Environment-friendly light foam concrete as well as preparation method and application thereof

Abstract

The invention discloses environment-friendly lightweight foam concrete as well as a preparation method and application thereof, and belongs to the technical field of lightweight concrete materials. The concrete comprises the following raw materials in percentage by weight: 30-50% of a gel material, 40-60% of waste aggregate, 0.5-1.5% of reinforced fibers, 0.8-1.2% of a composite microbial foaming agent, 1-2.5% of a functional additive and the balance of water, wherein the total amount is 100%. According to the invention, waste concrete is used for replacing a part of raw material cement, and compared with traditional concrete, the carbon emission fixed by a carbonization process is reduced, so that waste resources are effectively utilized; gas generated by metabolism of the microbial foaming agent forms a uniform pore structure, so that a sound wave transmission path caused by communicating pores is reduced. Compared with traditional concrete, the mass is reduced, and meanwhile the heat preservation and sound insulation performance is remarkably improved. In the concrete production process, additional equipment does not need to be added, the cost is lower, and the production efficiency is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lightweight concrete materials, and particularly relates to an environment-friendly lightweight foamed concrete, a preparation method thereof, and an application thereof. Background Art

[0002] As a porous lightweight building material, lightweight foamed concrete is widely used in the fields of building walls, road filling, roof insulation, etc. due to its low density, heat insulation, fire resistance, earthquake resistance and other characteristics. Traditional lightweight foamed concrete usually uses portland cement as the matrix, introduces pore structure through physical or chemical foaming processes, and supplements industrial solid wastes such as fly ash and slag as admixtures to reduce the material density and improve the environmental benefits. However, with the improvement of the comprehensive performance requirements of modern buildings, especially the high standards for sound insulation performance, mechanical strength and environmental friendliness, the defects of lightweight foamed concrete in the prior art are gradually exposed, and it is urgent to achieve breakthroughs through material design and process innovation.

[0003] Sound insulation performance is a key index of building envelopes, and the acoustic characteristics of lightweight foamed concrete are closely related to its pore structure. Existing patented technologies (such as CN109734397A, CN112194416A) generally use chemical foaming agents (such as hydrogen peroxide, aluminum powder) or surfactant-based foaming agents (such as sodium dodecyl sulfate) to form closed-cell or semi-closed-cell structures. Although certain sound insulation effects can be achieved by reflecting sound waves through pores, the following bottlenecks exist: Insufficient low-frequency sound insulation ability: The pore sizes formed by existing foaming processes mostly concentrate in the range of 0.5 - 2 mm, and the distribution uniformity is poor, resulting in low blocking efficiency of the material for low-frequency sound waves (<500 Hz). For example, the sound insulation amount of the foamed concrete disclosed in CN113636827A at a frequency of 100 Hz is only 25 dB, which is difficult to meet the requirements for isolating low-frequency noise in high-rise buildings or along traffic routes.

[0004] Sound bridge effect caused by pore connectivity: Some patents (such as CN111995258A) reduce the density by increasing the amount of foaming agent, but excessive foaming easily forms connected pores, and sound waves are transmitted through the vibration of the pore walls to form "sound bridges", which instead weakens the overall sound insulation performance. Tests show that when the density is lower than 300 kg / m³, the weighted sound insulation amount (Rw) of the material decreases by more than 15%.

[0005] Stability defects of organic foaming agents: Patents using protein-based or synthetic foaming agents (such as CN112125577A) can improve the pore size uniformity, but such foaming agents are easily decomposed in alkaline cement slurries, causing foam collapse, and finally resulting in cracks and pore collapse inside the hardened body, further reducing the sound insulation effect.

[0006] In addition, these traditional foamed concretes mostly use raw materials such as cement and natural aggregates, which have problems such as high resource consumption, high cost, and high carbon emissions.

[0007] In summary, there are significant technical bottlenecks in the sound insulation performance, mechanical strength, and environmental friendliness of existing lightweight foamed concretes. It is urgent to develop a new type of environmentally friendly material that can achieve the organic unity of high sound insulation, high compressive strength, and low carbon emissions by optimizing the foaming system, cementitious material composition, and preparation process while ensuring low density. Summary of the Invention

[0008] In view of the problems existing in the prior art, the present invention uses construction waste as raw material and is supplemented with a microbial foaming agent to prepare an environmentally friendly lightweight foamed concrete with excellent sound insulation performance. This material can effectively isolate low-frequency sound waves, reduce the sound bridge effect caused by pore connectivity, and improve the comprehensive performance such as sound insulation and heat insulation of the material.

[0009] To achieve the above technical objectives, the technical solution adopted by the present invention is as follows: An environmentally friendly lightweight foamed concrete, comprising raw materials in the following weight percentages: 30-50% of gel material, 40-60% of waste aggregate, 0.5-1.5% of reinforcing fiber, 0.8-1.2% of composite microbial foaming agent, 1-2.5% of functional auxiliary agent, and the balance is water, with a total of 100%.

[0010] Further, the gel material is portland cement, carbonized waste concrete fine powder, fly ash, and blast furnace slag micro powder; the proportion of each substance in parts by weight is 10-15 parts of portland cement, 15-25 parts of carbonized waste concrete fine powder, 3-7 parts of fly ash, and 2-5 parts of blast furnace slag micro powder.

[0011] Even further, the preparation method of the carbonized waste concrete fine powder is as follows: (1) Take waste cement concrete, crush it to a particle size less than 5 mm, and then grind it into recycled fine powder with a particle size less than 0.3 mm; (2) Mechanical activation: Add 1% of the activator based on the mass of the fine powder, mix evenly, and then use a planetary ball mill for dry grinding for 2-4 hours to increase its specific surface area; (3) High-efficiency carbonization: Place the fine powder obtained in step (2) in a carbonization furnace, evacuate the kettle to -60 kPa to remove air, and then inject CO 2 gas with a concentration exceeding 99.5% until the pressure reaches 10 kPa; carbonize at an ambient temperature of 20±1°C and a relative humidity of not less than 70% for 15-20 h; after carbonization, vacuum dry at 50-60°C for 24 h to obtain carbonized waste concrete fine powder.

[0012] Further, in step (2), the activator is triethanolamine and sodium hydroxide, and the mass ratio of the two is 1:1.

[0013] The present invention uses waste concrete as raw material to replace part of the cement raw material, which can greatly reduce the production and manufacturing cost. First, through mechanical crushing and ball milling, the original dense structure of waste concrete is destroyed to expose the internal free Ca(OH) 2 , unhydrated cement particles (C 2 S, C 3 S) and active components such as C-S-H gel. Subsequently, triethanolamine and sodium hydroxide with equal mass are used as activators. Among them, the strong alkaline environment provided by sodium hydroxide dissolves the silicate phase in the recycled fine powder (such as C-S-H gel, unhydrated (C 2 S / C 3 S), releasing Ca² + and active SiO 2 , and then can accelerate the reaction with CO 2 to generate CaCO 3 and silica gel (SiO 2 ·nH 2 O). The added triethanolamine forms a soluble complex by chelating Ca 2+ to promote ion migration; at the same time, as a surfactant, it improves the fluidity of the slurry and has a good activation effect on low-activity fine powder (such as waste concrete in old age). The two work together to achieve efficient activation of waste concrete powder. Subsequently, high-efficiency carbonation is carried out. The generated carbonate network bonds with the residual gel and fills the pores, overall improving the mechanical properties of the material. This carbonation process not only enhances the stability of the material but also endows it with good durability. It can effectively replace commercial cement raw materials as a gel material, greatly reducing the production cost and reducing the dependence on natural resources.

[0014] Further, the waste aggregate is obtained by mixing waste glass microspheres and waste EPS particles after being treated respectively. The specific preparation method is as follows: The waste glass microspheres are crushed and then sieved to obtain particles with a particle size of 0.5-2 mm, and metals and plastics are removed. Then, they are soaked in a 5% NaOH solution by mass for 30 minutes, and then dried to a moisture content <1% to obtain treated waste glass microspheres; the waste EPS particles are mechanically crushed into 3-5 mm fragments, and the surface oil is removed by washing with dilute sulfuric acid with a pH of 3. A silane coupling agent solution with a mass concentration of 0.5% is sprayed, and the spraying amount is 3%. It is dried and cured at 60 °C to reduce the water absorption rate; then, it is treated with hot air at 160 °C for 5 seconds to expand the internal micropores of the particles to obtain treated waste EPS particles; finally, the waste glass microspheres and the waste EPS particles are mixed according to a mass ratio of (5-10):(8-12) to obtain the waste aggregate.

[0015] The present invention uses waste glass microspheres and waste EPS particles as aggregates, and forms a rough surface through alkali etching to enhance the mechanical bite force between the glass microspheres and cement; the silane coating reduces the hydrophobicity difference of EPS particles and alleviates the risk of interfacial peeling. EPS and the microporous matrix synergistically absorb broadband noise and improve the sound insulation effect.

[0016] Furthermore, the reinforcing fiber is polypropylene fiber with a length of 10 - 20 mm.

[0017] Furthermore, the specific preparation method of the composite microbial foaming agent is as follows: Bacillus subtilis ( Bacillus subtilis ), Pediococcus acidilactici ( Pediococcus acidilactici ), and Saccharomyces cerevisiae ( Saccharomyces cerevisiae ) are activated and then inoculated into a liquid medium, and cultured on a shaker at 25 - 42 °C for 24 hours until the bacterial liquid concentration reaches 1×10 8 CFU / mL; the three bacterial liquids are mixed according to the volume ratio: Bacillus subtilis:Pediococcus acidilactici:Saccharomyces cerevisiae = 5:3:2, and 1% of cocamidopropyl betaine based on the mass of the mixed bacterial liquid is added, and then centrifuged and concentrated to a bacterial concentration of 5×10 9 CFU / mL to prepare a liquid bacterial agent, which is the composite microbial foaming agent.

[0018] Furthermore, the composition of the liquid medium is: glucose, yeast extract, peptone, and phosphate buffer solution, with a ratio of 10:5:5:2. After mixing, it is sterilized at a temperature of 121 °C for 15 minutes.

[0019] Furthermore, the strain number of Bacillus subtilis is CGMCC No.1.12939, and the original preservation date is May 30, 2014; the strain number of Pediococcus acidilactici is CGMCC No.1.12332, and the original preservation date is September 10, 2012; the strain number of Saccharomyces cerevisiae is CGMCC No.2.3875, and the original preservation date is June 5, 2008; the three strains are all purchased from the China General Microbiological Culture Collection Center, and can be purchased through public channels without the need for repeated biological preservation.

[0020] Traditional foamed concrete relies on chemical foaming agents (such as aluminum powder, hydrogen peroxide, etc.) or physical mechanical foaming, which has problems such as high cost, environmental pollution, and uneven pore sizes. Existing microbial foaming agents mostly use single strains, with low gas production efficiency and insufficient foam stability. The present invention achieves a balance between high - efficiency gas production and foam stability through the synergistic fermentation of a composite microbial community. Bacillus subtilis, Pediococcus acidilactici, and Saccharomyces cerevisiae are selected and compounded in a specific ratio, and respectively undertake gas production (CO 2), adjust the pH by producing acid, and secrete biosurfactants, forming a synergistic effect. Bacillus subtilis undergoes aerobic fermentation to produce CO 2 , and metabolizes to generate lipopeptide biosurfactants; Pediococcus acidilactici metabolizes to produce lactic acid, reducing the local environmental pH to inhibit miscellaneous bacteria and activate yeast activity. Saccharomyces cerevisiae metabolizes sugars to produce CO 2 and ethanol, and ethanol synergistically enhances the foam stability with lipopeptides. The three strains act synergistically. The liquid fermentation inoculant is directly added during the concrete mixing stage, and the microbial metabolism is activated by the heat released during cement hydration (40 - 50 °C), synchronously completing gas production and foaming and cement setting without additional temperature control equipment. Moreover, the generated bubbles are uniform and stable, enabling the lightweighting, heat insulation, and sound insulation performance of concrete to be improved.

[0021] Furthermore, the functional additive is a polycarboxylate water reducer.

[0022] A preparation method of an environment-friendly lightweight foam concrete includes the following steps: (1) Prepare carbonized waste concrete fine powder; (2) Mix Portland cement, carbonized waste concrete fine powder, fly ash, and blast furnace slag micro-powder evenly, add water and waste aggregates, and stir until a uniform slurry is obtained; (3) Prepare a composite microbial foaming agent, add it to the slurry, then add a functional additive and reinforcing fibers, and continue stirring for 10 - 15 minutes; (4) Let it stand for 2 - 4 hours at 25 - 40 °C, and the microorganisms metabolize to produce gas to form a uniform closed-cell structure; (5) Pour the obtained concrete slurry into a mold, demold the cured foam concrete, and place it in a room with a humidity of 90 - 95% and a temperature of 20 - 25 °C for curing to the specified age.

[0023] Beneficial effects: (1) In the present invention, waste concrete is used to replace a part of the raw material cement. After the carbonized waste concrete fine powder is mechanically activated and CO 2 -strengthened carbonization, its activity is significantly improved, and it synergistically enhances the matrix strength with Portland cement; the proportion of waste aggregates in the foam concrete of the present invention is high, effectively improving the utilization rate of construction waste, and the carbonization process fixes CO 2 The carbon emissions are reduced compared with traditional concrete, and waste resources are effectively utilized; (2) The gas generated by the metabolism of the microbial foaming agent forms a uniform pore structure, reducing the sound wave transmission path caused by connected pores. Through sound wave scattering and damping effects, low-frequency sound waves (100 - 500 Hz) are effectively blocked. Tests show that the sound insulation at 100 Hz in Example 1 reaches 38 dB, which is significantly improved compared with Comparative Example 1 (traditional chemical foaming); (3) In addition, the lightweight foamed concrete prepared by this method also shows improved mechanical properties, meeting the strength requirements of general construction projects. Compared with traditional concrete, it has a reduced mass while significantly enhancing the insulation and sound insulation properties. During the production process of the concrete, no additional equipment needs to be added, resulting in lower costs and greatly improving production efficiency. Description of the Drawings

[0024] Figure 1 Microstructure of the foam in the initial state of Example 1 and Comparative Examples 3 - 5 of the present invention; Figure 2 Section view of the foamed concrete specimen of Example 1 of the present invention; Figure 3 Section views of the foamed concrete specimens of Comparative Examples 1 - 6. Detailed Description of the Invention

[0025] The technical solution of the present invention will be further described below in conjunction with specific embodiments, but not limited thereto.

[0026] Example 1 An environmentally friendly lightweight foamed concrete, comprising the following raw materials in weight percentages: 50% of gel material, 40% of waste aggregate, 0.5% of reinforcing fiber, 1.2% of composite microbial foaming agent, 1% of functional additive, and the balance being water, with a total of 100%.

[0027] The gel material is Portland cement, carbonized waste concrete fine powder, fly ash, and blast furnace slag micro - powder; the proportion of each substance by weight is: 10 parts of Portland cement, 25 parts of carbonized waste concrete fine powder, 3 parts of fly ash, and 2 parts of blast furnace slag micro - powder.

[0028] The preparation method of the carbonized waste concrete fine powder is as follows: (1) Take waste cement concrete, crush it to a particle size less than 5 mm, and then grind it to prepare recycled fine powder with a particle size less than 0.3 mm; (2) Mechanical activation: Add 1% of the activator based on the mass of the fine powder, mix evenly, and then perform dry grinding for 2 hours using a planetary ball mill to increase its specific surface area; (3) High - efficiency carbonization: Place the fine powder obtained in step (2) in a carbonization furnace, evacuate the kettle to - 60 kPa to remove air, and then inject CO 2 gas until the pressure reaches 10 kPa; carbonize at an ambient temperature of 20 ± 1 °C and a relative humidity of not less than 70% for 15 h; after carbonization, perform vacuum drying at 50 - 60 °C for 24 h to obtain carbonized waste concrete fine powder.

[0029] In step (2), the activator is triethanolamine and sodium hydroxide, and the mass ratio of the two is 1:1.

[0030] The waste aggregate is obtained by mixing treated waste glass microspheres and waste EPS particles. The specific preparation method is as follows: The waste glass microspheres are crushed and then sieved to obtain particles with a particle size of 0.5 - 2 mm, and metals and plastics are removed. Then, they are soaked in a 5% NaOH solution by mass for 30 minutes, and then dried to a moisture content of <1% to obtain treated waste glass microspheres; The waste EPS particles are mechanically crushed into 3 - 5 mm fragments, and the surface oil is removed by washing with dilute sulfuric acid with a pH of 3. A silane coupling agent solution with a mass concentration of 0.5% is sprayed, and the spraying amount is 3%. It is dried and cured at 60°C to reduce the water absorption rate; Subsequently, it is treated with hot air at 160°C for 5 seconds to expand the internal micropores of the particles to obtain treated waste EPS particles; Finally, the waste glass microspheres and waste EPS particles are mixed according to a mass ratio of 5:12 to obtain the waste aggregate.

[0031] The reinforcing fiber is polypropylene fiber with a length of 10 - 20 mm.

[0032] The specific preparation method of the composite microbial foaming agent is as follows: Bacillus subtilis ( Bacillus subtilis ), Pediococcus acidilactici ( Pediococcus acidilactici ), and Saccharomyces cerevisiae ( Saccharomyces cerevisiae ) are activated and then inoculated into a liquid medium. They are cultured on a shaker at 25 - 42°C for 24 hours until the bacterial liquid concentration reaches 1×10 8 CFU / mL; The three bacterial liquids are mixed according to a volume ratio of Bacillus subtilis:Pediococcus acidilactici:Saccharomyces cerevisiae = 5:3:2, and 1% of cocamidopropyl betaine based on the mass of the mixed bacterial liquid is added. It is centrifuged and concentrated to a bacterial concentration of 5×10 9 CFU / mL to prepare a liquid bacterial agent, which is the composite microbial foaming agent.

[0033] The composition of the liquid medium is: glucose, yeast extract, peptone, and phosphate buffer solution, with a ratio of 10:5:5:2. After mixing, it is sterilized at a temperature of 121°C for 15 minutes.

[0034] The strain number of the Bacillus subtilis is CGMCC No.1.12939, and the original preservation date is May 30, 2014; The strain number of the Pediococcus acidilactici is CGMCC No.1.12332, and the original preservation date is September 10, 2012; The strain number of the Saccharomyces cerevisiae is CGMCC No.2.3875, and the original preservation date is June 5, 2008; The three strains are all purchased from the China General Microbiological Culture Collection Center and can be purchased through public channels without the need for repeated biological preservation.

[0035] The functional additive is a polycarboxylate water reducer.

[0036] A preparation method of an environment-friendly lightweight foamed concrete, comprising the following steps: (1) Prepare carbonized waste concrete fine powder; (2) Mix Portland cement, carbonized waste concrete fine powder, fly ash, and ground granulated blast-furnace slag evenly, add water and waste aggregate, and stir until a homogeneous slurry is obtained; (3) Prepare a composite microbial foaming agent, add it to the slurry, then add functional additives and reinforcing fibers, and continue stirring for 10 - 15 minutes; (4) Let it stand for 2 hours in an environment of 25 - 40 °C, and microbial metabolism produces gas to form a uniform closed-cell structure; (5) Pour the obtained concrete slurry into a mold, demold the cured foamed concrete, and place it in a room with a humidity of 90 - 95% and a temperature of 20 - 25 °C for curing to the specified age.

[0037] Example 2 An environment-friendly lightweight foamed concrete, comprising raw materials in the following weight percentages: 30% of gel material, 60% of waste aggregate, 1.5% of reinforcing fiber, 0.8% of composite microbial foaming agent, 2% of functional additives, and the balance is water, with a total of 100%.

[0038] The gel material is Portland cement, carbonized waste concrete fine powder, fly ash, and ground granulated blast-furnace slag; the proportion of each substance in parts by weight is 12 parts of Portland cement, 20 parts of carbonized waste concrete fine powder, 5 parts of fly ash, and 4 parts of ground granulated blast-furnace slag.

[0039] The preparation method of the carbonized waste concrete fine powder is as follows: (1) Take waste cement concrete, crush it to a particle size less than 5 mm, and then grind it into recycled fine powder with a particle size less than 0.3 mm; (2) Mechanical activation: Add an activator accounting for 1% of the mass of the fine powder, mix evenly, and then use a planetary ball mill for dry grinding for 3 hours to increase its specific surface area; (3) High-efficiency carbonization: Place the fine powder obtained in step (2) in a carbonization furnace, evacuate the kettle to -60 kPa to remove air, and then inject CO 2 gas until the pressure reaches 10 kPa; carbonize at an ambient temperature of 20 ± 1 °C and a relative humidity of not less than 70% for 15 h; after carbonization, vacuum dry at 50 - 60 °C for 24 h to obtain carbonized waste concrete fine powder.

[0040] The activator in step (2) is triethanolamine and sodium hydroxide, and the mass ratio of the two is 1:1.

[0041] The waste aggregate is obtained by mixing treated waste glass microspheres and waste EPS particles. The specific preparation method is as follows: Crush the waste glass microspheres and then screen them to obtain particles with a particle size of 0.5 - 2 mm. Remove metals and plastics, and then soak them in a 5% NaOH solution by mass for 30 minutes, followed by drying to a moisture content of <1% to obtain treated waste glass microspheres; Mechanically crush the waste EPS particles into 3 - 5 mm fragments, wash them with dilute sulfuric acid with a pH of 3 to remove surface oil stains, spray a silane coupling agent solution with a mass concentration of 0.5%, with a spraying amount of 3%, and dry and cure at 60°C to reduce the water absorption rate; Subsequently, perform hot air treatment at 160°C for 5 seconds to expand the internal micropores of the particles to obtain treated waste EPS particles; Finally, mix the waste glass microspheres and waste EPS particles in a mass ratio of 7:10 to obtain the waste aggregate.

[0042] The reinforcing fiber is polypropylene fiber with a length of 10 - 20 mm.

[0043] The specific preparation method of the composite microbial foaming agent is as follows: Activate Bacillus subtilis ( Bacillus subtilis ), Pediococcus acidilactici ( Pediococcus acidilactici ), and Saccharomyces cerevisiae ( Saccharomyces cerevisiae ), and then inoculate them into a liquid medium. Incubate them on a shaker at 25 - 42°C for 24 hours until the bacterial concentration reaches 1×10 8 CFU / mL; Mix the three bacterial solutions in a volume ratio of Bacillus subtilis:Pediococcus acidilactici:Saccharomyces cerevisiae = 5:3:2, add 1% of cocamidopropyl betaine based on the mass of the mixed bacterial solution, and centrifuge and concentrate to a bacterial concentration of 5×10 9 CFU / mL to prepare a liquid bacterial agent, which is the composite microbial foaming agent.

[0044] The composition of the liquid medium is: glucose, yeast extract, peptone, and phosphate buffer solution, with a ratio of 10:5:5:2. After mixing, perform sterilization treatment at a temperature of 121°C for 15 minutes.

[0045] The strain number of Bacillus subtilis is CGMCC No.1.12939, and the original preservation date is May 30, 2014; The strain number of Pediococcus acidilactici is CGMCC No.1.12332, and the original preservation date is September 10, 2012; The strain number of Saccharomyces cerevisiae is CGMCC No.2.3875, and the original preservation date is June 5, 2008; The three strains are all purchased from the China General Microbiological Culture Collection Center and can be purchased through public channels without the need for repeated biological preservation.

[0046] The functional auxiliary agent is a polycarboxylate water reducer.

[0047] A preparation method of an environment-friendly lightweight foamed concrete, comprising the following steps: (1) Prepare carbonized waste concrete fine powder; (2) Mix Portland cement, carbonized waste concrete fine powder, fly ash, and ground granulated blast-furnace slag evenly, add water and waste aggregate, and stir until a uniform slurry is obtained; (3) Prepare a composite microbial foaming agent, add it to the slurry, then add functional additives and reinforcing fibers, and continue stirring for 10 - 15 minutes; (4) Let it stand for 3 hours in an environment of 25 - 40 °C, and microbial metabolism generates gas to form a uniform closed-cell structure; (5) Pour the obtained concrete slurry into a mold, demold the cured foamed concrete, and place it in a room with a humidity of 90 - 95% and a temperature of 20 - 25 °C for curing to the specified age.

[0048] Example 3 An environment-friendly lightweight foamed concrete, comprising raw materials in the following weight percentages: 45% of gel material, 43% of waste aggregate, 1% of reinforcing fiber, 1% of composite microbial foaming agent, 2.5% of functional additives, and the balance is water, with a total of 100%.

[0049] The gel material is Portland cement, carbonized waste concrete fine powder, fly ash, and ground granulated blast-furnace slag; the proportion of each substance by weight is: 15 parts of Portland cement, 25 parts of carbonized waste concrete fine powder, 7 parts of fly ash, and 5 parts of ground granulated blast-furnace slag.

[0050] The preparation method of the carbonized waste concrete fine powder is as follows: (1) Take waste cement concrete, crush it to a particle size less than 5 mm, and then grind it into recycled fine powder with a particle size less than 0.3 mm; (2) Mechanical activation: Add 1% of an activator based on the mass of the fine powder, mix evenly, and then use a planetary ball mill for dry grinding for 2 - 4 hours to increase its specific surface area; (3) High-efficiency carbonization: Place the fine powder obtained in step (2) in a carbonization furnace, evacuate the kettle to -60 kPa to remove air, and then inject CO 2 gas until the pressure reaches 10 kPa; carbonize at an ambient temperature of 20 ± 1 °C and a relative humidity of not less than 70% for 20 h; after carbonization, conduct vacuum drying at 50 - 60 °C for 24 h to obtain carbonized waste concrete fine powder.

[0051] In step (2), the activator is triethanolamine and sodium hydroxide, and the mass ratio of the two is 1:1.

[0052] The waste aggregate is obtained by mixing treated waste glass microspheres and waste EPS particles. The specific preparation method is as follows: The waste glass microspheres are crushed and then sieved to obtain particles with a particle size of 0.5 - 2 mm, and metals and plastics are removed. Then, they are soaked in a 5% NaOH solution by mass for 30 minutes, and subsequently dried to a moisture content of <1% to obtain the treated waste glass microspheres; The waste EPS particles are mechanically crushed into 3 - 5 mm fragments, washed with dilute sulfuric acid with a pH of 3 to remove surface oil stains, sprayed with a silane coupling agent solution with a mass concentration of 0.5%, with a spraying amount of 3%, and dried and cured at 60°C to reduce the water absorption rate; Subsequently, they are treated with hot air at 160°C for 5 seconds to expand the internal micropores of the particles, obtaining the treated waste EPS particles; Finally, the waste glass microspheres and the waste EPS particles are mixed in a mass ratio of 10:12 to obtain the waste aggregate.

[0053] The reinforcing fiber is polypropylene fiber with a length of 10 - 20 mm.

[0054] The specific preparation method of the composite microbial foaming agent is as follows: Bacillus subtilis ( Bacillus subtilis ), Pediococcus acidilactici ( Pediococcus acidilactici ), and Saccharomyces cerevisiae ( Saccharomyces cerevisiae ) are activated and then inoculated into a liquid medium, and cultured on a shaker at 25 - 42°C for 24 hours until the bacterial liquid concentration reaches 1×10 8 CFU / mL; The three bacterial liquids are mixed in a volume ratio of Bacillus subtilis:Pediococcus acidilactici:Saccharomyces cerevisiae = 5:3:2, and 1% of cocamidopropyl betaine based on the mass of the mixed bacterial liquid is added, and then centrifuged and concentrated to a bacterial concentration of 5×10 9 CFU / mL to prepare a liquid bacterial agent, which is the composite microbial foaming agent.

[0055] The composition of the liquid medium is: glucose, yeast extract, peptone, and phosphate buffer solution, with a ratio of 10:5:5:2. After mixing, it is sterilized at a temperature of 121°C for 15 minutes.

[0056] The strain number of the Bacillus subtilis is CGMCC No.1.12939, and the original preservation date is May 30, 2014; The strain number of the Pediococcus acidilactici is CGMCC No.1.12332, and the original preservation date is September 10, 2012; The strain number of the Saccharomyces cerevisiae is CGMCC No.2.3875, and the original preservation date is June 5, 2008; The three strains are all purchased from the China General Microbiological Culture Collection Center, and can be purchased through public channels without the need for repeated biological preservation.

[0057] The functional auxiliary agent is a polycarboxylate water reducer.

[0058] A preparation method of an environment-friendly lightweight foamed concrete, comprising the following steps: (1) Prepare carbonized waste concrete fine powder; (2) Mix Portland cement, carbonized waste concrete fine powder, fly ash, and ground granulated blast-furnace slag evenly, add water and waste aggregate, and stir until a homogeneous slurry is obtained; (3) Prepare a composite microbial foaming agent, add it to the slurry, then add functional additives and reinforcing fibers, and continue stirring for 10 - 15 minutes; (4) Stand still for 4 hours in an environment of 25 - 40°C, and microbial metabolism produces gas to form a uniform closed-cell structure; (5) Pour the obtained concrete slurry into a mold, demold the cured foamed concrete, and place it in a room with a humidity of 90 - 95% and a temperature of 20 - 25°C for curing to the specified age.

[0059] Comparative Example 1 In this comparative example, compared with Example 1, in the preparation of carbonized waste concrete fine powder, only triethanolamine is used as the activator, and the other raw materials and preparation processes are the same as those in Example 1. That is: The preparation method of the carbonized waste concrete fine powder is as follows: (1) Take waste cement concrete, crush it to a particle size less than 5 mm, and then grind it into recycled fine powder with a particle size less than 0.3 mm; (2) Mechanical activation: Add 1% of the activator based on the mass of the fine powder, mix evenly, and then perform dry grinding for 2 - 4 hours using a planetary ball mill to increase its specific surface area; (3) High-efficiency carbonization: Place the fine powder obtained in step (2) in a carbonization furnace, evacuate the kettle to -60 kPa to remove air, and then inject CO 2 gas with a concentration exceeding 99.5% until the pressure reaches 10 kPa; carbonize at an ambient temperature of 20 ± 1°C and a relative humidity of not less than 70% for 20 h; after carbonization, perform vacuum drying at 50 - 60°C for 24 h to obtain carbonized waste concrete fine powder.

[0060] The activator in step (2) is triethanolamine.

[0061] Comparative Example 2 In this comparative example, compared with Example 1, in the preparation of carbonized waste concrete fine powder, only sodium hydroxide is used as the activator, and the other raw materials and preparation processes are the same as those in Example 1. That is: The preparation method of the carbonized waste concrete fine powder is as follows: (1) Take waste cement concrete, crush it to a particle size less than 5 mm, and then grind it into recycled fine powder with a particle size less than 0.3 mm; (2) Mechanical activation: Add an activator accounting for 1% of the mass of the fine powder, mix evenly, and then perform dry grinding for 2 hours using a planetary ball mill to increase its specific surface area; (3) High-efficiency carbonization: Place the fine powder obtained in step (2) in a carbonization furnace, evacuate the kettle to -60 kPa to remove air, and then inject CO 2 gas with a concentration exceeding 99.5% until the pressure reaches 10 kPa; carbonize at an ambient temperature of 20 ± 1 °C and a relative humidity of not less than 70% for 15 h; after carbonization, perform vacuum drying at 50 - 60 °C for 24 h to obtain carbonized waste concrete fine powder.

[0062] In step (2), the activator is sodium hydroxide.

[0063] Comparative Example 3 In this comparative example, compared with Example 1, in the preparation of the composite microbial foaming agent, except that Bacillus subtilis is not used as the microorganism, the remaining raw materials and preparation processes are the same as those in Example 1. That is: The specific preparation method of the composite microbial foaming agent is as follows: Activate Pediococcus acidilactici and Saccharomyces cerevisiae and then inoculate them into a liquid medium, culture at 25 - 42 °C on a shaker for 24 hours until the bacterial liquid concentration reaches 1×10 8 CFU / mL; Mix the two bacterial liquids in a volume ratio of Pediococcus acidilactici:Saccharomyces cerevisiae = 3:2, add cocamidopropyl betaine accounting for 1% of the mass of the mixed bacterial liquid, and centrifuge and concentrate to a bacterial concentration of 5×10 9 CFU / mL to prepare a liquid bacterial agent, which is the composite microbial foaming agent.

[0064] Comparative Example 4 In this comparative example, compared with Example 1, in the preparation of the composite microbial foaming agent, except that Pediococcus acidilactici is not used as the microorganism, the remaining raw materials and preparation processes are the same as those in Example 1. That is: The specific preparation method of the composite microbial foaming agent is as follows: Activate Bacillus subtilis and Saccharomyces cerevisiae and then inoculate them into a liquid medium, culture at 25 - 42 °C on a shaker for 24 hours until the bacterial liquid concentration reaches 1×10 8 CFU / mL; Mix the two bacterial liquids in a volume ratio of Bacillus subtilis:Saccharomyces cerevisiae = 5:2, add cocamidopropyl betaine accounting for 1% of the mass of the mixed bacterial liquid, and centrifuge and concentrate to a bacterial concentration of 5×10 9 CFU / mL to prepare a liquid bacterial agent, which is the composite microbial foaming agent.

[0065] Comparative Example 5 In this comparative example, compared with Example 1, in the preparation of the composite microbial foaming agent, except that Saccharomyces cerevisiae is not used as the microorganism, the remaining raw materials and preparation processes are the same as those in Example 1. That is: The specific preparation method of the composite microbial foaming agent is as follows: Activate Bacillus subtilis and Pediococcus acidilactici and inoculate them into a liquid medium. Incubate at 25 - 42°C on a shaker for 24 hours until the bacterial liquid concentration reaches 1×10 8 CFU / mL; Mix the two bacterial liquids according to the volume ratio: Bacillus subtilis:Pediococcus acidilactici = 5:3, add 1% of cocamidopropyl betaine based on the mass of the mixed bacterial liquid, and centrifuge and concentrate to a bacterial concentration of 5×10 9 CFU / mL to prepare a liquid bacterial agent, which is the composite microbial foaming agent.

[0066] Comparative Example 6 Compared with the traditional chemical foaming agent (hydrogen peroxide), that is, relative to Example 1, only the composite microbial foaming agent is replaced with a hydrogen peroxide foaming agent, and the other raw materials and preparation processes are the same as those in Example 1. That is: An environmentally friendly lightweight foamed concrete includes the following raw materials in weight percentages: 50% gel material, 40% waste aggregate, 0.5% reinforcing fiber, 1.2% foaming agent, 1% functional additive, and the balance is water, with a total of 100%.

[0067] A preparation method of an environmentally friendly lightweight foamed concrete includes the following steps: (1) Prepare carbonized waste concrete fine powder; (2) Dilute the foaming agent hydrogen peroxide with water at a dilution ratio of 1:30 to obtain a foaming agent solution; (3) Mix Portland cement, carbonized waste concrete fine powder, fly ash, and blast furnace slag micro powder evenly, add the foaming agent solution, then add the remaining water and waste aggregate, and stir until a uniform slurry; then add the functional additive and reinforcing fiber, and continue to stir for 10 - 15 minutes; (4) Since the decomposition rate of hydrogen peroxide is relatively fast, it is necessary to pour immediately after stirring. Pour the obtained concrete slurry into a mold, demold the cured foamed concrete, and place it in a room with a humidity of 90 - 95% and a temperature of 20 - 25°C for curing to the specified age.

[0068] Performance Test Comparison of the foaming performance of different foaming agents: Prepare the composite microbial foaming agent according to the methods of Example 1 and Comparative Examples 3 - 5. According to JC / T2199—2013 "Foaming Agent for Foamed Concrete", measure the foaming multiple, 1h sedimentation distance, and 1h bleeding rate of the microbial foaming agent; obtain the microscopic images of the foam using a super-depth-of-field microscope and process the images using Image-Pro plus software.

[0069] Table 1 Test Results of the Foaming Performance of the Foaming Agent As can be seen from Table 1, the foaming multiple, 1h settlement distance and 1h bleeding rate of Example 1 using the composite microbial foaming agent are all better than those of other comparative experiments. Especially the bleeding rate and settlement distance are significantly higher than those of Comparative Examples 3, 4, 5 and the hydrogen peroxide foaming agent. This result shows that the composite microbial foaming agent can meet the foaming performance requirements of foam concrete, and its foaming performance is equal to or even better than that of the traditional chemical hydrogen peroxide foaming agent, and it can replace the chemical foaming agent. At the same time, for Comparative Examples 4-5 with the changed microbial composition, due to the different microbial species used, the synergistic effect between strains disappeared, resulting in a decrease in foaming performance. From the microscopic structure of the foam in the initial state (when the foam was just prepared) Figure 1 It can be seen that the foam obtained by the foaming agent of Example 1 has clearer boundaries, better bubble independence, and uniform foam size and shape, while in the foam liquid film of Comparative Examples 3-5, there are doped with tiny bubbles, the foam boundaries are not clear, and the bubble independence is poor.

[0070] Performance Test of Foam Concrete According to the standard of "Foam Concrete" (JG / T 266-2011), the compressive and flexural strengths of the specimens cured for 28 days were tested. The dry density and water absorption of the specimens cured for 28 days were tested according to the method in "Foam Concrete" (JG / T 266-2011), and the size of the test block was 100 mm×100 mm×100 mm. Thermal conductivity test: The test was carried out with reference to GB / T 10294—2008. Sound insulation performance: According to GB / T 19889.3-2005, the sound insulation quantity in the frequency band of 100-5000 Hz was tested by the standing wave tube method. The weighted sound insulation quantity (Rw) was calculated according to ISO 717-1. The specimens were scanned using a nanoVoxel-2740E type X-ray high-precision industrial CT, and the software Avizo was used to analyze the experimental results to obtain the two-dimensional pore structure of the samples. The test results are shown in Table 2: Table 2 Performance Test Results of Foam Concrete From the data in the table, we can see that the foamed concrete of the present invention is superior to the foamed concrete prepared by traditional hydrogen peroxide foaming agents in terms of compressive and flexural strengths, has a lower dry density, a smaller water absorption rate, and especially has a significantly improved sound insulation performance. This indicates that the composite microbial foaming agent not only improves the mechanical properties of the foamed concrete but also significantly enhances its heat insulation and sound insulation effects, providing a new direction for the optimization of building materials. For Comparative Examples 4-5 in which the types of microorganisms in the foaming agent were changed, both their mechanical properties and heat insulation and sound insulation effects decreased, verifying the importance of the synergistic effect of the strains. At the same time, the experimental data also show that with the effective activation of sodium hydroxide and triethanolamine, the gel performance of waste concrete is effectively improved, which can replace part of the cement use, reduce costs, and is more environmentally friendly. From the two-dimensional slice images of the foamed concrete cases of Example 1 of the present invention and Comparative Examples 1-6, it can also be seen that the pores inside the foamed concrete are evenly distributed, and a small number of large pores are occasionally seen, while Comparative Examples 1-6 all show an obvious large pore structure, with increased pore connectivity and significant differences in pore size, resulting in a decrease in strength performance and sound insulation performance.

[0071] It should be noted that the above-mentioned embodiments are only some of the embodiments of the preferred implementation manners of the present invention, rather than all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

Claims

1. An environmentally friendly lightweight foamed concrete, characterized in that: The raw materials include the following weight percentages: 30-50% of gel material, 40-60% of waste aggregate, 0.5-1.5% of reinforcing fiber, 0.8-1.2% of composite microbial foaming agent, 1-2.5% of functional additive, and the balance is water, and the total amount is 100%.

2. The environmentally friendly lightweight foamed concrete according to claim 1, characterized in that: The gel material is silicate cement, carbonized waste concrete powder, fly ash and blast furnace slag powder; the proportion of each material in parts by weight is: 10-15 parts of silicate cement, 15-25 parts of carbonized waste concrete powder, 3-7 parts of fly ash, and 2-5 parts of blast furnace slag powder.

3. The environmentally friendly lightweight foamed concrete according to claim 2, characterized in that: The preparation method of the carbonized waste concrete fine powder is: (1) taking waste cement concrete, crushing it to a particle size of less than 5 mm, and then grinding it to prepare recycled micro powder, wherein the particle size of the recycled micro powder is less than 0.3 mm; (2) Mechanical activation: Add 1% of the powder mass of the activator, mix well, and use a planetary ball mill for 2-4 hours to dry grind to increase its specific surface area; (3) High-efficiency carbonization: The fine powder obtained in step (2) is placed in a carbonization furnace, the interior of the reactor is evacuated to -60 kPa to exclude air, and then CO2 gas with a concentration exceeding 99.5% is injected until the pressure reaches 10 kPa; carbonization is performed for 15-20 hours at an ambient temperature of 20±1°C and a relative humidity of not less than 70%; after the carbonization is completed, vacuum drying is performed at 50-60°C for 24 hours to obtain carbonized waste concrete fine powder.

4. The environmentally friendly lightweight foamed concrete according to claim 3, characterized in that: In step (2), the activator is triethanolamine and sodium hydroxide, and the mass ratio of the two is 1:

1.

5. The environmentally friendly lightweight foamed concrete according to claim 1, characterized in that: The waste aggregate is obtained by mixing waste glass microspheres and waste EPS particles after being treated respectively. The specific preparation method is as follows: the waste glass microspheres are crushed and sieved to obtain particles with a particle size of 0.5-2 mm, and metals and plastics are removed, and then the particles are soaked in a 5% by mass NaOH solution for 30 minutes, and then dried to a moisture content of less than 1% to obtain treated waste glass microspheres; the waste EPS particles are mechanically crushed into 3-5 mm particles, washed with dilute sulfuric acid with pH=3 to remove surface oil stains, sprayed with a silane coupling agent solution with a mass concentration of 0.5%, a spraying amount of 3%, and dried at 60°C for curing to reduce water absorption; then hot air treatment is performed at 160°C for 5 seconds to obtain treated waste EPS particles; finally, the waste glass microspheres and waste EPS particles are mixed in a mass ratio of (5-10): (8-12) to obtain waste aggregate.

6. The environmentally friendly lightweight foamed concrete according to claim 1, characterized in that: The reinforcing fiber is polypropylene fiber with a length of 10-20 mm.

7. The environmentally friendly lightweight foamed concrete according to claim 1, characterized in that: The specific preparation method of the composite microbial foaming agent is: Bacillus subtilis ( Bacillus subtilis ), Pediococcus acidilactici ( Pediococcus acidilactici ) and Saccharomyces cerevisiae ( Saccharomyces cerevisiae ) After activation, it was inoculated into liquid culture medium and cultured on a shaker at 25-42°C for 24 hours until the bacterial liquid concentration reached 1×10 8 CFU / mL; the three bacterial solutions were mixed in a volume ratio of Bacillus subtilis: Pediococcus acidilactici: Saccharomyces cerevisiae = 5:3:2, and 1% of the mass of the mixed bacterial solution was added with cocamidopropyl betaine, and centrifuged to concentrate the bacterial concentration to 5×10 9 CFU / mL, made into liquid bacterial agent, that is, composite microbial foaming agent.

8. The environmentally friendly lightweight foamed concrete according to claim 1, characterized in that: The strain number of the Bacillus subtilis is CGMCC No.1.12939; the strain number of the Pediococcus acidilactici is CGMCC No.1.12332; the strain number of the Saccharomyces cerevisiae is CGMCC No.2.3875; all three strains were purchased from the China General Microbiological Collection Center.

9. The environmentally friendly lightweight foamed concrete according to claim 1, characterized in that: The functional additive is a polycarboxylic acid water reducer.

10. A method for preparing the environmentally friendly lightweight foamed concrete according to any one of claims 1 to 9, characterized in that: The following steps are involved: (1) Preparing carbonized waste concrete fine powder; (2) Mixing silicate cement, carbonized waste concrete fine powder, fly ash, and blast furnace slag fine powder evenly, adding water and waste aggregate, and stirring until a uniform slurry is obtained; (3) preparing a composite microbial foaming agent and adding it to the slurry, then adding a functional additive and reinforcing fiber, and continuing to stir for 10-15 minutes; (4) Standing at 25-40°C for 2-4 hours, the microorganisms metabolize and produce gas to form a uniform closed-cell structure; (5) The obtained concrete slurry is poured into a mold, and the solidified foamed concrete is demoulded and placed in a room with a humidity of 90-95% and a temperature of 20-25°C for curing to a specified age.

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