Prediction of chloride penetration rates in Hawaiian concrete in a marine environment

Abstract

A study was conducted to evaluate the chloride concentrations of reinforced concrete specimens exposed to a marine environment made with Hawaiian aggregates including various corrosion inhibiting admixtures and pozzolans intended to reduce the chloride penetration rates through the concrete and thus reducing the amount and rate of corrosion of the reinforcing steel therein. Field panels were constructed and placed at Pier 38 in Honolulu Harbor on the island of Oahu in 2002 and 2003 and first sampled for chloride concentrations in 2004 from a previous phase of this overall study. Additional collected samples from 2006 and 2008 were also included in this study. The corrosion inhibiting admixtures included in the field panel mixtures were Darex Corrosion Inhibitor (DCI), Rheocrete CNI, Rheocrete 222+, FerroGard 901, Xypex Admix C-2000, latex modifier, and Kryton KIM. The pozzolanic admixture materials included fly ash and silica fume. The focus on this study was to compare the chloride concentration results from the field panels to that of the computer program Life-365 which is designed to predict chloride concentrations in reinforced concrete. This report limited the analysis of the admixtures to DCI, Rheocrete CNI, Rheocrete 222+, fly ash and silica fume as these are the only admixture options currently available in the Life-365 software. Modified parameters were needed for all of the predicted chloride concentrations of Life-365 as most of the program default parameters overestimated the concentrations through the depth of the specimen when compared to the field panel results. The predicted chloride concentration results were best for the silica fume admixture. In addition, the final half-cell results for the selected admixtures previously listed along with each corresponding visual observation of the field panels were included in this report to provide conclusions to the performances of the concrete constituents included in the field panels. Generally, concrete mixtures with a lower water-cement ratio performed better than those made with higher ratios as concluded from the control panels. The calcium nitrite type admixtures, CNI and Rheocrete CNI, indicated better performance to corrosion resistance with a higher dosage of 4 gal/yd³ compared to the mixtures with 2 gal/yd³. The replacement of 15% fly ash with cementitious materials performed the best and gave the most consistent results. Both the final half-cell readings and visual observations concluded that corrosion was least probable in the field panel. The panels including the remaining admixtures, Rheocrete 222+ and silica fume, exhibited inconsistent results.