Wakkanai Port, located in the northernmost part of Japan, has a breakwater called “North Breakwater Dome, ” which is reminiscent of ancient Greek architecture. Construction of the North Breakwater Dome was completed in 1936, and an overall rehabilitation was conducted from 1978 to 1981. Currently, the deterioration of the dome is becoming apparent. We examined the remedial measures for deterioration, but the issues were to devise a method for assessing the performance of reinforced concrete members and a reasonable repair method. This is because the inspection range is very large, and the structure of the Dome is a civil engineering heritage. To solve the issues, we devised the deterioration mapping that is created by subdividing of large inspection areas, and by grading into five grades of deterioration based on damage. By using deterioration mapping, it is possible to quantitatively grasp damages in large areas, to quantitatively understand the corrosion state of reinforced concrete members, and to implement reasonable repair on an unit area basis. This paper discusses the effectiveness of the deterioration mapping using the case study of the North Breakwater Dome maintenance.
Non-destructive tests with ultrasonic waves are often used to examine grouting conditions in tendon-duct of post-tensioned prestressed concrete bridges. Wide-range ultrasonic testing (WUT), a kind of the NDT technique, has an advantage that it is applicable even in relatively thick PC girders. WUT is often employed in box-girders of PC bridge because the grout inspection can be conducted at the inner space of the girder without a scaffolding. WUT analyses the reflection ultrasonic waves and evaluates voids from the observed high-frequency waves. The observed ultrasonic waves include reflection waves from the end-face of girder in addition to the reflection waves from the voids. It is well known that the former reflection waves are generally greater than the latter. The influence of reflection waves from the end-face should be evaluated properly to detect the voids of PC duct. To improve the accuracy of void detection by WUT, this study aims at examining the influence of reflection waves from the duct and the end-face. The study conducted the fundamental experiment using 4 test specimens: A) concrete embedding a void-duct; B) concrete embedding a grout-filled duct; C) plain concrete of 240 mm thick; and D) plain concrete of 135 mm thick. The paper reports the influence of reflection waves from the end-face on the void detection of WUT.
To quantitatively evaluate the performance of epoxy resins for crack injection in cold environment, we performed injection tests using cylindrical specimens with controlled crack widths during which the changes in viscosity and temperature of the epoxy resins were measured during the injection. This paper presents the results of the areal rate into a crack under various temperatures and injection rates.
As a result, the injection performance of epoxy resins depends on the environmental temperature inside the crack because the resin changes its temperature very little due to its chemical reaction in low temperature environments. In addition, the injection areal rate has a correction with the environmental temperatures of 5°C or less. From this correlation, it is possible to quantitatively evaluate the injection performance of epoxy resin for crack injection in cold environment at the design stage.
In this study, triaxial tests were performed on compacts of leached/unleached cement paste, calcium hydroxide, and synthesized C-S-H to understand the deformation mechanisms of cement paste and concrete under high pressure and also the mechanism of higher strength and density development of crushed concrete through compaction when the concrete powder is wet. It was found that compact of calcium hydroxide significantly reduced strength and stiffness when it was wet. The synthesized C-S-H reduced the stiffness under high confining pressure, but the effect of moisture was small compared with that of calcium hydroxide. Based on the obtained results, the process of the strength gain of crushed concrete through compaction is explained as follows: C-S-H, which deformed easily, was squeezed out, the calcium hydroxide structure was formed, and the structure deformation occurred readily when the concrete was wet. These findings are useful for understanding the deformation mechanisms of ordinary concrete and cement paste.
It is essential to develop an inspection method capable of diagnosis for corrosion of reinforcing steel inside the concrete structure since the aging of reinforced concrete (RC) structures is in progress. However, in the conventional methods, it is necessary to partially destroy the existing structure to measure the corrosion rate of the reinforcing steel. In this work, to develop a non-destructive method to measure the corrosion rate of the steel inside the existing structure using a four-probe AC impedance method, the impedance is measured for mortar and concrete specimens. Also, current dispersion analysis clears the change of the measurement value depending on the probe distance and the rebar depth.
As a result, we succeeded in proposing a condition capable of applying the method and an index capable of converting into a corrosion rate under the condition. It is shown that we can set a measurement condition according to a targeted concrete structure and evaluate the corrosion rate of the reinforcing steel using the non-destructive method.
The purpose of this study was to clarify the relationship between air permeability and mass transfer resistance of concrete subjected to various deterioration factors. This was done by analysing cores collected from actual structures and the relationship between air permeability and the progress of deterioration was studied.
Experiments were carried out and it was observed that the air permeability coefficient of the deteriorated part was clearly larger than the healthy part. It was also estimated that the higher the air permeability and the larger the oxygen supply amount, the sooner the deterioration such as peeling occured. Rebar corrosion progressed rapidly due to the effects of deterioration factors like the CO2, chloride ions and water ingress. Therefore, in the environmental range of the actual structure studied this time, it was suggested that the damage could be quantitatively assessed by measuring the air permeability coefficient using core at any given location.
The aim of this study was to find out the punching shear failure mechanism of RC slabs through experimental investigation and nonlinear finite element analysis. In the nonlinear finite element analysis, 3D Nonlinear Cementitious 3 constitutive model was specifically applied to concrete material to express the stress – strain relationship of concrete subjected to triaxial compressive stress states. As a result, it was found that triaxial compressive region was formed in the vicinity of the loading plate, and the compression failure of concrete in this region caused punching shear failure of the RC slab. Therefore, a pyramid shell model was proposed based on the load bearing mechanism formed around the vicinity of the loading plate. Finally, the evaluation formula for the punching shear resistance derived from this pyramidal shell model was in good agreement with the previous experimental results.
The aim of this study was to investigate the effect of in-plane confining pressure on the punching shear resistance of RC slabs through punching shear loading test and non-linear finite element analysis. In order to analyze the punching shear fracture behavior of RC slabs subjected to in-plane confining pressures, it was specifically essential to use a constitutive model that can appropriately express the stress-strain relationship of concrete under triaxial compressive stress. As a result, it was shown that the punching shear resistance of RC slabs subjected to in-plane confining pressure could be evaluated from the pyramidal shell model based on the punching shear fracture load bearing mechanism by treating the in-plane confining pressure as an equivalent conversion rebar ratio. Furthermore, in this study, the design formulae of punching shear resistance considering the influence of in-plane confining pressure in the design standards of foreign countries were also examined.
Experimental studies were conducted on fundamental properties, shrinkage properties, thermal properties, and wear properties of self-compacting concrete mixed with seawater and limestone aggregate derived from corals assuming use on isolated islands. As a result, the concrete using this aggregates with many voids had excellent fluidity, moderate segregation resistance, and the same strength development as when using ordinary aggregates. In addition, shrinkage and thermal expansion coefficient were smaller than that of concrete using ordinary aggregate. Furthermore, even when coral aggregate was used, abrasion resistance of concrete equivalent to that when using ordinary aggregate could be secured by setting the water cement ratio and unit coarse aggregate volume small.