Concrete using seawater as the mixing water contains NaCl. NaCl is often added when evaluating the alkali-silica reactivity of concrete. However, there have been few reports of the compressive strength of concrete which NaCl has been added under the sealed curing. In this study, the concrete specimens with NaCl added were cured in water or sealed condition, and the compressive strength was measured at each age. In addition, the hydration reaction analysis and the autogenous shrinkage measurement were carried out.

 From these results, in the case of the sealed curing, it was confirmed that the compressive strength of initial age decreased as the increment of NaCl addition. From the results of the hydration reaction analysis, it was guessed that the decrease in compressive strength was caused by the phenomenon that the cement hydration was obstructed by the generation of the alumina gel. Moreover, in the sealed curing, in addition to the effect of obstructing the cement hydration, it was guessed that the formation of alumina gel increased self-desiccation and caused a decrease in compressive strength.

 Cracks at the outer surface of the web or the bottom flange of a pretensioned PC hollow slab girder, which often develop axially along the PC bars, are investigated by applying a multi-scale analysis coupled with material and structural behavior. Such cracks are generally considered to be caused by steel corrosion, alkali-silica reaction, insufficient cover depth, etc. This study, however, shows that even with standard design and materials, careful curing and construction, cracks may appear a decade or two later in service due to seasonal variations in temperature and humidity. Sensitivity analyses under different environmental conditions are also conducted to investigate the causes of cracking, and it is confirmed that the cracks have little influence on load carrying capacity of the PC girder. Based on the analytical results, suggestions for future countermeasures are also made.

 The paper aims to elucidate shear resisting and failure mechanism of RC beams without stirrups under fatigue loading. In this study, crack widths and sliding displacements at a shear crack in RC beams under static and fatigue test were carefully measured by a sampling moire method. Shear resisting forces at concrete compression zone and a shear crack were calculated using strains observed and existing shear transfer models. The differences of those shear resisting forces between static and fatigue tests were examined. As a result, it was experimentally clarified that no reduction of shear resisting force by aggregate interlocking would occur under fatigue loading and the fatigue life might be determined by fatigue failure at concrete compression zone under compressive and shear stress variation.

 In this study, a shear strength prediction AI model was developed for RC beams without shear reinforcements. The AI model is a neural network model which contains explanatory variables derived from mechanical interpretation such as the neutral axis and also variables on details of tensile reinforcing bars. The AI model can predict experimental results which contains wide range of shear span to effective depth ratio with high accuracy rather than a conventional neural network model and empirical shear strength equations. The AI model can apply to new data set without dependence on the train data. Furthermore, the AI model, in which Young’s modulus of the FRP reinforcements was taken into consideration in explanatory variables, can predict shear strengths of concrete beams reinforced with FRP reinforcements correctly.

 Expansive concrete has been utilized to suppress cracks of concrete for a longer time particularly for the symmetrical cross-sectional dimensions structures by using chemical prestress technology of that is introduced by the expansive additive. In order to widen the application of this technology to various concrete structures, estimating method of chemical prestress in the unsymmetrical cross-sectional dimensions concrete was proposed and was evaluated on a full-scale road bridge specimen using expansive concrete slab and wall fences. As a result, it was clarified that the chemical prestress introduced unsymmetrical crosssectional dimensions can be evaluated by the proposed estimation method. In addition, it was observed that the shrinkage cracks on the wall fences were suppressed by the chemical prestress.

 In order to expand the application range of precast method, we have proceeded with development the “hybrid PC (HPC) structure”, that is jointed pre-tensioned member to additional post-tensioned member by re-tensioning PC steel stands extended from pre-tensioned member. In this study, we carried out experiments on the development length and re-tensioning in pre-tensioned member. Experimental parameter are concrete strength and with or without the epoxy coating of PC steel strands. And we considered the adhesive mechanism of PC steel strands when introducing prestress and re-tensioning in pre-tensioned member from result of these experiments. The relationship between the adhesive stress and slip of PC steel strands obtained from these experiments were introduced into the nonlinear FEM analysis, and tried reproduction analysis the adhesive behavior of PC steel strands.

 As a result, The adhesion mechanism are different in the introducing prestress and the re-tensioning, and with or without epoxy resin coating on PC steel strands. And we have found high strength concrete are suitable for HPC structure. In addition, FEM analysis are able to reproduce the adhesive behavior of PC steel strands to a certain degree.

 This study discusses effect of surface coating on suppress of rebar corrosion in concrete with combined deterioration of internal chloride and carbonation, highlighting such different properties as initial W/C ratio, initial chloride content, crack on the coating, and carbonation area assumed during the service life. Cylinder specimens with electrically connected split rebar elements embedded in the concrete were produced, and the corrosion rate of the rebar of each specimen was monitored while they were exposed to an accelerated wet and dry cyclic regime for several months. The results showed that the corrosion rates of the steel bar embedded in the specimens with a higher W/C ratio and a deeper carbonation penetration on the coating were significantly greater than those without crack generation on the coating surface. The rebars embedded in the specimens with initial high chloride content, regardless of the carbonation progress, showed still higher corrosion rates after a crack was generated on the coating surface. Therefore, the corrosion suppress performance of the surface coating was not fully expected for such cases.

 In order to cope with various design conditions of concrete structures, a prediction equation for the shrinkage strain of concrete has been developed, which allows input of the effects of cement type, the aggregate shrinkage strain, and the application of liquid water, in addition to the conventionally indicated mix proportion of concrete and ambient relative humidity. The prediction equation is formulated based on the 3D material-structure interaction analysis system (DuCOM-COM3), and is characterized by its applicability to the long-term age of shrinkage strain, including the thickness of members and concrete with low water-binder ratio, assuming that the concrete structure is in service. It was also confirmed that the prediction equation can explain the phenomena that appear to be caused in part by concrete shrinkage, such as strain of concrete in prestressed concrete (PC) girders in service using the blast furnace cement concrete (Class B) and the deflection in PC ridged-frame bridges.

 Two indices for local damage of concrete, i.e. the averaged second invariant of deviatoric strain and the averaged normalized accumulated strain energy, which had been proposed for two-dimensional models, were extended to three-dimensional space and were verified for reinforced concrete members failing in different modes. The verified indices were then applied to the analyses of the RC members showing three-dimensional responses owing to their shapes and support conditions, and of the members subjected to complex combination of external actions. As a result, the damage propagation and capacity of the members could be well evaluated in terms of a combination of the indices. The proposed indices enable performance evaluation of reinforced concrete structures with revealing their internal load-carrying mechanism, independent of shapes, boundary conditions and load combinations of constitutive members.

 The interfacial transition zones (ITZ) form around aggregates have a significant effect on the permeability of concrete. This is because ITZ has a higher pore volume and connectivity compared to the cement matrix. Therefore, understanding of the effects of ITZ is important for understanding of the physical properties of concrete.

 In this study, the specimens contains ITZ using different aggregates and different mineral admixtures were prepared. Zeta potentials of the aggregate surface were measured on those samples. In addition, we investigated the influence on the thickness and the content of Ca(OH)₂ of ITZ.

 As a result, the lower the zeta potential on the surface of the aggregate, the higher content of calcium hydroxide was obtained. Moreover, the use of silica fume produce the complicated pore system and the diffusion coefficient in ITZ is reduced.