Biochar concrete and preparation method thereof

Abstract

The invention provides charcoal concrete and a preparation method thereof, and relates to the technical field of building materials. The biochar concrete comprises the following raw materials: cement, coal ash, coarse aggregate, fine aggregate, an additive and water, wherein the cement contains 1-10wt% of biochar. According to the method, tobacco leaves and wood are treated in a pyrolysis carbonization mode, and compared with a traditional method for preparing biochar through combustion, greenhouse gas is not additionally discharged outwards in the production process of the technology; the prepared biochar is an efficient carbon sequestration material, the biochar concrete is prepared by adding the biochar into a cement material, and the biochar concrete is applied to constructional engineering, so that carbon neutralization in the construction industry can be realized in an assisted manner. A certain amount of biochar is loaded in the biochar concrete, and experiments show that the biochar concrete can improve the compressive strength of the concrete and has a certain early strength effect on the concrete.

Description

Technical Field

[0001] The present application relates to the technical field of building materials, and in particular to a biochar concrete and a preparation method thereof. Background Art

[0002] The construction sector is one of the main areas of energy consumption and carbon emissions in my country. As the urbanization rate and residents' living standards continue to increase, my country's energy consumption and carbon dioxide emissions in the construction sector will maintain rigid growth. In the context of "dual carbon", the construction industry is under tremendous pressure to reduce carbon emissions.

[0003] The carbon trading mechanism allocates emission reduction targets to each member country, which is then allocated to each enterprise by each member country according to the national allocation plan. If an enterprise achieves the requirements of reducing carbon dioxide emissions through technological upgrades and transformations, it can sell the unused emission rights to other enterprises that have not yet achieved their emission reduction targets. The carbon trading mechanism is a trading market based on greenhouse gas emission reductions, which uses emission rights as a commodity. It helps to use market mechanisms to allocate resources more effectively and control greenhouse gas emissions.

[0004] Negative carbon technology generally refers to the technology of capturing, utilizing and storing carbon dioxide. There are two main ways to achieve carbon removal: one is based on nature, that is, using biological processes to increase carbon removal and store it in forests, soil or wetlands; the other is through technical means, that is, directly removing carbon from the air or inhibiting the natural carbon removal process to accelerate carbon storage.

[0005] However, there are relatively few applications of removing carbon from the air or inhibiting natural carbon removal in the field of building materials. How to store carbon in building materials while ensuring or improving material performance and achieving carbon sequestration and carbon trading is an urgent problem to be solved by technicians in this field. Summary of the invention

[0006] The purpose of this application is to provide a biochar concrete and a preparation method thereof, wherein the biochar concrete can be used for carbon neutrality in the construction industry, and the biochar loaded therein can improve the compressive strength of the concrete and enhance the early strength effect.

[0007] The purpose of this application is achieved through the following technical solutions:

[0008] In one aspect, the present application provides a biochar concrete, wherein the raw materials of the biochar concrete include cement, fly ash, coarse aggregate, fine aggregate, admixture and water, and the cement contains 1-10 wt% of biochar. .

[0009] In another aspect, the present application provides a method for preparing biochar concrete, comprising the following steps:

[0010] S1, drying, pyrolyzing, cooling and crushing the carbon raw material to obtain biochar;

[0011] S2. Add the biochar into cement in proportion, then add fly ash, coarse aggregate, fine aggregate and water, then add admixtures, stir evenly to form, and finally cure to obtain biochar concrete.

[0012] Beneficial effects of this application:

[0013] 1. This application uses pyrolysis carbonization to process tobacco leaves and wood. Compared with the traditional combustion method to prepare biochar, the process of this application does not emit additional greenhouse gases during the production process; the prepared biochar is a highly efficient carbon-fixing material. Adding it to cement materials to prepare a biochar concrete, and applying it to construction projects, can help achieve "carbon neutrality" in the construction industry.

[0014] 2. The biochar concrete of this application is loaded with a certain amount of biochar. Experiments have shown that it improves the compressive strength of concrete and can play a certain role in early strengthening of concrete.

[0015] The aforementioned main scheme of the present application and its further options can be freely combined to form multiple schemes, all of which are schemes that can be adopted and claimed for protection in the present application; and in the present application, (non-conflicting options) can also be freely combined with each other and with other options. After understanding the scheme of the present application, those skilled in the art can understand that there are many combinations based on the prior art and common knowledge, all of which are technical schemes to be protected by the present application, and they are not exhaustively listed here. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a flow chart of the biochar production process of Example 2 of the present application. DETAILED DESCRIPTION

[0017] The following non-limiting examples are provided to illustrate the present application.

[0018] A biochar concrete, the raw materials of which include cement, fly ash, coarse aggregate, fine aggregate, admixture and water, wherein the cement contains 1-10wt% of biochar.

[0019] In some embodiments of the present application, the water-cement ratio of the above-mentioned biochar concrete is 0.52; each cubic meter of the above-mentioned biochar concrete contains 250kg of cement, 80kg of fly ash, 1000kg of coarse aggregate, 893kg of fine aggregate, and 170-170kg of water; the addition amount of the above-mentioned admixture is 2.1% of the total amount of other raw materials.

[0020] In some embodiments of the present application, the cement is silicate cement, the molar ratio of hydrogen content to organic carbon content in the biochar is H / Corg < 0.7, and the molar ratio of oxygen content to organic carbon content is O / Corg ≤ 0.3.

[0021] In some embodiments of the present application, the above-mentioned coarse aggregate is crushed stone with a particle size of less than 31.5 mm and a moisture content of less than 0.2%.

[0022] In some embodiments of the present application, the fine aggregate is coarse sand and medium sand, the mass ratio of the coarse sand and medium sand is 2:1, and the moisture content of the fine aggregate is less than 0.5%.

[0023] A method for preparing biochar concrete comprises the following steps:

[0024] S1, drying, pyrolyzing, cooling and crushing the carbon raw material to obtain biochar;

[0025] S2. Add the biochar into cement in proportion, then add fly ash, coarse aggregate, fine aggregate and water, then add admixtures, stir evenly to form, and finally cure to obtain biochar concrete.

[0026] In some embodiments of the present application, the charcoal raw materials in the above step S1 include wood and tobacco leaves.

[0027] In some embodiments of the present application, the drying temperature in the above-mentioned S1 step is 150-200°C, and the drying is carried out to a moisture content of ≤20%; the pyrolysis comprises drying, pre-carbonization, carbonization and combustion steps in sequence; wherein the drying temperature is 100-160°C, and the drying time is 80-100min; the pre-carbonization temperature is 160-280°C, and the pre-carbonization time is 120-180min; the carbonization temperature is 280-450°C, and the carbonization time is 180-240min; the combustion temperature is 450-1000°C, and the combustion time is 60-80min.

[0028] In some embodiments of the present application, the biochar after crushing in the above step S1 is passed through an 80-mesh sieve, where the mesh refers to the number of sieve holes in a length of 2.54 cm (1 inch) in the Taylor standard sieve, and is referred to as mesh for short. The aperture of the 80-mesh sieve is 0.18 mm, i.e., 180 microns. Before crushing, the biochar needs to be dried to a constant weight at a drying temperature of 30-50°C.

[0029] In some embodiments of the present application, the curing temperature in the above step S2 is 18-22° C., and the relative humidity of the curing environment is >95%.

[0030] Traditional biochar is charcoal with extremely rich carbon content, which refers to a type of refractory, stable, highly aromatic, carbon-rich solid material produced by high-temperature slow pyrolysis (usually <700°C, the target product is charcoal) in the absence of oxygen, so it is generally used as fuel. The biochar of the present application is produced by high-temperature pyrolysis (>700°C) in a non-anaerobic environment. It is a porous material with high specific surface area and high adsorption properties, so it has better carbon collection and storage effects.

[0031] The principle of adding biochar to cement to improve compressive strength and early strength (i.e. accelerate early strength development) can be mainly attributed to the following aspects:

[0032] 1. Increase of hydration products

[0033] The addition of biochar will cause cement to form more hydration products, especially Ca(OH)2, which indicates that the hydration reaction is more complete, thereby increasing the hydration degree of cement. The increase in hydration products helps to form a denser and stronger cement stone structure, thereby improving the compressive strength of concrete.

[0034] 2. Improvement of microstructure

[0035] Biochar has a porous structure and a large specific surface area. These characteristics enable biochar to be filled into the cement matrix as micro-aggregate, reducing porosity and improving the density of the material. At the same time, the oxygen-containing functional groups on the surface of biochar can adsorb free water produced during cement hydration, promote the crystallization and growth of hydration products, and thus optimize the microstructure of concrete. This improvement in microstructure is an important factor in improving compressive strength.

[0036] 3. Promotion of carbonization reaction

[0037] The addition of biochar can also promote the carbonation reaction of concrete. Carbonation is the process in which calcium hydroxide (Ca(OH)2) in concrete reacts with carbon dioxide to form calcium carbonate (CaCO3). The formation of calcium carbonate can fill the pores inside the concrete, improving the density and strength of the concrete. The porous structure and adsorption capacity of biochar provide channels and space for the adsorption of carbon dioxide, promote the carbonation reaction, and thus improve the compressive strength of concrete.

[0038] 4. Accelerated development of early strength

[0039] The addition of biochar can also accelerate the early strength development of cement. On the one hand, the porous structure of biochar can absorb the free water produced during the cement hydration process, making the hydration reaction between cement particles more rapid and sufficient; on the other hand, the filling effect of biochar can reduce the pores and defects in the cement matrix, making the cement stone structure more dense and stable. These two effects jointly promote the early strength development of cement.

[0040] The features and performance of the present application are further described in detail below in conjunction with the embodiments.

[0041] Example 1

[0042] This embodiment provides a concrete, which is prepared by the following method:

[0043] 173g of water, 250g of cement, 40g of Class I fly ash, 40g of Class II fly ash, 300g of medium sand, 593g of coarse sand, 1000g of crushed stone, and 2.1% of water reducing agent were added, stirred and mixed evenly, and made into 100mm×100mm×100mm cubic concrete blocks, and then cured under standard conditions of temperature of 18-22℃ and relative humidity of environment>95%, and the compressive strength of the concrete blocks was tested at 7 days, 28 days and 60 days of curing. The compressive strength test adopts the national standard method.

[0044] Example 2

[0045] This embodiment provides a biochar concrete, and its preparation method is basically the same as that of Example 1, except that 2.5 g of tobacco biochar is used instead of 2.5 g of cement in this embodiment.

[0046] The preparation method of tobacco biochar is as follows: before the carbonization process, the tobacco waste is dried at a low temperature of 150-200°C, and the moisture content of the tobacco waste after drying is ≤20%; at the same time, impurities are separated to meet production needs. Drying is the first stage of the carbonization process. The semi-finished biochar is gradually dried at a temperature of 100-160°C in the carbonization kiln for 80 minutes. White water vapor is generated in the carbonization kiln, and low molecular volatiles are gradually decomposed. Next, in the pre-carbonization stage, the temperature is controlled within the range of 160-280°C for 150 minutes. At this stage, the bonds of organic macromolecules are broken, and the unstable component hemicellulose begins to decompose. In the carbonization stage, the temperature is controlled at 280-450°C for 200 minutes, and cellulose, lignin, etc. begin to decompose violently, and the emitted substances include wood tar, carbon monoxide, methane and other gases. In the combustion stage, the temperature is controlled at 700-1000℃, the combustion time is 80min, the pyrolysis process is basically completed, and basically no gas is generated. The main discharge is the volatile matter remaining on the surface of the charcoal, increasing the fixed carbon content. The output of the pyrolysis combustion process is only biochar, and the pyrolysis gas is reused during the pyrolysis and burning process. After the charcoal is discharged, it enters the cooling furnace to cool the product, and finally it is packaged, and the dust is treated by the filter cartridge dust removal method. The process flow chart is as follows Figure 1 shown.

[0047] The tobacco biochar in this embodiment needs to be dried at 40° C. to a constant weight before preparing the biochar concrete, and then ground through an 80-mesh sieve.

[0048] Example 3

[0049] This embodiment provides a biochar concrete, and its preparation method is basically the same as that of Example 2, except that 12.5 g of tobacco biochar is used instead of 12.5 g of cement in this embodiment.

[0050] Example 4

[0051] This embodiment provides a biochar concrete, and its preparation method is basically the same as that of Example 2, except that 25g of tobacco biochar is used instead of 25g of cement in this embodiment.

[0052] Example 5

[0053] This embodiment provides a biochar concrete, and its preparation method is basically the same as that of Example 2, except that 2.5 g of wood biochar is used instead of 2.5 g of cement in this embodiment.

[0054] The preparation method of wood biochar is as follows: before the carbonization process, the wood waste is dried at a low temperature of 150-200°C, and the moisture content of the wood waste after drying is ≤20%; at the same time, impurities are separated to meet production needs. Drying is the first stage of the carbonization process. The semi-finished biochar is gradually dried at a temperature of 100-160°C in the carbonization kiln for 80 minutes. White water vapor is generated in the carbonization kiln, and low molecular volatiles are gradually decomposed. Next, in the pre-carbonization stage, the temperature is controlled within the range of 160-280°C for 150 minutes. At this stage, the bonds of organic macromolecules are broken, and the unstable component hemicellulose begins to decompose. In the carbonization stage, the temperature is controlled at 280-450°C for 200 minutes, and cellulose, lignin, etc. begin to decompose violently, and the emitted substances include wood tar, carbon monoxide, methane and other gases. In the combustion stage, the temperature is controlled at 750-1000℃, the combustion time is 80min, the pyrolysis process is basically completed, and basically no gas is generated. The main volatile matter remaining on the surface of the charcoal is discharged to increase the fixed carbon content. The output of the pyrolysis combustion process is only biochar, and the pyrolysis gas is reused during the pyrolysis and burning process. After the charcoal is discharged, it enters the cooling furnace to cool the product, and finally it is packaged, and the dust is treated by filter cartridge dust removal.

[0055] Example 6

[0056] This embodiment provides a biochar concrete, and its preparation method is basically the same as that of Example 5, except that 7.5 g of wood biochar is used instead of 7.5 g of cement in this embodiment.

[0057] Example 7

[0058] This embodiment provides a biochar concrete, and its preparation method is basically the same as that of Example 5, except that in this embodiment, 12.5 g of wood biochar is used instead of 12.5 g of cement.

[0059] Example 8

[0060] This embodiment provides a biochar concrete, and its preparation method is basically the same as that of Example 5, except that in this embodiment, 25g of wood biochar is used instead of 25g of cement.

[0061] The compressive strength of Examples 1-8 of the present application at different curing times is shown in Table 1.

[0062] Table 1

[0063]

[0064] The percentage in brackets represents the percentage of the benchmark strength required by the GB175-2023 "General Portland Cement" standard; through the comparative results analysis of Examples 1-8 in Table 1, it can be seen that adding 1% tobacco biochar has a certain effect on improving the compressive strength of concrete materials.

[0065] Moreover, the compressive strength of the concrete after adding 1% tobacco biochar at 7 days, 28 days and 60 days increased by 11.4%, 7% and 6.7% respectively compared with the baseline group, indicating that the addition of biochar enables the concrete material to exhibit some early strength properties.

[0066] The aforementioned basic examples and their further selected examples can be freely combined to form multiple embodiments, all of which are embodiments that can be adopted and claimed for protection in this application. In the scheme of this application, each selected example can be arbitrarily combined with any other basic examples and selected examples.

[0067] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A biochar concrete, characterized in that: The raw materials of the biochar concrete include cement, fly ash, coarse aggregate, fine aggregate, admixture and water, and the cement contains 1-10wt% of biochar.

2. The biochar concrete according to claim 1, characterized in that: The water-cement ratio of the biochar concrete is 0.52; each cubic meter of the biochar concrete contains 250kg of cement, 80kg of fly ash, 1000kg of coarse aggregate, 893kg of fine aggregate, and 170-170kg of water; the amount of the admixture added is 2.1% of the total amount of other raw materials.

3. The biochar concrete according to claim 1, characterized in that: The cement is silicate cement, the molar ratio of hydrogen content to organic carbon content in the biochar is H / Corg<0.7, and the molar ratio of oxygen content to organic carbon content is O / Corg≤0.

3.

4. The biochar concrete according to claim 1, characterized in that: The coarse aggregate is crushed stone with a particle size of less than 31.5 mm and a moisture content of less than 0.2%.

5. The biochar concrete according to claim 1, characterized in that: The fine aggregate is coarse sand and medium sand, the mass ratio of the coarse sand and medium sand is 2:1, and the moisture content of the fine aggregate is less than 0.5%.

6. A method for preparing biochar concrete according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1, drying, pyrolyzing, cooling and crushing the carbon raw material to obtain biochar; S2. Add the biochar into cement in proportion, then add fly ash, coarse aggregate, fine aggregate and water, then add admixtures, stir evenly to form, and finally cure to obtain biochar concrete.

7. The method for preparing biochar concrete according to claim 6, characterized in that: The charcoal raw materials in step S1 include wood and tobacco leaves.

8. The method for preparing biochar concrete according to claim 7, characterized in that: The drying temperature in the S1 step is 150-200°C, and the drying is performed until the moisture content is ≤20%; the pyrolysis comprises drying, pre-carbonization, carbonization and combustion steps in sequence; wherein the drying temperature is 100-160°C, and the drying time is 80-100min; the pre-carbonization temperature is 160-280°C, and the pre-carbonization time is 120-180min; the carbonization temperature is 280-450°C, and the carbonization time is 180-240min; the combustion temperature is 450-1000°C, and the combustion time is 60-80min.

9. The method for preparing biochar concrete according to claim 6, characterized in that: The biochar after crushing in the step S1 is passed through an 80-mesh sieve. Before crushing, the biochar is dried to a constant weight at a drying temperature of 30-50°C.

10. The method for preparing biochar concrete according to claim 6, characterized in that: The curing temperature in step S2 is 18-22° C., and the relative humidity of the curing environment is >95%.

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