Hybrid aluminum-SHCC/FRCM jacketing for axial strengthening of reinforced concrete columns: Promoting ductile behavior and superior energy absorption

Aging reinforced concrete (RC) columns frequently suffer axial capacity degradation, necessitating sustainable and high-performance retrofitting strategies. This study investigates a novel hybrid strengthening system combining near-surface-mounted (NSM) aluminum bars/angles with a strain-hardening cementitious composite (SHCC)/fabric-reinforced cementitious matrix (FRCM) jacket, complemented by glass fiber reinforced polymer (GFRP) mesh wrapping. Nine RC columns were experimentally tested under axial compression to evaluate load-carrying capacity, displacement ductility, and energy absorption. A validated three-dimensional nonlinear finite element model was developed to replicate the experimental response and facilitate a comprehensive parametric investigation. Results demonstrate that the hybrid aluminum-SHCC configuration significantly enhances structural performance, with ultimate load capacity increasing by up to 78% and energy absorption nearly tripling relative to unstrengthened specimens. The SHCC jacket effectively suppresses cover spalling and enables multiple micro-cracking, while aluminum reinforcement provides ductile confinement and delays failure. The hybrid system consistently outperforms conventional single-mechanism retrofits in strength and ductility and is expected to offer sustainability advantages, given the recyclability of aluminum and the epoxy-free nature of the SHCC/FRCM jacket. These findings establish the aluminum-SHCC/FRCM hybrid jacket as a robust and design-efficient solution for axial column retrofitting, with promising, though yet to be quantified, seismic resilience and sustainability benefits.