In a previous study, the authors carried out a series of running wheel load fatigue tests with stepped incremental loading by using model specimens of highway bridge RC deck slabs and proposed a calculation formula of the punching shear load-carrying capacity and S-N curve of highway RC deck slabs. However, no constant amplitude running wheel fatigue tests were carried out. Therefore, in the present study, constant amplitude running wheel fatigue tests were carried out to verify the validity of application of Miner's rule to fatigue life estimation and the consistency of the S-N curve obtained from our previous study. In addition, the validity of our calculation formula of the punching shear load-carrying capacity in consideration of some design parameters, such as concrete compressive strength, mechanical properties of re-bar and amount of re-bar, was investigated. Consequently, the consistency between the S-N curve obtained from the equivalent number of cycles based on stepped incremental loading fatigue tests results using the punching shear load-carrying capacity (P_s.max) proposed by the authors and the constant amplitude fatigue test results was well verified.

The authors studied cylindrical shear-keys for use instead of concrete roughening for seismic retrofitted joints. Assuming actual construction, combined use of post-installed anchors and cylindrical shear-keys was investigated. The ultimate purpose of the study was to elucidate the mechanical behavior of such combination and to propose a mechanical model. In this paper, the test results are organized for each failure model (bearing failure, shear-off failure), and a mechanical model of cylindrical shear-keys including the post-peak area is proposed. The mechanical model was shown to be capable of largely satisfactory reproduction of the test results.

This study aims to clarify the shear capacity of flanged L-shaped RC members. Three specific tests with a total of nine flanged L-shaped RC beams were carried out under four point bending conditions to investigate the influence of the shear reinforcing ratio (r_w) and the shear span ratio (a/d). The results show that the actual shear capacity of flanged L-shaped RC beams is at least 1.54 times larger than that calculated conventionally because a large number of stirrups support the shear force. Finally, based on the actual crack distribution, a two line model and a three line model for predicting the actual shear capacity of flanged L-shaped RC beams are presented.

In seismic-reinforced structures, the existing member and the newly added reinforcing member are usually joined using concrete roughening by the chipping method and post-installed anchors. However, the current structural design guideline considers only the shear strength of post-installed anchors. Methods to evaluate the mechanical behavior of post-installed anchor used in combination with concrete roughening are currently being evolved based on findings of past studies. As part of this research, we conducted tests using specimens that combine post-installed anchors and concrete roughening, and investigated if the experimental results can be reproduced through the cumulative use of a number of existing models. As a result, a model evolved by modifying the existing contact stress model and adjusting the joint gap and plastic hinge location was found to approximate reasonably well the test results for specimens that combine post-installed anchors and concrete roughening.

In seismically active areas, enhancing earthquake resistance performance of buildings is an important issue. Externally applied seismic retrofit is one of the methods for the seismic retrofit of existing members of a building. In such a building, combined stress acts on the post-installed anchors with large bending moment. In a previous study, the authors constructed a mechanical model to reproduce experimental results under pure shear and conducted cyclic loading tests on post-installed anchors under constant tensile force. In this paper, the authors sought to extend the proposed model to estimate the shear force-slip relation of post-installed anchors under combined stress. Finally, an extended model that use functions based on tensile stress ratio is proposed. As a result, the experimental results can be reproduced with high accuracy by this model.

Open channels made of reinforced concrete are subject to freeze–thaw cycles when used in cold regions for a long period. We conducted electron probe microanalysis to analyze surface elements of core samples from the exposed parts of channel sidewalls, and examined the deterioration of the concrete on the inner and outer surfaces of the sidewalls. Our study revealed that freeze–thaw cycles cause cracks in the outer surfaces that serve as passageways for water, and that the leaching of calcium around the cracks and the penetration of carbon dioxide into them cause calcium recrystallization and sulfur diffusion. Our study also showed that the calcium that leaches into the air voids near the inner surfaces of cracks recrystallizes, causing blockage of air voids.

Greater utilization of recycled aggregate concrete (RAC) is desirable to build a sustainable recycling oriented society that reduces carbon dioxide emissions. In this study, low-quality recycled concrete aggregate was improved by carbonation technology and the effect of the use of carbonated RAC as a partial replacement of aggregate on the properties of concrete was investigated. The carbonation of RAC was found to significantly improve the strength, freeze-thaw resistance, and durability of RAC, and also to reduce its shrinkage. This carbonation technology can be used also to reduce CO₂ emissions of energy plants.

In this study, we investigated the durability of high-volume ground granulated blast furnace slag (GGBS) blended cement concrete containing over 70％ of GGBS for possible general structural applications. The concrete specimens used were exposed to natural outdoor conditions for 41 years on a building rooftop. It was found that the carbonation depth of concrete specimens containing 70％ GGBS was about 7 to 9 mm, and about 15 mm for specimens containing 90％ GGBS. Despite the high volume of GGBS content (70％) in the concrete specimens, traces of Ca(OH)₂, which is involved in the chemical reaction of GGBS, were found in parts that remained uncarbonated. Ca(OH)₂ increases the alkalinity of the specimen and is thus considered to have a rebar corrosion-inhibiting effect.