Differences in salient beliefs associated with voluntary exercise training among South Korean firefighters before and after COVID-19

Background : Participating in voluntary exercise training is important to meet occupational requirements as well as firefighters’ health and safety. The purpose of this study is to identify salient beliefs associated with voluntary exercise training among firefighters in the pandemic era by comparing outcomes with those from a previous elicitation study, which was carried out before the COVID-19 outbreak. Methods : A total of 57 firefighters are recruited to participate in an elicitation study. Participants are requested to respond to six open-ended questions related to voluntary exercise training. Content analysis is used to create categories that combine similar factors in each belief. Beliefs mentioned by more than 30% of participants are used for comparison with the results of the previous research. Results : “Improves my physical ability” (n = 44) and “cause injury” (n = 17) are identified as behavioral beliefs in the present study, whereas “makes me tired” and “takes too much time” were also elicited in Lee’s study. Normative beliefs are “family members” (n = 45) and “colleagues” (n = 27) and these results are consistent with those in Lee’s study. “Lack of time” (n = 28), “exercise facilities” (n = 19), and “COVID-19” (n = 19) are elicited as control beliefs in the present study, whereas “physical condition” (n = 21) and “exercise partners” (n = 14) were elicited as other control beliefs, and “COVID-19” was not mentioned in Lee’s study. Conclusion : This study can contribute valuable information about salient beliefs associated with exercise training behavior among firefighters, particularly under pandemic conditions. Future researchers should develop tailored exercise training programs for firefighters based on current elicited beliefs.This research was supported by the Emergency Response to Disaster sites Research and Development Program funded by National Fire Agency(20013968)

Electrically cured ultra-high performance concrete (UHPC) embedded with carbon nanotubes for field casting and crack sensing

The effects of incorporating carbon nanotubes (CNTs) into ultra-high performance concrete (UHPC), thereby forming UHPC/CNT composites, were investigated in terms of electrical curing efficiency, mechanical properties, and crack sensing capability. The addition of CNTs significantly decreased the electrical resistivity of the UHPC, allowing effective electrical curing at low voltage; improved mechanical properties through bridging, pore filling, and calcium-silicate-hydrate (C-S-H) stiffening effects; and favorably influenced the deflection hardening and multiple cracking behavior under flexural stress. Furthermore, the developed UHPC/CNT composites subjected to compressive or flexural stress showed significant crack sensing capability due to the obtained low electrical resistivity. A dramatic fractional change in the resistivity (FCR) of the UHPC/CNT composites can represent the failure under compression or first cracking under flexure. Therefore, it was experimentally verified that the UHPC/CNT composites can extend the applications of UHPC materials especially for on-site casting and structural crack sensors for UHPC-based structures. (c) 2020 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Y

Investigation on the Micro-Grinding Induced Crystallographic Variations of Nine Different Clinkers

Abstract Although clinker has been used for many years, complicated mineralogical properties of clinker pose challenges for the precise quantification. In this study, the mineralogical and crystallographic properties of nine different clinkers according to grinding procedures were investigated. With the dry-grinding for 2 h, particle size reduction to 3 μm of median particle size with a substantial phase transition to an amorphous phase observed, to which alite (C3S) mainly contributed to the transition. Meanwhile, the crystallographic properties of the clinker phases were barely changed during the wet-grinding. In the wet-grinding program, the amount of ferrite solid solution (C4AF) with a high linear absorption coefficient was not underestimated. Furthermore, well-corrected preferred orientation effect on C3S was positively contributed to the analysis result of clinkers with the wet-grinding. Hence, it was suggested that the crystallographic effects observed in the wet-grinding program could produce more reliable results in phase analysis for the clinkers

Sustainable solar energy harvesting using phase change material (PCM) embedded pyroelectric system

This work proposes a smart control of pyroelectric energy harvesting, based on the form-stable phase change material (PCM) composites utilizing polyethylene glycol (PEG) and 1-tetradecanol (1-TD). Solar light transmitted into a pyroelectric system made of window glass and indium tin oxide (ITO) pyro-electrode can provoke thermoelectric energy conversion by the change of temperature difference. The transparent pyro-electrode allows the transmitted solar light to reach the other side of the window glass. The PCM composite placed at the side can reduce the temperature fluctuation to control the change of temperature difference during the light-on/-off process. Since pyroelectric harvesting effects depends on the intensity of sunlight, different solar irradiations (10, 15, and 20 mW/cm2) were applied to the energy harvesting system in this study. The pyro-electrode could generate stable and continuous electrical energy by the combination of PCM composites. In addition, the underlying physics behind the system are theoretically modeled by utilizing the finite element method (FEM).N

Micro- and meso-structural changes on electrically cured ultra-high performance fiber-reinforced concrete with dispersed carbon nanotubes

This study investigated the potential application of electrical curing method on ultra-high performance fiber-reinforced concrete (UHPFRC) by incorporating carbon nanotubes (CNTs) and resulting structural changes in micro- and meso-scale. The addition of CNTs significantly decreased the electrical resistance of the UHPFRC, and the temperature inside the UHPFRC was able to increase to 90 degrees C under low voltage by the Joule effect. This enabled electrical curing, which can produce a similar effect to steam curing but in a much more energetically efficient way. The added CNTs slightly hindered the hydration reaction of the UHPFRC, but it modified the formation of C-(A)-S-H to be denser, stiffer, and more complex which have been evidenced by observed partial cross-linking in the C-(A)-S-H and the higher fractal dimension of solid system. The results of this study are promising for using UHPFRC in on-site field condition and extending the application of CNTs in structural materials.N

Application of micro-CT to Mori-Tanaka method for non-randomly oriented pores in air-entrained cement pastes

The homogenization technique has played a key role in elucidating the mechanical, thermal, and chemical behaviors of composite materials. Specifically, the cement-based material is a representatively complex composite material consisting of various inclusions, such as pores, fibers, and aggregates. Recent studies have mathematically introduced the Mori-Tanaka method to express non-randomly oriented ellipsoidal inclusions. Therefore, the present study aimed to practically apply pore information obtained from micro-computed tomography (micro-CT) to the Mori-Tanaka method. Cement-paste samples were prepared with 0, 1, 2, 5, and 10 wt% of an air-entraining (AE) agent. The representative ellipsoidal shape and orientation distribution function (ODF) of the pores were obtained from the micro-CT, and this information was incorporated into the Mori-Tanaka method. The computation results revealed good agreement between the results of the Mori-Tanaka method and the finite-element method (FEM). Additional sensitivity studies using the Mori-Tanaka model allowed for quantifying the anisotropic degree of the pores in the AE-agent added cement pastes. (C) 2020 Elsevier Ltd. All rights reserved

Carbon Nanotube Embedded Nanostructure for Biometrics

Low electric energy loss is a very important problem to minimize the decay of transferred energy intensity due to impedance mismatch. This issue has been dealt with by adding an impedance matching layer at the interface between two media. A strategy was proposed to improve the charge transfer from the human body to a biometric device by using an impedance matching nanostructure. Nanocomposite pattern arrays were fabricated with shape memory polymer and carbon nanotubes. The shape recovery ability of the nanopatterns enhanced durability and sustainability of the structure. It was found that the composite nanopatterns improved the current transfer by two times compared with the nonpatterned composite sample. The underlying mechanism of the enhanced charge transport was understood by carrying out a numerical simulation. We anticipate that this study can provide a new pathway for developing advanced biometric devices with high sensitivity to biological information

Predicting airborne chloride deposition in marine bridge structures using an artificial neural network model

Chloride-induced corrosion of reinforcement is the most frequent durability problem in marine reinforced concrete (RC) structures. In particular, marine structures are intrinsically exposed to chloride ingress due to airborne chloride deposition. However, monitoring airborne chloride deposition in marine structures is difficult, since conventional on-site measurement is time-consuming and very hazardous. This study presents a prediction model for airborne chloride deposition in coastal bridges based on an artificial neural network (ANN) using local marine meteorological data. Two data sets were prepared for training: chloride deposition data in the (1) presence and (2) absence of scattered deicing salts. The proposed ANN model successfully predicted airborne chloride deposition at three different sampling sites in a coastal bridge, despite the complex relationship between airborne chloride deposition and meteorological parameters. The sampling site, such as one near a vehicle highway, was a more important factor for chloride deposition than the bridge height

Predicting airborne chloride deposition in marine bridge structures using an artificial neural network model

Chloride-induced corrosion of reinforcement is the most frequent durability problem in marine reinforced concrete (RC) structures. In particular, marine structures are intrinsically exposed to chloride ingress due to airborne chloride deposition. However, monitoring airborne chloride deposition in marine structures is difficult, since conventional on-site measurement is time-consuming and very hazardous. This study presents a prediction model for airborne chloride deposition in coastal bridges based on an artificial neural network (ANN) using local marine meteorological data. Two data sets were prepared for training: chloride deposition data in the (1) presence and (2) absence of scattered deicing salts. The proposed ANN model successfully predicted airborne chloride deposition at three different sampling sites in a coastal bridge, despite the complex relationship between airborne chloride deposition and meteorological parameters. The sampling site, such as one near a vehicle highway, was a more important factor for chloride deposition than the bridge height.N