In the operation and maintenance of the power plant, the investigation of concrete is done based on the law. So, the information of concrete structures has been stocked. Using this information, the method of calculating the maintenance cost that was considering the fluctuation of data was proposed. The main result is as follows. 1) The influence by the fly ash and the temperature on the appearance diffusion factor and the density of the surface chloride ion was evaluated. The reinforced concrete corrosion speed was investigated in two or more offshore structures, and it was indicated that it was 1-20μm/year. 2) Using this information, the method of calculating the maintenance cost that was considering the fluctuation of data was proposed. The case study of the maintenance cost was carried out with this technique. It was shown that the maintenance cost was able to be reduced with fly ash as a result of the trial calculation by about 10 percent, and the maintenance cost changed by about three times by the change of the reinforced concrete corrosion speed. 3) Moreover, it was shown to be able to reduce the maintenance cost by doing the maintenance management according to the importance in the power plant composed of two or more structures. Thus, it becomes possible to improve the accuracy of the deterioration prediction by evaluating the survey data enough, and, consequently, the maintenance cost can be decreased.
In this study, two kinds of: impact-elastic wave method and electromagnetic pulse method, are applied to lateral prestressing steel bars in existing prestressed concrete bridges to evaluate grouting conditions in tendon ducts. First of all, impact-elastic wave method was perfomed to evaluate the grouting condition in tendon ducts to measure elastic wave velocities. Then, electromagnetic pulse method was applied to detect voids in tendon ducts just below the measurement points by using maximum amplitude of received elastic waves. The evaluation results is verified by drilling and observing the actual grouting condition in tendon ducts. Non-destructive evaluation results show good agreement with those of visiual inspection.
Shear loading test has been conducted with deep beam scale models in order to establish shear strengthening design procedure to existing beam by DFRCC (Ductile Fiber Reinforced Cementitious Composite) U-shaped winding. Finite element nonlinear analysis has been also carried out to explain not only test results but observed significant phenomena as well. Through comparison with past studies including rebar anchorage, steel plate and reinforced fiber sheet strengthening technologies, it is presented that further more shear capacity increase can be assured by the present construction joint technique with water jet treatment to existing beam. Practical design equation applicable even up to full winding is conclusively proposed focusing on additional shear capacity increase due to crack width control by DFRCC winding.
In this study, continuous fiber ropes were applied for shear reinforcement of RC members such as beams and columns. The fixing and covering materials for the rope on concrete surface and the rope winding interval were examined. Shear loading tests were conducted to RC beams reinforced with a continuous fiber rope. In order to utilize the capacity of continuous fiber ropes for shear reinforcement of RC members, we proposed a method to fix ropes with acrylic resin and then to cover them with HPFRCC (High Performance Fiber-Reinforced Cementitious Composite) on concrete surface.
Recently, it was being revealed that the performance of repaired reinforced concrete (RC) members and re-repaired RC members was different from the performance of RC members. In previous studies, we revealed the performance (re-)repaired RC members was affected by damage degree of longitudinal reinforcements, repairing materials and repairing methods. In this paper, we tried to quantify the performance of (re-)repaired RC members. Firstly, we proposed the seven models of stiffness and maximum capacity point of (re-)repaired RC members, and proposed the tri-linear skeleton model of them. Secondly, by using these models, we evaluated the seismic performance of repaired rigid-frame viaducts.
We aimed at the establishment as a large quantity of recycling methods of a shell holding and carried out various research works for use of the scallop shell to concrete. Because it was difficult to crush it into the appopriate size that could apply a scallop shell as fine aggregate, we took up a rotary crushing machine with the results as the shell crusher and examined the crush performance. And, about shell concrete that uses scallop shell as fine aggregate, we carried out various indoor examinations to grasp basic properties and field proof examinations aiming at verification of the problem towards utilization. From the results of indoor experiments and field examinations, the basic property and utility of the shell concrete are confirmed. Shell sand concrete has almost same properties in comparison with the normal concrete.
Under an economic crisis, bridge management system has been a critical issue to maintain bridge stock in efficient way. However, calculated LCC from the deterioration prediction is largely differed from the LCC of real bridges. One of the reasons is due to spatial variation of deterioration that caused by fluctuation of environmental and structural conditions in time and space. Maintenance scenarios that were calculated from deterministic deterioration prediction could not cover the variation. This paper aims to the scenarios generation with consideration of the spatial variation of deterioration. The target bridge is virtually subdivided into a discrete number of elements having its own deterioration rate. Those elements are classified into several groups according to state of deterioration. As the most deteriorated group has reached the condition level, maintenance scenario will be generated for the group while leaving the other groups untouched. As a result, more practical LCC and maintenance scenario can be calculated accordingly.
The external cable method is significant not only as a prestressing method in prestressed concrete structures but also as a strengthening system. Continuous Fiber Reinforcing Materials should be applied to the concrete structures under deteriorating conditions as tendons because it is non-corrosive, high strength and also possess other superior qualities. However, the flexural tensile strength will be decreased at the bent-up portions of the beam. This paper deals with the causes and the mechanism of decrement in flexural tensile strength of CFRP strands based on the experimental data. Also from the experimental data, relationship between flexural tensile strength and corresponding parameters, such as bent-up angle, diameter ratio of deviator to CFRP strands are derived. Moreover, the design concept of deviator and the control of prestressing as external tendons using CFRP strands were discussed.
Loading test of RC deep beams with solid circular cross section having a/d=1.0 under simply supported and anti-symmetric moment was carried out and shear failure behavior was investigated. As a result, it was confirmed that a compression strut forms between opposing corners of span under anti-symmetric moment and shear capacity decreases compared to that under simply supported condition. Longitudinal bars arranged around the cross section increases the shear capacity regardless of the supporting condition as well as observed in beams of rectangular cross section. The existing prediction equation for RC deep beams of rectangular cross section underestimates the shear capacity under simply supported condition, while it can properly predict the shear capacity under anti-symmetric moment by using total length of a span for shear span length. In addition, it was revealed that the effect of shear reinforcements under simply supported condition is provided by the confinement effect of concrete, while that under anti-symmetric moment is provided by a combination of confinement effect and the shear resisting force at a diagonal crack.
This study presents experimental work on bending strength and fracture energy of hybrid fibres reinforced high-strength concrete (HFRHSC) which were conducted during and after heating (i.e. hot and residual tests). It was observed that hot test results showed lower bending strength compared to residual one. This is considered to be mainly due to deterioration of ITZ during heating which significantly affects the bending strength of HSC. As for the fracture toughness, notably HFRHSC in hot test showed lower fracture energy compared to residual test. This is considered to be mainly due to the decrease of the bond strength between steel fibre and concrete matrix during heating. Additionally, hybrid fibre reinforcement is efficient in maintaining the bending strength, and is importantly effective to improve the fracture toughness of HSC both during and after heating. Thus, the hot test should be conducted for evaluating fractural properties of HSC due to its severity compared to residual test.
Durability of concrete structures depends on the mass transfer resistance of cover concrete. Therefore, the quality of the cover concrete is very important for ensuring the concrete structures' durability. For the reason, in order to ensure the durability of concrete structures, quality control of concrete based on mass transfer resistance of the structural cover concrete should be performed. To accomplish this, this study focused on the air permeability, one indicator of mass transfer resistance. When evaluating the test results, it is necessary to understand characteristics of the surface air permeability test, factors which may influence the measured values. As a result, considering the effect of dimensions of members on air permeability, it was found that the air permeability is less affected if the concrete age is more than 56 days. Therefore, it was found that one technique to solve influence of the age of concrete is to conduct the evaluation with the same water content comparing standard specimen to structural cover concrete under the same curing and conditions. in concrete having the same water-cement ratio it was clear that the surface air permeability was affected by the difference in bleeding properties even in the standard specimens. It is very important to take the bleeding properties into consideration in addition to water-cement ratio of concrete for predicting the surface air permeability as an indicator of durability.
The quality of structural concrete, which is affected by the execution conditions of construction works such as casting and consolidation method, is different from test specimens. Durability of concrete structures depends on the mass transfer resistance of cover concrete. Therefore, the quality of the cover concrete is very important for ensuring the concrete structures' durability. Currently, effects of concrete types and construction for the mass transfer resistance is not understood quantitatively. This study investigates the influence of bleeding of concrete, re-vibration, arrangement of steel bar, and change of mix proportions on quality of cover-concrete. As a result, it was clearly shown that the surface air permeability at the upper layers was larger than the lower layers, and the variation in height could be explained by the bleeding quantity of concrete. When examining the effect of reinforcement, it was found that the presence of reinforcement reduced the amount of coarse aggregate of cover concrete which caused an increase in air permeability. However, there was less vertical variation in the air permeability when using reinforcement than without reinforcement. This may be due to the reduction of consolidation by self weight as a driving force for bleeding due to the resistance of reinforcement and formwork. In addition, the improvement of surface air permeability by re-vibration after casting was quantitatively shown, as the effective time of re-vibration after casting depends on the properties of concrete such as slump.
In this research, the relationship between the results of the non-destructive surface air permeability test and the carbonation rate of concrete was examined in order to facilitate smooth information processing from the design stage to the construction, inspection, and maintenance stage. Corrosion of reinforcement due to carbonation was set as the cause of deterioration of the concrete structure. Although the examined experimental conditions were limited, the coefficient of air permeability of surface concrete can be formulated as a function of water-cement ratio, amount of bleeding water, and placement height per layer. The mix proportioning method, inspection system, and initial performance of structural concrete based on the proposed method are discussed.
In this study a multi-scale constitutive model for shrinkage behavior is enhanced with the purpose of expanding its applicability and increasing the precision. The enhancement focuses on the intrinsic driving forces of shrinkage at the microscale, whereas the existing time-dependent constitutive law remains unchanged. First, with regard to the rapid development of autogenous shrinkage of low w/c ratio concrete at early age, the contribution of chemical shrinkage is taken into account in the enhanced model and quantified according to the dispersion and hydration of cement particles. Furthermore, the driving forces until long time are deeply discussed and reconstructed based on the moisture state in micro-pores with different sizes. Capillary tension is assumed only active in coarse pores, while disjoining pressure dominates in fine pores with nanoscale. With the enhanced model, autogenous and drying shrinkage behaviors with various w/c ratios and relative humidity can be simulated reasonably.