• Title/Summary/Keyword: Mixed sand

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Characteristics of Shear Waves in Controlled Low Strength Material with Curing Time (양생시간에 따른 유동성 채움재의 전단파 특성)

  • Han, Woojin;Lee, Jong-Sub;Byun, Yong-Hoon;Cho, Samdeok;Kim, Juhyong
    • Journal of the Korean GEO-environmental Society
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    • v.17 no.3
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    • pp.13-19
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    • 2016
  • The ultrasonic waves for monitoring concrete materials have been used to investigate the setting and hardening process of concrete. This paper presents the application of bender elements for monitoring the hardening properties of Controlled Low Strength Material (CLSM) and the characterization of shear waves in CLSM according to curing time. To ensure the early age properties and flow, the CLSM consists of CSA cement, sand, silt, water, fly ash, and accelerator. In addition, three different type specimens according to fine contents are mixed. A couple of bender elements are installed at the wall of measurement cell and the CLSM specimen are prepared at the measurement cell for 28 days. Experimental results show that the resonant frequency and shear wave velocities increase with an increase in the curing time, regardless of the fine contents. Up to ten hours, the amplitudes of shear waves also increase, and the resonant frequency and shear wave velocities at the same time increase as the fine contents increase. The shear wave measurement technique using the bender elements may be effectively used to evaluate the hardening properties of CLSM along the curing time.

Propagation by Cutting Method of Korea Rare Endemic Thuja koraiensis Nak. (희귀식물(稀貴植物) 눈측백나무(Thuja koraiensis Nak.)의 삽목증식(揷木增殖))

  • Song, Jeong-Ho;Lee, Jung-Joo;Koo, Yeong-Bon;Lee, Kab-Yeon;Han, Sang-Don;Yang, Byeung-Hoon
    • Journal of Korean Society of Forest Science
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    • v.95 no.4
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    • pp.393-397
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    • 2006
  • Thuja koraiensis Nak. is a short and creeping evergreen shrub which reaches about 3 m in height and only occurs in the northeast China and in high mountains over the Korea. It's designated as a rare and endangered tree species in Korea and DD (data deficient) in Red List Category & Criteria of IUCN. This study was carried out to develop the propagation technique by cutting for conservation of genetic resources of T. koraiensis. The rooting responses of branch cuttings, obtained from hard (May) and semi-hard wood shots (August) to three plant growth regulators (PGRs), namely, IAA, IBA, and NAA applied at various concentrations (0, 100, 500, 1000, 2000, and 3000 mg/l) were examined in sand and mixed soil media. Percentage of rooting showed significant difference between cutting time, among kinds and among concentration of PGRs. The optimum cutting time was April to May in hardwood cutting. The application of IAA 1000 mg/l and NAA 500mg/l were effective in callus formation and rooting of cutting. Relatively, rooting of cutting of the control taken in May was above 93%.

Prediction of Succession and Silvicultural Control in the Black Locust(Robinia pseudoacacia L.) Plantation (아까시나무(Robinia pseudoacacia L.) 조림지(造林地)에서 천이(遷移)의 예측(豫測)과 조림학적(造林學的) 제어(制御))

  • Yun, Chung Weon;Oh, Seung Hwan;Lee, Joon Hyouk;Joo, Sung Hyun;Hong, Sung Cheon
    • Journal of Korean Society of Forest Science
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    • v.88 no.2
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    • pp.229-239
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    • 1999
  • To get ecological information necessary for the prediction on succession and the silvicultural control of the black locust(R. pseudoacacia) plantation, classification of vegetation unit. competition of major species, and succession were analyzed. The results were as follows. Vegetation units classified in R. pseudoacacia forest were Quercus variabilis community, Persicaria perfoliata community, Styrax japonica community, Acalypha australis community, Typical community. Species diversity indices showed significant difference among the vegetation units. As a result of stand ordination by CCA method, arrangement of stands on Axis I was correlated significantly with altitude, sand, silt and available phosphorus contents, and that on Axis II was with total nitrogen, exchangeable calcium and kalium contents. It was judged that R. pseudoacacia plantation would be replaced by the mixed forest including Quercus spp., Acer spp., and Prunus spp. etc., native to Korea with the progression of succession as the results of analyses on competition of major species and successional tendency in R. pseudoacacia plantation.

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A Study on the Fabrication of Shrinkage-Free Mullite--$ZrO_2$ Ceramics with Al-Additives (Al첨가에 의한 무수축 Mullite-$ZrO_2$ 요업체의 제조에 관한 연구)

  • Kim, Jeong-Uk;Kim, Il-Su
    • Korean Journal of Materials Research
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    • v.5 no.7
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    • pp.888-896
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    • 1995
  • In this paper the manufacture of shrinkage-free in situ Mullite-ZrO$_2$ceramics through the addition of Al base metal powder to the mixture of ZrSiO$_4$and A1$_2$O$_3$was attempt. The ZrO$_2$-strengthened mullite ceramics was prepared after the following reaction form, 3(Al+Al$_2$O$_3$)+2ZrSiO$_4$longrightarrow3A1$_2$O$_3$.2SiO$_2$+2ZrO$_2$Al metal powder was added from none to 30 weight percent to the A1$_2$O$_3$. The powders were mechanically mixed, isostatically pressed and reaction sintered at 1450-1$600^{\circ}C$ for 3hours. The specimens were sintered with and without intrim soaking time for 5 hours at 125$0^{\circ}C$ for the oxidation of Al-powder The addition of aluminium accelerates the reaction and compensate the shrinkage during the sintering through an increase in volume of oxidized Al. Because coarse flake type Al metal powders were not effectively milled, oxidized Al resulted in the relative large pore in the specimen.

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Purity of γ-Dicalcium Silicate with Synthetic and Raw Materials Conditions (합성 및 원료 조건에 따른 γ-C2S의 순도)

  • Lee, Seok-Hee;Cho, Hyeong-Kyu
    • Journal of the Korea Institute of Building Construction
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    • v.20 no.2
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    • pp.123-128
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    • 2020
  • γ-dicalcium silicate(γ-C2S) is known as a polymorphism of belite. Due to its high CO2 fixing capacity and the production process with low CO2 emission, γ-C2S has attracted more attention of researchers. For the further development of γ-C2S applications in construction industry, this study aims to investigate the method for synthesizing high purity of γ-C2S. The influence of raw materials and calcination temperatures on the purity of γ-C2S was evaluated. Several Ca bearing materials were selected as the calcium source, the materials which's main component is SiO2 were used as the silicon source. Raw materials were mixed and calcined under different temperatures. The results revealed that the highest purity could be obtained using Ca(OH)2 and SiO2 powder as raw materials. In addition, a relatively economic synthesis method using natural mineral materials-limestone and silica sand as raw materials were developed for the practical application. The purity of synthetic γ-C2S was recorded up to 77.6%.

A Study on the Reduced Rebound Method of Surface Finishing Spray Photocatalytic Mortar (표면 마감 광촉매 스프레이 모르타르의 리바운드량 저감 방안 연구)

  • Baek, Hyo-Seon;Park, Jeong-Hwan
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.21 no.9
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    • pp.604-609
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    • 2020
  • There are various methods of finishing concrete surfaces, and when considering workability, the spray method is effective, but rebound occurs. The allocation of rebound occurrence control should be adjusted according to the materials used. Thus, a basic study was conducted on multiple techniques for reducing the rebound incidence that are suitable for surface finishing materials containing a photocatalyst. A prior study derived the reduction effect and optimal mix ratio for photocatalytic performance. Based on that study, the rebound reduction was verified according to the specifications of the content and the mechanical durability characteristics of the mixed materials. Rebound, compressive strength, flexural rigidity, and table flow tests were done. The flow was fixed at 170±10 mm considering the workability of the mortar spray equipment. For the experimental variables, the rebound number was adjusted to the silica sand variables relative to the cement weight, and silica sands No. 5 and No. 7 were used. The results show the highest compression strength in the final S-1 variable, and the amount of rebound was minimized. These results were sufficiently filled with the bindings of the silica pores, which increased the binding force between the aggregates, resulting in a lower amount of rebound.

Effect of Fines on Unconfined Compressive Strength of Cemented Sands (세립분이 고결모래의 일축압축강도에 미치는 영향)

  • Park, Sung-Sik;Choi, Sun-Gyu
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.31 no.6C
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    • pp.213-220
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    • 2011
  • Fines such as silt or clay are usually mixed with granular particles in natural or reclaimed soils which are slightly cemented. Such fines contained within weakly cemented soils may influence permeability and also mechanical behavior of the soils. In this study, a series of unconfined compression tests on weakly cemented sands with fines are carried out in order to evaluate the effect of fines on unconfined compressive strength (UCS) of cemented soils. Two different cement ratios and fine types were used and fine contents varied by 5, 10, and 15%. Two types of specimens were prepared in this testing. One is the specimen with the same compaction energy applied. The other is the one with the same dry density by varying compaction energy. When the same amount of compaction energy was applied to a specimen, its density increased as a fine content increased. As a result, the UCS of cemented soils with fines increased up to 2.6 times that of one without fines as an amount of fines increased. However, when the specimen was prepared to have the same density, its UCS slightly decreased and then increased a little as a fine content increased. Under the same conditions, a UCS of the specimen with silt was stronger than the one with kaolin. As a cement ratio increased, a UCS increased regardless of fine type and content.

Hydrogeochemical Characteristics and Occurrences of High-Saline Ground Water at Seocheon Area, Korea (서천 길산천 소유역의 고염분 지하수 수질과 산출 특성)

  • Moon, Sang-Ho;Lee, Bong-Joo;Park, Kwon-Gyu;Ko, Kyung-Seok
    • Economic and Environmental Geology
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    • v.42 no.3
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    • pp.235-246
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    • 2009
  • High-saline ground water, whose eclectrical conductivity value ranges from 12,000 to 21,000 $\mu$S/cm, occurs at the small catchment of Gilsan stream near Geum-river estuary dike. These high-saline ground water comes form three different aquifers consisting of two horizons of sand sediments and one weathered zone with top part of unconformity. For these three aquifers showing mutual independence in terms of hydrogeological and hydrogeochemical connection, we examined characteristics of aqifer occurrences and their water chemistry, and observed and analyzed the fluctuations of the ground water level and electrical conductivity. Our study results indicate that the high-saline characteristics of ground water in this study area should not come from dynamic recent seawater intrusion, but might be due to the fossil saline water included and isolated within the paleo-sediments or weathered zone and their upper unconformity part. This high-saline water seems to be now partially mixed and affected by freshwater in the higher inland reach of Gilsan stream.

The Solidification Characteristics of Recycled Aggregate Mixed with Incineration Ash and Waste Concrete (소각재와 폐콘크리트를 이용한 재생골재의 고형화 특성)

  • Yeon, Ikjun;Ju, Soyoung;Lee, Sangwoo;Shin, Taeksoo;Kim, Kwangyul
    • Journal of the Korean GEO-environmental Society
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    • v.9 no.5
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    • pp.5-13
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    • 2008
  • In this study, It was carried out to evaluate the feasibility of recycled crushed concrete as aggregate used cement mortar replace sand and to investigate engineering properties of recycled aggregate for hazardous waste solidification. The compressive strength of cement mortar replaced 5-15% (wt.) recycled aggregate was over $163kgf/cm^2$ which is the standard of first grade concrete block class C. And cement mortar was examined to evaluate the stability by leaching test. Cu, Cd, Pb, Cr, and As as the heavy metals were proved very stable but mercury (Hg) was leached high concentration because it was simply tied to the cement surface. We investigated the crystal structures of cement mortar and they had shown the peaks of $Ca(OH)_2$, ettringite, and CSH (calcium silicate hydrate). As the result, the longer curing time, the higher CSH peak that means to increase compressive strength and the cement mortar was more stable. Therefore it was shown that it may be possible to apply hazardous waste solidification using recycled aggregate, fly ash and sewage sludge ash.

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Classification of Various Severe Hazes and Its Optical Properties in Korea for 2011~2013 (2011~2013년 한반도에서 관측된 다양한 연무의 분류 및 광학특성)

  • Lee, Kyu-Min;Eun, Seung-Hee;Kim, Byung-Gon;Zhang, Wenting;Park, Jin-Soo;Ahn, Jun-Young;Chung, Kyung-Won;Park, Il-Soo
    • Atmosphere
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    • v.27 no.2
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    • pp.225-233
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    • 2017
  • Korea has recently suffered from severe hazes, largely being long-range transported from China but frequently mixed with domestic pollution. It is important to identify the origin of the frequently-occurring hazes, which is however hard to clearly determine in a quantitative term. In this regard, we suggest a possible classification procedure of various hazes into long-range transported haze (LH), Yellow Sand (YS), and urban haze (UH), based on mass loading of fine particles, time lag of PM mass concentrations between two sites aligned with dominant wind direction, backward trajectory of air mass, and the mass ratio of PM2.5 to PM10. The analysis sites are Seoul (SL) and Baengnyeongdo (BN), which are distant about 200 km from each other in the west to east direction. Aerosol concentrations at BN are overall lower than those of SL, indicative of BN being a background site for SL. We found distinct time lag of PM2.5 and PM10 concentrations between BN and SL in case of both LH and YS, but the intensity of YS being stronger than LH. Time scale (e-folding time scale) of LH appears to be longer and more variable than YS, which implies that LH covers much larger spatial scale. In addition, we found linear and significant correlations between ${\tau}_a$ obtained from sunphotometer and ${\tau}_{cal}$ calculated from surface aerosol scattering coefficient for LH episodes, relative to few correlation between those for YS, which might be associated with transported height of YS being much higher than LH. Therefore surface PM concentrations for the YS period are thought to be not representative for vertical integrated amount of aerosol loadings, probably by virtue of decoupled structure of aerosol vertical distribution. Improvement of various hazes classification based on the current result would provide the public as well as researchers with more accurate information of LH, UH, and YS, in terms of temporal scale, size, vertical distribution of aerosols, etc.