Method for preparing slurry-coated recycled aggregate by utilizing carbon mineralization

Abstract

A method for preparing slurry-coated recycled aggregate by utilizing carbon mineralization comprises the following steps: carrying out carbon mineralization treatment on collected recycled concrete aggregate until carbon is completely mineralized to obtain primarily mineralized recycled aggregate, soaking the primarily mineralized recycled aggregate by utilizing a saturated calcium hydroxide solution, and drying to obtain the slurry-coated recycled aggregate. And then wrapping the soaked recycled aggregate with newly mixed cement paste with a low water-binder ratio, then adjusting the water content of the slurry-wrapped recycled aggregate through drying treatment, and finally mineralizing the slurry-wrapped recycled aggregate again by using CO2 to obtain the high-quality carbon mineralized slurry-wrapped recycled aggregate. According to the method, rapid and high-degree carbon mineralization of the recycled aggregate is achieved, and then the recycled aggregate which is compact in structure, low in porosity, low in water absorption rate, low in crushing index and excellent in mechanical property and permeation resistance is obtained; meanwhile, construction waste is effectively recycled and utilized, and the raw material cost, energy consumption and carbon emission in the concrete preparation process are reduced.

Description

Technical Field

[0001] The invention relates to a method for preparing recycled aggregate of building materials, in particular to a method for preparing cladding recycled aggregate. Background Art

[0002] In recent years, with the implementation of my country's sustainable development and environmental protection strategy, the development and application of waste concrete has received more and more attention. Recycling recycled aggregates from waste concrete is considered to play an important role in reducing the amount of natural aggregates and reducing environmental pollution.

[0003] Recycled aggregate is produced by processing and crushing discarded concrete components. Recycled aggregate usually consists of virgin aggregate, attached mortar, and the interface transition zone between the attached mortar and virgin aggregate. This leads to significant differences between recycled aggregate and natural aggregate, with higher porosity and more microcracks in existing recycled aggregate, resulting in poorer performance of existing recycled aggregate.

[0004] In recent years, in order to improve the performance of recycled aggregates, a large number of researchers at home and abroad have used carbon mineralization methods to treat recycled aggregates. This treatment method can make the alkaline hydration products in the attachment mortar react with CO2 to generate calcium carbonate and silica with volcanic ash activity. Calcium carbonate and calcium silicate hydrate generated by the volcanic ash reaction can be filled into the attachment mortar and the interface transition zone, making the microstructure of the recycled aggregate more compact and improving its performance.

[0005] However, the effect of the current carbon mineralization treatment technology on improving the performance of recycled aggregate decreases as the amount of mortar attached to the surface decreases. The reason is that the content of carbon mineralizable components, especially the content of hydration products with high mineralization activity such as calcium hydroxide, is low. This leads to poor improvement in the microstructure density, mechanical properties, and durability of recycled aggregates with less attached mortar after treatment with existing carbon mineralization technology. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the above-mentioned defects existing in the prior art and provide a method for rapidly and highly mineralizing recycled aggregates with a small amount of mortar attached to the surface, thereby obtaining recycled aggregates with dense microstructure.

[0007] The technical solution adopted by the present invention to solve the technical problem is a method for preparing high-quality cladding recycled aggregate by using carbon mineralization, comprising the following steps:

[0008] (1) Initial carbon mineralization treatment of recycled aggregate: The recycled aggregate is placed in a carbon mineralization device and treated with carbon mineralization using CO2 until the carbon mineralization is initially and completely completed, thereby obtaining recycled aggregate with initial carbon mineralization;

[0009] (2) Soaking in a calcium hydroxide solution: Soaking the regenerated aggregate with preliminary carbon mineralization obtained in step (1) in a calcium hydroxide solution;

[0010] (3) coating with fresh cement slurry: fully mixing the recycled aggregate soaked in step (2) with the fresh cement slurry to obtain coated recycled aggregate;

[0011] (4) Moisture content adjustment: drying the clad recycled aggregate obtained in step (3) to adjust the moisture content of the clad recycled aggregate;

[0012] (5) Re-carbon mineralization treatment: The clad recycled aggregate treated in step (4) is subjected to carbon mineralization treatment again with CO2 to obtain high-quality clad recycled aggregate.

[0013] Preferably, in step (1), the recycled aggregate is non-alkaline pebbles and / or crushed stones with a particle size of ≤30 mm prepared from construction waste.

[0014] Preferably, in steps (1) and (5), during the carbon mineralization treatment, the relative humidity of the mineralization treatment site is 30%-80%.

[0015] Preferably, in steps (1) and (5), during the carbon mineralization treatment, the CO2 volume concentration in the mineralization treatment site is ≥5% (preferably 50%, more preferably 70%, further preferably 90%, and further ≥98%).

[0016] Preferably, the method for preparing high-quality clad recycled aggregate by carbon mineralization is characterized in that the carbon mineralization time in the carbon mineralization treatment in steps (1) and (5) is ≥ 1 hour.

[0017] Preferably, in step (2), the mass concentration of the calcium hydroxide solution is ≥10%.

[0018] Preferably, the soaking time in the calcium hydroxide aqueous solution in step (2) is ≥2 hours, preferably ≥4 hours.

[0019] Preferably, the fresh cement slurry described in step (3) is prepared by mixing silicate cement and water, and the mixing time is ≥ 60 seconds.

[0020] Preferably, in step (3), the silicate cement in the fresh cement slurry can be partially replaced by an auxiliary cementitious material, and the auxiliary cementitious material can be one or more of the auxiliary cementitious materials rich in silica such as fly ash, silica fume, slag, etc.; the total replacement rate of the auxiliary cementitious material is ≤30%.

[0021] Preferably, the water-to-cement ratio of the fresh cement slurry described in step (3) is ≥0.25.

[0022] Preferably, the method for preparing high-quality clad recycled aggregate by carbon mineralization is characterized in that the mixing time of the fresh cement slurry and the soaked recycled aggregate in step (3) is ≥ 60 seconds.

[0023] Preferably, in step (4), after the drying, the moisture content of the slurry-coated recycled aggregate drops to 10%-30%.

[0024] The principle of the present invention: Saturated calcium hydroxide solution as an external calcium source can enter the interior of the recycled aggregate by immersion, especially the interface transition zone between the aggregate and the attached mortar, thereby increasing the content of calcium hydroxide, a high-carbon mineralization active ingredient, in the recycled aggregate. On the other hand, wrapping the surface of the recycled aggregate with fresh cement slurry is equivalent to increasing the amount of cement slurry attached to the surface of the recycled aggregate. This method can also increase the calcium content in the recycled aggregate. Through the above two methods, the content of carbon-mineralizable substances in the recycled aggregate is significantly increased, and the activity is enhanced after mineralization, which in turn makes the mineralization degree and performance of the recycled aggregate after carbon mineralization treatment, including mechanical properties and microstructural density, significantly improved.

[0025] The present invention has the following advantages: 1) Compared with the recycled aggregate obtained by the existing ordinary carbon mineralization technology, the microstructure of the recycled aggregate prepared by the present invention is denser, especially the interface transition zone between the aggregate and the attached mortar is denser, the porosity of the recycled aggregate is low, the water absorption rate is low, the crushing index is low, and thus the mechanical properties and anti-penetration properties are better; 2) For more types of recycled aggregates, especially recycled aggregates with less surface attached mortar and larger aggregate size, the carbon mineralization efficiency is higher, and the quality of the recycled aggregate after carbon mineralization treatment is higher; 3) The whole process is green and environmentally friendly, and can reduce carbon emissions in the construction industry while recycling construction waste; 4) The main raw materials used in the whole processing process, including calcium hydroxide and cement clinker, are low in price, very common and easy to obtain. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with the examples. Obviously, the examples given below are part of the embodiments of the present invention. Based on the examples in the present invention, modifications and equivalent changes made by ordinary technicians in the field without departing from the idea of ​​the present invention all belong to the protection scope of the patent of the present invention.

[0027] The recycled aggregate raw materials used in each embodiment are aggregates with a particle size range of 9.5-19 mm recovered from waste concrete with a strength grade of C40, which are cleaned and dried in an oven at 105° C. for 1 day.

[0028] Example 1

[0029] The method of preparing high-quality cladding recycled aggregate by carbon mineralization in this embodiment comprises the following steps:

[0030] (1) The recycled aggregate raw materials are placed in a reactor for preliminary carbon mineralization treatment: potassium bromide is used to control the humidity in the reactor to 50%, and the CO2 volume concentration is 99%; the carbon mineralization time is 4 hours;

[0031] (2) soaking the regenerated aggregate preliminarily mineralized in step (1) in a calcium hydroxide solution for 24 hours; the calcium hydroxide solution is prepared by 495 g of water and 55 g of calcium hydroxide;

[0032] (3) Take the recycled aggregate soaked in calcium hydroxide solution and coat the surface of the recycled aggregate with fresh cement paste; the cement paste used for coating is prepared by mixing PI 42.5 cement with water, with a water-cement ratio of 0.30, and slowly stir for 100 seconds and then quickly stir for 100 seconds; the coating operation is as follows: pour the recycled aggregate into a mixing pot filled with fresh cement, stir it manually with a trowel for 120 seconds, and after the stirring is completed, take out the coated recycled aggregate with tweezers and place it on a tray;

[0033] (4) Allow the clad recycled aggregate placed on the tray to dry until its moisture content reaches 20%;

[0034] (5) After the clad recycled aggregate dried in step (4) reaches the target moisture content, it is placed in a reactor for carbon mineralization treatment again, and the humidity in the reactor is controlled to be 50% with a saturated lithium chloride solution, the CO2 volume concentration is 99%, and the mineralization time is 4 hours; thus, high-quality clad recycled aggregate is obtained.

[0035] Example 2

[0036] The method of preparing high-quality cladding recycled aggregate by carbon mineralization in this embodiment comprises the following steps:

[0037] (1) The recycled aggregate raw materials are placed in a reactor for preliminary carbon mineralization treatment: the humidity in the reactor is controlled to 0% with potassium bromide, the CO2 volume concentration is 99%; the carbon mineralization time is 4 hours;

[0038] (2) soaking the regenerated aggregate preliminarily mineralized in step (1) in a calcium hydroxide solution for 48 hours; the calcium hydroxide solution is prepared by mixing 495 g of water with 110 g of calcium hydroxide;

[0039] (3) Take the recycled aggregate soaked in step (1) and coat the surface of the recycled aggregate with fresh cement paste. The cement paste used for coating is made by mixing PI 42.5 cement with water, with a water-cement ratio of 0.30, and slowly stir for 100 seconds and then quickly stir for 100 seconds; the coating operation is as follows: pour the recycled aggregate into a mixing pot filled with fresh cement, stir manually for 120 seconds with a trowel, and after the stirring is completed, take out the coated recycled aggregate with tweezers and place it on a tray;

[0040] (4) Allow the clad recycled aggregate placed on the tray to dry until its moisture content reaches 20%;

[0041] (5) After the patina is stable, the patina regenerated aggregate is placed in a reactor for re-carbon mineralization treatment. The humidity in the reactor is controlled to 50% with potassium bromide and the CO2 concentration is 99%. The mineralization time is 8 hours, and the patina regenerated aggregate is obtained.

[0042] The performance (including water absorption rate and apparent density) of the grout-coated recycled aggregate prepared by carbon mineralization was investigated. The present invention tested the performance of the original recycled aggregate (i.e., the recycled aggregate that was not mineralized and mineralized, which was used as a blank control) and the high-quality grout-coated recycled aggregate obtained in Examples 1 and 2. The water absorption rate and apparent density of the recycled aggregate were tested with reference to GB / T 25177-2010 "Recycled coarse aggregate for concrete", and the crushing value index of the recycled aggregate was tested according to GB / T 14685-2011 "Pebbles and crushed stones for construction", and the results are shown in Table 1 below:

[0043] Table 1 Water absorption, crushing index and apparent density of high-quality cladding recycled aggregate prepared by carbon mineralization

[0044]

[0045]

[0046] As can be seen from Table 1, the water absorption rate and crushing index of the clad recycled aggregate prepared in the embodiment of the present invention are significantly lower than those of the control group, and its apparent density is also slightly lower than that of the control group. This shows that the properties of the recycled aggregate can be significantly improved by using the present invention. In addition, it can be seen that the water absorption rate and crushing index of the high-quality clad recycled aggregate prepared in Example 2 are further reduced compared with the water absorption rate and crushing index of the high-quality clad recycled aggregate prepared in Example 1, which shows that increasing the calcium hydroxide soaking time and the carbon mineralization time can further improve the properties of the high-quality clad recycled aggregate.

Claims

1. A method for preparing cladding recycled aggregate by using carbon mineralization, characterized in that: The steps include: (1) Carbon mineralization treatment of recycled aggregates: placing the recycled aggregates in a carbon mineralization device and using CO2 for mineralization treatment until the carbon is initially and completely mineralized, thereby obtaining recycled aggregates with initial carbon mineralization; (2) Soaking in a calcium hydroxide solution: Soaking the regenerated aggregate with preliminary carbon mineralization obtained in step (1) in a calcium hydroxide solution; (3) coating with fresh cement slurry: fully mixing the recycled aggregate soaked in step (2) with the fresh cement slurry to obtain coated recycled aggregate; (4) Moisture content adjustment: drying the clad recycled aggregate obtained in step (3) to adjust the moisture content of the clad recycled aggregate; (5) Re-carbon mineralization treatment: The clad recycled aggregate dried in step (4) is treated with CO2 for mineralization again, thereby obtaining high-quality clad recycled aggregate.

2. The method for preparing cladding recycled aggregate by carbon mineralization according to claim 1, characterized in that: In step (1), the recycled aggregate is non-alkaline pebbles and / or crushed stones with a particle size of ≤30 mm prepared from construction waste.

3. A method for preparing cladding recycled aggregate by carbon mineralization according to claim 1 or 2, characterized in that: In steps (1) and (5), during the carbon mineralization treatment, the relative humidity of the mineralization treatment site is 30%-80%.

4. A method for preparing cladding recycled aggregate by carbon mineralization according to claim 1 or 2, characterized in that: In steps (1) and (5), during the carbon mineralization treatment, the volume concentration of CO2 in the mineralization treatment site is ≥5%.

5. The method for preparing cladding recycled aggregate by carbon mineralization according to claim 1 or 2, characterized in that: In steps (1) and (5), the carbon mineralization time during the carbon mineralization treatment is ≥ 1 hour.

6. A method for preparing cladding recycled aggregate by carbon mineralization according to claim 1 or 2, characterized in that: In step (2), the mass concentration of the calcium hydroxide solution is ≥10%.

7. A method for preparing cladding recycled aggregate by carbon mineralization according to claim 1 or 2, characterized in that: In step (2), the immersion time of the calcium hydroxide aqueous solution is ≥ 2 hours.

8. The method for preparing cladding recycled aggregate by carbon mineralization according to claim 1 or 2, characterized in that: In step (3), the fresh cement slurry is prepared by mixing silicate cement and water, and the mixing time is ≥ 60 seconds.

9. A method for preparing cladding recycled aggregate by carbon mineralization according to claims 1 and 8, characterized in that: In step (3), the silicate cement in the fresh cement slurry is partially replaced by an auxiliary cementitious material, wherein the auxiliary cementitious material is one or more of fly ash, silica ash, and slag rich in silicon dioxide; and the total replacement rate of the auxiliary cementitious material is ≤30%.

10. A method for preparing cladding recycled aggregate by carbon mineralization according to claims 1 and 8, characterized in that: In step (3), the water-cement ratio of the fresh cement slurry is ≥0.25.

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