In situ Determination of Moisture Levels in Structural Concrete by a Modified Nuclear Magnetic Resonance (NMR) Method

摘要

The prototype bridge deck Nuclear Magnetic Resonance (NMR) Moisture Measurement System was modified to improve its usefulness and field tested in Wichita Falls, Texas, and at the FHWA Turner-Fairbank Research Center in Mclean, Virginia. Modifications included addition of an external control unit to provide for selection of desired measurement depths and automatic adjustment of the RF pulses and magnetic field for the selected measurement depth and rebar depth. Field tests were conducted on 8 bridge decks having a variety of overlays in the Wichita Falls area and on 12 concrete test slabs having a variety of rehabilitation systems at the FHWA center. Good qualitative agreement was obtained between the NMR moisture results and those obtained from dry core samples at selected locations, except that the NMR results tended to be more consistent. For the FHWA test slabs, the NMR moisture values for the concrete were found to increase with increasing water/cement ratio and decrease with increasing concrete density.