Durability and microstructural evolution of high-performance ecological geopolymer concrete under low-pressure-salt-erosion-freeze-thaw cycling conditions

Environmental characteristics such as low pressure, high-frequency freeze-thaw cycles, and salt erosion in a plateau region have a significant impact on the mechanical properties and durability of concrete. To reveal the damage mechanism of high-performance ecological geopolymer concrete (HPEGPC) incorporating tunnel spoils, slag, and fly ash (FA) in extreme environments, this study used HPEGPC with 12 % alkali-activated binders (AABS) and a binding material to machine-made sand ratio of 0.36 and ordinary Portland cement concrete (OPCC) with 12.4 % cement and a water-cement ratio of 0.5 to simulate the deterioration process of mechanical properties and durability under the action of low-pressure-salt-erosion-freeze-thaw cycles. The mass, compressive strength, relative dynamic elastic modulus loss rate, microstructure, and pore evolution patterns of HPEGPC and OPCC were analysed using experimental and microscopic tests. The results showed that the HPEGPC was significantly more resistant to freezing and salt erosion than the OPCC in both standard and hypobaric environments. The interfaces of HPEGPC before and after the low-pressure-salt-erosion-freeze-thaw cycles underwent a developmental process from a dense structure with microcracks to microcracks expanding into fracture surfaces and the dispersion of hydration products. The cementitious materials of HPEGPC have a high percentage of non-hazardous and less hazardous pores, and their dense structure results in a high resistance to freezing and salt erosion. In addition, by establishing a damage decay model and damage accumulation model for the compressive strength and relative dynamic elastic modulus, this paper provides theoretical guidance for the application of HPEGPC under low pressure, salt erosion, and freeze-thaw cycle environments of the plateau.