Systems Approach to Concrete Durability

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Title: Systems Approach to Concrete Durability

Author(s): N. S. Berke, M. C. Hicks and K. J. Folliard

Publication: Special Publication

Volume: 170

Issue:

Appears on pages(s): 1293-1316

Keywords: Admixtures; calcium; chlorides; corrosion; durability; epoxy resins;permeability; pozzolans; reinforcing steels; shrinkage; silica fume.

Date: 7/1/1997

Abstract:
Reinforced concrete is one of the most durable building materials in use today. However, it is often used in applications in which it is subjected to chloride ingress. When the chloride reaches the reinforcing steel corrosion initiates and the subsequent expansive corrosion products cause the concrete to crack or spall. This results in an acceleration of the corrosion and the need for repair. Numerous approaches have been utilized to prevent corrosion of embedded steel in concrete. Data from long-term laboratory tests over periods exceeding 3 years are presented for several commonly used methods to extend durability against corrosion of the reinforcing steel. The data show that reducing concrete permeability to chloride ingress by lowering the water-to-cement ratio or adding pozzolans are not sufficient for long-term performance in severe chloride environments. Furthermore, some of these mixture designs can result in increased shrinkage and thermal cracking compromising long-term performance. The conclusions from the studies performed in our laboratory are that a systems approach is needed for long-term durability for steel reinforced concrete in severe chloride exposures. It starts with low permeability concrete mixture designs that have reduced drying and thermal shrinkage. Corrosion inhibitors are added to protect the reinforcing steel which may or may not be coated. This is known as a ‘belt and suspenders approach, and has the added advantage of being amenable to modeling.