Experimental study on dynamic mechanical properties of concrete for hydraulic dams with PVA fiber

To investigate the improvement effect of PVA fibers on the dynamic mechanical properties of concrete in water conservancy dams under dry-wet cycles and impact loads, C40 plain concrete and PVA fiber concrete were selected as the research objects. 0 to 120 dry-wet cycle tests and SHPB dynamic compression tests under different air pressures of 0.2 to 0.5 MPa were carried out. The evolution laws of damage degree, stress-strain curves, peak stress, toughness, energy dissipation and fracture fragmentation morphology of the specimens were systematically analyzed to reveal the strengthening and toughening mechanism of PVA fibers.The results show that the increase in the number of dry-wet cycles and the increase in impact pressure significantly affect the mechanical properties of concrete. The damage degree of both types of concrete increases with the increase in the number of cycles, and the peak stress and toughness continuously decrease.Under the same conditions, the damage degree of PVA fiber concrete is significantly lower than that of plain concrete. Its peak stress, toughness and dissipation energy are all higher than those of plain concrete, and the rate of performance degradation is slower.As the number of dry-wet cycles increases, the internal cracks in the plain concrete rapidly expand and penetrate, showing obvious brittle disintegration characteristics. Meanwhile, the PVA fibers form a three-dimensional network structure in the matrix. Through bridging crack resistance, stress dispersion and energy absorption and toughening effects, they inhibit crack initiation and propagation, delay damage accumulation, and transform the failure mode from brittle fracture to ductile progressive failure.Research has confirmed that PVA fibers can effectively enhance the dry-wet cycle resistance, dynamic bearing capacity and impact toughness of hydraulic concrete, significantly improving its durability and structural safety in complex service environments. This provides experimental basis and theoretical support for the application of high-performance fiber concrete in water conservancy projects.