Abstract

Public infrastructures like bridges typically have a design lifetime of 100 years or more. When selecting protective coatings in such a long term perspective, focus should be on life cycle costs and not only the costs in the construction phase, since the maintenance costs may be considerable and dominate the total cost of ownership. Coating selection standards like ISO 12944 are not intended for such a long timescale, and there is little documentation in the literature of coating performance with lifetimes of more than about 20 years. Owners of structures with very long lifetimes have little information to base their coating selection on, besides their own experiences. Thermal spray zinc (TSZ) duplex coatings have been shown to be highly durable, as evidenced by more than 50 years of successful use since first specified by the Norwegian Public Roads Administration (NPRA). The paper will summarize field examinations, maintenance costs, coating lifetime expectations and life cycle cost estimates for steel bridges as a function of the environmental corrosivity category (C1-C5) and make comparisons to alternative coatings that are less expensive to apply but that have shorter lifetime expectancy.

Introduction

Very often the life of a corrosion protection paint coating system will not meet the design life of the steel structure it is supposed to protect. Decisions about coating selection are usually focusing on the costs for the initial construction, ignoring the certain future maintenance costs. The total cost of ownership includes the initial cost plus the maintenance, operating and finance costs over the life of a structure. Repeated maintenance operations, and resulting downtime, can add significantly to the total cost of ownership.

For public infrastructure, the appropriateness of the maintenance strategy, and the point of intervention for renewal or rehabilitation should be planned. The process requires proactive assessment which must be based on the performance expected of the structure, the consequences and probabilities of failures occurring, and the subsequent level of maintenance needed to keep the structure sound.

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