mechanical grinding utilizes ball mills, optimized ball mills, vertical eccentric grinding devices, and horizontal rotary grinding devices to remove old mortar from the surface of recycled aggregates to a certain extent, improving their quality. Heated grinding removes old mortar from the surface of recycled aggregates by heating before grinding; this method is more effective than mechanical grinding but is more complex. Particle shaping uses high-speed self-impact and friction to remove mortar or cement paste adhering to the aggregate surface, eliminating prominent edges on coarse aggregate particles and resulting in cleaner, smoother recycled aggregates. Chemical strengthening involves using chemical reagents to soak and alter the microstructure and phase properties of recycled aggregate ITZ, thereby modifying and strengthening ITZ. This includes chemical soaking, mineral admixture modification, and carbonization strengthening.

[0004] Currently, there are methods for strengthening recycled coarse aggregates using biotechnology. For example, patent CN110398538A discloses a method for studying the effect of Bacillus coccidioides mineralization deposition on the compressive strength of recycled concrete. The method includes: aggregate pretreatment, impregnation, preparation of recycled concrete specimens, wave velocity measurement, strength and acoustic emission parameter testing, and parameter analysis. This method is applicable to microbially modified recycled concrete. By designing different pH conditions for treating recycled aggregates with Bacillus coccidioides bacterial solutions, the determination of calcium ion concentration reflects the degree of Bacillus coccidioides mineralization deposition. Simultaneously, the compressive strength and damage characteristics of the recycled concrete specimens are measured. Patent CN118598566A discloses a method for strengthening recycled aggregates based on microbial mineralization and synergistic struvite deposition. This method utilizes urease-type microbial induced calcium carbonate precipitation (MICP) technology to strengthen recycled aggregates, and introduces Mg into the reaction system at appropriate times. 2+ and HPO4 2- The NH4 generated during the reaction + The process transforms ammonia byproducts from microbial mineralization into struvite (MgNH4PO4·6H2O). This method not only converts ammonia byproducts from the microbial mineralization process into struvite, avoiding environmental pollution, but the generated struvite also has a synergistic effect with microbially induced calcium carbonate, improving the strengthening effect of recycled aggregate. Patent CN115340313A discloses a method for strengthening recycled aggregate using physical composite microbial technology. The recycled aggregate is mixed with solid steel balls, stirred, and then the steel balls are removed. Small-diameter coarse recycled aggregate particles are sieved out to obtain mechanically ground recycled aggregate. This is then placed in a container, and a prepared microbial solution is poured in. After treatment, the recycled aggregate strengthened by physical composite microbial technology is obtained. The technical performance of recycled aggregates is significantly improved through physical, biological, and synergistic effects, including increased apparent density, reduced water absorption and crushing index, and optimized particle morphology. When used in concrete, the calcium carbonate particles precipitated on the aggregate surface can stimulate cement hydration, promote the bonding between aggregates and hydration products, and improve concrete strength. This effectively solves the problems of poor workability, low strength, and poor durability of recycled concrete, and is conducive to further improving the resource utilization rate of demolition waste. Patent CN112851170A discloses a method for strengthening recycled aggregate concrete using microbial denitrification and the recycled aggregate concrete. The method for strengthening recycled aggregate concrete using microbial denitrification includes the following steps: (1) soaking the recycled aggregate in the bacterial solution of denitrifying bacteria to obtain recycled aggregate with denitrifying bacteria attached; (2) soaking the recycled aggregate with denitrifying bacteria obtained in step (1) in a calcium salt solution / or spraying the calcium salt solution onto the surface of the recycled aggregate with denitrifying bacteria obtained in step (1); (3) mixing concrete: replacing the natural aggregate with the recycled aggregate treated in step (2) for mixing to obtain recycled aggregate concrete.

[0005] The aforementioned methods for strengthening recycled coarse aggregate using biotechnology are all based on microbial mineralization and deposition to generate calcium carbonate, thereby strengthening the recycled coarse aggregate. However, microbial mineralization and deposition are time-consuming and have low production efficiency, resulting in limited strengthening efficiency for recycled coarse aggregate. Therefore, this invention utilizes the consolidation capabilities of desert algae microorganisms to modify recycled aggregate, preparing recycled aggregate concrete and improving its performance. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for enhancing recycled coarse aggregate using biotechnology. Based on desert algae, this invention utilizes the adhesion and entanglement of algal filaments on the surface and microcracks of recycled coarse aggregate. The metabolites, including extracellular polysaccharides, possess cohesive power. Through the mechanical binding effect of the desert algae filaments and the adhesive effect of their metabolites, the microcracks on the surface and inside of the coarse aggregate are filled, causing the coarse aggregate to bond with the old mortar, thereby improving the performance of the recycled coarse aggregate.

[0007] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0008] In a first aspect, the present invention provides a method for enhancing recycled coarse aggregate using biotechnology, comprising the following steps: mixing algae slurry with compound fertilizer evenly, then evenly sprinkling the mixture onto the surface of recycled coarse aggregate for inoculation and cultivation, and after curing, obtaining modified recycled coarse aggregate;

[0009] The method for preparing the algal slurry includes the following steps:

[0010] Desert algae were cultured, and the supernatant was removed from the culture to obtain algal slurry;

[0011] The desert algae species include one or more of the genera *Pseudobranchia*, *Nostoc*, *Symplocos*, *Syngonium*, *Syngonium*, *Oscillatoria*, and *Eyebrowella*.

[0012] The method provided by this invention involves uniformly mixing algae slurry with compound fertilizer, then evenly sprinkling the mixture onto the surface of recycled coarse aggregate for inoculation and cultivation. After curing, modified recycled coarse aggregate with improved strength is obtained. The recycled coarse aggregate is obtained from waste concrete through crushing, baking and inactivation, and soaking treatment. This invention prepares recycled coarse aggregate suitable for preparing recycled concrete through crushing, with a particle size of 5-25 mm. The coarse aggregate particles obtained from crushed waste concrete have old mortar adhering to their surface and contain numerous microcracks caused by mechanical / manual crushing. Baking and inactivation treatment of the coarse aggregate particles prevents the presence of other microorganisms that could affect algae growth on the surface and inside the particles. During the treatment process, the containers holding the coarse aggregate particles must also be kept clean and sterile. Soaking the coarse aggregate particles ensures that the surface and internal moisture content of the particles reaches a suitable environment for algae growth. Simultaneously, to prevent secondary pollution from the soaking water, the containers should be disinfected and sterilized beforehand. The algal slurry used in this invention is obtained by culturing and separating desert algae. The algae can be a combination of one or more algae to achieve sufficient survival. The desert algae used in this invention require a weakly alkaline environment and sufficient moisture for development. By subjecting the coarse aggregate particles to high-temperature inactivation and soaking treatment, the weakly alkaline coarse aggregate particles become a carrier adapted to the survival and development of the desert algae. This invention mixes the algal slurry with compound fertilizer and then inoculates it onto the surface of recycled coarse aggregate. By adjusting the inoculation amount, environmental moisture content, light, temperature, and other conditions, the algae can achieve the optimal survival rate, thereby allowing the algal filaments to adhere to and entwine on the surface and microcracks of the recycled coarse aggregate. Its mechanical binding effect can wrap around microparticles such as old cement, and metabolic products, including extracellular polysaccharides, can fill the microcracks, giving the surface of the recycled coarse aggregate a certain degree of cohesion. At the same time, the extracellular polysaccharides have strong water absorption; after absorbing water and swelling, they further fill the microcracks and increase the roughness between the recycled coarse aggregates, so that the final modified recycled coarse aggregate can improve the mechanical properties of concrete. In addition, extracellular polysaccharides can adsorb elements such as Ca and Si. Mineral particles, rich in Ca, are adsorbed on and near the surface of the algal filament sheath. These mineral elements play a regulatory role in the cement hydration process: on the one hand, they can regulate the hydration rate of C3A in cement, reduce the heat of hydration, and prevent cracks from forming in the transition zone between recycled coarse aggregate and cement mortar; on the other hand, the excess Ca and Si on the surface of the recycled coarse aggregate increase the Ca content in the solution during hydration. 2+ Si 4+ Ion concentration promotes the formation of CSH gel, effectively improving the strength of the transition zone at the interface between recycled coarse aggregate and cement mortar, thereby significantly improving the strength of recycled concrete.

[0013] Preferably, when the desert algae species are a mixture of multiple species from the genera *Hymenopterus*, *Pseudoclado*, *Nostoc*, *Symplocos*, *Hymenopterus*, *Oscillatoria*, and *Eyebrowella*, the mixing ratio (fresh weight ratio) of the desert algae species is as follows:

[0014] *Pseudobrya* : *Pseudobrya* = (7:3) ~ (9:1);

[0015] *Nostoc* : *Nostoc* = (5:5) ~ (8:2);

[0016] *Pterocarya* : *Pterocarya* = (6:4) ~ (8:2);

[0017] *Pterocarya* : *Pterocarya* = (6.5 : 3.5) ~ (9 : 1);

[0018] *Pseudococcus*: *Pseudococcus*: *Nostoc* = (6:3:1) ~ (8:1:1);

[0019] The ratio of *Pseudobrya* to *Pseudobrya* to *Pseudobrya* is (7:2.5:0.5) ~ (9:0.3:0.7).

[0020] The ratio of *Euphorbia* to *Pseudobranchia* to *Euphorbia* is (7:2.1:0.9) ~ (8.5:0.5:1).

[0021] The ratio of *Euphorbia* to *Pseudobranchia* to *Oscillatoria* is (6:1.3:2.7) ~ (8.7:0.2:1.1).

[0022] Preferably, in the method for preparing the algal slurry, the desert algae strain is cultured under continuous light for 24 hours with a light intensity of 50-100 μEm. -2 s -1 .

[0023] Specifically, the method for preparing the algal slurry is as follows:

[0024] (1) Weigh 10-15 g of desert algal crust soil samples selected in the field, place them in 100-160 mL of BG11 culture medium, shake evenly for 12 h, and separate the algal liquid.

[0025] (2) The desert algae in the algal solution were separated and purified; the purified algae were placed in BG11 or BG110 medium and cultured in a light incubator at 25±3 ℃ for 30 days; when the algae were cultured until the desert algae biomass in each liter of culture exceeded 0.2 g, the algae were collected and the supernatant was removed to obtain algal slurry.

[0026] Preferably, the desert algal crust soil samples are taken from fixed sand dunes that are more than 3 years old, and artificial biological soil crusts in the field with different regions, different slope aspects, and different crust growth times are selected; when sampling, three 1000 mm × 1000 mm quadrats are selected in each sample area, and the crust samples are cylinders with a diameter of 50 mm and a column height of 10 mm.

[0027] Preferably, the mass ratio of the algae slurry to the compound fertilizer is (1:0.5) to (1:1.5).

[0028] Preferably, the compound fertilizer is a nitrogen-phosphorus-potassium compound fertilizer.

[0029] Preferably, before evenly sprinkling the mixture of algae slurry and compound fertilizer onto the surface of the recycled coarse aggregate, the recycled coarse aggregate is spread out in a flat layer with a thickness of 100-200 mm.

[0030] Preferably, the inoculation dose is 5~20 μg / cm³. 2 (Based on chlorophyll a content).

[0031] Preferably, the algae slurry is cultured on the surface of the recycled coarse aggregate under light; specifically, it is illuminated for 16 hours every 24 hours, with a light intensity of 300~600 μEm. -2 s -1 The temperature conditions were 25±3 ℃, and the CO2 concentration was 500~800 mg·L. -1 .

[0032] Preferably, the maintenance includes: regular watering and regular replenishment of the culture medium.

[0033] There are many specific operations for the regular watering and replenishment of the culture medium. The specific operation of the maintenance process of this invention is as follows: daily micro-spraying watering, and replenishment of the culture medium every other day; wherein, the amount of watering is to ensure that the moisture content of the recycled coarse aggregate is 8%~15%; specifically, the moisture content of the recycled coarse aggregate can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%. The culture medium is PDA medium, Ashby nitrogen-free medium, phosphorus-solubilizing medium, or BG medium. 11 One or more of the culture media are mixed, with a mass fraction of 0.15% to 2.5%, and a daily volume of 30 to 100 mL / g of culture medium.

[0034] Preferably, the maintenance period is 7 to 8 days.

[0035] Preferably, the recycled coarse aggregate is obtained from waste concrete through processing, including the following steps:

[0036] (1) The waste concrete is crushed and screened to obtain coarse aggregate particles;

[0037] (2) The coarse aggregate particles are baked and then cooled;

[0038] (3) Soak the cooled coarse aggregate particles in pure water. After soaking, sieve out excess water to obtain recycled coarse aggregate. The pure water is distilled and inactivated water with a pH of 5.0~7.0, a total bacterial count ≤20 cfu / ml, and a coliform count ≤3MPN / 100 mL.

[0039] Preferably, in step (1), the original compressive strength of the waste concrete is 30~50 MPa; specifically, the original compressive strength of the waste concrete can be 30 MPa, 35 MPa, 40 MPa, 45 MPa or 50 MPa.

[0040] Preferably, in step (1), the particle size of the coarse aggregate particles is 5~25 mm.

[0041] Preferably, in step (1), the content of old mortar on the surface of the coarse aggregate particles is 8%~20% (mass percentage); the mud content on the surface of the coarse aggregate particles is less than 4.0%; specifically, the content of old mortar on the surface of the coarse aggregate particles can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%; the mud content on the surface of the coarse aggregate particles can be 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5% or 4.0%.

[0042] Preferably, in step (2), the baking process involves spreading the coarse aggregate particles evenly in a drying oven and baking them for 5-6 hours at a temperature of 95±5 ℃; the thickness of the spread coarse aggregate particles is less than 2 cm; specifically, during the baking process, the thickness of the spread coarse aggregate particles can be 0.5 cm, 1.0 cm, 1.5 cm or 2.0 cm.

[0043] Preferably, in step (3), the container holding the coarse aggregate particles soaked in pure water is soaked in nitric acid or hydrochloric acid with a mass fraction of 10% for more than 8 hours before use, and then rinsed with pure water before use to ensure that the container is free of bacteria; the pure water is distilled and inactivated water with a pH value of 5.0~7.0, a total bacterial count ≤20 cfu / ml, and a coliform count ≤3MPN / 100 mL.

[0044] Preferably, in step (3), the coarse aggregate particles are soaked in pure water for 24 hours.

[0045] Preferably, in step (3), the moisture content of the recycled coarse aggregate is 8% to 15%; specifically, the moisture content of the recycled coarse aggregate can be 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%.

[0046] Specifically, the method for enhancing recycled coarse aggregate using biotechnology includes the following steps:

[0047] P1. After crushing the waste concrete, screen and collect coarse aggregate particles with a particle size of 5~25 mm.

[0048] P2. Spread the coarse aggregate particles evenly in a drying oven and bake for 5-6 hours, then cool and set aside for use.

[0049] P3. Soak the cooled coarse aggregate particles in pure water for 24 hours. After soaking, remove them and repeatedly sift them through a sieve with a mesh size of 3-5 mm to remove excess water, thus obtaining recycled coarse aggregate. Spread the recycled coarse aggregate evenly with an average thickness of 100-200 mm.

[0050] P4. Mix the algae slurry with NPK compound fertilizer evenly, spray evenly onto the surface of the spread recycled coarse aggregate for inoculation and cultivation. The inoculation amount is 5~20μg / cm³. 2 (Based on chlorophyll a content); During the maintenance period, water regularly and replenish the culture solution regularly until 7-8 days later when the recycled coarse aggregate is collected, the moisture is dried, and the modified recycled coarse aggregate is obtained.

[0051] Secondly, the present invention provides modified recycled coarse aggregate prepared by the method described above.

[0052] Thirdly, the present invention provides a recycled concrete comprising the modified recycled coarse aggregate.

[0053] Preferably, the recycled concrete comprises the following raw materials in parts by weight: 750-920 parts of modified recycled coarse aggregate, 120-800 parts of fine aggregate, 150-225 parts of cement, 130-195 parts of fly ash, 140-210 parts of water, and 3-20 parts of admixture.

[0054] Compared with the prior art, the advantages of the present invention are:

[0055] (1) This invention utilizes desert algae to grow on recycled coarse aggregate, and uses the filaments of the desert algae to mechanically bind the microparticles of old cement mortar. The metabolites, including extracellular polysaccharides, adhere to and fill the microcracks on the surface and inside of the recycled coarse aggregate, forming aggregated microparticles, which significantly improves the density of the microstructure of the recycled coarse aggregate. At the same time, the extracellular polysaccharides encapsulate the recycled coarse aggregate, giving the surface of the recycled coarse aggregate a certain degree of cohesion, which makes the bond between the prepared modified recycled coarse aggregate and the new mortar stronger. Furthermore, the extracellular polysaccharides have strong water absorption. After absorbing water and swelling, they further fill the microcracks, increasing the surface roughness of the recycled coarse aggregate. At the same time, the extracellular polysaccharides also play a water storage role, releasing water during the later stage of hydration. When the recycled coarse aggregate of this invention is used in recycled concrete, it can perform secondary curing of the recycled concrete and significantly improve the strength of the recycled concrete. In addition, extracellular polysaccharides can adsorb elements such as Ca and Si. Mineral particles adsorbed on and near the surface of the algal filament sheath are rich in Ca. These mineral elements can regulate the cement hydration rate, reduce the heat of hydration, and prevent cracks from forming in the transition zone between recycled coarse aggregate and cement mortar. At the same time, it promotes the formation of CSH gel, effectively improves the strength of the transition zone between recycled coarse aggregate and cement mortar, thereby significantly improving the strength of recycled concrete.

[0056] (2) This invention strengthens recycled coarse aggregate through biotechnology, thereby reducing the water absorption, improving the compressive strength, increasing the density and apparent density of the recycled coarse aggregate, and improving its compatibility with new mortar. The interface transition zone between recycled coarse aggregate and new mortar is denser and the bonding force is significantly improved, thereby increasing the strength of recycled concrete and making the application range of recycled concrete wider, enabling the application of large quantities of construction waste concrete.

[0057] (3) The growth of desert algae is a process of carbon absorption and nitrogen fixation. Introducing desert algae into recycled coarse aggregate for growth and development can utilize recycled concrete to absorb carbon dioxide from the air in a low-cost and more ecological way. The widespread application of this recycled concrete can effectively improve the greenhouse effect.

[0058] (4) The bio-binding ability of desert algae species is used to improve the performance of recycled coarse aggregate, which has a certain degree of reversibility. The solid phase after the hydration of traditional cement is inorganic substances such as hydrated calcium silicate, calcium hydroxide, and calcium sulfoaluminate. These substances have good stability and cannot be degraded. They can be decomposed through weathering, water erosion, etc., which takes hundreds of years and has a great impact on the environment. However, the extracellular polysaccharides metabolized by the desert algae species used in this invention are organic matter, which is easy to decompose and degrade, and has a small environmental impact. Detailed Implementation

[0059] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] This invention provides a method for enhancing recycled coarse aggregate using biotechnology, comprising the following steps: mixing algae slurry and compound fertilizer evenly, then evenly sprinkling the mixture onto the surface of the recycled coarse aggregate for inoculation and cultivation, and after curing, obtaining modified recycled coarse aggregate;

[0061] The method for preparing the algal slurry includes the following steps:

[0062] Desert algae were cultured, and the supernatant was removed from the culture to obtain algal slurry;

[0063] The desert algae species include one or more of the genera *Pseudobranchia*, *Nostoc*, *Symplocos*, *Syngonium*, *Syngonium*, *Oscillatoria*, and *Eyebrowella*.

[0064] In some examples, the compound fertilizer is a nitrogen-phosphorus-potassium compound fertilizer, which can be obtained through conventional purchase or prepared by oneself; in the following specific embodiments and comparative examples, the nitrogen-phosphorus-potassium compound fertilizer was purchased from Shandong Sanfang Chemical Group.

[0065] In some examples, the desert algae strain is cultured under continuous light for 24 hours with a light intensity of 50-100 μEm in the algal slurry preparation method. -2 s -1 .

[0066] In some examples, the mass ratio of algae slurry to compound fertilizer is (1:0.5) to (1:1.5); in the following specific embodiments, the mass ratio of algae slurry to compound fertilizer is 1:1.

[0067] In some examples, the recycled coarse aggregate is spread evenly on the surface of the recycled coarse aggregate before the mixture of algae slurry and compound fertilizer is evenly sprinkled. The thickness of the spread is 100-200 mm.

[0068] In some examples, the inoculation dose is 5–20 μg / cm³. 2 (Based on chlorophyll a content).

[0069] In some examples, the algal slurry is cultured on the surface of the recycled coarse aggregate under light; for example, 16 hours of light per 24 hours, with a light intensity of 300-600 μEm. -2 s -1 The temperature conditions were 25±3 ℃, and the CO2 concentration was 500~800 mg·L.-1 .

[0070] In some examples, the maintenance includes regular watering and regular replenishment of the culture medium. There are many specific methods for regular watering and replenishment of the culture medium; the specific operation of the maintenance process in this invention is as follows: daily micro-spraying watering, and replenishment of the culture medium every other day; wherein, the amount of watering is to ensure that the moisture content of the recycled coarse aggregate is 8%~15%; for example, the moisture content of the recycled coarse aggregate can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%; the culture medium is PDA medium, Ashby nitrogen-free medium, phosphorus-solubilizing medium, or BG medium. 11 One or more of the culture media are mixed, with a mass fraction of 0.15% to 2.5%, and a daily volume of 30 to 100 mL / g of culture medium.

[0071] In some examples, the maintenance period in step S4 is 7 to 8 days.

[0072] The recycled coarse aggregate is obtained from waste concrete through processing, including the following steps:

[0073] (1) The waste concrete is crushed and screened to obtain coarse aggregate particles;

[0074] (2) The coarse aggregate particles are baked and then cooled;

[0075] (3) Soak the cooled coarse aggregate particles in pure water. After soaking, sieve out excess water to obtain recycled coarse aggregate. The pure water is distilled and inactivated water with a pH of 5.0~7.0, a total bacterial count ≤20 cfu / ml, and a coliform count ≤3MPN / 100 mL.

[0076] In some examples, in step (1), the original compressive strength of the waste concrete is 30~50 MPa; for example, the original compressive strength of the waste concrete can be 30 MPa, 35 MPa, 40 MPa, 45 MPa or 50 MPa.

[0077] In some examples, in step (1), the old mortar content on the surface of the coarse aggregate particles is 8% to 20% (by mass); the mud content on the surface of the coarse aggregate particles is less than 4.0%; for example, the old mortar content on the surface of the coarse aggregate particles can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%; the mud content on the surface of the coarse aggregate particles can be 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5% or 4.0%.

[0078] In some examples, in step (2), the baking process involves spreading the coarse aggregate particles evenly in a drying oven and baking them for 5-6 hours at a temperature of 95±5 ℃; the thickness of the spread coarse aggregate particles is less than 2 cm; for example, during the baking process, the thickness of the spread coarse aggregate particles can be 0.5 cm, 1.0 cm, 1.5 cm or 2.0 cm.

[0079] In some examples, in step (3), the container holding the coarse aggregate particles soaked in pure water is soaked in nitric acid or hydrochloric acid with a mass fraction of 10% for more than 8 hours before use, and then rinsed with pure water before use to ensure that the container is free of bacteria; the pure water is distilled and inactivated water with a pH value of 5.0~7.0, a total bacterial count ≤20 cfu / ml, and a coliform count ≤3 MPN / 100 mL.

[0080] In some examples, in step (3), the moisture content of the recycled coarse aggregate is 8% to 15%; for example, the moisture content of the recycled coarse aggregate may be 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%.

[0081] In the following examples and comparative examples, unless otherwise specified, the original compressive strength of the waste concrete is 43.6 MPa (obtained by actual measurement); the desert algal crust soil samples were collected from five desert areas in Gansu, Ningxia, and Xinjiang, and were labeled as crust soil sample N1, crust soil sample N2, crust soil sample N3, crust soil sample N4, and crust soil sample N5, respectively; the recycled concrete contains the following raw materials in parts by weight: 750 parts recycled coarse aggregate, 300 parts fine aggregate, 175 parts cement, 130 parts fly ash, 210 parts water, and 15 parts admixture; wherein, the fine aggregate is natural river sand with a particle size of 0-5 mm and a fineness modulus of 2.4; the cement is Huaxin 42.5 ordinary Portland cement; the fly ash is Grade I fly ash produced by Wuhan Yangluo Power Plant; and the admixture is a polycarboxylate-based high-efficiency water-reducing agent.

[0082] Example 1

[0083] A method for preparing bio-enhanced recycled coarse aggregate includes the following steps:

[0084] S1. Crush the waste concrete until its particle size reaches 5-25 mm for reuse. The surface of the coarse aggregate particles contains 16.7% old mortar and 3.89% mud.

[0085] S2. Spread the coarse aggregate particles evenly to a thickness of 1.5 mm, place them in a drying oven and bake for 5.5 hours, then cool.

[0086] S3. Soak the container in 10% nitric acid for 10 hours. After soaking, rinse with purified water to ensure the container is free of bacteria. Place the cooled coarse aggregate particles in the container and soak in purified water for 24 hours. Remove the particles and repeatedly sift them through a 3-5 mm mesh to remove excess water, obtaining recycled coarse aggregate with a moisture content of 12.6%. Spread the recycled coarse aggregate evenly with an average thickness of 150 mm.

[0087] S4. Weigh 10 g of each desert algal crust soil sample N1 and place it in 100 mL of BG11 culture medium. Shake well for 12 h to separate the algal solution.

[0088] S5. The desert algae species in the algal solution were isolated and purified. After artificial preparation, the ratio of algae species was: *Pseudococcus*: *Pseudococcus*: *Pseudococcus* = 7:2.1:0.9. The algae species were placed in BG11 medium and cultured in a light incubator at 25±3 ℃ with aeration for 30 days. The algae species were collected when the biomass of desert algae species in each liter of culture exceeded 0.2 g, and the supernatant was removed to obtain algal slurry.

[0089] S6. Add nitrogen, phosphorus, and potassium compound fertilizer to the algae slurry, mix thoroughly, and spray evenly onto the surface of the flat-laid recycled coarse aggregate for inoculation and cultivation. The inoculation amount is 15 μg / cm³. 2 (Based on chlorophyll a content). During the maintenance period, water is sprayed regularly every day, and the culture solution is replenished every other day until the recycled coarse aggregate is collected after 8 days. The moisture is dried to obtain modified recycled coarse aggregate.

[0090] Example 2

[0091] A method for preparing bio-enhanced recycled coarse aggregate includes the following steps:

[0092] S1. Crush the waste concrete until its particle size reaches 5-25 mm for reuse. The surface of the coarse aggregate particles contains 16.7% old mortar and 3.89% mud.

[0093] S2. Spread the coarse aggregate particles evenly to a thickness of 1.5 mm, place them in a drying oven and bake for 5.5 hours, then cool.

[0094] S3. Soak the container in 10% nitric acid for 10 hours. After soaking, rinse with purified water to ensure the container is free of bacteria. Place the cooled coarse aggregate particles in the container and soak in purified water for 24 hours. Remove the particles and repeatedly sift them through a 3-5 mm mesh to remove excess water, obtaining recycled coarse aggregate with a moisture content of 12.6%. Spread the recycled coarse aggregate evenly with an average thickness of 150 mm.

[0095] S4. Weigh 10 g of desert algal crust soil sample N2 per portion, place it in 100 mL of BG11 culture medium, shake well for 12 h, and separate the algal solution.

[0096] S5. The desert algae species in the algal solution were isolated and purified. After artificial preparation, the ratio of algae species was 8.2:1.8: *Pseudoclado*. The algae species were placed in BG11 medium and cultured in a light incubator at 25±3 ℃ with aeration for 30 days. The algae species were collected when the biomass of desert algae species in each liter of culture exceeded 0.2 g, and the supernatant was removed to obtain algal slurry.

[0097] S6. Add nitrogen, phosphorus, and potassium compound fertilizer to the algae slurry, mix thoroughly, and spray evenly onto the surface of the flat-laid recycled coarse aggregate for inoculation and cultivation. The inoculation amount is 15 μg / cm³. 2 (Based on chlorophyll a content). During the maintenance period, water is sprayed regularly every day, and the culture solution is replenished every other day until the recycled coarse aggregate is collected after 8 days. The moisture is dried to obtain modified recycled coarse aggregate.

[0098] Example 3

[0099] A method for preparing bio-enhanced recycled coarse aggregate includes the following steps:

[0100] S1. Crush the waste concrete until its particle size reaches 5-25 mm for reuse. The surface of the coarse aggregate particles contains 16.7% old mortar and 3.89% mud.

[0101] S2. Spread the coarse aggregate particles evenly to a thickness of 1.5 mm, place them in a drying oven and bake for 5.5 hours, then cool.

[0102] S3. Soak the container in 10% nitric acid for 10 hours. After soaking, rinse with purified water to ensure the container is free of bacteria. Place the cooled coarse aggregate particles in the container and soak in purified water for 24 hours. Remove the particles and repeatedly sift them through a 3-5 mm mesh to remove excess water, obtaining recycled coarse aggregate with a moisture content of 12.6%. Spread the recycled coarse aggregate evenly with an average thickness of 150 mm.

[0103] S4. Weigh 10 g of each desert algal crust soil sample N3 and place it in 100 mL of BG11 culture medium. Shake well for 12 h to separate the algal solution.

[0104] S5. The desert algae species in the algal solution were isolated and purified. After artificial preparation, the ratio of algae species was 8.7:1.3: *Pseudobrya*. The algae species were placed in BG11 medium and cultured in a light incubator at 25±3 ℃ with aeration for 30 days. The algae species were collected when the biomass of desert algae species in each liter of culture exceeded 0.2 g, and the supernatant was removed to obtain algal slurry.

[0105] S6. Add nitrogen, phosphorus, and potassium compound fertilizer to the algae slurry, mix thoroughly, and spray evenly onto the surface of the flat-laid recycled coarse aggregate for inoculation and cultivation. The inoculation amount is 15 μg / cm³. 2 (Based on chlorophyll a content). During the maintenance period, water is sprayed regularly every day, and the culture solution is replenished every other day until the recycled coarse aggregate is collected after 8 days. The moisture is dried to obtain modified recycled coarse aggregate.

[0106] Example 4

[0107] A method for preparing bio-enhanced recycled coarse aggregate includes the following steps:

[0108] S1. Crush the waste concrete until its particle size reaches 5-25 mm for reuse. The surface of the coarse aggregate particles contains 16.7% old mortar and 3.89% mud.

[0109] S2. Spread the coarse aggregate particles evenly to a thickness of 1.5 mm, place them in a drying oven and bake for 5.5 hours, then cool.

[0110] S3. Soak the container in 10% nitric acid for 10 hours. After soaking, rinse with purified water to ensure the container is free of bacteria. Place the cooled coarse aggregate particles in the container and soak in purified water for 24 hours. Remove the particles and repeatedly sift them through a 3-5 mm mesh to remove excess water, obtaining recycled coarse aggregate with a moisture content of 12.6%. Spread the recycled coarse aggregate evenly with an average thickness of 150 mm.

[0111] S4. Weigh 10 g of each desert algal crust soil sample N4 and place it in 100 mL of BG11 culture medium. Shake well for 12 h to separate the algal solution.

[0112] S5. The desert algae species in the algal solution were isolated and purified. After artificial preparation, the algae species were 100% *Gnaphalium*. The algae species were placed in BG11 medium and cultured in a light incubator at 25±3 ℃ with aeration for 30 days. The algae species were collected when the biomass of desert algae species in each liter of culture exceeded 0.2 g, and the supernatant was removed to obtain algal slurry.

[0113] S6. Add nitrogen, phosphorus, and potassium compound fertilizer to the algae slurry, mix thoroughly, and spray evenly onto the surface of the flat-laid recycled coarse aggregate for inoculation and cultivation. The inoculation amount is 15 μg / cm³. 2(Based on chlorophyll a content). During the maintenance period, water is sprayed regularly every day, and the culture solution is replenished every other day until the recycled coarse aggregate is collected after 8 days. The moisture is dried to obtain modified recycled coarse aggregate.

[0114] Example 5

[0115] A method for preparing bio-enhanced recycled coarse aggregate includes the following steps:

[0116] S1. Crush the waste concrete until its particle size reaches 5-25 mm for reuse. The surface of the coarse aggregate particles contains 16.7% old mortar and 3.89% mud.

[0117] S2. Spread the coarse aggregate particles evenly to a thickness of 1.5 mm, place them in a drying oven and bake for 5.5 hours, then cool.

[0118] S3. Soak the container in 10% nitric acid for 10 hours. After soaking, rinse with purified water to ensure the container is free of bacteria. Place the cooled coarse aggregate particles in the container and soak in purified water for 24 hours. Remove the particles and repeatedly sift them through a 3-5 mm mesh to remove excess water, obtaining recycled coarse aggregate with a moisture content of 12.6%. Spread the coarse aggregate particles evenly with an average thickness of 150 mm.

[0119] S4. Weigh 10 g of each desert algal crust soil sample N5 and place it in 100 mL of BG11 culture medium. Shake well for 12 h to separate the algal solution.

[0120] S5. The desert algae species in the algal solution were isolated and purified. After artificial preparation, the ratio of algae species was 7.5:2.5: *Nostoc*. The algae species were placed in BG11 medium and cultured in a light incubator at 25±3 ℃ with aeration for 30 days. The algae species were collected when the biomass of desert algae species in each liter of culture exceeded 0.2 g, and the supernatant was removed to obtain algal slurry.

[0121] S6. Add nitrogen, phosphorus, and potassium compound fertilizer to the algae slurry, mix thoroughly, and spray evenly onto the surface of the flat-laid recycled coarse aggregate for inoculation and cultivation. The inoculation amount is 15 μg / cm³. 2 (Based on chlorophyll a content). During the maintenance period, water is sprayed regularly every day, and the culture solution is replenished every other day until the recycled coarse aggregate is collected after 8 days. The moisture is dried to obtain modified recycled coarse aggregate.

[0122] Comparative Example 1

[0123] A recycled coarse aggregate, the preparation method includes the following steps:

[0124] S1. Crush the waste concrete until its particle size reaches 5-25 mm for reuse. The surface of the coarse aggregate particles contains 16.7% old mortar and 3.89% mud.

[0125] S2. Spread the coarse aggregate particles evenly to a thickness of 1.5 mm, place them in a drying oven and bake for 5.5 hours, then cool.

[0126] S3. Soak the container in 10% nitric acid for 10 hours. After soaking, rinse with pure water to ensure that the container is free of bacteria. Place the cooled coarse aggregate particles in the container and soak in pure water for 24 hours. After soaking, remove the particles and repeatedly sift them through a sieve with a pore size of 3-5 mm to remove excess water. Dry the particles to obtain recycled coarse aggregate.

[0127] Comparative Example 2

[0128] A recycled coarse aggregate, the preparation method includes the following steps:

[0129] S1. Crush the waste concrete until its particle size reaches 5-25 mm for reuse. The surface of the coarse aggregate particles contains 16.7% old mortar and 3.89% mud.

[0130] S2. Spread the coarse aggregate particles evenly to a thickness of 1.5 mm, place them in a drying oven and bake for 5.5 hours, then cool. Spread the cooled coarse aggregate particles evenly to an average thickness of 150 mm.

[0131] S3. Weigh 10 g of each desert algal crust soil sample N1 and place it in 100 mL of BG11 culture medium. Shake well for 12 h to separate the algal solution.

[0132] S4. The desert algae species in the algal solution were isolated and purified. After artificial preparation, the ratio of algae species was: *Pseudococcus*: *Pseudococcus*: *Pseudococcus* = 7.3:1.5:1.2. The algae species were placed in BG11 medium and cultured in a light incubator at 25±3℃ with aeration for 30 days. The algae species were collected when the biomass of desert algae species in each liter of culture exceeded 0.2 g, and the supernatant was removed to obtain algal slurry.

[0133] S5. Add NPK compound fertilizer to the algae slurry and mix thoroughly. Spray the mixture evenly onto the surface of the flat-laid recycled coarse aggregate for inoculation and cultivation. The inoculation amount is 15 μg / cm³. 2 (Based on chlorophyll a content). During the maintenance period, water is sprayed regularly every day, and the culture solution is replenished every other day until the recycled coarse aggregate is collected after 8 days. The moisture is dried to obtain modified recycled coarse aggregate.

[0134] Comparative Example 3

[0135] A recycled coarse aggregate, the preparation method includes the following steps:

[0136] S1. Crush the waste concrete until its particle size reaches 5-25 mm for reuse. The surface of the coarse aggregate particles contains 16.7% old mortar and 3.89% mud.

[0137] S2. Spread the coarse aggregate particles evenly to a thickness of 1.5 mm, place them in a drying oven and bake for 5.5 hours, then cool.

[0138] S3. Soak the container in 10% nitric acid for 10 hours. After soaking, rinse with purified water to ensure the container is free of bacteria. Place the cooled coarse aggregate particles in the container and soak in purified water for 24 hours. Remove the particles and repeatedly sift them through a 3-5 mm mesh to remove excess water, obtaining recycled coarse aggregate with a moisture content of 12.6%. Spread the coarse aggregate particles evenly with an average thickness of 150 mm.

[0139] S4. Weigh 10 g of each desert algal crust soil sample N1 and place it in 100 mL of BG11 culture medium. Shake well for 12 h to separate the algal solution.

[0140] S5. The desert algae species in the algal solution were isolated and purified. After artificial preparation, the ratio of algae species was: *Pseudococcus*: *Pseudococcus*: *Pseudococcus* = 7.3:1.5:1.2. The algae species were placed in BG11 medium and cultured in a light incubator at 25±3℃ with aeration for 30 days. The algae species were collected when the biomass of desert algae species in each liter of culture exceeded 0.2 g, and the supernatant was removed to obtain algal slurry.

[0141] S6. Add nitrogen, phosphorus, and potassium compound fertilizer to the algae slurry, mix thoroughly, and spray evenly onto the surface of the flat-laid recycled coarse aggregate for inoculation and cultivation. The inoculation amount is 15 μg / cm³. 2 (Based on chlorophyll a content). During the curing period, the culture medium was replenished every other day until the recycled coarse aggregate was collected after 8 days. The moisture was dried to obtain the modified recycled coarse aggregate.

[0142] Comparative Example 4

[0143] A recycled coarse aggregate, the preparation method includes the following steps:

[0144] S1. Crush the waste concrete until its particle size reaches 5-25 mm for reuse. The surface of the coarse aggregate particles contains 16.7% old mortar and 3.89% mud.

[0145] S2. Soak the container in 10% nitric acid for 10 hours. After soaking, rinse with purified water to ensure the container is free of bacteria. Place the coarse aggregate particles in the container and soak in purified water for 24 hours. Remove the particles and repeatedly sift them through a 3-5 mm mesh to remove excess water, obtaining recycled coarse aggregate with a moisture content of 12.6%. Spread the coarse aggregate particles evenly with an average thickness of 150 mm.

[0146] S3. Weigh 10 g of each desert algal crust soil sample N1 and place it in 100 mL of BG11 culture medium. Shake well for 12 h to separate the algal solution.

[0147] S4. The desert algae species in the algal solution were isolated and purified. After artificial preparation, the ratio of algae species was: *Pseudococcus*: *Pseudococcus*: *Pseudococcus* = 7.3:1.5:1.2. The algae species were placed in BG11 medium and cultured in a light incubator at 25±3℃ with aeration for 30 days. The algae species were collected when the biomass of desert algae species in each liter of culture exceeded 0.2 g, and the supernatant was removed to obtain algal slurry.

[0148] S5. Add NPK compound fertilizer to the algae slurry and mix thoroughly. Spray the mixture evenly onto the surface of the flat-laid recycled coarse aggregate for inoculation and cultivation. The inoculation amount is 15 μg / cm³. 2 (Based on chlorophyll a content). During the maintenance period, water is sprayed regularly every day, and the culture solution is replenished every other day until the recycled coarse aggregate is collected after 8 days. The moisture is dried to obtain modified recycled coarse aggregate.

[0149] Comparative Example 5

[0150] A method for preparing recycled concrete includes the following steps:

[0151] Preparation of recycled coarse aggregate:

[0152] S1. Crush the waste concrete until its particle size reaches 5-25 mm for reuse. The surface of the coarse aggregate particles contains 16.7% old mortar and 3.89% mud.

[0153] S2. Spread the coarse aggregate particles evenly to a thickness of 1.5 mm, place them in a drying oven and bake for 5.5 hours, then cool.

[0154] S3. Soak the container in 10% nitric acid for 10 hours. After soaking, rinse with pure water to ensure that the container is free of bacteria. Place the cooled coarse aggregate particles in the container and soak in pure water for 24 hours. After soaking, remove the particles and repeatedly sift them through a sieve with a pore size of 3-5 mm to remove excess water. Dry the particles to obtain recycled coarse aggregate.

[0155] Preparation of algal slurry:

[0156] S1. Weigh 10 g of desert algal crust soil sample N1 and place it in 100 mL of BG11 culture medium. Shake well for 12 h to separate the algal solution.

[0157] S2. The desert algae species in the algal solution were isolated and purified. After artificial preparation, the ratio of algae species was: *Pseudococcus*: *Pseudococcus*: *Pseudococcus* = 7.3:1.5:1.2. The algae species were placed in BG11 medium and cultured in a light incubator at 25±3℃ with aeration for 30 days. The algae species were collected when the biomass of desert algae species in each liter of culture exceeded 0.2 g, and the supernatant was removed to obtain algal slurry.

[0158] Preparation of recycled concrete:

[0159] 750 parts of recycled coarse aggregate, 300 parts of fine aggregate, 175 parts of cement, 130 parts of fly ash, 210 parts of water, and 15 parts of admixture were mixed with algae slurry (the amount of algae slurry was the same as in Example 1) to prepare recycled concrete. Its compressive strength was tested after 28 days of standard curing.

[0160] Comparative Example 6

[0161] A method for preparing bio-enhanced recycled coarse aggregate includes the following steps:

[0162] S1. Crush the waste concrete until its particle size reaches 5-25 mm for reuse. The surface of the coarse aggregate particles contains 16.7% old mortar and 3.89% mud.

[0163] S2. Spread the coarse aggregate particles evenly to a thickness of 1.5 mm, place them in a drying oven and bake for 5.5 hours, then cool.

[0164] S3. Soak the container in 10% nitric acid for 10 hours. After soaking, rinse with purified water to ensure the container is free of bacteria. Place the cooled coarse aggregate particles in the container and soak in purified water for 24 hours. Remove the particles and repeatedly sift them through a 3-5 mm mesh to remove excess water, obtaining recycled coarse aggregate with a moisture content of 12.6%. Spread the recycled coarse aggregate evenly with an average thickness of 150 mm.

[0165] S4. Collect the red algae when the biomass in each liter of culture exceeds 0.2 g, remove the supernatant, and obtain algal slurry.

[0166] S5. Add NPK compound fertilizer to the algae slurry and mix thoroughly. Spray the mixture evenly onto the surface of the flat-laid recycled coarse aggregate for inoculation and cultivation. The inoculation amount is 15 μg / cm³. 2 (Based on chlorophyll a content). During the maintenance period, water is sprayed regularly every day, and the culture solution is replenished every other day until the recycled coarse aggregate is collected after 8 days. The moisture is dried to obtain modified recycled coarse aggregate.

[0167] Referring to GB / T 14685-2022 "Construction Gravel and Crushed Stone" and GB / T 25177-2010 "Recycled Coarse Aggregate for Concrete" standards, the water absorption rate, crushing resistance index, and apparent density of the recycled coarse aggregates finally obtained in Examples 1-5 and Comparative Examples 1-6 were tested. The test results are shown in Table 1.

[0168] The content of attached extracellular polysaccharides in the recycled coarse aggregates obtained in Examples 1-5 and Comparative Examples 1-6 was extracted and determined as follows: 200 g of recycled coarse aggregate sample was placed in a 1000 mL beaker, 600 mL of distilled water was added, and the mixture was magnetically stirred for 15 min. This stirring and addition of distilled water was repeated three times. The sample was centrifuged at 6000 g for 15 min, and the supernatant was collected after three centrifugations. 2.0 mL of the solution was taken, and 1.0 mL of 6% phenol and 5.0 mL of 2M concentrated sulfuric acid were added. The mixture was shaken well and cooled. The absorbance at 490 nm was measured using a spectrophotometer. The polysaccharide content was calculated using glucose standard solution as a reference. The results are shown in Table 1.

[0169] The recycled coarse aggregates obtained in Examples 1-5 and Comparative Examples 1-4 and 6 were mixed with fine aggregates, cement, fly ash, water, and admixtures in a specific ratio to prepare recycled concrete, which was then cured under standard conditions for 28 days. The compressive strength of the recycled concretes in Examples 1-5 and Comparative Examples 1-6 was tested. The compressive strength values ​​were tested according to GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Ordinary Concrete" and GB / T50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete". The test results are shown in Table 1.

[0170] Table 1: Performance test results of recycled coarse aggregate and recycled concrete in Examples 1-5 and Comparative Examples 1-6

[0171]

[0172] As shown in Table 1, the recycled coarse aggregates prepared in Examples 1-5 of this invention have a water absorption rate of 2.8%-4.6%, a crushing resistance index of 10.7%-14.6%, and an apparent density of 2599-2793 kg / m³. 3 The content of attached extracellular polysaccharides is 1.11~3.96 mg / g. The compressive strength of the recycled concrete prepared using the recycled coarse aggregates of Examples 1~5 of this invention is 43.1~52.7 MPa. Compared with the recycled coarse aggregates in Comparative Example 1 that have not undergone biotechnology treatment, the water absorption rate of this invention is reduced by 50.0%~69.6%, the crushing resistance index is reduced by 17.9%~42.1%, the apparent density is increased by 12.4%~20.8%, and the compressive strength of the recycled concrete is increased by 5.5~15.1 MPa.

[0173] In Comparative Example 2, the recycled coarse aggregate was not soaked, and its surface moisture content was low, which failed to provide a favorable environment for the growth of desert algae. The content of attached extracellular polysaccharides was only 0.67 mg / g, and the strengthening effect of the recycled coarse aggregate was not obvious.

[0174] In Comparative Example 3, the recycled coarse aggregate was not replenished with water regularly during the curing process, resulting in insufficient water for the growth of desert algae, poor growth, and an attached extracellular polysaccharide content of only 0.43 mg / g, indicating that the strengthening effect of the recycled coarse aggregate was not obvious.

[0175] In Comparative Example 4, the recycled coarse aggregate was not baked and inactivated. Other microorganisms that endanger the growth of desert algae were present on the surface and inside, resulting in almost no growth of desert algae. The content of attached extracellular polysaccharides was only 0.04 mg / g, and the recycled coarse aggregate had no strengthening effect.

[0176] In Comparative Example 5, the algal species were not cultured and failed to grow enough algal filaments or secrete enough extracellular polysaccharides. The extracellular polysaccharide content was only 0.06 mg / g, and the regenerated coarse aggregate had no strengthening effect.

[0177] In Comparative Example 6, red algae were used instead of the desert algae species of the present invention. The content of the extracellular polysaccharides secreted by the red algae was extremely low, and there was no significant strengthening effect on the regenerated coarse aggregate.

[0178] In summary, this invention prepares recycled coarse aggregate with enhanced strength through steps such as crushing, baking and inactivating, soaking, inoculating with algae, cultivating and curing waste concrete. Specifically, this invention utilizes the mechanical binding effect of desert algae filaments and the adhesion and adsorption of mineral elements by metabolic products, including extracellular polysaccharides, to fill micro-cracks on the surface and inside of the recycled coarse aggregate. This allows the recycled coarse aggregate to bond with the old mortar, improving its compressive strength and achieving performance similar to natural aggregate, thus demonstrating great application potential.

[0179] The above detailed embodiments describe the implementation of the present invention; however, the present invention is not limited to the specific details described in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A method for enhancing recycled coarse aggregate using biotechnology, characterized in that, Includes the following steps: After the algae slurry and compound fertilizer are mixed evenly, they are evenly sprinkled on the surface of the recycled coarse aggregate for inoculation and cultivation. After curing, the modified recycled coarse aggregate is obtained. The method for preparing the algal slurry includes the following steps: Desert algae were cultured, and the supernatant was removed from the culture to obtain algal slurry; The desert algae species include one or more of the genera *Euphorbia*, *Pseudobranchia*, *Nostoc*, *Symplocos*, *Euphorbia*, *Oscillatoria*, and *Euphorbia*. The recycled coarse aggregate is obtained from waste concrete through processing, including the following steps: (1) The waste concrete is crushed and screened to obtain coarse aggregate particles; (2) The coarse aggregate particles are baked and then cooled; (3) Soak the cooled coarse aggregate particles in pure water. After soaking, sieve out the excess water to obtain recycled coarse aggregate.

2. The method for enhancing recycled coarse aggregate using biotechnology according to claim 1, characterized in that, The mass ratio of algae slurry to compound fertilizer is (1:0.5) to (1:1.5).

3. The method for enhancing recycled coarse aggregate using biotechnology according to claim 1, characterized in that, The compound fertilizer is a nitrogen-phosphorus-potassium compound fertilizer.

4. The method for enhancing recycled coarse aggregate using biotechnology according to claim 1, characterized in that, The algae slurry was cultured on the surface of the recycled coarse aggregate under light, with a light intensity of 300–600 μEm. -2 s -1 The temperature conditions were 25±3 ℃, and the CO2 concentration was 500~800 mg·L. -1 .

5. A method for enhancing recycled coarse aggregate using biotechnology according to claim 1, characterized in that, The specific maintenance procedures are as follows: daily micro-spraying watering, with replenishment of culture medium every other day; the amount of water sprayed is to ensure that the moisture content of the recycled coarse aggregate is 8%~15%; the culture medium is PDA medium, Ashby nitrogen-free medium, phosphorus-solubilizing medium, and BG medium. 11 One or more of the culture media are mixed, with a mass fraction of 0.15% to 2.5%, and a daily volume of 30 to 100 mL / g of culture medium.

6. A method for enhancing recycled coarse aggregate using biotechnology according to claim 1, characterized in that, In step (2), the baking time is 5-6 hours and the baking temperature is 95±5℃.

7. A method for enhancing recycled coarse aggregate using biotechnology according to claim 1, characterized in that, In step (3), the container holding the coarse aggregate particles soaked in pure water is soaked in nitric acid or hydrochloric acid for more than 8 hours before use, and then rinsed with pure water before use.

8. Modified recycled coarse aggregate prepared by any one of claims 1 to 7.

9. A type of recycled concrete, characterized in that, Includes the modified recycled coarse aggregate as described in claim 8.

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