Innovative confinement of concrete using passive, active, and hybrid FRP–SMA systems: Experimental evaluation of mechanical performance

Concrete is recognized for its exceptional compressive strength; however, it exhibits inherent brittleness when subjected to uniaxial compressive stress, which restricts its structural resilience and ductility. Improving these characteristics is essential for sophisticated engineering applications, and lateral confinement has proven to be an effective strategy for reducing brittle failure and enhancing energy absorption. Confinement can be implemented in either passive or active forms: passive confinement involves the use of internal transverse reinforcements (such as spirals, stirrups, and hoops), external steel spirals, steel jackets, or fiber-reinforced polymer (FRP) jackets, while active confinement entails the application of pre-stressing in transverse directions before loading. Recent advancements, including the utilization of shape memory alloys (SMAs) for active confinement and hybrid systems that integrate FRP layers with SMA spirals, show significant potential for optimizing concrete performance. This research investigates the impact of various factors on the behavior of confined concrete cylinders, focusing on confinement methods (passive, active, and hybrid), confinement pressure, concrete compressive strength, types of FRP, and three techniques for applying hybrid confinement (conventional, groove, and talc powder methods). Twenty-four cylindrical specimens (152 × 305 mm) were subjected to uniaxial compressive loading. The results indicate that confinement markedly improves peak strength, ultimate stress, strain capacity, and energy absorption while decreasing dilation compared to unconfined specimens. Among passive methods, CFRP layers are particularly effective in enhancing strength, whereas steel spirals are superior in improving strain capacity and energy absorption. Active and hybrid confinement methods surpass passive techniques, with the talc powder method for hybrid confinement yielding the most favorable overall performance. These results highlight the advantages of integrating passive and active confinement to enhance the mechanical properties of concrete, offering valuable insights for advanced structural design. • Proposing innovative active and hybrid confinement techniques using FRP and SMA materials. • Exploring the integration of SMAs for active confinement in concrete cylindrical specimens. • Evaluating the superior performance of active and hybrid confinement methods compared to passive techniques. • Highlighting the potential of hybrid confinement using talc powder to optimize concrete's mechanical properties. • Comparing the effectiveness of groove and conventional methods for applying hybrid confinement.