Implications of chloride ion binding for rapid chloride ion resistancetests for concrete

摘要

The durability of reinforced concrete structures exposed to chloride-laden environments is determined,at least in part, by the chloride penetration resistance of the concrete. Many tests have been proposed torapidly evaluate concrete chloride penetrability. One aspect of chloride resistance of concrete that is not normallyconsidered in evaluating the results of these accelerated tests, however, is the chloride ion binding ability of theconcrete. As chloride ions penetrate the concrete matrix, they interact with the pore surfaces and a portion ofthe ions will be bound, either physically or chemically. This binding serves to immobilize some ions and toreduce the free chloride ion concentration of the pore solution. These interactions can occur within a short timeframe. The specific amount of chloride ion binding depends not only upon the chloride ion concentration, butalso upon the properties of the concrete matrix. The impact that chloride ion binding has on the test proceduresand on interpreting the rapid test results are discussed for three separate accelerated test methods that have beenproposed in the literature: 1) the Non-Steady State Migration Test by Tang and Nilsson (1991), 2) the Steady-StateMigration Test by Dhir et al. (1990), and 3) the Chloride Conduction Test by Streicher and Alexander (1995).