Study on performance damage mechanism of cementitious materials under marine environmental temperature cycling

With the rapid development of marine infrastructure, the durability of concrete structures under cyclic temperature variations in marine environments has become a critical engineering challenge. To clarify the thermal damage mechanism of cementitious materials in marine-relevant thermal cycling environments, this research explores the damage processes occurring in cement-based materials subjected to moderate thermal cycles (10°C-60°C), specifically examining ordinary Portland cement pastes with water-to-cement ratios of 0.35, 0.45, and 0.55. The experimental results demonstrate that thermal cycling markedly diminishes the mechanical properties, microhardness, pore structure integrity, morphology, and hydration product composition of cement pastes. By quantifying the coarsening of pores through MIP (such as the increase of P55 capillary pores from 22.07% to 32.02%), and combining nanoindentation analysis of the C-S-H phase transformation (HD-C-S-H decreased from 22% to 14%), the coupling relationship between pore evolution and phase softening under mild thermal cycling was established for the first time.Samples with higher water-to-cement ratios were observed to experience more severe deterioration. Detailed microstructural assessments revealed substantial pore coarsening, characterized by the growth of capillary pores and a concurrent decline in gel pores. Additionally, thermal cycling induced progressive microcracking and the formation of interconnected crack networks within the matrix. Nanoindentation analyses further substantiated these observations, showing a distinct decrease in high-density (HD) C-S-H phases and a significant increase in lower-density (LD and LP) C-S-H phases, indicative of microstructural softening. Collectively, the findings emphasize the critical role of water-to-cement ratios and clarify the underlying mechanisms responsible for thermal degradation in cementitious materials.