What type of thin concrete reinforcement is sold in rolls?

The correct answer is WWM, which stands for Welded Wire Mesh. This type of reinforcement consists of a series of wires arranged in a grid pattern that are welded together at their intersections. It is commonly used in various concrete applications to improve the tensile strength and prevent cracking. WWM is produced in sheets and rolls, making it convenient for various construction projects. When sold in rolls, it is particularly beneficial for large areas, allowing for easier handling and installation.

The other options do not fit the description of thin concrete reinforcement sold in rolls. BRC refers to British Reinforcement Concrete and is a type of mesh but is not typically sold in the same roll format. Sheet mesh usually refers to flat sheets of mesh, and while chain link is a type of fencing material, it is not used for concrete reinforcement. This further contextualizes why WWM is the best answer, as it is specifically made for reinforcing thin concrete and is available in roll formats.