Long-term Performance of Concrete Containing Hydrated Hydraulic Lime as an Admixture

About the report:

In 1941 two bridges were constructed with decks using concrete incorporating as an experimental feature the use of hydrated lime as an admixture in amounts varying from zero to 12%. After 35 years of service the decks were scheduled for repairs to correct surface spalling caused by corrosion of the reinforcing steel. Performance surveys were made including the measurement of electrical corrosion potential. Cores were removed for petrographic examination, chloride content and analysis by X-ray diffraction. Based upon these observations it was concluded that: 1. The performance of the concrete in the decks has been excellent considering the age of the structure and the lack of air entrainment. There is no significant scaling or other general deterioration. 2. The major defect is surface spalling from corrosion of the reinforcement. This is not surprising in view of the high chloride levels and comparatively shallow concrete cover above the top reinforcement 3. Based upon electrical potential measurements, the corrosion potential decreases with increasing additions of hydraulic lime, for additions of 4% and 8%, and increases slightly between 8% and 12%. If this reduction is real, it must be related to some initial passivation of the reinforcement from either the lime itself or included alkalies that over the years was overcome but which still is reflected in the extent of corrosion. 4. The overall excellent durability of the concrete in these decks as compared with the concrete in contemporary decks undoubtedly reflects the greater than average testing and inspection exercised in connection with the experimental features of the project. 5. Within the limits of the chemical and petrographic analyses, no unusual reaction products or characteristics were observed among the several types of concrete used.

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