Method for improving chloride ion curing capacity of limestone calcined clay cement paste

Abstract

The invention discloses a method for improving the chloride ion curing capacity of limestone calcined clay cement paste, and belongs to the technical field of cement concrete. According to the method, layered double hydroxides are doped into a limestone calcined clay cement-based material, the cement-based material comprises cement, metakaolin, limestone powder, a water reducing agent and water, and the layered double hydroxides are CaAl-NO3 LDHs; the doping amount of the CaAl-NO3 LDHs is 0.9%-3% of the weight of the cement-based material. By doping CaAl-NO3 LDHs, the chloride ion curing capacity of cement paste can be improved, and the chloride ion diffusion coefficient of an LC3 system is always lower than that of an OPC system. The total chloride ion content and the free chloride ion content of the OPC-L2 system at the depth of 0-5 mm are respectively reduced by 10.3% and 10.0%, and the total chloride ion content and the free chloride ion content of the LC55-L2 system at the depth of 0-5 mm are respectively reduced by 23.4% and 10.1%.

Description

Technical Field

[0001] This invention belongs to the field of cement concrete technology, specifically relating to a method for improving the chloride ion curing ability of limestone-calcined clay cement paste. Background Technology

[0002] Limestone calcined clay cement (LC) 3 Limestone powder and calcined clay are used to replace part of the cement clinker in a ternary composite cementitious material. It combines the chemical reaction between alumina in the calcined clay and carbonates in the limestone, the pozzolanic effect of the calcined clay, and the filling effect of the limestone, creating a synergistic effect among the cement clinker, calcined clay, and limestone. This results in a denser microstructure and excellent mechanical properties and durability. Furthermore, due to the denser microstructure and stronger chloride ion binding capacity, LC... 3 The system exhibits excellent resistance to chloride ion diffusion and good resistance to sulfate attack. Although LC 3 The system performs well in terms of durability, but in complex, salty environments, corrosion of the matrix is ​​still unavoidable.

[0003] Layered double hydroxides (LDHs), also known as layered double hydroxide composite metal hydroxides, are two-dimensional nanosheet materials with layered structures possessing ion exchange properties and "structural memory" capabilities. Due to the layered structure of LDHs, the anions between the layers are connected by hydrogen bonds, thus enabling the exchangeability of these anions. Generally, higher-valence anions are more easily exchanged into the interlayer space, while lower-valence anions are more easily exchanged out. The general ion exchange sequence followed by interlayer anions in LDHs is CO32-. 2- >SO4 2- >Cl - >NO3 - >NO2 - Furthermore, calcined LDHs can restore their original layered framework structure in anionic solutions, allowing anions to be inserted between the layers, thus exhibiting a higher anion adsorption capacity. Due to their unique layered structure and ion exchange properties, they can be used as auxiliary reinforcing materials in concrete structures to adsorb corrosive ions and improve the durability of concrete structures.

[0004] Currently, there are numerous reports on the application of LDHs in cement-based materials, and research on the combination of LDHs with LC... 3 No research has been reported on systems to resist the erosion of cement-based materials in chloride salt environments. Summary of the Invention

[0005] One technical problem solved by this invention is to provide a method for improving the chloride ion curing ability of limestone-calcined clay cement paste. By optimizing the LDHs system, a controlled-release, long-lasting, and targeted chloride ion curing LDHs protection system is obtained, laying the foundation for improving the durability and engineering application of long-life LC3 marine concrete structures.

[0006] Technical Solution: To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A method for improving the chloride ion curing ability of limestone-calcined clay cement paste involves incorporating layered double hydroxides into the limestone-calcined clay cement-based material. The cement-based material is composed of cement, metakaolin, limestone powder, water-reducing agent, and water, and the layered double hydroxides are CaAl-NO3 LDHs.

[0008] The method comprises the following cement-based material components and contents: 230-260g cement, 120-140g metakaolin, 60-70g limestone powder, 2-3g water-reducing agent, and 210-230g water; preferably, 247.5g cement, 135.0g metakaolin, 67.5g limestone powder, 2.5g water-reducing agent, and 225g water; the water-cement ratio is 0.5.

[0009] In the method described, the amount of CaAl-NO3 LDHs incorporated is 0.9%-3% of the weight of the cement-based material; preferably, 1%-2%.

[0010] The method wherein the cement is one of grade 42.5 Portland cement, grade 42.5 ordinary Portland cement, or grade 52.5 Portland cement, preferably grade 42.5 ordinary Portland cement, with an apparent density and specific surface area of ​​2080 kg / m³. 3 and 385m 2 / kg; the metakaolin is one of water-washed calcined kaolin, coal-series calcined kaolin, or calcined coal gangue, preferably water-washed calcined metakaolin with an apparent density of 2520 kg / m³. 3 Specific surface area 16800 m² 2 / kg; the limestone powder is one of high-calcium limestone powder, magnesium limestone powder, or dolomite powder, preferably 600-mesh calcareous limestone powder with an apparent density of 2720 kg / m³. 3 Specific surface area 795 kg / m² 3 .

[0011] The method described, the method for preparing cement paste, includes the following steps:

[0012] (1) Add cement, metakaolin, limestone powder, water-reducing agent and hydrotalcite to the cement paste mixer;

[0013] (2) Add mixing water and continue stirring. After stirring, pour it into a mold and transfer it to a constant temperature and humidity chamber for standard curing for 28 days. After curing, limestone calcined clay cement paste is obtained.

[0014] The method described herein, the preparation of CaAl-NO3 LDHs, includes the following steps:

[0015] (1) Dissolve Ca(NO3)2·4H2O and Al(NO3)3·9H2O in deionized water;

[0016] (2) Add the metal salt solution from step (1) dropwise to the sodium nitrate solution;

[0017] (3) The reaction is carried out in a temperature-controlled magnetic stirrer, and crystallization is performed after the addition is complete;

[0018] (4) The obtained white precipitate was filtered with a vacuum filter, the obtained white filter cake was washed with deionized water, the precipitate was dried, and then ground to obtain hydrotalcite CaAl-NO3 LDHs powder.

[0019] The molar ratio of Ca(NO3)2·4H2O and Al(NO3)3·9H2O in the method is 1.8:1-2.5:1, preferably 2:1; the total molar concentration of the metal salt solution is 1.8-2.5 mol / L, preferably 2 mol / L.

[0020] In the method described, the concentration of the sodium nitrate solution is 1.8-2.5 mol / L, preferably 2 mol / L. While adding the sodium nitrate solution dropwise, 0.8-1.2 mol / L of sodium hydroxide solution is added dropwise to maintain the pH value of the mixed solution system at 11.8-12.2. Preferably, the concentration of the sodium hydroxide solution is 1 mol / L, adjusting the solution system to maintain a pH of 12.

[0021] The method involves magnetic stirring at a speed of 800-1200 r / s and maintaining a temperature of 23-27°C for 1.8-2.5 hours; after the addition is complete, crystallization is carried out at 65-75°C for 16-20 hours; preferably, magnetic stirring at a speed of 1000 r / s and maintaining a temperature of 25°C for 2 hours; after the addition is complete, crystallization is carried out at 70°C for 18 hours.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0023] (1) The addition of CaAl-NO3 LDHs can improve the chloride ion curing ability of cement paste. 3The chloride ion diffusion coefficient of the OPC-L2 system was consistently lower than that of the OPC system. In the OPC-L2 system, the total chloride ion and free chloride ion contents decreased by 10.3% and 10.0% at a depth of 0-5 mm, respectively, while in the LC55-L2 system, they decreased by 23.4% and 10.1%, respectively.

[0024] (2) CaAl-NO3 LDHs and LC 3 The composite system exhibited better resistance to chloride ion penetration than OPC. The chloride ion diffusion coefficients of the OPC-L2 system and the LC55-L2 system were 6.26 × 10⁻⁶ and 6.26 × 10⁻⁶, respectively. -12 m 2 / s and 2.67×10 -12 m 2 / s, compared with the control group, decreased by 15.1% and 45.2%, respectively. Increasing the CaAl-NO3 LDHs doping did not further reduce the chloride ion diffusion coefficient.

[0025] (3) XRD analysis results showed that the incorporation of CaAl-NO3 LDHs increased the Friedel's salt content of the paste and decreased the calcium hydroxide peak, indicating that more chloride ions were solidified in the matrix. LC 3 Regardless of whether CaAl-NO3LDHs were incorporated into the system, Friedel's salt peak was always higher than that of the OPC-L3 group.

[0026] (4) Thermogravimetric analysis results showed that the OPC-L0 group had the highest calcium hydroxide content and the lowest Friedel's salt content. After incorporating the highest amount of CaAl-NO3 LDHs, the Friedel's salt content in the hydration products of the OPC system increased from 2.53% to 2.91%. 3 The system concentration increased from 3.34% to 4.13%. Compared to the OPC system, CaAl-NO3 LDHs and LC 3 The composite exhibits better resistance to chloride ion penetration.

[0027] (5) The present invention aims to optimize the design of the LDHs system in order to obtain a controlled-release, long-lasting, targeted curing chloride ion LDHs protection system, laying the foundation for improving the durability and engineering application of long-life LC3 marine concrete structures. Attached Figure Description

[0028] Figure 1 XRD diffraction pattern of synthetic hydrotalcite ( Figure 1 a) TG-DSC chart Figure 1 b) FTIR plot ( Figure 1 c) and SEM image ( Figure 1 d);

[0029] Figure 2 The total chloride ion content (TCI) of two types of paste samples after soaking in NaCl solution for 120 days is ( ). Figure 2 a, 2b) and free chloride ions ( Figure 2 c) Distribution diagram of 2d)

[0030] Figure 3 XRD patterns of different neat cement paste samples after 120 days of etching in NaCl solution. Figure 3 a) TG chart ( Figure 3 b) and DTG diagram ( Figure 3 c). Detailed Implementation

[0031] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0032] The cement is P·O 42.5 ordinary Portland cement (OPC) produced by Hubei Huangshi Huaxin Cement Plant, with an apparent density and specific surface area of ​​2080 kg / m³. 3 and 385m 2 / kg; chemical composition is shown in Table 1.

[0033] Metakaolin (MK) is a water-washed and calcined metakaolin with an apparent density of 2520 kg / m³. 3 Specific surface area 16800 m² 2 / kg; chemical composition is shown in Table 1.

[0034] Limestone powder (LP) is 600-mesh calcareous limestone powder with an apparent density of 2720 kg / m³. 3 Specific surface area 795 kg / m² 3 The chemical composition is shown in Table 1.

[0035] The cement paste mixing water used is Wuhan municipal tap water.

[0036] The water-reducing agent used is a polycarboxylate water-reducing agent produced by Jiangsu Subote Co., Ltd., with a solid content of 33% and a water reduction rate of 35%.

[0037] Synthetic hydrotalcite and chloride ion analysis were performed using ultrapure water produced by a pure water system.

[0038] Chemical reagents: Aluminum nitrate (Ca(NO3)2·4H2O), calcium nitrate (Al(NO3)3·9H2O), sodium nitrate (NaNO3), silver nitrate (AgNO3), and sodium hydroxide (NaOH) were purchased from Sinopharm Chemical Reagent Co., Ltd., while NaCl, nitric acid, potassium chromate, phenolphthalein, etc. were purchased from Xilong Scientific Co., Ltd., and all were of analytical grade.

[0039] Table 1. Chemical composition (wt%) of cement, metakaolin, and limestone powder

[0040] Components CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> MgO <![CDATA[SO3]]> LOI OPC 63.83 19.21 4.18 3.35 1.65 3.32 1.11 LS 51.33 0.31 0.13 0.05 0.77 0.02 42.6 MK 0.18 54.62 43.21 0.78 0.08 0.01 1.04

[0041] Example 1

[0042] The CaAl-NO3 LDHs were synthesized using a coprecipitation method. The specific synthesis steps are as follows:

[0043] (1) Dissolve analytical grade Ca(NO3)2·4H2O and Al(NO3)3·9H2O in deionized water at a molar ratio of 2:1, and make the total molar concentration 2 mol / L;

[0044] (2) Add the metal salt solution from step (1) dropwise to 200 mL of 2 mol / L sodium nitrate solution. At the same time, add 1 mol / L sodium hydroxide solution dropwise to keep the pH of the mixed solution system at around 12.

[0045] (3) The entire reaction process was carried out in a temperature-controlled magnetic stirrer at a speed of 1000 r / s and a temperature of 25°C for 2 hours; after the addition was completed, it was crystallized at 70°C for 18 hours.

[0046] (4) The obtained white precipitate was filtered with a vacuum filter, and the obtained white filter cake was washed with deionized water 4 times to remove residual nitrates adhering to the surface of the product. Finally, the precipitate was dried in a drying oven at 105°C for 12 hours, and then taken out and ground to obtain hydrotalcite CaAl-NO3 LDHs white powder.

[0047] Figure 1 a is the XRD diffraction pattern of the synthesized hydrotalcite. As can be seen from the figure, most diffraction peaks correspond to the characteristic diffraction peaks of CaAl-NO3LDHs, and the peak shapes are very sharp with high intensity, proving that the synthesized CaAl-NO3LDHs has high purity, complete crystal form, and good crystallinity. The first strong peak in the figure corresponds to the d

[003] crystal plane, with a corresponding diffraction angle of 2θ = 10.26°. This hydrotalcite belongs to the hexagonal crystal system, with cell parameters c = 3d003 = 2.587 nm and a cell parameter a = 2d003. 110=0.305nm. Subtracting the layer thickness from d003 yields the interlayer channel height. The peaks of the CaAl-NO3 LDHs in the figure are very sharp, and the baseline is low and stable, both indicating good crystallinity and high interlayer regularity of the synthesized CaAl-NO3 LDHs. The spectrum also shows that CO2 still entered the solution during synthesis, causing the formation of some CaAl-CO3 LDHs and CaCO3 byproducts. However, the peak intensities of both are low, indicating minimal impurity contamination and no impact on subsequent experiments.

[0048] Figure 1 b is the TG-DSC chromatogram of the synthesized CaAl-NO3 LDHs. The chromatogram shows that CaAl-NO3 LDHs exhibited significant loss of water of crystallization at 70.8℃. With increasing temperature, the water of crystallization was completely removed, and interlayer water began to be removed, resulting in a sharp endothermic peak at 175.8℃, indicating the decomposition of hydroxyl groups on the main layer into water. As the temperature continued to rise, the layered structure of CaAl-NO3 LDHs was disrupted, with a significant endothermic peak appearing at 595.8℃, representing the decomposition of nitrates into nitrogen dioxide. This indicates that the interlayer anions in the CaAl-NO3 LDHs were mostly nitrate. During the temperature rise to 1000℃, a few broad small peaks were observed, mainly due to the decomposition of carbonates within this temperature range, indicating the presence of a small amount of carbonate impurities in the synthesized hydrotalcite.

[0049] The FTIR spectra of the synthesized CaAl-NO3 LDHs are as follows: Figure 1 As shown in c, it can be seen from the figure that 3610cm -1 and 3470cm -1 The two strong peaks at 1620 cm⁻¹ correspond to the stretching vibrations of the water of crystallization and the Ca-OH group, respectively. -1 The infrared peak at 1380 cm⁻¹ corresponds to the bending vibration of the HOH group in the interlayer water molecules. -1 The splitting peak at 795 cm⁻¹ corresponds to the stretching vibration peak of nitrate ions, indicating that nitrate ions have successfully intercalated into the interlayer. -1 and 555cm -1 The results reflect the stretching and deformation vibrations of the Al-OH group. These results demonstrate the successful synthesis of nitrate hydrotalcite.

[0050] Figure 1 Image d shows the SEM image of the synthesized CaAl-NO3 LDHs. As can be seen, there are many irregular layered flakes with layers stacked on top of each other. The CaAl-NO3 LDHs have small grain sizes and complete crystal growth, and the unique layered structure of hydrotalcite is clearly visible, further confirming the synthesis of CaAl-NO3 LDHs.

[0051] Example 2

[0052] The preparation of LC55-L1 paste includes the following steps:

[0053] (1) Add 247.5g of cement, 135.0g of metakaolin, 67.5g of limestone powder, 2.5g of water-reducing agent and 4.5g of hydrotalcite to a cement paste mixer and mix for 2 minutes; the water-cement ratio is 0.5.

[0054] (2) Add 225g of mixing water and continue stirring. After stirring, pour the mixture into a 40mm×40mm×160mm mold and transfer it to a constant temperature and humidity chamber for standard curing for 28 days. After curing, you will get LC55-L1 pure pulp.

[0055] After adding the weighed cementitious material and hydrotalcite, remove the product, coat the surrounding area with epoxy resin, and then immerse it in the etching solution. After reaching the specified curing age, remove the product and take samples at 0-5mm, 5-10mm, 10-15mm, and 15-20mm diameters for grinding and titration.

[0056] Example 3

[0057] The mixing ratio of LC55-L2 cement paste is: 247.5g cement, 135.0g metakaolin, 67.5g limestone powder, 2.5g water-reducing agent, 9g hydrotalcite, and 225g water. The preparation method is the same as in Example 2.

[0058] Example 4

[0059] The mixing ratio of LC55-L3 cement paste is: 247.5g cement, 135.0g metakaolin, 67.5g limestone powder, 2.5g water-reducing agent, 13.5g hydrotalcite, and 225g water. The preparation method is the same as in Example 2.

[0060] Comparative Example 1

[0061] The mixing ratio of LC55-L0 cement paste is: 247.5g cement, 135.0g metakaolin, 67.5g limestone powder, 2.5g water-reducing agent, and 225g water. The preparation method is the same as in Example 2.

[0062] Comparative Example 2

[0063] The mixing ratio of OPC-L0 cement paste is: 450.0g cement and 225g water. The preparation method is the same as in Example 2.

[0064] Comparative Example 3

[0065] The mixing ratio of OPC-L1 cement paste is: 450.0g cement, 4.5g hydrotalcite, and 225g water. The preparation method is the same as in Example 2.

[0066] Comparative Example 4

[0067] The mixing ratio of OPC-L2 cement paste is: 450.0g cement, 9g hydrotalcite, and 225g water. The preparation method is the same as in Example 2.

[0068] Comparative Example 5

[0069] The mixing ratio of OPC-L3 cement paste is: 450.0g cement, 13.5g hydrotalcite, and 225g water. The preparation method is the same as in Example 2.

[0070] Test methods

[0071] After oxidation, remove the slurry, coat it with epoxy resin around the edges, and then immerse it in an etching solution (3.5% NaCl solution). After reaching the specified curing time, remove the slurry and take samples at 0-5mm, 5-10mm, 10-15mm, and 15-20mm diameters for grinding and titration.

[0072] According to JGJ / T 322—2013 "Technical Specification for Testing Chloride Ion Content in Concrete", the total chloride ion content is tested by acid dissolution method, and the free chloride ion content is determined by water dissolution method.

[0073] (1) The total chloride ion content of the paste sample after soaking in NaCl solution for 120 days was tested. Figure 2 a, 2b) and free chloride ions ( Figure 2 c, 2d) Distribution

[0074] Total chloride ions in a paste sample soaked in NaCl solution for 120 days ( Figure 2 a, 2b) and free chloride ions ( Figure 2 c) Distribution of CaAl-NO3 LDHs. It can be seen that the incorporation of CaAl-NO3 LDHs reduces both the total chloride ion content and the free chloride ion content of the sample, and both gradually decrease with increasing depth. For the OPC system, CaAl-NO3 LDHs have a reducing effect on chloride ion content at depths within 15 mm. Specifically, compared with OPC-L0, OPC-L1, OPC-L2, and OPC-L3 show reductions in total chloride ion content of 5.3%, 10.3%, and 30.5% at depths of 0-5 mm, respectively, and reductions in free chloride ion content of 3.1%, 10.0%, and 49.3%, respectively. For LC... 3 Compared to LC55-L0, the systems with incorporation amounts of LC55-L1, LC55-L2, and LC55-L3 showed reductions in total chloride ion content of 19.1%, 23.4%, and 21.2% at depths of 0-5 mm, respectively, and reductions in free chloride ion content of 12.6%, 10.1%, and 37.3%, respectively. However, with increasing depth, the chloride ion content of the OPC system paste gradually became more uniform. Compared to the OPC system, LC55-L1, LC55-L2, and LC55-L3 showed... 3The system exhibits significantly lower total chloride ion content and free chloride ion content, with the total chloride ion content continuously decreasing as the LDH dosage increases. This is attributed, on the one hand, to the filling effect of limestone powder and the pozzolanic effect of calcined clay, which refine the matrix pore structure while simultaneously enhancing chloride ion binding capacity, thus improving the LC... 3 Compared to the OPC system, this system exhibits stronger resistance to chloride ion penetration. This is partly due to the interlayer anion exchange property of CaAl-NO3 LDHs, which allows chloride ions to be adsorbed.

[0075] (2) Test the apparent chloride ion diffusion coefficient of the sample

[0076] According to Fick's second law, the apparent chloride ion diffusion coefficient of the sample was calculated using the free chloride ion content. A higher chloride ion diffusion coefficient indicates that chloride ions can more easily penetrate into the cementitious material. For the OPC system, the chloride ion diffusion coefficient of the OPC-L0 sample was 7.37 × 10⁻⁶. -12 m 2 / s, the chloride ion diffusion coefficients of OPC-L1, OPC-L2 and OPC-L3 samples were 6.71×10⁻⁶. -12 m 2 / s, 6.26×10 -12 m 2 / s and 7.22×10 -12 m 2 / s, representing reductions of 9.0%, 15.1%, and 2.0%, respectively. For LC 3 The system, sample LC55-L0, has a chloride ion diffusion coefficient of 4.87 × 10⁻⁶. -12 m 2 / s, the chloride ion diffusion coefficients of LC55-L1, LC55-L2 and LC55-L3 samples were 3.58×10⁻⁶ / s, respectively. -12 m 2 / s, 2.67×10 -12 m 2 / s and 4.11×10 -12 m 2 / s, compared to 26.5%, 45.2%, and 15.6%, respectively. It can be seen that with the increase of CaAl-NO3 LDHs doping, the OPC system and LC... 3 The chloride ion diffusion coefficients of the system samples all showed a trend of first decreasing and then increasing. LC 3 The chloride ion diffusion coefficient of the system is always lower than that of the OPC system.

[0077] In summary, the chloride ion diffusion coefficients of LC55-L1 and LC55-L2 are significantly reduced, while the chloride ion diffusion coefficient of the LC55-L3 system is increased. This indicates that appropriate amounts of CaAl-NO3 LDHs help to slow down chloride ion diffusion. Furthermore, it can be seen that hydrotalcite and LC55-L3... 3 Cement-based composites exhibit better resistance to chloride ion penetration than OPC. This is because CaAl-NO3 LDHs can activate the pozzolanic activity of calcined clay, promoting LC... 3 Early hydration of cement generates more hydration products, and this hydration product can react with chloride ions to form more Friedel's salts, thereby increasing LC. 3 The system's ability to cure chloride ions.

[0078] (3) XRD analysis of different cement paste samples after 120 days of etching in NaCl solution

[0079] Figure 3 a shows the XRD patterns of different paste samples after 120 days of etching in NaCl solution. Friedel's salt peaks were observed in all samples. The Friedel's salt peak was enhanced in the OPC-L3 system, while the peak of ettringite (AFt) was weakened because CaAl-NO3 LDHs preferentially react with SO4. 2- The combination promotes the conversion of more C3A to Friedel's salt, thus limiting the formation of AFt. The Friedel's salt peak variation in the LC55-L3 system is smaller, while the AFt peak is enhanced. Comparing the OPC-L3 group and the LC55-L0 group of pulp, it can be seen that LC... 3 Regardless of whether CaAl-NO3 LDHs were incorporated into the system, its Friedel's salt peak was consistently higher than that of the OPC-L3 group, indicating that the incorporation of CaAl-NO3 LDHs significantly improved the OPC and LC ratios. 3 The curing effect of the LC system on chloride ions is better than that of the OPC system. 3 The system exhibits strong resistance to chloride ion penetration. Furthermore, it can be observed that, except for the OPC-L0 group, the calcium hydroxide diffraction peaks of the other groups of paste are relatively low. This is because CaAl-NO3 LDHs have a large specific surface area, and during mixing, they absorb some water, resulting in incomplete hydration and reduced calcium hydroxide formation.

[0080] (4) Test the TG and DTG of different pastes after soaking in NaCl solution for 120 days.

[0081] TG of different pastes soaked in NaCl solution for 120 days Figure 3 b) and DTG diagram ( Figure 3c). As shown in the figure, there are four weight loss peaks: 60-200℃ represents the dehydration of C-(A)-SH gel and the decomposition of ettringite; 300-350℃ represents the decomposition of Friedel's salt peak; 400-500℃ represents the decomposition of calcium hydroxide; and 600-800℃ represents the decomposition range of calcium carbonate. It can be seen that the OPC-L0 group has a distinct calcium hydroxide peak compared to other groups, which is consistent with the XRD analysis results.

[0082] (5) Calculate the calcium hydroxide and Friedel's salt content of different types of paste.

[0083] Table 2 shows the calculated calcium hydroxide and Friedel's salt contents of different pastes using TG curves. It can be seen that the OPC-L0 group has the highest calcium hydroxide content and the lowest Friedel's salt content, while the calcium hydroxide content in LC55-L0 / L3 is not significantly different. With the addition of CaAl-NO3 LDHs, the Friedel's salt content increased in both systems. This indicates that the addition of CaAl-NO3 LDHs can improve the chloride ion binding capacity of the system. Among all pastes, the LC55-L3 group has the highest content, indicating that LC55-L0... 3 Combining the system with CaAl-NO3 LDHs can significantly improve the system's resistance to chloride ion penetration.

[0084] Table 3. Content of hydration products (%)

[0085] OPC-L0 OPC-L3 LC55-L0 LC55-L3 CH 10.76 4.22 2.90 3.12 Friedel's salt 2.53 2.91 3.34 4.4

[0086] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for improving the chloride ion curing ability of limestone-calcined clay-cement paste, characterized in that, Layered double hydroxides are added to limestone-calcined clay cement-based materials. The cement-based materials are composed of cement, metakaolin, limestone powder, water-reducing agent, and water. The layered double hydroxides are CaAl-NO3 LDHs.

2. The method according to claim 1, characterized in that, The specific components and dosage of cement-based materials are as follows: 230-260g cement, 120-140g metakaolin, 60-70g limestone powder, 2-3g water-reducing agent, and 210-230g water.

3. The method according to claim 1, characterized in that, The amount of CaAl-NO3 LDHs incorporated is 0.9%-3% of the weight of the cement-based material.

4. The method according to claim 1, characterized in that, The cement is one of grade 42.5 silicate cement, grade 42.5 ordinary silicate cement, or grade 52.5 silicate cement; the metakaolin is one of water-washed calcined kaolin, coal-series calcined kaolin, or calcined coal gangue; the limestone powder is one of high-calcium limestone powder, magnesium limestone powder, or dolomite powder.

5. The method according to claim 1, characterized in that, The method for preparing cement paste includes the following steps: (1) Add cement, metakaolin, limestone powder, water-reducing agent and hydrotalcite to the cement paste mixer; (2) Add mixing water and continue stirring. After stirring, pour it into a mold and transfer it to a constant temperature and humidity chamber for standard curing for 28 days. After curing, limestone calcined clay cement paste is obtained.

6. The method according to claim 1, characterized in that, The preparation of CaAl-NO3 LDHs includes the following steps: (1) Dissolve Ca(NO3)2·4H2O and Al(NO3)3·9H2O in deionized water; (2) Add the metal salt solution from step (1) dropwise to the sodium nitrate solution; (3) The reaction is carried out in a temperature-controlled magnetic stirrer, and crystallization is performed after the addition is complete; (4) The obtained white precipitate was filtered with a vacuum filter, the obtained white filter cake was washed with deionized water, the precipitate was dried, and then ground to obtain hydrotalcite CaAl-NO3 LDHs powder.

7. The method according to claim 6, characterized in that, The molar ratio of Ca(NO3)2·4H2O and Al(NO3)3·9H2O is 1.8:1-2.5:1, and the total molar concentration of the metal salt solution is 1.8-2.5 mol / L.

8. The method according to claim 6, characterized in that, The concentration of sodium nitrate solution is 1.8-2.5 mol / L. While adding sodium nitrate solution dropwise, 0.8-1.2 mol / L sodium hydroxide solution is added dropwise to maintain the pH value of the mixed solution system at 11.8-12.

2.

9. The method according to claim 6, characterized in that, The magnetic stirrer is operated at 800-1200 r / s and the temperature is maintained at 23-27℃. The reaction lasts for 1.8-2.5 hours. After the addition is complete, the mixture is crystallized at 65-75℃ for 16-20 hours.

Images