A modified biochar-based carbon-fixing cementitious material and its preparation method

Abstract

The present invention discloses a modified biochar-based carbon-fixing cementitious material. The raw materials and their mass percentages are as follows: 50-80% of a modified biochar / fly ash composite material and 20-50% of cement. Among them, in the modified biochar / fly ash composite material, the components and their mass percentages are: 28-45% of modified biochar, 45-62% of high-calcium fly ash, and 6-20% of amino silane. The present invention gives full play to the balanced and synergistic effects of biochar, high-calcium fly ash, and amino silane, can realize the high-value utilization of large dosages of biochar and high-calcium fly ash in construction engineering, effectively reduce the cement dosage, and can effectively solidify carbon dioxide in the air; it has significant economic and environmental benefits and is suitable for popularization and application.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and particularly relates to a modified biochar-based carbon sequestration cementitious material and a preparation method thereof. Background Art

[0002] As the most widely used building material in structural engineering, cement-based concrete has the advantages of excellent strength, abundant raw materials, and suitable price. However, its adverse impact on the environment is also very prominent. To alleviate the carbon emission pressure caused by cement production and promote the green production innovation of the concrete industry, it is urgent to use other green materials to partially or even completely replace cement for concrete production.

[0003] Biochar is a porous material formed by biomass, municipal waste, and other organic materials through gasification, pyrolysis and other processes in an oxygen-limited environment. It has a high specific surface area, high porosity, and high affinity for non-polar compounds. Compared with commonly used cement replacement materials such as fly ash and slag powder, using biochar to replace part of the cement can not only reduce the environmental pressure caused by cement, but also has good adsorption for carbon dioxide in the air and has extremely high carbon sequestration potential. It is an ideal green raw material. At present, biochar has been proven to be used as a admixture or modifier to refine the pore structure of cement-based materials, thereby improving their comprehensive performance. However, the content of active components in biochar itself is low, and the porosity is relatively high. Using it to replace cement will lead to problems such as reduced mechanical properties and durability of concrete. Therefore, the current suitable dosage in concrete is very low, and it is impossible to achieve large-scale application in construction projects.

[0004] High-calcium fly ash has higher pozzolanic activity compared with the fly ash commonly used in current concrete production, which is beneficial to promoting the hydration of the cementitious system, increasing the content of hydration products, and can be used to improve the adverse effects of biochar on the performance of concrete. However, there is more free calcium oxide in high-calcium fly ash, which is easy to cause concrete cracking, resulting in serious safety accidents and significant economic losses, restricting its large-scale application in concrete. Summary of the Invention

[0005] The main purpose of the present invention is to provide a modified biochar-based carbon sequestration cementitious material in view of the application problems and deficiencies of existing biochar and high-calcium fly ash in the field of concrete, effectively promoting the wide application of biochar and high-calcium fly ash in cementitious materials, reducing the cement consumption, and reducing the carbon emissions of the concrete industry.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A modified biochar-based carbon-fixing cementitious material, the raw materials and their mass percentages include: 50-80% of modified biochar / fly ash composite, 20-50% of cement; among them, in the modified biochar / fly ash composite, the components and their mass percentages include: 28-45% of modified biochar, 45-62% of high-calcium fly ash, and 6-20% of amino silane.

[0008] In the above scheme, the modified biochar is obtained by impregnating biochar in an alkaline solution, followed by filtration, washing, and drying.

[0009] In the above scheme, the alkaline solution can be selected as sodium hydroxide solution, etc., with a concentration of 0.2-0.3 mol / L; the solid-liquid ratio of biochar to alkaline solution is 1 g:(1-3) mL.

[0010] In the above scheme, the impregnation treatment time is 20-30 min.

[0011] In the above scheme, the biochar is obtained by pyrolyzing biomass agricultural waste in a low-temperature anaerobic environment, and its main elements include: C 46-79 wt%, O 5-38 wt%; the specific surface area is 300-550 m 2 / kg; the pore volume is 0.01-0.3 cm 3 / g; the pore diameter is 1-35 nm.

[0012] Furthermore, the biomass agricultural waste can be selected from biomass straw such as corn, wheat, soybeans, etc.

[0013] In the above scheme, the high-calcium fly ash is fly ash with a relatively high calcium oxide content discharged from a coal-fired power plant, with a CaO content > 10%, a free calcium oxide content of 1.7-3.6%, a SiO2 content > 35%, and an Al2O3 content > 25%; the fineness is 13-18%, the loss on ignition is 2.1-3.9%, and the specific surface area is 240-410 m 2 / kg.

[0014] In the above scheme, the amino silane can be selected from one or more of silanes containing amino functional groups such as KH-550, KH-540, KH-792, APTES, etc.

[0015] In the above scheme, the cement can be selected from one or more of P·O 42.5, P·O 52.5, P·Ⅰ42.5, P·Ⅰ52.5, P·Ⅱ42.5, P·Ⅱ52.5, etc.

[0016] The preparation method of the above modified biochar-based carbon-fixing cementitious material includes the following steps:

[0017] 1) Dry the biomass agricultural waste, then pyrolyze it, cool it, grind it and screen it to obtain biochar;

[0018] 2) Add the biochar into an alkali solution for impregnation treatment, filter, wash and dry it to obtain modified biochar;

[0019] 3) Mix high-calcium fly ash with an amino-silane solution and conduct primary heating and stirring; then add the modified biochar and conduct secondary heating and stirring, filter, wash and dry it to obtain a modified biochar / fly ash composite material;

[0020] 4) Stir the modified biochar / fly ash composite material in an environment with a high carbon dioxide concentration to obtain a carbon adsorption modified biochar / fly ash composite material;

[0021] 5) Mix and stir the carbon adsorption modified biochar / fly ash composite material with cement to obtain a modified biochar-based carbon sequestration cementitious material.

[0022] In the above scheme, the drying temperature adopted in step 1) is 55 - 60 °C and the time is 10 - 12 h.

[0023] In the above scheme, the pyrolysis step in step 1) includes: heating up to 500 - 550 °C at a rate of 8 - 12 °C / min and holding for 2 - 3 h.

[0024] In the above scheme, in step 1), mechanically grind for 20 - 30 min and retain the biochar passing through a 0.1 - 0.15 mm sieve.

[0025] In the above scheme, in step 3), the amino-silane solution is formed by mixing amino-silane and water in a mass ratio of 1:(3 - 4).

[0026] In the above scheme, in step 3), the mass ratio of high-calcium fly ash to the introduced amino-silane is (2 - 10):1.

[0027] In the above scheme, the temperature of the primary heating and stirring is 40 - 50 °C, the stirring rate is 600 - 650 rpm, and the time is 2 - 3 h.

[0028] In the above scheme, in step 3), the mass ratio of high-calcium fly ash to the modified biochar is (1 - 2):1.

[0029] In the above scheme, the temperature of the secondary heating and stirring is 40 - 50 °C, the stirring rate is 600 - 650 rpm, and the time is 1 - 2 h.

[0030] In the above scheme, in step 4), the concentration of carbon dioxide is 40 - 80 vol%, and the stirring time is 2 - 3 h.

[0031] In the above solution, in step 5), the mass ratio of the modified biochar / fly ash composite to cement is (1-4):1, and the stirring time is 5-10 min.

[0032] The principle of the present invention is as follows:

[0033] The present invention gives full play to the balanced and synergistic effects of biochar, high-calcium fly ash and amino silane, realizes the large-scale high-value utilization of biochar and high-calcium fly ash in construction engineering, and comprehensively improves the performance of concrete:

[0034] 1) Aiming at the problems such as the deterioration of concrete performance caused by the low self-gelling activity and high porosity of biochar, the high pozzolanic activity of high-calcium fly ash is used to increase the content of hydration products in the gelling system, and at the same time, the contents of components such as silicon, aluminum and calcium in the gelling system are increased to enhance its reaction ability with carbon dioxide. Aiming at the problem of poor bonding between high-calcium fly ash and biochar, on the one hand, the biochar surface is impregnated with sodium hydroxide solution to increase the oxygen-containing functional groups on the biochar surface; on the other hand, by introducing organosilane, the good bonding effect of silane with the oxygen-containing functional groups on the surfaces of both biochar and high-calcium fly ash is utilized to achieve the efficient composite of biochar and high-calcium fly ash.

[0035] 2) Aiming at the problem that high-calcium fly ash reduces the carbon dioxide adsorption capacity of biochar, by introducing amino silane, on the one hand, the amino functional group is used to improve the binding ability of the gelling system with carbon dioxide, and on the other hand, the hydrophobic alkyl group is used to strengthen its adsorption effect on carbon dioxide, comprehensively improving the carbon sequestration performance of the gelling system. In addition, the formed hydration products and carbon dioxide mineralization products can directly improve the concrete strength, and can also fill the internal pores of biochar and the gelling system, improve the weak interfacial transition zone, and thus improve the mechanical properties and durability of concrete.

[0036] 3) Aiming at the problems such as the high content of free calcium oxide in high-calcium fly ash, which leads to easy cracking of concrete, biochar and amino silane are used to improve the carbon dioxide adsorption capacity of the gelling system, and promote the chemical reaction of components such as silicon, aluminum and calcium in the system with carbon dioxide. While effectively consuming the free calcium oxide in high-calcium fly ash, the formed calcium carbonate crystals can be used as hydration nucleation sites to promote the hydration of the gelling system, refine the pore structure of concrete, and enhance the matrix density.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] 1) In view of the problems that biochar leads to the reduction of concrete strength and durability, and high-calcium fly ash is prone to cause concrete cracking, the present invention first proposes to combine the characteristics of the two, utilize the strong adsorption of modified biochar to carbon dioxide, consume the free calcium oxide in high-calcium fly ash, and effectively reduce the risk of concrete cracking; utilize the pozzolanic activity of high-calcium fly ash to mitigate the adverse effects of biochar on concrete strength and durability; in addition, in view of the problems such as poor direct combination effect of the two and easy reduction of carbon dioxide adsorption capacity in simple compounding, further combine means such as sodium hydroxide impregnation and introduction of organosilicon components to synergistically improve the overall compounding effect and carbon sequestration performance, effectively play the balancing role of biochar and high-calcium fly ash, and realize the large-scale high-value utilization of the two in concrete production;

[0039] 2) On the basis of balancing the disadvantages of biochar and high-calcium fly ash, the present invention further introduces aminosilane to give full play to the synergistic effect of the three and improve the carbon sequestration performance of concrete from multiple angles, while significantly improving the mechanical properties and durability of concrete: First, based on the adsorption of carbon dioxide by biochar itself, utilize high-calcium fly ash to provide more components such as calcium, silicon, and aluminum, and at the same time play the double-strengthening effect of aminosilane on carbon dioxide adsorption and reaction, and increase the surface alkalinity and oxygen-containing functional groups of biochar through sodium hydroxide treatment, significantly enhancing the carbon dioxide curing effect of the gelling system; Second, the calcium carbonate formed by the carbon dioxide curing reaction can not only fill the internal pores of biochar and the gelling system, but also serve as a nucleation site to promote the hydration reaction of the gelling system, thus significantly improving the mechanical properties of concrete; Third, biochar plays the role of "micro-skeleton", combined with the bridging and hydrophobic effects of aminosilane, regulates the growth of hydration products of the gelling system, forms a dense gel network structure, optimizes the pore structure, and improves the overall hydrophobic performance of concrete, thereby enhancing the durability of concrete;

[0040] 3) The present invention uses biochar / modified high-calcium fly ash to replace cement, which can effectively reduce the cement dosage and can effectively solidify carbon dioxide in the air; starting from the low-carbon and carbon sequestration directions in a coordinated manner, promoting the green production innovation of the concrete industry, and having significant economic and environmental benefits. Specific embodiments

[0041] The present invention is not limited to the above embodiments. For those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as within the protection scope of the present invention. The content not described in detail in this specification belongs to the prior art well-known to those skilled in the art.

[0042] In the following examples, the biomass straw used is corn straw recycled from waste, and the C content of the biochar obtained by pyrolysis is 63%, and the O content is 24%; the specific surface area is 450m 2 / g; the pore volume is 0.17 cm 3 / g; the pore diameter is 1 - 15 nm, and the average pore diameter is about 5 nm.

[0043] The high-calcium fly ash used is the untreated high-calcium fly ash discharged from a thermal power plant in Wuhan, Hubei. Its CaO content is 17.6%, the free calcium oxide content is 2.8%, the SiO2 content is 41.2%, and the Al2O3 content is 28.5%; the specific surface area is 285 m 2 / kg.

[0044] The amino silane used is KH-550 provided by Quanzhou Sikon New Materials Co., Ltd. Its appearance is colorless and transparent liquid, and the purity is 99 wt%.

[0045] The cement used is P·O 42.5 ordinary Portland cement. Its specific surface area is 370 m 2 / kg, the initial setting time is 210 min, the final setting time is 270 min, the 3-day compressive strength is 29.6 MPa, and the 28-day compressive strength is 47.3 MPa.

[0046] Example 1

[0047] A modified biochar-based carbon sequestration cementitious material, the raw materials and their contents are: 50% of modified biochar / fly ash composite, 50% of cement; among them, the components and contents of the modified biochar / fly ash composite are: 45% of modified biochar, 45% of high-calcium fly ash, and 10% of amino silane; the specific preparation steps include:

[0048] 1) Dry the corn straw at 60 °C for 12 h, then place it in a muffle furnace, heat it to 550 °C at a heating rate of 10 °C / min, and hold it at this temperature for 2 h; after natural cooling, mechanically grind the pyrolysis product for 20 min, and retain the biochar passing through a 0.1 mm sieve;

[0049] 2) Immerse 450 g of biochar in 450 mL of sodium hydroxide solution (2 mol / L) for 12 h, filter and wash with deionized water, and then dry it to constant weight at 105 °C to obtain modified biochar;

[0050] 3) Mix 450 g of high-calcium fly ash with 500 g of amino silane solution (the mass of amino silane is 100 g), stir at a rate of 600 rpm at 40 °C for 2 h; then add 450 g of modified biochar, and continue to stir at a rate of 600 rpm at 40 °C for 1.5 h, filter and wash with deionized water, and dry it to constant weight at 105 °C to obtain the modified biochar / fly ash composite;

[0051] 4) Stir the modified biochar / fly ash composite material in an environment with a carbon dioxide concentration of 60 vol% for 2 h to obtain a carbon adsorption modified biochar / fly ash composite material;

[0052] 5) Mix 1000 g of the carbon adsorption modified biochar / fly ash composite material with 1000 g of cement and stir for 5 min to obtain a modified biochar-based carbon sequestration cementitious material.

[0053] Example 2

[0054] A modified biochar-based carbon sequestration cementitious material, the preparation method of which is substantially the same as that of Example 1, except that the components and their mass percentages are as follows: 65% of the modified biochar / fly ash composite material and 35% of cement; among them, the components and contents of the modified biochar / fly ash composite material are: 36% of biochar, 53% of high-calcium fly ash, and 11% of amino silane.

[0055] Example 3

[0056] A modified biochar-based carbon sequestration cementitious material, the preparation method of which is substantially the same as that of Example 1, except that the components and their mass percentages are as follows: 80% of the modified biochar / fly ash composite material and 20% of cement; among them, the components and contents of the modified biochar / fly ash composite material are: 29% of biochar, 59% of high-calcium fly ash, and 12% of amino silane.

[0057] Comparative Example 1

[0058] A modified biochar-based carbon sequestration cementitious material, the preparation method of which is substantially the same as that of Example 3, except that the biochar is not treated with sodium hydroxide impregnation.

[0059] Comparative Example 2

[0060] A modified biochar-based carbon sequestration cementitious material, the preparation method of which is substantially the same as that of Example 3, except that only the modified biochar, high-calcium fly ash and cement are mixed without adding amino silane.

[0061] Comparative Example 3

[0062] A modified biochar-based carbon sequestration cementitious material, the preparation method of which is substantially the same as that of Example 3, except that only the modified biochar and cement are mixed without adding high-calcium fly ash and amino silane.

[0063] Comparative Example 4

[0064] A modified biochar-based carbon sequestration cementitious material, the preparation method of which is substantially the same as that of Example 3, except that only the high-calcium fly ash and cement are mixed without adding biochar and amino silane.

[0065] The gelling materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were applied to the preparation of concrete, with the water-binder ratio taken as 0.4. The raw materials and their masses were as follows: 400 kg / m of the modified biochar-based carbon-fixing gelling material 3 , 650 kg / m of sand 3 , 1050 kg / m of stone 3 , 8 kg / m of water-reducing agent 3 , 160 kg / m of water 3 ; among them, washed sand was used, with a fineness modulus of 2.6 and an MB value of 2.0; the stone was ordinary crushed stone with a continuous gradation of 5 - 20 mm, and the crushing index was 8.2%; the water-reducing agent was a polycarboxylate-based water-reducing agent, with a solid content of 20% and a water-reducing rate of 17%.

[0066] Meanwhile, a cement-based concrete was set as the reference sample (all the gelling materials were cement), and the workability, mechanical properties, impermeability, and carbon-fixing properties were tested respectively. The results are shown in Table 1. Among them, the slump and spread of the concrete mixture were tested in accordance with GB / T 50080—2016 "Standard Test Method for Properties of Ordinary Concrete Mixtures"; the 3 / 28-day compressive strength of the concrete specimens was tested in accordance with GB / T 50081-2019 "Standard Test Method for Physical and Mechanical Properties of Concrete"; the 28-day impermeability of the concrete specimens was tested in accordance with GB / T 50082-2009 "Standard Test Method for Long-Term Performance and Durability of Ordinary Concrete"; the calcium carbonate content in the concrete at the age of 28 days was calculated using the thermogravimetric test results to evaluate the carbon-fixing properties of the concrete specimens.

[0067] Table 1 Test Results of Concrete Performance

[0068]

[0069] The above results show that the modified biochar-based carbon-fixing gelling material obtained in this invention has excellent workability, mechanical properties, impermeability, and carbon-fixing properties, can promote the large-scale resource utilization of biochar and low-quality high-calcium fly ash, and can significantly reduce the carbon emissions in the concrete industry.

[0070] Obviously, the above examples are only for clearly illustrating the examples and not for limiting the implementation methods. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. And the obvious changes or variations thus derived are still within the protection scope of this invention.

Claims

1. A modified biochar-based carbon-fixing cementitious material, characterized in that: The raw materials and their weight percentages include: 50-80% of modified biochar / fly ash composite material and 20-50% of cement; wherein, the components and their weight percentages in the modified biochar / fly ash composite material include: 28-45% of modified biochar, 45-62% of high-calcium fly ash, and 6-20% of aminosilane; The modified biochar is obtained by adding biochar into an alkaline solution for immersion treatment, and then filtering, washing, and drying; The high calcium fly ash has a CaO content greater than 10%, a free calcium oxide content of 1.7 to 3.6%, a SiO2 content greater than 35%, and an Al2O3 content greater than 25%. The ignition loss is 2.1 to 3.9%, and the specific surface area is 240 to 410 m 2 / kg; Before use, the modified biochar / fly ash composite material is prepared by compounding modified biochar, high-calcium fly ash, and aminosilane, and then placing the compound in a high carbon dioxide concentration environment and stirring the compound to obtain a carbon adsorption modified biochar / fly ash composite material. The compounding steps include: mixing high-calcium fly ash with aminosilane solution, heating and stirring the mixture once at a temperature of 40 to 50°C for 2 to 3 hours; then adding the modified biochar, heating and stirring the mixture twice at a temperature of 40 to 50°C for 1 to 2 hours, filtering, washing, and drying the mixture to obtain the modified biochar / fly ash composite material.

2. The modified biochar-based carbon-fixing cementitious material according to claim 1, characterized in that: The biochar is obtained by pyrolyzing biomass agricultural waste in a low-temperature oxygen-free environment. Its main elements include: C 46-79wt%, O 5-38wt%; and a specific surface area of 300-550m 2 / kg; pore volume is 0.01~0.3cm 3 / g; pore diameter is 1~35nm.

3. The modified biochar-based carbon-fixing cementitious material according to claim 1, characterized in that: The aminosilane is one or more of KH-550, KH-540, KH-792, and APTES.

4. The method for preparing the modified biochar-based carbon-fixing cementitious material according to any one of claims 1 to 3, characterized in that: The steps include: 1) Drying the biomass agricultural waste, pyrolyzing it, cooling it, grinding it, and screening it to produce biochar; 2) adding the biochar into an alkaline solution for immersion treatment, filtering, washing, and drying to obtain modified biochar; 3) mixing high-calcium fly ash and aminosilane solution, heating and stirring once; then adding modified biochar, heating and stirring twice, filtering, washing, and drying to obtain a modified biochar / fly ash composite material; 4) stirring the modified biochar / fly ash composite material in a high carbon dioxide concentration environment to obtain a carbon adsorption modified biochar / fly ash composite material; 5) The carbon adsorption modified biochar / fly ash composite material is mixed and stirred with cement to obtain a modified biochar-based carbon-fixing cementitious material.

5. The preparation method according to claim 4, characterized in that The stirring rate of the primary heating and stirring is 600-650 rpm.

6. The preparation method according to claim 4, characterized in that The stirring rate of the secondary heating stirring is 600-650 rpm.

7. The preparation method according to claim 4, characterized in that In step 4), the concentration of carbon dioxide is 40-80 vol%, and the stirring time is 2-3 h.

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