Capacitance-based nondestructive detection of aggregate proportion variation in a cement-based slab

This paper reports unprecedentedly capacitance-based nondestructive detection of aggregate proportion variation in cement-based materials. It uses the fringing electric field of a capacitor comprising a cement-based slab and two relatively small copper electrodes. The aggregate volume fraction increases from cement paste to mortar and to concrete, thus causing the apparent permittivity (high due to the fringing field) to decrease in the same order. Each slab consists of two regions with different aggregate proportions. The through-thickness and in-plane capacitances are measured using sandwiching and coplanar electrodes, respectively. To locate the interface, the capacitance is innovatively measured using a series of electrodes.