Experimental and theoretical analysis of auxetic cementitious composite: A comparative study with recycled and virgin steel fibers

This research investigated the development of auxetic cementitious composites (ACC) reinforced with recycled steel fibers (ranging from 0 % to 2 % volume in increments of 0,5 %). The mechanical and auxetic properties of these composites were compared to an ACC reinforced with virgin steel fibers. Additionally, a theoretical model was developed to understand stress-strain behavior, specific energy absorption, and their corresponding measured errors. This novel material has the potential to significantly impact global infrastructure resilience, offering solutions for seismic protection, impact absorption, and collision mitigation. Additive manufacturing techniques were employed to produce the ACCs. The study utilized an Ultra-High Performance Concrete (UHPC) formulation tailored for both high strength and workability. The ACCs underwent mechanical testing and physical characterization, including measurements of Poisson's ratio. The results revealed that ACCs reinforced with recycled steel fibers achieved the desired properties, comparable to those of the virgin fiber-reinforced ones. Notably, Poisson's ratio reached-1,12, signifying pronounced auxetic behavior. This implies that under longitudinal compression, the specimen would contract in the transverse direction by up to 112 % of its vertical strain, exceeding the typical strain recoveries (15-30 %) of conventional construction materials like concrete and steel. Furthermore, the specific deformation energy absorption of the auxetic specimen reached 0,92 cm3J. This research successfully developed and characterized auxetic cementitious composites using recycled steel fibers, contributing to the material's sustainability and offering a promising solution for global challenges in infrastructure resilience and energy efficiency.