PSI - Issue 70

Abutu Simon John Smith et al. / Procedia Structural Integrity 70 (2025) 59–66

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1. Introduction The structural performance of ultra-high performance fiber reinforced concrete (UHPFRC) is greatly influenced by crack development especially when its members are subjected to substantial amount of load or when they are exposed to harsh environmental conditions (Xi et al., 2023). Cracks in UHPFRC members like beam, column and slab can reduce its structural resistance against shear, flexure, deflection and corrosion as reported in literature that cracks can reduce UHPFRC beam’s structural integrity, causing it to have low bearing capacity, high susceptibility to water and chemical attack (Xi et al., 2023; Zhang et al., 2022; Walker, 2024). Due to the effect of cracks on UHPFRC’s structural performance, researchers have opined that incorporating self -healing technology in UHPFRC members can help mitigate the effects of cracks on UHPFRC members (Rathore, 2021; Zhang et al., 2020; Jonkers, 2007). Niu et al. (2021) subjected a UHPFRC specimen reinforced with hybrid steel fibers to flexural loading to investigate its crack propagation behavior; and they reported that crack propagates rapidly in UHPFRC with longer fibers at the initial cracking stage before dramatically dropping in speed. UHPFRC containing coarse aggregate (UHPFRC-CA) has been reported to provide better resistance to crack widening than UHPFRC due to its rocky and hard nature (Smith and Xu, 2024). Yang et al. (2019) also investigated the migration techniques for autogenous shrinkage of UHPFRC-CA; and found that the addition of coarse aggregate in UHPFRC does not only mitigate its shrinkage cracking but help to improve its mechanical and durability properties. Most of the existing studies on UHPFRC- CA beam’s shear performance are more inclined to its resistance against ultimate load and deflection with the analyses of its crack behavior limited to only crack pattern and failure mode, despite its importance in understanding UHPFRC- CA beam’s ductility, nature of stresses, energy absorption and dissipation, neutral axis position and location of cracks that cause failure (Kodur et al., 2018). The lack of much attention on the analyses of UHPFRC- CA beam’s crack behavior by researchers has not only resulted in little findings on its crack behavior but have also impacted experimentation in such a way that beams designed to fail in shear sometimes end up failing in flexure as reported in Smith and Xu (2023). This research work is targeted at investigating the crack behavior of UHPFRC-CA beam subjected to shear loading by comparing its flexural crack with its diagonal crack in terms of crack width, number of cracks formed at failure stage, crack distance from the nearest support, and crack angle, in order to establish how the knowledge of the aforementioned crack performances can be used by researchers during experimental design stage and research analyses.

Nomenclature UHPFRC

Ultra-high performance fiber reinforced concrete UHPFRC-CA Ultra-high performance fiber reinforced concrete containing coarse aggregate

2. Materials and Methods The materials utilized for this study were designed using Funk and Dinger (1994) model as illustrated in Eq. (1); and the mix ratios presented in Table 1 for UHPFRC-CA containing 2% and 3% volume of straight steel fiber ( V f ) were used for the study. ( ) = 100 ⨯ − − (1) where P ( D ) is the volume fraction of the total solids smaller than size D , D is the particle size, D max is the optimum particle size, D min is the smallest particle size, q is the distribution modulus. Four UHFRC-CA beam specimens (see Figure 1) of 1200mmX200mmX100mm size were prepared in accordance with EN 1992-1-1, BS 8110-1, Merchand (2009) and Narayanan and Darwish (1987) design principles to have a cover of 15mm, longitudinal reinforcement ratio ( ρ ) of 0.0373, tensile reinforcement steel of 2Φ20,