Title:
A Collaborative Study for the Development of a Standard Critical Chloride Threshold Test Method
Author(s):
Ceki Halmen; Goran Adil
Publication:
CRC
Volume:
Issue:
Appears on pages(s):
Keywords:
reinforced, concrete, corrosion, steel, carbon dioxide, chlorides,
DOI:
Date:
1/11/2020
Abstract:
One of the most important and costly deterioration mechanisms affecting reinforced concrete
structures is the corrosion of the embedded steel reinforcement. Steel reinforcement is unlikely to
corrode in good quality concrete due to the formation of a thin protective oxide film (passive
film) in the highly alkaline concrete pore solution [1]. Steel bars remain passive as long as the
high alkalinity of concrete pore solution is sustained. However, the passive film can break down
causing initiation of active corrosion due to two major causes; presence of chlorides at the steelconcrete interface above a threshold amount and carbonation [2]. Carbonation is the decrease of
alkalinity in concrete environment and is caused by reactions of carbon dioxide (CO2) penetrating
into the concrete from the atmosphere. Chlorides may penetrate concrete from external sources
such as seawater and deicing salts or may be admixed with concrete ingredients during concrete
production. The amount of chlorides at the steel-concrete interface necessary to initiate corrosion
is referred to as the critical chloride threshold (Ccrit) [3, 4]. The Ccrit for steel reinforcement
in concrete is thought to be a distribution of values dependent on the quality of the constructed
concrete, constituent materials and their proportions, exposure environment, and the laboratory
test method used.
Over the last several decades chloride-induced corrosion of reinforcement in concrete has
been studied extensively and numerous laboratory test methods have been developed to quantify
the Ccrit [5]. A literature survey reported that 29 authors published a wide range of different Ccrit
values based on over 20 different test methods, criterion, and/or materials. The Ccrit data collected
and published with these different laboratory test methods in the literature exhibits significant
1
scatter and varies between 0.1 and 3.1% by weight of binder [4]. Important differences between
the test methods used and differences between the physical and chemical properties of materials
used in different studies contribute to the large scatter of published data. Development of a standard
laboratory critical chloride threshold test method to decrease the variability in the reported Ccrit
data is necessary. This study developed a framework for a standard laboratory test method and
evaluated two different test methods developed within this framework by two different groups.
Test methods were evaluated through a round robin test with participation of multiple laboratories.