Journal of Advanced Concrete Technology最新文献

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.

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)].

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.

To better utilize topology optimization theory to assist in designing reinforced concrete (RC) D-region members, a novel application mode, the Genetic Bi-directional Evolutionary Structural Optimization (GBESO) method based on Finite Element Analysis (FEA) with discrete models is proposed. Correspondingly a design method for reinforcement layout of RC D-region members is also derived. Non-linear FEA verification is conducted on numerical examples involving deep beams with openings. The results demonstrate that the GBESO algorithm exhibits better global optimization capacities compared to Evolutionary Structural Optimization-type (ESO-type) algorithms. It also provides rebar topologies that are more in line with the optimization objective, bringing lower steel consumption and higher rebar utilization rates. Moreover, by introducing inclined rebar to the members, their shear strength is enhanced to a level comparable to the flexural one, significantly improving ultimate load-bearing capacity, elastoplastic deformation capacity, and better ductility compared to empirical method.

Steam curing is a widely used technique for producing precast concrete components in practical engineering. Chloride attack is a main factor that leads to the corrosion of rebars in concrete structures, which significantly affects the durability and safety of concrete structures in marine environments. In this paper, XRD, LF-NMR, ²⁹Si NMR, and ²⁷Al NMR were used to investigate the microstructure evolution of steam-cured concrete and standard-cured concrete. Then, the steam-cured and standard-cured concrete were subjected to actual marine exposure tests to explore the microstructure evolution of concrete and the chloride erosion behavior in the tidal zone. The results showed that steam-curing can increase the average molecular chain length (MCL) and polymerization degree of C-(A)-S-H, promote the transformation of silicon-oxygen tetrahedral dimer to polymer, and increase the Q²/Q¹ value of steam-cured concrete to twice that of standard-cured concrete. Compared to standard-cured specimens, steam-cured concrete specimens had significantly more harmful pores and multi-harmful pores. With the increase of exposure time to the marine environment, the depth of the convection zone inside the concrete did not change significantly, however, the peak value of chloride concentration increased gradually. The addition of SCMs to steam-cured concrete reduced the content of free and total chloride, which was well explained by microscopic tests. The concentration of chloride on the surface and chloride diffusion coefficient of steam-cured concrete showed a quadratic function relationship with the increase of slag content, and an exponential decay relationship with the content of fly ash.

The accurate numerical solution of a one-dimensional two-component reaction-diffusion equation including a second-order chemical reaction between concrete constituents and carbon dioxide to generate carbonated products was approximated by a simple analytical function which was given as a function of the effective diffusion coefficient of CO₂, the rate constant of CO₂ absorption, and parameters determined by the initial and the boundary conditions of the system. The pseudo-analytical solution thus obtained showed that the depth profile of carbonation shifts in parallel with square-root of time, and the rate constant of carbonation is determined from the location where the amount of the carbonated product is a half of the maximum amount. Comparison of the pseudo-analytical solution with an observed depth profile of concrete carbonation makes it possible to directly extract the rate constant of concrete carbonation that is necessary for predicting the future progress of the carbonation.

Six square steel tube-encased concrete (SC) columns confined by bolted circular thin steel tube were fabricated and tested under cyclical reversed lateral load to investigate their structural behavior. The primary experimental variables included the axial load ratio, the grade of the encased square steel tubes (FB rank and FC rank), the infilling of concrete into the encased steel tube, and the thickness of outer circular bolted thin steel tubes. Experimental results revealed that confinement by the bolted circular thin steel tube with outer-diameter-to-thickness ratio of 189 could ensure sufficient ductility to the SC columns, and the bolted thin steel tube did not rupture until the drift angle of about 0.09 rad. Furthermore, a simple evaluation method for the ultimate flexural strength of SC column section was proposed along with a numerical analytical method to predict the overall behavior of SC columns. The proposed methods can take the confinement effect by the bolted circular steel tube into consideration. Fairly good agreement between the experimental results and the calculated ones verified the reliability and accuracy of the proposed methods.

This study is a continuation of the published research studies relevant to self-compacting geopolymer mortar (SCGM) prototype using fly ash. The aim of this study was to investigate the effect of fly ash quantity on the rheological properties of SCGM. The flow properties include relative flow area (G_m) and relative funnel speed (R_m) is determined with the variation of fly ash to sand ratio (FA/S), volume of water to powder ratio (Vw/Vp), and superplasticizer to powder ratio (Sp/P). The test results exhibited that the increase in FA/S from 0.5 to 1.0 positively affected the G_m and R_m of SCGM. The maximum G_m of 10.90 and R_m of 1.43 were obtained for the SCGM mix having FA/S of 1.0, Vw/Vp of 1.02, and Sp/P of 3%. Overall, test results exhibited that with an increase in FA/S comparable flow properties of SCGM were achieved even at lower Vw/Vp and Sp/P. The recommended boundary for SCGM is proposed by comparing the experimental test result of this study with previous studies.

Paste volumes protected by air voids against frost attacks were estimated using Dirichlet tessellation tiles. Each tile was regarded as an area protected by air voids. The characteristic distance was defined by the largest tile size to reach a cumulative area fraction of 0.95. The significance of this distance was verified by a Monte Carlo test for the simulation of random point patterns. Comparing the characteristic distance and conventional spacing factor, the latter corresponds to the actual distance required for protecting the local region with the highest vulnerability to frost attack. The tessellation model provides the protection characteristic distance without overlaps even in the region of clustered air voids.

Reinforced concrete shear walls are commonly used in buildings to resist lateral loads due to wind and seismic action. They are typically either cast-in-place or precast, with the latter solution used to achieve high construction speed and quality control. At the same time, the main challenge with precast solutions is to ensure appropriate connections between the adjacent walls, as well as the anchorage of the walls in the foundations. A hybrid structural system combining precast and cast-in-place concrete can provide the advantages of both methods such as faster construction, better quality control, improved structural performance, and durability. This study focuses on investigating the shear behaviour of squat hybrid shear walls through full-scale experimental testing. The tests include one conventional cast-in-place wall and one hybrid wall with a pre-wall system (two precast walls) and cast-in-place concrete core. Detailed measurements and kinematic-based modelling are used to develop comprehensive understanding of the behaviour of the test specimens. It is shown that the hybrid method of construction does not affect the stiffness of the walls and results in a slight reduction of shear strength. It is also shown that the three-parameter kinematic theory can be used to predict the shear strength and key deformation components of the tested walls.