Concrete is everywhere, but it`s bad for the planet, generating large amounts of carbon dioxide – alternatives are being developed

混凝土随处可见，但它对地球有害，会产生大量二氧化碳 - 正在开发替代品

A  Concrete is the second most used substance in the global economy, after water – and one of the world`s biggest single sources of greenhouse gas emissions. The chemical process by which cement, the key ingredient of concrete, is created results in large quantities of carbon dioxide. The UN estimates that there will be 9.8 billion people living on the planet by mid-century. They will need somewhere to live. If concrete is the only answer to the construction of new cities, then carbon emissions will soar, aggravating global warming. And so scientists have started innovating with other materials, in a scramble for alternatives to a universal commodity that has underpinned our modern life for many years.

混凝土是全球经济中使用量仅次于水的物质，也是世界上最大的温室气体排放源之一。水泥是混凝土的主要成分，其生产的化学过程会产生大量二氧化碳。据联合国估计，到本世纪中叶，地球上将有 98 亿人。他们需要地方居住。如果混凝土是建设新城市的唯一办法，那么碳排放量将激增，加剧全球变暖。因此，科学家们开始使用其他材料进行创新，争相寻找替代品，以取代这种多年来一直支撑着我们现代生活的通用商品。

B  The problem with replacing concrete is that it is so very good at what it does. Chris Cheeseman, an engineering professor at Imperial College London, says the key thing to consider is the extent to which concrete is used around the world, and is likely to continue to be used. `Concrete is not a high-carbon product. Cement is high carbon, but concrete is not. But it is the scale on which it is used that makes it high carbon. The sheer scale of manufacture is so huge, that is the issue.`

取代混凝土的问题在于它的性能非常出色。伦敦帝国理工学院工程学教授 Chris Cheeseman 说，关键是要考虑混凝土在全球的使用程度，以及是否会继续使用。混凝土不是高碳产品。水泥是高碳产品，但混凝土不是。但正是混凝土的使用规模使其成为高碳产品。生产规模如此之大，这就是问题所在。

C  Not only are the ingredients of concrete relatively cheap and found in abundance in most places around the globe, the stuff itself has marvellous properties: Portland cement, the vital component of concrete, is mouldable and pourable, but quickly sets hard. Cheeseman also notes another advantage: concrete and steel have similar thermal expansion properties, so steel can be used to reinforce concrete, making it far stronger and more flexible as a building material than it could be on its own. According to Cheeseman, all these factors together make concrete hard to beat. `Concrete is amazing stuff. Making anything with similar properties is going to be very difficult.`

混凝土的成分不仅相对便宜，而且在全球大多数地方都能大量找到，混凝土本身也具有奇妙的特性： 波特兰水泥是混凝土的重要成分，具有可塑性和可浇注性，但很快就会凝固变硬。切斯曼还指出了另一个优点：混凝土和钢材具有相似的热膨胀特性，因此可以用钢材来加固混凝土，使其作为建筑材料的强度和灵活性远远超过混凝土本身。Cheeseman 认为，所有这些因素加在一起，使混凝土变得难以超越。混凝土是一种神奇的材料。制造具有类似性能的任何东西都会非常困难。

D  A possible alternative to concrete is wood. Making buildings from wood may seem like a rather medieval idea, but climate change is driving architects to turn to treated timber as a possible resource. Recent years have seen the emergence of tall buildings constructed almost entirely from timber. Vancouver, Vienna and Brumunddal in Norway are all home to constructed tall, wooden buildings.

混凝土的一个可能替代品是木材。用木材建造建筑似乎是一个相当中世纪的想法，但气候变化正促使建筑师将处理过的木材作为一种可能的资源。近年来，出现了几乎完全用木材建造的高层建筑。温哥华、维也纳和挪威的布鲁蒙德达尔都是木制高层建筑的发源地。

E  Using wood to construct buildings, however, is not straightforward. Wood expands as it absorbs moisture from the air and is susceptible to pests, not to mention fire. But treating wood and combining it with other materials can improve its properties. Cross-laminated timber is engineered wood. An adhesive is used to stick layers of solid-sawn timber together, crosswise, to form building blocks. This material is light but has the strength of concrete and steel. Construction experts say that wooden buildings can be constructed at a greater speed than ones of concrete and steel and the process, it seems, is quieter.

然而，使用木材建造建筑物并不简单。木材在吸收空气中的水分后会膨胀，而且容易受到虫害，更不用说火灾了。但是，对木材进行处理并将其与其他材料相结合，可以改善木材的特性。交叉层压木材是一种工程木材。使用粘合剂将一层层实木锯材横向粘在一起，形成建筑砌块。这种材料重量轻，但具有混凝土和钢的强度。建筑专家说，木制建筑的建造速度比混凝土和钢筋建筑快，而且建造过程似乎更安静。

F  Stora Enso is Europe`s biggest supplier of cross-laminated timber, and its vice-president Markus Mannström reports that the company is seeing increasing demand globally for building in wood, with climate change concerns the key driver. Finland, with its large forests, where Stora Enso is based, has been leading the way, but the company is seeing a rise in demand for its timber products across the world, including in Asia. Of course, using timber in a building also locks away the carbon that it absorbed as it grew. But even treated wood has its limitations and only when a wider range of construction projects has been proven in practice will it be possible to see wood as a real alternative to concrete in constructing tall buildings.

斯道拉恩索公司是欧洲最大的交错层压木材供应商，其副总裁马库斯-曼斯特罗姆（Markus Mannström）报告说，该公司看到全球对木结构建筑的需求日益增长，而气候变化问题是主要驱动因素。斯道拉恩索公司总部所在的芬兰拥有大片森林，在这方面一直处于领先地位，但该公司看到，包括亚洲在内的世界各地对其木材产品的需求都在增加。当然，在建筑中使用木材也会锁住木材在生长过程中吸收的碳。但是，即使是经过处理的木材也有其局限性，只有当更多的建筑项目在实践中得到验证后，才有可能将木材视为建造高层建筑时混凝土的真正替代品。

G  Fly ash and slag from iron ore are possible alternatives to cement in a concrete mix. Fly ash, a byproduct of coal-burning power plants, can be incorporated into concrete mixes to make up as much as 15 to 30% of the cement, without harming the strength or durability of the resulting mix. Iron-ore slag, a byproduct of the iron-ore smelting process, can be used in a similar way. Their incorporation into concrete mixes has the potential to reduce greenhouse gas emissions.

来自铁矿石的粉煤灰和矿渣是混凝土混合料中水泥的可能替代品。粉煤灰是燃煤发电厂的副产品，可掺入混凝土混合料中，占水泥的 15% 至 30%，而不会损害混合料的强度或耐久性。铁矿渣是铁矿石冶炼过程中产生的副产品，也可以类似的方式使用。将它们加入混凝土混合料中有可能减少温室气体排放。

But Anna Surgenor, of the UK`s Green Building Council, notes that although these waste products can save carbon in the concrete mix, their use is not always straightforward. `It`s possible to replace the cement content in concrete with waste products to lower the overall carbon impact. But there are several calculations that need to be considered across the entire life cycle of the building – these include factoring in where these materials are being shipped from. If they are transported over long distances, using fossil fuels, the use of alternative materials might not make sense from an overall carbon reduction perspective.`

但英国绿色建筑委员会的 Anna Surgenor 指出，虽然这些废品可以在混凝土混合料中节约碳，但使用起来并不总是那么简单。用废品替代混凝土中的水泥成分可以降低整体的碳影响。但是，在建筑物的整个生命周期中，有几项计算需要考虑，其中包括这些材料的运输地点。如果使用化石燃料进行长途运输，那么从整体碳减排的角度来看，使用替代材料可能并不合理。

H  While these technologies are all promising ideas, they are either unproven or based on materials that are not abundant. In their overview of innovation in the concrete industry, Felix Preston and Johanna Lehne of the UK`s Royal Institute of International Affairs reached the conclusion that, `Some novel cements have been discussed for more than a decade within the research community, without breaking through. At present, these alternatives are rarely as cost-effective as conventional cement, and they face raw-material shortages and resistance from customers.`

虽然这些技术都是很有前景的想法，但它们要么未经证实，要么基于并不丰富的材料。英国皇家国际事务研究所的费利克斯-普雷斯顿（Felix Preston）和约翰娜-莱恩（Johanna Lehne）在对混凝土行业的创新进行概述后得出结论："一些新型水泥在研究界已经讨论了十多年，但仍未取得突破。目前，这些替代品很少具有传统水泥的成本效益，而且面临原材料短缺和客户抵制的问题。