• Advances in concrete construction
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• 제17권1호
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• pp.13-26
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• 2024

Due to its capacity to address urgent environmental challenges connected to urbanization and stormwater management, pervious concrete, a sustainable and innovative material, has attracted a lot of attention recently. The aim of this study was to find the engineering characteristics of pervious concrete made from recycled aggregate (RA) at various aggregate-to-cement ratios (A/C) and the addition of 5% (by weight of total aggregate) of both natural and recycled fine aggregate to produce a very sustainable concrete product for a variety of applications. The three distinct aggregate-to-cement ratios, 6, 5, and 4, were used to produce pervious concrete using recycled aggregate in the research approach. The ratio of water to cement (w/c) was maintained at 0.3. Pervious concrete was created using single-sized recycled aggregate that passed through a 12.5 mm sieve and was held on a 9.5 mm sieve, as well as natural and recycled sand that passed through a 4 mm sieve. The production of twelve distinct concrete mixtures resulted in the testing of each concrete sample for dry density, abrasion resistance, compressive and splitting tensile strengths, porosity, and water permeability. A statistical method called GLM-ANOVA was also used to assess the characteristics of pervious concrete made using recycled aggregate. According to the experimental results, lowering the aggregate-to-cement ratio enhances the pervious concrete's overall performance. Additionally, a modest amount of fine aggregate boosts mechanical strength while lowering void content and water permeability. However, it was noted that such concretes' mechanical qualities were adversely affected to some extent. The results of this study offer insight into the viability of using recycled aggregates in order to achieve both structural integrity and environmental friendliness, which helps to optimize pervious concrete compositions.

• 한국주조공학회지
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• 제38권1호
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• pp.1-8
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• 2018

In this study, we focused on the correlation between the solidification structure, heat treatment and mechanical properties of the A356 alloy according to the conditions of Sr modification. The microstructural evolution of the eutectic Si and ${\alpha}-Al$ phase in the A356 alloy castings depending on the amount of Sr were investigated during solid solution heat treatment using an optical microscope, a scanning electron microscope and an image analyzer. In addition, tensile tests on the heat treated materials examined the relationship between the microstructure and the fracture surface. The as-cast A356 alloys under 40 ppm Sr showed an undermodified microstructure, but that of the added 60-80 ppm Sr had well modified structure of fine fibrous silicon. After solid solution treatment, the microstructure of the undermodified A356 alloy exhibited a partially spheroidized morphology, but the remainder showed the fragmentation of fibrous shaped silicon. The spheroidization of the eutectic silicon in the modified A356 alloys was completed during heat treatment, which was very effective in increasing the elongation. This is supported by the fracture surface in the tensile test.

• 지질공학
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• 제1권1호
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• pp.2-10
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• 1991

이 보문은 리비아의 트리폴리 지역에서 건설공사를 할 경우 지반공학적으로 고려하여야할 점을 기술한 것이다. 지반자료는 이 지역에서 수행된 학교와 주택건설을 위한 부지지반조사에서 얻은 것이다. 자파라 평원의 지표하 10m까지 표층의 대부분은 보통 조밀한 실트질 모래로 구성되어 있다. 그러나 지역적으로는 표토가 빈약하고 석회암이나 석회사암의 호층으로 구성되어 있기도 하며 산지 지역은 대부분 표토의 발달이 거의 없다. 원지반의 실트질 모래는 확대기초나 줄기초를 적용할 경우 일반적으로 150kN/$m^2$의 지내력을 가진다고 추정된다. 트리폴리 지역에서 콘크리트에 적합한 골재의 분포는 매우 제한되어 있으며 조골재는 주로 백운암 석산을 개발하여 공급된다.

• 콘크리트학회논문집
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• 제25권3호
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• pp.347-354
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• 2013

최근 천연모래의 부족으로 부순 잔골재가 널리 사용되고 있다. 우리나라에서는 부순 잔골재 중의 0.08 mm 이하 미립분을 7% 이하로 제한하고 있으며 이는 ASTM의 규정과 유사한 것이나 그 외의 다른 나라의 규정과 비교할 때 상당히 엄격한 규정이다. 또한 부순 잔골재 중에는 파쇄 시에 발생하는 0.08 mm 이하 미립분을 20% 정도 포함하게 되며 물로 씻어내는 일도 용이하지 않을 뿐 아니라 자원이용의 극대화를 위해서도 잔입자량 한도의 상향 조정 가능 여부에 대한 검토가 필요하다. 그래서 이 연구에서는 0.08 mm 이하 미립분에 대한 특성 및 콘크리트 품질에 미치는 영향에 대한 실험을 실시하였으며, 비교를 위하여 실트 및 점성토 중의 미립분을 사용한 실험을 병행하였다. 미립분에 대해 실험한 결과 메틸렌블루 값은 부순 잔골재 중의 석분에 비하여 실트 및 점성토 중의 미립분에 대한 값이 보다 크게 나타났으며 또한 메틸렌블루 값은 packing density 및 액성한계, 소성한계와 높은 상관관계를 가지는 것으로 나타났다. 콘크리트 실험에서 동일한 슬럼프를 얻기 위한 고성능 감수제의 소요량은 미립분의 대체 사용량 증가에 따라 커지며, 메틸렌블루 값이 큰 미립분을 사용할 때 보다 크게 나타났다. 한편 부순 잔골재 중의 미립분을 20% 이내에서 대체 사용한 경우, 고성능감수제를 사용하여 반죽질기를 같게 한 콘크리트의 압축강도와 인장강도는 거의 변화가 없었으며 콘크리트의 건조수축량도 큰 차이를 보이지 않았다. 그러나 실트 및 점성토 중의 미립분을 대체 사용한 경우는 콘크리트의 강도가 현저히 저하하고 건조수축량도 크게 증가하는 것으로 나타났다.

• 한국수산과학회지
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• 제32권3호
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• pp.345-352
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• 1999

이 연구는 제주도 함덕연안에 분포하는 구멍연잎성게의 생태 및 번식생활사에 관한 연구보고서이다. 시료는 북제주군 함덕에서 SCUBA를 통하여 채집하였으며, 실험실로 옮긴 뒤, 크기 및 생식소에 대한 분석을 수행하였다. 구멍연잎성게의 크기는 각장 80$\~$200mm 이었으며, 각장 140$\~$170mm 의 개체가 주를 이루었다 (N=129). 구멍연잎성게는 세립질 또는 미립질 ($125\~250\mu$m ($2\~3\phi$))의 사질에 주로 분포하였으며, 퇴적물내의 유기물을 섭취하는 퇴적물식자로 확인되었다. 성숙한 암컷의 생식소는 보라색을 띠며, 수컷은 짙은 노란색을 띤다. 암, 수 모두 11$\~$3월 사이 휴지기를 거쳐 6월경에 성숙하며, 주 방란 방정은 7$\~$10월 사이에 이루어진 것으로 추정된다. 암컷의 경우 성숙한 난은 그 직경이 평균 381$\mu$m이었다.

• 한국도로학회논문집
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• 제4권2호
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• pp.19-31
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• 2002

대표적인 산업부산물인 폐주물사와 플라이애쉬의 재활용은 매우 시급한 현안중의 하나이다. 이러한 산업부산물의 재활용을 위해 저강도 콘크리트 개념을 적용한 유동성채움재(CLSM)로의 재활용을 위한 기본 연구가 지난 3년간 수행되었다. 본 연구에서는 폐주물사중 환경오염문제의 발생 가능성이 적은 것을 선별하여 CLSM용 잔골재로 이용하였다. 특히, 폐주물사에 화학약품처리를 하여 재활용 잔골재로 이용하는 방식사 역시 실험 재료로 이용하였다. 실험은 기존에 보편적으로 이용되는 뒤채움재 시공시 발생하는 사일로 토압에 대한 검증과 토압 경감효과에 대한 연구를 수행하였다. 실험결과 CLSM은 기존의 뒤채움재와는 그 성질이 매우 달라서, 옹벽배면과 절개면사이의 거리가 짧아서 발생하는 사일로 토압효과는 나타나지 않았다. 이는 기존의 뒤채움재와는 상당히 다른 재료이고, 또한, 기존에 이용되는 각종 토압론의 공식적용에 다소 신중해야 할 것으로 판단된다. 사용된 잔골재용 시료중에서는 방식사가 가장 큰 토압경감 효과를 나타냈고, 사용된 CLSM의 잔골재 특성에 따라 토압경감 효과에 다소 시간적인 차이는 있으나, 그 절대값은 어느 정도 일정한 값으로 수렴하는 것으로 나타났다.

• Advances in materials Research
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• 제11권2호
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• pp.121-146
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• 2022

In the recent years, the use of agricultural waste in green cement mortar and concrete production has attracted considerable attention because of potential saving in the large areas of landfills and potential enhancement on the performance of mortar. In this research, microparticles of palm oil fuel ash (POFA) obtained from a multistage thermal and mechanical treatment processes of raw POFA originating from palm oil mill was utilized as a pozzolanic material to produce high-performance cement mortar (HPCM). POFA was used as a partial replacement material to ordinary Portland cement (OPC) at replacement levels of 0, 5, 10, 15, 20, 25, 30, 35, 40% by volume. Sand with particle size smaller than 300 ㎛ was used to enhance the performance of the HPCM. The HPCM mixes were tested for workability, compressive strength, ultrasonic pulse velocity (UPV), porosity and absorption. The results portray that the incorporation of micro POFA in HPCMs led to a slight reduction in the compressive strength. At 40% replacement level, the compressive strength was 87.4 MPa at 28 days which is suitable for many high strength applications. Although adding POFA to the cement mixtures harmed the absorption and porosity, those properties were very low at 3.4% and 11.5% respectively at a 40% POFA replacement ratio and after 28 days of curing. The HPCM mixtures containing POFA exhibited greater increase in strength and UPV as well as greater reduction in absorption and porosity than the control OPC mortar from 7 to 28 days of curing age, as a result of the pozzolanic reaction of POFA. Micro POFA with finely graded sand resulted in a dense and high strength cement mortar due to the pozzolanic reaction and increased packing effect. Therefore, it is demonstrated that the POFA could be used with high replacement ratios as a pozzolanic material to produce HPCM.

• Geomechanics and Engineering
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• 제33권2호
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• pp.221-230
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• 2023

The liquefaction of soil occurs when a soil loses strength and stiffness because of applied stress, such as an earthquake or other changes in stress conditions that result in a loss of cohesion. Hence, a method for improving the strength of liquefiable soil needs to be developed. Many techniques have been presented for their possible applications to mitigate liquefiable soil. Recently, alternative methods using biopolymers (such as xanthan gum, guar gum, and gellan gum), nontraditional additives, have been introduced to stabilize fine-grained soils. However, no studies have been done on the use of carrageenan as a biopolymer for soil improvement. Due to of its rheological and chemical structure, carrageenan may have the potential for use as a biopolymer for soil improvement. This research aims to investigate the effect of adding carrageenan on the soil strength of treated liquefiable soil. The biopolymers used for comparison are carrageenan (as a novel biopolymer), xanthan gum, and guar gum. Then, sand samples were made in cylindrical molds (5 cm × 10 cm) by the dry mixing method. The amount of each biopolymer was 1%, 3%, and 5% of the total sample volume with a moisture content of 20%, and the samples were cured for seven days. In terms of observing the effect of temperature on the carrageenan-treated soil, several samples were prepared with dry sand that was heated in an oven at various temperatures (i.e., 20℃ to 75℃) before mixing. The samples were tested with the direct shear test, UCS test, and SEM test. It can increase the cohesion value of liquefiable soil by 22% to 60% compared to untreated soil. It also made the characteristics of the liquefiable increase by 60% to 92% from very loose sandy soil (i.e., ϕ=29°) to very dense sandy soil. Carrageenan was also shown to have a significant effect on the compressive strength and to exceed the liquefaction limit. Based on the results, carrageenan was found to have the potential for use as an alternative biopolymer.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.107-110
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• 1999

The objective of this study is to obtain characteristics of early age pore-structure and carbonation of concrete using ground granulated blast furnace slag (GGBFS). The durability of GGBFS concrete should be evaluated for wide use of the GGBFS. As for that evaluation, an analysis on early age pore-structure characteristics of GGBFS concrete are very important, Carbonation depths of GGBFS concrete, which are known to be larger than that of OPC, are different according to replacement ratios and fineness of slag. Because sea sand as fine aggregate is much used recently, it is also necessary to analyze characteristics of carbonation of GGBFS concrete. In this study, The micro-pore structure formation characteristics of GGBFS concrete are obtained through the test of GGBFS mortars with different fineness and replacement ratio of GGBFS. The carbonation of GGBFS concrete is also investigated by acclerated carbonation test for early age GGBFS concrete.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2004년도 추계학술대회 논문집
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• pp.1071-1076
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• 2004

The purpose. in this study. is to analyze liquefaction potential of Inchon International Airport at the Area Phase ' I ' for Railway Construction of all, seismic response was analyzed using the computer program, Shake91. Four methods proposed by Seed & Idriss. Eurocode, Iwasaki & Tatsuoka. and Ishihara were used for assessment of liquefaction potential and safety factors calculated form these methods are compared. Based on the results of seismic response analysis, the maximum acceleration at the ground surface is larger than that evaluated site factor effect by using site factor because these areas are composed of very loose sand clay. Especially, in the case of analysis with long period earthquake data. it is appeared that the acceleration of earthquake is amplified more largely. Therefore, accurate seismic response analysis is suggested for the design on the important structures on reclaimed land. The analytical results of liquefaction potential show that the increments of N-value and effective overburden pressure with remediation make safety factors increase. Through comparing the safety factors evaluated from four method, the safety factor calculated by See & Idriss method in the lowest one and it is found that the SPT N-value effect the safety factor very largely. And, Iwasaki & Tatsuoka method is affected by various factors such as average grain size. fine contents, confining pressure. In conclusion. to minimize earthquake Risk by liquefaction, the efficient remediation is essential and seismic response analysis should be carride out.