Durability of concrete structures are seriously suffered from cracking in early age concrete. Since the early age cracking is influenced by a lot of factors which are highly interacted each other to affect the hydration process, and strain and stress development, the cracking behavior is very complicated and any rational controlling methodologies for the cracking have not been established yet. In spite of the complexity, high strength concrete has been used more and more and the number of massive concrete structures has increased. These trends require more rational methodologies for the control. In this report, recent research trends on the mechanisms to cause the complex phenomena and on the methodologies to control the early age cracking are reviewed.

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X-ray technique with contrast medium is studied for the practical application as one of the non-destructive tests of concrete structures. This method can detect crack tip position and crack shape of the concrete member inside at the good accuracy. In addition, this method may be able to quantitatively examine the degree of the deterioration from the microcrack generation condition in collected concrete test piece. This paper described present state of the research.

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A shortage of high quality natural sand and the environmental constraints make the availability and the use of them less attractive for concrete. Fine aggregate manufactured by crushing a granulated blast furnace slag are used for concrete as one of replacements of natural sand. In that manufacturing process, anti-bonding agent is usually added to the blast furnace slag fine aggregate, in order to suppress their hydration and keep a long term storage in summer season. The authors have developed an advanced anti-bonding agent comprising oxycarboxylate derivative. The agent performs well for a longer term storage. On the constrary, the effects of the agent on the concrete properties were negligible.

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In this paper, the fracture mechanism of concrete subjected to combined stress (so-called mixed mode fracture) and the modeling methodology are studied based on the literature. The test methods to examine the mechanism and the examples of the numerical analyses are introduced. Finally, the numerical issues to simulate the mixed mode fracture and research tasks in the future are pointed out.

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This paper contains a summary of the technical contents in the Common parts on Design, Materials and Construction, and Maintenance of the Asian Concrete Model Code 2001 and the underlining needs for the Code by Asia. The main features of the Code, namely the “Performance-based concept” and “Multilevel document structure” and the Code's relationship with ISO and its future direction are presented.

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