Underwater Concrete Repair – Part One

Causes of Defects, Methods of Inspection and Evaluation of Underwater Concrete Defects Based on ACI 546.2R Standard

Underwater concrete repair is one of the most challenging and sensitive aspects of civil engineering and marine structures. Underwater environments create specific conditions for concrete and repair materials due to hydrostatic pressure, continuous presence of water, temperature changes, and the chemical composition of water. Success in underwater concrete repair operations requires precise understanding of technical requirements, selection of appropriate materials, and use of advanced execution techniques.

The requirements for underwater concrete repair include structural damage assessment, environmental condition evaluation, and adaptation of repair methods to international standards. The main goal of these operations is to restore structural integrity, increase durability, and improve resistance against damaging environmental factors. In this context, using specific methods such as injection, underwater concreting, or waterproof repair materials plays a key role in achieving sustainable results.

This article/report reviews key requirements, materials used, and effective techniques in underwater concrete repair, and provides practical solutions to extend the service life of these structures. Precise planning and the use of specific methods and standards are essential.

• Importance of underwater concrete structures (such as bridges, dams, piers, and tanks).
• Specific challenges related to underwater concrete repair.
• The role of ACI 546.2R standard in providing repair guidelines.

Necessity of Underwater Concrete Repair

Underwater concrete is widely used in marine structures, bridges, dams, and other water-related projects. These structures are exposed to various damaging factors such as corrosion, erosion, abrasion, freeze-thaw cycles, dynamic loads, etc., which can cause serious damage to underwater concrete and reduce its strength and service life.

Repairing underwater concrete is crucial to maintain the strength and safety of structures throughout their service life. This process involves identifying and assessing defects, selecting appropriate repair methods, and precise implementation. The purpose of underwater concrete repair is to restore the strength and performance of concrete to its original level and prevent further damage.

Causes of Defects in Underwater Concrete

1. Chemical and Biological Reactions

• Alkali-Silica Reaction (ASR).
• Sulfate attack.
• Growth of microorganisms and algae.

2. Mechanical and Hydraulic Forces

• Erosion and abrasion caused by water flow.
• Impact from floating objects or ship collisions.

3. Design or Construction Deficiencies

• Poor quality of concrete raw materials.
• Incomplete compaction or presence of air bubbles.
• Problems in reinforcement or concrete cover.

4. Environmental Factors

• Freeze-thaw cycles.
• Chloride penetration and rebar corrosion.
• Changes in water level and hydrostatic pressure.

Inspection and Evaluation of Underwater Concrete Defects

According to ACI 546.2R, the evaluation process includes:

1. Initial Observation and Inspection:

• Use of professional divers for visual inspection.
• Underwater photography and imaging.

2. Mechanical and Non-destructive Testing:

• Schmidt hammer test to assess surface concrete strength.
• Ultrasonic Pulse Velocity (UPV) test to identify cracks and voids.
• Core sampling to check crack depth and material quality.

3. Chemical Analysis:

• Chloride analysis to evaluate reinforcement corrosion.
• pH measurement to determine penetration of aggressive substances.

4. Advanced Evaluation Using Equipment:

• Ground Penetrating Radar (GPR) to identify weak zones.
• Electrical current testing to detect active corrosion in reinforcement.

Classification of Defects Based on ACI 546.2R

Based on damage extent, underwater concrete defects are classified into:

1. Surface Defects:

• Fine cracks and spalling.
• Erosion limited to surface layers.

2. Structural Defects:

• Deep or widespread cracks affecting strength.
• Severe reinforcement corrosion and load capacity reduction.

3. Functional Defects:

• High permeability allowing water or aggressive ions to pass.
• Damage to the designed structural performance.

Design Principles for Underwater Concrete Repair

Repair design must consider factors such as defect type, environmental constraints, climatic conditions, dynamic loads, etc. Important principles include:

• Identifying defect type and cause before repair.
• Selecting repair materials and methods compatible with defect type and environment.
• Designing repair structure to be compatible with the original structure.
• Considering environmental limitations like water depth, climate, and water flow.
• Ensuring safety for workers and environmental protection during repair design.

Repair Methods and Execution Steps

Various methods exist for underwater concrete repair, selected based on defect type and environment. Common methods include:

• Polymer-based repairs for crack and erosion repair.
• Portland cement concrete repair for severe damage like cavities and fractures.
• Flexible materials for structures under dynamic loads.
• Electrochemical methods to prevent reinforcement corrosion.

Steps for Executing Underwater Concrete Repair

• Surface preparation: Fully prepare the concrete surface before repair.
• Cleaning: Remove all contaminants and chemicals from the concrete surface.
• Formwork installation: Securely install formwork if needed.
• Repair execution: Apply repair materials according to specifications and standards.
• Inspection: Conduct thorough inspection after repair completion.

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References

• ACI 546.2R: Guide to Underwater Repair of Concrete
• Other related sources on concrete repair techniques and global standards