AKA Thermite welding.
Uses a graphite form which is placed around the conductors, and filled with a mixture of powdered filler metal (copper for electrical work), an oxidizer, and a top layer of some kind of ignitor powder (magnesium powder?).
Used for creating "radial" ground systems at AM broadcast tower bases, and other places where the highest connection reliability is desired. Also used for welding rebar, railroad tracks, etc.
http://www.cadweld.com/erico_public/product/Cadweld.asp
