Conference Agenda

This study analyzes the influence of fiber orientation on the scatter of fatigue life in fiber-reinforced concrete (FRC). For this purpose, prismatic specimens with three fiber contents were manufactured and subsequently subjected to bending fatigue under identical relative stress levels. Fiber orientation and distribution were characterized using micro-computed tomography prior to testing. The results show that fiber orientation parameters (mean angle relative to the longitudinal axis and orientation factor along this axis) clearly correlate with fatigue life. Specimens with better-aligned fibers endured a greater number of cycles, and this relationship was observed both in the combined analysis of all series and in separate studies. Furthermore, fiber orientation affects the rate of fatigue damage propagation. These findings contribute to reducing uncertainty in fatigue tests, optimizing fatigue design criteria.

Most classical formulations of S-N fatigue curves in concrete assume that, when the maximum cycling is equal to the static strength of concrete, the element fails during the first cycle. However, this assumption ignores that the concrete strength depends on the load application rate. In this work, an S-N curve expression is proposed assuming that failure for N= 1 occurs when the dynamic strength of concrete is reached, which depends on the frequency and the stress range. To validate it, the new equation is fitted to several sets of experimental data. The results reveal that this curve reflects more accurately the test results, with higher R2 coefficients than the classical S-N curves.

This contribution focusses on the fatigue damage assessment of concrete samples using wide-range experimental data. Within this study, the concrete samples were tested under various loading conditions: static fracture, low-cycle and high cycle fatigue. This allowed us to obtain static load-CMOD, S-N curves for fatigue lifetime assessment, and mainly CMOD-N curves showing the stiffness degradation at high-cycle fatigue load regime. The low-cycle fatigue resistance is assessed from stepwise load-CMOD curves with increasing CMOD value every step, allowing to analyse damage growth between each load cycle. This study investigates the fatigue resistance of concrete samples by combining all of these experimental data and could provide useful recommendation for structural design.

This study explores the influence of sodium gluconate (SG), an organic electrolyte, on the rheology and mechanical properties of ultra-high-performance fiber-reinforced concrete (UHPFRC). SG was incorporated at varying dosages (0.03%-0.15%) to assess its effects on workability, hydration, porosity, and fracture behavior. Key findings demonstrate that SG effectively retards hydration by inhibiting gypsum dissolution and AFt formation, resulting in significant delays in setting time—up to 295% with higher SG content. Furthermore, increased SG dosages improved workability, with a slump diameter increase of up to 56%, facilitating better fiber distribution and bonding. No major chemical changes were observed in the concrete matrix; however, SG decreased macropores (> 10μm) and increased micropores (< 0.1μm), which contributed to enhanced mechanical performance. Compressive strength rose by 9.5%, and flexural cracking initiation improved by 38% for Mix-0.15. Residual flexural strengths also showed substantial increases (up to 38%), attributed to improved fiber-matrix adhesion. These findings highlight SG’s potential to improve UHPFRC’s mechanical properties and durability, making it a promising additive for high-strength construction applications.