PSI - Issue 68

Rami Hawileh et al. / Procedia Structural Integrity 68 (2025) 259–265 R. Hawileh et al./ Structural Integrity Procedia 00 (2025) 000–000

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HSC is its poor performance under fire conditions, primarily due to the occurrence of explosive spalling (Assad et al., (2023); Karaki et al., (2021), (2024); Ngo et al., (2013); Nguyen et al., (2018)). Polypropylene (PP) fibers offer several advantages when incorporated into concrete, particularly in enhancing its performance under high-temperature conditions (Park et al., (2019); Sciarretta et al., (2021)). One of the primary benefits of PP fibers is their ability to mitigate explosive spalling during elevated temperatures. When exposed to heat, the fibers melt, creating voids that allow steam pressure to escape. This significantly reduces the risk of spalling (Li & Zhang, (2021)). Additionally, the inclusion of PP fibers improves the tensile strength and ductility of concrete, contributing to overall durability (Alsalman et al., (2017)). These fibers also enhance the workability of concrete mixtures, facilitating better mixing and placement (He et al., (2021)). Being lightweight, PP fibers help decrease the overall weight of concrete elements without compromising strength (Lande & Thorstensen, (2023)). Unlike steel fibers, PP fibers do not corrode, making them suitable for applications where corrosion resistance is crucial (J. Yang et al., (2019)). Economically, PP fibers are generally more cost-effective than some other synthetic fibers, providing an attractive option for enhancing concrete performance (Ding et al., (2016)). Furthermore, they increase the flexural strength of concrete, making it more resistant to bending forces (Bangi & Horiguchi, (2012)). Their use can also contribute to more sustainable construction practices by improving the longevity of concrete structures, potentially reducing maintenance and repair needs (Peng et al., (2006)). Lastly, PP fibers are versatile and can be employed in various concrete applications, including pavements, precast elements, and shotcrete, adapting well to different mixing processes and environmental conditions (Kodur et al., (2003)). In a study performed by Yang et al. (2018), a comparison between high-strength fiber-reinforced concrete (HSFRC) and HSC beams under flexural loading revealed several key insights. HSFRC beams demonstrated superior crack control, with narrower cracks and more resistance to crack propagation compared to HSC beams. While HSC beams failed suddenly due to crushing in the compression zone, HSFRC beams exhibited a more gradual failure as steel fibers pulled out of the concrete matrix. Crack stiffness in HSFRC beams was significantly higher, especially at higher rebar ratios, where the ductility of HSFRC beams also improved, unlike the brittle behavior seen in HSC beams. Although HSC beams showed higher toughness at low rebar ratios, HSFRC beams surpassed them in flexural toughness at higher rebar ratios, making HSFRC more effective for energy absorption and durability in reinforced structures (Yang et al., (2018)). Explosive spalling of concrete causes concrete fissures, loss of concrete cover, and fire exposure of steel reinforcement, all of which degrade building load-carrying capability. Based on earlier research, the emergence of "moisture clogs" and the accumulation of water vapor pressure within the pores of concrete are recognized as key factors influencing the occurrence of explosive spalling in concrete. When concrete exhibits adequate permeability, the release of water vapor can happen before substantial pressure accumulates, effectively reducing the likelihood of explosive spalling (Li et al., (2019)). Permeability is a factor that assesses the capacity of porous materials to allow the movement of fluids in response to pressure differences. It stands as a crucial determinant in regulating the rate at which water vapor is transported and in the build-up of pore pressure within concrete structures. In a comparative study done by (Li et al., (2019)), various compositions of PP and steel fibers were subjected to elevated temperatures to evaluate their effects on explosive spalling. The findings demonstrated a positive correlation between the dosage of steel fibers and the severity of explosive spalling; as the amount of steel fibers increased, so did the spalling severity. On the other hand, the introduction of PP fibers effectively reduced the effect of explosive spalling. However, even with higher dosages (4 kg/m³ and 6 kg/m³), the PP fibers did not bridge cracks resulting from aggregate expansion and cement paste drying. Instead, significant radial cracks developed, causing the specimens to fragment into multiple sections (Li et al., (2019)). This study aims to investigate the effect of using PP fibers on the performance of HSC under elevated temperatures. Standard cylinders are preheated to various temperatures and their residual compressive strength is evaluated. The overall behavior and extent of spalling are observed and evaluated.