Email this article Detection of Thermal Cracks in Early-Age Concrete by AE
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Early-age cracking after casting is a fundamental problem for the durability of concrete structures. Recently, thermal cracks and early-age cracks have been observed in concrete containing Portland cement with blast-furnace slag in Japan. In order to reduce the number of these cracks, fly ash is substituted for cement or sand. Fly ash is one of the popular admixtures as a waste material from coal-fired power plants. To evaluate the effect of fly ash on early-age cracks, experimental studieswere performed. In order to detect micro-cracking in concrete, acoustic emission (AE) measurement was applied. In experiments, two types of fly ash, typeⅡ and Ⅳ categorized by JIS were employed. The ratio to substitute cement and sand was 10% and 20%. As a result, micro-cracks in concrete were detected by the AE method. Resultsshow that substitution of fly ash for cement and sand is effective to reduce micro-cracking due to thermal changes which occurs from 20 to 30 hours elapsed after casting of concrete.
Keywords
thermal cracks; AE method; blast-furnace slag; fly ash, early-age cracks
References
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Son, H. N., Hosoda, A. and Watanabe, T. Characterization of Microcracking in Very Early Age Concrete subjected to Elevated Temperature by AE, Proceedings of The Japan Concrete Institute, 2001, 31: pp. 323-328
