C E M E N T
8% of the world's CO2 emissions? That is 2.2 billion tonnes of CO2 every year. That's (are you sitting down?) 350 times the Great Pyramid of Giza. So why is cement not an integral part of any discussion of climate change? You have to question the sanity of Homo sapiens (Wise Man) when around the world, there are currently hundreds if not thousands of projects in the advanced stages of planning and construction which involve colossal quantities of concrete. We'll look at some of these later in this section. For now, a quick look at the process of cement production will reveal the source of these vast quantities of CO2.
The raw materials limestone and clay, once crushed, are mixed with iron ore and/or silica sand.
These are ground down into a fine powder.
The powder must be heated to 1,450°C to convert the limestone into lime.
For stage 3, fossil fuels are used to heat the powder in huge rotating kilns and fossil fuels release CO2 when burnt.
When limestone is converted to lime, CO2 is given off as a waste product.
The end result is clinker which is cooled, ground down and mixed with gypsum and limestone. Result - cement.
Two sources of CO2:
60%: thermal (heating the kiln). 60-70% of cement kilns use coal for heating, the worst of the fossil fuels in terms of CO2 emissions.
40%: chemical (limestone to lime).
In an article for the BBC, Lucy Rodgers highlighted the little-known and certainly little-discussed problem associated with man's obsession with concrete:
"Concrete is the most widely used man-made material in existence. It is second only to water as the most-consumed resource on the planet."
"Cement - the key ingredient in concrete - is the source of about 8% of the world's carbon dioxide (CO2) emissions, according to thinktank Chatham House."
"If the cement industry were a country, it would be the third largest emitter in the world - behind China and the US."
One kilogram of limestone produces one kilogram of CO2 in the overall process (thermal + chemical.)
Figure 1
By Braunposc237 - Own work, CC BY-SA 4.0,
During that time, the Chinese economy was growing at warp speed. The country was and is urbanizing at a historic rate. More than 20 million Chinese relocate to cities each year. In 1978, less than 20% of China’s population lived in cities. By 2020, that proportion was 65 percent. A gargantuan quantity of cement went into building high rise flats for this influx. By 2009, China had 221 cities with more than a million people in them, compared with only 35 in Europe.
But there's more to the Chinese cement story than just tower blocks. Dams use enormous amounts of concrete, no more so than China's Three Gorges Dam across the Yangtze River (Fig. 2 below). Sometimes touted as China’s “new Great Wall”, the dam includes 27.2 million cubic metres of concrete.
In just three years, 2011-13, China used more cement than the US did in the entire 20th Century.
Think cement, think China.
It's hard to believe but China has built no fewer than 106 dams in the 21st Century. It's worth mentioning here that many of these are now functioning hydroelectric power stations. Indeed, the Three Gorges Dam is the world's largest power station in terms of capacity. Here lies the great contradiction - huge carbon emissions from billions of tonnes of cement which was used to build over a hundred dams producing 390 gigawatts of power, enough to supply 290 million homes.
But we're not finished yet. China has a water supply problem - a humid south with a relatively low population density and an arid north with a high population density. The solution, Chinese style, is the transfer of water along three canal systems, the South–North Water Transfer Project.
Figure 2
Rehman - Three_Gorges_Dam,_Yangtze_River,_China.jpg, CC BY 2.0,
Figure 3 shows the start of the Central route which runs 1264 km to Beijing. This was completed in 2014. The Eastern Route project is 1,156km in length and carries water driven along by 23 pumping stations. The third 'canal', the Western Route is projected to start in 2050. Thus far, China has spent an eye-watering $79 billion making it the world's most ambitious and expensive engineering project.
Figure 3
It goes without saying that this project requires a fair amount of concrete. Two and half thousand kilometers of aqueduct capable of transporting over 16 cubic kilometers of water each year. By 2012, some 22 million cubic meters of concrete had been laid. Based on a 1:8 cement:sand/gravel ratio in the concrete mix, this quantity of concrete will have resulted in the release, over the span of 10 years construction, of 4.95 billion tonnes of CO2.
On the flip side of the coin, these high carbon-emission projects have provided millions of Chinese with improved food security by making more water available for irrigation. Water quality in the north has also improved reducing the incidence of waterborne diseases. Together with the mitigation of droughts in the north and floods in the south, the benefits to Chinese living in rural areas is enormous. This takes us back yet again to the uncomfortable truth: the fast route to a comfortable, healthy lifestyle is down the high carbon-emission road. Affluent developed nations have already travelled that road. China is a long way down it. India is close behind. So too are many African nations. Investment in renewable energy simply isn't keeping pace with energy demand. That's why atmospheric CO2 concentration keeps on rising. And +3°C creeps ever closer.
Concrete will be with us as the go-to building material for years to come and work is proceeding apace to come up with ways of reducing its carbon-emission footprint. Read about these in the slowing climate change section. It can and must be done. Every 1% reduction in carbon-emissions is going to make a difference to the chances of avoiding +3°C.