How Can We Reduce Concrete's Hefty Carbon Footprint?


Publication:
Date: 
April 13, 2016
Bit by bit, innovators are chipping away at this ubiquitous material’s environmental downsides

A roomful of materials scientists, gathered at UCLA for a recent conference on “grand challenges in construction materials,” slowly passed a brick-size white block around the room. They held in their hands, briefly, part of the solution to one of those grand challenges. The white block, rock solid and surprisingly lightweight, was a new alternative to cement, the glue that holds together aggregate, or crushed rock, to make the world’s most ubiquitous building material: concrete.

Production of cement — and by extension, concrete — has a large environmental footprint, mostly due to the huge amount of energy it takes to heat limestone, cement’s key ingredient, and the subsequent chemical process it undergoes. The process of creating cement emits upwards of 80 percent of the cement’s weight in carbon dioxide and accounts for about 5 percent of human-generated CO2 emissions annually. Though the white block’s production still requires some of the CO2-emitting fuel use of typical cement making, CO2 is also one of the ingredients used to create it. About one-third CO2 by mass, the cementlike substance reduces its carbon footprint by sequestering CO2 inside the finished product.

Concrete, and the cement that binds it, is the most widely used material in the world, and its usage is on the rise. From 2011 through 2013, China used more than 6.5 billion metric tons (7.2 billion tons) of cement — more than the U.S. used in the entire 20th century. Between 2006 and 2050, global production of cement is expected to increase to between 3.7 billion metric tons (4.1 billion tons) and about 4.4 billion metric tons (4.9 billion tons) a year. Since concrete’s not going away, reducing the carbon intensity of its production is becoming a global imperative. New technologies and approaches are being developed to cut down on concrete’s environmental downsides — everything from utilizing industrial by-products to reduce cement usage, to recycling existing concrete, to producing self-healing concretes that reduce the need for new concrete, to creating entirely new materials. ...