Method for improving carbon sequestration rate of cement-based material

Abstract

The invention provides a method for improving the carbon sequestration rate of cement, which comprises the following steps: mixing a cement-based material, secondary alcohol amine and water, uniformly stirring to form flowing slurry, pouring and molding, demolding to obtain a cement test block, and carrying out CO2 curing on the cement test block, the mass percentage of the secondary alcohol amine in the flowing slurry is 0.01-0.05 wt%. According to the invention, the secondary alcohol amine is used as an additive to carry out CO2 curing on the cement-based material, the carbon sequestration rate of the cement-based material is obviously improved, the external carbon sequestration rate of the cement-based material is improved by 36.8% compared with that of common CO2 curing, and the addition of the secondary alcohol amine can capture a part of CO2, accelerate the conversion of CO2 into carbonate ions and improve the reaction efficiency of cement hydration products and unhydrated minerals with CO2; the carbon sequestration rate is increased by 67.08% compared with that of common CO2 curing, a channel is provided for diffusion of CO2 into a cement test block through addition of secondary alcohol amine, CO2 sealing in the cement test block is facilitated, the carbon sequestration rate of a cement material is increased while the mechanical property of the cement material is guaranteed, and a new thought is provided for improvement of the carbon sequestration rate and the mechanical property of the cement-based material.

Description

Technical Field

[0001] The invention belongs to the technical field of cement-based materials and relates to a method for improving the carbon fixation rate of cement-based materials. Background Art

[0003] Carbon mineralization technology is a key technology in carbon utilization and storage. Its main principle is to form carbonates through the reaction of CO2 with alkaline or alkaline earth metal oxides to permanently fix carbon. At present, cement as an alkali source for carbon mineralization has been widely studied, and CO2 curing of cement is the main method to achieve carbon mineralization. After the hydration reaction, cement contains hydration products CSH, Ca(OH)2, Aft, etc., as well as unhydrated phases C3S, C2S and C4AF. These substances can react with CO2 to form CaCO3, thereby filling the pores in cement and improving the strength of cement materials. Therefore, CO2 curing can accelerate the curing efficiency of cement and achieve the purpose of sealing CO2. At the same time, CO2 curing can be carried out under normal temperature and pressure conditions, with low operating costs, and is an effective method for preparing low-carbon green building materials. Cement is a material with good carbon fixation potential, but the current research on cement carbon fixation is far lower than its theoretical carbon fixation rate. Therefore, while ensuring the strength of cement materials, improving its carbon fixation rate requires more in-depth research. In order to improve the mechanical properties of cement materials and their carbon fixation rate during CO2 curing, adding admixtures to cement materials is one of the effective research directions for scholars.

[0004] A Chinese patent (CN 117567089A) discloses a method for adding modified biochar to cement-based materials to improve carbon fixation rate and compressive strength. The biomass raw material used in this patent is corn stalks, and the modified solution used is a mixture of citric acid, anhydrous ethanol, distilled water, ammonia water, tetraethyl silicate, and calcium chloride. Adding 3% modified biochar to cement-based materials obtains the optimal compressive strength and carbon fixation rate. Its compressive strength after standard curing for 7 days reaches 49.9MPa, which is 14.2% higher than the control group. The carbon fixation growth rate after CO2 curing is 1.14%, which is 16.3% higher than the control group.

[0005] A Chinese patent (CN 117383861 A) discloses a method for improving the carbon fixation capacity of cement-based materials by incorporating MOFs nanozymes into standard cement paste or mortar. The patent prepared MOFs nanozymes, which were incorporated into cement-based materials at an amount of 0.01-0.1% of the mass of cement clinker, and carbon-fixed and cured for 1-7 days at a temperature of 20±2°C and a CO2 pressure of 0.1-0.4MPa. Incorporating MOFs nanozymes into cement-based materials can improve the CO2 absorption capacity of the material, while reducing the porosity and improving the strength of the material.

[0006] A Chinese patent (CN 117645443 A) discloses a high carbon fixation fiber cement board and its preparation method. The patent adds kraft pulp fiber or cellulose fiber to the cement board and performs carbonation curing in a CO2 environment. The incorporation of porous fibers provides a gas channel for CO2, which is conducive to improving the efficiency of carbonation curing.

[0007] In summary, the admixtures currently added to cement-based materials mainly include biochar, nanomaterials, fibers, etc., but their preparation process is relatively complicated, and some porous biochar or fiber materials will increase the porosity of cement-based materials, which may reduce the strength of the materials. Although CO2 curing can offset some of the adverse effects of porous materials, it is still necessary to explore the types of materials and reaction conditions to achieve better results. The carbonation reaction of cement materials mainly involves the diffusion of CO2 and the reaction of CO2, among which the diffusion of CO2 plays a leading role in the carbonation reaction. Increasing the curing temperature and pressure can increase the diffusion rate of CO2, but it will also increase the curing cost accordingly. The addition of most admixtures mainly plays a positive role in the diffusion of CO2, providing a channel for CO2 to enter the cement material, increasing the diffusion rate of CO2, and thus increasing its carbon fixation rate. However, the addition of admixtures will also affect the strength change of cement materials. Therefore, how to simplify the process and improve its carbon fixation rate while ensuring the mechanical properties of cement materials is the current research goal. Summary of the invention

[0008] The object of the present invention is to provide a method for improving the carbon fixation rate of cement, comprising the following steps:

[0009] S1: Mix cement-based materials, secondary alcohol amine and water, and stir them evenly to form a flowing slurry; the mass percentage of the secondary alcohol amine in the flowing slurry is 0.01-0.05wt%;

[0010] S2 is cast and then demoulded to obtain a cement test block;

[0011] S3 performs CO2 curing on the cement test block.

[0012] The water-cement ratio (W / C) of the fluid slurry is 0.3 to 0.6.

[0013] The secondary alcohol amine includes one or more of diethanolamine (DEA), diisopropanolamine (DIPA) and N-methylaminoethanol (MMEA). Furthermore, the secondary alcohol amine is MMEA.

[0014] The cement-based material includes freshly mixed cement, mortar or concrete.

[0015] It also includes recycled aggregate, which is obtained by crushing and screening one or more of waste cement, waste mortar and waste concrete.

[0016] The curing conditions are: CO2 curing temperature is 20-50°C, humidity is 50-80%, pressure is 0-0.2MPa, CO2 concentration is 20-100%, and curing time is 2-48h.

[0017] The present invention also provides a cement-based material product obtained by the method.

[0018] Beneficial effects of the present invention: The present invention uses secondary alcohol amines as additives to perform CO2 curing on cement-based materials, and the carbon fixation rate of cement-based materials is significantly improved. The external carbon fixation rate is 36.8% higher than that of ordinary CO2 curing. The addition of secondary alcohol amines can capture a portion of CO2, accelerate the conversion of CO2 into carbonate ions, and improve the efficiency of the reaction between cement hydration products and unhydrated minerals and CO2; the internal carbon fixation rate is 67.08% higher than that of ordinary CO2 curing. The addition of secondary alcohol amines provides a channel for CO2 to diffuse into the interior of the cement test block, which is beneficial to the sealing of CO2 inside the cement test block, while ensuring the mechanical properties of the cement material and improving its carbon fixation rate. In addition, by using MMEA as an additive, the compressive strength of the obtained cement material is increased by 15.7% compared with ordinary CO2 curing, and the carbon fixation rate and compressive strength can be improved at the same time. It provides a new idea for improving the carbon fixation rate and mechanical properties of cement-based materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is the compressive strength of each group of cement test blocks.

[0020] Figure 2 is the external carbon fixation rate of each group of cement test blocks.

[0021] Figure 3 is the internal carbon fixation rate of each group of cement test blocks. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is explained below through specific implementation methods. After reading the present invention, the various equivalent forms of modifications made by technicians to the present invention all fall within the scope defined by the claims attached to this application.

[0023] The cement used in the examples is PO 42.5R ordinary Portland cement.

[0024] The CO2 absorption test inside and outside the test block is as follows: After the compressive strength test, the fragments within 1 cm from the surface of the test block (outside) and the fragments within 1 cm from the center of the test block (inside) are collected, soaked in anhydrous ethanol to stop hydration and dried, ground into powder, and thermogravimetric tests are performed on the outside and inside respectively, the weight loss of CaCO3 is recorded, and the CO2 absorption is calculated based on the obtained data to obtain the carbon fixation rate.

[0025] Example 1

[0026] Cement and water were prepared with a water-cement ratio of 0.5, and DEA was added thereto, stirred evenly to form a flowing slurry, in which the mass fraction of DEA was 0.03wt%. The slurry was poured into a 40*40*40mm mold and allowed to stand in a natural environment for molding, and demolded after molding. The demolded cement test block was placed in a CO2 curing kettle for CO2 curing for 24 hours. The curing conditions were: temperature of 20±2℃, humidity of 70±10%, pressure of normal pressure, and CO2 concentration of 20%. After the curing, the test block was taken out for subsequent testing. Its compressive strength was 20.9MPa, the carbon fixation rate of the external test block was 25.69%, and the carbon fixation rate of the internal test block was 12.25%.

[0027] Example 2

[0028] Cement and water were prepared with a water-cement ratio of 0.5, and DIPA was added thereto, stirred evenly to form a flowing slurry, in which the mass fraction of DIPA was 0.03wt%. The slurry was poured into a 40*40*40mm mold and allowed to stand in a natural environment for molding, and demolded after molding. The demolded cement test block was placed in a CO2 curing kettle for CO2 curing for 24 hours. The curing conditions were: temperature of 20±2℃, humidity of 70±10%, pressure of normal pressure, and CO2 concentration of 20%. After the curing, the test block was taken out for subsequent testing. Its compressive strength was 21.6MPa, the carbon fixation rate of the external test block was 20.52%, and the carbon fixation rate of the internal test block was 14.72%.

[0029] Example 3

[0030] Cement and water were prepared with a water-cement ratio of 0.5, and MMEA was added thereto, stirred evenly to form a flowing slurry, in which the mass fraction of MMEA was 0.03wt%. The slurry was poured into a 40*40*40mm mold and allowed to stand in a natural environment for molding, and demolded after molding. The demolded cement test block was placed in a CO2 curing kettle for CO2 curing for 24 hours. The curing conditions were: temperature of 20±2℃, humidity of 70±10%, pressure of normal pressure, and CO2 concentration of 20%. After the curing, the test block was taken out for subsequent testing. Its compressive strength was 25.0MPa, the external carbon fixation rate of the test block was 28.02%, and the internal carbon fixation rate of the test block was 14.41%.

[0031] Comparative Example 1

[0032] Cement and water were prepared with a water-cement ratio of 0.5, without adding any admixtures, and stirred evenly to form a flowing slurry. The slurry was poured into a 40*40*40mm mold and allowed to stand in a natural environment for molding, and then demolded. The demolded cement block was placed in a CO2 curing kettle for CO2 curing for 24 hours. The curing conditions were: temperature of 20±2℃, humidity of 70±10%, pressure of normal pressure, and CO2 concentration of 20%. After the curing, the test block was taken out for subsequent testing. Its compressive strength was 21.6MPa, the external carbon fixation rate of the test block was 20.48%, and the internal carbon fixation rate of the test block was 8.81%.

[0033] Comparative Example 2

[0034] Cement and water were prepared with a water-cement ratio of 0.5, and ethanolamine (MEA) was added thereto, and stirred evenly to form a flowing slurry, in which the mass fraction of MEA was 0.03wt%. The slurry was poured into a 40*40*40mm mold and allowed to stand in a natural environment for molding, and then demolded. The demolded cement block was placed in a CO2 curing kettle for CO2 curing for 24 hours. The curing conditions were: temperature of 20±2℃, humidity of 70±10%, pressure of normal pressure, and CO2 concentration of 20%. After the curing, the test block was taken out for subsequent testing. Its compressive strength was 25.0MPa, the carbon fixation rate of the external test block was 17.53%, and the carbon fixation rate of the internal test block was 9.67%.

[0035] Comparative Example 3

[0036] Cement and water were prepared with a water-cement ratio of 0.5, and triethanolamine (TEA) was added thereto, and stirred evenly to form a flowing slurry, in which the mass fraction of TEA was 0.03wt%. The slurry was poured into a 40*40*40mm mold and allowed to stand in a natural environment for molding, and then demolded. The demolded cement block was placed in a CO2 curing kettle for CO2 curing for 24 hours. The curing conditions were: temperature of 20±2℃, humidity of 70±10%, pressure of normal pressure, and CO2 concentration of 20%. After the curing, the test block was taken out for subsequent testing. Its compressive strength was 23.3MPa, the carbon fixation rate of the external test block was 16.96%, and the carbon fixation rate of the internal test block was 9.23%.

[0037] Comparative Example 4

[0038] Cement and water were prepared with a water-cement ratio of 0.5, and triisopropanolamine (TIPA) was added thereto, and stirred evenly to form a flowing slurry, wherein the mass fraction of TIPA was 0.03wt%. The slurry was poured into a 40*40*40mm mold and allowed to stand in a natural environment for molding, and then demolded. The demolded cement block was placed in a CO2 curing kettle for CO2 curing for 24 hours. The curing conditions were: temperature of 20±2℃, humidity of 70±10%, pressure of normal pressure, and CO2 concentration of 20%. After the curing, the test block was taken out for subsequent testing. Its compressive strength was 23.5MPa, the carbon fixation rate of the external test block was 14.53%, and the carbon fixation rate of the internal test block was 8.31%.

[0039] Table 1 shows the compressive strength and external and internal carbon fixation rates of the test blocks of each embodiment and comparative example. By comparison, it can be seen that the external and internal carbon fixation rates of the test blocks with secondary alcohol amines DEA, DIPA, and MMEA as admixtures are significantly improved compared with the test blocks of comparative example 1 without adding admixtures. The external carbon fixation rate is increased by up to 36.8%, and the internal carbon fixation rate is increased by up to 67.08%. And compared with the primary alcohol amines and tertiary alcohol amines of comparative examples 2 to 4, their external and internal carbon fixation rates also have obvious advantages. The addition of secondary alcohol amines has a more significant effect on improving the internal carbon fixation rate of the test block. It provides a channel for CO2 to diffuse into the interior of the cement test block, which is beneficial to the sealing of CO2 inside the cement test block, and improves the carbon fixation rate while ensuring the mechanical properties of the cement material. Among them, in Example 3, the test block with secondary alcohol amine MMEA as an admixture not only has a higher carbon fixation rate, but also has a significant improvement in its compressive strength, which is 15.7% higher than that of comparative example 1. After comparison, MMEA is the most preferred. Cement test blocks with MMEA as an admixture can simultaneously improve the carbon fixation rate and compressive strength.

[0040] Table 1 Compressive strength (MPa) and carbon fixation rate (%) of Examples 1 to 3 and Comparative Examples 1 to 4

[0041]

Claims

1. A method for improving cement carbon fixation rate, characterized in that: The steps include: S1: mixing cement-based materials, secondary alcohol amine and water, and stirring them evenly to form a flowing slurry, wherein the mass percentage of the secondary alcohol amine in the flowing slurry is 0.01-0.05wt%; S2 is cast and then demoulded to obtain a cement test block; S3 performs CO2 curing on the cement test block.

2. A method for improving cement carbon fixation rate according to claim 1, characterized in that: The water-cement ratio of the fluid slurry is 0.3-0.

6.

3. A method for improving cement carbon fixation rate according to claim 1, characterized in that: The secondary alcohol amine includes one or more of diethanolamine, diisopropanolamine and N-methylaminoethanol.

4. A method for improving cement carbon fixation rate according to claim 1, characterized in that: The cement-based material includes freshly mixed cement, mortar or concrete.

5. A method for improving cement carbon fixation rate according to claim 4, characterized in that: The cement-based material also includes recycled aggregate, which is obtained by crushing and screening one or more of waste cement, waste mortar and waste concrete.

6. A method for improving cement carbon fixation rate according to claim 1, characterized in that: The CO2 curing temperature is 20-50°C, the humidity is 50-80%, the pressure is 0-0.2MPa, the CO2 concentration is 20-100%, and the curing time is 2-48h.

7. A cement-based material product obtained by the method of claim 1.

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