Dry-wet cycle resistant concrete and preparation method thereof

Abstract

The invention relates to the technical field of building materials, and discloses dry-wet cycle resistant concrete and a preparation method thereof. The concrete is prepared from 500 to 900 parts of a cementing material, 1000 to 1600 parts of sand and 225 to 360 parts of water, wherein the cementing material is prepared from 125 to 675 parts of cement and 125 to 675 parts of beta-C2S. The preparation method comprises the following steps: mixing the cement, beta-C2S and sand, adding water, stirring to form slurry, molding, demolding, and carrying out CO2 curing. According to the invention, cement is partially replaced by beta-C2S, and a specific CO2 curing process is combined, so that harmful expansion of concrete in a dry-wet cycle environment is remarkably reduced, the volume stability and long-term durability are improved, and carbon sequestration and emission reduction are realized at the same time.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a concrete material suitable for wet-dry cycle environments and its preparation method, particularly a concrete whose volume stability is improved through composition optimization and CO2 curing process. Background Technology

[0002] CO2 curing technology for concrete can effectively solidify CO2 emissions from industry and improve the early performance of concrete, making it a promising low-carbon building material technology. However, traditional silicate cement, after CO2 curing, generates a large amount of silica gel with high polymerization degree and high specific surface area. This silica gel repeatedly absorbs and dehydrates in wet-dry cycles, generating significant expansion and contraction stresses, which can easily lead to concrete cracking in the long term, impairing its durability and limiting the application of CO2-cured concrete in complex environments.

[0003] In existing technologies, various special admixtures, fibers, or complex chemical additives are often added to improve concrete performance, but this approach suffers from high costs and complex processes. Therefore, there is an urgent need to develop a technical solution that uses simple raw materials, has controllable costs, and can fundamentally improve the resistance to wet-dry cycles in CO2-cured concrete. Summary of the Invention

[0004] To address the problems of poor volume stability and easy expansion and cracking of existing CO2-cured concrete under wet-dry cycles, this invention aims to provide a concrete resistant to wet-dry cycles and its preparation method. This solution effectively inhibits harmful expansion and improves long-term durability through synergistic material composition design and curing process.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a concrete resistant to wet-dry cycles, which is prepared from the following raw materials in parts by weight: 500-900 parts of cementitious material; 1000-1600 parts of sand; 225-360 parts water; The cementitious material comprises 125-675 parts of cement and 125-675 parts of β-C2S.

[0006] Preferably, the cement is ordinary Portland cement.

[0007] Secondly, the present invention provides a method for preparing the above-mentioned concrete resistant to wet-dry cycles, comprising the following steps: S1: Mix cement, β-C2S and sand evenly; S2: Add water and stir evenly to obtain concrete slurry; S3: The concrete slurry is molded and demolded to obtain a concrete specimen; S4: The concrete specimens are cured with CO2.

[0008] Preferably, the CO2 curing is carried out under a pressure of 0.15 MPa to 0.25 MPa.

[0009] Preferably, the conditions for CO2 curing also include: humidity of 55%-65% and curing time of 2-4 hours.

[0010] Preferably, before CO2 curing, the method further includes a step of drying the demolded specimens until the water-cement ratio is not higher than 0.3.

[0011] Preferably, in step S2, the water-cement ratio is 0.45.

[0012] Preferably, the mixing is performed using a high-speed mixer for 3 minutes.

[0013] The beneficial effects of this invention are as follows: (1) Excellent volume stability: This invention fundamentally changes the microstructure of CO2 curing products by introducing β-C2S to partially replace cement. The incorporation of β-C2S significantly reduces the degree of polymerization of the silica phase, making it form a low-polymerization phase that is closer to a stable CSH gel, rather than a highly expansive, high-polymerization silica gel. At the same time, the addition of β-C2S changes the pore structure of the material, increases the porosity and optimizes the pore size distribution, providing a physical buffer space for potential volume changes. The synergistic optimization of chemical and physical structures is the core mechanism by which the technical solution of this invention can effectively suppress the harmful expansion of the material under wet-dry cycles, thereby obtaining "wet-dry cycle resistant" performance.

[0014] (2) Low carbon, environmental protection and cost-effectiveness: β-C2S itself is a low carbon cementitious material, and its large-scale replacement of cement directly reduces the carbon emissions of raw materials. Combined with CO2 curing process, it achieves the solidification of greenhouse gases, resulting in double carbon reduction. At the same time, the raw materials are simple, no expensive additives are required, the process is easy to control, and the production cost and the whole life cycle maintenance cost are reduced. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 This is a flowchart of the method for preparing concrete resistant to wet-dry cycles provided by the present invention.

[0016] Figure 2 These are the FTIR spectra of the silica phases of the embodiments and comparative examples of the present invention after CO2 curing. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0018] This invention provides a concrete resistant to wet-dry cycles, prepared from the following raw materials in parts by weight: 500-900 parts of cementitious material; 1000-1600 parts of sand; 225-360 parts water; The cementitious material comprises 125-675 parts of cement and 125-675 parts of β-C2S.

[0019] The cement is ordinary Portland cement.

[0020] Please see Figure 1 As shown, the present invention also provides a method for preparing the aforementioned concrete resistant to wet-dry cycles, comprising the following steps: S1: Mix cement, β-C2S and sand evenly; S2: Add water and stir evenly to obtain concrete slurry; S3: The concrete slurry is molded and demolded to obtain a concrete specimen; S4: The concrete specimens are cured with CO2.

[0021] In step S1, the mixing is performed using a high-speed mixer for 3 minutes.

[0022] In step S4, the CO2 curing is carried out under a pressure of 0.15 MPa to 0.25 MPa.

[0023] The conditions for CO2 curing also include: humidity of 55%-65% and curing time of 2-4 hours.

[0024] Before CO2 curing, the process also includes drying the demolded specimens until the water-cement ratio is no higher than 0.3.

[0025] Specifically, in step S2, the water-cement ratio is 0.45.

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to embodiments and comparative examples, but the scope of protection of this invention is not limited thereto.

[0027] This invention discovers that by introducing a specific proportion of β-C2S to partially replace cement, the chemical composition (reducing the degree of polymerization of the silica phase) and microphysical structure (increasing and optimizing porosity) of CO2 curing products can be actively regulated, thereby synergistically solving the problem of volume instability under wet-dry cycles.

[0028] Raw material description: Cement: PI 42.5 ordinary Portland cement conforming to GB 8076-2008.

[0029] β-C2S (β-type dicalcium silicate): prepared by mixing limestone and shale in an appropriate molar ratio, calcining at 1300°C for 2 hours, and then cooling to room temperature at a rate of about 60°C / min.

[0030] Sand: Standard sand.

[0031] Water: tap water.

[0032] CO2: Industrially pure carbon dioxide gas.

[0033] Preparation of Examples and Comparative Examples: The following examples all follow the general steps for sample preparation, with the only difference being the composition of the cementitious material, as shown in Table 1 below.

[0034] Mixing: According to the proportions in Table 1, dry mix the cementitious materials (cement and β-C2S) and sand in a high-speed mixer for 1 minute. Then add all the water and continue mixing for 3 minutes at a water-cement ratio of 0.45 to form a uniform slurry.

[0035] Molding and Pretreatment: The slurry was poured into a cubic steel mold with a side length of 20 mm, vibrated to compact it, covered and cured for 24 hours, and then demolded. The demolded specimens were dried at room temperature until the remaining water-cement ratio was approximately 0.25.

[0036] CO2 curing: Place the pretreated specimens in a sealed curing chamber. Introduce CO2 gas into the chamber to stabilize the pressure at 0.2 MPa and maintain the ambient humidity at approximately 60%. Curing is carried out under these conditions for 3 hours.

[0037] Table 1: Raw material ratios (parts by weight) for each embodiment and comparative example Performance testing and results analysis: Pore ​​structure and mechanical properties: Mercury intrusion porosimetry and compressive strength tests were performed on the specimens after CO2 curing. Detailed results are shown in Tables 2 to 4 below.

[0038] Table 2: Pore structure distribution and length variation of specimens after CO2 curing without wet-dry cycling Table 3: Pore structure distribution and length variation of specimens after CO2 curing under 40 wet-dry cycles Table 4: Pore structure distribution and length variation of specimens after CO2 curing under 60 wet-dry cycles As shown in Tables 2-4, the introduction of β-C2S significantly improved the volume stability of CO2-cured mortar under wet-dry cycling, effectively reducing its volume change. Comparative Example A0 (pure cement mortar) showed significant expansion after 40 cycles, with a length change of 298 µε, and still exhibited a net expansion of 215 µε after 60 cycles. In contrast, Example A1, incorporating 25% β-C2S, had a length of -198 µε after 40 cycles, while the volume change decreased to -68 µε after 60 cycles, with an overall fluctuation much smaller than that of A0. When the β-C2S content increased to 50% (A2) and 75% (A3), the volume change was further controlled during long-term cycling: A2 had a length of -120 µε after 60 cycles, and A3 had -621 µε. Both showed volume recovery and a more stable state after the expansion peak in the middle of the cycle. This indicates that the addition of β-C2S inhibits the expansion of carbon dioxide-cured concrete.

[0039] After CO2 curing, the porosity of the pure cement sample (A0-CO2) was 21.09%. However, the porosity of all samples increased significantly after the addition of β-C2S: 26.67% for the A1-CO2 group, 30.89% for the A2-CO2 group, and 28.69% for the A3-CO2 group. This indicates that the addition of β-C2S increases the porosity of the cement paste after CO2 curing. The addition of β-C2S alters the pore structure of the material, increasing the porosity and providing a buffer space for volume changes, thus increasing volume stability.

[0040] Analysis of the degree of polymerization of silica phase: FTIR spectroscopy was used to analyze the silicon-oxygen tetrahedra (Q) in CO2 curing products. 0 Q 1 Q 2 Q 3 Q 4 ) structural distribution, and used (Q 3 +Q 4 ) / (Q 1 +Q 2The ratio represents the average degree of polymerization of the silicon phase. Detailed original data and calculation results are shown in Table 5 below.

[0041] Table 5: Distribution and Degree of Polymerization of Silicon-Oxide Tetrahedral Structures in Products After CO2 Curing Figure 2 The FTIR spectra and analytical data in Table 5 clearly show that the degree of polymerization ratio of the silica phase in the pure cement group (A0) is as high as 0.85, indicating the formation of a large amount of highly polymerized Q phase. 3 Q 4 Structure (silicone). In embodiments A1-A3 employing the technical solution of this invention, the degree of polymerization ratio is significantly reduced to 0.19-0.64, and the Q of high polymerization degree... 3 Q 4 The proportion of the structure decreased significantly, and the Q of low polymerization degree 1 Q 2 The increased proportion of the structure directly proves the core chemical mechanism of "reducing the degree of polymerization of the silica phase to form a more stable CSH-like gel," providing a fundamental chemical basis for "improving volume stability."

[0042] In summary, this invention, by partially replacing cement with β-C2S and combining it with a specific CO2 curing process, achieves the aforementioned beneficial effects through the synergistic effect of both chemical structure (significantly reducing the degree of polymerization of the silica phase, as shown in Table 5) and physical structure (increasing total porosity and optimizing pore size distribution, as shown in Tables 2-4), and successfully solves the technical problem of poor resistance to wet-dry cycles in CO2-cured concrete.

[0043] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Various changes and modifications made by those skilled in the art within the scope defined by the claims fall within the protection scope of the present invention.

Claims

1. A type of concrete resistant to wet-dry cycles, characterized in that, It is prepared from the following raw materials in parts by weight: 500-900 parts of cementitious material; 1000-1600 parts of sand; 225-360 parts water; The cementitious material comprises 125-675 parts of cement and 125-675 parts of β-C2S; the β-C2S accounts for 25wt% to 75wt% of the total weight of the cementitious material.

2. The concrete resistant to wet-dry cycles according to claim 1, characterized in that, The cement is ordinary Portland cement.

3. A method for preparing concrete resistant to wet-dry cycles as described in any one of claims 1-2, characterized in that, Includes the following steps: S1: Mix cement, β-C2S and sand evenly; S2: Add water and stir evenly to obtain concrete slurry; S3: The concrete slurry is molded and demolded to obtain a concrete specimen; S4: The concrete specimens are cured with CO2.

4. The method for preparing concrete resistant to wet-dry cycles according to claim 3, characterized in that, The CO2 curing was carried out under pressures ranging from 0.15 MPa to 0.25 MPa.

5. The method for preparing concrete resistant to wet-dry cycles according to claim 3, characterized in that, The conditions for CO2 curing also include: humidity of 55%-65% and curing time of 2-4 hours.

6. The method for preparing concrete resistant to wet-dry cycles according to claim 3, characterized in that, Before CO2 curing, the process also includes drying the demolded specimens until the water-cement ratio is no higher than 0.

3.

7. The method for preparing concrete resistant to wet-dry cycles according to claim 3, characterized in that, In step S2, the water-cement ratio is 0.

45.

8. The method for preparing concrete resistant to wet-dry cycles according to claim 3, characterized in that, Mix using a high-speed mixer for 3 minutes.

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