Which statement about fiber reinforcement in concrete is accurate?

• A. It primarily improves long-term color stability.
• B. It provides an immediate, large increase in strength with no cracking.
• C. It makes finishing harder due to roughness.
• D. Crack control and post-crack toughness in some mixes.

Answer: (D)

Fiber reinforcement in concrete mainly provides crack control and post-crack toughness. Fibers bridge cracks as they form, carrying some tensile load across the crack, slowing crack growth, and increasing energy absorption after cracking. This leads to improved durability and ductility in certain mixes such as slabs and pavements where shrinkage or fatigue cracking is a concern. Because of that, the statement about crack control and post-crack toughness in some mixes best describes what fibers do.

Color stability isn’t a function of fiber reinforcement, so that isn’t the right focus. Fibers don’t typically produce an immediate, large increase in strength or prevent cracking entirely, so the claim about a big early strength gain with no cracking isn’t accurate. Finishing can be affected in some cases, but the primary and most reliable benefit of fiber reinforcement is crack control and post-crack toughness.