Getty ImagesConcrete is perhaps the most commonly used building material in the world. With a bit of tweaking, it could help to power our homes too.On a laboratory bench in Cambridge, Massachusetts, a stack of polished cylinders of black-coloured concrete sit bathed in liquid and entwined in cables. To a casual observer, they aren't doing much. But then Damian Stefaniuk flicks a switch. The blocks of human-made rock are wired up to an LED – and the bulb flickers into life."At first I didn't beli...