| In the present investigation, a series of experiments were conducted to examine the effect of two commercially available calcium nitrite inhibitors (designated CN1 and CN2, respectively) and laboratory grade calcium nitrate. Studies of steel in synthetic concrete pore solution and of cement paste were conducted. Two types of cement were used: white Type 50 and grey Type 10 (Ordinary Portland Cement - OPC). Corrosion measurements in synthetic concrete pore solution found that none of the inhibitors inhibited or delayed the onset of corrosion. These tests also showed that a solid precipitate containing chlorides forms in all solutions, with the highest chloride concentration being in the precipitate from the solution containing CN1.; Mercury intrusion porosimetry determined the effect of the admixtures on the total, capillary and gel porosities of two types of hardened cement pastes containing admixtures (Type 50 White and Type 10 Grey), both prior to and after exposure to a 2% chloride ponding solution. Inhibitors had the greatest effect on the gel porosity, decreasing the proportions compared to the Control mixes both before and after exposure to 2% Cl− ponding solution. Acid soluble chloride titration showed that all mixes had lower total chloride concentrations than expected based on the volume of ponding solution absorbed by cylinders. This indicates that water is entering the sample at a faster rate than chlorides.; Three forms of bound chlorides were detected by thermal analysis: Friedel's salt, calcium hydroxychloride and Cl− in the C-S-H. The latter forms were found only in the cylinders made from OPC, and were highest in concentration in the OPC paste made with CN1. A sequence for formation of bound chlorides is proposed based on these observations and other currently unpublished research.; Using pore solution expression, it was determined that only a minor fraction of the admixed nitrites or nitrates is present in the pore water, indicating that nitrite and nitrate are incorporated into the solid cement hydration products. Chloride concentrations in ponded cylinders were also found to be disproportionate to the amount of ponding solution absorbed. (Abstract shortened by UMI.)... |
