Metal

Metal is used in construction in various forms and products. It appears as an end product such as structural steel beams and columns, as metal studs for walls, C channels for roof trusses, handrails, staircases, as well as steel reinforcement embedded in concrete framed buildings.

Atmospheric corrosion

Defect risk related to moisture is corrosion as water is an important electrolyte as the catalyst for an ionic reaction that causes corrosion. The atmosphere always has a quantity of water vapour present and the value is measured as relative humidity (RH%). Any moisture that lingers on metal surfaces from condensation may become alkaline due to reaction with metal surfaces or become acidic as it absorbs carbon dioxide from the air. This aggressive electrolyte promotes corrosion on unprotected metal surfaces.

Worse, corrosive contaminants suspended in the air from traffic or industrial smoke particles landing on metal surfaces can accumulate and in high humidity condition, causes corrosion on metal surfaces.

In iron, a critical humidity level of 60% is known as a factor that promotes corrosion. Atmospheric corrosion proceeds by balancing the anodic and cathodic reactions, where anodic oxidation attacks the metal and cathodic reaction is the oxygen reduction reaction shown in the figure above.

We will explore the topic of metal defects further in detail in the coming weeks and explain the mechanism of failure and ways to mitigate it.