Effect of Admixed and External Chlorides on the Transport of Chlorides in Concrete

The binding of chlorides by the hydration products of cement in concrete is one of the factors that affects the rate of chloride ingress, which in turn can influence the time to corrosion initiation of reinforcing steel in concrete. Theoretical assessments of the influence of chloride binding on the chloride ingress and service life estimates are often based on empirically developed chloride binding isotherms to account for the interaction between the concrete matrix and external chlorides. While being useful, these assessments disregard the binding influence of admixed chlorides that may be present in the concrete from the early stages of hydration. It is suspected that the presence of free admixed chlorides can influence the diffusivity of chlorides in concrete. This work focuses on determining the binding behavior of admixed chlorides and proposes a modified diffusion model that takes chloride binding from admixed and external chlorides into consideration. Keywords: admixed chlorides; chloride binding capacity; external chlorides; finite elemental analysis.