Corrosion Protection of Injection Molded Porous 440C Stainless Steel by Electroplated Zinc Coating

Zinc electroplating was used to enhance corrosion resistance of porous metal injection molded 440C stainless steel. Controlled porosity was achieved by the powder space holder technique and by using sodium chloride as a space holder material. The internal pore structure of porous 440C was deposited by zinc using electroplating with three different electrolytes of zinc acetate, zinc sulfate, and zinc chloride. Our results show that all zinc depositions on porous 440C samples significantly improved corrosion resistance. The lowest corrosion was observed with zinc acetate at 30 wt.% porosity. The developed zinc coated porous 440C samples have potential in applications in corrosive environments.

Study on the Effects of Ultrasonic Agitation on CO2 Adsorption Efficiency Improvement of Cement Paste

To realize high-efficiency CO2 absorption by fresh cement paste, ultrasonic vibration technology is introduced into the CO2 absorption test device used in this study. Influences of ultrasonic frequency on the CO2 absorption rate (CO2 AR) and the ultimate absorption amount of fresh cement paste are analyzed. Furthermore, the influencing laws of the CO2 absorption amount (CO2 AA) on the fluidity, pore distribution, and mechanical properties of cement paste under ultrasonic vibrating agitation are analyzed by measuring the variations of the CO2 AA of cement paste. Results demonstrate that ultrasonic vibrating agitation not only can increase the CO2 AR and ultimate absorption amount of fresh cement paste, but also can optimize the internal pore structure of materials and compressive strength of cement-based materials.

Synchrotron X-ray microtomography and multifractal analysis for the characterization of pore structure and distribution in softwood pellet biochar

Biochar pores in the micrometer range (1–100 µm) derive from cellular structures of the plant biomass subjected to pyrolysis or can be the result of mechanical processing, such as pelleting. In this study, synchrotron X-ray microtomography was used to investigate the internal pore structure of softwood pellet biochar produced by slow pyrolysis at 550 and 700 °C. The microtomographic data sets consisted of 2025 images of 2560 × 2560 voxels with a voxel side length of 0.87 µm. The three-dimensional reconstructions revealed that pelleting and pyrolysis significantly altered the pore structures of the wood feedstock, creating a network of connected pores between fragments that resembled the wood morphology. While higher pyrolysis temperature increased the specific surface area (as determined by BET nitrogen adsorption), it did not affect the total observed porosity. Multifractal analysis was applied to assess the characteristics of the frequency distribution of pores along each of the three dimensions of reconstructed images of five softwood pellet biochar samples. The resulting singularity and Rényi spectra (generalized dimensions) indicated that the distribution of porosity had monofractal scaling behavior, was homogeneous within the analyzed volumes and consistent between replicate samples. Moreover, the pore distributions were isotropic (direction-independent), which is in strong contrast with the anisotropic pore structure of wood. As pores at the scale analyzed in this study are relevant, for example, for the supply of plant accessible water and habitable space for microorganisms, our findings combined with the ability to reproduce biochar with such pore distribution offer substantial advantages in various biochar applications.

Study on the Process and Characteristics of Clogging for Ceramic Permeable Brick

A ceramic permeable brick was selected for study in a device that was designed to fully investigate the process and characteristics of clogging in permeable bricks. In order to evaluate the permeability influenced by clogging, a simulated rainfall was filtered through the permeable brick placed in an innovative device. The macroscopic and microscopic changes in the brick and the filtrate were all measured to fully investigate the causes and process of clogging. Then, the mechanism of clogging in the permeable brick pores was further discussed. The results showed that the clogging risk of permeable brick was extremely high, and it can result in a complete clogging in only 5–10 years under the experimental conditions. The permeability coefficient and porosity both decreased exponentially with the increase in filtrate, which was attributed to the clogging of the internal pore structure due to particle interception. The chord size distribution results stressed that the blockage mainly occurred in the upper layer pores in the range of 0.5–1.5 mm, which is relatively sensitive to clogging due to the particle size distribution in rain water. The particle size distribution of the influent and effluent indicated that the clogging process could completely remove particles larger than 88 µm but showed variable removal efficiency for particles with sizes of 20–88 µm. This research offers new insight into the clogging of permeable bricks and provides theoretical guidance for restoring the brick permeability.

Study on the Deterioration of Concrete under Dry–Wet Cycle and Sulfate Attack

In order to study the deterioration and mechanism of dry–wet cycles and sulfate attack on the performance of concrete in seaside and saline areas, the deterioration of compressive strength of concrete with different water cement ratios under different erosion environments (sodium sulfate soaking at room temperature and coupling of dry–wet cycling and sodium sulfate) was studied here. At the same time, ICT (industrial computed tomography) and NMR (nuclear magnetic resonance) techniques were used to analyze the internal pore structure of concrete under different erosion environments. The results show that the compressive strength under different erosion environments increases first and then decreases, and the dry–wet cycle accelerates the sulfate erosion. With the increase of dry and wet cycles, larger pores are filled with erosion products and developed into small pores in the early stage of erosion; in the later stage of erosion, the proportion of larger pores increases, and cracks occur inside the sample. In the process of sulfate soaking and erosion, the smaller pores in the concrete account for the majority. As the sulfate erosion continues, the T2 spectrum distribution curve gradually moves right, and the signal intensity of the larger pores increases.

Minimizing Drying Shrinkage and Enhancing Impermeability of Foam Concrete Modified with Epoxy Resin

Relatively high drying shrinkage and permeability were two of the major challenges associated with foam concrete (FC), primarily due to its high porosity nature. This study was aimed at reducing the drying shrinkage and improving the impermeability of FC by blending and modifying it with epoxy resin (EP). Extensive laboratory testing yielded an optimum content of 4.0% EP, corresponding to a minimum drying shrinkage rate of 1.47 mm/m, which was 48% lower than that of the unmodified FC. At this optimum dosage of 4.0% EP, the permeability pressure was at a maximum level of 1.4 MPa, whereas the permeability coefficient was at its lowest value of 0.75 × 10−9 mm/h. Internal pore structure and EP distribution were characterized using the scanning electron microscopy and indicated that a microgrid structure of the FC was formed internally, featuring an increase in the number of pores, a reduction in the average pore size, and a uniform pore size distribution. Similarly, surface energy measurements using the tensiometry method yielded maximum surface energy values at 4.0% EP content, which could be used to explain the reduced drying shrinkage and the enhanced impermeability characteristics of the modified FC.

Influences of High-Sulphur Fly Ash on the Properties of Lightweight Cement-Treated Materials Subjected to Sulphate Corrosion

In this study, the effects of high-sulphur fly ash on the properties of lightweight cement-treated materials (LCMs) immersed in sodium sulphate solutions were studied. The unconfined compressive strength of LCMs corroded by sulphate was tested. The microscopic properties were characterised by X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The results show that high-sulphur fly ash has an adverse effect on the structural strength of LCMs after corrosion, but when the content of fly ash is less than 75%, the effect of fly ash on the strength is small. A small amount of high-sulphur fly ash can improve the density of the material structure; the internal pore structure of LCMs provides space for the growth of ettringite and other corrosive substances and relieves the expansion pressure. LCMs mixed with high-sulphur fly ash have a certain resistance to sodium sulphate corrosion.

Effect of CaSO4 Incorporation on Pore Structure and Drying Shrinkage of Alkali-Activated Binders

This present study investigates the effects of CaSO4 incorporation on the pore structure and drying shrinkage of alkali-activated slag and fly ash. The slag and fly ash were activated at a 5:5 ratio by weighing with a sodium silicate. Thereafter, 0%, 5%, 10%, and 15% of CaSO4 were incorporated to investigate the changes in phase formation and internal pore structure. X-Ray Diffraction (XRD), thermogravimetry (TG)/derivative thermogravimetry (DTG), mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), and drying shrinkage tests were carried out to find the correlation between the pore structure and drying shrinkage of the specimens. The results showed that CaSO4 incorporation increased the formation of thenardite, and these phase changes affected the pore structure of the activated fly ash and slag. The increase in the CaSO4 content increased the pore distribution in the mesopore. As a result, the capillary tension and drying shrinkage decreased.