Diffusion vs. concentration of chloride ions in concrete.

PDFTech ReportBDK79-977-03Reinforced concreteDurabilityChloridesSeawaterBridge substructuresConcentration (Chemistry)IonsThermal diffusionUnderwater structuresCementFloridaFlorida. Dept. of Transportation. Research CenterPresuel-Moreno, Francisco J.Arias, WendyEchevarria, VictorShill, ScottWu, Yu-YouFlorida Atlantic University. Dept. of Ocean EngineeringUS Transportation CollectionThis investigation was performed to gain insight and assist in determining the long-term durability ofreinforced concrete structures where the external chloride concentrations are different than those typicallyobserved at the permanently immersed, tidal, and splash zones of partially immersed bridges. Insight intothe diffusion properties of the concrete at these locations may lead to changes in the state\ue2\u20ac\u2122s policy oncorrosion control of reinforced concrete structures. Structures at locations where the external chlorideconcentrations may have spatial, let alone time, variation are of interest. Additionally, at elevations abovethe splash zone, the amount of chlorides deposited would be lower, and the concrete close to the surface notsaturated. Similarly, the section of structures that extend inland would be subjected to seawater spray andthe concrete close to the surface would usually not be water saturated.The performance in regard to chloride penetration of specimens made with three base compositions (thesupplementary cementitious materials were: 20% fly ash; 20% fly ash + 8% silica fume; and 50% slag),and water-to-cementitious ratios of 0.35, 0.41, or 0.47 were investigated here. Experiments investigatedthe diffusion of chloride ions into concrete samples that were exposed in scenarios that simulated thesplash, tidal, and immersed portions of a marine structure, with the solution ranging from brackish water to10% seawater, to seawater. Bulk diffusion experiments were conducted in solutions that contained 0.6%,3%, and 16.5% NaCl. Rapid migration tests and resistivity measurements were also performed severaltimes over two years, and the non-saturated migration coefficient vs. resistivity values were correlated. Theapparent diffusion values from the bulk diffusion tests were correlated to corresponding equivalentresistivity values. Samples exposed for over 18 years, simulating tidal exposure were also part of thisinvestigation. The field component investigated the chloride concentration as a function of elevation. Otherexperiments were conducted which involved controlling the degree of saturation and exposing a designatedsurface to finely ground salt. These apparent diffusion results were compared to the apparent diffusionresults from specimens in which the chloride transport was due to natural marine atmosphere