Service Life Demonstration Based on Simulated Exposure and Numerical Modeling

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Title: Service Life Demonstration Based on Simulated Exposure and Numerical Modeling

Author(s): N. R. Buenfeld

Publication: Special Publication

Volume: 212

Issue:

Appears on pages(s): 1-10

Keywords: cement; chloride; concrete; life prediction; numerical modelling; simulated exposure

Date: 6/1/2003

Abstract:
Modelling chloride transport is usually an integral part of demonstrating that a concrete structure in a chloride-rich environments will have the required service life. Ideally this should take account of spacial and temporal variations in exposure environment and concrete properties. This paper describes how this may be approached through a combination of simulated natural exposure and numerical modelling. This approach helps to reduce the errors associated with coupling different transport processes. The example taken is a reinforced concrete tunnel exposed to chloride-contami-nated groundwater. In a laboratory experiment, opposite faces of specimens of tunnel lining concrete were exposed to the maximum hydrostatic head (30m) of groundwater and the minimum relative humidity (35%) expected inside the tunnel and water outflow and chloride accumulation were monitored over a 3 year period. Water vapourdiffusion, chloride binding and porosity measurements were made on parallel specimens. The measurements were used as inputs to a numerical model of water and chloride transport to extrapolate from the measured chloride profiles to predict future chloride profiles. The results were very sensitive to ground water chloride concentration and chloride threshold level, but relatively insensitive to hydrostatic head.