Concrete is the most widely used construction material in the world.
混凝土是世界上使用最廣泛的建築材料。
It can be found in swathes of city pavements, bridges that span vast rivers, and the tallest skyscrapers on earth.
它常見於一條條城市道路，跨江大橋和高聳入雲的摩天大樓。
But this sturdy substance does have a weakness:
但是這種堅固的物質有一個弱點：
it's prone to catastrophic cracking that costs tens of billions of dollars to repair each year.
容易出現毀滅性的裂縫，每年要花費數百億美元來修補這些裂縫。
But what if we could avoid that problem, by creating concrete that heals itself?
如果我們能發明自我修復的混凝土來避免這個問題呢？
This idea isn't as far-fetched as it may seem.
這個想法並不像看上去那麼遙不可及。
It boils down to an understanding of how concrete forms, and how to exploit that process to our benefit.
簡單來說是要明白混凝土是怎麼形成的，並且要知道怎樣才能利用這一過程。
Concrete is a combination of coarse stone and sand particles, called aggregates,
混凝土是一種混合物，由粗石料和沙礫，稱為集料，
that mix with cement, a powdered blend of clay and limestone.
與水泥混合，水泥是黏土和石灰巖構成的粉狀混合物。
When water gets added to this mix, the cement forms a paste and coats the aggregates,
在混合物中加入水後，水泥變成糊狀物，包裹住集料，
quickly hardening through a chemical reaction called hydration.
通過化學反應迅速硬化，這一過程即水合反應。
Eventually, the resulting material grows strong enough to prop up buildings that climb hundreds of meters into the sky.
最終形成的材料十分強固，足以用來建設百米高樓，高聳入雲。
While people have been using a variety of recipes to produce cement for over 4,000 years,
雖然人們嘗試了各種方法生產水泥，已經有4000多年的歷史了，
concrete itself has a surprisingly short lifespan.
但混凝土本身的壽命卻出人意料地短暫。
After 20 to 30 years, natural processes like concrete shrinkage, excessive freezing and thawing, and heavy loads can trigger cracking.
混凝土澆築二三十年後，自然過程，例如混凝土收縮、過度融凍及負荷過重都會引發裂縫。
And it's not just big breaks that count: tiny cracks can be just as dangerous.
危險的不僅僅是大裂縫，小裂縫也同樣危險。
Concrete is often used as a secondary support around steel reinforcements.
混凝土一般用作鋼結構周圍的二級支撐。
In this concrete, even small cracks can channel water, oxygen, and carbon dioxide that corrode the steel and lead to disastrous collapse.
混凝土中的小裂縫會成為水、氧氣和二氧化碳的通道，而這些物質會腐蝕鋼結構，導致災難性坍塌。
On structures like bridges and highways that are constantly in use,
針對橋梁、道路這類頻繁使用的結構物，
detecting these problems before they lead to catastrophe becomes a huge and costly challenge.
在災難形成前，進行問題排查，是一項巨大而昂貴的挑戰。
But not doing so would also endanger thousands of lives.
但不這麼做的話，又會危及數千條生命。
Fortunately, we're already experimenting with ways this material could start fixing itself.
幸運的是，我們正在試驗各種方法，讓混凝土進行自我修復。
And some of these solutions are inspired by concrete's natural self-healing mechanism.
其中一些方法，靈感來自於混凝土天然的自我修復機制。
When water enters these tiny cracks, it hydrates the concrete's calcium oxide.
水進入小裂縫之後，會與混凝土的氧化鈣發生水合作用。
The resulting calcium hydroxide reacts with carbon dioxide in the air, starting a process called autogenous healing,
產生的氫氧化鈣與空氣中的二氧化碳反應，於是，混凝土開始了自我修復，
where microscopic calcium carbonate crystals form and gradually fill the gap.
也就是微小的額碳酸鈣晶體形成，逐漸填補裂縫的過程。
Unfortunately, these crystals can only do so much, healing cracks that are less than 0.3mm wide.
不幸的是，碳酸鈣晶體「能力有限」，只能填補寬度小於0.3mm的裂縫。
Material scientists have figured out how to heal cracks up to twice that size by adding hidden glue into the concrete mix.
材料科學家已經找到了讓修復寬度翻一倍的方法，即在混凝土混合物中加入膠粘劑。
If we put adhesive-filled fibers and tubes into the mixture,
如果我們將纖維膠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.
那麼在出現裂縫時，纖維膠液管就會破裂，釋放出膠粘劑修復裂縫。
But adhesive chemicals often behave very differently from concrete,
但是膠粘劑化學物質的運動與混凝土截然不同，
and over time, these adhesives can lead to even worse cracks.
所以時間一長，膠粘劑反而會造成更大的裂縫。
So perhaps the best way to heal large cracks is to give concrete the tools to help itself.
或許大裂縫最好的修複方式是給混凝土提供自我癒合的工具。
Scientists have discovered that some bacteria and fungi can produce minerals,
科學家已經發現一些細菌和真菌能夠生成礦物質，
including the calcium carbonate found in autogenous healing.
還有可以自我癒合的碳酸鈣。
Experimental blends of concrete include these bacterial or fungal spores alongside nutrients in their concrete mix,
混凝土試配中，在混凝土混合物中加入細菌和真菌孢子以及養分，
where they could lie dormant for hundreds of years.
這些孢子可以在此休眠，時間長達數百年。
When cracks finally appear and water trickles into the concrete,
最終當裂縫出現，水滲入混凝土裂縫時，
the spores germinate, grow, and consume the nutrient soup that surrounds them,
孢子就會開始發芽生長，消耗周圍養分，
modifying their local environment to create the perfect conditions for calcium carbonate to grow.
改變周圍環境，為碳酸鈣的形成創造完美條件。
These crystals gradually fill the gaps, and after roughly three weeks,
碳酸鈣晶體會慢慢填補裂縫，大約三周後，
the hard-working microbes can completely repair cracks up to almost 1mm wide.
這些勤勤懇懇的微生物就能完全修復寬達1mm的裂縫。
When the cracks seal, the bacteria or fungi will make spores and go dormant once more
當裂縫修復後，這些細菌和真菌會重新回到孢子狀態，重新進入休眠狀態，
ready to start a new cycle of self-healing when cracks form again.
等待裂縫再次出現時，開始新一輪的自我修復。
Although this technique has been studied extensively,
雖然這項技術已經被廣泛研究，
we still have a ways to go before incorporating it in the global production of concrete.
但是將這種辦法用於全球混凝土生產，還有很長的路要走。
But, these spores have huge potential to make concrete more resilient and long-lasting
不過這些孢子擁有巨大的潛力，能使混凝土更加持久耐用，
which could drastically reduce the financial and environmental cost of concrete production.
這能大大降低混凝土生產的資金和環境成本。
Eventually, these microorganisms may force us to reconsider the way we think about our cities,
最後，或許這些微生物會促使我們重新審視我們看待城市的方式，
bringing our inanimate concrete jungles to life.
讓毫無生氣的混凝土叢林煥發勃勃生機。