Slurry-coated recycled aggregate based on tea stem cellulose and tea saponin and low-alkali ecological preparation process of slurry-coated recycled aggregate

Abstract

The invention discloses a slurry-coated recycled aggregate based on tea stem cellulose and tea saponin and a low-alkali ecological preparation process of the slurry-coated recycled aggregate. According to the method, tea stem recycling grading treatment is adopted, tea stem cellulose is prepared through an acid hydrolysis method, tea saponin is purified through an ethanol soaking method, and the tea stem cellulose and the tea saponin are synergistically applied to a recycled aggregate surface modification system. The wrapping slurry is mainly prepared from the following raw materials in parts by weight: 50 parts of ordinary Portland cement, 20 parts of silica fume, 30 parts of fly ash, 10 parts of polyvinyl alcohol fiber, 10 parts of carbon fiber and 0.3 part of tea stem cellulose. A compact interface layer is formed on the surface of the recycled aggregate through a wet slurry wrapping process of a pelletizer, interface bonding of tea stem cellulose and a cement matrix is enhanced by utilizing the surface activity effect of tea saponin, and a cement hydration product Ca (OH) 2 is promoted to react with CO2 to generate CaCO3 in combination with a carbonization curing process, so that the pH value of a system is remarkably reduced, and low-alkalization regulation and control are realized. The modified slurry-coated recycled aggregate not only has better mechanical properties, but also is improved in durability, and can replace natural aggregate to prepare high-performance concrete. According to the invention, through high-value utilization of the waste tea stems, the problems of insufficient mechanical properties and enrichment of alkaline substances of the recycled aggregate are synchronously solved, and an innovative path with low carbon emission and ecological benefits is provided for recycling of building solid wastes.

Description

Technical Field

[0001] The invention relates to the technical field of concrete, and in particular to a grout-coated recycled aggregate and a low-alkali ecological preparation process thereof. Background Art

[0002] With the acceleration of urbanization, the renewal of the construction industry is becoming more and more frequent, and the amount of construction waste generated is also increasing year by year. Crushing concrete to produce recycled aggregate is an important way to recycle construction waste. Although it has a high resource utilization efficiency, the strength of the recycled aggregate is relatively low due to the attachment of old mortar on the surface of the recycled aggregate and a large number of microcracks inside. At present, the methods to improve recycled aggregates mainly include mechanical treatment, immersion treatment, and acid corrosion. Although these methods can partially improve the strength of recycled aggregates, there are still risks of incomplete interface strengthening and alkaline enrichment. However, the interface bonding between traditional encapsulating slurry and recycled aggregate is weak, and microcracks cannot be effectively closed, resulting in limited improvement in mechanical properties. In addition, the hydration of cement-based materials produces a large amount of Ca(OH) 2 , the pH value of the system is as high as 12-13, which can easily cause alkali-aggregate reaction in concrete and reduce durability.

[0003] Therefore, the existing technology lacks efficient recycled aggregate modification technology that combines mechanical strengthening, low-alkali regulation and solid waste synergy.

[0004] In addition, with the rapid development of the tea processing industry, the annual output of tea stems as the main by-product has exceeded 10 million tons. Traditional treatment methods mostly use open-air incineration or simple landfill, which not only wastes biomass resources, but also releases a large amount of greenhouse gases and dust pollutants. Although the existing tea stem resource technology involves activated carbon preparation or composting, there are generally bottlenecks such as low product added value and high process energy consumption. It is difficult to achieve efficient graded extraction and functional application of organic components, which restricts the construction of a circular economy system for the tea industry. Summary of the invention

[0005] The present invention provides a pulp-coated recycled aggregate based on tea stem cellulose and tea saponin, which has the advantages of mechanical strengthening, low alkali regulation and solid waste synergy, and breaks through the limitations of the existing technology. The pulp-coated recycled aggregate strengthening technology with tea stem cellulose and tea saponin adopts a mechanical granulation process to form a coating slurry layer on the aggregate surface to close microcracks. The process achieves uniform coating by regulating the wetting and particle adsorption process in stages, and combines carbonization curing technology to promote CO 2 It reacts with the slurry to mineralize, improves the mechanical properties of recycled aggregate and the durability of concrete, and realizes CO 2 Permanent storage effectively reduces carbon emissions throughout the entire cycle of resource utilization of construction solid waste.

[0006] The paste-coated recycled aggregate of the invention is composed of the following raw materials in parts by mass: 80-120 parts of recycled aggregate with a particle size of 4.75-9.5 mm, 40-55 parts of cement, 15-20 parts of silica fume, 30-40 parts of fly ash, 10-15 parts of polyvinyl alcohol fiber, 8-10 parts of carbon fiber, 0.1-0.5 parts of tea stem cellulose, 0.01-0.05 parts of tea saponin and water.

[0007] Preferably, silicate cement, silica fume, fly ash, polyvinyl alcohol fiber, carbon fiber and tea stem cellulose are mixed to obtain coated powder, tea saponin is prepared into a tea saponin solution with a concentration of 0.1%-0.5%, the tea saponin solution is sprayed on the recycled aggregate in a granulator once, and the coating powder is added once, and this cycle is repeated multiple times until the tea saponin solution and the coating powder are added, thereby obtaining the slurry-coated recycled aggregate.

[0008] Preferably, the tea stem cellulose in the component is obtained by acid hydrolysis purification, water washing, freeze drying and grinding of the tea stems; and the tea saponin is obtained by defatting the tea stems, extracting with alcohol and filtering.

[0009] Preferably, the extraction steps of tea stem cellulose are as follows: (1) raw material pretreatment: dehydrating the tea stems to a moisture content of less than 5%, crushing them into 80-100 mesh powders by a pulverizer, then sieving to remove impurities, and collecting the sieve material; (2) acid hydrolysis purification: putting sulfuric acid solution and tea stem powder into a reactor, continuously stirring the reaction mechanically in a constant temperature water bath at 30-55°C to destroy the lignin-hemicellulose composite structure; (3) water washing: transferring the acid hydrolysis residue into distilled water to further remove residual acid on the residue surface; (4) finished product preparation: using a freeze-drying process to solidify the fibers, followed by dry grinding with a ball mill to obtain tea stem cellulose powder.

[0010] Preferably, the extraction steps of tea saponin are as follows: (1) acetone defatting pretreatment: tea stem powder and acetone are loaded into a filter paper tube at a weight ratio of 1:4-6, extracted in a water bath at 60-100°C to remove oil impurities, the extracted tea stem powder is collected, and dried until there is no acetone smell; (2) ethanol gradient extraction: defatted tea powder and 60% ethanol are added at a solid-to-liquid ratio of 1:8-15, and ultrasonic enhanced extraction is performed; (3) finished product preparation: the extract is filtered to obtain a solid, a saturated sodium chloride solution is added at a volume ratio of solid to saturated sodium chloride solution of 1:1-2, and the precipitate is collected by centrifugation.

[0011] Preferably, the cement is silicate cement, the fly ash is primary fly ash, the polyvinyl alcohol fiber is a high modulus type with a single filament diameter of 20-40 μm, and the carbon fiber is a polyacrylonitrile-based carbon fiber with a single filament diameter of 7-12 μm.

[0012] The present invention also provides a low-alkali ecological preparation process of the above-mentioned pulp-coated recycled aggregate, comprising the following steps:

[0013] S1, pre-mix 40-55 parts of Portland cement, 15-20 parts of silica fume, 30-40 parts of fly ash, 10-15 parts of polyvinyl alcohol fiber, 8-10 parts of carbon fiber and 0.1-0.5 parts of tea stem cellulose to prepare a coating powder;

[0014] S2. Put the recycled aggregate into the opened granulator and spray 0.1%-0.5% tea saponin solution with a watering can to make the surface of the recycled aggregate evenly covered with the solution;

[0015] S3, adding the coating powder to make granules. Thereafter, the spraying and powder adding process in S2-S3 is repeated, that is, before adding the coating powder each time, the surface of the recycled aggregate is sprayed with the tea saponin solution using a watering can;

[0016] S4, after multiple wrapping, the processed slurry-coated recycled aggregate is obtained and carbonization curing is performed. Preferably, the rotation speed of the granulator in step S3 is 30-50r / min.

[0017] Preferably, during the mixing process of step S1, the stirring rate is controlled to ensure that each component can be fully and evenly dispersed to form a uniformly coated powder, wherein the stirring speed is 30 r / min and the time is 1 min.

[0018] Preferably, in step S2, the recycled aggregate is put into a granulator, the tea saponin solution is sprayed with a watering can and the granulator is turned on so that the surface of the recycled aggregate is evenly covered with the solution, and the tea saponin solution can be dynamically spread on the surface of the recycled aggregate; the granulator speed is set to 10r / min and the time is 30s.

[0019] Preferably, in step S3, before each addition of the coating powder, the surface of the recycled aggregate is first moistened with a watering can. The purpose of moistening is to form a layer of water film on the surface of the recycled aggregate, thereby enhancing the adhesion between the coating powder and the recycled aggregate, and also facilitating the uniform distribution of the powder on the surface of the aggregate. By adding powder in small amounts multiple times, the thickness of the coating layer can be gradually increased to ensure the uniformity and density of the coating layer.

[0020] Preferably, in step S4, after multiple wrapping operations, the processed slurry-coated recycled aggregate is obtained. At this time, the surface of the recycled aggregate has been evenly coated with a layer of composite slurry composed of cement, silica fume, fly ash, polyvinyl alcohol fiber, carbon fiber and tea stem cellulose. The slurry coating layer can effectively improve the surface properties of the recycled aggregate, improve its mechanical properties and durability, and provide a good foundation for subsequent carbonization curing and other processes. Afterwards, the prepared slurry-coated recycled aggregate is placed in a carbonization curing box, and the carbon dioxide partial pressure should be controlled at 0.2-0.8MPa to ensure sufficient carbon dioxide concentration to promote the carbonization reaction. The carbonization curing time is usually 1-5 days.

[0021] The present invention also provides the use of the above-mentioned mortar-coated recycled aggregate in construction, for example, in the preparation of concrete, preparation of environmentally friendly building materials, preparation of load-bearing structures, etc.

[0022] The research ideas of the present invention are as follows:

[0023] The tea stem cellulose introduced in this process improves the performance of recycled aggregate through the following synergistic mechanisms: on the one hand, the abundant hydroxyl groups on the surface of tea stem cellulose react with cement mineral C 3 S.C. 2 S chemically bonds to promote heterogeneous nucleation of calcium silicate hydrate (CSH) gel, which reduces the porosity of the encapsulation layer. On the other hand, the carboxyl functional groups (-COOH) on the surface of tea stem cellulose preferentially bond with CO during the carbonization curing stage. 2 reaction, generating nano calcium carbonate crystal nuclei and accelerating Ca(OH) 2 conversion, thereby reducing the pH value of the system.

[0024] Furthermore, it has been found through research that tea saponin can be mixed with water in advance as a spray solution, and the amount of tea saponin used can be greatly saved by spraying.

[0025] The experimental results show that the spreading speed of tea saponin solution on the surface of recycled aggregate is much higher than that of single water, achieving dynamic spreading, and tea saponin and tea stem cellulose form a "surfactant-fiber" composite carrier to drive the capillary penetration of the wrapped slurry along the cracks.

[0026] Furthermore, the powder for wrapping the recycled aggregate in the present invention is a composite powder of cement, fly ash, silica fume, polyvinyl alcohol fiber, carbon fiber and tea stem cellulose. Silica fume has high volcanic ash activity and can react with calcium hydroxide, a cement hydration product, to generate more hydrated calcium silicate gel, filling the pores generated by crushing the recycled aggregate, significantly improving the strength of the recycled aggregate; secondly, fly ash can replace part of the cement, reduce the cost of the wrapping slurry, and at the same time improve the working performance of the recycled aggregate, improve the fluidity and pumpability of the wrapping slurry, and reduce the amount of water used.

[0027] Furthermore, the polyvinyl alcohol fiber is a polymer fiber made of polyvinyl alcohol through a spinning process, and the length is generally 6-12 mm; the polyvinyl alcohol fiber in the coating material has good hydrophilicity and chemical stability, and can form a good interface bonding with the cement matrix.

[0028] At the same time, polyvinyl alcohol fiber has a synergistic effect with silica fume and fly ash. The interfacial bonding strength between polyvinyl alcohol fiber and cement matrix will be affected by fly ash and silica fume. Fly ash can reduce the chemical bonding and interfacial friction between fiber and matrix, thereby inhibiting the premature breakage of fiber during the pull-out process and improving the ductility of the composite material. The addition of silica fume helps to enhance the interfacial bonding strength.

[0029] Furthermore, carbon fiber is a fiber material with a carbon content of more than 90% made from polyacrylonitrile, asphalt or viscose fibers through high temperature carbonization. The main role of carbon fiber in the coating material in the powder coating is to improve mechanical properties, improve durability and enhance crack resistance, which helps to reduce maintenance requirements and cement consumption, thereby indirectly reducing carbon dioxide emissions.

[0030] Furthermore, the tea stem cellulose that wraps the powder forms a three-level reinforcement system with polyvinyl alcohol fibers and carbon fibers. The synergistic effect is specifically manifested in that the surface hydroxyl groups of the tea stem cellulose form a hydrogen bond network with the polyvinyl alcohol segments of the PVA fibers, the tea stem cellulose bridges nanoscale cracks, the PVA fibers dissipate mesoscale crack energy through plastic deformation, and the carbon fibers inhibit the expansion of macroscopic cracks. The three-level reinforcement system can greatly improve the tensile strength compared with a single reinforcement system.

[0031] Furthermore, it was found that through the mechanical action of rolling and rubbing the granulator, the recycled aggregate is selectively arranged according to the largest contact area, and the particles inside the spherical pellets are further compacted, so that the thin film water layer may contact each other; in the subsequent process, wetting and mechanical action play a leading role, so that the surface of the recycled aggregate is further compacted by the slurry wrapped. The working performance of the granulator is mainly determined by the rotation time and rotation speed, which is 30-50r / min.

[0032] The present invention uses a composite powder material reinforced with tea stem cellulose to coat the surface of the recycled aggregate, and forms a uniform and dense reinforcement layer on the aggregate surface by optimizing the powder particle size distribution and the tea saponin-assisted wetting process; in the regulated pulp coating granulation process, the granulator adopts a specific rotation speed (30-50r / min) and cooperates with the tea saponin-modified water spraying system to promote the adhesion effect between the tea stem cellulose and the powder. 2 A directional mineralization reaction occurs, which fills the surface cracks while reconstructing the interface transition zone of the old mortar, forming a carbonized product layer with a fiber reinforcement effect, so that the mechanical properties and durability of the recycled aggregate can be improved simultaneously.

[0033] The beneficial effects of the present invention are:

[0034] (1) The present invention innovatively realizes the synergistic utilization of tea stem cellulose and tea saponin in tea stems. Through the acid hydrolysis-ethanol extraction combined technology, tea stem cellulose and tea saponin are extracted from the discarded tea stems in a graded manner, thus solving the problem of resource waste and pollution in traditional tea stem processing.

[0035] (2) Tea stem cellulose, with its high specific surface area and abundant hydroxyl / carboxyl functional groups, forms a three-dimensional network structure in the encapsulated slurry, enhances the interfacial bonding of the cement matrix through hydrogen bonding, and promotes the directional growth of calcium carbonate crystals as a mineralization nucleation site; tea saponin plays the role of a surfactant, reduces the surface tension of the solution, drives the tea stem cellulose to penetrate along the cracks of the recycled aggregate, and inhibits the precipitation of alkaline substances through the chelation of saponin molecules with calcium ions.

[0036] (3) The present invention constructs a dual mechanism for improving the performance of recycled aggregates by coupling the wet slurry coating process of the granulator with the carbonization curing technology. The granulator uses a gradient speed of 30-50r / min and a tea saponin modified wetting process to form a dense and uniform composite coating layer on the surface of the recycled aggregate through the "dynamic wetting-layer-by-layer coating" mode, effectively sealing microcracks and reconstructing the interface transition zone.

[0037] (4) The low-alkali ecologically recycled aggregate prepared through the above-mentioned technological innovation has an alkalinity regulation mechanism embodied in the following aspects: tea stem cellulose accelerates CO 2 The mineralization reaction consumes alkaline substances, and carbonization curing causes the pH value of the system to decrease. This technology can absorb a large amount of tea stem waste every year, while reducing the amount of construction solid waste landfill by tens of millions of tons, solving the problem of poor mechanical properties of recycled aggregates, and providing the construction industry with a three-in-one sustainable development path of "solid waste resource utilization-carbon sequestration-low alkali".

[0038] (5) The carbonization curing method of the present invention is to carry out carbonization curing after the coated recycled aggregate is formed. Compared with the traditional standard curing, it can fix carbon dioxide and is environmentally friendly. Secondly, the calcium carbonate formed by carbonization curing can further fill the gap between the coated slurry and the recycled aggregate, further enhancing the strength of the recycled aggregate.

[0039] The present invention comprehensively constructs a tea stem-construction solid waste collaborative disposal system, realizes efficient separation of tea stem cellulose and tea saponin through the acid hydrolysis-ethanol extraction combined technology, and develops a synergistically enhanced composite modified slurry. The preparation process combines the toughening effect of tea stem cellulose with the surface activity of tea saponin to form a dense interface transition layer during the wet granulation process, and cooperates with the carbonization curing process to promote the directional conversion of hydration products, and simultaneously realizes the improvement of the mechanical properties of recycled aggregates and the regulation of the pH value of the system. This process not only provides a new idea for the disposal of tea stem waste and the utilization of recycled aggregates, but also conforms to the national development strategy of "carbon peak and carbon neutrality", and has the benefits of low-alkali ecology, so it has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The present invention provides a flow chart of the preparation process.

[0041] Figure 2This is the step of extracting tea stem cellulose.

[0042] Figure 3 This is the extraction step of tea saponin. DETAILED DESCRIPTION

[0043] The present invention provides a pulp-coated recycled aggregate based on tea stem cellulose and tea saponin and its low-alkali ecological preparation. The present invention is further described below in conjunction with specific embodiments, but is not intended to be a limitation of the present invention.

[0044] In the following examples, tea stem cellulose and tea saponin are obtained from discarded tea stems, and the method of obtaining them is as follows:

[0045] (1) Extraction of tea stem cellulose: The tea stems were placed in a 60°C drying oven for dehydration until the moisture content was less than 5%, and then crushed into 80-100 mesh powder using a pulverizer. Subsequently, the 0.15 mm standard sieve was vibrated and sieved for 5 min to remove inorganic impurities such as sand, gravel, and soil, and the sieve was collected; a 3 wt % sulfuric acid solution was prepared, and the tea stem powder was mixed with the mixture in a solid-liquid ratio of 1:15 and put into a reactor, and the mixture was continuously stirred mechanically in a 45°C constant temperature water bath for 30 min; the acid hydrolysis residue was then transferred to distilled water for treatment for 30 min to further remove the residual acid on the residue surface; the fiber was solidified by freeze drying, and then dry ground in a ball mill for 15 min to obtain tea stem cellulose powder with good fluidity.

[0046] (2) Extraction of tea saponin: 100 g of tea stem powder was weighed and loaded into a filter paper tube, and 500 mL of acetone was added. The mixture was extracted in a water bath at 85°C for 1 hour to remove oil impurities. The extracted tea stem powder was collected and air-dried at 60°C for 1 hour until there was no acetone odor. Defatted tea powder and 60% ethanol were added in a solid-liquid ratio of 1:12, and ultrasonic-enhanced extraction was performed for 30 minutes. The extract was vacuum-filtered through a Buchner funnel, and a saturated sodium chloride solution was added in a volume ratio of 1:1.2, and the mixture was allowed to stand for 12 hours. The precipitate was collected by centrifugation.

[0047] Example 1

[0048] (1) Preparation of coated powder: 50 parts of silicate cement, 20 parts of silica fume, 30 parts of fly ash, 10 parts of polyvinyl alcohol fiber, 10 parts of carbon fiber and 0.1 parts of tea stem cellulose were weighed and mixed in advance, and stirred in a mixer at a speed of 30 r / min for 1 min to prepare coated powder.

[0049] (2) Wet granulation process: 100 parts of recycled aggregate were placed in the granulator and the granulator was turned on. The coating powder was added in 5 times. Before each addition of the coating powder, the surface of the recycled aggregate or particles was first sprayed with a 0.1% tea saponin solution using a watering can to wet it once. The number of spraying times during the entire wet granulation process was 5 times, and the amount of each spray was about 2g; the granulator speed was 45r / min, and the duration was 3min.

[0050] (3) Carbonization curing process: After multiple wrappings, the processed slurry-coated recycled aggregate is subjected to carbonization curing, with the carbon dioxide partial pressure controlled at 0.5 MPa for 3 days.

[0051] Example 2

[0052] (1) Preparation of coated powder: 50 parts of silicate cement, 20 parts of silica fume, 30 parts of fly ash, 10 parts of polyvinyl alcohol fiber, 10 parts of carbon fiber and 0.3 parts of tea stem cellulose were weighed and mixed in advance, and stirred in a mixer at a speed of 30 r / min for 1 min to prepare coated powder.

[0053] (2) Wet granulation process: The concentration of the tea saponin solution sprayed is 0.3%, and the rest of the process is the same as Example 1.

[0054] (3) Carbonization curing process: After multiple wrappings, the processed slurry-coated recycled aggregate is subjected to carbonization curing, with the carbon dioxide partial pressure controlled at 0.5 MPa for 3 days.

[0055] Example 3

[0056] (1) Preparation of coated powder: 50 parts of silicate cement, 20 parts of silica fume, 30 parts of fly ash, 10 parts of polyvinyl alcohol fiber, 10 parts of carbon fiber and 0.5 parts of tea stem cellulose were weighed and mixed in advance, and stirred in a mixer at a speed of 30 r / min for 1 min to prepare coated powder.

[0057] (2) Wet granulation process: The concentration of the tea saponin solution sprayed is 0.5%, and the rest of the process is the same as Example 1.

[0058] (3) Carbonization curing process: After multiple wrappings, the processed slurry-coated recycled aggregate is subjected to carbonization curing, with the carbon dioxide partial pressure controlled at 0.5 MPa for 3 days.

[0059] Example 4

[0060] (1) Preparation of coated powder: 50 parts of silicate cement, 20 parts of silica fume, 30 parts of fly ash, 10 parts of polyvinyl alcohol fiber, 10 parts of carbon fiber and 0.3 parts of tea stem cellulose were weighed and mixed in advance, and stirred in a mixer at a speed of 30 r / min for 1 min to prepare coated powder.

[0061] (2) Wet granulation process: the granulator speed is 30 r / min, and the rest of the process is the same as in Example 1.

[0062] (3) Carbonization curing process: After multiple wrappings, the processed slurry-coated recycled aggregate is subjected to carbonization curing, with the carbon dioxide partial pressure controlled at 0.5 MPa for 3 days.

[0063] Example 5

[0064] (1) Preparation of coated powder: 50 parts of silicate cement, 20 parts of silica fume, 30 parts of fly ash, 10 parts of polyvinyl alcohol fiber, 10 parts of carbon fiber and 0.3 parts of tea stem cellulose were weighed and mixed in advance, and stirred in a mixer at a speed of 30 r / min for 1 min to prepare coated powder.

[0065] (2) Wet granulation process: the granulator speed is 50 r / min, and the rest of the process is the same as in Example 1.

[0066] (3) Carbonization curing process: After multiple wrappings, the processed slurry-coated recycled aggregate is subjected to carbonization curing, with the carbon dioxide partial pressure controlled at 0.5 MPa for 3 days.

[0067] Example 6

[0068] (1) Preparation of coated powder: 40 parts of silicate cement, 15 parts of silica fume, 30 parts of fly ash, 12 parts of polyvinyl alcohol fiber, 8 parts of carbon fiber and 0.3 parts of tea stem cellulose were weighed and mixed in advance, and stirred in a mixer at a speed of 30 r / min for 1 min to prepare coated powder.

[0069] (2) Wet granulation process: 80 parts of recycled aggregate were placed in a granulator, and the process was the same as in Example 1.

[0070] (3) Carbonization curing process: After multiple wrappings, the processed slurry-coated recycled aggregate is subjected to carbonization curing, with the carbon dioxide partial pressure controlled at 0.5 MPa for 3 days.

[0071] Example 7

[0072] (1) Preparation of coated powder: 45 parts of silicate cement, 17 parts of silica fume, 30 parts of fly ash, 14 parts of polyvinyl alcohol fiber, 9 parts of carbon fiber and 0.3 parts of tea stem cellulose were weighed and mixed in advance, and stirred in a mixer at a speed of 30 r / min for 1 min to prepare coated powder.

[0073] (2) Wet granulation process: 90 parts of recycled aggregate were placed in a granulator, and the process was the same as in Example 1.

[0074] (3) Carbonization curing process: After multiple wrappings, the processed slurry-coated recycled aggregate is subjected to carbonization curing, with the carbon dioxide partial pressure controlled at 0.5 MPa for 3 days.

[0075] Example 8

[0076] (1) Preparation of coated powder: 55 parts of silicate cement, 20 parts of silica fume, 40 parts of fly ash, 15 parts of polyvinyl alcohol fiber, 10 parts of carbon fiber and 0.3 parts of tea stem cellulose were weighed and mixed in advance, and stirred in a mixer at a speed of 30 r / min for 1 min to prepare coated powder.

[0077] (2) Wet granulation process: 120 parts of recycled aggregate were placed in a granulator, and the process was the same as in Example 1.

[0078] (3) Carbonization curing process: After multiple wrappings, the processed slurry-coated recycled aggregate is subjected to carbonization curing, with the carbon dioxide partial pressure controlled at 0.5 MPa for 3 days.

[0079] Comparative Example 1

[0080] (1) Preparation of coated powder: 50 parts of silicate cement, 20 parts of silica fume, 30 parts of fly ash, 10 parts of polyvinyl alcohol fiber and 10.3 parts of carbon fiber were weighed and mixed in advance, and stirred in a mixer at a speed of 30 r / min for 1 min to prepare coated powder.

[0081] (2) Wet granulation process: spray distilled water, the process is the same as Example 1.

[0082] (3) Carbonization curing process: After multiple wrappings, the processed slurry-coated recycled aggregate is subjected to carbonization curing, with the carbon dioxide partial pressure controlled at 0.5 MPa for 3 days.

[0083] Comparative Example 2

[0084] (1) Preparation of coated powder: 50 parts of silicate cement, 20 parts of silica fume, 30 parts of fly ash, 10 parts of polyvinyl alcohol fiber, 10 parts of carbon fiber and 0.33 parts of tea stem cellulose were weighed and mixed in advance, and stirred in a mixer at a speed of 30 r / min for 1 min to prepare coated powder.

[0085] (2) Wet granulation process: spray distilled water, and the rest of the process is the same as Example 1.

[0086] (3) Carbonization curing process: After multiple wrappings, the processed slurry-coated recycled aggregate is subjected to carbonization curing, with the carbon dioxide partial pressure controlled at 0.5 MPa for 3 days.

[0087] Comparative Example 3

[0088] (1) Preparation of coated powder: 50 parts of silicate cement, 20 parts of silica fume, 30 parts of fly ash, 10 parts of polyvinyl alcohol fiber and 10.3 parts of carbon fiber were weighed and mixed in advance, and stirred in a mixer at a speed of 30 r / min for 1 min to prepare coated powder.

[0089] (2) Wet granulation process: The concentration of the tea saponin solution sprayed is 3.3%, and the rest of the process is the same as Example 1.

[0090] (3) Carbonization curing process: After multiple wrappings, the processed slurry-coated recycled aggregate is subjected to carbonization curing, with the carbon dioxide partial pressure controlled at 0.5 MPa for 3 days.

[0091] Comparative Example 4

[0092] (1) Preparation of coated powder: 50 parts of silicate cement, 20 parts of silica fume, 30 parts of fly ash, 10 parts of polyvinyl alcohol fiber, 10 parts of carbon fiber and 0.3 parts of tea stem cellulose were weighed and mixed in advance, and stirred in a mixer at a speed of 30 r / min for 1 min to prepare coated powder.

[0093] (2) Wet granulation process: The process is the same as in Example 1.

[0094] (3) Natural curing process: After multiple wrappings, the processed recycled aggregate is obtained, the temperature is controlled at 20 °C, the relative humidity is 95%, and the curing is carried out for 3 days.

[0095] Performance Testing Process

[0096] (1) Compressive strength test: The aggregate after carbonization curing is subjected to compressive strength test according to the "Test Method for Strength of Cement Mortar" (GB / T 17671-2021);

[0097] (2) Water absorption test: Take another 20g of aggregate and put it into a constant temperature drying oven, set the temperature to 105±5℃, dry it for 24 hours until constant weight is reached, and weigh the mass of the dried sample with an electronic balance (M 1 ), then completely immerse the sample in 25℃ deionized water. After 6 hours, take out the sample and wipe the surface adsorbed water with wet filter paper. Immediately weigh the mass of the sample after water absorption (M 2 ),

[0098] (3) Dynamic monitoring of pH value: The treated recycled aggregate was immersed in deionized water (solid-liquid ratio 1:5), and the pH value was measured using a pH meter after 28 days. The performance test results of the above embodiments and comparative examples are summarized in Table 1.

[0099] Table 1 Batting material ratio and performance test

[0100]

[0101] From the comparison of Examples 1-3 in Table 1, it can be seen that as the amount of tea stem cellulose increases from 0.1 to 0.3 parts, the compressive strength is significantly improved, indicating that tea stem cellulose improves mechanical properties by filling pores and enhancing interface bonding. However, when the amount increases to 0.5 parts, the compressive strength decreases to 46.1 MPa. Excessive tea stem cellulose causes agglomeration and weakens the structural density. In addition, as the concentration of tea saponin increases from 0.1% to 0.5%, the pH value of the extract decreases from 10.5 to 9.5, indicating that tea saponin improves mechanical properties by chelating free Ca 2+ Inhibit cement hydration product Ca(OH) 2 of precipitation, thereby reducing the alkalinity of the system.

[0102] From the comparison between Example 2 and Example 4-5 in Table 1, it can be seen that at a speed of 45 r / min, the tea saponin and tea stem cellulose have the best dispersion uniformity, forming a dense three-dimensional network structure, which effectively enhances the mechanical properties of the aggregate wrapping layer; 30 r / min speed is too low, resulting in uneven mixing of particles, local agglomeration of the wrapping slurry, and weakening the compressive strength; 50 r / min speed is too high, which may cause excessive shearing and destroy the reinforcing effect of the wrapping slurry. From the comparison between Example 2 and Example 6-8 in Table 1, it can be seen that the material combination within the scope of claim 1 can prepare qualified recycled aggregates with high strength, low water absorption and low alkalinity.

[0103] From the comparison between Example 2 and Comparative Examples 1-3 in Table 1, it can be seen that the synergistic enhancement effect of tea stem cellulose and tea saponin is that the compressive strength of Example 2 (containing 0.3 parts of tea stem cellulose + 0.3% tea saponin) is 49.7MPa, which is significantly higher than that of Comparative Examples 1-3; tea saponin chelates Ca through hydroxyl groups and carboxylic acid groups. 2+ , inhibiting Ca(OH) 2 The dense structure of tea stem cellulose hinders OH - Diffusion, the pH value of the leaching solution of Example 2 is 9.8, which is significantly better than 12.3, 11.8 and 10.9 of the comparative examples. Tea stem cellulose and tea saponin synergistically reduce the alkalinity of the system. It can be seen from Example 2 and Comparative Example 4 that carbonization curing has an improving effect on compressive strength and an inhibitory effect on water absorption. The water absorption rate of Example 2 is only 1.9%, which is 39% lower than 3.1% of Comparative Example 4, and it has a regulating effect on pH value. The pH value of the leaching solution of Example 2 is 9.8, while the pH of Comparative Example 4 (uncarbonized) is as high as 12.1.

[0104] The above specific implementation modes are used to explain the present invention rather than to limit the present invention. Any modification and change made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A pulp-coated recycled aggregate based on tea stem cellulose and tea saponin, characterized in that: The invention is composed of the following raw materials in parts by mass: 80-120 parts of recycled aggregate with a particle size of 4.75-9.5 mm, 40-55 parts of cement, 15-20 parts of silica fume, 30-40 parts of fly ash, 10-15 parts of polyvinyl alcohol fiber, 8-10 parts of carbon fiber, 0.1-0.5 parts of tea stem cellulose, 0.01-0.05 parts of tea saponin and water.

2. The paste-coated recycled aggregate according to claim 1, characterized in that: Portland cement, silica fume, fly ash, polyvinyl alcohol fiber, carbon fiber and tea stem cellulose are mixed to obtain coated powder, tea saponin is prepared into a tea saponin solution with a concentration of 0.1%-0.5%, the tea saponin solution is sprayed on the recycled aggregate in a granulator once, and the coating powder is added once, and this cycle is repeated for multiple times until the tea saponin solution and the coating powder are added, thereby obtaining the coated recycled aggregate.

3. The paste-coated recycled aggregate according to claim 1, characterized in that: The tea stem cellulose in the components is obtained by acid hydrolysis, purification, water washing, freeze drying and grinding of the tea stems; and the tea saponin is obtained by defatting the tea stems, extracting with alcohol and filtering.

4. The paste-coated recycled aggregate according to claim 3, characterized in that: The extraction steps of tea stem cellulose are as follows: (1) raw material pretreatment: dehydrating the tea stems to a moisture content of less than 5%, crushing them into 80-100 mesh powders through a pulverizer, then sieving to remove impurities, and collecting the sieve undersize; (2) acid hydrolysis purification: putting sulfuric acid solution and tea stem powder into a reactor, continuously mechanically stirring the reaction in a constant temperature water bath of 30-55°C to destroy the lignin-hemicellulose composite structure; (3) water washing: transferring the acid hydrolysis residue into distilled water to further remove the residual acid on the residue surface; (4) finished product preparation: using a freeze-drying process to solidify the fibers, and then dry grinding them with a ball mill to obtain tea stem cellulose powder.

5. The paste-coated recycled aggregate according to claim 3, characterized in that: The extraction steps of tea saponin are as follows: (1) acetone defatting pretreatment: tea stem powder and acetone are loaded into a filter paper tube at a weight ratio of 1:4-6, and extracted in a water bath at 60-100°C to remove oil impurities, and the extracted tea stem powder is collected and dried until there is no acetone smell; (2) ethanol gradient extraction: defatted tea powder and 60% ethanol are added at a solid-liquid ratio of 1:8-15, and ultrasonic enhanced extraction is performed; (3) finished product preparation: the extract is filtered to obtain a solid, a saturated sodium chloride solution is added at a volume ratio of solid: saturated sodium chloride solution of 1:1-2, and the precipitate is collected by centrifugation.

6. The paste-coated recycled aggregate according to claim 1, characterized in that: The cement is silicate cement, the fly ash is first-grade fly ash, the polyvinyl alcohol fiber is a high modulus type with a single filament diameter of 20-40 μm, and the carbon fiber is a polyacrylonitrile-based carbon fiber with a single filament diameter of 7-12 μm.

7. A low-alkali preparation method for paste-coated recycled aggregate according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1, pre-mix 40-55 parts of Portland cement, 15-20 parts of silica fume, 30-40 parts of fly ash, 10-15 parts of polyvinyl alcohol fiber, 8-10 parts of carbon fiber and 0.1-0.5 parts of tea stem cellulose to prepare a coating powder; S2. Put the recycled aggregate into the turned-on granulator and spray 0.1%-0.5% tea saponin solution with a watering can; S3, adding the coating powder to make granules. Thereafter, the spraying and powder adding process in S2-S3 is repeated, that is, before adding the coating powder each time, the surface of the recycled aggregate is sprayed with the tea saponin solution using a watering can; S4. After multiple wrappings, the processed slurry-coated recycled aggregate is obtained and carbonization curing is carried out.

8. The preparation method according to claim 7, characterized in that: In step S3, the rotation speed of the granulator is 30-50 r / min.

9. The preparation method according to claim 8, characterized in that: In the carbonization curing method in step S4, the carbon dioxide partial pressure in the carbonization curing box is controlled at 0.2-0.8 MPa, and the curing time is 1-5 days.

10. Use of the mortar-coated recycled aggregate according to any one of claims 1 to 6 in construction.

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