Pretreated reinforced recycled aggregate concrete and method for preparing the same

Abstract

This invention relates to a pretreated reinforced recycled aggregate concrete and its preparation method, comprising the following raw materials: 320-360 parts cement; 20-40 parts fly ash; 80-120 parts mineral powder; 585-670 parts manufactured sand; 1050-1200 parts recycled coarse aggregate; 156-172 parts water; and 11-12.3 parts admixtures. After pretreatment, the concrete prepared from the recycled coarse aggregate exhibits significantly improved performance compared to the untreated recycled coarse aggregate. The synergistic effect of multiple pretreatment methods significantly improves the water absorption, crushing index, and apparent density of the raw coarse aggregate. Pretreatment of the recycled coarse aggregate provides enhanced conditions for internal hydration in the recycled concrete and simultaneously improves the surface roughness of the recycled coarse aggregate, thus enhancing the workability and increasing the strength of the concrete.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, and in particular to a pretreated reinforced recycled aggregate concrete and its preparation method. Background Technology

[0002] With the continuous advancement of urban modernization, building materials have entered an era of widespread use. Construction of houses, roads, bridges, and other projects has expanded significantly, leading to a surge in demand for concrete. However, as urbanization progresses, the requirements for building materials also increase. Concrete materials are gradually developing towards intelligent, high-performance, and multi-functional directions, resulting in the replacement of many old concrete structures. Simultaneously, non-compliant construction and unfinished projects exist during urban development, leading to a growing amount of urban construction waste. To alleviate the pressure of urban construction waste and reduce the mining of natural stone and other materials, recycled concrete will be one of the main development directions for future building materials.

[0003] Recycled concrete refers to new concrete made by crushing, washing, and grading waste concrete blocks, mixing them with aggregates in a certain proportion, and partially or completely replacing natural aggregates such as sand and gravel (mainly coarse aggregates), then adding cement and water. Recycled aggregates, obtained from crushed construction waste, have low density, high water absorption and porosity, and poor mechanical properties, which negatively impact the quality of recycled concrete, resulting in low strength, high strain, and poor durability. Using aggregate carbonation technology allows the remaining paste in the recycled aggregate to react and generate CaCO3, thereby increasing the aggregate density and reducing water absorption.

[0004] By using wet-heat carbonization modification technology for recycled aggregates, the various properties of recycled aggregates can be improved and their application range can be expanded. This not only solves the pressure of urban solid waste disposal but also reduces the use of natural minerals, which is conducive to promoting green ecological development and realizing a circular economy. Summary of the Invention

[0005] The purpose of this invention is to provide a pretreated reinforced recycled aggregate concrete and its preparation method to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The present invention provides a pretreated reinforced recycled aggregate concrete and a method for preparing the same.

[0007] In a first aspect, the present invention provides a pretreated reinforced recycled aggregate concrete and a method for preparing the same, employing the following technical solution:

[0008] A pretreated reinforced recycled aggregate concrete is made from raw materials comprising the following parts by weight:

[0009] Cement 320-360 parts; fly ash 20-40 parts; mineral powder 80-120 parts; fine aggregate 585-670 parts; pretreated recycled coarse aggregate 1050-1200 parts; water 156-172 parts; admixtures 11-12.3 parts;

[0010] Preferably, the cement is P.O42.5 ordinary Portland cement; the pretreated recycled coarse aggregate has a particle size of 5-25mm, continuous gradation, mud content of 0.4%, water absorption of 4.6%, crushing index of 16.4%, and apparent density of 2440kg / m³; the fly ash is Grade I fly ash; and the mineral powder is S105 grade mineral powder.

[0011] Preferably, the pretreated recycled coarse aggregate includes the following pretreatment steps:

[0012] S1. Pickling: The recycled coarse aggregate is first soaked in a 12%-16% glacial acetic acid solution for 12 hours, then washed with water, and then soaked in a 5%-8% phosphoric acid solution for 12 hours. After being removed, it is washed with water 3-4 times and dried to obtain acidified recycled coarse aggregate.

[0013] S2. Aggregate strengthening: The acidified recycled coarse aggregate obtained in S1 is immersed in aggregate strengthening slurry for 6 hours and then dried in a microwave drying instrument for 2 hours to obtain strengthened recycled coarse aggregate.

[0014] S3. Pore sealing: The reinforced recycled coarse aggregate obtained in S2 is placed in the surface modification solution to be fully wetted, dried, and then sealed and stored to obtain surface-modified recycled coarse aggregate.

[0015] S4. Wet heat carbonization: The surface-modified recycled coarse aggregate obtained in S3 is subjected to wet heat carbonization treatment. The conditions for wet heat carbonization pretreatment are: pressure of 0.5-0.8MPa, carbon dioxide concentration of 45-60%, temperature of 50-60℃, relative humidity of 50-70%, and carbonization time of 24h to obtain pretreated recycled coarse aggregate.

[0016] Preferably, the reinforced slurry comprises, by weight, the following components: 66-72 parts γ-C2S mineral powder, 35-40 parts fatty alcohol polyoxyethylene ether, 1-3 parts methylcellulose, 15-30 parts calcium carbonate whiskers, 5-9 parts organosilicon, and 79-85 parts water.

[0017] The preferred surface-modifying solution, by mass, comprises 23.7-66.3 parts C of the following components. 18 H 37 -POSS (octadecyl cage-like silsesquioxane), 57.4-65.4 parts of organic solvent.

[0018] Preferably, the organic solvent in the surface modification solution is any one of 1,4-dioxane, acetone, and 2-MeTHF.

[0019] Preferably, the additive is a polycarboxylate superplasticizer.

[0020] Preferably, the application provides a method for preparing pretreated reinforced recycled aggregate concrete as described in any of the preceding claims, comprising the following steps:

[0021] SS1. First, pour the pretreated recycled coarse aggregate, cement, fly ash, mineral powder and fine aggregate into the horizontal mixer in sequence, and dry mix for 30 seconds.

[0022] SS2. Add the admixture to 70% of the mixing water, keep the mixer running, add the mixture to the premixed materials, stir for 3 minutes, add the remaining 30% of the mixing water, stir for 2 minutes to obtain high-strength pretreated reinforced recycled aggregate concrete.

[0023] Through the above technical solution, this application has the following beneficial effects:

[0024] (1) This application uses reinforced slurry-soaked recycled coarse aggregate prepared from γ-C2S, calcium carbonate whiskers, and carbon dioxide-loving fatty alcohol polyoxyethylene ether. On the one hand, γ-C2S generates CSH gel and calcium hydroxide in the hydration reaction, which effectively fills the microcracks and pores on the aggregate surface and reduces the water absorption rate. At the same time, calcium carbonate whiskers enter the aggregate pores through physical intercalation, forming a three-dimensional network structure on the aggregate surface. This improves the aggregate's crush resistance through crack deflection and bridging mechanisms, and forms a dense protective layer in conjunction with the hydration products. On the other hand, fatty alcohol polyoxyethylene ether, as a surfactant, can improve the wettability of the slurry to the aggregate, promote the uniform coating of the aggregate surface by the hydration products, and reduce ITZ microcracks. Methylcellulose delays water evaporation through thickening and water retention, ensuring that the hydration reaction proceeds fully.

[0025] (2). This application adopts the method of C 18 H 37 Regenerated coarse aggregate is impregnated with a surface-modified solution prepared by reacting 1,4-dioxane, acetone, or 2-MeTHF with octadecyl silsesquioxane (POSS). On one hand, after being dispersed in the organic solvent, POSS molecules can penetrate into the microcracks and pores on the surface of the recycled aggregate. When the solvent evaporates, the POSS molecules form a nanoscale hydrophobic barrier, reducing the water absorption rate of the recycled aggregate. Simultaneously, long-chain alkyl groups (C... 18 H 37The POSS molecule forms a low surface energy monolayer (contact angle > 110°) on the surface of recycled aggregate, giving it superhydrophobicity and further reducing water intrusion. On the other hand, the silicon-oxygen framework (Si-O) of the POSS molecule forms Si-O-Si covalent bonds with the hydroxyl groups (-OH) on the aggregate surface, enhancing the interfacial bonding between the aggregate and the cement paste. Furthermore, the rigid cage-like structure of the POSS molecule not only effectively disperses stress to avoid stress concentration and inhibit the formation of microcracks, but also forms a ceramic-like protective layer on the surface of the recycled coarse aggregate, further improving the aggregate's crushing performance.

[0026] (3) The wet heat carbonization treatment of recycled coarse aggregate can effectively improve the physical properties of the aggregate and reduce the water absorption rate and crushing value. Carbon dioxide in the outside world enters the pores through the capillary of hardened cement paste, and reacts with the cement hydration products calcium hydroxide and hydrated calcium silicate gel dissolved in the pore liquid to form calcium carbonate, which fills the pores of the aggregate, thereby reducing the water absorption rate and crushing value of the recycled aggregate.

[0027] Furthermore, the carbonization conditions for recycled coarse aggregate are: pressure of 0.5-0.8 MPa, carbon dioxide concentration of 50-60%, temperature of 50-60℃, relative humidity of 50-70%, and carbonization time of 24h.

[0028] By adopting the above technical solution and selecting the above carbonization treatment conditions, the mechanical properties of recycled coarse aggregate are further improved. The natural carbonization rate of recycled aggregate is slow (carbon dioxide diffusion coefficient is 10⁻⁸ cm³ / s). Applying a pressure of 0.5-0.8 MPa to the carbonization environment increases the diffusion rate of carbon dioxide. It is important to note that the pressure should not be too high or too low; excessive pressure may damage the structure of the recycled coarse aggregate, while insufficient pressure will not significantly enhance its carbonization gain. Similarly, the carbon dioxide concentration, ambient temperature, and relative humidity should not be too high or too low, otherwise it will affect the formation of carbonization products and cause product instability. Because the carbonization reaction repairs the micropores of the recycled aggregate, and the pre-wetting and pressurization allow moisture to enter the aggregate interior, under high temperature conditions, it promotes further reaction of unhydrated cement particles in the old mortar on the surface of the recycled aggregate, thereby strengthening the matrix. By selecting the above control parameter range, the carbon fixation rate and amount of recycled coarse aggregate can be improved while ensuring the stability of the carbonization products, thus improving the mechanical properties of the recycled coarse aggregate. Simultaneously, the wet-heat carbonization process synergistically complements the previous pretreatment process. After carbonization, the hydration products of γ-C2S mineral powder will be converted into calcium carbonate and silica gel. The physical intercalation of calcium carbonate whiskers and the filling of calcium carbonate achieve an "anchoring effect," while the C2S prepared in step S3... 18 H 37 - The POSS sealing layer allows selective CO2 permeation. Although the hydrophobic long-chain alkyl groups block the intrusion of water molecules, they allow CO2 (a non-polar molecule) to diffuse. The rigid framework of POSS can also protect carbonization products from being destroyed. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] This invention provides a pretreated reinforced recycled aggregate concrete and its preparation method:

[0031] Example of preparation of pretreated recycled coarse aggregate

[0032] Preparation Example 1

[0033] The pretreatment steps for the pretreated recycled aggregate are as follows:

[0034] S1. Pickling: The recycled coarse aggregate is first soaked in a 12% glacial acetic acid solution for 12 hours, then washed with water, and then soaked in an 8% phosphoric acid solution for 12 hours. After being removed, it is washed with water three times and dried to obtain acidified recycled coarse aggregate.

[0035] S2. Aggregate strengthening: The acidified recycled coarse aggregate obtained in S1 is immersed in aggregate strengthening slurry for 6 hours and then dried in a microwave drying instrument for 2 hours to obtain strengthened recycled coarse aggregate.

[0036] S3. Pore sealing: The reinforced recycled coarse aggregate obtained in S2 is placed in the surface modification solution to be fully wetted, dried, and then sealed and stored to obtain surface-modified recycled coarse aggregate.

[0037] S4. Wet heat carbonization: The surface-modified recycled coarse aggregate obtained in S3 is subjected to wet heat carbonization treatment. The conditions for wet heat carbonization pretreatment are: pressure of 0.8 MPa, carbon dioxide concentration of 45%, temperature of 60℃, relative humidity of 50%, and carbonization time of 24 h to obtain pretreated recycled coarse aggregate.

[0038] The reinforced slurry comprises the following components by weight: 72 parts γ-C2S mineral powder, 35 parts fatty alcohol polyoxyethylene ether, 3 parts methylcellulose, 15 parts calcium carbonate whiskers, 9 parts organosilicon, and 79 parts water.

[0039] The surface modification solution, by mass, comprises the following components: 66.3 parts C 18 H 37 -POSS (octadecyl cage-like silsesquioxane), 57.4 parts organic solvent.

[0040] The organic solvent is 1,4-dioxane.

[0041] Preparation Example 2

[0042] S1. Pickling: The recycled coarse aggregate is first soaked in a 16% glacial acetic acid solution for 12 hours, then washed with water, and then soaked in a 5% phosphoric acid solution for 12 hours. After being removed, it is washed with water 4 times and dried to obtain acidified recycled coarse aggregate.

[0043] S2. Aggregate strengthening: The acidified recycled coarse aggregate obtained in S1 is immersed in aggregate strengthening slurry for 6 hours and then dried in a microwave drying instrument for 2 hours to obtain strengthened recycled coarse aggregate.

[0044] S3. Pore sealing: The reinforced recycled coarse aggregate obtained in S2 is placed in the surface modification solution to be fully wetted, dried, and then sealed and stored to obtain surface-modified recycled coarse aggregate.

[0045] S4. Wet heat carbonization: The surface-modified recycled coarse aggregate obtained in S3 is subjected to wet heat carbonization treatment. The conditions for wet heat carbonization pretreatment are: pressure of 0.5 MPa, carbon dioxide concentration of 60%, temperature of 50℃, relative humidity of 70%, and carbonization time of 24 h to obtain pretreated recycled coarse aggregate.

[0046] The reinforced slurry comprises the following components by weight: 66 parts γ-C2S mineral powder, 40 parts fatty alcohol polyoxyethylene ether, 1 part methylcellulose, 30 parts calcium carbonate whiskers, 5 parts organosilicon, and 85 parts water.

[0047] The surface modification solution, by mass, comprises the following components: 23.7 parts C 18 H 37 -POSS (octadecyl cage-like silsesquioxane), 65.4 parts organic solvent.

[0048] In the surface modification solution, the organic solvent is acetone.

[0049] Preparation Example 3

[0050] S1. Pickling: The recycled coarse aggregate is first soaked in a 14% glacial acetic acid solution for 12 hours, then washed with water, and then soaked in a 6% phosphoric acid solution for 12 hours. After being removed, it is washed with water 4 times and dried to obtain acidified recycled coarse aggregate.

[0051] S2. Aggregate strengthening: The acidified recycled coarse aggregate obtained in S1 is immersed in aggregate strengthening slurry for 6 hours and then dried in a microwave drying instrument for 2 hours to obtain strengthened recycled coarse aggregate.

[0052] S3. Pore sealing: The reinforced recycled coarse aggregate obtained in S2 is placed in the surface modification solution to be fully wetted, dried, and then sealed and stored to obtain surface-modified recycled coarse aggregate.

[0053] S4. Wet heat carbonization: The surface-modified recycled coarse aggregate obtained in S3 is subjected to wet heat carbonization treatment. The conditions for wet heat carbonization pretreatment are: pressure of 0.6 MPa, carbon dioxide concentration of 55%, temperature of 55℃, relative humidity of 60%, and carbonization time of 24 h to obtain pretreated recycled coarse aggregate.

[0054] The reinforced slurry comprises the following components by weight: 68 parts γ-C2S mineral powder, 38 parts fatty alcohol polyoxyethylene ether, 2 parts methylcellulose, 15-30 parts calcium carbonate whiskers, 7 parts organosilicon, and 83 parts water.

[0055] The surface modification solution, by mass, comprises the following components: 56.3 parts C 18 H 37 -POSS (octadecyl cage-like silsesquioxane), 62.4 parts of organic solvent.

[0056] In the surface modification solution, the organic solvent is 2-MeTHF.

[0057] Preparation Example 4

[0058] S1. Pickling: The recycled coarse aggregate is first soaked in a 12% glacial acetic acid solution for 12 hours, then washed with water, and then soaked in a 7% phosphoric acid solution for 12 hours. After being removed, it is washed with water three times and dried to obtain acidified recycled coarse aggregate.

[0059] S2. Aggregate strengthening: The acidified recycled coarse aggregate obtained in S1 is immersed in aggregate strengthening slurry for 6 hours and then dried in a microwave drying instrument for 2 hours to obtain strengthened recycled coarse aggregate.

[0060] S3. Pore sealing: The reinforced recycled coarse aggregate obtained in S2 is placed in the surface modification solution to be fully wetted, dried, and then sealed and stored to obtain surface-modified recycled coarse aggregate.

[0061] S4. Wet heat carbonization: The surface-modified recycled coarse aggregate obtained in S3 is subjected to wet heat carbonization treatment. The conditions for wet heat carbonization pretreatment are: pressure of 0.7 MPa, carbon dioxide concentration of 45%, temperature of 55℃, relative humidity of 50%, and carbonization time of 24 h to obtain pretreated recycled coarse aggregate.

[0062] The reinforced slurry comprises the following components by weight: 69 parts γ-C2S mineral powder, 35 parts fatty alcohol polyoxyethylene ether, 2 parts methylcellulose, 15 parts calcium carbonate whiskers, 8 parts organosilicon, and 79 parts water.

[0063] The surface modification solution, by mass, comprises the following components: 48.9 parts C 18 H 37-POSS (octadecyl cage-like silsesquioxane), 57.4 parts organic solvent.

[0064] In the surface modification solution, the organic solvent is 1,4-dioxane.

[0065] Preparation Example 5

[0066] The difference from Preparation Example 3 is that the γ-C2S mineral powder in the aggregate strengthening slurry used in the pretreatment step S2 is replaced with ordinary mineral powder.

[0067] Preparation Example 6

[0068] The difference from Preparation Example 3 is that the calcium carbonate whiskers in the strengthening slurry used for aggregate strengthening in pretreatment step S2 are removed.

[0069] Preparation Example 7

[0070] The difference from Preparation Example 3 is that the surface modification solution used for pore sealing in the pretreatment step S3 is replaced with silicone oil.

[0071] Preparation Example 8

[0072] The difference from Preparation Example 3 is that the S2 aggregate strengthening pretreatment was not performed.

[0073] Preparation Example 9

[0074] The difference from Preparation Example 3 is that the S3 pore sealing pretreatment was not performed.

[0075] Preparation Example 10

[0076] The difference from Preparation Example 3 is that the S4 wet heat carbonization pretreatment was not performed.

[0077] Table 1: Properties of Pretreated Recycled Coarse Aggregate are shown in the following table.

[0078] Group Clay content / % Water absorption rate / % Crushing value / % Apparent density / kg / m³ Ordinary recycled coarse aggregate 0.40 4.6 16.4 2440 Preparation Example 1 0.12 1.2 11.6 2480 Preparation Example 2 0.05 1.1 10.5 2520 Preparation Example 3 0.1 0.8 8.6 2550 Preparation Example 4 0.1 1.0 10.7 2500 Preparation Example 5 0.1 1.8 13.9 2450 Preparation Example 6 0.1 2.8 14.7 2420 Preparation Example 7 0.1 2.6 11.5 2470 Preparation Example 8 0.1 3.7 15.9 2400 Preparation Example 9 0.1 2.8 12.3 2460 Preparation Example 10 0.1 2.0 14.5 2430

[0079] Comparing the performance indicators of Preparation Example 3 and Preparation Examples 5, 6, and 8, the following conclusions can be drawn: (1) γ-C2S generates CSH gel and calcium hydroxide in the hydration reaction, which effectively fills the microcracks and pores on the aggregate surface and reduces the water absorption rate. At the same time, γ-C2S can combine with CO2 to undergo carbonation reaction, which further promotes the hydration reaction rate. When ordinary mineral powder is used to replace γ-C2S mineral powder, the activity of ordinary mineral powder is insufficient, resulting in insufficient pore filling. At the same time, due to the reduction of hydration products, the effect of calcium carbonate whiskers entering the aggregate pores through physical insertion is weakened, and the bridging network formed on the aggregate surface is not dense enough. The micropore filling density of the recycled coarse aggregate is reduced, resulting in increased water absorption rate and crushing index, and deterioration of the performance of the recycled coarse aggregate. (2) Calcium carbonate whiskers mainly form a three-dimensional network structure through physical insertion and filling. Their absence leads to the ineffective filling of micropores on the surface of the recycled coarse aggregate, and the crack deflection and bridging mechanism fails. Removing the calcium carbonate whisker component from the reinforced slurry caused the water absorption rate of the recycled coarse aggregate to increase from 0.8% to 2.8%, the crushing value to increase from 8.6% to 14.7%, and the apparent density to decrease by 130 kg / m³, further demonstrating the reduced structural compactness. (3) The removal of the pretreatment step S2 aggregate reinforcement resulted in the loss of the synergistic filling and bridging effect of γ-C2S and calcium carbonate whiskers on the internal pores of the recycled coarse aggregate, and the ability to strengthen the interface transition zone and restrict the development of microcracks was further weakened. Fatty alcohol polyoxyethylene ether, as a surfactant, can improve the wettability of the slurry on the aggregate, and methylcellulose can effectively optimize the hydration process. The absence of both will lead to incomplete pore repair and complete loss of the strengthening effect. The pretreated recycled coarse aggregates prepared in Examples 5, 6, and 8 do not meet the performance index requirements for Class I recycled coarse aggregates in GB / T 25177-2010 "Recycled Coarse Aggregate for Concrete".

[0080] Comparing the performance indicators of Preparation Example 3 and Preparation Example 9, the following conclusions can be drawn: Eliminating the pretreatment step S3 (pore sealing) results in the loss of the nanoscale hydrophobic barrier formed by POSS molecules. The micropores on the surface of the recycled coarse aggregate are not sealed by the nanoscale barrier, water permeation channels are retained, and the water absorption rate of the recycled aggregate rebounds to 2.8%. Simultaneously, the lack of long-chain alkyl groups (C...) 18 H 37The monolayer formed on the surface of recycled aggregate causes it to lose its hydrophobicity, further deteriorating its water absorption capacity. On the other hand, the hydroxyl groups (-OH) on the aggregate surface cannot form Si-O-Si covalent bonds with the silicon-oxygen framework (Si-O) of the POSS molecules, reducing interfacial bonding strength. Stress concentration occurs on the microcracks on the surface of the recycled coarse aggregate, further reducing the crushing index. Comparing the performance indicators of Preparation Example 3 and Preparation Example 10, the following conclusions can be drawn: By eliminating the pretreatment step S4 (wet heat carbonation), the hydration products of γ-C2S mineral powder, calcium hydroxide and CSH gel, cannot react with CO2 to generate calcium carbonate and silica gel. The pores on the surface of the recycled coarse aggregate are not filled, and the lack of calcium carbonate as a framework support leads to reduced mechanical properties. Simultaneously, the wet heat environment, which should promote the secondary hydration of unhydrated cement particles in the old mortar, is missing, resulting in insufficient matrix strengthening and further deterioration of the crushing index. Furthermore, the absence of the wet heat carbonation step disrupts the process synergy, and the C2S prepared in step S3... 18 H 37 - The POSS sealing layer allows selective CO2 permeation. Although the hydrophobic long-chain alkyl group blocks the intrusion of water molecules, it allows CO2 (a non-polar molecule) to diffuse. The rigid framework of POSS can also protect the carbonization products from being destroyed. In Preparation Example 10, the sealing layer only plays a static hydrophobic role and does not cooperate with dynamic carbonization.

[0081] Example

[0082] Example 1

[0083] An internally cured recycled concrete and its preparation method, the preparation steps are as follows:

[0084] Step 1: First, pour 1100 parts of recycled coarse aggregate, 340 parts of cement, 30 parts of fly ash, 100 parts of mineral powder, and 620 parts of fine aggregate into a horizontal mixer in sequence, and pre-dry mix for 30 seconds.

[0085] Step 2: Prepare 11 parts of admixture and 162 parts of water. Mix the admixture and add it to 70% of the mixing water. Continuously start the mixer and add the mixture to the premixed materials. Stir for 3 minutes, then add the remaining 30% of the mixing water and stir for 2 minutes to obtain high-strength pretreated reinforced recycled aggregate concrete.

[0086] In this embodiment, the recycled coarse aggregate was prepared in Preparation Example 3.

[0087] Example 2

[0088] An internally cured recycled concrete and its preparation method differ from Example 1 in that the material proportions in step one are 1200 parts recycled coarse aggregate, 320 parts cement, 40 parts fly ash, 120 parts mineral powder, and 585 parts fine aggregate, and in step two, 10.2 parts admixture and 155 parts water.

[0089] Example 3

[0090] An internally cured recycled concrete and its preparation method differ from Example 1 in that the material proportions in step one are 1050 parts recycled coarse aggregate, 360 parts cement, 20 parts fly ash, 80 parts mineral powder, and 670 parts fine aggregate, and in step two, 12.3 parts admixture and 172 parts water.

[0091] Example 4

[0092] An internally cured recycled concrete and its preparation method are disclosed. The difference between this and Example 1 is that the recycled coarse aggregate in step one is prepared in Example 5.

[0093] Example 5

[0094] An internally cured recycled concrete and its preparation method are disclosed. The difference between this and Example 1 is that the recycled coarse aggregate in step one is prepared in Example 6.

[0095] Example 6

[0096] An internally cured recycled concrete and its preparation method are disclosed. The difference between this and Example 1 is that the recycled coarse aggregate in step one is prepared in Example 7.

[0097] Example 7

[0098] An internally cured recycled concrete and its preparation method are disclosed. The difference between this and Example 1 is that the recycled coarse aggregate in step one is prepared in Example 8.

[0099] Example 8

[0100] An internally cured recycled concrete and its preparation method are disclosed. The difference between this and Example 1 is that the recycled coarse aggregate in step one is prepared in Example 9.

[0101] Example 9

[0102] An internally cured recycled concrete and its preparation method are disclosed. The difference between this and Example 1 is that the recycled coarse aggregate in step one is prepared in Example 10.

[0103] Table 2: Concrete performance indicators of the control group and Examples 1-6 are shown in the following table:

[0104] Rewinding time / s Slump / mm Expansion / mm 2h slump / mm 2h expansion / mm 7d strength / MPa 28d strength / MPa Control group 1 9.8 200 530 170 460 45.3 58.7 Example 1 3.8 230 650 200 610 54.8 68.9 Example 2 4.3 220 625 190 600 52.3 65.9 Example 3 4.6 220 620 190 595 53.6 67.1 Example 4 6.5 215 620 190 595 48.6 61.7 Example 5 7.4 210 615 185 590 47.8 60.5 Example 6 8.9 200 590 180 555 53.3 66.9 Example 7 9.8 195 520 170 485 46.5 59.7 Example 8 10.2 195 515 165 480 48.1 61.4 Example 9 6.8 210 615 190 590 47.8 60.9

[0105] According to the proportions of cement, mineral powder, fly ash, fine aggregate, natural aggregate, and admixtures in the control group and Examples 1-9, recycled aggregate concrete was molded into 150mm×150mm×150mm specimens, with 3 specimens in each group. The 7-day and 28-day compressive strength of each group of specimens was tested according to the provisions of GB / T50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete".

[0106] As shown in the table above, the recycled concrete prepared from recycled coarse aggregate before pretreatment has poor performance. Furthermore, due to the porosity and rough surface of the recycled coarse aggregate, its workability decreases significantly over time, and its non-dense structure leads to a decline in strength. Examples 1-3 demonstrate that the performance of concrete prepared from recycled coarse aggregate after pretreatment is significantly improved compared to that prepared from raw coarse aggregate. The synergistic effect of multiple pretreatment methods significantly improves the water absorption, crushing index, and apparent density of the raw coarse aggregate. Pretreatment of the recycled coarse aggregate provides enhanced conditions for internal hydration in the recycled concrete and also improves the surface roughness, thus enhancing the workability and increasing the strength of the concrete. Examples 4-9, however, show that the absence of one or more steps in the recycled aggregate pretreatment process, as well as modifications to the treatment scheme, can severely affect the performance of the prepared concrete. The specific performance impact mechanism is detailed above and will not be elaborated further here.

[0107] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A pretreated reinforced recycled aggregate concrete, characterized in that, The raw materials include: 320-360 parts cement, 20-40 parts fly ash, 80-120 parts mineral powder, 585-670 parts fine aggregate, 1050-1200 parts pretreated recycled coarse aggregate, 156-172 parts water, and 11-12.3 parts admixtures; the pretreated recycled coarse aggregate has a particle size of 5-25 mm, continuous gradation, and a mud lump content of 0.4%. The following preprocessing steps are included: S1. Pickling: The recycled coarse aggregate is first soaked in a 12%-16% glacial acetic acid solution for 12 hours, then washed with water, and then soaked in a 5%-8% phosphoric acid solution for 12 hours. After being removed, it is washed with water 3-4 times and dried to obtain acidified recycled coarse aggregate. S2. Aggregate strengthening: The acidified recycled coarse aggregate obtained in S1 is soaked in aggregate strengthening slurry for 6 hours and then dried in a microwave drying instrument for 2 hours to obtain strengthened recycled coarse aggregate. S3. Pore sealing: The reinforced recycled coarse aggregate obtained in S2 is placed in the surface modification solution to be fully wetted, dried, and then sealed and stored to obtain surface-modified recycled coarse aggregate. S4. Wet heat carbonization: The surface-modified recycled coarse aggregate obtained in S3 is subjected to wet heat carbonization treatment. The pretreatment conditions for wet heat carbonization are: pressure 0.5-0.8 MPa, carbon dioxide concentration 45-60%, temperature 50-60℃, relative humidity 50-70%, and carbonization time 24h, to obtain pretreated recycled coarse aggregate. The reinforcing slurry comprises the following components by weight: 66-72 parts γ-C2S mineral powder, 35-40 parts fatty alcohol polyoxyethylene ether, 1-3 parts methylcellulose, 15-30 parts calcium carbonate whiskers, 5-9 parts organosilicon, and 79-85 parts water. The surface modification solution comprises the following components by weight: 23.7-66.3 parts C 18 H 37 -POSS, 57.4-65.4 parts of organic solvent; the organic solvent of the surface modification solution is any one of 1,4-dioxane, acetone, and 2-MeTHF.

2. The method for preparing pretreated reinforced recycled aggregate concrete according to claim 1, characterized in that: The fine aggregate is manufactured sand with a fineness modulus of 2.7-2.

9.

3. The method for preparing pretreated reinforced recycled aggregate concrete according to claim 1, characterized in that, Prepared using the following steps: SS1. First, pour the pretreated recycled coarse aggregate, cement, fly ash, mineral powder and fine aggregate into the horizontal mixer in sequence, and dry mix for 30 seconds. SS2. Add the admixture to 70% of the mixing water, keep the mixer running, add the mixture to the premixed materials, stir for 3 minutes, add the remaining 30% of the mixing water, stir for 2 minutes to obtain high-strength pretreated reinforced recycled aggregate concrete.