The construction industry confronts its carbon footprint

FANS of cement like to point out that it is the most widely used substance on the planet after water. Unfortunately it is also one of the most polluting. The main ingredient in concrete, cement is made by heating limestone and clay until they fuse into a material called clinker, which is then ground up and mixed with various additives. Both the heating, which is normally fuelled by coal, and the chemical reaction it induces release large amounts of carbon dioxide, and so contribute to global warming. By the industry's own admission, cement-making accounts for some 5% of the world's emissions of greenhouse gases—twice the amount attributed to aviation.

The European Union already restricts emissions from cement kilns, and other jurisdictions are likely to follow suit. The biggest cement firms have joined an outfit called the Cement Sustainability Initiative, which promises to realise voluntary emissions cuts—doubtless in the hope of heading off further regulation. But with demand for cement growing by around 5% annually, the industry's environmental headaches are only likely to grow.

Lafarge, Holcim and Cemex, the three biggest firms in the business, have all pledged to cut the emissions from each tonne of cement they make: the first two by a fifth by 2010 and Cemex by a quarter by 2015. So far, they are all more or less on track. In 2006, for example, Holcim's emissions per tonne were 16% below the level of 1990.

The cuts come in three main areas. First, cement-makers are trying to make their kilns more efficient and so reduce the amount of energy needed per unit of output. Second, they are replacing fossil fuels such as coal and coke with alternatives such as farm waste or used tyres. Third, they are mixing more additives into their cement, and so reducing the proportion of emissions-intensive clinker.

But all three tactics have their limits. Cement-makers have been improving the efficiency of their kilns for over a century, leaving relatively little scope for further big gains. Fuel substitution is also difficult: environmental activists worry that burning waste might release noxious chemicals. Indeed, Greenpeace's campaigns against cement plants have focused more on the dangers of waste incineration than on their role in climate change. And building codes limit the extent to which cement can be diluted with additives.

Moreover, these measures yield only marginal benefits. Demand for cement is growing faster than emissions per tonne are falling, leading to an overall increase in emissions. Holcim's total emissions, for example, have risen by two-thirds since 1990. Lafarge has pledged to cut its overall emissions in rich countries, where demand is growing relatively sluggishly. But at the same time it hopes to expand rapidly in emerging markets. In mid-December it agreed to buy the cement division of Orascom, an Egyptian conglomerate, for €8.8 billion ($12.9 billion).

Cement firms see no way to alter the basic chemistry of cement-making. In time, they say, they may be able to capture the carbon dioxide they produce and store it underground, just as some utilities propose to do with some power stations. They also point out that the stronger and more flexible varieties of cement and concrete they have developed can be used more sparingly. Bruno Lafont, the boss of Lafarge, proudly indicates a photograph of an impossibly thin pedestrian bridge built with one such miracle product. Instead of blaming the cement industry, he says, anxious environmentalists should take on the construction industry as a whole. Buildings could be more energy-efficient with such materials, and smarter architecture and city planning could reduce the demand for cement and concrete.

David Santillo of Greenpeace supports such initiatives, but argues that the industry will ultimately need to come up with a substitute for cement. There are various alternatives, including binding agents derived from oil and silicon—but none has achieved much commercial success. Mr Lafont, meanwhile, says he spends a week in the laboratory every year, urging Lafarge's boffins on.

source: economist