File Name: pore structure of cement based materials testing interpretation and requirements .zip
Mercury intrusion porosimetry MIP is questioned for possibly damaging the micro structure of cement-based materials CBMs , but this theme still has a lack of quantitative evidence.
- Pore Structure of Cement-Based Materials: Testing, Interpretation and Requirements
- Pore structure of cementitious material enhanced by graphitic nanomaterial: a critical review
- Cement and Concrete Research
Pore Structure of Cement-Based Materials: Testing, Interpretation and Requirements
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To more quantitatively and subtly analyze effects of carbonation on the pore structure of well cement by supercritical CO 2 under carbon capture and storage CCS conditions, a digital scanning electron microscopy-backscattered electron SEM-BSE image analysis with a combination of nontoxic low-melting point metal intrusion is used to characterize the exposed cements to humid supercritical CO 2 for 10 and 20 days.
The porous area fraction PAF and pore size distribution PSD profiles obtained by slicing operation are used to describe the pore structure variation along the corrosion direction in a two-dimensional 2D plane. The results show that the image-based method with the combination of metal intrusion is an effective method for characterizing the layer structure of exposed cement and getting quantitative information about the pore structure.
From the surface to the core, the main altered layers in exposed cement for 10 days include the partially leached layer, the carbonated layer, and the calcium hydroxide CH -dissolved layer. For the exposed cement for 20 days, the main altered layers include the porous leached layer, the partially leached layer, the carbonated layer, and the carbonated transition layer. The nonporous carbonated layer can effectively block the flow parallel to the corrosion direction, while the porous leached layer can facilitate the flow perpendicular to the corrosion direction.
Findings from this study will provide valuable information for understanding the effects of carbonation on the pore structure of well cement under CCS conditions. Figure 4. Typical BSE image a , the gray-level histogram b , and a binary image c of pores black of epoxy-impregnated cement. Figure 5. Figure 6. Pictures and XRD patterns of cement pastes with different layers exposed at CO 2 conditions a pictures of the cement pastes; b XRD patterns of the cement paste exposed for 10 days in CO 2 condition; c XRD patterns of the cement paste exposed for 20 days in CO 2 condition.
Figure 9. BSE and binary images of the exposed sample for 10 days: a-1 the stitched BSE image of exposed cement; a-2 the binary image of a pore system black of exposed cement; b-1, c-1, d-1, and e-1 magnified BSE images of different layers; b-2, c-2, d-2, and e-2 magnified binary images of pores in different layers; b-3, c-3, d-3, and e-3 the pore shape factor of exposed cement with different layers. Figure BSE and binary images of exposed sample for 20 days: a-1 the stitched BSE image of exposed cement; a-2 the binary image of the pore system black of exposed cement; b-1, c-1, d-1, e-1, and f-1 magnified BSE images of different layers; b-1, c-1, d-1, e-1, and f-2 magnified binary images of pores in different layers; b-3, c-3, d-3,e-3, and f-3 the PSF of exposed cement with different layers.
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. More by Tao Gu. More by Youcheng Zheng. More by Hong Yue. More by Youzhi Zheng. Cite this: ACS Omega , 6 , 3 , — Published by American Chemical Society. Article Views Altmetric -.
Abstract High Resolution Image. Climate change is one of the biggest urgent challenges that human beings are facing today, which is mainly attributed to the increase in carbon dioxide CO 2 emission from fossil fuels. For a geologic carbon storage project, the wellbore is the key channel for both storing CO 2 and monitoring its reservoir migration. Therefore, the long-term integrity of wellbore is a critical issue for the success of using CCS.
Step 1: Formation of carbonic acid 1. Step 2: Carbonation of the hydration products 2 3. Step 3: Bicarbonation and calcium leaching 4 5. Step 4: Decalcification of CSH 6. Carbonic acid formed when CO 2 is dissolved in pore solution of cement or formation of water eq 1. This process is called as carbonation and is known to reduce cement porosity for CaCO 3 precipitation in innate pores of cement.
Due to higher solubility of Ca HCO 3 2 , this process causes calcium to be leached out of the cement matrix gradually. Amorphous silica gel is porous and lacks structure.
Eventually, Ca-leaching will lead to significant changes in the microstructure and properties of well cement. Cement-based materials are a porous medium with a wide range of pore sizes from the micrometer to the nanoscale.
Presently, some analytical methods, such as nitrogen gas adsorption, mercury intrusion porosimetry MIP , X-ray microtomography XMT , and image-based analysis based on scanning electron microscopy-backscattered electron SEM-BSE imaging on polished epoxy-impregnated cement , have been applied to characterize pore structure changes of well cement and to evaluate the degradation of cement by supercritical CO 2.
As mentioned above, a multilayer structure with different mineral compositions and pore structures will be formed in the carbonated cement, which directly relates to the performances of exposed cement. An additional limitation of MIP and BET methods is they cannot offer a visible interpretation of pores, such as connectivity and shape.
Image analysis based on BSE imaging is an effective way to offer quantitative information about the pore structures of porous media, such as cement-based materials on a fine scale. It has been well demonstrated that the replacement of metal to epoxy can significantly improve the contrast and resolution of pores under BSE imaging because of the massive atomic number difference between the metal and the cement matrixes. Then, a scheme based on the combination of nontoxic low-melting point metal intrusion and BSE image analysis was applied.
Based on the pore structure analysis results from the BSE image analysis, the variation characteristics of the pore structure of exposed cement along the corrosion direction in a two-dimensional 2D plane were analyzed. Experimental Methods.
Conventional density cement slurry was designed to conduct the experiments, as shown in Table 1. Table 1.
Formulation of the Cement Sample a. Table 2. The exposed durations were selected as 10 and 20 days. Then, X-ray diffraction was applied to test the XRD patterns of the cement pastes with different curing conditions at a scanning rate of 0.
Figure 1. Schematic of the experimental setup and sample loading. High Resolution Image. After drying, the samples were divided into two parallel groups. For the epoxy resin impregnation process, the parallel samples used for metal intrusion were impregnated under vacuum with epoxy resin. Subsequently, the impregnated samples were kept in ambient for 2 days until the epoxy was totally solidified.
Then, the samples were also finely polished down to 0. Binary images of the pores were obtained by thresholding of pores. Solid inclusions within pores were considered in the calculation of pore fraction. Then, the metal-intruded pores were identified in a single threshold to produce a binary image.
Afterward, each set of BSE images and corresponding binary images were stitched together in turn to get the 2D panoramas of exposed cement. The actual porosity or pore volume of cement is a concept in the three-dimensional 3D plane; however, it is evident that the binary image only shows the distribution of the pores in a two-dimensional 2D plane.
Therefore, the porous area fraction PAF is adopted, which is defined by the area of the pores divided by the total area of the investigated sample. To quantitatively analyze the distribution of 2D PAF along with the corrosion direction, a slicing operation was conducted. Then, the regional PAF of each sliced picture was measured.
By this process, the PAF profile can be obtained. Figure 2. Schematic of slicing operation. Pore size is the key parameter to characterize pore structures, which is often expressed in terms of pore diameter. However, the actual shape of pores in cement is irregular. Here, equivalent pore diameter d p is used as illustrated in Figure 3.
For noncircular pores, d p is the diameter of a circular pore with an equivalent area and is given as follows: 8 where P area is the area of the pore from the image analysis. Figure 3. Schematic for the d p calculation. Using the slicing operation, the pore size distribution PSD of each section and the PSD profile along with the corrosion direction can be obtained. For porous media, the pore shape factor PSF is another important parameter to describe the 2D pore structure.
This parameter is usually used to analyze the morphological characteristics of pores, which reflects the roundness degree of pores. Also, a complex pore shape has the lower pore shape factor. For example, the PSF for rectangular pores and triangular pores are 0. Yang et al. Results and Discussion. According to the principle of BSE imaging, the intensity of the BSE signal and the brightness of an image is mainly a function of the atomic number of the atoms in the sample. The relatively high brightness of unhydrated grains contributes to analysis of the mineral phase composition, hydration degree, and hydration process of cement by image analysis on the basis of the gray level.
Therefore, the pores filled by metal in the BSE image are white color. In order to clearly observe the pore characterization, the BSE image is analyzed by binary image analysis; the pores are colored using black color. A magnified view Figure 5 b illustrates that both the large capillary pores and small capillary pores in porous CSH gel are well filled with metal and showed much higher resolution and contrast. The high resolution and contrast of pores can guarantee a significant gray level difference between metal-filled pores and solid phases hydration products, unhydrated cement grains, etc.
Moreover, it is clearly shown that the geometry of pores in cement is irregular and complicated. As shown in Figure 5 c, there is a separate peak for metal-filled pores in paste, which was quite beneficial to distinguish the pores from cement during image analysis.
Pore structure of cementitious material enhanced by graphitic nanomaterial: a critical review
Carbon nano tubes CNT has been introduced as an efficient nanomaterial in order to improve the mechanical and durability properties of concrete. The effect of CNT on the microstructures of cementitious materials has been widely reported. This paper combines a critical review on the effect of CNTon the pore and microstructure of cement composite with a discussion on the porosity measurement of pastes containing CNT using mercury intrusion porosimetry techniques MIP. In this scope, this review paper involves analyzing the effect of CNT on the microstructure and the pore structure of cementitious materials. The existing methods of measuring the porosity of cementitious material are reviewed, in particular, the contact angle measurement is discussed in detail in which the most effective parameters and possible errors of calculation is presented. This is a preview of subscription content, access via your institution. Please try refreshing the page.
Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. DOI: Aligizaki Published Materials Science. Specimen Pretreatment. Mercury Intrusion Porosimetry. Gas Adsorption.
Pore Structure of Cement-Based Materials: Testing, Interpretation and Requirements · 1. Introduction. · 2. Specimen Pretreatment. · 3. Mercury Intrusion.
Cement and Concrete Research
Concrete is a composite material that consists of a binding medium and aggregate particles and can be formed in several types. It may be considered to consist of three phases: a cement paste, the aggregate, and the interfacial transition zone ITZ between them. In addition to ordinary Portland cement, the essential components of the base of concrete are aggregates and water.