To predict the progression of ASR, both chemical aspect and physical aspect should be taken into consideration. As first step of this study, chemical analysis and diffusion analysis were carried out. Through these investigations, we developed chemical model for the generation of ASR gel and the consumption of alkali by reactive aggregate. We also developed physical model which predicts concrete expansion from the amount of ASR gel. Our physical model indirectly considers the influences of damages induced in concrete matrix during expansion process. As second step of this study, we considered about the mechanism of the unique phenomenon that ASR expansion is significantly reduced when rebar restrains concrete somewhat. We developed ASR expansion model which evaluates the restraint effect of rebars by expressing the migration of ASR gel into capillary pores with pore size distribution function (PSD function). By comparing with experimental results of concrete bar specimens, our model was verified to predict the expansion of reinforced concrete due to ASR.
This study aimed at evaluating the corrosion behavior of steel bars in reinforced concrete members constructed under the airtight underground space. Construction works of structures were carried out in the air condition, and structures were initially exposed to oxidizing environment. Structures were afterwards buried in the underground, and the environmental condition surrounding the structures were gradually shifted to the reducing environment. In this study, such environment was experimentally reproduced and corrosion rate of steel bars in concrete were estimated using the various electrochemical methods. As a result, the following conclusions were obtained. (1) The corrosion rate in oxidizing environment at temperature of 20°C was 0.001~0.011μA/cm2 , and the corrosion rate after being shifted was 0.013~0.056μA/cm2 in reducing environment at temperature of 50°C. These values were equivalent to the reported rates by the electrochemical methods so far. (2) The accuracy of various polarization methods was greatly influenced by a potential sweep rate. (3) "The passive maintaining current method" proposed by the study was very effective so as to evaluate the corrosion rate in reducing environment.
This paper proposes the framework of detailed damage assessment of RC frame structures subjected to reversed cyclic loading based on the damage and failure of constitutive materials, which can be applied, in the future, to the safety and repairability verification of RC structures. The evaluation scheme based on the spatially-averaged strain-based indices incorporated to the damage of constitutive materials, which are calculated from the local stresses and strains at each integration point in the finite elements, are verified for nine RC column specimens fail in shear and flexure. Furthermore, the damage level and deterioration process upto failure of RC frame structures are fully evaluated using the verified method, by conducting the nonlinear finite element analyses of 1- and 2-layer RC frame and RC box culvert specimens.
First, in a pretension hollow slab girder bridge severely damaged due to sodium chloride used as deicing salt, the detailed field inspection was performed. Next, using concrete cores sampled from the blocks of girders, the mechanical properties and chloride ion concentration of concrete were measured. Further, by removing whole concrete from blocks, the corrosion condition of steel inside was observed. From the results of these inspections, it was recognized that some girders involved highly-concentrated chloride ions and this fact resulted in not only chloride induced deterioration but also severe frost damage. Thus, additional experiments simulating actual concrete properties and environmental conditions were conducted. The experimental results revealed that Non-AE concrete involving highly-concentrated chloride ion remarkably accelerated frost damage under deicing salt.
Completely non-destructive technique of surface water absorption test (SWAT) for newly-constructed and existing concrete structures was developed by the authors. SWAT can measure absorped water volume continuously and accurately immediately after filling up water. Through the measurement by SWAT in 10 minutes, several indicators for resistance against water absorption are obtained, and covercrete quality from the surface to some depth can be evaluated by these indicators. In this research, the following three investigations were conducted; 1) tests for concretes with different constituent materials, W/C, and curing conditions without the effect of rainfall, 2) tests for concretes in different exposure environment, 3) measurement of actual structures. SWAT could detect the effects of W/C and curing condition on covercrete quality for concretes with OPC and slag cement. It was proved that water absorption rate at 10 minutes obtained from actual structures could be considered to follow normal distribution. In order to establish inspection system with SWAT, a method to set threshold value and a way of judgment in inspection were proposed based on a statistical approach. As practical applications of SWAT, analyzing the adverse effect of microcrack on covercrete quality, and detecting the effects of expansive additive and silane type water repellent on improving covercrete quality were introduced.
In recent years, continuous fiber reinforcing materials are expected to use strongly for maintenance of concrete structures as repair or strengthening materials. Especially, CFRP strands are the most suitable materials as tendons, for example, ground anchor methods, external or inner cables of prestressed concrete structures, because CFRP strands have many superior mechanical properties obtained from our previous fundamental studies. The important mechanical properties of CFRP strands are high tensile strength, relaxation and fatigue characteristics as tendons. These properties have not been discussed quantitatively and qualitatively. In this paper, the important mechanical properties of CFRP strands as tendons are summarized with new innovation. The abundant experimental data were reverent and a prerequisite for repairs, strengthening design as well as for the new construction design of concrete structures.
It is necessary that bridge foundation remains elastic even under a large earthquake to guarantee the rehabilitation of the structure. RC piles using the high-strength concrete and rebars, and prestress technology has been developed to increase the lateral capacity of pile foundation. The carbon fiber sheets are attached on the proposed RC pile in order that the cover concrete can contribute to increasing the flexural capacity. The static and cyclic bending test are conducted to investigate the structural performance of RC piles. In addition, full scale cyclic loading tests of proposed pile embedded into the ground are conducted. Based on the comparison with the behavior of conventional concrete pile, the proposed pile subjected to higher lateral load could remain elastic. It is possible to evaluate the seismic performance of the proposed pile using the conventional methods of structural analysis for concrete piles.
UFC is one of the cementitious materials which have outstanding properties such as more than 200 MPa compressive strength, high ductility and durability. The permanent formwork for RC structures is one of the promising applications of UFC. This research is aimed to investigate the shear behavior of RC beams using a U-shaped UFC permanent formwork. Eight RC beams using a U-shaped UFC permanent formwork were tested by four-point bending test. The experimental parameters were the presence of shear keys at the internal surface of a UFC U-shaped permanent formwork, presence of screws and bolts, thickness of formwork, shear span to effective depth ratio and presence of stirrups. The experimental results indicated that a U-shaped UFC permanent formwork enhanced the shear capacity of RC beams more than twice compared to normal RC beams. In addition, the shear resistance mechanisms were investigated. By using a UFC formwork with shear keys and screwed bolts, the UFC formwork intercepted widening of diagonal cracks inside a RC part. Finally, the shear carried by a UFC permanent formwork was investigated. The proposed calculation method can provide a good agreement with the experimental values.