Mechanical and seepage characteristics of polyvinyl alcohol fiber concrete under stress-seepage coupling

Abstract

This study presents an experimental investigation of the coupled stress and seepage water pressure loading test conducted on polyvinyl alcohol (PVA) fiber concrete, which had undergone salt attack freeze-thaw (F-T) cycles. This study delves into the influence of the number of salt attack F-T cycles, as well as the magnitude of seepage water pressure, on the triaxial compression seepage mechanical properties and permeability evolution of the specimens. Additionally, the nuclear magnetic resonance (NMR), scanning electron microscope (SEM) and X-ray diffraction (XRD) test results were analyzed, revealing that sodium sulfate solution penetrates the interior of PVA fiber concrete and reacts with cement stone to form ettringite and gypsum, which initially fills and compacts the pore structure. The increased production of such compounds causes pore structure to expand, with the maximum number of mesopores and macropores increasing by 115.5%. Macroscopically, it was observed that the mass and peak strength of the specimens increased at the beginning of the cycle, and the initial permeability decreased. However, the opposite phenomenon occurred after 15 cycles. When seepage water pressure was increased from 1 MPa to 3 MPa, the crack initiation stress, crack damage stress, and peak stress of the specimens decreased by 13.1%, 16.9%, and 15.6% on average, respectively, and the initial permeability increased by 69.3% on average. The deformation process of PVA fiber concrete under stress-seepage coupling loading was divided into five stages, including the initial compaction stage, elastic deformation stage, crack initiation and stable propagation stage, crack unstable propagation stage, and post-peak deformation stage. Correspondingly, the permeability exhibited a rapid decline, followed by a relatively stable phase, a slow rise, a rapid rise, and a continuous increase. Besides, the relationship between permeability and volume strain in compression and expansion stages was clarified.