雅思阅读 79: The Ancient Secret of Roman Concrete（罗马混凝土的古老秘密）

改编自 Smithsonian Magazine / Nature Communications（2025年12月）。雅思阅读 Section 3 难度，约 1050 词。 素材来源：https://www.smithsonianmag.com/smart-news/this-ancient-construction-site-in-the-ruins-of-pompeii-is-revealing-new-secrets-about-the-2000-year-old-recipe-for-roman-concrete-180987845/

Reading Passage

A. Travel across southern Europe today and the hand of ancient Rome is everywhere: amphitheatres, aqueducts, harbours, walls and bridges raised two millennia ago that still stand. Their survival is owed largely to the concrete the Romans mixed, a material that seems to defy the forces that crumble modern structures within decades. The contrast is starkest at the coast, where Roman harbour walls have sat submerged in salt water for two thousand years and, rather than decaying, appear to have grown stronger. Modern concrete piers built in the same sea, by contrast, often crack and spall within a single human lifetime. For generations, engineers wondered what the ancients knew that modern builders had forgotten. The Roman writer Vitruvius left tantalising clues about volcanic ash and lime, but no complete recipe. Only recently, by examining the actual chemistry of the ruins, has the secret begun to yield — and it turns out to rest on a mixing method that modern engineers once dismissed as a clumsy mistake rather than a deliberate technique. The puzzle is not purely academic. Concrete is the most widely used manufactured material on Earth, and its production contributes a substantial share of global carbon emissions. If a cleaner, longer-lasting formulation inspired by Roman practice could be adopted, the environmental payoff would be enormous. That practical prize is what has turned dusty ruins into a cutting-edge materials-research programme.

B. The latest evidence comes from an unlikely place: an unfinished construction site frozen in time at Pompeii. Buried by the eruption of Mount Vesuvius in 79 CE, the city offers something almost no other Roman site can — building materials captured mid-process, before two thousand years of weathering and repair. In 2025, researchers published a study comparing samples from finished walls, walls still under construction, and piles of dry, raw ingredients lying nearby. The comparison, they wrote, "unequivocally" supported a long-suspected theory. Admir Masic, an engineer at the Massachusetts Institute of Technology and a co-author, described the site as a true "snapshot" of Roman building practice. Unlike a finished monument, which has been altered by centuries of decay, the Pompeii deposits preserve the ingredients as they were stacked, mixed and placed — letting chemists read the process backwards from the raw materials that the builders themselves left behind.

C. The method at the heart of the discovery is called "hot mixing". Modern concrete is typically made by blending wet, pre-slaked lime with aggregates. The Romans, the evidence now suggests, did something different. They combined volcanic ash — a sandy material from the region around the Bay of Naples — with dry "quicklime", a highly reactive form of limestone. When water was added, the quicklime reacted violently, releasing so much heat that the mixture steamed. That high temperature, rather than being a nuisance, changed the chemistry of the paste. Crucially, the hot process left behind small, uneven chunks of calcium scattered through the concrete — the "lime clasts" that chemists had noticed for decades without fully understanding. For years, these white lumps were written off as signs of careless mixing, the marks of labourers who had not bothered to work the lime thoroughly. The new reading reverses that judgement entirely.

D. Those lumps, it turns out, are the source of the concrete's extraordinary durability. When a crack eventually forms in a Roman wall — and all concrete cracks eventually — water seeps along it. The water encounters a lime clast, dissolves the calcium within it, and carries that calcium-rich solution further into the gap. In time the dissolved mineral recrystallises, depositing fresh calcium carbonate that fills the crack from the inside out. The material, in effect, repairs itself. Provided water keeps reaching the clasts, the process can continue for centuries, sealing micro-cracks before they widen into structural flaws. In seawater, the same mechanism is thought to combine with the volcanic ash to grow reinforcing minerals that knit the whole mass together more tightly as the years pass. A material that begins to heal itself the moment it is damaged is not a luxury but a fundamental redesign of how concrete should behave. Ordinary modern concrete, by contrast, is deliberately mixed so that its ingredients react completely during pouring; once set, it has no spare chemistry left over, and any crack that opens simply widens as water, ice and salt work their way in. Roman concrete, in effect, was built with an internal reserve — a chemical battery that could be drawn on again and again, for as long as the structure stood.

E. The reassignment of the lime clasts from accident to design is a small lesson in humility. Masic has said he found it "really difficult to believe that ancient Roman engineers would not do a good job", given how carefully they chose and processed their other materials. What looked like sloppiness to twentieth-century eyes was, on closer inspection, a deliberate feature. The implications extend beyond archaeology. Researchers have already developed a modern, Roman-inspired cement that incorporates the same hot-mixed lime clasts, claiming it can seal its own cracks within roughly two weeks. If the approach can be scaled affordably, it might produce roads, bridges and sea defences that mend themselves rather than requiring costly, repeated repair. The Romans, it seems, did not merely build for the ages by luck. They hit on a self-healing chemistry that modern engineering is only now beginning to catch up with. Whether that ancient recipe can be reproduced at industrial scale, at a price the construction industry will accept, remains an open question. The earliest Roman-inspired cements work in the laboratory, but proving they last for decades in real weather and real seawater will take trials measured in years rather than weeks.

Questions 1-4

Choose the correct heading for paragraphs B, C, D and E from the list of headings below.

List of Headings i. The puzzle of why Roman concrete lasts so long ii. The Pompeii construction site as a frozen snapshot iii. The hot-mixing recipe and its surprising by-product iv. How lime clasts heal cracks from within v. From "bad mixing" to a design we are relearning vi. The political decline of the Roman empire vii. Why modern concrete is cheaper to manufacture

1. Paragraph B: ____
2. Paragraph C: ____
3. Paragraph D: ____
4. Paragraph E: ____

Questions 5-8

Choose the correct letter, A, B, C or D.

5. What is striking about Roman harbour walls in the sea? A. They have crumbled within a few decades. B. They have apparently grown stronger after two thousand years submerged. C. They were built from pure marble blocks. D. They were constructed by modern engineers.

6. Why was the Pompeii construction site especially valuable? A. It contained a hoard of buried gold. B. It preserved materials mid-process, before weathering. C. It had been rebuilt many times over the centuries. D. It proved the Romans used no concrete at all.

7. What happens during the Roman "hot mixing" process? A. Wet lime is blended with cold aggregates. B. Dry quicklime and volcanic ash react with water, releasing heat. C. The wet concrete is baked in a large oven. D. Salt water is added instead of fresh water.

8. How do the lime clasts make concrete self-healing? A. They expand on their own without water. B. Water dissolves their calcium, which recrystallises to fill cracks. C. They make the concrete completely waterproof. D. They attract sea creatures to repair the gaps.

Questions 9-13

Do the following statements agree with the claims of the writer?

Write:

• TRUE if the statement agrees with the information
• FALSE if the statement contradicts the information
• NOT GIVEN if there is no information on this

9. Roman harbour walls have been submerged in the sea for around two thousand years.
10. Modern engineers initially thought the lime clasts indicated poor mixing.
11. The hot-mixing process produces almost no heat.
12. The Pompeii construction site was buried by a volcanic eruption.
13. Roman concrete was invented around 100 CE by the emperor Augustus.

Questions 14-15

Complete the summary below using NO MORE THAN TWO WORDS from the passage.

Water seeping into a crack dissolves calcium from (14) __________, which then recrystallises to fill the gap, giving Roman concrete its (15) __________ property.

答案与解析

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