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Yonathan Reches 한국콘크리트학회 2020 International Journal of Concrete Structures and M Vol.14 No.4
The exposure of concrete to gamma radiation gives rise to a set of physical and chemical processes over multiple length scales, from molecular to bulk. The literature includes a number of bulk-scale studies which report the radiogenic heating of concrete and the loss of water (unbound, physically-bound, and/or chemically-bound) due to irradiation. This paper mechanistically quantifies observations by these studies, and presents a continuum framework to model the effects of gamma photons on concrete. A basis is presented for comparing otherwise disparate results in the literature for radiolysis rates. The Stefan–Boltzmann Law, adapted to include a gamma heat source term, reasonably describes radiogenic heating in concrete specimens. In multiple studies, the primary mechanism for dehydration is the loss of liquid water in the pore network of the cement product, rather than of water which is physically or chemically bound in a solid state.
흙의 동상 민감도 특성 정의를 위한 동결융해 시험 방법에 관한 연구
Yonathan Alemu Yami,박용부,박종배,노승현 한국도로학회 2022 한국도로학회논문집 Vol.24 No.5
PURPOSES : The aim of this study is to review freeze-and-thaw testing apparatuses, develop a freeze-and-thaw testing setup with a test protocol, test the freeze-and-thaw properties of soils collected from different parts of South Korea, and suggest an index for frost susceptibility criteria for soils found in South Korea. METHODS : Based on a literature review, a new freeze-thaw testing setup was developed. In addition, a test protocol was developed for freeze-thaw testing. Soils collected from different parts of South Korea and bedding sand used for block pavements were tested to determine whether the measurements from the newly developed test setup could capture important freeze-thaw characteristics of the soils. Finally, to develop local frost susceptibility criteria, a parameter including both the vertical deformation and thermal conductivity characteristics of the soils was suggested. RESULTS : The results from the laboratory experiments indicate that the newly developed freeze-and-thaw setup captures the required parameters to quantify the responses of soils subjected to cyclic freeze-and-thaw testing. In addition, a vertical deformation of up to 2.437 mm is measured. Moreover, seven soils out of the nine tested soils are classified as having a medium frost susceptibility, whereas the remaining two show low frost susceptibility. The bedding sand experiment also shows that there is a possibility of having a frost susceptible condition based on the moisture content. When submerged, the bedding sand is classified as having a medium frost susceptibility. CONCLUSIONS : The "HEART" freeze-thaw testing setup was able to capture the parameters required for evaluating the frost susceptibility of soils. This setup and testing procedure could be further used to test and prepare criteria for classifying the frost susceptibility of soils found in South Korea.
Dynamic Mechanical Properties of Elastomeric Nanoparticle Composites
Sungwon Ma,Yonathan Thio 한국고분자학회 2016 Macromolecular Research Vol.24 No.10
The blends of two crosslinked polystyrene-b-polyisoprene (PS-b-PI) copolymers with homopolystyrene were investigated for their dynamic mechanical properties. Elastomeric block copolymer nanofibers utilized as filler were prepared by employing the phase separation property of a polystyrene-b-polyisoprene copolymer, which was then exposed to a crosslinking agent (S2Cl2) for cold vulcanization. The crosslinking density and morphology of nanofillers resulted in three elastomeric block copolymer nanofillers: fully crosslinked nanofiber (FCF), fully crosslinked multi-junctioned nanofiber (FCM), and partially crosslinked multi-junctioned sample (PCM). Uncrosslinked PS-PI block copolymer (UBC) was also studied as a comparison. Crosslinking density was calculated by measuring the change in intensity of the double bond peaks using FTIR spectroscopy. Thermo-mechanical properties and morphology of the blends were characterized by dynamic mechanical analysis (DMA) and scanning electron microscope (SEM). DMA results show that modulus increases with increasing filler loading in the terminal region for both PS/FCM and PS/FCF systems and the increasing rate is related to crosslinking density.
Dispersion stability and its effect on tape casting of solvent-based SiC slurries
이종현,Weon-Ju Kim,Ji-Yeon Park,Parlindungan Yonathan,윤당혁 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.3
Slurries containing well-dispersed ceramic particles are essential for further processing, such as tape casting and infiltration to a woven fabric, to produce high quality products. In this study, various types of suspensions were prepared with 4 different types of commercial dispersants to examine the dispersion mechanism and determine the optimum conditions for the microsized α- and 50 nm-sized β-SiC systems in a toluene/ethanol mixed solvent. According to the sedimentation and rheological results, 3 and 20 wt.% of a polyester/polyamine co-polymeric dispersant were found to be the most effective dispersant for α- and β-SiC suspensions, respectively. An electrostatic mechanism did not play a major role in the mixed solvent system when a dispersant was added. The optimum amount of dispersant for the slurry was less than that for the suspension due to the dispersing effect of the polyvinyl butyral (PVB) binder. Due to the high specific surface area of the nano-sized β-SiC powder, 40 wt.% binder resin was needed to achieve a tape with desirable properties, while 15 wt.% of binder was adequate for the slurry with α-SiC with a lower surface area. Overall, the tape properties, such as green morphology and density, were strongly related to the dispersion state of the slurry. Slurries containing well-dispersed ceramic particles are essential for further processing, such as tape casting and infiltration to a woven fabric, to produce high quality products. In this study, various types of suspensions were prepared with 4 different types of commercial dispersants to examine the dispersion mechanism and determine the optimum conditions for the microsized α- and 50 nm-sized β-SiC systems in a toluene/ethanol mixed solvent. According to the sedimentation and rheological results, 3 and 20 wt.% of a polyester/polyamine co-polymeric dispersant were found to be the most effective dispersant for α- and β-SiC suspensions, respectively. An electrostatic mechanism did not play a major role in the mixed solvent system when a dispersant was added. The optimum amount of dispersant for the slurry was less than that for the suspension due to the dispersing effect of the polyvinyl butyral (PVB) binder. Due to the high specific surface area of the nano-sized β-SiC powder, 40 wt.% binder resin was needed to achieve a tape with desirable properties, while 15 wt.% of binder was adequate for the slurry with α-SiC with a lower surface area. Overall, the tape properties, such as green morphology and density, were strongly related to the dispersion state of the slurry.