A modified recycled aggregate, its preparation method and application

Abstract

The present invention belongs to the technical field of building materials, and discloses a modified recycled aggregate, a preparation method thereof, and an application thereof. The preparation method of the modified recycled aggregate of the present invention comprises the following steps: soaking the recycled aggregate in an alkaline solution containing calcium, then adding ethyl orthosilicate and tetrabutyl titanate, then adding a plant-active silicon oxide compound and conducting a hydrothermal reaction, filtering, and uniformly dispersing the mineralized bacteria on the surface of the filtrate to obtain the aggregate. The modified recycled aggregate prepared by the present invention has a significantly lower saturated surface dry water absorption rate than that before modification, and compared with the concrete prepared from the unmodified aggregate, the slump, 28d compressive strength and impermeability of the recycled aggregate concrete prepared from the modified recycled aggregate of the present invention are significantly improved. In summary, the modified recycled aggregate prepared by the present invention realizes resource utilization and performance optimization, which is of great significance for environmental protection, low-carbon development and sustainable development of concrete.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials, and particularly relates to a modified recycled aggregate and a preparation method and application thereof. Background Art

[0002] In recent years, with the continued development of urbanization in my country and the gradual renewal of cities, the demolition and renovation of existing buildings in urban construction projects such as shantytown redevelopment, roads, and bridges has generated a large amount of construction waste. However, much of this waste remains untreated and is transported to suburban or urban areas for simple landfill or open-air storage. This not only wastes land and resources but also pollutes the environment. However, upstream in product production, with the increasing population, the construction industry's demand for sand and gravel aggregates continues to grow. For a long time, due to their widespread availability and low price, sand and gravel aggregates were considered an inexhaustible raw material and were thus arbitrarily mined. This, in turn, has led to resource depletion, landslides, riverbed diversion, and severe damage to the natural environment. Therefore, recycled concrete aggregates have emerged.

[0003] Aggregate made from waste concrete is called recycled concrete aggregate (abbreviated as recycled aggregate). The production and utilization of recycled aggregate from construction waste is of great significance for resource conservation, environmental protection, and the sustainable development of the construction industry. Recycled aggregate produced through simple crushing and screening processes has angular particles, a rough surface, and contains hardened cement mortar. Furthermore, the crushing process accumulates damage within the concrete blocks, creating numerous microcracks. This results in high porosity, high water absorption, low packing density, high void ratio, and a high crushing index. Recycled concrete made from this type of recycled aggregate has a high water content, low hardened strength, and a low elastic modulus. Furthermore, its durability properties, such as impermeability, frost resistance, carbonation resistance, shrinkage, creep, and chloride ion permeability resistance, are inferior to those of conventional concrete. Due to the wide variation in the quality of waste concrete, the performance of recycled aggregate produced through simple processes also varies significantly, hindering the widespread application of recycled aggregate.

[0004] To improve the performance of recycled concrete, low-quality recycled aggregates obtained through simple crushing must be strengthened, particularly by controlling their water absorption. Currently, the main methods for modifying recycled aggregate to control water absorption include: 1) physical modification: mechanically breaking weak recycled crushed stone particles or removing residual mortar adhering to the crushed stone surface to reduce porosity; and 2) chemical modification: improving the surface condition of the recycled aggregate by filling and sealing cracks with active admixtures and inorganic salt additives. While these methods have improved the performance of recycled aggregate to some extent, they also have drawbacks: physical modification processes are complex, the improvement process is cumbersome, and the equipment is bulky, power-intensive, and costly. Traditional chemical methods are limited by the inherent properties of the aggregate, making it difficult to accurately determine the optimal ratio, yield, and concentration of additives. This results in either ineffective production or waste of resources. Therefore, an optimization method that effectively addresses these contradictions and challenges is crucial for improving the strength of recycled concrete and promoting its widespread use. Summary of the Invention

[0005] In view of the problems and shortcomings in the prior art, the present invention aims to provide a modified recycled aggregate and a preparation method and application thereof.

[0006] Based on the above purpose, the present invention adopts the following technical solutions:

[0007] The first aspect of the present invention provides a method for preparing a modified recycled aggregate, comprising the following steps:

[0008] (1) Adding recycled aggregate to a calcium-containing alkaline solution and soaking it at 40-80°C to obtain premix A;

[0009] (2) Ethyl orthosilicate, tetrabutyl titanate, and ethanol are mixed and added to premix A and stirred to obtain premix B;

[0010] (3) Adding the plant-active silicon oxide compound to premix B, dispersing the mixture evenly and then allowing it to stand to obtain premix C; adding premix C to a reactor and heating it to 300-400°C for hydrothermal reaction to obtain premix D;

[0011] The preparation method of the plant active silicon oxide compound is as follows: fresh grass plant leaves are placed in water for dispersion treatment, precipitates are collected after filtering, and then the precipitates are dried to obtain the compound;

[0012] (4) After filtering the premix D, the filtrate is collected. After the filtrate is cooled, the mineralizing bacteria are evenly dispersed on the surface of the filtrate to obtain the modified recycled aggregate.

[0013] Preferably, the recycled aggregate is crushed stone particles with a particle size of 5-35 mm, mortar particles with a particle size of 0.075-5 mm, or brick particles with a particle size of 5-35 mm.

[0014] Preferably, the calcium-containing alkaline solution is a mixture of a sodium hydroxide aqueous solution and a calcium hydroxide aqueous solution; the mass fraction of the sodium hydroxide aqueous solution is 10%-52%; the calcium hydroxide aqueous solution is a saturated calcium hydroxide aqueous solution; and the volume ratio of the sodium hydroxide aqueous solution to the calcium hydroxide aqueous solution is (3-4): (1-2).

[0015] More preferably, the amount of the calcium-containing alkaline solution added is based on completely immersing the recycled aggregate. In order to reduce the raw material cost of the calcium-containing alkaline solution, the mass ratio of the recycled aggregate to the calcium-containing alkaline solution is 5:(2-4).

[0016] Preferably, the mass ratio of the plant-active silicon oxide compound to the recycled aggregate is (0.5-2): 100. More preferably, the optimal ratio of the plant-active silicon oxide compound is related to the type of recycled aggregate.

[0017] Preferably, in the method for preparing the plant-active silicon oxide compound, the dispersion treatment method is ultrasonic treatment for 6-8 hours; the water temperature during the dispersion treatment is 25-80° C.; and the drying temperature is 30-80° C. More preferably, the water temperature during the dispersion treatment is 25-40° C.; and the drying temperature is 40-60° C.

[0018] Preferably, the mass ratio of the recycled aggregate to tetraethyl orthosilicate, tetrabutyl titanate, and ethanol is 100:(5-8):(6-10):(2-5).

[0019] Preferably, the mineralizing bacteria are calcium carbonate mineralizing bacteria; and the mass ratio of the mineralizing bacteria to the recycled aggregate is (0.01-0.1):100.

[0020] Preferably, the soaking time in step (1) is 4-6 hours.

[0021] More preferably, during the stirring process in step (2), the solution in the premix will become turbid and turn into milky white, and the stirring end point is when the milky white phenomenon no longer changes.

[0022] Preferably, the dispersion method in step (3) is ultrasonic treatment; the standing time is 6-8 hours; and the hydrothermal reaction time is 24-48 hours.

[0023] Preferably, the temperature of the filtrate after cooling in step (4) does not exceed 60°C; the method for uniformly dispersing the mineralized bacteria on the surface of the filtrate is to atomize the suspension of the mineralized bacteria and then uniformly spray it on the surface of the filtrate.

[0024] The second aspect of the present invention provides a modified recycled aggregate prepared by any of the preparation methods described in the first aspect.

[0025] The third aspect of the present invention provides use of the modified recycled aggregate described in the second aspect in recycled aggregate concrete.

[0026] A fourth aspect of the present invention provides a modified recycled aggregate concrete, wherein the modified recycled aggregate concrete is prepared from cement, fly ash, sand, modified recycled aggregate, water and admixtures; the modified recycled aggregate is the modified recycled aggregate described in the second aspect above;

[0027] The mass ratio of the cement, fly ash, sand, modified recycled aggregate and water is (28-35): (8-15): (70-85): (95-115): (14-20); the amount of the admixture is 1%-3% of the mass of the cement.

[0028] More preferably, the admixture is an anti-mud polycarboxylic acid-based high-performance water reducer.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The present invention first adds the recycled aggregate to a calcium-containing alkaline solution for alkaline excitation treatment; then adds ethyl orthosilicate and tetrabutyl titanate to generate sodium titanate with strong adsorption and certain ability to dissolve metal oxides, so that the sodium titanate is completely wrapped and attached to the surface of the recycled aggregate, and a certain amount of active metal cations such as calcium ions are dissolved, enriching a large amount of active silicon and aluminum; then adds a biologically active silicon oxide compound (specifically extracted from the surface of the leaves of grass plants, a type of micro-nano particles and fiber structures mainly composed of silicon oxide compounds), which penetrates into the gaps of the recycled aggregate to react with calcium ions, plays a role in building a micro-skeleton, crystal nucleus and filling the recycled aggregate, and promotes the sealing and closure of the cracks in the recycled aggregate. In one embodiment, the saturated dry water absorption rate of the modified recycled aggregate prepared by the present invention is 1.1%, which is 7.3% lower than that before modification; the slump of the recycled aggregate concrete prepared by the present invention is 160mm, the 28d compressive strength is 39.8MPa, and the impermeability is 0.48×10 -6 mm / s, the slump of unmodified recycled aggregate concrete increased by 63%, the 28-day compressive strength increased by 23%, and the impermeability increased by three times. Therefore, the modified recycled aggregate prepared by the present invention achieves resource utilization and performance optimization, which is of great significance for environmental protection, low-carbon development, and the sustainable development of concrete.

[0031] (2) Finally, the present invention adds mineralizing bacteria to the surface of the recycled aggregate. The mineralizing bacteria convert the calcium hydroxide precipitated and attached to the surface of the recycled aggregate into calcium carbonate, further improving and reinforcing the surface of the recycled aggregate, reducing the water absorption rate of the recycled aggregate, and improving the overall performance of the recycled aggregate. In addition, the mineralizing bacteria can further participate in the mineralization reaction in the modified recycled aggregate concrete, further improving the density and strength of the concrete.

[0032] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below through examples. It should be understood that the specific examples described herein are only used to explain the present invention and are not intended to limit the present invention.

[0034] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the embodiments.

[0035] Example 1: Effects of plant-active silicon oxides on the properties of modified recycled aggregate and modified recycled aggregate concrete

[0036] To investigate the effects of plant-active silicon oxide compounds on the properties of modified recycled aggregate and modified recycled aggregate concrete, the inventors conducted the following experiments, namely Examples 1-1 to 1-3. The corresponding methods of adding the plant-active silicon oxide compounds and the test results of the properties of the modified recycled aggregate and modified recycled aggregate concrete prepared therefrom are shown in Table 1. The saturated surface dry water absorption of the modified recycled aggregate was determined according to the test method specified in JGJ52; the slump of the modified recycled aggregate concrete was determined according to the test method specified in GB50080; the 28-day compressive strength was determined according to the test method specified in GB50081; and the impermeability was determined according to the water seepage height method specified in GB50082.

[0037] Example 1-1

[0038] This embodiment provides a modified recycled aggregate, the preparation method of which includes the following steps:

[0039] (1) 52% sodium hydroxide aqueous solution and saturated calcium hydroxide aqueous solution were mixed in a volume ratio of 2:1 to obtain a calcium-containing alkaline solution. Then, 100 parts of recycled aggregate were added to 40 parts of the calcium-containing alkaline solution and soaked at 75°C for 4 hours to obtain premix A.

[0040] The recycled aggregate is crushed stone particles with a particle size of 5-35 mm.

[0041] (2) After evenly mixing 5 parts of ethyl orthosilicate, 10 parts of tetrabutyl titanate, and 3 parts of ethanol, slowly drip into premix A and stir until the solution in the premix turns turbid to milky white, thereby obtaining premix B.

[0042] (3) Add 1.5 parts of powdered plant-active silicon oxide to premix B, disperse evenly by ultrasonication, and allow to stand and soak for 8 hours to obtain premix C;

[0043] The preparation method of the plant-active silicon oxide compound comprises: taking fresh grass plant leaves (leaves of Elymus dahliae, the surface of which has plant-active silicon oxide compounds in various forms, such as serrated rods and hair fibers), subjecting the leaves to ultrasonic dispersion treatment for 6 hours in water at a temperature of 30°C, collecting the precipitate after filtration, and then drying the precipitate at 60°C to obtain the plant-active silicon oxide compound.

[0044] (4) Premix C was added to a hydrothermal synthesis reactor and heated to 400°C for a hydrothermal reaction for 48 h to obtain premix D.

[0045] (5) After premix D is filtered, the filtrate is collected. After the filtrate is cooled to 60°C, 0.02 parts of calcium carbonate mineralized bacterial capsules are made into a suspension, atomized, and evenly dispersed on the surface of the filtrate. After natural drying, the modified recycled aggregate is obtained.

[0046] This embodiment also provides a modified recycled aggregate concrete. The raw materials for preparing each cubic meter of the modified recycled aggregate concrete include: 290 kg of PO42.5 cement, 100 kg of fly ash, 780 kg of sand, 1060 kg of the modified recycled aggregate prepared in this embodiment, 175 kg of water, and 7.8 kg of PCE (polycarboxylate-based high-performance water reducer). The preparation method includes the following steps: first, adding cement, fly ash, sand, and modified recycled aggregate, thoroughly mixing them, then simultaneously adding water and the water reducer, stirring until the slurry is uniform, and then forming the slurry to obtain the modified recycled aggregate concrete.

[0047] Example 1-2

[0048] The content of a modified recycled aggregate is substantially the same as that of Example 1-1, except that the recycled aggregate in step (1) is mortar particles with a particle size of 0.075-5 mm.

[0049] The content of a modified recycled aggregate concrete is basically the same as that of Example 1-1, except that the modified recycled aggregate in the raw materials is prepared in this example.

[0050] Examples 1-3

[0051] The content of a modified recycled aggregate is substantially the same as that of Example 1-1, except that the preparation in step (3) is not performed, and the premix B prepared in step (2) is directly added to the reactor instead of the premix C in step (4) to prepare the premix D.

[0052] The content of a modified recycled aggregate concrete is basically the same as that of Example 1-1, except that the modified recycled aggregate in the raw materials is prepared in this example.

[0053] Examples 1-4

[0054] The content of a modified recycled aggregate is substantially the same as that of Example 1-1, except that: the recycled aggregate in step (1) is mortar particles with a particle size of 0.075-5 mm; and step (3) is not performed, and the premix B prepared in step (2) is directly added to the reactor instead of the premix C in step (4) to prepare the premix D.

[0055] The content of a modified recycled aggregate concrete is basically the same as that of Example 1-1, except that the modified recycled aggregate in the raw materials is prepared in this example.

[0056] Examples 1-5

[0057] The content of a modified recycled aggregate is substantially the same as that of Example 1-1, except that in step (3), 1.5 parts of nano-active silica powder is added to premix B instead of 1.5 parts of plant-active silicon oxide to prepare premix C.

[0058] The content of a modified recycled aggregate concrete is basically the same as that of Example 1-1, except that the modified recycled aggregate in the raw materials is prepared in this example.

[0059] Examples 1-6

[0060] The content of a modified recycled aggregate is substantially the same as that of Example 1-1, except that: the recycled aggregate in step (1) is mortar particles with a particle size of 0.075-5 mm; and in step (3), 1.5 parts of nano-active silica powder is added to premix B instead of 1.5 parts of plant-active silicon oxide to prepare premix C.

[0061] The content of a modified recycled aggregate concrete is basically the same as that of Example 1-1, except that the modified recycled aggregate in the raw materials is prepared in this example.

[0062] Table 1 Effects of plant-based active silicon oxides on the properties of modified recycled aggregates

[0063]

[0064] Comparing Examples 1-1, 1-3, and 1-5, it can be seen that when the type of recycled aggregate is the same as crushed stone particles, the saturated surface dry water absorption rate data of Example 1-3 without the addition of plant-active silicon oxide is the highest, the saturated surface dry water absorption rate data of Example 1-5 with nano-active silica instead of plant-active silicon oxide is second, and the saturated surface dry water absorption rate data of Example 1-1 with the addition of plant-active silicon oxide is the lowest. The properties of the modified recycled aggregate concrete, such as slump, 28d compressive strength, and impermeability, are all affected by the saturated surface dry water absorption rate of the modified recycled aggregate and show the same trend. Comparing Examples 1-2, 1-4, and 1-6, it can be seen that this trend also occurs when the type of recycled aggregate is the same as mortar particles. It should be noted that the inventors also conducted a comparative experiment on brick particles with a particle size of 5-35 mm, but because brick particles have fewer application scenarios, the data is not released. The data trend is the same as that of crushed stone particles and mortar particles. This is because plant-activated silica compounds, after ultrasonic dispersion, enter the cracks of aggregate and participate in hydration reactions under alkaline conditions, sealing and reinforcing the cracks, increasing aggregate density, and further improving the overall performance of concrete. While nano-activated silica can act as a crystal nucleus to induce cement hydration, thus providing reinforcement, its effectiveness is significantly inferior to plant-activated silica compounds. Therefore, the plant-activated silica compounds prepared in this experiment are preferred for modifying recycled aggregate, and when optimizing modification conditions, the saturated dry water absorption data of the modified recycled aggregate should be prioritized.

[0065] Example 2: Effect of water temperature on the properties of modified recycled aggregate during the preparation of plant-active silicon oxide compounds

[0066] In order to explore the effect of water temperature in the preparation method of plant-active silicon oxide compounds on the saturated dry water absorption rate of modified recycled aggregate, the inventors conducted the following experiments, namely Examples 1-1, 2-1 to 2-4, and the measurement results of the water temperature in the preparation method of plant-active silicon oxide compounds and the saturated dry water absorption rate of the modified recycled aggregate prepared therefrom are shown in Table 2.

[0067] Example 2-1

[0068] The content of a modified recycled aggregate is substantially the same as that of Example 1-1, except that in the preparation method of the plant-active silicon oxide compound in step (3), the water temperature for ultrasonic dispersion treatment is 25°C.

[0069] Example 2-2

[0070] The content of a modified recycled aggregate is substantially the same as that of Example 1-1, except that in the preparation method of the plant-active silicon oxide compound in step (3), the water temperature for ultrasonic dispersion treatment is 40°C.

[0071] Example 2-3

[0072] The content of a modified recycled aggregate is substantially the same as that of Example 1-1, except that in the preparation method of the plant-active silicon oxide compound in step (3), the water temperature for ultrasonic dispersion treatment is 80°C.

[0073] Examples 2-4

[0074] The content of a modified recycled aggregate is substantially the same as that of Example 1-1, except that in the preparation method of the plant-active silicon oxide compound in step (3), the water temperature for ultrasonic dispersion treatment is 100°C.

[0075] Table 2 Effect of water temperature on the properties of modified recycled aggregate in the preparation method of plant-active silicon oxide compounds

[0076]

[0077] By comparing Examples 1-1, 2-1 to 2-4, it can be seen that when the drying temperature for fixing the plant-active silicon oxide compound is 60°C and other conditions such as the amount added are met, the saturated surface dry water absorption rate of the modified recycled aggregate shows a trend of first decreasing and then increasing with the increase of the water temperature of the ultrasonic dispersion treatment, and reaches a minimum value when the dispersion temperature is 30°C. This is because under room temperature conditions, plant cells are still active, which can ensure the integrity and continuity of the structure of the generated plant-active silicon oxide compound, and the morphology is better. After the temperature rises, the morphology and structure of the silicon oxide compound in the plant body are affected, which affects the subsequent reaction with the recycled aggregate. In addition, the inventors also carried out the above modification process using mortar particles as recycled aggregate, and the trend of its saturated surface dry water absorption rate was the same as that of sand and gravel particles. Therefore, in subsequent experiments, a water temperature of 30°C is preferably used for the preparation of plant-active silicon oxide compounds.

[0078] Example 3: Effect of Drying Temperature on the Properties of Modified Recycled Aggregates in the Preparation Method of Plant-Active Silicon Oxide Compounds

[0079] In order to explore the effect of the drying temperature in the preparation method of the plant-active silicon oxide compound on the saturated surface dry water absorption rate of the modified recycled aggregate, the inventors conducted the following experiments, namely Examples 1-1, 3-1, and 3-2. The corresponding drying temperatures in the preparation method of the plant-active silicon oxide compound and the saturated surface dry water absorption rate of the modified recycled aggregate prepared therefrom are shown in Table 3.

[0080] Example 3-1

[0081] The content of a modified recycled aggregate is substantially the same as that of Example 1-1, except that in the preparation method of the plant-active silicon oxide compound in step (3), the drying temperature is 40°C.

[0082] Example 3-2

[0083] The content of a modified recycled aggregate is substantially the same as that of Example 1-1, except that in the preparation method of the plant-active silicon oxide compound in step (3), the drying temperature is 80°C.

[0084] Table 3 Effect of drying temperature on the properties of modified recycled aggregate in the preparation method of plant-active silicon oxide compounds

[0085]

[0086] By comparing Examples 1-1, 3-1, and 3-2, it can be seen that when the water temperature for the ultrasonic treatment of the fixed plant-active silicon oxide compound is 30°C and other conditions such as the amount added are met, the saturated surface dry water absorption rate of the modified recycled aggregate shows a trend of first decreasing and then increasing with the increase of the drying temperature. This is because after the plant-active silicon oxide compound is taken out, when the temperature is low, its activity is improved as the temperature increases, but when the temperature is too high, its activity is affected, so the temperature is limited to no more than 80°C. In addition, the inventors also carried out the above modification process using mortar particles as recycled aggregate, and the trend of its saturated surface dry water absorption rate was the same as that of sand and gravel particles. Therefore, in subsequent experiments, a drying temperature of 60°C is preferably used for the preparation of plant-active silicon oxide compounds.

[0087] Example 4: Effect of the amount of plant-active silicon oxide added on the properties of modified recycled aggregate

[0088] In order to explore the effect of the amount of plant-active silicon oxide added on the saturated surface dry water absorption rate of the modified recycled aggregate, the inventors conducted the following experiments, namely Examples 1-1, 4-1 to 4-7, and the corresponding amounts of plant-active silicon oxide added and the saturated surface dry water absorption rate of the modified recycled aggregate prepared therefrom are shown in Table 4.

[0089] Example 4-1

[0090] The content of a modified recycled aggregate is substantially the same as that of Example 1-1, except that the amount of plant-active silicon oxide added in step (3) is 0.5 parts.

[0091] Example 4-2

[0092] The content of a modified recycled aggregate is substantially the same as that of Example 1-1, except that: the recycled aggregate in step (1) is mortar particles with a particle size of 0.075-5 mm; and the amount of plant-active silicon oxide added in step (3) is 0.5 parts.

[0093] Example 4-3

[0094] The content of a modified recycled aggregate is substantially the same as that of Example 1-1, except that the amount of plant-active silicon oxide compound added in step (3) is 1 part.

[0095] Example 4-4

[0096] The content of a modified recycled aggregate is substantially the same as that of Example 1-1, except that: the recycled aggregate in step (1) is mortar particles with a particle size of 0.075-5 mm; and the amount of plant-active silicon oxide added in step (3) is 1 part.

[0097] Examples 4-5

[0098] The content of a modified recycled aggregate is substantially the same as that of Example 1-1, except that the recycled aggregate in step (1) is mortar particles with a particle size of 0.075-5 mm.

[0099] Examples 4-6

[0100] The content of a modified recycled aggregate is substantially the same as that of Example 1-1, except that the amount of plant-active silicon oxide compound added in step (3) is 2 parts.

[0101] Examples 4-7

[0102] The content of a modified recycled aggregate is substantially the same as that of Example 1-1, except that: the recycled aggregate in step (1) is mortar particles with a particle size of 0.075-5 mm; and the amount of plant-active silicon oxide added in step (3) is 2 parts.

[0103] Table 4 Effect of the addition amount of plant-active silicon oxides on the properties of modified recycled aggregates

[0104]

[0105] Comparison of Examples 4-1, 4-3, 1-1, and 4-6 reveals that, when the recycled aggregate is all crushed stone particles, the saturated surface dry water absorption of the modified recycled aggregate initially decreases and then increases with increasing amounts of plant-active silicon oxide compounds. This is because an appropriate amount of plant-active silicon oxide compounds effectively fills gaps in the aggregate, while excessive addition can squeeze cracks and pores, leading to secondary cracking. Furthermore, excess unreacted plant-active silicon oxide compounds adhere to the aggregate surface as fine powder, increasing its water absorption.

[0106] The inventors also conducted the above modification process using mortar particles as recycled aggregate. Comparing Examples 4-2, 4-4, 4-5, and 4-7, it can be seen that the saturated surface dry water absorption rate trends are similar to those of sand and gravel particles, but the optimal addition amount of the plant-active silica compound is different. This is because the crack size and dimensions of the fine and coarse aggregates in the mortar differ, resulting in different optimal addition amounts.

[0107] Therefore, the amount of plant-active silicon oxide compound added can be optimized according to the type of recycled aggregate to modify it.

[0108] Example 5

[0109] This embodiment provides a modified recycled aggregate, the preparation method of which includes the following steps:

[0110] (1) A 10% sodium hydroxide aqueous solution and a saturated calcium hydroxide aqueous solution were mixed at a volume ratio of 4:1 to obtain a calcium-containing alkaline solution. Then, 100 parts of recycled aggregate were added to 80 parts of the calcium-containing alkaline solution and soaked at 40°C for 6 hours to obtain a premix A.

[0111] The recycled aggregate is crushed stone particles with a particle size of 5-35 mm.

[0112] (2) After evenly mixing 5 parts of ethyl orthosilicate, 6 parts of tetrabutyl titanate, and 5 parts of ethanol, slowly drip into premix A and stir until the solution in the premix turns turbid to milky white, thereby obtaining premix B.

[0113] (3) Add 0.5 parts of powdered plant-active silicon oxide to premix B, disperse evenly by ultrasonication, and then let it stand and soak for 8 hours to obtain premix C;

[0114] The preparation method of the plant-active silicon oxide compound comprises: taking fresh grass plant leaves (ryegrass leaves, the plant-active silicon oxide compound having a pointed shape on the leaf surface) and performing ultrasonic dispersion treatment in water at a temperature of 80° C. for 6 hours, collecting the precipitate after filtration, and then drying the precipitate at 80° C. to obtain the plant-active silicon oxide compound.

[0115] (4) Premix C was added to a hydrothermal synthesis reactor and heated to 300°C for hydrothermal reaction for 24 h to obtain premix D.

[0116] (5) After premix D was filtered and the filtrate was collected, the filtrate was cooled to 60°C, and 0.01 parts of calcium carbonate mineralized bacterial capsules were made into a suspension and atomized and evenly dispersed on the surface of the filtrate. After natural drying, the modified recycled aggregate was obtained. The saturated surface dry water absorption of the modified recycled aggregate was measured to be 3.2%.

[0117] This embodiment also provides a modified recycled aggregate concrete, wherein the raw materials for preparing each cubic meter of the modified recycled aggregate concrete include: 290kg P.O42.5 cement, 100kg fly ash, 780kg sand, 1060kg modified recycled aggregate prepared in this embodiment, 175kg water, and 7.8kg PCE. The preparation method includes the following steps: first, cement, fly ash, sand, and modified recycled aggregate are added and mixed thoroughly, then water and a water reducer are added simultaneously, stirred until the slurry is uniform, and then formed to obtain the modified recycled aggregate concrete. The slump of the modified recycled aggregate concrete was measured to be 160mm, the 28d compressive strength was 37.8MPa, and the impermeability was 1.02×10 -6 mm / s.

[0118] Example 6

[0119] The content of a modified recycled aggregate is basically the same as that of Example 5, except that the recycled aggregate in step (1) is mortar particles with a particle size of 0.075-5 mm. The saturated surface dry water absorption rate of the modified recycled aggregate is 2.1%.

[0120] The content of a modified recycled aggregate concrete is basically the same as that of Example 5, except that the modified recycled aggregate in the raw materials is prepared in this example. The slump of the modified recycled aggregate concrete was measured to be 155 mm, the 28d compressive strength was 36.8 MPa, and the impermeability was 1.11×10 -6 mm / s.

[0121] Example 7

[0122] This embodiment provides a modified recycled aggregate, the preparation method of which includes the following steps:

[0123] (1) 30% sodium hydroxide aqueous solution and saturated calcium hydroxide aqueous solution were mixed in a volume ratio of 3:2 to obtain a calcium-containing alkaline solution. Then, 100 parts of recycled aggregate were added to 60 parts of the calcium-containing alkaline solution and soaked at 60°C for 5 hours to obtain premix A.

[0124] The recycled aggregate is crushed stone particles with a particle size of 5-35 mm.

[0125] (2) After mixing 8 parts of ethyl orthosilicate, 10 parts of tetrabutyl titanate, and 2 parts of ethanol, slowly drop them into premix A and stir until the solution in the premix turns turbid and milky white, thereby obtaining premix B.

[0126] (3) Add 2 parts of powdered plant-active silicon oxide to premix B, disperse evenly by ultrasonication, and then let it stand and soak for 6 hours to obtain premix C;

[0127] The preparation method of the plant-active silicon oxide compound comprises: taking fresh grass plant leaves (ice grass leaves, the leaf surface of which has active silicon oxide compounds in the shape of needles) and subjecting them to ultrasonic dispersion treatment in water at a temperature of 40°C for 8 hours, collecting the precipitate after filtration, and then drying the precipitate at 60°C to obtain the plant-active silicon oxide compound.

[0128] (4) Premix C was added to a hydrothermal synthesis reactor and heated to 320°C for a hydrothermal reaction for 36 h to obtain premix D.

[0129] (5) After premix D was filtered and the filtrate was collected, the filtrate was cooled to 60°C, and 0.1 parts of calcium carbonate mineralized bacterial capsules were made into a suspension and atomized and evenly dispersed on the surface of the filtrate. After natural drying, the modified recycled aggregate was obtained. The saturated surface dry water absorption of the modified recycled aggregate was measured to be 2.4%.

[0130] This embodiment also provides a modified recycled aggregate concrete, wherein the raw materials for preparing each cubic meter of the modified recycled aggregate concrete include: 290kg P.O42.5 cement, 100kg fly ash, 780kg sand, 1060kg modified recycled aggregate prepared in this embodiment, 175kg water, and 7.8kg PCE. The preparation method includes the following steps: first, adding cement, fly ash, sand, and modified recycled aggregate, and mixing them thoroughly, then adding water and a water reducer simultaneously, stirring until the slurry is uniform, and then forming to obtain the modified recycled aggregate concrete. The slump of the modified recycled aggregate concrete was measured to be 160mm, the 28d compressive strength was 37.2MPa, and the impermeability was 0.89×10 -6 mm / s.

[0131] Example 8

[0132] The content of a modified recycled aggregate is basically the same as that of Example 7, except that the recycled aggregate in step (1) is mortar particles with a particle size of 0.075-5 mm. The saturated surface dry water absorption rate of the modified recycled aggregate is 1.6%.

[0133] The content of a modified recycled aggregate concrete is basically the same as that of Example 7, except that the modified recycled aggregate in the raw materials is prepared in this example. The slump of the modified recycled aggregate concrete was measured to be 155 mm, the 28d compressive strength was 36.5 MPa, and the impermeability was 1.01×10 -6 mm / s.

[0134] Example 9

[0135] This embodiment provides a modified recycled aggregate, the preparation method of which includes the following steps:

[0136] (1) 20% sodium hydroxide aqueous solution and saturated calcium hydroxide aqueous solution were mixed in a volume ratio of 2:1 to obtain a calcium-containing alkaline solution, and then 100 parts of recycled aggregate were added to 50 parts of the calcium-containing alkaline solution and soaked at 80°C for 4 hours to obtain premix A;

[0137] The recycled aggregate is crushed stone particles with a particle size of 5-35 mm.

[0138] (2) After uniformly mixing 6 parts of ethyl orthosilicate, 8 parts of tetrabutyl titanate, and 4 parts of ethanol, slowly drip into premix A and stir until the solution in the premix turns turbid to milky white, thereby obtaining premix B.

[0139] (3) Add 1 part of powdered plant-active silicon oxide compound to premix B, disperse evenly by ultrasonication, and then let it stand and soak for 7 hours to obtain premix C;

[0140] The preparation method of the plant-active silicon oxide compound comprises: taking fresh grass plant leaves (leaves of Elymus dahliae, the surface of which has plant-active silicon oxide compounds in various forms, such as serrated rods and hair fibers), subjecting the leaves to ultrasonic dispersion treatment for 8 hours in water at a temperature of 30°C, collecting the precipitate after filtration, and then drying the precipitate at 50°C to obtain the plant-active silicon oxide compound.

[0141] (4) Add premix C into a hydrothermal synthesis reactor and heat to 360°C for 48 h to obtain premix D.

[0142] (5) After premix D was filtered and the filtrate was collected, the filtrate was cooled to 60°C, and 0.05 parts of calcium carbonate mineralized bacterial capsules were made into a suspension and atomized and evenly dispersed on the surface of the filtrate. After natural drying, the modified recycled aggregate was obtained. The saturated surface dry water absorption of the modified recycled aggregate was measured to be 1.1%.

[0143] This embodiment also provides a modified recycled aggregate concrete, wherein the raw materials for preparing each cubic meter of the modified recycled aggregate concrete include: 290kg P.O42.5 cement, 100kg fly ash, 780kg sand, 1060kg modified recycled aggregate prepared in this embodiment, 175kg water, and 7.8kg PCE. The preparation method includes the following steps: first, cement, fly ash, sand, and modified recycled aggregate are added and mixed thoroughly, then water and a water reducer are added simultaneously, stirred until the slurry is uniform, and then formed to obtain the modified recycled aggregate concrete. The slump of the modified recycled aggregate concrete was measured to be 160mm, the 28d compressive strength was 39.8MPa, and the impermeability was 0.88×10 -6 mm / s.

[0144] Example 10

[0145] The content of a modified recycled aggregate is basically the same as that of Example 9, except that the recycled aggregate in step (1) is mortar particles with a particle size of 0.075-5 mm. The saturated surface dry water absorption rate of the modified recycled aggregate is determined to be 0.8%.

[0146] The content of a modified recycled aggregate concrete is basically the same as that of Example 9, except that the modified recycled aggregate in the raw materials is prepared in this example. The slump of the modified recycled aggregate concrete was measured to be 160 mm, the 28d compressive strength was 39.3 MPa, and the impermeability was 0.92×10 -6 mm / s.

[0147] Example 11

[0148] The contents of a modified recycled aggregate were substantially the same as those of Example 1-1, except that, in the preparation method of the plant-active silicon oxide compound in step (3), the water temperature for ultrasonic dispersion treatment was 25°C, and the drying temperature was 30°C. The saturated surface dry water absorption of the modified recycled aggregate was determined to be 2.2%.

[0149] The content of a modified recycled aggregate concrete is basically the same as that of Example 1-1, except that the modified recycled aggregate in the raw materials is prepared in this example. The slump of the modified recycled aggregate concrete was measured to be 160 mm, the 28d compressive strength was 38.1 MPa, and the impermeability was 1.23×10 -6 mm / s.

[0150] Example 12

[0151] The content of a modified recycled aggregate is substantially the same as that of Example 11, except that the recycled aggregate in step (1) is mortar particles with a particle size of 0.075-5 mm. The saturated surface dry water absorption of the modified recycled aggregate is determined to be 2.1%.

[0152] The modified recycled aggregate concrete has the same contents as Example 11, except that the modified recycled aggregate in the raw materials is prepared in this example. The slump of the modified recycled aggregate concrete was 155 mm, the 28d compressive strength was 36.5 MPa, and the impermeability was 1.12×10 -6 mm / s.

[0153] Comparative Example 1

[0154] The content of a recycled aggregate concrete is basically the same as that of Example 1-1, except that the modified recycled aggregate is replaced by unmodified recycled aggregate in the raw materials, and the unmodified recycled aggregate is crushed stone particles with a particle size of 5-35 mm.

[0155] The saturated surface dry water absorption of the unmodified recycled aggregate was 8.4%; the slump of the modified recycled aggregate concrete was 110 mm, the 28-day compressive strength was 32.4 MPa, and the impermeability was 1.92×10 -6 mm / s.

[0156] Comparative Example 2

[0157] The content of a recycled aggregate concrete is basically the same as that of Example 1-1, except that the modified recycled aggregate is replaced by unmodified recycled aggregate in the raw materials, and the unmodified recycled aggregate is mortar particles with a particle size of 0.075-5 mm.

[0158] The saturated surface dry water absorption of the unmodified recycled aggregate was 12.8%; the slump of the modified recycled aggregate concrete was 90 mm, the 28-day compressive strength was 25.7 MPa, and the impermeability was 2.87×10 -6 mm / s.

[0159] In summary, the present invention effectively overcomes the deficiencies in the prior art and has a high industrial application value. The above embodiments serve to illustrate the substantial content of the present invention, but are not intended to limit the scope of protection of the present invention. Those skilled in the art will appreciate that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of protection of the technical solutions of the present invention.

Claims

1. A method for preparing modified recycled aggregate, characterized in that: The steps include: (1) Adding recycled aggregate to a calcium-containing alkaline solution and soaking it at 40-80°C to obtain premix A; (2) Ethyl orthosilicate, tetrabutyl titanate, and ethanol are mixed and added to premix A and stirred to obtain premix B; (3) Adding the plant-active silicon oxide compound to premix B, dispersing the mixture evenly and then allowing it to stand to obtain premix C; adding premix C to a reactor and heating it to 300-400°C for hydrothermal reaction to obtain premix D; The preparation method of the plant active silicon oxide compound is as follows: fresh grass plant leaves are placed in water for dispersion treatment, the precipitate is collected after filtering, and the precipitate is dried to obtain the compound; (4) After filtering the premix D, the filtrate is collected, and after the filtrate is cooled, the mineralizing bacteria are evenly dispersed on the surface of the filtrate to obtain the modified recycled aggregate; the calcium-containing alkaline solution is a mixture of sodium hydroxide aqueous solution and calcium hydroxide aqueous solution.

2. The preparation method according to claim 1, characterized in that In the preparation method of the plant-active silicon oxide compound, the water temperature during the dispersion treatment process is 25-80°C; and the drying temperature is 30-80°C.

3. The preparation method according to claim 2, characterized in that The mass ratio of the plant active silicon oxide compound to the recycled aggregate is (0.5-2):

100.

4. The preparation method according to claim 3, characterized in that The mass ratio of the recycled aggregate to tetraethyl orthosilicate, tetrabutyl titanate and ethanol is 100:(5-8):(6-10):(2-5).

5. The preparation method according to claim 4, characterized in that The mass fraction of the sodium hydroxide aqueous solution is 10%-52%; the calcium hydroxide aqueous solution is a saturated calcium hydroxide aqueous solution; and the volume ratio of the sodium hydroxide aqueous solution to the calcium hydroxide aqueous solution is (3-4): (1-2).

6. The preparation method according to claim 5, characterized in that The mineralizing bacteria are calcium carbonate mineralizing bacteria; the mass ratio of the mineralizing bacteria to the recycled aggregate is (0.01-0.1):

100.

7. The preparation method according to claim 6, characterized in that The recycled aggregate is crushed stone particles with a particle size of 5-35 mm, mortar particles with a particle size of 0.075-5 mm, or brick particles with a particle size of 5-35 mm.

8. The modified recycled aggregate prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the modified recycled aggregate according to claim 8 in recycled aggregate concrete.

10. A modified recycled aggregate concrete, characterized in that: The modified recycled aggregate concrete is prepared from cement, fly ash, sand, modified recycled aggregate, water and admixtures; the modified recycled aggregate is the modified recycled aggregate according to claim 8; The mass ratio of the cement, fly ash, sand, modified recycled aggregate and water is (28-35): (8-15): (70-85): (95-115): (14-20); the amount of the admixture is 1%-3% of the mass of the cement.

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