It's improved health, school attendance, agricultural productivity and farm worker wages, but concrete has a poor reputation. It takes a lot of energy to produce and releases a great deal of CO2 in the process. However, architects appreciate its versatility and there are few more important inventions. Tim Harford tells the remarkable hidden story of a ubiquitous, unloved material.

(Image: Masons hands spread concrete, Credit: APGuide/Shutterstock)