What is popout and how can you prevent it?

• A. Popouts are surface cracks caused by drying; prevent by keeping surface wet
• B. Popouts are large voids caused by rebar spacing; prevent by repositioning rebar
• C. Popouts are small crater-like voids from aggregate pockets; prevent by selecting proper aggregate, ensuring proper curing, and avoiding aggressive finishing near aggregates
• D. Popouts are surface staining from chemicals; prevent by sealing with epoxy

Answer: (C)

Popouts are surface voids that show up as small crater-like pits caused by pockets within the aggregate pulling away from the surrounding cement paste. This usually happens when certain aggregates have weak or reactive pockets that expand or separate under moisture and alkali conditions, pushing paste outward and leaving a tiny cavity at the surface. The best way to prevent them is to choose aggregates that are suitable for the mix (low reactivity and clean, well-graded material), ensure proper curing to minimize internal stresses and shrinkage, and avoid aggressive finishing practices near aggregates that can disrupt the paste around those pockets. Other options describe different surface problems—drying cracks, voids from rebar spacing, or chemical staining—not the same mechanism as popouts.