Calcium nitrite has been used as a corrosion inhibitor against chloride attack and as a set accelerator in concrete for more than 20 years. Considerable data are available concerning its effects on corrosion inhibition, setting times, freeze-thaw resistance, strength, and other properties. Although much of the data have been published in the open literature, a full-scale review is not available. This paper reviews past and present research on the properties of calcium nitrite in concrete. While the bulk of the data have been generated by W.R. Grace & Co., considerable information is available from outside sources, including the U.S. Federal Highway Administration (FHWA), departments of transportation, universities, and independent test laboratories. It is shown that calcium nitrite is an effective corrosion inhibitor for steel in concrete, based upon extensive corrosion testing in laboratory and field concrete specimens. The effects of mix design and concrete cover on corrosion resistance with calcium nitrite are also discussed. Furthermore, in most cases, calcium nitrite improves the compressive strength of the concrete mix and, with proper air entrainment, is freeze-thaw durable. In conclusion, the data generated in the last 20 years show that calcium nitrite is a proven corrosion-inhibiting admixture to be used to protect concrete structures in a chloride environment.
Samenvatting