According to the lack of river aggregate, the usage of sea sand has been reached the great quantities. The corrosion protection of reinforcing steel in concrete with sea sand becomes the most important matter in the southan part of Mainland and Okinawa Islands in Japan. This paper deals with the outline of corrosion protection, standing position of inhibiter in corrosion protection of reinforcing steel, chemical role of inhibiter, and the quality and methods of tests which were newly established standard JIS A 6205 (Corrosion Inhibiter for Reinforcing Steel in Concrete).

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First of all it is shown that the structure of a composite material such as concrete can be subdivided into different levels. Characteristic properties of hardened cement paste will be described in terms of the micro-level. Pores, cracks and inclusions are introduced on the meso-level. On the macrolevel the material is looked upon to be quasi homogeneous. On this level material laws are developed. Mechanics and mechanisms of deformation and crack formation can be discussed on the corresponding levels. It is pointed out in particular that mechanisms of the micro-level cannot be linked directly with the material behaviour, this implies that mechanisms derived from direct observation of macroscopical behaviour are generally meaningless. It is important to note that different mechanisms must be related to the observed materials response according to the hierarchic structural system. On the micro-level the Munich Model is introduced. The influence of moisture content on creep and strength of hardened cement paste can be described satisfactorily by means of this model. The influence of porosity on strength is also discussed on the micro-level. As a typical example for the mechanisms involved on the meso-level, crack propagation from large pores and cracks and interfaces is treated. This is essentially a micromechanics approach of a composite porous material. It can be concluded that numerical methods have become a powerful tool to complement experimental research. It is possible to base material laws for application in structural engineering on results gained on the micro-level and on the meso-level if the hierarchic structural system is taken into consideration.

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Due to its effectiveness in construction, expansive concrete was applied as a measure to prevent further crack damage in the highway bridge reinforced concrete deck slabs of the Kuroishihama Bridge along the Nagasaki Expressway. Expansion, drying shrinkage, and conditions of crack production of the concrete deck slabs were investigated over a two year period. Results are summarized here. Consequently, it was confirmed that expansive concrete deck slabs crack less than those of normal concrete and have the strength to withstand loads. An explanation on the causes of cracking is added based on results obtained from durability inspections and endurance tests.

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The Nishikigaoka No.3 Overbridge of the Hokkaido (traversing) Expressway, a PC diagonal tension bridge, which is the first full-fledged highway bridge ever constructed in Japan. The bridge constructcion has a 3 chamber box girder with 2 continuous spans of an independent single column 3 layer harp type. The main tower constructed by a post tension system is eccentricall positioned in both the axial direction of the bridge and the right angle direction of the bridge axis, resulting in continuous torsions. Using the Freyssinet method (27H15), the diagonal tension cables were inserted after the installation of protective pipes. This study covers the design and construction of the bridge.

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Based on past experience with earthquakes the aseismicity of RC buildings has been highlighted. Conventionally, studies on improvements in aseismicity have been conducted using methods in which main bars are arranged parallelly. In this paper, an X type arrangement of reinforcement, a new method which has been studied and developed, was adopted as an approach to improve aseismic performance. This approach aims at improving aseismic performance by arranging main bars in diagonal directoins. In this report, emphasis was placed on a design and construction enabling the improvements above.

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This is a record on the five high piers which were constructed in the substructure construction of Numao River Bridge of Kanetsu Expressway. With regard to over 60 meters high pier construction, climlring form work method, block installation method of reinforcement bavs, and concrete placing method for high place were applied with a view to easiness of construction work, safeness in construction, progress of work, and etc.. The following is a report of these three methods.

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