Identification of Cracks

Question 1:

a) Mode of Failure / Damage Type

Image 1: Localized Spalling of Concrete

• Mode: This damage is a localized spalling of the beam corner, likely due to corrosion of embedded reinforcement.
• Cause: Moisture ingress leads to steel corrosion, causing expansion and cracking of the concrete cover.
• Repairable: Yes. Spalled concrete due to corrosion is typically repairable.

Image 2: Major Cracks and Delamination

• Mode: Shows vertical and diagonal cracking along with large areas of delaminated concrete, indicating shear failure or poor bonding.
• Cause: Could be due to inadequate reinforcement, earthquake loads, or poor-quality concrete.
• Repairable: Technically yes, using methods like epoxy grouting, jacketing, or FRP wrapping, but may require detailed structural evaluation.

Image 3: Cracks at Beam-Column Joint

• Mode: Cracking at the beam-column junction, which is a highly stressed region.
• Cause: Common in seismic zones due to joint weakness, improper detailing, or differential settlement.
• Repairable: Yes, with epoxy injection, polymer-modified mortar, or retrofitting with steel jacketing.

General Repair Measures

1. Remove loose concrete around the damaged zone.
2. Clean and treat exposed rebars with anti-corrosion agents.
3. Apply bonding agent to enhance new concrete adhesion.
4. Use non-shrink repair mortar to fill the cavity.
5. For major cases, apply jacketing, FRP wraps, or steel plates.

Preventive Actions

• Proper waterproofing to prevent moisture ingress.
• Use of corrosion-resistant rebars or coatings.
• Regular structural health monitoring.

Question 2:

a)

Mode of Failure:

1. Image 1: Diagonal Shear Failure / Corrosion Damage
• The diagonal cracking and spalling suggest shear failure, likely exacerbated by corrosion of reinforcement.
• The concrete has detached, exposing corroded reinforcement.
• Likely due to inadequate shear reinforcement or high lateral loads (e.g., seismic).
2. Image 2: Corrosion-Induced Spalling
• The large area of delaminated concrete and exposed steel indicate rebar corrosion.
• Cracks run along rebar lines—classic symptoms of carbonation or chloride ingress.
• This damage compromises both strength and durability.
3. Image 3: Corner Crushing and Column-Connection Failure
• Shows concrete crushing and bond failure at a junction (probably beam-column).
• Likely due to poor anchorage, under-reinforced detailing, or impact/loading.

Are the Damages Repairable?

Yes, repairs are possible, but the feasibility depends on the extent of the damage:

Suggested Repair Methods:

For Minor to Moderate Damage:

• Remove all loose/delaminated concrete.
• Clean corroded rebars (mechanically or chemically).
• Apply anti-corrosion coating on reinforcement.
• Rebuild section with polymer-modified mortar or non-shrink repair grout.
• Use epoxy injection for crack sealing if needed.

For Severe Damage:

• Retrofitting using:
• Steel jacketing or
• Ferrocement wrapping or
• FRP wrapping (Fiber-Reinforced Polymer)
• Consider load redistribution or temporary propping during repairs.
• Structural strengthening may be needed if loss of cross-sectional area is significant.

In Case of Critical Structural Damage:

• If >25–30% of the cross-section or multiple rebars are affected, partial replacement or heavy retrofitting may be necessary.

A structural engineer must inspect onsite and validate the repair method.