Concrete experiences a three-dimensional variable stress state during its service life. To explore the permeability evolution and mechanism under such conditions, a permeability test was conducted on double damage basalt fiber concrete subjected to loading and unloading of twice confining pressure. Pore structure and microstructure of specimens were analyzed before and after permeability test. The findings reveal that the reduction in permeability after primary cycle of confining pressure loading and unloading is significantly higher than that after secondary cycle, and residual deformation is also more pronounced after primary cycle. Both high temperature and salt freeze-thaw cycles induce initial damage to specimens, consequently altering internal pore structure and subsequently impacting initial permeability. Notably, initial permeability decreases in the case of 10th salt freeze-thaw cycles, while it increases under other conditions. The greater the initial extent of damage to the specimen, the higher the permeability damage coefficient and the permeability damage rate. As the confining pressure decreases, the attenuated permeability increases, with the permeability decay rate reaching a significant 88.53 %. Plastic deformation of pores during loading and unloading process cannot be fully reversed, leading to the development of macropores and mesopores into smaller pore sizes, resulting in a remarkable 87.17 % increase in the proportion of micropores. Microscopic observations reveal smaller pores within the matrix, shorter crack lengths, and narrower crack widths in the specimen. The application of confining pressure reduces permeability channels within specimens, ultimately causing a decline in permeability.

中文翻译：

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三维变应力状态下双损伤玄武岩纤维混凝土渗流特性及机理


混凝土在其使用寿命期间经历三维可变应力状态。为了探讨该条件下渗透率的演变及机理，对两次围压加卸载下的双损伤玄武岩纤维混凝土进行了渗透试验。在渗透性试验前后对试件的孔隙结构和微观结构进行了分析。研究结果表明，一次围压加卸荷循环后渗透率下降幅度明显高于二次循环后，残余变形也更加明显。高温和盐冻融循环都会引起样品的初始损坏，从而改变内部孔隙结构，从而影响初始渗透率。值得注意的是，在第 10 次盐冻融循环的情况下，初始渗透率降低，而在其他条件下则增加。试件的初始损伤程度越大，渗透性损伤系数和渗透性损伤率越高。随着围压的降低，渗透率衰减率增大，渗透率衰减率达到显着的88.53%。加卸载过程中孔隙的塑性变形无法完全逆转，导致大孔和中孔向更小的孔径发展，导致微孔比例显着增加87.17%。显微镜观察揭示了基体内较小的孔隙、较短的裂纹长度以及样品中较窄的裂纹宽度。施加围压会减少样本内的渗透性通道，最终导致渗透性下降。