High Performance Concrete, which was developed by the group in the University of Tokyo, is originally designed with low water-cement ratio for the purpose of self-compactability. Therefore, this concrete has sufficient performance in hardened state for ordinary concrete structures even when it is not well cured. In this study, systematic experiments are carried out in order to evaluate the durability of hardened High Performance Concrete when it is stripped at early ages. Two types of High Performance Concrete are used. Some properties related to the durability, such as compressive strength, drying shrinkage, cracking resistance, carbonation, salt penetration and freezing-thawing, are examined. The applicability of High Performance Concrete for early form-removal is discussed based on the experimental results.

View full abstract

This paper describes the development of a new mixture for surface course using cement and emulsified asphalt as base materials. The mixture was requested following points.
(1) Construction should be conducted at normal temperature.
(2) It is highly resistable to rutting caused by plastic flow of asphalt.
(3) It is almost free from shrinkage cracking and the pavement using this material doesn't need any joint.
(4) The widely used devices for asphalt pavement construction are also applicable for it.
(5) The pavement can be opened for traffics shortly after construction helped by high early strength of it.
This project was started seven years ago in 1986. After three years' studies in situ, several field tests were carried out at heavy traffic roads. Results show every request mentioned above is nearly satisfied.

View full abstract

The purpose of this study is to estimate of the effect of hydration of cement after initial curing on carbonation rate. The depth of carbonation of mortar under accelerated condition and the degree of hydration of cement under water desorption and absorption conditions were measured. The hydration process of cement and the change in physical and chemical properties of mortar, -pore volume and amount of calciumu hydroxide-, due to hydration of cement were formulated.
Based on these results, the depth of carbonation can be predicted in consideration of hydration of cement after initial curing.

View full abstract

Diagonal tension failure of concrete beams without web reinforcement is one of the most important research topics in concrete mechanics. The size effect on the shear strength has been confirmed experimentally. In the standard specification for design and construction of concrete structures of JSCE, the design equation considering the size effect was specified. However, with the increase in the size of concrete structures, huge concrete structures, which are outside the limit of the specification, will be built and the experimental verification will be substantially impossible. In this paper, the size effect on the shear strength of concrete beams is predicted numerically by the fracture mechanics.

View full abstract

Many new types of PC structures have recently been developed and some of them has a feature that its ultimate strength and failure mode are controlled by combined axial tensile force and flexure. To investigate the response of prestressed concrete members under such loading, experimental studies were first performed using a box girder bridge with partially prestressed concrete cable stays as a proto-type model structure. Next, analytical approach was taken, with a tension stiffening model of concrete, to compare with the experimental results, and then to evaluate its tension stiffening effect.
Finally, using the above model, non-linear analysis was performed to evaluate the effects of the redistribution and tensile stiffness on the ultimate strength of the overall structure.

View full abstract

The objective of this study is toinvestigate the flexural behavior of externally prestressed concrete beams. First, series of test specimens of PC beams with external, internal unbonded tendons and bonded PC beam were conducted. It was found that the effect of change of tendon's eccentricity (secondary effect) is dominant in flexural strength of externally PC beams. Second, the established analytical approach based on the compatibility of deformation and change of eccentricity effect showed a good agreement with test results. Finally, design equations to predict flexural strength of such an externally PC beam were proposed and the better accuracy of prediction based on this proposed equations was obtained when compared with the other investigator's proposed equations.

View full abstract

To capture the shear resisting mechanism of reinforced concrete beams, such as the occurrence of diagonal cracking, the yielding of shear reinforcement, and the crush of web concrete and also construct a practical macroscopic shear resisting model, the lattice model, that can be considered as a simplified analytical model, has been newly developed. The applicability of the lattice model is examined by proposed equations and existing experimental data. After the verification for the lattice model, the validity and problems of the modified truss analogy are examined using the lattice model.

View full abstract

Shear strength of concrete beamss reinforced with FRP was studied through experiment and analysis. The effect of stiffness of longitudinal tensile reinforcement on the diagonal tension failure strength was calculated using the extended modified compression fields theory, and the evaluation method was proposed based on the analytical results. Furthermore, shear strength of the beams which fail due to the rupture of FRP stirrups was well evaluated by considering the lower stiffness and the strength reduction of FRP at bent corner.

View full abstract

In this paper, the thermal stress of precast concrete pavement (PCCP) is discussed based on the experiment and FEM analysis. The thermal strains measured in the test pavement were divided into three components; axial, warping and nonlinear components, and examined by FEM. Axial and nonlinear components were small in the term of tensile stress, and could be neglected in the structural design. On the other hand, warping component was found to be significant and could be estimated by FEM with appropriate subbase model.

View full abstract