Journal of Advanced Concrete Technology
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Volume 12 , Issue 3
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Scientific paper
  • Gyu Yong Kim, Gyeong Choel Choe, Yeon Woo Kang, Tae Gyu Lee
    Volume 12 (2014) Issue 3 Pages 82-90
    Released: March 27, 2014
    JOURNALS FREE ACCESS
    Since the 1960’s, various studies have been carried out on the internal and external factors that might affect heated con-crete in terms of compressive strength, elastic modulus and thermal stress. In particular, thermal properties of aggregate and cooling methods are known to have a significant influence on concrete residual mechanical properties. This study aims to assess concrete mechanical properties based on the types of aggregate and cooling methods used. The used coarse aggregate in concrete was granite, ash-clay and clay type. The circular concrete specimens of Ø100×200mm used in the experiment were heated to the target temperature to test the mechanical properties at a high temperature, slow cooling (room temperature) and water cooling (quenching) conditions. In conclusion, the research finding reveals that the smaller the thermal expansion of the aggregate, the higher the strain at a high temperature while the more dete-riorated the mechanical characters. In addition, the lightweight aggregate concrete was greatly affected by the cooling velocity although the thermal expansion strain of aggregates as the thermal expansion of aggregates took place to a smaller extent, the strength at high temperature remained, while the mechanical properties deteriorated with cooling accelerated. In addition, light-weight aggregate concrete which ash-clay and clay aggregates is greatly affected by the cooling velocity depending on aggregate although the thermal expansion strain of the aggregates was shown to be within a similar range.
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  • Han-Seung Lee, Myoung-Won Cho, Hyun-Min Yang, Sung-Bok Lee, Won-Jun Pa ...
    Volume 12 (2014) Issue 3 Pages 91-100
    Released: March 26, 2014
    JOURNALS FREE ACCESS
    The quality requirements of concrete have become more stringent in recent times; therefore, the quality control of early-age concrete has become an extremely important task at construction sites. Among the various factors affecting the quality performance of concrete, its curing temperature and compressive strength were focused upon in this study. A curing temperature management system was developed for in-place concrete that enables direct, real-time measure-ments and continuous monitoring of the internal temperature of concrete via an all-in-one wireless sensor network (WSN) during the early curing stages. The system can also suggest an informed decision about stripping of the form-works without having to consider the wiring at the construction site. To validate the system, its performance in monitor-ing curing temperature was investigated and verified by its application in indoor tests and at real construction sites. The compressive strength of concrete was predicted using several functions based on the maturity and the curing tempera-ture. Then, a field experiment was performed to measure the curing temperature of concrete using the developed system. After fresh concrete was poured into the formworks, the WSN signals were measured at a 150-m radius from the field office. The signals were acquired for 28 days without any dispersion or interruption at the construction site. Therefore, it is concluded that the developed system can improve the measurement accuracy of concrete curing temperatures and can also be used at an actual construction site.
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  • Sinan T. Erdoğan, Derya Över, Mustafa Tokyay
    Volume 12 (2014) Issue 3 Pages 101-110
    Released: March 29, 2014
    JOURNALS FREE ACCESS
    The chemical composition and heat evolution of <45 μm (fine), and > 45 μm (coarse) portions of interground, natural pozzolan-blended cements were investigated. Cements with four different pozzolan contents were ground to 300 m2/kg, 500 m2/kg, and 600 m2/kg fineness and sieved through a 45 μm sieve. Clinker, pozzolan, and gypsum contents in the fine and coarse portions after sieving were determined and compared with the unsieved cements. Heat of hydration evolution of the samples were determined up to 48 h using isothermal calorimetry. The fine portions of the cements always contained more gypsum, had higher pozzolan-to-clinker ratios, and slightly higher tricalcium silicate contents, which influenced the rate of heat development at early ages. The fine portions contribute more to the total early heat evolved than the coarse portions. A small amount of pozzolan enhances early hydration. The heat evolved up to 24 h was related linearly to the heat evolved up to 48 h. Such observations could be useful in the modeling of early hydra-tion of blended cements.
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