Abstract: Cementing loose coral sand to reduce the permeability of island reef formations is one of the key approaches to enhancing freshwater retention in ecological islands. To this end, a permeability test was conducted on zinc sulfate-bonded coral sand, analyzing the effects of varying immersion durations, zinc sulfate solution concentrations, and initial dry densities on its permeability. The durability was verified through dry-wet cycling tests, while the microscopic cementation mechanism was investigated using XRD(X-ray diffraction), SEM(scanning electron microscope), EDS(energy dispersive spectrometer) and CT(computed tomography) scanning. The test results show that: (1) the permeability coefficient of coral sand is reduced by 70.17% to 95.79% after cementation with zinc sulfate. (2) After undergoing 16 dry-wet cycles and 36 hours of cementation, the mass loss rate of the cemented coral sand samples does not exceed 4%, and the variation of permeability coefficient is less than 1.0×10⁻³ cm/s, indicating excellent durability of the samples. (3) Additionally, the reaction between coral sand and zinc sulfate produces dihydrate gypsum and smithsonite, filling the pores of the samples, resulting in a decrease in the average pore-throat radius and coordination number, and a significant reduction in pore connectivity. This technology holds significant engineering application value, as it can be applied to sand fixation and erosion prevention in the initial stage of island reef reclamation, improving foundation bearing capacity and reducing permeability to promote groundwater conservation and eco-island construction.

Key words: zinc sulfate, coral sand, permeability coefficient, dry-wet cycles, reef island