Cement and Global Warming

Concrete structure under construction.
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It is not an activity we think of often, but cement production is a very important source of greenhouse gases, which are responsible for global climate change.

What Is Cement?

We often confound cement and concrete, using the terms interchangeably. What is cement? Cement usually comes in dry powder form, which when mixed with water undergoes a chemical reaction and becomes a strong binding agent. It can be used to make mortar to hold bricks and stones together, or mixed with crushed stone, gravel, or sand to create concrete.

Concrete is used for making infrastructure like sidewalks, road surfaces, foundations, buildings, dams, reservoirs, and bridges. It is also used for smaller home projects like fence footings, below-ground pools, even kitchen counter tops. Enormous volumes of concrete are mixed every year, all over the globe, putting high demands on cement production.

A Primer on Cement Production

To produce cement, calcium carbonate must be heated to high temperatures to produce lime (CaO). As part of that chemical reaction, the greenhouse gas carbon dioxide (CO2) is released to the atmosphere. Lime is then further refined to produce cement powder. The calcium carbonate-to-lime chemical reaction accounts for 50% of CO2 emissions associated with cement. Another 40% of emissions come from burning the fuel used to achieve the high temperatures needed, and the remaining 10% is emitted during the grinding and transportation phases.

Due to the large amounts of carbon dioxide produced in the manufacturing of cement, and the vast amounts of concrete mixed worldwide every year (>3.4 billion tons), the cement industry is responsible for 5% of all greenhouse gas emissions.

Cement Demand Is Dynamic

The demand for cement in China has risen to dizzying heights in recent years, driven by housing needs for a growing population in a fast growing economy.

In addition, even more cement has been going into the construction of roads, bridges, and dams. Notably, the Three Gorges Dam on the Yangtze River in China necessitated the pouring of 27 million cubic meters of concrete. In 2012, China was responsible for two thirds of the entire world’s use of cement. The country’s recent economic woes, however, have cut deeply in the cement industry: for the first time in 15 years, production has been decreasing in 2015.

In the United States, the demand for cement cooled off ahead of the 2008 recession, but has picked up since. A healthier construction sector and the need to replace the rapidly aging road infrastructures should continue to fuel cement needs for many years.

What Can Be Done?

Since the need for concrete is not likely to abate soon, can the CO2 emissions coming from cement manufacturing be reduced? Newer cement plans are designed to improve efficiency in the production process, and cleaner-burning alternatives to coal can be used as fuel sources. However, climate change mitigation through greenhouse gas emission reductions seem to be most feasible by reducing our total needs for production of cement. To do that, higher strength concretes are developed, volume-saving molds are used, and different cement compositions are tested.

One promising avenue is the use of fly ash in concrete mixtures. Fly ash is one of the by-products originating from the combustion of coal, and when integrated in the concrete production process it can reduce the amount of cement needed in the mix. Fly ash can also be used to produce cement at much lower temperatures than when using conventional ingredients, reducing the amount of heating fuel needed, thus reducing greenhouse gas emissions.  

Sources

Amato, I. 2013. Green Cement: Concrete Solutions. Nature Vol. 494.

Globe and Mail. 2015. China’s Cement Alley in Decline as Economy Falters.

IPCC 2013. Fifth Assessment Report. Chapter 10: Industry.