听力音频：
L1
讲座
1. What is the lecture mainly about?
Reasons why some structures from the Roman Empire are still standing
How concrete reacts under extreme weather conditions
New developments in concrete formulation and repair
Properties of concrete that is reinforced with steel
2. What current problems with concrete does the professor mention?（多选题）
The concrete discolors when exposed to sunlight.
The concrete is expensive to maintain.
The concrete does not adjust easily to sudden temperature changes.
The concrete is difficult to inspect when used on long bridges
3. Why does the professor mention a paper cut?
To help students understand a concrete-repair process
To illustrate the size of a typical crack in concrete
To warn students about the sharp edges of broken concrete
To imply that most cracks in concrete are straight rather than jagged
4. What point does the professor make about the microcapsules in the coating developed in South Korea?
They can be used instead of steel bars.
They contain a toxic material
They work effectively without a chemical agent serving as a catalyst.
Their contents form a substance that hardens when exposed to rainwater.
5. What does the professor imply about a composite material that contains micro fibers?（多选题）
It has the ability to bend
It is not expected to last as long as Roman concrete.
Ice is unable to form on its surface
Any cracks that develop in it can repair themselves.
6. What does the professor say regarding the high cost of constructing highways using new materials?
Governments should pay for the additional costs by raising the tax on fuel.
The high cost will probably lead to fewer highways being built.
The materials should not be used until scientists find ways to lower costs.
Lower maintenance costs might help to offset higher construction costs.
