Muhaimin, A. A., M. Adel, and K. Nagai, "Investigating the effect of repeated high water pressure on the compressive and bond strength of concrete with/without steel bar", Materials, vol. 14, issue 3, pp. 527, 2021.
Adel, M., K. Matsumoto, T. Ueda, and K. Nagai, "Material comparative analysis of crack-bridging degradation of SFRC structural beams under flexural fatigue loading", Construction and Building Materials, vol. 339, issue 127642, 2022.
ADEL, M., P. Jiradilok, K. Matsumoto, and K. Nagai, Evaluation of crack-bridging strength degradation in SFRC structural beams under flexural fatigue, , vol. 244, pp. 112267, 2020. AbstractWebsite

Steel fiber reinforced concrete (SFRC) at the structural scale exhibits an enhanced fatigue performance compared to conventional reinforced concrete (RC) with lower stress levels and longer fatigue life. The steel fibers contribute to the crack-bridging strength of the concrete, but how this degrades in the tensile stress zone of an SFRC structural beam during flexural cyclic loading remains unknown. This makes the fatigue design and safety verification of SFRC beams an unexplored area. In this work, the degradation in crack-bridging strength of SFRC structural beams with 1.5% by volume of hooked-end steel fibers under different flexural fatigue stress levels is evaluated over the fatigue life using an inverse analysis method. The experimental flexural response is monitored during static and fatigue tests, and compared with the calculated one from the section analysis calculations through the execution of the inverse analysis method. Based on the results, the crack-bridging strength is shown to degrade gradually at different flexural fatigue stress levels over the fatigue life. Further, the residual flexural capacity at the end of fatigue life is shown to be little different from the original capacity obtained in static loading when the flexural fatigue stress level is low.

ADEL, M., H. Yokoyama, H. Tatsuta, T. Nomura, Y. Ando, T. Nakamura, H. Masuya, and K. Nagai, Early damage detection of fatigue failure for RC deck slabs under wheel load moving test using image analysis with artificial intelligence, , vol. 246, pp. 113050, 2021/11/01. Abstract

Reinforced concrete (RC) bridge decks suffer from cracking damages caused by traffic loading and environmental-related defects, such as the alkali-silica reaction (ASR). These require inspections involving measuring crack width and density followed by essential maintenance and repair works, however, there are no signs for fatigue failure. In this study, the out-of-plane shear deformations which cause small delaminations (pits) along surface cracks are proposed as an early indicator for fatigue failure. Thus, un-damaged and ASR-damaged RC deck slabs are tested under moving wheel loading and, using image-recognition for surface cracks detection, the pits along surface cracks are captured using an artificial intelligence (AI) model. The results show that, while both crack and pit density increase over the fatigue life of un-damaged slabs, there is an earlier sudden increase in pit density. In the case of the ASR-damaged slab, surface cracking is almost constant over the fatigue life until a sudden increase just prior to failure. Pit density, however, increases over the fatigue life with an earlier rapid increase before failure. The density of pits along cracks would be, therefore, a significantly earlier indicator of fatigue failure than crack density, offering the potential for more efficient and automatable bridge inspections.

ADEL, M., K. Matsumoto, and K. Nagai, Crack-bridging Degradation and Evolution in SFRC Structural Beams under Variable Amplitude Flexural Cyclic Loading, , vol. 272, pp. 114176, 2021/05/01. Abstract

A few studies have demonstrated a degradation in the performance of the steel-fibers in bridging cracks over the lifetime of steel-fiber reinforced concrete (SFRC) structures but only considered for constant amplitude cyclic loading. However, SFRC structures in practice are subjected to variable amplitude loading, thus their crack-bridging would be influenced by the preceding loading history. This concern has so far remained unexplored. This study presents experimental and analytical flexural cyclic responses of SFRC structural beams under constant and variable amplitudes. The crack-bridging stresses are evaluated using a proposed inverse method based on sectional analysis calculations. Besides, the maximum rebar strain level is correlated with the crack-bridging degradation law, aiming at reflecting the beam’s macroscopic response. The results show that crack-bridging stress increases if the fatigue load level increases, indicating that new fibers play a role in bridging cracks along the crack length. Further, decreasing the fatigue load level leads to an instant decrease in crack-bridging, which is followed by a stabilization as the pullout stress applied to the bridging fibers is reduced. Finally, a diagram of crack-bridging degradation and evolution is proposed regarding the maximum rebar strain, which is supposed to be a valuable tool in the SFRC structural design.