Sulphoaluminate cement based on hydration-carbonization regulation and preparation method thereof

Abstract

The invention provides sulphoaluminate cement based on hydration-carbonization regulation and a preparation method of the sulphoaluminate cement. The preparation method comprises the following steps: mixing sulphoaluminate cement and water, and stirring to obtain sulphoaluminate cement slurry; forming and hardening the sulphoaluminate cement slurry in a standard environment to obtain a cement test piece; the cement test piece is placed in a normal pressure environment with the temperature of 20 + / -2 DEG C, the concentration of 20%-25% and the relative humidity of 70 + / -5% to be subjected to accelerated carbonization treatment, or placed in an environment with the temperature of 20 + / -2 DEG C, the pressure of 0.2 + / -0.05 MPa, the concentration of 99.5%-99.9% and the relative humidity of 55 + / -5% to be subjected to pressurized carbonization treatment, and the sulphoaluminate cement based on hydration-carbonization regulation and control is obtained. According to the invention, short-term carbonization treatment is carried out at the early stage of sulfoaluminate cement hydration, so that the early strength of the sulfoaluminate cement is further improved.

Description

Technical Field

[0001] This invention relates to the field of special cement-based materials technology, specifically to a sulfoaluminate cement based on hydration-carbonation regulation and its preparation method. Background Technology

[0002] It is reported that the construction industry emits approximately 3.5 to 11 billion tons of carbon annually, accounting for 10% to 23% of global greenhouse gas emissions. In 2016, emissions from building materials production processes totaled approximately 1.8 billion tons, representing about 5% of global CO2 emissions. Specifically, the production of one ton of silicate cement clinker generates approximately 0.87 tons of CO2 equivalent emissions. Furthermore, significant amounts of CO2 are released annually due to building demolition and reconstruction. Therefore, the high carbon emissions associated with the silicate cement industry have attracted considerable attention globally, prompting extensive research into various carbon reduction strategies.

[0003] As a low-carbon cement, sulfoaluminate cement has received increasing attention in recent years. This special cement was independently developed in my country in the 1970s and is the second most widely used cement in the country after silicate cement. It possesses excellent properties such as rapid setting and hardening, high early strength, low shrinkage, frost resistance, impermeability, and corrosion resistance, making it particularly suitable for emergency repairs, rapid construction, waterproofing projects, and marine engineering construction and maintenance. Its main mineral composition includes calcium sulfoaluminate (C4A3Š), belite (C2S), gypsum dihydrate (CŠH2), anhydrous gypsum (CŠ), and iron phase.

[0004] Carbonation refers to the chemical reaction between carbon dioxide and alkaline components in cementitious materials (such as calcium hydroxide, ettringite, and hydrated calcium silicate) to produce products such as calcium carbonate. As a carbon dioxide capture method, carbonation technology is receiving increasing attention, not only for its ability to seal carbon dioxide and reduce emissions, but also for its ability to improve the compressive strength of cement through reaction products. In recent years, carbonation methods have become increasingly diverse, but research on the carbonation of sulfoaluminate cement remains relatively limited. Previous studies have mainly focused on the carbonation resistance of sulfoaluminate cement combined with various mineral admixtures (SCMs), and have used long-term carbonation methods (at least 28 days). Currently, there is a lack of systematic understanding of the impact mechanism of a short-term, controllable carbon dioxide treatment process applied during the early hydration stage, and the immediate and sustained effects of this combined effect on the microstructure evolution and macroscopic performance development of cement. Therefore, conducting research on the close integration of early hydration and short-term carbonation on the early strength of sulfoaluminate cement is both necessary and feasible. Summary of the Invention

[0005] The purpose of this invention is to provide a sulfoaluminate cement based on hydration-carbonation regulation and its preparation method, which further improves the early strength of sulfoaluminate cement by performing short-term carbonation treatment in the early stage of hydration.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a method for preparing sulfoaluminate cement based on hydration-carbonation regulation. The method includes: mixing sulfoaluminate cement and water to obtain a sulfoaluminate cement slurry; hardening the sulfoaluminate cement slurry under standard conditions to obtain cement specimens; subjecting the cement specimens to accelerated carbonation treatment at normal pressure (20±2℃, 20%~25% carbon dioxide concentration, and 70±5% relative humidity), or subjecting them to pressurized carbonation treatment at 20±2℃, 0.2±0.05 MPa pressure, 99.5%~99.9% carbon dioxide concentration, and 55±5% relative humidity, to obtain the sulfoaluminate cement based on hydration-carbonation regulation.

[0007] Furthermore, after obtaining the cement specimens, the cement specimens are placed in a standard environment for secondary curing; wherein the secondary curing time is 0 to 6 days. Preferably, it is 0 (i.e., no secondary curing), 2 days (secondary curing age is 2 days), or 6 days (secondary curing age is 6 days).

[0008] Furthermore, the water-cement ratio of the sulfoaluminate cement and water is 0.4~0.5, and the mixing time is 2~3 minutes. Furthermore, before the sulfoaluminate cement slurry undergoes molding and hardening, it is first poured into a mold with dimensions of 20 mm × 20 mm × 20 mm; the molding and hardening time is 1 day.

[0009] Furthermore, the standard environment is 20±2℃ and 95±3% relative humidity.

[0010] Furthermore, the accelerated carbonization treatment or pressurized carbonization treatment takes 1 day.

[0011] Furthermore, the preparation method specifically includes the following steps: Step 1: Mix sulfoaluminate cement and water at a water-cement ratio of 0.4 and 0.5, and then mix for 2-3 minutes to obtain sulfoaluminate cement slurry; Step 2: Pour the sulfoaluminate cement slurry into a 20 mm × 20 mm × 20 mm mold, and allow it to harden at 20±2℃ and 95±3% relative humidity for 1 day to obtain a cement specimen; Step 3: After demolding the cement specimen, place it in a secondary curing environment at 20±2℃ and 95% relative humidity for 0, 2, and 6 days respectively to obtain a secondary cured cement specimen; Step 4: Place the secondary cured cement specimen in a carbonization curing chamber at 20±2℃, 20%~25% carbon dioxide concentration, and 70±5% relative humidity under normal pressure for 1 day of accelerated carbonization treatment, or place it in a carbonization curing chamber at 20±2℃ and 0.2±0.05% relative humidity. The sulfoaluminate cement based on hydration-carbonation regulation was obtained by subjecting the cement to a pressure of MPa, a carbon dioxide concentration of 99.5%~99.9%, and a relative humidity of 55±5% for one day.

[0012] The present invention also provides a sulfoaluminate cement prepared by the above-mentioned method for preparing sulfoaluminate cement based on hydration-carbonation regulation.

[0013] Furthermore, the early compressive strength of the sulfoaluminate cement based on hydration-carbonation regulation reaches up to 48 MPa.

[0014] The present invention also provides an application of the above-mentioned sulfoaluminate cement based on hydration-carbonation regulation in the field of rapid construction.

[0015] Compared with the prior art, the technical solution provided by the present invention has at least the following advantages: (1) Two short-term carbonation treatments promoted the carbonation reaction of ettringite and dicalcium silicate in low water-cement ratio sulfoaluminate cement specimens, generating products such as calcite and forming a denser microstructure. Especially under accelerated carbonation conditions, the carbonation reaction of the two was more significant, and 1 day of carbonation also promoted the hydration reaction of sulfoaluminate cement stone at 3 and 7 days of curing age. After only 1 day of carbonation treatment, the compressive strength can be increased by up to 41.6%, and the compressive strength can reach 48 MPa, effectively improving the early compressive strength of the cement.

[0016] (2) The two short-term carbonation treatments improved the internal pore structure of sulfoaluminate cement, reduced the overall pore size, and significantly reduced the volume of macropores, transforming them into smaller pores. This densification process further enhanced the early strength of sulfoaluminate cement. Attached Figure Description

[0017] Figure 1The graph shows the compressive strength test results of cement specimens under different treatment methods at three different curing ages. Figure 2 These are microstructure morphology images of specimens treated with different methods at an age of 1 day; Figure 3 These are microstructure morphology images of specimens treated with different methods at an age of 3 days. Figure 4 These are microstructure morphology images of specimens treated with different methods at an age of 7 days. Figure 5 This is a distribution of relaxation time (T2) of specimens under different treatment methods when the specimen age is 1 day; Figure 6 This is a distribution of relaxation time (T2) of specimens under different treatment methods at an age of 3 days; Figure 7 This is a distribution of relaxation time (T2) of specimens under different treatment methods at an age of 7 days; Figure 8 This is a porosity distribution curve of specimens treated with different methods at an age of 3 days; Figure 9 This is a graph showing the pore volume results of specimens treated with different methods at an age of 3 days. Detailed Implementation

[0018] Background research indicates that existing studies have largely focused on the carbonation mechanism of sulfoaluminate cement. However, previous research primarily concentrated on the carbonation resistance of sulfoaluminate cement combined with various supplemental cementitious materials (SCMs). The sulfoaluminate cement used in these studies had been hydrated for at least 28 days before carbonation. Given the rapid hydration rate and early strength development of sulfoaluminate cement, early carbonation may significantly affect the evolution of its hydration products, pore structure formation, and strength development process. However, related studies often neglect the coupling relationship between early carbonation, hydration reactions, and early strength evolution, making in-depth research in this area necessary.

[0019] This invention addresses the aforementioned gap by focusing on the coupling effect between early hydration and carbonation in sulfoaluminate cement, thus filling the research gap in the early carbonation mechanism of this cement. By applying short-term carbonation treatment in the early stage of hydration, the early strength of sulfoaluminate cement is effectively improved, making it more suitable for engineering scenarios requiring rapid construction. This early strength enhancement effect has not been fully emphasized in previous studies.

[0020] The present invention will now be described in detail with reference to specific embodiments.

[0021] In the following examples: The sulfoaluminate cement (grade 42.5) produced in Tangshan City, Hebei Province, has the following chemical composition by mass percentage: 37.4% CaO, 18.0% SiO2, 27.7% Al2O3, 13.8% SO3, 2.71% Fe2O3, and 0.39% other impurities. Its mineral composition by mass percentage includes: 40.24% C4A3Š, 21.88% C2S, 21.41% CŠ, 5.16% C4AF, 5.86% C3A, 4.35% CŠH2, and 1.1% amorphous matter. The above-mentioned mineral composition in the technical solution of this invention can all be quantitatively analyzed using TOPAS 4.2.

[0022] The meanings of the English abbreviations used in this invention are shown in the table below:

[0023] Example 1 This embodiment provides a method for preparing sulfoaluminate cement based on hydration-carbonation regulation, the specific method including the following steps: Step 1: Mix sulfoaluminate cement and water, controlling the water-cement ratio (the weight ratio of water to cement) to 0.4, and mix for a short time of 2-3 minutes to obtain sulfoaluminate cement paste. Step 2: Pour the cement grout obtained in Step 1 into a 20×20×20 mm grout container. 3 The mold was filled and hardened for 1 day under standard conditions (20±2℃, 95% relative humidity); Step 3: Demold the cement specimens that have been formed and hardened in Step 2 and place them in a standard environment for secondary curing. Step four: Place the cement specimens that have undergone secondary curing in step three into a carbonation curing chamber at 20±2℃, 20%~25% carbon dioxide concentration and 70±5% relative humidity under normal pressure for accelerated carbonation treatment.

[0024] After 0 days, 2 days, and 6 days of secondary curing, accelerated carbonation was carried out for 1 day, and the compressive strength of the cement blocks obtained after carbonation in Example 1 was then tested.

[0025] Example 2 The preparation, curing and carbonation methods of the sulfoaluminate cement test blocks in this embodiment are the same as those in Embodiment 1, except that the water-cement ratio is 0.5. The specific method process is as follows.

[0026] Step 1: Mix sulfoaluminate cement and water, controlling the water-cement ratio to 0.5, and mix for 2-3 minutes to obtain sulfoaluminate cement paste. Step 2: Pour the cement slurry obtained in Step 1 into the mold of Example 1 and perform molding and curing (i.e., the above-mentioned 1-day molding and hardening). Step 3: Demold the cement specimens that have been molded and cured in Step 2 and place them in a standard environment for secondary curing. Step four: Place the cement specimens that have undergone secondary curing in step three into a carbonation curing chamber at 20±2℃, 20~25% carbon dioxide concentration and 70±5% relative humidity under normal pressure for accelerated carbonation treatment.

[0027] After 0 days, 2 days, and 6 days of secondary curing, accelerated carbonization was carried out for 1 day, and the compressive strength of the cement specimens obtained after carbonization in Example 2 was then tested.

[0028] Example 3 The preparation, curing, and water-cement ratio of the sulfoaluminate cement test blocks in this embodiment are the same as in Example 1. The difference is that a pressure carbonization method is used for carbonation treatment, and the specific method process is as follows.

[0029] Step 1: Mix sulfoaluminate cement and water, controlling the water-cement ratio to 0.4, and mix for 2-3 minutes to obtain sulfoaluminate cement paste. Step 2: Pour the cement slurry obtained in Step 1 into the mold of Example 1 and perform molding and curing. Step 3: Demold the cement specimens that have been molded and cured in Step 2 and place them in a standard environment for secondary curing. Step four: Place the cement specimens that have undergone secondary curing in step three into a carbonation chamber at normal pressure with an environment of 20±2℃, 0.2±0.05 MPa pressure, 99.5%~99.9% carbon dioxide concentration and 55±5% relative humidity for pressurized carbonation treatment.

[0030] After 0 days, 2 days, and 6 days of secondary curing, the cement blocks were subjected to 1 day of pressurized carbonation, and the compressive strength of the cement blocks obtained after carbonation in Example 3 was then tested.

[0031] Example 4 The preparation, curing, and water-cement ratio of the sulfoaluminate cement test blocks in this embodiment are the same as in Example 2. The difference is that a pressure carbonization method is used for carbonation treatment, and the specific method process is as follows.

[0032] Step 1: Mix sulfoaluminate cement and water, controlling the water-cement ratio to 0.5, and mix for 2-3 minutes to obtain sulfoaluminate cement paste. Step 2: Pour the cement slurry obtained in Step 1 into the mold of Example 1 and perform molding and curing. Step 3: Demold the cement specimens that have been molded and cured in Step 2 and place them in a standard environment for secondary curing. Step four: Place the cement specimens, after secondary curing in step three, into a carbonation chamber at 20±2℃, 0.2±0.05 MPa pressure, 99.5%~99.9% carbon dioxide concentration, and 55±5% relative humidity for pressurized carbonation treatment. After 0 days, 2 days, and 6 days of secondary curing, the cement blocks were subjected to 1 day of pressurized carbonation, and the compressive strength of the cement blocks obtained after carbonation in Example 4 was then tested.

[0033] It is understandable that in Examples 1 to 4, the total curing period is 1 day, 3 days and 7 days, respectively, with 1 day of molding curing plus 0 days, 2 days and 6 days of secondary curing.

[0034] Comparative Example 1 The preparation, curing parameters, and water-cement ratio of the sulfoaluminate cement test blocks in this comparative example are the same as in Example 1. The difference is that carbonation treatment is not performed after curing. The specific method and process are as follows.

[0035] Step 1: Mix sulfoaluminate cement and water, controlling the water-cement ratio to 0.4, and mix for a short time to obtain sulfoaluminate cement paste. Step 2: Pour the cement slurry obtained in Step 1 into the mold and allow it to set and cure. Step 3: Demold the cement specimens that have been molded and cured in Step 2 and place them in a standard environment for secondary curing. The compressive strength of the specimens obtained in Comparative Example 1 was tested at curing times of 1 day, 3 days, and 7 days.

[0036] Comparative Example 2 The preparation, curing parameters, and water-cement ratio of the sulfoaluminate cement test blocks in this comparative example are the same as in Example 2. The difference is that carbonation treatment is not performed after curing. The specific method and process are as follows.

[0037] Step 1: Mix sulfoaluminate cement and water, control the water-cement ratio to 0.5, and mix for a short time to obtain sulfoaluminate cement paste. Step 2: Pour the cement slurry obtained in Step 1 into the mold and allow it to set and cure. Step 3: Demold the cement specimens that have been molded and cured in Step 2 and place them in a standard environment for secondary curing. The compressive strength of the specimens obtained in Comparative Example 1 was tested at curing times of 1 day, 3 days, and 7 days.

[0038] Analysis of experimental results: (1) Compressive strength of the specimen: Figure 1The figures show the compressive strength test results of cement specimens from Examples 1-4 and Comparative Examples 1 and 2 at different curing ages. Under a water-cement ratio of 0.4, the early compressive strength of the untreated sample after 1 day was 29 MPa, after accelerated carbonation it was 35-37 MPa, and after pressurized carbonation it was 33.2-35 MPa. The untreated strength after 3 days was 33 MPa, after accelerated carbonation it was 46.5-48 MPa, and after pressurized carbonation it was 36-38 MPa. The untreated strength after 7 days was 32 MPa, after accelerated carbonation it was 42-44 MPa, and after pressurized carbonation it was 34-35.5 MPa. Under a water-cement ratio of 0.5, the early compressive strength of cement specimens after 1 day of untreated treatment was 18 MPa, increasing to 21.5–23 MPa after accelerated carbonation and 19.9–21 MPa after pressurized carbonation. After 3 days of untreated treatment, the strength was 25.5 MPa, increasing to 31–33.5 MPa after accelerated carbonation and 28.5–30 MPa after pressurized carbonation. After 7 days of untreated treatment, the strength was 19.5 MPa, increasing to 30–34.5 MPa after accelerated carbonation and 24–26 MPa after pressurized carbonation. It can be seen that under water-cement ratios of 0.4 and 0.5, the strength of cement specimens at all ages improved after implementing both short-term carbonation methods. Under a water-cement ratio of 0.4, after accelerated carbonation treatment at three different curing ages, the compressive strength of cement specimens increased by 23.4% (1 day), 36.0% (3 days), and 28.8% (7 days), respectively. In comparison, the compressive strength of cement specimens treated with pressure carbonation increased by 16.6% (1 day), 5.9% (3 days), and 2.7% (7 days), respectively. Furthermore, cement specimens treated with both short-term (1-day) carbonation methods already achieved compressive strength levels comparable to uncarbonized cement specimens at 3 and 7 days of curing under the same conditions, even after only 1 day of curing. At a water-cement ratio of 0.5, accelerated carbonation increased the compressive strength of cement specimens by 14.9% (1 day), 22.0% (3 days), and 48.7% (7 days). Under pressure carbonation, the compressive strength increased by 5.9% (1 day), 12.5% ​​(3 days), and 21.8% (7 days), respectively. These data demonstrate that both accelerated and pressure carbonation methods significantly improve the early strength of sulfoaluminate cement during the early stages of hydration. Meanwhile, the accelerated carbonation treatment method for short-term carbonation has a significantly more prominent effect on improving the early compressive strength of sulfoaluminate cement compared to pressure carbonation.

[0039] Since a water-cement ratio of 0.4 significantly improves the strength of sulfoaluminate cement after short-term carbonation treatment, and the effect is more pronounced, further analysis will be conducted on cement specimens with a water-cement ratio of 0.4 in the future.

[0040] (2) Quantitative analysis of the composition of cement specimens Tables 1, 2, and 3 show the quantitative analysis results of cement specimens from Examples 1, 3, and 1 (Comparative Example 1) at curing ages of 1 day, 3 days, and 7 days, respectively. At a curing period of 1 day (see Table 1), the ettringite content in cement specimens after both carbonation treatments was lower than that in uncarbonized specimens. This can be attributed to the carbonation reaction of ettringite. Furthermore, the ettringite content in specimens treated with accelerated carbonation was lower than that in specimens treated with pressure carbonation, while the contents of gypsum and calcite, the products of the ettringite carbonation reaction, were higher. This indicates that the carbonation reaction of ettringite was more significant under accelerated carbonation conditions. Table 1 also shows that the contents of calcium sulfoaluminate and gypsum in specimens treated with both carbonation treatments were higher than those in uncarbonized specimens, indicating that the hydration reaction of calcium sulfoaluminate in the specimens was inhibited by the carbonation environment. In addition, the content of dicalcium silicate in cement specimens decreased under both carbonation treatments, and the content of dicalcium silicate was even lower under accelerated carbonation conditions, which also indicates that the dicalcium silicate underwent a carbonation reaction. As described above, the reduction in ettringite content in the carbonized cement specimens is not only due to its own carbonization decomposition, but also to the inhibited hydration reaction of calcium sulfoaluminate, resulting in less ettringite formation. The increase in calcite content in the carbonized specimens also comes from both the carbonization of ettringite and the carbonization of dicalcium silicate.

[0041] At a curing period of 3 days (see Table 2), the content of ettringite decreased in both types of carbonized specimens, while the contents of gypsum dihydrate and calcite increased, and this phenomenon was more pronounced after accelerated carbonization treatment. Unlike the curing period of 1 day, the calcium sulfoaluminate content decreased in both types of carbonized specimens after 3 days of curing, indicating that carbonization treatment promoted the hydration reaction of calcium sulfoaluminate in the specimens at a 3-day hydration period. Furthermore, the content of dicalcium silicate in the specimens treated with pressure carbonization was lower than that in the specimens treated with accelerated carbonization, indicating that the pressure carbonization environment at a 3-day curing period intensified the carbonization reaction of dicalcium silicate.

[0042] When the curing period was 7 days (see Table 3), the carbonized specimens had a slightly lower content of ettringite and an increased content of gypsum dihydrate and calcite, which further confirmed the occurrence of the carbonization reaction. At the same time, the decrease in the content of anhydrous gypsum and calcium sulfoaluminate indicated that the hydration reaction of calcium sulfoaluminate was promoted in both carbonization environments.

[0043] Table 1. Quantitative XRD results of cement specimens treated with different methods at a curing age of 1 day (in wt.%)

[0044] Table 2. Quantitative XRD results of cement specimens treated with different methods at a curing period of 3 days (in wt.%)

[0045] Table 3. Quantitative XRD results of cement specimens treated with different methods at a curing age of 7 days (in wt.%)

[0046] (3) Microscopic morphology analysis of the specimen Figure 2 , Figure 3 and Figure 4 The images show the microstructure of different cement specimens from Examples 1, 3, and 1 Comparative Example 1 at curing ages of 1 day, 3 days, and 7 days, respectively.

[0047] As shown in the figure, at a curing age of 1 day, a large number of needle-like ettringite crystals were observed in the uncarbonized cement specimens, accompanied by flocculent aluminum hydroxide. In the carbonized samples, aggregated calcite crystals and small amounts of flocculent and fibrous aluminum hydroxide were observed in the pressure-carbonized specimens, forming a complete structure. For the accelerated carbonized samples, a large amount of amorphous aluminum hydroxide coexisted with agglomerated calcite. The presence of both structures significantly contributed to the strength increase of the two types of specimens after carbonization.

[0048] At a curing age of 3 days, a small amount of fibrous aluminum hydroxide and angular calcite crystals were observed in the uncarbonized specimens. Under pressure carbonization conditions, the calcite produced by carbonization formed cubic clusters in the cement specimens, accompanied by obvious fibrous aluminum hydroxide. This combination of structures made the microstructure of the specimens more compact. Under accelerated carbonization conditions, calcite crystals aggregated into larger particles, and a large amount of amorphous aluminum hydroxide adhered to their surface, effectively filling the pore structure. Therefore, the pore structure of the specimens was improved, the microstructure became more compact, and the specimen strength was thus enhanced.

[0049] At a curing period of 7 days, the microstructure of the specimens was similar to that at a curing period of 3 days; for uncarbonized specimens, needle-like ettringite and fibrous aluminum hydroxide were still present. Under pressure carbonization conditions, due to the decomposition of ettringite, flocculent aluminum hydroxide was found to adhere to the prismatic calcite. Under accelerated carbonization conditions, a cohesive structure was observed formed between the prismatic calcite and a large amount of amorphous and fibrous aluminum hydroxide, further densifying the microstructure of the specimens.

[0050] (4) Analysis of the hole structure of the specimen Figure 5 , Figure 6 and Figure 7The figures show the relaxation time (T2) distribution of cement specimens at three different curing ages. Generally, the T2 peak can be divided into three regions: 0.1–1 ms corresponds to water in gel pores, 1–10 ms corresponds to water in capillary pores, and 10–100 ms corresponds to water in microcracks or voids. As shown in the figure, all three types of specimens exhibit two distinct T2 peaks, with the main peak located in the 1–10 ms range and the secondary peak located in the 10–100 ms range.

[0051] At a curing age of 1 day, the primary T2 values ​​of both types of carbonized cement specimens showed a decreasing trend, and the secondary T2 peaks also showed the same trend. This indicates that the pore size of the carbonized specimens decreased, especially in the specimens treated with accelerated carbonation, where the smallest T2 value was observed. This represents the smallest pore size and improved pore structure in the accelerated carbonization specimens, which also corresponds to the results of the compressive strength test. In addition, the peak area (0.1~1 ms) of water in the gel pores of the carbonized specimens decreased, with the smallest area observed in the pressurized carbonization specimens, representing the smallest gel pore volume. Similarly, the peak area (1~10 ms) of water in the capillary pores was ranked as follows: uncarbonized specimens > pressurized carbonization specimens > accelerated carbonization specimens, indicating that the accelerated carbonization specimens had the smallest capillary pore volume.

[0052] At a curing age of 3 days, the decrease in both the primary and secondary T2 peak values ​​of the cement specimens after both carbonation treatments indicates that carbonation reduced the pore size of the specimens. The peak area of ​​the gel pores (0.1–1 ms) also shows that carbonation reduced the gel pore content in the specimens. At a curing age of 7 days, the primary T2 peak value decreased only under accelerated carbonation. The primary and secondary T2 peaks under pressure carbonation were similar to those of the uncarbonized specimens. The overall gel pore and capillary pore content of the carbonized specimens decreased. Notably, the specimens after accelerated carbonation had the lowest capillary pore content and overall pore size, corresponding to their highest compressive strength.

[0053] Figure 8 The figure shows the nanopore distribution of specimens cured for 3 days under different treatments. Pore size can generally be categorized into different ranges: gel pores (pore size < 10 nm), mesopores (10 nm < pore size ≤ 50 nm), medium capillary pores (50 nm < pore size ≥ 100 nm), and large capillary pores (pore size > 100 nm). The median pore sizes of these specimens are 25.05 nm, 19.10 nm, and 22.84 nm, respectively, indicating that carbonation treatment reduces the median pore size of the cement specimens. Furthermore, the figure also shows that carbonation treatment significantly reduces the volume of large capillary pores (≥ 100 nm). Figure 9 According to Figure 8The calculated pore volumes showed that, compared to uncarbonized specimens, the gel pore volume increased after pressure carbonization, but decreased after accelerated carbonization. Furthermore, the pore volumes of mesopores (10–50 nm) and mesocapillary pores (50–100 nm) increased after carbonization, while the volumes of large capillary pores (≥100 nm) decreased. This indicates that short-term carbonization reduces the volume of large capillary pores and increases the volume of mesopores and mesocapillary pores in sulfoaluminate cement specimens, improving the pore structure and corresponding to the increased compressive strength of the cement specimens after short-term carbonization.

[0054] Those skilled in the art will understand that the above embodiments are specific examples of implementing the present invention, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of the present invention. Any person skilled in the art can make their own modifications and alterations without departing from the spirit and scope of the present invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for the production of sulphoaluminate cement based on hydration-carbonation regulation, characterized by, The preparation method comprises the following steps: mixing sulphoaluminate cement and water, and then performing mixing to obtain a sulphoaluminate cement paste; performing moulding and hardening of the sulphoaluminate cement paste under standard environment to obtain a cement test piece; placing the cement test piece in an accelerated carbonation treatment under normal pressure environment of 20±2℃, 20%-25% carbon dioxide concentration and 70±5% relative humidity, or in a pressurized carbonation treatment under 20±2℃, 0.2±0.05 MPa pressure, 99.5%-99.9% carbon dioxide concentration and 55±5% relative humidity environment, to obtain the sulphoaluminate cement based on hydration-carbonation regulation.

2. The method for producing a sulphoaluminate cement based on hydration-carbonation regulation according to claim 1, characterized in that, after obtaining the cement test piece, the cement test piece is further placed in a standard environment for secondary curing; the time for the secondary curing is 0-6 days.

3. The method for producing a sulphoaluminate cement based on hydration-carbonation regulation according to claim 1, characterized in that, the water-cement ratio of the sulphoaluminate cement and water is 0.4-0.5, and the mixing time is 2-3 minutes.

4. The method for producing a sulphoaluminate cement based on hydration-carbonation regulation according to claim 1, characterized in that, the sulphoaluminate cement paste is first poured into a mould with a size of 20 mm×20 mm×20 mm before performing moulding and hardening; and the time for the moulding and hardening is 1 day.

5. The method for producing a sulphoaluminate cement based on hydration-carbonation regulation according to claim 1, characterized in that, the standard environment is 20±2℃ and 95±3% relative humidity.

6. The method for producing a sulphoaluminate cement based on hydration-carbonation regulation according to claim 1, characterized in that the time for the accelerated carbonation treatment or the pressurized carbonation treatment is 1 day.

7. The method for producing a sulphoaluminate cement based on hydration-carbonation regulation according to claim 1, characterized in that, The preparation method specifically comprises the following steps: Step one, mixing sulphoaluminate cement and water at a water-cement ratio of 0.4-0.5, and then performing mixing for 2-3 minutes to obtain a sulphoaluminate cement paste; Step two, pouring the sulphoaluminate cement paste into a mould with a size of 20 mm×20 mm×20 mm, and performing moulding and hardening for 1 day under 20±2℃ and 95±3% relative humidity to obtain a cement test piece; Step three, after demoulding the cement test piece, placing the cement test piece under 20±2℃ and 95±3% relative humidity for 0, 2 and 6 days of secondary curing respectively to obtain cement test pieces after secondary curing; Step four, placing the cement test pieces after secondary curing in a carbonation curing box under 20±2℃, 20%-25% carbon dioxide concentration and 70±5% relative humidity for 1 day of accelerated carbonation treatment, or under 20±2℃, 0.2±0.05 MPa pressure, 99.5%-99.9% carbon dioxide concentration and 55±5% relative humidity for 1 day of pressurized carbonation treatment, to obtain the sulphoaluminate cement based on hydration-carbonation regulation.

8. The sulphoaluminate cement based on hydration-carbonation regulation prepared by the preparation method of the sulphoaluminate cement based on hydration-carbonation regulation according to any one of claims 1-7.

9. Sulphoaluminate cement based hydration-carbonation regulation according to claim 8, characterized in that, The early compressive strength of the sulphoaluminate cement based on hydration-carbonation regulation is up to 48 MPa.

10. Application of the sulphoaluminate cement based on hydration-carbonation regulation according to claim 8 in the field of rapid construction.

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