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*2.2.2建房材料
非常非常类似的原文：
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.
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.
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.
cement是用来建房子的材料。生产它的过程是把limestone还有clay加一起烧。这个过程需要用fuel。需要加addictive。生产C会产生好多二氧化碳，导致温室效应。所以EU要求节能减排。他们的工场开始响应号召，想减低CO2的排放。三个措施：（1）提高cement-kiln(大概是这么个词，不知道什么意思）的效率（efficiency)。（2）替换加热能源。不用fuel而用farm waste来做fuel--但是这个方案不好（后文提到），因为会有有毒气体产生（3）生产过程中加入更多的添加剂（additives）。
下一段总起说这些措施不靠谱：（1）水泥企业已经经历了很长时间的发展，效率已经到了极限，没有多少提高的空间。（2）忘了。。。。（3）添加剂不能加太多。实际上建筑标准（construction coding)水泥里成分比例有规定，CL不能太少。然后环保人士在此处的看法：他们其实不关心CO2，而是关心burning waste：燃烧废气）
此外（Moreover），水泥需求的增加速度远远超过了排放的下降速度。所以水泥企业说他们将，虽然暂时还不能，像有些人提议的那样，把排放的东西埋到地下去。有人提议把应该把建筑物作为一个整体来考虑，整体造的好的建筑，也许能在其他方面减少排放。建议去咨询建筑学家，也许他们能想出办法，让水泥里所必须的CL成分少一些。 |
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