VOA科学技术2023--Scientists Study Long-lasting Ancient Structures

Scientists Study Long-lasting Ancient Structures

Ancient builders across the world created structures that are still standing¹ today, thousands of years later.

Roman engineers built thick concrete sea barriers, for example. Mayan builders created sculptures to their gods, and Chinese builders raised walls against invaders².

But 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.

A 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.

The research has turned up a surprising list of materials that were mixed into old buildings. They include tree bark, volcanic³ ash, rice, beer and even urine. These unexpected materials could have the ability to get stronger over time and "heal" cracks when they form.

Figuring 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 infrastructure⁴, it cannot compete with the endurance of these ancient materials.

With 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 emissions⁵ worldwide. Cement production alone makes up more than 7 percent of those emissions.

Is ancient Roman concrete better?

Many 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.

Even 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.

Most modern concrete starts with Portland cement, a powder made by heating limestone⁶ 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 gravel⁷ are added.

Records 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.

Now, 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.

Admir Masic is a civil and environmental engineer at the Massachusetts Institute of Technology. In a study, he said this power comes from chunks⁹ 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.

Instead, 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 activates¹⁰ the leftover¹¹ lime, creating new chemical reactions that can fill in the damaged sections.

Ancient Roman ... skyscrapers¹³?

Today'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 skyscraper¹² with Roman concrete," Oleson said. "It would collapse¹⁴ when you got to the third story."

Instead, 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.

People 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 demolition¹⁵, less maintenance and less material in the long run."

Words in This Story

concrete — n. a hard, strong material that is used for building and made by mixing cement, sand, and broken rocks with water

infrastructure — n. the basic equipment and structures that are needed for a country, region, or organization to function properly

endurance — n. the ability to do something difficult for a long time

sustainable — adj. able to be used without being completely used up or destroyed

emissions — n. the act of producing or sending out something from a source

aqueduct — n. a structure that looks like a bridge and that is used to carry water over a valley

paste — n. a soft, wet mixture of usually a powder and a liquid

chunk⁸ — n. a thick piece of something

demolition — n. deliberate destruction of a building or other structure

1 standing   

n.持续，地位；adj.永久的，不动的，直立的，不流动的

参考例句：

• After the earthquake only a few houses were left standing.地震过后只有几幢房屋还立着。
• They're standing out against any change in the law.他们坚决反对对法律做任何修改。

2 invaders   

入侵者，侵略者，侵入物( invader的名词复数 )

参考例句：

• They prepared to repel the invaders. 他们准备赶走侵略军。
• The family has traced its ancestry to the Norman invaders. 这个家族将自己的世系追溯到诺曼征服者。

3 volcanic   

adj.火山的；象火山的；由火山引起的

参考例句：

• There have been several volcanic eruptions this year.今年火山爆发了好几次。
• Volcanic activity has created thermal springs and boiling mud pools.火山活动产生了温泉和沸腾的泥浆池。

4 infrastructure   

n.下部构造，下部组织，基础结构，基础设施

参考例句：

• We should step up the development of infrastructure for research.加强科学基础设施建设。
• We should strengthen cultural infrastructure and boost various types of popular culture.加强文化基础设施建设，发展各类群众文化。

5 emissions   

排放物( emission的名词复数 )； 散发物（尤指气体）

参考例句：

• Most scientists accept that climate change is linked to carbon emissions. 大多数科学家都相信气候变化与排放的含碳气体有关。
• Dangerous emissions radiate from plutonium. 危险的辐射物从钚放散出来。

6 limestone   

n.石灰石

参考例句：

• Limestone is often used in building construction.石灰岩常用于建筑。
• Cement is made from limestone.水泥是由石灰石制成的。

7 gravel   

n.砂跞；砂砾层；结石

参考例句：

• We bought six bags of gravel for the garden path.我们购买了六袋碎石用来铺花园的小路。
• More gravel is needed to fill the hollow in the drive.需要更多的砾石来填平车道上的坑洼。

8 chunk   

n.厚片，大块，相当大的部分（数量）

参考例句：

• They had to be careful of floating chunks of ice.他们必须当心大块浮冰。
• The company owns a chunk of farmland near Gatwick Airport.该公司拥有盖特威克机场周边的大片农田。

9 chunks   

厚厚的一块( chunk的名词复数 )； （某物）相当大的数量或部分

参考例句：

• a tin of pineapple chunks 一罐菠萝块
• Those chunks of meat are rather large—could you chop them up a bIt'smaller? 这些肉块相当大，还能再切小一点吗？

10 activates   

使活动，起动，触发( activate的第三人称单数 )

参考例句：

• Activates the window and displays it in its current size and position. 激活窗口，保持当前的大小及位置不变。
• Pulling out the alarm switch activates alarm and pushing it deactivates it. 闹钟的开和关是通过拔出和按入闹铃开关实现的。

11 leftover   

n.剩货，残留物，剩饭；adj.残余的

参考例句：

• These narrow roads are a leftover from the days of horse-drawn carriages.这些小道是从马车时代沿用下来的。
• Wonder if that bakery lets us take leftover home.不知道那家糕饼店会不会让我们把卖剩的带回家。

12 skyscraper   

n.摩天大楼

参考例句：

• The skyscraper towers into the clouds.那幢摩天大楼高耸入云。
• The skyscraper was wrapped in fog.摩天楼为雾所笼罩。

13 skyscrapers   

n.摩天大楼

参考例句：

• A lot of skyscrapers in Manhattan are rising up to the skies. 曼哈顿有许多摩天大楼耸入云霄。
• On all sides, skyscrapers rose like jagged teeth. 四周耸起的摩天大楼参差不齐。

14 collapse   

vi.累倒；昏倒；倒塌；塌陷

参考例句：

• The country's economy is on the verge of collapse.国家的经济已到了崩溃的边缘。
• The engineer made a complete diagnosis of the bridge's collapse.工程师对桥的倒塌做了一次彻底的调查分析。

15 demolition   

n.破坏,毁坏,毁坏之遗迹

参考例句：

• The church has been threatened with demolition for years. 这座教堂多年来一直面临拆毀的威胁。
• The project required the total demolition of the old bridge. 该项目要求将老桥完全拆毁。