Concrete Corrosion Inhibitors Association (CCIA)

  "Long-Term
  Performance of an
  Organic Corrosion
  Inhibitor"

  "Corrosion Inhibition
  Properties of a
  Complex Inhibitor -
  Mechanism of
  Inhibition"

  "The Effects of
  Calcium Nitrite and
  Mix Design on the
  Corrosion Resistance
  of Steel in Concrete"

  "Modelling Chloride
  Diffusion in Concrete.
  Effect of Fly Ash and
  Slag"

"Modelling Chloride Diffusion in Concrete. Effect of Fly Ash and Slag", M. D. A. Thomas and P. B. Bamforth, Cement and Concrete Research 29 (1999) 487-495.

As portland cement hydrates in concrete and porosity diminishes, the diffusion coefficient of chloride ion decreases from the value measured at 28 days. This decrease in diffusion coefficient is even more dramatic in concrete made with fly ash (30% replacement of cement) or slag (GGBS, 70% replacement of cement). The diffusivity of

plain portland cement concrete,
concrete with 25-30% fly ash prelacement, and
concrete with moderate levels of slag (about 50%)

would be expected to be similar at early ages (1 month), that is, 8 x 10-12 m2/s. After about two years, however, the diffusivity of the fly ash and slag concretes may be a factor of 10 lower than for the plain portland cement concrete. This has a significant impact on the interpretation of date from short term or accelerated tests.

Chloride penetration of reinforced concrete blocks exposed to a sea front splash zone in southeast England was followed by coring and analysis. After 3 years, the chloride content in plain portland cement concrete was found to be above 0.40% chloride ion by weight of cement (0.05% by weight of concrete), which is the threshhold level for corrosion. The first 10 mm of flyash concrete (30% replacement) was initially penetrated fairly rapidly, but the rate diminished sharply with time, so that the threshhold level of the 0.4% Cl/cement had not penetrated a depth of 30 mm even after 8 years. Model calculations estimate it would take almost 200 years for the chloride ion in this environment to reach the threshhold level at a depth of 50 mm. This emphasizes the importance of depth of cover in preventing corrosion.

A model has been designed to use time-dependent transport coefficients in modelling chloride ingress in concrete for the long term. [Elements of this model have been included in Life-365, which also incoroporates silica fume addition.]

C.C.I.A. Members:
Axim Concrete Technologies | Euclid Chemical Company | Grace Construction Products
BASF Admixtures | Sika Corporation

Concrete Corrosion Inhibitors Association
Arnie Rosenberg, Executive Director
Email: info@corrosioninhibitors.org
Phone: 301-340-7368