Protecting Steel and Concrete from Corrosion in Bangladesh's Climate

Bangladesh's climate is hard on buildings. High humidity, intense monsoon rainfall, flooding and — in coastal districts — salt-laden air all accelerate corrosion of steel, whether it is a PEB frame or reinforcement inside concrete. Corrosion is slow and often hidden, but it steadily reduces strength and can eventually threaten safety.

How reinforcement corrodes inside concrete

Concrete is naturally alkaline, which protects embedded steel. This protection is lost in two main ways:

• Carbonation — carbon dioxide from the air slowly reduces the alkalinity of the concrete from the surface inward. When it reaches the steel, corrosion can begin.
• Chlorides — from sea air, contaminated sand or water, or salty groundwater — break down the protective layer even in alkaline concrete.

As steel corrodes, the rust occupies more volume than the original steel, cracking and spalling the concrete cover and accelerating further damage.

Protecting RCC structures

• Adequate cover — the concrete between the steel and the surface is the first line of defence. Specify cover suited to the exposure, and enforce it on site with cover blocks.
• Dense, well-cured concrete — low water–cement ratio, proper compaction and curing reduce permeability.
• Clean materials — avoid salty sand and water; test where in doubt.
• Crack control — good detailing limits crack widths that let water in.
• Protective coatings and waterproofing on exposed surfaces, roofs and basements.

Protecting structural steel

• Surface preparation — blast cleaning before painting makes coatings last far longer.
• Coating system — choose primer and finish coats suited to the environment; coastal and chemical environments need more robust systems.
• Galvanising for secondary members, fasteners and items that are hard to maintain.
• Detailing — avoid pockets that trap water and debris; seal gaps; keep column bases above the floor where water collects.
• Roofing — specify sheeting with appropriate coating type and weight for the location.

Inspection and maintenance

Corrosion is far cheaper to manage early. A simple annual inspection should look for rust stains, cracks along the line of bars, spalling, coating breakdown on steel, and leaks around roof fixings and gutters. Touch-up painting and crack sealing are inexpensive; replacing corroded members is not.

Repairing corrosion damage

Where corrosion has damaged concrete, repair involves removing contaminated concrete behind the bars, cleaning or replacing corroded steel, applying protective treatments and reinstating cover with suitable repair mortar. Where section loss is significant, the member may need strengthening. A condition assessment, including half-cell and carbonation testing, identifies the extent before repairs are designed.

Contact us if you are seeing rust staining or spalling in your building.