A mix-design method based on packing model was used to optimize the mix proportion of Reactive Powder Concrete (RPC) containing phosphorous slag in this paper. The design aimed to achieve a densely compacted matrix by applying the modified Andreasen particle packing model, i.e., the Dinger-Funk particle size distribution (PSD) equation. MATLAB and Excel Solver Tool were utilized to implement the calculation of the design with four steps. The outcome of the design was quite similar to another two results obtained respectively through the method for minimum water demand of paste and through the orthogonal design for mix proportion of RPC. According to these three mix proportions, RPC specimens with volume fraction of steel fiber of 1% were produced after they had been cured in 95°C steam for 72 hours. Their compressive and flexural strength are more than 180 MPa and 28 MPa, respectively. Microstructural investigation of specimens through mercury intrusion porosimetry and scanning electron microscopy confirms the very low porosity and quite compact microstructure of the RPC.

Due to their wide applicability in inspection of concrete structures, there is considerable interest in the development of automated crack detection method by image processing. However, the accuracy of existing methods tends to be influenced by the existence of traces of tie-rod holes and formworks. In order to reduce these influences, this paper proposes a crack detection method based on semantic segmentation by deep learning. The accuracy of developed method is investigated by the photos of concrete structures with lots of adverse conditions including shadow and dirt, and it is found that not only the crack region could be detected but also the trace of tie-rod holes and formworks could be removed from the detection result with high accuracy. This paper is the English translation from the authors' previous work [Yamane, T. and Chun, P., (2019). “Crack detection from an image of concrete surface based on semantic segmentation by deep learning.” Journal of Structural Engineering, 65A, 130-138. (in Japanese)].

Aiming at improving bond strengths between FRP sheet and concrete, the FRP sheet bonding method using high elongation elastic resin as a buffer layer was developed. In this study, bonding tests was conducted to clarify the basic bond characteristics of FRP strand sheet-concrete interface with a polyurea resin. As a result of the bonding tests, it was found that the use of the polyurea resin as a buffer layer significantly improved the bond strength and the interfacial fracture energy between FRP sheets and concrete. In addition, bond stress-slip relationships with a polyurea resin were proposed. Finally, numerical analyses of bonding CFRP strand sheets and concrete were conducted so as to verify va-lidity of the proposed bond stress-slip relationships. This paper is an extended version in English from the authors’ previous work [Kobayashi, A., Ozaki, M., Sato, Y., Arazoe, M., Tateishi, A. and Komori, A., (2020). “Study on bonding behavior of FRP sheets and concrete bonded with high elongation elastic resin.” Journal of Structural Engineering, JSCE, 66A, 855-867. (in Japanese)].

The adhesion failure of the interface between concrete and rendering mortars often leads to the degradation of the reinforced concrete building envelopes. Although several methods to improve the adhesion properties between concrete and rendering mortar have been proposed, there is no system to evaluate the effectiveness of these methods from the perspective of durability. To this end, this study proposed an experimental method to evaluate the durability of rendering mortar and concrete adhesion systems at the laboratory level. In this technique, a cyclic thermal load is applied to a part of the rendering mortar surface to accelerate the degradation; this part represents an external wall subjected to solar radiation. Subsequently, appropriate constraints are applied to the loaded part of the mortar to reproduce the actual degradation mechanism. Numerical simulation and experimental results support the effectiveness of the proposed accelerated degradation method. Considering the rate of decrease in the bond strength as a criterion to evaluate the durability, the influence of several known factors on the durability can be explicitly ranked. The durability assessment method can facilitate the comparison of novel solutions during the development stage.

In this research, concrete-filled braided carbon fibre-reinforced polymer (CFRP) tubular beams and arches were constructed. CFRP tubes and concrete-filled CFRP tubular cylinders were compressed to investigate the constraint effect of the CFRP tube on the concrete. Long and short beams were bent to reveal the deformation styles and the failure modes controlled the flexure and the shear, respectively. All of these experiments on cylinders and beams supply basic data to judge the failure load of the concrete-filled tubular arch. Blast resistance of the concrete-filled tubular arch was investigated by explosion experiments and evaluated by the residual static load-carrying capacity of the exploded arches. Constrained by the CFRP tube, the protective arch has excellent blast resistance. A hybrid compression-bending failure criterion was proposed to estimate the static structural performance, and the prediction is consistent with the experiment.