Concrete is the most widely used construction material in the world. It can be found in swathes of city pavements, bridges that span vast rivers, and the tallest skyscrapers on earth. But this sturdy substance does have a weakness: it’s prone to catastrophic cracking that costs tens of billions of dollars to repair each year. But what if we could avoid that problem, by creating concrete that heals itself?
Beton je najzastupljeniji građevinski materijal na svijetu. Može se naći svuda, od pločnika, mostova nad velikim rijekama, do najviših nebodera na svijetu. Ali ova tvrda supstanca ima jednu slabost: sklona je katastrofalnom pucanju, i desetine milijardi dolara se godišnje troše na popravke. Ali šta ako se problem može izbjeći stvaranjem betona koji se sam oporavlja? Ideja nije tako neostvariva
This idea isn’t as far-fetched as it may seem. It boils down to an understanding of how concrete forms, and how to exploit that process to our benefit. Concrete is a combination of coarse stone and sand particles, called aggregates, that mix with cement, a powdered blend of clay and limestone. When water gets added to this mix, the cement forms a paste and coats the aggregates, quickly hardening through a chemical reaction called hydration. Eventually, the resulting material grows strong enough to prop up buildings that climb hundreds of meters into the sky.
kao što se možda čini. Svodi se na razumijevanje toga kako beton nastaje, i kako taj proces može da ide u našu korist. Beton je kombinacija grubih kamenih i pješčanih čestica ili agregata, koji se miješaju sa cementom, tj. praškom od gline i krečnjaka. Kada se ovoj mješavini doda voda, cement formira pastu i oblaže agregate, koji očvrsnu kroz hemijsku reakciju koja se zove hidracija. Materijal koji nastaje u tom procesu je dovoljno snažan da čini zgrade stotinama metara visokim.
While people have been using a variety of recipes to produce cement for over 4,000 years, concrete itself has a surprisingly short lifespan. After 20 to 30 years, natural processes like concrete shrinkage, excessive freezing and thawing, and heavy loads can trigger cracking. And it’s not just big breaks that count: tiny cracks can be just as dangerous. Concrete is often used as a secondary support around steel reinforcements. In this concrete, even small cracks can channel water, oxygen, and carbon dioxide that corrode the steel and lead to disastrous collapse. On structures like bridges and highways that are constantly in use, detecting these problems before they lead to catastrophe becomes a huge and costly challenge. But not doing so would also endanger thousands of lives.
Iako su ljudi koristili razne recepte za cement tokom 4 000 godina, beton i dalje ima iznenađujuće kratak životni vijek. Nakon 20 do 30 godina, prirodni procesi poput skupljanja, pretjeranog zaleđivanja i topljenja, kao i teškog tereta mogu izazvati pucanje. I nijesu važne samo velike pukotine: sitne mogu biti jednako opasne. Beton se često koristi kao sekundarna podrška oko čeličnih nosača. Kod ovakvog betona, čak i male pukotine mogu kanalisati vodu, kiseonik i ugljen-dioksid koji razjedaju čelik i dovode do krupnih urušavanja. Na mostivima i auto-putevima koji se stalno koriste, uočavanje tih problema prije nego što izazovu katastrofu je ogroman i skup izazov. Ali ignorisanje problema ugrožava na hiljade života.
Fortunately, we’re already experimenting with ways this material could start fixing itself. And some of these solutions are inspired by concrete’s natural self-healing mechanism. When water enters these tiny cracks, it hydrates the concrete’s calcium oxide. The resulting calcium hydroxide reacts with carbon dioxide in the air, starting a process called autogenous healing, where microscopic calcium carbonate crystals form and gradually fill the gap. Unfortunately, these crystals can only do so much, healing cracks that are less than 0.3mm wide.
Srećom, već eksperimentišemo kako bi ovaj materijal mogao sam da se oporavlja. I neka od rješenja su inspirisana njegovim prirodnim metodama samoizlječenja. Kada voda uđe u ove male napukline, hidrira kalcijum oksid u betonu. Kalcijum hidroksid koji nastaje reaguje sa ugljen-dioksidom u vazduhu, i započinje proces autogenog oporavka, pri čemu nastaju mikroskopski kristali kalcijum karbonata i postepeno popunjavaju pukotine. Nažalost, ovi kristali mogu samo dijelom popraviti pukotine, one uže od 0,3 mm.
Material scientists have figured out how to heal cracks up to twice that size by adding hidden glue into the concrete mix. If we put adhesive-filled fibers and tubes into the mixture, they’ll snap open when a crack forms, releasing their sticky contents and sealing the gap. But adhesive chemicals often behave very differently from concrete, and over time, these adhesives can lead to even worse cracks.
Naučnici za materijale su shvatili kako da i dvostruko veće pukotine poprave dodavanjem lijepka u mješavinu za beton. Ako dodamo adhezivna vlakna i cjevčice u mješavinu, otvoriće se kada nastane pukotina i osloboditi ljepljivi sadržaj koji će popuniti pukotinu. Ali adhezivna sredstva se često ponašaju znatno drugačije od betona, i vremenom ovi adhezivi mogu stvoriti još gore pukotine.
So perhaps the best way to heal large cracks is to give concrete the tools to help itself. Scientists have discovered that some bacteria and fungi can produce minerals, including the calcium carbonate found in autogenous healing. Experimental blends of concrete include these bacterial or fungal spores alongside nutrients in their concrete mix, where they could lie dormant for hundreds of years. When cracks finally appear and water trickles into the concrete, the spores germinate, grow, and consume the nutrient soup that surrounds them, modifying their local environment to create the perfect conditions for calcium carbonate to grow. These crystals gradually fill the gaps, and after roughly three weeks, the hard-working microbes can completely repair cracks up to almost 1mm wide. When the cracks seal, the bacteria or fungi will make spores and go dormant once more— ready to start a new cycle of self-healing when cracks form again.
Tako da je možda najbolji način za popravku većih pukotina davanje alata betonu da se sam zaliječi. Naučnici su otkrili da pojedine bakterije i gljive proizvode minerale, uključujući kalcijum karbonat, koji pomažu autogeni oporavak. Eksperimentalne mješavine betona uključuju ove bakterije ili spore gljiva pored nutrijenata u betonskoj smješi, gdje mogu opstati uspavane stotinama godina. Kada dođe do pukotine i voda uđe u beton, spore klijaju, rastu i hrane se nutrijentima koji ih okružuju, mijenjaju lokalnu sredinu i stvaraju savršene uslove za rast kalcijum karbonata. Ovi kristali polako popunjavaju pukotine, i, otprilke, nakon tri sedmice, vrijedni mikrobi mogu potpuno da poprave pukotine širine do gotovo jednog milimetra. Kada se pukotine popune, bakterije i gljive prave spore i onda pređu u uspavano stanje - spremne da započnu novi ciklus oporavka kada se pukotine opet pojave.
Although this technique has been studied extensively, we still have a ways to go before incorporating it in the global production of concrete. But, these spores have huge potential to make concrete more resilient and long-lasting— which could drastically reduce the financial and environmental cost of concrete production. Eventually, these microorganisms may force us to reconsider the way we think about our cities, bringing our inanimate concrete jungles to life.
Iako je ova tehnika dugo vremena izučavana, pred nama je dug put prije nego što se uvede u svjetsku proizvodnju betona. Ali ove spore imaju ogroman potencijal da beton učine otpornijim i trajnijim - što bi drastično smanjilo finansijsku i ekološku cenu proizvodnje betona. Na kraju, ovi mikroorganizmi nas tjeraju da promijenimo način razmišljanja o gradovima, tako što beživotnim betonskim džunglama udahnjuju život.