Service Life Model for Concrete Structures in Chloride Laden Environments

Abstract

Bridges are a major element in ground transportation networks. Of the present $70 billion backlog of bridge rehabilitation needs, $28 billion dollars is attributed to the corrosion of steel in concrete. The chloride corrosion of steel in concrete structures is not confined to bridges but also reduces the service life of parking garages and sea and coastal structures. The service life model for reinforced concrete structures in chloride laden environments consists of the following serial phases: diffusion to the depth of the steel that would precipitate first maintenance actions; corrosion of the steel at the first maintenance depth until cracking and spalling occurs; and continue spalling until a damage level is reached which is defined as the end-of-functional service life for an element or structure. The diffusion phase is described by Fick's Law and the boundary conditions define the solution form. The time-to-cracking model is dependent upon factors as concrete strength properties, cover depth, and corrosion rate. Corrosion rate has a significant influence on the time-to-cracking, which typically occurs 3-7 years after initiation. The utility of the model in estimating the service life of corrosion protection systems as increased cover depth, corrosion inhibitors, and low permeable concrete is presented. As is the means for determining the time-to-first maintenance and annual maintenance requirements to the end-of-functional service life. The model in conjunction with a life-cycle cost model will enable the selection of the least cost solution to corrosion protection.