PSI - Issue 68

Asad Zia et al. / Procedia Structural Integrity 68 (2025) 231–237 A. Zia et al. / Structural Integrity Procedia 00 (2025) 000–000

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4. Discussion and Conclusions 4.1. Discussion

The experimental results for water absorption, compressive strength, and split tensile strength provide valuable insights into the performance of fiber-reinforced recycled aggregate concrete (RAC), specifically with the inclusion of industrial steel fibers (ISFs) and end-of-life tire fibers (EFs). These findings hold significant implications for enhancing the durability and crack resistance of concrete structures such as canal linings, beam-column joints, and rigid pavements, while simultaneously advancing sustainability goals. (A) Water Absorption and Durability: The water absorption results indicate that both ISFs and EFs contribute to reducing the water absorption of RAC, which is crucial for improving the durability of concrete in moisture-sensitive applications. The 6IS7R mixture, containing industrial steel fibers, exhibited a 12% reduction in water absorption compared to plain concrete, while the 6EF7R mixture, with end-of-life tire fibers, showed a 3% reduction. This decrease in water absorption is likely due to the ability of the fibers to disrupt capillary pathways within the concrete matrix, reducing porosity and limiting moisture ingress. Lower water absorption rates directly enhance the long-term durability of concrete, particularly in structures exposed to water and harsh environmental conditions, such as canal linings. These improvements also mitigate the risk of cracking due to freeze-thaw cycles and chloride ingress, making fiber-reinforced RAC a viable option for sustainable infrastructure. (B) Compressive Strength and Energy Absorption The results for compressive strength demonstrate that the inclusion of both ISFs and EFs has a negligible effect on the overall compressive strength of RAC. However, the compressive total energy (CTE) and compression toughness index (CTI) results reveal significant enhancements in energy absorption and toughness. The CTE for 6IS7R increased by 6% and for 6EF7R by 1%, while the CTI values showed increases of 27% and 16%, respectively, compared to plain concrete. These improvements in toughness are critical for applications subjected to dynamic loads and high-stress environments, such as beam-column joints and rigid pavements. The increased energy absorption capacity indicates that fiber-reinforced concrete can better resist crack propagation under compressive loading, thereby enhancing the lifespan and structural integrity of concrete elements. The use of EFs, in particular, offers a sustainable alternative to industrial fibers, aligning with the need to reduce CO2 emissions and the environmental impact of fiber production. (C) Split Tensile Strength and Crack Resistance The split tensile strength results highlight a notable improvement in the tensile properties of RAC when reinforced with fibers. The 6IS7R mixture exhibited a 46% increase in split tensile strength compared to plain concrete, while 6EF7R showed a 10% improvement. This enhancement in tensile capacity is crucial for improving crack resistance in concrete structures. In applications such as canal linings, where tensile stresses from water pressure can lead to cracking, or in beam-column joints, where high tensile forces are encountered, the use of fiber-reinforced concrete can significantly reduce crack formation and propagation. Additionally, the increased tensile strength also benefits rigid pavements, which are prone to cracking due to repeated traffic loads. The higher tensile strength of fiber-reinforced concrete, especially with ISFs, provides better resistance to cracking and enhances the structural performance of pavements. (D) Sustainability Implications From a sustainability perspective, the use of end-of-life tire fibers (EFs) is particularly promising. While ISFs offer superior mechanical performance, the environmental impact associated with their production is considerable due to high energy consumption and CO 2 emissions. EFs, derived from waste materials, offer a sustainable alternative by repurposing waste tires, which not only reduces landfill waste but also contributes to lowering the carbon footprint of concrete production. Although the performance of EFs is slightly lower than that of ISFs, the moderate improvements in water absorption, compressive toughness, and split tensile strength indicate that EFs can still provide substantial benefits in enhancing the durability and crack resistance of RAC. For projects prioritizing sustainability, such as green infrastructure initiatives, the use of EFs in concrete offers an environmentally friendly option without compromising structural integrity.