Influence of material and design parameters on the mechanical performance and specific energy absorption of auxetic HPCC

This research systematically investigates the mechanical performance and specific energy absorption (SEA) of auxetic cementitious composites, focusing on the influence of fiber type, length, and specimen scale. The study utilized a high-performance cementitious composite (HPCC) and incorporated three fiber types: recycled steel (rSF), polypropylene (PF), and glass (GF), each at two distinct lengths. To assess the scale effect, three auxetic specimen dimensions were evaluated (150 mm,200 mm, and 250 mm overall scales). The stress-strain behavior in compression and SEA were measured for all fiber-reinforced auxetic specimens. Experimental results demonstrated that rSF consistently provided superior mechanical properties and the highest SEA, reaching a maximum of ≈ 0.45 J/cm³ (in 150 mm specimens). This performance signifies a substantial enhancement in toughness compared to the brittle unreinforced reference. PF offered high ductility but intermediate strength, while GF composites exhibited minimal mechanical benefits. The central finding is that the efficacy of fiber reinforcement is highly scale-dependent. As the internal auxetic cell size increases, the resulting crack width exceeds the critical anchorage length of shorter fibers, leading to a substantial loss of SEA performance. The study concludes that energy absorption is dictated more by the internal cell geometry than by the overall specimen scale, underscoring that optimal fiber selection must be governed by the specific cellular design to guarantee desired toughness. • Fibre type, length and specimen scale influence mechanical performance of auxetic high-performance cement composites. • Fibre addition, notably 13 mm recycled steel, improved mechanics and SEA in auxetic specimens. • Internal ellipses size is the key parameter for energy absorption, surpassing specimen size effects. • Ellipse size affects crack bridging, making optimal fiber length and type crucial for performance.