The slab is 7.5 inches thick (19 cm), and consists of two layers. The bottom 4-inch (10-cm) layer is made up of regular concrete, while the top layer consists of 1 percent carbon fiber combined with a special mix of cement, sand and rocks. Sandwiched between those layers are six electrodes (per slab) that are hard-wired to a power supply in a nearby hangar.

When the electrodes are remotely powered up via an app, they send an electrical current through the top layer. The carbon fiber content makes the concrete electrically conductive, yet there's still enough resistance that heat is generated. That heat makes the surface of concrete hot enough to melt away accumulated ice and snow, yet still safe to touch.

[Source]