Date palm fibers (from Najran city) as reinforcement in UHPC: Design, performance, and microstructural analysis

To preserve the ecosystem and mitigate pollution, it is vital to appropriately manage the diverse range of agricultural residues arising from date cultivation. The objective of this study is to develop environmentally conscious, economically feasible, and sustainable ultra-high-performance concrete (UHPC) by substituting conventional steel fibers with date palm fibers (DPFs) collected from Najran City, Kingdom of Saudi Arabia. This research entailed generating numerous UHPC specimens with varying proportions of DPF substitution for steel fibers in the range of 0%–100%. The designed mixtures were evaluated in terms of compressive strength, density, water absorption, ultrasonic velocity, flexural strength, compressive stress–strain behavior, compressive energy absorption capability, load–displacement characteristics, and scanning electron microscopy analysis. The results indicated that the compressive strength decreased by 76% compared with the substitution of 100% steel fibers with DPF. In addition, the load–displacement behavior was nearly identical for all UHPC samples except when 100% DPF was used, and the mixture in which 15% DPF was used exhibited remarkable performance. Moreover, the displacement energy absorption capability decreased in the innovative UHPC with increasing amounts of DPF from 0% to 100%, owing to the lower stiffness of the DPF.