Ball Milling–Alkali Synergy: Mechanochemical Degradation of Phenolic Resin and Its Impact on the Performance Evolution of Rock Wool-Based Alkali-Activated Cementitious Composites

Rock wool trim waste (RWTW) presents considerable recycling difficulties due to the release of toxic volatiles from phenolic resin binders during pyrolysis, which also hinders its effective utilization in rock wool-based alkali-activated cementitious composites (RWACCs). Traditional thermal and chemical resin removal approaches are energy-consuming, produce secondary pollutants, and can diminish the aluminosilicate reactivity of RWTW. This study introduces an innovative mechanochemical ball milling pretreatment aimed at selectively breaking resin C−O bonds while maintaining the integrity of the mineral phase, thus facilitating eco-friendly and efficient RWTW recycling. By applying different milling durations (30–120 min), the properties of RWTW particles were systematically characterized through granulometry, XRD, SEM, and FT-IR. The hydration kinetics, compressive strength, and microstructure of RWACC pastes were thoroughly examined. Key findings confirm that 120 min is the optimum ball milling duration, as validated by weighted sum analysis. This duration yielded a median particle size (D50) of 7.15 μm, significantly increased reactivity (evidenced by a 28-day activity index of 85.3%), and outstanding mechanical properties, achieving flexural and compressive strengths of 15.73 MPa and 97.27 MPa, respectively. The mechanochemical process successfully encapsulated organic residues within the geopolymer matrix, preventing toxic emissions. This synergistic approach between resin degradation and enhanced reactivity demonstrates a viable route for the industrial-scale valorization of RWTW. It significantly contributes to the circular economy objectives in the construction sector.