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Title: Laboratory Studies and Calculations on the Influence of Crack Width on Chloride-Induced Corrosion of Steel in Concrete

Author(s): Peter Schiessl and Michael Raupach

Publication: 318Reference



Appears on pages(s): 56-61

Keywords: chlorides; concretes; corrosion; cover; cracking (fracturing); crack width and spacing; humidity; reinforced concretes; reinforcing steels; water-cement ratio;


Date: 1/1/1997

Laboratory tests were performed on cracked reinforced concrete beams to clarify the corrosion mechanism and dominant influencing variables, especially the influence of crack width. Test results and a mathematical model were then used to calculate the effect of crack distance and crack width limitation by reducing the rod diameters on the steel removal rates due to chloride-induced corrosion. The results show that after local depassivation of the steel surface by chlorides penetrating through cracks in concrete, the steel in the cracked zone acts as an anode (iron removal) and the steel between the cracks as a cathode (oxygen reduction). Therefore the corrosion rate in the crack zone is influenced considerably by the conditions between the cracks. It has been found that thickness and quality of concrete cover influence the corrosion rate much more than crack width. By simplified calculations it was shown that a crack width limitation by reducing rod diameters from about 0.4 mm (0.016 in.) to lower crack widths results in increasing losses of steel diameter. As a consequence, corrosion protection must be assured primarily through adequate concrete quality and cover.