PSI - Issue 82

Asad Zia et al. / Procedia Structural Integrity 82 (2026) 234–238

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A. Zia, I. Holly/ Structural Integrity Procedia 00 (2026) 000–000

While the mechanical properties of TDF-reinforced concrete have been extensively studied, research on its durability characteristics, such as water absorption, carbonation resistance, and linear shrinkage, remains relatively limited (Zia et al., 2023a; Zia and Holly, 2025a). Moreover, most of the available data pertain to standard curing ages, typically up to 28 days (Prokop et al., 2025; Sengul, 2016; Tahwia et al., 2024). Only a few recent studies have examined long-term performance, extending to 120 or even 600 days. The combination of TDFs with industrial fibers, especially hook-end steel fibers, has been shown to enhance both mechanical and durability properties more effectively than using raw TDFs alone (Balea et al., 2021; Zia et al., 2023b; Zia and Holly, 2025b). However, long-term investigations on such hybrid fiber-reinforced concretes are still scarce. Therefore, the present study aims to explore the long-term performance of hybrid TDF-reinforced concrete at an extended curing age of 599 days. Key properties, including water absorption, carbonation depth, and split tensile strength, are experimentally evaluated and discussed to provide insights into the performance of hybrid fiber reinforced concrete. 2. Materials and Tests The experimental program was conducted using locally produced C20/25 concrete from Bratislava, Slovakia, reinforced with industrial hook-end steel fibers (IHFs) and an IHF combined tire-derived steel fiber mix (CTFs). The IHFs used had a length of 30 mm and a diameter of 0.80 mm. The hybrid fiber mix consisted of tire-derived steel fibers (TDFs) blended with 30% IHFs by mass to enhance performance. Details of the TDFs and their characterization can be found in the authors’ previous studies (Zia et al., 2023c). A representative sample of the TDFs used in this work is shown in Fig. 1, illustrating that smaller-sized fibers were dominant in the raw TDF blend. For experimental evaluation, 100 mm concrete cubes aged 599 days were tested for split-tensile strength, water absorption, and carbonation depth. The testing procedures and loading rates were kept consistent for all specimens to ensure reliable comparison of results.

Fig. 1. Tire-derived steel fibers

3. Test outcomes 3.1. Water absorption

The water absorption results of 599-day-old specimens, which were immersed in water for an additional 81 days until reaching an age of 680 days, are presented in Fig. 2. The findings indicate that hybrid fiber-reinforced concrete exhibited superior resistance to water ingress. The lowest water absorption value of 7%, representing a 5.6% reduction compared to the mix containing only industrial hook-end fibers (0.5HIF), was observed for the hybrid mix reinforced with 0.70% combined industrial and tire-derived fibers (0.7CTF). This improvement demonstrates the effectiveness of hybrid fibers in mitigating capillary transport. Although the inclusion of fibers increases matrix heterogeneity, the combined action of industrial and tire-derived fibers disrupts