Real time monitoring of concrete resistivity in cracking concrete

Abstract

Cracks are almost inevitable in a heterogeneous material such as concrete. However their presence weakens the porous matrix resistance and constitutes a preferential flow path for fluid, gas and pollutants : material durability is therefore seriously affected. This paper deals with the feasibility of transfer properties measurement tests during the post-peak cracking phase of concrete. A proper description of the evolution of these properties should be monitored in real-time as cracks open in the specimen. In this work, attention is focused on the mechanical test and the geometrical characterization of the cracks by means of a displacement measurement system together with a digital image correlation technique. The mechanical test is then enhanced in order to establish a real-time relation between the evolution of the electrical resistance and the crack width opening in a saturated concrete sample. The experimental results show that the electrical resistance is constant before the peak (when no crack is observed) and decreases only when the peak of load is reached and when a crack is initiated. No threshold value and no phase shift between the crack opening and the resistance evolution have been observed, even in the case of a breathing crack. The evolution of the conductance has then been modeled by taking into account the (simplified) morphology of the crack and assuming a constant value for the electrolyte conductivity. The model and the experimental conductance through a traversing crack have proved to be in good agreement