Final answer:
Concrete is a mixture of Portland cement, sand, gravel, and water that cures into a solid, durable mass. It has an excellent compressive strength and is a fundamental material in construction. The Romans significantly improved concrete by adding volcanic ash, known as pozzolana.
Step-by-step explanation:
The correct answer to the question is d) Concrete. Concrete is a composite material that significantly contributed to construction ever since the Romans advanced its usage. It consists of a mixture of Portland cement, fine aggregates like sand, and coarse aggregates such as gravel or crushed stone, mixed with water. When the mixture cures, it turns into a solid mass renowned for its impressive compressive strength.
Portland cement serves as the binder in concrete, while the sand and gravel act as fillers to give it structure and volume. The water initiates the chemical reaction that allows the cement to harden and bind the aggregate into a solid mass. Notably, ancient Romans improved upon concrete by adding pozzolana, volcanic ash that provides additional strength and durability, even allowing concrete to set underwater.
Over time, the evolution of concrete has led to a variety of mixes, including lightweight concrete, which uses aggregates like shale, clay, or slate, offering advantages such as reduced load and better thermal protection. This adaptability and the material's inherent characteristics make concrete an indispensable material in modern construction.