Size effect on the fragmentation of plain and steel fiber-reinforced concrete induced by soundless chemical demolition agents

Soundless chemical demolition agents (SCDAs) offer an eco-friendly alternative for concrete dismantling, yet scaling laboratory results to field applications is severely hindered by the size effect and fiber reinforcement. This study investigates the size-dependent fragmentation behavior of plain concrete (PC) and steel fiber-reinforced concrete (SFRC) under SCDA-induced pressure which cover specimen sizes from 150 to 300 mm. A combined experimental and 3D numerical framework was established, utilizing digital image correlation (DIC) and acoustic emission (AE) to track the spatiotemporal damage evolution. Experiments were conducted on PC and SFRC specimens with side lengths of 150–300 mm at a fixed borehole diameter of D = 30 mm. A numerical model validated against the experimental results was subsequently adopted for a parametric analysis at D = 28–34 mm. The simulations reveal a non-monotonic, bell-shaped relationship between specimen size and crack volume within the investigated numerical range, indicating the existence of an optimal specimen size for fragmentation. For PC, this optimal size shifts toward larger values as D increases, with the maximum crack volume reaching 3.12 × 10⁵ mm³ at D = 34 mm. The incorporation of steel fibers markedly suppress crack opening, resulting in a reduction in crack volume of more than 40% in large specimens (≥250 mm) and shifting the optimal fragmentation size toward smaller values. The findings indicate that increasing borehole diameter can effectively enhance fragmentation efficiency in PC. For SFRC, a moderate borehole diameter combined with a denser hole spacing is recommended to compensate for fiber-induced energy dissipation. This study provides quantitative guidance for optimizing SCDA-assisted demolition across different specimen sizes.