NASCLA Accredited Commercial General ContractorConcreteMedium
A concrete general contractor is tasked with overseeing the repair of a heavily trafficked concrete bridge deck. The repair involves removing deteriorated concrete and patching with a specialized rapid-setting repair mortar. Before applying the new repair material, what critical step must be ensured regarding the prepared substrate to achieve a durable bond?
- AThe substrate must be completely dry to prevent dilution of the repair material.
- BThe substrate must be saturated surface dry (SSD) to prevent premature drying of the repair material.
- CThe substrate must be left rough and dusty to provide mechanical keying.
- DThe substrate should be coated with a bond breaker for easier future repairs.
Show answer & explanationAnswer & explanation
Correct answer: B. The substrate must be saturated surface dry (SSD) to prevent premature drying of the repair material.
For most concrete repair materials, especially cementitious ones, the substrate must be saturated surface dry (SSD). This condition means the concrete pores are filled with water, but no free water is present on the surface. This prevents the dry substrate from absorbing water from the fresh repair material, which could lead to premature drying, poor hydration, and a weak bond.
Why the other options are wrong
- A. A completely dry substrate will absorb water from the repair material, leading to a weak bond.
- C. While a rough surface is good for mechanical keying, a dusty surface prevents good bonding.
- D. A bond breaker would prevent adhesion, which is contrary to the goal of a durable repair.
Saturated Surface Dry (SSD)
A condition of aggregate or concrete substrate where the pores are filled with water, but no free water exists on the surface.
- Crucial for proper bonding of cementitious repair materials.
- Prevents substrate from absorbing water from fresh mix.
- Achieved by pre-wetting and then allowing surface water to evaporate.
Memory trick: Clean, sound, and just wet enough for a strong blend.