Crushed sand can be used as fine aggregate only blended with beach sand or river sand because of its angularity. It was ascertained with concrete and mortar that crushed sand with surface configurations improved by the high-quality crushed sand manufacturing system proposed in this study can be used for the entire content of fine aggregate with more or less equal unit water content as when using river sand. It was shown that the amount of bleeding is not increased, and that strength is not decreased with improvement in surface configuration of crushed sand. The high-quality crushed sand manufacturing system for improving the surface configurations of crushed sand consists of a high-quality crushed sand manufacturing machine, crushed sand moisture separation apparatus, and slurry treatment apparatus.
It has been pointed out that the degree of damage of concrete structures due to the alkalisilica reaction varies widely depending on environments. However, there were only a few studies concerning the progress of deterioration on reactive aggregate-bearing concretes under different environments over a long period. In this study, reactive aggregate-bearing concretes were exposed to the two different natural environments. The influence of the environments on the alkali-silica reaction was investigated by measuring expansion and monitoring cracking of them. The concretes having the same mix proportions were stored in a moist environment at 38°C. The difference between the alkali-silica expansion under the natural environments and in the laboratory test was investigated. From the point of view of deterioration of concrete due to the alkali-silica reaction, the exposure test condition under the natural environments was severer than the accelerated test condition in a moist environment at 38°C.
This paper discusses the application of Neural Network Theory to the scene evaluation of concrete structures using plants. At first, sensory evaluation method about concrete structures using plant is carried out and person's landscape images of these structures are classified into typical groups by Main Factor Analysis and Cluster Analysis. Second, main factors which affect the landscape images of concrete structures using plants are picked up from these groups. These factors are constituted from thirty units, that is, the area ratio of planting, the arrangement of planting at concrete structures, the kind of plants and etc. Third, the relationship between the main factors and sensory evaluation results is modeled by Artificial Neural Network system. This Neural Network system is composed of 30 input units (some of categorized main factors affect the scene landscape image of concrete structures using plant) and 3 output units (some of categorized sensory evaluation, “High”, “Middle” and “Low”). The usefulness of the Neural Network theory to evaluate the landscape of concrete structures using plants ara proved in this study.
In order to apply limit state design method to tube structure like tunnels the authors conducted loading tests on a tube model and verified the fracture process for tube structures. According to the test results, even when the sectional force locally exceeded the sectional force capacity in the tube structure and cracking developed, the structural body did not collapse, and it was confirmed that the structural force capacity was greater than the sectional force capacity. With the design of tube structures, regarding the point when the sectional forces reach the force capacity as one of the limit states, the sectional force and the force capacity were checked. In calculation of the sectional force capacity, it was decided that it was all right to consider this as the state when cracking occurred. With steel fiber reinforced concrete (SFRC), it was seen that the sectional force capacity becomes larger than that of plain concrete, and that the force capacity differs depending on factors such as the shape and content of steel fibers, because the tensile stress is transmitted through the steel fibers intersecting the crack surface even after cracking has developed. However there are almost no methods to calculate the sectional force capacity, with consideration of the tensile stress transmitted through the steel fibers, and there are few examples of applying steel fiber reinforced concrete to structural members. Therefore in this paper a method to calculate the sectional force capacity in steel fiber reinforced concrete is proposed based on fracture mechanics.
In this model, the residual strength criteria is introduced, and the Mohr-Coulomb's failure criterion is expansively appllied to the modelling of the strain softening under compression. The cohesion and the friction coefficient are assumed as functions of tangential component of sliding displacement in the shear band. The strain softening response is described in connection with the sliding mechanism. The functions of the cohesion and the friction coefficient are evaluated based on the stress-strain relationships obtained from experimental data which are carried by authors.
A lot of study has been executed on the bending-shear force bearing capacity and flexural deformation capability of concrete filled steel tube (CFT). Especially, the confined effect to the in-filled concrete by the steel tube has been the main theme to be estimated exactly. But in case of the CFT in which high compressive strength concrete such as 1 000 kg/cm2 is used, the contribution of the confined effect to the ultimate bending strength has not yet been estimated numerically. In this study, we did the experimental researches to investigate the flexural strength and flexural deformation capability of a CFT which has square hollow section tube and 1 000 kg/cm2 compressive strength filled concrete. The CFT is completed by using centrifugal compaction and autoclaved curing. The experimental process, results and observations are reported in the paper.
This paper describes the finite element method to predict the long-term behavior of partially prestressed concrete (PPC) beams. The concept of the tension stiffening after cracking is also added in the time-dependent FEM analysis, using the strain softening diagrahm. The results of calculation give a good agreement with several avairable test data. The creep properties of PPC beam are revealed under several prestressing force by parametric analyses. This present method is suitable to predict the creep behavior of PPC beams.
The appearance of concrete walls or concrete structures changes with the distance between the viewpoint and the place where the concrete stands. The finding is that the concrete with smooth surface, such as casted in coated plywood, metal or pervious sheet forms scarcely makes people feels changes of appearance with distance, whereas concrete with modified texture does people various changes of appearance. This concept is to applicable to design and to select surface finishing of concrete. The seventeen concrete specimens of surface finishing were used for the test.
Influence of microstructural changes in high strength concrete on toughening mechanism is studied. Load-displacement curves of notched beams of various types of concrete are analyzed by means of an inverse analysis technique to obtain the tension softening diagrams. Parameters of the bilinear tension softening diagram are discussed in relation to dynamic Young's modulus, compressive strength, tensile strength and porosity. A brittleness index was also proposed, which is defined as a function of fracture energy, tensile strength and Young's modulus. These results are useful to determine the tension softening diagram of concrete on the basis of general standard test results.
The present paper deals with a uniaxial member involving strain localization, making emphasis on deformational characteristics and stability analysis. Localization phenomena are classified into the semi-localization for concrete in compression and the perfect-localization for concrete in tension. Equivalent constitutive equations are formulated for both cases. An incremental calculation method to incorporate the snapback behavior is then presented. Stability/Instability condition is analytically derived based upon second variation of total potential energy for inelastic materials. In addition, an kinetic energy to evaluate snapdown instability of a localized member is proposed.