A probabilistic framework to justify allowable admixed chloride limits in concrete

Chloride induced corrosion in concrete is a well-known issue. Although numerous researchers have attempted to quantify the chloride threshold limits (C_T) in different concrete systems (with little consensus), the issue of allowable admixed chlorides (C_A) in concrete is still very much unresolved. For example, The C_A limits specified by the American Concrete Institute (ACI) committees range from 0.06 to 1 percent by the weight of cement or cementitious materials. Similarly, the C_A limits published by the State Highway Agencies in the U.S. vary significantly from one State to another (up to 9000 times difference). These significant differences and the variability in the published C_A values can have significant economic and engineering risks. Therefore, it is essential that a standardized approach be developed to minimize these risks. The objective of the present study is to introduce a framework to remove subjectivity and variability in the decision-making process regarding C_A. This paper provides a description of the development of the framework and economic assessment of selecting C_A based on the first-order reliability method (FORM), spatial modeling techniques, and quantitative decision making tools. The proposed framework would help policy and decision makers realize the significant influence of C_A on the corrosion of reinforcing steel in concrete and life-cycle cost of a project, and ultimately assisting them in making unbiased decisions that have scientific underpinnings.