We report a unique approach for the patterned growth of single-crystalline tungsten oxide (WOx) nanowires based on localized stress-induction. Ions implanted into the desired growth area of WOx thin ...films lead to a local increase in the compressive stress, leading to the growth of nanowire at lower temperatures (600 °C vs. 750-900 °C) than for equivalent non-implanted samples. Nanowires were successfully grown on the microscale patterns using wafer-level ion implantation and on the nanometer scale patterns using a focused ion beam (FIB). Experimental results show that nanowire growth is influenced by a number of factors including the dose of the implanted ions and their atomic radius. The implanted-ion-assisted, stress-induced method proposed here for the patterned growth of WOx nanowires is simpler than alternative approaches and enhances the compatibility of the process by reducing the growth temperature.
This study investigated changes in the interfacial properties of epoxy-coated concrete exposed to various conditions, regarding the epoxy type, coating equipment, and exposure environment and period. ...The measured coating thickness and pull-off bond strength exhibited diverse trends, depending on the exposure period and conditions. In the real sea (RS) environment, the average bond strengths for bisphenol A (BPA) (E1), BPA with zinc powder (E2), and BPA with cresyl glycidyl ether (E3) were 1.26, 1.93, and 1.92 MPa, respectively. The coating method did not significantly affect the measured coating thickness and strength values. The conventional roller (D1) exhibited the highest thickness variation, with a value of 214.45 μm. The RS condition significantly increased the coating thickness (34% to 158%) compared to the tap water (TW) condition. The exposure conditions had little impact on bond strength except for E3, which showed an increased strength (2.71 MPa) over 7–91 days, especially under RS conditions, while E2 remained constant at approximately 1.82 MPa. This study offers insights into factors influencing marine concrete coating performance and discusses limitations and future work.
The present study investigated the structural evolution of Portland cement (PC) incorporating supplementary cementitious materials (SCMs) exposed to seawater. The samples were made with replacing ...Portland cement with 10 mass-% silica fume, metakaolin or glass powder. The reaction degree of SCMs estimated by the portlandite consumption shows that metakaolin has the highest reaction degree, thus metakaolin-blended PC exhibits the highest strength. The control exposed to seawater exhibited 14.82% and 12.14% higher compressive strengths compared to those cured in tap water at 7 and 28 days. The samples incorporating metakaolin showed the highest compressive strength of 76.60 MPa at 90 days tap water curing and this was 17% higher than that of the control. Exposure to seawater is found to retard the rate of hydration in all SCM-incorporating systems, while the strength development of the neat PC system is enhanced. The main reaction product that forms during exposure to seawater is Cl-AFm and brucite, while it is predicted by the thermodynamic modelling that a significant amount of M-S-H, calcite and hydrotalcite is to form at an extended period of exposure time.
Multi-vibrational-mode electrostatic energy harvesters are designed and micro-machined utilizing a simple silicon-on-insulator (SOI) wafer-based process. Enhanced adaptability to various vibrational ...environments is achieved in the proposed design by using serpentine springs attached to the fishbone-shaped inertial mass. The experimental results show that the developed device could convert an input vibration of 6 g at 1272 Hz to 2.96, 3.28, and 2.30 μW for different vibrational directions of 0°, 30°, and 45° with respect to a reference direction, respectively, when all serpentine springs are identical. An alternative device design using serpentine springs with different stiffnesses between x- and y-axes exhibited resonance frequencies at 1059 and 1635 Hz for an input vibrational direction of 45° and acceleration amplitude of 4 g, successfully generating 0.723 and 0.927 μW of electrical power at each resonance, respectively.
This study characterizes alkali-activated fly ash/slag (AFS) blends with reactive MgO under an accelerated carbonation condition. XRD, DTG, FT-IR, solid-state 29Si, and 27Al MAS NMR analyses were ...conducted to investigate the microstructural and gel phase changes caused by the addition of MgO under a high CO2 condition. The addition of reactive MgO to the AFS blends confirmed the formation of a hydrotalcite-like phase with a higher Al uptake level rather than Al substitution for Si in C-S-H gel. The incorporated MgO reacted with CO2 to precipitate as magnesium carbonate and an amorphous hydrotalcite-like phase, which mitigated the carbonation of the C-S-H gel by retarding the penetration of CO2. The carbonated samples showed the presence of aluminosilicate gel with Q3 and Q4 sites stemming from the decalcification of C-(A-)S-H gel and highly cross-linked C-(N-)A-S-H gel.
A widely tunable variable capacitor using mechanical switching and a reversible latching mechanism was developed. This variable capacitor can increase the total capacitance by utilizing three ...discrete switches to sequentially connect four sets of fixed capacitors arranged in parallel. Continuous fine tuning is achieved by closing gaps with these interdigitated capacitors, and connected states are maintained through the use of a mechanical latching mechanism. By combining switching and gap-closing modes, a maximum tuning ratio of 9.42 was obtained.
•A modified Darter and Barenberg’s equation to predict crack widths of thin FRC overlays.•Previously constructed full-scale thin FRC overlays subjected to environmental loadings.•A simple ...two-dimensional finite element model for the cracking and debonding of thin FRC overlays.•Validation of predicted crack widths through the comparison with measured crack widths from field studies.
This study aims to predict the early-age crack width of thin fiber reinforced concrete (FRC) overlays through the modified prediction equation and finite element modeling. The equation which was originally developed to predict the joint opening width of plain concrete pavements, was modified in this study to either consider the fiber aspect ratio or the residual strength ratio of FRC. The predicted crack widths were compared and validated against the measured crack widths of full-scale FRC overlays constructed in the field. Thin FRC overlays in the field had varied joint spacing from 1.12 to 3.35m and were subjected to only environmental loading, rather than traffic loading. A finite element model was generated using fracture energy to account for the fiber-bridging effect and tensile bond strength for interface bonding with the underling structures. The results from a sensitivity analysis indicated that the crack width, vertical lift-off, and debonding length all decreased as the fracture energy of the FRC increased, or as the interfacial tensile bond increased. The proposed equation was found to predict the field crack width within 0.19mm or 26% difference.
The management of plastic waste is a massive challenge and the recycling of plastics for newer applications is a potential solution. This study investigates the feasibility of using polyethylene ...terephthalate (PET) powder in cementitious composites. The changes in the strength and microstructure of Portland cement incorporating PET powder with different replacement ratios were systematically analyzed through the measurements of compressive strength, isothermal calorimetry, X-ray diffraction, thermogravimetric analysis, and Raman spectroscopy. In addition, the possible chemical changes of cement paste samples were studied upon exposure to different conditions, including deionized water, seawater, and simulated pore solution. Based on the test results and analysis, no apparent chemical changes were observed in the cement paste samples, regardless of the exposure conditions. In contrast, the PET powder incorporated into concrete exhibited remarkable changes, which may have occurred during the mixing process. The results also suggested that the maximum replacement ratio of PET powder should be less than 10% of the binder (by mass) to minimize its influence on cement hydration, due to the interaction between water and PET. The PET-containing samples showed the presence of calcium aluminate hydrates which were absent in the neat paste sample.
Supplementary cementitious materials (SCMs) are used to partially replace Portland cement (PC) to reduce the CO2 footprint of concrete. Although many studies have been conducted regarding the uses of ...SCMs as well as oyster shell (OS) with PC, there has been limited investigation into the use of OS coupled with SCMs to replace PC. This study investigated the properties of different types of ternary cement containing OS powder. Ternary cement samples consisting of PC-calcium sulfoaluminate (CSA)-blast furnace slag (BFS) or PC-CSA-metakaolin (MK) were prepared and characterized after 28 and 90 days of curing. The addition of OS formed monocarbonate and hemicarbonate instead of monosulfate, stabilizing ettringite in the samples. As a result, the hydration degree was higher in the CSA-containing samples, whereas the extent of OS consumption was greater in the BFS-containing samples. The results provide new insights into the achievement of an optimal mixture when ternary cements are used with OS.
This study investigated the effects of seawater exposure on the mechanical, durability, and microstructural properties of cement mortars, which contained silica fume, metakaolin, or glass powder at ...two different replacement ratios. Test variables included the exposure conditions, exposure periods, supplementary cementitious material types, and replacement ratios. Compressive, flexural, and pull-off strengths were measured periodically. Mass change, water absorption, and rapid chloride permeability tests were conducted to evaluate the durability performance of Portland cement mortars (PCMs). Microcomputed tomography was utilized to obtain the pore information from representative PCMs. Test results revealed that seawater exposure yielded positive effects, including flexural strength and durability improvements during short-term exposure periods while those effects might not be last for long period. Metakaolin was the most effective supplementary cementitious material to minimize the reduction in compressive strength, while silica fume contributed to durability improvements. On the other hand, PCM containing GP did not show significant changes in strength and durability. Strong correlations between the flexural strength and durability were observed, and it was explained by additional hydration (i.e., matrix densification) of PCMs (except for the GP) due to the seawater curing which filled specific size of pores ranging 50–200 µm.
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