2019 CSCE Annual Conference - Laval (Greater Montreal)

2019 CSCE Annual Conference - Laval (Greater Montreal) Conference

Relationships between free and water-soluble chloride concentrations in concrete

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Mr. Mehdi Shafikhani, McMaster University (Presenter)
Dr. Samir Chidiac, McMaster University

Corrosion of metals embedded in concrete is pivotal when studying durability of reinforced concrete structures. Chloride ions present in the vicinity of steel reinforcements tend to initiate and/or accelerate their corrosion.  Chloride ions are either bound physically or chemically to the cementing material or free in the pore solution, and only the latter can be transported. Free chloride concentration Cf was measured by pore solution expression method however it is found to be very difficult in low water to cement ratios. Water extraction method is used to measure water-soluble chloride concentration Cw in concrete, however the results are found to be highly depend on liquid to solid ratio, temperature, size of particles, and extraction method. The aim of this study is to experimentally evaluate current standard test methods, standard test method for acid-soluble chloride (ASTM C1152-04 [1]) and water-soluble chloride (ASTM C1218-15 [2]) in mortar and concrete, and the relationships between Cw and Cf.

Sixteen concrete mixes containing Portland-limestone (CSA type GUL) cement with and without supplementary cementing materials including silica fume and/or ground granulated blast-furnace slag were subjected to a non-steady state migration experiment. The acid-soluble and water-soluble chloride concentration at different layers of the samples were determined at 84 days based on ASTM C1152-04 [1] and C1218-15 [2] test methods, respectively. Freundlich isotherm was employed along with total chloride concentration data to determine free chloride Cf values. Linear relationships between Cw and Cf were observed with a significant dependence on binder composition.