治愈混凝土顽疾

Curing concrete cancer

Two Australian bridges try to stand the test of time

治愈混凝土顽疾

两座澳大利亚桥梁将试图经受住时间的考验

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What have the Romans done for us?

罗马人为我们做了什么？

Modern civilization is built on concrete and steel. Put the two together, though, and you can generate a problem. Reinforcing concrete with steel rods called rebars is the basis of modern construction. But because water gets in through tiny cracks, the rebars rust. This causes them to expand, widening the cracks and weakening the concrete. Hence such structures require constant attention and often have design lives of only 60-100 years. That is pitiful compared with, say, the concrete dome of the Pantheon in Rome—which was completed in 125ad and still stands.

现代文明是建立在混凝土和钢材之上的。但是，将两者放在一起，就可能会产生问题。钢筋混凝土是现代建筑的基础。但是由于水通过微小的裂缝渗入易导致钢筋生锈。这导致钢筋膨胀、裂缝扩张并削弱混凝土。因此，这种结构需要持续的关注，并且设计寿命通常只有60-100年。这与保留至今的古代建筑（例如罗马万神殿的混凝土穹顶）相比，显得微不足道，罗马万神殿建成于公元125年，至今仍然屹立不倒。

Various ways of delaying or preventing concrete cancer, as this corrosion is known colloquially, have been tried. These include recipes for concrete that is less permeable to water, andrebars made from rust-resistant materials such as stainless-steel or composites. Such approaches work, but they can be expensive.

混凝土的易腐蚀性众所周知，人们已经尝试了各种延迟或预防混凝土腐蚀的方法。这包括采用低透水性的混凝土配方，以及由防锈材料（例如不锈钢或复合材料）制成的钢筋。这样的方法是可行的，但价格昂贵。

This may be about to change. Next year, if all goes well, a pair of footbridges intended to be cancer-proof will open in Geelong, a town 75km south-west of Melbourne, Australia. These bridges, which will act as prototypes for more than 150 others planned for the expanding city, will be constructed using a novel approach that combines glass-fibre and carbon-fibre rebars. They will, though, cost about the same as equivalent conventional bridges.

情况可能会发生改变。如果一切顺利，明年两座旨在终结混凝土腐蚀问题的的行人天桥将在澳大利亚墨尔本西南75公里的吉朗（Geelong）开通。这两座桥梁采用新型的组合玻璃纤维和碳纤维建造，将成为城市规划中另外的150多座桥梁的原型。此外，他们的建造成本与传统桥梁大致相同。

The new design is the brainchild of a joint team of researchers from Deakin, a local university, and Austeng, the firm contracted to build the bridges. This team began with commercially available rebars made from carbon-fibre composite. Although these are as strong as steel ones, they are expensive. They are, therefore, most often used in specialist structures such as buildings to house mri hospitals canners, where electromagnetic interference from metal can cause problems.

这项新设计是由当地大学迪肯（Deakin）和承包建造桥梁的公司奥斯汀（Austeng）组成的联合研究小组的创意。这个团队开始使用碳纤维复合材料，尽管它们与钢筋一样坚固，但价格高昂。因此，碳纤维复合材料主要用于特种结构中，例如用于容纳医用扫描仪的建筑物，在这些建筑物中，金属的电磁干扰会给仪器带来问题。

To get around this the team have worked out how to minimise cost by using carbon-fibre rebars only where strictly necessary. In other places they use glass fibre, which is cheaper. Theresult is a frame that acts as a skeleton for precast concrete sections which can then be assembled into a bridge.

为了解决这个问题，团队已经研究出如何仅在严格必要的位置才使用碳纤维钢筋来最小化成本。在其它地方，他们使用便宜的玻璃纤维。这样便可制成预制混凝土节段，然后再组装成桥。

According to Mahbube Subhani, one of the researchers at Deakin, a three-metre-long version of such asection has just been tested and has passed local building codes. The group is now pressing ahead with the first of the ten-metre sections needed to construct the bridges themselves.

根据Deakin的研究人员之一Mahbube Subhani的说法，3米长的新型混凝土节段刚刚经过了测试，并通过了当地建筑规范。该小组目前正在推进用于组装实际桥梁的第一个10米长混凝土节段的工作。

The new castings are, as was hoped, both stronger and lighter than steel-reinforced concrete. Tests showed that the prototype’s load-carrying capacity was 20% better, even though its cross-section was 15% smaller. Production costs are “a little bit higher”, DrSubhani admits. But in the long run, he says, the bridges will work out cheaper because they should last for at least 100 years without any maintenance being required.

如所希望的，新型混凝土比钢筋混凝土更坚固，更轻。测试表明，即使横截面减少15％，其承载能力却提高20％。 Subhani博士承认，新型混凝土的生产成本“略微高一点”。但是从长远来看，这样的桥梁造价会更低，因为它们至少可以使用100年，而无需任何维护。

They will also be more environmentally friendly, for the concrete surrounding the skeleton is unconventional, too. Normal concrete is bound with Portland cement, which is made by roasting a mixture that includes limestone (calcium carbonate). This process drives off carbon dioxide, a greenhouse gas, and cement-making is a big source of such emissions.

它们也将更加环保，因为使用的混凝土也是非常规的。普通混凝土由硅酸盐水泥制成，硅酸盐水泥是通过焙烧包含石灰石（碳酸钙）的混合物制成的。这个过程会排除温室气体二氧化碳，而水泥制造是二氧化碳排放的主要来源。

Geelong’s bridges, by contrast, will be made with geopolymer concrete. This uses cement made from a different mixture of ingredients, including furnace fly-ash, which do not release carbon dioxide when being processed.

相比之下，吉朗的桥梁将由地聚合物混凝土（geopolymer concrete）制成。这类混凝土使用由不同成分的混合物制成的水泥（包括炉灰），且在加工时不会释放二氧化碳。

Further down the line Deakin’s researchers are looking into making rebars out of basalt, an abundant volcanic rock, by melting it and extruding it into fibres. That could provide a cheaper and greener alternative to carbon fibres, which are usually made from oil-based polymers. Some commercial basalt-fibre composites are already available, but the team think they can improve the performance of such fibres further, by adding other materials.

迪肯的研究人员正在进一步研究，通过将玄武岩（一种丰富的火山岩）融化并将其挤压成纤维。这可以为通常由油基聚合物制成的碳纤维提供一种更便宜、更环保的替代品。一些商用玄武岩纤维复合材料已经面市，但研究小组认为，通过添加其他材料，它们可以进一步改善此类纤维的性能。

Coincidentally, one of the ingredients of the Pantheon’s concrete dome is pumice, another volcanic rock.Whether basalt-fibre concrete will similarly stand the test of time only future architects will know.

巧合的是，万神殿混凝土穹顶的成分之一便是另一种火山岩—浮石（pumice）。未来的建筑师将见证，玄武岩纤维混凝土（basalt-fibre concrete）是否同样能经受住时间的考验。

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（本文原载于2019.11.02 The Economist)