In this paper, a strain space based plasticity model, which was previously proposed by the authors to represent the compressive softening behavior as well as hardening behavior of concrete materials, has been applied to assess the capability to predict the path-dependent behavior of concrete under the conditions such as (1) monotonically increasing confining pressures, (2) suddenly increasing confining pressures, and (3) suddenly reducing confining pressures. Firstly, a proposed model has been briefly reviewed, and a detail modeling that can treat a path-dependent behavior of concrete has been explained by introducing a damage concept of concrete material. Secondly, the general incremental stress-strain relation has been given in a tensorial form. Finally, the model predictions have been compared with the experimental data available from triaxial compression tests under three types of confining pressure loadings. It has been concluded that the proposed model can well predict the general path-dependent behavior of concrete materials particularly in the softening region.
A new test system to quantitatively evaluate alkali-silica reactivity of aggregate is proposed. In this test system, at first, change of soluble silica content of aggregate with the passage of time is measured by a leaching test at various temperatures. The results obtained from this test are analyzed on the basis of kinetics in order to obtain alkali diffusion coefficient in aggregate and alkali-silica ratio of reaction products, and also to evaluate the effect of temperature on diffusion coefficient, which are main factors in predicting the progress of ASR. Expansion behaviors and ultimate expansion ratios of mortar bars can be calculated by using these values. And expansion curves of mortar bars observed experimentally almost coincide with the calculated expansion curves. It was also found that the alkali diffusion coefficients in sedimentary rocks change during ASR.
The present paper proposes the general form of the tangential constitutive equation of a reinforced concrete uniaxial member, emphasizing on the cracks' opening and closing behavior. In the model, the tension stiffening factor makes the most important role in describing the varying stiffness due to cracks generation and slippage between concrete and reinforcement. The proposed constitutive model can realistically represent the cyclic behavior in tension and in reversed loading to compressive zone and agrees relatively well with experimental results.
This paper deals with the shear capacity of existing reinforced concrete member with carbon fibre sheet, and mechanical behaviours of stirrup in concrete and carbon fibre sheet. Most of existing structures cannot be rounded with carbon fibre sheet except columns. In this study two types of reinforcement was examined, one was rounded with carbon fibre sheet, and the other was stuck to the side of concrete member. The results of this tests show that the reinforcement with carbon fibre sheet will improve the shear capacity. The strain of carbon fibre sheet differ from the strain of stirrup, and near the crack increase rapidly because fibre sheet was stuck to surface of concrete structures. Therefore fibre carry the higher shear strength than the strength calculated from the rate of fibre and stirrup.
In regard to antiwashout underwater concrete using three-component cement, technique for reduction of heat generation with addition of anhydrite and characteristics of granulated blast-furnace slag (G. B. F. S.) were studied. We also examine stability and hydrate texture of the low-heat concrete, to which this technique was applied. Increasing the fineness and the basicity of G. B. F. S. and adding of anhydrite in adequate blending rate obtain low-heat and long-term strength development. Quantity of aluminium trioxide, fineness, basicity of G. B. F. S. influence the effect of anhydrite adding. Addition of anhydrite also changes kind of hydrate products and texture of concrete on account of consumption of anhydrite adding and product of ettringite since early age on hardening. It consequently affect the strength, heat generation, expansibility of concrete.
There is a method called “generalized superpose flexural strength method” which is widely used to calculate ultimate flexural bearing capacity of Steel Reinforced Concrete Structures in Japan. This method is easier and more practical than a method calculate ultimate strength of structural members based on equilibrium of stresses and compatibility of strains. On the other hand, this method overestimates flexural bearing capacity in a certain case that concrete reaches ultimate strain yielding of steels. The author proposes a modified method which solves problem of overestimation. The modified method evaluates the yielding condition of steels properly in and case, and estimates flexural bending capacity and deformation of Steel-Concrete composite members preisely.
There are multiple processes of damage with a lot of damage factors in existing concrete bridges in service. Although it is very difficult to define such damage processes quantitatively, it can be assumed that the bridge engineers who deal with bridge repair works have their own concepts of bridge rating system in their minds based on past engineering experiences and knowledges. In this paper, it has been proposed a global hierarchy model of damage factors for concrete bridges based on the Fuzzy Hierarchy Structural Modeling. Since the knowledges about the relation with damage factors were picked out through a questionnaire to a few experts, subjective uncertainties were included in the results. In order to deal with such uncertainties, the concepts of basic probability according to the Dempster & Shafer theory were applied. The final hierarchy model was selected from among several models in the viewpoint of simplicity and relation to available literature. This hierarchy model can be effectively utilized into the bridge rating system.
The salt attack on RC structure causes cracking and spalling of cover concrete due to the corrosion of embedded steel bars. The main purpose of this study is to evaluate the corrosion preventive effectiveness of the existing repairing method composed of coating of steel, patching by mortar materials and surface coating of concrete. The conclusions obtained from this study are as follows (1) Coating of steel does not have a significant corrosion preventive effectiveness in the repairing method. (2) The corrosion preventive effectiveness of the two concrete repairing materials used in this study is almost same. (3) The corrosion preventive effectiveness of the surface coating of concrete depends on cracks between concrete and patching mortar, that is, the effectiveness becomes greater with the cracks. (4) Moisture and chloride contents in concrete are significant factors which affect the corrosion preventive effectiveness of repairing.
Soiling on the exposed concrete surface is serious problem from the view point of marring the appearance of concrete structures and the landscape. In order to obtain a basic knowledge about the soiling on exposed concrete surface, the effect of mortar surface properties on the adhesion of suspended particles on mortar surface was studied. The mortar surface which the coefficient of water penetration is high or which the coefficient of adhesive roughness is high has a tendency that the amount of particles adhesing on the mortar surface is high.