Seismic evaluations of existing RC buildings have been extensive in Japan since earthquake of 1995. According to some reports, seismic evaluations found many RC buildings of very low concrete strength, i.e. less than half of the design concrete strength. It is necessary for evaluation and retrofitting to clarify the mechanical characteristics of low strength concrete and seismic performance of low strength concrete members and frames. In this report, the outline of the previous studies on the low strength concrete is described and the possibilities of strengthening are investigated through the experimental works.

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A concrete drying shrinkage rate was prescribed for at the AIJ (Architectural Institute of Japan) and the JSCE (Japan Society of Civil Engineers). But, it isn't prescribed for JIS A 5308 as the quality requirement items Because of that, the countermeasure to decrease drying shrinkages wasn't examined in the ready-mixed concrete factory with no shipping experience the construction work of the large metropolitan area in many cases. As one of the guarantee measures concerning the drying shrinkage rate against the purchaser, National Federation ready-mixed concrete industrial association did investigation of actual conditions of the ready-mixed concrete factory in 2008 and 2009 years.

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[in Japanese]

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[in Japanese]

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