• Journal of the Korean Wood Science and Technology
• /
• v.48 no.4
• /
• pp.458-471
• /
• 2020

Effect of pre-treatment and compression ratio on specific gravity (SG) and dimensional stability improvement of three lesser-used wood species from natural forest area of North Kalimantan Province, Indonesia had been investigated. Hot soaking at 80℃ for 3 hours within 2 and 5% of boron solution was applied as pre-treatment, while compression ratio applied was 20 and 40% from the initial thickness. Densification was conducted using hot pressing machine at 30 kg/㎠ of pressure and 160℃ of temperature for 15 minutes. Specific gravity was measured gravimetrically, while dimensional stability was evaluated through thickness swelling and water absorption as the indicator. Results show that SG of densified wood was influenced by wood species and compression ratio, but not by pre-treatment applied; while dimensional stability was influenced by wood species, compression ratio, and pre-treatment. Specific gravity and water absorption of densified wood was improved significantly. Specific gravity increased 28.86-63.03%, while water absorption decreased 12.80-15.89%. Thickness swelling of 20% densified wood was lower than that of 40% densified wood.

• The Journal of the Petrological Society of Korea
• /
• v.3 no.3
• /
• pp.234-240
• /
• 1994

The Wongyeong site, one of massive pinkish granite quarries in the Mungyeong area, was drilled to study the physical and chemical properties following the rock classification from fresh rock to highly, moderately and slightly weathered one. The physical properties such as specific gravity, absorption ratio, porosity and compressive strength were tested from the core samples. Specific gravity and absorption ratio are 2.37-2.64 and 0.27-1.87% respectively, while porosity and compressive strength are 0.70-4.38% and 110- 1, 695 kg/$cm^2$. With increased weathering, absorption ratio vs. porosity shows a positive correlation. The absorption ratio is in reverse proportion to compressive strength. Toward the surface in the drilled core, the $SiO_2$, CaO and $K_2O$ contents slightly decrease, but the $Al_2O_3$+FeO(t) contents increase by the enrichment of residual clay in the weathered rock.

• Economic and Environmental Geology
• /
• v.32 no.1
• /
• pp.1-11
• /
• 1999

In the last decade, the supply of natural aggregates has been continuously increased due to the other types of aggregates. In general, aggregates constitute 70-80% of the total volume of concrete, so the quality of aggregates is main factor controlling physical characteristics of concrete. For this reason, physical properties of aggregate according to different rock types were studied. The majority of crushed aggregates is taken out of granite, gneiss, sandstone, andesite, basalt and so forth. The physical properties of these rock types were tested and most of them fell within the acceptable limit on the base of Korean standard regulation. The major lithology of the crushed aggregates is granite and gneiss, both of which are marked for more than 50% of total lithology thpes in Korea. A to the physical properties of granite, the high specific gravity coincides with low porosity, low absorption ratio, while the abrasion and soundness index show, in general, no specific trend. It has been assumed that slight differences of the physical properties of granite aggregates are related with those of the mineral composition, grain size, and so on. In comparison to granite, the physical properties of gneiss have little correlation one after another. This trend is related to different mineral composition, grain size and typical sheet fractures typically prevailing in the texture of gneiss. Spatial pattern of physical properties shows that high specific gravity of granite coincides only with low porosity and absorption ratio in all provinces except Cheolla province, and high specific gravity of gneiss coincides with low porosity and absorption ratio only in Cheolla and Gandwon provinces.

• Journal of the Korea Concrete Institute
• /
• v.15 no.4
• /
• pp.566-573
• /
• 2003

This study was performed to manufacture a rigid sound absorbing material by increasing the continuous void ratio of cellular concrete, thereby achieving an increase in sound absorption ratio and an enhancement in strength of the cellular concrete. By the experiments, it was determined that an increase in sound absorption ratio is achieved by increasing the added amount of air voids, thereby increasing the continuous void ratio. When the material had a thickness of 5 cm, a satisfactory average sound absorption ratio of 70% was obtained at a continuous void ratio of 40% or more. An increase in the thickness of the sound absorbing material resulted in an increase in sound absorption ratio in a super bass range. The specific gravity of cellular concrete meeting an average sound absorption ratio of 70% was 0.4 at a material thickness of 5 cm, and 0.6 or less at a material thickness of 7 cm. The compressive strength of the cellular concrete having a specific gravity of 0.4 meeting an average sound absorption ratio of 70% or more was 1.37 Mpa at a cement fineness of 3,000. This compressive strength was increased to 3.34 MPa at a cement fineness of 8,000. Accordingly, it was determined that the compressive strength of cellular concrete having continuous voids increases with a higher cement fineness.

• Journal of the Architectural Institute of Korea Structure & Construction
• /
• v.34 no.2
• /
• pp.49-56
• /
• 2018

The use of highly absorptive materials in cement-based materials is increasing for internal curing purpose. However, calculation of correct absorption capacity of such materials is not easy, which leads to change in the effective water-to-cement ratio of cement paste by either absorbing or releasing water. In this study, effective absorption capacity of a highly absorptive material was found using isothermal calorimetry. Moreover, the effect of specific surface area was investigated. It was found that the method was capable of finding effective water absorption capacity of activated carbon fiber. For the activated carbon fiber used in this research, the effect of specific surface area was negligible because the high BET surface area was due to micropores less than 1nm, which does not affect the rate of hydration curve. Thus, the effective absorption capacity of such materials can be found successfully using this method.

• International Journal of Highway Engineering
• /
• v.15 no.2
• /
• pp.57-63
• /
• 2013

PURPOSES : This study was performed to investigate a feasibility of job-site use of recycled concrete aggregate exceeding 3% of absorption rate. Test variables are coarse aggregate types such as natural aggregate, job-site processed recycled aggregate, and recycled aggregate processed from the intermediate waste treatment company. METHODS : First, aggregate properties such as gradation, specific gravity and absorption rate were determined. Next a basic series of mechanical properties of concrete was tested. RESULTS : All strength test results such as compression, flexure and modulus were satisfied for the minimum requirements. Finally up to first 48 elapsed days the shrinkage strains of concretes made from both recycled aggregates (in case of volume-surface ratio of 300) appeared to be greater than 26% of the companion concretes made from natural aggregates. CONCLUSIONS : Drying shrinkage result is ascribed to greater absorption rate and specific gravity of those specimens made from recycled aggregate. This may be reduced with an addition of admixtures.

• Tunnel and Underground Space
• /
• v.23 no.3
• /
• pp.212-218
• /
• 2013

Tuff specimens were thermally treated with predetermined temperatures of 200, 400 and $600^{\circ}C$ to construct specimens simulating weathered tuff rocks. Specific gravity, absorption ratio, elastic wave velocity, uniaxial compressive strength, Brazilian tensile strength, Young's modulus, Poisson's ratio and slake-durability index were measured for pre-heated specimens. Heating of rock specimens entailed the degradation of material properties except for slake-durability index. It was found that correlations among P-wave velocity, uniaxial compressive strength, Brazilian tensile strength, Young's modulus and absorption ratio are high. Regression equations which use the P-wave velocity as an independent variable were presented to evaluate uniaxial compressive strength, Brazilian tensile strength, Young's modulus and absorption ratio.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.04a
• /
• pp.327-332
• /
• 2000

The objective of this study was to improve the defects of lightweight cement concrete by treating with redispersible polymer powders. The statistical relationships of water-cement ratios, contents of lightweight aggregates and polymer powers and be used for predicting the concrete strength. It was found that the varieties and techniques adopted in this experiment were capable of identifying the influence of various tested for air contents, flow test, water absorption, specific gravity, flexural and compressive strength. This study showed that fundamental properties were very affected by cement- lightweight aggregate ratio, polymer-cement ratio and water-cement ratio.

• The Journal of the Korea Contents Association
• /
• v.13 no.2
• /
• pp.308-313
• /
• 2013

In this paper, we measured specific absorption rate (SAR) using characteristic variables such as flip angle, repetition time (TR) and echo time (TE) at magnetic resonance imaging. The subject was applied to same scan technique from body weight 10 kg to 90 kg, were measured for the average SAR and the peak SAR values according to the change of parameter. SAR with different body weight levels was not seen a significant change at TE but it increased in the larger flip angle and the shorter TR. SAR value was within the limits of human head acceptable standard and SNR in segmental body weights was not proportional to the increase of body weights. In conclusion, this study can be helpful for diagnosis by using appropriate parameters which obtained the various contrast and SNR.

• ETRI Journal
• /
• v.46 no.4
• /
• pp.571-580
• /
• 2024

A compact triple-band porous electromagnetic bandgap structure-loaded coplanar-waveguide-fed wearable antenna is introduced for applications of wireless body area networks. The porous structure is aimed to create a stopband or bandgap in the electromagnetic spectrum and increase breathability. The holes in the bottom electromagnetic bandgap surface increase the inductance, which in turn increases the bandwidth. The final design resonates at three bands with impedance bandwidths of 264 MHz, 100 MHz, and 153 MHz and maximum gains of 2.18 dBi, 6.75 dBi, and 9.50 dBi at 2.45 GHz, 3.5 GHz, and 5.5 GHz, respectively. In addition, measurements indicate that the proposed design can be deformed up to certain curvature and withstand human tissue loading. Moreover, the specific absorption rate remains within safe levels for humans. Therefore, the proposed antenna can suitably operate in the industrial, scientific, and medical, Bluetooth, Wi-Fi, and WiMAX bands for potential application to wireless body area networks.