What is the primary function of rebar in concrete?

The primary function of rebar, or reinforcing bar, in concrete is to improve tensile strength, which directly influences its structural integrity. Concrete is excellent at resisting compressive forces but lacks tensile strength; it tends to crack under tension. By incorporating rebar into the concrete mix, the tensile strength is significantly enhanced, allowing the concrete to handle stress more effectively. This reinforcement helps to keep cracks tightly closed when they do form, which mitigates any further expansion and maintains the overall durability and longevity of the concrete structure.

While other options presented may reference different characteristics or perceived functionalities, they do not accurately reflect the primary purpose of rebar. For instance, rebar does not primarily facilitate easier pouring, add aesthetic value, or provide insulation. Instead, its main role is critical in ensuring that the concrete can withstand various loads and stresses that could lead to cracking.