Moisture State of Concrete in a Coastal Ridge


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Title: Moisture State of Concrete in a Coastal Ridge

Author(s): E.J. Sellevold, C. K. Larsen and A. A. Blankvoll

Publication: Special Publication

Volume: 170


Appears on pages(s): 823-834

Keywords: Bridges (structures); concretes; electrical properties; moisture; porosity; water.

Date: 7/1/1997

This paper presents results from the OFU Bridge Repair Project on the Gimsarystraumen bridge near Svolvaer, Norway. The results are mainly of laboratory measurements on concrete samples taken undisturbed from the bridge to determine: 1) the relative humidity exerted by the pore water, 2) the pore water content and degree of capillary saturation of the concrete, and 3) the electrical resistivity of the concrete at two temperatures. The laboratory results are related to field monitoring of relative humidity, electrical resistance and temperature at various positions in the bridge over a 2 year period. The results show that the moisture state of the concrete a few mm from the surface and to 40 mm depth vary very little over both time and position on the bridge. The relative humidity is in the range 70 - 80% RH, while the degree of capillary saturation is in the range 80 - 90%. The electrical resistivity of the concrete is a very strong function of both the degree of capillary saturation (about 5% change in resistivity per 1% change in saturation at 3.5’ C and 85% degree of capillary saturation) and the temperature. Interpretation of electrical resistance measurements in the field is difficult with present techniques, but the method is considered promising for routine monitoring of moisture state in the field. It is concluded that any field monitoring method of moisture state must be supplemented by laboratory measurements on undisturbed concrete samples taken from the structure.