A long-period carbonization maintenance process for seawater-sea sand concrete

Abstract

This invention proposes a long-cycle carbonation curing process for seawater sand concrete. It employs a three-stage synergistic approach: "pre-curing-free demolding – long-cycle carbonation – subsequent water curing," eliminating the need for traditional pre-curing. Through vibration compaction and shortened in-membrane curing, direct demolding and carbonization are achieved, overcoming the obstruction of CO2 diffusion channels caused by premature surface dehydration and densification. Under the synergistic effects of 95% high CO2 concentration, 45℃ medium temperature, and 60% RH, the process significantly enhances the CO2 penetration rate and mineralization reactivity in low water-cement ratio seawater sand concrete, ensuring uniform deep carbonization from the surface to the interior within a 28-day long-cycle curing period. Subsequent water curing up to 56 days activates the continuous hydration of unhydrated clinker, effectively eliminating the risk of carbonation brittleness. The resulting concrete possesses excellent mechanical strength, carbon sequestration capacity, and resistance to chloride ion penetration, making it suitable for marine engineering structures.

Description

[Technical Field] This invention belongs to the field of concrete curing technology, and particularly relates to a long-cycle carbonation curing process for seawater sand concrete. [Background Technology] Carbon dioxide (CO2) curing technology, as a green curing method, utilizes the carbonation reaction between concrete cementitious materials and hydration products to generate stable products such as calcium carbonate to fill internal pores, thereby improving the microstructure of concrete and enhancing early compressive strength, thus achieving both carbon emission reduction and performance enhancement benefits.

[0001] However, existing carbonation curing technologies are mostly carried out under normal pressure and low CO2 concentration environments, which have drawbacks such as low carbonation efficiency, uneven depth, and poor quality control. For low water-cement ratio (w / b) or highly dense concrete, poor internal pore connectivity leads to a large boost from CO2 penetration, limiting the modification effect.

[0002] Furthermore, current research on CO2 curing of cement-based materials largely focuses on early, short-term treatments (typically 4-24 hours). This short-cycle curing only improves surface properties and fails to achieve deep CO2 sequestration and long-term optimization of matrix minerals. In particular, for seawater-sand concrete systems, the high concentrations of chloride and sulfate ions in seawater lead to complex competitive reactions with carbonation products. Short-cycle curing not only fails to effectively activate the pozzolanic activity of admixtures such as fly ash, but also is insufficient to form a stable chloride-solidified phase and impermeability barrier in the matrix, resulting in limited improvement in the long-term durability of concrete in marine environments. [Summary of the Invention] The purpose of this invention is to provide a long-cycle carbonation curing process for seawater sand concrete, which solves the technical problems of low curing efficiency, low carbon sequestration, and insufficient durability of conventional carbonation curing methods for seawater sand concrete.

[0003] This invention is achieved by the following technical solution: A long-cycle carbonation curing process for seawater sand concrete includes the following steps: S1. Pouring: Pour the seawater sand concrete mixture into the mold for pouring, and then compact it on a vibrating table to obtain the seawater sand concrete specimen. S2. Demolding: After the seawater sand concrete specimen has been cured in the mold for 6 hours, it is demolded. S3. Carbonation curing: The demolded seawater sand concrete specimens are placed in a carbonation device and carbonized at 95% CO2, 45℃ and 60%RH for 28 days. S4. Subsequent water curing: After the carbonization curing is completed, the seawater sand concrete specimens are water-cured until the total age is 56 days.

[0004] The mold is a detachable mold. Compared to non-detachable molds, this detachable design facilitates quick assembly and disassembly and smooth demolding, effectively reducing the edge damage rate and surface defects of concrete specimens; each connecting component can be disassembled independently, facilitating the thorough removal of residual slurry and replacement of locally worn parts, avoiding the complete scrapping of the mold due to single-point damage, and significantly extending its service life.

[0005] This invention eliminates the need for traditional pre-curing, allowing for direct demolding and carbonation after shortened in-membrane curing. This avoids premature dehydration and densification of the concrete surface, which hinders CO2 diffusion channels. Combined with a high CO2 concentration of 95%, a moderate temperature of 45℃, and 60% RH, it significantly enhances the CO2 penetration rate and reactivity in low water-cement ratio seawater sand concrete, achieving uniform and deep CO2 carbonization from the surface to the interior within a 28-day long-term curing period. Simultaneously, the CaCO3 crystals generated during carbonization directionally fill the micropores and aggregate-slurry interface transition zone, effectively severing the pore connectivity network while moderately increasing the critical pore size. This achieves a dual improvement in both high carbon sequestration and resistance to chloride ion penetration.

[0006] Preferably, the seawater and sea sand concrete mixture in step S1 includes the following components: coarse aggregate, sea sand, cement, fly ash, seawater, and water-reducing agent.

[0007] This invention uses sea sand as fine aggregate and seawater directly as mixing water. The sea sand contains trace amounts of Cl. - SO4 2- It can effectively stimulate the early hydration activity of cement, accelerate the formation of initial CSH gel and ettringite, and build a richer network of reaction sites. During the subsequent 28-day long-term carbonation curing process at 95% CO2 and 45℃, CO2 diffuses deeply and undergoes a full mineralization reaction with the pore solution and early hydration products, promoting the full consumption of Ca(OH)2 and Friedel's salt and their transformation into highly dense calcite-type CaCO3 crystals. These CaCO3 crystals directionally fill the micropores of the matrix, helping to reduce the total porosity of seawater sand concrete.

[0008] Preferably, the preparation method of the seawater and sea sand concrete mixture is as follows: weigh coarse aggregate, sea sand, cement, fly ash, seawater and water-reducing agent; first, mix the coarse aggregate and sea sand for the first time, then add cement and fly ash for the second time, and finally add seawater and water-reducing agent for the third time to obtain the seawater and sea sand concrete mixture.

[0009] Preferably, the sea sand contains 0.0199% chloride ions and 0.0396% sulfate ions.

[0010] Preferably, the coarse aggregate has a particle size of 5-20 mm; the sea sand has a particle size of 0.25-0.5 mm.

[0011] This invention limits the particle size of sea sand to 0.25~0.5mm. Its moderate specific surface area, combined with coarse aggregate of 5~20mm, forms a continuous gradation skeleton, effectively improving the initial bulk density of concrete and optimizing the rheological properties of the paste under a low water-cement ratio system. During the subsequent 28-day long-term carbonation curing process at 95% CO2 and 45℃, the uniform particle distribution avoids the blockage of gas diffusion paths by ultrafine powder agglomeration, promoting the uniform penetration of CO2 from the surface to the interior along the continuous pore network, and undergoing a deep mineralization reaction with the pore solution and early hydration products. The calcite-type CaCO3 crystals generated in situ by this reaction precipitate directionally in the homogeneous matrix and block the pore throats, helping to reduce pore connectivity and significantly improve the carbonation uniformity and overall density of seawater sand concrete.

[0012] Preferably, the seawater is artificial seawater, comprising the following components: NaCl 24.53 g / L, MgCl 25.2 g / L, Na2SO4 4.09 g / L, CaCl 21.16 g / L and KCl 0.695 g / L.

[0013] This invention uses artificial seawater as the mixing water, and its formulation simulates the ionic composition of natural seawater to ensure that Cl is present in different batches of preparation. - SO4 2- / Mg 2+ / Ca 2+ The constant concentration effectively eliminates interference from natural seawater components in carbonization maintenance. At this ratio, the Cl released by NaCl and MgCl2... - Disruption of the electrical double layer on the surface of cement particles accelerates the early dissolution of C3S, while Na2SO4 provides SO42-. 2- Promotes rapid formation of ettringite, and CaCl2 replenishes free Ca. 2+ This reserves sufficient active sites for subsequent carbonization reactions.

[0014] Preferably, the water-cement ratio of the seawater-sand concrete mixture in step S1 is 0.35~0.55.

[0015] This invention proposes a long-cycle carbonation curing process for seawater sand concrete. It employs a three-stage synergistic approach: "pre-curing-free demolding – long-cycle carbonation – subsequent water curing," eliminating the need for traditional pre-curing. Through vibration compaction and shortened in-membrane curing, direct demolding and carbonization are achieved, overcoming the obstruction of CO2 diffusion channels caused by premature surface dehydration and densification. Under the synergistic effects of 95% high CO2 concentration, 45℃ medium temperature, and 60% RH, the process significantly enhances the CO2 penetration rate and mineralization reactivity in low water-cement ratio seawater sand concrete, ensuring uniform deep carbonization from the surface to the interior within a 28-day long-cycle curing period. Subsequent water curing up to 56 days activates the continuous hydration of unhydrated clinker, effectively eliminating the risk of carbonation brittleness. The resulting concrete possesses excellent mechanical strength, carbon sequestration capacity, and resistance to chloride ion penetration, making it suitable for marine engineering structures. [Attached Image Description] To more clearly illustrate the technical solutions in the embodiments of the invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0016] Figure 1 This is a schematic diagram showing the degree of carbonation of seawater and sea sand concrete specimens under different curing ages using the carbonation curing method of this invention. Figure 2 This is a schematic diagram showing the degree of carbonation of seawater and sea sand concrete specimens under different curing ages using conventional carbonation curing methods, as described in this invention. Figure 3 This is a schematic diagram showing the degree of carbonation of ordinary concrete specimens under different curing ages using the concrete carbonation curing method of this invention. Figure 4 This is a schematic diagram of the gradation curves of different fine aggregates with the same particle size.

Detailed Implementation Methods

[0017] A long-cycle carbonation curing process for seawater sand concrete includes the following steps: S1. Pouring: Pour the seawater sand concrete mixture into a detachable mold for pouring, and then compact it on a vibrating table to obtain a seawater sand concrete specimen. S2. Demolding: After the seawater sand concrete specimen has been cured in the detachable mold for 6 hours, it is demolded. S3. Carbonation curing: The demolded seawater sand concrete specimens are placed in a carbonation device and carbonized at 95% CO2, 45℃ and 60%RH for 28 days. S4. Subsequent water curing: After the carbonization curing is completed, the seawater sand concrete specimens are water-cured until the total age is 56 days.

[0018] Example 2 The difference from Example 1 is as follows: Preparation of seawater and sea sand concrete mixture: According to Table 1, weigh out coarse aggregate, sea sand, cement, fly ash, seawater and water-reducing agent; first mix the coarse aggregate and sea sand, then add cement and fly ash for a second mixing, and finally add seawater and water-reducing agent for a third mixing to obtain a seawater and sea sand concrete mixture with a water-cement ratio of 0.50.

[0019] Example 3 The difference from Example 1 is as follows: Preparation of seawater and sea sand concrete mixture: According to Table 1, weigh out coarse aggregate, sea sand, cement, fly ash, seawater and water-reducing agent; first mix the coarse aggregate and sea sand, then add cement and fly ash for a second mixing, and finally add seawater and water-reducing agent for a third mixing to obtain a seawater and sea sand concrete mixture with a water-cement ratio of 0.55.

[0020] Comparative Example 1 Preparation of seawater and sea sand concrete mixture: According to Table 1, weigh out coarse aggregate, sea sand, cement, fly ash, seawater and water-reducing agent; first mix the coarse aggregate and sea sand, then add cement and fly ash for a second mixing, and finally add seawater and water-reducing agent for a third mixing to obtain a seawater and sea sand concrete mixture with a water-cement ratio of 0.45.

[0021] A concrete carbonation curing process includes the following steps: S1. Pouring: Pour the seawater sand concrete mixture into a non-removable mold for pouring, and then compact it on a vibrating table to obtain a seawater sand concrete specimen. S2. Demolding: After the seawater sand concrete specimen has been cured in the non-removable mold for 12 hours, it is demolded. S3. Pre-curing: The demolded seawater sand concrete specimens are placed in an air curing chamber at 25°C for 18 hours for pre-curing to remove free water from the seawater sand concrete specimens. S4. Carbonation curing: The pre-cured seawater sand concrete specimens are placed in a carbonation device and carbonized at 95% CO2, 25℃ and 60% RH for 28 days. S5. Subsequent water curing: After the carbonization curing is completed, the seawater sand concrete specimens are water-cured until the total age is 56 days.

[0022] Comparative Example 2 The difference from Comparative Example 1 is: Preparation of seawater and sea sand concrete mixture: According to Table 1, weigh out coarse aggregate, sea sand, cement, fly ash, seawater and water-reducing agent; first mix the coarse aggregate and sea sand, then add cement and fly ash for a second mixing, and finally add seawater and water-reducing agent for a third mixing to obtain a seawater and sea sand concrete mixture with a water-cement ratio of 0.50.

[0023] Comparative Example 3 The difference from Comparative Example 1 is: Preparation of seawater and sea sand concrete mixture: According to Table 1, weigh out coarse aggregate, sea sand, cement, fly ash, seawater and water-reducing agent; first mix the coarse aggregate and sea sand, then add cement and fly ash for a second mixing, and finally add seawater and water-reducing agent for a third mixing to obtain a seawater and sea sand concrete mixture with a water-cement ratio of 0.55.

[0024] Comparative Example 4 Preparation of ordinary concrete mixture: According to Table 1, weigh out coarse aggregate, river sand, cement, fly ash, laboratory tap water, and water-reducing agent; first, mix the coarse aggregate and river sand, then add cement and fly ash for a second mixing, and finally add laboratory tap water and water-reducing agent for a third mixing to obtain a common concrete mixture with a water-cement ratio of 0.45.

[0025] A long-cycle carbonation curing process for concrete includes the following steps: S1. Pouring: Pour the ordinary concrete mixture into a detachable mold for pouring, and then compact it on a vibrating table to obtain ordinary concrete specimens; S2. Demolding: After the ordinary concrete specimen has been cured in the detachable mold for 6 hours, it is demolded. S3. Carbonation curing: The demolded ordinary concrete specimens are placed in carbonation equipment and carbonized at 95% CO2, 45℃ and 60%RH for 28 days. S4. Subsequent water curing: After the carbonation curing is completed, the ordinary concrete specimens are water-cured until the total age is 56 days.

[0026] Comparative Example 5 The difference from Comparative Example 4 is: Preparation of ordinary concrete mixture: According to Table 1, weigh out coarse aggregate, river sand, cement, fly ash, laboratory tap water, and water-reducing agent; first, mix the coarse aggregate and river sand, then add cement and fly ash for a second mixing, and finally add laboratory tap water and water-reducing agent for a third mixing to obtain a common concrete mixture with a water-cement ratio of 0.50.

[0027] Comparative Example 6 The difference from Comparative Example 4 is: Preparation of ordinary concrete mixture: According to Table 1, weigh out coarse aggregate, river sand, cement, fly ash, laboratory tap water, and water-reducing agent; first, mix the coarse aggregate and river sand, then add cement and fly ash for a second mixing, and finally add laboratory tap water and water-reducing agent for a third mixing to obtain a concrete mixture with a water-cement ratio of 0.55.

[0028] Table 1 Concrete mix proportions of the examples and comparative examples

[0029] Specifically, the components of Examples 1-3 and Comparative Examples 1-6 are shown in Table 2. The quality indicators of the cement used are shown in Table 3. The chemical composition of the cement and fly ash used was determined using X-ray fluorescence spectrometry (XRF), and the results are shown in Table 4.

[0030] Table 2 Components of Concrete Mixtures in Examples and Comparative Examples

[0031] Table 3 Quality Indicators of P.O42.5 Grade Ordinary Portland Cement

[0032] Table 4 Quality Indicators of Cement and Fly Ash

[0033] The seawater and sea sand concrete specimens of Examples 1-3 and Comparative Examples 1-3, and the ordinary concrete specimens of Comparative Examples 4-6 were tested under the following conditions: Carbonization degree test: Before carbonation curing, paraffin wax was evenly applied to the top and bottom surfaces of 100mm×100mm×400mm concrete specimens to completely seal them, ensuring carbonation proceeds along the sides. The degree of concrete carbonation was tested at 3, 7, 14, and 28 days of carbonation curing. During testing, to avoid erosion of the cross-section by the cutting cooling water, [further details were provided]. - Loss of colorimetric reagent affected the colorimetric reaction. A pressure testing machine with a standard splitting fixture was used to split the specimen perpendicular to its long axis, cutting a short segment approximately 100 mm in length for this test. Immediately after splitting, phenolphthalein indicator was evenly sprayed onto the fresh fracture surface. After standing for 30 seconds, the degree of carbonization was determined by calculating the ratio of the carbonized area (colorless region) to the total cross-sectional area of ​​the specimen, as shown in equation (1-1). After sampling was completed, the remaining specimen fracture surfaces were recoated with paraffin wax and sealed, then placed in a carbonization chamber for further curing until the next measurement.

[0034]

[0035] Equation (1-1) Depend on Figures 1 to 3 It can be seen that the degree of carbonation of concrete is affected by the water-cement ratio, curing age, matrix type, and curing method: The degree of carbonization increases significantly with increasing water-to-binder ratio (w / b). Figure 1 Taking seawater and sea sand concrete as an example: after 3 days of curing, the carbonation degree of the specimen with w / b=0.45 was 21%, while that of the specimen with w / b=0.55 reached 32%. The mechanism is that the water-cement ratio directly determines the initial porosity of the matrix. A higher w / b ratio forms a more open capillary network, significantly reducing the CO2 diffusion resistance and accelerating the advancement of the carbonation reaction front inward.

[0036] The degree of carbonation in concrete increases with the extension of curing age, but the rate of increase slows down. Figure 3 Taking ordinary concrete with a w / b ratio of 0.55 as an example: the degree of carbonation is 52% after 3 days of carbonation curing, reaching 90% after 28 days. This is because as the reaction proceeds, the thickness of the carbonated layer increases, and CO2 needs to travel a longer diffusion path to reach the unreacted area. The accumulated mass transfer resistance leads to a decrease in the reaction rate. In other words, the increase in the degree of carbonation of concrete in the later stages of carbonation curing is much smaller than in the early stages.

[0037] Under the same curing methods and age, ordinary concrete exhibits a higher degree of carbonation than seawater-sand concrete. For example... Figure 1 and Figure 3 Comparison: At a curing age of 28 days, the carbonation degree of seawater sand concrete with a w / b ratio of 0.55 was 90%, while that of ordinary concrete was close to 100%. (Combined) Figure 4 Aggregate gradation analysis shows that sea sand, due to its more rounded particle morphology and superior continuous gradation, can form a denser structure under the same water-cement ratio, thus inhibiting CO2 diffusion.

[0038] Depend on Figure 1 and Figure 2 The comparison shows that this invention significantly improves carbonation efficiency and depth through the precise synergy of parameters: 95% CO2, 45℃, and 60% RH. Taking seawater sand concrete with a w / b ratio of 0.55 as an example: under conventional carbonation curing methods, the carbonation degree after 28 days is 65%; while using the carbonation curing method of this invention, the carbonation degree at the same age is increased to 89%, an increase of 24%; and this synergistic effect is consistent under different water-cement ratios.

[0039] Further integration Figure 3Analysis shows that ordinary concrete exhibits a superior carbonation response under the carbonation curing method of this invention, indicating the universality of this carbonation curing method. Taking w / b=0.55 as an example: the carbonation degree can reach over 95% after 28 days, approaching complete carbonation; even for specimens with a low water-cement ratio (w / b=0.45), the carbonation degree after 28 days is still over 60%. Compared with seawater and sea sand concrete, ordinary concrete has a slightly higher carbonation degree under the same process, mainly attributed to the continuous gradation characteristics and particle morphology advantages of sea sand, which help increase the aggregate bulk density, making the paste-aggregate interface transition zone more compact and slightly increasing the CO2 diffusion resistance.

[0040] The above description is one implementation method provided in conjunction with specific content. It is not intended that the specific implementation of the present invention is limited to these descriptions. Any technical deductions, substitutions, improvements, etc., that are similar to or based on the present invention should be considered within the scope of protection of this patent.

Claims

1. A long-cycle carbonation curing process for seawater sand concrete, characterized in that: Includes the following steps: S1. Pouring: Pour the seawater sand concrete mixture into the mold for pouring, and then compact it on the vibrating table to obtain the seawater sand concrete specimen. S2. Demolding: After the seawater sand concrete specimen has been cured in the mold for 6 hours, it is demolded. S3. Carbonation curing: The demolded seawater sand concrete specimens are placed in a carbonation device and carbonized at 95% CO2, 45℃ and 60%RH for 28 days. S4. Subsequent water curing: After the carbonization curing is completed, the seawater sand concrete specimens are water-cured until the total age is 56 days.

2. The long-cycle carbonation curing process for seawater sand concrete according to claim 1, characterized in that: The seawater and sea sand concrete mixture described in step S1 includes the following components: coarse aggregate, sea sand, cement, fly ash, seawater, and water-reducing agent.

3. The long-cycle carbonation curing process for seawater sand concrete according to claim 2, characterized in that: The preparation method of the seawater and sea sand concrete mixture is as follows: weigh coarse aggregate, sea sand, cement, fly ash, seawater and water-reducing agent; first, mix the coarse aggregate and sea sand for the first time, then add cement and fly ash for the second time, and finally add seawater and water-reducing agent for the third time to obtain the seawater and sea sand concrete mixture.

4. The long-cycle carbonation curing process for seawater sand concrete according to claim 2, characterized in that: The sea sand contained 0.0199% chloride ions and 0.0396% sulfate ions.

5. The long-cycle carbonation curing process for seawater sand concrete according to claim 2, characterized in that: The sea sand has a particle size of 0.25~0.5mm.

6. The long-cycle carbonation curing process for seawater sand concrete according to claim 2, characterized in that: The seawater is artificial seawater, comprising the following components: NaCl 24.53 g / L, MgCl2 5.2 g / L, Na2SO4 4.09 g / L, CaCl2 1.16 g / L and KCl 0.695 g / L.

7. The long-cycle carbonation curing process for seawater sand concrete according to claim 1, characterized in that: The water-cement ratio of the seawater-sand concrete mixture in step S1 is 0.35~0.55.

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