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Modeling of Mechanical Properties of Concrete Mixed with Expansive Additive
Hyeonggil Choi,Takafumi Noguchi 한국콘크리트학회 2015 International Journal of Concrete Structures and M Vol.9 No.4
This study modeled the compressive strength and elastic modulus of hardened cement that had been treated with an expansive additive to reduce shrinkage, in order to determine the mechanical properties of the material. In hardened cement paste with an expansive additive, hydrates are generated as a result of the hydration between the cement and expansive additive. These hydrates then fill up the pores in the hardened cement. Consequently, a dense, compact structure is formed through the contact between the particles of the expansive additive and the cement, which leads to the manifestation of the strength and elastic modulus. Hence, in this study, the compressive strength and elastic modulus were modeled based on the concept of the mutual contact area of the particles, taking into consideration the extent of the cohesion between particles and the structure formation by the particles. The compressive strength of the material was modeled by considering the relationship between the porosity and the distributional probability of the weakest points, i.e., points that could lead to fracture, in the continuum. The approach used for modeling the elastic modulus considered the pore structure between the particles, which are responsible for transmitting the tensile force, along with the state of compaction of the hydration products, as described by the coefficient of the effective radius. The results of an experimental verification of the model showed that the values predicted by the model correlated closely with the experimental values.
Heesup Choi,Hyeonggil Choi,Myungkwan Lim,Masumi Inoue,Ryoma Kitagaki,Takafumi Noguchi 한국콘크리트학회 2016 International Journal of Concrete Structures and M Vol.10 No.1
In this study, a quantitative review was performed on the mechanical performance, permeation resistance of concrete, and durability of surface-modified coarse aggregates (SMCA) produced using low-quality recycled coarse aggregates, the surface of which was modified using a fine inorganic powder. The shear bond strength was first measured experimentally and the interface between the SMCA and the cement matrix was observed with field-emission scanning electron microscopy. The results showed that a reinforcement of the interfacial transition zone (ITZ), a weak part of the concrete, by coating the surface of the original coarse aggregate with surface-modification material, can help suppress the occurrence of microcracks and improve the mechanical performance of the aggregate. Also, the use of low-quality recycled coarse aggregates, the surfaces of which were modified using inorganic materials, resulted in improved strength, permeability, and durability of concrete. These results are thought to be due to the enhanced adhesion between the recycled coarse aggregates and the cement matrix, which resulted from the improved ITZ in the interface between a coarse aggregate and the cement matrix.
양생조건에 따른 섬유보강 시멘트계 복합재료(FRCC)의 균열 자기치유 특성
최희섭 ( Heesup Choi ),최형길 ( Hyeonggil Choi ) 한국건축시공학회 2016 한국건축시공학회지 Vol.16 No.4
In this study, the self-healing effect of a fiber-reinforced cement composite (FRCC) was examined using a drying-wetting test and an outdoor exposure test. The influence of various curing conditions on the self-healing effect of the FRCC was also investigated. The effect of self-healing was evaluated using a permeability coefficient and by investigating the cracks using a optical microscope. The results confirmed that the FRCC was capable of self-healing under a long wetting time and a low drying temperature. In addition, watertight performance by self-healing was shown to have a significant influence on wetting time. Meanwhile, this self-healing effect was enhanced by hydration as a result of rainfall when the FRCC was put under actual environmental conditions. Moreover, it was determined that cracking self-healing can be improved by using the appropriate admixture materials.
Strength Reduction of Concrete Subjected to High Temperatures: Effects of Various Aggregates
Wonchang Kim(Wonchang Kim),Keesin Jeong(Keesin Jeong),Hyeonggil Choi(Hyeonggil Choi),Taegyu Lee(Taegyu Lee) 한국화재소방학회 2023 International Journal of Fire Science and Engineer Vol.37 No.1
Previous studies on the strength degradation of concrete subjected to high temperatures were analyzed. To analyze the effect of the coarse-aggregate type on strength degradation, data from previous studies were collected, and the coarse aggregate used, physical properties of the aggregate, and heating conditions were analyzed. The concrete types were classified into normal, heavyweight, and lightweight concrete. Their high-temperature characteristics were analyzed and evaluated according to the mixed coarse aggregate. Finally, the correlations derived from the analysis results were compared with the CEB Code. The analysis results were different for different concrete and coarse-aggregate types, and different tendencies from the CEB Code were observed.
양생조건에 따른 섬유보강 시멘트계 복합재료(FRCC)의 균열 자기치유 특성
최희섭,최형길,Choi, Heesup,Choi, Hyeonggil 한국건축시공학회 2016 한국건축시공학회지 Vol.10 No.4
양생조건의 차이가 섬유보강 시멘트계 복합재료(FRCC)의 자기치유에 미치는 영향을 검토하기 위해, 건습 반복시험 및 옥외 폭로시험을 실시하여 FRCC의 자기치유 효과에 대해 검토했다. 투수계수 및 마이크로스코프에 의한 균열조사에 의해 FRCC의 자기치유 효과에 대해 평가한 결과, 수중에의 침지시간이 길고, 건조온도가 낮은 경우 균열의 자기치유 효과는 큰 것을 확인할 수 있었다. 또한, 자기치유에 있어서의 수밀성능은 습윤 시간에 크게 영향을 받는 것을 확인했다. 한편, 실환경 조건에 있어서 강우에 의한 수분 공급에 의해 자기치유는 진전하는 것을 확인했으며, 혼화재료를 적절히 병용하여 사용하는 것으로 균열의 자기치유 성능을 향상할 수 있다고 판단된다. In this study, the self-healing effect of a fiber-reinforced cement composite (FRCC) was examined using a drying-wetting test and an outdoor exposure test. The influence of various curing conditions on the self-healing effect of the FRCC was also investigated. The effect of self-healing was evaluated using a permeability coefficient and by investigating the cracks using a optical microscope. The results confirmed that the FRCC was capable of self-healing under a long wetting time and a low drying temperature. In addition, watertight performance by self-healing was shown to have a significant influence on wetting time. Meanwhile, this self-healing effect was enhanced by hydration as a result of rainfall when the FRCC was put under actual environmental conditions. Moreover, it was determined that cracking self-healing can be improved by using the appropriate admixture materials.
Van, Nguyen Duc,Choi, Hyeonggil,Hama, Yukio Elsevier 2019 Construction and Building Materials Vol.223 No.-
<P><B>Abstract</B></P> <P>Although expansive additives have been widely used to efficiently reduce shrinkage cracking in concrete, little research has been undertaken to model the hydration reaction of cement and expansive additive blends. This paper presents a hydration model that describes the hydration reaction that occurs when expansive additives are mixed at an early stage and an equation to predict the compressive strength of expansive concrete. Using the proposed model, this study predicted the hydration degree, rate of heat evolution, and gel/space ratio of the hardening cement–expansive additive paste. The results indicated good agreement of the calculated data with the measured data. From the relationship between the gel/space ratio and compressive strength, an equation was deduced for prediction of the development of compressive strength of expansive concrete. Furthermore, this work also found that the model parameters can be represented as a function of the mineral composition of the cement. The results demonstrate that the proposed model is effective and useful in predicting the hydration and mechanical properties of expansive concrete.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Proposed a hydration model of cement-expansive additive paste. </LI> <LI> Relationship between mineral composition and model parameters is clearly explained. </LI> <LI> Predicted gel/space ratio using proposed model. </LI> <LI> A conversion coefficient is deduced for predicting compressive strength. </LI> <LI> Predicted compressive strength development of expansive concrete. </LI> </UL> </P>
2차원 확산파 해석모형을 통한 침사지겸 저류지의 친환경 조립식 빗물침투저류시설 적용 타당성 분석
김호진 ( Kim Ho-jin ),최희용 ( Choi Hee-yong ),이태규 ( Lee Tae-gyu ),최형길 ( Choi Hyeonggil ) 한국건축시공학회 2022 한국건축시공학회 학술발표대회 논문집 Vol.22 No.2
In this study, a numerical analysis was conducted using a two-dimensional diffusion-wave analysis model to analyze the validity about the application of eco-friendly prefabricated rainwater detention system in grit chamber and permanent pond. As a result of the analysis, it is confirmed that the flood prevention effect, such as a decrease in peak flow rate and a delay in peak time, is excellent, so it is considered reasonable to apply eco-friendly prefabricated rainwater detention system in grit chamber and permanent pond.