Many modern concrete structures degrade within decades, but ancient Roman harbor walls have survived intact for over two thousand years. Researchers studying these ancient structures discovered that the Romans used a unique mixture of volcanic ash and lime. When exposed to seawater, this volcanic material triggers a chemical reaction that crystallizes a rare mineral called aluminous tobermorite. This crystallization process actively reinforces the concrete's structure over time, filling microscopic cracks before they can expand. Thus, rather than eroding, Roman marine concrete actually becomes stronger when submerged in seawater.
Which choice best states the main idea of the text?
- AModern concrete structures fail to survive as long as Roman harbor walls because modern builders do not use volcanic materials.
- BAll ancient Roman structures were built using volcanic ash and lime to ensure they would remain durable for thousands of years.
- A chemical reaction triggered by seawater causes ancient Roman marine concrete to strengthen over time.Answer
- DThe crystallization of aluminous tobermorite is a mineral process that weakens the structural integrity of ancient concrete.
Answer
A chemical reaction triggered by seawater causes ancient Roman marine concrete to strengthen over time.
The correct option accurately states the main idea of the passage: that Roman marine concrete contains volcanic materials which react with seawater to trigger crystallization, actively strengthening the concrete over time and explaining its long-term durability.
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Key Concept
Identifying the central idea of a passage