Coating Requirement for Concrete Surfaces [SAES-H-003] – Civil QC Notes Part-4

Below are some technical definitions and explanations for civil qc and engineers:

1. Light Duty Surface: This refers to a concrete surface that is exposed to relatively mild environmental conditions, such as occasional exposure to salt, minor chemical spills, moderate industrial fumes, or other forms of mild attack.
2. Heavy Duty Surface: This term describes a concrete surface that faces more severe conditions, including continuous immersion, frequent chemical spills, heavy chemical fumes, severe abrasion, or physical abuse.
3. Laitance: Laitance is a layer of fine particles that can accumulate on the surface of fresh concrete due to the upward movement of water. It can affect the quality of the concrete surface and may need to be addressed before applying coatings.
4. DFT (Dry Film Thickness): DFT refers to the thickness of a coating once it has dried and cured. It is an essential parameter to ensure that the coating provides adequate protection.
5. Carbonation: Carbonation is a chemical process where carbon dioxide reacts with calcium hydroxide present in cement, neutralizing it to form calcium carbonate. This process can affect the durability of concrete structures.
6. Chloride Ion Attack: Chloride ion attack occurs when chloride ions come into contact with concrete. It can happen due to the inclusion of chlorides in the concrete mix, using chloride-contaminated aggregates, or exposing concrete to chloride-containing solutions. Chloride ions can damage steel reinforcement within concrete, leading to rust and potentially causing concrete spalling.
7. RSA (Responsible Standardization Agency Representative): The RSA is a Coating Engineer designated by the Manager of the Consulting Services Department. They are responsible for product approvals and serve as the primary contact for matters related to the interpretation and application of the coating specifications mentioned in the document.
8. Approved Product: An approved product is a coating material that has received approval from the RSA. It must meet the requirements of the applicable APCS (Aramco Product and Service Catalog) or SAMSS (Saudi Aramco Material System Specifications). If no relevant APCS or SAMSS specification exists, the RSA can certify in writing that the product is suitable for the intended service. Only approved products can be used on Saudi Aramco projects to ensure quality and compliance with specifications.

Concrete Surface Preparation Requirements

1. Surface Requirements

The surface requirements for concrete prior to coating. It specifies the curing time and provides two methods for measuring concrete moisture content to determine whether it’s ready for coating. Let’s break down each part:

1. Concrete Cure:

• New concrete must undergo a minimum curing period of 28 days before applying any coatings.
• Shorter curing times are acceptable only if the concrete passes specific moisture cure tests mentioned in following paragraphs.

2. Concrete Moisture Content – ASTM D4263 “Plastic Sheet Method”:

This method is used to assess concrete moisture content.

a) Test Procedure:

Tape a 4 mil thick (0.1 mm), 18″ x 18″ (450 mm x 450 mm) clear plastic sheet to the concrete surface to be coated using 2″ wide (50 mm) duct tape. Ensure the sheet is taped on all sides to prevent air leaks.

b) Duration:

Allow the plastic sheet to remain in place for a minimum of 16 hours.

c) Moisture Check:

After 16 hours, remove the plastic sheet and visually check the underside for moisture.

d) Results:

If no moisture is observed on the underside of the sheet after 16 hours, the concrete is considered ready for coating.

e) If Moisture is Present:

• If droplets of moisture are present, the concrete is not ready for coating, and the test should be repeated after allowing more time for curing.

3. Concrete Moisture Content – Elcometer Method:

This is an alternative method for measuring concrete moisture content.

a) Test Procedure:

Drill two small holes approximately 6 mm in diameter, 25 mm in depth, and 150 mm apart in the concrete (these holes must be repaired afterward).

b) Probes and Sealing:

Insert probes into the drilled holes and seal them with silicone putty.

c) Waiting Period:

Wait approximately 24 hours to allow the side-effects of drilling to stabilize, and then take measurements.

d) Coating Start Threshold:

Begin coating only if the moisture content is less than 4%.

2. Environmental Conditions During Surface Preparation:

2.1 Relative Humidity:

Relative humidity should be maintained at a level less than 85%. High humidity can affect the adhesion and drying of coatings.

2.2 Surface Dryness:

The surface to be coated should be tested for dryness after specific events, including rain, water blasting, or heavy overnight fog. Ensuring that the surface is dry is essential for proper adhesion of coatings.

2.3 Wind Conditions:

Wind conditions should be such that they allow for the complete cleanup of dust and dirt on the areas to be coated. Adequate wind control helps maintain a clean and debris-free surface, which is important for achieving a smooth and defect-free coating application.

Texture and Cleanliness of Prepared (Blast Cleaned) Surfaces.

Focuses on the texture and cleanliness requirements for prepared (blast cleaned) surfaces, particularly for new concrete surfaces intended for light-duty service.

New Concrete – Light Duty Service:

a) Surface Scouring:

• The goal is to remove any protrusions and sharp edges on the new concrete surface.
• This can be achieved through various methods, including using an abrasive brick (carborundum), power grinding, or power brushing.
• To check the overall surface soundness, scratch the surface with a screwdriver or pocket knife.
• If the metal object moves smoothly over the surface without loosening any particles and leaves only a shiny mark, the surface is considered sound.
• If the surface is not sound, continue scouring until it meets this criteria.

b) Removal of Surface Contaminants:

• Surface contaminants like laitance and form oils must be removed.
• Form oils, grease, and other contaminants can generally be removed by steam cleaning with a water-emulsifiable detergent added.
• Laitance can be removed by wire brushing.
• Hydrochloric acid is used for etching, and it should be diluted as specified (10/90 to 20/80 with water).
• Apply acid etching at the rate of 1.0 liter/m².
• Allow the acid to react with the concrete surface for 5 to 10 minutes.
• Flush the surface with water while scrubbing.
• Ensure the surface is fully neutralized before proceeding with coating application. This can be checked with Litmus or pH paper.

c) Surface Roughening:

• The surface of the new concrete should be roughened to the texture of medium grit sandpaper.
• This can be achieved through either of the following methods:
  1) Dry Abrasive Blasting:
  – Maintain a specific blast nozzle distance to achieve results similar to a brush-off blast.
  2) Wet Abrasive Blasting:
  – This method offers advantages such as easy cleanup, minimal dust, and generally more uniform surface etching.

These steps and methods are essential for preparing the new concrete surface to meet the required texture and cleanliness standards, ensuring that the subsequent coating application will adhere effectively and perform as expected. Proper surface preparation is critical for the long-term durability of coatings on concrete surfaces.

Environmental Conditions During Coating Application:

1. Relative Humidity:

• Relative humidity should be less than 85% during coating application. High humidity can impact the drying and curing of coatings.

2. Surface Temperature:

• The surface temperature should not fall below 10°C (50°F). Coating application at lower temperatures can affect the performance of coatings.

3. Dew Point:

• The surface temperature must be greater than 3°C (5°F) above the dew point. This helps prevent condensation on the surface, which can interfere with coating adhesion.

4. Surface Dryness:

• The surface to be coated should be tested for dryness after specific events, including rain, water blasting, or heavy overnight fog. Ensuring that the surface is dry is crucial for proper coating adhesion.

5. Wind Conditions:

• Wind conditions should be such that they prevent the accumulation of dust and dirt on the surface to be coated. Clean conditions are essential for achieving a smooth and defect-free coating finish.

Coating and Lining Inspection:

1. Surface Temperature and Humidity:

• Surface temperature and humidity readings should be recorded during the coating application process.
• Work should not proceed if the substrate temperature or relative humidity falls outside the limits specified by the coating or lining manufacturer’s data sheets.

2. Visual Inspection:

• The coating or lining should be visually inspected for defects.
• It should meet the requirements specified in the coating or lining manufacturer’s data sheets.

3. Wet Film Thickness:

• Wet film thickness should be monitored during coating application.
• At least three wet film gauge readings should be taken per 100 ft² to ensure that the coating is applied at the specified thickness.

These environmental conditions and inspection requirements are critical to ensuring that the coating application is carried out correctly and that the coatings meet the necessary quality standards. Adhering to these guidelines helps achieve a successful and durable coating on the concrete surface.