The circular economy and sustainable concrete

Do engineers need to significantly change how we use materials to make what we build sustainable? I've been thinking recently about this question in the context of concrete, one of the most frequently used materials in construction. In this post I'll be exploring the two main problems with concrete: that it is extremely energy-intensive to manufacture, and it is difficult to re-use without downgrading the quality.

For example, industry statistics show that last year the UK construction industry used 15 million cubic metres (37.5 million tonnes) of ready-mix concrete and 25 million tonnes of concrete products from blocks and pre-cast walls to driven piles.  

Castleton cement works in Derbyshire
(picture by Dave Pape)

Concrete is formed from two materials: cement and aggregate. Quarrying is required for both elements (with attendant environmental and landscape impacts), but the cement also requires a chemical reaction to occur: calcium carbonate (ie limestone) is heated to a high temperature (300 degrees C) to drive off CO2 and form calcium oxide instead. Therefore making cement produces CO2 both from the fuel used for heating and from the reaction itself (although this can be somewhat recovered when used, as hardening cement absorbs CO2 to form calcium carbonate again).