This Paper presents experimental and numerical results on axial tensile tests of prism members with HPFRM (High Performance Fiber Reinforced Mortar) and conventional reinforcing bar. With increasing fiber content in the HPFRM, the tension stiffening effect was improved as well as cracks being distributed with finer crack width. In addition the orientation of the fibers affected both the tension stiffening and the crack distribution. To evaluate these structural behaviors the analytical simulation using 2D Rigid Body Spring Model was applied with some improvements on the material constitutive law for unique characteristics on the HPFRM.
Time-dependent constitutive law of Rigid-Body Spring Model (RBSM) was developed by separating mortar deformation into four components based on material information from micro to meso scale. In addition, the analysis could track residual strength up to the failure under creep and fatigue loading by installing a new method for determining failure state for load-controlled analysis. The analytical model could simulate mortar behavior under monotonic, creep and fatigue loading in terms of change in strength, stress-strain-time and S-N relationship. Furthermore, fracture mechanism of mortar under creep and fatigue loading was numerically explained. That is, failure happens when the material strength becomes less than the applied stress as a result of crack propagation with stress release-redistribution due to relaxation or unloading-reloading.
This study was carried out to make clear the behavior of macro-cell corrosion generated in RC slabs repaired by partial patching. Macro-cell corrosion current in patched test slabs was periodically measured for about 2 years using segmented steel bars. Based on the test results, the following topics were particularly discussed: 1) Mechanism of the macro-cell corrosion of steel bars in patched concrete, 2) The effect of intersections of steel bars on the behavior of macro-cell corrosion, and 3) The possibility of corrosion of steel bars in the patched area. Through the analysis of test results, the following conclusions were obtained: 1) The steel bar in chloride-contaminated concrete near the joint acted as macro-cell cathode in the early stage of exposure, however, the electrochemical incompatibility in the RC member made the steel bar anodic. 2) Corrosion currents at the intersections in chloride-contaminated concrete were re-markably large in the early stage of exposure. It was considered to be caused by the flow of a two-dimensional electrical current. 3) Steel bars in patched area had the possibility of macro-cell corrosion formation.
First, in PC bridge girders severely damaged by chloride induced deterioration on the Japan Sea Shore in Aomori, the field inspection was performed. Next, using concrete cores sampled from the blocks of girders, the compressive strength, Young’s modulus, carbonation depth, and chloride ion concentration of concrete were measured. Additionally, by removing whole concrete from blocks, the corrosion condition of steel inside was observed. After measuring the mass loss of steel due to corrosion, the load-elongation relation of steel was examined. From the results of these inspections and experiments, it was recognized that this bridge was exposed to an extremely severe corrosive environment. Further, the influence of various factors on the corrosion of steel, and the relation between mechanical properties of steel and its mass loss due to corrosion were revealed.
The authors have developed a constitutive model of the three dimensional Rigid-Body-Spring Model with random geometry for quantitative evaluation of the response of concrete subjected to active lateral pressure and uniaxial compression. In the present study, numerical analyses of confined concrete specimens under uniaxil compression using the proposed model were conducted for validation of the applicability to the compressive response subjected to passive lateral pressure. By comparing analytical results with empirical formula or the experimental results, we confirmed that the proposed model can reasonably evaluate the compressive strength, the softening behavior and the localization behavior. In addition, the failure process and the stress transfer mechanism of confined concrete were discussed.
A permeable pavement, which is one of pavements with various advanced functions, has been expected to improve the urban environments by the pervious surface structures. Because we need to determine the water retention and permeability characteristics of pavement materials in order to evaluate the rainfall storage and infiltration facilities of the permeable pavement, we conducted a series of laboratory tests using porous asphalt mixture specimens having a diameter of 150mm which consist of several different kinds of maximum grain size, void ratio and specimen length. The experimental results show that the Van Genuchten model predicts the water retention curves and the Irmay model predicts the unsaturated permeability coefficients of such materials very well, respectively.
Corroded beam specimens, sawn from reinforced concrete bridge which was constructed about 80 years ago in the coast of the Japan sea, is loaded until failure. The structural performance of beam specimens are subjected to the effectiveness of lap splice because each beam specimens contain several corroded lap splices. The reduction in load carrying capacity is comparable to the corrosion rate when lap splices work effectively. On the other hand, load carrying capacity is significantly reduced when lap splices are degraded due to severe corrosion. FE analysis are conducted to be compared with test results. FE analysis can estimate the load carrying capacity of beam specimen by considering average corrosion rate when lap splice works well. On the other hand, the effectiveness of each lap splices should be preliminary known if we want to simulate the structural performance of severely deteriorated beam specimen accurately.
Gaps between superstructures and abutment parapets should be small for increasing the life of expansion joints and for reducing noise from joints. However, to prevent the collision of superstructures with seismic-isolation bearing into parapets, the gaps should be large. In this study, the noise from expansion joints and load bearing capacity of abutment parapet of bridges were investigated. On the basis of the results, concrete blocks with unique shapes were made with high performance fiber reinforced cement composite and foamed polystyrene for aiming at giving the following functions to the blocks: Having sufficient load bearing capacity for the vertical wheel load at ordinary times. Following the seismic displacement of the superstructure by deforming largely in horizontal direction. Enabling the restoration of damaged members easier by having an easy-replaceable module structure. The loading tests of the blocks revealed that they had highly anisotropic mechanical performances and high deformability of compressive strain of more than 20%, as had been expected. In addition, it was clarified that fibers could prevent spalling of concrete fragment after the fracture of the block. Polystyrene form helped to decrease the residual strain of blocks after being unloaded less than the half of its maximum strain during loading test.
The purpose of this study is the development of design structural material which has strength and durability with design of a traditional landscape in Japan. In this study, the mechanical properties and the color evaluation of mortar and concrete colored by using 8 types of the waste earthenware powder were examined. As a result, it was verified that the strength and durability of the colored concrete were equivalent to those of normal concrete by determining the mix proportion appropriately. And the color of the colored concrete was generally in agreement with that of wall materials in the traditional area. Furthermore, the effects of coloring by using waste earthenware powder and surface treatment methods of design of concrete wall were examined.
In this paper, deterioration of concrete structures due to sulfate or sulfate ion which are contained in ground were discussed. First, examples of collapse due to deterioration of concrete housing foundations on land developed with coal waste in an old coal-mining area was explained. Damage occurred on the land developed with mudstones of Neogene formations was also explained. These deterioration and damage were caused by sulfate or sulfate ion which are contained in soil. The process that pyrite was oxidized by bacteria and sulfate ion was formed in deposited layer was examined. Moreover, the review on sulfate ion content in ground in Japan was carried out. As the results, hazard map of deterioration due to sulfate attack concerning was geological and meteorological factors was proposed.
The long-term durability against leaching is necessary and currently treated as an important issue, and there are many investigations on the evaluation of the durability against leaching. Especially, many researches have been reported with using the numerical analysis for deterioration due to leaching. On the other hand, the electrical treatment, which can accelerate the deterioration due to leaching with high magnification, has been used to evaluate the long-term durability against leaching. However the ion migration mechnism in the electrical treatment is different from that in the real situation. Therefore, it is important to obtain the data, such as pore structure and diffusion coefficient, after electrical treatment and evaluate the leaching behavior in the electrical treatment for the applicability. The purposes of this research were to investigate 1) the chemical alteration, such as decrease of Ca(OH)2 and Ca/Si ratio of C-S-H, 2) the phyisical alteration, such as increase of cumulative pore volume and threshold pore and 3) the feasivility of the electrical treatment for evaluation of diffusion coefficient alteration due to leaching with void ratio.As the results of this study, the important data were obtained for underestanding the leaching alteration by electrical treatment and indicating the feasivility. Espacially, the following items for using electrical treatment were obtained. 1) Decrease of Ca(OH)2 and Ca/Si ratio of C-S-H were confirmed. 2) Cumulative pore volume and pore ratio were increased. It can be said that the electrical treatment is useful for evaluating the alteration of cementitious material due to leaching. 3) The relationship between void ratio and diffusion coefficient which was obtained by electrical treatment was similar to the modeled one in previous studies. Therefore, this result were showing the applicability of the electrical treatment for leaching alteration.
C-S-H is a dominant hydration product of cementitious materials. Therefore, its composition and properties affect the properties of concrete. However, the composition and the properties of C-S-H, and the relation between both have not been completely clarified. The purpose of this study is to estimate chemical composition and physical properties of C-S-H, such as density and specific surface area. Chemical compositions of C-S-H were calculated from the mass balance between starting materials and hydration products. The density and specific surface area of synthesized C-S-H and C-S-H generated from various cementitious materials were measured. From the experimental results, H/S ratio of C-S-H is in proportional to C/S ratio independent of kind of binder and mix proportion. The density and specific surface area are affected by C/S ratio, and linear relationships between C/S ratio and these physical properties are recognized respectively independent of kind of binder and mix proportion.