Meso-structural insights into post-peak behaviors of micro steel fiber-reinforced recycled aggregate concrete using in-situ 4D CT and DVC techniques

Amid rising concerns over sustainability, recycled aggregate concrete (RAC) has emerged as a key focus in the construction industry. This study investigates the post-peak behavior of micro steel fiber-reinforced RAC (MSF-RAC) using in-situ 4D computed tomography (CT) and digital volume correlation (DVC) with fiber dosages of 1.0 %, 2.0 %, and 2.5 %. Results demonstrate that micro steel fibers enhance RAC's toughness and ductility, reducing crack volume by 12.3 % and crack width by 28.7 %. Fiber bridging is shown to control crack propagation and redistribute stress, with 4D CT and DVC revealing concentrated strain at fiber aggregation points that stabilize the matrix and promote ductile failure. These findings provide a theoretical foundation for optimizing MSF-RAC designs and advancing its sustainable applications.