Su-Ho Bae

Evaluation on Mix Characteristics of Concrete Using Fine Sand of Nakdong-River

Abstract The purpose of this experimental research is to suggest a base data to utilize the fine sand of Nakdong-River actively as an alternative aggregate for concrete. For this purpose, after the typical fine sand samples were collected at the mid stream and down stream of main stream of Nakdong-River, the physical properties of them and the mix characteristics of concrete using those were estimated. As a result, it was observed from the test result that mix characteristics between concrete using fine sand and concrete using well-graded reference sand made little differences since unit water content and unit cement content of concrete using fine sand increased only a little than those of concrete using reference sand for specified compressive strength. Key Words : Fine sand of Nakdong-River, Mix characteristics, Physical property, Unit cement content, Unit water content 본 연구는 국토해양부 지역기술혁신사업의 연구비지원(과제번호 : 11CRTI-C059640-01)에 의해 수행되었습니다. * Corresponding Author : Su-Ho Bae(Andong National Univ.)Tel: +82-54-820-5896 email: shbae@andong.ac.krReceived January 28, 2013 Revised (1st February 14, 2013, 2nd March, 4, 2013) Accepted March 7, 2013

Aggregate Utilization Estimation of River Sand according to Typical Location of Main Stream of Nakdong-River

Due to the recent shortage of well-graded river sand resulting from a rapid growth of concrete construction, sea sand, crushed sand, and etc. are increasingly used instead. It is, however, well noted that non-washed sea sand leads to corrosion of the reinforcing steel in concrete, and thus eventually results in damage to concrete. Also, the crushed sand is not being widely used, since it is difficult to maintain the allowable amount of passing 0.08mm sieve and to adjust grading. On the other hand, because the fine sand of Nakdong-River has a poor grading but good quality as a fine aggregate for concrete, it is strongly needed to investigate the fine sand as an alternative fine aggregate. Thus, the purpose of this research is to evaluate the physical properties of the fine sand of Nakdong-River to utilize it actively as a fine aggregate. For this purpose, after the sand samples were collected according to typical location of main stream of Nakdong-River, the physical properties such as density in oven-dry condition, grading, unit volume mass, and etc. of them were estimated. It was observed from the test results that physical properties of the fine sand of Nakdong-River except grading were found to be excellent.

Long-Term Durability Estimation of Cementless Concrete Based on Alkali Activated Slag

최근, 우리나라는 세계 10위 온실가스 배출국 선정 및 지구온난 화 문제의 이슈화로 인해 탄소저감 기술 개발을 위한 지속적인 노 력을 하고 있다(Kim 2010). 국내 건설 산업 분야에서도 이산화탄소 배출량을 줄이기 위한 연구가 진행되고 있는데(Bae et al. 2013), 이는 콘크리트의 주 원료인 시멘트의 생산과정에서 전체 탄소 배 출량의 약 6.5%인 연간 4,500만톤의 CO2를 배출하기 때문이다 (Jung et al. 2015). 이에 따라 결합재로서 시멘트 대신에 고로슬래 그 미분말(ground granulated blast furnace slag, GGBFS)이나 플라이애시(fly ash)의 비소성 바인더를 사용한 무시멘트 콘크리 트에 관한 연구들이 활발히 진행되고 있다(Kim et al. 2014; Park et al. 2015). 무시멘트 콘크리트를 활용하면 대폭적인 탄소배출량 저감 효과 뿐만 아니라 높은 초기 강도 및 고강도 발현 등의 장점이 있다(Oh 2014). 무시멘트 콘크리트는 알칼리 활성화제의 종류 및 첨가량에 따 라 콘크리트의 특성 변화가 심해 제어가 어려울 뿐만 아니라 급격 한 유동성 손실이라는 단점을 가지고 있으나(Collins and Sanjayan 1999), GGBFS를 콘크리트에 적정량 활용함으로써 장기강도 증진, 수화열 저감, 수밀성·내해수성·내화학성 증대 등의 다양한 효과 를 가져올 수 있다. 한편, 콘크리트의 내구수명을 저하시키는 대표적인 요인으로 알칼리 활성 슬래그 기반 무시멘트 콘크리트의 장기 내구성 평가 Long-Term Durability Estimation of Cementless Concrete Based on Alkali Activated Slag

Workability and Mechanical Properties of Hybrid Fiber Reinforced Concrete Using Amorphous Steel Fiber and Polyamide Fiber

Many studies have been performed on hybrid fiber reinforced concrete for years, which is to improve some of the weak material properties of concrete. Studies on characteristics of hybrid fiber reinforced concrete using amorphous steel fiber and polyamide fiber, however, yet remain to be done. The purpose of this experimental research is to evaluate the workability and mechanical properties of hybrid fiber reinforced concrete using amorphous steel fiber and polyamide fiber. For this purpose, the hybrid fiber reinforced concrete containing amorphous steel fiber(ASF) and polyamide fiber(PAF) were made according to their total volume fraction of 0.5 % for water-binder ratio of 33 %, and then the mechanical properties such as the compressive strength, direct tensile strength, flexural strength, and flexural toughness of those were estimated. It was observed from the test results that the compressive strength was slightly decreased with increasing ASF and decreasing PAF and the effect of fiber combination on the flexural strength was not much but the flexural toughness was relatively largely increased with decreasing ASF and increasing PAF.

Durability Evaluation of Concrete Using Fine Sand of Nakdong-River

It is strongly needed to investigate the fine sand as an alternative fine aggregate of well-graded river sand because the fine sand which is being enormously distributed in the midstream and downstream of Nakdong-River in Korea has a poor grading but good quality as a fine aggregate for concrete. Thus, the purpose of this experimental research is to evaluate the durability of concrete using the fine sand to utilize it actively as a fine aggregate. For this purpose, the concrete specimens using different fine sand were made for the specified concrete strength of 35MPa, and then their durability such as the resistance to freezing and thawing and carbonation, and drying shrinkage were evaluated. It was observed from the test results that the resistance to freezing and thawing and carbonation of concrete using the fine sand was similar to that of concrete using reference sand, but the drying shrinkage of concrete using the fine sand with small fineness was comparatively lager than that of concrete using reference sand.

Characteristics for Reinforcement Corrosion and Chloride Ion Diffusion of High Volume Fly Ash Concrete

(Received February 25, 2014 / Revised March 17, 2014 / Accepted March 19, 2014)The purpose of this experimental research is to evaluate the resistance of reinforcement corrosion and chloride ion penetration of highvolume fly ash (HVFA) concrete. For this purpose, concrete test specimens were made for various strength level and replacement ratioof fly ash, and then compressive strength and diffusion coefficient for chloride ion of them were measured for 28, 91 and 182 d ays, respectively. Also, corrosion monitoring by half cell potential method was carried out for the made lollypop concrete test spec imens to detect the time of corrosion initiation for reinforcement in concrete. As a result, it was observed from the test results that compressivestrength of HVFA concrete was decreased with increasing replacement ratio of fly ash but long-term resistance against reinforce mentcorrosion and chloride ion penetration of that was increased.키워드 : 하이볼륨 플라이애시 콘크리트, 철근부식 모니터링, 자연전위, 염소이온 확산계수Keywords : High Volume Fly Ash Concrete, Reinforcement Corrosion Monitoring, Self-Potential, Diffusion Coefficient for Chloride Ion* Corresponding author E-mail: shbae@andong.ac.kr