cement and the environment

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cement and the environment

Postby Paul Clerkin » Tue Jan 29, 2008 4:33 pm

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 is cement, 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 per cent 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 realize voluntary emissions cuts – doubtless in the hope of heading off further regulation.

But with demand for cement growing by around 5 per cent 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: 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 per cent 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 tires.
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.

Cement firms see no way to alter the 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, a senior scientist for 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.

None, however, has achieved much commercial success.
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Re: cement and the environment

Postby PTB » Wed Jan 30, 2008 8:49 am

What about the cement made from the slag from Iron smelting? I thought that was fairly eco-friendly. Its used quite a lot in the Benelux nations.
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Re: cement and the environment

Postby Paul Clerkin » Thu Jan 31, 2008 4:01 am

Greener cement production starts soon

A factory on the outskirts of Melbourne, Australia could be about to provide a big step forward for green building. It's the first commercial enterprise in the world dedicated to transforming waste from power stations and blast furnaces into geopolymer concrete, said by the manufacturer to offer significant savings in carbon emissions compared to normal cement based concrete.

The factory, owned by the company Zeobond, is due to start operations in February.

Geopolymers, the basic substance of Zeobond's E-crete are a type of inorganic polymer formed at room temperature by using industrial waste, fly ash and bottom ash from power stations, blast furnace slag from iron making plants, and recycled cement waste to form a solid binder that looks like and performs a similar function to ordinary Portland cement.

According to the World Business Council for Sustainable Development (WBCSD), “Concrete is the most widely used material on earth apart from water, with nearly three tons used annually for each man, woman, and child.” Cement is made by burning fossil fuels when the limestone and clay are heated to over 1300°C and CO2 is liberated from the decomposed limestone.

The hugely energy intensive calcination step is a necessary key to cement production. Therefore, the focus of reductions in CO2 emissions during cement manufacturing is on energy use.

However, emissions reduction is ultimately limited by two factors: (1) the high temperature needed to drive the calcination of limestone, and (2) 60% of CO2 produced in cement manufacture arises from the calcination reaction itself.

The manufacture of cement produces about 0.9 kilograms of CO2 for every kilogram of cement. At least 4% of global CO2 emissions result from cement manufacture, making this product one of the more polluting activities undertaken by mankind.

One of the primary advantages of geopolymers over traditional cements from an environmental perspective is largely associated with the much lower CO2 emissions from geopolymer manufacture compared to OPC production. This is mainly due to the absence of the high-temperature calcination step in geopolymer synthesis.

While the activators used in geopolymers do reintroduce some CO2 cost, the overall CO2 saving due to widespread geopolymer utilisation is in the order of 80-90% when compared with Portland cement.

Zeobond is currently involved in an accreditation process and Life Cycle Analysis with a view to having the environmental benefits of geopolymers officially acknowledged by the relevant Australian and international bodies.

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