Chloride diffusion in concrete with silica fume under early-age exposure

This study investigates chloride diffusion in marine concrete structures during early-age curing, specifically slip-formed caissons and cast-in-place quay walls where concrete experiences chloride ingress before achieving full strength. The research examines how early-age exposure affects long-term chloride diffusion coefficients in conventional concrete and silica fume-modified concrete. Early-age chloride exposure critically compromises marine concrete durability, yet standardized testing typically evaluates concrete at 28 days or later. Understanding this impact is essential for accurate service-life prediction, but conventional concentration profile methods are labor-intensive and expensive, necessitating more efficient assessment techniques. We employed a rapid colorimetric technique under natural diffusion conditions to determine apparent chloride diffusion coefficients () for concrete mixes with water-cement ratios of 0.3, 0.4, and 0.5, both with and without 10% silica fume. The study compared diffusion coefficients across multiple exposure intervals from casting (0 days) to 1, 3, 7, 28, and 180 days. Results show early-age exposure significantly elevates long-term : for plain concrete, 0−180 days exposure increased by 58% compared to standard 28−180 days exposure. The colorimetric method revealed an even more pronounced effect (235% increase) for silica fume concrete. Diffusion coefficients for 0−1-day intervals were approximately 82 times higher than 0−180-day intervals. Silica fume reduced by 65% for 0−180 days and 81% for 28−180 days compared to control mixes. The findings demonstrate that early-age chloride exposure substantially impacts long-term durability, with the colorimetric method providing a more conservative assessment than traditional methods. Delaying exposure by just three days significantly improves performance, with 3−180 days exposure showing only 8% higher than standard exposure. These results emphasize the necessity of accounting for early-age chloride ingress in coastal infrastructure design and validate silica fume as an effective material for enhancing marine concrete resilience.