A method for preparing a surface layer of calcium carbonate crystals on a cement-based material

Abstract

The application discloses a preparation method of a cement-based material surface calcium carbonate crystalline layer, and comprises the following steps: step one, mixing cement and water, pouring into a mold for curing, demolding and curing to obtain a cement test block which is not completely hydrated; step two, adding sodium chloride, sodium sulfate, potassium chloride and sodium bicarbonate into deionized water to prepare an inorganic ion solution, and the concentration of sodium bicarbonate is greater than or equal to 0.20 g / kg; step three, soaking the cement test block which is not completely hydrated obtained in step one into the inorganic ion solution prepared in step two, rinsing the surface after taking out, terminating hydration, vacuum drying, and obtaining a cement test block surface calcium carbonate crystalline layer. The prepared crystalline layer is uniform and dense, the operation is simple, the surface mineralization can be carried out by using bicarbonate ions in the inorganic ion solution, the penetration of chloride ions and the potential negative effects accompanied by the penetration of chloride ions are avoided, and the cement test block can be further modified by silane to obtain high hydrophobicity and resist moisture infiltration.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a crystalline layer, in particular to a preparation method of a calcium carbonate crystalline layer on the surface of a cement-based material. BACKGROUND

[0002] The surface of a cement-based material is often porous, which leads to the penetration of water and ions on the surface, and further causes the denaturation and expansion of the hydration products of the matrix and the corrosion and expansion of the steel bars contained therein, thereby causing the destruction of the structure due to the superposition of internal and external stresses, and causing great harm and hidden dangers to the national economy and people's livelihood. Mineralization treatment is performed on the surface to obtain a crystalline layer, which can increase the surface density and slow down the penetration of water. In addition, the surface roughness obtained by micro-nano scale crystallization can further improve the surface hydrophobicity after surface hydrophobization treatment, and the water invasion is resisted by changing the surface wettability. However, the existing mineralization treatment method for the surface of a cement-based material is relatively complicated. A method for biomimetic induced mineralization of the surface of a cement-based material is disclosed in the literature, which uses a polydopamine coating as a mineralization point to perform surface mineralization. The polydopamine coating is deposited on the surface of the cement-based material, and then the cement-based material is alternately immersed in CaCl2 and NaHCO3 solutions for induced mineralization. It is pointed out that a relatively dense surface mineralization layer can be obtained after fifteen times of alternating immersion treatment, but the water absorption rate of the cement-based test block is only slightly affected by the mineralization layer, and the water absorption rate is almost the same as that of the untreated cement-based test block after being soaked in water for 40 min. The water absorption rate can be significantly reduced only after surface hydrophobization.

[0003] Therefore, the existing mineralization method for the surface of a cement-based material needs to use high-cost hydrochloric acid dopamine as a raw material to deposit a polydopamine coating as an induced mineralization point, and the treatment solution needs to be prepared manually, so the operation process is relatively complex and time-consuming, labor-intensive and energy-consuming. SUMMARY

[0004] The purpose of the present application is to overcome the deficiencies in the prior art, and to provide a preparation method of a calcium carbonate crystalline layer on the surface of a cement-based material, which is uniform and dense and easy to operate.

[0005] Technical scheme: The preparation method of a calcium carbonate crystalline layer on the surface of a cement-based material comprises the following steps:

[0006] Step one, mixing cement and water, pouring into a mold for curing, and then demolding to obtain a cement test block which is not completely hydrated;

[0007] Step two, adding sodium bicarbonate into deionized water to prepare an inorganic ion solution, and the concentration of the sodium bicarbonate is greater than or equal to 0.20 g / kg;

[0008] Step three, after the un-hydrated cement test block obtained in step one is cured, it is soaked in the inorganic ion solution configured in step two, and after being taken out, the surface is rinsed, the hydration is terminated, and vacuum drying or air drying is performed to obtain a calcium carbonate crystalline layer on the surface of the cement test block.

[0009] Further, in step one, the mass ratio of cement to water is 10:3-5. The curing time is 1-2 days. The mixing is first slow stirring for 50-60 s, and then fast stirring for 20-30 s.

[0010] Further, in step two, the inorganic ion solution further comprises sodium chloride, sodium sulfate, potassium chloride, and the mass ratio of sodium chloride, sodium sulfate, potassium chloride, and sodium bicarbonate is 0-125:0-21:0-3.5:1, and the mass ratio is preferably 119.65:20.05:3.4:1.

[0011] Further, in step three, the curing time is 0-7 days, the soaking time is more than 3 days, and is preferably 6-14 days. The surface is rinsed with deionized water. Ethanol soaking is used to terminate the hydration. The temperature for vacuum drying is 35-45 DEG C, and the time is 0-3 days, or the cement test block can be naturally air dried at room temperature. The particle size distribution of the crystalline particles of the calcium carbonate crystalline layer is 2-10 microns.

[0012] Further, the cement test block with the calcium carbonate crystalline layer on the surface is subjected to silanization treatment to obtain a cement test block with a hydrophobic surface.

[0013] Carbon dioxide is dissolved in seawater, river water, and other surface water, so natural water contains bicarbonate ions as a carbon source for carbonization of calcium ions. The inorganic ion solution configured in the application simulates the composition of natural water, and the bicarbonate ions in the inorganic ion solution are used as a carbon source to mineralize the surface of the cement-based material. Prior to this, it was generally believed that natural water containing chloride ions, such as seawater, has a negative effect on cement-based materials, and the chloride salt in the natural water penetrates into the cement-based material from the porous surface of the cement-based material, causing corrosion of the steel bars in the cement-based material.

[0014] Preparation principle: The inorganic ion aqueous solution configured in the application simulates the composition of natural water, and the bicarbonate ions in the inorganic ion aqueous solution are used as a carbon source to mineralize the surface of the cement-based material. The obtained mineralized layer is uniform and dense, the operation is simple, and the bicarbonate ions in the aqueous solution can be consumed. The un-hydrated cement-based material is immersed in the inorganic ion aqueous solution. Since calcium hydroxide is leached from the un-hydrated cement-based material, the calcium ions enriched on the surface of the cement-based material combine with the bicarbonate ions in the aqueous solution to form a mineralized crystalline layer. The bicarbonate ions contained in the artificially prepared inorganic ion aqueous solution can be used as a continuous carbon source. Therefore, the obtained mineralized layer is continuous and dense, and when the chloride ions have not penetrated into the matrix, the mineralized layer on the surface avoids the penetration of the chloride ions.

[0015] Beneficial effects: Compared with the prior art, the present application has the following significant features: the prepared crystalline layer is uniform and dense, the operation is simple, the surface mineralization can be carried out by using bicarbonate in an inorganic ion solution simulating the composition of natural water, the penetration of chloride ions and the potential negative effects accompanying the penetration of chloride ions are avoided, the calcium carbonate crystalline layer can be further modified by silane to obtain high hydrophobicity, and water infiltration is resisted. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a scanning electron microscope characterization diagram of embodiment 1 of the present application, wherein (a) is the surface and (b) is the cross section;

[0017] Figure 2 is an energy spectrum element analysis diagram of the mineralized layer of embodiment 1 of the present application;

[0018] Figure 3 is an energy spectrum element analysis diagram of the substrate close to the mineralized layer of embodiment 1 of the present application;

[0019] Figure 4 is a water absorption change curve diagram of embodiment 1, embodiment 2 and the comparative example of the present application;

[0020] Figure 5 is a surface contact angle measurement result diagram of embodiment 1 of the present application, wherein (a) is before hydrophobization treatment and (b) is after hydrophobization treatment. DETAILED DESCRIPTION

[0021] Embodiment 1

[0022] A preparation method of a calcium carbonate crystalline layer on the surface of a cement-based material, comprising the following steps:

[0023] (1) Mix cement and water at a mass ratio of water-cement ratio 4:10, first slowly stir for 60 s, then quickly stir for 30 s, pour the stirred mixture into a mold, demold after solidification for 1 d to obtain a not fully hydrated cement test block.

[0024] (2) Prepare an inorganic ion aqueous solution containing sodium chloride 23.93 g / kg, sodium sulfate 4.01 g / kg, potassium chloride 0.68 g / kg and sodium bicarbonate 0.20 g / kg.

[0025] (3) Put the not fully hydrated cement test block obtained in step (1) into the inorganic ion aqueous solution prepared in step (2) for soaking for 7 days, then rinse the surface with deionized water, soak in ethanol for 2 days to terminate hydration, and dry in a vacuum oven under vacuum condition at 40℃ for 2 d to obtain a cement test block with a calcium carbonate crystalline layer on the surface.

[0026] The surface and cross-sectional morphology of the calcium carbonate crystalline layer are characterized by a scanning electron microscope, and the results are as follows Figure 1As shown in Figure 1 It can be seen that the crystalline particles in the crystalline layer have a cubic morphology and a close-packed feature. The crystalline particle size distribution is ~2-10 μm, and the crystalline layer is a single layer of crystalline particles in thickness.

[0027] The cross-section of the cement-based material with a calcium carbonate crystalline layer was analyzed by energy dispersive spectrometer, as shown in Figure 2 The crystalline composition of the crystalline layer should be calcium carbonate. As shown in Figure 3 The matrix portion near the crystalline layer did not detect the penetration of chloride ions.

[0028] Example 2

[0029] A method for preparing a calcium carbonate crystalline layer on the surface of a cement-based material, comprising the following steps:

[0030] (1) Mix cement and water at a water-cement ratio of 4:10 by mass ratio, first slowly stir for 60 s, then quickly stir for 30 s, pour the stirred mixture into a mold, and after curing for 1 d, remove the mold to obtain a partially hydrated cement test block.

[0031] (2) Prepare an inorganic ion aqueous solution containing sodium chloride 23.93 g / kg, sodium sulfate 4.01 g / kg, potassium chloride 0.68 g / kg, and sodium bicarbonate 0.20 g / kg.

[0032] (3) After the partially hydrated cement test block obtained in step (1) is cured in a standard curing room for 7 d, it is immersed in the inorganic ion aqueous solution prepared in step (2) for 7 d, then the surface is washed with deionized water, immersed in ethanol for 2 d to terminate hydration, and dried in a vacuum oven at 40°C under vacuum conditions for 2 d to obtain a cement test block with a calcium carbonate crystalline layer on the surface.

[0033] Comparative Example

[0034] The remaining steps of this comparative example are the same as those of Example 1, except that step (3) is replaced by curing the partially hydrated cement test block obtained in step (1) in a standard curing room for 7 d.

[0035] The cement test blocks with a calcium carbonate crystalline layer prepared in Example 1 and Example 2 were immersed in deionized water, and the change in water absorption with time was measured, with a cement test block with a calcium carbonate crystalline layer cured for 7 d in a standard curing room as a control group, and the results are shown in Figure 4 As shown in Figure 4It can be seen that, compared with the standard curing, the water absorption rate of the cement test block with the surface having calcium carbonate crystallization obtained in Example 1 soaked in the aqueous inorganic ion solution for the same hydration time is greatly reduced, and the water absorption rate is reduced by about 27.0% after 24 h of water immersion, compared with the control group. Compared with Example 1, Example 2 is cured for 7 d under standard curing conditions before soaking in the aqueous inorganic ion solution, and the internal structure is more compact, so the water absorption rate is reduced by a greater degree of about 50.1%, compared with the control group.

[0036] The cement test block obtained in Example 1 was placed in an ethanol solution of hexadecyltrimethoxysilane and heated to 60°C for surface silane modification, as shown in Figure 5 The obtained silane hydrophobic modified surface is highly hydrophobic, and the water contact angle in air reaches 139.7±0.1°, which can further hinder the penetration of moisture.

[0037] Example 3

[0038] A method for preparing a surface calcium carbonate crystalline layer of a cement-based material, comprising the following steps:

[0039] (1) The cement and water are mixed at a mass ratio of water-cement ratio of 3:10, first slowly stirred for 50 s, then quickly stirred for 20 s, the stirred mixture is poured into a mold, and after 2 d of solidification, the mold is removed to obtain a cement test block that is not completely hydrated.

[0040] (2) An aqueous inorganic ion solution containing sodium bicarbonate 0.20 g / kg is prepared.

[0041] (3) The cement test block that is not completely hydrated obtained in step (1) is placed in the aqueous inorganic ion solution prepared in step (2) after being cured in a standard curing room for 3 d, soaked for 6 days, the surface is washed with deionized water after being taken out, soaked in ethanol for 2 days to terminate hydration, and naturally air-dried at room temperature to obtain a cement test block with a surface calcium carbonate crystalline layer.

[0042] Example 4

[0043] A method for preparing a surface calcium carbonate crystalline layer of a cement-based material, comprising the following steps:

[0044] (1) The cement and water are mixed at a mass ratio of water-cement ratio of 5:10, first slowly stirred for 55 s, then quickly stirred for 25 s, the stirred mixture is poured into a mold, and after 1 d of solidification, the mold is removed to obtain a cement test block that is not completely hydrated.

[0045] (2) An aqueous inorganic ion solution containing sodium chloride 25 g / kg, sodium sulfate 4.2 g / kg, potassium chloride 0.7 g / kg, and sodium bicarbonate 0.20 g / kg is prepared.

[0046] (3) The incompletely hydrated cement test block obtained in step (1) is placed in the inorganic ion aqueous solution prepared in step (2) after being cured in a standard curing room for 4d, and soaked for 14d. After being taken out, the surface is washed with deionized water, soaked in ethanol for 2d to terminate hydration, and dried in a vacuum oven under vacuum at 45℃ for 0.5d to obtain a cement test block with a calcium carbonate crystalline layer on the surface.

[0047] Example 5

[0048] A method for preparing a calcium carbonate crystalline layer on the surface of a cement-based material, comprising the following steps:

[0049] (1) Cement and water are mixed at a mass ratio of water-cement ratio of 4:10, slowly stirred for 52s and then rapidly stirred for 28s. The mixed mixture is poured into a mold, and after being cured for 2d, the mold is removed to obtain an incompletely hydrated cement test block.

[0050] (2) An inorganic ion aqueous solution is prepared, containing sodium chloride 12g / kg, sodium sulfate 2.04g / kg, potassium chloride 0.39g / kg and sodium bicarbonate 0.20g / kg.

[0051] (3) The incompletely hydrated cement test block obtained in step (1) is placed in the inorganic ion aqueous solution prepared in step (2) after being cured in a standard curing room for 5d, and soaked for 3d. After being taken out, the surface is washed with deionized water, soaked in ethanol for 2d to terminate hydration, and dried in a vacuum oven under vacuum at 35℃ for 3d to obtain a cement test block with a calcium carbonate crystalline layer on the surface.

Claims

1. A method for preparing a calcium carbonate crystal layer on the surface of a cement-based material, characterized in that: The following steps are involved: Step 1: Mix cement and water, pour into a mold, solidify, and then remove the mold to obtain an incompletely hydrated cement test block; Step 2: Add sodium bicarbonate to deionized water to prepare an inorganic ion solution, wherein the concentration of sodium bicarbonate is ≥ 0.20 g / kg; Step 3: After curing the incompletely hydrated cement test block obtained in Step 1, soak it in the inorganic ion solution prepared in Step 2, take it out, rinse the surface, and vacuum dry it or air dry it to obtain a calcium carbonate crystal layer on the surface of the cement test block; In the step 2, the inorganic ion solution further comprises sodium chloride, sodium sulfate, and potassium chloride, and the mass ratio of the sodium chloride, sodium sulfate, potassium chloride, and sodium bicarbonate is 0-125:0-21:0-3.5:1; In the step 3, the curing time is 0 to 7 days, and the soaking time is 6 to 14 days.

2. The method for preparing a calcium carbonate crystal layer on the surface of a cement-based material according to claim 1, characterized in that: In the step 1, the mass ratio of cement to water is 10:3-5.

3. The method for preparing a calcium carbonate crystal layer on the surface of a cement-based material according to claim 1, characterized in that: In the step 1, the curing time is 1 to 2 days.

4. The method for preparing a calcium carbonate crystal layer on the surface of a cement-based material according to claim 1, wherein: In step 1, the mixing is performed by first slowly stirring for 50 to 60 seconds and then rapidly stirring for 20 to 30 seconds.

5. The method for preparing a calcium carbonate crystal layer on the surface of a cement-based material according to claim 1, characterized in that: In the step 3, the surface is rinsed using deionized water.

6. The method for preparing a calcium carbonate crystal layer on the surface of a cement-based material according to claim 1, characterized in that: In the step 3, the vacuum drying temperature is 35-45°C and the time is 0-3 days.

7. The method for preparing a calcium carbonate crystal layer on the surface of a cement-based material according to claim 1, wherein: In the step 3, the particle size of the calcium carbonate crystal layer is distributed in the range of 2 to 10 μm.

8. The method for preparing a calcium carbonate crystal layer on the surface of a cement-based material according to claim 1, characterized in that: The cement test block is subjected to silanization treatment after a calcium carbonate crystal layer is formed on the surface of the cement test block to obtain a cement test block with a hydrophobic surface.

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