Modified recycled coarse aggregate concrete and method for preparing the same

Abstract

The application relates to a modified recycled coarse aggregate concrete and a preparation method thereof, which comprises the following raw material components in mass fractions: cement 300-450 parts, zeolite powder 30-50 parts, sodium silicate modified red brick powder 150-300 parts, sodium hydroxide 15-50 parts, machine-made sand 750-900 parts, modified recycled coarse aggregate 850-1000 parts, and water 150-200 parts; the preparation process of the modified recycled coarse aggregate is as follows: the recycled coarse aggregate is calcined, and the modified recycled coarse aggregate is obtained after cooling. Compared with the prior art, the recycled coarse aggregate has higher strength, can be effectively applied to high-strength high-performance concrete, and the modified recycled coarse aggregate concrete with high strength is obtained.

Description

Technical Field

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

[0002] The application of recycled aggregate concrete in the construction field has achieved certain results. It is widely used in the construction of foundations, columns, beams, slabs, and other components of various buildings, and its strength and durability can meet the requirements of general construction projects. Despite these achievements, recycled aggregate concrete still faces some challenges. The poor quality stability of recycled aggregates is a major problem. Because recycled aggregates have waste cement paste and mortar adhering to their surface, their apparent density and bulk density are lower than those of natural aggregates. Furthermore, the existing cement paste and mortar on the surface can cause cracks, resulting in higher crushing index and water absorption. Additionally, insufficient adhesion between the recycled aggregate surface and the cementitious material prevents its application in the preparation of high-strength concrete. These problems affect the compressive strength and durability of recycled concrete.

[0003] Therefore, if recycled aggregates can be applied to high-strength, high-performance concrete and meet the relevant performance requirements, it will greatly expand the application of recycled aggregates in concrete.

[0004] Patent publication number CN115650688A discloses a prefabricated aerated concrete panel and method prepared using recycled concrete aggregate. However, in this method, the organic matter in the recycled concrete aggregate is removed by microwave sintering, which does not involve the decomposition of the recycled aggregate. In addition, the treatment of recycled concrete aggregate particles and red brick particles are used as aggregates in the aerated concrete. These two types of particles have low density and are less likely to float or sink during the preparation of aerated concrete, which helps to reduce the shrinkage of alkali-activated aerated concrete, rather than promoting alkali activation. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art by providing a modified recycled coarse aggregate concrete and its preparation method, so that the recycled coarse aggregate has high strength and can be effectively applied to high-strength and high-performance concrete to obtain high-strength modified recycled coarse aggregate concrete.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] In one aspect, the present invention provides a modified recycled coarse aggregate concrete, comprising the following raw material components in parts by weight: 300-450 parts cement, 30-50 parts zeolite powder, 150-300 parts sodium silicate (Na2SiO3) modified red brick powder, 15-50 parts sodium hydroxide (NaOH), 750-900 parts manufactured sand, 850-1000 parts modified recycled coarse aggregate, and 150-200 parts water.

[0008] The preparation process of the modified recycled coarse aggregate is as follows: the recycled coarse aggregate is calcined and cooled to obtain the modified recycled coarse aggregate, which contains a large amount of calcium oxide (CaO) substances formed by the decomposition of calcium carbonate (CaCO3) and calcium hydroxide (Ca(OH)2) on its surface and inside.

[0009] Furthermore, the calcination temperature is 600~1100℃, and the calcination time is 2~4h.

[0010] Furthermore, the modified recycled coarse aggregate has a particle size of 5~25mm.

[0011] Furthermore, the Na2SiO3 modified red brick powder is modified before use. The modification process is as follows: the red brick powder is soaked in Na2SiO3 solution, and then dried to obtain modified red brick powder, so that the modified red brick powder contains sodium silicate.

[0012] Furthermore, the drying process is described as sun-drying or air-drying.

[0013] Furthermore, the composition of the red brick powder, by mass percentage, includes: 55%-60% silicon dioxide (SiO2), 15%-25% calcium oxide (CaO), 5%-10% iron oxide (FeO), 0-5% iron oxide (Fe2O3), and 0-5% aluminum oxide (Al2O3);

[0014] When the Fe2O3 content is 0, it means that the red brick powder does not contain Fe2O3. When the Al2O3 content is 0, it means that the red brick powder does not contain Al2O3.

[0015] Furthermore, the average particle size of the red brick powder is 20~50μm.

[0016] Furthermore, the red brick powder is obtained by crushing and grinding red bricks from demolished old buildings, and has a large number of nanoscale pores and irregular particle shapes.

[0017] Furthermore, the Na2SiO3 solution has a mass concentration of 20wt%-40wt%, the red brick powder is completely immersed in the sodium silicate solution, and the soaking time is 2-10h, preferably 3-6h.

[0018] Furthermore, the zeolite powder includes natural zeolite powder or synthetic zeolite powder, which is loosely aggregated and has a large number of nanoscale pores. The particles are irregular in shape and have the function of absorbing and solidifying carbon dioxide (CO2).

[0019] Furthermore, the manufactured sand is medium-coarse sand with a fineness modulus of 2.1 to 3.0.

[0020] Furthermore, the purity of the NaOH is 99%~99.99%.

[0021] In another aspect, the present invention also provides a method for preparing modified recycled coarse aggregate concrete, comprising the following steps:

[0022] Modified recycled coarse aggregate is obtained by calcining and cooling recycled coarse aggregate.

[0023] A sodium NaOH solution is obtained by mixing water and NaOH.

[0024] Modified recycled coarse aggregate, manufactured sand, zeolite powder, Na2SiO3 modified red brick powder, and cement are mixed and stirred. The sodium hydroxide solution is then added, and the mixture is stirred evenly to obtain modified recycled coarse aggregate concrete.

[0025] Further, water and NaOH are mixed and stirred evenly, then cooled to obtain a sodium hydroxide solution.

[0026] Further, the modified recycled coarse aggregate, manufactured sand, zeolite powder, red brick powder, and cement are mixed and stirred for 10-60 seconds, and the NaOH solution is added and stirred for 60-120 seconds to obtain modified recycled coarse aggregate concrete.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] (1) In this invention, recycled coarse aggregate is calcined to obtain modified recycled coarse aggregate, so that CaCO3 and Ca(OH)2 in the recycled aggregate can decompose to produce CaO; red brick powder is soaked in Na2SiO3 solution to obtain Na2SiO3 modified red brick powder. After the release of Na2SiO3 in the red brick powder, it not only plays a role in solidifying the recycled aggregate, but also acts as an alkali activator, so that the red brick powder and CaO wrapped on the surface and inside of the modified recycled coarse aggregate form an alkali activated cementitious material under the activation of Na2SiO3 and NaOH, which improves the bonding force between the surface of the recycled coarse aggregate and the alkali activated cementitious material, thereby greatly weakening the defects caused by insufficient bonding force between the surface of the recycled coarse aggregate and the alkali activated cementitious material, and thus providing support for the modified recycled coarse aggregate concrete.

[0029] (2) For ordinary recycled coarse aggregate concrete, the compressive strength is lower than that of ordinary concrete due to the presence of hardened mortar and a large number of interfacial structures on the surface of the recycled coarse aggregate. In this invention, the recycled coarse aggregate is calcined at 600~1100℃ to obtain modified recycled coarse aggregate, so that Ca(OH)2 in the recycled aggregate can decompose to produce CaO.

[0030] (3) This invention utilizes Na2SiO3 to soak and modify red brick powder, resulting in Na2SiO3-modified red brick powder. The red brick powder has a large number of distributed near-spherical micropores, which can absorb and store Na2SiO3. After the red brick powder is air-dried, sodium silicate can be effectively retained in the micropores. When the Na2SiO3-modified red brick powder is used in recycled coarse aggregate concrete, Na2SiO3 will be released to chemically solidify and modify the recycled coarse aggregate, thus mitigating the disadvantage that the recycled coarse aggregate cannot increase its strength due to its inherent defects.

[0031] (4) Since modified red brick powder is a low-calcium, high-silicon alkali-activated raw material, adjusting the amount of modified recycled coarse aggregate and modified red brick powder can effectively adjust the overall calcium oxide content in the modified red brick powder, thereby obtaining the optimal Ca / Si ratio. Under the action of Na2SiO3 and NaOH, CaO promotes the alkali-activated reaction, improves the strength of alkali-activated cementitious materials, and thus enhances the strength of modified recycled coarse aggregate concrete.

[0032] (5) Zeolite powder itself contains porous material and acts as an inorganic internal curing agent. Simultaneously, zeolite powder possesses two major adsorption characteristics: selective adsorption and high-efficiency adsorption, enabling it to effectively adsorb CO2. This invention utilizes zeolite powder. When CO2 in the air erodes low-carbon concrete, the zeolite powder inside the modified recycled coarse aggregate can adsorb CO2. Furthermore, when the zeolite powder cannot absorb excess CO2, the CO2 will react with the calcium hydroxide in the residual cement paste on the surface of the modified recycled coarse aggregate to produce calcium carbonate, blocking more micropores and defects on the surface of the modified recycled coarse aggregate, thus alleviating the problem of the inability to improve the strength of the modified recycled coarse aggregate concrete due to defects in the modified recycled coarse aggregate.

[0033] (6) This invention organically combines the inherent characteristics of modified recycled coarse aggregate, the inherent characteristics of Na2SiO3 modified red brick powder, the combined effect of modified recycled coarse aggregate and Na2SiO3 modified red brick powder, and the effect of zeolite powder. This results in the modified recycled coarse aggregate having a large amount of CaO obtained from the calcination and decomposition of CaCO3 and Ca(OH)2 inside and on its surface. This allows the modified recycled coarse aggregate to provide CaO to some of the red brick powder, and promotes alkali activation under the action of Na2SiO3 provided in Na2SiO3 modified red brick powder and the added NaOH. In addition, Na2SiO3 in the modified red brick powder can chemically solidify the surface of the modified recycled coarse aggregate. Finally, the CO2 absorbed by the zeolite powder reacts with the Ca(OH)2 involved in the modified recycled coarse aggregate to fill the pores on the surface of the modified recycled coarse aggregate. Under the combined effect of these three effects, the strength of the modified recycled coarse aggregate concrete can be greatly and effectively improved.

[0034] (7) This invention organically combines and utilizes the physical and chemical properties of construction waste, which can effectively solve the problem of poor strength of recycled coarse aggregate concrete caused by the inherent defects of recycled aggregate itself. Detailed Implementation

[0035] The present invention will now be described in detail with reference to specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. All other embodiments obtained by those skilled in the art based on the given embodiments without creative effort are within the scope of protection of this application.

[0036] Unless otherwise specified, the reagents, methods, instruments and equipment used in this invention are conventional reagents, methods, instruments and equipment in the art.

[0037] A modified recycled coarse aggregate concrete comprises the following raw material components in parts by weight: 300-450 parts cement, 30-50 parts zeolite powder, 150-300 parts Na2SiO3 modified red brick powder, 15-50 parts NaOH, 750-900 parts manufactured sand, 850-1000 parts modified recycled coarse aggregate, and 150-200 parts water.

[0038] The preparation process of the modified recycled coarse aggregate is as follows: the recycled coarse aggregate is calcined and cooled to obtain the modified recycled coarse aggregate, so that its surface and interior contain a large amount of CaCO3 and Ca(OH)2 decomposed into CaO substances.

[0039] In some specific embodiments, the calcination temperature is 600~1100℃ and the calcination time is 2~4h.

[0040] In some specific embodiments, the particle size of the modified recycled coarse aggregate is 5~25mm.

[0041] In some specific embodiments, the Na2SiO3 modified red brick powder is modified before use. The modification process is as follows: the red brick powder is soaked in Na2SiO3 solution, and then dried to obtain modified red brick powder, so that the modified red brick powder contains sodium silicate.

[0042] In some specific implementations, the drying process involves sun drying or air drying.

[0043] In some specific embodiments, the composition of the red brick powder, by mass percentage, includes: 55%-60% SiO2, 15%-25% CaO, 5%-10% FeO, 0-5% Fe2O3, and 0-5% Al2O3;

[0044] When the Fe2O3 content is 0, it means that the red brick powder does not contain Fe2O3; when the Al2O3 content is 0, it means that the red brick powder does not contain Al2O3.

[0045] In some specific embodiments, the average particle size of the red brick powder is 20~50μm.

[0046] In some specific embodiments, the red brick powder is obtained by crushing and grinding red bricks from demolished old buildings, and has a large number of nanoscale pores and irregular particle shape.

[0047] In some specific embodiments, the mass concentration of the Na2SiO3 solution is 20wt%-40wt%, the red brick powder is completely immersed in the sodium silicate solution, and the soaking time is 2-10h.

[0048] In some specific embodiments, the zeolite powder includes natural zeolite powder or synthetic zeolite powder, which is loosely aggregated and has a large number of nanoscale pores and irregular particle shape, and at the same time has the function of absorbing and solidifying CO2.

[0049] In some specific embodiments, the manufactured sand is medium-coarse sand with a fineness modulus of 2.1 to 3.0.

[0050] In some specific embodiments, the purity of the NaOH is 99% to 99.99%.

[0051] A method for preparing modified recycled coarse aggregate concrete includes the following steps:

[0052] Modified recycled coarse aggregate is obtained by calcining and cooling recycled coarse aggregate.

[0053] A sodium NaOH solution is obtained by mixing water and NaOH.

[0054] Modified recycled coarse aggregate, manufactured sand, zeolite powder, Na2SiO3 modified red brick powder, and cement are mixed and stirred. The sodium hydroxide solution is then added, and the mixture is stirred evenly to obtain modified recycled coarse aggregate concrete.

[0055] Further, water and NaOH are mixed and stirred evenly, then cooled to obtain a sodium hydroxide solution.

[0056] Further, the modified recycled coarse aggregate, manufactured sand, zeolite powder, red brick powder, and cement are mixed and stirred for 10-60 seconds, and the NaOH solution is added and stirred for 60-120 seconds to obtain modified recycled coarse aggregate concrete.

[0057] Example 1

[0058] A modified recycled coarse aggregate concrete comprises, by mass parts: 300 parts cement, 40 parts zeolite powder, 300 parts Na2SiO3 modified red brick powder, 40 parts NaOH, 800 parts manufactured sand, 950 parts modified recycled coarse aggregate, and 200 parts water.

[0059] A method for preparing modified recycled coarse aggregate concrete includes the following steps:

[0060] S1. Calcine the recycled coarse aggregate at 1050℃ for 3 hours, and then cool it to obtain modified recycled coarse aggregate. The particle size of the modified recycled coarse aggregate is 5~25mm.

[0061] S2. Red bricks from demolished old buildings are crushed and ground into powder to obtain red brick powder. The average particle size of the red brick powder is 20~50μm, and its composition by mass percentage includes: SiO2 content 55%-60%, CaO content 15%-25%, FeO content 5%-10%, Fe2O3 content 0-5%, and Al2O3 content 0-5%. When the Fe2O3 content is 0, it means that the red brick powder does not contain Fe2O3; when the Al2O3 content is 0, it means that the red brick powder does not contain Al2O3.

[0062] S3. Place the red brick powder in a 30wt% sodium silicate solution to completely immerse it for 4 hours. After immersion, air dry it to obtain Na2SiO3 modified red brick powder, so that the Na2SiO3 modified red brick powder contains Na2SiO3.

[0063] S4. Mix 200 parts water and 40 parts NaOH, stir until homogeneous, and cool to obtain a sodium hydroxide solution.

[0064] S5. Pour 950 parts of modified recycled coarse aggregate, 800 parts of manufactured sand, 40 parts of zeolite powder, 300 parts of Na2SiO3 modified red brick powder, and 300 parts of cement into a mixer and mix thoroughly for 30 seconds. Add the NaOH solution and stir for 90 seconds until the mixture is uniform to obtain modified recycled coarse aggregate concrete.

[0065] In this embodiment, the recycled coarse aggregate is recycled coarse aggregate from waste concrete, with a particle size of 5-20mm. During use, it is washed with water to remove surface debris, dust, and impurities, and then dried. The red bricks are selected from red bricks from demolished old buildings. The zeolite powder is natural zeolite powder, commercially available, produced in Xinyang, Henan Province. It is loosely aggregated and has numerous nanoscale pores with irregular particle shapes, and also has the function of absorbing and solidifying CO2. The manufactured sand is medium-coarse sand with a fineness modulus of 2.1-3.0. The cement is Conch PO42.5 ordinary Portland cement. The sodium hydroxide has a purity of 99.5% and is industrially purified sodium hydroxide.

[0066] Example 2

[0067] Compared with Example 1, most of the components are the same, except that the modified recycled coarse aggregate concrete consists of the following components by mass parts: 325 parts cement, 40 parts zeolite powder, 275 parts Na2SiO3 modified red brick powder, 36 parts NaOH, 800 parts manufactured sand, 950 parts modified recycled coarse aggregate, and 200 parts water.

[0068] Example 3

[0069] Compared with Example 1, most of the components are the same, except that the modified recycled coarse aggregate concrete consists of the following components by mass parts: 350 parts cement, 40 parts zeolite powder, 250 parts Na2SiO3 modified red brick powder, 32 parts NaOH, 800 parts manufactured sand, 950 parts modified recycled coarse aggregate, and 200 parts water.

[0070] Example 4

[0071] Compared with Example 1, most of the components are the same, except that the modified recycled coarse aggregate concrete consists of the following components by mass parts: 375 parts cement, 40 parts zeolite powder, 225 parts Na2SiO3 modified red brick powder, 28 parts NaOH, 800 parts manufactured sand, 950 parts modified recycled coarse aggregate, and 200 parts water.

[0072] Example 5

[0073] Compared with Example 1, most of the components are the same, except that the modified recycled coarse aggregate concrete consists of the following components by mass parts: 400 parts cement, 40 parts zeolite powder, 200 parts Na2SiO3 modified red brick powder, 24 parts NaOH, 800 parts manufactured sand, 950 parts modified recycled coarse aggregate, and 200 parts water.

[0074] Example 6

[0075] Compared with Example 1, most of the components are the same, except that the modified recycled coarse aggregate concrete consists of the following components by mass parts: 425 parts cement, 40 parts zeolite powder, 175 parts Na2SiO3 modified red brick powder, 20 parts NaOH, 800 parts manufactured sand, 950 parts modified recycled coarse aggregate, and 200 parts water.

[0076] Example 7

[0077] Compared with Example 1, most of the components are the same, except that the modified recycled coarse aggregate concrete consists of the following components by mass parts: 450 parts cement, 40 parts zeolite powder, 150 parts Na2SiO3 modified red brick powder, 16 parts NaOH, 800 parts manufactured sand, 950 parts modified recycled coarse aggregate, and 200 parts water.

[0078] Example 8

[0079] Compared with Example 1, most of the components are the same, except that the modified recycled coarse aggregate concrete consists of the following components by mass parts: 300 parts cement, 40 parts zeolite powder, 300 parts Na2SiO3 modified red brick powder, 40 parts NaOH, 800 parts manufactured sand, 850 parts modified recycled coarse aggregate, and 200 parts water.

[0080] Example 9

[0081] Compared with Example 1, most of them are the same, except that the modified recycled coarse aggregate concrete has the following composition by mass parts: 300 parts cement, 40 parts zeolite powder, 300 parts Na2SiO3 modified red brick powder, 40 parts NaOH, 800 parts manufactured sand, 1000 parts modified recycled coarse aggregate, and 200 parts water.

[0082] Example 10

[0083] Compared with Example 1, most of the contents are the same, except that the recycled coarse aggregate is calcined at 1000°C for 4 hours to obtain modified recycled coarse aggregate.

[0084] Example 11

[0085] Compared with Example 1, most of the contents are the same, except that the recycled coarse aggregate is calcined at 1100°C for 2 hours to obtain modified recycled coarse aggregate.

[0086] Comparative Example 1

[0087] A type of fly ash ordinary concrete comprises, by weight parts: 950 parts crushed stone, 800 parts ordinary sand, 550 parts cement, 100 parts fly ash, 16 parts water-reducing agent, and 200 parts water.

[0088] A method for preparing fly ash ordinary concrete involves pouring 950 parts crushed stone and 800 parts ordinary sand into a mixer, adding 550 parts cement and 100 parts fly ash, mixing for 30 seconds, and finally adding 200 parts water mixed with 16 parts water-reducing agent, mixing evenly to obtain C30 fly ash ordinary concrete.

[0089] In this embodiment, the crushed stone is modified recycled crushed stone with a particle size range of 5-31.5 mm. The crushed stone is calcined at 1050℃ for 3 hours to obtain modified recycled crushed stone; the cement is Conch PO42.5 ordinary Portland cement; the fly ash is Grade I fly ash, taken from Yuanyuan Thermal Power Plant in Jilin City, with a density of 2868 kg / m³. 3 The specific surface area is 5.1%, the water demand ratio is 94.1%, the loss on ignition is 4.76%, and the SO3 content is 0.48%. The water-reducing agent is a naphthalene-based high-efficiency water-reducing agent (sodium β-naphthalenesulfonate formaldehyde condensate), with a water reduction rate of 18%-28%, and the quality indicators meet the requirements of the "Concrete Admixtures" (GB8076-2008) standard.

[0090] Comparative Example 2

[0091] Compared with Example 5, most of them are the same, except that the 950 parts of modified recycled coarse aggregate were changed to 712 parts of modified recycled coarse aggregate and 238 parts of crushed stone.

[0092] Comparative Example 3

[0093] Compared with Example 5, most of them are the same, except that the 950 parts of modified recycled coarse aggregate are changed to 475 parts of modified recycled coarse aggregate and 475 parts of crushed stone.

[0094] Comparative Example 4

[0095] Compared with Example 5, most of them are the same, except that the 950 parts of modified recycled coarse aggregate were changed to 238 parts of modified recycled coarse aggregate and 712 parts of crushed stone.

[0096] Comparative Example 5

[0097] Compared with Example 1, most of them are the same, except that the modified recycled coarse aggregate is replaced with recycled coarse aggregate and is not calcined or modified.

[0098] Comparative Example 6

[0099] Compared with Example 1, most of them are the same, except that the Na2SiO3 modified red brick powder is replaced with red brick powder and is not modified.

[0100] Table 1 shows the composition (by mass parts) of Examples 1-9 and Comparative Examples 2-6.

[0101] Table 1. Composition of Examples 1-9 and Comparative Examples 2-6 (by parts by mass)

[0102]

[0103] Setting time and compressive strength tests were conducted on Examples 1-9 and Comparative Examples 1-6. The setting time test method was carried out in accordance with the method in GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures"; the compressive strength test method was carried out in accordance with the method in GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete".

[0104] Table 2 shows the anticoagulation time and compressive strength test results of Examples 1-9 and Comparative Examples 1-8.

[0105] Table 2. Anticoagulation time and compressive strength tests of Examples 1-10 and Comparative Examples 1-7

[0106]

[0107] Comparative Examples 1, 5, and 6 show that the modified recycled coarse aggregate concrete prepared using modified recycled coarse aggregate and Na2SiO3-modified red brick powder has higher strength. When the recycled coarse aggregate is not calcined or modified, or the red brick powder is not modified with Na2SiO3, and only ordinary recycled coarse aggregate or ordinary red brick powder is used, the strength of the prepared recycled coarse aggregate concrete decreases. This indicates that the modified recycled aggregate and Na2SiO3-modified red brick powder work together to promote the alkali-activated reaction, which is beneficial to improving the concrete strength. This invention involves calcining recycled coarse aggregate to obtain modified recycled coarse aggregate, enabling the CaCO3 and Ca(OH)2 in the recycled aggregate to decompose and produce CaO. Red brick powder is then soaked in a Na2SiO3 solution to obtain Na2SiO3-modified red brick powder. The release of Na2SiO3 into the red brick powder not only solidifies the recycled aggregate but also acts as an alkali activator. Under the activation of sodium silicate and sodium hydroxide, the red brick powder and the CaO encapsulated on and inside the modified recycled coarse aggregate form an alkali-activated cementitious material, improving the adhesion between the surface of the recycled coarse aggregate and the alkali-activated cementitious material. This significantly reduces defects caused by insufficient adhesion between the recycled coarse aggregate itself and the alkali-activated cementitious material, thus providing support for the modified recycled coarse aggregate concrete.

[0108] Zeolite powder itself contains porous material, acting as an inorganic internal curing agent. Simultaneously, zeolite powder possesses two major adsorption characteristics: selective adsorption and high-efficiency adsorption, effectively adsorbing CO2. This invention utilizes zeolite powder; when CO2 in the air erodes low-carbon concrete, the zeolite powder inside the modified recycled coarse aggregate can adsorb CO2. Furthermore, when the zeolite powder cannot absorb excess CO2, the CO2 will react with Ca(OH)2 in the residual cement paste on the surface of the modified recycled coarse aggregate to produce CaCO3, blocking more micropores and defects on the surface of the modified recycled coarse aggregate, thus alleviating the problem of the modified recycled coarse aggregate concrete's strength not being improved due to defects in the modified recycled coarse aggregate.

[0109] By comparing Examples 1-7, with the amount of modified recycled coarse aggregate remaining constant, the overall calcium oxide content in both the modified recycled aggregate and the Na2SiO3-modified red brick powder was adjusted by varying the amount of Na2SiO3-modified red brick powder. It can be seen that different ratios of modified recycled aggregate to Na2SiO3-modified red brick powder affect both materials. Examples 5, 6, and 7 exhibited the best mechanical properties, reaching or even exceeding those of C30 fly ash ordinary concrete (Comparative Example 1), with Example 7 showing the best effect. Under the influence of Na2SiO3 and NaOH, CaO promotes the alkali-activated reaction, increases the strength of the alkali-activated cementitious material, and thus enhances the strength of the modified recycled coarse aggregate concrete.

[0110] Observations of Example 5 and Comparative Examples 2-4 show that as the content of modified recycled coarse aggregate gradually decreases, the mechanical properties of modified recycled coarse aggregate concrete show a gradual decreasing trend. This indicates that as the amount of modified recycled aggregate decreases, the overall calcium oxide content in the modified recycled coarse aggregate and modified red brick powder decreases. When the calcium oxide content is low, it is not conducive to the development of the strength of alkali-activated cementitious materials in modified recycled coarse aggregate concrete, resulting in lower strength of modified recycled coarse aggregate concrete.

[0111] In summary, modified recycled coarse aggregate concrete has good mechanical properties and high strength, which is superior to recycled coarse aggregate concrete prepared using ordinary recycled coarse aggregate. When the amount of modified recycled coarse aggregate and modified red brick powder is appropriate (as in Examples 5, 6, and 7), its mechanical properties are in a better state, which can reach or even exceed those of C30 fly ash ordinary concrete (Comparative Example 1).

[0112] Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A modified recycled coarse aggregate concrete, characterized in that, The raw material components include the following parts by weight: 300-450 parts cement, 30-50 parts zeolite powder, 150-300 parts sodium silicate modified red brick powder, 15-50 parts sodium hydroxide, 750-900 parts manufactured sand, 850-1000 parts modified recycled coarse aggregate, and 150-200 parts water. The preparation process of the modified recycled coarse aggregate is as follows: the recycled coarse aggregate is calcined at 600~1100℃ and cooled to obtain the modified recycled coarse aggregate. The calcination time is 2~4h, so that Ca(OH)2 in the recycled aggregate can decompose to produce CaO. The sodium silicate modified red brick powder is modified before use. The modification process is as follows: the red brick powder is soaked in sodium silicate solution, and then dried to obtain modified red brick powder.

2. The modified recycled coarse aggregate concrete according to claim 1, characterized in that, The modified recycled coarse aggregate has a particle size range of 5~25mm.

3. The modified recycled coarse aggregate concrete according to claim 1, characterized in that, The composition of the red brick powder, by mass percentage, includes: 55%-60% SiO2, 15%-25% CaO, 5%-10% FeO, 0-5% Fe2O3, and 0-5% Al2O3. When the Fe2O3 content is 0, it means that the red brick powder does not contain Fe2O3. When the Al2O3 content is 0, it means that the red brick powder does not contain Al2O3.

4. The modified recycled coarse aggregate concrete according to claim 1, characterized in that, The average particle size of the red brick powder is 20~50μm.

5. The modified recycled coarse aggregate concrete according to claim 1, characterized in that, The sodium silicate solution has a mass concentration of 20wt%-40wt%, and the soaking time is 2-10h.

6. The modified recycled coarse aggregate concrete according to claim 1, characterized in that, The zeolite powder includes natural zeolite powder or synthetic zeolite powder.

7. The modified recycled coarse aggregate concrete according to claim 1, characterized in that, The manufactured sand is medium-coarse sand with a fineness modulus of 2.1 to 3.

0.

8. A method for preparing modified recycled coarse aggregate concrete as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Modified recycled coarse aggregate is obtained by calcining and cooling recycled coarse aggregate. Water and sodium hydroxide are mixed to obtain a sodium hydroxide solution; Modified recycled coarse aggregate, manufactured sand, zeolite powder, sodium silicate modified red brick powder, and cement are mixed and stirred. The sodium hydroxide solution is then added, and the mixture is stirred evenly to obtain modified recycled coarse aggregate concrete.

Images