Study on microscopic deterioration of cement mortar under mechano-acid coupling erosion based on NMR

To explore the microscopic deterioration mechanism of cement mortar under mechano-acid coupling erosion, low-field nuclear magnetic resonance (NMR) technology was used for non-destructive testing on specimens immersed in acidic solutions with pH values of 3 and 5 and subjected to 10% uniaxial compressive loading. The deterioration mechanism of the specimens was analyzed through pore size distribution, pore sensitivity, and fractal characteristics. The results showed that acid erosion significantly reduced the pore structure stability, large pores were more prone to compaction and form microcracks under loading, leading to an increase in gel pore content and a decrease in average pore radius. Gel pores and capillary pores exhibit different sensitivities to the acid environment. Capillary pores with the T₂ spectrum range of 0.4~2.0 ms showed positive sensitivity, while those in the range of 2.0~10.0 ms showed negative sensitivity. Mechano-acid coupling enhanced the sensitivity of capillary pores and weakened that of gel pores. Both acid erosion and mechano-acid coupling reduced the pore fractal dimension, with the coupling effect leading to the most significant simplification of the pore structure, indicating that loading exacerbates the complexity of the acid-eroded pore system. The research results can provide a reference for evaluating the durability of cement-based materials in complex environments.