Concrete Spalling

The terms "open" and "closed" in the context of concrete spalling relate to the extent of the damage and the visibility of the underlying issues:

Open Spalls:

• Description: Open spalls are characterized by visible sections where flakes of concrete have fallen away from the surface. These spalls expose the underlying reinforcement steel (typically rebar) or aggregate. Flakes are typically as thick as the concrete covering the steel. Thinner flakes may separate as the result of a weak plane between the surface layer and underlying layers due to poor finishing or curing practices.
• Causes: Spalling may be caused by the expansion of rusting steel reinforcement, freeze-thaw cycles, or chemical reactions like alkali-silica reaction (ASR) that lead to internal pressure and subsequent separation of flakes.
• Appearance: The surface of the concrete shows clear signs of damage, with pieces of concrete having fallen away.

Closed Spalls:

• Description: Closed spalls refer to situations where a concrete flake is in the process of debonding from the underlying layer but has not yet completely separated and fallen away. The damage may not be obvious at the surface. Once debonding is complete the flake will fall and it will become an open spall.
• Causes: These can be due to early stages of corrosion, where the rusting steel has not yet expanded enough to cause open spalling, or due to other internal stresses that have not yet produced enough pressure to cause the flake to fully separate and fall.
• Appearance: The concrete might show only minor surface imperfections, sometimes some displacement, but internal deterioration is taking place that could eventually lead to open spalls if not addressed.

Key Differences:

• Visibility: Open spalls are visible and expose the underlying issues, while closed spalls might not show much significant surface damage, hiding the internal problems.
• Stage of Damage: Open spalls indicate advanced stages of deterioration, whereas closed spalls represent earlier stages where the damage is still contained within the concrete.
• Urgency of Repair: Open spalls require immediate attention to prevent further structural compromise, while closed spalls might be addressed through preventative measures to halt the progression of internal damage.

Understanding these differences is important in order for inspectors to make appropriate comments about the existence and severity of the problem.

Repairing spalls

If spalling is due to corroded steel the corrosion process can be stopped by treating the exposed steel with chemicals. Depending on the situation it may be sandblasted first. After any necessary blasting and treatment a rust-inhibiting coating is applied and the spall is patched with an appropriate material. Spalling due to other causes may require the application of stabilizing and bonding agents before the spall is patched. Repair methods vary according to cause.

RATING REINFORCED CONCRETE DAMAGE