Title: EFFECT OF FLY ASH AND SILICA FUME ON TIME TO CORROSION INITIATION FOR SPECIMENS EXPOSED LONG TERM TO SEAWATER
Author(s): Francisco J. Presuel-Moreno, Eric I. Moreno
Publication: Symposium Paper
Appears on pages(s): 1-20
Keywords: Chloride Diffusivity, Chloride Threshold, Fly Ash, Resistivity, Silica Fume, Time to Corrosion Initiation
The aim of this study was to determine the chloride threshold concentration of carbon steel rebar embedded in high performance concrete under exposure conditions relevant to the substructure of coastal bridge in Florida. The experiments were based upon a series of reinforced and non-reinforced concrete specimens that contained 1) 20, 35 and 50 percent cement replacement by fly ash, 2) 6, 15 and 27 percent cement replacement by silica fume, and 3) control specimens (no pozzolanic admixture). All specimens had a target w/cm ratio of 0.37. The specimens have been exposed to one week wet - one week dry ponding cycle with natural seawater since January, 1995. Rebar potential values were monitored with time in order to determine when corrosion initiated. The rebar of several specimens activated after 15.6 to 17 years of exposure, and selected specimens were terminated for forensic examination and extent of corrosion. Cores were obtained to determine the extent of chloride ingress, the apparent diffusion coefficient (Dapp) and concrete resistivity. The chloride concentration above the rebar trace was also measured on most of the terminated specimens. The value for Dapp was correlated against the corresponding measured resistivity. Specimens with 50 percent FA had the lowest Dapp but also the lowest chloride threshold.