• 한국건설순환자원학회논문집
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• 제5권4호
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• pp.421-426
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• 2017

본 연구에서는 초음파 속도 측정 실험을 이용하여 동결 융해 작용을 받는 시멘트 모르타르의 동탄성 계수 및 공극 구조 변화를 평가하기 위한 연구를 수행하였다. 초음파 속도는 동결융해 시험 중 매 30cycle마다 시편을 꺼낸 후 측정하였으며, MIP를 이용한 porosity 분석도 수행하였다. 초음파 속도 측정 결과를 이용하여 동탄성계수를 계산한 결과 300cycle 이후 약 13%가 감소하는 것으로 나타났다. porosity는 초기에 대비해서 약 30%가량 증가하였으며, 초음파 속도 측정으로부터 계산된 porosity는 MIP를 통해 측정한 porosity와 약 5~30% 차이를 보였지만 유사한 증가 경향을 보이는 것으로 확인되었다. 이를 통해 초음파 속도 측정 결과를 이용하여 시멘트 모르타르의 porosity 변화를 예측하는 것은 타당한 방법으로 볼 수 있으며, 이를 이용하여 확산계수 등 내구성 평가 지수를 예측할 수 있는 것을 확인할 수 있었다.

• 한국의류학회지
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• 제23권6호
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• pp.820-828
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• 1999

The purpose of this study was to investigate the changes of pore area and water vapour transport by the changes of moisture regain and fabric structure of wool fabrics, As specimens 4 worsted wool fabrics were used. The pore area were measured by image analysis method and dinamic vapour transport and water reisitance was determined by clothing-environment-body modelling system. The pore area was changed by the moisture regain of wool fabrics. The change of pore area was influenced by the yarn twist thread count and cover factor and the weave type. The water vapour transport was changed by the moisture regain. The change of water vapour transport was influenced by the change of pore aree which was determined by image analysis.

• 한국분말재료학회지
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• 제4권4호
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• pp.283-290
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• 1997

$Ti_5Si_3$ intermetallics containing 0-6 wt% of Cu were made by reactive sintering (RS) under vacuum using elemental powder mixtures (Process 1), electro-pressure sintering (EPS) using RS'ed materials (Process2), and EPS using elemental powder mixtures (Process 3). Relatively low dense titanium silicides were gained by process 1, in which porosity decreased with increasing Cu content. For example, porosity changed from 42 to 19.4% with the increase in Cu content from 0 to 6 wt%, indicating that Cu is a useful sintering aid. The titanium silicides fabricated by Process 2 had a higher density than those by Process 1 at given composition, and porosity decreased with increasing Cu content. For example, porosity decreased from 38 to 6.8% with the change in Cu content from 0 to 6 wt%. A high dense titanium silicides were obtained by Process 3. In this Process, porosity decreased a little by Cu addition, and was almost insensitive to Cu content. Namely, about 9 or 7% of porosity was shown in 0 or 1-6 wt% Cu containing silicides, respectively. The hardeness increased by Cu addition, and was not changed markedly with Cu content for the silicides fabricated by Process 3. This tendency was considered to be resulted from porosity, hardening of grain interior by Cu addition, and softening of grain boundary by Cu-base segregates. All these results suggested that EPS using elemental powder mixtures (Process 3) is an effective processing method to achieve satisfactorily dense titanium silicides.

• Geomechanics and Engineering
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• 제35권6호
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• pp.627-636
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• 2023

The essence of subgrade mud pumping under train load is the migration of fine particles in subgrade soil. The migration of fine particles will change the pore structure of overlying ballast, thus affecting the mechanical properties and hydraulic properties of ballast layer. It is of great theoretical significance and engineering value to study the effect of fine particle migration on the pore structure of ballast layer under cyclic loading. In this paper, a tailor-made subgrade mud pumping test model and an X-ray computed tomography (CT) scanning equipment were used to study the influence of migration of fine particles in subgrade soil on the pore parameters (plane porosity, volume porosity, pore distribution and pore connectivity) of overlying ballast under cyclic loading. The results show that the compression of ballast pores and the blockage of migrated fine particles make the porosity of ballast layer decreases gradually. And the percentage of small pores in ballast layer increases, while the percentage of large pores decreases; the connectivity of pores also gradually decreases. Based on the test results, an empirical model of ballast porosity evolution under cyclic loading is established and verified.

• 한국세라믹학회지
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• 제25권5호
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• pp.532-540
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• 1988

Even the finest cement as having a specific surface area of 6.000~8.500$\textrm{cm}^2$/g (Blaine) is to convert into low-porosity hardened cement paste by the use of appropriate plasticizer. In this study, tests were carried out on such a special cement mix(fineness of 6.000$\textrm{cm}^2$/g, Ca-lignosulfonate plus k2CO3 as plasticizer and W/C=0.25) in comparison with ordinary Portland cement. Owing mainly to the high fineness of the cement powder and the low water-to-cement ratio, the hardened low-porosity cement paste showed a very tight microstructure, the pore texture of which consisted of micropores and wide pores only of small radii. The consequence of such mix was hence that the low-porosity special cement had excellent properties of early-high and very high strengths as compared to ordinary Portland cement. Its volume change when dried in the air or re-wetted, exhibited superor behaviour as well.

• 펄프종이기술
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• 제41권4호
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• pp.58-64
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• 2009

This study was carried out to prepare high porosity pulp for oil and air filter media from commercial grade NBKP with 6 - 20% NaOH treatment. The fiber width of NBKP remarkably decreased by NaOH pretreatment. The air permeability of the test sheet prepared from alkali-pretreated NBKP increased with increasing NaOH concentration up to 15%. The burst factor was greatly decreased by alkali pretreatment. By 15 - 20% NaOH pretreatment of NBKP, it could be possible to prepare a high porosity pulp. It seems that the high porosity of the pulp was due to a strong swelling and a great change of the cellulose crystalline lattice from cellulose I to cellulose II with NaOH treatment of NBKP. The study suggested that alkali- pretreated NBKP could be used for manufacturing oil and air filter media.

• Advances in nano research
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• 제7권5호
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• pp.325-335
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• 2019

In the present study, nonlocal strain gradient theory (NSGT) is developed for wave propagation of functionally graded (FG) nanoscale plate in the thermal environment by considering the porosity effect. $Si_3N_4$ as ceramic phase and SUS304 as metal phase are regarded to be constitutive material of FG nanoplate. The porosity effect is taken into account on the basis of the newly extended method which considers coupling influence between Young's modulus and mass density. The motion relation is derived by applying Hamilton's principle. NSGT is implemented in order to account for small size effect. Wave frequency and phase velocity are obtained by solving the problem via an analytical method. The effects of different parameters such as porosity coefficient, gradient index, wave number, scale factor and temperature change on phase velocity and wave frequency of FG porous nanoplate have been examined and been presented in a group of illustrations.

• Coupled systems mechanics
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• 제11권5호
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• pp.389-409
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• 2022

During the manufacture of FGM plates, defects such as porosities can appear. Those can change the entire behavior of these plates. This paper aims to investigate the free vibration characteristics of porous functionally graded (FG) plates resting on elastic foundations. The Young's modulus of the plate is assumed to vary continuously through the thickness according to a power-law formulation, and the Poisson ratio is held constant. Different types of porosity distribution rates are considered. To examine the accuracy of the present formulation, several comparison studies are investigated. Effects of variation of porosity distribution rate, foundation parameter, power-law index and thickness ratio on the fundamental frequency of plates have been investigated.

• 한국세라믹학회지
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• 제31권6호
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• pp.581-586
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• 1994

Effect of excess and deficiency of PbO on the sintering and electrical properties of tetragonal Pb(Zr0.5Ti0.5)O3 were investigated. Fired density revealed maximum value with 4 wt% of excess PbO, and decreased with increasing amount of both excess and deficient PbO. Grain size increased with excess PbO, and decreased with deficiency of PbO. It appeared that excess PbO forms a liquid phase to enhance grain growth and completely volatilizes after sintering, whereas ZrO2 particles formed in PbO-deficient PZT inhibit grain growth. The change in the values of the equivalent circuit elements of PZT corresponded well with thar of porosity formed by excess and deficiency of PbO; kp, Co and Cm decreased while Qm, Rm and Lm increased conosiderably with porosity. This change was more pronounced in PbO-deficient type probably due to change in Zr/Ti ratio of PZT.

• 한국세라믹학회지
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• 제47권4호
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• pp.276-282
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• 2010

There are the impregnating layer formation by surface protective materials or impregnants and the adhesion method by polymer, FRP sheet or steel plate in the surface protective method of concrete structure. The surface impregnation method by impregnants improves the durability of concrete structure by modifying the structure of the concrete surface and also have a merit that can be shortly applied in place without the decrease of concrete surface appearance and is easily applied again. This study is interested in manufacturing the concrete surface impregnants including lithium and potassium silicate for the repair of the exposed concrete and the color concrete requiring the advanced function in view of the concrete appearance. The durability and porosity properties was tested for the review of application. The result of this study show that the effective content of silicate ranges 5 to 20% and the separate application of the first impregnant and the second impregnant is effective for the optimum performance. The adhesion in tension is slightly increased but the reinforcement of concrete substrate is slight. So, the concrete impregnant of this study is more desirable for the improvement of durability rather than the reinforcement.