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성능기준 확립을 위한 공항 줄눈 콘크리트포장의 초기거동 조사
썬 런쥬안(Sun Renjuan),최기효(Choi Ki Hyo),정진훈(Jeong Jin Hoon),권수안(Kwon Soo Ahn) 대한토목학회 2007 대한토목학회논문집 D Vol.27 No.3D
콘크리트포장 줄눈의 초기균열발생과 움직임에 영향을 주는 중요한 인자는 콘크리트 내부의 온도와 습도이므로 이를 측정하고 분석하는 것은 매우 중요하다. 이를 연구하기 위해 인천국제공항 포장공사 지역에 Thermocouple과 Vibrating wire strain gauge, Demec disk, 습도측정장치 등을 설치하였다. 줄눈부 균열의 발생을 육안으로 확인하였고, Demec gauge를 사용하여 균열의 초기거동을 측정하였다. 분석결과, 콘크리트포장의 온도는 줄눈거동에 크게 영향을 주는 것으로 나타났다. 성숙도를 이용하여 콘크리트 슬래브의 경화시간을 측정하였다. 콘크리트 슬래브 변형률은 초기경화 시간이후부터 일정한 경향을 갖고 움직이기 시작하였고, 이는 센서가 설치된 슬래브내 각 위치와 깊이에서 서로 다른 값을 나타냈다. 줄눈에 발생한 균열의 폭은 콘크리트슬래브의 열팽창의 영향으로 온도가 하강하는 야간이나 새벽에 증가하고, 온도가 상승하는 주간에는 줄어드는 것을 확인할 수 있었다. 균열이 발생하지 않은 줄눈의 거동은 이와는 반대의 경향을 나타내었다. 또한, 최종 경화 시 슬래브 내 온도분포의 영향으로 오전 타설 구간과 오후 타설 구간은 서로 다른 균열발생률을 나타내었다. The temperature and moisture variations of concrete pavement at its early-age significantly affect the initiation and movement of joint cracks. Thermocouples, moisture measurement device, vibrating wire strain gages, and Demec disks were installed in 2 slabs of the IIA (Incheon International Airport) concrete pavement to investigate the environmental effect on the behavior of the concrete pavements. The results showed temperature of the concrete slab significantly affected the joint movement. The setting time of the concrete was determined by using the penetration test results. The strain data was analyzed from the initial setting time based on the test results. The strains measured at different locations and different depths of the slabs showed different variation characteristics. The widths of the joint cracks increased early in the morning when the temperature significantly dropped but, those decreased at daytime when the temperature rose due to the effect of thermal expansion of the concrete. The movements of the joints where the cracks never developed showed opposite trend to the cracked joints.
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Yanhua Guan,Jiajie Wu,Renjuan Sun,Hongzhi Zhang,Yanqiu Hu,Fei Wang 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.8
Orthotropic steel bridge deck system usually consists of an orthotropic steel deck and an asphalt overlay. Fatigue cracks of the orthotropic steel deck and premature damage of the asphalt overlay are frequently reported for such system. Engineering cementitious composites (ECC) was therefore proposed to replace the asphalt overlay to address the aforementioned issues. The current study presents an investigation on the transversal flexural behaviour of the ECC under bending forces. Influence of the bending force direction, cover thickness, the number of longitudinal reinforcement steel bars on the flexural performance was revealed. Responses with regard to the load-deflection curve, failure mode, the ultimate capacity, the cracking behaviour, the interfacial slip between ECC and steel deck and the nominal cracking stresses were analysed. The results showed that the load-deflection response under both negative and positive bending forces exhibits elastic stage, crack-developing stage and yield stage. Compared with the reinforcement ratio, cover thickness plays a more significant role on the flexural performances. When the cover thickness decreases from 35 mm to 25 mm, the peak load increases by 21% − 25%. ECC maintains its feature of being ductile, with high tensile and compressive strain capacity in the composite slab. From the design point of view, reducing the cover thickness and increasing the reinforcement ratio can improve the ultimate load and cracking stress, and reduce the internal slip, strain and crack width of the composite slab. It is expected that the current study can provide basic knowledge to the design and application of the steel-ECC composite deck system.
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Huaqiang Yuan,Chuanyi Ma,Jiemin Liu,Zhi Ge,Yifeng Ling,Hongzhi Zhang,Abdullah M. Tawfek,Renjuan Sun 대한토목학회 2024 KSCE Journal of Civil Engineering Vol.28 No.5
This article aims to study the effects of particle packing and inter-particle force on the rheological behaviors of binary cement paste. Fly ash (FA), ground granulated blast furnace slag (GGBFS), and limestone powder (LP) were added by 10 − 40% of cement weight to prepare the binary binder. The particle packing of each binary binder was analyzed based on the close packing theory and bulk density test. Atomic force microscopy and direct shear method were used to investigate the Hamaker constant and friction coefficient of different binders. Fresh pastes of every binder were prepared with variable solid volume fractions (w/b is 0.50, 0.55, and 0.60), and the rheology was measured by a rotary rheometer. Eventually, two empirical models were proposed to predict the yield stress and plastic viscosity of paste based on the porosity, friction coefficient, and w/b obtained from the experiments, and the accuracy of these new models was verified by ANOVA and p-value approach. The results show that particle packing and inter-particle force play a collaborative role in determining the rheological behavior of paste. Increasing particle packing or reducing inter-particle force (i.e., decreasing porosity or friction coefficient) benefits the enhancement of paste rheology. Moreover, an increase in the Hamaker constant leads to higher friction coefficients for binders. Comparisons between the predicted and experimental results demonstrated that these empirical models accurately capture the rheological behaviors of fresh pastes.
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