corrosion monitoring in concrete

Corrosion Monitoring in Reinforced Concrete (Construction, Civil Engineering):

Corrosion of steel reinforced concrete structures is a major corrosion problem in North America, Europe, the Middle-East and other parts of the world. Chloride induced rebar corrosion damage results mainly from the use of de-icing salts in cold climates and/or exposure to marine environments. Carbonation damage is a further important degradation mechanism.

"To build environmentally sustainable concrete structures, it is clear that instead of strength, the 21st century concrete practice must be driven by considerations of durability."

from P.K. Mehta and R.W. Burrows: "Building Durable Structures in the 21st Century", Concrete International, March 2001, pp.57-63.

In view of the enormous scale and costs associated with the deteriorating reinforced concrete infrastructure, corrosion monitoring is becoming increasingly important for maintenance scheduling and life prediction purposes.

Dr John Broomfield has outlined the uses of corrosion monitoring of steel in concrete (Reference: MonoSys Guide to Monitoring 21), including the following:

Ensuring that structures remain safe and fully operational.
Information for timely and cost-effective intervention to prevent unacceptable damage and also service life extension.
Durability modeling, and related predictive elements.
Enhanced understanding of micro and macro corrosion environments.

Corrosion monitoring of reinforcing steel poses many challenges such as:

Direct inspection of the rebar or corrosion coupons, sensors is almost impossible as these are embedded in concrete.
Retrofitting of corrosion probes/sensors is difficult.
Concrete is actually a complex composite material, whose structure and properties tend to change with time. It does not "behave" like simple aqueous corrosion systems.
Cracks in the concrete may represent a major factor in the severity of corrosion damage.
Chloride induced rebar corrosion tends to be of the localized variety.
Corrosion damage is typically manifested over many years of exposure.

Existing corrosion monitoring and assessment methods include electrochemical techniques, ER probes, examination of extracted core samples, measurement of chloride concentration profiles in the concrete and carbonation depths, tests for the "soundness" and permeability of concrete, and visual inspection.

References/Literature:

ASTM C876 Standard: "Standard Test Method for Half Cell Potentials of Reinforcing Steel in Concrete", American Society for Testing and Materials, West Conshohocken, PA.

J.P. Broomfield, P.E. Langford and A.J. Ewins: "The Use of a Potential Wheel to Survey Reinforced Concrete Structures", Corrosion Rates of Steel in Concrete, ASTM STP 1065, American Society for Testing and Materials, West Conshohocken, PA., 1990, pp.157-173.

B. Elsener and H. Bohni: "Potential Mapping and Corrosion of Steel in Concrete", Corrosion Rates of Steel in Concrete, ASTM STP 1065, American Society for Testing and Materials, West Conshohocken, PA., 1990, pp.143-156.

K.R. Gowers, S.G. Millard, J.S. Gill and R.P. Gill: "Programmable linear polarisation meter for determination of corrosion rate of reinforcement in concrete structures, British Corrosion Journal,Vol.29, No.1, 1994, pp.25-32.

J. Flis, H.W. Pickering and K. Osseo-Asare: "Assessment of data from Three Electrochemical Instruments for Evaluation of Reinforcement Corrosion Rates in Concrete Bridge Components", Corrosion, Vol.51, No.8, August 1995, pp.602-609.

M.I. Jafar, J.L. Dawson and D.G. John: "Electrochemical Impedance and Harmonic Analysis Measurements on Steel in Concrete", Electrochemical Impedance: Analysis and Interpretation, ASTM STP 1188, American Society for Testing and Materials, West Conshohocken, PA, 1993, pp.384-403.

More comprehensive texts on concrete and durability.......

P.K. Mehta and R.W. Burrows: "Building Durable Structures in the 21st Century", Concrete International, March 2001, pp.57-63.

P.K. Mehta: "Durability - Critical Issues for the Future", Concrete International, July 1997, pp.27-33.

J.P. Broomfield: "Corrosion of Steel in Concrete", E&FN Spon, 1997.

C.M. Hansson: "Concrete: The Advanced Material for the 21st Century", Metallurgical and Materials Transactions A, 1995, pp.1321-1341.

Links:
Paper on electrochemical rebar monitoring techniques:
published at www.corrosionsource.com
(other related papers are on this site).

FHWA Office of Research, Development and Technology - Document "Corrosion Protection: Concrete Bridges" at
http://www.tfhrc.gov/structur/corros/corros.htm