Field Performance of Portland Cement and Fly Ash Concrete Subjected to Flowing seawater

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Title: Field Performance of Portland Cement and Fly Ash Concrete Subjected to Flowing seawater

Author(s): Vute Sirvivatnanon, P. Marsh, and P. Nelson

Publication: Special Publication

Volume: 163

Issue:

Appears on pages(s): 463-480

Keywords: carbonation; chlorides; half-cell potential; permability; portland cement; pozzolan cements; Materials Research

Date: 8/1/1996

Abstract:
The concrete lining the outfall canal of Munmorah Power Station, built by the Electricity Commission of New South Wales (now operating as Pacific Power) in the mid-1960s, has been subjected to flowing seawater for 30 years. Two types of concrete, a portland cement concrete and a fly ash concrete, were used for the construction of the canal. This presented an ideal opportunity for a comparison to be made of the performance of the two binders in concretes which were subjected to the same aggressive environment. Limited information was available on the concretes from trial mixture records. A recent field investigation revealed similar chloride ingress into the two concretes in the tidal zone. This was so despite the fact that the fly ash concrete had a lower binder content than the portland cement concrete. As such, a lower strength grade and, hence, a fly ash concrete with higher water permeability can perform as well as a portland cement concrete. In the dry area above the high tide mark, the carbonation depth of the fly ash concrete was greater than the portland cement concrete. No corrosion was found in any reinforcing steel, as there was sufficient cover in both concretes to prevent the chloride ions or carbonation front reaching the steel. The effectiveness of a number of investigative techniques was evaluated during the investigation. It was found that the apparent chloride diffusion coefficients, determined from short-term immersion, the water permeability coefficients, and copper to copper sulfate half-cell potential measurements were poor indicators of the real long- term performance.