A magnetic method for non destructive monitoring of fiber dispersion and orientation in Steel Fiber Reinforced Cementitious Composites – part 1: method calibration

Steel fiber reinforced concrete (SFRC) is a composite material which is becoming more and more widely employed in building construction. The mechanical behaviour of the material and the performance of structural elements may significantly depend on the fiber dispersion and orientation with respect to the stress pattern. Non-destructive monitoring of fiber dispersion related issues hence becomes of the foremost importance in order to reliably anticipate the structural performance of elements made with fiber reinforced cementitious composites (FRCCs), as well as for quality control during manufacturing. In this paper a new method for the detection of fiber density and orientation is presented, which is based on the employment of a probe sensitive to the magnetic properties of the steel fibers. The presence and the relative position of steel fibers modify the flux linked by the winding of the probe thus resulting in an impedance variation. The local average concentration and orientation of the fibers can be thus assessed by measuring the variation of the probe inductance. The performance of the method has been analyzed with reference to a self-consolidating high performance FRCC slab and thoroughly verified by means of comparison with destructive monitoring of fiber local concentration and orientation. Besides its good sensitivity, the method is also characterized by ease of use, since it just requires to lean the probe on the surface of the specimen, without any particular care about the coupling. This guarantees a high degree of repeatability and low uncertainty in the measurements, even, e.g. on vertical elements or slabs accessible from the bottom.