Repair Methods, Placement, and Curing
Domain focus
This domain tests correct execution: forming, bonding, placing, consolidating, finishing, and curing repairs in horizontal, vertical, and overhead orientations.
Core rules
- Repair methods include formed repairs, shotcrete, hand placement, and proprietary systems. Select based on depth, orientation, access, and structural requirements.
- Bond is achieved through sound preparation, correct bonding agent or scrub coat, and proper moisture condition. Do not let a cementitious bonding slurry dry out before placing the repair material.
- Place cementitious repairs against SSD substrate. Dry substrate absorbs mix water and causes shrinkage cracking and weak bond.
- Consolidate to eliminate voids, especially at the repair perimeter and around reinforcement. Avoid overvibration and segregation.
- Cure cementitious repairs moist for about 7 days per ACI 308, or use an approved curing compound. Cure epoxy and polymer systems per the manufacturer; they may require only protection from moisture loss.
- Crack repair may use epoxy injection for structural cracks, polyurethane grout for water-bearing cracks, routing and sealing, or stitching. Reinforcement with significant section loss must be cleaned or supplemented.
Worked example
A 75 mm deep vertical spall on a column is to be repaired. Reasoning: saw-cut square edges, remove unsound concrete, clean reinforcement, and pre-wet the substrate to SSD. Use a non-sag cementitious repair or a formed flowable microconcrete, apply a compatible bonding agent, and consolidate carefully at the form. Cure moist for 7 days. Do not hand-pack a dry, absorbent substrate or rely on a bonding agent that has filmed over.
Traps
- Placing cementitious repair on dry substrate.
- Using a bonding agent outside its open time.
- Insufficient curing, especially in hot or windy conditions.
- Overhead repairs that sag because a non-sag material was not used.