Pretreatment reinforced recycled aggregate concrete and preparation method thereof

Abstract

The invention relates to pretreatment reinforced recycled aggregate concrete and a preparation method thereof. The pretreatment reinforced recycled aggregate concrete comprises the following raw materials: 320-360 parts of cement; 20 to 40 parts of fly ash; 80 to 120 parts of mineral powder; 585 to 670 parts of machine-made sand; 1050 to 1200 parts of recycled coarse aggregate; 156 to 172 parts of water; and 11-12.3 parts of an additive. After the recycled coarse aggregate is pretreated, the performance of the concrete prepared from the recycled coarse aggregate is remarkably improved compared with that of the concrete prepared from the recycled coarse aggregate before pretreatment, and the synergistic effect of multiple pretreatment modes has an obvious improvement effect on the water absorption rate, the crushing index and the apparent density of the raw coarse aggregate; the pretreated recycled coarse aggregate provides a gain condition for internal hydration of the recycled concrete, and meanwhile, the problem that the surface of the recycled coarse aggregate is rough is solved, so that the workability of the concrete is enhanced, and the strength of the concrete is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete, and particularly relates to a pre-treated and strengthened recycled aggregate concrete and a preparation method thereof. Background Art

[0002] With the continuous advancement of urban modernization, building materials have entered an era of high promotion and use. Projects such as housing construction, roads, and bridges have been greatly expanded, and at the same time, there is also a huge demand for the use of concrete. However, with the improvement of urbanization construction, the requirements for building materials have also increased. Concrete materials are gradually developing towards multi-functional directions such as intelligent and high-performance, resulting in the elimination and renewal of many waste concrete buildings. At the same time, there are also phenomena such as non-compliant construction and unfinished projects during urban construction, leading to an increasing amount of urban construction waste. In order to relieve the pressure of urban construction waste and reduce the exploitation of natural stones, etc., recycled concrete will be one of the main development directions of future building materials.

[0003] Recycled concrete refers to new concrete prepared by crushing, cleaning, and grading waste concrete blocks, mixing them in a certain proportion and gradation, partially or completely replacing natural aggregates such as sand and gravel (mainly coarse aggregates), and then adding cement, water, etc. Recycled aggregates are produced by crushing construction waste, and they have low density, high water absorption and porosity, and low mechanical properties, which have an adverse impact on the quality of recycled concrete, resulting in low strength, high strain, and poor durability. Using the aggregate carbonization technology can make the remaining slurry in the recycled aggregate react to generate CaCO3, thereby increasing the aggregate density and reducing the water absorption.

[0004] Through the recycled aggregate hydrothermal carbonization modification technology, the performance of recycled aggregates is improved, and the application range of recycled aggregates is expanded. This not only solves the stacking pressure of urban solid construction waste, but also reduces the use of natural minerals, which is conducive to promoting green ecological development and realizing circular economy. Summary of the Invention

[0005] The purpose of the present invention is to provide a pre-treated and strengthened recycled aggregate concrete and a preparation method thereof to solve the problems raised in the above background art.

[0006] To achieve the above purpose, the present invention provides the following technical solutions: The present invention provides a pre-treated and strengthened recycled aggregate concrete and a preparation method thereof.

[0007] In the first aspect, the present invention provides a pre-treated and strengthened recycled aggregate concrete and a preparation method thereof, adopting the following technical solutions:

[0008] A pre-treated and strengthened recycled aggregate concrete is made from raw materials including the following parts by weight:

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

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

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

[0012] S1. Acid pickling: First, put the recycled coarse aggregate into an ice acetic acid solution with a concentration of 12% - 16% and soak for 12 h. Take it out, wash it with water, then put it into a phosphoric acid solution with a concentration of 5% - 8% and soak for 12 h. Take it out and wash 3 - 4 times, then dry to obtain acidified recycled coarse aggregate.

[0013] S2. Aggregate strengthening: Put the acidified recycled coarse aggregate obtained in S1 into the aggregate strengthening slurry and soak for 6 h, then put it into a microwave drying instrument and dry for 2 h to obtain strengthened recycled coarse aggregate.

[0014] S3. Pore sealing: Put the strengthened recycled coarse aggregate obtained in S2 into the surface modification solution to fully wet it, air dry it and then store it sealed to obtain surface - modified recycled coarse aggregate.

[0015] S4. Hydrothermal carbonation: Carry out hydrothermal carbonation treatment on the surface - modified recycled coarse aggregate obtained in S3. The conditions for hydrothermal carbonation pretreatment are: pressure of 0.5 - 0.8 MPa, carbon dioxide concentration of 45% - 60%, temperature of 50 - 60 °C, relative humidity of 50% - 70%, and carbonation time of 24 h to obtain pretreated recycled coarse aggregate.

[0016] Preferably, the strengthening slurry includes the following components by mass: 66 - 72 parts of γ - C2S slag powder, 35 - 40 parts of fatty alcohol polyoxyethylene ether, 1 - 3 parts of methyl cellulose, 15 - 30 parts of calcium carbonate whiskers, 5 - 9 parts of silicone, and 79 - 85 parts of water.

[0017] Preferably, the surface modification solution includes the following components by mass: 23.7 - 66.3 parts of C 18 H 37 -POSS (octadecylcage silsesquioxane), 57.4 - 65.4 parts of organic solvent.

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

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

[0020] Preferably, the application provides a preparation method of the pretreated reinforced recycled aggregate concrete as described in any one of the above, comprising the following steps:

[0021] SS1. First, sequentially pour the pretreated recycled coarse aggregate, cement, fly ash, mineral powder, and fine aggregate into a horizontal mixer, and pre-mix and stir for 30 s.

[0022] SS2. Mix the admixture and add it to 70% of the mixing water. Continuously start the mixer, add the mixture to the pre-mixed materials, stir for 3 min, add the remaining 30% of the mixing water, and stir for 2 min to obtain high-strength pretreated reinforced recycled aggregate concrete.

[0023] Through the above technical solutions, the present application has the following beneficial effects:

[0024] (1). The present application uses a strengthening paste prepared from γ-C2S, calcium carbonate whiskers, and carbon dioxide-philic fatty alcohol polyoxyethylene ether to soak the recycled coarse aggregate; on the one hand, γ-C2S generates C-S-H gel and calcium hydroxide during the hydration reaction, effectively filling the micro-cracks and pores on the surface of the aggregate and reducing the water absorption rate. At the same time, the calcium carbonate whiskers physically intercalate into the pores of the aggregate to form a three-dimensional network structure on the surface of the aggregate, improving the crushing resistance of the aggregate through the crack deflection and bridging mechanisms, and cooperating with the hydration products to form a dense protective layer. On the other hand, as a surfactant, fatty alcohol polyoxyethylene ether can improve the wettability of the paste to the aggregate, promote the uniform coating of the hydration products on the surface of the aggregate, and reduce the micro-cracks in the ITZ. And methyl cellulose delays the evaporation of water through thickening and water retention effects to ensure the full progress of the hydration reaction.

[0025] (2). The present application uses a surface modification solution prepared from C 18 H 37 -POSS (octadecylcage silsesquioxane) and any one of the organic solvents of 1,4-dioxane, acetone, and 2-MeTHF to soak the recycled coarse aggregate. On the one hand, after the POSS molecules are dispersed in the organic solvent, they can penetrate into the micro-cracks and pores on the surface of the recycled aggregate. When the solvent volatilizes, the POSS molecules will form a nano-scale hydrophobic barrier to reduce the water absorption rate of the recycled aggregate. At the same time, the long-chain alkyl group (C 18 H 37)(3) It will form a low surface energy monolayer (contact angle > 110°) on the surface of recycled aggregate, endowing the recycled aggregate with superhydrophobicity and further reducing the intrusion of moisture. On the other hand, the silicon-oxygen skeleton (Si-O) of POSS molecules forms Si-O-Si covalent bonds with the hydroxyl groups (-OH) on the aggregate surface, enhancing the interfacial bonding force between the aggregate and the cement paste. Moreover, the rigid cage-like structure of POSS molecules can not only effectively disperse stress to avoid stress concentration and inhibit the generation of microcracks, but also form a ceramic-like protective layer on the surface of recycled coarse aggregate, further improving the crushing index of the aggregate.

[0026] (3) The physical properties of recycled coarse aggregate can be effectively improved by hydrothermal carbonation treatment, and the water absorption rate and crushing value can be reduced. Carbon dioxide in the external environment enters the pores through the capillary pores of the hardened cement paste and reacts with the hydrated calcium hydroxide and hydrated calcium silicate gel dissolved in the pore liquid to generate calcium carbonate, thereby filling the pores of the aggregate, and then reducing the water absorption rate and crushing value of the recycled aggregate.

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

[0028] By adopting the above technical solutions and selecting the above carbonation treatment conditions, the mechanical properties of recycled coarse aggregate are further improved; the natural carbonation 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 carbonation environment can increase the diffusion rate of carbon dioxide. It should be noted that the pressure cannot be too high or too low. Too high may cause damage to the structure of recycled coarse aggregate, and too low will not have an obvious carbonation gain; the carbon dioxide concentration, environmental temperature, and relative humidity cannot be too high or too low either, otherwise it will affect the formation of carbonation products and cause instability of the products, etc.; because the carbonation reaction repairs the micro-pores of recycled aggregate, and pre-wetting and pressurization make water enter the interior of the aggregate, promoting the further reaction of unhydrated cement particles in the old mortar on the surface layer of recycled aggregate under high temperature conditions, achieving the effect of strengthening the matrix. Selecting the above control parameter range can ensure the stability of carbonation products while increasing the carbon sequestration rate and carbon sequestration amount of recycled coarse aggregate, and then improving the mechanical properties of recycled coarse aggregate. At the same time, hydrothermal carbonation can play a synergistic role with the previous pretreatment process. After carbonation, the hydration products of γ-C2S mineral powder will be converted into calcium carbonate and silica gel. The physical intercalation and filling of calcium carbonate whiskers achieve the "anchoring effect", and the C 18 H 37 -POSS sealing layer allows selective permeation of CO2. The hydrophobic long-chain alkyl groups block the intrusion of water molecules, but allow the diffusion of CO2 (non-polar molecules). The rigid skeleton of POSS can also protect the carbonation products from being damaged. Specific Embodiments

[0029] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0030] The present invention provides a pre-treated strengthened recycled aggregate concrete and its preparation method:

[0031] Preparation Example of Pre-treated Recycled Coarse Aggregate

[0032] Preparation Example 1

[0033] The pre-treatment steps of the pre-treated recycled aggregate are as follows:

[0034] S1. Acid pickling: First, put the recycled coarse aggregate into an ice acetic acid solution with a concentration of 12% and soak for 12 hours. After taking it out, wash it with water, then put it into a phosphoric acid solution with a concentration of 8% and soak for 12 hours. After taking it out, wash it 3 times with water and dry it to obtain acidified recycled coarse aggregate.

[0035] S2. Aggregate strengthening: Put the acidified recycled coarse aggregate obtained in S1 into the aggregate strengthening slurry and soak for 6 hours, then put it into a microwave drying instrument and dry for 2 hours to obtain strengthened recycled coarse aggregate.

[0036] S3. Pore sealing: Put the strengthened recycled coarse aggregate obtained in S2 into the surface modification solution to fully wet it, air dry it and then store it sealed to obtain surface-modified recycled coarse aggregate.

[0037] S4. Hydrothermal carbonation: Perform hydrothermal carbonation treatment on the surface-modified recycled coarse aggregate obtained in S3. The conditions for hydrothermal carbonation pretreatment are: pressure of 0.8 MPa, carbon dioxide concentration of 45%, temperature of 60 °C, relative humidity of 50%, and carbonation time of 24 hours to obtain pre-treated recycled coarse aggregate.

[0038] The described strengthening slurry includes the following components by mass: 72 parts of γ-C2S mineral powder, 35 parts of fatty alcohol polyoxyethylene ether, 3 parts of methyl cellulose, 15 parts of calcium carbonate whiskers, 9 parts of silicone, and 79 parts of water.

[0039] The described surface modification solution includes the following components by mass: 66.3 parts of C 18 H 37 -POSS (octadecylcage silsesquioxane), 57.4 parts of organic solvent.

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

[0041] Preparation Example 2

[0042] S1. Pickling: The recycled coarse aggregate is first put into a 16% glacial acetic acid solution and soaked for 12 h, taken out and washed with water, then put into a 5% phosphoric acid solution and soaked for 12 h, taken out and washed 4 times with water, and dried to obtain acidified recycled coarse aggregate.

[0043] S2. Aggregate strengthening: The acidified recycled coarse aggregate obtained in S1 is put into an aggregate strengthening slurry and soaked for 6 h, then put into a microwave drying instrument and dried for 2 h to obtain strengthened recycled coarse aggregate.

[0044] S3. Pore sealing: The strengthened recycled coarse aggregate obtained in S2 is put into a surface modification solution to be fully wetted, air-dried and then stored in a sealed manner to obtain surface-modified recycled coarse aggregate.

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

[0046] The said strengthening slurry, by mass, comprises the following components: 66 parts of γ-C2S mineral powder, 40 parts of fatty alcohol polyoxyethylene ether, 1 part of methyl cellulose, 30 parts of calcium carbonate whiskers, 5 parts of silicone, and 85 parts of water.

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

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

[0049] Preparation Example 3

[0050] S1. Pickling: The recycled coarse aggregate is first put into a 14% glacial acetic acid solution and soaked for 12 h, taken out and washed with water, then put into a 6% phosphoric acid solution and soaked for 12 h, taken out and washed 4 times with water, and dried to obtain acidified recycled coarse aggregate.

[0051] S2. Aggregate strengthening: The acidified recycled coarse aggregate obtained in S1 is put into an aggregate strengthening slurry and soaked for 6 h, then put into a microwave drying instrument and dried for 2 h to obtain strengthened recycled coarse aggregate.

[0052] S3. Pore sealing: The strengthened recycled coarse aggregate obtained in S2 is put into a surface modification solution to be fully wetted, air-dried and then stored in a sealed manner to obtain surface-modified recycled coarse aggregate.

[0053] S4. Hydrothermal carbonization: The surface-modified recycled coarse aggregate obtained in S3 is subjected to hydrothermal carbonization treatment. The conditions for hydrothermal carbonization pretreatment are as follows: the pressure is 0.6 MPa, the carbon dioxide concentration is 55%, the temperature is 55 °C, the relative humidity is 60%, and the carbonization time is 24 h to obtain pretreated recycled coarse aggregate.

[0054] The reinforcing paste described above includes the following components by mass: 68 parts of γ-C2S mineral powder, 38 parts of fatty alcohol polyoxyethylene ether, 2 parts of methyl cellulose, 15 - 30 parts of calcium carbonate whiskers, 7 parts of silicone, and 83 parts of water.

[0055] The surface-modifying solution described above includes the following components by mass: 56.3 parts of C 18 H 37 -POSS (octadecylcage silsesquioxane), 62.4 parts of organic solvent.

[0056] In the surface-modifying solution described above, the organic solvent is 2-MeTHF.

[0057] Preparation Example 4

[0058] S1. Pickling: The recycled coarse aggregate is first put into a 12% glacial acetic acid solution and soaked for 12 h, taken out and washed with water, then put into a 7% phosphoric acid solution and soaked for 12 h, taken out and washed 3 times, and dried to obtain acidified recycled coarse aggregate.

[0059] S2. Aggregate strengthening: The acidified recycled coarse aggregate obtained in S1 is put into the aggregate strengthening paste and soaked for 6 h, then put into a microwave drying instrument and dried for 2 h to obtain strengthened recycled coarse aggregate.

[0060] S3. Pore sealing: The strengthened recycled coarse aggregate obtained in S2 is put into the surface-modifying solution to be fully wetted, air-dried and then sealed for storage to obtain surface-modified recycled coarse aggregate.

[0061] S4. Hydrothermal carbonization: The surface-modified recycled coarse aggregate obtained in S3 is subjected to hydrothermal carbonization treatment. The conditions for hydrothermal carbonization pretreatment are as follows: the pressure is 0.7 MPa, the carbon dioxide concentration is 45%, the temperature is 55 °C, the relative humidity is 50%, and the carbonization time is 24 h to obtain pretreated recycled coarse aggregate.

[0062] The reinforcing paste described above includes the following components by mass: 69 parts of γ-C2S mineral powder, 35 parts of fatty alcohol polyoxyethylene ether, 2 parts of methyl cellulose, 15 parts of calcium carbonate whiskers, 8 parts of silicone, and 79 parts of water.

[0063] The surface-modifying solution described above includes the following components by mass: 48.9 parts of C 18 H 37-POSS (octadecylcage silsesquioxane), 57.4 parts of organic solvent.

[0064] In the surface modification solution described above, 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 strengthening slurry used for strengthening the aggregate 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 strengthening the aggregate in the 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 is not carried out.

[0073] Preparation Example 9

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

[0075] Preparation Example 10

[0076] The difference from Preparation Example 3 is that the S4 hydrothermal carbonization pretreatment is not carried out.

[0077] Table 1: The properties of the pretreated recycled coarse aggregate are as follows

[0078] Group Clay lump 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 indexes of Preparation Example 3 with those of Preparation Examples 5, 6, and 8, the following conclusions can be drawn: (1) γ-C2S generates C-S-H gel and calcium hydroxide during the hydration reaction, effectively filling the microcracks and pores on the aggregate surface, reducing the water absorption rate. At the same time, γ-C2S can combine with CO2 to undergo carbonation reaction, further promoting the hydration reaction rate. When replacing γ-C2S mineral powder with ordinary mineral powder, the insufficient activity of ordinary mineral powder results in insufficient pore filling. Meanwhile, due to the reduction of hydration products, the role of calcium carbonate whiskers entering the aggregate pores through physical intercalation weakens, and the bridging network formed on the aggregate surface is not tight enough, resulting in a decrease in the filling density of the micro-pores of recycled coarse aggregate, leading to an increase in water absorption rate and crushing index, and the deterioration of the performance of recycled coarse aggregate. (2) Calcium carbonate whiskers mainly form a three-dimensional network structure through physical intercalation and filling. The absence thereof leads to the ineffective filling of the micro-pores on the surface of recycled coarse aggregate, and the crack deflection and bridging mechanism fail. Removing the calcium carbonate whisker component in the strengthening paste causes the water absorption rate of recycled coarse aggregate to rise from 0.8% to 2.8%, the crushing value to rise from 8.6% to 14.7%, and the apparent density to decrease by 130 kg / m³, further proving the reduction of structural compactness. (3) Canceling the pretreatment step S2 of aggregate strengthening results in the lack of the synergistic filling and bridging effects of γ-C2S and calcium carbonate whiskers on the internal pores of recycled coarse aggregate, and further weakens the ability to strengthen the interfacial transition zone and limit the development of microcracks. As a surfactant, fatty alcohol polyoxyethylene ether can improve the wetting degree of the paste to the aggregate, and methyl cellulose can effectively optimize the hydration process. The absence of both will lead to incomplete pore repair and the complete loss of strengthening effect. The pretreated recycled coarse aggregates prepared in Preparation Examples 5, 6, and 8 do not meet the performance index requirements for Class I recycled coarse aggregates in "Recycled Coarse Aggregates for Concrete" GB / T 25177-2010.

[0080] Comparing the performance indexes of Preparation Example 3 with those of Preparation Example 9, the following conclusions can be drawn: Canceling the pretreatment step S3 of pore sealing. On the one hand, the nano-scale hydrophobic barrier formed by POSS molecules is lost, the micro-pores on the surface of recycled coarse aggregate are not sealed by the nano-barrier, the water penetration channels are retained, and the water absorption rate of recycled aggregate rises back to 2.8%. At the same time, the long-chain alkyl (C 18 H 37) forms a monomolecular layer on the surface of the recycled aggregate, the recycled aggregate loses its hydrophobicity, and the water absorption performance of the aggregate further deteriorates. On the other hand, the hydroxyl group (-OH) on the aggregate surface cannot form a Si-O-Si covalent bond with the silicon-oxygen skeleton (Si-O) of the POSS molecule, the interfacial bonding strength is reduced, the stress concentration appears on the microcracks on the surface of the recycled coarse aggregate, and the crushing index is further reduced. By comparing the various performance indicators of Preparation Example 3 and Preparation Example 10, the following conclusions can be drawn: by canceling the pretreatment step S4 wet heat carbonization, the hydration products of γ-C2S mineral powder, calcium hydroxide and CSH gel, cannot react with CO2 to form calcium carbonate and silica gel, the pores on the surface of the recycled coarse aggregate cannot be filled, and there is a lack of calcium carbonate as a skeleton support, resulting in reduced mechanical properties. At the same time, the wet heat environment can promote the secondary hydration of unhydrated cement particles in the old mortar. The lack of this environmental factor leads to insufficient matrix strengthening and further deterioration of the crushing index. Furthermore, the lack of the wet heat carbonization step destroys the synergy of the process. The C prepared in step S3 18 H 37 -The POSS sealing layer allows CO2 to selectively permeate. Although the hydrophobic long-chain alkyl blocks the invasion of water molecules, it allows CO2 (non-polar molecules) to diffuse. The rigid skeleton of POSS can also protect the carbonization product 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 internal curing type recycled concrete and a preparation method thereof, 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, 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, keep the mixer running, add the mixed liquid to the premixed material, 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;

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

[0087] Example 2

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

[0089] Example 3

[0090] An internally cured recycled concrete and its preparation method. Different from Example 1, in Step 1, the material quantities are 1050 parts of recycled coarse aggregate, 360 parts of cement, 20 parts of fly ash, 80 parts of slag powder, and 670 parts of fine aggregate. In Step 2, the admixture is 12.3 parts and the water is 172 parts.

[0091] Example 4

[0092] An internally cured recycled concrete and its preparation method. Different from Example 1, in Step 1, the recycled coarse aggregate is obtained from Preparation Example 5.

[0093] Example 5

[0094] An internally cured recycled concrete and its preparation method. Different from Example 1, in Step 1, the recycled coarse aggregate is obtained from Preparation Example 6.

[0095] Example 6

[0096] An internally cured recycled concrete and its preparation method. Different from Example 1, in Step 1, the recycled coarse aggregate is obtained from Preparation Example 7.

[0097] Example 7

[0098] An internally cured recycled concrete and its preparation method. Different from Example 1, in Step 1, the recycled coarse aggregate is obtained from Preparation Example 8.

[0099] Example 8

[0100] An internally cured recycled concrete and its preparation method. Different from Example 1, in Step 1, the recycled coarse aggregate is obtained from Preparation Example 9.

[0101] Example 9

[0102] An internally cured recycled concrete and its preparation method. Different from Example 1, in Step 1, the recycled coarse aggregate is obtained from Preparation Example 10.

[0103] Table 2: The concrete performance indexes of the control group and Examples 1 - 6 are as follows:

[0104] Inversion cylinder time / s Slump / mm Spread / mm 2h slump / mm 2h spread / 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] Weigh according to the proportions of each component of cement, slag powder, fly ash, fine aggregate, natural aggregate, and admixture in the control group and Examples 1 - 9. The recycled aggregate concrete is formed into specimens with dimensions of 150 mm × 150 mm × 150 mm, with 3 specimens in each group. Test the 7-day and 28-day compressive strengths of each group of specimens according to the regulations in the "Standard Test Method for Mechanical Properties of Ordinary Concrete" GB / T 50081 - 2002.

[0106] As can be seen from the above table, the performance of recycled concrete prepared from recycled coarse aggregate before pretreatment is poor. Due to the porous and rough surface of the recycled coarse aggregate, the workability of its concrete has a large time-dependent loss, and the lack of density in the structure leads to a decrease in strength. It can be seen from Examples 1-3 that after the recycled coarse aggregate is pretreated, the performance of the concrete prepared from the recycled coarse aggregate is significantly improved compared with that before pretreatment. The synergistic effect of multiple pretreatment methods has an obvious improvement effect on the water absorption rate, crushing index and apparent density of the raw coarse aggregate. The pretreated recycled coarse aggregate provides beneficial conditions for the internal hydration of recycled concrete, and at the same time improves the problem of the rough surface of the recycled coarse aggregate. Therefore, the workability of the concrete is enhanced and its strength is improved. Examples 4-9 show that the absence of one or more steps and the change of the treatment plan in the pretreatment process of recycled aggregate will seriously affect the performance of the prepared concrete. The specific performance impact mechanism is described in detail in the previous text and will not be elaborated here.

[0107] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used 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 perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A pre-treatment enhanced recycled aggregate concrete, characterized in that, It includes the following raw materials: 320 - 360 parts of cement, 20 - 40 parts of fly ash, 80 - 120 parts of slag powder, 585 - 670 parts of fine aggregate, 1050 - 1200 parts of pretreated recycled coarse aggregate, 156 - 172 parts of water, and 11 - 12.3 parts of admixture.

2. The pretreated enhanced recycled aggregate concrete according to claim 1, wherein The particle size of the pretreated recycled coarse aggregate is 5 - 25 mm, with continuous grading and a mud lump content of 0.4%.

3. The pre-treatment enhanced recycled aggregate concrete according to any one of claims 1-2, wherein It includes the following pretreatment steps: S1. Pickling: First, put the recycled coarse aggregate into an ice acetic acid solution with a concentration of 12% - 16% and soak for 12 h. After taking it out, wash it with water, then put it into a phosphoric acid solution with a concentration of 5% - 8% and soak for 12 h. After taking it out, wash it 3 - 4 times and dry it to obtain acidified recycled coarse aggregate. S2. Aggregate strengthening: Put the acidified recycled coarse aggregate obtained in S1 into the aggregate strengthening slurry and soak for 6 h, then put it into a microwave drying instrument and dry for 2 h to obtain strengthened recycled coarse aggregate. S3. Pore sealing: Put the strengthened recycled coarse aggregate obtained in S2 into the surface modification solution to fully wet it, air-dry it and then store it sealed to obtain surface-modified recycled coarse aggregate. S4. Hydrothermal carbonation: Carry out hydrothermal carbonation treatment on the surface-modified recycled coarse aggregate obtained in S3. The conditions for hydrothermal carbonation pretreatment are: pressure of 0.5 - 0.8 MPa, carbon dioxide concentration of 45% - 60%, temperature of 50 - 60 °C, relative humidity of 50% - 70%, and carbonation time of 24 h to obtain pretreated recycled coarse aggregate.

4. The pre-treated enhanced recycled aggregate concrete according to claim 3, wherein The strengthening slurry includes the following components by mass: 66 - 72 parts of γ-C2S slag powder, 35 - 40 parts of fatty alcohol polyoxyethylene ether, 1 - 3 parts of methyl cellulose, 15 - 30 parts of calcium carbonate whisker, 5 - 9 parts of silicone, and 79 - 85 parts of water.

5. The pre-treated and strengthened recycled aggregate concrete according to claim 3, characterized in that, The surface modification solution comprises the following components by mass: 23.7 - 66.3 parts of C 18 H 37 -POSS, and 57.4 - 65.4 parts of organic solvent.

6. The pre-treated enhanced recycled aggregate concrete according to claim 5, wherein The organic solvent of the surface modification solution is any one of 1,4-dioxane, acetone, and 2-MeTHF.

7. The preparation method of a pre-treated and strengthened recycled aggregate concrete according to claim 1, wherein: The fine aggregate is manufactured sand with a fineness modulus of 2.7 - 2.

9.

8. The preparation method of a pre-treated and enhanced recycled aggregate concrete according to claim 1, characterized in that, It is prepared by the following steps: SS1. First, pour the pretreated recycled coarse aggregate, cement, fly ash, slag powder, and fine aggregate into a horizontal mixer in sequence and premix and stir for 30 s. SS2. Mix the admixture and add it to 70% of the mixing water. Continuously start the mixer, add the mixed liquid to the premixed materials, stir for 3 min, add the remaining 30% of the mixing water, and stir for 2 min to obtain high-strength pretreated strengthened recycled aggregate concrete.