Influence of crack propagation on electrical resistivity and ultrasonic characteristics of normal concrete assessed by sequential TPB fracture test

• We measured electrical resistivity and ultrasonic parameters of fractured concrete.
• The parameters indicate the quality of concrete for structural durability assessment.
• Sequential three-point bending test was utilised to drive the crack propagation.
• Electrical resistivity increases when fracture propagates through dry concrete only.
• Ultrasound passing time increases when both dry and wet specimens fracture.

The paper is focused on the investigation of the effect of tensile failure propagation on the change in values of electrical resistivity and ultrasound pulse passing time within the central section of beam bend specimens made of normal concrete. These two physical characteristics may be employed as a quality indicator of the concrete cover within the procedures of the assessment of the structural durability. The three-point bending test configuration was utilised to drive the crack propagation process through several loading–unloading cycles, between which, the electrical resistivity and ultrasonic measurements over the fractured region were performed. Equivalent elastic crack model was used for estimation of the fracture progression (described via the effective crack length increment) at those loading stages. The relationships between changes of the non-destructively determined parameters, the effective crack length and the distance from crack tip are discussed with respect to two variants of treatment of the test specimens’ surface: the pre-dried surface and the wet surface. A difference between the ultrasonic and electrical resistivity measurements ability with respect to crack width is found in the case of wet samples.