• International Journal of Concrete Structures and Materials
• /
• 제3권2호
• /
• pp.81-90
• /
• 2009

This paper proposes a semi analytical model to describe the pore structure of concrete by a set of simple equations. The relationship between the porosity and the microstructure of concrete has been considered when constructing the analytical model. The microstructure includes the interface transition zone (ITZ) between aggregates and cement paste. The predicting model of porosity was developed with considering the ITZ for various mixing of mortar and concrete. The proposed model is validated by the rapid experimental programs. Although the proposed model is semi-analytical and relatively simple, this model could be reasonably utilized for the durability design and adapted for predicting the service life of concrete structures.

• 한국도로학회논문집
• /
• 제20권1호
• /
• pp.59-67
• /
• 2018

PURPOSES : This paper presents a mix design method for using steel slag as an aggregate for asphalt mixtures. METHODS : Steel slag has a different density and absorption rate than natural aggregates. The asphalt content was calculated according to the steel slag characteristics, and the formula for aggregate-gradation correction was presented. RESULTS : The asphalt mix was designed using the proposed equations. Using the proposed mix design method, it was possible to design the asphalt mixture according to the target-usage amount of the recycled aggregate. CONCLUSIONS : The suggested method can be used for asphalt mix design using aggregates with different densities and absorption rates. It is expected to contribute to quality improvement by ensuring accurate calculation of mixing ratios for steel slag asphalt mixtures.

• Fibers and Polymers
• /
• 제5권3호
• /
• pp.187-197
• /
• 2004

The compressive and flexural properties of hemp fiber reinforced concretes (FRC) were examined in this paper. Natural hemp fiber was mixed using dry and wet mixing methods to fabricate the FRC. Mechanical properties of the FRC were investigated. The main factors affecting compressive and flexural properties of the FRC materials were evaluated with an orthogonal test design. Fiber content by weight has the largest effect. The method for casting hemp FRC has been optimised. Under the optimum conditions, compressive strength increased by 4 %, flexural strength increased by 9 %, flexural toughness increased by 144 %, and flexural toughness index increased by 214 %.

• Architectural research
• /
• 제11권1호
• /
• pp.25-33
• /
• 2009

This study presents the testing of 15 hwangtoh-based cementless concrete mixes to explore the significance and limitations of the development of eco-friendly concrete without carbon dioxide emissions while maintaining various beneficial effects. Hwangtoh, which is a kind of kaolin, was incorporated with inorganic materials, such as calcium hydroxide, to produce a cement-less binder. The main variables investigated were the water-to-binder ratio and fine aggregate-to-total aggregate ratio to ascertain the reliable mixing design of hwangtoh-based cementless concrete. The variation of slump with elapsed time was recorded in fresh concrete specimens. Mechanical properties of hardened concrete were also measured: including compressive strength gain, splitting tensile strength, moduli of rupture and elasticity, stress-strain relationship, and bond resistance. In addition, mechanical properties of hwangtoh-based cement-less concrete were compared with those of ordinary portland cement (OPC) concrete and predictions obtained from the design equations specified in ACI 318-05 and CEB-FIP for OPC concrete, wherever possible. Test results show that the mechanical properties of hwangtoh-based concrete were significantly influenced by the water-to-binder ratio and to less extend by fine aggregate-to-total aggregate ratio. The moduli of rupture and elasticity of hwangtoh-based concrete were generally lower than those of OPC concrete. In addition, the stress-strain and bond stress-slip relationships measured from hwangtoh-based concrete showed little agreement with the design model specified in CEB-FIP. However, the measured moduli of rupture and elasticity, and bond strength were higher than those given in ACI 318-05 and CEB-FIP. Overall, the test results suggest that the hwangtoh-based concrete shows highly effective performance and great potential as an environmental-friendly building material.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
• /
• pp.377-380
• /
• 2008

Fiber Cocktail을 혼입유무에 따른 40${\sim}$100 MPa 고강도 콘크리트 구조부재의 고온영역에서 재료적 물리적 역학적 특성을 규명한 후, 유한요소해석법(ABAQUS)을 적용한 구조요소 화재거동 시뮬레이션 해석을 수행한 결과, 다음과 같은 결론을 얻었다. 첫째, 콘크리트 Fiber Cocktail을 혼입한 실험체는 무혼입 실험체에 비해 최대수축이 제어되는 것으로 해석되었으며, 그 제어 범위는 혼입실험체 대비 약 25%${\sim}$55%로 분석되었다. 이는 고강도 콘크리트 기둥에서 Fiber Cocktail 혼입을 통해 기둥변위 수축제어가 가능한 것으로 분석되었다. 둘째, 본 연구는 고강도 콘크리트의 내부 공극압에 의한 폭렬 특성이 반영되지 않은 화재 거동 해석으로서 향 후 콘크리트 내부 공극압에 대한 특성 반영, 다양한 고강도 콘크리트 및 강재의 강도별, 내부온도별 재료 특성 DB가 구축된다면 성능기반 내화구조 설계를 위한 기술적 기반이 이루어질 것으로 판단된다.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
• /
• pp.997-1002
• /
• 2001

Tensile strength of CFRP (Carbon Fiber Reinforced Polymer) is approximately 10 times higher than that steel reinforcement, but the design strength of CFRP is normally reduced by the bond failure between RC and CFRP. Many researches have been carried out, concerned with bond behavior between RC and CFRP to prevent the unpredicted bond failure of RC beam strengthened by CFRP, but the national design code for design bond strength of CFRP hasn't been constructed. In this study, 3 beams specimen strengthened by CFRP under the variable of bonded length were tested to derive the design bond strength of CFRP to the RC flexural members. Also 2 beams specimen strengthened by CFRP were tested to inspect the construction environment effects such as mixing error of epoxy resin and the amount of primer epoxy resin. From the test results, It is concluded that the maximum design bond strength of CFRP to RC flexural member is considered to be $\tau_{a}$=8kgf/$cm^{2}$.

• International Journal of Concrete Structures and Materials
• /
• 제10권sup3호
• /
• pp.65-74
• /
• 2016

During concrete pumping, the migration and redistribution of particles occur in a pipe and the lubrication layer that forms between the bulk concrete and the pipe wall is the governing factor determining the flow behavior. In order to identify flow behavior of pumping, in this study, the viscoelastic properties related to the microstructural behavior of a flocculated suspension were examined by using dynamic oscillatory measurements. Cement paste is assumed to be a constituent material of the lubrication layer and ten cases of mixing design are employed by changing the proportions of mineral admixtures. The relationship between the yield stress obtained from the steady shear test and the dynamic modulus resulted from the oscillatory shear measurement was derived and the implications of the correlation are discussed. Moreover, based on the investigation of the viscoelastic properties with oscillatory measurements, the initial behavior of pumped concrete was analyzed systematically.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 1997년도 봄 학술발표회 논문집
• /
• pp.643-648
• /
• 1997

P.C Bearing Plate method, corresponding to the existing steel plate build-up method, is developed by the very first in domestic and is applied to the foundation in the HYUNDAI building at Kang-Nam. P. C Bearing Plate produced in ourself P.C plant can stand against vertical load of 7,000ton obtaining allowable force of soil. It is possible to minmize cost expediting, do site assembling and omit unnecessary excavation work by plant prefabrication of foundation member. The purpose of this paper is to study the optimum mixing design of Ultra-high strength concrete ($\acute{f}_{C91}$= 950kg/$\textrm{cm}^2$), crack control through measuring the heat of hydration, mock up test for the optimum curing method. As mentioned above, developing the Ultra-high strength Precast Concrete Bearing Plate set up successfully in the site foundation work of the HYUNDAI Building at Kang-Nam.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2018년도 추계 학술논문 발표대회
• /
• pp.149-150
• /
• 2018

The RC buildings which are constructed on the seaside are followed by KBC(2016) to achieve the minimization of durability damage. To control the corrosion of the reinforced steel bar by salt attack, W/C should be under 0.4 and specified concrete strength is more than 35MPa in the concrete/building construction standard specification. Ready mixed concretes which have usually include the admixtures in Busan were tested to certify the salt attack durability. In the same specified concrete strength, remarkable salt attack durability was evaluated in comparison to OPC.

• 한국건설순환자원학회논문집
• /
• 제7권2호
• /
• pp.123-130
• /
• 2019

본 연구에서는 순환잔골재의 혼입률에 따른 콘크리트의 강도 특성을 실험을 통해 확인하고, 전과정평가(LCA, Life Cycle Assessmet) 기법을 이용하여 순환잔골재의 전과정 환경영향을 평가하여, 콘크리트를 제조함에 있어서 순환잔골재 사용의 유효성을 확인하여 순환골재 콘크리트 활용을 위한 기초적 자료로 사용하는 것을 목적으로 한다. 이를 위해, 목표설계기준압축강도는 27MPa로 하였으며, 순환골재 실용화를 고려하여 순환잔골재의 혼입률을 0, 30, 60, 100%로 설정하여 굳지 않은 콘크리트 및 굳은 콘크리트에 대한 실험을 통해 슬럼프, 공기량, 압축강도 등을 확인하였고, 순환잔골재의 전과정 환경영향을 평가하고 타 골재와 환경영향을 비교 분석 하였다.