Effect of constrictivity of gel/capillary pores in concrete on chloride ions migration

Abstract

Abstract Corrosion of steel bars due to chloride ions in seawater migration into reinforced concrete (RC) lining is a major factor affecting the lifetime of subsea tunnels. To improve the safety assessment of existing subsea tunnels, a coupled hydraulic-mechanical-chemical (H-M-C) model is proposed to simulate the chloride ions migration process with hydrostatic pressure in the RC lining of subsea tunnels for obtaining the long-term distribution of chloride ions in the RC lining more accurately. In the H-M-C coupled model, the volume fluid fraction and convection velocity obtained from the bidirectionally coupled hydraulic and mechanic analysis are unidirectionally considered in the analysis of convection, diffusion, and adsorption of chloride ions in the RC lining. In addition, to consider the influence of concrete microscopic pores (e.g., gel pores and capillary pores) size on chloride ion migration, the classic expression of the effective diffusion coefficient is modified by considering a constrictivity factor that varies nonlinearly with the microscopic pore size. Results indicate that in the diffusion zone, the concentration of chloride ions significantly increases with increasing gel/capillary pores radius (rpeak), leading to a rapid non-linear decrease in the service time of the RC subsea tunnel. Afterward, to more clearly ascertain the sensitivity of the effects of constrictivity of gel/capillary pores in concrete on chloride ion migration, the sensitivity analyses are carried out on four sets of parameters (i.e., saturated permeability, van Genuchten parameters, initial saturation, and binding capacity parameters). The results of the sensitivity analyses suggest that the effects of capillary pores radius (rpeak) on the penetration process of chloride ions in the concrete lining of subsea tunnels are more sensitive to the initial saturation (Se) than the vG parameters (a and m). Furthermore, with the increase of capillary pores radius (rpeak), the sensitivity of the chloride ion penetration to capillary pores radius the under different chloride binding conditions is increasing.