Concrete is one of the most widely used construction materials in the world. In 2013, four billion tons of concrete were produced, according to a report published by the US Geological Survey in February 2014.However, the environmental impact of this omnipresent material is rarely discussed. Yet, according to several studies, producing a ton of cement emits about 900kg of CO2.Cement is a powder. When mixed with water, it sets after a few hours, then hardens into an extremely resistant material. To make the cement powder, you start by heating the raw materials (limestone and clay) at an extremely high temperature (1450°C) into a substance called clinker. This heating process explains why cement manufacturing uses so much energy.Julien Blanchard and David Hoffman wanted to invent a new construction material, that would be just as solid as concrete but much more environmentally friendly to manufacture.