A Reactive Transport Model for Concrete Exposed to Cyclic Wetting/Drying: Salt Crystallization, Carbonation, Leaching, and Beyond

Abstract

The durability of concrete structures in marine and salt lake has been of great concern to civil engineering community. As a better alternative to durability assessment and service-life prediction, physical-based models have been widely accepted and employed. Among these models, while either transport behavior or reaction issues of concrete have been essentially stressed, coupling of both transport and reaction remains an open question. A comprehensive reactive transport model, accounting for hydro-ionic chloride transport, chloride binding, salt crystallization, natural carbonation, and leaching, is developed in this work to investigate the evolutions of chloride distribution, phase assemblage, and porosity of concrete exposed to different wetting/drying regimes and different concentrations of immersed salt solutions. Model results show that a high wetting/drying ratio facilitates leaching of concrete, leading to a pronounced increase in porosity and penetration depth of chloride; compared with the filling effect of calcium carbonate on porosity induced by natural carbonation, leaching plays a dominating role in elevation of porosity of cover concrete. NaCl crystals are absent when concrete is exposed to marine environment (3.5 wt.% NaCl); however, in salt-lake environment (10 wt.% NaCl, 15 wt.% NaCl), NaCl crystals precipitate on superficial region of concrete; the higher the exposure time, immersion solution concentration and wetting/drying ratio are, the higher the ratio of [Cl⁻]/[OH⁻] of the pore solution in concrete is, and the deeper the potential corrosion depth is.