We optimized the test conditions for evaluating the hydrogen embrittlement susceptibility of High-strength steel used in prestressed concrete. Through experiments, we clarified the effects of an applied potential and ammonium thiocyanate (NH4SCN) concentration on hydrogen content. An applied potential of −1.0 V versus Ag-AgCl Electrode (SSE) and an NH4SCN concentration of 1.0 wt. % were optimal for the test. We also determined the dimensions of the test cell and test temperature. Experiments in which we soaked different lengths of specimens and changed the solution volume to specimen area ratio led us to design a test cell with a soaking length of 15 cm and an inner diameter of 8 cm. A test temperature of 50°C was chosen for acceleration of hydrogen embrittlement.

To examine rebar corrosion in cracked concrete, we have exposed cracked test pieces of pre-stressed concrete containing two rebars to the outdoors and observed the electrochemical behavior. After one year from the start of the exposure test, the potential difference between rebars increased, so it seemed one of rebars has corroded. However, as the exposure test proceeded, the potential difference decreased to the initial state. In addition, destructive observations of test piece revealed that only one rebar had corroded. These results indicate that just one rebar was repassivated after the depassivation in cracked concrete.

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It may be possible to estimate the hydrogen embrittlement process by statistically analyzing the fracture time of high strength steel. In this study, we derived transition probability λ t representing the degradation rate by statistically analyzing the fracture time of high strength steel using a stochastic process model. The analysis revealed that λ t decreased rapidly after the start of the test and then became a constant value. This behavior differs from general hydrogen entr y behavior, suggesting that the fracture time of high strength steel is not uniquely determined only by the amount of hydrogen in the specimen.

To verify the applicability of glass-fiber reinforced plastics with an unsaturated polyester matrix in manhole environments, degradation characteristics in a weak alkaline aqueous solution were evaluated by conducting a solution immersion test. We were able to clarify that diffusion of alkaline ions is slower than that of water, effect of accelerated deterioration due to alkali remaining on the sample surface, resin fiber interface preferentially deteriorates due to the diffusion of water, and that the decrease in flexural strength is in good agreement with the logarithmic approximation formula.