A preparation method of carbon mineralization regenerated micro powder, a carbon mineralization enhanced solid waste based low-carbon concrete and a preparation method thereof

Abstract

The application discloses a preparation method of carbon-mineralized regenerated micro powder, a carbon-mineralized enhanced solid waste-based low-carbon concrete and a preparation method thereof. The solid waste-based low-carbon concrete disclosed by the application takes waste concrete regenerated micro powder as an object, obtains a strengthened product through carbon dioxide mineralization, is compounded with calcined clay, cement clinker and gypsum to prepare a low-carbon composite cementing material, replaces part of natural sand and stone with regenerated coarse aggregate and fine aggregate, and prepares low-carbon concrete under carbon dioxide curing. The application solves the efficient resource utilization of building solid waste, realizes chemical solidification of carbon dioxide, provides a new synergistic technical route for the low-carbon development of the cement industry, and improves the overall mechanical properties of the concrete by improving the interface density of the regenerated aggregate.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of building materials, and particularly relates to a preparation method of carbon-mineralized regenerated micro powder, and a carbon-mineralized enhanced solid waste-based low-carbon concrete and a preparation method thereof. BACKGROUND

[0002] Carbon dioxide capture, storage and utilization technology (CCUS) can realize the resource utilization of CO2, and has a strong development momentum, which is of great significance to solve the "double carbon" target of the cement industry.

[0003] China's rapid urbanization and infrastructure construction have driven the huge increase in cement consumption. The cement industry promotes economic development while consuming a large amount of resources and energy. The main carbon emissions of the cement industry are generated during the cement production process, of which 40% of the carbon emissions are due to energy consumption, and 60% of the carbon emissions are due to the decomposition of calcium carbonate in the cement raw materials. In order to reduce the carbon emissions of the cement industry, the following methods can be taken: (1) improving the energy utilization efficiency in the cement production process; (2) using clean energy to produce cement; (3) using auxiliary cementitious materials to replace cement to reduce the amount of cement clinker. At present, auxiliary cementitious materials such as fly ash and ground slag have been widely used in the cement and concrete industry. However, with the continuous development of the cement and concrete industry, the commonly used auxiliary cementitious materials such as fly ash and ground slag have the disadvantages of uneven regional distribution, large quality difference, and difficult quality control, and at a large dosage, they will affect the development of the early strength of cement-based materials, which restricts their more extensive application in cement and concrete. Therefore, finding a low-carbon composite cementitious material with controllable material performance and comparable strength development characteristics to ordinary portland cement is an effective way for the cement industry to reduce CO2 emissions.

[0004] At the same time, with the rapid growth of infrastructure construction, the demand for concrete is still at a high point, constantly consuming natural sand and stone resources. Therefore, the building materials industry urgently needs to find suitable alternative resources for river sand.

[0005] In summary, in the face of the urgent need for resource utilization of waste concrete and development of low-carbon cementitious materials in the construction industry, it is necessary to find a proper treatment method, which can consume CO2-rich tail gas emitted in the production of the cement industry and other industries, has important environmental benefits, and helps to promote the early realization of the "double carbon" target of China. SUMMARY

[0006] To solve the problems existing in the prior art, the application provides a preparation method of carbon-mineralized recycled micro powder and a solid waste-based low-carbon concrete with carbon-mineralized enhancement and a preparation method thereof.The solid waste-based low-carbon concrete provided by the application takes waste concrete recycled micro powder as the object, obtains a strengthened product through carbon dioxide mineralization, and is compounded with calcined clay, cement clinker and gypsum to prepare a low-carbon composite cementitious material, and then recycled coarse aggregate and fine aggregate are used to replace part of natural sand and stone to prepare low-carbon concrete under the carbon dioxide curing, so that the application solves the efficient resource utilization of building solid waste, realizes the chemical solidification of carbon dioxide, and provides a new synergistic technical route for the low-carbon development of the cement industry.

[0007] The application provides a preparation method of carbon-mineralized recycled micro powder, which comprises the following steps:

[0008] (1) mixing the recycled micro powder and solution I to obtain a first mixture;

[0009] The mass ratio of the recycled micro powder to solution I is 1:(5-50);

[0010] The recycled micro powder is obtained from waste concrete and waste mortar generated in the process of waste building demolition and the process of commercial concrete mixing station, and has a particle size of less than 0.075 mm after crushing, grinding and screening.

[0011] The solution I is a mixed aqueous solution of a surfactant, a calcium ion complexing agent and calcium carbonate seeds;

[0012] The surfactant is selected from one or more than one of soluble phosphate and soluble aluminum salt, and the molar concentration of the surfactant in the solution I is 0.01 mol / L-10 mol / L;

[0013] The calcium ion complexing agent is selected from one or more than one of sodium ethylenediaminetetraacetate, polyvinyl alcohol and triethanolamine, and the mass fraction of the calcium ion complexing agent in the solution I is 0.01%-2%;

[0014] The calcium carbonate seeds are beneficial to accelerating the carbon mineralization reaction and deposition, have a purity of more than 70%, a particle size of 0.5-1.5 mm and a length of 20-40 mm, and the mass fraction of the calcium carbonate seeds in the recycled micro powder is 0.01%-0.5%;

[0015] (2) passing carbon dioxide gas into the first mixture in step (1) and heating to perform a carbonization reaction to obtain a second mixture;

[0016] In step (2), the concentration of carbon dioxide is not less than 5%, the carbonization reaction temperature is 40-120 DEG C, and the reaction time is 0.5-24 h;

[0017] (3) After mixing the second mixture in step (2) with a soluble alkaline solution for a period of time, solid product and by-product solution are obtained after solid-liquid separation. Then, the solid product is further subjected to vacuum drying to obtain the carbon mineralization regenerated micro powder of the present invention.

[0018] The soluble alkali can improve the purity of the generated calcium carbonate and convert the silica gel and alumina gel in the carbon mineralization reaction products into soluble silicates, aluminates or aluminosilicates. In the system combined with calcined clay, a higher calcium carbonate content is beneficial to the strength development of cement-based materials.

[0019] The molar concentration of the soluble alkali is 0.5 mol / L to 10 mol / L, and the mass ratio of the alkali to the second mixture is 5:1 to 20:1; the mixing temperature in step (3) is 20 to 100°C, and the mixing time is 0.5 to 24 h.

[0020] Specifically, in step (1), the waste concrete and waste mortar are mainly composed of limestone, and also contain a small amount of hydration products CSH, CH, AFt and unhydrated minerals C2S, C3S and C4AF.

[0021] Specifically, in step (2), the carbon dioxide gas is an industrial exhaust gas or commercial gas with a concentration of not less than 5%. The industrial exhaust gas comes from the exhaust gas of industries such as steel industry, cement industry, power industry, chemical industry, or any combination thereof.

[0022] Specifically, in step (3), the soluble alkali is selected from any one or more of KOH, LiOH, and NaOH; the by-product solution obtained in step (3) is a silicate, aluminate, or aluminosilicate solution.

[0023] Specifically, in step (3), the vacuum drying temperature is 45±5℃ and the drying time is 24~48h.

[0024] This invention also provides a carbon mineralization-reinforced solid waste-based low-carbon concrete comprising the carbon mineralization regenerated micro powder obtained by the above method, which is obtained by mixing low-carbon composite cementitious material with coarse aggregate, fine aggregate, water, and admixtures according to the following proportions, with the following weight parts of each component:

[0025]

[0026]

[0027] The low-carbon composite cementitious material is obtained by uniformly mixing the above-mentioned carbon mineralized recycled micro powder with calcined clay, cement clinker and gypsum.

[0028] The mass ratio of carbon mineralized recycled micro powder to calcined clay is (1-2.5):1, which is adjusted according to the CaCO3 and Al2O3 content. The mass of cement clinker accounts for 25%-60% of the mass of low-carbon composite cementitious material. The mass of gypsum accounts for 0%-5% of the mass of low-carbon composite cementitious material. The gypsum ratio is adjusted according to the gypsum content in the cement and the Al2O3 content in the calcined clay. There may be cases where no additional addition is required.

[0029] Specifically, the coarse aggregate is gravel, including natural coarse aggregate from natural mines and riverbeds, as well as recycled coarse aggregate obtained after crushing and screening waste concrete, wherein the recycled coarse aggregate accounts for 20% to 60% of the total mass of coarse aggregate.

[0030] The fine aggregate is sand, including natural fine aggregate from natural mines and riverbeds, as well as recycled fine aggregate obtained after crushing and screening waste concrete, wherein the recycled fine aggregate accounts for 10% to 40% of the total fine aggregate mass.

[0031] Specifically, the admixture is selected from any one or more of high-performance water-reducing agents, air-entraining agents, and defoamers used to adjust the workability of fresh concrete.

[0032] Specifically, the calcined clay is obtained by calcining clay whose main component is kaolin or metakaolin at 600-950°C, and then grinding and sieving it. The calcination temperature of the clay is 600-950°C, during which the structural water of the clay is continuously lost, achieving dehydroxylation, destroying the crystal lattice structure, and generating a large amount of active Al2O3 and SiO2.

[0033] Specifically, the gypsum is preferably dihydrate gypsum, and the cement clinker is selected from either silicate cement or sulfoaluminate cement.

[0034] This invention also provides a method for preparing the above-mentioned carbon mineralization-enhanced solid waste-based low-carbon concrete, comprising:

[0035] (1) The above-mentioned carbon mineralized recycled micro powder, calcined clay, cement clinker and gypsum are mixed evenly in proportion to obtain a low-carbon composite cementitious material.

[0036] (2) The low-carbon composite cementitious material described in step (1) is mixed with sand, stone aggregate, water and admixtures according to the mixing ratio and molded together. The mixture is then placed in a carbonization reactor for carbon dioxide pre-curing to obtain the solid waste-based low-carbon concrete of the present invention.

[0037] Specifically, the carbon dioxide curing conditions in step (2) are as follows: the carbonization reactor is a high-pressure carbonization reactor, the carbon dioxide concentration is not less than 10%, the curing temperature is 40-100℃, the curing relative humidity is 70%-95%, the curing pressure is ≥0.1MPa, and the curing time is 10-48h.

[0038] This invention obtains carbon mineralized recycled micro powder through carbonization reaction, and uses this carbon mineralized recycled micro powder to make a carbon mineralized reinforced solid waste-based low-carbon concrete. This not only realizes the full utilization of waste concrete or waste mortar, but also provides low-carbon composite cementitious materials and concrete CCUS technology. On the one hand, the high carbonization activity of hydration products CSH, CH, AFt and unhydrated minerals C2S, C3S and C4AF in recycled micro-powder enables carbon dioxide capture and mineralization. The original CaCO3 in the recycled micro-powder acts as a template during carbon mineralization, promoting the conversion of reactants into crystalline CaCO3. On the other hand, the CaCO3 products generated by carbon mineralization and the main component of the recycled micro-powder itself further react with active Al2O3 in calcined clay to produce hydrated calcium aluminate carbohydrate, achieving performance comparable to that of ordinary silicate cement hydration products, significantly reducing the amount of cement clinker used. Simultaneously, to maximize the utilization of waste concrete or waste mortar, the recycled coarse and fine aggregates prepared from them are used to prepare recycled concrete, and carbon dioxide wet curing technology is employed to improve the overall mechanical properties of the concrete by increasing the interfacial density of the recycled aggregates. The technical solution provided by this invention can significantly reduce carbon emissions throughout the entire life cycle of concrete, achieving efficient synergistic utilization of solid waste and gaseous waste, which has significant social and environmental implications. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the preparation process of the carbon mineralization-enhanced solid waste-based low-carbon concrete described in this invention. Detailed Implementation

[0040] To better understand the present invention, the following description, in conjunction with embodiments, further illustrates the content of the invention. However, the content of the present invention is not limited to the scope described in the embodiments. Rather, these embodiments are provided to explain the principles of the invention and its practical applications, thereby enabling other those skilled in the art to understand the various embodiments of the invention and various modifications suitable for specific intended applications.

[0041] This invention provides five comparative examples, namely ordinary concrete and solid waste-based low-carbon concrete without carbon mineralization enhancement treatment. Eight implementation examples are provided by adjusting the composition of the low-carbon composite cementitious material and the aggregate composition. These examples use one type of cement clinker, two types of recycled micro-powder, two types of calcined clay, and two types of recycled aggregate. The calcination temperature of the calcined clay is 950℃. The chemical composition of each raw material is shown in Table 1, and the performance of the aggregate is shown in Table 2. Recycled coarse aggregate I and recycled fine aggregate I are obtained from waste concrete with an original strength grade of C45 after crushing and screening. Recycled coarse aggregate II and recycled fine aggregate II are obtained from waste concrete with an original strength grade of C30 after crushing and screening. The mix proportions of each comparative example and implementation example are shown in Table 3, and the composition of the low-carbon composite cementitious material is shown in Table 4. The slump and compressive strength test values ​​of the concrete prepared in Examples 1-8 and Comparative Examples 1-5 of this invention are shown in Table 5.

[0042] The method for preparing carbon mineralization regenerated micro powder according to the present invention includes:

[0043] (1) Mix the regenerated micro powder and solution I to obtain the first mixture;

[0044] The mass ratio of the regenerated micro powder to solution I is 1:(5-50);

[0045] Solution I is a mixed aqueous solution of surfactant, calcium ion complexing agent and calcium carbonate seed crystals;

[0046] The surfactant is selected from any one or more of soluble phosphates and soluble aluminum salts, and the molar concentration of the surfactant in solution I is 0.01 mol / L to 10 mol / L;

[0047] The calcium ion complexing agent is selected from any one or more of sodium ethylenediaminetetraacetate, polyvinyl alcohol, and triethanolamine, and the mass fraction of the calcium ion complexing agent in solution I is 0.01% to 2%.

[0048] The calcium carbonate seed crystals are beneficial for accelerating the carbon mineralization reaction and deposition. They have a purity greater than 70%, a particle size of 0.5–1.5 mm, and a length of 20–40 mm. The calcium carbonate seed crystals are 0.01%–0.5% of the mass of the regenerated micro powder.

[0049] (2) In step (1), carbon dioxide gas with a concentration of not less than 5% is introduced into the first mixture; and the mixture is heated to carry out a carbonization reaction to obtain a second mixture;

[0050] The carbonization reaction temperature is 40–120°C, and the reaction time is 0.5–24 h.

[0051] (3) After mixing the second mixture in step (2) with a soluble alkaline solution for a period of time, solid product and by-product solution are obtained after solid-liquid separation. Then, the solid product is further subjected to vacuum drying to obtain the carbon mineralization regenerated micro powder of the present invention.

[0052] The soluble alkali can improve the purity of the generated calcium carbonate, and the carbon mineralization reaction will also generate other products. In the system combined with calcined clay, a higher calcium carbonate content is beneficial to the strength development of cement-based materials.

[0053] The molar concentration of the soluble alkali is 0.5 mol / L to 10 mol / L, and the mass ratio of the alkali to the second mixture is 5:1 to 20:1; the mixing temperature in step (3) is 20 to 100°C, and the mixing time is 0.5 to 24 h.

[0054] Table 1 Chemical composition of raw materials

[0055]

[0056]

[0057] Table 2 Mechanical properties of aggregates

[0058] Material Crushing value / % Apparent density / kg / m 3 ]] Water absorption / % Natural coarse aggregate 9.1 2650 0.2 Natural fine aggregate / 2740 2.1 Recycled coarse aggregate I 12.3 2590 3.1 Recycled fine aggregate I / 2680 5.3 Recycled coarse aggregate II 15.4 2540 5.4 Recycled fine aggregate II / 2610 8.1

[0059] Table 3 Concrete mix proportions (kg / m³) 3 )

[0060]

[0061]

[0062] Table 4. Mix proportions of low-carbon composite cementitious materials (kg / m³) 3 )

[0063]

[0064] Note: The regenerated micro powder in Comparative Example 5 was not carbonized.

[0065] Example 1

[0066] Carbonized recycled micro powder A and calcined clay A are used, with the two replacing 40% of the cement clinker. Recycled aggregate from source I replaces 30% of the natural aggregate to prepare concrete, which is then pre-cured in a carbonization reactor.

[0067] First, carbonized regenerated micropowder was prepared under the following conditions: commercially available carbon dioxide gas was used, with a flow rate adjusted to 0.1 L / min to achieve a concentration of 10% entering the reactor; the carbonization temperature was 80℃; the reaction time was 2 h; and the mass ratio of regenerated micropowder A to the solution in the first mixture was 1:20. The solution was prepared as follows: a 0.08% (w / w) triethanolamine solution was prepared in deionized water; soluble calcium phosphate was added to adjust its molar concentration to 0.1 mol / L; and calcium carbonate seed crystals with a purity of 75%, a particle size of 1 mm, and a length of 25 mm were added, with a mass of 0.01% of the regenerated micropowder mass. After the carbonization reaction, 1 mol / L sodium hydroxide was added to the second mixture, and the mixture was stirred at 40℃ for 1 h. The solid-liquid mixture was then separated using a filter, and the solid was repeatedly washed with deionized water. Finally, the solid was dried in a vacuum oven at 45±5℃ for 48 h to obtain the carbonized regenerated micropowder.

[0068] The proportions of each raw material in the low-carbon cementitious material were determined based on the chemical composition of carbonized recycled micro powder A and calcined clay A, and mixed evenly. The proportions are shown in Table 4. Concrete was prepared according to the proportions in Table 3, wherein the mass ratio of water-reducing agent to air-entraining agent in the admixtures was 10:1. The concrete was then placed in a carbonization reactor with the mold in place for curing. The carbon dioxide concentration was 15%, the reaction pressure was 0.1 MPa, the curing temperature was 70℃, the curing humidity was 80%, and the curing time was 12 hours.

[0069] Example 2

[0070] Carbonized recycled micro powder B and calcined clay A were used, with the two replacing 40% of the cement clinker. Recycled aggregate from source I replaced 30% of the natural aggregate to prepare concrete, which was then pre-cured in a carbonization reactor. The carbonization curing conditions for recycled micro powder B and low-carbon concrete, as well as the concrete mix proportions, were the same as in Example 1. The difference lay in the mix proportions of the raw materials in the low-carbon cementitious material, as detailed in Table 4.

[0071] Example 3

[0072] Carbonized recycled micro powder A and calcined clay B were used, with the two replacing 40% of the cement clinker. Recycled aggregate from source I replaced 30% of the natural aggregate to prepare concrete, which was then pre-cured in a carbonization reactor. The carbonization curing conditions for recycled micro powder A and low-carbon concrete, as well as the concrete mix proportions, were the same as in Example 1. The difference lay in the mix proportions of the raw materials in the low-carbon cementitious material, as detailed in Table 4.

[0073] Example 4

[0074] Carbonized recycled micro powder A and calcined clay A were used, with the two replacing 60% of the cement clinker. Recycled aggregate from source I replaced 30% of the natural aggregate to prepare concrete, which was then pre-cured in a carbonization reactor. The carbonization curing conditions for recycled micro powder A and low-carbon concrete, as well as the concrete mix proportions, were the same as in Example 1. The difference lay in the mix proportions of the raw materials in the low-carbon cementitious material, as detailed in Table 4.

[0075] Example 5

[0076] Carbonized recycled micro powder A and calcined clay A were used, with the two replacing 40% of the cement clinker. Recycled aggregate from source II replaced 30% of the natural aggregate to prepare concrete, which was then pre-cured in a carbonization reactor. The carbonization curing conditions for recycled micro powder A and low-carbon concrete, as well as the concrete mix proportions, were the same as in Example 1. The difference lay in the mix proportions of the raw materials in the low-carbon cementitious material, as detailed in Table 4.

[0077] Example 6

[0078] Carbonized recycled micro powder A and calcined clay A were used, with the two replacing 40% of the cement clinker. Recycled aggregate from source I replaced 30% of the natural aggregate to prepare concrete, which was then pre-cured in a carbonization reactor. The mix proportions of each raw material in recycled micro powder A and low-carbon cementitious materials, as well as the mix proportions of the concrete, were the same as in Example 1. The difference lay in the carbonization curing conditions of the recycled micro powder and the low-carbon concrete.

[0079] The carbonization conditions for the regenerated micro powder are as follows: the carbon dioxide gas is commercially available, the gas flow rate is adjusted to 0.1 L / min, the concentration of which enters the reactor is 20%, the carbonization temperature is 80℃, the reaction time is 4 h, and the mass ratio of regenerated micro powder A to solution in the first mixture is 1:20.

[0080] The curing conditions for low-carbon concrete are: carbon dioxide concentration of 25%, reaction pressure of 0.2 MPa, curing temperature of 70℃, curing humidity of 80%, and curing time of 4 hours.

[0081] Example 7

[0082] Carbonized recycled micro powder A and calcined clay A were used, with the two replacing 40% of the cement clinker. Recycled aggregate from source I replaced 30% of the natural aggregate in the concrete preparation, and pre-curing was carried out in a carbonization reactor. The mix proportions of each raw material in recycled micro powder A and low-carbon cementitious materials, the concrete mix proportions, and the carbonization curing conditions for both the recycled micro powder and the low-carbon concrete were the same as in Example 1. The difference lay in the selection of solution I and the soluble alkaline solution during the preparation of the recycled micro powder.

[0083] In the first mixture, the mass ratio of regenerated micropowder A to the solution is 1:20. The specific preparation process of solution I is as follows: a mixed solution of triethanolamine and sodium ethylenediaminetetraacetate with a mass fraction of 0.2% is prepared in deionized water at a mass ratio of 1:1. Then, soluble calcium aluminate is added to adjust its molar concentration to 1 mol / L, and calcium carbonate seed crystals with a purity of 90%, a particle size of 0.8 mm, and a length of 20 mm are added, with a mass of 0.02% of the regenerated micropowder mass. After the carbonization reaction is complete, 5 mol / L potassium hydroxide is added to the second mixture, and the mixture is stirred at 40°C for 1 hour. The solid-liquid mixture is then separated using a filtration device, and the solid material is repeatedly washed with deionized water. Finally, the solid material is dried in a vacuum oven at 45±5°C for 48 hours to obtain the carbonized regenerated micropowder.

[0084] The curing conditions for low-carbon concrete are: carbon dioxide concentration of 15%, reaction pressure of 0.1 MPa, curing temperature of 70℃, curing humidity of 80%, and curing time of 12 hours.

[0085] Example 8

[0086] Carbonized recycled micro powder A and calcined clay A were used, with the two replacing 30% of the cement clinker. Recycled aggregate from source I replaced 25% of the natural aggregate in the concrete preparation, and pre-curing was carried out in a carbonization reactor. The mix proportions of each raw material in the low-carbon concrete and low-carbon cementitious materials are detailed in Tables 3 and 4, respectively. The mass ratio of water-reducing agent to defoamer in the admixtures was 10:1. The carbonization curing conditions for both the recycled micro powder and the low-carbon concrete were the same as in Example 1.

[0087] Comparative Example 1

[0088] Concrete was prepared using silicate cement and natural coarse and fine aggregates, following the molding methods and standard curing conditions for ordinary concrete. The curing conditions were 20±2℃ and a relative humidity of not less than 95%. The properties of the raw materials are shown in Tables 1 and 2, and the specific mix proportions are shown in Table 3. The water-cement ratio was 0.4, the sand ratio was 0.36, and only water-reducing agents were used as admixtures.

[0089] Comparative Example 2

[0090] Recycled micro powder A was blended with silicate cement at a mass ratio of 3:7. 30% of the natural aggregate was replaced with recycled aggregate from source I. The concrete was prepared according to the molding method and curing conditions of ordinary concrete. The properties of the raw materials are shown in Tables 1 and 2, and the specific mix proportions are shown in Table 3. The water-cement ratio was 0.4, the sand ratio was 0.36, and the mass ratio of water-reducing agent to air-entraining agent in the admixtures was 10:1.

[0091] Comparative Example 3

[0092] Low-carbon composite cementitious material was prepared by using carbonized recycled micro powder A, calcined clay A, cement clinker and gypsum in the proportions shown in Table 4. Natural coarse aggregate and natural fine aggregate were used entirely. Concrete was prepared according to the molding method and curing conditions of ordinary concrete. The properties of the raw materials are shown in Tables 1 and 2, and the specific mix proportions are shown in Table 3. The water-cement ratio was 0.4, the sand ratio was 0.36, and the mass ratio of water-reducing agent and air-entraining agent in the admixtures was 10:1.

[0093] Comparative Example 4

[0094] Low-carbon composite cementitious material was prepared by using carbonized recycled micro powder A, calcined clay A, cement clinker and gypsum in the proportions shown in Table 4. 30% of the natural aggregate was replaced with recycled aggregate from source I. Concrete was prepared according to the molding method and curing conditions of ordinary concrete. The properties of the raw materials are shown in Tables 1 and 2, and the specific mix proportions are shown in Table 3. The water-cement ratio was 0.4, the sand ratio was 0.36, and the mass ratio of water-reducing agent and air-entraining agent in the admixtures was 10:1.

[0095] Comparative Example 5

[0096] Uncarbonized recycled micro powder A, calcined clay A, cement clinker, and gypsum were compounded according to the proportions in Table 4. The total mass ratio of recycled micro powder and calcined clay to cement clinker was 3:7. 25% of the natural aggregate was replaced with recycled aggregate from source I. Concrete was prepared according to the molding method and curing conditions of ordinary concrete. The properties of the raw materials are shown in Tables 1 and 2, and the specific mix proportions are shown in Table 3. The water-cement ratio was 0.45, the sand ratio was 0.37, and the mass ratio of water-reducing agent to defoamer in the admixtures was 10:1.

[0097] Table 5 Performance of Solid Waste-Based Low-Carbon Concrete

[0098]

[0099] According to Table 5, Comparative Example 1 had the highest slump, and also the highest compressive strength at 3 days and 28 days. Comparative Example 2 used uncarbonized recycled micro-powder A and recycled aggregate with a 30% replacement rate. Comparative Example 3 used a low-carbon composite cementitious material made from a mixture of carbonized recycled micro-powder, calcined clay, and cement clinker. The aggregate consisted entirely of natural coarse and fine aggregates, and conventional curing methods were used. The compressive strength at 3 days and 28 days were 85.6% and 91.4% of that of Comparative Example 1, respectively. Comparative Example 4 used the same low-carbon composite cementitious material as Comparative Example 3, and the same proportions of recycled coarse and fine aggregates as Comparative Example 2 to replace natural aggregates. After conventional curing, the concrete strength was lower than that of Comparative Example 3, indicating that the strength of the concrete decreased after the recycled aggregates replaced the natural aggregates, but was slightly higher than that of Comparative Example 2. This suggests that carbonation curing of the recycled micropowder promoted the conversion of some hydration products into calcium carbonate, forming a more dense hydration product. At the same time, the calcium carbonate reacted further with the active Al2O3 in the calcined clay to form calcium carbonate-aluminum-silica hydrate, which has a higher strength than the hydrated alumina hydrate without calcium carbonate. Comparative Example 5 had a water-to-cement mass ratio (water-cement ratio) of 0.45, higher than the other comparative examples. It used uncarbonized recycled micropowder A and recycled aggregates with a 25% replacement rate. Although clay was added and conventional curing was used, the overall strength was lower than that of Comparative Example 2.

[0100] Example 1, based on Comparative Example 3, involves carbonation curing of concrete. The 3-day and 28-day strengths of the concrete increased by 7.7% and 9.3% respectively compared to Comparative Example 1. This indicates that carbonation curing further promotes the formation of denser hydration products in low-carbon cementitious materials and also enhances the interfacial transition zone of recycled aggregates.

[0101] The CaO content in the recycled micro-powder used in Example 2 was lower than that in Example 1. Under the same carbonization conditions and curing regime, the strength of its low-carbon concrete was lower than that of Example 1. This is because the composition of the hydration products of the low-carbon composite cementitious material depends on the molar ratio of CaCO3 in the recycled micro-powder to Al2O3 in the calcined clay. When the molar ratio is 1:1, a full reaction can be achieved, generating hydrated mono-aluminate or hydrated hemi-aluminate with higher density, thus refining the pore structure and increasing the content of hydration products, thereby promoting the improvement of the strength of the cement-based material. When the CaCO3 content is low, excessive Al2O3 reacts with gypsum to form ettringite, which has a slightly lower strength. Conversely, if the Al2O3 content in the calcined clay is low, excessive CaCO3 can only play a filling effect due to its fine particle characteristics, contributing little to the strength. A comparison of the test results of Example 3 and Example 1 shows that the Al2O3 content of the calcined clay used in Example 3 is lower than that in Example 1, which leads to its slightly lower strength.

[0102] In Example 4, the proportion of carbonized recycled micro powder and calcined clay replacing cement clinker reached 60%. Other conditions were the same as in Example 1. The compressive strength at 3 days and 28 days decreased by 16.9% and 11.9%, respectively. This indicates that the low-carbon composite cementitious material proposed in this patent does not completely replace silicate cement to obtain cement concrete of the same strength grade. However, it can be confirmed that this system can be used to formulate cement concrete and its products with slightly lower strength grades, which greatly reduces the energy consumption and carbon emissions of cement production.

[0103] In Example 5, recycled aggregates from a different source than those in Example 1 were used. The resulting virgin concrete had lower strength, slightly higher water absorption and crushing index, and slightly lower apparent density. In other words, the quality of recycled aggregate II was inferior to that of recycled aggregate I. Using the same formulation, the low-carbon concrete obtained in Example 5 had lower strength than that in Example 1. This confirms the influence of recycled aggregate quality on the performance of low-carbon concrete. The difference in recycled aggregate quality mainly stems from the hardened cement paste adhering to its surface. The carbonation curing method proposed in this patent further enhances the quality of recycled aggregates to obtain reinforced low-carbon concrete, achieving efficient utilization of all components of waste concrete or waste mortar.

[0104] In Example 6, the same raw materials as in Example 1, such as recycled micro powder, clay, and recycled aggregate, were used. However, the carbonization and curing conditions were different. In particular, during the carbon mineralization process of the recycled micro powder, the carbon dioxide concentration was increased and the reaction time was prolonged. During the carbonization process of the low-carbon concrete, the carbon dioxide concentration and reaction pressure were increased, resulting in the final low-carbon concrete having a higher strength than the low-carbon concrete in Example 1.

[0105] In Example 7, the same raw materials as in Example 1, such as recycled micro powder, clay, and recycled aggregate, were used, and the carbonation curing conditions were the same. However, the solutions used were different. In particular, solution I used calcium carbonate seed crystals with higher purity and smaller particle size, which played a better role in the nucleation effect, promoted the formation of more calcium carbonate products during the carbonation process of the recycled micro powder, and further improved the strength of the low-carbon concrete.

[0106] In Example 8, the water-to-cement ratio (water-cement ratio) was increased compared to other examples, resulting in lower strength. The same recycled powder, clay, and recycled aggregate as Comparative Example 5 were used, but the recycled powder was carbonized and the prepared concrete was carbonized and cured, thereby increasing the strength of the recycled concrete.

Claims

1. A carbon mineralization-reinforced solid waste-based low-carbon concrete, characterized in that, It is prepared by mixing low-carbon composite cementitious material with coarse aggregate, fine aggregate, water, and admixtures according to the following proportions, and the weight parts of each component are as follows: 270-450 parts of low-carbon composite cementitious material 650-850 parts fine aggregate, 800-1250 parts coarse aggregate 130-200 parts water 2-20 parts of admixture; The low-carbon composite cementitious material is obtained by uniformly mixing the above-mentioned carbon mineralized recycled micro powder with calcined clay, cement clinker and gypsum. The mass ratio of carbon mineralized recycled micro powder to calcined clay is (1~2.5):1, the mass of cement clinker accounts for 25%~60% of the mass of low-carbon composite cementitious material, and the mass of gypsum accounts for 0%~5% of the mass of low-carbon composite cementitious material; The coarse aggregate is gravel, including natural coarse aggregate from natural mines and riverbeds, as well as recycled coarse aggregate obtained after crushing and screening waste concrete, wherein the recycled coarse aggregate accounts for 20% to 60% of the total mass of coarse aggregate; The fine aggregate is sand, including natural fine aggregate from natural mines and riverbeds, as well as recycled fine aggregate obtained after crushing and screening waste concrete, wherein the recycled fine aggregate accounts for 10% to 40% of the total fine aggregate mass; The method for preparing the carbon mineralization regenerated micro powder includes: (1) Mix the regenerated micro powder and solution I to obtain the first mixture; The mass ratio of the regenerated micro powder to solution I is 1:(5~50); The recycled micro powder is made from waste concrete and waste mortar generated during the demolition of old buildings and the production process of commercial concrete mixing plants. The powder has a particle size of less than 0.075 mm after crushing, grinding and screening. Solution I is a mixed aqueous solution of surfactant, calcium ion complexing agent and calcium carbonate seed crystals; (2) In step (1), carbon dioxide gas is introduced into the first mixture and heated to carry out a carbonization reaction to obtain a second mixture; In step (2), the carbon dioxide concentration is not less than 5%, the carbonization reaction temperature is 40~120℃, and the reaction time is 0.5~24h; (3) After mixing the second mixture in step (2) with a soluble alkaline solution for a period of time, solid product and by-product solution are obtained after solid-liquid separation. Then, the solid product is further subjected to vacuum drying to obtain the carbon mineralization regenerated micro powder.

2. The carbon mineralization-reinforced solid waste-based low-carbon concrete according to claim 1, characterized in that, The surfactant mentioned in step (1) is selected from any one or a mixture of soluble phosphates and soluble aluminum salts, and the molar concentration of the surfactant in solution I is 0.01 mol / L to 10 mol / L; The calcium ion complexing agent is selected from any one or a mixture of more than one of sodium ethylenediaminetetraacetate, polyvinyl alcohol, and triethanolamine, and the mass fraction of the calcium ion complexing agent in solution I is 0.01% to 2%. The calcium carbonate seed crystals have a purity greater than 70%, a particle size of 0.5~1.5mm, and a length of 20~40mm. The calcium carbonate seed crystals are 0.01%~0.5% of the mass of the regenerated micro powder. In step (1), the waste concrete and waste mortar are mainly composed of limestone, and also contain a small amount of hydration products CSH, CH, AFt and unhydrated minerals C2S, C3S and C4AF.

3. A carbon mineralization-reinforced solid waste-based low-carbon concrete according to claim 1 or 2, characterized in that, In step (2), the carbon dioxide gas is an industrial exhaust gas or commercial gas with a concentration of not less than 5%. The industrial exhaust gas comes from the exhaust gas of the steel industry, cement industry, power industry, chemical industry or any combination thereof.

4. A carbon mineralization-reinforced solid waste-based low-carbon concrete according to claim 1 or 2, characterized in that, In step (3), the molar concentration of the soluble alkali is 0.5 mol / L to 10 mol / L, and the mass ratio of the alkali to the second mixture is 5:1 to 20:

1. The mixing temperature in step (3) is 20~100℃ and the mixing time is 0.5~24h.

5. The carbon mineralization-reinforced solid waste-based low-carbon concrete according to claim 4, characterized in that, In step (3), the soluble base is selected from any one or a mixture of more than one of KOH, LiOH, and NaOH; the by-product solution obtained in step (3) is a silicate, aluminate, or aluminosilicate solution.

6. The carbon mineralization-reinforced solid waste-based low-carbon concrete according to claim 1, characterized in that, In step (3), the vacuum drying temperature is 45±5℃ and the drying time is 24~48h.

7. The carbon mineralization-reinforced solid waste-based low-carbon concrete according to claim 1, characterized in that, The calcined clay is obtained by calcining clay whose main component is kaolin or metakaolin at 600~950℃, and then grinding and sieving it. The gypsum is dihydrate gypsum; The cement clinker is selected from either silicate cement clinker or sulfoaluminate cement clinker. The admixture is selected from any one or more of the following: high-performance water-reducing agents, air-entraining agents, and defoamers, which are used to adjust the workability of fresh concrete.

8. A method for preparing carbon mineralization-reinforced solid waste-based low-carbon concrete according to any one of claims 1 to 7, characterized in that, include: (1) The above-mentioned carbon mineralized recycled micro powder, calcined clay, cement clinker and gypsum are mixed evenly in proportion to obtain a low-carbon composite cementitious material. (2) The low-carbon composite cementitious material described in step (1) is mixed with sand, stone aggregate, water and admixture according to the mixing ratio, and then placed together with the mold in a carbonization reactor for carbon dioxide pre-curing to obtain the solid waste-based low-carbon concrete.

9. The method for preparing carbon mineralization-reinforced solid waste-based low-carbon concrete according to claim 8, characterized in that, The carbon dioxide curing conditions in step (2) are as follows: the carbonization reactor is a high-pressure carbonization reactor, the carbon dioxide concentration is not less than 10%, the curing temperature is 40~100℃, the curing relative humidity is 70%~95%, the curing pressure is ≥0.1MPa, and the curing time is 10~48h.

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