The paper discussed corrosion of reinforcing bars embedded in concrete specimens and change of concrete properties, after being left for five years at the tidal zone of the experimental pool which simulated the natural condition of the ebb and flow.
　The cylinder specimens (φ15×30cm) included such factors as kind of cement, content of SO3, kind of mixing water and concrete cover. Though the experimental results at present showed no distinct difference regarding concrete properties, reinforcing bars in concrete mixed with the sea water and thinner concrete cover qualitatively tended to corrode.
　The prism specimens (10×10×80cm)　had been in advance cracked.
It was likely that residual crack became constant in excess of 0.2mm of crack width at loading, and no visible corrosion was observed precluding cracked section when using the service water for mixed water and concrete cover of 4cm. Reinforcing bars at cracked section corroded by 35 percents among whole crack width of less than 0.1mm, and half of them showed distinct observed corrosion.