Compressive and environmental behavior of prestressed CFRP-confined concrete with coal gangue sand

This paper investigates the axial compressive mechanical properties and environmental benefits of prestressed CFRP-confined coal gangue sand concrete (PCFRP-CGSC) by considering the coal gangue sand replacement ratio (r _GS), prestressing level (m), and concrete strength grade. The results indicate that PCFRP-CGSC specimens exhibit a brittle failure mode characterized by rupture of the CFRP sheet. A higher prestressing level leads to a larger failure area of the CFRP sheet and more severe concrete spalling. Applying prestress significantly enhances the mechanical properties of the specimens; the ultimate bearing capacity (N _u,e) increases by up to 18.7%, while an increase in r _GS causes a slight decrease in mechanical properties, with a maximum reduction of 8.4%. FE analysis reveals that the enhancement effect of m on N _u,e diminishes with increasing concrete strength grade (13.3% increase for C30 vs. only 8.9% for C60) and with increasing cross-sectional size (13.6% increase for 200 mm diameter vs. 9.6% for 800 mm diameter). However, the enhancement is more pronounced for concrete with a high coal gangue sand replacement ratio (at r _GS = 100%, the reduction in bearing capacity narrows from 9.2% without prestress to 7.4% with prestress). Compared with other FRP types, CFRP exhibits higher confinement efficiency, and this advantage is further amplified after applying prestress (a 27.81% increase over GFRP). Based on the experimental data, a calculation formula for the ultimate bearing capacity and a full-range stress-strain constitutive model for PCFRP-CGSC were established, with deviations between predicted, experimental, and simulated values all within 8.0%. Full-range parametric analysis shows that increasing r _GS enhances the confinement effectiveness of the prestressed CFRP.The LCA demonstrates that increasing the prestressing level significantly reduces the carbon emission equivalent per unit bearing capacity (γ) without increasing raw material consumption. When the coal gangue sand replacement ratio is 100%, increasing m from 0 to 0.2 reduces γ from 0.690 to 0.581 kgCO₂-eq/kN, a reduction of 15.9%. This study confirms that prestressed CFRP confinement technology can effectively compensate for the performance deficiencies of coal gangue sand aggregate, achieving synergistic optimization of the mechanical properties and environmental benefits of coal gangue sand concrete.