A compensated magnetic probe for steel fiber reinforced concrete monitoring

SFRC, steel fiber reinforced concrete, is a widely employed material in building construction. The fibers assure a better mechanical behavior with respect to plain concrete. Testing the material "on the site" represents a very important goal. In particular, there is a strong need to have a reliable measurement method available which allows assessing information about size, orientation and concentration of the fibers. Currently, the measurement techniques present some important restrictions (laboratory applications only, sensitivity to the humidity, complexity, cost etc). This paper presents a new approach, based on a simple, low-cost sensor employing a C-shaped ferrite core. Four coils have been wound on it: two provides the generation of the magnetic flux and two allow picking up the emf. By leaning the probe on the SFRC surface and by measuring the variation of the mutual inductance between the two pairs of winding, it is possible to discriminate the average orientation of the fibers, and to obtain information about their concentration. It has also been proven that the size and the geometrical properties of the fibers result in a variation of the power losses.