We do go on about the carbon footprint of concrete, noting that its manufacture is the source of about 5% of the CO2 emitted each year. There is a lot less talk about the stuff that makes up about 85% of concrete, and that is the aggregate that is mixed with cement. The true environmental cost of concrete has to take this into account.
Professor Ugo Bardi of the University of Florence shows this incredible graph, showing the amount of sand and rock that is dug up each year. It astonishing. He writes:
This graph is taken from an article by Krausmann et al., (see below). It is not unexpected to see that the growth of all mineral commodities has been increasing during the past century. But what's impressive is the growth of "construction minerals" which stands for sand, rock, cement and the like.... Think about that: 25 billion tons per year corresponds to more than three tons per person. Think of a ten kg cube [22 lbs] of rock and cement delivered to you and deposited in front of your door every morning, every day of the year.
So far, it seems that we have been able to pave just a few percent of the planet's surface but, given the beauty of exponential growth, the day when we will have transformed the Earth into a shiny ball of concrete can't be too far away.