Embedded Resistivity Sensor for Concrete Materials and Structures: Vision and Prototype

The Performance Engineered Mixtures (PEM) approach, standardized in AASHTO R101, calls for evaluation of the concrete Formation Factor (FF) as an indication of permeability and thus resilience of the materials to ingress of aggressive ions. FF is defined as the ratio of the electrical resistivity of the bulk concrete mixture over the resistivity of the concrete pore solution. The AASHTO TP 119 and AASHTO T 358 standards were developed to measure the concrete bulk resistivity and surface resistivity, respectively. However, there are no standard equipment or test methods for non-destructive measurement of the pore solution resistivity (PSR), and the only available methods involve labor-intensive laboratory extraction of the pore solution. An embedded sensor system for measuring concrete PSR is under development, funded by the USDOT Federal Highway Administration (FHWA). This paper discusses the vision for the devised sensor system, the corresponding test procedure, potential applications in practice, and test results using the manufactured prototypes. The use of the sensor system in cylindrical concrete samples will improve concrete mix design and construction quality control to produce concrete materials that are less permeable to aggressive ions, which can corrode steel reinforcement and accelerate deterioration. The sensor can also be embedded inside concrete structures for monitoring changes in chloride content and detection of aggressive ions in a timely manner to preserve and prolong service life.