CHLORIDE BINDING IN CONCRETE EXPOSED TO SEA WATER AND SALT SOLUTIONS

Author(s): H. Justnes, K. De Weerdt and M.R. Geiker
Paper category: Proceedings
Book title: Proceedings of CONSEC13 Seventh International Conference on Concrete under Severe Conditions - Environment and Loading Volume I
Editor(s): Z.J. Li, W. Sun, C.W. Miao, K.Sakai, O.E. Gjørv, N.Banthia
ISBN: 978-2-35158-124-7
e-ISBN: 978-2-35158-134-6
Publisher: RILEM Publications SARL
Publication year: 2013
Pages: 653-665
Total Pages: 961
Language : English

Abstract: A concrete wall exposed to sea water in the tidal zone for 10 years in the Trondheim fjord has an observed total chloride concentration at 1 mm of 0.96% total Cl- of concrete mass. Assuming that the pore water at this depth should have a chloride concentration equal to the concentration of sea water, and using chloride binding data for sodium chloride from literature, a surface concentration of only 0.21% total Cl- of concrete mass was calculated. One reason for the discrepancy is that magnesium in seawater ion exchange with calcium and release this into the pore solution so that the compound CaCl2·3Ca(OH)2·12H2O can form in the concrete pores, and also magnesium chloride in contact with already precipitated brucite can form the compound MgCl2·5Mg(OH)2·8H2O. Chloride binding isotherms using sodium, calcium and magnesium chloride show that Cl- associated with Na+ only bind half as much as when associated with Ca2+ and Mg2+ for whatever reason, and that chlorides associated with the two latter cations bind equally much in accordance with theory. However, even when taking into account the increased binding by magnesium chloride, the observed surface concentration of chlorides is still much higher than calculated (0.32%). The main reason for the difference between field and lab observed surface concentration of chlorides is the formation of CaCl2·3Ca(OH)2·12H2O in the field concrete as documented by SEM.

Online publication : 2013
Publication type : full_text
Public price (Euros) : 0.00