Non destructive monitoring of fiber dispersion and flow-induced orientation in self-compacting SFRC: a method based on magnetic properties

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 sig-nificantly depend on the fiber dispersion and orientation with respect to the stress pattern. Non-destructive monitoring of fiber dispersion related issues hence be-comes of the foremost importance in order to reliably anticipate the structural per-formance of elements made with fiber reinforced cementitious composites, as well as for quality control during manufacturing. In this paper a new method for the de-tection of fiber density and orientation is presented, which is based on the em-ployment 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 ana-lyzed with reference to a self-consolidating high performance fiber reinforced ce-mentitious composite slab. Besides its good sensitivity, the method is also charac-terized 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 ver-tical elements or slabs accessible from the bottom.