Steel fibers are ferromagnetic and they
have the property of altering the magnetic field around
them. This paper discusses a method and gives a
practical example to measure, non-destructively, the
amount and orientation of fibers from cubic concrete
specimens (150 mm). This is possible because the
fibers affect inductance of a sensor (an inductive coil)
that is wrapped around the specimen.
Torrents, J. [et al.]. Inductive method for assessing the amount and orientation of steel fibers in concrete. "Materials and structures", 24 Abril 2012, vol. 45, núm. 10, p. 1577-1592.