In polymer-modified concrete (PMC), the role of the polymer component is to: 

Explanation:

In polymer-modified concrete (PMC), the polymer component is added to improve the properties of conventional concrete.

The key roles of the polymer include:

1. Reduce water permeability: The polymer creates a dense and cohesive bond between the particles of the concrete, which significantly reduces the passage of water and other fluids.

2. Increase flexibility: The polymer enhances the elastic properties of concrete, making it more flexible and less brittle, which improves its ability to resist cracking under stress or deformation.

Additional Information

1. Increase setting time significantly: Polymers generally do not increase setting time significantly; in fact, some may accelerate the curing process.

2. Reduce strength and durability: The use of polymers generally improves strength, durability, and other performance characteristics of concrete.

3. Increase brittleness: Polymers increase flexibility and reduce brittleness, not the other way around.