A Sliding Evaluation Method for the Microstructure of the Interface Transition Zone of Building Materials

Abstract

The present invention belongs to the field of characterization of building material properties, and particularly relates to a sliding evaluation method for the microstructure of the interfacial transition zone of building materials. It includes: processing the test specimen to be tested; performing tomographic scanning imaging once respectively under the original and imaging states of the specimen with the same parameters; using image registration technology to spatially match the results of the two scans; obtaining the local porosity inside the specimen according to the change in gray values at the same positions in the results of the two scans; using sub-regions with different widths to slide across the interfacial transition zone of concrete. As the width of the sub-region increases, the peak of the one-dimensional porosity distribution curve gradually disappears; the width of the sub-region when the peak of the curve is about to disappear is taken as the width of the interfacial transition zone, and at this time, the peak is the width of the interfacial transition zone. The present invention adopts the method of moving average, which can overcome the problems of irregular shape and insufficient CT resolution of the interfacial transition zone and characterize the microstructure of the interfacial transition zone of concrete.

Description

Technical Field

[0001] The present invention belongs to the field of characterization of building material properties, and particularly relates to a sliding evaluation method for the microstructure of the interfacial transition zone of building materials. Background Art

[0002] Concrete is still the building material with the largest consumption and the widest application range at present. However, due to the presence of aggregates, the performance of the cement paste will be disturbed on the surface of the aggregates, forming a transition zone, that is, the interfacial transition zone of cement-based materials. Compared with the hardened cement paste, the chemical composition and microscopic morphology of the interfacial transition zone both show certain specificities; at the same time, the interfacial transition zone often enriches macropores. These characteristics make the interfacial transition zone very fragile, thereby causing the decline of the mechanical and durability properties of concrete.

[0003] A large number of simulation and experimental studies have been carried out around the interfacial transition zone, forming the side-wall effect and micro-bleeding effect theories to explain the formation reasons of the interfacial transition zone.

[0004] However, regarding the microstructure of the interfacial transition zone, such as its width and porosity, relatively few related studies have been carried out. Taking experimental research as an example, predecessors often used scanning electron microscopy and nanoindentation to study the microstructure of the interfacial transition zone. However, the above-mentioned equipment can only observe two-dimensional interfacial characteristics, which may be different from the three-dimensional properties of the interfacial transition zone; predecessors have also used mercury intrusion porosimetry (MIP) to analyze the interface, but since the sampling scale of the mercury intrusion porosimeter is much higher than that of the interfacial transition zone, the information obtained does not completely come from the interfacial transition zone; some scientific researchers have also tried to use X-ray computed tomography (CT) to analyze the interfacial characteristics. Unfortunately, the CT resolution is generally dozens of micrometers, which is very close to the scale of the interface, so it is difficult to analyze.

[0005] In addition, since the scale of the interfacial transition zone is generally lower than the representative elementary volume (REV), its performance is not stable and will change randomly with the sampling position. Therefore, for general analysis methods, since the information of each local part is not statistically analyzed, the interfacial information obtained may not reflect the overall microstructure of the interfacial transition zone. Summary of the Invention

[0006] The purpose of the present invention is to provide a sliding evaluation method for the microstructure of the interfacial transition zone of building materials to solve the problems that the shape of the interfacial transition zone is irregular and it is difficult to accurately characterize its three-dimensional structure.

[0007] The technical solution for realizing the purpose of the present invention is: a sliding evaluation method for the microstructure of the interfacial transition zone of building materials, comprising the following steps:

[0008] S1: Process the specimen to be tested and perform the first computed tomography imaging CT on the specimen in the original state;

[0009] S2: Change the linear absorption coefficient of the pores inside the specimen, and conduct a second CT test on the specimen with the same parameters;

[0010] S3: Spatially match the scanning results of steps S1 and S2, and obtain the local porosity of the specimen based on the change in gray values at the same positions in the two scans;

[0011] S4: Obtain the spatial distribution of the local porosity of the specimen based on the results of the local porosity;

[0012] S5: Select a sub-region, and count the porosity of the sub-region; Slide the sub-region uniformly from one building material area into another building material to obtain the one-dimensional distribution of the porosity of the sub-region;

[0013] S6: Gradually increase the width of the sub-region, and count the porosity of the sub-region; Slide the sub-region uniformly from one building material area into another building material to draw a new one-dimensional porosity distribution curve;

[0014] S7: Record the critical point where the peak disappears on the one-dimensional porosity distribution curve. At this time, the width of the sub-region is the statistical width of the interface transition zone, and the peak porosity at this time is the porosity of the interface transition zone.

[0015] Furthermore, in step S1, the specimen to be tested is a specimen containing an interface of cement paste-aggregate, alkali-activated paste-aggregate, or cement paste-alkali-activated paste.

[0016] Furthermore, in step S1, the radiation source used for tomographic imaging is X-ray, gamma ray, or neutron ray.

[0017] Furthermore, in step S2, the linear absorption coefficient of the pores is changed by saturating, drying, or imaging the specimen.

[0018] Furthermore, the imaging in step S2 is achieved by immersing in potassium iodide or cesium chloride solution.

[0019] Furthermore, in step S3, the matching method for "spatially matching the scanning results of steps S1 and S2" is image registration.

[0020] Furthermore, in step S3, the local porosity of the specimen is obtained by the following formula:

[0021]

[0022] where Φ is the local porosity of the specimen, %; G

[0019] , 孔隙前 , 第一次 , ,

[0021] ,

[0020] , , 孔隙后 , 第二次 ,

[0022] , , , G 第一次 are the gray values of the same position of the specimen in the second and the first time respectively; G 孔隙后 , G 孔隙前They are the gray values of the pores at the second time and the first time under the same test parameters respectively.

[0023] Compared with the prior art, the significant advantages of the present invention are as follows:

[0024] The present invention adopts the method of moving average, which can overcome the problems of irregular shape of the interfacial transition zone and insufficient CT resolution, and characterize the microstructure of the concrete interfacial transition zone. Description of the Drawings

[0025] Figure 1 It is the three-dimensional porosity distribution result of the alternating 3D printed specimen of the sliding evaluation method for the microstructure of the interfacial transition zone of the building materials of the present invention;

[0026] Figure 2 It is the two-dimensional porosity distribution result of the alternating 3D printed specimen of the sliding evaluation method for the microstructure of the interfacial transition zone of the building materials of the present invention, and a-a' is the line scan analysis area;

[0027] Figure 3 It is the one-dimensional porosity distribution result of the alternating 3D printed specimen of the sliding evaluation method for the microstructure of the interfacial transition zone of the building materials of the present invention;

[0028] Figure 4 It is the one-dimensional porosity distribution curve obtained by sliding with sub-regions of different widths in the embodiment. Detailed Embodiment

[0029] The present invention will be further described in detail below with reference to the drawings.

[0030] The present invention provides a method for characterizing the spatial distribution of concrete components by combining dissolution and image registration, including the following steps:

[0031] S1. Process the specimen to be tested, and perform the first tomographic imaging (CT) on the specimen in the original state;

[0032] S2. Change the linear absorption coefficient of the pores inside the specimen, and perform the second CT test on the specimen with the same parameters;

[0033] S3. Spatially match the scanning results, and obtain the local porosity of the specimen according to the change of the gray values at the same positions in the two scans;

[0034]

[0035] Among them, Φ is the local porosity (%) of the specimen; G 第二次 , G 第一次 are the gray values of the same position of the specimen at the second time and the first time respectively; G 孔隙后 , G 孔隙前They are the gray values of pores at the second and first times under the same test parameters, respectively;

[0036] S4. Obtain the spatial distribution of the local porosity of the specimen based on the results of the local porosity;

[0037] S5. Select a sub-region and count the porosity of the sub-region; Slide the sub-region uniformly from one building material region into another building material to obtain the one-dimensional distribution of the porosity of the sub-region;

[0038] S6. Gradually increase the width of the sub-region and count the porosity of the sub-region; Slide the sub-region uniformly from one building material region into another building material and draw a new one-dimensional porosity distribution curve;

[0039] S7. Record the critical point at which the peak disappears on the one-dimensional porosity curve. At this time, the width of the sub-region is the statistical width of the interfacial transition zone, and the peak porosity at this time is the porosity of the interfacial transition zone.

[0040] In the above S1, the specimen to be tested is a specimen containing an interface of cement paste-aggregate, alkali-activated paste-aggregate, or cement paste-alkali-activated paste.

[0041] In the above S1, the radiation source of the tomographic imaging device is X-ray, gamma ray, or neutron ray.

[0042] In the above S2, the linear absorption coefficient of the pores can be changed by saturating, drying the specimen, or immersing it in heavy metal solutions such as potassium iodide and cesium chloride (for contrast).

[0043] In the above S3, the method of spatially matching the results of multiple CT scans is generally image registration.

[0044] Example

[0045] A sliding evaluation method for the microstructure of the interfacial transition zone of building materials, comprising the following steps:

[0046] S1. Process the specimens to be tested. Use 2.6 - 2.8 kg of slag, 3.0 - 3.3 kg of standard sand, 0.26 - 0.32 kg of silica fume, 880 - 1000 g of water, 2 - 3 g of sodium gluconate retarder, and 50 - 60 g of UEA expansion agent (an alkali activator containing 45 - 55 g of sodium hydroxide and 160 - 220 g of sodium silicate) to prepare alkali-activated slag ink. Use 2.6 - 2.8 kg of P·II 52.5 cement, 3.0 - 3.3 kg of standard sand, 0.26 - 0.32 kg of silica fume, 880 - 1000 g of water, 2 - 3 g of sodium gluconate retarder, and 1.5 - 2.2 g of high-range water reducer to prepare cement-based ink. Use a concrete 3D printer produced by Nanjing Zhuochunni Intelligent Technology Co., Ltd. to prepare specimens. After printing, place the specimens under standard curing conditions for 28 days, and then cut the specimens to appropriate sizes.

[0047] S2. Place the specimens in boiling water that has been cooled, evacuate and saturate them with water for 28 days, and then conduct the first CT scan on the specimens.

[0048] S3. Take the specimens and put them into a vacuum drying oven, dry them for 28 days, and then conduct the second CT scan on the specimens using the same test parameters; use image registration to match the results of the two scans.

[0049] S4. Calculate the three-dimensional distribution (see <Object: Figure 1 ), two-dimensional distribution (see <Object: Figure 2 ), and one-dimensional distribution (see <Object: Figure 3 ) of the local porosity of the specimens. Use sliding frames of different widths to slide from the left end to the right end of each specimen. The widths of the sub-regions are respectively selected as 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, and 350 μm. Slide one pixel each time to obtain the one-dimensional sub-region porosity distribution curve (see <Object: Figure 4 ).

[0050] S5. When the width of the sub-region is 50 μm, two porosity peaks can be seen, corresponding to the double-interface transition zone of the alternating 3D printing structure; if the width of the sub-region is increased to 100 μm and 150 μm, the fluctuations of the one-dimensional porosity curve gradually decrease, but the peaks still exist; if the width of the sub-region is increased to 200 μm, the peak on the left disappears, and a platform and a peak appear on the curve; if the width of the sub-region is increased to 250 μm, the peak on the curve disappears, and only the platform area can be seen.

[0051] S6. Record the width of the sub-region when the peak first disappears as the width of the interface transition zone, which is 200 μm, corresponding to a porosity of approximately 9.6%.

Claims

1. A method for sliding evaluation of the microstructure of the interfacial transition zone of building materials, characterized in that, It includes the following steps: S1: Process the specimen to be tested, and conduct the first computed tomography (CT) scan on the specimen in its original state; S2: Change the linear absorption coefficient of the pores inside the specimen, and conduct the second CT test on the specimen using the same parameters; S3: Spatially match the scan results of steps S1 and S2, and obtain the local porosity of the specimen based on the change in gray values at the same positions in the two scans; S4: Based on the results of the local porosity, obtain the spatial distribution of the local porosity of the specimen; S5: Select a sub-region and count the porosity of the sub-region; Slide the sub-region uniformly from one building material region into another building material to obtain the one-dimensional distribution of the porosity of the sub-region; S6: Gradually increase the width of the sub-region and count the porosity of the sub-region; Slide the sub-region uniformly from one building material region into another building material to plot a new one-dimensional porosity distribution curve; S7: Record the critical point where the peak disappears on the one-dimensional porosity distribution curve. At this time, the width of the sub-region is the statistical width of the interfacial transition zone, and the peak porosity at this time is the porosity of the interfacial transition zone.

2. The method according to claim 1, characterized in that, In step S1, the specimen to be tested is a specimen containing an interface of cement paste-aggregate, alkali-activated paste-aggregate, or cement paste-alkali-activated paste.

3. The method according to claim 2, wherein, In step S1, the radiation source used for computed tomography scanning is X-ray, gamma ray, or neutron ray.

4. The method according to claim 3, wherein In step S2, the linear absorption coefficient of the pores is changed by saturating, drying, or contrast-enhancing the specimen.

5. The method according to claim 4, wherein The contrast-enhancing in step S2 is achieved by immersing in potassium iodide or cesium chloride solution.

6. The method according to claim 5, wherein In step S3, the matching method used for "spatially matching the scan results of steps S1 and S2" is image registration.

7. The method according to claim 6, wherein In step S3, the local porosity of the specimen is obtained using the following formula: where Φ is the local porosity of the specimen; G 第二次 , G 第一次 are the gray values of the same position of the specimen at the second and first times respectively; G 孔隙后 , G 孔隙前 are the gray values of the pores at the second and first times under the same test parameters respectively.

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