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이차돈 ( Lee¸ Chadon ),정상모 ( Chung¸ Sang-mo ),원종필 ( Won¸ Jong-pil ),이승환 ( Lee¸ Seung-hwan ),방정환 ( Bang¸ Jeong-hwan ) 한국구조물진단유지관리공학회 2002 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.6 No.2
Experiments were performed in order to examine the effectiveness of strengthening the reinforced concrete beams by the method of Near Surface Mounted(NSM) fiber reinforced plastic rebars(FRP rebars). Test results showed that NSM strengthening method with FRP rebars inserted directly into the grooves adequately increased the flexural strength. Using the theoretical model, parametric studies were performed. It was theoretically observed that identical flexural behavior of strengthened beams can be obtained if the concept of equivalent sectional areas based on the ratio of moduli of elasticity between different FRP rods is used.
Lee, Chadon,Lee, Songhee,Nguyen, Ngocchien Korea Concrete Institute 2016 International Journal of Concrete Structures and M Vol.10 No.2
High-early-strength-concrete (HESC) made of Type III cement reaches approximately 50-70 % of its design compressive strength in a day in ambient conditions. Experimental investigations were made in this study to observe the effects of temperature, curing time and concrete strength on the accelerated development of compressive strength in HESC. A total of 210 HESC cylinders of $100{\times}200mm$ were tested for different compressive strengths (30, 40 and 50 MPa) and different curing regimes (with maximum temperatures of 20, 30, 40, 50 and $60^{\circ}C$) at different equivalent ages (9, 12, 18, 24, 36, 100 and 168 h) From a series of regression analyses, a generalized rate-constant model was presented for the prediction of the compressive strength of HESC at an early age for its future application in precast prestressed units with savings in steam supply. The average and standard deviation of the ratios of the predictions to the test results were 0.97 and 0.22, respectively.
Optimization of Curing Regimes for Precast Prestressed Members with Early-Strength Concrete
Lee, Songhee,Nguyen, Ngocchien,Le, Thi Suong,Lee, Chadon Korea Concrete Institute 2016 International Journal of Concrete Structures and M Vol.10 No.3
Early-strength-concrete (ESC) made of Type I cement with a high Blaine value of $500m^2/kg$ reaches approximately 60 % of its compressive strength in 1 day at ambient temperature. Based on the 210 compressive test results, a generalized rateconstant material model was presented to predict the development of compressive strengths of ESC at different equivalent ages (9, 12, 18, 24, 36, 100 and 168 h) and maximum temperatures (20, 30, 40, 50 and $60^{\circ}C$) for design compressive strengths of 30, 40 and 50 MPa. The developed material model was used to find optimum curing regimes for precast prestressed members with ESC. The results indicated that depending on design compressive strength, conservatively 25-40 % savings could be realized for a total curing duration of 18 h with the maximum temperature of $60^{\circ}C$, compared with those observed in a typical curing regime for concrete with Type I cement.