Concrete Conductivity/Resistivity with Conductive Aggregate

The electrical properties of concrete (formation factor) are often used as a surrogate test method to assess fluid transport in concrete primarily because resistivity (or conductivity) can be measured rapidly and economically. While electrical properties have been measured for nearly a century, the recent rise in handheld, battery-operated testing tools coupled with the desire to quantify the transport performance of concrete has caused a sudden spike in interest in electrical property measurements as a quality control or quality acceptance tool. Standards have been developed (AASHTO T 358, AASHTO T 402, ASTM C1876) with an emphasis on the role of sample conditioning. Some users have reported that the use of certain aggregates tends to reduce the resistivity values (increase the conductivity) when compared with concrete made using the same matrix but different aggregates. This paper examines a fundamental assumption of the electrical testing, i.e., that the aggregate is resistive or non-conductive. It explores the implications if the aggregate is conductive using both an analytical and finite element approach to determining the impact of aggregate with a lower resistivity and discusses a procedure to account for aggregate conductivity.