Method for reinforcing recycled coarse aggregate by using biotechnology

Abstract

The invention provides a method for reinforcing recycled coarse aggregate by using a biotechnology, and belongs to the technical field of recycled aggregate concrete. The recycled coarse aggregate with improved strength is prepared through the steps of crushing, baking and inactivating, soaking treatment, algae seed inoculation, culture, maintenance and the like on the waste concrete; wherein the algae species comprise one or a mixture of more of coleus, pseudocladosporium, nostoc, schizonepeta, coleus, oscillatoria and eyebrow algae, and the algae species comprise one or more of the coleus, the pseudocladosporium, the nostoc, the schizonepeta, the oscillatoria and the eyebrow algae. According to the invention, the desert algae are utilized to reinforce the recycled coarse aggregate, reduce the water absorption, improve the compression resistance and increase the compactness, so that the recycled coarse aggregate has better compatibility with new mortar, the interface transition area of the recycled coarse aggregate and the new mortar is more compact, and the binding power is obviously improved, thereby further improving the strength of the recycled concrete; the application range of the recycled concrete is wider, so that the application of bulk building waste concrete is realized.

Description

Technical Field

[0001] The invention relates to the technical field of recycled aggregate concrete, and in particular to a method for strengthening recycled coarse aggregate by utilizing biotechnology. Background Art

[0002] Recycled aggregate concrete technology is one of the most common and direct ways to recycle construction waste resources. 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 adhered to old mortar, which has defects such as strong water absorption, high porosity and low strength. During pouring, an aggregate-mortar interface transition zone (ITZ) with complex microstructure and abnormally weak bonding performance is formed between the recycled coarse aggregate and the new mortar, resulting in reduced performance of recycled aggregate concrete.

[0003] The performance improvement technology of recycled concrete mainly focuses on the modification of recycled aggregates, including physical and chemical methods. Physical strengthening, that is, without changing the microstructure and physical properties of recycled aggregates, uses mechanical equipment to reprocess the simply crushed recycled aggregates to remove the cement mortar and the edges and corners of particles with weak connections on the surface of the recycled aggregates, including mechanical grinding, heating grinding, particle shaping, etc. The mechanical grinding method uses devices such as ball milling, optimized ball milling, vertical eccentric device grinding and horizontal rotary device grinding to remove the old mortar on the surface of recycled aggregates to a certain extent and improve the quality of recycled aggregates. The heating grinding method uses the method of heating first and then grinding to remove the old mortar on the surface of recycled aggregates. This method is better than the mechanical grinding method, but the procedure is more complicated. The particle shaping method uses "high-speed self-impact and friction of recycled aggregates" to knock off the mortar or cement stone attached to the surface of the aggregates, remove the more prominent edges and corners on the coarse aggregate particles, and make it a relatively clean and smooth recycled aggregate. Chemical strengthening is the use of chemical reagent soaking and other means to change the microstructure and phase properties of recycled aggregate ITZ, so that ITZ is modified and strengthened, including chemical soaking method, mineral admixture modification method, carbonization strengthening method, etc.

[0004] At present, there are methods for strengthening recycled coarse aggregate using biotechnology. For example, patent CN110398538A discloses a method for studying the effect of mineralized deposition of Bacillus cohnii on the compressive strength of recycled concrete. The method process includes: aggregate pretreatment - impregnation - preparation of recycled concrete specimens - wave velocity measurement - strength and acoustic emission parameter testing - parameter analysis. This method is applicable to recycled concrete modified by microorganisms. By designing Bacillus cohnii bacterial liquid under different pH conditions to treat recycled aggregate, the determination of calcium ion concentration reflects the degree of mineralized deposition of Bacillus cohnii, and the compressive strength and damage characteristics of recycled concrete specimens are determined at the same time. Patent CN118598566A discloses a method for strengthening recycled aggregate based on microbial mineralization and coordinated struvite deposition. On the basis of strengthening recycled aggregate using urease-type microbial induced calcium carbonate precipitation (MICP) technology, Mg is introduced into the reaction system at an appropriate time. 2+ and HPO 4 2- , the NH4 generated during the reaction + Converted to struvite (MgNH 4 PO 4 6H 2O). This method can not only convert the ammonia byproducts in the microbial mineralization process into struvite to avoid environmental pollution, but also the generated struvite can achieve a synergistic effect with the calcium carbonate induced by microorganisms to improve the strengthening effect of recycled aggregate. Patent CN115340313A discloses a physical composite microbial technology to strengthen the method of recycled aggregate, the recycled aggregate is mixed with solid steel balls, the steel balls are taken out after stirring, the recycled coarse aggregate particles with small particle size are screened out, and the recycled aggregate after mechanical grinding is obtained; then placed in a container, the configured microbial bacterial liquid is poured into it, and the recycled aggregate after physical composite microbial technology is strengthened by treatment. The technical performance of the recycled aggregate is significantly improved under the synergistic effect of physics, biology and physicobiology, which is manifested in the increase of apparent density, the decrease of water absorption rate and the decrease of crushing index, and the optimization of particle morphology. When used in concrete, the calcium carbonate particles precipitated on the surface of the aggregate have the effect of stimulating cement hydration, promoting the combination of aggregate and hydration products, and improving the strength of concrete. It effectively solves the problems of poor workability, low strength and poor durability of recycled concrete, which is conducive to further improving the utilization rate of demolition waste resources. Patent CN112851170A discloses a method for strengthening recycled aggregate concrete by utilizing microbial denitrification phenomenon and recycled aggregate concrete. The method for strengthening recycled aggregate concrete by utilizing microbial denitrification phenomenon comprises the following steps: (1) soaking the recycled aggregate in a bacterial solution of denitrifying bacteria to obtain recycled aggregate attached with denitrifying bacteria; (2) soaking the recycled aggregate attached with denitrifying bacteria obtained in step (1) in a calcium salt solution / or spraying the calcium salt solution on the surface of the recycled aggregate attached with denitrifying bacteria obtained in step (1); (3) mixing concrete: stirring the recycled aggregate treated in step (2) instead of natural aggregate to obtain recycled aggregate concrete.

[0005] The above-mentioned methods of strengthening recycled coarse aggregate using biotechnology are all based on the generation of calcium carbonate by microbial mineralization and deposition to achieve the strengthening of recycled coarse aggregate. Since microbial mineralization and deposition take too long and have low production efficiency, the strengthening efficiency of recycled coarse aggregate is limited. Based on this, the present invention utilizes the consolidation ability of desert algae microorganisms to modify the recycled aggregate, prepare recycled aggregate concrete, and improve its performance. Summary of the invention

[0006] In view of the deficiencies of the above-mentioned prior art, the present invention provides a method for strengthening recycled coarse aggregate using biotechnology. The present invention is based on desert algae species, and utilizes their algae filaments to adhere to and entangle on the surface of recycled coarse aggregate and grow in micro-cracks, including the metabolic products of extracellular polysaccharides having cohesive force. Through the mechanical binding effect of the desert algae species filaments and the adhesion effect of their metabolic products, the micro-cracks on the surface and inside of the coarse aggregate are filled, the coarse aggregate is bonded together with the old mortar, and the performance of the recycled coarse aggregate is improved.

[0007] To achieve the above purpose, the specific technical solutions of the present invention are as follows:

[0008] In a first aspect, the present invention provides a method for strengthening recycled coarse aggregate using biotechnology, comprising the following steps: uniformly mixing algae slurry and compound fertilizer, uniformly sprinkling on the surface of recycled coarse aggregate for inoculation and cultivation, and curing to obtain modified recycled coarse aggregate;

[0009] The method for preparing the algae pulp comprises the following steps:

[0010] Cultivating desert algae species, and removing the supernatant from the culture to obtain algae slurry;

[0011] The desert algae species include a mixture of one or more of the genera of Sphingomyelia, Pseudocloma, Nostoc, Root Mullet, Sphingomyelia, Oscillatoria, and Glechoma.

[0012] The method provided by the present invention is to mix algae slurry and compound fertilizer evenly, and then evenly sprinkle them on the surface of regenerated coarse aggregate for inoculation and cultivation, and obtain modified regenerated coarse aggregate with improved strength after curing. Wherein, the regenerated coarse aggregate is obtained by crushing, baking inactivation, soaking and other steps of waste concrete. The present invention prepares regenerated coarse aggregate suitable for preparing regenerated concrete by crushing, and its particle size is 5~25 mm. The surface of the coarse aggregate particles obtained by crushing the waste concrete is bonded with old mortar, and there are a large number of micro cracks inside caused by mechanical / artificial crushing. By baking and inactivating the coarse aggregate particles, other microorganisms that affect the growth of algae species are prevented from existing on the surface and inside of the coarse aggregate particles. During the treatment process, the container for holding the coarse aggregate particles also needs to be kept clean and sterile. The coarse aggregate particles are soaked to ensure that the water content on the surface and inside of the coarse aggregate particles reaches a suitable environment for the growth of algae species. At the same time, in order to prevent secondary pollution caused by soaking water, the container should be disinfected and sterilized in advance. The algae slurry used in the present invention is obtained by culturing and separating desert algae species, and the algae species can be a combination of one or more algae to achieve a sufficient survival amount; the development of the desert algae species used in the present invention requires a weakly alkaline environment and sufficient water, and the coarse aggregate particles are inactivated at high temperature and soaked to make the weakly alkaline coarse aggregate particles become carriers suitable for the survival and development of desert algae species. The present invention mixes the algae slurry with compound fertilizer, and then inoculates it on the surface of the regenerated coarse aggregate. By adjusting the inoculation amount, environmental moisture content, light, temperature and other conditions, the algae species can reach the optimal survival amount, and then the algae filaments are adhered and entangled on the surface of the regenerated coarse aggregate and grow in microcracks. Its mechanical binding effect can wrap around microparticles such as old cement, and the metabolic products including extracellular polysaccharides can fill the microcracks, so that the surface of the regenerated coarse aggregate has a certain cohesion; at the same time, the extracellular polysaccharide has strong water absorption, and after absorbing water and swelling, it further fills the microcracks, and also increases the roughness between the regenerated coarse aggregates, so that the modified regenerated coarse aggregate finally obtained can improve the mechanical properties of concrete. In addition, extracellular polysaccharides can absorb elements such as Ca and Si. Mineral particles are adsorbed on and near the surface of the algae filamentous sheath, which is rich in Ca. These mineral elements play a regulatory role in the cement hydration process: on the one hand, they can regulate the C content in cement. 3 A hydration rate, reduce hydration heat, prevent cracks in the transition zone between recycled coarse aggregate and cement mortar interface; on the other hand, the excess Ca, Si and other elements are on the surface of recycled coarse aggregate, increasing Ca in the solution during hydration. 2+ 、Si 4+ ion concentration, promotes the formation of CSH gel, effectively improves the strength of the transition zone between recycled coarse aggregate and cement mortar interface, and thus significantly improves the strength of recycled concrete.

[0013] Preferably, when the desert algae species is a mixture of multiple species of the genera of Sphaerotheca, Pseudocranium, Nostoc, Pseudocranium, Sphaerotheca, Oscillatoria, and Glechoma, the mixing ratio (fresh weight ratio) of the desert algae species is as follows:

[0014] Scalycophytes: Pseudoclophytes = (7:3)~(9:1);

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

[0016] Sclerotium: Pseudomonas = (6:4) ~ (8:2);

[0017] Sclerotium: Pheromycetes = (6.5:3.5)~(9:1);

[0018] Scalycophytes: Pseudoclatomium: Nostoc = (6:3:1)~(8:1:1);

[0019] Scalycophytes: Pseudoclae: Pseudoclae = (7:2.5:0.5)~(9:0.3:0.7);

[0020] Scalycophytes: Pseudoclaphytes: Scalycophytes = (7:2.1:0.9)~(8.5:0.5:1);

[0021] Oscillatoria: Pseudocloma: Oscillatoria / Browworm = (6:1.3:2.7) ~ (8.7:0.2:1.1).

[0022] Preferably, in the method for preparing algae slurry, the culture environment of the desert algae species is 24 h continuous illumination, and the light intensity is 50-100 μEm -2 s -1 .

[0023] Specifically, the preparation method of the algae pulp is as follows:

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

[0025] (2) Separate and purify the desert algae species in the algae liquid; place the purified algae species in BG11 or BG11 0 The culture medium was cultured in a light incubator at 25±3°C with aeration for 30 days; the algae were cultured until the biomass of desert algae per liter of culture exceeded 0.2 g, and then the algae slurry was obtained by removing the supernatant.

[0026] Preferably, the desert algae crust soil samples are sampled from sand dunes fixed for more than 3 years, and field artificial biological soil crusts are selected from different regions, different slope aspects, and different crust growth times; when sampling, 3 1000 mm×1000 mm sample plots 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 and potassium compound fertilizer.

[0029] Preferably, before the mixture of algae slurry and compound fertilizer is evenly sprinkled on the surface of the recycled coarse aggregate, the recycled coarse aggregate is spread flat with a thickness of 100 to 200 mm.

[0030] Preferably, the inoculation amount is 5-20 μg / cm 2 (measured in chlorophyll a content).

[0031] Preferably, the algae slurry is cultured on the surface of the recycled coarse aggregate under light culture conditions; specifically, the light is illuminated for 16 h every 24 h, and the light intensity is 300-600 μEm -2 s -1 , temperature condition is 25±3℃, CO 2 Concentration: 500~800 mg·L -1 .

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

[0033] There are many specific operations for regular watering and regular supplementation of culture solution. The specific operation of the maintenance process of the present invention is as follows: micro-spray watering at regular intervals every day, and supplementation of culture solution every other day; wherein, the watering amount is to ensure that the water content of the recycled coarse aggregate is 8% to 15%; specifically, the water content of the recycled coarse aggregate can be 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%. The culture solution is PDA culture medium, Ashby nitrogen-free culture medium, phosphate-dissolving culture medium, BG 11 A mixture of one or more of the culture media, the mass fraction of the culture medium is 0.15%~2.5%, and the daily dosage of the culture medium is 30~100 mL / g.

[0034] Preferably, the curing time is 7 to 8 days.

[0035] Preferably, the recycled coarse aggregate is obtained by processing waste concrete, comprising the following steps:

[0036] (1) Crushing and screening the waste concrete to obtain coarse aggregate particles;

[0037] (2) baking and cooling the coarse aggregate particles;

[0038] (3) Soaking the cooled coarse aggregate particles in pure water, and after soaking, sieving out excess water to obtain recycled coarse aggregate; the pure water is distilled inactivated water with a pH value of 5.0-7.0, a total colony count of ≤20 cfu / ml, and a coliform count of ≤3 MPN / 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 may 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 to 25 mm.

[0041] Preferably, in step (1), the content of old mortar on the surface of the coarse aggregate particles is 8% to 20% (mass percentage); the mud content on the surface of the coarse aggregate particles is lower than 4.0%; specifically, the content of old mortar on the surface of the coarse aggregate particles may 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 may be 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5% or 4.0%.

[0042] Preferably, in step (2), the baking treatment is to spread the coarse aggregate particles in a drying oven and bake them for 5 to 6 hours at a baking temperature of 95±5°C; the thickness of the coarse aggregate particles is less than 2 cm; specifically, during the baking treatment, the thickness of the 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 containing the coarse aggregate particles immersed in pure water is soaked in 10% by mass nitric acid or hydrochloric acid for more than 8 h before use, and then rinsed with pure water before use to ensure that the container is free of bacteria; the pure water is distilled inactivated water with a pH value of 5.0-7.0, a total colony count of ≤20 cfu / ml, and a coliform colony count of ≤3 MPN / 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 may be 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%.

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

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

[0048] P2. Spread the coarse aggregate particles flatly and place them in a drying oven for 5-6 hours, then cool them for later use;

[0049] P3. Soak the cooled coarse aggregate particles in pure water for 24 hours, remove them, and repeatedly sieve out excess water on a sieve with a pore size of 3-5 mm to obtain recycled coarse aggregate; lay the recycled coarse aggregate flat with an average laying thickness of 100-200 mm;

[0050] P4. Mix the algae slurry and nitrogen, phosphorus and potassium compound fertilizer evenly, and spray them evenly on the surface of the paved recycled coarse aggregate for inoculation and cultivation. The inoculation amount is 5~20μg / cm 2 (measured in terms of chlorophyll a content); during the curing period, water the soil regularly and replenish the culture medium regularly until the recycled coarse aggregate is collected 7 to 8 days later, the moisture is dried, and the modified recycled coarse aggregate is obtained.

[0051] In a second aspect, the present invention provides modified recycled coarse aggregate prepared by the method.

[0052] In a third aspect, 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 the 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 present invention is beneficial in that:

[0055] (1) The present invention allows desert algae to grow on recycled coarse aggregate, uses the filaments of desert algae to mechanically bind old cement mortar microparticles, and uses its metabolic products including extracellular polysaccharides to adhere to and fill the surface and internal microcracks of the recycled coarse aggregate to form agglomerated microparticles, thereby significantly improving the density of the microstructure of the recycled coarse aggregate; at the same time, the extracellular polysaccharides wrap the recycled coarse aggregate, so that the surface of the recycled coarse aggregate has a certain cohesive force, so that the bonding force between the prepared modified recycled coarse aggregate and the new mortar is stronger; in addition, the extracellular polysaccharides have strong water absorption, and after absorbing water and expanding, they further fill the microcracks and increase the surface roughness of the recycled coarse aggregate; at the same time, the extracellular polysaccharides also play a role in water storage, and release water in the later stage of hydration. The recycled coarse aggregate of the present invention is used in recycled concrete, which can be used for secondary maintenance of the recycled concrete, thereby significantly improving the strength of the recycled concrete. In addition, extracellular polysaccharides can absorb elements such as Ca and Si. Mineral particles are adsorbed on the surface and vicinity of the algal filament sheath, which is rich in Ca. These mineral elements can adjust the cement hydration rate, reduce the hydration heat, and prevent cracks from forming in the transition zone between the recycled coarse aggregate and cement mortar. At the same time, they promote the formation of CSH gel, effectively improve the strength of the transition zone between the recycled coarse aggregate and cement mortar, and thus significantly improve the strength of the recycled concrete.

[0056] (2) The present invention strengthens recycled coarse aggregate through biotechnology, so that the water absorption of recycled coarse aggregate is reduced, the compressive resistance is improved, the density is improved, the apparent density is increased, the compatibility with new mortar is better, the transition zone between the recycled coarse aggregate and the new mortar interface is more compact, and the bonding force is significantly improved, thereby improving the strength of recycled concrete, making the application range of recycled concrete wider, and realizing the application of large-scale construction waste concrete.

[0057] (3) The growth of desert algae species is a process of absorbing carbon and fixing nitrogen. By introducing desert algae species into recycled coarse aggregate for growth and development, recycled concrete can be used 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 biocementation ability of desert algae species is utilized to improve the performance of recycled coarse aggregate, which has a certain degree of reversibility. The solid phase of traditional cement after hydration is inorganic substances such as hydrated calcium silicate, calcium hydroxide, and calcium sulfoaluminate, which are stable and cannot be degraded. They need hundreds of years to decompose through weathering, water erosion, etc., which has a great impact on the environment. The extracellular polysaccharides metabolized by the desert algae species used in the present invention are organic matter, which is easy to decompose and degrade, and has little impact on the environment. DETAILED DESCRIPTION

[0059] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] The present invention provides a method for strengthening recycled coarse aggregate by using biotechnology, comprising the following steps: uniformly mixing algae slurry and compound fertilizer, uniformly sprinkling on the surface of recycled coarse aggregate for inoculation and cultivation, and curing to obtain modified recycled coarse aggregate;

[0061] The method for preparing the algae pulp comprises the following steps:

[0062] Cultivating desert algae species, and removing the supernatant from the culture to obtain algae slurry;

[0063] The desert algae species include a mixture of one or more of the genera of Sphingomyelia, Pseudocloma, Nostoc, Root Mullet, Sphingomyelia, Oscillatoria, and Glechoma.

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

[0065] In some examples, in the method for preparing algae slurry, the culture environment of the desert algae species is 24 hours of continuous light, and the light intensity is 50-100 μEm -2 s -1 .

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

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

[0068] In some examples, the inoculation amount is 5-20 μg / cm 2 (measured in chlorophyll a content).

[0069] In some examples, the algae slurry is cultured on the surface of the recycled coarse aggregate under light culture conditions; for example, light is applied for 16 h every 24 h, and the light intensity is 300-600 μEm -2 s -1 , temperature condition is 25±3℃, CO 2Concentration: 500~800 mg·L -1 .

[0070] In some examples, the maintenance includes: regular watering and regular replenishment of culture solution. There are many specific operations for regular watering and regular replenishment of culture solution. The specific operation of the maintenance process of the present invention is as follows: regular micro-spraying watering every day, replenishing culture solution every other day; wherein, the watering amount is to ensure that the water content of the recycled coarse aggregate is 8% to 15%; for example, the water content of the recycled coarse aggregate can be 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%; the culture solution is PDA culture medium, Ashby nitrogen-free culture medium, phosphate-dissolving culture medium, BG 11 A mixture of one or more of the culture media, the mass fraction of the culture medium is 0.15%~2.5%, and the daily dosage of the culture medium is 30~100 mL / g.

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

[0072] The recycled coarse aggregate is obtained by processing waste concrete, comprising the following steps:

[0073] (1) Crushing and screening the waste concrete to obtain coarse aggregate particles;

[0074] (2) baking and cooling the coarse aggregate particles;

[0075] (3) Soaking the cooled coarse aggregate particles in pure water, and after soaking, sieving out excess water to obtain recycled coarse aggregate; the pure water is distilled inactivated water with a pH value of 5.0-7.0, a total colony count of ≤20 cfu / ml, and a coliform count of ≤3 MPN / 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 may be 30 MPa, 35 MPa, 40 MPa, 45 MPa or 50 MPa.

[0077] In some examples, in step (1), the content of old mortar on the surface of the coarse aggregate particles is 8% to 20% (mass percentage); the mud content on the surface of the coarse aggregate particles is less than 4.0%; for example, the content of old mortar on the surface of the coarse aggregate particles may 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 may 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 treatment is to spread the coarse aggregate particles flatly in a drying oven for baking for 5 to 6 hours at a baking temperature of 95±5°C; the thickness of the coarse aggregate particles spread flatly is less than 2 cm; for example, during the baking treatment, the thickness of the coarse aggregate particles spread flatly can be 0.5 cm, 1.0 cm, 1.5 cm or 2.0 cm.

[0079] In some examples, in step (3), in step (3), the container containing the coarse aggregate particles immersed in pure water is soaked in 10% by mass nitric acid or hydrochloric acid 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 inactivated water with a pH value of 5.0-7.0, a total colony count of ≤20 cfu / ml, and a coliform colony count of ≤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 can be 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%.

[0081] In the following embodiments and comparative examples, unless otherwise specified, the original compressive strength of the waste concrete is 43.6 MPa (obtained through actual measurement); the desert algae crust soil samples were sampled from 5 desert areas in Gansu, Ningxia and Xinjiang, and were marked 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 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; 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 Class I fly ash produced by Wuhan Yangluo Power Plant; and the admixture is a polycarboxylic acid-based high-efficiency water reducer.

[0082] Example 1

[0083] A method for preparing recycled coarse aggregate by using biotechnology comprises the following steps:

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

[0085] S2. Spread the coarse aggregate particles 1.5 mm thick, place them in a drying oven and bake for 5.5 h, then cool them.

[0086] S3. Soak the container in 10% nitric acid for 10 h, rinse with pure water to ensure that the container is free of bacteria, place the cooled coarse aggregate particles in the container and soak them in pure water for 24 hours, then remove them and repeatedly sieve out excess water on a sieve with an aperture of 3-5 mm to obtain recycled coarse aggregate. The water content of the coarse aggregate particles is 12.6%. Spread the recycled coarse aggregate flat with an average laying thickness of 150 mm.

[0087] S4. Weigh 10 g of the desert algae crust soil sample N1, place it in 100 mL of BG11 culture medium, shake it evenly for 12 hours, and separate the algae liquid.

[0088] S5. Separate and purify the desert algae species in the algae liquid. After artificial blending, the ratio of algae species is: Sphingomyces: Pseudoclones: Sphingomyces = 7:2.1:0.9. Place the algae species in BG11 culture medium and culture them in a light incubator at 25±3 ℃ with ventilation for 30 days. Cultivate the algae species until the biomass of desert algae species exceeds 0.2 g per liter of culture, collect them, and remove the supernatant to obtain algae slurry.

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

[0090] Example 2

[0091] A method for preparing recycled coarse aggregate by using biotechnology comprises the following steps:

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

[0093] S2. Spread the coarse aggregate particles 1.5 mm thick, place them in a drying oven and bake for 5.5 h, then cool them.

[0094] S3. Soak the container in 10% nitric acid for 10 h, rinse with pure water to ensure that the container is free of bacteria, place the cooled coarse aggregate particles in the container and soak them in pure water for 24 hours, then remove them and repeatedly sieve out excess water on a sieve with an aperture of 3-5 mm to obtain recycled coarse aggregate. The water content of the coarse aggregate particles is 12.6%. Spread the recycled coarse aggregate flat with an average laying thickness of 150 mm.

[0095] S4. Weigh 10 g of the desert algae crust soil sample N2, place it in 100 mL of BG11 culture medium, shake it evenly for 12 hours, and separate the algae liquid.

[0096] S5. Separate and purify the desert algae species in the algae liquid. After artificial blending, the ratio of algae species is: Scalycophytes: Pseudoclophytes = 8.2:1.8. Place the algae species in BG11 culture medium and culture them in a light incubator at 25±3 ℃ with ventilation for 30 days. Cultivate the algae species until the biomass of desert algae species exceeds 0.2 g per liter of culture, collect them, and remove the supernatant to obtain algae slurry.

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

[0098] Example 3

[0099] A method for preparing recycled coarse aggregate by using biotechnology comprises the following steps:

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

[0101] S2. Spread the coarse aggregate particles 1.5 mm thick, place them in a drying oven and bake for 5.5 h, then cool them.

[0102] S3. Soak the container in 10% nitric acid for 10 h, rinse with pure water to ensure that the container is free of bacteria, place the cooled coarse aggregate particles in the container and soak them in pure water for 24 hours, then remove them and repeatedly sieve out excess water on a sieve with an aperture of 3-5 mm to obtain recycled coarse aggregate. The water content of the coarse aggregate particles is 12.6%. Spread the recycled coarse aggregate flat with an average laying thickness of 150 mm.

[0103] S4. Weigh 10 g of the desert algae crust soil sample N3, place it in 100 mL of BG11 culture medium, shake it evenly for 12 hours, and separate the algae liquid.

[0104] S5. Separate and purify the desert algae species in the algae liquid. After artificial blending, the ratio of algae species is: Scalycophytes: Pseudoclophytes = 8.7:1.3. Place the algae species in BG11 culture medium and culture them in a light incubator at 25±3 ℃ with ventilation for 30 days. Cultivate the algae species until the biomass of desert algae species exceeds 0.2 g per liter of culture, collect them, and remove the supernatant to obtain algae slurry.

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

[0106] Example 4

[0107] A method for preparing recycled coarse aggregate by using biotechnology comprises the following steps:

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

[0109] S2. Spread the coarse aggregate particles 1.5 mm thick, place them in a drying oven and bake for 5.5 h, then cool them.

[0110] S3. Soak the container in 10% nitric acid for 10 h, rinse with pure water to ensure that the container is free of bacteria, place the cooled coarse aggregate particles in the container and soak them in pure water for 24 hours, then remove them and repeatedly sieve out excess water on a sieve with an aperture of 3-5 mm to obtain recycled coarse aggregate. The water content of the coarse aggregate particles is 12.6%. Spread the recycled coarse aggregate flat with an average laying thickness of 150 mm.

[0111] S4. Weigh 10 g of desert algal crust soil sample N4, place it in 100 mL of BG11 culture medium, shake it evenly for 12 hours, and separate the algal liquid.

[0112] S5. Separate and purify the desert algae species in the algae liquid. After artificial blending, the algae species are 100% of the genus Sphaerotheca. Place the algae species in BG11 culture medium and culture them in a light incubator at 25±3℃ with aeration for 30 days. Cultivate the algae species until the biomass of the desert algae species per liter of culture exceeds 0.2 g, collect them, and remove the supernatant to obtain the algae slurry.

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

[0114] Example 5

[0115] A method for preparing recycled coarse aggregate by using biotechnology comprises the following steps:

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

[0117] S2. Spread the coarse aggregate particles 1.5 mm thick, place them in a drying oven and bake for 5.5 h, then cool them.

[0118] S3. Soak the container in 10% nitric acid for 10 hours, rinse it with pure water to ensure that there are no bacteria in the container, put the cooled coarse aggregate particles in the container and soak them in pure water for 24 hours, then take them out and repeatedly sieve out excess water on a sieve with an aperture of 3-5 mm to obtain recycled coarse aggregate. The water content of the coarse aggregate particles is 12.6%. Spread the coarse aggregate particles flatly with an average laying thickness of 150 mm.

[0119] S4. Weigh 10 g of desert algae crust soil sample N5, place it in 100 mL of BG11 culture medium, shake it evenly for 12 hours, and separate the algae liquid.

[0120] S5. Separate and purify the desert algae species in the algae liquid. After artificial blending, the algae species ratio is: Scalycophyte: Nostoc = 7.5:2.5. Place the algae species in BG11 culture medium and culture them in a light incubator at 25±3 ℃ with aeration for 30 days. Cultivate the algae species until the biomass of the desert algae species exceeds 0.2 g per liter of culture, collect them, and remove the supernatant to obtain the algae slurry.

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

[0122] Comparative Example 1

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

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

[0125] S2. Spread the coarse aggregate particles 1.5 mm thick, place them in a drying oven and bake for 5.5 h, then cool them.

[0126] S3. Soak the container in 10% nitric acid for 10 h, rinse it with pure water to ensure that there is no bacteria in the container, put the cooled coarse aggregate particles in the container and soak them in pure water for 24 hours, then take them out, repeatedly sift out excess water on a sieve with a pore size of 3-5 mm, and dry them to obtain recycled coarse aggregate.

[0127] Comparative Example 2

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

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

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

[0131] S3. Weigh 10 g of desert algal crust soil sample N1, place it in 100 mL of BG11 culture medium, shake it evenly for 12 hours, and separate the algal liquid.

[0132] S4. Separate and purify the desert algae species in the algae liquid. After artificial blending, the ratio of algae species is: Scalycophytes: Pseudocycophytes: Scalycophytes = 7.3:1.5:1.2. Place the algae species in BG11 culture medium and culture them in a light incubator at 25±3℃ with ventilation for 30 days. Cultivate the algae species until the biomass of desert algae species exceeds 0.2 g per liter of culture, collect them, and remove the supernatant to obtain algae slurry.

[0133] S5. Add nitrogen, phosphorus and potassium compound fertilizer to the algae slurry and mix evenly, then spray evenly on the surface of the flat recycled coarse aggregate for inoculation and cultivation. The inoculation amount is 15 μg / cm 2 (measured in chlorophyll a content). During the curing period, water was sprayed regularly every day, and the culture solution was replenished every other day until the recycled coarse aggregate was collected after 8 days. The water was dried to obtain the modified recycled coarse aggregate.

[0134] Comparative Example 3

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

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

[0137] S2. Spread the coarse aggregate particles 1.5 mm thick, place them in a drying oven and bake for 5.5 h, then cool them.

[0138] S3. Soak the container in 10% nitric acid for 10 hours, rinse it with pure water to ensure that there are no bacteria in the container, put the cooled coarse aggregate particles in the container and soak them in pure water for 24 hours, then take them out and repeatedly sieve out excess water on a sieve with an aperture of 3-5 mm to obtain recycled coarse aggregate. The water content of the coarse aggregate particles is 12.6%. Spread the coarse aggregate particles flatly with an average laying thickness of 150 mm.

[0139] S4. Weigh 10 g of the desert algae crust soil sample N1, place it in 100 mL of BG11 culture medium, shake it evenly for 12 hours, and separate the algae liquid.

[0140] S5. Separate and purify the desert algae species in the algae liquid. After artificial blending, the ratio of algae species is: Sphingomyces: Pseudoclones: Sphingomyces = 7.3:1.5:1.2. Place the algae species in BG11 culture medium and culture them in a light incubator at 25±3℃ with ventilation for 30 days. Cultivate the algae species until the biomass of desert algae species exceeds 0.2 g per liter of culture, collect them, and remove the supernatant to obtain algae slurry.

[0141] S6. Add nitrogen, phosphorus and potassium compound fertilizer to the algae slurry and mix evenly, then spray evenly on the surface of the flat recycled coarse aggregate for inoculation and cultivation. The inoculation amount is 15 μg / cm 2 (measured in terms of chlorophyll a content). During the curing period, the culture medium is added every other day until the recycled coarse aggregate is collected after 8 days. The water is dried to obtain the modified recycled coarse aggregate.

[0142] Comparative Example 4

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

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

[0145] S2. Soak the container in 10% nitric acid for 10 hours, rinse it with pure water to ensure that there are no bacteria in the container, put the coarse aggregate particles in the container and soak them in pure water for 24 hours, then take them out and repeatedly sieve out excess water on a sieve with an aperture of 3-5 mm to obtain recycled coarse aggregate. The water content of the coarse aggregate particles is 12.6%. Spread the coarse aggregate particles flatly with an average laying thickness of 150 mm.

[0146] S3. Weigh 10 g of desert algal crust soil sample N1, place it in 100 mL of BG11 culture medium, shake it evenly for 12 hours, and separate the algal liquid.

[0147] S4. Separate and purify the desert algae species in the algae liquid. After artificial blending, the ratio of algae species is: Scalycophytes: Pseudocycophytes: Scalycophytes = 7.3:1.5:1.2. Place the algae species in BG11 culture medium and culture them in a light incubator at 25±3℃ with ventilation for 30 days. Cultivate the algae species until the biomass of desert algae species exceeds 0.2 g per liter of culture, collect them, and remove the supernatant to obtain algae slurry.

[0148] S5. Add nitrogen, phosphorus and potassium compound fertilizer to the algae slurry and mix evenly, then spray evenly on the surface of the flat recycled coarse aggregate for inoculation and cultivation. The inoculation amount is 15 μg / cm 2 (measured in chlorophyll a content). During the curing period, water was sprayed regularly every day, and the culture solution was replenished every other day until the recycled coarse aggregate was collected after 8 days. The water was dried to obtain the modified recycled coarse aggregate.

[0149] Comparative Example 5

[0150] A recycled concrete preparation method comprises the following steps:

[0151] Preparation of recycled coarse aggregate:

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

[0153] S2. Spread the coarse aggregate particles 1.5 mm thick, place them in a drying oven and bake for 5.5 h, then cool them.

[0154] S3. Soak the container in 10% nitric acid for 10 h, rinse it with pure water to ensure that there is no bacteria in the container, put the cooled coarse aggregate particles in the container and soak them in pure water for 24 hours, then take them out, repeatedly sift out excess water on a sieve with a pore size of 3-5 mm, and dry them to obtain recycled coarse aggregate.

[0155] Preparation of algal slurry:

[0156] S1. Weigh 10 g of desert algal crust soil sample N1, place it in 100 mL of BG11 culture medium, shake it evenly for 12 hours, and separate the algal liquid.

[0157] S2. Separate and purify the desert algae species in the algae liquid. After artificial blending, the ratio of algae species is: Sphingomyces: Pseudoclones: Sphingomyces = 7.3:1.5:1.2. Place the algae species in BG11 culture medium and culture them in a light incubator at 25±3℃ with ventilation for 30 days. Cultivate the algae species until the biomass of desert algae species exceeds 0.2 g per liter of culture, collect them, and remove the supernatant to obtain algae 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 the algae slurry was the same as that in Example 1) to prepare recycled concrete, and its compressive strength was tested after standard curing for 28 days.

[0160] Comparative Example 6

[0161] A method for preparing recycled coarse aggregate by using biotechnology comprises the following steps:

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

[0163] S2. Spread the coarse aggregate particles 1.5 mm thick, place them in a drying oven and bake for 5.5 h, then cool them.

[0164] S3. Soak the container in 10% nitric acid for 10 h, rinse with pure water to ensure that the container is free of bacteria, place the cooled coarse aggregate particles in the container and soak them in pure water for 24 hours, then remove them and repeatedly sieve out excess water on a sieve with an aperture of 3-5 mm to obtain recycled coarse aggregate. The water content of the coarse aggregate particles is 12.6%. Spread the recycled coarse aggregate flat with an average laying thickness of 150 mm.

[0165] S4. Cultivate the red algae until the biomass exceeds 0.2 g per liter of culture, collect the cultured algae, and remove the supernatant to obtain the algae slurry.

[0166] S5. Add nitrogen, phosphorus and potassium compound fertilizer to the algae slurry and mix evenly, then spray evenly on the surface of the flat recycled coarse aggregate for inoculation and cultivation. The inoculation amount is 15 μg / cm 2 (measured in chlorophyll a content). During the curing period, water was sprayed regularly every day, and the culture solution was replenished every other day until the recycled coarse aggregate was collected after 8 days. The water was dried to obtain the modified recycled coarse aggregate.

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

[0168] The attached extracellular polysaccharide content of the recycled coarse aggregate finally obtained in Examples 1 to 5 and Comparative Examples 1 to 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 magnetic stirring was performed for 15 min, and distilled water was added and stirred three times. Centrifugation was performed at 6000 g for 15 min, and the supernatant was taken after centrifugation three times. 2.0 mL of the solution was taken, 1.0 mL of 6% phenol and 5.0 mL of 2M concentrated sulfuric acid were added, and the solution was shaken and cooled. The absorbance at a wavelength of 490 nm was measured by a spectrophotometer, and the polysaccharide content was calculated with reference to the glucose standard solution. The test results are shown in Table 1.

[0169] The recycled coarse aggregate finally obtained in Examples 1 to 5 and Comparative Examples 1 to 4 and 6 was mixed with fine aggregate, cement, fly ash, water, and admixtures in proportion to prepare recycled concrete, which was cured for 28 days. The compressive strength of the recycled concrete in Examples 1 to 5 and Comparative Examples 1 to 6 was tested, and the compressive strength value was tested in accordance with 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", and the test results are shown in Table 1.

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

[0171]

[0172] From the test results in Table 1, it can be seen that the water absorption rate of the recycled coarse aggregate prepared in Examples 1 to 5 of the present invention is 2.8% to 4.6%, the crushing resistance index is 10.7% to 14.6%, and the apparent density is 2599 to 2793 kg / m 3 , the content of attached extracellular polysaccharide is 1.11~3.96 mg / g, and the compressive strength of the recycled concrete prepared by the recycled coarse aggregate of Examples 1 to 5 of the present invention is 43.1~52.7 MPa. Compared with the recycled coarse aggregate not treated by biotechnology in Comparative Example 1, the water absorption rate of the present invention is reduced by 50.0%~69.6%, the anti-crushing 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 water content was low, which failed to provide a favorable environment for the growth of desert algae species. 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 a lack of water for the growth of the desert algae species, poor growth, and a content of attached extracellular polysaccharides of only 0.43 mg / g. The strengthening effect of the recycled coarse aggregate was not obvious.

[0175] In Comparative Example 4, the recycled coarse aggregate was not subjected to baking and inactivation treatment, and other microorganisms that endangered the growth of desert algae species existed on its surface and inside, resulting in almost no growth of desert algae species. 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 algae species were not cultured, failed to grow sufficient algal filaments and secrete sufficient extracellular polysaccharides, and the extracellular polysaccharide content was only 0.06 mg / g, and the recycled coarse aggregate had no strengthening effect.

[0177] In Comparative Example 6, red algae was used to replace the desert algae species of the present invention, and the content of extracellular polysaccharides secreted by red algae was extremely low, and the regenerated coarse aggregate had no obvious strengthening effect.

[0178] In summary, the present invention prepares recycled coarse aggregate with improved strength by crushing, baking and inactivating, soaking, algae seed inoculating, culturing and curing the waste concrete. The present invention utilizes the mechanical bundling effect of desert algae seed filaments and the adhesion and adsorption of mineral elements of metabolites including extracellular polysaccharides to fill the micro-cracks on the surface and inside of the recycled coarse aggregate, so that the recycled coarse aggregate is bonded with the old mortar, thereby improving the compressive resistance of the recycled coarse aggregate and achieving performance similar to that of natural aggregate. The present invention has great application prospects.

[0179] The above specific embodiments describe the implementation of the present invention in detail, but the present invention is not limited to the specific details in the above embodiments. Within the scope of the claims and technical concept of the present invention, the technical solution of the present invention can be modified and changed in many simple ways, and these simple modifications all belong to the protection scope of the present invention.

Claims

1. A method for strengthening recycled coarse aggregate using biotechnology, characterized in that: The following steps are involved: After the algae slurry and compound fertilizer are evenly mixed, the mixture is evenly sprinkled on the surface of the recycled coarse aggregate for inoculation and cultivation, and then the modified recycled coarse aggregate is obtained after curing; The method for preparing the algae pulp comprises the following steps: Cultivating desert algae species, and removing the supernatant from the culture to obtain algae slurry; The desert algae species include a mixture of one or more of the genera of Sphingomyelia, Pseudocloma, Nostoc, Root Mullet, Sphingomyelia, Oscillatoria, and Glechoma.

2. The method of utilizing biotechnology to strengthen recycled coarse aggregate according to claim 1, characterized in that: The recycled coarse aggregate is obtained by processing waste concrete, comprising the following steps: (1) Crushing and screening the waste concrete to obtain coarse aggregate particles; (2) baking and cooling the coarse aggregate particles; (3) Soaking the cooled coarse aggregate particles in pure water. After soaking, screen out excess water to obtain recycled coarse aggregate.

3. The method of utilizing biotechnology to strengthen recycled coarse aggregate according to claim 1, characterized in that: The mass ratio of the algae slurry to the compound fertilizer is (1:0.5) to (1:1.5).

4. The method of utilizing biotechnology to strengthen recycled coarse aggregate according to claim 1, characterized in that: The compound fertilizer is a nitrogen, phosphorus and potassium compound fertilizer.

5. The method of utilizing biotechnology to strengthen recycled coarse aggregate according to claim 1, characterized in that: The algae slurry is cultured on the surface of the recycled coarse aggregate under the condition of light culture, and the light intensity is 300-600 μEm -2 s -1 , temperature conditions are 25±3 ℃, CO2 concentration is 500~800 mg·L -1 .

6. The method of utilizing biotechnology to strengthen recycled coarse aggregate according to claim 1, characterized in that: The specific operation of the maintenance is: regular micro-spraying watering every day, and replenishing the culture medium every other day; wherein the amount of water sprayed is to ensure that the moisture content of the recycled coarse aggregate is 8% to 15%; the culture medium is PDA culture medium, Ashby nitrogen-free culture medium, phosphate-dissolving culture medium, BG 11 A mixture of one or more of the culture media, the mass fraction of the culture medium is 0.15%~2.5%, and the daily dosage of the culture medium is 30~100 mL / g.

7. The method of utilizing biotechnology to strengthen recycled coarse aggregate according to claim 2, characterized in that: In step (2), the baking time is 5 to 6 hours, and the baking temperature is 95±5°C.

8. The method of utilizing biotechnology to strengthen recycled coarse aggregate according to claim 2, characterized in that: In step (3), the container containing the coarse aggregate particles and soaking them 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.

9. The modified recycled coarse aggregate prepared by the method according to any one of claims 1 to 8.

10. A recycled concrete, characterized in that: Comprising the modified recycled coarse aggregate as claimed in claim 9.

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