Cement industry accounts for about 8% of CO2 emissions. One startup seeks to change that.

Cement is the most widely-used substance on Earth after water. When mixed with water, it forms concrete that becomes the backbone of buildings, roads, dams and bridges. 

But the cement industry is responsible for about 8% of planet-warming carbon dioxide emissions — far more than global carbon emissions from aviation. If the cement industry were a country, it would be the third-largest emitter of carbon dioxide in the world, after the U.S. and China. 

One startup seeks to change that. At the California-based company Brimstone, CEO Cody Finke and his team in Oakland have discovered a potentially game-changing solution: the world's first carbon-negative cement, made from calcium silicate rocks.