Long-Term Corrosion Resistance of Steel in Silica Fume and/or Fly Ash Containing Concretes


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Title: Long-Term Corrosion Resistance of Steel in Silica Fume and/or Fly Ash Containing Concretes

Author(s): N. S. Berke, M. J. Scali, J. C. Regan, and D. F. Shen

Publication: Special Publication

Volume: 126


Appears on pages(s): 393-422

Keywords: carbonation; chlorides; corrosion; electron microscopes; fly ash; hydration; microstructure; permeability; resistivity; silica fume; x-ray analysis; Materials Research

Date: 8/1/1991

Silica fume and/or fly ash concretes were produced to determine the long-term effects of these pozzolans on chloride ingress, electrical resistivity, microstructure, and the subsequent effect on corrosion of embedded steel reinforcement. Initial results of these experiments showed that there was a good relationship between the 28-day compressive strength, rapid chloride permeability, and electrical resistivity. In this paper the long-term corrosion performance, electrical resistivity, chloride ingress, and microstructure are examined after 3 years of partial ponding in 3 percent NaCL. These results are compared to the initial concrete properties to determine how well early measurements of the properties relate to long-term corrosion resistance and chloride ingress. Also, long-term changes in the concrete microstructures are documented. The results show that concrete resistivity and rapid chloride permeability measurements are better indicators of corrosion resistance than concrete strength. In general, increasing silica fume and/or fly ash contents and/or reducing water-cementitious ratios improves corrosion resistance. However, for mixes with over 20 percent pozzolans by mass of cement, some carbonation has occurred next to cracks where the reinforcement exited (the nonsubmerged sections of the samples). The significance of these findings is discussed.