What is the typical function of fiber reinforcement in concrete?

• A. To increase workability in all mixes.
• B. To significantly raise density.
• C. To act as a substitute for reinforcing steel.
• D. To improve crack control and post-crack toughness in some mixes.

Answer: (D)

Fiber reinforcement mainly acts to bridge cracks and boost post-crack toughness. As cracks form in concrete, fibers span the openings and carry load across the cracks, slowing crack growth and increasing residual strength. This helps control cracking and improves toughness in many mixes, especially in slabs, pavements, and shotcrete where crack resistance is important. It isn’t meant to increase density or replace reinforcing steel in structural members; steel bars provide primary tensile resistance, while fibers offerDistributed secondary reinforcement and enhanced post-crack behavior. Fiber addition can also affect workability, often reducing it if not properly dosed. So the typical function is to improve crack control and post-crack toughness in some mixes.