Underwater Concrete Repair - Part 2

Requirements for Underwater Concrete Repair According to ACI 546.2R
Preparation, Formwork, Methods, and Materials

Civil structures such as bridges, hydraulic structures, and marine docks are often constructed in tidal zones or underwater environments. These structures are generally made of reinforced concrete (RC), and when submerged, they are referred to as underwater concrete structures. These structures may become damaged due to abrasive erosion or impact. If the deteriorated and worn-out parts of concrete structures are not properly repaired, their service life will be significantly reduced, and the life-cycle maintenance costs will increase dramatically.

Repairing underwater concrete structures is typically a challenging task that requires specialized materials and installation systems. Underwater concrete, due to its unique environmental conditions—such as permanent or intermittent water exposure—is subject to various types of degradation including chemical attacks, leaching of cementitious materials, cracking, and erosion. Repairing concrete in such environments requires adherence to specific standards.

In this article, the requirements for preparation, formwork, repair methods, and materials used for underwater concrete repair according to ACI 546.2R are discussed.

1. Surface Preparation for Underwater Concrete Repair:

Surface preparation is one of the most critical steps in the underwater concrete repair process. It refers to a series of actions taken before applying the repair materials to ensure the damaged concrete surface is ready for restoration. These actions include surface evaluation, cleaning, removal of damaged concrete, creating an appropriate surface profile, and controlling surface conditions (such as saturation). The goal is to ensure a strong and durable bond between the substrate and the repair material, even in underwater conditions. According to ACI 546.2R, the following steps are essential:

1.1: Evaluation of the Damaged Concrete Surface:

Evaluating the condition of the damaged underwater concrete surface is a vital step before repair. It helps identify the type, extent, and depth of damage, allowing for the selection of appropriate repair methods and materials.

• Identifying damage types: Including cracks, delamination, erosion, or surface layer debonding.

• Assessing the extent of deterioration: Determining the degree and depth of damage using methods such as Schmidt hammer test, ultrasonic testing, or core sampling.

1.2: Cleaning the Concrete Surface:

Removal of contaminants, deposits, and grease using mechanical or chemical methods.

• Hydro-demolition: High-pressure water jetting is one of the most effective methods for preparing underwater concrete. It cleans the surface without causing cracks or damage to sound areas.
• Removing weak or damaged concrete: All loose or delaminated concrete must be removed to provide a solid and clean substrate for bonding with the repair material.

1.3: Creating an Appropriate Surface Profile:

The surface profile refers to the roughness and texture created on the concrete surface using mechanical or chemical techniques. The surface must have sufficient roughness to allow both mechanical (frictional) and chemical (adhesive) bonding of repair materials.

• According to ACI, the surface should be roughened to ensure proper adhesion.
• Methods like sandblasting, pneumatic chisels, or high-pressure water jets are recommended.

1.4: Surface Saturation Before Repair:

Pre-wetting the concrete before applying the repair materials is essential. This reduces the risk of water absorption from the repair mix and prevents shrinkage or weak bonding.

• The concrete surface must be saturated surface dry (SSD), meaning saturated but with no free water on the surface, to prevent the repair material from losing moisture into the substrate.

2. Formwork for Underwater Concrete Repair:

Formwork in underwater repair is one of the most challenging stages due to specific environmental conditions such as water pressure, flow, and limited visibility. The main goal of underwater formwork is to create a sealed, stable structure that holds fresh concrete or repair material in place, preventing washout.

2.1: Choosing Formwork Materials:

• Impermeable materials: Use tightly sealed forms to prevent leakage of repair materials.
• Pressure-resistant forms: Forms must withstand hydrostatic pressure.

2.2: Underwater Formwork Methods:

• Injectable forms: Designed for injecting repair materials without disturbing the underwater environment.
• Flexible forms: Used to shape irregular surfaces precisely.

All forms must be carefully inspected and installed before applying repair materials to ensure there is no leakage.

2.3: Formwork Sealing:

• Use of rubber strips or sealing gels at form joints to prevent water infiltration.
• Water pressure testing: Forms must be pressure-tested before injecting materials.

3. Underwater Concrete Repair Methods:

Injection of repair materials underwater is an effective method for repairing cracks, voids, or damage caused by pressure or corrosion. These methods are widely used in underwater structures like dams, bridges, and piers. Proper material placement is essential to ensure waterproof sealing and long-term effectiveness.

Repair method selection depends on damage type, depth, and environmental conditions. The following methods are recommended by ACI 546.2R:

3.1: Injection of Repair Materials:

• Epoxy Injection: Due to excellent adhesion and chemical resistance, epoxies are suitable for cracks and delaminated areas.
• Cementitious Injection: Used for larger cracks or voids and for deeper sections of damaged
• concrete.

Implementation:

• High-pressure pumps are used for injection.
• Inject from bottom to top to ensure complete filling of cracks and voids.

Concrete placement below water level

3.2: Underwater Concrete Placement:

• High Bonding Ability: Prevents washout of cement and aggregate separation.

• Anti-Washout Additives: Use of additives to maintain concrete integrity in water.

• Workability: Concrete should have adequate flowability to fill forms and voids.

• High Strength: Should withstand hydrostatic pressure, abrasion, and chemical exposure.

• Controlled Setting Time: Additives like retarders may be needed to adjust the setting behavior underwater.

3.3: Use of Repair Mortars:

• Cement-Based Repair Mortars: For small to medium repairs.
• Polymer and Epoxy Repair Mortars: For environments requiring higher chemical resistance or adhesion.

3.4: Mechanical Repair Methods:

• Use of steel plates or carbon fiber laminates to reinforce weak spots or large cracks.
• Grouting beneath reinforcement plates to transfer load and stabilize the structure.

4. Materials Used for Underwater Concrete Repair:

According to ACI 546.2R, the repair materials must meet the following requirements:

4.1: High Adhesion to Existing Concrete:

Materials must be capable of forming strong bonds in wet environments.

4.2: Resistance to Washout:

Use of grouts or concretes with anti-washout admixtures.

4.3: Durability Against Chemical Attacks:

Materials should resist sulfate and chloride attacks in environments such as seawater or polluted water.

4.4: Appropriate Setting Time:

Materials must have suitable setting times to avoid washout during application and curing.

4.5: Types of Materials Used:

• Polymer-Modified Concrete and Grout: High adhesion and durability.
• Epoxies: Ideal for crack injection and bonding.
• Anti-Washout Cement-Based Mortars: Suitable for filling underwater voids.

Abadgaran Chemical Industries, a knowledge-based industrial company, has developed advanced products such as ABADUR MP-25/45, ABADUR MP-5/25 repair mortars, ABAINJECT EPW-210H high-viscosity epoxy injection adhesive, and ABABUILD-100 grout admixture for underwater concrete repair and rehabilitation. These products offer effective solutions with high bonding strength, washout resistance, and long-term durability in aquatic environments.

References:

• ACI 546.2R Standard