Directions for teachers: Ask students to read the online Science News article “These chemists cracked the code to long-lasting Roman concrete” and have them answer the following questions. A version of the article “Chemists Crack the Code to Ancient Roman Concrete” appears in the February 11, 2023 issue of Science News.

1. What components are in modern concrete?

Cement, gravel, sand and water are common ingredients in concrete.

2. Why do chemists want to understand how the ancient Romans made concrete?

Chemists want to improve modern concrete production. The concrete made by the ancient Romans has lasted much longer than concrete made nowadays.

3. Whose writings did the scientists read to learn how the Romans made concrete? What pieces of information did those early Roman writers provide?

The scientists read works by the historian Pliny and the architect Vitruvius. From the writings, the scientists learned that quicklime used to make concrete should be made from high-quality limestone and that heat is produced when quicklime, volcanic ash and water are combined.

4. What is the chemical name for quicklime, and what element in the chemical name also appears in Roman concrete?

Calcium oxide is the chemical name for quicklime. One of the elements in quicklime is calcium. Roman concrete contains lots of small calcium-rich rocks.

5. How might the presence of calcium-rich rocks improve the quality of Roman concrete? Explain the interaction between the calcium and the concrete that might make the concrete last longer.

The scientists think the presence of calcium-rich rocks allows the concrete to heal itself when it cracks. It’s like the concrete has a built-in repair kit. The calcium can dissolve when it gets wet and then it moves into cracks and hardens (or re-crystallizes), and thereby fixes the concrete.

6. How did chemist Admir Masic and his team go about making their version of Roman concrete? What is the name of the method they used?

The scientists had to use “hot mixing” to make concrete that was high in calcium. In hot mixing, calcium oxide and ash are mixed, and then water is added.

7. How did the team test its version of the Roman concrete?

After the scientists made their concrete, they tested it to see whether it behaved like Roman concrete. The researchers did this by breaking the concrete, dripping water between the pieces and verifying that the breaks did heal.

8. What is the environmental cost of modern concrete manufacturing, and what would be the environmental benefit of making concrete that is more like Roman concrete?

Manufacturing concrete contributes significantly to greenhouse gas emissions every year. Approximately 8 percent of annual carbon dioxide emissions are a result of concrete manufacturing. Making concrete with the long-lasting properties of Roman concrete would reduce the need to replace structures and would decrease the need to produce as much of the building material.