Experimental results on the breakdown behaviour of concrete immersed in water

The efficiency of the electric impulse fragmentation of dielectric solids immersed in water is determined by the characteristics of the discharge channel propagating from the electrode tip through the solid to the grounded electrode plate. Voltage and current measurements indicate, that the pre-breakdown phase strongly depends on the arrangement of the solid material within the discharge gap. Short discharge delay times and low energy losses can only be observed, if the electrode gap is completely filled by solid material. In this case the channel resistance calculated from the measurements shows high values. If the channel has to bridge an intermediate water gap, the discharge delay times and the energy losses increase. Compared to a channel through solid material a discharge channel in water exhibits a low channel resistance, providing a poor energy transfer into the channel. Further experiments clearly indicate that gaseous inclusions in the solid material play an important role in discharge development in minerals.