Mechanical properties and damage analysis of polymer fiber reinforced concrete in low vacuum environments based on acoustic emission technology

• The mechanical properties of concrete in low vacuum environments were improved by polymer fiber reinforcement. • Acoustic emission technology was utilized for mechanical damage analysis. • High-content polyethylene fibers and coarse aggregates effectively enhanced confinement and reduced damage. This study addresses the performance degradation of concrete materials in low vacuum environments by investigating the mechanical properties and damage mechanisms of polyethylene (PE) and polypropylene (PP) fiber-reinforced concrete. Two types of polymer fiber-reinforced concrete (PEFC and PPFC) were designed. The effects of varying fiber contents (0.75 % and 1.50 %) and 20 % coarse aggregate substitution on material performance were analyzed under atmospheric drying (AD) and low vacuum drying (VD, 100 Pa) using acoustic emission (AE) technology and SEM. The findings reveal that PEFC exhibits ductile failure under flexural loads, while PPFC undergoes brittle fracture. The low vacuum condition enhances fiber-matrix interfacial bonding, increasing energy dissipation and AE signals during fiber debonding and pullout, promoting strain-hardening in PEFC. Higher fiber content improves peak load and hardening behavior, with PE fibers and coarse aggregates forming a robust confinement network driven by slow fiber pullout. Conversely, PP fibers show weaker synergy, failing mainly through rapid pullout and fracture. Energy absorption capacity and AE ringing counts correlate strongly with loading conditions, highlighting the importance of material composition and environmental factors. The b-value effectively captures damage characteristics, providing early warning indicators, with shorter warning times under VD. AF-RA images suggest VD accelerates shear crack formation. Optimizing PE fiber content (1.50 %) and combining it with coarse aggregates offers significant improvement in low vacuum concrete performance, providing insights for applications in high-speed maglev systems and space structural engineering.