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Concrete is the most widely used construction material in the world.
混凝土是世界上使用最广泛的建筑材料。
It can be found in swathes of city pavements, bridges that span vast rivers, and the tallest skyscrapers on earth.
它常见于一条条城市道路，跨江大桥和高耸入云的摩天大楼。
But this sturdy substance does have a weakness:
但是这种坚固的物质有一个弱点：
it's prone to catastrophic cracking that costs tens of billions of dollars to repair each year.
容易出现毁灭性的裂缝，每年要花费数百亿美元来修补这些裂缝。
But what if we could avoid that problem, by creating concrete that heals itself?
如果我们能发明自我修复的混凝土来避免这个问题呢？
This idea isn't as far-fetched as it may seem.
这个想法并不像看上去那么遥不可及。
It boils down to an understanding of how concrete forms, and how to exploit that process to our benefit.
简单来说是要明白混凝土是怎么形成的，并且要知道怎样才能利用这一过程。
Concrete is a combination of coarse stone and sand particles, called aggregates,
混凝土是一种混合物，由粗石料和沙砾，称为集料，
that mix with cement, a powdered blend of clay and limestone.
与水泥混合，水泥是黏土和石灰岩构成的粉状混合物。
When water gets added to this mix, the cement forms a paste and coats the aggregates,
在混合物中加入水后，水泥变成糊状物，包裹住集料，
quickly hardening through a chemical reaction called hydration.
通过化学反应迅速硬化，这一过程即水合反应。
Eventually, the resulting material grows strong enough to prop up buildings that climb hundreds of meters into the sky.
最终形成的材料十分强固，足以用来建设百米高楼，高耸入云。
While people have been using a variety of recipes to produce cement for over 4,000 years,
虽然人们尝试了各种方法生产水泥，已经有4000多年的历史了，
concrete itself has a surprisingly short lifespan.
但混凝土本身的寿命却出人意料地短暂。
After 20 to 30 years, natural processes like concrete shrinkage, excessive freezing and thawing, and heavy loads can trigger cracking.
混凝土浇筑二三十年后，自然过程，例如混凝土收缩、过度融冻及负荷过重都会引发裂缝。
And it's not just big breaks that count: tiny cracks can be just as dangerous.
危险的不仅仅是大裂缝，小裂缝也同样危险。
Concrete is often used as a secondary support around steel reinforcements.
混凝土一般用作钢结构周围的二级支撑。
In this concrete, even small cracks can channel water, oxygen, and carbon dioxide that corrode the steel and lead to disastrous collapse.
混凝土中的小裂缝会成为水、氧气和二氧化碳的通道，而这些物质会腐蚀钢结构，导致灾难性坍塌。
On structures like bridges and highways that are constantly in use,
针对桥梁、道路这类频繁使用的结构物，
detecting these problems before they lead to catastrophe becomes a huge and costly challenge.
在灾难形成前，进行问题排查，是一项巨大而昂贵的挑战。
But not doing so would also endanger thousands of lives.
但不这么做的话，又会危及数千条生命。
Fortunately, we're already experimenting with ways this material could start fixing itself.
幸运的是，我们正在试验各种方法，让混凝土进行自我修复。
And some of these solutions are inspired by concrete's natural self-healing mechanism.
其中一些方法，灵感来自于混凝土天然的自我修复机制。
When water enters these tiny cracks, it hydrates the concrete's calcium oxide.
水进入小裂缝之后，会与混凝土的氧化钙发生水合作用。
The resulting calcium hydroxide reacts with carbon dioxide in the air, starting a process called autogenous healing,
产生的氢氧化钙与空气中的二氧化碳反应，于是，混凝土开始了自我修复，
where microscopic calcium carbonate crystals form and gradually fill the gap.
也就是微小的额碳酸钙晶体形成，逐渐填补裂缝的过程。
Unfortunately, these crystals can only do so much, healing cracks that are less than 0.3mm wide.
不幸的是，碳酸钙晶体“能力有限”，只能填补宽度小于0.3mm的裂缝。
Material scientists have figured out how to heal cracks up to twice that size by adding hidden glue into the concrete mix.
材料科学家已经找到了让修复宽度翻一倍的方法，即在混凝土混合物中加入胶粘剂。
If we put adhesive-filled fibers and tubes into the mixture,
如果我们将纤维胶液管加入到混凝土混合物中，
they'll snap open when a crack forms, releasing their sticky contents and sealing the gap.
那么在出现裂缝时，纤维胶液管就会破裂，释放出胶粘剂修复裂缝。
But adhesive chemicals often behave very differently from concrete,
但是胶粘剂化学物质的运动与混凝土截然不同，
and over time, these adhesives can lead to even worse cracks.
所以时间一长，胶粘剂反而会造成更大的裂缝。
So perhaps the best way to heal large cracks is to give concrete the tools to help itself.
或许大裂缝最好的修复方式是给混凝土提供自我愈合的工具。
Scientists have discovered that some bacteria and fungi can produce minerals,
科学家已经发现一些细菌和真菌能够生成矿物质，
including the calcium carbonate found in autogenous healing.
还有可以自我愈合的碳酸钙。
Experimental blends of concrete include these bacterial or fungal spores alongside nutrients in their concrete mix,
混凝土试配中，在混凝土混合物中加入细菌和真菌孢子以及养分，
where they could lie dormant for hundreds of years.
这些孢子可以在此休眠，时间长达数百年。
When cracks finally appear and water trickles into the concrete,
最终当裂缝出现，水渗入混凝土裂缝时，
the spores germinate, grow, and consume the nutrient soup that surrounds them,
孢子就会开始发芽生长，消耗周围养分，
modifying their local environment to create the perfect conditions for calcium carbonate to grow.
改变周围环境，为碳酸钙的形成创造完美条件。
These crystals gradually fill the gaps, and after roughly three weeks,
碳酸钙晶体会慢慢填补裂缝，大约三周后，
the hard-working microbes can completely repair cracks up to almost 1mm wide.
这些勤勤恳恳的微生物就能完全修复宽达1mm的裂缝。
When the cracks seal, the bacteria or fungi will make spores and go dormant once more
当裂缝修复后，这些细菌和真菌会重新回到孢子状态，重新进入休眠状态，
ready to start a new cycle of self-healing when cracks form again.
等待裂缝再次出现时，开始新一轮的自我修复。
Although this technique has been studied extensively,
虽然这项技术已经被广泛研究，
we still have a ways to go before incorporating it in the global production of concrete.
但是将这种办法用于全球混凝土生产，还有很长的路要走。
But, these spores have huge potential to make concrete more resilient and long-lasting
不过这些孢子拥有巨大的潜力，能使混凝土更加持久耐用，
which could drastically reduce the financial and environmental cost of concrete production.
这能大大降低混凝土生产的资金和环境成本。
Eventually, these microorganisms may force us to reconsider the way we think about our cities,
最后，或许这些微生物会促使我们重新审视我们看待城市的方式，
bringing our inanimate concrete jungles to life.
让毫无生气的混凝土丛林焕发勃勃生机。
