The Effects of Cement Alkalinity upon the Pore Water Alkalinity and the Chloride Threshold Level of Reinforcing Steel in Concrete

Nam Jingak;Hartt William H.;Kim Kijoon

  • 발행 : 2004.08.01


Cement of three alkalinities (equivalent alkalinities of 0.36,0.52 and 0.97) was employed in fabricating a set of classical G109 type specimens. To-date, these have been subjected to a one week wet-one week dry cyclic pending using 15 w/o NaCl solution. At the end of the dry period, potential and macro-cell current were measured to indicate whether the top reinforcing steel was in the passive or active state. Once this bar became active, the specimen was autopsied and the extent of corrosion was documented. Subsequent to visual inspection, concrete powder samples were collected from the upper region of the top rebar trace; and at a certain times concrete cores were taken from non-reinforced specimens. Using these, determinations were made of (1) critical chloride concentration for corrosion initiation ($Cl_{th}^-$), (2) effective chloride diffusion coefficient ($D_e$), and (3) pore water alkalinity ($[OH^-]$). The pore water alkalinity was strongly related to the alkali content of cement that was used in the mix. The chloride concentration, ($Cl^-$), was greater at active than at passive sites, presumably as a consequence of electro migration and accumulation of these species at active site subsequent to corrosion initiation. Accordingly, ($Cl^-$) at passive sites was considered indicative of the threshold concentration fur corrosion initiation. The $Cl_{th}^-$ was increased with increasing Time-to-corrosion ($T_i$). Consequently, the HA(High Alkalinity) specimens exhibited the highest $Cl_{th}^-$ and the NA(Normal Alkalinity) was the least. This range exceeds what has previously been reported in North America. In addition, the effective diffusion coefficient, $D_e$, was about 40 percent lower for concrete prepared with the HA cement compared to the NA and LA(Low Alkalinity) ones.


concrete;cement alkalinity;reinforcing steel;corrosion;chloride threshold concentration;air voids


  1. L. Li, A. A. Sagues and N. Poor, 'In situ leaching investigation of pH and nitrite concentration in concrete pore solution,' Cement and Concrete Research, Vol.29, March 1999, pp.315~321
  2. J. Nam, W. Hartt, K. Kim and L. Li, 'Effect ofcement alkalinity upon time-to-corrosion ofreinforcing steel in concrete undergoing chloride exposure,' NACE, paper No.03290, Corrosion 2003, pp.1~31
  3. D. A. Hausmann, 'Steel corrosion in concrete- How does it occur?' Material Protection, Vol.6, 1967, pp.19~23
  4. P. Snadberg, 'Studies of chlorides binding in concrete exposed in a marine environment,' Cement and concrete research, Vol.29, 1999, pp.473~477
  5. B. M.Perez, H. Zibara, R. D. Hooton and M. D. A. Thomas, 'A study of the effect of chloride binding on service life predictions,' Cement and concrete research, Vol.30, 2000, pp.1215~1223
  6. C. Alonso, C. Andrade, M. Castellote, and P. Castro, 'Chloride threshold values to depassivate reinforcing bars embedded in a standardized OPC mortar,' Cement and Concrete Research, Vol. 30, 2000, pp.1047~1055
  7. D. S. Spellman, and R. F. Stratfull, 'Concrete Variables and Corrosion Testing,' Highway Research Record, No.423, 1963, 27pp
  8. K. C. Clear, 'Time-to-Corrosion of Reinforcing Steel in Concrete Slabs,' Report No. FHWA-RD-76-70, Federal Highway Administration, Washington, D.C., 1976, 7pp
  9. J. P. Broomfield, 'Corrosion ofSteel in Concrete,' E&FN Spon, London, 1997, pp.22~25
  10. L. Li, and A.A. Sagues, 'Chloride Corrosion Threshold of Reinforcing Steel in Alkaline Solutions-Open-Circuit Immersion Tests,' Corrosion, Vol. 57, 2001, 19pp
  11. G. K. Glass, and N. R. Buenfeld, 'Chloride Threshold Levels for Corrosion Induced Deterioration ofSteel in Concrete,' paper No.3 presented at RlLEM International Workshop on Chloride penetration into Concrete, Oct. 15-18, 1995, Saint Remy-les- Chevreuse
  12. ASTM Standard Test Method G 109-99, 'Determining the Effect ofChemical Admixtures on the Corrosion ofEmbedded Steel Reinforcement in Concrete Exposed to Chloride Environments,' Annual Book of ASTM Standards, Vol. 03.02, American Society for Testing and Materials, 100 Barr Harbor Drive, West Conshohcken, PA
  13. ASTM Standard Test Method C876-99, 'Half-cell potentials of uncoated reinforcing steel in concrete,' Annual Book of ASTM Standards, Vol. 03.02, American Society for Testing and Materials, 100 Barr Harbor Drive, West Conshohcken, PA
  14. FDOT, 'The Florida method of test for determining low level of chlorides in concrete and raw materials,' designation FM 5-516, Florida Department of Transportation, Sept 1994, pp.1~3
  15. Li, L., Nam, J., and Hartt, W.H., 'Ex-Situ Leaching Measurement ofConcrete Alkalinity,' NACE paper No.03299. Corrosion 2003, pp.1~9
  16. E. Samson , G. Lemaire, J. Marchand, and J. J. Beaudoin, 'Modeling chemical activity effects in strong ionic solutions,' Computational Materials Science, Vol.15, 1999, pp.285~294
  17. J. Tritthart, 'Chloride Binding in Concrete. II. The Influence of the Hydroxide Concentration in the Pore Solution of Hardened Cement Paste on Chloride Binding,' Cement and Concrete Research, Vol.19, 1989, 683pp
  18. S. Diamond, 'Effects of Two Danish Fly Ashes on Alkali Contents of Pore Solutions of Cement-Fly Ash Pastes,' Cement and Concrete Research, Vol. 11 , 1981, 383pp
  19. S. Diamond, 'Effects of Microsilica (Silica Fume) on Pore Solution Chemistry of Cement Pastes,' Communications of Am. Ceramics Soc., 1983, 82pp
  20. C. Arya, and Y. Xu, 'Effect of Cement Type on Chloride Binding and Corrosion of Steel in Concrete,' Cement and Concrete Research, Vo.25, 1995, 893pp
  21. D. Constantiner, and S. Diamond, 'Pore Solution Analysis: Are There Pressure Effects,' in Mechanisms of Chemical Degradation of Cement-based Systems, Eds: K.L. Scrivener and J.F. Young, E&FN SPON, London, 1997, 22pp
  22. M. Kawamura, O. A. Kayyali, and M. N. Haque, 'Effects of a Fly Ash on Pore Solution Composition in Calcium and Sodium Chloride-Bearing Mortars,' Cement and Concrete Research, Vol.18, 1988, 763pp
  23. O. A. Kayyali, and M. N. Haque, 'Environmental Factor and Concentration of Cl$^-$ and OH$^-$ in Mortars,' Journal of Materials in Civil Engineering, Vol.2, 1990, 24pp
  24. J.A. Larbi, A.L.A. Fraay, and J. L. Bijen, 'The Chemistry of the Pore Fluid of Silica Fume-Blended Cement Systems,' Cement and Concrete Research, Vol.20, 1990, pp. 506~516
  25. J. Duchesne, and M.A. Berube, 'Evaluation of the Validity of the Pore Solution Expression Method from Hardened Cement Pastes and Mortars,' Cement and Concrete Research, Vol. 24, 1994, pp.456-462
  26. C.L. Page, and O. Vennesland, 'Pore Solution Composition and Chloride Binding Capacity of Silica Fume Cement Pastes,' Materials and Structures, Vol. 16, 1983, pp.19-25
  27. O. Francy and R. Francois, 'Measuring chloride diffusion coefficient from non-steady state diffusion tests,' Cement and concrete research, Vol.28, 1998, pp.947-953
  28. G. Achari, S. Chatterji and R. C. Joshi, 'Evidence of the concentration dependent ionic diffusivity through saturated porous media,' RlLEM, No.9, 1997, pp.74-76
  29. P. Sandberg and J. Larsson, 'Chloride binding in cement pastes in equilibrium with synthetic pore solutions,' Chloride penetration in concrete structures, Ed. L.-O Nilsson, Nordic Miniseminar, Goiteborg, 1993, 98pp
  30. G. E. Monfore and G. J. Verbeck, 'Corrosion of prestressed wire in concrete,' ACI Journal, Vol.32, 1960, 491pp
  31. T.U. Mohammed, T. Fukute, T. Yamaji, and H. Hamada, 'Long Term Durability of Concrete Made with Different Water Reducing Chemical Admixtures under Marine Environment,' in Concrete for Extreme Conditions, Eds: R.K Dhir, M.J. McCarthy, M.D. Newlands, Thomas Telford, London, 2002, 233pp