Scientists Study Long-lasting Ancient Structures
2023-10-10
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1Ancient builders across the world created structures that are still standing today, thousands of years later.
2Roman engineers built thick concrete sea barriers, for example.
3Mayan builders created sculptures to their gods, and Chinese builders raised walls against invaders.
4But there are many recent structures that are already starting to fail.
5The concrete that makes up much of our modern world lasts around 50 to 100 years.
6A growing number of scientists have been studying materials from long-ago.
7They are breaking apart pieces of buildings and reading historical texts hoping to learn how they have stood for thousands of years.
8The research has turned up a surprising list of materials that were mixed into old buildings.
9They include tree bark, volcanic ash, rice, beer and even urine.
10These unexpected materials could have the ability to get stronger over time and "heal" cracks when they form.
11Figuring out how to copy these features could have real impacts today.
12While our modern concrete has the strength to hold up very tall buildings and heavy infrastructure, it cannot compete with the endurance of these ancient materials.
13With the rising threats of climate change, there is a growing call to make construction more sustainable.
14A recent UN report estimates that the built environment is responsible for more than a third of carbon dioxide emissions worldwide.
15Cement production alone makes up more than 7 percent of those emissions.
16Many researchers have turned to the Romans.
17Starting around 200 BCE, the Roman Empire was building concrete structures that have stood the test of time.
18That includes the Pantheon to the aqueducts that still carry water today.
19Even in places where seawater has been hitting structures for ages, you will find concrete "basically the way it was when it was poured 2,000 years ago," said John Oleson.
20He is an archaeologist at the University of Victoria in Canada.
21Most modern concrete starts with Portland cement, a powder made by heating limestone and clay to super-high temperatures and grinding them up.
22That cement is mixed with water to create a paste.
23Then, materials like rock and gravel are added.
24Records from ancient builders show the Roman process was similar.
25The ancient builders mixed materials like burnt limestone and volcanic sand with water and gravel, creating chemical reactions to tie everything together.
26Now, scientists think they have found an important reason why some Roman concrete has held up structures for thousands of years.
27The ancient material has an unusual power to repair itself.
28Exactly how is not yet clear, but scientists are starting to find reasons why.
29Admir Masic is a civil and environmental engineer at the Massachusetts Institute of Technology.
30In a study, he said this power comes from chunks of limestone throughout the Roman material that is not mixed in evenly.
31Researchers used to think these chunks were a sign that the Romans were not mixing up their materials well enough.
32Instead, the scientists found that the chunks could fuel the material's "self-healing" abilities.
33When cracks form, water enters the concrete, Masic explained.
34That water activates the leftover lime, creating new chemical reactions that can fill in the damaged sections.
35Today's builders cannot just copy the ancient processes.
36Even though Roman concrete lasted a long time, it could not hold up heavy buildings.
37"You couldn't build a modern skyscraper with Roman concrete," Oleson said.
38"It would collapse when you got to the third story."
39Instead, researchers are trying to take some of the ancient materials and add them into modern mixes.
40Masic is part of a company that is trying to build new projects using "self-healing" concrete.
41People do not need to make things last quite as long as the Romans did to have an impact, Masic said.
42If we add 50 or 100 years to concrete's lifespan, he said, "we will require less demolition, less maintenance and less material in the long run."
43I'm Dan Novak.
1Ancient builders across the world created structures that are still standing today, thousands of years later. 2Roman engineers built thick concrete sea barriers, for example. Mayan builders created sculptures to their gods, and Chinese builders raised walls against invaders. 3But there are many recent structures that are already starting to fail. The concrete that makes up much of our modern world lasts around 50 to 100 years. 4A growing number of scientists have been studying materials from long-ago. They are breaking apart pieces of buildings and reading historical texts hoping to learn how they have stood for thousands of years. 5The research has turned up a surprising list of materials that were mixed into old buildings. They include tree bark, volcanic ash, rice, beer and even urine. These unexpected materials could have the ability to get stronger over time and "heal" cracks when they form. 6Figuring out how to copy these features could have real impacts today. While our modern concrete has the strength to hold up very tall buildings and heavy infrastructure, it cannot compete with the endurance of these ancient materials. 7With the rising threats of climate change, there is a growing call to make construction more sustainable. A recent UN report estimates that the built environment is responsible for more than a third of carbon dioxide emissions worldwide. Cement production alone makes up more than 7 percent of those emissions. 8Is ancient Roman concrete better? 9Many researchers have turned to the Romans. Starting around 200 BCE, the Roman Empire was building concrete structures that have stood the test of time. That includes the Pantheon to the aqueducts that still carry water today. 10Even in places where seawater has been hitting structures for ages, you will find concrete "basically the way it was when it was poured 2,000 years ago," said John Oleson. He is an archaeologist at the University of Victoria in Canada. 11Most modern concrete starts with Portland cement, a powder made by heating limestone and clay to super-high temperatures and grinding them up. That cement is mixed with water to create a paste. Then, materials like rock and gravel are added. 12Records from ancient builders show the Roman process was similar. The ancient builders mixed materials like burnt limestone and volcanic sand with water and gravel, creating chemical reactions to tie everything together. 13Now, scientists think they have found an important reason why some Roman concrete has held up structures for thousands of years. The ancient material has an unusual power to repair itself. Exactly how is not yet clear, but scientists are starting to find reasons why. 14Admir Masic is a civil and environmental engineer at the Massachusetts Institute of Technology. In a study, he said this power comes from chunks of limestone throughout the Roman material that is not mixed in evenly. Researchers used to think these chunks were a sign that the Romans were not mixing up their materials well enough. 15Instead, the scientists found that the chunks could fuel the material's "self-healing" abilities. When cracks form, water enters the concrete, Masic explained. That water activates the leftover lime, creating new chemical reactions that can fill in the damaged sections. 16Ancient Roman ... skyscrapers? 17Today's builders cannot just copy the ancient processes. Even though Roman concrete lasted a long time, it could not hold up heavy buildings. "You couldn't build a modern skyscraper with Roman concrete," Oleson said. "It would collapse when you got to the third story." 18Instead, researchers are trying to take some of the ancient materials and add them into modern mixes. Masic is part of a company that is trying to build new projects using "self-healing" concrete. 19People do not need to make things last quite as long as the Romans did to have an impact, Masic said. If we add 50 or 100 years to concrete's lifespan, he said, "we will require less demolition, less maintenance and less material in the long run." 20I'm Dan Novak. 21Dan Novak adapted this story for VOA Learning English based on reporting by The Associated Press. 22_______________________________________ 23Words in This Story 24concrete - n. a hard, strong material that is used for building and made by mixing cement, sand, and broken rocks with water 25infrastructure - n. the basic equipment and structures that are needed for a country, region, or organization to function properly 26endurance - n. the ability to do something difficult for a long time 27sustainable - adj. able to be used without being completely used up or destroyed 28emissions - n. the act of producing or sending out something from a source 29aqueduct - n. a structure that looks like a bridge and that is used to carry water over a valley 30paste - n. a soft, wet mixture of usually a powder and a liquid 31chunk - n. a thick piece of something 32demolition - n. deliberate destruction of a building or other structure