Research Progress on Static-Cracking Demolition of Reinforced Concrete: Reinforcement Restraint, Directional Cracking and Engineering Application

To address the low demolition efficiency of static-cracking technology in reinforced concrete structures under sensitive environments, which is primarily caused by the reinforcement restraint effect, this paper presents a narrative review based on a systematic literature-search procedure and case-study compilation. Starting from the hydration-expansion mechanism of static-cracking agents, the work systematically examines how critical parameters—including borehole diameter, spacing, water-to-agent ratio, and reinforcement ratio—affect cracking performance. Three representative published engineering projects are reviewed to extract empirical design parameters and illustrate typical application scenarios under sensitive-environment conditions. Literature synthesis and case-study compilation indicate that static cracking can fully split structural members when the reinforcement ratio is ≤0.8%; local steel pre-cutting or densified boreholes are required when the reinforcement ratio ranges from 0.8% to 1.2%; and the cracking agent becomes almost ineffective when the reinforcement ratio exceeds 1.5%. Under standard laboratory conditions at 25 °C with a water-to-agent ratio of 0.3, expansion pressure at the borehole bottom reaches 80% of orifice pressure when drilling depth is less than 1.5 m, and declines to 50–60% when the depth is between 2 m and 3 m. As reported in the literature, grooves machined on borehole inner walls can reduce crack initiation pressure by 30–50%, with directional deviation remaining within 10°. It is suggested that three technical paths may hold promise for breaking the existing application limits of static-cracking technology: developing composite expansive materials, deploying lightweight digital-twin design schemes, and formulating multi-process collaborative demolition workflows.