Reinforced concrete (RC) structures in cold regions are susceptible to surface deterioration due to freeze-thaw cycles (FTC). For sustainable development goals (SDGs) and a decarbonized society, damaged structures should be repaired and reinforced. Post-installed anchors are commonly used for seismic retrofitting and equipment fixation. However, research on the bond characteristics of damaged concrete is limited. Therefore, in this study, the bonding performance of adhesive anchors in damaged concrete was investigated. Liquid nitrogen was employed to subject the concrete surface to FTC; subsequently, bond-slip tests were conducted with the degree of deterioration serving as a parameter. The results suggested, the bond strength decreased as the degree of damage increased. The reduction ratios of the post-installed anchor with epoxy and cement-based resins were almost identical. Furthermore, a bond strength equation was proposed by referring to the bond-slip model between the rebar and concrete (fib 1990). The test results were well predicted with a correlation coefficient of 0.94. This study is based on previous studies (Yano et al. 2022, 2023) but presents new findings.

Electric Arc Furnace slag (EAF slag) reuse is currently limited by its inconsistent chemical composition and volume instability. However, the alkaline composition suggests the possibility to use this material for carbon capture and storage. This study investigated the CO₂ uptake of EAF slag using a direct aqueous carbonation technique. The process was implemented at room temperature and ambient pressure, with minimized energy consumption. The CO₂-reactive phases were identified through X-ray diffraction analysis. Different CO₂ quantification techniques were employed: thermogravimetric analysis, acid digestion and thermal decomposition. The replicability of experiments and quantification techniques was assessed through analysis of variance and pairwise comparisons. The average CO₂ uptake and coefficient of variation resulted respectively 7.9% and 9.0%, with a carbonation degree of about 34%, proving that this simple mineralization process can be promising even in mild conditions.

Effects of fly ash (FA) content and environmental factors on the water permeability were studied, and the similarity relationship of time-dependent water permeability coefficient in site and laboratory environment was discussed. Meanwhile, the main microstructure parameters and their time-dependent characteristics were analyzed by the NMR method. Finally, the correlation between water permeability and porosity in two environments was analyzed. Results show that water permeability coefficient of FA concrete both decreased with exposure time in two environments. FA can effectively improve the water impermeability, and the improvement effect increased with FA content in the later exposure period. Laboratory environment accelerated the decrease of water permeability and porosity. However, in the later stage, the decrease degree was not as good as that in the site environment. Pores with size of 10 to 100 nm occupy the main part of pores in FA concrete and the proportion of harmful pores of diameter 100 nm or larger decreased with exposure time. The water permeability coefficient and porosity of concrete exposed for 520 days in laboratory are close to that exposed for 800 to 1000 days in site, showing a good time dependent correlation in both environments, and the correlation with exposure time is stronger than that considering FA content.

Current practice reveals that no adaptation of self-healing concrete mix designs are made for the introduction of healing agents. However, the inclusion of healing agent may downgrade the concrete properties to some extent. Therefore, an optimization of mix design is necessary in order to eliminate the possible negative effects induced by the healing agents and also to potentially improve the self-healing and self-sealing abilities. In this paper, seven concrete mix designs were studied with crystalline admixture (CA) as a prospective healing agent to stimulate the autogenous healing mechanism. Several design parameters were opted namely (1) dosage of CA from 0 to 2% by cement mass, (2) water-cement (w/c) ratio between 0.46 and 0.52, and (3) cement content in the range of 320 to 360 kg/m³. The self-healing and self-sealing performances were investigated by the indicators of crack closure and the permeability rate, respectively. Results showed that the addition of CA demonstrated an advanced progress on the crack closure with increasing the healing time. The size of the crack considerably influenced healing performance. All in all, the effects of mix design parameters in terms of improvements of healing and sealing efficiencies are discussed and a recommendation for optimizing the mix design is proposed.

In previous studies on the bond behaviors of FRP sheets attached to concrete, specimens for bond tests that contained FRP sheets with relatively low stiffnesses were used. However, in actual strengthening design, high stiffnesses of FRP sheets are required because the scale of the structure is very large. Therefore, in this study, bond tests were conducted using specimens with many different sheet stiffnesses and with polyurea resin. As a result, the bond strength increased as the stiffness increased with multiple CFRP sheets. Nevertheless, existing bond strength models overestimated the bond strength when the stiffness exceeded 200 kN/mm. In addition, 3D scanning measurements of patterned and indented concrete thin layers behind CFRP sheets revealed that the interfacial fracture energy was strongly related to the surface area of the concrete thin layer, not to the CFRP sheet stiffness or the resin properties.

This paper is an English translation of the authors’ previous work [Ozaki, M., Sato, Y., Yoshida, E., Takeuchi, A., Yamada, Y. and Nagashima, F., (2023). “Assessment on bond strength of CFRP sheet bonded to concrete focused on sheet stiffness.” Journal of JSCE, 79(6), 22-00289. (in Japanese)].