Journal of Advanced Concrete Technology(2024 - 2024)
Assessment on Bond Strength of CFRP Sheet Bonded to Concrete Focused on Sheet Stiffness
Ozaki M.; Sato Y.; Yoshida E.; Takeuchi A.; Yamada Y.; Nagashima F.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, 2024, APR.
(https://doi.org/10.3151/jact.22.190)
Abstract
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. Copyright c 2024 Japan Concrete Institute.
Bond Strength of Post-installed Anchor Adhering to Damaged Concrete by Freeze-thaw Action
Yano Y.; Shiokoshi T.; Takase Y.; Ishida Y.; Abe T.; Takahashi M.; Ishigaki T.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, 2024, APR.
(https://doi.org/10.3151/jact.22.178)
Abstract
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. c 2024 Japan Concrete Institute. All rights reserved.
Effect of Fly Ash Content on Rheological Properties of Self-compacting Geopolymer Mortar
Ghafoor M.T.; Fujiyama C.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, 2024, MAR.
(https://doi.org/10.3151/jact.22.103)
Abstract
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 (Gm) and relative funnel speed (Rm) 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 Gm and Rm of SCGM. The maximum Gm of 10.90 and Rm 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. c 2024 Japan Concrete Institute.
Extraction of Carbonation Rate from Depth Profile of Concrete Carbonation by using Pseudo-analytical Solution of Two-component Reaction-diffusion Equation
Ichikawa T.; Haga K.; Yamada K.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, 2024, MAR.
(https://doi.org/10.3151/jact.22.139)
Abstract
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. Copyright c 2024 Japan Concrete Institute.
Estimation of the Protected Paste Volume by Spatial Tessellation Associated with the Point Pattern of Air Voids
Ohyama K.; Yamashita S.; Igarashi S.-I.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, 2024, MAR.
(https://doi.org/10.3151/jact.22.128)
Abstract
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. c 2024 Japan Concrete Institute.
Structural Behaviors of Steel Tube-encased Concrete Columns Confined by Bolted Circular Thin Steel Tube
Zhang C.; Yamaoka K.; Fujinaga T.; Sun Y.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, 2024, MAR.
(https://doi.org/10.3151/jact.22.115)
Abstract
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. c 2024 Japan Concrete Institute. All rights reserved.
Development of Post-installed Headed Bars Embedded into Grouted Holes with Enlarged Ends
Ousalem H.; Horiuchi G.; Hamada A.; Takatsu H.; Idosako Y.; Masuda H.; Hiroshima Y.
Journal of Advanced Concrete Technology, Japan Concrete Institute, Vol.22, 2024, JAN.
(https://doi.org/10.3151/jact.22.62)
Abstract
To secure good quality post-installed anchors with a relatively short anchorage length and sufficient pull-out/shear resistance, an anchoring method with enlarged diameter at the end of drilled holes has been developed. Anchors were provided with head plates and fixed into the enlarged holes using non-shrinkage high-strength cementitious grout. Pull-out and shear preliminary tests were conducted to investigate the behavior and evaluate the strength of such anchors set in concrete. Furthermore, an evaluation method, based on the Japanese recommendations for design of composite constructions, was proposed. The evaluated pullout and shear capacities of all tested anchors designed to fail by steel yielding ensured sufficient safety margin as to test results, whereas those of some anchors designed to fail by concrete cone breakout should be reduced. c 2024 Japan Concrete Institute.