Xiao, Yu; Sun, Wenjing; Sun, De'an; Tan, Yunzhi; Zhang, Mingzhong; (2025) Mechanical behaviour of marine mud solidified by phosphogypsum-based cementitious materials under seawater wetting-drying cycles. Construction and Building Materials , 476 , Article 141278. 10.1016/j.conbuildmat.2025.141278.

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Abstract

Phosphogypsum‐based cementitious materials (PGCM), produced by alkali-activate of solid waste, such as phosphogypsum and granulated blast furnace slag, offer a sustainable and economically viable solution for stabilizing marine mud. Nevertheless, the resistance of PGCM-solidified marine mud (PGCM-S) to seawater erosion and its durability under seawater wetting-drying cycles, remains inadequately explored. This study aims to investigate the impacts of seawater erosion and wetting-drying cycles on mechanical and microstructural properties of PGCM-S, utilizing unconfined compressive strength (UCS), X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses. The results showed that after 180 days of seawater erosion, the UCS of PGCM-S reached 537 kPa, 16 % higher than that of ordinary Portland cement (OPC)-solidified marine mud (OPC-S). Furthermore, XRD and SEM analyses confirmed the formation of hydration products, including ettringite and C(N)-A-S-H gel, which enhanced the densification and cohesion of PGCM-S. This process mitigated the adverse effects of seawater ions, imparting PGCM-S with superior resistance to seawater erosion compared to OPC-S. Additionally, the UCS of PGCM-S decreased by 61 % and 79 % following 20 wetting-drying cycles with freshwater and seawater, respectively. This suggests that factors, such as ion erosion and salt crystallization, induced by seawater cycling, accelerated the propagation of internal microcracks and the decomposition of hydration products, ultimately reducing the strength of PGCM-S. Moreover, an energy evolution model was applied to quantitatively describe the relationship between deterioration progression and the number of wetting-drying cycles. This model facilitated the identification of three stages of deterioration: emergence, expansion, and acceleration. The findings of this study offer a theoretical application of the comprehensive utilization of PGCM-S as a backfill material in marine engineering applications.

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