Sesc Pompeia / Lina Bo Bardi. Image © Fernando Pires

混凝土的环境成本
The Environmental Cost of Cement, and What to Do About It

由专筑网李韧，邢子编译

几千年来，混凝土一直是建筑环境的重要基础，同时也是全球使用最为广泛的人造材料。然而，无论是建筑师还是大众，都愈发开始关注气候变化的影响与其成因，那么混凝土对于环境负面影响就已经不是一个小问题了。

Lucy Rodgers为BBC News写了一篇深刻的文章，其中说到，在全球二氧化碳排放量总数里，来源于混凝土的二氧化碳大约为8%。这篇文章的背景是于波兰召开的联合国气候变化大会（COP24），为了满足于2015年制定的《巴黎气候协议》，在2030年，混凝土的碳排放量必须下降16%。

“如果混凝土工业是一个国家，那么它会成为世界第三大排放国，仅次于中国和美国。相比起航天燃料（2.5%），混凝土甚至能够排放更多的二氧化碳，同时这也远超过全球农业的排放量（12%）。”——Lucy Rodgers, BBC News

For thousands of years, concrete has been a foundation of the built environment: the most widely used man-made material on the planet. However, as architects, and the public alike, sharpen their focus on the causes and effects of climate change, the environmental damage caused by cement has become a subject of unease.
As exhibited in a recent in-depth article by Lucy Rodgers for BBC News, cement is the source of about 8% of global CO2 emissions. The piece was written off the back of the UN’s COP24 climate change conference in Poland and found that in order to meet the requirements of the 2015 Paris Climate Agreement, annual cement emissions must fall by 16% by 2030.
“If the cement industry were a country, it would be the third largest emitter in the world – behind China and the US. It contributes more CO2 than aviation fuel (2.5%) and is not far behind the global agriculture business. (12%).”
-Lucy Rodgers, BBC News


Alexandra and Ainsworth estate / Neave Brown. Image © Fernando Pires

混凝土的起源可以追溯到公元前6000年的叙利亚与约旦，另外，诸如罗马万神庙等建筑也能更清晰地表达混凝土的应用，在19世纪与20世纪，混凝土的应用范围突然倍增。自上世纪50年代以来，混凝土产业甚至增加了30倍，到了90年代又增加了4倍，原因是欧洲战后建筑业的发展，以及90年代之后亚洲的经济增长。

如今，每年生产的混凝土超过40亿吨，释放的二氧化碳超过15亿吨。中国是混凝土与混凝土相关产品的生产大国，其次是印度、欧洲、美国等等。然而，中国混凝土的消费反过来也使得全球混凝土消费自2014年起就稳定在40亿吨左右。在未来，建筑市场会逐步向东南亚以及非洲撒哈拉地区转移，到了2030年，混凝土产品的用量也许还要增加25%，这样才能跟得上时代的发展。

Although the origins of concrete and cement can be traced back to Syria and Jordan in 6000BC, and more articulately by the Ancient Romans in magnificent structures such as the Pantheon, the 19th and 20th century saw an explosion in cement use. Production of cement has increased thirtyfold since 1950, and a further fourfold since 1990, driven by postwar building in Europe, and building booms across China and Asia from the 1990s onwards.
Today, over 4 billion tonnes of cement are produced each year, releasing over 1.5 billion tonnes of CO2. China is the top producer of cement and cement-related emissions, followed by India, the EU, and the US. However, the leveling off of Chinese consumption of cement has, in turn, caused global cement production to level off from 2014 onwards at the 4-billion tonne mark. As the future markets in construction move towards South East Asia and sub-Saharan Africa, it is predicted that cement production may have to increase by 25% by 2030 to keep pace.


The Barbican Estate / Chamberlin, Powell and Bon Architects. Image © Joas Souza

那么，混凝土为什么会成为如此严重的污染物呢？采石与运输过程占了混凝土排放量的不到10%。BBC曾经报道，超过90%的排放可能是来源于煤渣的制作过程，这是混凝土生产的关键要素。

在这个过程中，回转窑的温度会达到1,400C (2,600F)，其原料是石灰石、粘土、铁矿石、灰末的混合。这些混合物经过加热会分解为氧化钙与二氧化碳，那么二氧化碳就会释放出来，形成大理石般的灰球，这就是所谓的“煤渣”了，然后煤渣会经过冷却、研磨，再与石灰石、石膏混合，最终形成能够运输使用的混凝土。

So why is cement such a heavy polluter? The blame is frequently laid at the foot of quarrying and transport process, however this only accounts for less than 10% of cement-attributed emissions. As stressed by the BBC report, over 90% of the sector’s emissions can in fact be attributed to the process of making “clinker” – a key element of concrete.
This process sees a rotating kiln heated to over 1,400C (2,600F), fed with a quarried mix of ground limestone, clay, iron ore, and ash. The mixture is split into calcium oxide and C02, at which point the CO2 is released to leave behind marble-sized grey balls, called clinker. The clinker is then cooled, ground, and mixed with limestone and gypsum to form cement ready for transport.



而当前而言，许多人会不断呼吁利用木材等可持续材料来代替混凝土，同时人们对于混凝土对环境造成的影响的认识也不断提高，从而也会有一些可持续的产品来替代煤渣。最近，英国兰开斯特大学的研究者发现了一种新方法，那便是能够从胡萝卜和根类植物中提取纳米血小板来促进混凝土的混合。另外，Sandra Manso-Blanco博士所开发的“生物感受混凝土”也能够通过结构混凝土的分层来促进苔藓的生长，这种苔藓能够有效地吸收二氧化碳。

Taktl的策略围绕着“少即是多”的概念。其所用的高性能混凝土本质仍然是混凝土，但是其释放的二氧化碳会比传统混凝土要少很多，这说明达到相同的混凝土强度时，这种原材料所释放的二氧化碳会少一些。

As well as calls to move towards more sustainable primary building materials such as timber, the heightened awareness of the environmental damage caused by cement has led to the growth of new alternatives to the clinker process. Recently, researchers at Lancaster University in the UK unveiled a novel approach of using nanoplatelets extracted from carrots and root vegetables to enhance concrete mixes. Another trend of “bioreceptive concrete”, developed by Dr. Sandra Manso-Blanco, sees structural concrete layered with materials to encourage the growth of CO2-absorbing moss and lichen.
The approach of Taktl, meanwhile, is centered around the idea of "less is more." While this ultra-high-performance concrete is still concrete, it produces far less CO2 than traditional concrete by using less water and by being stronger, meaning you need less of it to achieve the same strength.


© Jacob Snavely

为了减少碳排放，加州的Watershed Materials公司也正在研发传统混凝土的替代策略，新型混凝土只使用少量的原材料，降低了二氧化碳的排放量，他们甚至在作品中应用了其中一种产品，希望能够完全替代传统混凝土。

新闻来源：BBC News

To further-curb runaway carbon emissions, a California-based company called Watershed Materials is developing alternatives to the traditional concrete block which uses less cement, dramatically reducing the amount of carbon dioxide produced; they even have a product in the works which they hope will offer a widely applicable concrete block alternative which uses no cement at all.
News via: BBC News