Evaluation method for crack self-repairing performance of cement-based material

Abstract

The invention discloses a method for evaluating the crack self-repairing performance of a cement-based material, and belongs to the field of cement-based materials. Comprising the following steps: (1) preparing a cement-based material test piece, and curing in a curing box; (2) manufacturing a through crack in the maintained test piece by using a splitting method, and placing the through crack in tap water to obtain a repaired test block; and (3) dividing the test block obtained in the step (2) into two halves along the crack, uniformly dropwise adding a copper sulfate solution along the crack surface, standing, and observing the color of each region. The evaluation method further comprises the following steps: acquiring a crack surface image, processing the crack surface image by using a binarization method, and calculating a crack surface repair rate. According to the evaluation method for the crack self-repairing performance of the cement-based material, the effect of qualitatively and quantitatively distinguishing the distribution condition of the hydrogel in the crack area can be achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to cement-based materials, in particular to a method for evaluating the crack self-repairing performance of a cement-based material. BACKGROUND

[0002] Cement-based materials refer to engineering materials that use cement as a cementitious material. Concrete and mortar are the most common cement-based materials. Some materials such as grouting materials and coatings can use organic cementitious materials or inorganic cementitious materials. If it is emphasized that it is cement-based, such as cement-based grouting materials and cement-based coatings, it means that it is based on cement as a cementitious material. Cement-based materials have the advantages of high compressive strength, low cost, good durability, etc., and have been widely used in civil engineering sub-fields such as building engineering, bridge engineering, and tunnel engineering. It is an indispensable main building material in the field of civil engineering. However, due to the low tensile strength of cement-based materials, cracks may occur during service due to various factors, which seriously reduces the waterproof performance of the structure, affects the normal use of the structure, and poses a significant threat to its safety and durability. Based on the continuous deepening of the concept of intelligence, developing new cement-based materials with biomimetic self-repairing ability has become a hot topic. At present, microbial mineralization technology occupies a central position in the field of crack self-repairing due to its environmental friendliness, long-term repair, and compliance with carbon neutralization goals. However, this repair method that relies on mineral deposition has a flaw, which is difficult to achieve high-level repair effect in a very short period of time. CN117209189A discloses a preparation method and application of a biomimetic composite repair material for biomineralization-strengthened hydrogel. This invention uses the special hydrophilicity of hydrogel to prepare a core-shell type repair agent that can quickly seal cracks in the crack area in a short time, and the hydrogel absorbs a large amount of water during expansion, providing sufficient water for microbial growth and mineralization. However, as a repair agent, most hydrogels are colorless and transparent colloids after absorbing water and expanding, making it difficult to directly observe the repair effect with the naked eye, which is not conducive to subsequent quantitative evaluation of repair effect. Therefore, it is necessary to explore a technology that can distinguish the distribution of hydrogel in the crack area. SUMMARY

[0003] The purpose of the present application is to provide a method for evaluating the crack self-repairing performance of a cement-based material that can qualitatively and quantitatively distinguish the distribution of hydrogel in the crack area.

[0004] Technical solution: The evaluation method for the crack self-repairing performance of a cement-based material according to the present application comprises the following steps:

[0005] (1) Prepare a cement-based material test piece and place it in a curing box for curing;

[0006] (2) In the test piece after maintenance, make a through crack, and place it in tap water to make it self-repair, and obtain the repaired test block;

[0007] (3) The test block obtained in step (2) is divided into two halves along the crack, and copper sulfate solution is uniformly added along the crack surface. After standing, the color of each region is observed, and the self-repairing performance is evaluated according to the color change.

[0008] Preferably, the evaluation method further comprises the following steps: taking the cross section after adding copper sulfate solution in step (3) as the crack surface image, processing it by binaryzation method, and calculating the crack surface repair rate.

[0009] Preferably, in step (1), the cement-based material test piece comprises cement and self-repairing agent, and the mass of the self-repairing agent is 1-15% of the mass of the cement.

[0010] Preferably, in step (1), the physicochemical properties of the solution in the cement crack area of the cement-based material test piece meet pH>12.

[0011] Preferably, in step (1), the cement in the cement-based material test piece is one of ordinary portland cement, slag portland cement, pozzolanic portland cement, fly ash portland cement, and composite portland cement.

[0012] Preferably, in step (1), the curing temperature is 20±0.5℃, and the humidity is 95%±0.5.

[0013] Preferably, in step (1), the curing time is 25-30 days.

[0014] Preferably, in step (2), the method for making a through crack is the splitting method.

[0015] Preferably, in step (2), the self-repairing time is 25-30 days.

[0016] Preferably, in step (3), the concentration of the copper sulfate solution is 0.3-0.7 mol / L.

[0017] Invention principle: The present application aims to provide a method for evaluating the self-repairing performance of cement-based materials. By adding blue copper sulfate solution to the cement-based material, the area covered by hydrogel appears blue due to the adsorption of copper sulfate solution, while the area not covered by hydrogel remains basically unchanged due to the inability to adsorb copper sulfate. In this way, the distribution area of hydrogel in the cement-based material is qualitatively judged, and the self-repairing performance of the cement-based material is indirectly evaluated. The cement-based material itself is a porous material, and the copper sulfate solution dropped in the area without hydrogel will be quickly absorbed and diffused into the deep pores, resulting in a too low surface concentration to show blue. The presence of hydrogel hinders this diffusion, as it has a three-dimensional network structure that can adsorb and fix copper sulfate solution, preventing its rapid penetration or loss. This allows copper ions to accumulate in the hydrogel, reaching a concentration visible to the naked eye. In addition, the surface of the cement-based material is rough, and the light scattering is strong, which will weaken the visibility of the color; while the surface of the hydrogel is relatively smooth, which enhances the contrast of the color. In addition, the present application uses the binary method to calculate the ratio of the area covered by hydrogel to the entire cross-sectional area, to quantitatively judge the distribution of hydrogel in the cement-based material. This method solves the problem of direct observation of the repair effect by the naked eye when using hydrogel to repair cracks, and provides great convenience for quantitative evaluation of the repair effect.

[0018] Advantages: Compared with the prior art, the present application has the following significant advantages: (1) The present application adds blue copper sulfate solution to the cement-based material, making the distribution of areas covered and not covered by hydrogel appear different colors, which can qualitatively judge the distribution of hydrogel in the cement-based material, and indirectly evaluate the self-repairing performance of the cement-based material; (2) The present application uses the binary method to quantitatively judge the distribution of hydrogel in the cement-based material; (3) This method solves the problem of direct observation of the repair effect by the naked eye when using hydrogel to repair cracks, and provides great convenience for quantitative evaluation of the repair effect. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The image after binary processing for Example 1;

[0020] Figure 2 The color development of the test piece before and after adding copper sulfate solution for Example 1, wherein (a) is before adding, and (b) is after adding;

[0021] Figure 3 The color development of the test piece before and after adding copper sulfate solution for Example 2, wherein (a) is before adding, and (b) is after adding;

[0022] Figure 4 The color development of the test piece before and after adding copper sulfate solution for Example 3, wherein (a) is before adding, and (b) is after adding;

[0023] Figure 5 The color development of the specimens before and after adding copper sulfate solution in Example 4 is shown in (a) before addition and (b) after addition.

[0024] Figure 6 The color development of the specimens before and after adding copper sulfate solution is shown in Comparative Example 1. (a) is before adding the solution, and (b) is after adding the solution. Detailed Implementation

[0025] The technical solution of the present invention will be further described below with reference to the embodiments.

[0026] The self-healing agent used in this invention is prepared according to the method disclosed in the patent document with publication number CN117209189A entitled "Preparation method and application of a biomimetic composite repair material of biomineralized reinforced hydrogel". The effective component of the self-healing agent is a hydrogel solid powder loaded with microorganisms.

[0027] Example 1

[0028] The method for evaluating the self-healing performance of cement-based materials with cracks as described in this invention includes qualitative evaluation and quantitative evaluation. The qualitative evaluation specifically includes the following steps:

[0029] (1) Mix ordinary silicate cement, water and self-healing agent in a mass ratio of 1432.5:252:67.5, pour into a mold, prepare a cylindrical cement-based material specimen with a diameter of 100 mm and a height of 100 mm, demold after curing at room temperature for 1 day, and then place in a standard curing box with a temperature of 20±0.5℃ and a humidity of 95%±0.5 for 28 days.

[0030] (2) After curing, remove it and use the splitting method to make a through crack with a width of 0.4mm. Then place it in tap water to allow it to repair itself for 28 days.

[0031] (3) Divide the repaired test block into two halves along the crack, and uniformly drip a copper sulfate solution with a concentration of 0.5 mol / L along the entire crack cross section. After standing for 1 minute, it can be clearly observed that the area with hydrogel is blue, while the area without hydrogel almost maintains the color of the matrix itself.

[0032] The quantitative evaluation includes the following steps: using an industrial camera, the cross-section after adding copper sulfate solution in step (3) is used as the crack surface image, and imported into Photoshop software. After binarization, a black and white image with only black and white is obtained. The white area represents the area covered by hydrogel. The area ratio of the white area is used as the crack surface repair rate. This area ratio is equivalent to the ratio of the overall cumulative gray values ​​of the binary image. The repair rate can be indirectly calculated through the cumulative gray values. The repair rate is 74.25%. The calculation method of the ratio of the overall cumulative gray values ​​is as follows: first calculate the overall cumulative gray values ​​of the binary image, then process the white area into black and calculate the overall cumulative gray values ​​again, and finally calculate the ratio of the two overall cumulative gray values.

[0033] Example 2

[0034] The similarities between this embodiment and Embodiment 1 will not be repeated here. The differences are as follows:

[0035] The composition of the cement-based material specimen was: ordinary Portland cement, water, sand, and self-healing agent in a mass ratio of 450:225:1282.5:67.5.

[0036] Quantitative evaluation showed that the repair rate was 66.37%.

[0037] Example 3

[0038] The similarities between this embodiment and Embodiment 1 will not be repeated here. The differences are as follows:

[0039] The composition of the cement-based material specimen was: ordinary Portland cement, water, sand, gravel, and self-healing agent in a mass ratio of 352:155:663.5:1010:67.5.

[0040] Quantitative evaluation showed that the repair rate was 62.37%.

[0041] Example 4

[0042] The similarities between this embodiment and Embodiment 1 will not be repeated here. The differences are as follows:

[0043] The composition of the cement-based material specimen was: ordinary Portland cement, water, sand, and self-healing agent in a mass ratio of 450:225:1336.5:13.5.

[0044] Quantitative evaluation showed a repair rate of 12.91%.

[0045] Comparative Example 1

[0046] The similarities between this comparative example and Example 4 will not be repeated here. The difference is that in the cement-based material specimen, the mass ratio of ordinary silicate cement, water and sand is 450:225:1350, and the amount of self-healing agent added is 0.

[0047] Experimental data shows that the evaluation method provided by this invention can qualitatively and quantitatively evaluate the self-healing performance of cracks in cement-based materials. Regardless of whether the cement-based material contains sand or gravel, as long as the following condition is met: the physicochemical properties of the solution in the crack area satisfy pH > 12, this method can be used for evaluation. After uniformly adding copper sulfate solution to the cross-section of the cement-based material, it can be clearly observed that the area with hydrogel is blue, while the area without hydrogel almost retains the color of the matrix itself.

Claims

1. A method for evaluating the self-healing performance of cracks in cement-based materials, characterized in that, Includes the following steps: (1) Prepare cement-based material specimens and then place them in a curing box for curing; (2) Create through cracks in the cured specimen and place it in tap water to allow it to self-repair, thus obtaining a repaired specimen; (3) Divide the test block obtained in step (2) into two halves along the crack, add copper sulfate solution evenly along the crack surface, observe the color of each area after standing, and evaluate its self-healing performance based on the color change.

2. The evaluation method according to claim 1, characterized in that, It also includes the following steps: The cross section after adding copper sulfate solution in step (3) is used as the crack surface image. The crack surface repair rate is obtained by binarization.

3. The evaluation method according to claim 1, characterized in that, The cement-based material specimens described in step (1) include cement and self-healing agent, with the mass of the self-healing agent being 1-15% of the mass of the cement.

4. The evaluation method according to claim 1, characterized in that, In the cement-based material specimens described in step (1), the physicochemical properties of the solution in the cement crack zone satisfy pH > 12.

5. The evaluation method according to claim 1, characterized in that, In step (1), the cement in the cement-based material specimen is one of ordinary Portland cement, slag Portland cement, pozzolanic Portland cement, fly ash Portland cement, or composite Portland cement.

6. The evaluation method according to claim 1, characterized in that, The curing temperature in step (1) is 20±0.5℃ and the humidity is 95%±0.5%.

7. The evaluation method according to claim 1, characterized in that, The maintenance period mentioned in step (1) is 25-30 days.

8. The evaluation method according to claim 1, characterized in that, The method for creating a through crack described in step (2) is the splitting method.

9. The evaluation method according to claim 1, characterized in that, The self-repair time mentioned in step (2) is 25-30 days.

10. The evaluation method according to claim 1, characterized in that, The concentration of the copper sulfate solution mentioned in step (3) is 0.3-0.7 mol / L.

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