A Multiscale Computational Framework for Predicting Chloride Ingress and Reinforcement Corrosion Initiation in Tropical Marine Concrete

Chloride-induced reinforcement corrosion remains the dominant durability failure mechanism for coastal reinforced concrete infrastructure in tropical marine environments, yet predictive models for corrosion initiation time in Nigerian coastal structures lack the multiscale physical basis needed to account for the combined effects of tropical temperature cycling, episodic tidal exposure, and locally variable concrete microstructure. This study develops a multiscale computational framework for predicting chloride ingress and corrosion initiation in tropical marine concrete, integrating molecular dynamics simulations of chloride ion transport in calcium silicate hydrate gel pores with mesoscale lattice Boltzmann modelling of chloride diffusion in the concrete pore network and macroscale finite element modelling of structural member exposure and service life. Molecular dynamics simulations were calibrated using neutron scattering data on calcium silicate hydrate pore structure, and mesoscale model parameters were validated against mercury intrusion porosimetry measurements on Nigerian coastal concrete cores. The macroscale service life model was validated against a 10-year chloride profile database from structural elements at three coastal sites in Lagos and Delta States in the South West and South South geopolitical zones. Results demonstrate that the multiscale model predicts chloride threshold depth with a mean absolute error of 11 percent, outperforming single-scale Fickian diffusion models which showed 28 percent mean absolute error on the same validation dataset. The model correctly captured the non-Fickian chloride binding behaviour attributed to Friedel's salt formation in fly ash-blended cements. The framework is applied to generate service life design charts for cover depths in XS2 and XS3 marine exposure classes under Nigeria's tropical coastal climate. Keywords: chloride ingress, corrosion initiation, multiscale modelling, tropical marine concrete, service life.